Abstract

Although the numerous advantages of polymer optical fiber (POF) sensors have been applied in different fields, the measurement consistency and sensitivity of POF evanescent wave (EW) sensors are still affected by its thermal stability and water absorption. Therefore, we perform a study to demonstrate the mechanism of the effect of heat treatments on physical and optical properties of POF EW sensors. We investigate the surface morphology, composition, refractive index, geometry, and weight of the fiber-sensing region subjected to water and vacuum heat treatments. We examine the spectral transmission and transmitted light intensity of POF sensors. We present a theoretical investigation of the effect of heat treatments on the sensitivity of POF EW sensors. The performance of the prepared sensor is evaluated using glucose and Chlorella pyrenoidosa analytes. We discovered that the spectral transmission and transmitted light intensity of the fibers shows little effect of vacuum heat treatments. In particular, the sensors, which subject to vacuum heat treatment at 110 °C for 3 h, exhibit temperature-independent measuring consistency and high sensitivity in glucose solutions in the temperature range 15–60 °C and also show high sensitivity in Chlorella pyrenoidosa solutions.

© 2016 Optical Society of America

1. Introduction

Polymer optical fibers (POFs) are widely applied in fiber optic communications and optical sensors because of their various potential advantages, including low cost, large-diameter core, large numerical aperture, and high degree of flexibility [1–3]. In particular, in sensor applications, the large diameter and numerical aperture of the fibers can increase the optical transmission capacity, and the high flexibility of the fibers can be easily fabricated into various shapes [4]; these advantages give enormous opportunity for fabricating a high-sensitivity and large-measurement range fiber-optic sensor. However, the commercial POFs are almost entirely composed of fluorinated polymer (fiber cladding) and poly(methyl methacrylate) (PMMA; fiber core); the physical and optical properties of the polymer and PMMA materials are easily affected by their thermal stability and water absorption [5]. Hence, the properties of sensors fabricated using the commercial POFs are also significantly affected by the temperature-dependence in vacuum or water. In particular, when the cladding and even the core material were exposed to a high temperature, which was above the glass transition temperature of PMMA.

In recent decades, numerous studies have reported on the influence of heat treatments on the physical and optical properties of POFs. Takezawa et al. [6] discovered that the attenuation loss of POFs increases with long use at high temperatures because of the increase in electronic transition absorption loss caused by a thermal oxidation reaction of the core polymer in the POF; particularly, they also noted that the Rayleigh scattering loss was due to fluctuations of the density and the refractive index (RI) in the core polymer subjected to heat treatment at 150 °C in air. Makino et al. [7] discovered that a temperature increase will induce a significant increase in the attenuation of the POFs, because the polymeric material has a narrow low attenuation window based on the carbon-hydrogen (C-H) vibrational absorption. Further, Sato et al. [8] discovered that PMMA will absorb 2 wt.% of water when the PMMA bulk is placed in hot water at 60 °C and revealed that the attenuation increment of POF is mainly due to scattering loss caused by some large aggregation of water molecules which depends on the affinity of water to the polymer matrix. Dai et al. [9] also confirmed that the absorbed water molecules in the POF cannot be uniformly dispersed but must be aggregated to form heterogeneities in the RI of the polymer matrix, causing large light attenuation from the scattering loss and O-H stretching vibration absorption. Stajanca et al. [10] further observed that the POF shrinkage increment is proportional to relative humidity level at temperature 90 °C due to the plasticizing effect of water molecules on the polymer structure; they discovered that the shrinkage rate of POF will affect the heterogeneity of molecular arrangement in the POF, and that the increased heterogeneity will influence fiber optical properties. However, these studies mainly focused on the effects of the POF subjected to water/vacuum heat treatments on fiber optic communications.

In the recent years, a number of researchers investigated the various technologies that can improve the stable performance of POF sensors. Yuan et al. [11] and Fasano et al. [12] have identified the effect of UV-induced heating on the POF grating and discovered that fiber Bragg grating sensors (FBGs) in annealed commercial POFs can offer more stable performance at higher temperature. Woyessa et al. [13] discovered that annealing at high humidity and high temperature can improve the performances of mPOFBGs in terms of stability and sensitivity to humidity; to create a humidity insensitive high temperature FBGs, Woyessa et al. [14] further created a FBG sensor by using a step-index single mode and humidity insensitive POF with core made from TOPAS 5013S-04 with a glass transition temperature of 134°C and a cladding from ZEONEX 480R with a glass transition temperature of 138°C. Markos et al. [15] presented FBGs in the high-Tg TOPAS mPOF are able to stably operate at 110°C. Ivan-Lazar Bundalo, et al. [16] reported that short writing time of FBG in mPOFs can significantly improve the grating stability. Despite the fact that effect of POFs treatments on the performance of the POFs sensors was already reported, very few studies have been reported on the effects of heat treatments on performance of POF EW sensors. In particular, prolonged heat treatment in vacuum and water changes in the fiber’s physical properties—the changes in surface morphology and composition—and their effects on optical transmission (spectrum and intensity), sensitivity, and measurement consistency of the POF sensor have not been examined. More importantly, we have discovered that the optical transmission, sensitivity and measurement consistency POF EW sensors are very different when the POF was subject to the vacuum and water heat treatment, respectively. These observations have yet to be explained in the literature. Thus, an understanding of mechanism of the effects of heat treatments on the properties of POFs is required to facilitate the fabrication of high-quality POF EW sensors.

In the present study, in order to reveal the mechanism of the effects of heat treatments on the physical and optical properties of POF EW sensors, we investigate the surface morphology, composition, RI, geometry, and weight of the D-shaped fiber-sensing region subjected to water and vacuum heat treatments. We also examine the spectral transmission and transmitted light intensity of POF EW sensors subjected heat treatment in vacuum and distilled water. We perform theoretical investigation of the effect of heat treatments on the sensitivity parameters of POF EW sensors. In addition, we evaluate the sensitivity and measurement consistency of our sensor using glucose solutions and Chlorella pyrenoidosa solutions.

2. Sensor sensitivity analysis

As is well known, the performance of POF EW sensors depends on the attenuation of the evanescent waves (EWs) and decrement in the number of modes propagating within the fiber. Furthermore, for a given analyte, the attenuation of the EWs is determined by their penetration depth and intensity; in particular, the EW intensity is further affected by the effective incident light intensity, number of total reflections, and effective EW optical path length on the unclad fiber surface. Thus, before we investigate the heat treatments on the effect of performance of POF EW sensors, we first examine these parameters.

2.2.1 Number of modes

It is well known that the light transmission in an optical fiber is the light guide mode. The number of modes in a fiber is proportional to the square of the normalized frequency of the fiber (i.e., V-parameter) which is related to the core radius and the NA of the fiber, the V-parameter is given by,

V=2πrλn22n12
where r is the radius of the sensing region; λ denotes the light wavelength; n2, n1 are, respectively, of the RI of the dense and rare media. Equation (1) shows that the light passing through an optical fiber is affected by a change in the physical structure of the fiber and or a change in the RI of the fiber. Thus, when the POF cladding is removed and the core is in direct contact with the aqueous medium, we can obtain the functional relationship between a small change in n and change in V as follows:
ΔV=πrnλn22n2Δn
where n is RI of the aqueous medium (analyte). We see that ΔV increases with decreasing n2 and increasing r if λ, n, and Δn are constant. Thus, the decrement in the number of modes propagating within the fiber also increases with decreasing n2 and increasing r.

2.2.2 EW penetration depth

The effective penetration depth of EWs is another important parameter that affects the attenuation of EWs. For a normal thin fiber, if the angle of incidence is larger than the critical angle (θiθc), the penetration depth is given by (Dp),

Dp=λ2π[n22sin2θin2]1/2

Equation (3) shows that Dp is a fraction of the wavelength if θi is perpendicular to the fiber–media interface and can be as large as several wavelengths if θi = θc. Thus, a small change in n causes a corresponding change in Dp as follows,

ΔDp=λn2π(n22sin2θin2)3/2×Δn

2.2.3 Incident light intensity

According to reports in the literature [17–19], the initial effective intensity of EWs, Iew, decreases with decreasing Iin for standard unclad fibers. Thus, when the unclad fiber is subjected to heat treatments, Iew will decrease because the scattering-refraction-absorption (IS-R) increases. The increased IS-R is due to the uneven distribution of amorphous region in fiber core, absorbed water molecules in PMMA, and increase in surface roughness of the unclad fiber. Therefore, when the transmitted light intensity of the fiber is described by Iout, Iew can be expressed as,

Iew=IinIoutISR

This fact reveals that Iew decreases with increasing IS-R, which degrades the POF EW sensor sensitivity.

2.2.4 Number of total reflections

As is well known, the EW generates by total reflection; at each point of reflection, the EW decays because it is absorbed by the analyte. Hence, the EW intensity and its attenuation are significantly affected by the number of total reflections. To investigate the number of total reflections, we defined the path length of light through two consecutive total internal reflections as l. Then, the number of reflections of light rays in the unclad fiber region can be expressed as,

N=2Ll=L4rtanθi

2.2.5 EW optical path length

The effective EW optical path length is another important parameter that affects the EW intensity. For a typical D-shaped fiber, by using Eq. (3) and Eq. 6, the effective optical path length Lew of EWs at the fiber–media interface can be obtained as,

Lew=Lλ4πrtanθi[n22sin2θin2]1/2tan[arcsin(nn2sinθi)]

Thus, a small change in n causes a corresponding change in Lew of the fibers as follows,

ΔLew=Lλ(XY)4πn2rsinθi[n22sin2θin2]tan2[arcsin(nn2sinθi)]×Δn
X=ntan[arc(nn2sinθi)][n22sin2θin2]1/2
Y=nsinθi[n22sin2θin2]1/2sec2[arcsin(nn2sinθi)][n22(nsinθi)2]1/2

The above analysis clearly shows the effect of fiber core parameters (n2 and r) on the sensitivity parameters of the POF EW sensors. To quantitatively assess the effects of n2 and r on ΔV, ΔDP, N, and ΔLew, we perform numerical simulations using Eqs. (2), (4), (6), and (8). The simulation parameters and results are listed in Table 1.

Tables Icon

Table 1. Simulation Parameters and Results

Table 1 shows that ΔV, ΔDP, and ΔLew increase, while N decreases, when the POF is subjected to heat treatments. More importantly, the sensitivity parameters of the POF EW sensors are very different when the POF is subject to the vacuum and water heat treatment, respectively. Thus, to exploit a high-performance POF EW sensor, it is necessary to expand this experimental study of the effect of heat treatments on the performance of POF EW sensor.

3. Materials and methods

3.1 Preparation of D-shaped POFs

We used plastic optical fibers [Jiangxi Daishing (China) POF Co., Ltd., Jiangxi, China; fiber diameters, cladding diameters and core diameters of 3000 ± 50, 2000 ± 5 and 1800 ± 5 μm respectively] with a core material made of PMMA, fiber cladding material composed of fluorinated polymer, numerical aperture of 0.5, core RI of 1.4920, cladding RI of 1.4057 (of core RI and cladding RI are measurement at a wavelength of 600 nm), PMMA glass transition temperature Tg = 105 °C, and operating temperature range of −50 to 70 °C. In this work, the studied sensors were prepared as follows. First, both ends of the POFs of length 35 cm were polished with 3-μm polishing paper. Second, the coatings of central region of the fibers were removed over a length of 30 mm using a fiber optic stripping tool (84-870, Stanley, USA). Third, the thin fiber was prepared by polishing the uncoated region held using a V grooved block; then, the uncoated region of the fiber and the V-grooved block were polished (thin) using precise machining (YM-36XL, Shenzhen Dajing Grinding Technology Co., Ltd, Shenzhen, China) with 3-μm polishing paper, and the polishing depth of the uncoated fiber was 500 ± 5 μm. The shape of the polished POFs is same as the previous paper [4]. Fourth, the normal and thin region of the POFs were inserted to a cylindrical steel tube with inner diameter of 5.5 mm and thickness 1 mm to reduce the deformation of POFs subjected heat treatment in vacuum and distilled water. The thin (D-shaped) region of the POFs was used as the sensing region of the POF EW sensor.

3.2 Experimental conditions

Regarding the heat treatments in distilled water, the temperature of the water was controlled using a high and low constant temperature bath with an operating temperature range of −20–200 °C, temperature stability of ± 0.03 °C, liquid tank size 320 × 180 × 150 mm, heating power of 2000 W, and refrigerating power of 250 W (FCH6-20, Jinan Hanon Instruments Co., Ltd.. Jinan, China); the moisture on the surface of the heating-treated fibers was dried at 25 °C using argon gas. Second, regarding the heat treatments in vacuum, the temperature of the vacuum was controlled using a vacuum oven with an operating temperature range of 10–250 °C, temperature stability of ± 1 °C, and working volume of 415 × 370 × 345 mm (DZF-6050D, Beijing Zhongkehuanshi Instrument Co., Ltd.. Beijing, China). In this work, the heating rate of the water and vacuum was set at 2 °C/min.

The surface morphology of the heat-treated fibers (D-shaped fiber surface) was examined using a scanning electron microscope (SEM, TESCAN vega3, Czech Republic). The compositions of the D-shaped POFs were analyzed using Fourier transform infrared (FT-IR) spectroscopy (IR spectrophotometer, Nicolet iN10, Thermofisher, USA) and XPS (XSAM800, Kratos Co., UK). The RI of the fibers (D-shaped fiber region) was measured using a refractometer with a resolution of ± 0.0002 at a wavelength of 600 nm (NAR-1T solid, ATAGO, Japan). An optical microscope system (IX81, Olympus, Japan) with a resolution of ± 1 μm was used to measure the diameter and width of the fibers. The D-shaped fiber length was checked using a digital micrometer with a resolution of 1 µm. The weight of the fibers (D-shaped fiber region) was determined using a microbalance with a resolution of 1 μg (XP56, Mettler Toledo, USA). To record the transmitted spectrum and transmitted light intensity of the fibers, both ends of the prepared sensors were directly coupled with the light source (AvaLight-DHS, Avantes, Apeldoorn, the Netherlands) and the optical spectrometer (Avantes 2048, Avantes, Apeldoorn, the Netherlands) or a power meter (NBET-36R, Newport Corporation, USA, obtained from the NBeT Group Corp., China); the wavelength range of the light source is 210–2500 nm, the working wavelength range of the spectrometer is 200–1100 nm, the power range of the power meter is 100 pW–0.2 W, and the maximum uncertainty of the power meter is 4% over a wavelength range of 200–1100 nm. In this work, the heat-treated fibers’ diameter, length, curvature, RI, and weight were analyzed at room temperature (25 °C); each experiment was repeated more than ten times.

3.3 Analytical methods

To accurately record the responses of the prepared sensors for the analytes, the glucose solutions were prepared by mixing a weighed amount of glucose (reagent-grade glucose) into distilled water. The concentrations and RI of the glucose solutions ranged from 0 to 12.5 g/100 ml and 1.3319 to 1.3468, respectively. The Chlorella pyrenoidosa solutions were made using cultivated Chlorella pyrenoidosa with a dry weight of 2.5 g/l and distilled water (the cultivation conditions and synthetic medium of the microalgae are the same as in previous work [20]). The heat-treated sensors were fixed in a flow cell (60 × 40 × 100 mm), which was covered by aluminum film; the transmitted light intensity of the sensors was recorded with a time interval of 2 min. Furthermore, in the data analysis, to effectively assess the sensitivity of the prepared sensors, the relative change in the transmitted light intensity (RCTLI) of the sensors was used. In particular, the parameter RCTLI_i was defined as RCTLI_i = (Ic,iI0,i)/I0,i, (i = I, II, III, …, VIII), where, Ic,i and I0,i denote the transmitted light intensities of the prepared sensor, i.e. sensor_i, in an analyte at concentration c and in its reference sample (distilled water), respectively.

4. Results and discussion

4.1. Physical and optical properties of POFs

As it is well known, the performance of a POF sensor are dependent on the spectral transmission and transmitted light intensity of the fiber, which are affected by the fiber parameters, including the geometry structure, composition, RI, and surface morphology. However, these parameters are easily affected by varying the water/vacuum heat treatment temperature and duration because of the low thermal stability and water absorption of PMMA. Hence, to assess the effects of heat treatments on the performance of a POF sensor, we first studied changes in the weight and geometry of the D-shaped region subjected to distilled water and vacuum heat treatments, as shown in Fig. 1. Subsequently, we verified the changes in composition, RI, and surface morphology of the D-shaped POFs with water and vacuum heat treatments, as shown in Fig. 2. Then, we examined the spectral transmission and transmitted light intensity of the POFs in air as shown in Fig. 3. In the experiments, the samples of the D-shaped POFs of length 30 ± 1 mm were prepared using the purchased POF. In this work, the Samples A to G are defined as follows, Sample A: normal POF, Sample B: POF was heated to 110 °C in water; Sample C: POF was treated in water at 110 °C for 1 h; Sample D: POF was treated in water at 110 °C for 3 h; Sample E: POF was heated to 110 °C in vacuum; Sample F: POF was treated in vacuum at 110 °C for 1 h; Sample G: POF was treated in vacuum at 110 °C for 3 h.

 

Fig. 1 (a–d) Weight, length, diameter, and width changes in D-shaped fibers as a function of heat treatment time at temperature 110 °C; the inset of Figs. 1(a)–1(d) shows that weight, length, diameter, and width of the D-shaped fibers changes with increasing temperature in the range of 20–110 °C (heating rate of the water and vacuum is 2 °C/min).

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Fig. 2 (a) XPS spectra of PMMA subjected water and vacuum heat treatment, (b) FT-IR spectra of PMMA subjected water and vacuum heat treatment, (c) RI change as a function of time at temperature 110 °C, the inset shows that RI changes with increasing temperature in the range of 20–110 °C (heating rate of the water and vacuum is 2 °C/min), (d) the picture and optical micrographs of the D-shaped region (d_1 represents the picture of the D-shaped region, d_2 is the optical micrograph (4 X) of the boundary between the normal region (NR) and polished region (PR), and d_2 is the optical micrograph (4 X) of the D-shaped surface), and (e) scanning electron microscopy (SEM) images (3.00 KX) of the D-shaped surface.

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Fig. 3 (a) spectral transmission of the fibers subjected to water and vacuum heat treatments (the spectral scanning time of Samples A, E, F and G was 1 ms, the scanning time of Sample B was 2 ms, and the scanning time of Samples C–D was 30 ms), (b) transmitted light intensity of the fibers change as a function of time at temperature 110 °C, the inset shows that transmitted light intensity of the fibers changes with increasing temperature in the range of 20–110 °C.

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Figure 1(a) shows that the weight of the D-shaped POF subjected to vacuum heat treatment at 110 °C decreases with the time in the range 0–120 min; however, when the POF was subjected to distilled water heat treatment at 110 °C, its weight increases with time in the range 0–180 min. Furthermore, in the inset of Fig. 1(a), one can see that the weight of the POF subjected to vacuum heat treatments still decreases with increasing temperature; however, the weight of the D-shaped POF first decreases and subsequently rapidly increases with increasing water temperature. The decrease in weight is attributed to a readjustment of the uneven distribution of molecular weight and an increase in the thermal decomposition of the residual monomers (methyl methacrylate, MMA) in the polymers with increasing temperature [21,22]. The increased weight of the POF with water heat treatment is due to the fact that some amount of water is absorbed by the fiber core material (PMMA) because of the affinity of water with the polymer matrix, and the amount of absorbed water increases with increasing temperature and prolonged time in the water [23]. The constant-weight of the vacuum heat-treated POFs can be attributed the fact that the glass transition, polymer chain reorientation, and thermal decomposition of the residual monomers have been completed; in particular, for the water heat-treated POFs, the thermal oxidation reaction of the PMMA in the POF has also been completed.

In the inset of Fig. 1(b), we note that the length shrinkage of the POFs is slow at first in the water/vacuum and then decreases rapidly in the temperature range 70–110 °C. Furthermore, one can see that the length shrinkage of the POF is still slow with the increasing time in the vacuum at temperature 110 °C, and then remains constant when the time is above 120 min. However, the length shrinkage rate is still rapid with increase of water-aging time in the range 0–120 min, and then it also remains constant after 180 min. The length shrinkage increment of the water heat-treated POF is about 15.2 times than that of the vacuum heat-treated POF after 3 h. The behavior of the slight decrease in vacuum is because the POF undergoes glass transition and the spontaneous reforming of polymer bonds; the constant level is because the residual stresses of the PMMA in the D-shaped POF disappear and the polymer chain reorientation has been completed. The POF exhibits large length shrinkage in water because of degradation of the polymer network. This is due to the reaction of the water molecules with the polymer chain or the vibration of the absorbed water molecules, which results in the production of a shorter chain [24] and the increase of diameter and width.

Figures 1(c) and 1(d), respectively, show that the diameter and width of the D-shaped POFs in vacuum still remain constant; however, the diameter and width of the D-shaped POFs subjected water heat treatment increase rapidly when the temperature is above 70 °C (see the inset of Figs. 1(c) and 1(d)) and subsequently remains constant when the treatment time is, respectively, increased to 180 min and 150 min. The constant level in the vacuum can be attributed to the fact that the thermal expansion coefficient of the POF in the diameter and width directions was destroyed by a large disturbance in the polymer chain in-length orientation caused by polymer chain shrinkage [25] and the decomposition of the residual monomers in the polymer. The significant increases in diameter and width of the POFs are mainly due to an increase in the thermal expansion coefficient, the formation of hydrogen bonds between the carbonyl groups in PMMA with hydroxyl groups in water caused by the absorbed water molecules [9], and that the mobility of absorbed water molecules has significantly lowered around polymer chains for both translational and rotational motions [26].

Figure 2(a) shows representative X-ray photoelectron spectroscopy (XPS) spectra of the normal D-shaped POF and POFs subjected to heat treatments. The five samples, i.e., Samples A, B, D, E and G, exhibit the same peaks at 1072, 1023, 979, 689, 533, 285, 154, and 103 eV, corresponding to Na 1s, Zn 2p, oxygen Auger peak intensity (O-KLL), F 1s, O 1s, C 1s, Si 2s, and Si 2p, implying that sodium, zinc, oxygen, fluorine, carbon and silicon dioxide must exist in the POF. To clarify the effects of the heat treatments on the functional groups of the PMMA material, the FT-IR spectra of PMMA was examined as shown in Fig. 2(b). Clearly, all the D-shaped POF samples exhibit the same absorption peaks at approximately 1694 cm−1 (carbonyl stretching), 1884 cm−1 (carbonyl fluoride groups), 2237 cm−1 (acrylonitrile in grafted copolymer), 2490 cm−1 (O–D stretching mode) and 3864 cm−1 (O–H stretching vibrations). We can note that the FTIR spectra of Sample A and Samples E–G (the three samples subjected to vacuum heat treatments) still show the same absorptions around 704 cm−1 (C–H out of plane bending vibrations of the polymers basal) and 3300 cm−1 (vibrational feature of the N–H bands); the results verify that the functional groups of the POFs do not change with the vacuum heat treatment temperature and duration. Furthermore, comparing Sample A with Samples E–G, one can see that the absorption peak in the range of 3630–3885 cm−1 shifts to shorter wavelength with increase of heat treatment time in vacuum at 110 °C; this indicates that the alcohol group decreases because of the high temperature decomposition of the residual monomers in the PMMA in vacuum. However, comparing Sample A with Samples B–D, it is clear that the bands at 704 and 3300 cm−1 gradually disappear with increase of the heat treatment time and a new absorption peak is observed at 1694 cm−1 (carbonyl stretching) in Sample Ddue to the thermal oxidation reaction of core polymer [6].

In the inset of Fig. 2(c), we note that the RI of the PMMA in the POF is nearly unchanged with increasing temperature in the range 20–50 °C and then rapidly decreases. In particular, the decrease rate of the RI of the POF subjected to vacuum heat treatment is higher than that of the water heat-treated POF when the temperature is above 60 °C. Furthermore, one can see that the RI was also significantly affected by the heat treatment time. The RI rapidly decreases at first, and then decreases slowly and thereafter remains constant when the POF is heat-treated in vacuum and water for 120 min and 150 min, respectively. The decrement of the RI of the POFs with vacuum heat treatment is about 1.4 times than that of the POFs subjected water heat treatment after 3 h. Herein, the unchanged RI results from the polymer chain shrinkage, and water absorption of the PMMA in the POF, being nearly unchanged in the temperature range 20–50 °C. The sharply decreased RI of the POFs subjected vacuum heat treatments can be attributed to the negative thermo-optic coefficient of PMMA; the constant level of RI can be explained by the fact that the decomposition of the residual monomers, glass transition of the PMMA, and the spontaneous reforming of the polymer bonds in POF have been completed. However, when the POFs were subjected to water heat treatment, the decreased RI can be attributed to the fact that although the RI mainly depends on the negative thermo-optic coefficient of PMMA [27], the RI of PMMA slightly increases with increasing absorbed moisture. The RI of water treated POF shows only a slight decrease and then remains constant; this behavior can be explained as follows. First, the thermal oxidation reaction, decomposition of the residual monomers, glass transition of the PMMA, and the spontaneous reforming of the polymer bonds in POF have been completed when the heat treatment time is above 150 min in water. The second is the balance among the absorption of water molecules and the negative thermo-optic coefficient [27–29].

Figure 2(d) shows the initial structure of the D-shaped region of POFs. In Fig. 2(e), compared with Samples A–D, one can see that a swelling and roughness structure gradually emerges with increasing heat treatment time in water at temperature 110 °C; this behavior can be attributed to the absorbed water molecules by the PMMA, and the water molecules are uniformly dispersed in the POF, which leads to further differences in local interfacial tension, local thermal expansion coefficient, and amorphous PMMA [30]. Furthermore, compared with Samples A and Samples E–G, we note that a dense structure with a slight local defect emerges with increasing heat treatment time in vacuum at temperature 110 °C; this fact can be explained by the thermal decomposition and slight thermal polymer chain shrinkage.

Figure 3(a) clearly shows that spectral transmission of the fibers rapidly decreases with increasing heat treatment time in water at temperature 110 °C. In particular, the transmission spectrum in the wavelength intervals 477–535 nm and 663–706 nm completely disappear. However, when the fibers were heat-treated in vacuum at temperature 110 °C, although spectral transmission power of the fibers also slightly decreases with increase in the time, the fibers, i.e., Samples A, E, F, and G, still show the similar spectral transmission characteristics. The decrement of spectral transmission power can be explained as follows. Although the decomposition of residual monomers can reduce the Rayleigh scattering losses, the length shrinkage can reduce the optical path, and the decrease in RI can improve the light transmission rate; the local deformation of the heat-treated POF causes ineffective optical transmission in the fiber core because of the effect of skew rays on the bending losses [31]. Second, fluctuations of the density and the distribution of amorphous domains might introduce additional scattering loss. Third, the local surface defects also excite and enhance the attenuation of the scattering, refraction, and EW at the D-shaped surface. However, for the fibers subjected to water heat treatment, its spectral transmission power experiences a strong attenuation in the observed spectral region, and the main reasons are as follows. The water-treated fiber absorbs a lot of water molecules, which are uniformly dispersed in the fiber core and shows a large deformation (length, diameter, and width) and large surface defects, which result in deterioration of light transmission in the POF. Further, the disappeared transmission spectrum of the water-treated fibers is due to the disappearance of C–H out of plane bending vibrations of the polymers basal and vibrational feature of the N–H bands, as well as to the appearance of conjugated carbonyl groups by thermal oxidation reactions, leading to a significant increase in electronic transition absorption loss caused by the n→ π* transition of the carbonyl group (>C = O) [6].

To quantify the effects of the heat treatments on light transmission of the fibers, the transmitted light intensity of the heat-treated fibers was checked as shown in Fig. 3(b). In the inset of Fig. 3(b), we note that the transmitted light intensity initially slightly increases with an increase in temperature (20–70 °C) and subsequently decreases; in particular, the intensity of the fiber subjected to water heat treatment decreases sharply when the temperature is above 80 °C. Further, the transmitted light intensity of the fibers decreases with increase of heat treatment time at temperature 110 °C, and the transmitted intensity of the fibers with heat treatment in water and vacuum from about 260 nW decreases, respectively, to 1 nW and 223 nW. Herein, the reasons for the decrease in the transmitted light intensity of the heat-treated fibers can be obtained from the explanations of the Fig. 3(a). Importantly, one can see that the transmitted intensity is unchanged with the heat treatment time when the time is greater than 3 h at temperature 110 °C, and the spectral transmission and transmitted light intensity of the POFs subjected to vacuum heat treatment still maintain at high-level. The high-level spectral transmission and transmitted light intensity are because of the slight deformation, appropriate surface roughness, unchanged material composition, low RI, and lack of water molecules. The constant level of the spectral transmission and transmitted light intensity are also due to the facts that the glass transition, polymer chain reorientation, and thermal decomposition of the residual monomers have been completed. In particular, for the water heat-treated POFs, the absorption of water and the thermal oxidation reaction of the PMMA in the POF have also been completed.

The above analysis clearly shows the effect of the vacuum and water heat treatments on the physical and optical properties of the POF EW sensors. However, the focus of this study is to clarify the effect of the heat treatments on the performance of the POF EW sensors and to realize a high-performance sensor. This aspect of the study is presented in the following section.

4.2. Performance of D-shaped POF EW sensors

To quantify the effects of the heat treatments on performance (sensitivity and measuring consistency) of POF sensors, we examined the response of the prepared sensors to glucose and Chlorella pyrenoidosa analytes as shown in Fig. 4.

 

Fig. 4 (a–g) RCTLI_i,, (i = I, II, III, …, VII), as a function of glucose concentration; where, in Figs. 4(a)–4(g), the sensors were, respectively, from the Samples A–G, (h–i) absorption spectra and RCTLI_VIII of the prepared D-shaped POF sensors in Chlorella pyrenoidosa solution (D-shaped POF sensors were, respectively, normal POF sensor and subjected to heat treatment in water and vacuum at 110 °C for 3 h; particularly, the Chlorella pyrenoidosa concentration was 1.3 g/l), and (j) is the micrograph (200 X) of Chlorella pyrenoidosa.

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Figure 4(a) clearly shows that the relative change in the transmitted light intensity (RCTLI) of the normal D-shaped POF EW sensors (RCTLI_I) exhibits a positive slope with increasing glucose concentration at 15 °C. However, the positive slope of the sensors changed to a negative slope with increasing glucose concentration at 30 °C, and the negative slope increased with increasing temperature in the glucose solutions. The increased RCTLI_I at 15 °C is explained as follows. First is the decrease in random scattering and refraction of light at the fiber surface because the difference in the RI between the fiber and glucose solution decreases due to the increasing glucose concentration. Second, the normal POF sensor exhibits low-level evanescent field intensity, therefore, the transmitted intensity of the light is almost unaffected by the evanescent field intensity. The change in the slope of RCTLI_I from positive to negative can be explained as follows. The inner structure and D-shaped surface of the fiber changed because of the change in the orientation of the polymer chain with increasing temperature, resulting in the light intensity at the D-shaped surface layer-analyte interface increasing, and the light could be efficiently attenuated by the glucose solution; in particular, when the attenuation intensity of the light is greater than that of the coupling intensity, the positive slope changed to a negative slope. The increased negative slope can be attributed the fact that the ΔV, ΔDP, and ΔLew increase.

Figures 4(b)–4(c) show the response of D-shaped POF EW sensors, which were subjected to water heat treatments, to the glucose solutions in the temperature range 15–60 °C. We note that the positive slope of the RCTLI_II changed to a negative slope of the RCTLI_III with increasing glucose concentration at 15 °C when the POF was heat-treated at temperature 110 °C for 1 h. This change can be explained as follows. Although the spectral transmission and transmitted light intensity of the heat-treated fibers decrease (the decrease will reduce the EW intensity), the fiber geometry structure, surface morphology and RI of the fiber also changed, which can change the core and cladding modes (light-transmission modes) in the D-shaped region and increase the EW intensity, EW penetration depth, and EW optical path length at the fiber–analyte interface (see Tab. 1); hence, the attenuation increases with increasing glucose concentration, which leads to the transmitted light intensity of the POFs decreasing with increase in glucose concentration and the attenuation intensity of the light at the fiber–analyte interface is greater than that of the coupling intensity.

Importantly, compared Figs. 4(a)–4(c), one can see that the RCTLI_IVs of the D-shaped POF sensor subjected to heat treatment at temperature 110 °C for 3 h show almost the same slope in the temperature range of 15 to 60 °C with increasing glucose concentration. This fact is due to the stable geometry, weight, RI, material composition, surface morphology, spectral transmission and transmitted light intensity, and these parameters are not affected by heat treatment time at temperature 110 °C in water; that is the sensor sensitivity parameters independence on the heat treatments, because the glass transition, thermal decomposition, thermal oxidation reaction, absorption of water molecules, and reorientation of polymer chain have been completed after 3 h. The maximum relative error (MRE) of the RCTLI_IVs in the temperatures range of 15–60 °C was determined to be 9.2%, which can be attributed to the change in the spacing of water and glucose molecules with increasing temperature [32] and to the adhesion of microbubbles on the D-shaped surface.

Compared Fig. 4(a) and Figs. 4(e)–4(g), one can also see that the positive slope of the RCTLI_I and RCTLI_V changed to a negative slope of the RCTLI_VI with increasing glucose concentration at 15 °C when the POF was heat-treated in vacuum at 110 °C for 1 h, and it appears that the curves for the temperatures range 15–60 °C have approximately the same negative slope when the POF was heat-treated in vacuum at 110 °C for 3 h. The changed slope can be attributed the fact that the decrease of RI and dense surface morphology with slight roughness change the light transmission modes in the POF and enhance the luminous intensity [4,33], EW penetration depth, and EW optical path length at the fiber surface (see Tab. 1), which can produce strong light absorption at the fiber–analyte interface by glucose solution. The decrease in the RI of the fiber core can help much of the light escaping from the sensing region (decrease in the number of modes propagating within the fiber as shown in Tab. 1) at the fiber–analyte interface with the increase of the glucose concentration according to the ray theory and Snell's Law. Hence, the attenuation intensity of the light is greater than that of the coupling intensity in the glucose solutions. Furthermore, we note that the sensitivity of the POF EW sensors increases with increasing heat treatment time, because the sensor sensing parameters, including ΔV, ΔDP, and ΔLew, increase with increasing the time (see Tab. 1). In Fig. 4(g), the near-uniformity of slope is also because the glass transition, thermal decomposition, and reorientation of polymer chain of the PMMA have been completed in vacuum at 110 °C for 3 h. The MRE of the RCTLI_VIIs in the temperature range 15–60 °C was determined to be 7.9%, which can also be attributed to the change in the spacing of water and glucose molecules with increasing temperature and to the adhesion of microbubbles on the sensing surface.

Comparing Figs. 4(a) and 4(d), we note that the sensitivity of the water-heat-treated POF sensors decreases, especially when the glucose solutions was set at 60 °C. This result can be explained as follows. First is the increase of the electronic transition absorption loss from the conjugated carbonyl groups caused by the thermal oxidation reaction of the core polymer in the POF. Second, the aggregation of water molecules is uniformly dispersed in the core of the POF, which leads to the formation of heterogeneities in the RI of the polymer matrix; therefore, an excess scattering loss appears and the attenuation increases with increasing aggregated water molecules in the polymer. Third, compared to normal POF fibers, the increased surface roughness makes some of the light ineffective for optical signal transmission, leading to an increase of the light-scattering and refraction loss at the sensing region [20,34]. Furthermore, the number of total reflections decreases when the POF is subjected to water heat-treatment (see Tab. 1). These attenuations will result in a decrease in intensity of EWs at the fiber–analyte interface, compared with the normal POF and extremely low total attenuation of EWs by absorption and scattering in the glucose solutions. However, comparing Figs. 4(a) and 4(g), the sensitivity of the D-shaped POF EW sensors subjected vacuum heat treatment at 110 °C for 3 h is 1.4 times that that of the normal D-shaped POF EW sensors. The increment of the sensitivity is attributed to the fact that the vacuum heat-treated POF still maintains the same spectral transmission and fiber diameter as the normal POF, the transmitted light intensity has only a slight loss (8.5%), and the fiber length causes only a slight shortening (3.2%); the RI of PMMA in the POF significantly decreased helping much of the light escaping from the fiber and increasing EW penetration depth and EW optical path length at the sensing region with the increase of the glucose concentration; the slightly increased surface roughness can also increase the intensity of EWs compared with the normal POF, leading to the increase of EWs attenuation [14].

In addition, comparing Figs. 4(d) and 4(g), we note that although the heat-treated sensors show a high degree of consistency in measurements of glucose solution concentration, the sensitivity of the vacuum heat-treated sensors is 1.7 times than that of the water heat-treated sensors. This fact can be explained as follows. Although the increased fiber diameter, which is subjected water heat treatment, increases ΔV with increasing glucose concentration, the water heat-treated POF with stronger length shrinkage leads to larger decrease of the number of total reflections at fiber-analyte interface compared with the vacuum heat-treated POF (see Tab. 1); the transmitted light intensity of the water heat-treated POF is smaller than that of vacuum heat-treated POF, which results in the intensity of EWs also being lower than that of the vacuum heat-treated sensor; hence, the total amount of EW attenuation of the water heat-treated sensor is lower than that of the vacuum heat-treated sensor. Second, the RI of the vacuum heat-treated fiber core is lower than that of the water heat-treated fiber core, and thus the EW penetration depth and EW optical path length at the surface of the vacuum heat-treated fiber is higher than that of the water heat-treated fibers with the increase of the glucose concentration (see Tab. 1). These results clearly show that although the POF EW sensors subjected vacuum and water heat treatment at 110 °C for 3 h show temperature-independent measuring consistency for the glucose solutions in the temperature range 15–60 °C, the sensitivity of the vacuum heat-treated sensor is higher than that of the normal and water heat-treated sensors.

In this work, to further investigate the prepared sensors application in bioanalysis, we examined the response of the sensors to the Chlorella pyrenoidosa solutions. In Fig. 4(h), we note that the absorption spectra of the vacuum heat-treated sensor is better than that of the normal POF sensor and the water heat-treated sensor because the higher intensity of the EW produces a larger EW attenuation by the Chlorella pyrenoidosa and the lower RI induces larger EW penetration depth and EW optical path length at the surface of fiber. In Fig. 4(i), the RCTLI_VIIIs of the prepared D-shaped POF sensors decrease with increasing Chlorella pyrenoidosa concentration because the contribution of the light attenuation at fiber-solution interface is caused by the absorption and scattering of the Chlorella pyrenoidosa (the average diameter was approximately 5.4 μm, as shown in Fig. 4(j)) and the attenuation increases with increasing Chlorella pyrenoidosa concentration. Importantly, the sensitivity of D-shaped POF EW sensors subjected vacuum heat treatment is also higher than that of the normal POF sensor (about 1.6 times) and water heat-treated sensors (about 1.9 times) in measurement of Chlorella pyrenoidosa solutions. The better sensitivity of the vacuum heat-treated is due to the larger ΔV, ΔDP and ΔLew (see Tab. 1), the better spectral transmission and transmitted light intensity, and appropriate surface roughness. These facts further verify that vacuum heat treatment technology can help to create high-sensitivity PO FEW sensors for application in the fields of chemistry, biochemistry, biomedical, and environmental sciences.

Conclusions

While POF EW sensors have been rapidly developed in recent decades and have been widely used in various areas, the measurement consistency and sensitivity of POF EW sensors are still affected by their thermal stability and water absorption. Hence, we explored the mechanism of the effects of heat treatments on the physical and optical properties of POF EW sensors. We summarize our findings as follows.

The spectral transmission and transmitted light intensity of the fibers subjected to water heat treatments experienced a strong attenuation because the absorbed water molecules are uniformly dispersed in the fiber core, which led to large deformations (length, diameter and width), large surface defects, and changing the core and cladding modes. The appearance of conjugated carbonyl groups by thermal oxidation reactions leads to a significant increase in electronic transition absorption loss caused by the n → π* transition of the carbonyl group (>C = O); however, the vacuum heat-treated POF showed little attenuation because the POF was only affected by a slight deformation, increase in surface roughness, and fluctuations of the density caused by the polymer chain shrinkage and thermal decomposition of the residual monomers.

The D-shaped POF EW sensors subjected water/vacuum heat treatment at temperature 110 °C for 3 h showed constant transmitted light intensity and temperature-independent measuring consistency in the glucose solutions in the temperature range 15–60 °C because the polymer chain reorientation, glass transition, and thermal decomposition of the residual monomers had been completed. In particular, for the POFs subjected to water heat treatment, the absorption of water and thermal oxidation reaction of the PMMA in the POF had also been completed, and these parameters were not affected by temperature variations over the range 15–60 °C. The sensitivity of the sensors subjected to vacuum heat treatment is still higher than that of the water heat-treated sensors in measurement of glucose and Chlorella pyrenoidosa analytes, because of the lager ΔV, ΔDP and ΔLew, the better spectral transmission and transmitted light intensity, and appropriate surface roughness when the POF was heat-treated in vacuum at 110 °C for 3 h.

In summary, our investigation of the mechanism of the effects of heat treatments on measurement consistency and sensitivity of POF EW sensors can be used to significantly improve the performance of POF-based sensors and extend their application in optical sensing. We believe that the valuable results of this research can significantly contribute to the development of POF-based FOEW sensors, telecommunication and data networks.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (NSFC) (no. 51406020, 51276209), the Key Projects of the National Natural Science Foundation of China (no. 51136007), the Research Project of Chinese Ministry of Education (no. 113053A), and the Youth Fund Project Supported by Department of Education of Guizhou Province under Grant (No. KY[2015]457).

References and links

1. A. F. Garito, J. Wang, and R. Gao, “Effects of random perturbations in plastic optical fibers,” Science 281(5379), 962–967 (1998). [CrossRef]   [PubMed]  

2. Y. Koike and M. Asai, “The future of plastic optical fiber,” NPG Asia Mater. 1(1), 22–28 (2009). [CrossRef]  

3. M. Rahlves, M. Rezem, K. Boroz, S. Schlangen, E. Reithmeier, and B. Roth, “Flexible, fast, and low-cost production process for polymer based diffractive optics,” Opt. Express 23(3), 3614–3622 (2015). [CrossRef]   [PubMed]  

4. N. Zhong, Q. Liao, X. Zhu, M. Zhao, Y. Huang, and R. Chen, “Temperature-independent polymer optical fiber evanescent wave sensor,” Sci. Rep. 5, 11508 (2015). [CrossRef]   [PubMed]  

5. L. Beverina, M. Crippa, M. Sassi, A. Monguzzi, F. Meinardi, R. Tubino, and G. A. Pagani, “Perfluorinated nitrosopyrazolone-based erbium chelates: a new efficient solution processable NIR emitter,” Chem. Commun. (Camb.) 34(34), 5103–5105 (2009). [CrossRef]   [PubMed]  

6. Y. Takezawa, S. Tanno, N. Taketani, S. Ohara, and H. Asano, “Analysis of thermal degradation for plastic optical fibers,” J. Appl. Polym. Sci. 42(10), 2811–2817 (1991). [CrossRef]  

7. K. Makino, T. Kado, A. Inoue, and Y. Koike, “Low loss graded index polymer optical fiber with high stability under damp heat conditions,” Opt. Express 20(12), 12893–12898 (2012). [CrossRef]   [PubMed]  

8. M. Sato, M. Hirai, T. Ishigure, and Y. Koike, “High temperature resistant graded-index polymer optical fiber,” J. Lightwave Technol. 18(12), 2139–2145 (2000). [CrossRef]  

9. J. He, Z. M. Liu, X. C. Ai, G. Y. Yang, B. X. Han, and J. Xu, “Stability of high-bandwidth graded-index polymer optical fiber,” J. Appl. Polym. Sci. 91(4), 2330–2334 (2004). [CrossRef]  

10. P. Stajanca, O. Cetinkaya, M. Schukar, and K. Krebber, “Molecular alignment relaxation in polymer optical fibers for sensing applications,” Opt. Fiber Technol. 28, 11–17 (2016). [CrossRef]  

11. W. Yuan, A. Stefani, M. Bache, T. Jacobsen, B. Rose, N. Herholdt-Rasmussen, F. K. Nielsen, S. Andresen, O. B. Sørensen, K. S. Hansen, and O. Bang, “Improved thermal and strain performance of annealed polymer optical fiber Bragg gratings,” Opt. Commun. 284(1), 176–182 (2011). [CrossRef]  

12. A. Fasano, G. Woyessa, P. Stajanca, C. Markos, A. Stefani, K. Nielsen, H. K. Rasmussen, K. Krebber, and O. Bang, “Fabrication and characterization of polycarbonate microstructured polymer optical fibers for high-temperature-resistant fiber Bragg grating strain sensors,” Opt. Mater. Express 6(2), 649–659 (2016). [CrossRef]  

13. G. Woyessa, K. Nielsen, A. Stefani, C. Markos, and O. Bang, “Temperature insensitive hysteresis free highly sensitive polymer optical fiber Bragg grating humidity sensor,” Opt. Express 24(2), 1206–1213 (2016). [CrossRef]   [PubMed]  

14. G. Woyessa, A. Fasano, A. Stefani, C. Markos, K. Nielsen, H. K. Rasmussen, and O. Bang, “Single mode step-index polymer optical fiber for humidity insensitive high temperature fiber Bragg grating sensors,” Opt. Express 24(2), 1253–1260 (2016). [CrossRef]   [PubMed]  

15. C. Markos, A. Stefani, K. Nielsen, H. K. Rasmussen, W. Yuan, and O. Bang, “High-Tg TOPAS microstructured polymer optical fiber for fiber Bragg grating strain sensing at 110 degrees,” Opt. Express 21(4), 4758–4765 (2013). [CrossRef]   [PubMed]  

16. I. L. Bundalo, K. Nielsen, C. Markos, and O. Bang, “Bragg grating writing in PMMA microstructured polymer optical fibers in less than 7 minutes,” Opt. Express 22(5), 5270–5276 (2014). [CrossRef]   [PubMed]  

17. Y. B. Zhao, D. Y. Wang, X. Q. Guo, and J. G. Xu, “A new spectrum technique based on direct detection of light intensity absorbed,” Sci. China, Ser. Biol. Chem. 41, 239–246 (1998).

18. J. Heo, M. Rodrigues, S. J. Saggese, and G. H. Sigel Jr., “Remote fiber-optic chemical sensing using evanescent-wave interactions in chalcogenide glass fibers,” Appl. Opt. 30(27), 3944–3951 (1991). [CrossRef]   [PubMed]  

19. N. Zhong, X. Zhu, Q. Liao, Y. Wang, R. Chen, and Y. Sun, “Effects of surface roughness on optical properties and sensitivity of fiber-optic evanescent wave sensors,” Appl. Opt. 52(17), 3937–3945 (2013). [CrossRef]   [PubMed]  

20. Q. Liao, L. Li, R. Chen, and X. Zhu, “A novel photobioreactor generating the light/dark cycle to improve microalgae cultivation,” Bioresour. Technol. 161, 186–191 (2014). [CrossRef]   [PubMed]  

21. H. C. Yu, A. Argyros, G. Barton, M. A. van Eijkelenborg, C. Barbe, K. Finnie, L. Kong, F. Ladouceur, and S. McNiven, “Quantum dot and silica nanoparticle doped polymer optical fibers,” Opt. Express 15(16), 9989–9994 (2007). [CrossRef]   [PubMed]  

22. A. G. El-Deen, N. A. M. Barakat, K. A. Khalil, and H. Y. Kim, “Development of multi-channel carbon nanofibers as effective electrosorptive electrodes for a capacitive deionization process,” J. Mater. Chem. A Mater. Energy Sustain. 1(36), 11001–11010 (2013). [CrossRef]  

23. T. Ishigure, M. Sato, A. Kondo, Y. Tsukimori, and Y. Koike, “Graded-index polymer optical fiber with high temperature and high humidity stability,” J. Lightwave Technol. 20(10), 1818–1825 (2002). [CrossRef]  

24. S. O. Han and L. T. Drzal, “Water absorption effects on hydrophilic polymer matrix of carboxyl functionalized glucose resin and epoxy resin,” Eur. Polym. J. 39(9), 1791–1799 (2003). [CrossRef]  

25. M. Ree, T. L. Nunes, and K. J. R. Chen, “Structure and properties of a photosensitive polyimide: Effect of photosensitive group,” J. Polym. Sci. Pol. Phys. 33(3), 453–465 (1995). [CrossRef]  

26. Y. Tamai, H. Tanaka, and K. Nakanishi, “Molecular dynamics study of polymer-water interaction in hydrogels. 2. Hydrogen-bond dynamics,” Macromolecules 29(21), 6761–6769 (1996). [CrossRef]  

27. M. Silva-López, A. Fender, W. N. MacPherson, J. S. Barton, J. D. Jones, D. Zhao, H. Dobb, D. J. Webb, L. Zhang, and I. Bennion, “Strain and temperature sensitivity of a single-mode polymer optical fiber,” Opt. Lett. 30(23), 3129–3131 (2005). [CrossRef]   [PubMed]  

28. C. Sheng, H. Liu, S. Zhu, and D. A. Genov, “Active control of electromagnetic radiation through an enhanced thermo-optic effect,” Sci. Rep. 5, 8835 (2015). [CrossRef]   [PubMed]  

29. C. A. F. Marques, G. D. Peng, and D. J. Webb, “Highly sensitive liquid level monitoring system utilizing polymer fiber Bragg gratings,” Opt. Express 23(5), 6058–6072 (2015). [CrossRef]   [PubMed]  

30. J. B. Puthoff, J. E. Jakes, H. Cao, and D. S. Stone, “Investigation of thermally activated deformation in amorphous PMMA and Zr-Cu-Al bulk metallic glasses with broadband nanoindentation creep,” J. Mater. Res. 24(03), 1279–1290 (2009). [CrossRef]  

31. J. Arrue, J. Zubia, G. Durana, and J. Mateo, “Parameters affecting bending losses in graded-index polymer optical fibers,” IEEE J. Sel. Top. Quant. 7(5), 836–844 (2001). [CrossRef]  

32. E. G. Strekalova, M. G. Mazza, H. E. Stanley, and G. Franzese, “Large decrease of fluctuations for supercooled water in hydrophobic nanoconfinement,” Phys. Rev. Lett. 106(14), 145701 (2011). [CrossRef]   [PubMed]  

33. H. E. Arabi, S. An, and K. Oh, “Fiber optic engine for micro projection display,” Opt. Express 18(5), 4655–4663 (2010). [CrossRef]   [PubMed]  

34. N. Zhong, Q. Liao, X. Zhu, and R. Chen, “A fiber-optic sensor for accurately monitoring biofilm growth in a hydrogen production photobioreactor,” Anal. Chem. 86(8), 3994–4001 (2014). [CrossRef]   [PubMed]  

References

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  1. A. F. Garito, J. Wang, and R. Gao, “Effects of random perturbations in plastic optical fibers,” Science 281(5379), 962–967 (1998).
    [Crossref] [PubMed]
  2. Y. Koike and M. Asai, “The future of plastic optical fiber,” NPG Asia Mater. 1(1), 22–28 (2009).
    [Crossref]
  3. M. Rahlves, M. Rezem, K. Boroz, S. Schlangen, E. Reithmeier, and B. Roth, “Flexible, fast, and low-cost production process for polymer based diffractive optics,” Opt. Express 23(3), 3614–3622 (2015).
    [Crossref] [PubMed]
  4. N. Zhong, Q. Liao, X. Zhu, M. Zhao, Y. Huang, and R. Chen, “Temperature-independent polymer optical fiber evanescent wave sensor,” Sci. Rep. 5, 11508 (2015).
    [Crossref] [PubMed]
  5. L. Beverina, M. Crippa, M. Sassi, A. Monguzzi, F. Meinardi, R. Tubino, and G. A. Pagani, “Perfluorinated nitrosopyrazolone-based erbium chelates: a new efficient solution processable NIR emitter,” Chem. Commun. (Camb.) 34(34), 5103–5105 (2009).
    [Crossref] [PubMed]
  6. Y. Takezawa, S. Tanno, N. Taketani, S. Ohara, and H. Asano, “Analysis of thermal degradation for plastic optical fibers,” J. Appl. Polym. Sci. 42(10), 2811–2817 (1991).
    [Crossref]
  7. K. Makino, T. Kado, A. Inoue, and Y. Koike, “Low loss graded index polymer optical fiber with high stability under damp heat conditions,” Opt. Express 20(12), 12893–12898 (2012).
    [Crossref] [PubMed]
  8. M. Sato, M. Hirai, T. Ishigure, and Y. Koike, “High temperature resistant graded-index polymer optical fiber,” J. Lightwave Technol. 18(12), 2139–2145 (2000).
    [Crossref]
  9. J. He, Z. M. Liu, X. C. Ai, G. Y. Yang, B. X. Han, and J. Xu, “Stability of high-bandwidth graded-index polymer optical fiber,” J. Appl. Polym. Sci. 91(4), 2330–2334 (2004).
    [Crossref]
  10. P. Stajanca, O. Cetinkaya, M. Schukar, and K. Krebber, “Molecular alignment relaxation in polymer optical fibers for sensing applications,” Opt. Fiber Technol. 28, 11–17 (2016).
    [Crossref]
  11. W. Yuan, A. Stefani, M. Bache, T. Jacobsen, B. Rose, N. Herholdt-Rasmussen, F. K. Nielsen, S. Andresen, O. B. Sørensen, K. S. Hansen, and O. Bang, “Improved thermal and strain performance of annealed polymer optical fiber Bragg gratings,” Opt. Commun. 284(1), 176–182 (2011).
    [Crossref]
  12. A. Fasano, G. Woyessa, P. Stajanca, C. Markos, A. Stefani, K. Nielsen, H. K. Rasmussen, K. Krebber, and O. Bang, “Fabrication and characterization of polycarbonate microstructured polymer optical fibers for high-temperature-resistant fiber Bragg grating strain sensors,” Opt. Mater. Express 6(2), 649–659 (2016).
    [Crossref]
  13. G. Woyessa, K. Nielsen, A. Stefani, C. Markos, and O. Bang, “Temperature insensitive hysteresis free highly sensitive polymer optical fiber Bragg grating humidity sensor,” Opt. Express 24(2), 1206–1213 (2016).
    [Crossref] [PubMed]
  14. G. Woyessa, A. Fasano, A. Stefani, C. Markos, K. Nielsen, H. K. Rasmussen, and O. Bang, “Single mode step-index polymer optical fiber for humidity insensitive high temperature fiber Bragg grating sensors,” Opt. Express 24(2), 1253–1260 (2016).
    [Crossref] [PubMed]
  15. C. Markos, A. Stefani, K. Nielsen, H. K. Rasmussen, W. Yuan, and O. Bang, “High-Tg TOPAS microstructured polymer optical fiber for fiber Bragg grating strain sensing at 110 degrees,” Opt. Express 21(4), 4758–4765 (2013).
    [Crossref] [PubMed]
  16. I. L. Bundalo, K. Nielsen, C. Markos, and O. Bang, “Bragg grating writing in PMMA microstructured polymer optical fibers in less than 7 minutes,” Opt. Express 22(5), 5270–5276 (2014).
    [Crossref] [PubMed]
  17. Y. B. Zhao, D. Y. Wang, X. Q. Guo, and J. G. Xu, “A new spectrum technique based on direct detection of light intensity absorbed,” Sci. China, Ser. Biol. Chem. 41, 239–246 (1998).
  18. J. Heo, M. Rodrigues, S. J. Saggese, and G. H. Sigel., “Remote fiber-optic chemical sensing using evanescent-wave interactions in chalcogenide glass fibers,” Appl. Opt. 30(27), 3944–3951 (1991).
    [Crossref] [PubMed]
  19. N. Zhong, X. Zhu, Q. Liao, Y. Wang, R. Chen, and Y. Sun, “Effects of surface roughness on optical properties and sensitivity of fiber-optic evanescent wave sensors,” Appl. Opt. 52(17), 3937–3945 (2013).
    [Crossref] [PubMed]
  20. Q. Liao, L. Li, R. Chen, and X. Zhu, “A novel photobioreactor generating the light/dark cycle to improve microalgae cultivation,” Bioresour. Technol. 161, 186–191 (2014).
    [Crossref] [PubMed]
  21. H. C. Yu, A. Argyros, G. Barton, M. A. van Eijkelenborg, C. Barbe, K. Finnie, L. Kong, F. Ladouceur, and S. McNiven, “Quantum dot and silica nanoparticle doped polymer optical fibers,” Opt. Express 15(16), 9989–9994 (2007).
    [Crossref] [PubMed]
  22. A. G. El-Deen, N. A. M. Barakat, K. A. Khalil, and H. Y. Kim, “Development of multi-channel carbon nanofibers as effective electrosorptive electrodes for a capacitive deionization process,” J. Mater. Chem. A Mater. Energy Sustain. 1(36), 11001–11010 (2013).
    [Crossref]
  23. T. Ishigure, M. Sato, A. Kondo, Y. Tsukimori, and Y. Koike, “Graded-index polymer optical fiber with high temperature and high humidity stability,” J. Lightwave Technol. 20(10), 1818–1825 (2002).
    [Crossref]
  24. S. O. Han and L. T. Drzal, “Water absorption effects on hydrophilic polymer matrix of carboxyl functionalized glucose resin and epoxy resin,” Eur. Polym. J. 39(9), 1791–1799 (2003).
    [Crossref]
  25. M. Ree, T. L. Nunes, and K. J. R. Chen, “Structure and properties of a photosensitive polyimide: Effect of photosensitive group,” J. Polym. Sci. Pol. Phys. 33(3), 453–465 (1995).
    [Crossref]
  26. Y. Tamai, H. Tanaka, and K. Nakanishi, “Molecular dynamics study of polymer-water interaction in hydrogels. 2. Hydrogen-bond dynamics,” Macromolecules 29(21), 6761–6769 (1996).
    [Crossref]
  27. M. Silva-López, A. Fender, W. N. MacPherson, J. S. Barton, J. D. Jones, D. Zhao, H. Dobb, D. J. Webb, L. Zhang, and I. Bennion, “Strain and temperature sensitivity of a single-mode polymer optical fiber,” Opt. Lett. 30(23), 3129–3131 (2005).
    [Crossref] [PubMed]
  28. C. Sheng, H. Liu, S. Zhu, and D. A. Genov, “Active control of electromagnetic radiation through an enhanced thermo-optic effect,” Sci. Rep. 5, 8835 (2015).
    [Crossref] [PubMed]
  29. C. A. F. Marques, G. D. Peng, and D. J. Webb, “Highly sensitive liquid level monitoring system utilizing polymer fiber Bragg gratings,” Opt. Express 23(5), 6058–6072 (2015).
    [Crossref] [PubMed]
  30. J. B. Puthoff, J. E. Jakes, H. Cao, and D. S. Stone, “Investigation of thermally activated deformation in amorphous PMMA and Zr-Cu-Al bulk metallic glasses with broadband nanoindentation creep,” J. Mater. Res. 24(03), 1279–1290 (2009).
    [Crossref]
  31. J. Arrue, J. Zubia, G. Durana, and J. Mateo, “Parameters affecting bending losses in graded-index polymer optical fibers,” IEEE J. Sel. Top. Quant. 7(5), 836–844 (2001).
    [Crossref]
  32. E. G. Strekalova, M. G. Mazza, H. E. Stanley, and G. Franzese, “Large decrease of fluctuations for supercooled water in hydrophobic nanoconfinement,” Phys. Rev. Lett. 106(14), 145701 (2011).
    [Crossref] [PubMed]
  33. H. E. Arabi, S. An, and K. Oh, “Fiber optic engine for micro projection display,” Opt. Express 18(5), 4655–4663 (2010).
    [Crossref] [PubMed]
  34. N. Zhong, Q. Liao, X. Zhu, and R. Chen, “A fiber-optic sensor for accurately monitoring biofilm growth in a hydrogen production photobioreactor,” Anal. Chem. 86(8), 3994–4001 (2014).
    [Crossref] [PubMed]

2016 (4)

2015 (4)

M. Rahlves, M. Rezem, K. Boroz, S. Schlangen, E. Reithmeier, and B. Roth, “Flexible, fast, and low-cost production process for polymer based diffractive optics,” Opt. Express 23(3), 3614–3622 (2015).
[Crossref] [PubMed]

N. Zhong, Q. Liao, X. Zhu, M. Zhao, Y. Huang, and R. Chen, “Temperature-independent polymer optical fiber evanescent wave sensor,” Sci. Rep. 5, 11508 (2015).
[Crossref] [PubMed]

C. Sheng, H. Liu, S. Zhu, and D. A. Genov, “Active control of electromagnetic radiation through an enhanced thermo-optic effect,” Sci. Rep. 5, 8835 (2015).
[Crossref] [PubMed]

C. A. F. Marques, G. D. Peng, and D. J. Webb, “Highly sensitive liquid level monitoring system utilizing polymer fiber Bragg gratings,” Opt. Express 23(5), 6058–6072 (2015).
[Crossref] [PubMed]

2014 (3)

Q. Liao, L. Li, R. Chen, and X. Zhu, “A novel photobioreactor generating the light/dark cycle to improve microalgae cultivation,” Bioresour. Technol. 161, 186–191 (2014).
[Crossref] [PubMed]

I. L. Bundalo, K. Nielsen, C. Markos, and O. Bang, “Bragg grating writing in PMMA microstructured polymer optical fibers in less than 7 minutes,” Opt. Express 22(5), 5270–5276 (2014).
[Crossref] [PubMed]

N. Zhong, Q. Liao, X. Zhu, and R. Chen, “A fiber-optic sensor for accurately monitoring biofilm growth in a hydrogen production photobioreactor,” Anal. Chem. 86(8), 3994–4001 (2014).
[Crossref] [PubMed]

2013 (3)

2012 (1)

2011 (2)

W. Yuan, A. Stefani, M. Bache, T. Jacobsen, B. Rose, N. Herholdt-Rasmussen, F. K. Nielsen, S. Andresen, O. B. Sørensen, K. S. Hansen, and O. Bang, “Improved thermal and strain performance of annealed polymer optical fiber Bragg gratings,” Opt. Commun. 284(1), 176–182 (2011).
[Crossref]

E. G. Strekalova, M. G. Mazza, H. E. Stanley, and G. Franzese, “Large decrease of fluctuations for supercooled water in hydrophobic nanoconfinement,” Phys. Rev. Lett. 106(14), 145701 (2011).
[Crossref] [PubMed]

2010 (1)

2009 (3)

J. B. Puthoff, J. E. Jakes, H. Cao, and D. S. Stone, “Investigation of thermally activated deformation in amorphous PMMA and Zr-Cu-Al bulk metallic glasses with broadband nanoindentation creep,” J. Mater. Res. 24(03), 1279–1290 (2009).
[Crossref]

Y. Koike and M. Asai, “The future of plastic optical fiber,” NPG Asia Mater. 1(1), 22–28 (2009).
[Crossref]

L. Beverina, M. Crippa, M. Sassi, A. Monguzzi, F. Meinardi, R. Tubino, and G. A. Pagani, “Perfluorinated nitrosopyrazolone-based erbium chelates: a new efficient solution processable NIR emitter,” Chem. Commun. (Camb.) 34(34), 5103–5105 (2009).
[Crossref] [PubMed]

2007 (1)

2005 (1)

2004 (1)

J. He, Z. M. Liu, X. C. Ai, G. Y. Yang, B. X. Han, and J. Xu, “Stability of high-bandwidth graded-index polymer optical fiber,” J. Appl. Polym. Sci. 91(4), 2330–2334 (2004).
[Crossref]

2003 (1)

S. O. Han and L. T. Drzal, “Water absorption effects on hydrophilic polymer matrix of carboxyl functionalized glucose resin and epoxy resin,” Eur. Polym. J. 39(9), 1791–1799 (2003).
[Crossref]

2002 (1)

2001 (1)

J. Arrue, J. Zubia, G. Durana, and J. Mateo, “Parameters affecting bending losses in graded-index polymer optical fibers,” IEEE J. Sel. Top. Quant. 7(5), 836–844 (2001).
[Crossref]

2000 (1)

1998 (2)

A. F. Garito, J. Wang, and R. Gao, “Effects of random perturbations in plastic optical fibers,” Science 281(5379), 962–967 (1998).
[Crossref] [PubMed]

Y. B. Zhao, D. Y. Wang, X. Q. Guo, and J. G. Xu, “A new spectrum technique based on direct detection of light intensity absorbed,” Sci. China, Ser. Biol. Chem. 41, 239–246 (1998).

1996 (1)

Y. Tamai, H. Tanaka, and K. Nakanishi, “Molecular dynamics study of polymer-water interaction in hydrogels. 2. Hydrogen-bond dynamics,” Macromolecules 29(21), 6761–6769 (1996).
[Crossref]

1995 (1)

M. Ree, T. L. Nunes, and K. J. R. Chen, “Structure and properties of a photosensitive polyimide: Effect of photosensitive group,” J. Polym. Sci. Pol. Phys. 33(3), 453–465 (1995).
[Crossref]

1991 (2)

J. Heo, M. Rodrigues, S. J. Saggese, and G. H. Sigel., “Remote fiber-optic chemical sensing using evanescent-wave interactions in chalcogenide glass fibers,” Appl. Opt. 30(27), 3944–3951 (1991).
[Crossref] [PubMed]

Y. Takezawa, S. Tanno, N. Taketani, S. Ohara, and H. Asano, “Analysis of thermal degradation for plastic optical fibers,” J. Appl. Polym. Sci. 42(10), 2811–2817 (1991).
[Crossref]

Ai, X. C.

J. He, Z. M. Liu, X. C. Ai, G. Y. Yang, B. X. Han, and J. Xu, “Stability of high-bandwidth graded-index polymer optical fiber,” J. Appl. Polym. Sci. 91(4), 2330–2334 (2004).
[Crossref]

An, S.

Andresen, S.

W. Yuan, A. Stefani, M. Bache, T. Jacobsen, B. Rose, N. Herholdt-Rasmussen, F. K. Nielsen, S. Andresen, O. B. Sørensen, K. S. Hansen, and O. Bang, “Improved thermal and strain performance of annealed polymer optical fiber Bragg gratings,” Opt. Commun. 284(1), 176–182 (2011).
[Crossref]

Arabi, H. E.

Argyros, A.

Arrue, J.

J. Arrue, J. Zubia, G. Durana, and J. Mateo, “Parameters affecting bending losses in graded-index polymer optical fibers,” IEEE J. Sel. Top. Quant. 7(5), 836–844 (2001).
[Crossref]

Asai, M.

Y. Koike and M. Asai, “The future of plastic optical fiber,” NPG Asia Mater. 1(1), 22–28 (2009).
[Crossref]

Asano, H.

Y. Takezawa, S. Tanno, N. Taketani, S. Ohara, and H. Asano, “Analysis of thermal degradation for plastic optical fibers,” J. Appl. Polym. Sci. 42(10), 2811–2817 (1991).
[Crossref]

Bache, M.

W. Yuan, A. Stefani, M. Bache, T. Jacobsen, B. Rose, N. Herholdt-Rasmussen, F. K. Nielsen, S. Andresen, O. B. Sørensen, K. S. Hansen, and O. Bang, “Improved thermal and strain performance of annealed polymer optical fiber Bragg gratings,” Opt. Commun. 284(1), 176–182 (2011).
[Crossref]

Bang, O.

A. Fasano, G. Woyessa, P. Stajanca, C. Markos, A. Stefani, K. Nielsen, H. K. Rasmussen, K. Krebber, and O. Bang, “Fabrication and characterization of polycarbonate microstructured polymer optical fibers for high-temperature-resistant fiber Bragg grating strain sensors,” Opt. Mater. Express 6(2), 649–659 (2016).
[Crossref]

G. Woyessa, K. Nielsen, A. Stefani, C. Markos, and O. Bang, “Temperature insensitive hysteresis free highly sensitive polymer optical fiber Bragg grating humidity sensor,” Opt. Express 24(2), 1206–1213 (2016).
[Crossref] [PubMed]

G. Woyessa, A. Fasano, A. Stefani, C. Markos, K. Nielsen, H. K. Rasmussen, and O. Bang, “Single mode step-index polymer optical fiber for humidity insensitive high temperature fiber Bragg grating sensors,” Opt. Express 24(2), 1253–1260 (2016).
[Crossref] [PubMed]

I. L. Bundalo, K. Nielsen, C. Markos, and O. Bang, “Bragg grating writing in PMMA microstructured polymer optical fibers in less than 7 minutes,” Opt. Express 22(5), 5270–5276 (2014).
[Crossref] [PubMed]

C. Markos, A. Stefani, K. Nielsen, H. K. Rasmussen, W. Yuan, and O. Bang, “High-Tg TOPAS microstructured polymer optical fiber for fiber Bragg grating strain sensing at 110 degrees,” Opt. Express 21(4), 4758–4765 (2013).
[Crossref] [PubMed]

W. Yuan, A. Stefani, M. Bache, T. Jacobsen, B. Rose, N. Herholdt-Rasmussen, F. K. Nielsen, S. Andresen, O. B. Sørensen, K. S. Hansen, and O. Bang, “Improved thermal and strain performance of annealed polymer optical fiber Bragg gratings,” Opt. Commun. 284(1), 176–182 (2011).
[Crossref]

Barakat, N. A. M.

A. G. El-Deen, N. A. M. Barakat, K. A. Khalil, and H. Y. Kim, “Development of multi-channel carbon nanofibers as effective electrosorptive electrodes for a capacitive deionization process,” J. Mater. Chem. A Mater. Energy Sustain. 1(36), 11001–11010 (2013).
[Crossref]

Barbe, C.

Barton, G.

Barton, J. S.

Bennion, I.

Beverina, L.

L. Beverina, M. Crippa, M. Sassi, A. Monguzzi, F. Meinardi, R. Tubino, and G. A. Pagani, “Perfluorinated nitrosopyrazolone-based erbium chelates: a new efficient solution processable NIR emitter,” Chem. Commun. (Camb.) 34(34), 5103–5105 (2009).
[Crossref] [PubMed]

Boroz, K.

Bundalo, I. L.

Cao, H.

J. B. Puthoff, J. E. Jakes, H. Cao, and D. S. Stone, “Investigation of thermally activated deformation in amorphous PMMA and Zr-Cu-Al bulk metallic glasses with broadband nanoindentation creep,” J. Mater. Res. 24(03), 1279–1290 (2009).
[Crossref]

Cetinkaya, O.

P. Stajanca, O. Cetinkaya, M. Schukar, and K. Krebber, “Molecular alignment relaxation in polymer optical fibers for sensing applications,” Opt. Fiber Technol. 28, 11–17 (2016).
[Crossref]

Chen, K. J. R.

M. Ree, T. L. Nunes, and K. J. R. Chen, “Structure and properties of a photosensitive polyimide: Effect of photosensitive group,” J. Polym. Sci. Pol. Phys. 33(3), 453–465 (1995).
[Crossref]

Chen, R.

N. Zhong, Q. Liao, X. Zhu, M. Zhao, Y. Huang, and R. Chen, “Temperature-independent polymer optical fiber evanescent wave sensor,” Sci. Rep. 5, 11508 (2015).
[Crossref] [PubMed]

Q. Liao, L. Li, R. Chen, and X. Zhu, “A novel photobioreactor generating the light/dark cycle to improve microalgae cultivation,” Bioresour. Technol. 161, 186–191 (2014).
[Crossref] [PubMed]

N. Zhong, Q. Liao, X. Zhu, and R. Chen, “A fiber-optic sensor for accurately monitoring biofilm growth in a hydrogen production photobioreactor,” Anal. Chem. 86(8), 3994–4001 (2014).
[Crossref] [PubMed]

N. Zhong, X. Zhu, Q. Liao, Y. Wang, R. Chen, and Y. Sun, “Effects of surface roughness on optical properties and sensitivity of fiber-optic evanescent wave sensors,” Appl. Opt. 52(17), 3937–3945 (2013).
[Crossref] [PubMed]

Crippa, M.

L. Beverina, M. Crippa, M. Sassi, A. Monguzzi, F. Meinardi, R. Tubino, and G. A. Pagani, “Perfluorinated nitrosopyrazolone-based erbium chelates: a new efficient solution processable NIR emitter,” Chem. Commun. (Camb.) 34(34), 5103–5105 (2009).
[Crossref] [PubMed]

Dobb, H.

Drzal, L. T.

S. O. Han and L. T. Drzal, “Water absorption effects on hydrophilic polymer matrix of carboxyl functionalized glucose resin and epoxy resin,” Eur. Polym. J. 39(9), 1791–1799 (2003).
[Crossref]

Durana, G.

J. Arrue, J. Zubia, G. Durana, and J. Mateo, “Parameters affecting bending losses in graded-index polymer optical fibers,” IEEE J. Sel. Top. Quant. 7(5), 836–844 (2001).
[Crossref]

El-Deen, A. G.

A. G. El-Deen, N. A. M. Barakat, K. A. Khalil, and H. Y. Kim, “Development of multi-channel carbon nanofibers as effective electrosorptive electrodes for a capacitive deionization process,” J. Mater. Chem. A Mater. Energy Sustain. 1(36), 11001–11010 (2013).
[Crossref]

Fasano, A.

Fender, A.

Finnie, K.

Franzese, G.

E. G. Strekalova, M. G. Mazza, H. E. Stanley, and G. Franzese, “Large decrease of fluctuations for supercooled water in hydrophobic nanoconfinement,” Phys. Rev. Lett. 106(14), 145701 (2011).
[Crossref] [PubMed]

Gao, R.

A. F. Garito, J. Wang, and R. Gao, “Effects of random perturbations in plastic optical fibers,” Science 281(5379), 962–967 (1998).
[Crossref] [PubMed]

Garito, A. F.

A. F. Garito, J. Wang, and R. Gao, “Effects of random perturbations in plastic optical fibers,” Science 281(5379), 962–967 (1998).
[Crossref] [PubMed]

Genov, D. A.

C. Sheng, H. Liu, S. Zhu, and D. A. Genov, “Active control of electromagnetic radiation through an enhanced thermo-optic effect,” Sci. Rep. 5, 8835 (2015).
[Crossref] [PubMed]

Guo, X. Q.

Y. B. Zhao, D. Y. Wang, X. Q. Guo, and J. G. Xu, “A new spectrum technique based on direct detection of light intensity absorbed,” Sci. China, Ser. Biol. Chem. 41, 239–246 (1998).

Han, B. X.

J. He, Z. M. Liu, X. C. Ai, G. Y. Yang, B. X. Han, and J. Xu, “Stability of high-bandwidth graded-index polymer optical fiber,” J. Appl. Polym. Sci. 91(4), 2330–2334 (2004).
[Crossref]

Han, S. O.

S. O. Han and L. T. Drzal, “Water absorption effects on hydrophilic polymer matrix of carboxyl functionalized glucose resin and epoxy resin,” Eur. Polym. J. 39(9), 1791–1799 (2003).
[Crossref]

Hansen, K. S.

W. Yuan, A. Stefani, M. Bache, T. Jacobsen, B. Rose, N. Herholdt-Rasmussen, F. K. Nielsen, S. Andresen, O. B. Sørensen, K. S. Hansen, and O. Bang, “Improved thermal and strain performance of annealed polymer optical fiber Bragg gratings,” Opt. Commun. 284(1), 176–182 (2011).
[Crossref]

He, J.

J. He, Z. M. Liu, X. C. Ai, G. Y. Yang, B. X. Han, and J. Xu, “Stability of high-bandwidth graded-index polymer optical fiber,” J. Appl. Polym. Sci. 91(4), 2330–2334 (2004).
[Crossref]

Heo, J.

Herholdt-Rasmussen, N.

W. Yuan, A. Stefani, M. Bache, T. Jacobsen, B. Rose, N. Herholdt-Rasmussen, F. K. Nielsen, S. Andresen, O. B. Sørensen, K. S. Hansen, and O. Bang, “Improved thermal and strain performance of annealed polymer optical fiber Bragg gratings,” Opt. Commun. 284(1), 176–182 (2011).
[Crossref]

Hirai, M.

Huang, Y.

N. Zhong, Q. Liao, X. Zhu, M. Zhao, Y. Huang, and R. Chen, “Temperature-independent polymer optical fiber evanescent wave sensor,” Sci. Rep. 5, 11508 (2015).
[Crossref] [PubMed]

Inoue, A.

Ishigure, T.

Jacobsen, T.

W. Yuan, A. Stefani, M. Bache, T. Jacobsen, B. Rose, N. Herholdt-Rasmussen, F. K. Nielsen, S. Andresen, O. B. Sørensen, K. S. Hansen, and O. Bang, “Improved thermal and strain performance of annealed polymer optical fiber Bragg gratings,” Opt. Commun. 284(1), 176–182 (2011).
[Crossref]

Jakes, J. E.

J. B. Puthoff, J. E. Jakes, H. Cao, and D. S. Stone, “Investigation of thermally activated deformation in amorphous PMMA and Zr-Cu-Al bulk metallic glasses with broadband nanoindentation creep,” J. Mater. Res. 24(03), 1279–1290 (2009).
[Crossref]

Jones, J. D.

Kado, T.

Khalil, K. A.

A. G. El-Deen, N. A. M. Barakat, K. A. Khalil, and H. Y. Kim, “Development of multi-channel carbon nanofibers as effective electrosorptive electrodes for a capacitive deionization process,” J. Mater. Chem. A Mater. Energy Sustain. 1(36), 11001–11010 (2013).
[Crossref]

Kim, H. Y.

A. G. El-Deen, N. A. M. Barakat, K. A. Khalil, and H. Y. Kim, “Development of multi-channel carbon nanofibers as effective electrosorptive electrodes for a capacitive deionization process,” J. Mater. Chem. A Mater. Energy Sustain. 1(36), 11001–11010 (2013).
[Crossref]

Koike, Y.

Kondo, A.

Kong, L.

Krebber, K.

Ladouceur, F.

Li, L.

Q. Liao, L. Li, R. Chen, and X. Zhu, “A novel photobioreactor generating the light/dark cycle to improve microalgae cultivation,” Bioresour. Technol. 161, 186–191 (2014).
[Crossref] [PubMed]

Liao, Q.

N. Zhong, Q. Liao, X. Zhu, M. Zhao, Y. Huang, and R. Chen, “Temperature-independent polymer optical fiber evanescent wave sensor,” Sci. Rep. 5, 11508 (2015).
[Crossref] [PubMed]

Q. Liao, L. Li, R. Chen, and X. Zhu, “A novel photobioreactor generating the light/dark cycle to improve microalgae cultivation,” Bioresour. Technol. 161, 186–191 (2014).
[Crossref] [PubMed]

N. Zhong, Q. Liao, X. Zhu, and R. Chen, “A fiber-optic sensor for accurately monitoring biofilm growth in a hydrogen production photobioreactor,” Anal. Chem. 86(8), 3994–4001 (2014).
[Crossref] [PubMed]

N. Zhong, X. Zhu, Q. Liao, Y. Wang, R. Chen, and Y. Sun, “Effects of surface roughness on optical properties and sensitivity of fiber-optic evanescent wave sensors,” Appl. Opt. 52(17), 3937–3945 (2013).
[Crossref] [PubMed]

Liu, H.

C. Sheng, H. Liu, S. Zhu, and D. A. Genov, “Active control of electromagnetic radiation through an enhanced thermo-optic effect,” Sci. Rep. 5, 8835 (2015).
[Crossref] [PubMed]

Liu, Z. M.

J. He, Z. M. Liu, X. C. Ai, G. Y. Yang, B. X. Han, and J. Xu, “Stability of high-bandwidth graded-index polymer optical fiber,” J. Appl. Polym. Sci. 91(4), 2330–2334 (2004).
[Crossref]

MacPherson, W. N.

Makino, K.

Markos, C.

Marques, C. A. F.

Mateo, J.

J. Arrue, J. Zubia, G. Durana, and J. Mateo, “Parameters affecting bending losses in graded-index polymer optical fibers,” IEEE J. Sel. Top. Quant. 7(5), 836–844 (2001).
[Crossref]

Mazza, M. G.

E. G. Strekalova, M. G. Mazza, H. E. Stanley, and G. Franzese, “Large decrease of fluctuations for supercooled water in hydrophobic nanoconfinement,” Phys. Rev. Lett. 106(14), 145701 (2011).
[Crossref] [PubMed]

McNiven, S.

Meinardi, F.

L. Beverina, M. Crippa, M. Sassi, A. Monguzzi, F. Meinardi, R. Tubino, and G. A. Pagani, “Perfluorinated nitrosopyrazolone-based erbium chelates: a new efficient solution processable NIR emitter,” Chem. Commun. (Camb.) 34(34), 5103–5105 (2009).
[Crossref] [PubMed]

Monguzzi, A.

L. Beverina, M. Crippa, M. Sassi, A. Monguzzi, F. Meinardi, R. Tubino, and G. A. Pagani, “Perfluorinated nitrosopyrazolone-based erbium chelates: a new efficient solution processable NIR emitter,” Chem. Commun. (Camb.) 34(34), 5103–5105 (2009).
[Crossref] [PubMed]

Nakanishi, K.

Y. Tamai, H. Tanaka, and K. Nakanishi, “Molecular dynamics study of polymer-water interaction in hydrogels. 2. Hydrogen-bond dynamics,” Macromolecules 29(21), 6761–6769 (1996).
[Crossref]

Nielsen, F. K.

W. Yuan, A. Stefani, M. Bache, T. Jacobsen, B. Rose, N. Herholdt-Rasmussen, F. K. Nielsen, S. Andresen, O. B. Sørensen, K. S. Hansen, and O. Bang, “Improved thermal and strain performance of annealed polymer optical fiber Bragg gratings,” Opt. Commun. 284(1), 176–182 (2011).
[Crossref]

Nielsen, K.

Nunes, T. L.

M. Ree, T. L. Nunes, and K. J. R. Chen, “Structure and properties of a photosensitive polyimide: Effect of photosensitive group,” J. Polym. Sci. Pol. Phys. 33(3), 453–465 (1995).
[Crossref]

Oh, K.

Ohara, S.

Y. Takezawa, S. Tanno, N. Taketani, S. Ohara, and H. Asano, “Analysis of thermal degradation for plastic optical fibers,” J. Appl. Polym. Sci. 42(10), 2811–2817 (1991).
[Crossref]

Pagani, G. A.

L. Beverina, M. Crippa, M. Sassi, A. Monguzzi, F. Meinardi, R. Tubino, and G. A. Pagani, “Perfluorinated nitrosopyrazolone-based erbium chelates: a new efficient solution processable NIR emitter,” Chem. Commun. (Camb.) 34(34), 5103–5105 (2009).
[Crossref] [PubMed]

Peng, G. D.

Puthoff, J. B.

J. B. Puthoff, J. E. Jakes, H. Cao, and D. S. Stone, “Investigation of thermally activated deformation in amorphous PMMA and Zr-Cu-Al bulk metallic glasses with broadband nanoindentation creep,” J. Mater. Res. 24(03), 1279–1290 (2009).
[Crossref]

Rahlves, M.

Rasmussen, H. K.

Ree, M.

M. Ree, T. L. Nunes, and K. J. R. Chen, “Structure and properties of a photosensitive polyimide: Effect of photosensitive group,” J. Polym. Sci. Pol. Phys. 33(3), 453–465 (1995).
[Crossref]

Reithmeier, E.

Rezem, M.

Rodrigues, M.

Rose, B.

W. Yuan, A. Stefani, M. Bache, T. Jacobsen, B. Rose, N. Herholdt-Rasmussen, F. K. Nielsen, S. Andresen, O. B. Sørensen, K. S. Hansen, and O. Bang, “Improved thermal and strain performance of annealed polymer optical fiber Bragg gratings,” Opt. Commun. 284(1), 176–182 (2011).
[Crossref]

Roth, B.

Saggese, S. J.

Sassi, M.

L. Beverina, M. Crippa, M. Sassi, A. Monguzzi, F. Meinardi, R. Tubino, and G. A. Pagani, “Perfluorinated nitrosopyrazolone-based erbium chelates: a new efficient solution processable NIR emitter,” Chem. Commun. (Camb.) 34(34), 5103–5105 (2009).
[Crossref] [PubMed]

Sato, M.

Schlangen, S.

Schukar, M.

P. Stajanca, O. Cetinkaya, M. Schukar, and K. Krebber, “Molecular alignment relaxation in polymer optical fibers for sensing applications,” Opt. Fiber Technol. 28, 11–17 (2016).
[Crossref]

Sheng, C.

C. Sheng, H. Liu, S. Zhu, and D. A. Genov, “Active control of electromagnetic radiation through an enhanced thermo-optic effect,” Sci. Rep. 5, 8835 (2015).
[Crossref] [PubMed]

Sigel, G. H.

Silva-López, M.

Sørensen, O. B.

W. Yuan, A. Stefani, M. Bache, T. Jacobsen, B. Rose, N. Herholdt-Rasmussen, F. K. Nielsen, S. Andresen, O. B. Sørensen, K. S. Hansen, and O. Bang, “Improved thermal and strain performance of annealed polymer optical fiber Bragg gratings,” Opt. Commun. 284(1), 176–182 (2011).
[Crossref]

Stajanca, P.

Stanley, H. E.

E. G. Strekalova, M. G. Mazza, H. E. Stanley, and G. Franzese, “Large decrease of fluctuations for supercooled water in hydrophobic nanoconfinement,” Phys. Rev. Lett. 106(14), 145701 (2011).
[Crossref] [PubMed]

Stefani, A.

Stone, D. S.

J. B. Puthoff, J. E. Jakes, H. Cao, and D. S. Stone, “Investigation of thermally activated deformation in amorphous PMMA and Zr-Cu-Al bulk metallic glasses with broadband nanoindentation creep,” J. Mater. Res. 24(03), 1279–1290 (2009).
[Crossref]

Strekalova, E. G.

E. G. Strekalova, M. G. Mazza, H. E. Stanley, and G. Franzese, “Large decrease of fluctuations for supercooled water in hydrophobic nanoconfinement,” Phys. Rev. Lett. 106(14), 145701 (2011).
[Crossref] [PubMed]

Sun, Y.

Taketani, N.

Y. Takezawa, S. Tanno, N. Taketani, S. Ohara, and H. Asano, “Analysis of thermal degradation for plastic optical fibers,” J. Appl. Polym. Sci. 42(10), 2811–2817 (1991).
[Crossref]

Takezawa, Y.

Y. Takezawa, S. Tanno, N. Taketani, S. Ohara, and H. Asano, “Analysis of thermal degradation for plastic optical fibers,” J. Appl. Polym. Sci. 42(10), 2811–2817 (1991).
[Crossref]

Tamai, Y.

Y. Tamai, H. Tanaka, and K. Nakanishi, “Molecular dynamics study of polymer-water interaction in hydrogels. 2. Hydrogen-bond dynamics,” Macromolecules 29(21), 6761–6769 (1996).
[Crossref]

Tanaka, H.

Y. Tamai, H. Tanaka, and K. Nakanishi, “Molecular dynamics study of polymer-water interaction in hydrogels. 2. Hydrogen-bond dynamics,” Macromolecules 29(21), 6761–6769 (1996).
[Crossref]

Tanno, S.

Y. Takezawa, S. Tanno, N. Taketani, S. Ohara, and H. Asano, “Analysis of thermal degradation for plastic optical fibers,” J. Appl. Polym. Sci. 42(10), 2811–2817 (1991).
[Crossref]

Tsukimori, Y.

Tubino, R.

L. Beverina, M. Crippa, M. Sassi, A. Monguzzi, F. Meinardi, R. Tubino, and G. A. Pagani, “Perfluorinated nitrosopyrazolone-based erbium chelates: a new efficient solution processable NIR emitter,” Chem. Commun. (Camb.) 34(34), 5103–5105 (2009).
[Crossref] [PubMed]

van Eijkelenborg, M. A.

Wang, D. Y.

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C. Markos, A. Stefani, K. Nielsen, H. K. Rasmussen, W. Yuan, and O. Bang, “High-Tg TOPAS microstructured polymer optical fiber for fiber Bragg grating strain sensing at 110 degrees,” Opt. Express 21(4), 4758–4765 (2013).
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W. Yuan, A. Stefani, M. Bache, T. Jacobsen, B. Rose, N. Herholdt-Rasmussen, F. K. Nielsen, S. Andresen, O. B. Sørensen, K. S. Hansen, and O. Bang, “Improved thermal and strain performance of annealed polymer optical fiber Bragg gratings,” Opt. Commun. 284(1), 176–182 (2011).
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Zhong, N.

N. Zhong, Q. Liao, X. Zhu, M. Zhao, Y. Huang, and R. Chen, “Temperature-independent polymer optical fiber evanescent wave sensor,” Sci. Rep. 5, 11508 (2015).
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C. Sheng, H. Liu, S. Zhu, and D. A. Genov, “Active control of electromagnetic radiation through an enhanced thermo-optic effect,” Sci. Rep. 5, 8835 (2015).
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N. Zhong, Q. Liao, X. Zhu, M. Zhao, Y. Huang, and R. Chen, “Temperature-independent polymer optical fiber evanescent wave sensor,” Sci. Rep. 5, 11508 (2015).
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N. Zhong, Q. Liao, X. Zhu, and R. Chen, “A fiber-optic sensor for accurately monitoring biofilm growth in a hydrogen production photobioreactor,” Anal. Chem. 86(8), 3994–4001 (2014).
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N. Zhong, X. Zhu, Q. Liao, Y. Wang, R. Chen, and Y. Sun, “Effects of surface roughness on optical properties and sensitivity of fiber-optic evanescent wave sensors,” Appl. Opt. 52(17), 3937–3945 (2013).
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N. Zhong, Q. Liao, X. Zhu, and R. Chen, “A fiber-optic sensor for accurately monitoring biofilm growth in a hydrogen production photobioreactor,” Anal. Chem. 86(8), 3994–4001 (2014).
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Appl. Opt. (2)

Bioresour. Technol. (1)

Q. Liao, L. Li, R. Chen, and X. Zhu, “A novel photobioreactor generating the light/dark cycle to improve microalgae cultivation,” Bioresour. Technol. 161, 186–191 (2014).
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W. Yuan, A. Stefani, M. Bache, T. Jacobsen, B. Rose, N. Herholdt-Rasmussen, F. K. Nielsen, S. Andresen, O. B. Sørensen, K. S. Hansen, and O. Bang, “Improved thermal and strain performance of annealed polymer optical fiber Bragg gratings,” Opt. Commun. 284(1), 176–182 (2011).
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C. A. F. Marques, G. D. Peng, and D. J. Webb, “Highly sensitive liquid level monitoring system utilizing polymer fiber Bragg gratings,” Opt. Express 23(5), 6058–6072 (2015).
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N. Zhong, Q. Liao, X. Zhu, M. Zhao, Y. Huang, and R. Chen, “Temperature-independent polymer optical fiber evanescent wave sensor,” Sci. Rep. 5, 11508 (2015).
[Crossref] [PubMed]

C. Sheng, H. Liu, S. Zhu, and D. A. Genov, “Active control of electromagnetic radiation through an enhanced thermo-optic effect,” Sci. Rep. 5, 8835 (2015).
[Crossref] [PubMed]

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A. F. Garito, J. Wang, and R. Gao, “Effects of random perturbations in plastic optical fibers,” Science 281(5379), 962–967 (1998).
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Figures (4)

Fig. 1
Fig. 1 (a–d) Weight, length, diameter, and width changes in D-shaped fibers as a function of heat treatment time at temperature 110 °C; the inset of Figs. 1(a)–1(d) shows that weight, length, diameter, and width of the D-shaped fibers changes with increasing temperature in the range of 20–110 °C (heating rate of the water and vacuum is 2 °C/min).
Fig. 2
Fig. 2 (a) XPS spectra of PMMA subjected water and vacuum heat treatment, (b) FT-IR spectra of PMMA subjected water and vacuum heat treatment, (c) RI change as a function of time at temperature 110 °C, the inset shows that RI changes with increasing temperature in the range of 20–110 °C (heating rate of the water and vacuum is 2 °C/min), (d) the picture and optical micrographs of the D-shaped region (d_1 represents the picture of the D-shaped region, d_2 is the optical micrograph (4 X) of the boundary between the normal region (NR) and polished region (PR), and d_2 is the optical micrograph (4 X) of the D-shaped surface), and (e) scanning electron microscopy (SEM) images (3.00 KX) of the D-shaped surface.
Fig. 3
Fig. 3 (a) spectral transmission of the fibers subjected to water and vacuum heat treatments (the spectral scanning time of Samples A, E, F and G was 1 ms, the scanning time of Sample B was 2 ms, and the scanning time of Samples C–D was 30 ms), (b) transmitted light intensity of the fibers change as a function of time at temperature 110 °C, the inset shows that transmitted light intensity of the fibers changes with increasing temperature in the range of 20–110 °C.
Fig. 4
Fig. 4 (a–g) RCTLI_i,, (i = I, II, III, …, VII), as a function of glucose concentration; where, in Figs. 4(a)–4(g), the sensors were, respectively, from the Samples A–G, (h–i) absorption spectra and RCTLI_VIII of the prepared D-shaped POF sensors in Chlorella pyrenoidosa solution (D-shaped POF sensors were, respectively, normal POF sensor and subjected to heat treatment in water and vacuum at 110 °C for 3 h; particularly, the Chlorella pyrenoidosa concentration was 1.3 g/l), and (j) is the micrograph (200 X) of Chlorella pyrenoidosa.

Tables (1)

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Table 1 Simulation Parameters and Results

Equations (10)

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V = 2 π r λ n 2 2 n 1 2
Δ V = π r n λ n 2 2 n 2 Δ n
D p = λ 2 π [ n 2 2 sin 2 θ i n 2 ] 1 / 2
Δ D p = λ n 2 π ( n 2 2 sin 2 θ i n 2 ) 3 / 2 × Δ n
I e w = I i n I o u t I S R
N = 2 L l = L 4 r tan θ i
L e w = L λ 4 π r tan θ i [ n 2 2 sin 2 θ i n 2 ] 1 / 2 tan [ a r c sin ( n n 2 sin θ i ) ]
Δ L e w = L λ ( X Y ) 4 π n 2 r sin θ i [ n 2 2 sin 2 θ i n 2 ] tan 2 [ a r c sin ( n n 2 sin θ i ) ] × Δ n
X = n tan [ a r c ( n n 2 sin θ i ) ] [ n 2 2 sin 2 θ i n 2 ] 1 / 2
Y = n sin θ i [ n 2 2 sin 2 θ i n 2 ] 1 / 2 sec 2 [ a r c sin ( n n 2 sin θ i ) ] [ n 2 2 ( n sin θ i ) 2 ] 1 / 2

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