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Abstract
A ring resonator-based biochemistry sensor with a wide range, ultra-compact footprint, and high sensitivity is proposed, which utilizes a suspended slot hybrid plasmonic (SSHP) waveguide. The waveguide consists of a suspended Si nanowire separated from a Cu metal surface by a nanoscale air gap. The hybridization of fundamental mode of a Si channel waveguide with the surface plasmon polariton (SPP) mode of Cu-Si interface achieves a strong light confinement, high waveguide sensitivity (Sw), and low optical loss, showing a great potential in integrated optical sensor. The sensitivity, the detection limit and the detection range of the SSHP waveguide-based biochemistry sensor with a miniaturized radius of 1 µm are numerically demonstrated as 458.1 nm/RIU, 3.7 × 10−5 RIU and 0.225 RIU, respectively. These superior performances as well as the fully CMOS compatibility enable the integrated optical sensing applications.
© 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
Integrated silicon photonic sensors have attracted intensive attention in recent years for the applications such as environmental monitoring [1], industrial production [2], medical diagnosis [3], chemical analysis [4], etc., due to their high sensitivity, compact footprint, and mass production capabilities towards low-cost [5–10]. For the silicon photonic sensors, the optimization of waveguide sensitivity (Sw), expressed by the ratio of the waveguide effective refractive index change to the analytes refractive index change (Δneff/Δnc), plays a dominant role in enhancing the sensing performance [11]. Several waveguide structures have been proposed to improve the Sw, such as slot waveguide [12], suspended waveguide [13], and subwavelength grating waveguide (SWG) [14], etc.. However, devices based on these structures usually have a complicated fabrication process, or cannot be scaled down to a compact footprint due to the weak light confinement. Recently, a hybrid plasmonic (HP) waveguide was proposed [15–19], in which light is guided as a mixed mode, coupling between photonic mode and plasmonic mode in the nanoscale structure [11,20–22]. Compared to the pure plasmonic waveguide, the HP waveguide has the lower propagation loss and the similar waveguide sensitivity, and is easier to be integrated with the other silicon photonic devices. Currently, most of the HP waveguides are based on noble metals [23–26], which are not compatible with the complementary metal-oxide-semiconductor transistor (CMOS) technology and thus preventing the sensor from being mass-produced at a low cost. Therefore, it is of great significance to investigate the hybrid plasmonic waveguide with CMOS-compatible metals, such as Al, Cu, and TiN. Al cannot provide the same level of light confinement, and TiN is too lossy at telecom wavelengths [25]. HP waveguide based on Cu with optimal design is possible to achieve the lower optical propagation loss and the stronger mode confinement than HP waveguide based on noble metals, such as Au [27]. Hence, we proposed a novel suspended slot hybrid plasmonic (SSHP) waveguide based on Cu, which can achieve a strong light confinement and low optical loss.
To investigate sensing performance, ring resonator is usually adopted to transfer the index variations of the analyte to the optical intensity variation or wavelength shift, due to its high sensitivity and compact footprint. Nevertheless, ring resonator optical sensors suffer a free spectral range (FSR) of the micro ring small, which results in a small detection range (DR) of sensors. The working principle of the refractive index (RI) sensor is tracking the resonant shifts introduced by the changes of the analyte. However, the transmission spectrum of the ring resonator is periodic, leading to that adjacent resonance peaks can disturb the resonance tracking if the resonance shift is larger than the FSR. In other words, if the introduced resonant shift is large enough to overlap with the adjacent resonant position, the RI change driven resonant shifts cannot be accurately determined. Several solutions have been proposed before, such as the sensor based on cascade rings [28] and the sensor patterned with periodically arranged set of gold nanodisks [29], but they are bulky and complex to be fabricated. Enlarging the FSR of the ring resonator-based sensor to cover the range of resonance shift may be an efficient way. The ring resonator-based sensor employing the SSHP waveguide can achieve a large FSR by decreasing the radius, due to the strong light confinement of the SSHP waveguide.
In this work, we present a ring resonator-based silicon photonic sensor utilizing a novel CMOS-compatible SSHP waveguide on the silicon-on-insulator (SOI) platform numerically. The SSHP waveguide shows a Sw as high as 0.8 with the optical propagation loss of less than 0.08 dB/µm in the section 2, showing a potential in the integrated optical sensor. Hence, an ultra-compact, high-sensitivity, and wide DR silicon photonic sensor and its fabrication process flow were proposed. The ring resonator optical sensor with 1 µm-radius shows a sensitivity of 458.1 nm/RIU, a detection limit of 3.7 × 10−5 RIU, and the detection range of 0.225 RIU, which is ten times larger than that of the sensor reported before. Furthermore, this kind of resonator can also be used as a high-performance electric-optical (E-O) modulator by infilling a E-O material in the slot.
2. Suspended hybrid plasmonic waveguide
The sensitivity (S) of the waveguide-based devices can be divided into two parts S = Sd · Sw [30]. The one is the device sensitivity Sd, which is only determined by the configuration of the photonic device. The other is the waveguide sensitivity Sw, which is relevant to a waveguide structure regardless of the device configuration. These two parts can be enhanced separately to achieve the higher overall sensitivity. We focus on the latter in this work.
The 3D schematic and the cross-section of the proposed suspended HP waveguide with a horizontal slot are shown in Figs. 1(a) and 1(b). It consists of a silicon channel waveguide based on SOI and a metal (Cu) cladding supporting by a 10 nm-thick Si3N4 layer. The SiO2 surrounding the Si channel is removed by the hydrogen fluoride (HF) solution and a hollow waveguide structure with a horizontal slot is formed. The suspended structure can further enhance the Sw of the waveguide. The refractive index of Si and SiO2 are 3.45 and 1.45, respectively. The refractive index of Cu is 0.282 + 11.8i at a wavelength of 1550 nm [25]. The width of the Si ridge, the heights of the horizontal slot, Si ridge, Si slab, and the thickness of Cu film and Si3N4 film are denoted as Wsi, hslot, hsi, hslab, hCu, and hSiN, respectively. The thickness of the Si ridge hsi and Cu film are fixed as 340 nm and 100 nm, respectively. The surface plasmonic polariton (SPP) penetration depth in the metal is much smaller than the silicon [31]. The thickness of Cu is fixed at 100 nm, which is thick enough to prevent the electric field from penetrating through the metal. The hslot and Wsi are investigated in the simulations to optimize the structure. The numerical investigation of this structure is performed with 3D FDTD. Figure 1(c) presents the E-intensity distribution at the waveguide cross section. Transverse-magnetic (TM) polarizations mode can be supported and strong optical confinement is achieved at the gap between Cu and Si materials. The dielectric discontinuity at the Si-air interface produces a polarization charge that interacts with the plasma oscillations of the metal–oxide interface; that is, the gap region has an effective optical capacitance, which has been explained and demonstrated in [27,32]. Thus, the E-field in the slot is strongly confined and enhanced by the SPP effect.
Fig. 1. (a) The 3D schematic, and (b) the cross-section of the SSHP waveguide (not to scale); (c) The E-distribution at the cross-section of the waveguide.
The analysis of the electric field (E) intensity of the various heights of the slots, as shown in Fig. 2(a). The electromagnetic energy is confined in the gap, leading to the optical guiding and controlling with low mode loss in the nanoscale structure. The strong confinement in the slot mainly arises from the continuity of the displacement field at the material interface and the polarization charges at the Si-air interface interacts with the plasma oscillations of the metal-Si3N4 interface. The E-intensity of the slot increases with the decrease of hslot, due to the strong light confinement of the plasmonic layers in the narrower HP waveguide. The E-intensity of the slot is much stronger than that in the silicon waveguide and other regions, which is an ideal characteristic for enhancing the sensor sensitivity.
Fig. 2. Numerical results of (a) normalized E-intensity of the SSHP waveguide with the varied -hslot; (b) the effective refractive index, (c) the propagation loss, and (d) the waveguide sensitivity versus the width of the Si ridge, Wsi, for various gap thicknesses, hslot.
To better understand the proposed hybrid waveguide, the dependence of the effective refractive index (neff) on hslot and WSi is analyzed. The variation of neff versus the width of Si ridge with the different thicknesses of the slot are shown in Fig. 2(b). The neff increases with a wider silicon waveguide and a smaller gap. The former is due to the high refractive index of the silicon material, while the latter is because the surface plasmonic polariton effect are enhanced with the decrease of hslot. Figure 2(c) shows the dependence of propagation loss on hslot and WSi. The propagation loss is mainly introduced by the close vicinity of the metal layer (plasmonic loss). For a large hslot and a large WSi, the hybrid waveguide supports a low-loss mixed mode with more electromagnetic energy confined to the high refractive index core. Conversely, a small gap and a small width of the Si channel suffer a high loss. Figure 2(d) presents the waveguide sensitivity versus hslot and WSi. In the typical waveguide structures, the waveguide sensitivity is proportional to the optical confinement factor in the tested analytes. When the light confinement in the tested analytes is large, the neff is heavily modified by the concentration change of tested analytes such as isopropyl alcohol (IPA) solution or acetylene gas. The optical confinement factor (Γ) in the tested analytes region, which is defined by the Eq. (1) [33],
In summary, a novel SSHP waveguide is proposed and analyzed. The working principle of the proposed waveguide structure was illustrated comprehensively by the numerical investigation. Considering the light confinement, the propagation loss and the waveguide sensitivity, the dimensions of the waveguide are determined: hslot = 30 nm and WSi = 150 nm.
3. Numerical investigation the ring sensor with a SSHP waveguide
3.1 Schematic of the ring sensor with a SSHP waveguide
The proposed sensor based on microring resonator utilizing a SSHP waveguide is sketched in Fig. 3. The radius of the ring, the length of the coupling region of the ring, and the gap between the bus waveguide and the ring are 1 µm, 1.08 µm, and 0.3 µm, respectively. The light is coupled into the ring from the typical bus waveguide at the resonance wavelength.
Fig. 3. (a) The 3D schematic of the proposed sensor with SSHP waveguide; (b) cross section of the ring resonator. (not to scale)
The resonance wavelength λres of a micro-ring resonator depends on the effective refractive index neff and the ring circumference L: λres = neff·L/m. Quality factor (Q-factor) is the most significant parameter of ring resonator, which describes the photon lifetime in the resonator and represents the number of oscillations before the energy has decayed to 1/e. Q-factor is given by Eq. (2) [34,35]:
Figure 4 presents the detailed process flow of the proposed sensor. The fabrication starts from an 8-inch SOI wafers with 340 nm-thick top Si and 3 µm-thick buried SiO2. Deep ultraviolet (DUV) lithography is adopted to pattern the waveguide and grating structures on photoresist. Then, inductively coupled plasma (ICP) etching is performed to transfer the patterns from the photoresist to silicon to form the designed devices. After etching, 260 nm-thick SiO2 is deposited by plasma-enhanced chemical vapor deposition (PECVD), followed by chemical-mechanical polishing (CMP) to flatten the surface. Then, 10 nm-thick Si3N4 is deposited and patterned. After that, a 100 nm-thick Cu film is formed by single damascene process, which including Cu electro-chemical plating (ECP), annealing and CMP processes, and then followed by the SiO2 window opening. Then, HF wet-etching is adopted to form the slot and suspended structures, using the photoresist as the protect layer.
3.2 Numerical investigation of the ring sensor
The resonance peaks and transmission intensity change of ring resonators with SSHP waveguide depend on the effective refractive index of the sensing region. Analysis of the normalized transmission spectra has been performed to estimate the performance of the sensor with the proposed HP waveguide.
The E-intensity distribution of the optical ring resonator is shown in Fig. 5. It is evident that this mixed mode is supported by the SSHP waveguide, containing high-sensitivity plasmonic mode and low loss photonic mode. At resonant wavelength, the light in the bus waveguide can be coupled into the ring and enhanced by the resonance, as showed in Fig. 5(a). The E intensity of the cross-section is shown in Fig. 5(b), which significantly suggests that the E-field is tightly confined in the slot and greatly enhanced by the SPP effect. Conversely, when the wavelength cannot satisfy the resonance condition, the light cannot be coupled into the ring and passes through the waveguide, as shown in Figs. 5(c) and 5(d). The strong light confinement and the SPP effect can significantly enhance the performance of the sensor, mainly including sensitivity, figure of merit (FOM), detection limit (DL), and detection range (DR).
Fig. 5. (a) E-intensity distribution of the ring resonator at resonant wavelength; (b) E-intensity distribution of the cross-section at the resonant wavelength; (c) E-intensity distribution of the ring resonator at 50 nm-off the resonant wavelength; (d) E-intensity distribution of the cross section at 50 nm-off the resonant wavelength.
Sensitivity is the most crucial characteristic of the sensor, which represents the ratio of the shift of the resonance wavelength and the variation in the refractive index of the test analytes (S = ∂λres/∂nc). The electromagnetic fields of a photonic mode are confined in the slot and the electromagnetic fields of a plasmonic mode are concentrated at the surface of Cu layer, which can overlap with the analyte. These would introduce a large resonance shift of the sensor and hence a better sensitivity. Apart from sensitivity and to further evaluate the performance of the proposed sensor, FOM is introduced that simultaneously considers the sensitivity and the Q-factor of the ring resonator, which is independent of the signal-to-noise ratio and can be used for the performance estimation. It is defined as FOM = S/ΔλFWHM = S·Q/λ. Compared to the plasmonic mode, the mixed mode-based sensor tends to have a lager FOM due to the loss-less nature of the photonic mode which leads to a sharper resonance. Also, the DL is a key characteristic of sensors, which represents the smallest change in the refractive index that can be resolved. DL is equal to the resonance wavelength resolution divided by the FOM, which can be expressed as DL = R/FOM [36], where R is the wavelength resolution of the measured signal change, highly relying on the performance of the measuring system. Thus, the DL is significantly affected by the measurement accuracy and noise of the detection instruments. Moreover, a detection range (DR) is a key factor in whether the sensor can be applied in practice. To accurately describe the measuring range in the ring resonator-based sensor, a detection range (DR) is defined as DR = FSR/S, which suggests that enlarging the FSR or decreasing the sensitivity can widen the detection range. However, in most scenarios, sensitivity is one of the most crucial properties of the sensor, and sacrificing sensitivity to obtain a large DR is not desirable. Due to the strong light confinement of the SSHP, the proposed sensor can achieve a larger FSR by reducing the radius of the ring resonator and hence a larger DR.
To characterize the proposed sensor, the transmission responses are investigated, which are shown in Fig. 6(a). As the concentration of the IPA solution increases, the refractive index of the solution increases, leading to red shifts of the resonant wavelength. Figure 6(b) shows the wavelength shifts versus the refractive index change of the test solution, from which a nearly linear relationship between Δλ and Δn is observed. The slopes of the blue and the grey line are the sensitivity of the SSHP-waveguide based sensor and the typical strip waveguide-based sensor, respectively, indicating that the sensitivity of the sensor is 458.1 nm/RIU, which is about 6 times higher than that of the ring-type sensor based on the typical waveguide [37].
Fig. 6. Transmission responses of the MRR sensor with a SSHP waveguide infiltrated with different concentrations of NaCl solution; (b) wavelength shift versus refractive index change of the MRR sensor
Furthermore, the Q factor of the ring resonator with the HP waveguide is about 890, resulting in the FOM of the proposed sensor equal to 468, which is much higher than the hybrid sensor reported before [21]. In addition, the Q factor can be improved by enlarging the hslot, while the light confinement and the sensitivity will decrease. An optimized trade-off between the sensitivity and the Q factor should be achieved, depending on the applications. The DL of the sensor depends on the sensitivity, Q factor, as well as the resolution of the measurement equipment. The amount of noise on the measurement system, which causes uncertainty to the sensing performance. Following the resolution analysis in [38], resonance wavelength resolution is chosen as 10 pm in this work. Consequently, the detection limit is 3.7 × 10−5 RIU, which is smaller than that reported before.
As shown in Fig. 7, the FSR of the proposed ring resonator is 103.2 nm and the DR can be calculated as 0.225, which can cover the range of resonance shift due to variations of the concentration of the biochemical solutions. Compared with a conventional waveguide-based ring resonator with a radius of 10 µm, the FSR of the proposed sensor is ten times larger.
Fig. 7. FSR of the MRR sensor with a SSHP waveguide infiltrated with various concentrations of IPA solution.
Table 1 presents the characteristics of the proposed sensor and other demonstrated ring-type sensors. The proposed sensor in this work is better than those previously reported in terms of detection limit, detection range, and FOM, especially the detection range is 10 times larger than that reported before.
Table 1. Characteristics of different kinds of sensors based on ring resonator
Additionally, the structure can be further applied to E-O modulator. For an E-O modulator, waveguide sensitivity is also a dominant parameter in the performance of the modulator. The E-O polymer is infilled in the hollow region and its index is efficiently changed by the applied voltage. Also, the Cu cap-based SSHP waveguide can readily serve as one of the electrodes and therefore simplify the electrical circuits as well as fabrication processes.
4. Conclusion
We have proposed an ultra-compact, high-sensitivity, and wide detection range ring resonator optical sensor based on a novel SSHP waveguide. By optimizing the hybridization of fundamental mode of a Si channel waveguide with the SPP of Cu-Si interface, we can simultaneously achieve subwavelength confinement, high waveguide sensitivity, and low optical loss, which shows a great potential in integrated optical sensor. The ring resonator optical sensor based on the SSHP waveguide is numerically demonstrated, showing a sensitivity of 458.1 nm/RIU and a detection limit of 3.7 × 10−5 RIU, which are superior to sensors based on the typical dielectric waveguide and the hybrid plasmonic reported before. In addition, benefiting from the strong light confinement of the SSHP waveguide, the ring resonator sensor is accomplished with 1 µm-radius, leading to a large FSR of 103.2 nm and a detection range of 0.225 RIU, which is large enough to cover the resonance wavelength shifts and refractive index variations of most biochemical solutions. Furthermore, the ring resonator optical sensor is also compatible with CMOS technologies, and it can be easily integrated with other SOI devices.
Funding
National Natural Science Foundation of China (61904196).
Disclosures
The authors declare no conflicts of interest.
Data availability
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
References
1. Y. Tomono, H. Hoshi, and H. Shimizu, “CO2 Detection with Si Slot Waveguide Ring Resonators toward On-chip Specific Gas Sensing,” in 2019 Conference on Lasers and Electro-Optics (CLEO), 1–2 (2019).
2. L. Tombez, E. J. Zhang, J. S. Orcutt, S. Kamlapurkar, and W. M. J. Green, “Methane absorption spectroscopy on a silicon photonic chip,” Optica 4(11), 1322 (2017). [CrossRef]
3. Y. Chen, Z. Li, H. Yi, Z. Zhou, and J. Yu, “Microring resonator for glucose sensing applications,” Front. Optoelectron. China 2(3), 304–307 (2009). [CrossRef]
4. J. Tao, X. Wang, T. Sun, H. Cai, Y. Wang, T. Lin, D. Fu, L. L. Ting, Y. Gu, and D. Zhao, “Hybrid Photonic Cavity with Metal-Organic Framework Coatings for the Ultra-Sensitive Detection of Volatile Organic Compounds with High Immunity to Humidity,” Sci. Rep. 7(1), 41640 (2017). [CrossRef]
5. H. Nazemi, A. Joseph, J. Park, and A. Emadi, “Advanced Micro- and Nano-Gas Sensor Technology: A Review,” Sensors 19(6), 1285 (2019). [CrossRef]
6. A. Raza, S. Clemmen, P. Wuytens, M. de Goede, A. S. K. Tong, N. Le Thomas, C. Liu, J. Suntivich, A. G. Skirtach, S. M. Garcia-Blanco, D. J. Blumenthal, J. S. Wilkinson, and R. Baets, “High index contrast photonic platforms for on-chip Raman spectroscopy,” Opt. Express 27(16), 23067–23079 (2019). [CrossRef]
7. Q. Liu, X. Tu, K. W. Kim, J. S. Kee, Y. Shin, K. Han, Y.-J. Yoon, G.-Q. Lo, and M. K. Park, “Highly sensitive Mach–Zehnder interferometer biosensor based on silicon nitride slot waveguide,” Sens. Actuators, B 188, 681–688 (2013). [CrossRef]
8. S. Yoshida, S. Ishihara, T. Arakawa, and Y. Kokubun, “Highly sensitive optical biosensor based on silicon-microring-resonator-loaded Mach–Zehnder interferometer,” Jpn. J. Appl. Phys. 25(26), 33193 (2017). [CrossRef]
9. M. S. Rasras and O. Al Mrayat, “Lab-on-Chip Silicon Photonic Sensor,” The IoT Physical Layer 83–102 (2019). [CrossRef]
10. A. L. Washburn, M. S. Luchansky, M. S. McClellan, and R. C. Bailey, “Label-free, multiplexed biomolecular analysis using arrays of silicon photonic microring resonators,” Procedia Eng. 25, 63–66 (2011). [CrossRef]
11. X. Sun, L. Thylen, and L. Wosinski, “Hollow hybrid plasmonic Mach-Zehnder sensor,” Opt. Lett. 42(4), 807–810 (2017). [CrossRef]
12. F. Dell’Olio and V. M. N. Passaro, “Optical sensing by optimized silicon slot waveguides,” Opt. Express 15(8), 4977–4993 (2007). [CrossRef]
13. W. Zhou, Z. Cheng, X. Wu, B. Zhu, X. Sun, and H. K. Tsang, “Fully suspended slot waveguides for high refractive index sensitivity,” Opt. Lett. 42(7), 1245–1248 (2017). [CrossRef]
14. Z. Tu, D. Gao, M. Zhang, and D. Zhang, “High-sensitivity complex refractive index sensing based on Fano resonance in the subwavelength grating waveguide micro-ring resonator,” Opt. Express 25(17), 20911–20922 (2017). [CrossRef]
15. J. Tao, L. Wu, G. Zheng, and S. Yu, “Cherenkov polaritonic radiation in a natural hyperbolic material,” Carbon 150, 136–141 (2019). [CrossRef]
16. D. K. Gramotnev and S. I. Bozhevolnyi, “Plasmonics beyond the diffraction limit,” Nat. Photonics 4(2), 83–91 (2010). [CrossRef]
17. J. Tao, L. Wu, and G. Zheng, “Graphene surface-polariton in-plane Cherenkov radiation,” Carbon 133, 249–253 (2018). [CrossRef]
18. G. Dabos, A. Manolis, D. Tsiokos, D. Ketzaki, E. Chatzianagnostou, L. Markey, D. Rusakov, J.-C. Weeber, A. Dereux, A.-L. Giesecke, C. Porschatis, T. Wahlbrink, B. Chmielak, and N. Pleros, “Aluminum plasmonic waveguides co-integrated with Si3N4 photonics using CMOS processes,” Sci. Rep. 8(1), 13380 (2018). [CrossRef]
19. R. Kumar, S. Pal, N. Pal, V. Mishra, and Y. K. Prajapati, “High-performance bimetallic surface plasmon resonance biochemical sensor using a black phosphorus–MXene hybrid structure,” Appl. Phys. A 127(4), 259 (2021). [CrossRef]
20. F. Zhang, L. Yao, H. Zhang, L. Chong, and S. Liu, “On chip chirality-distinguishing beamsplitter,” Opt. Express 25(21), 24861–24871 (2017). [CrossRef]
21. R. F. Oulton, V. J. Sorger, D. A. Genov, D. F. P. Pile, and X. Zhang, “A hybrid plasmonic waveguide for subwavelength confinement and long-range propagation,” Nat. Photonics 2(8), 496–500 (2008). [CrossRef]
22. A. Manolis, E. Chatzianagnostou, G. Dabos, N. Pleros, B. Chmielak, A. L. Giesecke, C. Porschatis, P. J. Cegielski, L. Markey, J. C. Weeber, A. Dereux, and D. Tsiokos, “Plasmonics co-integrated with silicon nitride photonics for high-sensitivity interferometric biosensing,” Opt. Express 27(12), 17102–17111 (2019). [CrossRef]
23. N. Jiang, X. Zhuo, and J. Wang, “Active Plasmonics: Principles, Structures, and Applications,” Chem. Rev. 118(6), 3054–3099 (2018). [CrossRef]
24. A. Bozzola, S. Perotto, and F. De Angelis, “Hybrid plasmonic-photonic whispering gallery mode resonators for sensing: a critical review,” Analyst 142(6), 883–898 (2017). [CrossRef]
25. J. C. Weeber, J. Arocas, O. Heintz, L. Markey, S. Viarbitskaya, G. Colas-des-Francs, K. Hammani, A. Dereux, C. Hoessbacher, U. Koch, J. Leuthold, K. Rohracher, A. L. Giesecke, C. Porschatis, T. Wahlbrink, B. Chmielak, N. Pleros, and D. Tsiokos, “Characterization of CMOS metal based dielectric loaded surface plasmon waveguides at telecom wavelengths,” Opt. Express 25(1), 394–408 (2017). [CrossRef]
26. X. Huang, X. Ou, Z. Tang, H. C. Liu, and Q. Tan, “Integrated dual-channel sensing utilizing polarized dissimilation based on photonic spin-orbit interaction,” Opt. Lett. 44(15), 3757 (2019). [CrossRef]
27. D. Y. Fedyanin, D. I. Yakubovsky, R. V. Kirtaev, and V. S. Volkov, “Ultralow-Loss CMOS Copper Plasmonic Waveguides,” Nano Lett. 16(1), 362–366 (2016). [CrossRef]
28. Y. Liu, Y. Li, M. Li, and J. J. He, “High-sensitivity and wide-range optical sensor based on three cascaded ring resonators,” Opt. Express 25(2), 972–978 (2017). [CrossRef]
29. D. Urbonas, A. Balcytis, M. Gabalis, K. Vaskevicius, G. Naujokaite, S. Juodkazis, and R. Petruskevicius, “Ultra-wide free spectral range, enhanced sensitivity, and removed mode splitting SOI optical ring resonator with dispersive metal nanodisks,” Opt. Lett. 40(13), 2977–2980 (2015). [CrossRef]
30. A. Densmore, D. X. Xu, P. Waldron, S. Janz, P. Cheben, J. Lapointe, A. Delage, B. Lamontagne, J. H. Schmid, and E. Post, “A silicon-on-insulator photonic wire based evanescent field sensor,” IEEE Photonics Technol. Lett. 18(23), 2520–2522 (2006). [CrossRef]
31. M. Dragoman and D. Dragoman, “Plasmonics: Applications to nanoscale terahertz and optical devices,” Prog. Quantum Electron. 32(1), 1–41 (2008). [CrossRef]
32. S. Zhu, G. Q. Lo, and D. L. Kwong, “Cu-insulator-Si hybrid plasmonic waveguide based CMOS-compatible Nanophotonic Devices,” Nanoelectronics Conference (INEC), 2013 IEEE 5th International (2013).
33. N. N. Feng, J. Michel, and L. C. Kimerling, “Optical field concentration in low-index waveguides,” IEEE J. Quantum Electron. 42(9), 883–888 (2006). [CrossRef]
34. L. Chrostowski, S. Grist, J. Flueckiger, W. Shi, X. Wang, E. Ouellet, H. Yun, M. Webb, B. Nie, Z. Liang, K. Cheung, S. Schmidt, D. Ratner, and N. Jaeger, “Silicon photonic resonator sensors and devices,” Proceedings of SPIE - The International Society for Optical Engineering 8236, 823620 (2012). [CrossRef]
35. X. Fan, I. White, S. Shopova, H. Zhu, J. Suter, and Y. Sun, “Sensitive Optical Biosensors for Unlabeled Targets: A Review,” Anal. Chim. Acta 620(1-2), 8–26 (2008). [CrossRef]
36. I. White and X. Fan, “On the performance quantification of resonant refractive index sensors,” Opt. Express 16(2), 1020–1028 (2008). [CrossRef]
37. K. De Vos, I. Bartolozzi, E. Schacht, P. Bienstman, and R. Baets, “Silicon-on-Insulator microring resonator for sensitive and label-free biosensing,” Opt. Express 15(12), 7610–7615 (2007). [CrossRef]
38. T. Claes, J. Gironès, K. Vos, E. Schacht, R. Baets, and P. Bienstman, “Label-Free Biosensing With a Slot-Waveguide-Based Ring Resonator in Silicon on Insulator,” IEEE Photonics J. 1(3), 197–204 (2009). [CrossRef]
39. X. Sun, D. Dai, L. Thylén, and L. Wosinski, “Double-Slot Hybrid Plasmonic Ring Resonator Used for Optical Sensors and Modulators,” Photonics 2(4), 1116–1130 (2015). [CrossRef]
40. L. Zhou, X. Sun, X. Li, and J. Chen, “Miniature Microring Resonator Sensor Based on a Hybrid Plasmonic Waveguide,” Sensors 11(7), 6856–6867 (2011). [CrossRef]
