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Accepted papers to appear in an upcoming issue

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Soliton detuning of 68.5 THz in the near-infrared in a highly nonlinear suspended core tellurite fiber

Tanvi Karpate, Grzegorz Stepniewski, Dariusz Pysz, Anupamaa Rampur, Yuriy Stepanenko, Ryszard Buczynski, and Mariusz Klimczak

DOI: 10.1364/JOSAB.389303 Received 29 Jan 2020; Accepted 27 Mar 2020; Posted 27 Mar 2020  View: PDF

Abstract: We demonstrate an isolated phenomenon of soliton self-frequency shift over a bandwidth of 68.5 THz in the near-infrared spectral range. We designed, fabricated and characterized a suspended core microstructured fiber made of highly nonlinear tellurite glass. The fiber is designed for a flat anomalous dispersion to leverage on Raman scattering-assisted frequency shift of a fundamental order soliton. We demonstrate a prominent soliton with an input power-based tunabilty in the spectral range from the 1560 nm central pump wavelength up to around 2400 nm central wavelength of the frequency-shifted soliton, when the fiber is pumped with 90 fs pulses from a commercial, fiber-based mode-locked laser.

Femtosecond filamentation, supercontinuum generation and determination of n₂ in polycrystalline SBN

Rosvaldas Suminas, Nail Garejev, Agne Suminiene, Vytautas Jukna, Gintaras Tamosauskas, and Audrius Dubietis

DOI: 10.1364/JOSAB.391702 Received 27 Feb 2020; Accepted 27 Mar 2020; Posted 27 Mar 2020  View: PDF

Abstract: We demonstrate that polycrystalline strontium barium niobate (SBN) serves as an excellent nonlinear material for supercontinuum generation in the near- and mid-infrared, as pumped by femtosecond pulses in the regions of its normal, zero and anomalous group velocity dispersion. We also show that broadband, octave-spanning planar second harmonic emission generated via random quasi phase matching usefully serves to precisely monitor focusing/refocusing cycles of a filament and to determine position of the nonlinear focus in particular, which was used to estimate the nonlinear index of refraction of the material applying the Marburger‘s law. The measured n₂ values are remarkably large: 44±7 × 10-¹⁶ cm²/W at 1.2 μm, 81± × 10-¹⁶ cm²/W at 2.0 μm and 100±15 × 10-¹⁶ cm²/W at 2.4 μm, and thus imply very low energy (below 100 nJ) and power (below 1 MW) thresholds for filamentation and SC generation in the infrared spectral range.

Bandwidth analysis of optical parametric amplifier pumped by broadband pulses

Viktorija Tamuliene, Rytis Butkus, and Algirdas Stabinis

DOI: 10.1364/JOSAB.387592 Received 06 Jan 2020; Accepted 26 Mar 2020; Posted 27 Mar 2020  View: PDF

Abstract: We present analytical solution of nonlinear coupling equations for parametric down-conversion of broadband pump at large gain. The feasibility of analytical expressions is demonstrated for the case of a collinear type II parametric interaction in BBO crystal and group-velocity matching of signal and pump waves. The correlation function of amplified signal wave was obtained and it was revealed that the bandwidth of noise-seeded optical parametric amplifier increases with decrease of pump pulse duration, especially for femtosecond pump pulses.

Thermo-optic instabilities in asymmetric dual-core amplifiers

Jesper Laegsgaard, Federica Poli, Annamaria Cucinotta, and Stefano Selleri

DOI: 10.1364/JOSAB.389601 Received 03 Feb 2020; Accepted 26 Mar 2020; Posted 27 Mar 2020  View: PDF

Abstract: Dynamical thermo-optic instabilies in asymmetric dual-core fiber amplifiers are investigated by numerical simulations. A coupled-mode model capable of describing the asymmetric dual-core structure is derived, and structures with various levels of refractive-index asymmetry from 10$^{-6}$ to 10$^{-4}$ are studied. The most viable route to avoid thermally induced power signal field fluctuations is found to be core decoupling via large separation and strong refractive-index asymmetry. A design criterion for this strategy to be effective is suggested based on the numerical results.

Super-resolution imaging of nitrogen vacancy center with the competition between charge state conversion and stimulated emission

Bo Du, Xiangdong Chen, Shao-Chun Zhang, Yang Dong, Cuihong Li, Guang-can Guo, and Fang-Wen Sun

DOI: 10.1364/JOSAB.390157 Received 10 Feb 2020; Accepted 26 Mar 2020; Posted 26 Mar 2020  View: PDF

Abstract: Nitrogen-vacancy (NV) center in diamond has been widely used for quantum information processing, nanophotonics and biological imaging. In this work, we experimentally studied the charge state conversion and stimulated emission of NV center with a near-infrared (NIR) pumping laser. The competition between these two processes resulted in a non-monotonic dependence of NV center's fluorescence intensity on the NIR laser power. Fluorescence enhancement was observed with weak NIR laser, while fluorescence depletion was observed with high power NIR laser. It led to the non-monotonic change of the spatial resolution with stimulated emission depletion microscopy, which has been used for the sub-diffraction imaging of NV center. Our work can help to further understand the optical mechanism and extend the applications of NV center.

Strong coupling between excitons and guided modes in WS2-based nanostructures

Yeming Qing, Hui Feng Ma, and Tie Jun Cui

DOI: 10.1364/JOSAB.388016 Received 10 Jan 2020; Accepted 24 Mar 2020; Posted 24 Mar 2020  View: PDF

Abstract: Transition-metal dichalcogenides (TMDCs) exhibit great potential in light-matter interaction due to their distinct properties. Here a simple guided resonance structure is proposed and investigated to realize dual-band light absorption exploiting the guided mode resonance (GMR) in the system and the robust exciton in WS2 monolayer. By tuning the incident angle, the dispersive GMR can strong interact with the nondispersive exciton state, resulting in remarkable Rabi splitting and the emergence of two hybrid polariton bands. The strong GMR-exciton coupling behavior can be well described by the classic oscillator model. The influence of the geometrical parameters on the spectral response is investigated. In addition, we also find that the Rabi splitting is strongly affected by the position of WS2 monolayer in the spacer. Our findings provide a simple route for realization of hybrid light-TMDCs interactions, which may inspire related studies on compact, scalable and easy-to-fabricate TMDCs-based devices.

Modeling and experimental characterization of dual-wavelength Bi-doped fiber lasers with cascaded cavities

Galina Nemova, Xian Jin, Lawrence Chen, Sergey Firstov, and Onur Sezerman

DOI: 10.1364/JOSAB.390847 Received 18 Feb 2020; Accepted 24 Mar 2020; Posted 24 Mar 2020  View: PDF

Abstract: We present a comprehensive theoretical and experimental investigation of a dual-wavelength, bismuth-doped fiber (BDF) laser operating near 1700 nm based on cascaded cavities. The BDF provides optical gain from 1650 nm to 1800 nm when pumped at 1550 nm. The linear laser cavity is defined by a 90% fiber mirror on one end and two fiber Bragg gratings (FBGs) with two lengths of BDF in cascade on the other. The laser can operate at either wavelength alone, or both wavelengths simultaneously by simple adjustment of the pump power. We develop a model based on rate equations and radiation transport equations for two level BDF lasers which we then extend to the case for cascaded cavities. Experimental results agree with simulations.

Scalable multi-qubit quantum gates in quantum networks based on themicrotoroidal-resonator-mediated nitrogen-vacancy centers in diamond

Taian Wang and Yong Zhang

DOI: 10.1364/JOSAB.387055 Received 09 Jan 2020; Accepted 22 Mar 2020; Posted 23 Mar 2020  View: PDF

Abstract: In the paper, we present some schemes for implementing multi-qubit quantum gates in quantum network based on the nitrogen-vacancy (NV) centers in diamond. In our schemes, NV centers coupled to the whispering-gallery modes of microtoroidal resonators (MTRs) serve as quantum registers to store quantum information. By coding the qubits of NV centers into the decoherence-free subspaces (DFSs), quantum information encoded in logical qubits is protected from collective dephasing, and quantum controlled-NOT (CNOT) and Toffoli gates between logical qubits from same or different quantum nodes can be implemented. Compared to the previous works, our schemes are simpler and reduce the consumption of resource. Furthermore, the modularized design of multi-qubit quantum gates can be extended to other quantum platform, which maybe lead to more efficient construction of quantum networks for distributed quantum computation and quantum communication.

Asymmetric light transmission based on the 1D metal triangular gratings

yu Lin

DOI: 10.1364/JOSAB.387975 Received 14 Jan 2020; Accepted 21 Mar 2020; Posted 23 Mar 2020  View: PDF

Abstract: Here, we proposed the 1D isosceles triangular metal gratings covered with silver on the dielectric substrate, the gratings performance asymmetric light transmission characteristics for both lights with transverse magnetic (TM) polarization and transverse electric (TE) polarization at near 1.55μm waveband. Through the check of the efficiency of each diffraction order and the distribution of electromagnetic field, it was found that the asymmetric light transmission characteristics originate from the high transmitted or reflected diffraction channels excited by the forward and backward direction incidence. Different from the previously published results based on the 1D gratings, the gratings still show obvious asymmetric light transmission in a certain waveband when incident wavelengths are beyond their period, they may be the candidate structures for wideband asymmetric light transmission devices, and under oblique incidence, the contrast ratio (CR) of forward and backward transmittance for a certain wavelength can reach more than 29dB.

Characteristics of microwave photonic signal generation using vertical-cavity surface-emitting lasers with optical injection and feedback

Chenpeng Xue, Da Chang, Yuanlong Fan, Songkun Ji, Zuxing Zhang, Hong Lin, Paul Spencer, and Yanhua Hong

DOI: 10.1364/JOSAB.389890 Received 07 Feb 2020; Accepted 20 Mar 2020; Posted 20 Mar 2020  View: PDF

Abstract: Characteristics of microwave photonic signal generation based on P1 dynamic in an optically injected vertical-cavity surface-emitting lasers is studied systematically. The evolutions of the linewidth, power and second harmonic ratio of the generated microwave are investigated as a function of injection strength and frequency detuning. The effect of optical feedback on the linewidth and the phase noise of the generated microwave photonic signal is also studied in detail. With the help of optical feedback, the linewidth can be effectively reduced by increasing the feedback strength and feedback delay time. However, there is an optimal feedback delay time to minimize the phase noise.

Extra-cavity enhanced difference frequency generation at 1.63 μm

Zhiyuan Zhou, Chen Yang, Yan Li, Yinhai Li, Shi-Long Liu, Zhao-Huai Xu, Guang-can Guo, Bao-Sen Shi, and shi-Kai Liu

DOI: 10.1364/JOSAB.388669 Received 22 Jan 2020; Accepted 19 Mar 2020; Posted 20 Mar 2020  View: PDF

Abstract: The laser around 1632 nm has a highly important application in interfacing the wavelength at a rubidium atomic memory (795 nm) and the telecom band (typically 1550 nm) by quantum frequency conversion in three-wave mixing processes. We present a laser source at 1632 nm based on a pump-enhanced difference frequency generation (DFG) scheme, providing 300 mW output power at 55% quantum efficiency, and the experimental data of output power agree with our simulations. A power stability of 0.51% over one hour is achieved, and the 200 kHz linewidth is measured using delayed self-heterodyne method.

Technique for magnetic moment and magnetic state reconstruction of laser cooled atoms using direct imaging

Gehrig Carlse, Alex Pouliot, Thomas Vacheresse, Adam Carew, Hermina Beica, S Winter, and A Kumarakrishnan

DOI: 10.1364/JOSAB.388995 Received 24 Jan 2020; Accepted 18 Mar 2020; Posted 18 Mar 2020  View: PDF

Abstract: We describe a simple in situ technique for measuring the magnetic moment and magnetic sublevel distribution in optically pumped magneto-optical traps. The technique relies on free-expansion imaging of a cold atom cloud in a small magnetic field gradient without the need to detect spatial separation between magnetic sublevels. We find that the effective acceleration of the cloud can be used to characterize extreme state optical pumping. In the general case, we show that the integrated displacement of the falling cloud can be accurately modelled using rate equation simulations of magnetic sublevel populations, and knowledge of local magnetic fields, field gradients, and light intensities. The agreement between the model and the data allows the reconstruction of magnetic moments and population distributions for a range of optical pumping conditions.

Quantum phase transition of finite number of atoms in electromagnetically induced transparency media

Raúl Robles and Ray-Kuang Lee

DOI: 10.1364/JOSAB.386007 Received 16 Dec 2019; Accepted 18 Mar 2020; Posted 18 Mar 2020  View: PDF

Abstract: Instead of an infinite number of atoms in the thermodynamic limit, we study the ground states of a finite number of three-level atoms in the electromagnetically induced transparency (EIT) media. Through the help from a classical control field, critical coupling strengths are derived analytically for the existence of quantum phase transitions in the ground states of this extended Dicke model.Compared to the classical limit, evolution of a finite-size excitation during the storage and retrieval process is also illustrated, as well as atom-field entanglement.The results conducted in this work provide the connection not only to the Dicke model, but also to the Lipkin-Meshkov-Glick (LMG) model.

Enhancement of third harmonic yield in fused filaments due to Gouy shift suppression

Daria Mokrousova, Daniil Shipilo, Georgy Rizaev, Nikolay Panov, Elena Sunchugasheva, Anna Shalova, Andrey Ionin, Olga Kosareva, and Leonid Seleznev

DOI: 10.1364/JOSAB.386955 Received 26 Dec 2019; Accepted 17 Mar 2020; Posted 18 Mar 2020  View: PDF

Abstract: We have measured the absolute energy of the third harmonic generated by multiple filaments in the focusing geometry of 744 nm femtosecond pulse in air. The third harmonic energy from four, three or two colliding beamlets is an order of magnitude larger than the energy from a single beamlet of the same initial energy. 3D nonstationary numerical simulations show that even for sub-critical beamlets their nonlinear interaction makes the high-intensity region asymmetric with respect to the focus, suppresses the Gouy shift and preserves the third harmonic energy attained by the focus from down conversion.

Characterization of scattering losses in tapered optical fibers perturbed by a microfiber tip

Pengfei Zhang, Xin Wang, Lijun Song, Chenxi Wang, Gang Li, and Tiancai Zhang

DOI: 10.1364/JOSAB.388312 Received 15 Jan 2020; Accepted 17 Mar 2020; Posted 18 Mar 2020  View: PDF

Abstract: We demonstrate the characterization of the exponential-decay scattering losses in a tapered optical fiber (TOF) based on near-field-probe-induced scattering. A hemispherical microfiber tip (MFT) with a diameter of 37.3 μm is immersed into the evanescent field of a TOF and induces scattering losses of the TOF. The near-field scattering losses perturbed by the MFT depend on the distance between the MFT and the TOF. The MFT can elongate the penetrate depth of evanescent field significantly when the TOF diameter is small because the effective refractive index outside TOF is changed by the MFT. The relationship between the scattering loss and the TOF-MFT distance is measured experimentally and is in good agreement with the numerical simulations. The lengthened evanescent field of TOF can sense the multifarious matter on a substrate which is farther from the TOF sensitively.

Vacuum Transverse-Fields Acceleration of Electron Bunch.

Hai Lin and Chengpu Liu

DOI: 10.1364/JOSAB.391432 Received 25 Feb 2020; Accepted 17 Mar 2020; Posted 23 Mar 2020  View: PDF

Abstract: We propose a feasible novel scheme of efficiently accelerating electron bunch through a targeted-designed transverse-fields configuration which consists of a laser and a DC magnetic field. Its merit over well-known longitudinal-field acceleration is the independence of the acceleration quality on the initial phase of the accelerated charge relative to the accelerator. Such an initial phase is a probability factor difficult to be controlled. Strict theory and numerical experiment demonstrate that under available not-too-high strength such as $10^{16}W/cm^{2}$ and $1\sim 10Tesla$, electronic energy gain in such a configuration can reach GeV-level over a time scale lasting $1600$-fold laser cycle. The cost of achieving such an "accelerating ability" in the transverse-fields acceleration is far below that in the longitudinal-field acceleration. Other aspects of acceleration quality in such a transverse-fields configuration also display the advantage of the configuration in achieving a compact, high-gain accelerator.

Sensing and switching capabilities of a graphene-based perfect dual-band metamaterial absorber with analytical methods

Mohamad Nejat and Najmeh Nozhat

DOI: 10.1364/JOSAB.385839 Received 11 Dec 2019; Accepted 15 Mar 2020; Posted 18 Mar 2020  View: PDF

Abstract: In this paper, the simultaneously sensing and switching performances of a graphene-based plasmonic dual-band absorber in THz region have been demonstrated and investigated. Due to the high confinement of graphene surface plasmons and hydrophobic nature of graphene, the structure can be used as a refractive index sensor in biomedical applications such as detection of impurities of water, cancer cells and STMV virus. The simulation results show the ultrahigh sensitivity of 360 THz/RIU and figure of merit of 654.54 RIU-1. Moreover, variation of the graphene chemical potential leads to switching function between the perfect absorption and total reflection states, with the high extinction ratio of 12.15 dB and ultrafast response time of 1.5 ps. Two analytical methods of equivalent circuit model and transmission matrix have been used to validate the suggested idea of the proposed graphene-based structure. We have shown that there is a good agreement between the theoretical and simulation results. The specifications of our suggested structure are tunability, ultrahigh sensitivity, high extinction ratio, ultrafast response time and simple design, which pave the ways for design and implementation of other multi-application THz plasmonic structures based on graphene, in future.

On-chip silicon shallowly-etched TM0-to-TM1 mode-order converter with high conversion efficiency and low modal crosstalk

Yin Xu, Chenxi Zhu, Xin Hu, Yue Dong, Bo Zhang, and Yi Ni

DOI: 10.1364/JOSAB.387698 Received 07 Jan 2020; Accepted 11 Mar 2020; Posted 12 Mar 2020  View: PDF

Abstract: Ever-increasing capacity requirements of optical interconnects drive the emergence and fast development of mode-division-multiplexing (MDM) transmission on-chip, where the efficient mode control and conversion components become indispensable. Here, we propose an on-chip silicon TM0-to-TM1 mode-order converter by leveraging the shallowly-etched rectangular slots on the top surface of silicon nanowire. The mode conversion region consists of two rectangular slots on the same side of silicon nanowire and a smaller one between them to realize the efficient mode-order conversion from input TM0 to output TM1 mode with the help of multimode interference and accumulated phase difference. By studying the etching pattern on the silicon nanowire in detail, we have achieved an on-chip TM0-to-TM1 mode-order converter with high conversion efficiency 97.5% and low modal crosstalk <- dB in a conversion length of 11.8 um, and the insertion loss is only 0.29 dB at the wavelength of 1.55 um. Moreover, the device working bandwidth and fabrication tolerance are also analyzed. Note that the proposed shallowly-etched slots on the silicon nanowire can also be further developed to achieve the on-chip TM0-to-TM2 mode-order conversion. With these characteristics, such device could boost the development of MDM transmission on-chip with more TM-polarized mode channels.

Torsion and strain simultaneous measurement using a cascaded helical long period grating

Lunlun Xian, Li Li, and Dongdong Wang

DOI: 10.1364/JOSAB.381406 Received 28 Oct 2019; Accepted 11 Mar 2020; Posted 12 Mar 2020  View: PDF

Abstract: A cascaded helical long period grating (C-HLPG) with two different grating fabrication molten state duration times (MSDT) for simultaneous measurement of torsion and strain is proposed. The sensing system which can discriminate torsion and strain within ranges of 0–1744με and −240° ∼ 240° with accuracies to be ∼120με and ∼0.12rad respectively is demonstrated. The C-HLPG with different MSDT offers unique opportunities as torsion and strain sensors as well as providing a potential development for multi-parameter fiber optical sensors and new development in optical-fiber components.

Higher radial orders of Laguerre-Gaussian beams in two-wave mixing processes

Danilo Gomes Pires, José Carlos Rocha, Alcenisio Silva, and Eduardo Fonseca

DOI: 10.1364/JOSAB.384112 Received 26 Nov 2019; Accepted 10 Mar 2020; Posted 12 Mar 2020  View: PDF

Abstract: We generalize the study of Laguerre-Gaussian in two-wave mixing processes considering optical beams with both integer azimuthal and non-null radial mode index as input modes combined in the nonlinear crystal. Here, we present a deeper discussion on the generation of higher radial orders through two-wave mixing process leading to a more complete understanding on the nonlinear process considered.

3D adjoint-based marching scheme for optical propagation in inhomogeneous waveguides

HAO YANG and Zhifeng Tang

DOI: 10.1364/JOSAB.387287 Received 06 Jan 2020; Accepted 10 Mar 2020; Posted 12 Mar 2020  View: PDF

Abstract: This paper presents a three dimensional (3D) adjoint-based marching schemefor long-range inhomogeneous optical waveguide devices. Efficient numerical propagation computation of an optical waveguide terminated by perfectly matched layers is available by using our approach because it utilizes the new transmission and reflection operators through the one-way formulation of the complex Helmholtz-PML equation, and a novel design of the transverse and adjoint operators that calculate the coordinates through the bi-orthogonal of their eigenfunctions in each marching step. In addition, the validity and accuracy of our proposed method are demonstrated by analyzing a buried channel waveguide and a straight waveguide with varying refractive indices.

Back-action evading measurement of the collective mode of a Bose-Einstein condensate

Marjan Fani and Ali Dalafi

DOI: 10.1364/JOSAB.386227 Received 23 Dec 2019; Accepted 09 Mar 2020; Posted 10 Mar 2020  View: PDF

Abstract: In this paper, we investigate theoretically the backaction evading measurement of the collective mode of an interacting atomic Bose-Einstein condensate (BEC) trapped in an optical cavity which is driven coherently by a pump laser with a modulated amplitude. It is shown that for a specified kind of amplitude modulation of the driving laser, one can measure a generalized quadrature of the collective mode of the BEC indirectly through the output cavity field with a negligible back-action noise in the good-cavity limit. Nevertheless, the on-resonance added noise of measurement is suppressed below the standard quantum limit (SQL) even in the bad cavity limit. Moreover, the measurement precision can be controlled through the s-wave scattering frequency of atomic collisions.

Circular-side square microlasers with shifted output waveguide positions for mode and lasing spectrum control

Yong-Zhen Huang, yong-Heng zhang, Ya-Qian Ye, Yue-De Yang, and Jin-Long Xiao

DOI: 10.1364/JOSAB.387662 Received 07 Jan 2020; Accepted 09 Mar 2020; Posted 10 Mar 2020  View: PDF

Abstract: Circular-side square microlasers with shifted output waveguide positions are demonstrated for realizing mode and lasing spectrum control. Numerical simulation results indicate that the mode Q factors of the fundamental, first- and second-order transverse modes are modulated and the output coupling efficiency of the output waveguide is greatly improved by introducing the translation of the output waveguide. Single-mode lasing, dual-mode lasing and three-mode lasing are experimentally realized by changing the output waveguide positions. At the optimized shifted output waveguide position, the microlaser exhibits tunable single-mode behavior with a maximum output power of 120 μW, a side-mode suppression-ratio of 31 dB and a linewidth of 42MHz. Furthermore, lasing characteristics are compared for the microlasers with different circular-side deformation parameters.

Metasurfaces homogenization based on contravariant tensors averaging in smooth field approximation

Kofi EDEE

DOI: 10.1364/JOSAB.380169 Received 09 Oct 2019; Accepted 08 Mar 2020; Posted 10 Mar 2020  View: PDF

Abstract: Metasurfaces transverse parameters homogenization is introduced through the concept of covariant per- mittivity tensor averaging. The proposed scheme is based on covariant form of Maxwell equations writ- ten in the matched coordinates system. Therefore, the average characteristics of the periodic structure take account for, not only all physical boundary conditions, but also the geometrical details of the peri- odic structure which affect the electromagnetic field propagation. The proposed method is successfully applied to analyse the extraordinary optical transmission through a thick layer subwavelength periodic annular slits array.

Impact of tilted magnetic field on propagation of oblique waves in plasma superlattice

Denis Iakushev and Servando Lopez-Aguayo

DOI: 10.1364/JOSAB.382937 Received 12 Nov 2019; Accepted 08 Mar 2020; Posted 10 Mar 2020  View: PDF

Abstract: In its most general statement, we consider the problem of impact of external magnetic field on photonic properties of superlattice comprised of dielectric and conducting layers: the direction of the wave propagation as well as direction of the external magnetic field are assumed to be arbitrary. We show that even relatively weak external magnetic field can drastically alter the photonic spectrum of the superlattice since within the photonc gaps there emerge photonic bands making the superlattice transparent for incident radiation. We demonstrate that the spectral width of photonic bands can be effectively controlled by rotation of the static external magnetic field.

Si-MZI racetrack micro-ring resonator circuits for wavelength division adjustment – way to generate optical digital patterns

Masih Ghasemi, Seyyedeh Mehri Hamidi, A. Dehzangi, and Pankaj Choudhury

DOI: 10.1364/JOSAB.380360 Received 11 Oct 2019; Accepted 07 Mar 2020; Posted 10 Mar 2020  View: PDF

Abstract: Silicon (Si) photonic components, namely grating coupler and three-port splitter and coupler, were designed and combined to form double-stadium Si-Mach-Zehnder interferometer (MZI) racetrack ring resonator circuits for efficient control over resonance in certain wavelength range and free-spectral range (FSR). It was found that variable MZI stadium arms and the values of free-space distance (between the arms) as 200 nm and 5 micron can yield two and six OFF-phase zones, respectively, within the wavelength range of 1.5-1.6 micron. Furthermore, it was observed that the smaller arms downsize the FSR, whereas the larger arms upsize its value within the transmission spectrum. The usefulness of these structures can be conceptualized in the area of optical digital pattern code generation because suitably controlling the MZI arm lengths would create certain optical digital patterns in the frequency domain of operation.

Simultaneous detection of SRI and temperature with SLPFG sensor operating near PMTP

qiang ling, Zhengtian Gu, and Bo Pang

DOI: 10.1364/JOSAB.384767 Received 03 Dec 2019; Accepted 06 Mar 2020; Posted 06 Mar 2020  View: PDF

Abstract: In our paper, a superimposed long period fiber grating (SLPFG) sensor based on dual-peak resonance near phase-matching turning point (PMTP) for simultaneous dection of surrounding refractive index (SRI) and temperature is proposed. Two fiber grating with different periods are overlapped and written in the same fiber core. There are resonance peaks corresponding to different grating and different mode in the transmission spectrum. By theoretical design, one resonant peak corresponds to a little resonant state near PMTP, while the other one corresponds to the single peak state. When the SRI and temperature change, the resonance peak in a little resonance state will only have peak transmissivity response, but the peak wavelength will not change, while the resonance peak in a single peak state will shift the resonance wavelength. Results of numerical simulations demonstrate that SRI and temperature measurement can be simultaneously by monitoring the wavelength shift of the left peak and the transmissivity of right peak in the transmission spectrum. The SRI and temperature sensitivities of the left peak are -628.57nm/RIU and -0.20nm/℃, respectively. And SRI sensitivity is from -217.73dB/RIU to -682.47dB/RIU when the SRI range is from 1.330 to 1.360. The temperature sensitivity is from -0.044dB/℃ to -0.101dB/℃ in the temperature range from 20℃ to 120℃. The SRI and temperature sensitivities of the sensor are 7 times and 20 times higher than that of other types of fiber optic sensors with dual parameter modulation of intensity and wavelength. The proposed sensor with high sensitivity and simplified structure can be extended to multi-parameter measurement.

Reservoir-engineered optomechanically induced nonreciprocity

Bangpin Hou, Bei Tang, Xiaohui Zhao, Yi-Bing Qian, and Deng-Gao Liao

DOI: 10.1364/JOSAB.383905 Received 26 Nov 2019; Accepted 05 Mar 2020; Posted 26 Mar 2020  View: PDF

Abstract: The optical nonreciprocity in a three-mode optomechanical system within a common optical reservoir is considered. It is found that the optomechanically induced nonreciprocity is generated by the interference between the incoherent coupling induced by the common reservoir and the optomechanical coupling mediated by the interactions of two optical modes with a mechanical mode. There exist two symmetric nonreciprocal regimes which respectively correspond to the forward and backward photon transmitting directions, and the optical nonreciprocity for the relative phase φ between the optomechanical couplings is exchange symmetric with that for the phase 2Π-φ. Additionally, it is shown that the optimal nonreciprocity as well as the nonreciprocal amplification can be reached only by adjusting the optomechanical couplings. To compare the nonreciprocal behavior induced by the common reservoir (incoherent coupling) with that in the case of the coherent coupling, we consider the optomechanically induced nonreciprocity induced by the direct photon tunneling. The nonreciprocal behaviors and their differences in these two cases are explained by using analytic findings.

Chiral and Plasmonic Dimer Pair: Chirality and Plasmonic Resonance Induced Reversal of Near and Far Field Optical Binding Force

Naima Ahsan, Rafia Shamim, Mahdy Mahdy, Saikat Das, Chaity Dolon, Hamim Rivy, Maruf Hossain, and K.M Faisal

DOI: 10.1364/JOSAB.383004 Received 11 Nov 2019; Accepted 02 Mar 2020; Posted 03 Mar 2020  View: PDF

Abstract: In both the near (i.e. around 10 to 250 nm inter-particle distance) and far (i.e. around 1 µm to higher inter-particle distances) field region, controlling the mutual attraction and repulsion between chiral and plasmonic dimers by using light has not been reported so far. Such a control is termed as the reversal of optical binding force. In most of the set-ups, reversal of optical binding force between plasmonic hetero-dimers vanishes with inter-particle distance of around 100 nm and above due to the disappearance of the fano resonance. In this article, we have demonstrated a possible set-up illuminated by linearly polarized plane wave: chiral and plasmonic dimers over a plasmonic substrate, which supports the reversal of optical binding force both in near field and far field regions. At first, we have worked with two chiral homodimers and two plasmonic homodimers but we have not gotten the reversal of optical binding force by varying the inter-particle distance. Then we have placed a plasmonic and a chiral nanoparticle together to create dimer. Interestingly, we have found strong plasmonic resonance at far field but no reversal of optical binding force at far field region. Lastly, we have placed the same chiral – plasmonic dimers setup over a plasmonic substrate and the desired result has been observed mainly due to the induced lateral force on chiral object (in presence of the substrate) and the ‘fano type resonance’ in the system. Controlling both the near and far field optical binding force without using any chemical can be an important aspect for particle clustering, accumulation, crystallization and organization of templates for biological and colloidal sciences in near future.

Rainbow trapping in a tapered photonic crystal waveguide and its application for wavelength demultiplexing effect

Berkay Neseli, Emre Bor, Hamza Kurt, and Mirbek Turduev

DOI: 10.1364/JOSAB.388374 Received 16 Jan 2020; Accepted 02 Mar 2020; Posted 03 Mar 2020  View: PDF

Abstract: In this paper, numerical and experimental demonstration of a wavelength demultiplexer (WDM) based on photonic crystal (PC) is presented in which the waveguide has a tapered width. Owing to tapered waveguide, propagating light can be slowed down and be trapped by a local mode gap effect at certain distances from the entrance of waveguide. The corresponding effect leads to localization of four different wavelengths at different points inside the waveguide. The drop-channels are introduced at these specified locations to separate selected wavelengths. Here, we utilized an optimization algorithm to enhance the coupling efficiencies at the introduced drop-channels. The presented WDM PC separates the wavelengths of 22.29 mm (13.46 GHz), 21.63 mm (13.87 GHz), 20.80 mm (14.42 GHz), and 19.87 mm (15.10 GHz) into different drop-channels with coupling efficiencies at around 80%. Experimental verifications of the numerically presented results are realized at the microwave frequency regime where the coupling efficiencies of each drop-channel are measured as around 75%. The designed WDM PC structure is all-dielectric, compact and efficient, and exhibits low cross-talk between drop-channels. Numerical results and experimental measurements are in good agreement with each other that makes the proposed device a promising solution for optical wavelength division-multiplexing applications.

Performance of an optical single-sideband laser system for atom interferometry

Clemens Rammeloo, Lingxiao Zhu, Yu-Hung Lien, Kai Bongs, and Michael Holynski

DOI: 10.1364/JOSAB.385919 Received 18 Dec 2019; Accepted 28 Feb 2020; Posted 03 Mar 2020  View: PDF

Abstract: This paper reports on a detailed performance characterization of a recently developed optical single-sideband (OSSB) laser system based on an IQ modulator and second-harmonic generation for rubidium atom interferometry experiments. The measured performance is used to evaluate the noise contributions of this OSSB laser system when it is applied to drive stimulated Raman transitions in 87Rb for precision measurements of gravitational acceleration. The laser system suppresses unwanted sideband components, but additional phase shift compensation needs to be applied when performing frequency chirps with such an OSSB laser system. The total phase noise contribution of the OSSB laser system in the current experiment is 72 mrad for a single atom-interferometry sequence with interrogation times of 𝑇 = 120 ms, which corresponds to a relative precision of 32 n𝑔 per shot. The dominant noise sources are found in the relative intensity fluctuations between sideband and carrier components and the phase noise of the microwave source.

Stochastic and probabilistic equations for three- and four-level lasers

Colin McKinstrie

DOI: 10.1364/JOSAB.379976 Received 09 Oct 2019; Accepted 03 Feb 2020; Posted 03 Feb 2020  View: PDF

Abstract: In this tutorial, Langevin stochastic equations and Markov probability equations are used to model electron- and photon-number fluctuations in three- and four-level lasers. Equations are derived for the moments of the electron and photon numbers (means, variances and correlations). Both approaches produce the same moment equations. In the Langevin approach, the moments of the noise terms must be specified by other means, whereas in the Markov approach, they are determined self-consistently and satisfy the shot-noise rule: For each process that is modeled by the rate equations, the driving terms in the variance equations equal the moduli of the associated terms in the mean equations. The driving terms in the correlation equations have the same magnitudes as the variance terms, but can be positive or negative, depending on whether the changes in the electron and photon numbers are correlated or anti-correlated, respectively. Formulas are derived for the relative intensity noise and its spectrum. The consequences of these results for three- and four-level lasers are discussed.

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