Contents
2020
Volume: 8 Issue 2
15 Article(s)
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Editorials
Integrated Optics
3D integrated photonics platform with deterministic geometry control | Editors' Pick
Jérôme Michon, Sarah Geiger, Lan Li, Claudia Goncalves, Hongtao Lin, Kathleen Richardson, Xinqiao Jia, and Juejun Hu
3D photonics promises to expand the reach of photonics by enabling the extension of traditional applications to nonplanar geometries and adding novel functionalities that cannot be attained with planar devices. Available material options and device geometries are, however, limited by current fabrication methods. In this work, we pioneer a method that allows for placement of integrated photonic device arrays at arbitrary predefined locations in 3D using a fabrication process that capitalizes on the buckling of a 2D pattern. We present theoretical and experimental validation of the deterministic buckling process, thus demonstrating implementation of the technique to realize what we believe to be the first fully packaged 3D integrated photonics platform. Application of the platform for mechanical strain sensing is further demonstrated.3D photonics promises to expand the reach of photonics by enabling the extension of traditional applications to nonplanar geometries and adding novel functionalities that cannot be attained with planar devices. Available material options and device geometries are, however, limited by current fabrication methods. In this work, we pioneer a method that allows for placement of integrated photonic device arrays at arbitrary predefined locations in 3D using a fabrication process that capitalizes on the buckling of a 2D pattern. We present theoretical and experimental validation of the deterministic buckling process, thus demonstrating implementation of the technique to realize what we believe to be the first fully packaged 3D integrated photonics platform. Application of the platform for mechanical strain sensing is further demonstrated..
Photonics Research
- Publication Date: Jan. 31, 2020
- Vol. 8, Issue 2, 194 (2020)
Reviews
Fiber Optics and Optical Communications
Distributed curvature sensing based on a bending loss-resistant ring-core fiber
Li Shen, Hao Wu, Can Zhao, Lei Shen, Rui Zhang, Weijun Tong, Songnian Fu, and Ming Tang
A theoretical and experimental study on curvature sensing using a Brillouin optical time-domain analyzer based on the ring-core fiber (RCF) is reported. The Brillouin gain spectrum of the RCF is investigated, and the Brillouin frequency shift (BFS) dependence on temperature and strain is calibrated. We theoretically analyze the fiber bending-induced BFS and peak Brillouin gain variation for the RCF through a numerical simulation method, and the RCF is revealed to have a high curvature sensitivity. Distributed curvature sensing is successfully demonstrated, with the bending radius ranging from 0.5 to 1.5 cm, corresponding to a BFS variation from 32.90 to 7.81 MHz. The RCF takes advantage of great bending loss resistance, and the maximum macrobending loss at the extreme bending radius of 0.5 cm is less than 0.01 dB/turn. Besides, the peak Brillouin gain of the RCF is discovered to vary significantly in response to fiber bending, which is expected to be another parameter for distributed curvature determination. The results imply that the RCF is a promising candidate for highly sensitive distributed curvature measurement, especially in sharp bending circumstances.A theoretical and experimental study on curvature sensing using a Brillouin optical time-domain analyzer based on the ring-core fiber (RCF) is reported. The Brillouin gain spectrum of the RCF is investigated, and the Brillouin frequency shift (BFS) dependence on temperature and strain is calibrated. We theoretically analyze the fiber bending-induced BFS and peak Brillouin gain variation for the RCF through a numerical simulation method, and the RCF is revealed to have a high curvature sensitivity. Distributed curvature sensing is successfully demonstrated, with the bending radius ranging from 0.5 to 1.5 cm, corresponding to a BFS variation from 32.90 to 7.81 MHz. The RCF takes advantage of great bending loss resistance, and the maximum macrobending loss at the extreme bending radius of 0.5 cm is less than 0.01 dB/turn. Besides, the peak Brillouin gain of the RCF is discovered to vary significantly in response to fiber bending, which is expected to be another parameter for distributed curvature determination. The results imply that the RCF is a promising candidate for highly sensitive distributed curvature measurement, especially in sharp bending circumstances..
Photonics Research
- Publication Date: Jan. 29, 2020
- Vol. 8, Issue 2, 165 (2020)
Optical Devices
Broadband on-chip photonic spin Hall element via inverse design | On the Cover
Zhenwei Xie, Ting Lei, Haodong Qiu, Zecen Zhang, Hong Wang, and Xiaocong Yuan
The photonic spin Hall effect plays an important role in photonic information technologies, especially in on-chip spin Hall devices. However, conventional devices suffer from low efficiency or narrow bandwidth, which prevents their practical application. Here, we introduce a spin Hall device using inverse design to achieve both high efficiency and broadband. Spin-dependent light separation is enabled by a 2.4 μm circular device with 100 nm pixels. The photonic spin Hall element is fabricated on a silicon-on-insulator wafer compatible with a standard integrated photonic circuit. The spin light is detected and emitted with an efficiency of up to 22% and 35%, respectively, over a 200 nm bandwidth at optical wavelength.The photonic spin Hall effect plays an important role in photonic information technologies, especially in on-chip spin Hall devices. However, conventional devices suffer from low efficiency or narrow bandwidth, which prevents their practical application. Here, we introduce a spin Hall device using inverse design to achieve both high efficiency and broadband. Spin-dependent light separation is enabled by a 2.4 μm circular device with 100 nm pixels. The photonic spin Hall element is fabricated on a silicon-on-insulator wafer compatible with a standard integrated photonic circuit. The spin light is detected and emitted with an efficiency of up to 22% and 35%, respectively, over a 200 nm bandwidth at optical wavelength..
Photonics Research
- Publication Date: Jan. 22, 2020
- Vol. 8, Issue 2, 121 (2020)
Research Articles
Integrated Optics
Erbium-doped TeO2-coated Si3N4 waveguide amplifiers with 5 dB net gain
Henry C. Frankis, Hamidu M. Mbonde, Dawson B. Bonneville, Chenglin Zhang, Richard Mateman, Arne Leinse, and Jonathan D. B. Bradley
We demonstrate 5 dB net gain in an erbium-doped tellurium-oxide-coated silicon nitride waveguide. The amplifier design leverages the high refractive index and high gain in erbium-doped tellurite glass as well as the ultra-low losses and mature, reliable, and low-cost fabrication methods of silicon nitride waveguide technology. We show that the waveguide platform demonstrates low background propagation losses of 0.25 dB/cm based on a ring resonator device with a Q factor of 1.3×106 at 1640 nm. We measure 5 dB peak net gain at 1558 nm and >3 dB of net gain across the C band in a 6.7 cm long waveguide for 35 mW of launched 1470 nm pump power. Gain per unit length of 1.7 and 1.4 dB/cm is measured in a 2.2 cm long waveguide for 970 and 1470 nm pump wavelengths, respectively. Amplifier simulations predict that >10 dB gain can be achieved across the C band simply by optimizing waveguide length and fiber-chip coupling. These results demonstrate a promising approach for the monolithic integration of compact erbium-doped waveguide amplifiers on silicon nitride chips and within silicon-based photonic integrated circuits.We demonstrate 5 dB net gain in an erbium-doped tellurium-oxide-coated silicon nitride waveguide. The amplifier design leverages the high refractive index and high gain in erbium-doped tellurite glass as well as the ultra-low losses and mature, reliable, and low-cost fabrication methods of silicon nitride waveguide technology. We show that the waveguide platform demonstrates low background propagation losses of 0.25 dB/cm based on a ring resonator device with a
Photonics Research
- Publication Date: Jan. 22, 2020
- Vol. 8, Issue 2, 127 (2020)
Effects of coupling and phase imperfections in programmable photonic hexagonal waveguide meshes
Iman Zand, and Wim Bogaerts
We present a study of the effect of imperfections on the transmission and crosstalk in programmable photonic meshes with feedback loops consisting of tunable couplers and phase shifters. The many elements in such a mesh can generate a multitude of parasitic paths when the couplers and phase shifters deviate even slightly from their nominal value. Performing Monte Carlo simulations, we show that small stochastic imperfections in the phase and coupling (1.0%) can introduce unwanted interferences and resonances and significantly deteriorate the frequency response of the circuit. We also demonstrate that, in the presence of imperfections, the programming strategy of the unused couplers can reduce effects of such parasitics.We present a study of the effect of imperfections on the transmission and crosstalk in programmable photonic meshes with feedback loops consisting of tunable couplers and phase shifters. The many elements in such a mesh can generate a multitude of parasitic paths when the couplers and phase shifters deviate even slightly from their nominal value. Performing Monte Carlo simulations, we show that small stochastic imperfections in the phase and coupling (
Photonics Research
- Publication Date: Jan. 31, 2020
- Vol. 8, Issue 2, 211 (2020)
Lasers and Laser Optics
High-energy all-fiber gain-switched thulium-doped fiber laser for volumetric photoacoustic imaging of lipids
Can Li, Jiawei Shi, Xiatian Wang, Boquan Wang, Xiaojing Gong, Liang Song, and Kenneth K. Y. Wong
We demonstrate a high-energy all-fiber short wavelength gain-switched thulium-doped fiber laser for volumetric photoacoustic (PA) imaging of lipids. The laser cavity is constructed by embedding a short piece of gain fiber between a pair of fiber Bragg gratings (FBGs). Through using three pairs of FBGs with operation wavelengths at 1700, 1725, and 1750 nm, three similar lasers are realized with a cavity length of around 25 cm. Under a maximum pump energy of 300 μJ at 1560 nm, laser pulse energies of 58.2, 66.8, and 75.3 μJ are, respectively, achieved with a minimum pulse width of 16.7 ns at a repetition rate of 10 kHz. Volumetric imaging of lipids is validated through scanning a fat beef slice with a PA microscopy system incorporated with the newly developed source, and a lateral resolution of 18.8 μm and an axial resolution of 172.9 μm are achieved. Moreover, the higher shooting speed of the developed source can potentially allow for increasing at twice the frame rate of current intravascular PA imaging.We demonstrate a high-energy all-fiber short wavelength gain-switched thulium-doped fiber laser for volumetric photoacoustic (PA) imaging of lipids. The laser cavity is constructed by embedding a short piece of gain fiber between a pair of fiber Bragg gratings (FBGs). Through using three pairs of FBGs with operation wavelengths at 1700, 1725, and 1750 nm, three similar lasers are realized with a cavity length of around 25 cm. Under a maximum pump energy of 300 μJ at 1560 nm, laser pulse energies of 58.2, 66.8, and 75.3 μJ are, respectively, achieved with a minimum pulse width of
Photonics Research
- Publication Date: Jan. 27, 2020
- Vol. 8, Issue 2, 160 (2020)
Optical and Photonic Materials
Third-order nonlinear optical susceptibility of crystalline oxide yttria-stabilized zirconia
Guillaume Marcaud, Samuel Serna, Karamanis Panaghiotis, Carlos Alonso-Ramos, Xavier Le Roux, Mathias Berciano, Thomas Maroutian, Guillaume Agnus, Pascal Aubert, Arnaud Jollivet, Alicia Ruiz-Caridad, Ludovic Largeau, Nathalie Isac, Eric Cassan, Sylvia Matzen, Nicolas Dubreuil, Michel Rérat, Philippe Lecoeur, and Laurent Vivien
Nonlinear all-optical technology is an ultimate route for next-generation ultrafast signal processing of optical communication systems. New nonlinear functionalities need to be implemented in photonics, and complex oxides are considered as promising candidates due to their wide panel of attributes. In this context, yttria-stabilized zirconia (YSZ) stands out, thanks to its ability to be epitaxially grown on silicon, adapting the lattice for the crystalline oxide family of materials. We report, for the first time to the best of our knowledge, a detailed theoretical and experimental study about the third-order nonlinear susceptibility in crystalline YSZ. Via self-phase modulation-induced broadening and considering the in-plane orientation of YSZ, we experimentally obtained an effective Kerr coefficient of n^2YSZ=4.0±2×10?19 m2·W?1 in an 8% (mole fraction) YSZ waveguide. In agreement with the theoretically predicted n^2YSZ=1.3×10?19 m2· W?1, the third-order nonlinear coefficient of YSZ is comparable with the one of silicon nitride, which is already being used in nonlinear optics. These promising results are a new step toward the implementation of functional oxides for nonlinear optical applications.Nonlinear all-optical technology is an ultimate route for next-generation ultrafast signal processing of optical communication systems. New nonlinear functionalities need to be implemented in photonics, and complex oxides are considered as promising candidates due to their wide panel of attributes. In this context, yttria-stabilized zirconia (YSZ) stands out, thanks to its ability to be epitaxially grown on silicon, adapting the lattice for the crystalline oxide family of materials. We report, for the first time to the best of our knowledge, a detailed theoretical and experimental study about the third-order nonlinear susceptibility in crystalline YSZ. Via self-phase modulation-induced broadening and considering the in-plane orientation of YSZ, we experimentally obtained an effective Kerr coefficient of
Photonics Research
- Publication Date: Jan. 07, 2020
- Vol. 8, Issue 2, 110 (2020)
Thermometry strategy developed based on fluorescence contrast driven by varying excitations in codoped LiNbO3
Siwei Long, Shaopeng Lin, Decai Ma, Yunzhong Zhu, Huashan Li, and Biao Wang
We propose what we believe is a novel optical thermometry strategy (FIR-Ex) based on the fluorescence intensity ratio (FIR) between two radiations associated with the same emission peak but different excitation wavelengths, in contrast to the traditional approach (FIR-Em), which depends on the FIR at varying emission wavelengths. The temperature-dependent FIR within the FIR-Ex strategy arises from the different charge/energy evolution routes, rather than the distribution of thermally coupled levels within the FIR-Em strategy. Considerable diversity in thermal behaviors and luminescence mechanisms was demonstrated by analyzing the 618 nm red emission in Pr3+-doped congruent LiNbO3 (Pr:CLN) under 360 and 463 nm excitations. The temperature sensitivity was further improved via Mg2+ codoping due to the optimization of charge dynamics and energy transfer processes. Given its wide detection scope, relatively high absolute sensitivity at low temperature, and high tunability of temperature sensitivity, the FIR-Ex strategy is promising for developing optical temperature-sensing materials with high performance.We propose what we believe is a novel optical thermometry strategy (FIR-Ex) based on the fluorescence intensity ratio (FIR) between two radiations associated with the same emission peak but different excitation wavelengths, in contrast to the traditional approach (FIR-Em), which depends on the FIR at varying emission wavelengths. The temperature-dependent FIR within the FIR-Ex strategy arises from the different charge/energy evolution routes, rather than the distribution of thermally coupled levels within the FIR-Em strategy. Considerable diversity in thermal behaviors and luminescence mechanisms was demonstrated by analyzing the 618 nm red emission in
Photonics Research
- Publication Date: Jan. 22, 2020
- Vol. 8, Issue 2, 135 (2020)
Microcrystal modulated exciton-polariton emissions from single ZnO@ZnO:Ga microwire
Wangqi Mao, Mingming Jiang, Jiaolong Ji, Peng Wan, Xiangbo Zhou, and Caixia Kan
Due to their outstanding surface-to-volume ratio, highly smooth surface, and well-defined crystal boundary, semiconducting micro-/nanocrystals have been used as a pivotal platform to fabricate multifunctional optoelectronic devices, such as superresolution imaging devices, solar concentrators, photodetectors, light-emitting diodes (LEDs), and lasers. In particular, micro-/nanocrystals as key elements can be employed to tailor the fundamental optical and electronic transport properties of integrated hetero-/homostructures. Herein, ZnO microcrystal-decorated pre-synthesized Ga-doped ZnO microwire (ZnO@ZnO:Ga MW) was prepared. The single ZnO@ZnO:Ga MW can be used to construct optically pumped Fabry–Perot (F–P) mode microlasers, with the dominating lasing peaks centered in the violet spectral region. Stabilized exciton-polariton emissions from single ZnO@ZnO:Ga MW-based heterojunction diode can also be realized. The deposited ZnO microcrystals can facilitate the strong coupling of F–P optical modes with excitons, leading to the formation of exciton-polariton features in the ZnO@ZnO:Ga MW. Therefore, the waveguiding lighting behavior and energy-band alignment of ZnO microcrystal-sheathed ZnO:Ga MW radial structures should be extremely attractive for potential applications in semiconducting microstructure-based optoelectronic devices, such as micro-LEDs, laser microcavities, waveguides, and photodetectors.Due to their outstanding surface-to-volume ratio, highly smooth surface, and well-defined crystal boundary, semiconducting micro-/nanocrystals have been used as a pivotal platform to fabricate multifunctional optoelectronic devices, such as superresolution imaging devices, solar concentrators, photodetectors, light-emitting diodes (LEDs), and lasers. In particular, micro-/nanocrystals as key elements can be employed to tailor the fundamental optical and electronic transport properties of integrated hetero-/homostructures. Herein, ZnO microcrystal-decorated pre-synthesized Ga-doped ZnO microwire (ZnO@ZnO:Ga MW) was prepared. The single ZnO@ZnO:Ga MW can be used to construct optically pumped Fabry–Perot (F–P) mode microlasers, with the dominating lasing peaks centered in the violet spectral region. Stabilized exciton-polariton emissions from single ZnO@ZnO:Ga MW-based heterojunction diode can also be realized. The deposited ZnO microcrystals can facilitate the strong coupling of F–P optical modes with excitons, leading to the formation of exciton-polariton features in the ZnO@ZnO:Ga MW. Therefore, the waveguiding lighting behavior and energy-band alignment of ZnO microcrystal-sheathed ZnO:Ga MW radial structures should be extremely attractive for potential applications in semiconducting microstructure-based optoelectronic devices, such as micro-LEDs, laser microcavities, waveguides, and photodetectors..
Photonics Research
- Publication Date: Jan. 31, 2020
- Vol. 8, Issue 2, 175 (2020)
Characterization of Yb-doped ZBLAN fiber as a platform for radiation-balanced lasers
Mostafa Peysokhan, Esmaeil Mobini, Arman Allahverdi, Behnam Abaie, and Arash Mafi
Recent advances in power scaling of fiber lasers are hindered by the thermal issues, which deteriorate the beam quality. Anti-Stokes fluorescence cooling has been suggested as a viable method to balance the heat generated by the quantum defect and background absorption. Such radiation-balanced configurations rely on the availability of cooling-grade rare-earth-doped gain materials. Herein, we perform a series of tests on an ytterbium-doped ZrF4–BaF2–LaF3–AlF3–NaF (ZBLAN) optical fiber to extract its laser-cooling-related parameters and show that it is a viable laser-cooling medium for radiation balancing. In particular, a detailed laser-induced modulation spectrum test is performed to highlight the transition of this fiber to the cooling regime as a function of the pump laser wavelength. Numerical simulations support the feasibility of a radiation-balanced laser, but they highlight that practical radiation-balanced designs are more demanding on the fiber material properties, especially on the background absorption, than solid-state laser-cooling experiments.Recent advances in power scaling of fiber lasers are hindered by the thermal issues, which deteriorate the beam quality. Anti-Stokes fluorescence cooling has been suggested as a viable method to balance the heat generated by the quantum defect and background absorption. Such radiation-balanced configurations rely on the availability of cooling-grade rare-earth-doped gain materials. Herein, we perform a series of tests on an ytterbium-doped
Photonics Research
- Publication Date: Jan. 31, 2020
- Vol. 8, Issue 2, 202 (2020)
Quantum Optics
Quantum nonreciprocality in quadratic optomechanics
Xunwei Xu, Yanjun Zhao, Hui Wang, Hui Jing, and Aixi Chen
We propose to achieve nonreciprocal quantum control of photons in a quadratic optomechanical (QOM) system based on directional nonlinear interactions. We show that by optically pumping the QOM system in one side, the effective QOM coupling can be enhanced significantly in that side, but not for the other side. This, contrary to the intuitive picture, allows the emergence of a nonreciprocal photon blockade in such optomechanical devices with weak single-photon QOM coupling. Our proposal opens up the prospect of exploring and utilizing quantum nonreciprocal optomechanics, with applications ranging from single-photon nonreciprocal devices to on-chip chiral quantum engineering.We propose to achieve nonreciprocal quantum control of photons in a quadratic optomechanical (QOM) system based on directional nonlinear interactions. We show that by optically pumping the QOM system in one side, the effective QOM coupling can be enhanced significantly in that side, but not for the other side. This, contrary to the intuitive picture, allows the emergence of a nonreciprocal photon blockade in such optomechanical devices with weak single-photon QOM coupling. Our proposal opens up the prospect of exploring and utilizing quantum nonreciprocal optomechanics, with applications ranging from single-photon nonreciprocal devices to on-chip chiral quantum engineering..
Photonics Research
- Publication Date: Jan. 22, 2020
- Vol. 8, Issue 2, 143 (2020)
Strong mechanical squeezing in an optomechanical system based on Lyapunov control
Biao Xiong, Xun Li, Shi-Lei Chao, Zhen Yang, Wen-Zhao Zhang, Weiping Zhang, and Ling Zhou
We propose a scheme to generate strong squeezing of a mechanical oscillator in an optomechanical system through Lyapunov control. Frequency modulation of the mechanical oscillator is designed via Lyapunov control. We show that the momentum variance of the mechanical oscillator decreases with time evolution in a weak coupling case. As a result, strong mechanical squeezing is realized quickly (beyond 3 dB). In addition, the proposal is immune to cavity decay. Moreover, we show that the obtained squeezing can be detected via an ancillary cavity mode with homodyne detection.We propose a scheme to generate strong squeezing of a mechanical oscillator in an optomechanical system through Lyapunov control. Frequency modulation of the mechanical oscillator is designed via Lyapunov control. We show that the momentum variance of the mechanical oscillator decreases with time evolution in a weak coupling case. As a result, strong mechanical squeezing is realized quickly (beyond 3 dB). In addition, the proposal is immune to cavity decay. Moreover, we show that the obtained squeezing can be detected via an ancillary cavity mode with homodyne detection..
Photonics Research
- Publication Date: Jan. 24, 2020
- Vol. 8, Issue 2, 151 (2020)
Silicon Photonics
Real-time, in situ probing of gamma radiation damage with packaged integrated photonic chips
Qingyang Du, Jérôme Michon, Bingzhao Li, Derek Kita, Danhao Ma, Haijie Zuo, Shaoliang Yu, Tian Gu, Anuradha Agarwal, Mo Li, and Juejun Hu
Integrated photonics is poised to become a mainstream solution for high-speed data communications and sensing in harsh radiation environments, such as outer space, high-energy physics facilities, nuclear power plants, and test fusion reactors. Understanding the impact of radiation damage in optical materials and devices is thus a prerequisite to building radiation-hard photonic systems for these applications. In this paper, we report real-time, in situ analysis of radiation damage in integrated photonic devices. The devices, integrated with an optical fiber array package and a baseline-correction temperature sensor, can be remotely interrogated while exposed to ionizing radiation over a long period without compromising their structural and optical integrity. We also introduce a method to deconvolve the radiation damage responses from different constituent materials in a device. The approach was implemented to quantify gamma radiation damage and post-radiation relaxation behavior of SiO2-cladded SiC photonic devices. Our findings suggest that densification induced by Compton scattering displacement defects is the primary mechanism for the observed index change in SiC. Additionally, post-radiation relaxation in amorphous SiC does not restore the original pre-irradiated structural state of the material. Our results further point to the potential of realizing radiation-hard photonic device designs taking advantage of the opposite signs of radiation-induced index changes in SiC and SiO2.Integrated photonics is poised to become a mainstream solution for high-speed data communications and sensing in harsh radiation environments, such as outer space, high-energy physics facilities, nuclear power plants, and test fusion reactors. Understanding the impact of radiation damage in optical materials and devices is thus a prerequisite to building radiation-hard photonic systems for these applications. In this paper, we report real-time, in situ analysis of radiation damage in integrated photonic devices. The devices, integrated with an optical fiber array package and a baseline-correction temperature sensor, can be remotely interrogated while exposed to ionizing radiation over a long period without compromising their structural and optical integrity. We also introduce a method to deconvolve the radiation damage responses from different constituent materials in a device. The approach was implemented to quantify gamma radiation damage and post-radiation relaxation behavior of
Photonics Research
- Publication Date: Jan. 31, 2020
- Vol. 8, Issue 2, 186 (2020)
Fabrication-tolerant Fourier transform spectrometer on silicon with broad bandwidth and high resolution
Ang Li, Jordan Davis, Andrew Grieco, Naif Alshamrani, and Yeshaiahu Fainman
We report an advanced Fourier transform spectrometer (FTS) on silicon with significant improvement compared with our previous demonstration in [Nat. Commun.9, 665 (2018)2041-1723]. We retrieve a broadband spectrum (7 THz around 193 THz) with 0.11 THz or sub nm resolution, more than 3 times higher than previously demonstrated [Nat. Commun.9, 665 (2018)2041-1723]. Moreover, it effectively solves the issue of fabrication variation in waveguide width, which is a common issue in silicon photonics. The structure is a balanced Mach–Zehnder interferometer with 10 cm long serpentine waveguides. Quasi-continuous optical path difference between the two arms is induced by changing the effective index of one arm using an integrated heater. The serpentine arms utilize wide multi-mode waveguides at the straight sections to reduce propagation loss and narrow single-mode waveguides at the bending sections to keep the footprint compact and avoid modal crosstalk. The reduction of propagation loss leads to higher spectral efficiency, larger dynamic range, and better signal-to-noise ratio. Also, for the first time to our knowledge, we perform a thorough systematic analysis on how the fabrication variation on the waveguide widths can affect its performance. Additionally, we demonstrate that using wide waveguides efficiently leads to a fabrication-tolerant device. This work could further pave the way towards a mature silicon-based FTS operating with both broad bandwidth (over 60 nm) and high resolution suitable for integration with various mobile platforms.We report an advanced Fourier transform spectrometer (FTS) on silicon with significant improvement compared with our previous demonstration in [Nat. Commun. 9 , 665 (2018 )2041-1723 Nat. Commun. 9 , 665 (2018 )2041-1723
Photonics Research
- Publication Date: Jan. 31, 2020
- Vol. 8, Issue 2, 219 (2020)
Spectroscopy
Facilitated tip-enhanced Raman scattering by focused gap-plasmon hybridization
Houkai Chen, Yuquan Zhang, Yanmeng Dai, Changjun Min, Siwei Zhu, and Xiaocong Yuan
Tip-enhanced Raman scattering (TERS) spectroscopy is a nondestructive and label-free molecular detection approach that provides high sensitivity and nanoscale spatial resolution. Therefore, it has been used in a wide array of applications. We demonstrate a gap-plasmon hybridization facilitated by a bottom-illuminated TERS configuration. The gap-plasmon hybridization effect is first performed with the finite-difference time-domain method to optimize the parameters, and experiments are then conducted to calibrate the performance. The results demonstrate an enhancement factor of 1157 and a spatial resolution of 13.5 nm. The proposed configuration shows great potential in related surface imaging applications in various fields of research.Tip-enhanced Raman scattering (TERS) spectroscopy is a nondestructive and label-free molecular detection approach that provides high sensitivity and nanoscale spatial resolution. Therefore, it has been used in a wide array of applications. We demonstrate a gap-plasmon hybridization facilitated by a bottom-illuminated TERS configuration. The gap-plasmon hybridization effect is first performed with the finite-difference time-domain method to optimize the parameters, and experiments are then conducted to calibrate the performance. The results demonstrate an enhancement factor of 1157 and a spatial resolution of 13.5 nm. The proposed configuration shows great potential in related surface imaging applications in various fields of research..
Photonics Research
- Publication Date: Jan. 07, 2020
- Vol. 8, Issue 2, 103 (2020)
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