Contents
2017
Volume: 5 Issue 4
19 Article(s)
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Research Articles
Image Processing
Experimental investigation of ghost imaging of reflective objects with different surface roughness
Suqin Nan, Yanfeng Bai, Xiaohui Shi, Qian Shen, Lijie Qu, Hengxing Li, and Xiquan Fu
We present an experimental demonstration of ghost imaging of reflective objects with different surface roughness. The influence of the surface roughness, the transverse size of the test detector, and the reflective angle on the signal-to-noise ratio (SNR) is analyzed by measuring the second-order correlation of the light field based on classical statistical optics. It is shown that the SNR decreases with an increment of the surface roughness and the detector’s transverse size or a decrease of the reflective angle. Additionally, the comparative studies between the rough object and the smooth one under the same conditions are also discussed.We present an experimental demonstration of ghost imaging of reflective objects with different surface roughness. The influence of the surface roughness, the transverse size of the test detector, and the reflective angle on the signal-to-noise ratio (SNR) is analyzed by measuring the second-order correlation of the light field based on classical statistical optics. It is shown that the SNR decreases with an increment of the surface roughness and the detector’s transverse size or a decrease of the reflective angle. Additionally, the comparative studies between the rough object and the smooth one under the same conditions are also discussed..
Photonics Research
- Publication Date: Jul. 26, 2017
- Vol. 5, Issue 4, 372 (2017)
Lasers and Laser Optics
Multipoint fiber-optic laser–ultrasound generation along a fiber based on the core-offset splicing of fibers
Xiaolong Dong, Shimin Gao, Jiajun Tian, and Yong Yao
Fiber-optic laser–ultrasound generation is being used in an increasing number of applications, including medical diagnosis, material characterization, and structural health monitoring. However, most currently used fiber-optic ultrasonic transducers allow effective ultrasound generation at only a single location, namely, at the fiber tip, although there have been a few limited proposals for achieving multipoint ultrasound generation along the length of a fiber. Here we present a novel fiber-optic ultrasound transducer that uses the core-offset splicing of fibers to effectively generate ultrasound at multiple locations along the fiber. The proposed laser–ultrasonic transducer can produce a balanced-strength signal between ultrasonic generation points by reasonably controlling the offsets of the fibers. The proposed transducer has other outstanding characteristics, including simple fabrication and low cost.Fiber-optic laser–ultrasound generation is being used in an increasing number of applications, including medical diagnosis, material characterization, and structural health monitoring. However, most currently used fiber-optic ultrasonic transducers allow effective ultrasound generation at only a single location, namely, at the fiber tip, although there have been a few limited proposals for achieving multipoint ultrasound generation along the length of a fiber. Here we present a novel fiber-optic ultrasound transducer that uses the core-offset splicing of fibers to effectively generate ultrasound at multiple locations along the fiber. The proposed laser–ultrasonic transducer can produce a balanced-strength signal between ultrasonic generation points by reasonably controlling the offsets of the fibers. The proposed transducer has other outstanding characteristics, including simple fabrication and low cost..
Photonics Research
- Publication Date: Jun. 14, 2017
- Vol. 5, Issue 4, 287 (2017)
Fiber laser with random-access pulse train profiling for a photoinjector driver
Ekaterina I. Gacheva, Anatoly K. Poteomkin, Sergey Yu. Mironov, Viktor V. Zelenogorskii, Efim A. Khazanov, Konstantin B. Yushkov, Alexander I. Chizhikov, and Vladimir Ya. Molchanov
We report on the design and performance of a fiber laser system with adaptive acousto-optic macropulse control for a novel photocathode laser driver with 3D ellipsoidal pulse shaping. The laser system incorporates a three-stage fiber amplifier with an integrated acousto-optical modulator. A digital electronic control system with feedback combines the functions of the arbitrary micropulse selection and modulation resulting in macropulse envelope profiling. As a benefit, a narrow temporal transparency window of the modulator, comparable to a laser pulse repetition period, effectively improves temporal contrast. In experiments, we demonstrated rectangular laser pulse train profiling at the output of a three-cascade Yb-doped fiber amplifier.We report on the design and performance of a fiber laser system with adaptive acousto-optic macropulse control for a novel photocathode laser driver with 3D ellipsoidal pulse shaping. The laser system incorporates a three-stage fiber amplifier with an integrated acousto-optical modulator. A digital electronic control system with feedback combines the functions of the arbitrary micropulse selection and modulation resulting in macropulse envelope profiling. As a benefit, a narrow temporal transparency window of the modulator, comparable to a laser pulse repetition period, effectively improves temporal contrast. In experiments, we demonstrated rectangular laser pulse train profiling at the output of a three-cascade Yb-doped fiber amplifier..
Photonics Research
- Publication Date: Jun. 14, 2017
- Vol. 5, Issue 4, 293 (2017)
Exploiting a metal wire grating in total internal reflection geometry to achieve achromatic polarization conversion
Xudong Liu, Xuequan Chen, Edward P. J. Parrott, and Emma Pickwell-MacPherson
We demonstrate how a metal wire grating can work as a 45° polarization converter, a quarter-wave retarder, and a half-wave retarder over a broadband terahertz range when set up in total internal reflection geometry. Classical electromagnetic theory is applied to understand the mechanism, and equations to calculate the polarization state of reflected light are derived. We use a metal grating with a period of 20 μm and width of 10 μm on a fused silica surface: linearly polarized terahertz light incident from fused silica with a supercritical incident angle of 52° is totally reflected by the metal grating and air. The polarization of the terahertz light is rotated by 45°, 90°, and circularly polarized by simply rotating the wire grating. The performance is achromatic over the measured range of 0.1–0.7 THz and comparable to commercial visible light wave retarders.We demonstrate how a metal wire grating can work as a 45° polarization converter, a quarter-wave retarder, and a half-wave retarder over a broadband terahertz range when set up in total internal reflection geometry. Classical electromagnetic theory is applied to understand the mechanism, and equations to calculate the polarization state of reflected light are derived. We use a metal grating with a period of 20 μm and width of 10 μm on a fused silica surface: linearly polarized terahertz light incident from fused silica with a supercritical incident angle of 52° is totally reflected by the metal grating and air. The polarization of the terahertz light is rotated by 45°, 90°, and circularly polarized by simply rotating the wire grating. The performance is achromatic over the measured range of 0.1–0.7 THz and comparable to commercial visible light wave retarders..
Photonics Research
- Publication Date: Jun. 14, 2017
- Vol. 5, Issue 4, 299 (2017)
Effects of gain nonlinearities in an optically injected gain lever semiconductor laser | On the Cover
J. M. Sarraute, K. Schires, S. LaRochelle, and F. Grillot
The effects of gain compression on the modulation dynamics of an optically injected gain lever semiconductor laser are studied. Calculations reveal that the gain compression is not necessarily a drawback affecting the laser dynamics. With a practical injection strength, a high gain lever effect and a moderate compression value allow us to theoretically predict a modulation bandwidth four times higher than the free-running one without a gain lever, which is of paramount importance for the development of directly modulated broadband optical sources compatible with short-reach communication links.The effects of gain compression on the modulation dynamics of an optically injected gain lever semiconductor laser are studied. Calculations reveal that the gain compression is not necessarily a drawback affecting the laser dynamics. With a practical injection strength, a high gain lever effect and a moderate compression value allow us to theoretically predict a modulation bandwidth four times higher than the free-running one without a gain lever, which is of paramount importance for the development of directly modulated broadband optical sources compatible with short-reach communication links..
Photonics Research
- Publication Date: Jun. 29, 2017
- Vol. 5, Issue 4, 315 (2017)
Stable single-mode operation of a distributed feedback quantum cascade laser integrated with a distributed Bragg reflector
Feng-Min Cheng, Zhi-Wei Jia, Jin-Chuan Zhang, Ning Zhuo, Shen-Qiang Zhai, Li-Jun Wang, Jun-Qi Liu, Shu-Man Liu, Feng-Qi Liu, and Zhan-Guo Wang
We report an index-coupled distributed feedback quantum cascade laser by employing an equivalent phase shift (EPS) of quarter-wave integrated with a distributed Bragg reflector (DBR) at λ～5.03 μm. The EPS is fabricated through extending one sampling period by 50% in the center of a sampled Bragg grating. The key EPS and DBR pattern are fabricated by conventional holographic exposure combined with the optical photolithography technology, which leads to improved flexibility, repeatability, and cost-effectiveness. Stable single-mode emission can be obtained by changing the injection current or heat sink temperature even under the condition of large driving pulse width.We report an index-coupled distributed feedback quantum cascade laser by employing an equivalent phase shift (EPS) of quarter-wave integrated with a distributed Bragg reflector (DBR) at λ ～ 5.03 μm
Photonics Research
- Publication Date: Jun. 29, 2017
- Vol. 5, Issue 4, 320 (2017)
High power and beam quality continuous-wave Nd:GdVO4 laser in-band diode-pumped at 912 nm
Mohammad Nadimi, Tanant Waritanant, and Arkady Major
We report on the performance of a continuous-wave Nd:GdVO4 laser in-band diode-pumped at 912 nm with high output power and excellent beam quality. The laser produced an output power of 19.8 W at 1063 nm with an optical efficiency of 59.3% and slope efficiency of 62.7%. The laser threshold was ～2.04 W of the absorbed pump power, and laser output beam quality was ≤1.2 in the horizontal and vertical directions. The strength of thermal lensing at full output power (33.4 W of absorbed power) was measured to be an average of 8.6 diopters. It is shown that thermal lensing is reduced by a factor of 2 with respect to the Nd:YVO4 lasers, thus opening a way for further output-power scaling.We report on the performance of a continuous-wave Nd : GdVO 4 ～ 2.04 W ≤ 1.2 Nd : YVO 4
Photonics Research
- Publication Date: Jul. 05, 2017
- Vol. 5, Issue 4, 346 (2017)
Near-diffraction-limited linearly polarized narrow-linewidth random fiber laser with record kilowatt output
Jiangming Xu, Long Huang, Man Jiang, Jun Ye, Pengfei Ma, Jinyong Leng, Jian Wu, Hanwei Zhang, and Pu Zhou
In this paper, we propose and experimentally investigate a linearly polarized narrow-linewidth random fiber laser (RFL) operating at 1080 nm and boost the output power to kilowatt level with near-diffraction-limited beam quality using a master oscillation power amplifier. The RFL based on a half-opened cavity, which is composed of a linearly polarized narrow-linewidth fiber Bragg grating and a 500 m piece of polarization-maintained Ge-doped fiber, generates a 0.71 W seed laser with an 88 pm full width at half-maximum (FWHM) linewidth and a 22.5 dB polarization extinction ratio (PER) for power scaling. A two-stage fiber amplifier enhances the seed laser to the maximal 1.01 kW with a PER value of 17 dB and a beam quality of Mx2=1.15 and My2=1.13. No stimulated Brillouin scattering effect is observed at the ultimate power level, and the FWHM linewidth of the amplified random laser broadens linearly as a function of the output power with a coefficient of about 0.1237 pm/W. To the best of our knowledge, this is the first demonstration of a linearly polarized narrow-linewidth RFL with even kilowatt-level near-diffraction-limited output, and further performance scaling is ongoing.In this paper, we propose and experimentally investigate a linearly polarized narrow-linewidth random fiber laser (RFL) operating at 1080 nm and boost the output power to kilowatt level with near-diffraction-limited beam quality using a master oscillation power amplifier. The RFL based on a half-opened cavity, which is composed of a linearly polarized narrow-linewidth fiber Bragg grating and a 500 m piece of polarization-maintained Ge-doped fiber, generates a 0.71 W seed laser with an 88 pm full width at half-maximum (FWHM) linewidth and a 22.5 dB polarization extinction ratio (PER) for power scaling. A two-stage fiber amplifier enhances the seed laser to the maximal 1.01 kW with a PER value of 17 dB and a beam quality of
Photonics Research
- Publication Date: Jul. 10, 2017
- Vol. 5, Issue 4, 350 (2017)
Microscopy
Woofer– tweeter adaptive optical structured illumination microscopy
Qinggele Li, Marc Reinig, Daich Kamiyama, Bo Huang, Xiaodong Tao, Alex Bardales, and Joel Kubby
A woofer–tweeter adaptive optical structured illumination microscope (AOSIM) is presented. By combining a low-spatial-frequency large-stroke deformable mirror (woofer) with a high-spatial-frequency low-stroke deformable mirror (tweeter), we are able to remove both large-amplitude and high-order aberrations. In addition, using the structured illumination method, as compared to widefield microscopy, the AOSIM can accomplish high-resolution imaging and possesses better sectioning capability. The AOSIM was tested by correcting a large aberration from a trial lens in the conjugate plane of the microscope objective aperture. The experimental results show that the AOSIM has a point spread function with an FWHM that is 140 nm wide (using a water immersion objective lens with NA=1.1) after correcting a large aberration (5.9 μm peak-to-valley wavefront error with 2.05 μm RMS aberration). After structured light illumination is applied, the results show that we are able to resolve two beads that are separated by 145 nm, 1.62× below the diffraction limit of 235 nm. Furthermore, we demonstrate the application of the AOSIM in the field of bioimaging. The sample under investigation was a green-fluorescent-protein-labeled Drosophila embryo. The aberrations from the refractive index mismatch between the microscope objective, the immersion fluid, the cover slip, and the sample itself are well corrected. Using AOSIM we were able to increase the SNR for our Drosophila embryo sample by 5×.A woofer–tweeter adaptive optical structured illumination microscope (AOSIM) is presented. By combining a low-spatial-frequency large-stroke deformable mirror (woofer) with a high-spatial-frequency low-stroke deformable mirror (tweeter), we are able to remove both large-amplitude and high-order aberrations. In addition, using the structured illumination method, as compared to widefield microscopy, the AOSIM can accomplish high-resolution imaging and possesses better sectioning capability. The AOSIM was tested by correcting a large aberration from a trial lens in the conjugate plane of the microscope objective aperture. The experimental results show that the AOSIM has a point spread function with an FWHM that is 140 nm wide (using a water immersion objective lens with NA = 1.1 1.62 × Drosophila embryo. The aberrations from the refractive index mismatch between the microscope objective, the immersion fluid, the cover slip, and the sample itself are well corrected. Using AOSIM we were able to increase the SNR for our Drosophila embryo sample by 5 ×
Photonics Research
- Publication Date: Jun. 29, 2017
- Vol. 5, Issue 4, 329 (2017)
Nonlinear Optics
Fabrication and near-infrared optical responses of 2D periodical Au/ITO nanocomposite arrays
Zhengyuan Bai, Guiju Tao, Yuanxin Li, Jin He, Kangpeng Wang, Gaozhong Wang, Xiongwei Jiang, Jun Wang, Werner Blau, and Long Zhang
Two-dimensional (2D) periodical Au and indium tin oxide (ITO) nanocomposite arrays have been fabricated based on a self-assembled nanosphere lithography technique. A button-shaped Au nanoparticle was formed on each hollow hemisphere-shaped ITO shell. Importantly, the underlying formation mechanism during the thermal treatment has been thoroughly explored by comparing structures resulting from different deposition conditions in detail. Compared to the Au nanoparticle arrays without ITO shells, the Au/ITO nanocomposite arrays showed a stronger localized surface plasmon resonance effect and higher absorption in the near-infrared (NIR) region, benefiting from the free-electron interaction enhancement between Au and ITO. The nonlinear optical properties were investigated using a modified femtosecond intensity-scan system, and the results demonstrated Au/ITO nanocomposite arrays with a remarkable two-photon absorption saturation effect for femtosecond pulses at 1030 nm. The versatile NIR optical responses indicate the great potential of the elaborately prepared 2D periodical Au/ITO nanocomposite arrays in many applications such as solar cells, photocatalysis, and novel nano optoelectronic devices.Two-dimensional (2D) periodical Au and indium tin oxide (ITO) nanocomposite arrays have been fabricated based on a self-assembled nanosphere lithography technique. A button-shaped Au nanoparticle was formed on each hollow hemisphere-shaped ITO shell. Importantly, the underlying formation mechanism during the thermal treatment has been thoroughly explored by comparing structures resulting from different deposition conditions in detail. Compared to the Au nanoparticle arrays without ITO shells, the Au/ITO nanocomposite arrays showed a stronger localized surface plasmon resonance effect and higher absorption in the near-infrared (NIR) region, benefiting from the free-electron interaction enhancement between Au and ITO. The nonlinear optical properties were investigated using a modified femtosecond intensity-scan system, and the results demonstrated Au/ITO nanocomposite arrays with a remarkable two-photon absorption saturation effect for femtosecond pulses at 1030 nm. The versatile NIR optical responses indicate the great potential of the elaborately prepared 2D periodical Au/ITO nanocomposite arrays in many applications such as solar cells, photocatalysis, and novel nano optoelectronic devices..
Photonics Research
- Publication Date: Jun. 06, 2017
- Vol. 5, Issue 4, 280 (2017)
Nonlinear interaction between broadband single-photon-level coherent states
Yuanhua Li, Tong Xiang, Yiyou Nie, Minghuang Sang, and Xianfeng Chen
We experimentally demonstrate the nonlinear interaction between two chirped broadband single-photon-level coherent states. Each chirped coherent state is generated in independent fiber Bragg gratings. They are simultaneously coupled into a high-efficiency nonlinear waveguide, where they are converted into a narrowband single-photon state with a new frequency by the process of sum-frequency generation (SFG). A higher SFG efficiency of 1.06×10 7 is realized, and this efficiency may achieve heralding entanglement at a distance. This also made it possible to realize long-distance quantum communication, such as device-independent quantum key distribution, by directly using broadband single photons without filtering.We experimentally demonstrate the nonlinear interaction between two chirped broadband single-photon-level coherent states. Each chirped coherent state is generated in independent fiber Bragg gratings. They are simultaneously coupled into a high-efficiency nonlinear waveguide, where they are converted into a narrowband single-photon state with a new frequency by the process of sum-frequency generation (SFG). A higher SFG efficiency of 1.06 × 10 7
Photonics Research
- Publication Date: Jun. 29, 2017
- Vol. 5, Issue 4, 324 (2017)
Amplification assisted difference frequency generation for efficient mid-infrared conversion based on monolithic tandem lithium niobate superlattice
Tao Chen, Hao Liu, Wei Kong, and Rong Shu
We report the investigation on the performance of an amplification assisted difference frequency generation (AA-DFG) system driven by pulsed pump and continuous-wave primary signal lasers. A monolithic tandem lithium niobate superlattice was employed as the nonlinear crystal with a uniform grating section for the DFG process, followed by a chirp section for the optical parametric amplification process. The impacts of pump pulse shape, primary signal power, input beam diameter, and crystal structure on the pump-to-idler conversion efficiency of the AA-DFG system were comprehensively studied by numerically solving the coupled wave equations. It is concluded that square pump pulse and high primary signal power are beneficial to high pump-to-idler conversion efficiency. In addition, tighter input beam focus and smaller DFG length proportion could redeem the reduction in conversion efficiency resulting from wider acceptance bandwidths for the input lasers. We believe that such systems combining the merits of high stability inherited from cavity-free configuration and high efficiency attributed from the cascaded nonlinear conversion should be of great interest to a wide community, especially when the pulse shaping technique is incorporated.We report the investigation on the performance of an amplification assisted difference frequency generation (AA-DFG) system driven by pulsed pump and continuous-wave primary signal lasers. A monolithic tandem lithium niobate superlattice was employed as the nonlinear crystal with a uniform grating section for the DFG process, followed by a chirp section for the optical parametric amplification process. The impacts of pump pulse shape, primary signal power, input beam diameter, and crystal structure on the pump-to-idler conversion efficiency of the AA-DFG system were comprehensively studied by numerically solving the coupled wave equations. It is concluded that square pump pulse and high primary signal power are beneficial to high pump-to-idler conversion efficiency. In addition, tighter input beam focus and smaller DFG length proportion could redeem the reduction in conversion efficiency resulting from wider acceptance bandwidths for the input lasers. We believe that such systems combining the merits of high stability inherited from cavity-free configuration and high efficiency attributed from the cascaded nonlinear conversion should be of great interest to a wide community, especially when the pulse shaping technique is incorporated..
Photonics Research
- Publication Date: Jul. 13, 2017
- Vol. 5, Issue 4, 355 (2017)
Optical Vortices
Efficient separating orbital angular momentum mode with radial varying phase
Cheng Li, and Shengmei Zhao
It is shown that orbital angular momentum (OAM) is a promising new resource in future classical and quantum communications. However, the separation of OAM modes is still a big challenge. In this paper, we propose a simple and efficient separation method with a radial varying phase. In the method, specific radial varying phases are designed and modulated for different OAM modes. The resultant beam is focused to the spots with different horizontal and vertical positions after a convex lens, when the coordinate transformation, including two optical elements with coordinate transformation phase and correct phase, operates on the received beam. The horizontal position of the spot is determined by the vortex phases, and the vertical position of the spot is dependent on the radial varying phases. The simulation and experimental results show that the proposed method is feasible both for separation of two OAM modes and separation of three OAM modes. The proposed separation method is available in principle for any neighboring OAM modes because the radial varying phase is controlled. Additionally, no extra instruments are introduced, and there is no diffraction and narrowing process limitation for the separation.It is shown that orbital angular momentum (OAM) is a promising new resource in future classical and quantum communications. However, the separation of OAM modes is still a big challenge. In this paper, we propose a simple and efficient separation method with a radial varying phase. In the method, specific radial varying phases are designed and modulated for different OAM modes. The resultant beam is focused to the spots with different horizontal and vertical positions after a convex lens, when the coordinate transformation, including two optical elements with coordinate transformation phase and correct phase, operates on the received beam. The horizontal position of the spot is determined by the vortex phases, and the vertical position of the spot is dependent on the radial varying phases. The simulation and experimental results show that the proposed method is feasible both for separation of two OAM modes and separation of three OAM modes. The proposed separation method is available in principle for any neighboring OAM modes because the radial varying phase is controlled. Additionally, no extra instruments are introduced, and there is no diffraction and narrowing process limitation for the separation..
Photonics Research
- Publication Date: Jun. 06, 2017
- Vol. 5, Issue 4, 267 (2017)
Optics at Surfaces
Multiple resonant excitations of surface plasmons in a graphene stratified slab by Otto configuration and their independent tuning
Jin Yao, Ying Chen, Longfang Ye, Na Liu, Guoxiong Cai, and Qing Huo Liu
Multiple resonant excitations of surface plasmons in a graphene stratified slab are realized by Otto configuration at terahertz frequencies. The proposed graphene stratified slab consists of alternating dielectric layers and graphene sheets, and is sandwiched between a prism and another semi-infinite medium. Optical response and field distribution are determined by the transfer matrix method with the surface current density boundary condition. Multiple resonant excitations appear on the angular reflection spectrum, and are analyzed theoretically via the phase-matching condition. Furthermore, the effects of the system parameters are investigated. Among them, the Fermi levels can tune the corresponding resonances independently. The proposed concept can be engineered for promising applications, including angular selective or multiplex filters, multiple channel sensors, and directional delivery of energy.Multiple resonant excitations of surface plasmons in a graphene stratified slab are realized by Otto configuration at terahertz frequencies. The proposed graphene stratified slab consists of alternating dielectric layers and graphene sheets, and is sandwiched between a prism and another semi-infinite medium. Optical response and field distribution are determined by the transfer matrix method with the surface current density boundary condition. Multiple resonant excitations appear on the angular reflection spectrum, and are analyzed theoretically via the phase-matching condition. Furthermore, the effects of the system parameters are investigated. Among them, the Fermi levels can tune the corresponding resonances independently. The proposed concept can be engineered for promising applications, including angular selective or multiplex filters, multiple channel sensors, and directional delivery of energy..
Photonics Research
- Publication Date: Jul. 26, 2017
- Vol. 5, Issue 4, 377 (2017)
Quantum Optics
Optomechanically induced transparency in a spinning resonator
Hao Lü, Yajing Jiang, Yu-Zhu Wang, and Hui Jing
We study optomechanically induced transparency in a spinning microresonator. We find that in the presence of rotation-induced Sagnac frequency shift, both the transmission rate and the group delay of the signal are strongly affected, leading to a Fano-like spectrum of transparency. In particular, tuning the rotary speed leads to the emergence of nonreciprocal optical sidebands. This indicates a promising new way to control hybrid light–sound devices with spinning resonators.We study optomechanically induced transparency in a spinning microresonator. We find that in the presence of rotation-induced Sagnac frequency shift, both the transmission rate and the group delay of the signal are strongly affected, leading to a Fano-like spectrum of transparency. In particular, tuning the rotary speed leads to the emergence of nonreciprocal optical sidebands. This indicates a promising new way to control hybrid light–sound devices with spinning resonators..
Photonics Research
- Publication Date: Jul. 21, 2017
- Vol. 5, Issue 4, 367 (2017)
Resonators
Bandpass transmission spectra of a whispering-gallery microcavity coupled to an ultrathin fiber
Fuchuan Lei, Rafino M. J. Murphy, Jonathan M. Ward, Yong Yang, and Síle Nic Chormaic
Tapered fibers with diameters ranging from 1 to 4 μm are widely used to excite the whispering-gallery (WG) modes of microcavities. Typically, the transmission spectrum of a WG cavity coupled to a waveguide around a resonance assumes a Lorentzian dip morphology due to resonant absorption of the light within the cavity. In this paper, we demonstrate that the transmission spectra of a WG cavity coupled with an ultrathin fiber (500–700 nm) may exhibit both Lorentzian dips and peaks, depending on the gap between the fiber and the microcavity. By considering the large scattering loss of off-resonant light from the fiber within the coupling region, this phenomenon can be attributed to partially resonant light bypassing the lossy scattering region via WG modes, allowing it to be coupled both to and from the cavity, then manifesting as Lorentzian peaks within the transmission spectra. This implies the system could be implemented within a bandpass filter framework.Tapered fibers with diameters ranging from 1 to 4 μm are widely used to excite the whispering-gallery (WG) modes of microcavities. Typically, the transmission spectrum of a WG cavity coupled to a waveguide around a resonance assumes a Lorentzian dip morphology due to resonant absorption of the light within the cavity. In this paper, we demonstrate that the transmission spectra of a WG cavity coupled with an ultrathin fiber (500–700 nm) may exhibit both Lorentzian dips and peaks, depending on the gap between the fiber and the microcavity. By considering the large scattering loss of off-resonant light from the fiber within the coupling region, this phenomenon can be attributed to partially resonant light bypassing the lossy scattering region via WG modes, allowing it to be coupled both to and from the cavity, then manifesting as Lorentzian peaks within the transmission spectra. This implies the system could be implemented within a bandpass filter framework..
Photonics Research
- Publication Date: Jul. 18, 2017
- Vol. 5, Issue 4, 362 (2017)
Silicon Photonics
Characterization of geometry and depleting carrier dependence of active silicon waveguide in tailoring optical properties
Md Rezwanul Haque Khandokar, Masuduzzaman Bakaul, Md Asaduzzaman, Stan Skafidas, and Thas Nirmalathas
Changes in refractive index and the corresponding changes in the characteristics of an optical waveguide in enabling propagation of light are the basis for many modern silicon photonic devices. Optical properties of these active nanoscale waveguides are sensitive to the little changes in geometry, external injection/biasing, and doping profiles, and can be crucial in design and manufacturing processes. This paper brings the active silicon waveguide for complete characterization of various distinctive guiding parameters, including perturbation in real and imaginary refractive index, mode loss, group velocity dispersion, and bending loss, which can be instrumental in developing optimal design specifications for various application-centric active silicon waveguides.Changes in refractive index and the corresponding changes in the characteristics of an optical waveguide in enabling propagation of light are the basis for many modern silicon photonic devices. Optical properties of these active nanoscale waveguides are sensitive to the little changes in geometry, external injection/biasing, and doping profiles, and can be crucial in design and manufacturing processes. This paper brings the active silicon waveguide for complete characterization of various distinctive guiding parameters, including perturbation in real and imaginary refractive index, mode loss, group velocity dispersion, and bending loss, which can be instrumental in developing optimal design specifications for various application-centric active silicon waveguides..
Photonics Research
- Publication Date: Jun. 23, 2017
- Vol. 5, Issue 4, 305 (2017)
Numerical investigations of an optical switch based on silicon stripe waveguide embedded with vanadium dioxide layers
Lei Chen, Han Ye, Yumin Liu, Dong Wu, Rui Ma, and Zhongyuan Yu
A novel scheme for the design of an ultra-compact and high-performance optical switch is proposed and investigated numerically. Based on a standard silicon (Si) photonic stripe waveguide, a section of hyperbolic metamaterials (HMM) consisting of 20-pair alternating vanadium dioxide (VO2)/Si thin layers is inserted to realize the switching of fundamental TE mode propagation. Finite-element-method simulation results show that, with the help of an HMM with a size of 400 nm×220 nm×200 nm (width×height×length), the ON/OFF switching for fundamental TE mode propagation in an Si waveguide can be characterized by modulation depth (MD) of 5.6 dB and insertion loss (IL) of 1.25 dB. It also allows for a relatively wide operating bandwidth of 215 nm maintaining MD>5 dB and IL<1.25 dB. Furthermore, we discuss that the tungsten-doped VO2 layers could be useful for reducing metal-insulator-transition temperature and thus improving switching performance. In general, our findings may provide some useful ideas for optical switch design and application in an on-chip all-optical communication system with a demanding integration level.A novel scheme for the design of an ultra-compact and high-performance optical switch is proposed and investigated numerically. Based on a standard silicon (Si) photonic stripe waveguide, a section of hyperbolic metamaterials (HMM) consisting of 20-pair alternating vanadium dioxide ( VO 2 ) / Si 400 nm × 220 nm × 200 nm width × height × length MD > 5 dB IL < 1.25 dB VO 2
Photonics Research
- Publication Date: Jul. 05, 2017
- Vol. 5, Issue 4, 335 (2017)
Design of low-energy on-chip electro-optical 1 × M wavelength-selective switches
Richard Soref
A theoretical design is presented for a 1×M wavelength-selective switch (WSS) that routes any one of N incoming wavelength signals to any one of M output ports. This planar on-chip device comprises a 1×N demultiplexer, a group of N switching “trees” actuated by electro-optical or thermo-optical means, and an M-fold set of N×1 multiplexers. Trees utilize 1×2 switches. The WSS insertion loss is proportional to [log2 (M+N+1)]. Along with cross talk from trees, cross talk is present at each cross-illuminated waveguide intersection within the WSS, and there are at most N 1 such crossings per path. These loss and cross talk properties will likely place a practical limit of N=M=16 upon the WSS size. By constraining the 1×2 switching energy to ～1 fJ/bit, we find that resonant, narrowband 1×2 switches are required. The 1×2</iA theoretical design is presented for a 1 × M N M 1 × N N M N × 1 1 × 2 log 2 ( M + N + 1 ) N 1 N = M = 16 1 × 2 ～ 1 fJ / bit 1 × 2 1 × 2
Photonics Research
- Publication Date: Jul. 05, 2017
- Vol. 5, Issue 4, 340 (2017)
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