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2020
Volume: 8 Issue 8
19 Article(s)
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PEROVSKITE PHOTONICS
Triple-cation perovskite solar cells for visible light communications | Spotlight on Optics
Natalie A. Mica, Rui Bian, Pavlos Manousiadis, Lethy K. Jagadamma, Iman Tavakkolnia, Harald Haas, Graham A. Turnbull, and Ifor D. W. Samuel
Hybrid perovskite materials are widely researched due to their high absorptivity, inexpensive synthesis, and promise in photovoltaic devices. These materials are also of interest as highly sensitive photodetectors. In this study, their potential for use in visible light communication is explored in a configuration that allows for simultaneous energy and data harvesting. Using a triple-cation material and appropriate device design, a new record data rate for perovskite photodetectors of 56 Mbps and power conversion efficiencies above 20% under white LED illumination are achieved. With this device design, the −3 dB bandwidth is increased by minimizing the dominating time constant of the system. This correlation between the bandwidth and time constant is proved using measurements of time-resolved photoluminescence, transient photovoltage, and device resistance. Hybrid perovskite materials are widely researched due to their high absorptivity, inexpensive synthesis, and promise in photovoltaic devices. These materials are also of interest as highly sensitive photodetectors. In this study, their potential for use in visible light communication is explored in a configuration that allows for simultaneous energy and data harvesting. Using a triple-cation material and appropriate device design, a new record data rate for perovskite photodetectors of 56 Mbps and power conversion efficiencies above 20% under white LED illumination are achieved. With this device design, the
Photonics Research
- Publication Date: Jul. 14, 2020
- Vol. 8, Issue 8, A16 (2020)
Reviews
Optical Devices
Unidirectional reflection from an integrated “taiji” microresonator
A. Calabrese, F. Ramiro-Manzano, H. M. Price, S. Biasi, M. Bernard, M. Ghulinyan, I. Carusotto, and L. Pavesi
We study light transmission and reflection from an integrated microresonator device, formed by a circular microresonator coupled to a bus waveguide, with an embedded S-shaped additional crossover waveguide element that selectively couples counter-propagating modes in a propagation-direction-dependent way. The overall shape of the device resembles a “taiji” symbol, hence its name. While Lorentz reciprocity is preserved in transmission, the peculiar geometry allows us to exploit the non-Hermitian nature of the system to obtain high-contrast unidirectional reflection with negligible reflection for light incident in one direction and a significant reflection in the opposite direction.We study light transmission and reflection from an integrated microresonator device, formed by a circular microresonator coupled to a bus waveguide, with an embedded S-shaped additional crossover waveguide element that selectively couples counter-propagating modes in a propagation-direction-dependent way. The overall shape of the device resembles a “taiji” symbol, hence its name. While Lorentz reciprocity is preserved in transmission, the peculiar geometry allows us to exploit the non-Hermitian nature of the system to obtain high-contrast unidirectional reflection with negligible reflection for light incident in one direction and a significant reflection in the opposite direction..
Photonics Research
- Publication Date: Jul. 17, 2020
- Vol. 8, Issue 8, 1333 (2020)
Frequency stabilization and tuning of breathing solitons in Si3N4 microresonators
Shuai Wan, Rui Niu, Zheng-Yu Wang, Jin-Lan Peng, Ming Li, Jin Li, Guang-Can Guo, Chang-Ling Zou, and Chun-Hua Dong
Dissipative Kerr solitons offer broadband coherent and low-noise frequency combs and stable temporal pulse trains, having shown great potential applications in spectroscopy, communications, and metrology. Breathing solitons are a particular kind of dissipative Kerr soliton in which the pulse duration and peak intensity show periodic oscillation. Here we have investigated the breathing dissipative Kerr solitons in silicon nitride (Si3N4) microrings, while the breathing period shows uncertainties of around megahertz (MHz) order in both simulation and experiments. This instability is the main obstacle for future applications. By applying a modulated signal to the pump laser, the breathing frequency can be injection locked to the modulation frequency and tuned over tens of MHz with frequency noise significantly suppressed. Our demonstration offers an alternative knob for the control of soliton dynamics in microresonators and paves a new avenue towards practical applications of breathing solitons.Dissipative Kerr solitons offer broadband coherent and low-noise frequency combs and stable temporal pulse trains, having shown great potential applications in spectroscopy, communications, and metrology. Breathing solitons are a particular kind of dissipative Kerr soliton in which the pulse duration and peak intensity show periodic oscillation. Here we have investigated the breathing dissipative Kerr solitons in silicon nitride (
Photonics Research
- Publication Date: Jul. 21, 2020
- Vol. 8, Issue 8, 1342 (2020)
Physical Optics
All-fiber generation of arbitrary cylindrical vector beams on the first-order Poincaré sphere
Lipeng Feng, Yan Li, Sihan Wu, Xun Guan, Chen Yang, Weijun Tong, Wei Li, Jifang Qiu, Xiaobin Hong, Yong Zuo, Hongxiang Guo, Erhu Chen, and Jian Wu
We propose a linear mapping relationship between the polarization of the fundamental mode and the cylindrical vector (CV) modes on the first-order Poincaré sphere (FOPS) in fiber. The new method is based on the four-dimensional complex Jones matrices in terms of the linearly polarized mode bases. With our theoretical model, an all-fiber approach to generate arbitrary CV beams on the FOPS is proposed theoretically and verified experimentally. In the experiment, through the combination of a mode converter and a two-segment cascaded few-mode fiber with fixed stresses, it is possible to generate all CV modes on the FOPS by only adjusting the polarization of the fundamental mode. The Stokes parameters of the output light are measured to verify our scheme, which shows good agreement with the theoretical prediction. The method may provide a convenient way to generate CV beams and evolve the polarization states in any path on the FOPS, which is expected to have potential applications in encoding information and quantum computation.We propose a linear mapping relationship between the polarization of the fundamental mode and the cylindrical vector (CV) modes on the first-order Poincaré sphere (FOPS) in fiber. The new method is based on the four-dimensional complex Jones matrices in terms of the linearly polarized mode bases. With our theoretical model, an all-fiber approach to generate arbitrary CV beams on the FOPS is proposed theoretically and verified experimentally. In the experiment, through the combination of a mode converter and a two-segment cascaded few-mode fiber with fixed stresses, it is possible to generate all CV modes on the FOPS by only adjusting the polarization of the fundamental mode. The Stokes parameters of the output light are measured to verify our scheme, which shows good agreement with the theoretical prediction. The method may provide a convenient way to generate CV beams and evolve the polarization states in any path on the FOPS, which is expected to have potential applications in encoding information and quantum computation..
Photonics Research
- Publication Date: Jul. 10, 2020
- Vol. 8, Issue 8, 1268 (2020)
Geometric-phase-induced arbitrary polarization and orbital angular momentum generation in helically twisted birefringent photonic crystal fiber
Takeshi Fujisawa, and Kunimasa Saitoh
The evolutions of polarization and orbital angular momentum (OAM) states of light in helically twisted birefringent photonic crystal fibers (TB-PCFs) are analyzed. It is shown that a circular polarization (CP) component (S3 of a Stokes parameter) is periodically excited when usual linearly polarized (LP) modes of PCF are launched. The excitation originates from a geometric phase in TB-PCFs. The S3 excitation is larger for larger linear birefringence for a fixed twisting rate. If the linear birefringence is large enough, a CP filtering behavior can be seen in addition to the S3 excitation. From the analytical consideration of the sign of the geometric phase, the TB-PCF with periodical inversion of twisting is proposed to generate arbitrary polarization state on the Poincaré sphere. Next, an OAM state generation in multimode TB-PCFs is shown for higher-order LP mode input. By observing a far-field interference pattern from TB-PCF mixed with LP01 mode, a vortex associated with the OAM state can be seen. Similar to the single-mode case, by using periodical twisting inversion, efficient OAM generation is possible. These results indicate that by simply launching fiber’s LP mode into TB-PCF, arbitrary polarization and OAM states can be generated, leading to a novel mechanism for the manipulation of the spatial state of light.The evolutions of polarization and orbital angular momentum (OAM) states of light in helically twisted birefringent photonic crystal fibers (TB-PCFs) are analyzed. It is shown that a circular polarization (CP) component (
Photonics Research
- Publication Date: Jul. 10, 2020
- Vol. 8, Issue 8, 1278 (2020)
Research Articles
Imaging Systems, Microscopy, and Displays
Fast structured illumination microscopy via deep learning
Chang Ling, Chonglei Zhang, Mingqun Wang, Fanfei Meng, Luping Du, and Xiaocong Yuan
This study shows that convolutional neural networks (CNNs) can be used to improve the performance of structured illumination microscopy to enable it to reconstruct a super-resolution image using three instead of nine raw frames, which is the standard number of frames required to this end. Owing to the isotropy of the fluorescence group, the correlation between the high-frequency information in each direction of the spectrum is obtained by training the CNNs. A high-precision super-resolution image can thus be reconstructed using accurate data from three image frames in one direction. This allows for gentler super-resolution imaging at higher speeds and weakens phototoxicity in the imaging process.This study shows that convolutional neural networks (CNNs) can be used to improve the performance of structured illumination microscopy to enable it to reconstruct a super-resolution image using three instead of nine raw frames, which is the standard number of frames required to this end. Owing to the isotropy of the fluorescence group, the correlation between the high-frequency information in each direction of the spectrum is obtained by training the CNNs. A high-precision super-resolution image can thus be reconstructed using accurate data from three image frames in one direction. This allows for gentler super-resolution imaging at higher speeds and weakens phototoxicity in the imaging process..
Photonics Research
- Publication Date: Jul. 21, 2020
- Vol. 8, Issue 8, 1350 (2020)
Instrumentation and Measurements
Graphene metalens for particle nanotracking
Xueyan Li, Shibiao Wei, Guiyuan Cao, Han Lin, Yuejin Zhao, and Baohua Jia
Particle nanotracking (PNT) is highly desirable in lab-on-a-chip systems for flexible and convenient multiparameter measurement. An ultrathin flat lens is the preferred imaging device in such a system, with the advantage of high focusing performance and compactness. However, PNT using ultrathin flat lenses has not been demonstrated so far because PNT requires the clear knowledge of the relationship between the object and image in the imaging system. Such a relationship still remains elusive in ultrathin flat lens-based imaging systems because they operate based on diffraction rather than refraction. In this paper, we experimentally reveal the imaging relationship of a graphene metalens using nanohole arrays with micrometer spacing. The distance relationship between the object and image as well as the magnification ratio is acquired with nanometer accuracy. The measured imaging relationship agrees well with the theoretical prediction and is expected to be applicable to other ultrathin flat lenses based on the diffraction principle. By analyzing the high-resolution images from the graphene metalens using the imaging relationship, 3D trajectories of particles with high position accuracy in PNT have been achieved. The revealed imaging relationship for metalenses is essential in designing different types of integrated optical systems, including digital cameras, microfluidic devices, virtual reality devices, telescopes, and eyeglasses, and thus will find broad applications.Particle nanotracking (PNT) is highly desirable in lab-on-a-chip systems for flexible and convenient multiparameter measurement. An ultrathin flat lens is the preferred imaging device in such a system, with the advantage of high focusing performance and compactness. However, PNT using ultrathin flat lenses has not been demonstrated so far because PNT requires the clear knowledge of the relationship between the object and image in the imaging system. Such a relationship still remains elusive in ultrathin flat lens-based imaging systems because they operate based on diffraction rather than refraction. In this paper, we experimentally reveal the imaging relationship of a graphene metalens using nanohole arrays with micrometer spacing. The distance relationship between the object and image as well as the magnification ratio is acquired with nanometer accuracy. The measured imaging relationship agrees well with the theoretical prediction and is expected to be applicable to other ultrathin flat lenses based on the diffraction principle. By analyzing the high-resolution images from the graphene metalens using the imaging relationship, 3D trajectories of particles with high position accuracy in PNT have been achieved. The revealed imaging relationship for metalenses is essential in designing different types of integrated optical systems, including digital cameras, microfluidic devices, virtual reality devices, telescopes, and eyeglasses, and thus will find broad applications..
Photonics Research
- Publication Date: Jul. 15, 2020
- Vol. 8, Issue 8, 1316 (2020)
Lasers and Laser Optics
Reconfigurable time-stretched swept laser source with up to 100 MHz sweep rate, 100 nm bandwidth, and 100 mm OCT imaging range | Editors' Pick
Dongmei Huang, Feng Li, Chao Shang, Zihao Cheng, and P. K. A. Wai
The sweep rate, sweep range, and coherence length of swept sources, respectively, determine the acquisition rate, axial resolution, and imaging range of optical coherence tomography (OCT). In this paper, we demonstrate a reconfigurable high-speed and broadband swept laser by time stretching of a flat spectrum femtosecond pulse train with over 100 nm bandwidth and a repetition rate of 100 MHz. By incorporating an optical modulator and utilizing appropriate dispersive modules, the reconfiguration of the swept source is demonstrated with sweep rates of 25 and 2.5 MHz. The 2.5 MHz swept source enables an imaging range of >110 mm with 6 dB sensitivity roll-off in OCT, which is the longest imaging range ever reported for megahertz OCT.The sweep rate, sweep range, and coherence length of swept sources, respectively, determine the acquisition rate, axial resolution, and imaging range of optical coherence tomography (OCT). In this paper, we demonstrate a reconfigurable high-speed and broadband swept laser by time stretching of a flat spectrum femtosecond pulse train with over 100 nm bandwidth and a repetition rate of 100 MHz. By incorporating an optical modulator and utilizing appropriate dispersive modules, the reconfiguration of the swept source is demonstrated with sweep rates of 25 and 2.5 MHz. The 2.5 MHz swept source enables an imaging range of
Photonics Research
- Publication Date: Jul. 23, 2020
- Vol. 8, Issue 8, 1360 (2020)
Nanophotonics and Photonic Crystals
Design of a micrometer-long superconducting nanowire perfect absorber for efficient high-speed single-photon detection
Risheng Cheng, Sihao Wang, Chang-Ling Zou, and Hong X. Tang
Despite very efficient superconducting nanowire single-photon detectors (SNSPDs) reported recently, combining their other performance advantages such as high speed and ultralow timing jitter in a single device still remains challenging. In this work, we present a perfect absorber model and the corresponding detector design based on a micrometer-long NbN nanowire integrated with a 2D photonic crystal cavity of ultrasmall mode volume, which promises simultaneous achievement of near-unity absorption, gigahertz counting rates, and broadband optical response with a 3 dB bandwidth of 71 nm. Compared to previous stand-alone meandered and waveguide-integrated SNSPDs, this perfect absorber design addresses the trade space in size, efficiency, speed, and bandwidth for realizing large on-chip single-photon detector arrays.Despite very efficient superconducting nanowire single-photon detectors (SNSPDs) reported recently, combining their other performance advantages such as high speed and ultralow timing jitter in a single device still remains challenging. In this work, we present a perfect absorber model and the corresponding detector design based on a micrometer-long NbN nanowire integrated with a 2D photonic crystal cavity of ultrasmall mode volume, which promises simultaneous achievement of near-unity absorption, gigahertz counting rates, and broadband optical response with a 3 dB bandwidth of 71 nm. Compared to previous stand-alone meandered and waveguide-integrated SNSPDs, this perfect absorber design addresses the trade space in size, efficiency, speed, and bandwidth for realizing large on-chip single-photon detector arrays..
Photonics Research
- Publication Date: Jul. 14, 2020
- Vol. 8, Issue 8, 1260 (2020)
Nonlinear Optics
Second-harmonic generation and manipulation in lithium niobate slab waveguides by grating metasurfaces
Bin Fang, Hanmeng Li, Shining Zhu, and Tao Li
Nonlinear optical processes in waveguides play important roles in compact integrated photonics, while efficient coupling and manipulations inside the waveguides still remain challenging. In this work, we propose a new scheme for second-harmonic generation as well as beam shaping in lithium niobate slab waveguides with the assistance of well-designed grating metasurfaces at λ=1064 nm. By encoding the amplitude and phase into the holographic gratings, we further demonstrate strong functionalities of nonlinear beam shaping by the metasurface design, including dual focusing and Airy beam generation. Our approach would inspire new designs in the miniaturization and integration of compact multifunctional nonlinear light sources on chip.Nonlinear optical processes in waveguides play important roles in compact integrated photonics, while efficient coupling and manipulations inside the waveguides still remain challenging. In this work, we propose a new scheme for second-harmonic generation as well as beam shaping in lithium niobate slab waveguides with the assistance of well-designed grating metasurfaces at
Photonics Research
- Publication Date: Jul. 14, 2020
- Vol. 8, Issue 8, 1296 (2020)
Optical and Photonic Materials
Self-powered, flexible, and ultrabroadband ultraviolet-terahertz photodetector based on a laser-reduced graphene oxide/CsPbBr3 composite
Yifan Li, Yating Zhang, Zhiliang Chen, Qingyan Li, Tengteng Li, Mengyao Li, Hongliang Zhao, Quan Sheng, Wei Shi, and Jianquan Yao
Self-powered and flexible ultrabroadband photodetectors (PDs) are desirable in a wide range of applications. The current PDs based on the photothermoelectric (PTE) effect have realized broadband photodetection. However, most of them express low photoresponse and lack of flexibility. In this work, high-performance, self-powered, and flexible PTE PDs based on laser-scribed reduced graphene oxide (LSG)/CsPbBr3 are developed. The comparison experiment with LSG PD and fundamental electric properties show that the LSG/CsPbBr3 device exhibits enhanced ultrabroadband photodetection performance covering ultraviolet to terahertz range with high photoresponsivity of 100 mA/W for 405 nm and 10 mA/W for 118 μm at zero bias voltage, respectively. A response time of 18 ms and flexible experiment are also acquired at room temperature. Moreover, the PTE effect is fully discussed in the LSG/CsPbBr3 device. This work demonstrates that LSG/CsPbBr3 is a promising candidate for the construction of high-performance, flexible, and self-powered ultrabroadband PDs at room temperature.Self-powered and flexible ultrabroadband photodetectors (PDs) are desirable in a wide range of applications. The current PDs based on the photothermoelectric (PTE) effect have realized broadband photodetection. However, most of them express low photoresponse and lack of flexibility. In this work, high-performance, self-powered, and flexible PTE PDs based on laser-scribed reduced graphene oxide
Photonics Research
- Publication Date: Jul. 14, 2020
- Vol. 8, Issue 8, 1301 (2020)
Electrical properties and microstructure formation of V/Al-based n-contacts on high Al mole fraction n-AlGaN layers
Luca Sulmoni, Frank Mehnke, Anna Mogilatenko, Martin Guttmann, Tim Wernicke, and Michael Kneissl
The electrical and structural properties of V/Al-based n-contacts on n‐AlxGa1-xN with an Al mole fraction x ranging from x=0.75 to x=0.95 are investigated. Ohmic n-contacts are obtained up to x=0.75 with a contact resistivity of 5.7×10-4 Ω·cm2 whereas for higher Al mole fraction the IV characteristics are rectifying. Transmission electron microscopy reveals a thin crystalline AlN layer formed at the metal/semiconductor interface upon thermal annealing. Compositional analysis confirmed an Al enrichment at the interface. The interfacial nitride-based layer in n-contacts on n‐Al0.9Ga0.1N is partly amorphous and heavily contaminated by oxygen. The role and resulting limitations of Al in the metal stack for n-contacts on n-AlGaN with very high Al mole fraction are discussed. Finally, ultraviolet C (UVC) LEDs grown on n‐Al0.87Ga0.13N and emitting at 232 nm are fabricated with an operating voltage of 7.3 V and an emission power of 120 μW at 20 mA in cw operation.The electrical and structural properties of V/Al-based n-contacts on
Photonics Research
- Publication Date: Jul. 31, 2020
- Vol. 8, Issue 8, 1381 (2020)
Optoelectronics
Vortex Smith–Purcell radiation generation with holographic grating | On the Cover
Mengxuan Wang, Fang Liu, Yuechai Lin, Kaiyu Cui, Xue Feng, Wei Zhang, and Yidong Huang
Smith–Purcell radiation (SPR) is the electromagnetic wave generated by free electrons passing above a diffraction grating, and it has played an important role in free-electron light sources and particle accelerators. Orbital angular momentum (OAM) is a new degree of freedom that can significantly promote the capacity of information carried by an electro-magnetic beam. In this paper, we propose an integrable method for generating vortex Smith–Purcell radiation (VSPR), namely, SPR carrying OAM, by having free-electron bunches pass on planar holographic gratings. VSPRs generated by different electron energies, with different topological charges of the OAM, radiation angles, and frequencies are demonstrated numerically. It is also found that, for high-order radiation, the topological charge of the OAM wave will be multiplied by the radiation order. This work introduces a new way to generate SPR with OAM and provides a method to achieve an integratable and tunable free-electron OAM wave source at different frequency regions.Smith–Purcell radiation (SPR) is the electromagnetic wave generated by free electrons passing above a diffraction grating, and it has played an important role in free-electron light sources and particle accelerators. Orbital angular momentum (OAM) is a new degree of freedom that can significantly promote the capacity of information carried by an electro-magnetic beam. In this paper, we propose an integrable method for generating vortex Smith–Purcell radiation (VSPR), namely, SPR carrying OAM, by having free-electron bunches pass on planar holographic gratings. VSPRs generated by different electron energies, with different topological charges of the OAM, radiation angles, and frequencies are demonstrated numerically. It is also found that, for high-order radiation, the topological charge of the OAM wave will be multiplied by the radiation order. This work introduces a new way to generate SPR with OAM and provides a method to achieve an integratable and tunable free-electron OAM wave source at different frequency regions..
Photonics Research
- Publication Date: Jul. 15, 2020
- Vol. 8, Issue 8, 1309 (2020)
High-responsivity, self-driven photodetectors based on monolayer WS2/GaAs heterojunction
Kuilong Li, Wenjia Wang, Jianfei Li, Wenxin Jiang, Min Feng, and Yang He
Constructing two-dimensional (2D) layered materials with traditional three-dimensional (3D) semiconductors into complex heterostructures has opened a new platform for the development of optoelectronic devices. Herein, large-area high performance self-driven photodetectors based on monolayer WS2/GaAs heterostructures were successfully fabricated with a wide response spectrum band ranging from the ultraviolet to near-infrared region. The detector exhibits an overall high performance, including high photoresponsivity of 65.58 A/W at 365 nm and 28.50 A/W at 880 nm, low noise equivalent power of 1.97×10?15 W/Hz1/2, high detectivity of 4.47×1012 Jones, and fast response speed of 30/10 ms. This work suggests that the WS2/GaAs heterostructure is promising in future novel optoelectronic device applications, and also provides a low-cost, easy-to-process method for the preparation of 2D/3D heterojunction-based devices.Constructing two-dimensional (2D) layered materials with traditional three-dimensional (3D) semiconductors into complex heterostructures has opened a new platform for the development of optoelectronic devices. Herein, large-area high performance self-driven photodetectors based on monolayer
Photonics Research
- Publication Date: Jul. 24, 2020
- Vol. 8, Issue 8, 1368 (2020)
Quantum Optics
Pulse-width-induced polarization enhancement of optically pumped N-V electron spin in diamond
Yumeng Song, Yu Tian, Zhiyi Hu, Feifei Zhou, Tengteng Xing, Dawei Lu, Bing Chen, Ya Wang, Nanyang Xu, and Jiangfeng Du
The nitrogen-vacancy (N-V) center in diamond is a widely used platform for quantum information processing and sensing. The electron-spin state of the N-V center could be initialized, read out optically, and manipulated by resonate microwave fields. In this work, we analyze the dependence of electron-spin initialization on widths of laser pulses. We build a numerical model to simulate this process and to verify the simulation results in experiments. Both simulations and experiments reveal that shorter laser pulses are helpful to the electron-spin polarization. We therefore propose to use extremely short laser pulses for electron-spin initialization. In this new scheme, the spin-state contrast could be improved about 10% in experiments by using laser pulses as short as 4 ns in width. Furthermore, we provide a mechanism to explain this effect, which is due to the occupation time in the meta-stable spin-singlet states of the N-V center. Our new scheme is applicable in a broad range of N-V-based applications in the future.The nitrogen-vacancy (N-V) center in diamond is a widely used platform for quantum information processing and sensing. The electron-spin state of the N-V center could be initialized, read out optically, and manipulated by resonate microwave fields. In this work, we analyze the dependence of electron-spin initialization on widths of laser pulses. We build a numerical model to simulate this process and to verify the simulation results in experiments. Both simulations and experiments reveal that shorter laser pulses are helpful to the electron-spin polarization. We therefore propose to use extremely short laser pulses for electron-spin initialization. In this new scheme, the spin-state contrast could be improved about 10% in experiments by using laser pulses as short as 4 ns in width. Furthermore, we provide a mechanism to explain this effect, which is due to the occupation time in the meta-stable spin-singlet states of the N-V center. Our new scheme is applicable in a broad range of N-V-based applications in the future..
Photonics Research
- Publication Date: Jul. 14, 2020
- Vol. 8, Issue 8, 1289 (2020)
Silicon Photonics
Impact of carrier transport on the performance of QD lasers on silicon: a drift-diffusion approach
Marco Saldutti, Alberto Tibaldi, Federica Cappelluti, and Mariangela Gioannini
The operation of quantum dot lasers epitaxially grown on silicon is investigated through a quantum-corrected Poisson-drift-diffusion model. This in-house developed simulation framework completes the traditional rate equation approach, which models the intersubband transitions involved into simultaneous ground-state and excited-state lasing, with a physics-based description of carrier transport and electrostatic effects. The code is applied to look into some of the most relevant mechanisms affecting the lasing operation. We analyze the impact of threading dislocations on non-radiative recombination and laser threshold current. We demonstrate that asymmetric carrier transport in the barrier explains the ground-state power quenching above the excited-state lasing threshold. Finally, we study p-type modulation doping and its benefits/contraindications. The observation of an optimum doping level, minimizing the ground-state lasing threshold current, stems from the reduction of the electron density, which counteracts the benefits from the expected increase of the hole density. This reduction is due to electrostatic effects hindering electron injection.The operation of quantum dot lasers epitaxially grown on silicon is investigated through a quantum-corrected Poisson-drift-diffusion model. This in-house developed simulation framework completes the traditional rate equation approach, which models the intersubband transitions involved into simultaneous ground-state and excited-state lasing, with a physics-based description of carrier transport and electrostatic effects. The code is applied to look into some of the most relevant mechanisms affecting the lasing operation. We analyze the impact of threading dislocations on non-radiative recombination and laser threshold current. We demonstrate that asymmetric carrier transport in the barrier explains the ground-state power quenching above the excited-state lasing threshold. Finally, we study p-type modulation doping and its benefits/contraindications. The observation of an optimum doping level, minimizing the ground-state lasing threshold current, stems from the reduction of the electron density, which counteracts the benefits from the expected increase of the hole density. This reduction is due to electrostatic effects hindering electron injection..
Photonics Research
- Publication Date: Jul. 31, 2020
- Vol. 8, Issue 8, 1388 (2020)
Ultrafast Optics
Laser-driven self-exfoliation of graphene oxide layers on a fiber facet for Q switching of an Er-doped fiber laser at the longest wavelength
Byungjoo Kim, Seongjin Hong, Jaedeok Park, Yongsoo Lee, Dong-il Yeom, and Kyunghwan Oh
A new method to make an all-fiber nonlinear optic device for laser pulse generation is developed by depositing multi-layer graphene oxide (GO) selectively onto the core of the cleaved fiber facet by combining the electrical arc discharge and the laser-driven self-exfoliation. Using the GO colloid droplet with sub-nanoliter volume, we obtained a GO bulk layer deposited on a fiber facet of the order of milliseconds by using an electric arc. The prepared fiber facet was then included in an Er-doped fiber laser (EDFL) cavity and we obtained a few layers of GO having nonlinear optic two-dimensional (2D) characteristics selectively on the fiber core by the laser-driven self-exfoliation. The 2D GO layers on the fiber core served as a stable and efficient saturable absorber enabling robust pulse train generation at λ=1600.5 nm, the longest Q-switched laser wavelength in EDFLs. Pulse characteristics were analyzed as we varied the pump power at λ=980 nm from 105.2 mW to 193.6 mW, to obtain the maximum repetition rate of 17.8 kHz and the maximum output power of 2.3 mW with the minimum pulse duration of 7.8 μs. The proposed method could be further applied to other novel inorganic 2D materials opening a window to explore their novel nonlinear optic laser applications.A new method to make an all-fiber nonlinear optic device for laser pulse generation is developed by depositing multi-layer graphene oxide (GO) selectively onto the core of the cleaved fiber facet by combining the electrical arc discharge and the laser-driven self-exfoliation. Using the GO colloid droplet with sub-nanoliter volume, we obtained a GO bulk layer deposited on a fiber facet of the order of milliseconds by using an electric arc. The prepared fiber facet was then included in an Er-doped fiber laser (EDFL) cavity and we obtained a few layers of GO having nonlinear optic two-dimensional (2D) characteristics selectively on the fiber core by the laser-driven self-exfoliation. The 2D GO layers on the fiber core served as a stable and efficient saturable absorber enabling robust pulse train generation at
Photonics Research
- Publication Date: Jul. 17, 2020
- Vol. 8, Issue 8, 1324 (2020)
High-gain amplification for femtosecond optical vortex with mode-control regenerative cavity
Shuiqin Zheng, Zhenkuan Chen, Qinggang Lin, Yi Cai, Xiaowei Lu, Yanxia Gao, Shixiang Xu, and Dianyuan Fan
Ultra-intense femtosecond vortex pulses can provide an opportunity to investigate the new phenomena with orbital angular momentum (OAM) involved in extreme cases. This paper reports a high gain optical vortex amplifier for intense femtosecond vortex pulses generation. Traditional regeneration amplifiers can offer high gain for Gaussian mode pulses but cannot amplify optical vortex pulses while maintaining the phase singularity because of mode competition. Here, we present a regeneration amplifier with a ring-shaped pump. By controlling the radius of the pump, the system can realize the motivation of the Laguerre–Gaussian [LG0,1(?1)] mode and the suppression of the Gaussian mode. Without seeds, the amplifier has a donut-shaped output containing two opposite OAM states simultaneously, as our prediction by simulation. If seeded by a pulse of a topologic charge of 1 or ?1, the system will output an amplified LG0,1(?1) mode pulse with the same topologic charge as the seed. To our knowledge, this amplifier can offer the highest gain as 1.45×106 for optical vortex amplification. Finally, we obtain a 1.8 mJ, 51 fs compressed optical vortex seeded from a 2 nJ optical vortex.Ultra-intense femtosecond vortex pulses can provide an opportunity to investigate the new phenomena with orbital angular momentum (OAM) involved in extreme cases. This paper reports a high gain optical vortex amplifier for intense femtosecond vortex pulses generation. Traditional regeneration amplifiers can offer high gain for Gaussian mode pulses but cannot amplify optical vortex pulses while maintaining the phase singularity because of mode competition. Here, we present a regeneration amplifier with a ring-shaped pump. By controlling the radius of the pump, the system can realize the motivation of the Laguerre–Gaussian [
Photonics Research
- Publication Date: Jul. 24, 2020
- Vol. 8, Issue 8, 1375 (2020)
Errata
In situ optical backpropagation training of diffractive optical neural networks: publisher’s note
Tiankuang Zhou, Lu Fang, Tao Yan, Jiamin Wu, Yipeng Li, Jingtao Fan, Huaqiang Wu, Xing Lin, and Qionghai Dai
This publisher’s note corrects the authors’ affiliations in Photon. Res.8, 940 (2020).PRHEIZ2327-912510.1364/PRJ.389553This publisher’s note corrects the authors’ affiliations in Photon. Res. 8 , 940 (2020 ).PRHEIZ 2327-9125 10.1364/PRJ.389553
Photonics Research
- Publication Date: Jul. 15, 2020
- Vol. 8, Issue 8, 1323 (2020)
About the Cover
Generating “vortex Smith-Purcell radiation” by having periodically bunched free electrons pass on a holographic grating.
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