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2021
Volume: 9 Issue 8
26 Article(s)
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DEEP LEARNING IN PHOTONICS
Towards smart optical focusing: deep learning-empowered dynamic wavefront shaping through nonstationary scattering media
Yunqi Luo, Suxia Yan, Huanhao Li, Puxiang Lai, and Yuanjin Zheng
Optical focusing through scattering media is of great significance yet challenging in lots of scenarios, including biomedical imaging, optical communication, cybersecurity, three-dimensional displays, etc. Wavefront shaping is a promising approach to solve this problem, but most implementations thus far have only dealt with static media, which, however, deviates from realistic applications. Herein, we put forward a deep learning-empowered adaptive framework, which is specifically implemented by a proposed Timely-Focusing-Optical-Transformation-Net (TFOTNet), and it effectively tackles the grand challenge of real-time light focusing and refocusing through time-variant media without complicated computation. The introduction of recursive fine-tuning allows timely focusing recovery, and the adaptive adjustment of hyperparameters of TFOTNet on the basis of medium changing speed efficiently handles the spatiotemporal non-stationarity of the medium. Simulation and experimental results demonstrate that the adaptive recursive algorithm with the proposed network significantly improves light focusing and tracking performance over traditional methods, permitting rapid recovery of an optical focus from degradation. It is believed that the proposed deep learning-empowered framework delivers a promising platform towards smart optical focusing implementations requiring dynamic wavefront control.
Optical focusing through scattering media is of great significance yet challenging in lots of scenarios, including biomedical imaging, optical communication, cybersecurity, three-dimensional displays, etc. Wavefront shaping is a promising approach to solve this problem, but most implementations thus far have only dealt with static media, which, however, deviates from realistic applications. Herein, we put forward a deep learning-empowered adaptive framework, which is specifically implemented by a proposed Timely-Focusing-Optical-Transformation-Net (TFOTNet), and it effectively tackles the grand challenge of real-time light focusing and refocusing through time-variant media without complicated computation. The introduction of recursive fine-tuning allows timely focusing recovery, and the adaptive adjustment of hyperparameters of TFOTNet on the basis of medium changing speed efficiently handles the spatiotemporal non-stationarity of the medium. Simulation and experimental results demonstrate that the adaptive recursive algorithm with the proposed network significantly improves light focusing and tracking performance over traditional methods, permitting rapid recovery of an optical focus from degradation. It is believed that the proposed deep learning-empowered framework delivers a promising platform towards smart optical focusing implementations requiring dynamic wavefront control.
.Photonics Research
- Publication Date: Jul. 16, 2021
- Vol. 9, Issue 8, B262 (2021)
Deep learning in photonics: introduction
Li Gao, Yang Chai, Darko Zibar, and Zongfu Yu
The connection between Maxwell’s equations and neural networks opens unprecedented opportunities at the interface between photonics and deep learning. This feature issue highlights recent research progress at the interdisciplinary field of photonics and deep learning and provides an opportunity for different communities to exchange their ideas from different perspectives.
The connection between Maxwell’s equations and neural networks opens unprecedented opportunities at the interface between photonics and deep learning. This feature issue highlights recent research progress at the interdisciplinary field of photonics and deep learning and provides an opportunity for different communities to exchange their ideas from different perspectives.
.Photonics Research
- Publication Date: Jul. 19, 2021
- Vol. 9, Issue 8, DLP1 (2021)
Reviews
Physical Optics
Epsilon-near-zero photonics: infinite potentials
Jiaye Wu, Ze Tao Xie, Yanhua Sha, H. Y. Fu, and Qian Li
With its unique and exclusive linear and nonlinear optical characteristics, epsilon-near-zero (ENZ) photonics has drawn a tremendous amount of attention in the recent decade in the fields of nanophotonics, nonlinear optics, plasmonics, light-matter interactions, material science, applied optical science, etc. The extraordinary optical properties, relatively high tuning flexibility, and CMOS compatibility of ENZ materials make them popular and competitive candidates for nanophotonic devices and on-chip integration in all-optical and electro-optical platforms. With exclusive features and high performance, ENZ photonics can play a big role in optical communications and optical data processing. In this review, we give a focused discussion on recent advances of the theoretical and experimental studies on ENZ photonics, especially in the regime of nonlinear ENZ nanophotonics and its applications. First, we overview the basics of the ENZ concepts, mechanisms, and nonlinear ENZ nanophotonics. Then the new advancements in theoretical and experimental optical physics are reviewed. For nanophotonic applications, the recent decades saw rapid developments in various kinds of different ENZ-based devices and systems, which are discussed and analyzed in detail. Finally, we give our perspectives on where future endeavors can be made.With its unique and exclusive linear and nonlinear optical characteristics, epsilon-near-zero (ENZ) photonics has drawn a tremendous amount of attention in the recent decade in the fields of nanophotonics, nonlinear optics, plasmonics, light-matter interactions, material science, applied optical science, etc. The extraordinary optical properties, relatively high tuning flexibility, and CMOS compatibility of ENZ materials make them popular and competitive candidates for nanophotonic devices and on-chip integration in all-optical and electro-optical platforms. With exclusive features and high performance, ENZ photonics can play a big role in optical communications and optical data processing. In this review, we give a focused discussion on recent advances of the theoretical and experimental studies on ENZ photonics, especially in the regime of nonlinear ENZ nanophotonics and its applications. First, we overview the basics of the ENZ concepts, mechanisms, and nonlinear ENZ nanophotonics. Then the new advancements in theoretical and experimental optical physics are reviewed. For nanophotonic applications, the recent decades saw rapid developments in various kinds of different ENZ-based devices and systems, which are discussed and analyzed in detail. Finally, we give our perspectives on where future endeavors can be made..
Photonics Research
- Publication Date: Jul. 30, 2021
- Vol. 9, Issue 8, 1616 (2021)
Research Articles
Fiber Optics and Optical Communications
High-speed Stokes vector receiver enabled by a spin-dependent optical grating
Youpeng Xie, Ting Lei, Dawei Wang, Jianxin Ren, Yanmeng Dai, Yanjun Chen, Luping Du, Bo Liu, Zhaohui Li, and Xiaocong Yuan
Stokes vector direct detection is a promising, cost-effective technology for short-distance communication applications. Here, we design and fabricate a spin-dependent liquid crystal grating to detect light polarization states. By separating the circular and linear components of incident light, the polarization states can be resolved with accuracy of up to 0.25°. We achieved Stokes vector direct detection of quadrature phase-shift keying (QPSK), 8PSK, and 16-ary quadrature amplitude modulation signals with 32, 16, and 16 GBd rates, respectively. We integrated the system, including the grating, photodetectors, and optical elements, on a miniaturized printed circuit board and demonstrated high-speed optical communications with 16 GBd rate QPSK signals.Stokes vector direct detection is a promising, cost-effective technology for short-distance communication applications. Here, we design and fabricate a spin-dependent liquid crystal grating to detect light polarization states. By separating the circular and linear components of incident light, the polarization states can be resolved with accuracy of up to 0.25°. We achieved Stokes vector direct detection of quadrature phase-shift keying (QPSK), 8PSK, and 16-ary quadrature amplitude modulation signals with 32, 16, and 16 GBd rates, respectively. We integrated the system, including the grating, photodetectors, and optical elements, on a miniaturized printed circuit board and demonstrated high-speed optical communications with 16 GBd rate QPSK signals..
Photonics Research
- Publication Date: Jul. 15, 2021
- Vol. 9, Issue 8, 1470 (2021)
Hollow-core antiresonant terahertz fiber-based TOPAS extruded from a 3D printer using a metal 3D printed nozzle
Wanvisa Talataisong, Jon Gorecki, Lieke D. van Putten, Rand Ismaeel, James Williamson, Katie Addinall, Daniel Schwendemann, Martynas Beresna, Vasilis Apostolopoulos, and Gilberto Brambilla
We report the use of a terahertz (THz) transparent material, cyclic olefin copolymer (COC or TOPAS), for fabricating a hollow-core antiresonant fiber that provides an electromagnetic wave guidance in the THz regime. A novel fabrication technique to realize a hollow-core antiresonant polymer optical fiber (HC-ARPF) for THz guidance is proposed and demonstrated. The fiber is directly extruded in a single-step procedure using a conventional fused deposition modeling 3D printer. The fiber geometry is defined by a structured nozzle manufactured with a metal 3D printer, which allows tailoring of the nozzle design to the various geometries of microstructured optical fibers. The possibility to use the HC-ARPF made from TOPAS for guiding in the THz region is theoretically and experimentally assessed through the profile of mode simulation and time-frequency diagram (spectrogram) analysis.We report the use of a terahertz (THz) transparent material, cyclic olefin copolymer (COC or TOPAS), for fabricating a hollow-core antiresonant fiber that provides an electromagnetic wave guidance in the THz regime. A novel fabrication technique to realize a hollow-core antiresonant polymer optical fiber (HC-ARPF) for THz guidance is proposed and demonstrated. The fiber is directly extruded in a single-step procedure using a conventional fused deposition modeling 3D printer. The fiber geometry is defined by a structured nozzle manufactured with a metal 3D printer, which allows tailoring of the nozzle design to the various geometries of microstructured optical fibers. The possibility to use the HC-ARPF made from TOPAS for guiding in the THz region is theoretically and experimentally assessed through the profile of mode simulation and time-frequency diagram (spectrogram) analysis..
Photonics Research
- Publication Date: Jul. 20, 2021
- Vol. 9, Issue 8, 1513 (2021)
Si-substrate LEDs with multiple superlattice interlayers for beyond 24 Gbps visible light communication
Fangchen Hu, Shouqing Chen, Guoqiang Li, Peng Zou, Junwen Zhang, Jian Hu, Jianli Zhang, Zhixue He, Shaohua Yu, Fengyi Jiang, and Nan Chi
High-speed visible light communication (VLC) using light-emitting diodes (LEDs) is a potential complementary technology for beyond-5G wireless communication networks. The speed of VLC systems significantly depends on the quality of LEDs, and thus various novel LEDs with enhanced VLC performance increasingly emerge. Among them, InGaN/GaN-based LEDs on a Si-substrate are a promising LED transmitter that has enabled VLC data rates beyond 10 Gbps. The optimization on the period number of superlattice interlayer (SL), which is a stress-relief epitaxial layer in a Si-substrate LED, has been demonstrated to be an effective method to improve Si-substrate LED’s luminescence properties. However, this method to improve LED’s VLC properties is barely investigated. Hence, we for the first time experimentally studied the impact of SL period number on VLC performance. Accordingly, we designed and fabricated an integrated 4 × 4 multichromatic Si-substrate wavelength-division-multiplexing LED array chip with optimal SL period number. This chip allows up to 24.25 Gbps/1.2 m VLC transmission using eight wavelengths, which is the highest VLC data rate for an InGaN/GaN LED-based VLC system to the best of our knowledge. Additionally, a record-breaking data rate of 2.02 Gbps over a 20-m VLC link is achieved using a blue Si-substrate LED with the optimal SL period number. These results validate the effectiveness of Si-substrate LEDs for both high-speed and long-distance VLC and pave the way for Si-substrate LED design specially for high-speed VLC applications.High-speed visible light communication (VLC) using light-emitting diodes (LEDs) is a potential complementary technology for beyond-5G wireless communication networks. The speed of VLC systems significantly depends on the quality of LEDs, and thus various novel LEDs with enhanced VLC performance increasingly emerge. Among them, InGaN/GaN-based LEDs on a Si-substrate are a promising LED transmitter that has enabled VLC data rates beyond 10 Gbps. The optimization on the period number of superlattice interlayer (SL), which is a stress-relief epitaxial layer in a Si-substrate LED, has been demonstrated to be an effective method to improve Si-substrate LED’s luminescence properties. However, this method to improve LED’s VLC properties is barely investigated. Hence, we for the first time experimentally studied the impact of SL period number on VLC performance. Accordingly, we designed and fabricated an integrated 4 × 4 multichromatic Si-substrate wavelength-division-multiplexing LED array chip with optimal SL period number. This chip allows up to 24.25 Gbps/1.2 m VLC transmission using eight wavelengths, which is the highest VLC data rate for an InGaN/GaN LED-based VLC system to the best of our knowledge. Additionally, a record-breaking data rate of 2.02 Gbps over a 20-m VLC link is achieved using a blue Si-substrate LED with the optimal SL period number. These results validate the effectiveness of Si-substrate LEDs for both high-speed and long-distance VLC and pave the way for Si-substrate LED design specially for high-speed VLC applications..
Photonics Research
- Publication Date: Jul. 30, 2021
- Vol. 9, Issue 8, 1581 (2021)
Imaging Systems, Microscopy, and Displays
Flexible, video-rate, and aberration-compensated axial dual-line scanning imaging with field-of-view jointing and stepped remote focusing
Rui Jin, Yalan Yu, Dan Shen, Qingming Luo, Hui Gong, and Jing Yuan
Parallel dual-plane imaging with a large axial interval enables the simultaneous observation of biological structures and activities in different views of interest. However, the inflexibility in adjusting the field-of-view (FOV) positions in three dimensions and optical sectioning effects, as well as the relatively small effective axial range limited by spherical aberration, have hindered the application of parallel dual-plane imaging. Herein, we propose a flexible, video-rate, and defocus-aberration-compensated axial dual-line scanning imaging method. We used a stepped mirror to remotely generate and detect dual axial lines with compensation for spherical aberration and FOV-jointing to rearrange into a head-to-head line for high-speed optical sectioning acquisition. The lateral and axial positions of the two FOVs could be flexibly adjusted before and during imaging, respectively. The method also allows the adjustment of optical sectioning effects according to specific experimental requirements. We experimentally verified the consistent imaging performance over an axial range of 300 μm. We demonstrated high throughput by simultaneously imaging Brownian motions in two 250 μm×250 μm FOVs with axial and lateral intervals of 150 μm and 240 μm, respectively, at 24.5 Hz. We also showed potential application in functional imaging by simultaneously acquiring neural activities in the optic tectum and hindbrain of a zebrafish brain. The proposed method is, thus, advantageous compared to existing parallel dual-plane imaging and potentially facilitates intravital biological study in large axial range.Parallel dual-plane imaging with a large axial interval enables the simultaneous observation of biological structures and activities in different views of interest. However, the inflexibility in adjusting the field-of-view (FOV) positions in three dimensions and optical sectioning effects, as well as the relatively small effective axial range limited by spherical aberration, have hindered the application of parallel dual-plane imaging. Herein, we propose a flexible, video-rate, and defocus-aberration-compensated axial dual-line scanning imaging method. We used a stepped mirror to remotely generate and detect dual axial lines with compensation for spherical aberration and FOV-jointing to rearrange into a head-to-head line for high-speed optical sectioning acquisition. The lateral and axial positions of the two FOVs could be flexibly adjusted before and during imaging, respectively. The method also allows the adjustment of optical sectioning effects according to specific experimental requirements. We experimentally verified the consistent imaging performance over an axial range of 300 μm. We demonstrated high throughput by simultaneously imaging Brownian motions in two
Photonics Research
- Publication Date: Jul. 15, 2021
- Vol. 9, Issue 8, 1477 (2021)
Instrumentation and Measurements
Photonic extreme learning machine by free-space optical propagation
Davide Pierangeli, Giulia Marcucci, and Claudio Conti
Photonic brain-inspired platforms are emerging as novel analog computing devices, enabling fast and energy-efficient operations for machine learning. These artificial neural networks generally require tailored optical elements, such as integrated photonic circuits, engineered diffractive layers, nanophotonic materials, or time-delay schemes, which are challenging to train or stabilize. Here, we present a neuromorphic photonic scheme, i.e., the photonic extreme learning machine, which can be implemented simply by using an optical encoder and coherent wave propagation in free space. We realize the concept through spatial light modulation of a laser beam, with the far field acting as a feature mapping space. We experimentally demonstrate learning from data on various classification and regression tasks, achieving accuracies comparable with digital kernel machines and deep photonic networks. Our findings point out an optical machine learning device that is easy to train, energetically efficient, scalable, and fabrication-constraint free. The scheme can be generalized to a plethora of photonic systems, opening the route to real-time neuromorphic processing of optical data.Photonic brain-inspired platforms are emerging as novel analog computing devices, enabling fast and energy-efficient operations for machine learning. These artificial neural networks generally require tailored optical elements, such as integrated photonic circuits, engineered diffractive layers, nanophotonic materials, or time-delay schemes, which are challenging to train or stabilize. Here, we present a neuromorphic photonic scheme, i.e., the photonic extreme learning machine, which can be implemented simply by using an optical encoder and coherent wave propagation in free space. We realize the concept through spatial light modulation of a laser beam, with the far field acting as a feature mapping space. We experimentally demonstrate learning from data on various classification and regression tasks, achieving accuracies comparable with digital kernel machines and deep photonic networks. Our findings point out an optical machine learning device that is easy to train, energetically efficient, scalable, and fabrication-constraint free. The scheme can be generalized to a plethora of photonic systems, opening the route to real-time neuromorphic processing of optical data..
Photonics Research
- Publication Date: Jul. 08, 2021
- Vol. 9, Issue 8, 1446 (2021)
Brillouin-scattering-induced transparency enabled reconfigurable sensing of RF signals | Editors' Pick
Jaffar Kadum, Ranjan Das, Arijit Misra, and Thomas Schneider
Real-time spectrum sensing is essential to enable dynamic and rapid spectrum sharing of unused frequencies to cater the substantial demands of new wireless services deploying the existing RF bands. In this paper, we present a novel, real-time spectrum sensing approach for widely used RF signals based on Brillouin-scattering-induced transparency (BIT). A temporal discrimination of multi-channel input frequencies is achieved through the group delay tuning by BIT. By tuning the pump power and frequency, the proposed technique is fully reconfigurable and viable for a broad range of spectrum sensing. Several experimental illustrations of the time domain sensing are presented for two-tone channels with 0.9, 1.8, and 5 GHz frequencies to detect the unused spectrum within 3G, 4G, and 5G signals.Real-time spectrum sensing is essential to enable dynamic and rapid spectrum sharing of unused frequencies to cater the substantial demands of new wireless services deploying the existing RF bands. In this paper, we present a novel, real-time spectrum sensing approach for widely used RF signals based on Brillouin-scattering-induced transparency (BIT). A temporal discrimination of multi-channel input frequencies is achieved through the group delay tuning by BIT. By tuning the pump power and frequency, the proposed technique is fully reconfigurable and viable for a broad range of spectrum sensing. Several experimental illustrations of the time domain sensing are presented for two-tone channels with 0.9, 1.8, and 5 GHz frequencies to detect the unused spectrum within 3G, 4G, and 5G signals..
Photonics Research
- Publication Date: Jul. 20, 2021
- Vol. 9, Issue 8, 1486 (2021)
Integrated Optics
Hybrid-integrated high-performance microwave photonic filter with switchable response | Editors' Pick
Yuansheng Tao, Haowen Shu, Xingjun Wang, Ming Jin, Zihan Tao, Fenghe Yang, Jingbo Shi, and Jun Qin
The integrated microwave photonic filter (MPF), as a compelling candidate for next-generation radio-frequency (RF) applications, has been widely investigated for decades. However, most integrated MPFs reported thus far have merely incorporated passive photonic components onto a chip-scale platform, while all necessary active devices are still bulk and discrete. Though few attempts to higher photonic integration of MPFs have been executed, the achieved filtering performances are fairly limited, which impedes the pathway to practical deployments. Here, we demonstrate, for the first time to our knowledge, an all-integrated MPF combined with high filtering performances, through hybrid integration of an InP chip-based laser and a monolithic silicon photonic circuit consisting of a dual-drive Mach–Zehnder modulator, a high-Q ring resonator, and a photodetector. This integrated MPF exhibits a high spectral resolution as narrow as 360 MHz, a wide-frequency tunable range covering the S-band to K-band (3 to 25 GHz), and a large rejection ratio of >40 dB. Moreover, the filtering response can be agilely switched between the bandpass and band-stop function with a transient respond time (∼48 μs). Compared with previous MPFs in a similar integration level, the obtained spectral resolution in this work is dramatically improved by nearly one order of magnitude, while the valid frequency tunable range is broadened more than twice, which can satisfy the essential filtering requirements in actual RF systems. As a paradigm demonstration oriented to real-world scenarios, high-resolution RF filtering of realistic microwave signals aiming for interference rejection and channel selection is performed. Our work points out a feasible route to a miniaturized, high-performance, and cost-effective MPF leveraging hybrid integration approach, thus enabling a range of RF applications from wireless communication to radar toward the higher-frequency region, more compact size, and lower power consumption.The integrated microwave photonic filter (MPF), as a compelling candidate for next-generation radio-frequency (RF) applications, has been widely investigated for decades. However, most integrated MPFs reported thus far have merely incorporated passive photonic components onto a chip-scale platform, while all necessary active devices are still bulk and discrete. Though few attempts to higher photonic integration of MPFs have been executed, the achieved filtering performances are fairly limited, which impedes the pathway to practical deployments. Here, we demonstrate, for the first time to our knowledge, an all-integrated MPF combined with high filtering performances, through hybrid integration of an InP chip-based laser and a monolithic silicon photonic circuit consisting of a dual-drive Mach–Zehnder modulator, a high-
Photonics Research
- Publication Date: Jul. 30, 2021
- Vol. 9, Issue 8, 1569 (2021)
Lasers and Laser Optics
Vector harmonic mode-locking by acoustic resonance
Sergey Sergeyev, Stanislav Kolpakov, and Yury Loika
For an Er-doped fiber laser, for the first time, to the best of our knowledge, we demonstrate both experimentally and theoretically a novel mechanism of harmonic mode-locking based on the electrostriction effect leading to excitation of the torsional acoustic modes in the transverse section of the laser. The exited torsional acoustic modes modulate the fiber birefringence that results in synchronization of oscillations at the harmonic modes and the linewidth narrowing with the increased signal-to-noise ratio of 30 dB. By adjusting the in-cavity birefringence based on tuning the polarization controller, we enable the selection of the harmonic mode to be stabilized.For an Er-doped fiber laser, for the first time, to the best of our knowledge, we demonstrate both experimentally and theoretically a novel mechanism of harmonic mode-locking based on the electrostriction effect leading to excitation of the torsional acoustic modes in the transverse section of the laser. The exited torsional acoustic modes modulate the fiber birefringence that results in synchronization of oscillations at the harmonic modes and the linewidth narrowing with the increased signal-to-noise ratio of 30 dB. By adjusting the in-cavity birefringence based on tuning the polarization controller, we enable the selection of the harmonic mode to be stabilized..
Photonics Research
- Publication Date: Jul. 08, 2021
- Vol. 9, Issue 8, 1432 (2021)
Multigigawatt 50 fs Yb:CALGO regenerative amplifier system with 11 W average power and mid-infrared generation
Weizhe Wang, Han Wu, Cheng Liu, Biao Sun, and Houkun Liang
Lasers with high average and high peak power as well as ultrashort pulse width have been all along demanded by nonlinear optics studies, strong-field experiments, electron dynamics investigations, and ultrafast spectroscopy. While the routinely used titanium-doped sapphire (Ti:sapphire) laser faces a bottleneck in the average power upscaling, ytterbium (Yb)-doped lasers have remarkable advantages in achieving high average power. However, there is still a substantial gap of pulse width and peak power between the Ti:sapphire and Yb-doped lasers. Here we demonstrate a high-power Yb:CaAlGdO4 (Yb:CALGO) regenerative amplifier system, delivering 1040 nm pulses with 11 W average power, 50 fs pulse width, and 3.7 GW peak power at a repetition rate of 43 kHz, which to some extent bridges the gap between the Ti:sapphire and Yb lasers. An ultrabroadband Yb-doped fiber oscillator, specially designed spectral shapers, and Yb:CALGO gain medium with broad emission bandwidth, together with a double-end pumping scheme enable an amplified bandwidth of 19 nm and 95 fs output pulse width. To the best of our knowledge, this is the first demonstration of sub-100 fs regenerative amplifier based on Yb-doped bulk medium without nonlinear spectral broadening. The amplified pulse is further compressed to 50 fs via cascaded-quadratic compression with a simple setup, producing 3.7 GW peak power, which boosts the record of peak power from Yb:CALGO regenerative amplifiers by 1 order. As a proof of concept, pumped by the high-power, 50 fs pulses, 7.5–11.5 µm mid-infrared (MIR) generation via intrapulse difference-frequency generation is performed, without the necessity of nonlinear fiber compressors. It leads to a simple and robust apparatus, and it would find good usefulness in MIR spectroscopic applications.Lasers with high average and high peak power as well as ultrashort pulse width have been all along demanded by nonlinear optics studies, strong-field experiments, electron dynamics investigations, and ultrafast spectroscopy. While the routinely used titanium-doped sapphire (Ti:sapphire) laser faces a bottleneck in the average power upscaling, ytterbium (Yb)-doped lasers have remarkable advantages in achieving high average power. However, there is still a substantial gap of pulse width and peak power between the Ti:sapphire and Yb-doped lasers. Here we demonstrate a high-power
Photonics Research
- Publication Date: Jul. 08, 2021
- Vol. 9, Issue 8, 1439 (2021)
Low-latency deep-reinforcement learning algorithm for ultrafast fiber lasers
Qiuquan Yan, Qinghui Deng, Jun Zhang, Ying Zhu, Ke Yin, Teng Li, Dan Wu, and Tian Jiang
The application of machine learning to the field of ultrafast photonics is becoming more and more extensive. In this paper, for the automatic mode-locked operation in a saturable absorber-based ultrafast fiber laser (UFL), a deep-reinforcement learning algorithm with low latency is proposed and implemented. The algorithm contains two actor neural networks providing strategies to modify the intracavity lasing polarization state and two critic neural networks evaluating the effect of the actor networks. With this algorithm, a stable fundamental mode-locked (FML) state of the UFL is demonstrated. To guarantee its effectiveness and robustness, two experiments are put forward. As for effectiveness, one experiment verifies the performance of the trained network model by applying it to recover the mode-locked state with environmental vibrations, which mimics the condition that the UFL loses the mode-locked state quickly. As for robustness, the other experiment, at first, builds a database with UFL at different temperatures. It then trains the model and tests its performance. The results show that the average mode-locked recovery time of the trained network model is 1.948 s. As far as we know, it is 62.8% of the fastest average mode-locked recovery time in the existing work. At different temperatures, the trained network model can also recover the mode-locked state of the UFL in a short time. Remote algorithm training and automatic mode-locked control are proved in this work, laying the foundation for long-distance maintenance and centralized control of UFLs.The application of machine learning to the field of ultrafast photonics is becoming more and more extensive. In this paper, for the automatic mode-locked operation in a saturable absorber-based ultrafast fiber laser (UFL), a deep-reinforcement learning algorithm with low latency is proposed and implemented. The algorithm contains two actor neural networks providing strategies to modify the intracavity lasing polarization state and two critic neural networks evaluating the effect of the actor networks. With this algorithm, a stable fundamental mode-locked (FML) state of the UFL is demonstrated. To guarantee its effectiveness and robustness, two experiments are put forward. As for effectiveness, one experiment verifies the performance of the trained network model by applying it to recover the mode-locked state with environmental vibrations, which mimics the condition that the UFL loses the mode-locked state quickly. As for robustness, the other experiment, at first, builds a database with UFL at different temperatures. It then trains the model and tests its performance. The results show that the average mode-locked recovery time of the trained network model is 1.948 s. As far as we know, it is 62.8% of the fastest average mode-locked recovery time in the existing work. At different temperatures, the trained network model can also recover the mode-locked state of the UFL in a short time. Remote algorithm training and automatic mode-locked control are proved in this work, laying the foundation for long-distance maintenance and centralized control of UFLs..
Photonics Research
- Publication Date: Jul. 20, 2021
- Vol. 9, Issue 8, 1493 (2021)
Nonlinear Fourier transform enabled eigenvalue spectrum investigation for fiber laser radiation
Yutian Wang, Songnian Fu, Jian Kong, Andrey Komarov, Mariusz Klimczak, Ryszard Buczyński, Xiahui Tang, Ming Tang, Yuwen Qin, and Luming Zhao
Fiber lasers are a paradigm of dissipative systems, which distinguish themselves from a Hamilton system where energy is conservative. Consequently, pulses generated in a fiber laser are always accompanied by the continuous wave (CW). Under certain hypothesis, pulses generated in a fiber laser can be considered as a soliton, a product of a Hamilton system. Therefore, all the descriptions of solitons of a fiber laser are approximate. Coexistence of solitons and the CW from a fiber laser prevents unveiling of real nonlinear dynamics in fiber lasers, such as soliton interactions. Pulse behavior in a fiber laser can be represented by the state of single pulse, the state of period doubling of single pulse, the states of two pulses either tightly bound or loosely distributed, the states of three pulses, and various combinations of the above-mentioned states. Recently, soliton distillation was proposed and numerically demonstrated based on the nonlinear Fourier transform (NFT) [J. Lightwave Technol.39, 2542 (2021)JLTEDG0733-872410.1109/JLT.2021.3051036]. Solitons can be separated from the coherent CW background. Therefore, it is feasible to isolate solitons from CW background in a fiber laser. Here, we applied the NFT to various pulses generated in a fiber laser, including single pulse, single pulse in period doubling, different double pulses, and multiple pulses. Furthermore, with the approach of soliton distillation, the corresponding pure solitons of those pulses are reconstructed. Simulation results suggest that the NFT can be used to identify soliton dynamics excluding CW influence in a fiber laser, which paves a new way for uncovering real soliton interaction in nonlinear systems.Fiber lasers are a paradigm of dissipative systems, which distinguish themselves from a Hamilton system where energy is conservative. Consequently, pulses generated in a fiber laser are always accompanied by the continuous wave (CW). Under certain hypothesis, pulses generated in a fiber laser can be considered as a soliton, a product of a Hamilton system. Therefore, all the descriptions of solitons of a fiber laser are approximate. Coexistence of solitons and the CW from a fiber laser prevents unveiling of real nonlinear dynamics in fiber lasers, such as soliton interactions. Pulse behavior in a fiber laser can be represented by the state of single pulse, the state of period doubling of single pulse, the states of two pulses either tightly bound or loosely distributed, the states of three pulses, and various combinations of the above-mentioned states. Recently, soliton distillation was proposed and numerically demonstrated based on the nonlinear Fourier transform (NFT) [J. Lightwave Technol. 39 , 2542 (2021 )JLTEDG0 733-8724 10.1109/JLT.2021.3051036
Photonics Research
- Publication Date: Jul. 29, 2021
- Vol. 9, Issue 8, 1531 (2021)
Dynamic performance and reflection sensitivity of quantum dot distributed feedback lasers with large optical mismatch
Bozhang Dong, Jianan Duan, Heming Huang, Justin C. Norman, Kenichi Nishi, Keizo Takemasa, Mitsuru Sugawara, John E. Bowers, and Frédéric Grillot
This work reports on a high-efficiency InAs/GaAs distributed feedback quantum dot laser. The large optical wavelength detuning at room temperature between the lasing peak and the gain peak causes the static, dynamic, and nonlinear intrinsic properties to all improve with temperature, including the lasing efficiency, the modulation dynamics, the linewidth enhancement factor, and consequently the reflection insensitivity. Results reported show an optimum operating temperature at 75°C, highlighting the potential of the large optical mismatch assisted single-frequency laser for the development of uncooled and isolator-free high-speed photonic integrated circuits.This work reports on a high-efficiency InAs/GaAs distributed feedback quantum dot laser. The large optical wavelength detuning at room temperature between the lasing peak and the gain peak causes the static, dynamic, and nonlinear intrinsic properties to all improve with temperature, including the lasing efficiency, the modulation dynamics, the linewidth enhancement factor, and consequently the reflection insensitivity. Results reported show an optimum operating temperature at 75°C, highlighting the potential of the large optical mismatch assisted single-frequency laser for the development of uncooled and isolator-free high-speed photonic integrated circuits..
Photonics Research
- Publication Date: Jul. 29, 2021
- Vol. 9, Issue 8, 1550 (2021)
Nanophotonics and Photonic Crystals
In-plane excitation of a topological nanophotonic corner state at telecom wavelengths in a cross-coupled cavity | Editors' Pick
Xin-Tao He, Meng-Yu Li, Hao-Yang Qiu, Wen-Sheng Ruan, Li-Dan Zhou, Lin Liu, Xiao-Dong Chen, Wen-Jie Chen, Fu-Li Zhao, and Jian-Wen Dong
In silicon photonics, the cavity mode is a fundamental mechanism to design integrated passive devices for on-chip optical information processing. Recently, the corner state in a second-order topological photonic crystal (PC) rendered a global method to achieve an intrinsic cavity mode. It is crucial to explore such a topological corner state in silicon photonic integrated circuits (PICs) under in-plane excitation. Here, we study both theoretically and experimentally the topological nanophotonic corner state in a silicon-on-insulator PC cavity at a telecommunications wavelength. In theory, the expectation values of a mirror-flip operation for the Bloch modes of a PC slab are used to characterize the topological phase. Derived from topologically distinct bulk polarizations of two types of dielectric-vein PCs, the corner state is induced in a 90-deg-bend interface, localizing at the corner point of real space and the Brillouin zone boundary of reciprocal space. To implement in-plane excitation in an experiment, we fabricate a cross-coupled PC cavity based on the bend interface and directly image the corner state near 1383 nm using a far-field microscope. Finally, by means of the temporal coupled-mode theory, the intrinsic Q factor of a cross-coupled cavity (about 8000) is retrieved from the measured transmission spectra. This work gives deterministic guidance and potential applications for cavity-mode-based passive devices in silicon PICs, such as optical filters, routers, and multiplexers.In silicon photonics, the cavity mode is a fundamental mechanism to design integrated passive devices for on-chip optical information processing. Recently, the corner state in a second-order topological photonic crystal (PC) rendered a global method to achieve an intrinsic cavity mode. It is crucial to explore such a topological corner state in silicon photonic integrated circuits (PICs) under in-plane excitation. Here, we study both theoretically and experimentally the topological nanophotonic corner state in a silicon-on-insulator PC cavity at a telecommunications wavelength. In theory, the expectation values of a mirror-flip operation for the Bloch modes of a PC slab are used to characterize the topological phase. Derived from topologically distinct bulk polarizations of two types of dielectric-vein PCs, the corner state is induced in a 90-deg-bend interface, localizing at the corner point of real space and the Brillouin zone boundary of reciprocal space. To implement in-plane excitation in an experiment, we fabricate a cross-coupled PC cavity based on the bend interface and directly image the corner state near 1383 nm using a far-field microscope. Finally, by means of the temporal coupled-mode theory, the intrinsic
Photonics Research
- Publication Date: Jul. 08, 2021
- Vol. 9, Issue 8, 1423 (2021)
Negative refraction mediated by bound states in the continuum | On the Cover
Zhanyuan Zhang, Feifei Qin, Yi Xu, Songnian Fu, Yuncai Wang, and Yuwen Qin
Negative refraction might occur at the interface between a two-dimensional photonic crystal (PhC) slab and a homogeneous medium, where the guiding of the electromagnetic wave along the third dimension is governed by total internal reflection. Herein, we report on the observation of negative refraction in the PhC slab where the vertical guiding is enabled by a bound state in the continuum and essentially beyond the light cone. Such abnormal refraction and guiding mechanism are based on the synchronous crafting of spatial dispersion and the radiative lifetime of Bloch modes within the radiative continuum. Microwave experiments are provided to further validate the numerical proposal in an all-dielectric PhC platform. It is envisioned that the negative refraction observed beyond the light cone might facilitate the development of optical devices in integrated optics, such as couplers, multiplexers, and demultiplexers.Negative refraction might occur at the interface between a two-dimensional photonic crystal (PhC) slab and a homogeneous medium, where the guiding of the electromagnetic wave along the third dimension is governed by total internal reflection. Herein, we report on the observation of negative refraction in the PhC slab where the vertical guiding is enabled by a bound state in the continuum and essentially beyond the light cone. Such abnormal refraction and guiding mechanism are based on the synchronous crafting of spatial dispersion and the radiative lifetime of Bloch modes within the radiative continuum. Microwave experiments are provided to further validate the numerical proposal in an all-dielectric PhC platform. It is envisioned that the negative refraction observed beyond the light cone might facilitate the development of optical devices in integrated optics, such as couplers, multiplexers, and demultiplexers..
Photonics Research
- Publication Date: Jul. 30, 2021
- Vol. 9, Issue 8, 1592 (2021)
Optical and Photonic Materials
Modifying light–matter interactions with perovskite nanocrystals inside antiresonant photonic crystal fiber
Andrey A. Machnev, Anatoly P. Pushkarev, Pavel Tonkaev, Roman E. Noskov, Kristina R. Rusimova, Peter J. Mosley, Sergey V. Makarov, Pavel B. Ginzburg, and Ivan I. Shishkin
Structured environments are employed in a plethora of applications to tailor dynamics of light–matter interaction processes by modifying the structure of electromagnetic fields. The promising example of such a system is antiresonant photonic crystal fibers (AR-PCFs), which allow light–analyte interactions in a very long channel. Here we probe contribution of microstructuring and nontrivial mode hierarchy on light–matter interactions in AR-PCFs by investigating lifetime shortening of perovskite (CsPbBr3) nanocrystals grown to fiber capillaries. The crystals have been deposited using a wet chemistry approach and then excited by a supercontinuum source in the 450–500 nm range. Emission spectra have been measured and analyzed via the time-correlated single photon counting (TCSPC) technique, unravelling contributions of core and cladding modes. Fluorescence lifetime imaging inside an AR-PCF enables mapping input of various electromagnetic channels into light–matter interaction processes. Our results pave the way for tailoring the dynamics of high-order quantum processes, promoting the concept of AR-PCF as a light-driven reactor.Structured environments are employed in a plethora of applications to tailor dynamics of light–matter interaction processes by modifying the structure of electromagnetic fields. The promising example of such a system is antiresonant photonic crystal fibers (AR-PCFs), which allow light–analyte interactions in a very long channel. Here we probe contribution of microstructuring and nontrivial mode hierarchy on light–matter interactions in AR-PCFs by investigating lifetime shortening of perovskite (
Photonics Research
- Publication Date: Jul. 09, 2021
- Vol. 9, Issue 8, 1462 (2021)
Water-stable CsPbBr3 perovskite quantum-dot luminous fibers fabricated by centrifugal spinning for dual white light illumination and communication
Binhai Yu, Shunming Liang, Fengyi Zhang, Zongtao Li, Bin Liu, and Xinrui Ding
Lead halide perovskite quantum dots (PQDs) display remarkable photoelectric performance. However, defects such as weak stability in air and water environments limit the development of lead halide PQDs in solid-state light applications. Herein, centrifugal spinning is used for the fabrication of stable luminous CsPbBr3 PQD nanofibers. After immersion in water for 11 months, the PQD fibers still maintained considerable photoluminescence quantum yield, showing high stability in hostile environments. The water-stability mechanism of the fibers can be explained by the changing defect density, crystal growth of PQDs, and the molecular transformation at the fiber surface. The white LED based on the CsPbBr3 fibers exhibits satisfying color gamut performance (128% of National Television System Committee). Due to the short photoluminescence lifetime of CsPbBr3 PQDs, the communication potential is also considered. The CsPbBr3 fibers obtained by centrifugal spinning present a bandwidth of 11.2 MHz, showing promising performance for solid-state light and visible light communication applications.Lead halide perovskite quantum dots (PQDs) display remarkable photoelectric performance. However, defects such as weak stability in air and water environments limit the development of lead halide PQDs in solid-state light applications. Herein, centrifugal spinning is used for the fabrication of stable luminous
Photonics Research
- Publication Date: Jul. 29, 2021
- Vol. 9, Issue 8, 1559 (2021)
Optical Devices
Formation of a three-dimensional bottle beam via an engineered microsphere
Yan Zhou, and Minghui Hong
In this work, we propose a novel approach to produce three-dimensional (3D) optical trapping with sub-wavelength size through an engineered microsphere, under linear polarization states of an incident light. The engineered microsphere is designed to contain the segmented regions of diffractive patterns and made by focused ion beam fabrication. We simulate and experimentally characterize the focus performance of the engineered microsphere. The emitted light field from the exit surface of the engineered microsphere forms a pair of axially arranged focused beams, and they are connected with a continuous optical field embracing a 3D optical null at the center, forming the so-called optical bottle beam. Experimental results and numerical simulation are in good agreement. Such micro-optics can be used for precise and localized optical trapping.In this work, we propose a novel approach to produce three-dimensional (3D) optical trapping with sub-wavelength size through an engineered microsphere, under linear polarization states of an incident light. The engineered microsphere is designed to contain the segmented regions of diffractive patterns and made by focused ion beam fabrication. We simulate and experimentally characterize the focus performance of the engineered microsphere. The emitted light field from the exit surface of the engineered microsphere forms a pair of axially arranged focused beams, and they are connected with a continuous optical field embracing a 3D optical null at the center, forming the so-called optical bottle beam. Experimental results and numerical simulation are in good agreement. Such micro-optics can be used for precise and localized optical trapping..
Photonics Research
- Publication Date: Jul. 30, 2021
- Vol. 9, Issue 8, 1598 (2021)
Bidirectional cascaded deep neural networks with a pretrained autoencoder for dielectric metasurfaces
Weichao Kong, Jun Chen, Zengxin Huang, and Dengfeng Kuang
Metasurfaces composed of meta-atoms provide promising platforms for manipulating amplitude, phase, and polarization of light. However, the traditional design methods of metasurfaces are time consuming and laborious. Here, we propose a bidirectional cascaded deep neural network with a pretrained autoencoder for rapid design of dielectric metasurfaces in the range of 450 nm to 850 nm. The forward model realizes a prediction of amplitude and phase responses with a mean absolute error of 0.03. Meanwhile, the backward model can retrieve patterns of meta-atoms in an inverse-design manner. The availability of this model is demonstrated by database establishment, model evaluation, and generalization testing. Furthermore, we try to reveal the mechanism behind the model in a visualization way. The proposed approach is beneficial to reduce the cost of computation burden and improve nanophotonic design efficiency for solving electromagnetic on-demand design issues automatically.Metasurfaces composed of meta-atoms provide promising platforms for manipulating amplitude, phase, and polarization of light. However, the traditional design methods of metasurfaces are time consuming and laborious. Here, we propose a bidirectional cascaded deep neural network with a pretrained autoencoder for rapid design of dielectric metasurfaces in the range of 450 nm to 850 nm. The forward model realizes a prediction of amplitude and phase responses with a mean absolute error of 0.03. Meanwhile, the backward model can retrieve patterns of meta-atoms in an inverse-design manner. The availability of this model is demonstrated by database establishment, model evaluation, and generalization testing. Furthermore, we try to reveal the mechanism behind the model in a visualization way. The proposed approach is beneficial to reduce the cost of computation burden and improve nanophotonic design efficiency for solving electromagnetic on-demand design issues automatically..
Photonics Research
- Publication Date: Jul. 30, 2021
- Vol. 9, Issue 8, 1607 (2021)
Optoelectronics
Manipulation of blue TADF top-emission OLEDs by the first-order optical cavity design: toward a highly pure blue emission and balanced charge transport
Wanqi Ren, Kyung Rock Son, Tae Hoon Park, Vignesh Murugadoss, and Tae Geun Kim
The broad luminescence spectrum of a thermally activated delayed fluorescence (TADF) organic light-emitting diode (OLED) is a critical issue to overcome for its application in high-color-purity displays. Herein, a novel device structure that utilizes the first-order microcavity optical mode with a high radiance intensity is demonstrated to solve this problem by considering the charge transport properties through the analysis of hole-only and electron-only devices. In addition, by tuning the optical interference near the semitransparent top cathode layers consisting of thin silver and organic capping layers, light extraction is increased by nearly 2 times compared to the device without a capping layer. Consequently, the optimized blue TADF top-emission OLED exhibits much lower full width at half-maximum, higher maximum current efficiency, and external quantum efficiency compared to the device before optimization. This approach is expected to provide a simple but effective way to further enhance the spectral purity of the conventional TADF-based OLEDs.The broad luminescence spectrum of a thermally activated delayed fluorescence (TADF) organic light-emitting diode (OLED) is a critical issue to overcome for its application in high-color-purity displays. Herein, a novel device structure that utilizes the first-order microcavity optical mode with a high radiance intensity is demonstrated to solve this problem by considering the charge transport properties through the analysis of hole-only and electron-only devices. In addition, by tuning the optical interference near the semitransparent top cathode layers consisting of thin silver and organic capping layers, light extraction is increased by nearly 2 times compared to the device without a capping layer. Consequently, the optimized blue TADF top-emission OLED exhibits much lower full width at half-maximum, higher maximum current efficiency, and external quantum efficiency compared to the device before optimization. This approach is expected to provide a simple but effective way to further enhance the spectral purity of the conventional TADF-based OLEDs..
Photonics Research
- Publication Date: Jul. 20, 2021
- Vol. 9, Issue 8, 1502 (2021)
Physical Optics
Sub-diffraction dark spot localization microscopy
Chuankang Li, Yuzhu Li, Zhengyi Zhan, Yuhang Li, Xin Liu, Yong Liu, Xiang Hao, Cuifang Kuang, and Xu Liu
Single molecular localization microscopy (SMLM) is a useful tool in biological observation with sub-10-nm resolution. However, SMLM is incapable of discerning two molecules within the diffraction-limited region unless with the help of a stochastic on–off switching scheme which yet entails time-consuming processes. Here, we produce a novel kind of focal spot pattern, called sub-diffraction dark spot (SDS), to localize molecules within the sub-diffraction region of interest. In our proposed technique nominated as sub-diffracted dark spot localization microscopy (SDLM), multiple molecules within the diffraction-limited region could be distinguished without the requirement of stochastic fluorescent switches. We have numerically investigated some related impacts of SDLM, such as detection circle diameter, collected photon number, background noise, and SDS size. Simulative localization framework has been implemented on randomly distributed and specifically structured samples. In either two- or three-dimensional case, SDLM is evidenced to have ∼2 nm localization accuracy.Single molecular localization microscopy (SMLM) is a useful tool in biological observation with sub-10-nm resolution. However, SMLM is incapable of discerning two molecules within the diffraction-limited region unless with the help of a stochastic on–off switching scheme which yet entails time-consuming processes. Here, we produce a novel kind of focal spot pattern, called sub-diffraction dark spot (SDS), to localize molecules within the sub-diffraction region of interest. In our proposed technique nominated as sub-diffracted dark spot localization microscopy (SDLM), multiple molecules within the diffraction-limited region could be distinguished without the requirement of stochastic fluorescent switches. We have numerically investigated some related impacts of SDLM, such as detection circle diameter, collected photon number, background noise, and SDS size. Simulative localization framework has been implemented on randomly distributed and specifically structured samples. In either two- or three-dimensional case, SDLM is evidenced to have
Photonics Research
- Publication Date: Jul. 09, 2021
- Vol. 9, Issue 8, 1455 (2021)
Discrepancy between transmission spectrum splitting and eigenvalue splitting: a reexamination on exceptional point-based sensors
Qi Geng, and Ka-Di Zhu
In the study of exceptional point (EP)-based sensors, the concrete form of the output spectrum is often dismissed, and it is assumed that there is a corresponding relation between the peaks/valleys in the transmission spectrum and the real parts of the eigenvalues of the system. We point out that this assumption does not always hold. An effect, which is mathematically similar to electromagnetically induced transparency (EIT), may result in a ‘pseudo spectrum splitting’ that does not correspond to the splitting between the eigenvalues. The effect shall be taken care of when designing an EP-based sensor since it may cause measurement error and misunderstanding such as recognization of the spectrum splitting as the eigenvalue splitting at the exceptional point. We also propose to intentionally utilize this ‘pseudo splitting’ to design a sensor, which does not work at an EP, that has an EP-like spectrum splitting.In the study of exceptional point (EP)-based sensors, the concrete form of the output spectrum is often dismissed, and it is assumed that there is a corresponding relation between the peaks/valleys in the transmission spectrum and the real parts of the eigenvalues of the system. We point out that this assumption does not always hold. An effect, which is mathematically similar to electromagnetically induced transparency (EIT), may result in a ‘pseudo spectrum splitting’ that does not correspond to the splitting between the eigenvalues. The effect shall be taken care of when designing an EP-based sensor since it may cause measurement error and misunderstanding such as recognization of the spectrum splitting as the eigenvalue splitting at the exceptional point. We also propose to intentionally utilize this ‘pseudo splitting’ to design a sensor, which does not work at an EP, that has an EP-like spectrum splitting..
Photonics Research
- Publication Date: Jul. 30, 2021
- Vol. 9, Issue 8, 1645 (2021)
Quantum Optics
Quantum-limited localization and resolution in three dimensions
Ben Wang, Liang Xu, Jun-chi Li, and Lijian Zhang
As a method to extract information from optical systems, imaging can be viewed as a parameter estimation problem. The fundamental precision in locating one emitter or estimating the separation between two incoherent emitters is bounded below by the multiparameter quantum Cramér-Rao bound (QCRB). Multiparameter QCRB gives an intrinsic bound in parameter estimation. We determine the ultimate potential of quantum-limited imaging for improving the resolution of a far-field, diffraction-limited optical field within the paraxial approximation. We show that the quantum Fisher information matrix (QFIm) in about one emitter’s position is independent on its true value. We calculate the QFIm of two unequal-brightness emitters’ relative positions and intensities; the results show that only when the relative intensity and centroids of two-point sources, including longitudinal and transverse directions, are known exactly, the separation in different directions can be estimated simultaneously with finite precision. Our results give the upper bounds on certain far-field imaging technology and will find wide use in applications from microscopy to astrometry.As a method to extract information from optical systems, imaging can be viewed as a parameter estimation problem. The fundamental precision in locating one emitter or estimating the separation between two incoherent emitters is bounded below by the multiparameter quantum Cramér-Rao bound (QCRB). Multiparameter QCRB gives an intrinsic bound in parameter estimation. We determine the ultimate potential of quantum-limited imaging for improving the resolution of a far-field, diffraction-limited optical field within the paraxial approximation. We show that the quantum Fisher information matrix (QFIm) in about one emitter’s position is independent on its true value. We calculate the QFIm of two unequal-brightness emitters’ relative positions and intensities; the results show that only when the relative intensity and centroids of two-point sources, including longitudinal and transverse directions, are known exactly, the separation in different directions can be estimated simultaneously with finite precision. Our results give the upper bounds on certain far-field imaging technology and will find wide use in applications from microscopy to astrometry..
Photonics Research
- Publication Date: Jul. 23, 2021
- Vol. 9, Issue 8, 1522 (2021)
Surface Optics and Plasmonics
Negative refraction of ultra-squeezed in-plane hyperbolic designer polaritons
Qiaolu Chen, Yihao Yang, Li Zhang, Jialin Chen, Min Li, Xiao Lin, Rujiang Li, Zuojia Wang, Baile Zhang, and Hongsheng Chen
The in-plane negative refraction of high-momentum (i.e., high-k) photonic modes could enable many applications such as imaging, focusing, and waveguiding in a planar platform at deep-subwavelength scales. However, its practical implementation in experiments remains elusive so far. Here we propose a class of hyperbolic metasurfaces, which is characterized by an anisotropic magnetic sheet conductivity and can support the in-plane ultra-high-k magnetic designer polaritons. Based on such metasurfaces, we report the experimental observation of the all-angle negative refraction of designer polaritons at extremely deep-subwavelength scales. Moreover, we directly visualize the designer polaritons with hyperbolic dispersions. Importantly, for these hyperbolic polaritons, we find that their squeezing factor is ultra-large. To be specific, it can be up to 129 in the experiments, an ultra-high value exceeding those in naturally hyperbolic materials. This work may pave a way toward exploring the extremely high confinement and unusual propagation of magnetic designer polaritons over monolayer or twisted bilayer hyperbolic metasurfaces.The in-plane negative refraction of high-momentum (i.e., high-
Photonics Research
- Publication Date: Jul. 29, 2021
- Vol. 9, Issue 8, 1540 (2021)
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