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The image on the cover for Chinese Optics Letters Volume 19, Issue 11, summarizes the PAI techniques, imaging systems, and their biomedical applications in microrobots tracking in vitro and in vivo. From a robotic tracking perspective, some insight into the future of PAI technology in clinical applications is also provided.The image is based on original research by Dengfeng Li et al. presented in their paper "Review of photoacoustic imaging for microrobots tracking in vivo [Invited]", Chinese Optics Letters 19 (11), 111701 (2021).

The image on the cover for Photonics Research Volume 9, Issue 11, proposes a device that could be used for both display and visible light communication (VLC) applications. The semipolar blue &mu;LED array fabricated in this study shows a negligible wavelength shift, indicating a significant reduction in the quantum confined Stark effect. The image is based on original research by Tingzhu Wu et al. presented in their paper "Highly stable full-color display device with VLC application potential using semipolar &mu;LEDs and all-inorganic encapsulated perovskite nanocrystal", Photonics Research 9 (11), 11002132 (2021).

The image on the cover for Advanced Photonics Volume 3 Issue 5 depicts a novel spintronic-metasurface terahertz emitter, developed by researchers from Fudan University. Composed of alternating magnetic heterostructures, the emitter allows efficient, flexible generation and manipulation of chiral terahertz waves. Terahertz radiation is generated by exciting the emitter with laser pulses under an oriented external magnetic field. Transverse anisotropic confinement of the laser-induced charge currents imposed by the metasurface structure leads to chiralterahertz-wave emission.The image is based on original research presented in the report by Changqin Liu, Shunjia Wang, Sheng Zhang, and Qingnan Cai, et al., “Active spintronic-metasurface terahertz emitters with tunable chirality,” Adv. Photonics 3(5), 056002 (2021), doi: 10.1117/1.AP.3.5.056002.

The image on the cover of High Power Laser Science and Engineering Volume 9, Issue 3, presents an all-optical scheme to generate a high-energy &gamma;-photon beam with large beam angular momentum (BAM), small divergence, and high brilliance.The image is based on original research by Hao Zhang et al. presented in their paper "Efficient bright &gamma;-ray vortex emission from a laser-illuminated light-fan-in-channel target", High Power Laser Science and Engineering 9 (3), 03000e43 (2021).

The image on the cover for Chinese Optics Letters Volume 19, Issue 10, reviews the important parameters including the refractive index detection range, resonance wavelength, and spectral sensitivity responsible for the sensing properties of PCF-SPR sensors.The image is based on original research by Chao Liu et al. presented in their paper "Overview of refractive index sensors comprising photonic crystal fibers based on the surface plasmon resonance effect [Invited]", Chinese Optics Letters 19 (10), 102202 (2021).

Editors' Picks
Advances in quantum technologies over the past two decades have made possible an exciting breadth of applications in fields such as communications, and computation. Photon-pair generation based on the spontaneous parametric down conversion and four wave mixing processes have played an essential role in this revolution due to the ease with which the quantum entanglement characteristics of the emitted signal and idler photons may be tailored, and on account of their ability to propagate long distances either in free space or in optical fibers with minimal interaction with the environment.
Photonics Research
• Dec. 03, 2021
• Vol. 9, Issue 11 (2021)
Editors' Picks
Since the invention of tilted-pulse-front-pumped LiNbO3 (TPFP-LN) THz source in 2002, the maximum THz energy achieved by such sources has been increased by seven orders of magnitude, from 100 pJ to above 1 mJ. The few µJ THz energy and a few-hundred kV focused peak electric field achieved in 2007 have made it possible to perform THz pump – THz probe measurements and other nonlinear optical investigations. Because of this, TPFP LN THz source became the most widely used THz source in the lover than 2 THz frequency range.
Chinese Optics Letters
• Dec. 02, 2021
• Vol. 19, Issue 11 (2021)
On the Cover
The techniques of high-speed communication and high-resolution display kit are both essential to modern life, as they constitute the foundations of those attractive concepts: Internet of Things, virtual/augmented reality, and metverse. If they are expected to be integrated, being realized simultaneously in one single device in the form of visible light communication (VLC) and micro-LED (μLED) array, it will be thrilling that this new technique would combine the advantages of both, such as avoiding occupying the limited electromagnetic sources, confidentiality, energy saving, and large color gamut, etc.
Photonics Research
• Nov. 26, 2021
• Vol. 9, Issue 11 (2021)
AP Highlights
Similar to electrons, photons can carry angular momentum (AM). In general, photonic AM consists of spin angular momentum (SAM) and orbital angular momentum (OAM). The former is associated with rotating electric field vector, while the latter is linked to swirling phase. SAM associated with circularly polarization has been known for a very long time and extensively exploited in a wide array of applications ranging from materials metrology, chiral molecule detection and quantum optics. About 30 years ago, Allen et al discovered that optical field with spiral phase wavefront possesses OAM, offered a whole new degree of freedom for photonics. To this point, the SAM and OAM of light studied are parallel to the propagation direction of the beam, hence can be termed as longitudinal SAM and longitudinal OAM. About a decade ago, the existence of transverse SAM in both free space and localized optical fields has been revealed via both theoretical and experimental works. Light with transverse SAM exhibits distinctively different behaviors when interact with matters, rendering another degree of freedom for photonic AM. In 2020, Zhan et al demonstrated the controllable generation of light pulses containing pure transverse OAM. The last piece of the puzzle for photonic AM is finally in place.
• Nov. 25, 2021
• Vol. 3, Issue 6 (2021)
Editors' Picks
Spatiotemporal (ST) wavepacket has been widely investigated since the invention of ultrafast laser. Conventional research on ST wavepackets focuses on studying spatiotemporal uncoupled wavepacket, meaning the space domain property and time domain property of the wavepacket are exploited separately.
Photonics Research
• Nov. 24, 2021
• Vol. 9, Issue 11 (2021)
Enhanced absorption and electrical modulation of graphene based on the parity-time symmetry optical structure

In order to realize the ultrastrong absorption of graphene with electrical modulation properties, we designed a composite structure of graphene and parity

In order to realize the ultrastrong absorption of graphene with electrical modulation properties, we designed a composite structure of graphene and parity-time (PT) symmetry photonic crystal, which is achieved by placing the graphene layer on the top layer of the PT symmetry photonic crystal. In this paper, the absorption properties of graphene and the electrical modulating properties of the structure were theoretically analyzed based on the transfer matrix method. The result shows that the proposed structure can achieve the absorption of 31.5 dB for the communication wavelength of 1550 nm; meanwhile, by setting the electric field intensity to $±0.02 V/nm$, the absorption of graphene can be largely modulated to realize an electrically switchable effect, the modulation depth of graphene absorption can reach nearly 100%, and the operation speed is also close to 8.171 GHz. This investigation provides a novel approach to design graphene-based optoelectronic devices and optical communication devices.show less

• Dec.03，2021
• Chinese Optics Letters,Vol. 20, Issue 2
• 022201 (2022)
Design and fabrication of a compact, high-performance interference-filter-based external-cavity diode laser for use in the China Space Station

A hertz-linewidth ultra-stable laser (USL), which will be used to detect the clock transition line, in a strontium optical clock will be launched into the

A hertz-linewidth ultra-stable laser (USL), which will be used to detect the clock transition line, in a strontium optical clock will be launched into the China Space Station (CSS) in late 2022. As the core of the USL, an interference-filter-based external-cavity diode laser (IF-ECDL) was developed. The IF-ECDL has a compact, stable, and environmentally insensitive design. Performances of the IF-ECDL are presented. The developed IF-ECDL can pass the aerospace environmental tests, indicating that the IF-ECDL can be suitable for space missions in the CSS.show less

• Dec.03，2021
• Chinese Optics Letters,Vol. 20, Issue 2
• 021407 (2022)
Direct characterization of coherence of quantum detectors by sequential measurements

The quantum properties of quantum measurements are indispensable resources in quantum information processing and have drawn extensive research interest. T

The quantum properties of quantum measurements are indispensable resources in quantum information processing and have drawn extensive research interest. The conventional approach to revealing quantum properties relies on the reconstruction of entire measurement operators by quantum detector tomography. However, many specific properties can be determined by a part of the matrix components of the measurement operators, which makes it possible to simplify the characterization process. We propose a general framework to directly obtain individual matrix elements of the measurement operators by sequentially measuring two noncompatible observables. This method allows us to circumvent the complete tomography of the quantum measurement and extract the required information. We experimentally implement this scheme to monitor the coherent evolution of a general quantum measurement by determining the off-diagonal matrix elements. The investigation of the measurement precision indicates the good feasibility of our protocol for arbitrary quantum measurements. Our results pave the way for revealing the quantum properties of quantum measurements by selectively determining the matrix components of the measurement operators.show less

• Dec.03，2021
• Advanced Photonics,Vol. 3, Issue 6
• 066001 (2021)
Wide-steering-angle high-resolution optical phased array

Optical phased array (OPA) technology is considered a promising solution for solid-state beam steering to supersede the traditional mechanical beam steeri

Optical phased array (OPA) technology is considered a promising solution for solid-state beam steering to supersede the traditional mechanical beam steering. As a key component of the LIDAR system for long-range detection, OPAs featuring a wide steering angle and high resolution without beam aliasing are highly desired. However, a wide steering range requires a waveguide pitch less than half of the wavelength, which is easily subjected to cross talk. Besides, high resolution requires a large aperture, and it is normally achieved by a high count number of waveguides, which complicates the control system. To solve the mentioned issues, we design two high-performance 128-channel OPAs fabricated on a multilayered SiN-on-SOI platform. Attributed to the nonuniform antenna pitch, only 128 waveguides are used to achieve a 4 mm wide aperture. Besides, by virtue of innovative dual-level silicon nitride ($Si3N4$) waveguide grating antennas, the fishbone antenna OPA achieves a $100°×19.4°$ field of view (FOV) with divergence of $0.021°×0.029°$, and the chain antenna OPA realizes a $140°×19.23°$ FOV with divergence of $0.021°×0.1°$. To our best knowledge, 140° is the widest lateral steering range in two-dimensional OPA, and 0.029° is the smallest longitudinal divergence. Finally, we embed the OPA into a frequency-modulated continuous-wave system to achieve 100 m distance measurement. The reflected signal from 100 m distance is well detected with 26 dBm input transmitter power, which proves that OPA serves as a promising candidate for transceiving optical signal in a LIDAR system.show less

• Dec.03，2021
• Photonics Research,Vol. 9, Issue 12
• 12002511 (2021)

White light, which contains polychromic visible lights, affects the rhythm of organisms and has the potential for advanced applications of lighting, display, and communication. Compared

White light, which contains polychromic visible lights, affects the rhythm of organisms and has the potential for advanced applications of lighting, display, and communication. Compared with traditional incandescent bulbs and inorganic diodes, pure organic materials are superior in terms of better compatibility, flexibility, structural diversity and environmental friendliness. In the past few years, polychromic emission has been obtained based on organic aggregates, which provides a platform to achieve white-light emission. Several white-light emitters are sporadically reported, but the underlying mechanistic picture is still not fully established. Based on these considerations, this review will focus on the single-component and multi-component strategies to achieve efficient white-light emission from pure organic aggregates. Thereinto, single-component strategy is introduced from four parts: dual fluorescence, fluorescence and phosphorescence, dual phosphorescence with anti-Kasha’s behavior, and clusteroluminescence. Meanwhile, doping, supramolecular assembly, and cocrystallization are summarized as strategies for multi-component systems. Beyond the construction strategies of white-light emitters, their advanced representative applications, such as organic light-emitting diodes, white luminescent dyes, circularly polarized luminescence, and encryption, are also prospected. It is expected that this review will draw a comprehensive picture of white-light emission from organic aggregates as well as their emerging applicationsshow less

• Dec.03，2021

We designed a tunable wavelength-selective quasi-resonant cavity enhanced photodetector (QRCE-PD) based on high-contrast subwavelength grating (SWG). According to simulation results, it

We designed a tunable wavelength-selective quasi-resonant cavity enhanced photodetector (QRCE-PD) based on high-contrast subwavelength grating (SWG). According to simulation results, its peak quantum efficiency is 93.2%, 3-dB bandwidth is 33.5 GHz, spectral linewidth is 0.12nm, and wavelength-tuning range is 28 nm (1536 nm–1564 nm). The QRCE-PD contains a tunable Fabry-Perot filtering cavity (FPC), a symmetrical SWG deflection reflector (SSWG-DR) and a built-in p-i-n photodiode. The FPC and the SSWG-DR form an equivalent multi-region F-P cavity together by multiple mutual mirroring, which makes the QRCE-PD a multi-region resonant cavity enhanced photodetector. But QRCE-PD relies on the multiple-pass absorption enhanced effect to achieve high quantum efficiency, rather than the resonant cavity enhanced effect. This new photodetector structure is significant for the application in the dense wavelength division multiplexing (DWDM) systems. show less

• Dec.03，2021
• Chinese Optics Letters,Vol. 20, Issue 3
• (2022)

When two synchronized laser beams illuminate the inner surface of bulk lithium niobate crystals with magnesium doping (5% /mol ) under the condition of total reflection, the semi-degene

When two synchronized laser beams illuminate the inner surface of bulk lithium niobate crystals with magnesium doping (5% /mol ) under the condition of total reflection, the semi-degenerate four wave mixing (FWM) generates. On this basis, the research on more sophisticated frequency conversion process on the interface of nonlinear crystal have been taken. The generation mechanism is associated with the scattering light of the fundamental waves reflected on the inner surface of nonlinear crystal. Analysis of phase matching mechanism confirms that the FWM is stimulated by third-order nonlinear susceptibilities of nonlinear material. Theoretically calculated and experimentally measured corresponding data have been presented in this article. These results are expected to provide new inspiration for further experimental and theoretical research on frequency conversion in nonlinear crystals.show less

• Dec.03，2021
• Chinese Optics Letters,Vol. 20, Issue 3
• (2022)

The hole injection capability is essentially important for GaN-based vertical cavity surface emitting lasers (VCSELs) to enhance the laser power. In this work, we propose GaN-based VCSE

The hole injection capability is essentially important for GaN-based vertical cavity surface emitting lasers (VCSELs) to enhance the laser power. In this work, we propose GaN-based VCSELs with p-AlGaN/p-GaN structure as the p-type hole supplier to facilitate the hole injection. The p-AlGaN/p-GaN heterojunction is able to store the electric field and thus can moderately adjust the drift velocity and the kinetic energy for holes, which can improve the thermionic emission process for holes to travel across the p-type electron blocking layer (p-EBL). Besides, the valence band barrier height in the p-EBL can be reduced as a result of usage of the p-AlGaN layer. Therefore, the better stimulated radiative recombination rate and the increased laser power are obtained, thus enhancing the 3dB frequency bandwidth. Moreover, we also investigate the impact of p-AlGaN/p-GaN structure with various AlN compositions in the p-AlGaN layer on the hole injection capability, the laser power and the 3dB frequency bandwidth.show less

• Dec.03，2021
• Chinese Optics Letters,Vol. 20, Issue 3
• (2022)
Guilin, ChinaAugust 25-27, 2021
The image on the cover for Chinese Optics Letters Volume 19, Issue 11, summarizes the PAI techniques, imaging systems, and their biomedical applications in microrobots tracking in vitro and in vivo. From a robotic tracking perspective, some insight into the future of PAI technology in clinical applications is also provided.The image is based on original research by Dengfeng Li et al. presented in their paper "Review of photoacoustic imaging for microrobots tracking in vivo [Invited]", Chinese Optics Letters 19 (11), 111701 (2021).
• Journal
• 19th Nov，2021
The image on the cover for Photonics Research Volume 9, Issue 11, proposes a device that could be used for both display and visible light communication (VLC) applications. The semipolar blue &mu;LED array fabricated in this study shows a negligible wavelength shift, indicating a significant reduction in the quantum confined Stark effect. The image is based on original research by Tingzhu Wu et al. presented in their paper "Highly stable full-color display device with VLC application potential using semipolar &mu;LEDs and all-inorganic encapsulated perovskite nanocrystal", Photonics Research 9 (11), 11002132 (2021).
• Journal
• 19th Nov，2021