Contents 2 Issue (s), 13 Article (s)

Vol.4, Iss.3—May.1, 2022 • pp: 035001-036001 Spec. pp:

Vol.4, Iss.2—Mar.1, 2022 • pp: 020501-029901 Spec. pp:

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Vol.4, Iss.3-May..1,2022
Ultrafast and real-time physical random bit extraction with all-optical quantization
Ya Guo, Qiang Cai, Pu Li, Ruonan Zhang, Bingjie Xu, K. Alan Shore, and Yuncai Wang
Optical chaos generated by perturbing semiconductor lasers has been viewed, over recent decades, as an excellent entropy source for fast physical random bit generation (RBG) owing to its high bandwidth and large random fluctuations. However, most optical-chaos-based random bit generators perform their quantization process in the electrical domain using electrical analog-to-digital converters, so their real-time rates in a single channel are severely limited at the level of Gb/s due to the electronic bottleneck. Here, we propose and experimentally demonstrate an all-optical method for RBG where chaotic pulses are quantized into a physical random bit stream in the all-optical domain by means of a length of highly nonlinear fiber. In our proof-of-concept experiment, a 10-Gb/s random bit stream is successfully generated on-line using our method. Note that the single-channel real-time rate is limited only by the chaos bandwidth. Considering that the Kerr nonlinearity of silica fiber with an ultrafast response of few femtoseconds is exploited for composing the key part of quantizing laser chaos, this scheme thus may operate potentially at much higher real-time rates than 100 Gb/s provided that a chaotic entropy source of sufficient bandwidth is available.
Advanced Photonics
  • Publication Date: May. 02, 2022
  • Vol.4 Issue, 3 035001 (2022)
Organic room-temperature phosphorescent polymers for efficient X-ray scintillation and imagingArticle Video
Juan Wei, Yangyang Jiang, Chenyuan Liu, Jiayu Duan, Shanying Liu, Xiangmei Liu, Shujuan Liu, Yun Ma, and Qiang Zhao

Materials that exhibit visible luminescence upon X-ray irradiation show great potential in the medical and industrial fields. Pure organic materials have recently emerged as promising scintillators for X-ray detection and radiography, due to their diversified design, low cost, and facile preparation. However, recent progress in efficient radioluminescence has mainly focused on small molecules, which are inevitably associated with processability and repeatability issues. Here, a concise strategy is proposed to prepare radioluminescent polymers that exhibit multiple emission colors from blue to yellow with high brightness in an amorphous state by the radical copolymerization of negatively charged polyacrylic acid and different positively charged quaternary phosphonium salts. One of the obtained polymers exhibits excellent photostability under a high X-ray irradiation dosage of 27.35 Gy and has a detection limit of 149 nGy s - 1. This performance is superior to that of conventional anthracene-based scintillators. Furthermore, by simply drop-casting a polymer methanol solution on a quartz plate, a transparent scintillator screen was successfully fabricated for X-ray imaging with a resolution of 8.7 line pairs mm - 1. The pure organic phosphorescent polymers with a highly efficient radioluminescence were demonstrated for the first time, and the strategy reported herein offers a promising pathway to expand the application range of amorphous organic scintillators.

Advanced Photonics
  • Publication Date: May. 17, 2022
  • Vol.4 Issue, 3 035002 (2022)
Experimental verification of ill-defined topologies and energy sinks in electromagnetic continua
David E. Fernandes, Ricardo A. M. Pereira, Sylvain Lannebère, Tiago A. Morgado, and Mário G. Silveirinha
It is experimentally verified that nonreciprocal photonic systems with continuous translation symmetry may have an ill-defined topology. The topological classification of such systems is only feasible when the material response is regularized with a spatial-frequency cutoff. We experimentally demonstrate that adjoining a small air layer to the relevant material interface may effectively imitate an idealized spatial cutoff that suppresses the nonreciprocal response for short wavelengths and regularizes the topology. Furthermore, it is experimentally verified that nonreciprocal systems with an ill-defined topology may be used to abruptly halt the energy flow in a unidirectional waveguide due to the violation of the bulk-edge correspondence. In particular, we report the formation of an energy sink that absorbs the incoming electromagnetic waves with a large field enhancement at the singularity.
Advanced Photonics
  • Publication Date: May. 23, 2022
  • Vol.4 Issue, 3 035003 (2022)
Research Articles
Electro-optic tuning of a single-frequency ultranarrow linewidth microdisk laser
Jintian Lin, Saeed Farajollahi, Zhiwei Fang, Ni Yao, Renhong Gao, Jianglin Guan, Li Deng, Tao Lu, Min Wang, Haisu Zhang, Wei Fang, Lingling Qiao, and Ya Cheng
Single-frequency ultranarrow linewidth on-chip microlasers with a fast wavelength tunability play a game-changing role in a broad spectrum of applications ranging from coherent communication, light detection and ranging, to metrology and sensing. Design and fabrication of such light sources remain a challenge due to the difficulties in making a laser cavity that has an ultrahigh optical quality (Q) factor and supports only a single lasing frequency simultaneously. Here, we demonstrate a unique single-frequency ultranarrow linewidth lasing mechanism on an erbium ion-doped lithium niobate (LN) microdisk through simultaneous excitation of high-Q polygon modes at both pump and laser wavelengths. As the polygon modes are sparse within the optical gain bandwidth compared with the whispering gallery mode counterpart, while their Q factors (above 10 million) are even higher due to the significantly reduced scattering on their propagation paths, single-frequency lasing with a linewidth as narrow as 322 Hz is observed. The measured linewidth is three orders of magnitude narrower than the previous record in on-chip LN microlasers. Finally, enabled by the strong linear electro-optic effect of LN, real-time electro-optical tuning of the microlaser with a high tuning efficiency of ∼50 pm / 100 V is demonstrated.
Advanced Photonics
  • Publication Date: May. 03, 2022
  • Vol.4 Issue, 3 036001 (2022)
Vol.4, Iss.2-Mar..1,2022
Tunable metasurfaces towards versatile metalenses and metaholograms: a review
Jaekyung Kim, Junhwa Seong, Younghwan Yang, Seong-Won Moon, Trevon Badloe, and Junsuk Rho
Metasurfaces have attracted great attention due to their ability to manipulate the phase, amplitude, and polarization of light in a compact form. Tunable metasurfaces have been investigated recently through the integration with mechanically moving components and electrically tunable elements. Two interesting applications, in particular, are to vary the focal point of metalenses and to switch between holographic images. We present the recent progress on tunable metasurfaces focused on metalenses and metaholograms, including the basic working principles, advantages, and disadvantages of each working mechanism. We classify the tunable stimuli based on the light source and electrical bias, as well as others such as thermal and mechanical modulation. We conclude by summarizing the recent progress of metalenses and metaholograms, and providing our perspectives for the further development of tunable metasurfaces.
Advanced Photonics
  • Publication Date: Mar. 07, 2022
  • Vol.4 Issue, 2 024001 (2022)
Femtosecond laser-inscribed optical waveguides in dielectric crystals: a concise review and recent advances
Lingqi Li, Weijin Kong, and Feng Chen
Femtosecond laser inscription or writing has been recognized as a powerful technique to engineer various materials toward a number of applications. By efficient modification of refractive indices of dielectric crystals, optical waveguides with diverse configurations have been produced by femtosecond laser writing. The waveguiding properties depend not only on the parameters of the laser writing but also on the nature of the crystals. The mode profile tailoring and polarization engineering are realizable by selecting appropriate fabrication conditions. In addition, regardless of the complexity of crystal refractive index changes induced by ultrafast pulses, several three-dimensional geometries have been designed and implemented that are useful for the fabrication of laser-written photonic chips. Some intriguing devices, e.g., waveguide lasers, wavelength converters, and quantum memories, have been made, exhibiting potential for applications in various areas. Our work gives a concise review of the femtosecond laser-inscribed waveguides in dielectric crystals and focuses on the recent advances of this research area, including the fundamentals, fabrication, and selected photonic applications.
Advanced Photonics
  • Publication Date: Mar. 29, 2022
  • Vol.4 Issue, 2 024002 (2022)
Light-controllable time-domain digital coding metasurfacesArticle Video
Xin Ge Zhang, Ya Lun Sun, Bingcheng Zhu, Wei Xiang Jiang, Zaichen Zhang, and Tie Jun Cui

Programmable metasurfaces enable real-time control of electromagnetic waves in a digital coding manner, which are suitable for implementing time-domain metasurfaces with strong harmonic manipulation capabilities. However, the time-domain metasurfaces are usually realized by adopting the wired electrical control method, which is effective and robust, but there are still some limitations. Here, we propose a light-controllable time-domain digital coding metasurface consisting of a full-polarization dynamic metasurface and a high-speed photoelectric detection circuit, from which the microwave reflection spectra are manipulated by time-varying light signals with periodic phase modulations. As demonstrated, the light-controllable time-domain digital coding metasurface is illuminated by the light signals with two designed time-coding sequences. The measured results show that the metasurface can well generate symmetrical harmonics and white-noise-like spectra, respectively, under such cases in the reflected wave. The proposed light-controllable time-varying metasurface offers a planar interface to tailor and link microwaves with lights in the time domain, which could promote the development of photoelectric hybrid metasurfaces and related multiphysics applications.

Advanced Photonics
  • Publication Date: Apr. 18, 2022
  • Vol.4 Issue, 2 025001 (2022)
Research Articles
Revealing complex optical phenomena through vectorial metrics
Chao He, Jintao Chang, Patrick S. Salter, Yuanxing Shen, Ben Dai, Pengcheng Li, Yihan Jin, Samlan Chandran Thodika, Mengmeng Li, Aziz Tariq, Jingyu Wang, Jacopo Antonello, Yang Dong, Ji Qi, Jianyu Lin, Daniel S. Elson, Min Zhang, Honghui He, Hui Ma, and Martin J. Booth
Advances in vectorial polarization-resolved imaging are bringing new capabilities to applications ranging from fundamental physics through to clinical diagnosis. Imaging polarimetry requires determination of the Mueller matrix (MM) at every point, providing a complete description of an object’s vectorial properties. Despite forming a comprehensive representation, the MM does not usually provide easily interpretable information about the object’s internal structure. Certain simpler vectorial metrics are derived from subsets of the MM elements. These metrics permit extraction of signatures that provide direct indicators of hidden optical properties of complex systems, while featuring an intriguing asymmetry about what information can or cannot be inferred via these metrics. We harness such characteristics to reveal the spin Hall effect of light, infer microscopic structure within laser-written photonic waveguides, and conduct rapid pathological diagnosis through analysis of healthy and cancerous tissue. This provides new insight for the broader usage of such asymmetric inferred vectorial information.
Advanced Photonics
  • Publication Date: Mar. 10, 2022
  • Vol.4 Issue, 2 026001 (2022)
Research Articles
Second harmonic generation of laser beams in transverse mode locking statesArticle Video
Zilong Zhang, Yuan Gao, Xiangjia Li, Xin Wang, Suyi Zhao, Qiang Liu, and Changming Zhao

Nonlinear frequency conversion of structured beams has been of great interest recently. We present an intracavity second harmonic generation (SHG) of laser beams in transverse mode locking (TML) states with a specially designed sandwich such as a microchip laser. The intracavity nonlinear frequency conversion process of a laser beam in a TML state to its second harmonic is theoretically and experimentally investigated, considering different relative phase and weight parameters between the basic modes in the TML beam. Comparison between the far-field SHG beam patterns of fundamental frequency transverse modes in coherently locked and incoherently superposed states demonstrates that the SHG of TML beams can carry more information. Various rarely observed far-field SHG beam patterns are obtained, and they are consistent with the theoretical analysis and numerical simulations. With the obtained SHG beams, the characteristics of the structured fundamental frequency beams can also be conversely investigated or predicted. This work may have important applications in optical 3D printing, optical trapping of particles, and free-space optical communication areas.

Advanced Photonics
  • Publication Date: Mar. 14, 2022
  • Vol.4 Issue, 2 026002 (2022)
Research Articles
High-speed image reconstruction for optically sectioned, super-resolution structured illumination microscopy
Zhaojun Wang, Tianyu Zhao, Huiwen Hao, Yanan Cai, Kun Feng, Xue Yun, Yansheng Liang, Shaowei Wang, Yujie Sun, Piero R. Bianco, Kwangsung Oh, and Ming Lei
Super-resolution structured illumination microscopy (SR-SIM) is an outstanding method for visualizing the subcellular dynamics in living cells. To date, by using elaborately designed systems and algorithms, SR-SIM can achieve rapid, optically sectioned, SR observation with hundreds to thousands of time points. However, real-time observation is still out of reach for most SIM setups as conventional algorithms for image reconstruction involve a heavy computing burden. To address this limitation, an accelerated reconstruction algorithm was developed by implementing a simplified workflow for SR-SIM, termed joint space and frequency reconstruction. This algorithm results in an 80-fold improvement in reconstruction speed relative to the widely used Wiener-SIM. Critically, the increased processing speed does not come at the expense of spatial resolution or sectioning capability, as demonstrated by live imaging of microtubule dynamics and mitochondrial tubulation.
Advanced Photonics
  • Publication Date: Mar. 23, 2022
  • Vol.4 Issue, 2 026003 (2022)
Research Articles
Optical neural network quantum state tomography
Ying Zuo, Chenfeng Cao, Ningping Cao, Xuanying Lai, Bei Zeng, and Shengwang Du
Quantum state tomography (QST) is a crucial ingredient for almost all aspects of experimental quantum information processing. As an analog of the “imaging” technique in quantum settings, QST is born to be a data science problem, where machine learning techniques, noticeably neural networks, have been applied extensively. We build and demonstrate an optical neural network (ONN) for photonic polarization qubit QST. The ONN is equipped with built-in optical nonlinear activation functions based on electromagnetically induced transparency. The experimental results show that our ONN can determine the phase parameter of the qubit state accurately. As optics are highly desired for quantum interconnections, our ONN-QST may contribute to the realization of optical quantum networks and inspire the ideas combining artificial optical intelligence with quantum information studies.
Advanced Photonics
  • Publication Date: Mar. 24, 2022
  • Vol.4 Issue, 2 026004 (2022)