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2022
Volume: 10 Issue 3
28 Article(s)

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Special Issue on NEXT-GENERATION SILICON PHOTONICS
High-speed silicon microring modulator at the 2 µm waveband with analysis and observation of optical bistability
Weihong Shen, Gangqiang Zhou, Jiangbing Du, Linjie Zhou, Ke Xu, and Zuyuan He
Recently, significantly raised interests have emerged for the 2 µm waveband as an extended new window for fiber optic communication. Much research progress has been made on the photonic integrated circuits for the 2 µm waveband, especially on the CMOS-compatible silicon-on-insulator wafer. In this work, a silicon integrated microring modulator (MRM) with record high-speed performances at the 2 µm waveband was demonstrated. An L-shaped PN junction was specially designed for 2 µm to achieve a high modulation efficiency with VπL of 0.85 V·cm. The measured 3 dB bandwidth is 18 GHz, supporting up to 50 Gbps signaling at 2 µm. Additionally, optical bistability induced by the thermo-optical effect and nonlinear effects was analyzed theoretically and observed experimentally in the 2 µm MRM for the first time to our knowledge. Nonlinear coupled mode theory and the Runge–Kutta method were used to simulate the behaviors of bistability in the 2 µm MRM. The simulation and experimental results indicate that, when the MRM is launched by a high optical power, the distorted resonant spectrum under an optical bistable state deteriorates the modulation efficiency and signal performances. This work breaks the record of high-speed silicon MRM at 2 µm, drawing a promising prospect for the silicon photonic integration and high-speed interconnection at the 2 µm waveband, and it provides the referenceable analysis of optical bistability, which guides the design and experimental investigation of 2 µm MRM.
Photonics Research
  • Publication Date: Feb. 10, 2022
  • Vol. 10 Issue 3 03000A35 (2022)
Supercontinuum generation in silicon photonics platforms | Editors' Pick
Christian Lafforgue, Miguel Montesinos-Ballester, Thi-Thuy-Duong Dinh, Xavier Le Roux, Eric Cassan, Delphine Marris-Morini, Carlos Alonso-Ramos, and Laurent Vivien
Nonlinear optics has not stopped evolving, offering opportunities to develop novel functionalities in photonics. Supercontinuum generation, a nonlinear optical phenomenon responsible for extreme spectral broadening, attracts the interest of researchers due to its high potential in many applications, including sensing, imaging, or optical communications. In particular, with the emergence of silicon photonics, integrated supercontinuum sources in silicon platforms have seen tremendous progress during the past decades. This article aims at giving an overview of supercontinuum generation in three main silicon-compatible photonics platforms, namely, silicon, silicon germanium, and silicon nitride, as well as the essential theoretical elements to understand this fascinating phenomenon.
Photonics Research
  • Publication Date: Mar. 01, 2022
  • Vol. 10 Issue 3 03000A43 (2022)
Research Articles
Holography, Gratings, and Diffraction
Correlated triple hybrid amplitude and phase holographic encryption based on a metasurface | On the Cover
Hongqiang Zhou, Xin Li, Zhentao Xu, Xiaowei Li, Guangzhou Geng, Junjie Li, Yongtian Wang, and Lingling Huang
Metasurface holography is becoming a universal platform that has made a considerable impact on nanophotonics and information optics, due to its advantage of large capacity and multiple functionalities. Here, we propose a correlated triple amplitude and phase holographic encryption based on an all-dielectric metasurface. We develop an optimized holographic algorithm to obtain quantitatively correlated triple holograms, which can encrypt information in multiple wavelength and polarization channels. We apply the “static” and “dynamic” pixels in our design, respectively. Two kinds of isotropic square nanofins are selected, one functioning as a transmitter and the other functioning as a blocker counterintuitively at both working wavelengths, while another anisotropic rectangle nanofin can transmit or block light in co-polarization selectively, mimicking “dynamic” amplitude switches. Meanwhile, such “dynamic” nanofins can simultaneously function as a phase modulator in cross-polarization only at the transmission wavelength. That is, through smart design, different dielectric meta-atoms functioning as spectral filters as well as phase contributors can compositely achieve triple hybrid amplitude and phase holograms. Such strategy promises to be applied in compact large-capacity information storage, colorful holographic displays, optical encryption, multifunctional imaging devices, and so on.
Photonics Research
  • Publication Date: Feb. 22, 2022
  • Vol. 10 Issue 3 03000678 (2022)
Image Processing and Image Analysis
Antibunching and superbunching photon correlations in pseudo-natural light
Zhiyuan Ye, Hai-Bo Wang, Jun Xiong, and Kaige Wang
Since Hanbury Brown and Twiss revealed the photon bunching effect of a thermal light source in 1956, almost all studies in correlation optics have been based on light’s intensity fluctuation, regardless of fact that the polarization fluctuation is a basic attribute of natural light. In this work, we uncover the veil of the polarization fluctuation and corresponding photon correlations by proposing a new light source model, termed pseudo-natural light, embodying both intensity and polarization fluctuations. Unexpectedly, the strong antibunching and superbunching effects can be simultaneously realized in such a new source, whose second-order correlation coefficient g(2) can be continuously modulated across 1. For the symmetric Bernoulli distribution of the polarization fluctuation, particularly, g(2) can be in principle from 0 to unlimitedly large. In pseudo-natural light, while the bunching effects of both intensity and polarization fluctuations enhance the bunching to superbunching photon correlation, the antibunching correlation of the polarization fluctuation can also be extracted through the procedure of division operation in the experiment. The antibunching effect and the combination with the bunching one will arouse new applications in quantum imaging. As heuristic examples, we carry out high-quality positive or negative ghost imaging, and devise high-efficiency polarization-sensitive and edge-enhanced imaging. This work, therefore, sheds light on the development of multiple and broad correlation functions for natural light.
Photonics Research
  • Publication Date: Feb. 22, 2022
  • Vol. 10 Issue 3 03000668 (2022)
Fast and robust phase retrieval for masked coherent diffractive imaging
Li Song, and Edmund Y. Lam
Conventional phase retrieval algorithms for coherent diffractive imaging (CDI) require many iterations to deliver reasonable results, even using a known mask as a strong constraint in the imaging setup, an approach known as masked CDI. This paper proposes a fast and robust phase retrieval method for masked CDI based on the alternating direction method of multipliers (ADMM). We propose a plug-and-play ADMM to incorporate the prior knowledge of the mask, but note that commonly used denoisers are not suitable as regularizers for complex-valued latent images directly. Therefore, we develop a regularizer based on the structure tensor and Harris corner detector. Compared with conventional phase retrieval methods, our technique can achieve comparable reconstruction results with less time for the masked CDI. Moreover, validation experiments on real in situ CDI data for both intensity and phase objects show that our approach is more than 100 times faster than the baseline method to reconstruct one complex-valued image, making it possible to be used in challenging situations, such as imaging dynamic objects. Furthermore, phase retrieval results for single diffraction patterns show the robustness of the proposed ADMM.
Photonics Research
  • Publication Date: Mar. 01, 2022
  • Vol. 10 Issue 3 03000758 (2022)
Imaging Systems, Microscopy, and Displays
Axial gradient excitation accelerates volumetric imaging of two-photon microscopy
Yufeng Gao, Xianyuan Xia, Lina Liu, Ting Wu, Tingai Chen, Jia Yu, Zhili Xu, Liang Wang, Fei Yan, Zhuo Du, Jun Chu, Yang Zhan, Bo Peng, Hui Li, and Wei Zheng
Two-photon excitation fluorescence microscopy (TPM), owing to its capacity for subcellular resolution, intrinsic optical sectioning, and superior penetration depth in turbid samples, has revolutionized biomedical research. However, its layer-by-layer scanning to form a three-dimensional image inherently limits the volumetric imaging speed and increases phototoxicity significantly. In this study, we develop a gradient excitation technique to accelerate TPM volumetric imaging. The axial positions of the fluorophores can be decoded from the intensity ratio of the paired images obtained by sequentially exciting the specimen with two axially elongated two-photon beams of complementary gradient intensities. We achieved a 0.63 μm axial localization precision and demonstrate the flexibility of the gradient TPM on various sparsely labeled samples, including bead phantoms, mouse brain tissues, and live macrophages. Compared with traditional TPM, our technique improves volumetric imaging speed (by at least sixfold), decreases photobleaching (i.e., less than 2.07±2.89% in 25 min), and minimizes photodamages.
Photonics Research
  • Publication Date: Feb. 22, 2022
  • Vol. 10 Issue 3 03000687 (2022)
Integrated Optics
Compact electro-optic modulator on lithium niobate
Bingcheng Pan, Hongyuan Cao, Yishu Huang, Zong Wang, Kaixuan Chen, Huan Li, Zejie Yu, and Daoxin Dai
Fast electro-optic modulators with an ultracompact footprint and low power consumption are always highly desired for optical interconnects. Here we propose and demonstrate a high-performance lithium niobate electro-optic modulator based on a new 2×2 Fabry–Perot cavity. In this structure, the input and reflected beams are separated by introducing asymmetric multimode-waveguide gratings, enabling TE0-TE1 mode conversion. The measured results indicate that the fabricated modulator features a low excess loss of ∼0.9 dB, a high extinction ratio of ∼21 dB, a compact footprint of ∼2120 μm2, and high modulation speeds of 40 Gbps OOK and 80 Gbps PAM4 signals. The demonstrated modulator is promising for high-speed data transmission and signal processing.
Photonics Research
  • Publication Date: Feb. 22, 2022
  • Vol. 10 Issue 3 03000697 (2022)
Lasers and Laser Optics
Revealing the dynamics of intensity fluctuation transfer in a random Raman fiber laser
Jun Ye, Xiaoya Ma, Yang Zhang, Jiangming Xu, Hanwei Zhang, Tianfu Yao, Jinyong Leng, and Pu Zhou
Temporal intensity fluctuation is one of the inherent features of fiber lasers. When utilizing the fiber lasers to pump a random Raman fiber laser (RRFL), the intensity fluctuation transfer from the pump to the random lasing could affect the output performance significantly. In this paper, we comprehensively compared the spectral, temporal, and power characteristics of an RRFL pumped by two different fiber lasers—a temporally unstable fiber oscillator and a temporally stable amplified spontaneous emission (ASE) source. Owing to less impact of the intensity fluctuation transfer, the ASE source-pumped RRFL shows ∼45.3% higher maximum output power, higher spectral purity (>99.9%) and optical signal-to-noise ratio (>40 dB), weaker spectral broadening, and more stable temporal behavior compared to the fiber oscillator-pumped RRFL. Furthermore, based on the temporal-spatial-coupled Raman equations and the generalized nonlinear Schrödinger equations, we numerically revealed the impact of the pump intensity fluctuations on the output characteristics of RRFLs, and found that the temporal walk-off effect played an important role in the dynamics of intensity fluctuation transfer. This work may provide a reference for designing and implementing high-performance RRFLs and promote their practicability in sensing, telecommunications, and high-power applications.
Photonics Research
  • Publication Date: Feb. 09, 2022
  • Vol. 10 Issue 3 03000618 (2022)
Mode crossing induced soliton frequency comb generation in high-Q yttria-stabilized zirconia crystalline optical microresonators
Guoping Lin, and Tang Sun
We demonstrate for the first time, to the best of our knowledge, the fabrication of high-Q crystalline optical microresonators from cubic yttria-stabilized zirconia (YSZ). Intrinsic Q factors up to 80 million are obtained, indicating an upper bound absorption coefficient of 0.001 cm-1 for YSZ crystals at the telecom wavelength. Through laser-scanned spectroscopy on a few-mode YSZ microresonator with a radius of 300 μm, we find that the mode crossing effect in the case of weak coupling can induce a repelling disruption of free spectral range values between transverse mode families. Generation of soliton and soliton crystals in such a YSZ microcomb platform operated in the normal dispersion regime is observed. A breathing comb behavior is also reported. Our finding has enriched comb generation platforms with potential multidisciplinary capabilities linked to properties of YSZ crystals in superconducting films and sensors.
Photonics Research
  • Publication Date: Feb. 22, 2022
  • Vol. 10 Issue 3 03000731 (2022)
Nanophotonics and Photonic Crystals
Topological edge states at singular points in non-Hermitian plasmonic systems
Yin Huang, Yuecheng Shen, and Georgios Veronis
We introduce non-Hermitian plasmonic waveguide-cavity systems with topological edge states (TESs) at singular points. The compound unit cells of the structures consist of metal-dielectric-metal (MDM) stub resonators side-coupled to an MDM waveguide. We show that we can realize both a TES and an exceptional point at the same frequency when a proper amount of loss is introduced into a finite three-unit-cell structure. We also show that the finite structure can exhibit both a TES and a spectral singularity when a proper amount of gain is introduced into the structure. In addition, we show that we can simultaneously realize a unidirectional spectral singularity and a TES when proper amounts of loss and gain are introduced into the structure. We finally show that this singularity leads to extremely high sensitivity of the reflected light intensity to variations of the refractive index of the active materials in the structure. TESs at singular points could potentially contribute to the development of singularity-based plasmonic devices with enhanced performance.
Photonics Research
  • Publication Date: Feb. 22, 2022
  • Vol. 10 Issue 3 03000747 (2022)
Nonlinear Optics
Sub-50 fs pulses at 2050 nm from a picosecond Ho:YLF laser using a two-stage Kagome-fiber-based compressor
Krishna Murari, Giovanni Cirmi, Hüseyin Cankaya, Gregory J. Stein, Benoit Debord, Frederic Gérôme, Felix Ritzkosky, Fetah Benabid, Oliver Muecke, and Franz X. Kärtner
The high-energy few-cycle mid-infrared laser pulse beyond 2 μm is of immense importance for attosecond science and strong-field physics. However, the limited gain bandwidth of laser crystals such as Ho:YLF and Ho:YAG allows the generation of picosecond (ps) long pulses and, hence, makes it challenging to generate few-cycle pulse at 2 μm without utilizing an optical parametric chirped-pulse amplifier (OPCPA). Moreover, the exclusive use of the near-infrared wavelength has limited the generation of wavelengths beyond 4 μm (OPCPA). Furthermore, high harmonic generation (HHG) conversion efficiency reduces dramatically when driven by a long-wavelength laser. Novel schemes such as multi-color HHG have been proposed to enhance the harmonic flux. Therefore, it is highly desirable to generate few-cycle to femtosecond pulses from a 2 μm laser for driving these experiments. Here, we utilize two-stage nonlinear spectral broadening and pulse compression based on the Kagome-type hollow-core photonic crystal fiber (HC-PCF) to compress few-ps pulses to sub-50 fs from a Ho:YLF amplifier at 2 μm at 1 kHz repetition rate. We demonstrate both experimentally and numerically the compression of 3.3 ps at 140 μJ pulses to 48 fs at 11 μJ with focal intensity reaching 1013 W/cm2. Thereby, this system can be used for driving HHG in solids at 2 μm. In the first stage, the pulses are spectrally broadened in Kagome fiber and compressed in a silicon-based prism compressor to 285 fs at a pulse energy of 90 μJ. In the second stage, the 285 fs pulse is self-compressed in air-filled HC-PCF. With fine-tuning of the group delay dispersion (GDD) externally in a 3 mm window, a compressed pulse of 48 fs is achieved. This leads to a 70-fold compression of the ps pulses at 2050 nm. We further used the sub-50 fs laser pulses to generate white light by focusing the pulse into a thin medium of YAG.
Photonics Research
  • Publication Date: Feb. 09, 2022
  • Vol. 10 Issue 3 03000637 (2022)
Stimulated Brillouin scattering in chiral photonic crystal fiber | Editors' Pick
Xinglin Zeng, Wenbin He, Michael H. Frosz, Andreas Geilen, Paul Roth, Gordon K. L. Wong, Philip St.J. Russell, and Birgit Stiller
Stimulated Brillouin scattering (SBS) has many applications; for example, in sensing, microwave photonics, and signal processing. Here, we report the first experimental study of SBS in chiral photonic crystal fiber (PCF), which displays optical activity and robustly maintains circular polarization states against external perturbations. As a result, circularly polarized pump light is cleanly backscattered into a Stokes signal with the orthogonal circular polarization state, as is required by angular momentum conservation. By comparison, untwisted PCF generates a Stokes signal with an unpredictable polarization state, owing to its high sensitivity to external perturbations. We use chiral PCF to realize a circularly polarized continuous-wave Brillouin laser. The results pave the way for a new generation of stable circularly polarized SBS systems with applications in quantum manipulation, optical tweezers, optical gyroscopes, and fiber sensors.
Photonics Research
  • Publication Date: Feb. 22, 2022
  • Vol. 10 Issue 3 03000711 (2022)
Superior optical Kerr effects induced by two-dimensional excitons
Feng Zhou, Cacere Jelah Nieva, Dianyuan Fan, Shunbin Lu, and Wei Ji
Materials with strong optical Kerr effects (OKEs) are crucial for a broad range of applications, such as all-optical data processing and quantum information. However, the underlying OKE mechanism is not clear in 2D materials. Here, we reveal key insights of the OKE associated with 2D excitons. An admirably succinct formalism is derived for predicting the spectra and the magnitude of the nonlinear refractive index (n2) of 2D materials. The predicted n2 spectra are consistent with reported experimental data and exhibit pronounced excitonic resonances, which is distinctively different from bulk semiconductors. The n2 value is predicted to be 3×10-10 cm2/W for a 2D layered perovskite at low temperature as 7 K, which is four orders of magnitude larger than those of bulk semiconductors. The superior OKE induced by 2D excitons would give rise to a narrow refractive index-near-zero region for intense laser light. Furthermore, we demonstrate that the 2D layered perovskite should exhibit the best OKE efficiency (WFOM=1.02, TFOM=0.14) at 1550 nm, meeting the material requirements for all-optical switching. Our findings deepen the understanding of the OKE of 2D semiconducting materials and pave the way for highly efficient all-optical excitonic devices.
Photonics Research
  • Publication Date: Mar. 01, 2022
  • Vol. 10 Issue 3 03000834 (2022)
Optical and Photonic Materials
Surface ligand modified cesium lead bromide/silica sphere composites for low-threshold upconversion lasing
Qian Xiong, Sihao Huang, Zijun Zhan, Juan Du, Xiaosheng Tang, Zhiping Hu, Zhengzheng Liu, Zeyu Zhang, Weiwei Chen, and Yuxin Leng
In recent years, all-inorganic halide perovskite quantum dots (QDs) have drawn attention as promising candidates for photodetectors, light-emitting diodes, and lasing applications. However, the sensitivity and instability of perovskite to moisture and heat seriously restrict their practical application to optoelectronic devices. Recently, a facile ligand-engineering strategy to suppress aggregation by replacing traditional long ligands oleylamine (OAm) during the hot injection process has been reported. Here, we further explore its thermal stability and the evolution of photoluminescence quantum yield (PLQY) under ambient environment. The modified CsPbBr3 QDs film can maintain 33% of initial PL intensity, but only 17% is retained in the case of unmodified QDs after 10 h continuous heating. Further, the obtained QDs with higher initial PLQY (91.8%) can maintain PLQY to 39.9% after being continuously exposed in air for 100 days, while the PLQY of original QDs is reduced to 5.5%. Furthermore, after adhering CsPbBr3 QDs on the surface of a micro SiO2 sphere, we successfully achieve the highly-efficient upconversion random laser. In comparison with the unmodified CsPbBr3 QDs, the laser from the modified CsPbBr3 QDs presents a decreased threshold of 79.81 μJ/cm2 and higher quality factor (Q) of 1312. This work may not only provide a facile strategy to synthesize CsPbBr3 QDs with excellent photochemical properties but also a bright prospect for high-performance random lasers.
Photonics Research
  • Publication Date: Feb. 09, 2022
  • Vol. 10 Issue 3 03000628 (2022)
Submicrosecond electro-optical switching of one-dimensional soft photonic crystals
Lingling Ma, Chaoyi Li, Luyao Sun, Zhenpeng Song, Yanqing Lu, and Bingxiang Li
Photonics Research
  • Publication Date: Mar. 01, 2022
  • Vol. 10 Issue 3 03000786 (2022)
Optical Devices
Monitoring and identifying pendant droplets in microbottle resonators
Zijie Wang, Xiaobei Zhang, Qi Zhang, Yiqi Chen, Yong Yang, Yang Yu, Yang Wang, Yanhua Dong, Yi Huang, and Tingyun Wang
Optofluidic resonators are capable of characterizing various fluidic media. Here, we propose an optofluidic microbottle resonator (OFMBR) that is applied to generate pendant droplets, whose maximum mass is related to the liquid surface tension. Mass and type of droplets forming along the OFMBR stem can be monitored in real time by spectrum variation. As a pendant droplet grows, increased droplet gravity introduces a decreased coupling gap and compressive force between the tapered fiber and OFMBR, leading to a resonance wavelength shift. The operation mechanism of the proposed sensors is validated by theoretical simulation and experimental results. From the experimental spectra, a liquid mass sensor with maximum sensitivity of -3.34 pm/mg is obtained, and distilled water and alcohol can be identified. This scheme provides a new thread for droplet generation as well as fluidic properties characterization.
Photonics Research
  • Publication Date: Feb. 22, 2022
  • Vol. 10 Issue 3 03000662 (2022)
Single-sideband microwave-to-optical conversion in high-Q ferrimagnetic microspheres | Editors' Pick
Cheng-Zhe Chai, Zhen Shen, Yan-Lei Zhang, Hao-Qi Zhao, Guang-Can Guo, Chang-Ling Zou, and Chun-Hua Dong
Coherent conversion of microwave and optical photons can significantly expand the capabilities of information processing and communications systems. Here, we experimentally demonstrate the microwave-to-optical frequency conversion in a magneto-optical whispering gallery mode microcavity. By applying a magnetic field parallel to the microsphere equator, the intracavity optical field will be modulated when the magnon is excited by the microwave drive, leading to a microwave-to-optical conversion via the magnetic Stokes and anti-Stokes scattering processes. The observed single-sideband conversion phenomenon indicates a nontrivial optical photon–magnon interaction mechanism derived from the magnon that induced both the frequency shift and modulated coupling rate of optical modes. In addition, we demonstrate the single-sideband frequency conversion with an ultrawide tuning range up to 2.5 GHz, showing its great potential in microwave-to-optical conversion.
Photonics Research
  • Publication Date: Mar. 01, 2022
  • Vol. 10 Issue 3 03000820 (2022)
Fast extended depth of focus meta-optics for varifocal functionality
James E. M. Whitehead, Alan Zhan, Shane Colburn, Luocheng Huang, and Arka Majumdar
Extended depth of focus (EDOF) optics can enable lower complexity optical imaging systems when compared to active focusing solutions. With existing EDOF optics, however, it is difficult to achieve high resolution and high collection efficiency simultaneously. The subwavelength spacing of scatterers in a meta-optic enables the engineering of very steep phase gradients; thus, meta-optics can achieve both a large physical aperture and a high numerical aperture. Here, we demonstrate a fast (f/1.75) EDOF meta-optic operating at visible wavelengths, with an aperture of 2 mm and focal range from 3.5 mm to 14.5 mm (286 diopters to 69 diopters), which is a 250× elongation of the depth of focus relative to a standard lens. Depth-independent performance is shown by imaging at a range of finite conjugates, with a minimum spatial resolution of ∼9.84 μm (50.8 cycles/mm). We also demonstrate operation of a directly integrated EDOF meta-optic camera module to evaluate imaging at multiple object distances, a functionality which would otherwise require a varifocal lens.
Photonics Research
  • Publication Date: Mar. 01, 2022
  • Vol. 10 Issue 3 03000828 (2022)
Optoelectronics
Broadly tunable lens-coupled nonlinear quantum cascade lasers in the sub-THz to THz frequency range
Kazuue Fujita, Shohei Hayashi, Akio Ito, Tatsuo Dougakiuchi, Masahiro Hitaka, and Atsushi Nakanishi
Room-temperature terahertz (THz) quantum cascade laser sources with intracavity difference-frequency nonlinear mixing are electrically pumped monolithic semiconductor laser sources operating in the 0.6–6 THz spectral range. We report widely tunable, low-frequency THz quantum cascade laser sources using a lens-coupled Cherenkov waveguide scheme. Based on a watt-class high-power, λ∼13.7 μm quantum cascade laser, the monolithic THz source is strongly coupled with a high-resistivity silicon lens, which causes a major increase in the THz coupling efficiency and demonstrates significant performance improvements. A room-temperature 1.5 THz device produces a 0.2 mW peak output power with a high-quality beam pattern. Improved THz outcoupling efficiency using the lens-coupled scheme enabled the demonstration of a high-performance external-cavity semiconductor THz source that is tunable from 420 GHz to 2 THz. The external-cavity, lens-coupled device configuration can technically be assembled into a butterfly-style package for a thumb-sized, widely frequency tunable THz semiconductor source.
Photonics Research
  • Publication Date: Feb. 22, 2022
  • Vol. 10 Issue 3 03000703 (2022)
Significant sensing performance of an all-silicon terahertz metasurface chip for Bacillus thuringiensis Cry1Ac protein
Zijian Cui, Yue Wang, Yongqiang Shi, Yongqiang Zhu, Dachi Zhang, Zhiqi Hong, and Xuping Feng
The promising prospect of a terahertz metasurface in sensing and detection applications has attracted increasing attention because of its ability to overcome the classical diffraction limit and the enhancement of field intensity. In this work, a novel scheme based on an all-silicon terahertz plasmon metasurface is proposed and experimentally demonstrated to be a highly sensitive biosensor for the Bacillus thuringiensis Cry1Ac toxin. The regression coefficients between Bacillus thuringiensis protein concentrations and the spectral resonance intensity and frequency were 0.8988 and 0.9238, respectively. The resonance amplitude variation and frequency shift of the metasurface were investigated in terms of both thickness and permittivity change of the analyte, which reflected the protein residue in the actual process. Moreover, the reliability and stability of the metasurface chip were verified by time period, temperature, and humidity control. These results promise the ability of the proposed metasurface chip as a Bacillus thuringiensis protein sensor with high sensitivity and stability. In addition, this novel device strategy provides opportunities for the advancement of terahertz functional applications in the fields of biochemical sensing and detection.
Photonics Research
  • Publication Date: Feb. 22, 2022
  • Vol. 10 Issue 3 03000740 (2022)
Physical Optics
Terahertz bound states in the continuum with incident angle robustness induced by a dual period metagrating
Wenqiao Shi, Jianqiang Gu, Xingyuan Zhang, Quan Xu, Jiaguang Han, Quanlong Yang, Longqing Cong, and Weili Zhang
Metasurface-empowered bound state in the continuum (BIC) provides a unique route for fascinating functional devices with infinitely high quality factors. This method is particularly attractive to the terahertz community because it may essentially solve the deficiencies in terahertz filters, sensors, lasers, and nonlinear sources. However, most BIC metasurfaces are limited to specified incident angles that seriously dim their application prospects. Here, we propose that a dual-period dielectric metagrating can support multiple families of BICs that originate from guided mode resonances in the dielectric grating and exhibit infinite quality factors at arbitrarily tilted incidence. This robustness was analyzed based on the Bloch theory and verified at tilted incident angles. We also demonstrate that inducing geometric asymmetry is an efficient way to manipulate the leakage and coupling of these BICs, which can mimic the electromagnetically induced transparency (EIT) effect in our dual-period metagrating. In this demonstration, a slow-light effect with a measured group delay of 117 ps was achieved. The incidence-insensitive BICs proposed here may greatly extend the application scenarios of the BIC effect. The high Q factor and outstanding slow-light effect in the metagrating show exciting prospects in realizing high-performance filters, sensors, and modulators for prompting terahertz applications.
Photonics Research
  • Publication Date: Mar. 01, 2022
  • Vol. 10 Issue 3 03000810 (2022)
Quantum Optics
Mutually testing source-device-independent quantum random number generator
Jialin Cheng, Jiliang Qin, Shaocong Liang, Jiatong Li, Zhihui Yan, Xiaojun Jia, and Kunchi Peng
Quantum random numbers have an incomparable advantage over pseudo-random numbers since randomness originates from intrinsic property of quantum mechanics. The generation rate and the security of quantum random numbers are two significant indicators of a quantum random number generator (QRNG) for practical applications. Here we propose a mutually testing source-device-independent QRNG by simultaneously measuring a pair of conjugate quadratures from two separate parts of an untrusted continuous-variable quantum state. The amounts of randomness of the quadratures can be mutually estimated by each other via entropic uncertainty principle. Instead of randomly toggling between the conjugate quadratures of one state for collecting different types of data, two quadratures can generate check data and raw bits simultaneously and continuously in this mutually testing manner, which enhances the equivalent generation rate of private random bits to around 6 Gbit/s with a 7.5 mW laser beam. Moreover, the overall security is also improved by adjusting the conditional min-entropy in real time according to the continually monitored fluctuations of the local oscillator and the randomly measured electronic noise of homodyne detectors.
Photonics Research
  • Publication Date: Feb. 17, 2022
  • Vol. 10 Issue 3 03000646 (2022)
Deterministic distribution of orbital angular momentum multiplexed continuous-variable entanglement and quantum steering
Li Zeng, Rong Ma, Hong Wen, Meihong Wang, Jun Liu, Zhongzhong Qin, and Xiaolong Su
Orbital angular momentum (OAM) multiplexing provides an efficient method to improve data-carrying capacity in various quantum communication protocols. It is a precondition to distribute OAM multiplexed quantum resources in quantum channels for implementing quantum communication. However, quantum steering of OAM multiplexed optical fields and the effect of channel noise on OAM multiplexed quantum resources remain unclear. Here, we generate OAM multiplexed continuous-variable (CV) entangled states and distribute them in lossy or noisy channels. We show that the decoherence property of entanglement and quantum steering of the OAM multiplexed states carrying topological charges l=1 and l=2 are the same as that of the Gaussian mode with l=0 in lossy and noisy channels. The sudden death of entanglement and quantum steering of high-order OAM multiplexed states is observed in the presence of excess noise. Our results demonstrate the feasibility to realize high data-carrying capacity quantum information processing by utilizing OAM multiplexed CV entangled states.
Photonics Research
  • Publication Date: Mar. 01, 2022
  • Vol. 10 Issue 3 03000777 (2022)
Silicon Photonics
Toward calibration-free Mach–Zehnder switches for next-generation silicon photonics
Lijia Song, Tangnan Chen, Weixi Liu, Hongxuan Liu, Yingying Peng, Zejie Yu, Huan Li, Yaocheng Shi, and Daoxin Dai
Silicon photonic Mach–Zehnder switches (MZSs) have been extensively investigated as a promising candidate for optical systems. However, conventional 2×2 MZSs are usually prone to the size variations of the arm waveguides due to imperfect fabrication, resulting in considerable random phase imbalance between the two arms, thereby imposing significant challenges for further developing next-generation N×N MZSs. Here we propose a novel design toward calibration-free 2×2 and N×N MZSs, employing optimally widened arm waveguides, enabled by novel compact tapered Euler S-bends with incorporated mode filters. With standard 180 nm CMOS foundry processes, more than thirty 2×2 MZSs and one 4×4 Benes MZS with the new design are fabricated and characterized. Compared with their conventional counterparts with 0.45-μm-wide arm waveguides, the present 2×2 MZSs exhibit significant reduction in the random phase imbalance. The measured extinction ratios of the present 2×2 and 4×4 MZSs operating in the all-cross state are 27-49 dB and ∼20 dB across the wavelength range of ∼60 nm, respectively, even without any calibrations. This work paves the way toward calibration-free large-scale N×N MZSs for next-generation silicon photonics.
Photonics Research
  • Publication Date: Mar. 01, 2022
  • Vol. 10 Issue 3 03000793 (2022)
Spectroscopy
Ultrafast photocarrier and coherent phonon dynamics in type-II Dirac semimetal PtTe2 thin films probed by optical spectroscopy
Peng Suo, Shengnan Yan, Ruihua Pu, Wenjie Zhang, Di Li, Jiaming Chen, Jibo Fu, Xian Lin, Feng Miao, Shi-Jun Liang, Weimin Liu, and Guohong Ma
We report the ultrafast photocarrier dynamics and coherent phonon excitation in type-II Dirac semimetal platinum ditelluride (PtTe2) thin films via femtosecond (fs) pump-probe spectroscopy at room temperature. Quantitative analysis revealed that the incoherent electronic relaxation consists of two components: a subpicosecond fast relaxation process and a slow component with a time constant of hundreds of picoseconds (ps). Furthermore, the launch of a coherent acoustic phonon (CAP) in the 20 nm film but absence in the 6.8 nm film uncovers the dominant role of temperature gradient in producing a strain wave. The sound velocity and Young’s modulus in the thick PtTe2 are determined to be 1.736 km/s and 29.5 GPa, respectively. In addition, the coherent optical phonon (COP) with a frequency of 4.7 THz corresponding to Te atoms out-of-plane A1g vibration has been well resolved in all films, which is ascribed to displacive excitation of coherent phonon (DECP). The observation of a strong probe-wavelength dependent COP amplitude reveals the resonant feature of the optical excitation-induced atomic displacement in PtTe2. Our findings provide deep insight into the excitation and dynamics of CAP and COP as well as the photocarriers’ recovery pathway and lifetimes in PtTe2. Our study also demonstrates that the COP spectroscopy is a powerful tool to reveal the modulation of frequency-dependent optical constants induced by atomic vibrations, which may find applications in the fields of optoelectronics and ultrafast photonics.
Photonics Research
  • Publication Date: Feb. 17, 2022
  • Vol. 10 Issue 3 03000653 (2022)
Surface Optics and Plasmonics
Influence of non-Hermitian mode topology on refractive index sensing with plasmonic waveguides
Alessandro Tuniz, Markus A. Schmidt, and Boris T. Kuhlmey
We evaluate the sensing properties of plasmonic waveguide sensors by calculating their resonant transmission spectra in different regions of the non-Hermitian eigenmode space. We elucidate the pitfalls of using modal dispersion calculations in isolation to predict plasmonic sensor performance, which we address by using a simple model accounting for eigenmode excitation and propagation. Our transmission calculations show that resonant wavelength and spectral width crucially depend on the length of the sensing region, so that no single criterion obtained from modal dispersion calculations alone can be used as a proxy for sensitivity. Furthermore, we find that the optimal detection limits occur where directional coupling is supported, where the narrowest spectra occur. Such narrow spectral features can only be measured by filtering out all higher-order modes at the output, e.g., via a single-mode waveguide. Our calculations also confirm a characteristic square root dependence of the eigenmode splitting with respect to the permittivity perturbation at the exceptional point, which we show can be identified through the sensor beat length at resonance. This work provides a convenient framework for designing and characterizing plasmonic waveguide sensors when comparing them with experimental measurements.
Photonics Research
  • Publication Date: Feb. 22, 2022
  • Vol. 10 Issue 3 03000719 (2022)
Intelligent reconfigurable metasurface for self-adaptively electromagnetic functionality switching
Ying She, Chen Ji, Cheng Huang, Zuojun Zhang, Jianming Liao, Jiangyu Wang, and Xiangang Luo
Reconfigurable metasurfaces have attracted a deal of attention owing to their multifunctional and dynamic electromagnetic (EM) manipulation properties. However, most of the previous reconfigurable metasurfaces rely on manual control for function switching, which has huge limitations in practical application. Here, an intelligent metasurface with the self-adaptively EM manipulation capability is proposed. It integrates the sensing-and-feedback components to construct a closed-loop system, which can automatically adjust EM functionalities for the different incident power information. The sensing module in this metasurface can first perceive the incident EM power intensity and then provide the feedback signal to the field programmable gate array controlling platform that can send the corresponding instruction to the executing material for switching the EM functionality among transmission, reflection, and tunable absorption. Good self-adaptive reaction capability and practicability of the proposed metasurface have been demonstrated by the experiment. It has the capability of making a real-time response with adaptive EM behavior to the varying incoming wave power without the aid of human beings. Our design provides an avenue toward intelligent and cognitive metasurfaces, which has extensive application prospects in smart skin, intelligent absorber, and the related EM fields.
Photonics Research
  • Publication Date: Mar. 01, 2022
  • Vol. 10 Issue 3 03000769 (2022)
Ultrafast Optics
Powerful supercontinuum vortices generated by femtosecond vortex beams with thin plates
Litong Xu, Dongwei Li, Junwei Chang, Deming Li, Tingting Xi, and Zuoqiang Hao
We demonstrate numerically and experimentally the generation of powerful supercontinuum vortices from femtosecond vortex beams by using multiple thin fused silica plates. The supercontinuum vortices are shown to preserve the vortex phase profile of the initial beam for spectral components ranging from 500 nm to 1200 nm. The transfer of the vortex phase profile results from the inhibition of multiple filamentation and the preservation of the vortex ring with relatively uniform intensity distribution by means of the thin-plate scheme, where the supercontinuum is mainly generated from the self-phase modulation and self-steepening effects. Our scheme works for vortex beams with different topological charges, which provides a simple and effective method to generate supercontinuum vortices with high power.
Photonics Research
  • Publication Date: Mar. 01, 2022
  • Vol. 10 Issue 3 03000802 (2022)

About the Cover

Schematic illustration of a hybrid quantitative correlation amplitude and phase holographic display based on an all-dielectric metasurface. Based on the wavelength and polarization selectivity of nanoantennas, the correlated holograms are encrypted by the combination of discrete wavelengths and same/opposite handedness circular polarization channels.