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2022
Volume: 10 Issue 2
44 Article(s)

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Special Issue on NEXT-GENERATION SILICON PHOTONICS
Wafer-level hermetically sealed silicon photonic MEMS
Gaehun Jo, Pierre Edinger, Simon J. Bleiker, Xiaojing Wang, Alain Yuji Takabayashi, Hamed Sattari, Niels Quack, Moises Jezzini, Jun Su Lee, Peter Verheyen, Iman Zand, Umar Khan, Wim Bogaerts, Göran Stemme, Kristinn B. Gylfason, and Frank Niklaus
The emerging fields of silicon (Si) photonic micro–electromechanical systems (MEMS) and optomechanics enable a wide range of novel high-performance photonic devices with ultra-low power consumption, such as integrated optical MEMS phase shifters, tunable couplers, switches, and optomechanical resonators. In contrast to conventional SiO2-clad Si photonics, photonic MEMS and optomechanics have suspended and movable parts that need to be protected from environmental influence and contamination during operation. Wafer-level hermetic sealing can be a cost-efficient solution, but Si photonic MEMS that are hermetically sealed inside cavities with optical and electrical feedthroughs have not been demonstrated to date, to our knowledge. Here, we demonstrate wafer-level vacuum sealing of Si photonic MEMS inside cavities with ultra-thin caps featuring optical and electrical feedthroughs that connect the photonic MEMS on the inside to optical grating couplers and electrical bond pads on the outside. We used Si photonic MEMS devices built on foundry wafers from the iSiPP50G Si photonics platform of IMEC, Belgium. Vacuum confinement inside the sealed cavities was confirmed by an observed increase of the cutoff frequency of the electro-mechanical response of the encapsulated photonic MEMS phase shifters, due to reduction of air damping. The sealing caps are extremely thin, have a small footprint, and are compatible with subsequent flip-chip bonding onto interposers or printed circuit boards. Thus, our approach for sealing of integrated Si photonic MEMS clears a significant hurdle for their application in high-performance Si photonic circuits.
Photonics Research
  • Publication Date: Jan. 14, 2022
  • Vol. 10 Issue 2 A14 (2022)
Ultra-power-efficient heterogeneous III–V/Si MOSCAP (de-)interleavers for DWDM optical links
Stanley Cheung, Geza Kurczveil, Yingtao Hu, Mingye Fu, Yuan Yuan, Di Liang, and Raymond G. Beausoleil
We discuss the design and demonstration of various III–V/Si asymmetric Mach–Zehnder interferometer (AMZI) and ring-assisted AMZI (de-)interleavers operating at O-band wavelengths with 65 GHz channel spacing. The wafer-bonded III–V/Si metal-oxide-semiconductor capacitor (MOSCAP) structure facilitates ultra-low-power phase tuning on a heterogeneous platform that allows for complete monolithic transceiver photonic integration. The second- and third-order MOSCAP AMZI (de-)interleavers exhibit cross-talk (XT) levels down to -22 dB and -32 dB with tuning powers of 83.0 nW and 53.0 nW, respectively. The one-, two-, and three-ring-assisted MOSCAP AMZI (de-)interleavers have XT levels down to -27 dB, -22 dB, and -20 dB for tuning powers of 10.0 nW, 7220.0 nW, and 33.6 nW, respectively. The leakage current density is measured to be in the range of 1.6–27 μA/cm2. To the best of our knowledge, we have demonstrated for the first time, athermal III–V/Si MOSCAP (de-)interleavers with the lowest XT and reconfiguration power consumption on a silicon platform.
Photonics Research
  • Publication Date: Jan. 24, 2022
  • Vol. 10 Issue 2 A22 (2022)
Research Articles
Correction
Fiber Optics and Optical Communications
Intelligent all-fiber device: storage and logic computing
Zhihai Liu, Siying Cheng, Yu Zhang, Wei Jin, Xiang Li, Yaru Li, Yaxun Zhang, Xinghua Yang, Jianzhong Zhang, and Libo Yuan
The typical functions of the optical fiber are communication and sensing. However, the fiber functions need to extend to meet the requirements of the development of artificial intelligence. This paper achieves an all-fiber device with storage and logic computing functions using a single-mode fiber and Ge2Sb2Te5 (GST) material. We use the pulse amplitude modulation (the switching energy is about 50 nJ) to switch the GST state for performing the eight-level data storage (3-bit). The all-fiber memory device has the advantages of high optical contrast (about 38%), good reversibility, and high repeatability. We implement the all-optical logic operations (“AND” and “OR”) by using two memory cells in series and parallel. For the first time, we use the single-mode optical fiber to realize storage and computing functions, and this intelligent fiber has tremendous application potential in intelligent optical fiber communication and portends a new paradigm for brain-like computing.
Photonics Research
  • Publication Date: Jan. 14, 2022
  • Vol. 10 Issue 2 357 (2022)
Holography, Gratings, and Diffraction
Dynamic full-field refractive index distribution measurements using total internal reflection terahertz digital holography
Dayong Wang, Duoxuan Ma, Kunlun Li, Yaya Zhang, Jie Zhao, Yunxin Wang, and Lu Rong
Massive usage scenarios prompt the prosperity of terahertz refractive index (THz RI) measurement methods. However, they are very difficult in measuring the full-field dynamical RI distributions of either solid samples without a priori thickness or liquid samples. In this study, we propose total internal reflection THz digital holography and apply it for measuring RI distributions for both solid and liquid samples dynamically. An RI measurement model is established based on an attenuated total reflection prism with a pitching angle. The pitching angle and the field of view can be numerically calculated from the spectrogram of the off-axis Fresnel hologram, which solves the adjustment of the visually opaque prism irradiated by the invisible THz beam. Full-field RI distributions of the droplets of solid-state soy wax and distilled water are obtained and compared with THz time-domain spectroscopy. The evaporation of an ethanol solution droplet is recorded, and the variation of the RI distribution at the sample–prism interface is quantitatively visualized with a temporal resolution of 10 Hz. The proposed method greatly expands the sample range for THz RI measurements and provides unprecedented insight into investigating spontaneous and dynamic THz phenomena.
Photonics Research
  • Publication Date: Jan. 07, 2022
  • Vol. 10 Issue 2 289 (2022)
Lensless Fourier-transform terahertz digital holography for real-time full-field phase imaging
Yaya Zhang, Jie Zhao, Dayong Wang, Yunxin Wang, and Lu Rong
With the development of continuous-wave terahertz (THz) sources and array detectors, the pursuit of high-fidelity real-time imaging is receiving significant attention within the THz community. Here, we report a real-time full-field THz phase imaging approach based on lensless Fourier-transform THz digital holography. A triangular interferometric layout is proposed based on an oblique illumination of 2.52 THz radiation, which is different from other lensless holographic configurations at other frequencies. A spherical reference beam is generated by a reflective parabolic mirror with minor propagation loss. The complex-valued images are reconstructed using a single inverse Fourier transform of the hologram without complex calculation of the diffraction propagation. The experimental result for a Siemens star validates the lateral resolution of ∼346 μm in the diagonal direction. Sub-pixel image registration and image stitching algorithms are applied to enlarge the area of the reconstructed images. The dehydration process of an aquatic plant leaf (Hottonia inflata) is monitored for the first time, to the best of our knowledge, at the THz band. Rapid variations in water content and morphology are measured with a time interval of 0.6 s and a total time of 5 min from a series of reconstructed amplitude and phase images, respectively. The proposed method has the potential to become a powerful tool to investigate spontaneous phenomena at the THz band.
Photonics Research
  • Publication Date: Jan. 11, 2022
  • Vol. 10 Issue 2 323 (2022)
Instrumentation and Measurements
High-throughput microfabrication of axially tunable helices | Editors' Pick
He Cheng, Pooria Golvari, Chun Xia, Mingman Sun, Meng Zhang, Stephen M. Kuebler, and Xiaoming Yu
Helical structures exhibit novel optical and mechanical properties and are commonly used in different fields such as metamaterials and microfluidics. A few methods exist for fabricating helical microstructures, but none of them has the throughput or flexibility required for patterning a large surface area with tunable pitch. In this paper, we report a method for fabricating helical structures with adjustable forms over large areas based on multiphoton polymerization (MPP) using single-exposure, three dimensionally structured, self-accelerating, axially tunable light fields. The light fields are generated as a superposition of high-order Bessel modes and have a closed-form expression relating the design of the phase mask to the rotation rate of the beam. The method is used to fabricate helices with different pitches and handedness in the material SU-8. Compared to point-by-point scanning, the method reported here can be used to reduce fabrication time by two orders of magnitude, paving the way for adopting MPP in many industrial applications.
Photonics Research
  • Publication Date: Jan. 07, 2022
  • Vol. 10 Issue 2 303 (2022)
Time shifting deviation method enhanced laser interferometry: ultrahigh precision localizing of traffic vibration using an urban fiber link
Guan Wang, Zhongwang Pang, Bohan Zhang, Fangmin Wang, Yufeng Chen, Hongfei Dai, Bo Wang, and Lijun Wang
Using a fiber network as a huge sensing system will enrich monitoring methods of public infrastructures and geological disasters. With the traditional cross-correlation method, a laser interferometer has been used to detect and localize the vibration event. However, the random error induced by the cross-correlation method limits the localization accuracy and makes it not suitable for ultrahigh precision localizing applications. We propose a novel time shifting deviation (TSDEV) method, which has advantages over the cross-correlation method in practicability and localization accuracy. Three experiments are carried out to demonstrate the novelty of the TSDEV method. In a lab test, vibration localization accuracy of ∼2.5 m is realized. In field tests, TSDEV method enhanced interferometry is applied to monitor the urban fiber link. Traffic vibration events on the campus road and Beijing ring road have been precisely localized and analyzed, respectively. The proposed technique will extend the function of the existing urban fiber network, and better serve the future smart city.
Photonics Research
  • Publication Date: Jan. 24, 2022
  • Vol. 10 Issue 2 433 (2022)
Single-shot three-input phase retrieval for quantitative back focal plane measurement
Mengqi Shen, Qi Zou, Xiaoping Jiang, Fu Feng, and Michael G. Somekh
This paper presents quantitative measurements facilitated with a new optical system that implements a single-shot three-input phase retrieval algorithm. The new system allows simultaneous acquisition of three distinct input patterns, thus eliminating the requirement for mechanical movement and reducing any registration errors and microphonics. We demonstrate the application of the system for measurement and separation of two distinct attenuation measurements of surface waves, namely, absorption and coupling loss. This is achieved by retrieving the phase in the back focal plane and performing a series of virtual optics computations. This overcomes the need to use a complicated series of hardware manipulations with a spatial light modulator. This gives a far more accurate and faster measurement with a simpler optical system. We also demonstrate that phase measurements allow us to implement different measurement methods to acquire the excitation angle for surface plasmons. Depending on the noise statistics different methods have superior performance, so the best method under particular conditions can be selected. Since the measurements are only weakly correlated, they may also be combined for improved noise performance. The results presented here offer a template for a wider class of measurements in the back focal plane including ellipsometry.
Photonics Research
  • Publication Date: Feb. 01, 2022
  • Vol. 10 Issue 2 491 (2022)
Navigation-grade resonant fiber-optic gyroscope using ultra-simple white-light multibeam interferometry
Shuangxiang Zhao, Qingwen Liu, Yuanyuan Liu, Huilian Ma, and Zuyuan He
The miniaturization of the gyroscope is critical for spacecrafts, drones, wellbore surveys, etc. The resonant fiber-optic gyroscope (RFOG) is a competitive candidate due to its potential in both miniaturization and high resolution, while its actual performance is well below expectation because of laser-induced noise and complexity. Here we report the first navigation grade RFOG with a bias instability of 0.009°/h and an angle random walk of 0.0093°/h. The results are realized using a fiber resonator with finesse of 63 containing 100-m long fiber. Compared with the traditional RFOGs using narrow-linewidth lasers, the key feature of the proposed RFOG is that it is driven with a broadband light source. A white-light multibeam interference method is proposed to detect the Sagnac effect, representing the simplest scheme of RFOG to date. The complexity caused by multiple feedback loops and coherent noise suppression in traditional RFOG scheme is avoided. The minimal scheme and simple modulation algorithm will also promote the on-chip waveguide gyroscope.
Photonics Research
  • Publication Date: Feb. 01, 2022
  • Vol. 10 Issue 2 542 (2022)
Influence of light pattern thickness on the manipulation of dielectric microparticles by optoelectronic tweezers
Shuailong Zhang, Mohamed Elsayed, Ran Peng, Yujie Chen, Yanfeng Zhang, Steven L. Neale, and Aaron R. Wheeler
Optoelectronic tweezer (OET) is a useful optical micromanipulation technology that has been demonstrated for various applications in electrical engineering and most notably cell selection for biomedical engineering. In this work, we studied the use of light patterns with different shapes and thicknesses to manipulate dielectric microparticles with OET. It was demonstrated that the maximum velocities of the microparticles increase to a peak and then gradually decrease as the light pattern’s thickness increases. Numerical simulations were run to clarify the underlying physical mechanisms, and it was found that the observed phenomenon is due to the co-influence of horizontal and vertical dielectrophoresis forces related to the light pattern’s thickness. Further experiments were run on light patterns with different shapes and objects with different sizes and structures. The experimental results indicate that the physical mechanism elucidated in this research is an important one that applies to different light pattern shapes and different objects, which is useful for enabling users to optimize OET settings for future micromanipulation applications.
Photonics Research
  • Publication Date: Feb. 01, 2022
  • Vol. 10 Issue 2 550 (2022)
Integrated Optics
Silicon-integrated nonlinear III-V photonics | On the Cover
Weiqiang Xie, Chao Xiang, Lin Chang, Warren Jin, Jonathan Peters, and John E. Bowers
Mainstream silicon photonic integrated circuits are based on compact and low-loss silicon-on-insulator (SOI) waveguide platforms. However, monolithic SOI-based photonics provides only a limited number of functional device types. Here, to extend the on-chip capabilities, we propose a general heterogeneous integration approach to embed highly nonlinear III-V (AlGaAs) photonics into the SOI platform. We develop low-loss AlGaAs-on-SOI photonic circuits with integrated Si waveguides and showcase sub-milliwatt-threshold (∼0.25 mW) Kerr frequency comb generation in ultrahigh-Q AlGaAs microrings (Q over 106) at the telecom bands. Our demonstration complements existing mature Si photonics technology with efficient nonlinear functionalities provided by III-V and propels conventional Si photonics into emerging nonlinear photonic applications towards fully chip-based nonlinear engines.
Photonics Research
  • Publication Date: Feb. 01, 2022
  • Vol. 10 Issue 2 535 (2022)
High-sensitivity integrated SiN rib-waveguide long period grating refractometer
Clement Deleau, Han Cheng Seat, Olivier Bernal, and Frederic Surre
In this research, we demonstrate a high-sensitivity integrated silicon nitride long period grating (LPG) refractometer based on a rib waveguide with sinusoidally modulated width. While integrated LPG architectures typically achieve ultrahigh sensitivity only over a narrow optical bandwidth using a phase-matching turning-point optimization technique, our sensor exhibits a very high refractometric sensitivity that was designed to remain constant over a broad operational optical spectral bandwidth. The proposed design method relies on multi-modal dispersion tailoring that consists of homogenizing the spectral behaviors of both group and effective indices of the coupling modes. Experimental results are in agreement with numerical simulations, demonstrating not only a sensitivity reaching 11,500 nm/RIU but, more significantly, also that this sensitivity remains almost constant over a broad spectral range of at least 100 nm around 1550 nm. Additional advantages of the proposed sensor architecture encompass a low temperature sensitivity, down to -0.15 nm/K, and simplicity of the fabrication process. These results demonstrate the feasibility of chip-scale photonic integration to achieve both high sensitivity and large dynamic range of the proposed refractometer.
Photonics Research
  • Publication Date: Feb. 01, 2022
  • Vol. 10 Issue 2 564 (2022)
Lasers and Laser Optics
Near-optimal intense and powerful terahertz source by optical rectification in lithium niobate crystal
L. Guiramand, J. E. Nkeck, X. Ropagnol, T. Ozaki, and F. Blanchard
Photonics Research
  • Publication Date: Jan. 11, 2022
  • Vol. 10 Issue 2 340 (2022)
Principle and numerical demonstration of high power all-fiber coherent beam combination based on self-imaging effect in a square core fiber
Yuefang Yan, Yu Liu, Haoyu Zhang, Yue Li, Yuwei Li, Xi Feng, Donglin Yan, Jianjun Wang, Honghuan Lin, Feng Jing, Wenhui Huang, and Rumao Tao
The self-imaging effect in a square core fiber has been investigated, and an integrated all-fiber combiner has been proposed based on a large mode area double clad fiber, which can be employed to construct high power coherent beam combining sources in the all-fiber format. The influence of various parameters on beam quality (M2) and efficiency of the all-fiber coherent beam combiner has been studied numerically, which reveals that the near diffraction-limited laser beam can be achieved. A principle demonstration of the self-imaging effect has been carried out experimentally in a square core fiber, which proves the feasibility of beam combining with the square fiber, and that it is a promising way to develop high power coherent beam combination sources.
Photonics Research
  • Publication Date: Jan. 24, 2022
  • Vol. 10 Issue 2 444 (2022)
Sub-terahertz-repetition-rate frequency comb generated by filter-induced instabilities in passive driven fiber resonators
Pan Wang, Jiangyong He, Xiaosheng Xiao, Zhi Wang, and Yange Liu
Ultrahigh-repetition-rate frequency comb generation exhibits great potential in applications of optical waveform synthesis, direct comb spectroscopy, and high capacity telecommunications. Here we present the theoretical investigations of a filter-induced instability mechanism in passive driven fiber resonators with a wide range of cavity dispersion regimes. In this novel concept of modulation instability, coherent frequency combs are demonstrated numerically with rates up to sub-terahertz level. Floquet stability analysis based on the Ikeda map is utilized to understand the physical origin of the filter-induced instability. Comparison with the well-known Benjamin–Feir instability and parametric instability is performed, revealing the intrinsic distinction in the family of modulation instabilities. Our investigations might benefit the development of ultrahigh-repetition-rate frequency comb generation, providing an alternative method for the microresonators.
Photonics Research
  • Publication Date: Jan. 24, 2022
  • Vol. 10 Issue 2 465 (2022)
All-fiber spatiotemporal mode-locking lasers with large modal dispersion
Huaiwei Zhang, Yunhong Zhang, Jiying Peng, Xinyang Su, Xiaosheng Xiao, Dongjian Xu, Junhao Chen, Tianran Sun, Kai Zheng, Jianquan Yao, and Yi Zheng
It is a challenging problem to balance the modal walk-off (modal dispersion) between multiple transverse modes and chromatic dispersion in long step-index multimode fibers (MMFs). By properly designing the oscillator, we have overcome the difficulty and successfully obtained an all-fiber spatiotemporal mode-locked laser based on step-index MMFs with large modal dispersion for the first time, to our knowledge. Various proofs of spatiotemporal mode-locking (STML) such as spatial, spectral, and temporal properties, are measured and characterized. This laser works at a fundamental frequency of 28.7 MHz, and achieves a pulse laser with single pulse energy of 8 nJ, pulse width of 20.1 ps, and signal-to-noise ratio of ∼70 dB. In addition, we observe a dynamic evolution of the transverse mode energy during the STML establishment process that has never been reported before.
Photonics Research
  • Publication Date: Feb. 01, 2022
  • Vol. 10 Issue 2 483 (2022)
Spatial coherence of electrically pumped random terahertz lasers
Eva A. A. Pogna, Alessandra Di Gaspare, Kimberly Reichel, Chiara Liberatore, Harvey E. Beere, David A. Ritchie, and Miriam S. Vitiello
Light sources with high radiance and tailored coherence properties are highly desirable for imaging applications in the mid-infrared and terahertz (THz) spectral regions, which host a large variety of molecular absorptions and distinctive fingerprints to be exploited for sensing and tomography. Here, we characterize the spatial coherence of random multimode THz quantum cascade lasers (QCLs) emitting > mW optical power per mode and showing low divergence (10°–30°), performing a modified Young’s double-slit experiment. Partial spatial coherence values ranging between 0.16 and 0.34 are retrieved, depending on the specific degree of disorder. These values are significantly lower than those (0.82) of conventional Fabry–Perot THz QCLs exploiting an identical active region quantum design. We then incorporate the devised low spatial coherence random lasers into a confocal imaging system with micrometer spatial resolution and demonstrate notable imaging performances, at THz frequencies, against spatial cross talk and speckles.
Photonics Research
  • Publication Date: Feb. 01, 2022
  • Vol. 10 Issue 2 524 (2022)
Nanophotonics and Photonic Crystals
Multiparticle resonant optical sorting using a topological photonic structure
Bojian Shi, Yongyin Cao, Tongtong Zhu, Hang Li, Yanxia Zhang, Rui Feng, Fangkui Sun, and Weiqiang Ding
Resonance between light and object is highly desired in optical manipulation because the optical forces reach maximum values in this case. However, in traditional waveguide structures, the resonant interaction also greatly perturbs the incident field and weakens or completely destroys the manipulation on the subsequent particles. In order to avoid this dilemma, we propose to perform optical manipulation in a topological photonic structure. Owing to the topological protection, the light mode can almost keep its original form when an object is being manipulated. Therefore, resonant optical sorting can be achieved in a multiple and high throughput manner. The mechanism and results presented here pave the way for efficient on-chip optical sorting for biophysical and biochemical analysis.
Photonics Research
  • Publication Date: Jan. 07, 2022
  • Vol. 10 Issue 2 297 (2022)
Mid-infrared active metasurface based on Si/VO2 hybrid meta-atoms
Tongtong Kang, Boyu Fan, Jun Qin, Weihao Yang, Shuang Xia, Zheng Peng, Bo Liu, Sui Peng, Xiao Liang, Tingting Tang, Longjiang Deng, Yi Luo, Hanbin Wang, Qiang Zhou, and Lei Bi
Active metasurfaces whose optical properties can be tuned by an external stimulus have attracted great research interest recently. Introduction of VO2 phase change material in all-dielectric metasurfaces has been demonstrated to modulate the resonance wavelength and amplitude in the visible to near-infrared wavelength range. In this study, we report a mid-infrared active metasurface based on Si/VO2 hybrid meta-atoms. By incorporating VO2 thin films in different locations of Si/VO2 all-dielectric nanodisks, we demonstrate different modulation amplitude of the electric or magnetic resonance scattering cross sections, leading to drastically different transmission spectrum upon VO2 insulator to metal phase transition. The physical mechanism is originated from the field profiles of the resonance modes, which interact with VO2 differently depending on its locations. Based on this mechanism, we experimentally demonstrated a large modulation of the transmittance from 82% to 28% at the 4.6 μm wavelength. Our work demonstrates a promising potential of VO2-based active all-dielectric metasurface for mid-infrared photonic applications such as infrared camouflage, chemical/biomedical sensing, optical neuromorphic computing, and multispectral imaging.
Photonics Research
  • Publication Date: Jan. 14, 2022
  • Vol. 10 Issue 2 373 (2022)
Four-wave mixing in graphdiyne-microfiber based on synchronized dual-wavelength pulses
Xinxin Jin, Wenli Bao, Han Zhang, Zheng Zheng, and Meng Zhang
Photonics Research
  • Publication Date: Feb. 01, 2022
  • Vol. 10 Issue 2 503 (2022)
Nonlinear Optics
2 μm optical frequency comb generation via optical parametric oscillation from a lithium niobate optical superlattice box resonator | Spotlight on Optics
Xiaohan Wang, Kunpeng Jia, Mengwen Chen, Shanshan Cheng, Xin Ni, Jian Guo, Yihao Li, Huaying Liu, Liyun Hao, Jian Ning, Gang Zhao, Xinjie Lv, Shu-Wei Huang, Zhenda Xie, and Shi-Ning Zhu
Optical parametric oscillators (OPOs) can downconvert the pump laser to longer wavelengths with octave separation via χ(2), which is widely used for laser wavelength extension including mid-infrared (MIR) generation. Such a process can be integrated in monolithic resonators, being compact and low in threshold. In this work, we show that the monolithic χ(2) mini-OPO can also be used for optical frequency comb generation around 2096 nm and enters the boundary of MIR range. A new geometry called an optical superlattice box resonator is developed for this realization with near-material-limited quality factor of 4.0×107. Only a continuous-wave near-infrared pump laser is required, with OPO threshold of 80 mW and output power up to 340 mW. Revival temporal profiles are measured at a detectable repetition frequency of 1.426 GHz, and narrow beat note linewidth of less than 10 Hz shows high comb coherence. These results are in good agreement with our simulation for a stable comb generation. Such an OPO-based comb source is useful for carbon dioxide sensing or the mine prospect applications and can be generalized to longer MIR wavelengths for general gas spectroscopy.
Photonics Research
  • Publication Date: Feb. 01, 2022
  • Vol. 10 Issue 2 509 (2022)
Optical and Photonic Materials
SrAl2O4 crystallite embedded inorganic medium with super-long persistent luminescence, thermoluminescence, and photostimulable luminescence for smart optical information storage
Panpan Li, Youjie Hua, Renguang Ye, Muzhi Cai, Shiqing Xu, and Junjie Zhang
As a leader of long persistent luminescence (LPL) materials, the optical properties of aluminate phosphor have remained unsurpassed for many years. As a powder material, its practical application will always be limited to the field of security signs. In this paper, the SrAl2O4:Eu2+, Dy3+ inorganic solid material with comparable LPL properties to powder materials was obtained. The crystallization mechanism and crystallite micro-morphology of inorganic glass materials have been studied, and a new opinion is put forward that the large-size SrAl2O4 crystallites in the glass matrix are stacked by rod-shaped crystals arranged in a regular direction. In addition, the SrAl2O4:Eu2+, Dy3+ glass obtained cannot only collect high-energy photons but also is sensitive to low-energy sunlight. The results show that the material exhibits superior performance in LPL, thermoluminescence, and photostimulable luminescence. Based on this property, a new application of this material in the field of information storage was explored. This paper has a certain reference value for the development and application of aluminate LPL materials in the field of smart optical information storage.
Photonics Research
  • Publication Date: Jan. 14, 2022
  • Vol. 10 Issue 2 381 (2022)
Optical characteristics of self-trapped excitons in 2D (iso-BA)2PbI4 perovskite crystals
Haolin Li, Xuanyu Zhang, Haizhen Wang, Jiahao Yu, Kexue Li, Zhipeng Wei, Dehui Li, and Rui Chen
Organic–inorganic halide metal perovskites are an exciting class of two-dimensional (2D) materials that have sparked renewed interest for next-generation optoelectronics. In particular, the self-trapped excitons (STEs) in 2D perovskite with excellent optical properties suggest great potential in display and narrowband detection. A prerequisite of understanding STEs’ properties is correct identification of the underlying interaction that leads to STEs. Here, the optical properties of STEs in (iso-BA)2PbI4 are characterized through laser spectroscopy at various temperatures and excitation intensities. It is found that STEs are related to the octahedral distortion caused by strong electron–phonon interaction. Trapping and detrapping between STEs and free excitons (FEs) are clearly observed. With the increase in temperature, STEs and FEs will gain enough energy and migrate to each other. Moreover, by characterizing the thickness-dependent and two-photon excitation emission, it is confirmed that STEs exist inside the material because of their weak absorption. Our findings are of great significance for not only the fundamental understanding of STEs, but also the design and optimization of 2D-perovskite-based electronic and optoelectronic devices.
Photonics Research
  • Publication Date: Feb. 01, 2022
  • Vol. 10 Issue 2 594 (2022)
Optical Devices
Micro-LED backlight module by deep reinforcement learning and micro-macro-hybrid environment control agent
Che-Hsuan Huang, Yu-Tang Cheng, Yung-Chi Tsao, Xinke Liu, and Hao-Chung Kuo
This paper proposes a micro-LED backlight module with a distributed Bragg reflector (DBR) structure to achieve excellent micro-LED backlight module quality and uses deep reinforcement learning (DRL) architecture for optical design. In the DRL architecture, to solve the computing environment problems of the two extreme structures of micro-scale and macro-scale, this paper proposes an environment control agent and virtual-realistic workflow to ensure that the design environment parameters are highly correlated with experimental results. This paper successfully designed a micro-LED backlight module with a DBR structure by the abovementioned methods. The micro-LED backlight module with a DBR structure improves the uniformity performance by 32% compared with the micro-LED backlight module without DBR, and the design calculation time required by the DRL method is only 17.9% of the traditional optical simulation.
Photonics Research
  • Publication Date: Jan. 07, 2022
  • Vol. 10 Issue 2 269 (2022)
Directional emission in X-cut lithium niobate microresonators without chaos dynamics
Ang Gao, Chen Yang, Likun Chen, Ru Zhang, Qiang Luo, Wei Wang, Qitao Cao, Zhenzhong Hao, Fang Bo, Guoquan Zhang, and Jingjun Xu
We systematically investigate the field distribution of the transverse electric modes in X-cut lithium niobate disks as an example of circular microcavities with anisotropic refractive index. A conserved quantity is discovered, which indicates the absence of chaos that generally exists in deformed microcavities and leads to a nontrivial directional emission. The emission directionality was theoretically investigated and experimentally verified by exciting high-order modes of an X-cut lithium niobate microresonator assisted with second harmonics. The field distribution analysis can enrich the knowledge in designing photonic devices that need precise control of field distribution, such as phase matching in nonlinear processes. Furthermore, the discovered emission phenomenon is momentous in enhancing and controlling communications between on-chip photonic devices.
Photonics Research
  • Publication Date: Jan. 14, 2022
  • Vol. 10 Issue 2 401 (2022)
Flexoelectric-effect-based light waveguide liquid crystal display for transparent display
Yunho Shin, Yingfei Jiang, Qian Wang, Ziyuan Zhou, Guangkui Qin, and Deng-Ke Yang
We report a light waveguide liquid crystal display (LCD) based on the flexoelectric effect. The display consists of two parallel flat substrates with a layer of flexoelectric liquid crystal sandwiched between them. A light-emitting diode (LED) is installed on the edge of the display and the produced light is coupled into the display. When no voltage is applied, the liquid crystal is uniformly aligned and is transparent. The incident light propagates through the display by total internal reflection at the interface between the substrate and air, and no light comes out of the viewing side of the display. The display appears transparent. When a voltage is applied, the liquid crystal is switched to a micrometer-sized polydomain state due to flexoelectric interaction and becomes scattering. The incident light is deflected from the waveguide mode and comes out of the viewing side of the display. We achieved thin-film-transistor active matrix compatible driving voltage by doping liquid crystal dimers with large flexoelectric coefficients. The light waveguide LCD does not use polarizers as in conventional LCDs. It has an ultrahigh transmittance near 90% in the voltage-off state. It is very suitable for transparent display, which can be used for head-up display and augmented reality display.
Photonics Research
  • Publication Date: Jan. 24, 2022
  • Vol. 10 Issue 2 407 (2022)
Silicon nonlinear switch as a conditional circulator for monostatic LiDAR systems
Mingfei Ding, Yiwei Xie, Hao Yan, Abu Naim R. Ahmed, Reza Safian, Swapnajit Chakravarty, Leimeng Zhuang, Pengcheng Jiao, Huan Li, Liu Liu, and Daoxin Dai
All-optical silicon-photonics-based LiDAR systems allow for desirable features in scanning resolution and speed, as well as leverage other advantages such as size, weight, and cost. Implementing optical circulators in silicon photonics enables bidirectional use of the light path for both transmitters and receivers, which simplifies the system configuration and thereby promises low system cost. In this work, to the best of our knowledge, we present the first experimental verification of all-passive silicon photonics conditional circulators for monostatic LiDAR systems using a nonlinear switch. The proposed silicon nonlinear interferometer is realized by controlling signal power distribution with power-splitting circuits, allowing the LiDAR transmitter and receiver to share the same optical path. Unlike the traditional concept requiring a permanent magnet, the present device is implemented by using common silicon photonic waveguides and a standard foundry-compatible fabrication process. With several additional phase shifters, the demonstrated device exhibits considerable flexibility using a single chip, which can be more attractive for integration with photodetector arrays in LiDAR systems.
Photonics Research
  • Publication Date: Jan. 24, 2022
  • Vol. 10 Issue 2 426 (2022)
Optoelectronics
10 Gbps wavelength division multiplexing using UV-A, UV-B, and UV-C micro-LEDs | Editors' Pick
Daniel M. Maclure, Jonathan J. D. McKendry, Mohamed Sufyan Islim, Enyuan Xie, Cheng Chen, Xiaobin Sun, Xudong Liang, Xiaohui Huang, Hanaa Abumarshoud, Johannes Herrnsdorf, Erdan Gu, Harald Haas, and Martin D. Dawson
Deep ultraviolet (DUV) optical wireless communications have seen increased interest in recent years due to the unique properties of light in this spectral region. However, the reported DUV data rates remain significantly lower than comparable demonstrations at visible wavelengths due to lower modulation bandwidths and/or output power of the sources. Here, we present a wavelength division multiplexing demonstration using three UV micro-light-emitting diodes emitting at nominal peak wavelengths of 285, 317, and 375 nm, respectively, each with an emitting area of approximately 1369 μm2 (equivalent to circular device pixels of diameter ∼40 μm). Using orthogonal frequency division multiplexing, data rates of 4.17, 3.02, and 3.13 Gbps were achieved from the 285, 317, and 375 nm devices, respectively, for a combined data rate of 10.32 Gbps transmitted over a distance of 0.5 m.
Photonics Research
  • Publication Date: Feb. 01, 2022
  • Vol. 10 Issue 2 516 (2022)
N-polar InGaN nanowires: breaking the efficiency bottleneck of nano and micro LEDs | Editors' Pick
Xianhe Liu, Yi Sun, Yakshita Malhotra, Ayush Pandey, Ping Wang, Yuanpeng Wu, Kai Sun, and Zetian Mi
The efficiency of conventional quantum well light-emitting diodes (LEDs) decreases drastically with reducing areal size. Here we show that such a critical size scaling issue of LEDs can be addressed by utilizing N-polar InGaN nanowires. We studied the epitaxy and performance characteristics of N-polar InGaN nanowire LEDs grown on sapphire substrate by plasma-assisted molecular beam epitaxy. A maximum external quantum efficiency ∼11% was measured for LEDs with lateral dimensions as small as 750 nm directly on wafer without any packaging. The effect of electron overflow and Auger recombination on the device performance is also studied. This work provides a viable approach for achieving high-efficiency nano and micro LEDs that were not previously possible.
Photonics Research
  • Publication Date: Feb. 01, 2022
  • Vol. 10 Issue 2 587 (2022)
Physical Optics
Exceptional points and enhanced nanoscale sensing with a plasmon-exciton hybrid system
Hong Jiang, Weidong Zhang, Guowei Lu, Lulu Ye, Hai Lin, Jinglin Tang, Zhaohang Xue, Zheng Li, Haitan Xu, and Qihuang Gong
Singularities in the spectra of open systems, known as exceptional points (EPs), have been shown to exhibit nontrivial topological properties and enhanced sensitivities. Here, we propose a novel approach to realize the EPs in a plasmon-exciton hybrid system and explore their applications in enhanced nanoscale sensing technology. We consider a plasmon-exciton system composed of a gold nanorod and a monolayer WSe2. By controlling the geometric parameters of the nano-hybrid system, we obtain simultaneous coalescence of the resonance frequencies and loss rates of the hybrid system, which is a unique feature of EPs. Numerical simulations show its application in enhanced nanoscale sensing for environmental refractive indices. Our work opens the way to a new class of sensors based on EP-enhanced sensing, with intrinsic nanoscale sensitivity due to the sub-diffraction-limit size of the plasmon-exciton nano-hybrid system.
Photonics Research
  • Publication Date: Feb. 01, 2022
  • Vol. 10 Issue 2 557 (2022)
Direct observation of zero modes in a non-Hermitian optical nanocavity array
Flore Hentinger, Melissa Hedir, Bruno Garbin, Mathias Marconi, Li Ge, Fabrice Raineri, Juan A. Levenson, and Alejandro M. Yacomotti
Zero modes are symmetry protected ones whose energy eigenvalues have zero real parts. In Hermitian arrays, they arise as a consequence of the sublattice symmetry, implying that they are dark modes. In non-Hermitian systems that naturally emerge in gain/loss optical cavities, particle-hole symmetry prevails instead; the resulting zero modes are no longer dark but feature π/2 phase jumps between adjacent cavities. Here, we report on the direct observation of zero modes in a non-Hermitian three coupled photonic crystal nanocavities array containing quantum wells. Unlike the Hermitian counterparts, the observation of non-Hermitian zero modes upon single pump spot illumination requires vanishing sublattice detuning, and they can be identified through far-field imaging and spectral filtering of the photoluminescence at selected pump locations. We explain the zero-mode coalescence as a parity-time phase transition for small coupling. These zero modes are robust against coupling disorder and can be used for laser mode engineering and photonic computing.
Photonics Research
  • Publication Date: Feb. 01, 2022
  • Vol. 10 Issue 2 574 (2022)
Quantum Optics
Integrable high-efficiency generation of three-photon entangled states by a single incident photon
Yunning Lu, Zeyang Liao, Fu-Li Li, and Xue-Hua Wang
Generation of multi-photon entangled states with high efficiency in integrated photonic quantum systems is still a big challenge. The usual three-photon generation efficiency based on the third-order nonlinear effect is extremely low. Here, we propose a scheme to generate three-photon correlated states, which are entangled states in frequency space and bound states in real space, with high efficiency. This method relies on two crucial processes. On one hand, by employing a Sagnac interferometer, an incident photon can be transformed into a symmetric superposition of the clockwise and counterclockwise modes of the Sagnac loop, which can then be perfectly absorbed by the emitter. On the other hand, the coupling strengths of the two transition paths of the emitter to the Sagnac loop are set to be equal, under which the absorbed photon can be emitted completely from the cascaded transition path due to quantum interference. By adjusting the coupling strengths among the three transition paths of the emitter and the waveguide modes, we can control the spectral entanglement and spatial separation among the three photons. Our proposal can be used to generate three-photon entangled states on demand, and the efficiency can be higher than 90% with some practical parameters, which can find important applications in integrated quantum information processing.
Photonics Research
  • Publication Date: Jan. 14, 2022
  • Vol. 10 Issue 2 389 (2022)
Topologically protecting squeezed light on a photonic chip | Editors' Pick
Ruo-Jing Ren, Yong-Heng Lu, Ze-Kun Jiang, Jun Gao, Wen-Hao Zhou, Yao Wang, Zhi-Qiang Jiao, Xiao-Wei Wang, Alexander S. Solntsev, and Xian-Min Jin
Squeezed light is a critical resource in quantum sensing and information processing. Due to the inherently weak optical nonlinearity and limited interaction volume, considerable pump power is typically needed to obtain efficient interactions to generate squeezed light in bulk crystals. Integrated photonics offers an elegant way to increase the nonlinearity by confining light strictly inside the waveguide. For the construction of large-scale quantum systems performing many-photon operations, it is essential to integrate various functional modules on a chip. However, fabrication imperfections and transmission cross talk may add unwanted diffraction and coupling to other photonic elements, reducing the quality of squeezing. Here, by introducing the topological phase, we experimentally demonstrate the topologically protected nonlinear process of four-wave mixing, enabling the generation of squeezed light on a silica chip. We measure the cross-correlations at different evolution distances for various topological sites and verify the nonclassical features with high fidelity. The squeezing parameters are measured to certify the protection of cavity-free, strongly squeezed states. The demonstration of topological protection for squeezed light on a chip brings new opportunities for quantum integrated photonics, opening novel approaches for the design of advanced multi-photon circuits.
Photonics Research
  • Publication Date: Jan. 24, 2022
  • Vol. 10 Issue 2 456 (2022)
Quantum non-demolition measurement based on an SU(1,1)-SU(2)-concatenated atom-light hybrid interferometer
Gao-Feng Jiao, Keye Zhang, L. Q. Chen, Chun-Hua Yuan, and Weiping Zhang
Quantum non-demolition (QND) measurement is an important tool in the fields of quantum information processing and quantum optics. The atom-light hybrid interferometer is of great interest due to its combination of an atomic spin wave and an optical wave, which can be utilized for photon number QND measurement via the AC-Stark effect. In this paper, we present an SU(1,1)-SU(2)-concatenated atom-light hybrid interferometer, and theoretically study QND measurement of the photon number. Compared to the traditional SU(2) interferometer, the signal-to-noise ratio in a balanced case is improved by a gain factor of the nonlinear Raman process (NRP) in this proposed interferometer. Furthermore, the condition of high-quality QND measurement is analyzed. In the presence of losses, the measurement quality is reduced. We can adjust the gain parameter of the NRP in the readout stage to reduce the impact due to losses. Moreover, this scheme is a multiarm interferometer, which has the potential of multiparameter estimation with many important applications in the detection of vector fields, quantum imaging, and so on.
Photonics Research
  • Publication Date: Jan. 28, 2022
  • Vol. 10 Issue 2 475 (2022)
Silicon Photonics
Phase calibration for integrated optical phased arrays using artificial neural network with resolved phase ambiguity
Lemeng Leng, Zhaobang Zeng, Guihan Wu, Zhongzhi Lin, Xiang Ji, Zhiyuan Shi, and Wei Jiang
Phase calibration for optical phased arrays (OPAs) is a key process to compensate for the phase deviation and retrieve the initial working state. Conventional calibration approaches based on iterative optimization algorithms are tedious and time-consuming. The essential difficulty of such a problem is to inversely solve for the phase error distribution among OPA elements from the far-field pattern of an OPA. Deep-learning-based technology might offer an alternative approach without explicitly knowing the inverse solution. However, we find that the phase ambiguities, including conjugate ambiguity and periodic ambiguity, severely deter the accuracy and efficacy of deep-learning-based calibration. Device-physics-based analysis reveals the causes of the phase ambiguities, which can be resolved by creating a tailored artificial neural network with phase-masked far-field patterns in a conjugate pair and constructing a periodic continuity-preserving loss function. Through the ambiguity-resolved neural network, we can extract phase error distribution in an OPA and calibrate the device in a rapid, noniterative manner from the measured far-field patterns. The proposed approach is experimentally verified. Pure main-beam profiles with >12 dB sidelobe suppression ratios are observed. This approach can help overcome a crucial bottleneck for the further advance of OPAs in a variety of applications such as lidar.
Photonics Research
  • Publication Date: Jan. 11, 2022
  • Vol. 10 Issue 2 347 (2022)
Spectroscopy
Emission spectroscopy of NaYF4:Eu nanorods optically trapped by Fresnel lens fibers
Aashutosh Kumar, Asa Asadollahbaik, Jeongmo Kim, Khalid Lahlil, Simon Thiele, Alois M. Herkommer, Síle Nic Chormaic, Jongwook Kim, Thierry Gacoin, Harald Giessen, and Jochen Fick
NaYF4:Eu nanorods with high aspect ratios are elaborated and optically trapped using dual fiber optical tweezers in a counterpropagating geometry. High trapping efficiency is observed using converging beams, emitted from diffractive Fresnel lenses directly 3D printed onto cleaved fiber facets. Stable nanorod trapping and alignment are reported for a fiber-to-fiber distance of 200 μm and light powers down to 10 mW. Trapping of nanorod clusters containing one to three nanorods and the coupling of nanorod motion in both axial and transverse directions are considered and discussed. The europium emission is studied by polarization-resolved spectroscopy with particular emphasis on the magnetic and electric dipole transitions. The respective σ and π orientations of the different emission lines are determined. The angles with respect to the nanorod axes of the corresponding magnetic and electric dipoles are calculated. Mono-exponential emission decay with decay time of 4–5 ms is reported. It is shown that the nanorod orientation can be determined by purely spectroscopic means.
Photonics Research
  • Publication Date: Jan. 11, 2022
  • Vol. 10 Issue 2 332 (2022)
Surface Optics and Plasmonics
Ultra-sensitive Dirac-point-based biosensing on terahertz metasurfaces comprising patterned graphene and perovskites
Xin Yan, Tengteng Li, Guohong Ma, Ju Gao, Tongling Wang, Haiyun Yao, Maosheng Yang, Lanju Liang, Jing Li, Jie Li, Dequan Wei, Meng Wang, Yunxia Ye, Xiaoxian Song, Haiting Zhang, Chao Ma, Yunpeng Ren, Xudong Ren, and Jianquan Yao
Biosensors are a focus of research on terahertz metasurfaces. However, reports of ultra-sensitive biosensors based on Dirac points are rare. Here, a new terahertz metasurface is proposed that consists of patterned graphene and perovskites. This serves as an ultra-sensitive Dirac-point-based biosensor for qualitative detection of sericin. Theoretically, sericin may make graphene n-doped and drive the Fermi level to shift from the valence band to the Dirac point, causing a dramatic decrease in conductivity. Correspondingly, the dielectric environment on the metasurface undergoes significant change, which is suited for ultra-sensitive biosensing. In addition, metal halide perovskites, which are up-to-date optoelectronic materials, have a positive effect on the phase during terahertz wave transmission. Thus, this sensor was used to successfully detect sericin with a detection limit of 780 pg/mL, achieved by changing the amplitude and phase. The detection limit of this sensor is as much as one order of magnitude lower than that of sensors in published works. These results show that the Dirac-point-based biosensor is a promising platform for a wide range of ultra-sensitive and qualitative detection in biosensing and biological sciences.
Photonics Research
  • Publication Date: Jan. 07, 2022
  • Vol. 10 Issue 2 280 (2022)
Compact logic operator utilizing a single-layer metasurface
Zihan Zhao, Yue Wang, Xumin Ding, Haoyu Li, Jiahui Fu, Kuang Zhang, Shah Nawaz Burokur, and Qun Wu
In this paper, we design and demonstrate a compact logic operator based on a single-layer metasurface at microwave frequency. By mapping the nodes in the trained fully connected neural network (FCNN) to the specific unit cells with phase control function of the metasurface, a logic operator with only one hidden layer is physically realized. When the incident wave illuminates specific operating regions of the metasurface, corresponding unit cells are activated and can scatter the incident wave to two designated zones containing logical information in the output layer. The proposed metasurface logic operator is experimentally verified to achieve three basic logic operations (NOT, OR, and AND) under different input signals. Our design shows great application potential in compact optical systems, low-power consumption information transmission, and ultrafast wave-based full signal processing.
Photonics Research
  • Publication Date: Jan. 11, 2022
  • Vol. 10 Issue 2 316 (2022)
Dual-band multifunctional coding metasurface with a mingled anisotropic aperture for polarized manipulation in full space
Yibo Pan, Feng Lan, Yaxin Zhang, Hongxin Zeng, Luyang Wang, Tianyang Song, Guiju He, and Ziqiang Yang
Integrated metasurfaces with diversified functionalities have demonstrated promising prospects for comprehensive implementations in compact 5G/6G communication systems by flexibly manipulating electromagnetic (EM) waves. Increasingly emerged multifunctional metasurfaces have successfully revealed integrated wavefront manipulations via phase gradient arrays, coding apertures, independent polarization control, asymmetric transmission/reflection, etc. However, multifunctional metasurfaces with more degrees of freedom in terms of multi-band/broadband operation frequencies, full-space coverage, and computable array factors are still in dire demand. As a step forward in extending manipulation dimensions, we propose and corroborate a dual-band multifunctional coding metasurface for anomalous reflection, radar cross-section reduction, and vortex beam generation through full-wave analysis and experiment. Our tri-layer meta-device comprises a shared coding aperture of split-ring and cross-shaped resonators sandwiched between two layers of orthogonal wire gratings. With an approach of independent control of a reflection–transmission wavefront under orthogonal polarization states and Fabry–Perot-like constructive interference, the low-cross-talk shared coding aperture features a smooth phase shift and high efficiency for 3-bit coding in the K-band and 1-bit coding in the Ka-band. Both numerical and measured results verify that the proposed coding metasurface can effectively realize full-space EM control and improve the capacity of the information channel, which could be developed for potential applications in multifunctional devices and integrated systems.
Photonics Research
  • Publication Date: Jan. 24, 2022
  • Vol. 10 Issue 2 416 (2022)
Manipulating electromagnetic radiation of one-way edge states by magnetic plasmonic gradient metasurfaces
Huabing Wu, Xiang Xi, Ximing Li, Yin Poo, Shiyang Liu, and Rui-Xin Wu
We theoretically and experimentally demonstrate that magnetic plasmonic gradient metasurfaces (GMSs) can convert a spatially propagating wave to a one-way edge state or vice versa with high efficiency. Consisting of an array of ferrite rods with a rotation gradient introduced to the rod dimers in the unit cell, GMSs can covert an incident wave beam to a one-way edge state with efficiency over 77%, and almost fully radiate into free space from the one-way edge state. The phenomenon arises from the unidirectional coupling of the spatial electromagnetic wave with magnetic plasmonic GMSs, which is evidenced from the photonic band diagrams of the edge state. The one-way edge state can radiate to or be excited from air with different angles by either engineering the gradient of the GMSs or tuning the bias magnetic field. By designing magnetic plasmonic GMSs with more exquisite configurations, we can expect many more nonreciprocal properties, adding additional freedom in manipulating electromagnetic waves.
Photonics Research
  • Publication Date: Feb. 01, 2022
  • Vol. 10 Issue 2 610 (2022)
Ultrafast Optics
Synchronization of an optical frequency comb and a microwave oscillator with 53 zs/Hz1/2 resolution and 10-20-level stability
Changmin Ahn, Yongjin Na, Minji Hyun, Jinho Bae, and Jungwon Kim
Precise and stable synchronization between an optical frequency comb (femtosecond mode-locked laser oscillator or microresonator-based comb) and a microwave oscillator is important for various fields including telecommunication, radio astronomy, metrology, and ultrafast X-ray and electron science. Timing detection and synchronization using electro-optic sampling with an interferometer has been actively used for low-noise microwave generation, long-distance timing transfer, comb stabilization, time-of-flight sensing, and laser-microwave synchronization for ultrafast science facilities. Despite its outstanding performance, there has been a discrepancy in synchronization performance of more than 10 dB between the projected shot-noise-limited noise floor and the measured residual noise floor. In this work, we demonstrate the shot-noise-limited performance of an electro-optic timing detector-based comb-microwave synchronization, which enabled an unprecedented residual phase noise floor of -174.5 dBc/Hz at 8 GHz carrier frequency (i.e., 53 zs/Hz1/2 timing noise floor), integrated rms timing jitter of 88 as (1 Hz to 1 MHz), rms timing drift of 319 as over 12 h, and frequency instability of 3.6×10-20 over 10,000 s averaging time. We identified that bandpass filtering of the microwave signal and optical pulse repetition-rate multiplication are critical for achieving this performance.
Photonics Research
  • Publication Date: Jan. 14, 2022
  • Vol. 10 Issue 2 365 (2022)

About the Cover

Highly-nonlinear, high-Q III-microresonators, heterogeneously integrated with Si photonic integrated circuits, enable high-efficiency on-chip nonlinear processes. The demonstration lights up new opportunities for conventional Si photonics in implementing nonlinear light sources for innovative applications at system level on large scale.