Ultra-low V_(pp)and high-modulation-depth InP-based electro-optic microring modulator

A modulator is an essential building block in the integrated photonics,connecting the electrical with optical signals.The microring modulator gains much attention because of the small footprint,low drive voltage and high extinction ratio.An ultra-low V_(pp)and high-modulation-depth indium phosphide-based racetrack microring modulator is demonstrated in this paper.The proposed device mainly comprises one racetrack microring,incorporating a semiconductor amplifier,and coupling with a bus waveguide through a multimode interference coupler.Traveling wave electrodes are employed to supply bidirectional bias ports,terminating with a 50-Ω impedance.The on/off extinction ratio of the microring reaches 43.3 dB due to the delicately tuning of the gain.An 11 mV V_(pp),a maximum 42.5 dB modulation depth and a 6.6 GHz bandwidth are realized,respectively.This proposed microring modulator could enrich the functionalities and designability of the fundamental integrated devices.

35 km amplifier-less four-level pulse amplitude modulation signals enabled by a 23 GHz ultrabroadband directly modulated laser

The 4-level pulse amplitude modulation(PAM4)based on an 23 GHz ultrabroadband directly modulated laser(DML)was proposed.We have experimentally demonstrated that based on intensity modulation and direct detection(IMDD)56 Gbps per wavelength PAM4 signals transferred over 35 km standard single mode fiber(SSMF)without any optical amplification and we have achieved the bit error rate(BER)of the PAM4 transmission was under 2.9×10–4 by using feed forward equalization(FFE).

光学神经网络智能处理:技术演变与未来展望

卷积神经网络(CNN)以其卓越的特征提取能力,在人脸识别、图像分类、机器视觉、医学成像以及航空航天等领域展现出广泛的应用前景。然而,传统电学智能处理芯片受摩尔定律的制约,难以满足CNN算力需求的持续增长。光波以其超大宽带和超低损耗等特性,以光学或电学高维调控结构为基本单元,通过光的受控传播实现计算,是支撑下一代人工智能高算力需求的颠覆性技术。通过综述光学卷积神经网络的研究进展和技术突破,总结其发展的整体趋势,探讨未来需要解决的技术问题,并对光学卷积神经网络的应用前景进行展望。

4×112 Gb/s hybrid integrated silicon receiver based on photonic-electronic co-design

A 4×112 Gb/s hybrid-integrated optical receiver is demonstrated based on the silicon-photonic vertical p-i-n photodetector and silicon–germanium transimpedance amplifier.We propose a photonic-electronic co-design technique to optimize both the device-level and system-level performance,based on the end-to-end equivalent circuit model of the receiver.Continuous-time linear equalization and shunt peaking are employed to enhance the frequency response.Experimental results reveal that the optical-to-electrical 3-dB bandwidth of the receiver is 48 GHz.Clear open NRZ eye diagrams at56 Gb/s and PAM-4 eye diagrams at 112 Gb/s are achieved without an equalizer in the oscilloscope.The measured bit error rates for 56 Gb/s in NRZ and 112 Gb/s in PAM-4 reach 1×10^(-12)and 2.4×10^(-4)(KP4-FEC:forward error correction)thresholds under-4 dBm input power,respectively.Furthermore,the proposed receiver boasts a power consumption of approximately2.2 pJ/bit,indicating an energy efficient solution for data center traffic growth.

Recent advances in microwave photonics

Microwave photonics （MWP） is an interdisci- plinary field that combines two different areas of microwave engineering and photonics. It has several key features by transferring signals between the optical domain and microwave domain, which leads to the advantages of broad operation bandwidth for generation, processing and distribution of microwave signals and high resolution for optical spectrum measurement. In this paper, we comprehensively review past and current status of MWP in China by introducing the representative works from most of the active MWP research groups. Future prospective is also discussed fi＇om the national strategy to key enabling technology that we have developed.

Observation of parity-time symmetry in microwave photonics

Symmetry plays a crucial role in explorations of the laws of nature.Parity-time(PT)symmetry phenomena can lead to entirely real spectra in non-Hermitian systems,which attracts considerable attention in the fields of optics and electronics because these phenomena provide a new tool for the manipulation of oscillation modes and nonreciprocal signal transmission.A potential new field of application is microwave photonics,an interdisciplinary field in which the interaction between microwaves and optical signals is exploited.In this article,we report the experimental use of PT symmetry in an optoelectronic oscillator(OEO),a key microwave photonics system that can generate singlefrequency sinusoidal signals with high spectral purity.PT symmetry is theoretically analyzed and experimentally observed in an OEO with two mutually coupled active oscillation cavities via a precise manipulation of the interplay between gain and loss in the two oscillation cavities.Stable single-frequency microwave oscillation is achieved without using any optical/electrical filters for oscillation mode selection,which is an indispensable requirement in traditional OEOs.This observation opens new avenues for signal generation and processing based on the PT symmetry principle in microwave photonics.

Optoelectronic parametric oscillator

Oscillators are one of the key elements in various applications as a signal source to generate periodic oscillations.Among them,an optical parametric oscillator(OPO)is a driven harmonic oscillator based on parametric frequency conversion in an optical cavity,which has been widely investigated as a coherent light source with an extremely wide wavelength tuning range.However,steady oscillation in an OPO is confined by the cavity delay,which leads to difficulty in frequency tuning,and the frequency tuning is discrete with the minimum tuning step determined by the cavity delay.Here,we propose and demonstrate a counterpart of an OPO in the optoelectronic domain,i.e.,an optoelectronic parametric oscillator(OEPO)based on parametric frequency conversion in an optoelectronic cavity to generate microwave signals.Owing to the unique energy-transition process in the optoelectronic cavity,the phase evolution in the OEPO is not linear,leading to steady single-mode oscillation or multimode oscillation that is not bounded by the cavity delay.Furthermore,the multimode oscillation in the OEPO is stable and easy to realize owing to the phase control of the parametric frequency-conversion process in the optoelectronic cavity,while stable multimode oscillation is difficult to achieve in conventional oscillators such as an optoelectronic oscillator(OEO)or an OPO due to the mode-hopping and mode-competition effect.The proposed OEPO has great potential in applications such as microwave signal generation,oscillator-based computation,and radio-frequency phase-stable transfer.

Compact packaging for multi-wavelength DML TOSA

A compact multi-wavelength hybrid-integrated directly-modulated distributed-feedback laser(DML)transmitter optical sub-assembly(TOSA)has been achieved in our laboratory.The 8-channel distributed feedback(DFB)lasers are monolithically integrated based on the reconstruction-equivalent-chirp(REC)technology.With the high-density and high-speed packaging technique,the laser array and a multi-mode interference(MMI)multiplexer are assembled in the TOSA.The channel spacing of the TOSA is 200 GHz between adjacent lasers.It meets the 8 9 12.5 Gb/s operation demand and gives rather low channel crosstalk of less than-25 dB.This compact TOSA is of effective cost and shows good stability for mass production,which is expected to improve the performance of devices in access networks,data centers and supercomputing.

Recent advances in optoelectronic oscillators

An optoelectronic oscillator(OEO)is a microwave photonic system that produces microwave signals with ultralow phase noise using a high-quality-factor optical energy storage element.This type of oscillator is desired in various practical applications,such as communication links,signal processing,radar,metrology,radio astronomy,and reference clock distribution.Recently,new mode control and selection methods based on Fourier domain mode-locking and parity-time symmetry have been proposed and experimentally demonstrated in OEOs,which overcomes the long-existing mode building time and mode selection problems in a traditional OEO.Due to these mode control and selection methods,continuously chirped microwave waveforms can be generated directly from the OEO cavity and single-mode operation can be achieved without the need of ultranarrowband filters,which are not possible in a traditional OEO.Integrated OEOs with a compact size and low power consumption have also been demonstrated,which are key steps toward a new generation of compact and versatile OEOs for demanding applications.We review recent progress in the field of OEOs,with particular attention to new mode control and selection methods,as well as chip-scale integration of OEOs.

Dissipative microwave photonic solitons in spontaneous frequency-hopping optoelectronic oscillators

Dissipative solitons relying on the double balance between nonlinear and linear effects as well as cavity loss and gain have attracted increasing attention in recent years,since they give rise to novel operating states of various dissipative nonlinear systems.An optoelectronic oscillator(OEO)is a dissipative nonlinear microwave photonic system with a high quality factor that has been widely investigated for generating ultra-low noise single-frequency microwave signals.Here,we report a novel operating state of an OEO related to dissipative solitons,i.e.,spontaneous frequency hopping related to the formation of dissipative microwave photonic solitons.In this operating state,dissipative microwave photonic solitons occur due to the double balance between nonlinear gain saturation and linear filtering as well as cavity loss and gain in the OEO cavity,creating spontaneous frequencyhopping microwave signals.The generation of wideband tunable frequency-hopping microwave signals with a fast frequency-hopping speed up to tens of nanoseconds is observed in the experiment,together with the corresponding soliton sequences.This work reveals a novel mechanism between the interaction of nonlinear and linear effects in an OEO cavity,extends the suitability and potential applications of solitons,and paves the way for a new class of soliton microwave photonic systems for the generation,processing,and control of microwave and RF signals.

High-speed photodetectors in optical communication system

This paper presents a review and discussion for high-speed photodetectors and their applications on optical communications and microwave photonics. A detailed and comprehensive demonstration of high-speed photodetectors from development history, research hotspots to packaging technologies is provided to the best of our knowledge. A few typical applications based on photodetectors are also illustrated, such as free-space optical communications, radio over fiber and millimeter terahertz signal generation systems.

Serial time-encoded amplified microscopy for ultrafast imaging based on multi-wavelength laser

In this paper,a serial time-encoded amplified microscopy(STEAM)by employing a multi-wavelength laser as the light source is proposed and experimentally demonstrated.This system achieves ultrafast optical imaging with a tunable frame rate.The measuring range depends on the spectrum width of the multi-wavelength laser.Through tuning the speed of the modulating signal,the frame rate ranges from 100to 250 MHz.In addition,the spatial resolution can be improved by increasing the group velocity dispersion and reducing the wavelength spacing.Finally,with the development of photonic integrate circuits(PIC),the multi-wavelength laser source has the potential for integration on a photonic chip and thus the size of the proposed STEAM could be reduced in the future.

Optical length-change measurement based on an incoherent single-bandpass microwave photonic filter with high resolution

An optical length-change measurement technique is proposed based on an incoherent microwave photonic filter(MPF).The optical length under testing is inserted into an optical link of a single-bandpass MPF based on a polarization-processed incoherent light source.The key feature of the proposed technique is to transfer the length measurement in the optical domain to the electrical domain.In the electrical domain,the measurement resolution is extremely high thanks to the high-resolution measurement of microwave frequency response.In addition,since the MPF is a single-bandpass MPF,the optical length is uniquely determined by the central frequency of the MPF.A detailed investigation of the relation between the center frequency of the MPF and the optical length change is implemented.A measurement experiment is also demonstrated,and the experimental results show that the proposed technique has a measurement sensitivity of 1 GHz/mm with a high length-measurement resolution of 1 pm in theory.The proposed approach has the advantages of high sensitivity,high resolution,and immunity to power variation in electronic and optical links.

Single-photon microwave photonics

With the rapid development of microwave photonics technology, high-speed processing and ultra-weak signal detection capability have become the main bottlenecks in many applications. Thanks to the ultraweak signal detection capability and the extremely low timing jitter properties of single-photon detectors, the combination of single-photon detection and classical microwave photonics technology may provide a solution to break the above bottlenecks. In this paper, we first report a novel concept of singlephoton microwave photonics(SP-MWP), a SP-MWP signal processing system with phase shifting and frequency filtering functionalities is demonstrated based on a superconducting nanowire single photon detector(SNSPD) and a successive time-correlated single photon counting(TCSPC) module.Experimental results show that an ultrahigh optical sensitivity down to-100 d Bm has been achieved,and the signal processing bandwidth is only limited by the timing jitter of single-photon detectors. In the meantime, the proposed system demonstrates an ultrahigh anti-interference capability, only the signal which is phase locked by the trigger signal in TCSPC can be extracted from the detected signals combining with noise and strong interference. The proposed SP-MWP concept paves a way to a novel interdisciplinary field of microwave photonics and quantum mechanism, named by quantum microwave photonics.

Recent progresses on optical arbitrary waveform generation

This paper reviews recent progresses on optical arbitrary waveform generation （AWG） techniques, which could be used to break the speed and bandwidth bottle- necks of electronics technologies for waveform generation. The main enabling techniques for optically generating optical and microwave waveforms are introduced and reviewed in this paper, such as wavelength-to-time mapping techniques, space-to-time mapping techniques, temporal pulse shaping （TPS） system, optoelectronics oscillator （OEO）, programmable optical filters, optical differentiator and integrator and versatile electro-optic modulation implementations. The main advantages and challenges of these optical AWG techniques are also discussed.

112 Gbit/s transmitter optical subassembly based on hybrid integrated directly modulated lasers

Based on the hybrid integration technology, an ultra-compact and low cost transmitter optical subassembly module is proposed. Four directly modulated lasers are combined with a coarse wavelength division multiplexer operated at the O-band. The bandwidth for all channels is measured to be approximately 3 GHz. The 112 Gb∕s transmission is experimentally demonstrated for a 10 km standard single mode fiber（SSMF）, in which an optical isolator is used for avoiding the back-reflected and scattered light to improve the bit error rate（BER） performance. A low BER and clear eye opening are achieved for 10 km transmission.

Optically controlled phase array antenna [Invited]

To overcome the beam squint in wide instantaneous frequency, we review a number of system-level optical controlled phase array antennas for beam forming. The optical delay network based on a fiber device in terms of topological structure of an N-bit optical switch, fiber grating, high-dispersion fiber, and vector-sum technology is discussed, respectively. Lastly, an integrated circuit is simply summarized.

Large-scale coherent Ising machine based on optoelectronic parametric oscillator

Ising machines based on analog systems have the potential to accelerate the solution of ubiquitous combinatorial optimization problems.Although some artificial spins to support large-scale Ising machines have been reported,e.g.,superconducting qubits in quantum annealers and short optical pulses in coherent Ising machines,the spin stability is fragile due to the ultra-low equivalent temperature or optical phase sensitivity.In this paper,we propose to use short microwave pulses generated from an optoelectronic parametric oscillator as the spins to implement a large-scale Ising machine with high stability.The proposed machine supports 25,600 spins and can operate continuously and stably for hours.Moreover,the proposed Ising machine is highly compatible with high-speed electronic devices for programmability,paving a low-cost,accurate,and easy-to-implement way toward solving real-world optimization problems.

Reconfigurable single-shot incoherent optical signal processing system for chirped microwave signal compression

We propose and demonstrate a reconfigurable and single-shot incoherent optical signal processing system for chirped microwave signal compression, using a programmable optical filter and a multiwavelength laser(MWL). The system is implemented by temporally modulating a specially shaped MWL followed by a suitable linear dispersive medium. A microwave dispersion value up to 1.33 ns/GHz over several GHz bandwidth is achieved based on this approach. Here we demonstrate a singleshot compression for different linearly chirped microwave signals over several GHz bandwidth. In addition, the robustness of the proposed system when input RF signals are largely distorted is also discussed.

Surpassing the classical limit of the microwave photonic frequency fading effect by quantum microwave photonics

With energy-time entangled biphoton sources as the optical carrier and time-correlated single-photon detection for high-speed radio frequency(RF)signal recovery,the method of quantum microwave photonics(QMWP)has presented the unprecedented potential of nonlocal RF signal encoding and efficient RF signal distilling from the dispersion interference associated with ultrashort pulse carriers.In this paper,its capability in microwave signal processing and prospective superiority are further demonstrated.Both QMWP RF phase shifting and transversal filtering functionality,which are the fundamental building blocks of microwave signal processing,are realized.Besides good immunity to the dispersion-induced frequency fading effect associated with the broadband carrier in classical MWP,a native two-dimensional parallel microwave signal processor is provided.These results well demonstrate the superiority of QMWP over classical MWP and open the door to new application fields of MWP involving encrypted processing.