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).

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.

Recent advances in microwave photonics

微波 photonics (MWP ) 是联合微波工程和 photonics 的二个不同区域的一块学科交差的地。它由转移在光域和微波领域之间的信号有几特色，它为产生导致宽广操作带宽的优点，处理，微波的分发发信号并且为光光谱测量的高分辨率。在这篇论文，我们包括地由从大多数活跃 MWP 研究组介绍代表性的工作在中国考察过去和 MWP 的当前的地位。未来未来也从国家策略被讨论给我们开发了的创新技术调音。

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.

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.

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.

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.

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.

Recent progresses on optical arbitrary waveform generation

这份报纸在光任意的波形产生(美国线规) 上考察最近的进步技术，它能被用来为波形产生打破电子学技术的速度和带宽瓶颈。为光学地产生的主要启用技术光并且微波波形在这被介绍并且考察纸例如印射技术的 wavelength-to-time ， space-to-time 印射技术，塑造的时间的脉搏( TPS )系统，光电子振荡器( OEO )，可编程的光过滤器，光微分器和综合者和万用的电镀物品眼的调整实现。这些光美国线规技术的主要优点和挑战也被讨论。

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.

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 net work based on a fiber device in terms of topological structure of an Mbit optical switch, fiber grating, high-dispersion fiber, and vector-sum technology is discussed, respectively. Lastly, an integrated circuit is simply summarized.

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.

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.

An electrical-filtered optical heterodyne technique for tuning speed measurement of DBR lasers

A new scheme based on the electrical-filtered optical heterodyne technique is proposed for measuring the tuning speed of tunable distributed Bragg reflector (DBR) lasers. In this scheme, a 10 GHz high-pass electrical filter is used and the wavelength switching time of a tunable DBR laser for different tuning frequencies corresponding exactly to different delay lines is measured. The switching time is measured to be nearly 300 ns and can be improved by reducing the equivalent resistance-capacitance (RC) time constant of the device. The distribution of the beat signal of the DBR laser in the time domain is also obtained, and is a good match with the waveforms measured using an optical filter.

单光子微波光子学

伴随着微波光子学技术的迅速发展,超低功率下的高速微波光子信号检测、处理是一个限制微波光子应用领域的主要难点.考虑到单光子探测器具有超微弱光信号检测能力的同时还具有极低的时间抖动特性,将单光子检测与经典微波光子处理技术相结合是一种突破上述难点的潜在解决方案.基于此,本文提出了一种单光子微波光子系统.该系统使用单光子信号作为载波,通过微波强度改变光子探测几率,再通过单光子探测器得到光子探测几率复原微波信号.该系统成功实现了对单光子强度的微波光子信号进行滤波、移相的操作,而且系统的处理速度仅由单光子探测器时间抖动决定.此外,得益于系统所使用的信号恢复技术,该系统具有的优秀的抗干扰能力能够有效滤除噪声.该系统展示了一个微波光子学和量子光学学科交叉的范例,为之后量子微波光子学的发展奠定基础.

Few-mode vertical-cavity surface-emitting lasers for space-division multiplexing

In order to choose the proper radius of oxide aperture for few-mode vertical-cavity surface-emitting lasers （VCSELs）, the influences of oxide aperture size on the multi-transverse-mode behaviors are investigated in detail. By establishing the effective refractive index model to simulate VCSELs with different radii of oxide apertures, the wavelength and corresponding order of different modes are obtained. VCSELs with three kinds of oxide apertures are manufactured. Then the multi-transverse-mode spectra and near-field are measured. It is found that when the radius is between 1.5 and 4.5μm, few-mode VCSELs can be implemented. The 2.5μm VCSEL manufactured in this paper only emits LP01 mode and LP21 mode. Since the space distance between the two modes is 2μm, it is expected to realize direct-modulation few-mode VCSELs by channel etching or ion implantation between the two modes.

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.

All-optical temporal fractional order differentiator using an in-fiber ellipsoidal air-microcavity

An all-optical temporal fractional order differentiator with ultrabroad bandwidth （-1.6 THz） and extremely simple fabrication is proposed and experimentally demonstrated based on an in-fiber ellipsoidal air-microcavity. The ellipsoidal air-microcavity is fabricated by splicing a single mode fiber （SMF） and a photonic crystal fiber （PCF） together using a simple arc-discharging technology. By changing the arc-discharging times, the propagation loss can be adjusted and then the differentiation order is tuned. A nearly Gaussian-like optical pulse with 3 dB bandwidth of 8 nm is launched into the differentiator and a 0.65 order differentiation of the input pulse is achieved with a processing error of 2.55%.