Progress in integrating Ⅲ–Ⅴ semiconductors on silicon could drive silicon photonics forward

Why integratingⅢ–Ⅴsemiconductor on silicon Photonics is an enabling technology and play a significant role in today’s information age.In the last few decades,starting from the fiber long haul optical communications,optical interconnects have gradually replaced copper interconnects due to its advantage of the bandwidth distance product.As photonics is moving closer and closer to the processor and memory of computers,and eventually,to on-chip level,silicon photonics becomes a viable solution for future optical interconnections due to the feasibility of high-bandwidth,high-density I/O capability and dense integration enabled by the high index contrast.

High-performance polarization management devices based on thin-film lithium niobate

High-speed polarization management is highly desirable for many applications,such as remote sensing,telecommunication,and medical diagnosis.However,most of the approaches for polarization management rely on bulky optical components that are slow to respond,cumbersome to use,and sometimes with high drive voltages.Here,we overcome these limitations by harnessing photonic integrated circuits based on thin-film lithium niobate platform.We successfully realize a portfolio of thin-film lithium niobate devices for essential polarization management functionalities,including arbitrary polarization generation,fast polarization measurement,polarization scrambling,and automatic polarization control.The present devices feature ultra-fast control speeds,low drive voltages,low optical losses and compact footprints.Using these devices,we achieve high fidelity polarization generation with a polarization extinction ratio up to 41.9 dB and fast polarization scrambling with a scrambling rate up to 65 Mrad s−1,both of which are best results in integrated optics.We also demonstrate the endless polarization state tracking operation in our devices.The demonstrated devices unlock a drastically new level of performance and scales in polarization management devices,leading to a paradigm shift in polarization management.

Bias-drift-free Mach–Zehnder modulators based on a heterogeneous silicon and lithium niobate platform

Optical modulators have been and will continue to be essential devices for energy-and cost-efficient optical communication networks.Heterogeneous silicon and lithium niobate modulators have demonstrated promising performances of low optical loss,low drive voltage,and large modulation bandwidth.However,DC bias drift is a major drawback of optical modulators using lithium niobate as the active electro-optic material.Here,we demonstrate high-speed and bias-drift-free Mach–Zehnder modulators based on the heterogeneous silicon and lithium niobate platform.The devices combine stable thermo-optic DC biases in silicon and ultra-fast electro-optic modulation in lithium niobate,and exhibit a low insertion loss of 1.8 d B,a low half-wave voltage of 3 V,an electro-optic modulation bandwidth of at least 70 GHz,and modulation data rates up to 128 Gb/s.

Heterogeneously integrated,superconducting silicon-photonic platform for measurementdevice-independent quantum key distribution

Integrated photonics provides a route to both miniaturization of quantum key distribution(QKD)devices and enhancing their performance.A key element for achieving discrete-variable QKD is a singlephoton detector.It is highly desirable to integrate detectors onto a photonic chip to enable the realization of practical and scalable quantum networks.We realize a heterogeneously integrated,superconducting silicon-photonic chip.Harnessing the unique high-speed feature of our optical waveguide-integrated superconducting detector,we perform the first optimal Bell-state measurement(BSM)of time-bin encoded qubits generated from two independent lasers.The optimal BSM enables an increased key rate of measurement-device-independent QKD(MDI-QKD),which is immune to all attacks against the detection system and hence provides the basis for a QKD network with untrusted relays.Together with the timemultiplexed technique,we have enhanced the sifted key rate by almost one order of magnitude.With a 125-MHz clock rate,we obtain a secure key rate of 6.166 kbps over 24.0 dB loss,which is comparable to the state-of-the-art MDI-QKD experimental results with a GHz clock rate.Combined with integrated QKD transmitters,a scalable,chip-based,and cost-effective QKD network should become realizable in the near future.

1-Pbps orbital angular momentum fibre-optic transmission

Space-division multiplexing(SDM),as a main candidate for future ultra-high capacity fibre-optic communications,needs to address limitations to its scalability imposed by computation-intensive multi-input multi-output(MIMO)digital signal processing(DSP)required to eliminate the crosstalk caused by optical coupling between multiplexed spatial channels.By exploiting the unique propagation characteristics of orbital angular momentum(OAM)modes in ring core fibres(RCFs),a system that combines SDM and C+L band dense wavelength-division multiplexing(DWDM)in a 34 km 7-core RCF is demonstrated to transport a total of 24960 channels with a raw(net)capacity of 1.223(1.02)Peta-bit s−1(Pbps)and a spectral efficiency of 156.8(130.7)bit s−1 Hz−1.Remarkably for such a high channel count,the system only uses fixed-size 4×4 MIMO DSP modules with no more than 25 time-domain taps.Such ultra-low MIMO complexity is enabled by the simultaneous weak coupling among fibre cores and amongst non-degenerate OAM mode groups within each core that have a fixed number of 4 modes.These results take the capacity of OAM-based fibre-optic communications links over the 1 Pbps milestone for the first time.They also simultaneously represent the lowest MIMO complexity and the 2nd smallest fibre cladding diameter amongst reported few-mode multicore-fibre(FM-MCF)SDM systems of>1 Pbps capacity.We believe these results represent a major step forward in SDM transmission,as they manifest the significant potentials for further up-scaling the capacity per optical fibre whilst keeping MIMO processing to an ultra-low complexity level and in a modularly expandable fashion.

Optical generation of tunable and narrow linewidth radio frequency signal based on mutual locking between integrated semiconductor lasers

An integrated on-chip optical device consisting of two distributed feedback(DFB)lasers and one multimode semiconductor ring laser(SRL)has been numerically investigated.In this optical circuit,the two DFB lasers are injected into the SRL,and with the presence of the four-wave mixing effect and optical feedback,the three semiconductor lasers achieve mutual-locking state.The beating between the output optical spectral lines can generate readily tunable radio frequency signals with high spectral purity.

Digitally tunable optical delay line based on thinfilm lithium niobate featuring high switching speed and low optical loss

A tunable optical delay line(ODL) featuring high switching speed and low optical loss is highly desirable in many fields. Here, based on the thin-film lithium niobate platform, we demonstrate a digitally tunable on-chip ODL that includes five Mach–Zehnder interferometer optical switches, four flip-chip photodetectors, and four delayline waveguides. The proposed optical switches can achieve a switching speed of 13 ns and an extinction ratio of34.9 dB. Using a modified Euler-bend-based spiral structure, the proposed delay-line waveguide can simultaneously achieve a small footprint and low optical propagation loss. The proposed ODL can provide a maximum delay time of 150 ps with a resolution of 10 ps and feature a maximum insertion loss of 3.4 dB.

Manipulating optical vortices using integrated photonics

光旋涡(OV ) 与方位角地改变从极化旋转或从在量，水平对应于光子纺纱或轨道的尖 momenta 的波浪向量的尖设计产生的阶段术语指圆柱的光模式的一个班。OV 在光学和 photonics 的许多区域吸引了研究人员的注意，作为他们从光通讯的潜在的应用范围，光操作，成像，察觉到，到量信息。在最近的年里，综合 photonics 有成为操作 OV 的一个有效方法。在这份报纸，理论框架和为 OV 的操作的综合 photonics 的试验性的进步被考察。

Photonic integrated devices for exploiting the orbital angular momentum of light in optical communications

新兴的应用程序将多半基于带轨道的尖动量(操作维护管理) 的光横梁要求 photonic 为小型化，改进性能和提高的功能的综合设备和电路。这份报纸在光的操作维护管理的地里考察 state-of-the 艺术，在硅报导最近的开发综合操作维护管理 emitters，并且在能在未来操作维护管理被使用的综合操作维护管理设备基于的硅讨论应用潜力和挑战光通讯系统。

Locally periodically poled LNOI ridge waveguide for second harmonic generation [Invited]

Periodically poled lithium niobate on insulator(LNOI) ridge waveguides are desirable for high-efficiency nonlinear frequency conversions, and the fabrication process of such waveguides is crucial for device performance. In this work, we report fabrication and characterization of locally periodically poled ridge waveguides. Ridge waveguides were fabricated by dry etching, and then the high-voltage pulses were applied to locally poled ridge waveguides. Second harmonic generation with normalized conversion efficiency of 435.5% W^(-1)·cm^(-2) was obtained in the periodically poled LNOI ridge waveguide,which was consistent with the triangular domain structure revealed by confocal microscopy.

Route-asymmetrical light transmission of a fiber-chip-fiber optomechanical system

In this paper, we proposed and experimentally demonstrated a route-asymmetrical light transmission scheme based on the thermal radiative effect, which means that forward and backward propagations of an optical device have different transmittances provided they are not present simultaneously. Employing a fiber-chipfiber optomechanical system, our scheme has successfully achieved a broad operation bandwidth of at least 24 nm and an ultra-high route-asymmetrical transmission ratio （RATR） up to 63 dB. The route-asymmetrical device has been demonstrated effectively with not only the continuous-wave （CW） light but also 10 Gbit/s on-off-keying （OOK） digital signals. Above mentioned unique features can be mostly attributed to the significant characteristics of the thermal radiative effect, which could cause a fiber displacement up to tens of microns. The powerful and significant thermal radiative effect opens up a new opportunity and method for route-asymmetrical light transmission. Moreover, this research may have important applications in all-optical systems, such as the optical limiters and ultra-low loss switches.

Effect of dimension variation for second-harmonic generation in lithium niobate on insulator waveguide[Invited]

We study the effect of dimension variation for second-harmonic generation(SHG) in lithium niobate on insulator(LNOI)waveguides. Non-trivial SHG profiles in both type-0 and type-I quasi-phase matching are observed during the wavelength tuning of the fundamental light. Theoretical modeling shows that the SHG profile and efficiency can be greatly affected by the waveguide cross-section dimension variations, especially the thickness variations. In particular, our analysis shows that a thickness variation of tens of nanometers is in good agreement with the experimental results. Such investigations could be used to evaluate fabrication performance of LNOI-based nonlinear optical devices.