†All three authors contributed equally to this work pg. 2 Recent advances in nonlinear optics have revolutionized the area of integrated photonics, providing on-chip solutions to a wide range of new applications. Currently, the state of the art integrated nonlinear photonic devices are mainly based on dielectric material platforms, such as Si3N4 and SiO2. While semiconductor materials hold much higher nonlinear coefficients and convenience in active integration, they suffered in the past from high waveguide losses that prevented the realization of highly efficient nonlinear processes on-chip. Here we challenge this status quo and demonstrate an ultra-low loss AlGaAs-on-insulator (AlGaAsOI) platform with anomalous dispersion and quality (Q) factors beyond 1.5 × 10 6 . Such a high quality factor, combined with the high nonlinear coefficient and the small mode volume, enabled us to demonstrate a record low Kerr frequency comb generation threshold of ~36 µW for a resonator with a 1 THz free spectral range (FSR), ~100 times lower compared to that in previous semiconductor platform. Combs with >250 nm broad span have been generated under a pump power lower than the threshold power of state of the art dielectric micro combs. A soliton-step transition has also been observed for the first time from an AlGaAs resonator. This work is an important step towards ultra-efficient semiconductor-based nonlinear photonics and will lead to fully integrated nonlinear photonic integrated circuits (PICs) in near future. pg. 3 The extensive research on integrated nonlinear photonics in the last few years, driven by the breakthrough of the microcomb and other on-chip nonlinear devices, has opened up many new opportunities for on-chip integrated photonics, ranging from spectroscopy to atomic clock applications [1-3]. The demand to construct efficient nonlinear devices has motivated the development of different material platforms in nonlinear photonics. A common endeavor of those efforts is the reduction of the waveguide propagation loss, which is essential to enable high Q cavities so as to enhance the build-up power in the resonators and therefore increase the efficiency of the nonlinear optical processes [4]. In this regard, silica on silicon resonators [5-7] have long been dominant offering Q factors as high as 1 billion [6]. These devices can access a wide range of nonlinear effects including microwave rate soliton microcombs [8].However, over the last 5 years, there has been remarkable progress to significantly improve the Q factors of resonators in many other nonlinear integrated optical material platforms. One example is the Si3N4 platform, which delivers high performance in Kerr comb generation on chip [9][10][11]. The Si3N4 micro-resonators have enabled the generation of efficient frequency combs with repetition rates from microwave to THz frequencies [12] and improved Q factor of beyond 30 million [13,14]. Another material, which recently attracted attention, is LiNbO3. It offers additional opportunities for integrated nonlinear...

Microcombs have sparked a surge of applications over the past decade, ranging from optical communications to metrology1–4. Despite their diverse deployment, most microcomb-based systems rely on a large amount of bulky elements and equipment to fulfil their desired functions, which is complicated, expensive and power consuming. By contrast, foundry-based silicon photonics (SiPh) has had remarkable success in providing versatile functionality in a scalable and low-cost manner5–7, but its available chip-based light sources lack the capacity for parallelization, which limits the scope of SiPh applications. Here we combine these two technologies by using a power-efficient and operationally simple aluminium-gallium-arsenide-on-insulator microcomb source to drive complementary metal–oxide–semiconductor SiPh engines. We present two important chip-scale photonic systems for optical data transmission and microwave photonics, respectively. A microcomb-based integrated photonic data link is demonstrated, based on a pulse-amplitude four-level modulation scheme with a two-terabit-per-second aggregate rate, and a highly reconfigurable microwave photonic filter with a high level of integration is constructed using a time-stretch approach. Such synergy of a microcomb and SiPh integrated components is an essential step towards the next generation of fully integrated photonic systems.

We theoretically and experimentally demonstrate a significantly large modulation efficiency of a compact graphene modulator based on a silicon waveguide using the electro refractive effect of graphene. The modulation modes of electro-absorption and electro-refractive can be switched with different applied voltages. A high extinction ratio of 25 dB is achieved in the electro-absorption modulation mode with a driving voltage range of 0 V to 1 V. For electro-refractive modulation, the driving voltage ranges from 1 V to 3 V with a 185-pm spectrum shift. The modulation efficiency of 1.29 V · mm with a 40-μm interaction length is two orders of magnitude higher than that of the first reported graphene phase modulator. The realisation of phase and intensity modulation with graphene based on a silicon waveguide heralds its potential application in optical communication and optical interconnection systems.

Aluminum gallium arsenide (AlGaAs) and related III-V semiconductors have excellent optoelectronic properties. They also possess strong material nonlinearity as well as high refractive indices. In view of these properties, AlGaAs is a promising candidate for integrated photonics, including both linear and nonlinear devices, passive and active devices, and associated applications. Low propagation loss is essential for integrated photonics, particularly in nonlinear applications. However, achieving low-loss and high-confinement AlGaAs photonic integrated circuits poses a challenge. Here we show an effective reduction of surface-roughness-induced scattering loss in fully etched high-confinement AlGaAs-on-insulator nanowaveguides by using a heterogeneous wafer-bonding approach and optimizing fabrication techniques. We demonstrate ultrahigh-quality AlGaAs microring resonators and realize quality factors up to 3.52 × 106 and finesses as high as 1.4 × 104. We also show ultra-efficient frequency comb generations in those resonators and achieve record-low threshold powers on the order of ∼20 µW and ∼120 µW for the resonators with 1 THz and 90 GHz free-spectral ranges, respectively. Our result paves the way for the implementation of AlGaAs as a novel integrated material platform specifically for nonlinear photonics and opens a new window for chip-based efficiency-demanding practical applications.

The emergence of parallel convolution-operation technology has substantially powered the complexity and functionality of optical neural networks (ONN) by harnessing the dimension of optical wavelength. However, this advanced architecture faces remarkable challenges in high-level integration and on-chip operation. In this work, convolution based on time-wavelength plane stretching approach is implemented on a microcomb-driven chip-based photonic processing unit (PPU). To support the operation of this processing unit, we develop a dedicated control and operation protocol, leading to a record high weight precision of 9 bits. Moreover, the compact architecture and high data loading speed enable a preeminent photonic-core compute density of over 1 trillion of operations per second per square millimeter (TOPS mm−2). Two proof-of-concept experiments are demonstrated, including image edge detection and handwritten digit recognition, showing comparable processing capability compared to that of a digital computer. Due to the advanced performance and the great scalability, this parallel photonic processing unit can potentially revolutionize sophisticated artificial intelligence tasks including autonomous driving, video action recognition and image reconstruction.

The integrated microwave photonic filter (MPF), as a compelling candidate for next-generation radio-frequency (RF) applications, has been widely investigated for decades. However, most integrated MPFs reported thus far have merely incorporated passive photonic components onto a chip-scale platform, while all necessary active devices are still bulk and discrete. Though few attempts to higher photonic integration of MPFs have been executed, the achieved filtering performances are fairly limited, which impedes the pathway to practical deployments. Here, we demonstrate, for the first time to our knowledge, an all-integrated MPF combined with high filtering performances, through hybrid integration of an InP chip-based laser and a monolithic silicon photonic circuit consisting of a dual-drive Mach–Zehnder modulator, a high- Q ring resonator, and a photodetector. This integrated MPF exhibits a high spectral resolution as narrow as 360 MHz, a wide-frequency tunable range covering the S-band to K-band (3 to 25 GHz), and a large rejection ratio of > 40    dB . Moreover, the filtering response can be agilely switched between the bandpass and band-stop function with a transient respond time ( ∼ 48    μs ). Compared with previous MPFs in a similar integration level, the obtained spectral resolution in this work is dramatically improved by nearly one order of magnitude, while the valid frequency tunable range is broadened more than twice, which can satisfy the essential filtering requirements in actual RF systems. As a paradigm demonstration oriented to real-world scenarios, high-resolution RF filtering of realistic microwave signals aiming for interference rejection and channel selection is performed. Our work points out a feasible route to a miniaturized, high-performance, and cost-effective MPF leveraging hybrid integration approach, thus enabling a range of RF applications from wireless communication to radar toward the higher-frequency region, more compact size, and lower power consumption.

Optical evanescent sensors can non-invasively detect unlabeled nanoscale objects in real time with unprecedented sensitivity, enabling a variety of advances in fundamental physics and biological applications. However, the intrinsic low-frequency noise therein with an approximately 1/f-shaped spectral density imposes an ultimate detection limit for monitoring many paramount processes, such as antigen-antibody reactions, cell motions and DNA hybridizations. Here, we propose and demonstrate a 1/f-noise-free optical sensor through an up-converted detection system. Experimentally, in a CMOS-compatible heterodyne interferometer, the sampling noise amplitude is suppressed by two orders of magnitude. It pushes the label-free single-nanoparticle detection limit down to the attogram level without exploiting cavity resonances, plasmonic effects, or surface charges on the analytes. Single polystyrene nanobeads and HIV-1 virus-like particles are detected as a proof-of-concept demonstration for airborne biosensing. Based on integrated waveguide arrays, our devices hold great potentials for multiplexed and rapid sensing of diverse viruses or molecules.

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