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.

151 Eu 3+ -doped yttrium silicate ( 151 Eu 3+ : Y 2 SiO 5 ) crystal is a unique material that possesses hyperfine states with coherence time up to 6 h. Many efforts have been devoted to the development of this material as optical quantum memories based on the bulk crystals, but integrable structures (such as optical waveguides) that can promote 151 Eu 3+ : Y 2 SiO 5 -based quantum memories to practical applications, have not been demonstrated so far. Here we report the fabrication of type II waveguides in a 151 Eu 3+ : Y 2 SiO 5 crystal using femtosecond-laser micromachining. The resulting waveguides are compatible with single-mode fibers and have the smallest insertion loss of 4.95 dB. On-demand light storage is demonstrated in a waveguide by employing the spinwave atomic frequency comb (AFC) scheme and the revival of silenced echo (ROSE) scheme. We implement a series of interference experiments based on these two schemes to characterize the storage fidelity. Interference visibility of the readout pulse is 0.99 ± 0.03 for the spin-wave AFC scheme and 0.97 ± 0.02 for the ROSE scheme, demonstrating the reliability of the integrated optical memory.

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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.

Photon echo is a fundamental tool for the manipulation of electromagnetic fields. Unavoidable spontaneous emission noise is generated in this process due to the strong rephasing pulse, which limits the achievable signal-to-noise ratio and represents a fundamental obstacle towards their applications in the quantum regime. Here we propose a noiseless photon-echo protocol based on a four-level atomic system. We implement this protocol in a Eu3+:Y2SiO5 crystal to serve as an optical quantum memory. A storage fidelity of 0.952 ± 0.018 is obtained for time-bin qubits encoded with single-photon-level coherent pulses, which is far beyond the maximal fidelity achievable using the classical measure-and-prepare strategy. In this work, the demonstrated noiseless photon-echo quantum memory features spin-wave storage, easy operation and high storage fidelity, which should be easily extended to other physical systems.