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Location: Home / Technology / Microcomb-driven silicon photonic systems

Microcomb-driven silicon photonic systems

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Integrated photonics is profoundly impacting data communication and signal processing8,9,10. A crucial development in the past decade is the demonstration of Kerr microcombs, which provide mutually coherent and equidistant optical frequency lines generated by microresonators1,11,12. With a wide range of microcomb-based optoelectronic systems2,4,13,14,15,16,17,18 demonstrated recently, these integrated light sources hold the promise to extend the application space of integrated photonics to a much broader scope. However, despite the tremendous progress made in microcomb integration19,20,21,22,23, in almost all system-level demonstrations leveraging microcomb technologies, the passive comb generators are still the only integrated component. The rest of the system, including the comb pumping lasers, passive and active optical components, and the supporting electronics, usually rely on bulky, expensive and power-consuming equipment, thereby undermining the promised benefits of integrated photonics.

Microcomb-driven silicon photonic systems

In contrast, the advances in silicon photonics (SiPh) technology have provided a scalable and low-cost solution to miniaturize optical systems6,24,25, benefiting from complementary metal–oxide–semiconductor (CMOS)-compatible manufacturing. These ‘photonic engines’, have been commercialized in data interconnects26,27, and widely applied in other fields28,29,30,31. Yet, a key ingredient missing from foundry-based silicon-on-insulator (SOI) photonic integrated circuits (PICs) is the multiple wavelength source. For example, the current state-of-the-art photonic transceiver module contains an eight-channel distributed feedback laser (DFB) array for wavelength division multiplexing (WDM)32. Increasing the channel count in such a system requires considerable design effort, such as line-to-line spacing stabilization and increased assembly workload. Moreover, the lack of mutual coherence among channel lines restricts many applications, such as precise time–frequency metrology.

Although interfacing these two technologies is essential to address the aforementioned problems on both sides, until now, such a combination has remained elusive. Previously, although the combinations of a microcomb and other photonic components have shown potential in optical computation15, atomic clocks4 and synthesizer systems3, these integrated demonstrations usually rely on specialized fabrication processes unsuitable for high-volume production. Moreover, comb start-up33,34 and stabilization techniques35,36, which require high-performance discrete optics and electronic components, markedly increase the operation complexity and system size. Recent progress in hybrid or heterogeneous laser-microcomb integration enables on-chip comb generation in a simplified manner21,22,23, but these schemes add complexity in processing. These difficulties, along with the extra expenditures on multi-channel match-up and other pretreatments in system operations, have so far obstructed the implementation of a functional laser-microcomb system.

Here we make a key step in combining these two essential technologies. Using an aluminium gallium arsenide (AlGaAs)-on-insulator (AlGaAsOI) microresonator that can be directly pumped by a DFB on-chip laser, a dark-pulse microcomb is generated, which exhibits state-of-the-art efficiency, simple operation and long-time stability. Such a coherent comb is used to drive CMOS-foundry-based SiPh engines containing versatile functionality, which can be used for a wide range of applications (Fig. 1). On the basis of this approach, system-level demonstrations are presented for two major integrated photonics fields. (1) As a communications demonstration, we present a microcomb-SiPh transceiver-based data link with 100-Gbps pulse-amplitude four-level modulation (PAM4) transmission and 2-Tbps aggregate rate for data centres. (2) For microwave photonics, a compact microwave filter is demonstrated with tens-of-microseconds-level reconfiguration speed by an on-chip multitap delay-line processing scheme, whose tunable bandwidth and flexible centre frequency are capable of supporting fifth-generation (5G), radar and on-chip signal processing. This work paves the way towards the full integration of a wide range of optical systems, and will significantly accelerate the proliferation of microcombs and SiPh technologies for the next generation of integrated photonics.