Integrated photonics has profoundly affected a wide range of technologies underpinning modern society^1–4. The ability to fabricate a complete optical system on a chip offers unrivalled scalability, weight, cost and power efficiency^5,6. Over the last decade, the progression from pure III–V materials platforms to silicon photonics has significantly broadened the scope of integrated photonics, by combining integrated lasers with the high-volume, advanced fabrication capabilities of the commercial electronics industry^7,8. Yet, despite remarkable manufacturing advantages, reliance on silicon-based waveguides currently limits the spectral window available to photonic integrated circuits (PICs). Here, we present a new generation of integrated photonics by directly uniting III–V materials with silicon nitride waveguides on Si wafers. Using this technology, we present a fully integrated PIC at photon energies greater than the bandgap of silicon, demonstrating essential photonic building blocks, including lasers, amplifiers, photodetectors, modulators and passives, all operating at submicrometre wavelengths. Using this platform, we achieve unprecedented coherence and tunability in an integrated laser at short wavelength. Furthermore, by making use of this higher photon energy, we demonstrate superb high-temperature performance and kHz-level fundamental linewidths at elevated temperatures. Given the many potential applications at short wavelengths, the success of this integration strategy unlocks a broad range of new integrated photonics applications.

Heterogeneous silicon photonics is uniquely positioned to address the photonic sensing needs of upcoming autonomous cars and provide the necessary cost reduction for widespread deployment. This is because it allows for wafer-scale active/passive integration, including optical sources. We present our recent research and the development of interferometric optical gyroscopes and LiDAR sensors. More specifically, we show a fully integrated gyroscope front-end occupying an area of only 4.5 mm². We also show the first dense pitch optical phased array using heterogeneous phase shifters. The 4 µm pitch heterogeneous phase shifters provide very low V_2π of only 0.35-1.4 V across 200 nm, low residual amplitude modulation of only 0.1-0.15 dB for 2π phase shift, extremely low static power consumption ( 1 GHz). All of these factors make them ideal for next-generation LiDAR systems that employ optical phased arrays.

Heterogeneous silicon photonics using wafer bonding is reaching maturity with commercial products for the data center market being shipped in volume. Here we give an overview of recent research in the area showing record device performance by using the best of both worlds: III-V for light generation and Si for guiding the light. Utilizing the flexibility of the heterogeneous silicon platform, narrow-linewidth widely tunable lasers as well as fully integrated mode locked lasers with record pulse powers and pulse duration were demonstrated. The ability to perform multiple die bonding with optimized epitaxially grown layer stacks was used to realize high-performance photonic integrated circuits both for communications and sensing. In addition to III-V materials, nonreciprocal materials such as, for example, Ce:YIG can be bonded, providing additional functionality such as on-chip isolators and reconfigurable on-chip circulators. On-chip isolation will become necessary with the increase in complexity of photonic integrated chips as photonic components such as lasers are sensitive to feedback effects.

We demonstrate a fully integrated extended distributed Bragg reflector (DBR) laser with $\sim 1\mathrm{kHz}$ linewidth and over 37 mW output power, as well as a ring-assisted DBR laser with less than 500 Hz linewidth. The extended DBR lasers are fabricated by heterogeneously integrating III-V material on Si as a gain section plus a 15 mm long, low-kappa Bragg grating reflector in an ultralow-loss silicon waveguide. The low waveguide loss (0.16 dB/cm) and long Bragg grating with narrow bandwidth (2.9 GHz) are essential to reducing the laser linewidth while maintaining high output power and single-mode operation. The combination of narrow linewidth and high power enable its use in coherent communications, RF photonics, and optical sensing.

This paper presents recent results on widely-tunable narrow-linewidth semiconductor lasers using a ring-resonator based mirror as the extended cavity. Two generations of lasers on the heterogeneous Si/InP photonic platform are presented. The first-generation lasers, with a total footprint smaller than 0.81 $\text{mm}^2$ , showed an intrinsic linewidth of ~2 kHz over a 40 nm wavelength tuning range across C+L bands. The second-generation lasers using ultra-low loss silicon waveguides and a novel cavity design achieved an intrinsic linewidth below 220 Hz. The lasers also possess an ultrawide wavelength tuning range of 110 nm across three optical communication bands (S+C+L). These are records among all fully integrated semiconductor lasers reported in the literature.

We analyze optical phased arrays with aperiodic pitch and element-to-element spacing greater than one wavelength at channel counts exceeding hundreds of elements. We optimize the spacing between waveguides for highest side-mode suppression providing grating lobe free steering in full visible space while preserving the narrow beamwidth. Optimum waveguide placement strategies are derived and design guidelines for sparse (> 1.5 λ and > 3 λ average element spacing) optical phased arrays are given. Scaling to larger array areas by means of tiling is considered.