Nonlinear frequency conversion plays a crucial role in advancing the functionality of next-generation optical systems. Portable metrology references and quantum networks will demand highly efficient second-order nonlinear devices, and the intense nonlinear interactions of nanophotonic waveguides can be leveraged to meet these requirements. Here we demonstrate second harmonic generation (SHG) in GaAs-on-insulator waveguides with unprecedented efficiency of 40 W⁻¹ for a single-pass device. This result is achieved by minimizing the propagation loss and optimizing phase-matching. We investigate surface-state absorption and design the waveguide geometry for modal phase-matching with tolerance to fabrication variation. A 2.0 µm pump is converted to a 1.0 µm signal in a length of 2.9 mm with a wide signal bandwidth of 148 GHz. Tunable and efficient operation is demonstrated over a temperature range of 45 °C with a slope of 0.24 nm/°C. Wafer-bonding between GaAs and SiO₂ is optimized to minimize waveguide loss, and the devices are fabricated on 76 mm wafers with high uniformity. We expect this device to enable fully integrated self-referenced frequency combs and high-rate entangled photon pair generation.

The microscale integration of mid- and long-wave-infrared photonics could enable the development of fieldable, robust chemical sensors, as well as highly efficient infrared frequency converters. However, such technology would be defined by the choice of material platform, which immediately determines the strength and types of optical nonlinearities available, the optical transparency window, modal confinement, and physical robustness. In this work, we demonstrate a new platform, suspended AlGaAs waveguides integrated on silicon, providing excellent performance in all of these metrics. We demonstrate low propagation losses within a span of nearly two octaves (1.26–4.6 μm) with exemplary performance of 0.45 dB/cm at $\lambda =2.4\mathrm{\mu m}$. We exploit the high nonlinearity of this platform to demonstrate 1560 nm-pumped second-harmonic generation and octave-spanning supercontinuum reaching out to 2.3 μm with 3.4 pJ pump pulse energy. With mid-IR pumping, we generate supercontinuum spanning from 2.3 to 6.5 μm. Finally, we demonstrate the versatility of the platform with mid-infrared passive devices such as low-loss 10 μm-radius bends, compact power splitters with $96\pm 1\%$ efficiency, and edge couplers with $3.0\pm 0.1\mathrm{dB}$ loss. This platform has strong potential for multifunctional integrated photonic systems in the mid-infrared.

Heterogeneous integration enables the construction of silicon (Si) photonic systems, which are fully integrated with a range of passive and active elements including lasers and detectors. Numerous advancements in recent years have shown that heterogeneous Si platforms can be extended beyond near-infrared telecommunication wavelengths to the mid-infrared (MIR) (2-20 μm) regime. These wavelengths hold potential for an extensive range of sensing applications and the necessary components for fully integrated heterogeneous MIR Si photonic technologies have now been demonstrated. However, due to the broad wavelength range and the diverse assortment of MIR technologies, the optimal platform for each specific application is unclear. Here, we overview Si photonic waveguide platforms and lasers at the MIR, including quantum cascade lasers on Si. We also discuss progress toward building an integrated multispectral source, which can be constructed by wavelength beam combining the outputs from multiple lasers with arrayed waveguide gratings and duplexing adiabatic couplers.

Mid-infrared (MIR) silicon photonic systems show great promise for miniaturizing a variety of sensing and detection technologies. Rapid progress has been made in recent years, and numerous passive and active MIR devices have now been constructed on various silicon-based platforms. We previously reported the heterogeneous integration on silicon of Fabry–Perot and distributed feedback quantum cascade lasers (QCLs) operating at 4.8 μm. Interband cascade lasers (ICLs) will be preferred for many on-chip sensing technologies because they operate in the 3–6 μm range with threshold drive powers 1–2 orders of magnitude lower than QCLs. In this work, we demonstrate the integration of ICLs on a silicon substrate. These lasers emit 3.6 μm light into silicon-on-insulator waveguides in pulsed mode at temperatures up to 50°C. This represents an important step toward MIR photonic integrated circuits on silicon that operate with much lower drive power and therefore an even smaller footprint.

Nanophotonic waveguides with sub-wavelength mode confinement and engineered dispersion are an excellent platform for application-tailored nonlinear optical interactions at low pulse energies. We present fully air-clad suspended silicon waveguides for infrared frequency comb generation with optical bandwidth limited only by the silicon transparency. Precise lithographic control over the waveguide dispersion enables tailored infrared frequency comb generation across a bandwidth of 2.0–8.8 μm ($1130–5000{\mathrm{cm}}^{-1}$), with the broadest simultaneous bandwidth covering 2.0–7.7 μm. Novel fork-shaped couplers provide efficient input coupling with only 1.5 dB loss. The coherence, brightness, and stability of the generated light are highlighted in a dual-frequency comb setup in which individual comb lines are resolved with 30 dB extinction ratio and 100 MHz spacing in the wavelength range of 4.9–8.8 μm ($1130–2050{\mathrm{cm}}^{-1}$) using three different waveguide widths. These sources are used for broadband gas- and liquid-phase dual-comb spectroscopy with 100 MHz comb line resolution. We achieve a peak spectral signal-to-noise ratio of $10\sqrt{\mathrm{Hz}}$ across a simultaneous bandwidth of 6.3–8.2 μm ($1220–1590{\mathrm{cm}}^{-1}$) containing 112,200 comb lines. These results provide a pathway to further integration with the developing high-repetition-rate frequency comb lasers for compact sensors with applications in chip-based chemical analysis and spectroscopy.

We present the design of a novel platform that is able to combine optical frequency bands spanning 4.2 octaves from ultraviolet to mid-wave infrared into a single, low M² output waveguide. We present the design and realization of a key component in this platform that combines the wavelength bands of 350 nm – 1500 nm and 1500 nm – 6500 nm with demonstrated efficiency greater than 90% in near-infrared and mid-wave infrared. The multi-octave spectral beam combiner concept is realized using an integrated platform with silicon nitride waveguides and silicon waveguides. Simulated bandwidth is shown to be over four octaves, and measured bandwidth is shown over two octaves, limited by the availability of sources.