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An ideal photonic integrated circuit for nonlinear photonic applications requires high optical nonlinearities and low loss. This work demonstrates a heterogeneous platform by bonding lithium niobate (LN) thin films onto a silicon nitride (Si₃N₄) waveguide layer on silicon. It not only provides large second- and third-order nonlinear coefficients, but also shows low propagation loss in both the Si₃N₄ and the LN-Si₃N₄ waveguides. The tapers enable low-loss-mode transitions between these two waveguides. This platform is essential for various on-chip applications, e.g., modulators, frequency conversions, and quantum communications.

The mid-infrared spectral region, 2-20 μm, is of great interest for sensing and detection applications, in part because the vibrational transition energies of numerous molecules fall in that region. Silicon photonics is a promising technology to address many of these applications on a single integrated, low-cost platform. Near-infrared light sources, heterogeneously integrated on silicon, have existed for more than a decade, and there have been numerous incorporations of mid-infrared optical devices on silicon platforms. However, no lasers fully integrated onto silicon have previously been demonstrated for wavelengths longer than 2.0 μm. Here we report, to the best of our knowledge, the first quantum cascade lasers on silicon emitting 4.8 μm light, integrated with silicon-on-nitride-on-insulator (SONOI) waveguides, and operating in pulsed mode at room temperature. The broadband and versatile nature of both quantum cascade lasers and the SONOI platform suggests that this development can be expanded to build photonic integrated circuits throughout the near-and mid-infrared on the same chip.

Tremendous scientific progress has been achieved through the development of nonlinear integrated photonics. Prominent examples are Kerr frequency comb generation in microresonators, and supercontinuum generation and frequency conversion in nonlinear photonic waveguides. A high conversion efficiency is enabling for applications of nonlinear optics, including such broad directions as high‐speed optical signal processing, metrology, and quantum communication and computation. In this work, a gallium‐arsenide‐on‐insulator (GaAs) platform for nonlinear photonics is demonstrated. GaAs has among the highest second‐ and third‐order nonlinear optical coefficients, and the use of a silica cladding results in waveguides with a large refractive index contrast and low propagation loss for expanded designs of nonlinear processes. By harnessing these properties and developing nanofabrication with GaAs, a record normalized second‐harmonic efficiency of 13 000% W−1 cm−2 at a fundamental wavelength of 2 µm is reported. This work paves the way for high performance nonlinear photonic integrated circuits, which not only can transition advanced functionalities outside the lab through fundamentally reduced power consumption and footprint, but also enables future optical sources and detectors.

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 ℃ with a slope of 0.24 nm/℃. Wafer-bonding between GaAs and SiO 2 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.

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Here we experimentally demonstrate room temperature, continuous-wave (CW), 2.0 μm wavelength lasers heterogeneously integrated on silicon. Molecular wafer bonding of InP to Si is employed. These hybrid silicon lasers operate CW up to 35°C and emit up to 4.2 mW of single-facet CW power at room temperature. III-V tapers transfer light from a hybrid III-V/silicon optical mode into a Si waveguide mode. These lasers enable the realization of a number of sensing and detection applications in compact silicon photonic systems.

The microscale integration of mid-and longwave-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 to 4.6 µm) with exemplary performance of 0.45 dB/cm at λ = 2.4 µm. 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 ± 1% efficiency and edge couplers with 3.0 ± 0.1 dB loss. This platform has strong potential for multi-functional integrated photonic systems in the mid-IR. arXiv:1905.01380v1 [physics.app-ph] 3 May 2019 have suitable optical transparency [23], and strong optical nonlinearities are also required for the generation or broadening of frequency combs in the mid-IR [15]. While significant Kerr nonlinearity is present in silicon, germanium and chalcogenide materials, they lack intrinsic second-order optical nonlinearities for highly efficient frequency conversion [6,7,24,25] and electro-optic modulation [26].Alternatively, group III-V materials possess many desirable properties for multi-functional integrated photonic systems including a high refractive index, strong second-and third-order optical nonlinearities, and wide optical transparency windows into the LWIR. A practical advantage of these materials is the ability to grow a chemically selective etch stop underneath a high-quality epitaxial device (donor) film, enabling wafer or chip-bonding film transfer techniques for heterogeneous integration [27,28]. This has enabled high-index-contrast III-V waveguides on other substrates such as oxidized silicon and sapphire [29][30][31][32][33]. However, to take full advantage of the broad transparency window supported by III-V semiconductors, it is necessary to pursue alternative geometries such as air-clad suspended waveguides. But even this approach requires a degree of caution, as most materials readily form surface oxide layers that also introduce absorption. Undercut etching has been used to suspend GaAs waveguides engineered for mid-IR difference frequency generation [34]. While this represents a promising step in the development of nonlinear mid-IR photonics with III-V materials, many issues remain, such as the propagation loss in the mid-IR region, atmospheric stabilit...