Lasing is experimentally demonstrated in a direct bandgap GeSn alloy, grown directly onto Si(001). The authors observe a clear lasing threshold as well as linewidth narrowing at low temperatures.

/pdf/lasing-in-direct-bandgap-gesn-alloy-grown-on-si-515b98x7i8.pdf

Lasing in direct-bandgap GeSn alloy grown on Si

Recent developments in chip-based nonlinear photonics offer the tantalizing prospect of realizing many applications that can use optical frequency comb devices that have form factors smaller than 1 cm3 and that require less than 1 W of power. A key feature that enables such technology is the tight confinement of light due to the high refractive index contrast between the core and the cladding. This simultaneously produces high optical nonlinearities and allows for dispersion engineering to realize and phase match parametric nonlinear processes with laser-pointer powers across large spectral bandwidths. In this Review, we summarize the developments, applications and underlying physics of optical frequency comb generation in photonic-chip waveguides via supercontinuum generation and in microresonators via Kerr-comb generation that enable comb technology from the near-ultraviolet to the mid-infrared regime. This Review discusses the developments and applications of on-chip optical frequency comb generation based on two concepts—supercontinuum generation in photonic-chip waveguides and Kerr-comb generation in microresonators.

Photonic-chip-based frequency combs

The growing maturity of integrated photonic technology makes it possible to build increasingly large and complex photonic circuits on the surface of a chip. Today, most of these circuits are designed for a specific application, but the increase in complexity has introduced a generation of photonic circuits that can be programmed using software for a wide variety of functions through a mesh of on-chip waveguides, tunable beam couplers and optical phase shifters. Here we discuss the state of this emerging technology, including recent developments in photonic building blocks and circuit architectures, as well as electronic control and programming strategies. We cover possible applications in linear matrix operations, quantum information processing and microwave photonics, and examine how these generic chips can accelerate the development of future photonic circuits by providing a higher-level platform for prototyping novel optical functionalities without the need for custom chip fabrication. The current state of programmable photonic integrated circuits is discussed, including recent developments in their building blocks, circuit architectures, electronic control and programming strategies, as well as different application spaces.

https://biblio.ugent.be/publication/8677857/file/8677861.pdf

Programmable photonic circuits.

Recent developments in chip-based photonic quantum circuits have radically impacted quantum information processing. However, it is challenging for monolithic photonic platforms to meet the stringent demands of most quantum applications. Hybrid platforms combining different photonic technologies in a single functional unit have great potential to overcome the limitations of monolithic photonic circuits. Our Review summarizes the progress of hybrid quantum photonics integration, discusses important design considerations, including optical connectivity and operation conditions, and highlights several successful realizations of key physical resources for building a quantum teleporter. We conclude by discussing the roadmap for realizing future advanced large-scale hybrid devices, beyond the solid-state platform, which hold great potential for quantum information applications. The Review summarizes the progress of hybrid quantum photonics integration in terms of its important design considerations and fabrication approaches, and highlights some successful realizations of key physical resources for building integrated quantum devices, such as quantum teleporters, quantum repeaters and quantum simulators.

https://www.nature.com/articles/s41566-020-0609-x.pdf?proof=t

Hybrid integrated quantum photonic circuits.

A topical review of numerical and experimental studies of supercontinuum generation in photonic crystal fiber is presented over the full range of experimentally reported parameters, from the femtosecond to the continuous-wave regime. Results from numerical simulations are used to discuss the temporal and spectral characteristics of the supercontinuum, and to interpret the physics of the underlying spectral broadening processes. Particular attention is given to the case of supercontinuum generation seeded by femtosecond pulses in the anomalous group velocity dispersion regime of photonic crystal fiber, where the processes of soliton fission, stimulated Raman scattering, and dispersive wave generation are reviewed in detail. The corresponding intensity and phase stability properties of the supercontinuum spectra generated under different conditions are also discussed.

Supercontinuum generation, photonic crystal fiber

We demonstrate the generation of a stable supercontinuum in a 1-cm-long hydrogenated amorphous silicon waveguide by pumping the wire with 1950 nm picosecond pulses in the anomalous dispersion regime. The supercontinuum extends from 1460 to 2485 nm for a coupled peak power of 28.1 W.

/pdf/mid-infrared-to-telecom-band-stable-supercontinuum-1q44sv3474.pdf

Mid-infrared to telecom-band stable supercontinuum generation in hydrogenated amorphous silicon waveguides

In this paper we present our recent work on mid-infrared photonic integrated circuits for spectroscopic sensing applications. We discuss the use of silicon-based photonic integrated circuits (either based on silicon-on-insulator or germanium-on-silicon waveguide circuits) for this purpose and detail how a variety of optical functions in the mid-infrared besides passive waveguiding and filtering can be realized, either relying on nonlinear optics or on the integration of other materials such as GaSb-based compound semiconductors, GeSn epitaxy and PbS colloidal nanoparticles. The integration of photodetectors resulting in fully integrated mid-IR spectrometers, semiconductor laser sources and nonlinear optics based spectral translators between the telecommunication wavelength range and the mid-infrared are discussed.

/pdf/mid-ir-heterogeneous-silicon-photonics-1zbiyq90pf.pdf

Mid-IR heterogeneous silicon photonics

We present an inverse design method making waveguides with high performance and high robustness to fabrication errors. As an example, we show a 1-to-4 mode converter with > −1.5 dB conversion efficiency under geometric variations within fabrication tolerances.

Inverse Geometric Design of Fabrication-Robust Nanophotonic Waveguides

We demonstrate SiN-based passive waveguides with ultra-low thermo-optic effect, based on a novel waveguiding mechanism that confines light in the lower index of refraction. We demonstrate broadband operation over at least 200nm, with less than 0.01% change in the index over 200 degrees.

SiN-based waveguides with ultra-low thermo-optic effect

We demonstrate robust mode conversion up to the 12th higher order mode in silicon waveguides by using an optimized adiabatic directional coupler and using subwavelength waveguides. The conversion efficiency is better than −1.5 dB over a 75 nm bandwidth and tolerating ±30 nm fabrication variations. © 2019 The Author(s)

Utsav D. Dave

Papers

Mid-infrared to telecom-band stable supercontinuum generation in hydrogenated amorphous silicon waveguides

Mid-IR heterogeneous silicon photonics

Inverse Geometric Design of Fabrication-Robust Nanophotonic Waveguides

SiN-based waveguides with ultra-low thermo-optic effect

Efficient Conversion to Very High Order Modes in Silicon Waveguides