We present silicon-germanium on silicon waveguides as a suitable platform for on-chip supercontinuum generation in the mid-infrared. We report low propagation loss (<0.4dB∕cm) in the 3.5-5 μm range, leading to an octave spanning supercontinuum extending up to 8.5 μm with a high average power of more than 10 mW on-chip. Furthermore, we present the addition of a chalcogenide cladding layer as a simple post-processing technique to fine tune the waveguide dispersion which, in turn, governs the properties of the generated supercontinuum.
The future of exoplanet detection lies in the mid-infrared (MIR). The MIR region contains the blackbody peak of both hot and habitable zone exoplanets, making the contrast between starlight and planet light less extreme. It is also the region where prominent chemical signatures indicative of life exist, such as ozone at 9.7 μm. At a wavelength of 4 μm the difference in emission between an Earth-like planet and a star like our own is 80 dB. However a jovian planet, at the same separation exhibits 60 dB of contrast, or only 20 dB if it is hot due to its formation energy or being close to its host star. A two dimensional nulling interferometer, made with chalcogenide glass, has been measured to produce a null of 20 dB depth, limited by scattered light. Measures to increase the null depth to the theoretical limit of 60 dB are discussed.
Since many important molecules have strong “fingerprints” in the mid-infrared (mid-IR, between 3μm and 15μm), this wavelength spectrum is currently gaining significant attention for applications ranging from pollution detection, quality control in the food industry, early cancer diagnosis, security and safety [1, 2]. Molecular sensing devices in the mid-IR are currently being developed and are in the process of commercialization. An appealing approach is to create molecular sensing devices in the mid-IR based on low cost integrated mid-IR chips. A key building block is a high brightness integrated broadband light source that would allow the detection of several molecules characterized by distinct absorption lines in parallel. Such an integrated broadband source, referred to as a supercontinuum source, has been already demonstrated in the mid-IR on a chalcogenide chip . However, demonstrating mid-IR supercontinuum on group IV materials, in order to exploit the advantages of reliable CMOS fabrication technology, remains a challenge. So far, numerous CMOS-compatible supercontinuum sources have been demonstrated in silicon nitride-on-insulator [4, 5], silicon-on-insulator [6, 7], silicon germanium-on-insulator  and silicon-on-sapphire platforms . However, these sources are limited up to 3.5µm and 6µm due to the absorption in the silica and sapphire substrate, respectively. More recently, the silicon germanium-on-silicon platform [10, 11], emerged as an attractive platform for mid-IR photonics, with transparency potentially extending up to 15μm depending on the Ge content .
Here we report experimentally the first octave spanning supercontinuum generation from a SiGe waveguide in the actual mid-IR with 5mW on-chip power exceeding that produced so far in any other Si-based platform (0.15mW in SiGe/SiO2  and ~1mW in silicon-on-sapphire ). Our 4.25µm x 2.70µm cross-section air-clad SiGe-on-Si waveguide has been designed and manufactured to achieve single mode operation at 4µm, low anomalous dispersion and strong fundamental TE mode confinement in the core nonlinear material (~96% at 4μm). Losses as low as 0.4dB/cm were measured between 3.8 and 5µm. The achieved supercontinuum covered more than an octave between 2.95 and 6.0µm was generated by pumping a 7cm long waveguide with ~ 200fs pulses at 4.15µm and 63MHz repetition rate, as delivered by a Miropa-fs optical parameter amplifier. These results were supported by simulations and the related generation of a high brightness supercontinuum establishes silicon germanium-on-silicon as a promising platform for integrated nonlinear photonics in the mid-IR, with the potential to extend the operating range to beyond 8μm.
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In this paper we present high stimulated Brillouin scattering (SBS) gain in a chip-scale device. Narrowband gain of >50 dB is achieved in a chalcogenide waveguide with a bandwidth of ~10 MHz. Such a large gain is promising for on-chip amplification for the realization of integrated structures with many optical components, as well as for RF photonic and optical signal processing applications. We harness the highly efficient SBS interaction in the photonic chip to realize low-power RF filters, phase shifters and delay lines. Through the concept of RF interference an enhancement in the delay by almost a factor of 6 compared to pure SBS-based slow light is observed, making this technology promising for lowpower-budget RF photonic systems.
Photonic integrated circuits are established as the technique of choice for a number of astronomical processing functions due to their compactness, high level of integration, low losses, and stability. Temperature control, mechanical vibration and acoustic noise become controllable for such a device enabling much more complex processing than can realistically be considered with bulk optics. To date the benefits have mainly been at wavelengths around 1550 nm but in the important Mid-Infrared region, standard photonic chips absorb light strongly. Chalcogenide glasses are well known for their transparency to beyond 10000 nm, and the first results from coupler devices intended for use in an interferometric nuller for exoplanetary observation in the Mid-Infrared L’ band (3800-4200 nm) are presented here showing that suitable performance can be obtained both theoretically and experimentally for the first fabricated devices operating at 4000 nm.