Mid-IR silicon photonics

Abstract

Mid-IR silicon photonics is attracting interest due to a host of potential applications. As the mid-IR covers a wide range of wavelengths, there are several material platforms that are being investigated. Three of them will be presented in more details: silicon-on-insulator (SOI), suspended Si and Ge on Si. A number of passive and active devices have been demonstrated up to a wavelength of 4 µm, such as low loss SOI waveguides (rib, strip, slot) [1, 2], efficient couplers, filters, multiplexers and spectrometers [3], as well as modulators and detectors [4]. To extend transparency of SOI waveguides, bottom oxide cladding can be removed. A new technique based on subwavelength gratings has been developed [5] and a library of passive devices have been designed and fabricated. This approach involves only one dry etch step and offers more mechanically robust structures. Successful realisation of sub dB/cm waveguides and low loss bends, MMIs, MZIs, directional and grating couplers in the mid-IR will be presented. Ge on Si material can have larger transparency range than suspended Si [6]. Sub dB/cm waveguides and low loss passive devices in this platform have been demonstrated [7, 8], as well as all optical modulation [9] and two photon absorption measurements [10]. Finally a theoretical investigation free carrier optical modulation in Ge has been carried out [11].