Wideband mid-infrared group IV photonic devices and platforms

Abstract

Mid-infrared group IV photonics is a field which, by adapting techniques from silicon photonics at visible and near-infrared wavelengths and using mature semiconductor fabrication processes, could establish an enabling technology for a diverse range of applications in numerous areas. In particular, integrated photonic sensors could take advantage of the characteristic absorptions of many chemicals at mid-infrared wavelengths, due to strong fundamental molecular vibrations in this region. Such “lab-on-a-chip” devices would be applied to areas like medical diagnostics and environmental monitoring. To develop complex mid-infrared photonic integrated circuits, a set of core building-block components are required. Currently, the components in mid-infrared group IV photonics are limited to operating at relatively narrow wavelength ranges. This lack of spectral bandwidth is not an issue for some applications, but to unlock the full potential of the field, it is essential to develop wideband devices. The operating wavelength range of mid-infrared devices may be limited by absorptions of the material platform or the geometry of the component; this work considers both to increase the available spectral bandwidth. Silicon-on-insulator waveguides with propagation losses ∼1.5 dB/cm are shown to only support the fundamental mode over an octave of frequency, as an experimental demonstration of a technique that in principle will be applicable to much of the mid-infrared range. Beam splitters were fabricated on silicon-on-insulator platforms with low insertion losses and high performance over a bandwidth of 3.1 − 3.7 μm: multimode interferometers are shown with an insertion loss of <1 dB and imbalance of <0.5 dB; and an insertion loss of ∼0.2 dB was achieved for 50/50 Y-splitters. Further, considering material platforms, silicon membrane devices have been successfully transfer printed onto a high-transparency zinc selenide substrates, to develop waveguides without substrate absorption losses.

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