Experimental demonstration of high-Q MRR based on a germanium-on-insulator platform with an yttria insulator in the mid-IR range

Abstract

We experimentally demonstrate an all-pass microring resonator (MRR) based on a Y2O3 BOX germanium-on-insulator (GeOI) platform operating in the mid-IR region. The ring resonator was numerically designed to have a high quality (Q) factor in the 4.18 μm to 4.22 μm wavelength range in the fundamental TE mode. According to our design, the GeOI ring resonator was fabricated by the direct wafer-bonding technology with an yttria (Y2O3) buried oxide layer, which is transparent at the mid-IR region, for the bonding interface and the electron beam lithography. The experimental resonant characteristic was obtained using our fiber-based mid-IR measurement setup. The GeOI single MRR exhibited an extinction ratio (ER) of 15.28 dB and an insertion loss (IL) of 1.204 dB, and the racetrack showed an ER of 22.77 dB and an IL of 0.627 dB. Furthermore, the free spectral range of the device was 5.29 nm, and the loaded Q factor of 94,528 (176,158 of intrinsic Q factor) was extracted by the nonlinear least squares method. We believe this demonstration of our GeOI MRR offers a valuable opportunity to implement multipurpose devices such as optical sensors, switches, and filters in the mid-IR range.