Regular papers

Low-loss multilayer compatible a-Si:H optical thin films for photonic applications

Institute of Microsystem Technology, Hamburg University of Technology, 21073 Hamburg, Germany

^* timo.lipka@tu-harburg.de

Received: 7 May 2012
Revised: 20 July 2012

Abstract

This paper reports about hydrogenated amorphous silicon which can be employed as low-loss optical material for small footprint and cost-effective photonic integrated circuits. Basic waveguides, photonic wire based couplers, Mach-Zehnder interferometers, ring resonators and Mach-Zehnder assisted ring resonators were designed, fabricated, and optically characterised. The propagation loss of rib and photonic wire waveguides were determined to be 2 dB/cm and 5.3 dB/cm, respectively. The 90°bending losses of 5 µm curved photonic wires were determined to be 0.025 dB/90°. Three-dimensional tapers, which were fabricated without additional etching steps and were deposited on top of the fabricated photonic wires showed a net coupling loss of 4 dB/port. Multimode 3 dB-splitters were systematically investigated resulting in 49-51% splitting ratios. Mach-Zehnder interferometers that were realised with these splitters showed interference fringe depths of up to 25 dB for both polarisations. Compact ring resonators with 10 µm radius implemented as notch filters and in Mach-Zehnder coupled configurations provided extinction ratios of ≥20 dB and Q-factors up to 7500.