J. Eur. Opt. Soc. Rap. Publ. 7, 12033 (2012)

Silicon photonic devices are usually constructed from crystalline silicon owing to its high material quality and low optical absorption in the near- and mid-infrared, but scientists in Germany have now shown that a wide variety of low-loss passive devices can be made using thin films of hydrogenated amorphous silicon. Timo Lipka and co-workers from Hamburg University of Technology successfully fabricated waveguides, power-splitters, tapers, ring resonators and Mach–Zehnder interferometers using plasma-enhanced chemical vapour deposition. The researchers say that a low defect density was achieved by using a moderate deposition temperature of between 250 and 300 °C. Thin films of amorphous silicon were deposited onto substrates made from a variety of materials including Pyrex, BK-7 glass and silicon-dioxide-covered silicon wafers. Measurements indicate that at a wavelength of 1,550 nm, hydrogenated amorphous silicon rib waveguides had an average propagation loss of ∼2 dB cm−1, with the best devices reaching ∼1 dB cm−1. In addition, ring resonators with a 10-micrometre radius were demonstrated to have a Q-factor of up to 7,500, and 50:50 power-splitters were used to create Mach–Zehnder interferometers with interference fringes up to 25 dB deep. In the future, it is thought that such a-Si:H devices may suit on-chip integration and prove useful for applications in telecommunications and sensing.