Opt. Express 22, 12122–12132 (2014)

Fabrication imperfections can play havoc with the performance of high-contrast silicon photonic devices, with even only small deviations in geometry strongly affecting the operation wavelength. Now, Timo Lipka and co-workers from Hamburg University of Technology in Germany report that amorphous silicon devices can be successfully tuned or trimmed after fabrication to the preferred response by using ultraviolet radiation to alter the refractive index of the illuminated structure. The team demonstrated the scheme's utility by using fibre-coupled 405 nm radiation to tune the wavelength response of Mach–Zehnder interferometers and microring resonators. For compact ring resonators, a tuning range of 8 nm was achieved with an accuracy of 20 pm. Trimming adjustments were made at rates of up to 10 GHz. The devices did not show any significant degradation in operational capability after trimming. This post-fabrication passive approach avoids the need to use extra components and feedback circuitry, which are required by integrated, active adjustment schemes that involve microheaters, for example.