Athermal and wavelength-trimmable photonic filters based on TiO2-cladded amorphous-SOI.

Large-scale integrated silicon photonic circuits suffer from two inevitable issues that boost the overall power consumption. First, fabrication imperfections even on sub-nm scale result in spectral device non-uniformity that require fine-tuning during device operation. Second, the photonic devices need to be actively corrected to compensate thermal drifts. As a result significant amount of power is wasted if no athermal and wavelength-trimmable solutions are utilized. Consequently, in order to minimize the total power requirement of photonic circuits in a passive way, trimming methods are required to correct the device inhomogeneities from manufacturing and athermal solutions are essential to oppose temperature fluctuations of the passive/active components during run-time. We present an approach to fabricate CMOS backend-compatible and athermal passive photonic filters that can be corrected for fabrication inhomogeneities by UV-trimming based on low-loss amorphous-SOI waveguides with TiO2 cladding. The trimming of highly confined 10 µm ring resonators is proven over a free spectral range retaining athermal operation. The athermal functionality of 2nd-order 5 µm add/drop microrings is demonstrated over 40°C covering a broad wavelength interval of 60 nm.

Hydrogenated amorphous silicon photonic device trimming by UV-irradiation.

A method to compensate for fabrication tolerances and to fine-tune individual photonic circuit components is inevitable for wafer-scale photonic systems even with most-advanced CMOS-fabrication tools. We report a cost-effective and highly accurate method for the permanent trimming of hydrogenated amorphous silicon photonic devices by UV-irradiation. Microring resonators and Mach-Zehnder-interferometers were utilized as photonic test devices. The MZIs were tuned forth and back over their complete free spectral range of 5.5 nm by locally trimming the two MZI-arms. The trimming range exceeds 8 nm for compact ring resonators with trimming accuracies of 20 pm. Trimming speeds of ≥ 10 GHz/s were achieved. The components did not show any substantial device degradation.