| Summary: | Prototype silicon photonic circuits in a silicon-on-insulator (SOI) wafer fabricated using a CMOS-based single layer process, are thoroughly characterized. Thousands of devices were fabricated on a single 200 mm diameter wafer using deep UV lithography at the IMEC silicon photonics foundry. The devices studied integrate three key elements: i) input/output grating couplers, ii) waveguides, and iii) microcavities. The photonic crystal cavities are symmetrically coupled to input and output single mode channel waveguides, which couple light into tapered waveguides that are terminated by two-dimensional photonic crystal gratings couplers.
The grating coupler efficiencies and bandwidths are studied independently from the other device components, both experimentally and by simulations, using free-space optics. At a fixed angle of incidence, light over a bandwidth of approximately 14 nm (TE) and 30 nm (TM) is coupled from grating to grating, in both experiments and simulations. The centre frequency of this coupling spectrum is tuned by varying the angle of incidence on the grating, by coating the grating with photoresist, and by varying the size of the holes that form the grating.
The maximum net single-grating coupling efficiencies are measured to be 15% (26%) for TE (TM) coupling. Taking into account the limited aperture of the collection optics, and aberrations of the input coupling lenses, these measured net efficiencies are reasonably consistent with simulated true efficiencies of 21%(49%) found using Lumerical FDTD Solutions and MODE Solutions commercial software.
Resonant transmission measurements from free space, via an input grating, through the complete integrated photonic circuit, including the photonic crystal microcavity, and off-chip via an output grating are measured for a number of different cavities. The transmission of light from the end of one tapered waveguide, through the cavity, to the end of the other tapered waveguide is found to be ~10%. The maximum microcavity quality factor measured is ~ 5000.
This work demonstrates that fully integrated photonic circuits can be successfully fabricated using IMEC's CMOS foundry service. It further shows that useful overall coupling efficiencies can be realized using free space optics, which will be useful for probing such circuits when they are placed inside optical cryostats. === Science, Faculty of === Physics and Astronomy, Department of === Graduate
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