Cantilever couplers for intra-chip coupling to silicon photonic integrated circuits

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Abstract
An intra-chip coupling scheme from optical fibers to silicon strip waveguides is demonstrated. The couplers consist of silicon inverse width tapers embedded within silicon dioxide cantilevers that are deflected out-of-plane by residual stress. Deflection angles from 5 to 30 degrees are obtained and controlled by thermal annealing. Butt-coupling from tapered fibers or collimation-coupling from lensed fibers may be employed. The coupling scheme enables direct access to devices on the entire chip surface without dicing or cleaving the chip. Coupling efficiencies of 1.6 dB per connection for TE polarization and 2 dB per connection for TM polarization are achieved. The coupling efficiency shows little wavelength-dependence, with less than 1.6 dB fluctuation over the wavelength range of 1500 nm to 1560 nm.