Abstract
The ultimate goal of silicon photonics development is the monolithical
integration of a photonic layer with optical functions onto silicon IC chips.
This 3-D stacking can be obtained by wafer-to-wafer bonding leading to the
photonic layers to be embedded into the last levels of metalization above
the IC layer. We present a method that takes advantage of this integration
process in order to realize enhanced fiber grating couplers. Indeed, grating
structures are very attractive to couple the light between tiny silicon wires
to the external world, which is dominated by optical fibers. Moreover, the
insertion of a mirror below the grating is a well-known solution to increase
significantly the coupling efficiency. We propose a method to obtain this
bottom mirror by anticipating the grating coupler flip due to the wafer-to-wafer
bonding. To this end, the mirror is formed above the encapsulation layer of
the fiber grating coupler in order to appear below it after the optical layers
integration onto an IC wafer. In this way, the thickness between the grating
and the bottom mirror, which is a very sensitive parameter, remains under
control whatever wafer-to-wafer bonding process tolerances. Experimental results
with one single silicon layer as a bottom mirror exhibit coupling efficiency
up to 69%.
© 2011 IEEE
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