  In this paper we proposed a novel overlay alignment method using two sets of
identical photonic crystals (PhCs). In this method the reflection or
transmission spectrum of the two overlaid photonic crystals is measured to help
wafer tilt, yaw rotation, and translation aligning. The initial testing results
with two 1D photonic crystals and analysis of the alignment accuracy are
presented. This method is particularly useful in building photonic crystal
stacks with nanoimprint lithography (NIL).
