  We present a new fab-in-the-loop reinforcement learning algorithm for the
design of nano-photonic components that accounts for the imperfections present
in nanofabrication processes. As a demonstration of the potential of this
technique, we apply it to the design of photonic crystal grating couplers
fabricated on an air clad 220 nm silicon on insulator single etch platform.
This fab-in-the-loop algorithm improves the insertion loss from 8.8 to 3.24 dB.
The widest bandwidth designs produced using our fab-in-the-loop algorithm can
cover a 150 nm bandwidth with less than 10.2 dB of loss at their lowest point.
