  A photonic integrated circuit (PIC) for the coherent combination of 32 input
optical signals into a single output fiber is reported. The PIC was fabricated
using a low-loss thick silicon-on-insulator (SOI) process and packaged with 32
input and 1 output fibers. The basic building block is a 2x2 Mach-Zehnder
interferometer (MZI) with an external (to the MZI branches) and an internal
thermal phase shifter, and a bandwidth in excess of 80 kHz. The PIC
monolithically integrates 31 MZIs and 31 germanium photodetectors, and is
suitable in principle for turbulence mitigation in LEO-ground and horizontal
free space optics links. Improvements to the device for the coherent
combination of 64 inputs and for the reduction of insertion losses are also
discussed
