A Silicon Photonic 32-Input Coherent Combiner for Turbulence Mitigation in Free Space Optics Links

TL;DR

This paper presents a silicon photonic integrated circuit capable of coherently combining 32 optical inputs into a single output to mitigate turbulence effects in free space optical links, demonstrating high bandwidth and integration.

Contribution

It introduces a low-loss, monolithically integrated 32-input coherent combiner PIC fabricated on SOI, advancing turbulence mitigation in free space optics.

Findings

Successfully combines 32 inputs with high bandwidth

Monolithic integration of 31 MZIs and photodetectors

Potential for scaling to 64 inputs and reducing losses

Abstract

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