Empirical Analysis of Polarized Coherent Signal Loss from a Free Space Optical Communication Experimental Setup

The rapid growth of optical communications in space is driven by the need for higher data transmission rates to support the increasing demands of space missions. Our research focuses on a coherent free space optical communication (FSOC) setup, which serves as a framework for the development and experimental setup of optical communications hardware. By conducting an empirical examination of the propagation loss of coherent signals in FSOC systems, this study underscores the crucial influence of optical signal characteristics such as modulation schemes, polarization, and wavelength on system performance. With a 40GHz receiving bandwidth optical modulation analyzer (OMA), our experiments demonstrate a 3.5 dB loss of free space channel in lab for QPSK, 16QAM, 16APSK coherent optical signals at 1550 nm, regardless of polarization state (Linear and Circular). 1m space separation is set up between transmitter and receiver. This paper describes and characterizes a laboratory experiment setup and demonstrates how coherent signaling can leverage its inherent advantages to counteract the challenges of signal degradation in free-space optical links, thereby improving data rates and signal integrity over vast distances.