Improving lasercom terminals by reducing optical nonlinearities via hollow-core optical fibers

Hollow-Core Photonic Crystal Fibers (HC-PCFs) represent an innovative technology that alters the cross section of an optical fiber, guiding light via its photonic bandgap rather than through traditional total internal reflection. This method minimizes the overlap between the optical mode and the silica core, significantly reducing non-linear issues encountered in high peak power modulation formats. These issues currently restrict the data rate, range, and modulation options in free-space laser communication links due to the high launch peak powers from optical terminals. Traditional attempts to lessen non-linear impairment constrain optical terminal's fiber length. Such re-designs often leave critical components, like High Power Optical Amplifiers (HPOA), vulnerable to environmental factors, thereby decreasing system reliability. Moreover, they mandate an individual HPOA for each aperture, thus limiting system flexibility. Nonlinearities also limit the utilization of multiple wavelength channels, a technique that could otherwise improve communication link throughput. In this paper, we propose and investigate a solution to these challenges by replacing the Single-Mode Fiber (SMF) post-HPOA with HC-PCFs. Guiding high peak power light through a hollow-core fiber instead of an SMF mitigates nonlinearities. This decreases the system's Bit Error Rate (BER) for a given optical power and enhances the overall system reach by 10 dB compared to an SMF system with nonlinear constraints. Additionally, we present an analysis of various commercial HC-PCFs, describe a splicing method along with insertion loss for each type of hollow core fiber, and report on an experiment conducted to quantify the improvement in laser communication links offered by HC-PCFs.