Defocal Lens Assembly for Multi-Element Full-Duplex Free Space Optical Transceiver

Free-space optical communication presents a significant opportunity for next generation wireless communication and networking with high modulation speed, broad bandwidth, secure and direct line-of-sight link, and unlicensed spectrum. Multielement free-space optical transceivers can be used to improve the overall optical link performance as they offer spatial reuse, beam steering, and tolerance to mobility. In this paper, we explore the design and analysis of a fixed effective focal length lens system and the optical coupling efficiency that can be maximized by defocusing the beam footprint on the receiver side for a full-duplex free-space optical communication link. We propose a lens system with effective focal length of 49.5 mm, F/2, and field-of-view of 28° to collimate the transmit beam onto the receiver plane. We further present how to maximize the optical coupling efficiency and vibration tolerance by introducing small defocusing length between transmitter and lens assembly.