Off-axis catadioptric fisheye wide field- of-view optical receiver for free space optical communications

We propose a wide field-of-view optical receiver design based on a fisheye lens and an off-axis catadioptric structure for free-space optical communications. The design utilizes a novel fisheye lens group to compress a wide field angle into a narrow field angle and produce the appropriately collimated light that can effectively be coupled into the following aperture of a catadioptric telescope. An off-axis catadioptric telescope with aspheric surface mirrors is designed to compress the incident beam spot size, compensate for the high order optical aberrations and eliminate light loss due to an obstruction. The parallel exit rays are reflected on a double-level tracking mechanism by feeding the position signal from a quadrant detector to correct the pointing error and optimize the coupling efficiency into an optical fiber. The final wide field-of-view optical receiver design is presented along with the evaluation of optical performance results and tracking characteristics. The proposed optical receiver not only can provide a 60-deg wide field-of-view to expand the tracking range, but also mitigates optical aberrations to improve the tracking accuracy for free space optical communication systems in a turbulent atmosphere. Subject terms: free space optical communications; fisheye; wide-field-of-view; optical receiver; optical aberration. 1 Introduction An optical receiver is a key element in a long-haul free space optical (FSO) communication system. It combines the advantages of the high transmission capacity enabled by optical transmission device technologies and the inherent flexibility of wireless communication systems. 1,2 Because of the small beam divergence and the ultra long distance, optical links are strongly affected by atmospheric turbulence. Hence, acquisition, tracking, and pointing (ATP) mechanisms should be incorporated into optical receiver of such an FSO system. 3 However, the narrow field of view (FOV) and optical aberrations of the optical receiver increase the size of the tracking mechanism and degrade the tracking performance of the FSO communication systems. Therefore, it is necessary to analyze and investigate a wide FOV optical receiver in order to improve the performance of FSO communications in atmospheric turbulence.