Metalens wide-angle receiver for free space optical communications

Receiver field of regard is one of the major problems for free space optical (FSO) communications. Drift or vibrations in transceiver orientations reduces effective communication time. The methods implemented to overcome this limitation, often require bulky optical and complex mechanical assemblies with feedback control, that are not suitable for long run operation in an airborne system. In this paper, we propose a novel receiver system that can effectively reduce the impact of pointing errors. The system is composed of two metalenses and one off-the-shelf conventional lens. The first metalens focuses optical beam incident at different angles on the aperture, at different locations on focal plane. The second metalens is placed on the focal plane of first metalens. After passing through the second metalens, the beams become parallel to optical axis of the receiver optical system. The parallel beams are collected by a suitable off-the-shelf aspheric lens and focused back on single detector that sits on a point on the optical axis. The system is designed and analyzed by physical optics theory. With 0.5 mm receiver aperture and 50 mm diameter aspheric lens, Zemax simulation shows that the system can collect +/-5-degree incident angle with detector diameter of 273 mu m. COMSOL frequency domain simulation with smaller diameter beam shows that the efficiency of the 2 metalens system is about 80%. Efficient metalens design and beam compression at detector plane are two key features of the proposed system. The system relaxes the strict requirement of aligning the transmitter and receiver unit in FSO communication.