Passive Approach to Expand the Field of View of Receivers for Free-Space Laser Communications

Abstract

We present an unconventional approach to passively expand the field of view of optical receivers for free-space laser communications. The illumination area, given by the movement of a focused light spot due to different angles of reception, is reduced to a smaller area without expanding the propagation angle of the spot. The working principle of this approach is based on combining a photonic crystal's negative refractive behavior with properly bent crystal boundaries. The device's optical behavior is determined by means of rigorous electromagnetic computation, but the overall working principle of illumination area reduction can be well visualized by the ray trace method. In addition, we estimate the influence of light modulation for high-speed data transmission. Since the discrete structure of photonic crystals only approximates a bent boundary with an arbitrary inclination angle, a slight modification is introduced into the crystal's structure to enable a more flexible design. Although such a modification influences the negative refractive behavior, the function of field-of-view expansion is still verified and confirmed by means of electromagnetic computation.