Modified design of photonic crystals with negative refractive behavior to expand the field-of-view of optical receivers

An unconventional approach to passively expand the field-of-view of optical receivers for free-space laser communications is presented. Our device exploits the negative refractive behavior exhibited by photonic crystals. The particularity of this approach is seen by placing the device behind a lens, where the illumination area given by the ensemble of the focal spots of light received at different angle within a given angular range is reduced to a smaller area without any expansion in the propagation angle of the light for each individual spot. The fundamental idea of this approach is based on a combination of the crystal's negative refractive behavior and properly bended crystal boundaries interfacing with air. In a sample calculation, the reduction of the illumination area is estimated by the ray trace method and the preservation of propagation angles of the incoming beams is confirmed. Since the discrete structure of photonic crystals only approximates a bended boundary with an aribtrary inclination angle, a slight modification is introduced into the crystal's structure to allow 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.