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Conical refraction multiplexing for free-space optical communications

Conical refraction (CR) is proposed to increase the channel capacity for free space optical communication applications. We present the first investigations of cascaded CR with a linearly polarized input beam and experimentally prove that two oppositely oriented consecutive identical biaxial crystals perform a forward-backward transformation of the incident light beam. This forward-backward transformation is reported for different input beams with Gaussian, elliptical and angularly modulated transverse intensity profiles and is the basis for our novel proposal on multiplexing and demultiplexing of optical beams. We present experimental proof of usefulness and perspective of the CR multiplexing technique by increasing in one order of magnitude the channel capacity at optical frequencies. The technique is applicable to any wavelength in optical and telecommunication bands. It can be also properly upgraded with the WDM technique.