Active-fiber star coupler that uses arrays of microlenses and liquid-crystal modulators

An active-fiber star coupler that uses arrays of N x N microlenses and liquid-crystal modulators is presented. A simplified implementation of this device uses an 8 x 8 array of Fresnel microlenses fan out an incident beam into 64 focused spots (an 18 dB fan-out loss); on-off capability (270:1 extinction ratio) at each element is provided by liquid-crystal spatial light modulators. A row of focused spots is coupled into an array of 1 x 8 multimode fibers with a measured excess loss of 12 dB along each path (with an estimated overall loss of 30 dB in an 8 x 8 device). A modification of this device that is capable of wavelength selection at individual output fibers is proposed for wavelength division multiplexing applications.