Optical EngineeringHolographic 4x4 star-coupler in silver-halide sensitized gelatin
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Star couplers are fanin-fanout devices with each input beam split into several output beams with arbitrary intensities traveling at different angles. We demonstrate a 4 x 4 holographic star coupler fabricated as multiplexed holographic gratings in silver-halide sensitized gelatin (SHSG) derived from Agfa-Gevaert plates. The processing formula is modified to achieve high diffraction efficiency and an acceptable modulation transfer function within the region of spatial frequencies of interest. The holographic characteristics of the processed SHSG are measured. The required gratings are recorded simultaneously to avoid reciprocity law failure, which occurs in SHSG as well. The gratings are recorded to ensure equal grating strength, which gives an acceptable intensity ratio between the output beams. The star coupler is examined for use as a broadcast medium in fiber-based local area networks (LAN5), where relatively high loss and inhomogeneity between the outputs could be tolerated.