Preliminary Evaluation Of A 144 X 144 Holographic Interconnection System

We report on the design and experimental characterization of an holographic deflection system which enables slowly reconfigurable point-to-point interconnections. In this system collimated beams emerging from single-mode fibres at wavelength λl are deflected by a matrix of thin photothermoplastics holograms, recorded at λ2. We use presently Fresnel holograms for connecting two 12 x 12 2D arrays (with a 4 mm separation between neighbouring channels). Besides the improvement of the cyclability of the thermoplastics, the main problem to overcome are the aberrations (mainly astigmatism), due to high λ1/λ2 ratio (> 2). A suitable choice of both recording and reconstruction configurations allows to minimize astigmatism and other aberrations have been evaluated with a ray-tracing program. The predictions are in good agreement with the following experimental datas : λ1 = 1,334 nm, λ2 = 647 nm, mean deflection angle of 23°, input/output distance of 50 cm, maximum connection loss into a 600 μm silica fibre 16.5 dB (10 dB for diffraction efficiency, 5 dB for coupling efficiency and 1.5 for the aberrations). The crosstalk is lower than - 29 dB. Improvements allowing to achieve larger capacity and lower wavelength sensitivity are suggested.