Multimode y-coupler for heterodyne detection

It is suggested that a multimode waveguide Y-coupler may be used as a coherent multiplexer for heterodyne detection. The dependence of the mixing efficiency upon various parameters such as the asymmetry of the coupler, the intermediate frequency, the modal occupation and the dimensions is analysed and discussed. Numerical calculations indicate that the most important parameter is the symmetry of the Y-junction. For a symmetric Y-coupler, 1 cm long, a mixing efficiency of more than 60 per cent and bandwidth of the order of 50 GHz can be achieved. Experiments with AgC2:AgBr infrared fibers and preliminary experiments with As, Se, thin films seem to support the theory. This may be a first step towards the reali-zation of a coherent detector for integrated optics.