Electrically variable couplers for integrated optical circuits

Theory and optimisation of the design of electrically variable couplers for use in integrated optical circuits is presented. The recognition of the nonmonotonic change in the coupling coefficient of weakly coupled waveguides with change in the physical properties of the individual waveguides is utilised to design couplers that maximise the on/off ratio for a given length. This form of operation of the coupler may be designed to be quite insensitive to operating signal wavelength. Injection of carriers into the semiconductor to change the waveguide refractive index will be the process considered in the paper to produce electronically variable couplers. It is suggested that such couplers would also find convenient application in the design of optical switching matrices.