Multiplexing and demultiplexing using an AlGaAs nonlinear directional coupler

There has been a considerable amount of interest in utilising the nonresonant, third order, nonlinearity of optically transparent materials to implement all-optical switching and modulation operations. Such all-optical devices have considerable potential due to the instantaneous nature of the Kerr nonlinearity which makes possible ultrafast switching devices, which in turn would increase the usable bandwidth of optical fibres. In particular, devices formed in the AlGaAs material system have been shown to have several advantages, namely; they have a relatively large nonlinear coefficient, low propagation losses and can be operated in the 1.55 μm spectral region. The resulting devices are compact and resistant to environmental perturbations. To date several individual components have been demonstrated: the nonlinear directional coupler (NLDC), the nonlinear Mach-Zehnder interferometer and the X-junction. In order to be of practical interest the more complex functions of multiplexing and demultiplexing need to be demonstrated. These operations involve both a control and a signal pulse. In the implementations discussed a strong control pulse, with either a different polarisation, or wavelength, is used to modulate a weak signal pulse. This corresponds to a strong local pump source adding, or dropping, data from a data stream