Low-power low-loss acousto-optic fibre switch

We have previously reported a new design of all-fibre acousto-optic frequency shifter. It is based on a special asymmetric fused taper coupler which in the passive state does not actually couple light at any wavelength: the null coupler. An appropriate flexural acoustic wave imposed on the coupler causes light to couple between the fibres. This device can equally well function as a 2x2 all-fibre optical routing switch: the switch is in the "cross" state when the acoustic wave is on, and is in the "bar" state when the acoustic wave is off. Of particular interest are the switching time, insertion loss, crosstalk and drive power