Birks, T.A., Farwell, S.G., Russell, P.St.J. and Pannell, C.N.
Four-port fibre frequency-shifter with a null taper coupler
Optics Letters, 19, (23), . (doi:10.1364/OL.19.001964).
A prototype of a new design of fiber frequency shifter, based on a special four-port fused taper coupler with a null maximum coupling ratio, is reported. In this coupler the constituent fibers are so dissimilar that the maximum coupling is (ideally) zero. In the presence of a flexural acoustic wave, light is coupled between the fibers, acquiring a frequency shift in the process. Near 100% conversion with 30-dB sideband and carrier suppression is achieved, in an unoptimized device, for just 1 mW of electrical drive power.
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