Culverhouse, D.O., Farwell, S.G., Birks, T.A., Russell, P.St.J. and Pannell, C.N.
High-performance four-port acousto-optic frequency shifter at 1.55µm using standard single-mode telecommunications fibre.
In, Conference on Lasers and Electro-Optics (CLEO '95), Baltimore, US,
21 - 26 May 1995.
If a four-port fused-taper coupler is constructed from dissimilar fibers, the maximum splitting ratio can be close to zero over a broad spectral band. As previously shown, such a null coupler can be used to form an effective four-port acousto-optic frequency shifter. In Ref. 1, two dissimilar nonstandard fibers were used. Here we report the successful construction of a null coupler made by using standard telecommunications fiber. The procedure involves pretapering one of an identical pair of fibers to provide the necessary dissimilarity. In this way the device can be constructed entirely from one fiber type with four identical ports, and it can be made compatible with any existing network. Our present device used standard 125µm single-mode telecommunications fiber throughout, for operation at a wavelength of 1.55µm
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