Analysis of single-mode fused tapered fibre couplers

A fabrication technique for fused taper couplers is described. Coupling coefficients are calculated for fibres with raised, depressed and matched refractive-index profiles, and optimum V-values for coupling are found. These suggest a shorter coupler geometry differing from the biconical taper. The high taper loss in depressed cladding fibres is shown to correspond to the presence of the leaky LP01-mode. The wavelength response has been measured for various couplers and fitted theoretically. Coupling periods as small as 12 nm demonstrate potential use for couplers as wavelength-division multiplexers. The dependence of coupling on the refractive index of the surrounding medium has been measured. Thus couplers have also demonstrated potential as temperature sensors and optical switches.