Nondestructive measurement of the degree of fiber fusion in fused tapered couplers

Summary form only given. The enormous diversity of optical signal processing schemes available with fused tapered coupler devices, either in the passive or active state, explains why these devices have become one of the essential building blocks of fiberoptic systems. This large diversity of applications also justifies why it is important to be able to fully characterize this range of devices. Depending on the required bandwidth of the coupler, the waist region of the coupler may vary between 40 /spl mu/m diameter for large bandwidth splitters to 2 /spl mu/m diameter for grating-assisted filters, and depending on the polarization insensitivity required of the signal processing, the coupler´s waist cross section may vary between circularly fused to dumbbell-shaped cross section. The degree of fiber fusion of the waist region of a fused coupler therefore strongly influences the output characteristics of these devices in terms of polarization sensitivity and coupling coefficients, and any characterization method must be able to be function within this wide range of parameters. Using the acousto-optic effect, it is possible to nondestructively determine the degree of fiber fusion at a given position along a fiber coupler.