Temperature-Shifted White-Light Interferometry for Equalization of a Fiber Coupler to Near-Zero Path Length Difference

A method for equalizing the path lengths of two arms of an optical fiber coupler is presented as a critical step towards construction of a high-resolution 3-D interferometric imaging system. Based on white-light interferometry (WLI), the technique combines absolute measurement capability with the ability to accurately measure near-zero path length differences. A controlled temperature increase in one arm of the coupler generates a shift in the WLI measurement, allowing the fibers to be polished to near-equal lengths. The technique is demonstrated to equalize the fiber lengths to better than 0.6 mum.