Nondestructive determination of cladding thickness in D-fibers

We present a simple nondestructive method for determining the cladding thickness, to the fiber flat, in D-shaped optical fibers. Here, the thickness of the cladding is determined by immersing a section of the fiber in a thermooptic oil and monitoring the power transmission as a function of the temperature of the oil. Fitting the response to theoretical models provides an accurate determination of the cladding thickness.