Spot size measurements for single-mode fibers - A comparison of four techniques

Four techniques for measuring the spot size of a single-mode fiber are compared for accuracy and ease of use. The techniques are based upon imaging of the fiber near fields onto an infrared vidicon, measuring splice loss sensitivity to transverse offset, approximating the fiber far-field radiation pattern as a Gaussian beam, and using the inverse Hankel transform of the far-field radiation pattern. All four methods agree quite well (within 2 percent) considering that the Gaussian fields upon which spot size is based are only an approximation of the actual fields in the fiber. The far-field Gaussian beam technique was found to be the easiest and fastest of the four techniques.