Novel multifocus tomography for measurement of microstructured and multicore optical fibers

Abstract

A novel multifocus tomographic algorithm for reconstructing an optical fiber’s cross sectional refractive index distribution from transverse projections is described. This new algorithm is validated against measurements of both microstructured and multicore optical fibers, which were not previously measurable. Optical fiber tomographic measurements recently made by several research groups using different technologies have all suffered from the same limitation, namely that typical fiber diameters (several hundred microns) exceed the imaging depth-of-field (approximately one micron) by several orders of magnitude. The new algorithm combines data acquired from a multiplicity of focal planes to overcome this limitation, yielding measurements with extremely fine spatial resolution over large transverse dimensions, thereby providing the first-ever high quality measurements of microstructured and multicore fibers. This new measurement approach is broadly applicable to any tomographic problem in which the depthof- field is greatly exceeded by the transverse dimension of the specimen. Many types of transverse optical fiber measurement technologies, including interference microscopy, quantitative phase microscopy (QPM), residual stress measurement, differential interference contrast (DIC) microscopy, and spontaneous emission tomography will benefit from this new algorithm, which will greatly facilitate characterization of optical fibers for high-power applications.