Microinterferometric optical phase tomography for measuring small, asymmetric refractive-index differences in the profiles of optical fibers and fiber devices

Abstract

A new technique, microinterferometric optical phase tomography, is introduced for use in measuring small, asymmetric refractive-index differences in the profiles of optical fibers and fiber devices. The method combines microscopy-based fringe-field interferometry with parallel projection-based computed tomography to characterize fiber index profiles. The theory relating interference measurements to the projection set required for tomographic reconstruction is given, and discrete numerical simulations are presented for three test index profiles that establish the technique's ability to characterize fiber with small, asymmetric index differences. An experimental measurement configuration and specific interferometry and tomography practices employed in the technique are discussed.

Novel multifocus tomography for measurement of microstructured and multicore optical fibers

“…Over the past several years, various research groups [1][2][3][4][5][6][7][8][9] have reconstructed the complete two-dimensional cross section of an optical fiber sample from one-dimensional transverse projections acquired at a multiplicity of fiber angular orientations. The inverse Radon transform 10 , or a mathematically analogous algorithm, is used to synthesize the onedimensional projections into a single two-dimensional cross section.…”

“…Although only transverse interferometry 6 results are shown here, the new algorithm is broadly applicable to a wide variety of transverse optical fiber measurement technologies [1][2][3][4][5][7][8][9] . Figure 1(a) schematically illustrates the effect of finite depth-of-field on transverse one-dimensional projections of a non-azimuthally symmetric optical fiber, in this case a hypothetical three-core fiber.…”

Characterization of refractive index change and fabrication of long period gratings in pure silica fiber by femtosecond laser radiation

“…A microscopy approach called differential interference contrast (DIC) measures RIP using image contrast from the phase variation in optical fiber [20]. The computerized tomography (CT) enables three-dimensional measurement of RIP in optical fiber, for instance, at a grating [21]. Most of the reported techniques are either expensive and/or require a complex reconstruction method.…”

Multifocus tomographic algorithm for measuring optically thick specimens

“…Recently, tomographic algorithms originally developed for these situations have been applied by many research groups to the important problem of measuring the refractive index distribution of nonazimuthally symmetric optical fibers [2][3][4][5][6][7][8][9]. The transverse projection of features in an azimuthally symmetric optical fiber, such as conventional single-mode optical fiber, is unchanged by any amount of rotation about its central axis whereas the transverse projection of features inside a nonaximuthally symmetric fiber, such as a polarization-maintaining (PM) optical fiber, will change substantially when it is rotated about its central axis.…”

“…Quantifying the refractive index and geometry of such fibers is critically important for understanding their performance and optimizing their manufacture [11]. Such fibers have been measured by transverse tomographic interference microscopy [3,4,7,8], quantitative phase microscopy [2,6,9], or diffraction tomography [5]. The tomographic reconstruction algorithms used for these investigations assumed that the depth-of-field of the imaging system encompassed the transverse dimension of the fiber.…”