Two-dimensional refractive index distribution measurementof a GRIN lens

摘要

Based on the Fresnel's equations and the phase-shifting method; an alternative method for measuring the refractive index distribution of a GRIN lens is presented. A linearly/circularly polarized light in order enters a modified Twyman-Green interferometer; in which an electro-optical modulator is used as a phase shifter. In the interferometer; the light beam is divided by a beam-splitter into two beams; a reference beam and a test beam. After they are reflected by a plane mirror and the tested GRIN lens; respectively; they are combined together and pass through an analyzer. The analyzer extracts the same polarized components to interfere each other; and the full-field interference signals produced by the components of the s- and the p-polarizations can be obtained. The full-field interference signals are taken by a CMOS camera. The phase differences can be obtained by using the four-step phase-shifting interferometric method. Substituting these two groups of data into special equations derived from Fresnel equations; and the two-dimensional refractive index distribution of the GRIN lens can be calculated. Its validity is demonstrated and has some merits such as simple optical configuration; easy operation and high resolution.