Dispersion measurement of optical fiber using dual wavelength diffraction phase microscope

Abstract

Various quantitative phase microscopy (QPM) techniques for noninvasive and quantitative analysis of samples proposed based on imaging interferometry techniques over the last decade [1-4]. A phase image can be obtained with a single set of interference data in some types of phase microscopes such as diffraction phase microscope [5, 6]. They are suitable for studying rapidly varying phenomena with reduced concern for systematic and sample variations that may occur during the acquisition of the raw data. Dispersion measurements of a sample carry more information than refractive index of measurements at a single wavelength [7]. Knowledge of the optical dispersion for phase objects such as optical fibers, biological cells and micro-particles can provide very useful information about their property. In this work, we report on a common-path and dual wavelength quantitative phase microscope that simultaneously acquires two phase images at different wavelengths. The simultaneous dual-wavelength measurement was performed with a diffraction phase microscope based on a transmission grating and a spatial filter that form a common-path imaging interferometer. With a combined laser source that generates two-color light continuously, a different diffraction order of the grating was utilized for each wavelength component so that the dual-wavelength interference pattern could be distinguished by the distinct fringe frequencies. The refractive index profiles of fiber in both wavelengths were measured adequately by our DW-DPM system.