Chromatic dispersion measurement of few-mode fiber based on low coherence off-axis digital holography

Abstract

A method based on low coherence off-axis digital holography is proposed to measure the chromatic dispersion of few-mode fiber (FMF). A measurement system based on the Mach–Zehnder interferometer with a delay stage is established. The holograms, which vary with the delay stage at different wavelengths, are recorded using the system. The interference energy is extracted from the holograms to construct the time domain mode energy curve at each wavelength to obtain the delays of the fundamental mode and each higher-order mode. According to the relationship between the delay and the wavelength, the dispersion curves of the fundamental mode and each higher-order mode are calculated. The higher-order modes are selectively excited by controlling the tilt angle of the incident light to separate the higher-order modes with a close group delay in the short fiber in the time domain. The FMF is measured using this method, and the dispersion curves of the fundamental mode and each higher-order mode are obtained. The measurement results are consistent with the design parameters. This method is suitable for measuring short optical fibers and has several advantages, including high measurement resolution and simple experimental device.