Measurement of refractive index spectrum of optical material by phase detection with optical coherence tomography

Abstract

Refractive index (RI) is a fundamental parameter of optical material, and RI spectrum (RIS) is essential for many fields. Current RI measurement is only for some discrete spectral lines, and has extremely high requirements on measurement operation and accuracy. A measurement method of continuous RIS distribution in a wide spectral range was proposed in this work. A swept-source optical coherence tomography using a Mach-Zehnder configuration was used to detect interference spectrum signal, which phase was obtained by using Hilbert transform. By detecting the sample-induced phase and using the proposed equations, RIS of a sample could be obtained. Five measurements on the RIS distributions of two optical materials were conducted for a spectral range of 90 nm, and the results were in agreement with the theoretical distributions, verifying the method's validity. Its principle and operation are simple, and system has the potential to be miniaturized, making it possible to become a useful tool for RIS measurement, especially in some special occasions.