pISSN 0374-4914 eISSN 2289-0041

## Research Paper

New Phys.: Sae Mulli 2020; 70: 797-803

Published online September 29, 2020 https://doi.org/10.3938/NPSM.70.797

Copyright © New Physics: Sae Mulli.

## Analysis for Phase Control Condition of Ytterbium-doped Optical Fiber-based Phase Shifting Interferometer

Eun Sun KIM, Hui Won KANG, Hye Jun MA, Eun Seo CHOI*

Department of Physics, College of Natural Science, Chosun University, Gwangju 61452, Korea

Correspondence to:cesman@chosun.ac.kr

Received: May 27, 2020; Revised: July 17, 2020; Accepted: July 31, 2020

### Abstract

In this research, the optimum phase control condition was analyzed by calculating the change in the nonlinear refractive index induced in a ytterbium-doped optical fiber by using 980-nm pump light. Simulations were performed to obtain the characteristic of the refractive index change while varying the optical power of the pump light and the length of the optical fiber. By investigating this characteristic, we were able to determine the optimal optical fiber length at a specific pump light power and calculate the amount of phase change. As a result of the simulation on the 10-cm-long ytterbium-doped optical fiber, the pump light power required to induce the $\pi$ rad phase change of the 1330-nm signal light was calculated to be 8.5 mW. The pump light power applied to induce a $\pi$ rad phase change in the fiber optic Michelson interferometer experiment was 9.5 mW, which was very similar to the simulation result. Thus, we confirmed that the phase control required by the phase-shifting interferometer could be sufficiently achieved by using a low pump-light power and an optical fiber of several tens of cm in length.

Keywords: Nonlinear refractive index change, Phase-shifting interferometer, Phase shift