Experimental measurement of effective refractive index difference for few mode polarization maintaining fibers using S2method

Abstract

Polarization maintaining fibers (PMFs) can keep linear polarization state against external perturbations by inducing a high effective refractive index difference (Δneff) along one polarization axis. For few mode polarization maintaining fibers (FM-PMFs), Δneff is applicable between both orthogonal linear polarization modes (e.g. LP 01x and LP 01y ) and orthogonal degenerated modes (e.g. LP 11a and LP 11b ), which can enable advanced functionalities in multiple-input multiple- output-free spatial division multiplexing systems and optical fiber sensing systems. Therefore, the measurement of Δneff for polarization modes and degenerated modes is very important for determining the quality of a FM-PMF. However, measurement of the Δneff for FM-PMFs can be complicated due to the requirement for generating and demultiplexing of the higher order modes (HOMs). In this paper, we propose to measure the Δneff of FM-PMFs using Spatially and Spectrally resolved imaging (S 2 ) method for the first time. The presented method is simply by employing a tunable laser and an IR CCD camera, can avoid any mode converter or mode multiplexer/demultiplexer, featuring a rapid testing speed. A proof-of-concept experiment is carried out to measure FM-PMFs with a length of 1.1m and 5m. The Δneff between the orthogonal polarization modes (i.e. LP 11ax-11ay , LP 11bx-11by , LP 21ax-21ay , and LP21bx-21by) are characterized as 7.05×10 -4 , 6.91×10 -4 , 1.02×10 -3 and 1.04×10 -3 respectively. The Δneff of the orthogonal degenerated modes (i.e. LP 11ax-11bx , LP 11ay-11by , LP 21ax-21bx and LP 21ay-21by ) are also characterized to be 1.39×10 -4 , 1.24×10 -4 , 5.61×10 -5 and 6.53×10 -5 respectively.