Polarization averaged short-time Fourier transform technique for distributed fiber birefringence characterization using Brillouin gain Shangran Xie,1,2 Liang Chen,1 and Xiaoyi Bao1,* 1
Department of Physics, University of Ottawa, 150 Louis Pasteur, Ottawa, Ontario K1N6N5, Canada 2
Department of Electronic Engineering, Tsinghua University, Beijing 100084, China *Corresponding author:
[email protected] Received 6 March 2012; revised 27 April 2012; accepted 29 April 2012; posted 30 April 2012 (Doc. ID 163043); published 26 June 2012
A polarization averaged short-time Fourier transform (PASTFT) technique is developed for distributed fiber birefringence characterization based on counterpropagating stimulated Brillouin scattering (SBS) gain signal. This technique can be used for the birefringence characterization of the general elliptical birefringent fiber. A theoretical model on polarization matching of counterpropagating SBS process is established. The performance of the short-time Fourier transform (STFT) method and the PASTFT technique is analyzed by using the simulation of the theoretical model. Simulation results show that the process of polarization average could effectively reduce the birefringence characterization error caused by the polarization dependence of the local period of SBS gain. A less than 8% normalized root mean square error is achieved for the characterization of the length of the birefringence vector on elliptical birefringent fibers. The PASTFT technique is experimentally verified by the distributed measurement of beat length and differential group delay of a standard single-mode fiber via the Brillouin optical time domain analysis system. © 2012 Optical Society of America OCIS codes: 060.2270, 060.2370.
1. Introduction
Polarization mode dispersion (PMD) is a dominating factor that limits the transmission capacity of an optical fiber communication system. The impact of chromatic dispersion (CD) is static, which can be compensated by the dispersion shifted fiber or chirped Bragg grating; however, PMD varies with time and environmental condition. The physical origin of PMD effect is random fiber birefringence, which is the consequence of external perturbations as well as fiber drawing induced internal stress. It has been an important subject of fiber measurement over the past decades for monitoring and compensating of the PMD effect in standard communication single-mode fiber (SMF) by the mapping of fiber birefringence 1559-128X/12/194359-11$15.00/0 © 2012 Optical Society of America
characteristics. Currently, the standard method of fiber birefringence and PMD measurement can only provide the average value over the entire fiber link without distributed information [1–3]. However, in practice for a high PMD fiber link, there are often only one or a few bad sections. It is necessary to identify and replace these bad sections instead of the entire cable. Recently, several methods have been proposed for distributed fiber PMD monitoring. All reported methods are based on scattering techniques, e.g., Rayleigh scattering or Brillouin scattering. In the Rayleigh scattering regime, there are two methods being used for sensing: one is optical frequency-domain reflectometry (OFDR) [4–6]; the other is polarization-sensitive optical time-domain reflectometry (POTDR) [7–14]. The OFDR method has the advantage of high spatial resolution (less than 0.3 m in [4] and 20 μm in [6]); however, its short sensing range (
