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A novel modulation technique to enhance the optical intensity of referenced light for BOTDR’s high-accuracy signal interrogation

YAGE ZHAN1, KUN WANG1, LI LI1, YONG KONG1,* , FU YANG1, XIAOKAI ZHAO1

Affiliation

  1. Department of Physics, Donghua University, Shanghai 201602, P.R. China

Abstract

Heterodyne coherent detection is an optimal technique for Brillouin optical time domain reflectometer (BOTDR) on account of high resolution and good accuracy. Referenced light with enhanced intensity and with Brillouin frequency shift is important for BOTDR’s signal interrogation. A novel modulation technique, combining the regulating the DC bias voltage of electro-optic intensity modulator (EOIM) and the polarization state of the incident light, is proposed. Polarization influence on the intensity of sidebands generated by EOIM is investigated theoretically and experimentally. It is found that intensity of sideband change with the polarization state according to a 2 cos x relationship. Referenced light’s intensity can be enhanced further by adjusting the polarization state of the incident light after the action of DC voltage regulation has been exhausted. The intensity difference of 1st-order sideband and 0-order scattering (Rayleigh scattering), I1-I0, reaches maximum when polarization angle is 63.7O and the bias point of the EOIM is set in the nonlinear response range near the bottom. I1-I0 is 18dB higher than that of merely regulating DC bias voltage. Higher extinction ration (ER) of EOIM, higher I1-I0 can be achieved. When I1-I0 reaches maximum, the intensity difference between 1st-order sideband and other sidebands all reach maximum too. Meanwhile, the 1st-order sideband is best for being as referenced light for BOTDR’s signal interrogation..

Keywords

BOTDR, Signal interrogation, Modulation technique, Referenced light, Polarization.

Submitted at: Feb. 27, 2014
Accepted at: Sept. 11, 2014

Citation

YAGE ZHAN, KUN WANG, LI LI, YONG KONG, FU YANG, XIAOKAI ZHAO, A novel modulation technique to enhance the optical intensity of referenced light for BOTDR’s high-accuracy signal interrogation, Journal of Optoelectronics and Advanced Materials Vol. 16, Iss. 9-10, pp. 1039-1045 (2014)