Simplex coded polarization optical time domain reflectometry system.

In polarization optical time domain reflectometry (POTDR) system, the performance of polarimetric measurement is constrained by the low signal to noise ratio (SNR) due to the weak Rayleigh backscattering and the degradation of the degree of polarization (DOP) of signal light. Therefore, it is indispensable to improve the SNR without sacrificing the DOP of backscattered signal for a sufficient dynamic range. In this paper, a Simplex coded POTDR (sc-POTDR) system is proposed and demonstrated. The relationships between the signal's DOP and coding length/bit width are studied. Both numerical simulations and experimental results show that the length of Simplex code has no impact to the signal's DOP and the temporal depolarization effect can be suppressed just by reducing the bit width. Applying 511-bit Simplex code, a coding gain of 10.125 dB has been demonstrated. By taking advantage of high DOP and the coding gain, the changes of polarization state caused by a mechanical event in a long fiber link have been detected and located precisely.