Management of fiber physical effects in high-speed optical communication and sensor systems

Abstract

High-speed optical transmission networks have been studied for several decades and still attract a lot of attention. Optical fiber has been used in distributed sensing systems on measuring the temperature and strain along the fiber. However, the performance of both high-speed optical transmission networks and fiber sensing systems are affected by the physical effects of optical fiber. In this thesis, several topics on application of fiber nonlinear effects and management of degrading factors induced by fiber physical effects are studied.

Firstly, a high-speed multi-channel optical pulse train generation based on parametric process through highly-nonlinear fiber (HNLF) is demonstrated. The wavelength of pump pulse is optimized to satisfy phase-matching condition and obtain large gain and wide bandwidth. 6-channel 80-GHz optical pulse trains with high ER were generated using one pulsed pump and three continuous wave channels. The qualities of the amplified signal and generated idler channels are analyzed numerically by calculate the bit-error-rate of each channel.

Secondly, chromatic dispersion (CD) and polarization dispersion monitoring (PMD) method in high-speed transmission systems is proposed. The methods are based on radio frequency (RF) power measurement and optical filtering. In the absence of filter, RF power is affected by both CD and PMD. By filtering the optical components in one of sidebands, the CD effect can be eliminated and PMD measurement can be achieved. The power ratio of filtered and non-filtered signal is only affected by CD; therefore, PMD insensitive CD monitoring can be achieved. The center wavelength of optical filter can be optimized to achieve wide measurement range and high measurement resolution. Both simulation and experimental results show that the proposed method is efficient and cost effective.

Lastly, the polarization induced signal fluctuation in Brillouin distributed sensing system is studied. A polarization diversity scheme containing two polarization beam splitters (PBSs) and a piece of single-mode fiber (SMF) is proposed. Both theoretical analysis and experiment results show that the proposed scheme is efficient on eliminating polarization induced fluctuation in Brillouin Optical Time Domain Analysis (BOTDA) fiber optic distributed sensing system. This scheme does not need any feedback control and the measurement time is only 3 seconds. Stable distributed temperature and strain measurements are demonstrated along a 1.2 km SMF.