Double Rayleigh Scattering
Rayleigh backscattering in fibers is caused by scattering of light from small defects, which are randomly distributed along the fiber. Scatterings of light by Double Rayleigh scattering (DRS) cause a noise wave, which propagates in the direction of the transmitted wave along the fiber. This noise limits the performance of optical measurement systems and of analog applications, such as distributing clocks or high dynamic range signals.
While the backward Rayleigh scattering effect was intensively studied, the DRS effect was analyzed only in specific conditions and often by using numerical simulations. It is a challenging task to analyze and to understand the DRS effect since the scattered wave is affected by both the random distribution of the scatterers along the fiber and by the stochastic nature of the transmitted wave. We present in this work a comprehensive model to study DRS and give analytical results for several important cases. The model gives a deep physical insight to the DRS and it helps in finding optimal methods to suppress the DRS effect.
For deterministic signals, we obtained that DRS can be modeled by an effective low pass filter for amplitude changes in the signal and by a high pass filter for phase changes. The bandwidth of the effective filters is mainly determined by the fiber loss and not by the fiber length as might be expected. For stochastic signals, the DRS converts phase noise of the source into amplitude noise. We have studied the noise generated when the laser source has a phase noise, which is modeled by the Wiener process. Analytical results are given when the DRS noise is suppressed by modulating the laser frequency. Preliminary experimental results confirm the theoretical results on the frequency dependence of the DRS.
* M.Sc. student under the supervision of Professor Moshe Horowitz.