Abstract
Rayleigh scattering generates intensity noise close to an optical carrier that propagates in a single-mode optical fiber. This noise degrades the performance of optoelectronic oscillators and RF-photonic links. When using a broad linewidth laser, we previously found that the intensity noise power scales linearly with optical power and fiber length, which is consistent with guided entropy mode Rayleigh scattering (GEMRS), a third order nonlinear scattering process, in the spontaneous limit. In this work, we show that this behavior changes significantly with the use of a narrow linewidth laser. Using a narrow linewidth laser, we measured the bandwidth of the intensity noise plateau to be 10 kHz. We found that the scattered noise power scales superlinearly with fiber length up to lengths of 10 km in the frequency range of 500 Hz to 10 kHz, while it scales linearly in the frequency range of 10 Hz to 100 Hz. These results suggest that the Rayleigh-scattering-induced intensity noise cannot be explained by third-order nonlinear scattering in the spontaneous limit, as previously hypothesized.
Highlights
When light travels in a material, inhomogeneities in the material cause the light to scatter
We have shown that this noise can degrade the performance of optoelectronic oscillators (OEOs) [13], broadband analog RF-photonic fiber links [14], and narrowband analog RFphotonic fiber links that are used for frequency transfer [15]
When we measure the spectrum with a laser that has phase noise 104 times lower than the distributed feedback (DFB) laser used in [12], we find that the intensity noise plateau extends only to 10 kHz, a factor of 10 narrower than when measured with the standard DFB laser
Summary
When light travels in a material, inhomogeneities in the material cause the light to scatter. We can represent the inhomogeneities that scatter light with the permittivity. Fluctuations that occur on a molecular scale alter the tensor component of the permittivity, leading to Raman and Rayleigh-wing scattering [1]. Fluctuations of the thermodynamic properties—i.e. on the scale of many molecules—affect the scalar component of the permittivity. In this case, fluctuations in the density are the primary source of fluctuations in the permittivity, and other thermodynamic properties scatter light indirectly, via changes in the density [2].
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