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Abstract
Backward Rayleigh scattering in optical fibers due to the fluctuations that are "frozen-in" to the fiber during the manufacturing process may limit the performance of optical sensors and bidirectional coherent optical communication systems. In this manuscript we describe a comprehensive model for studying intensity noise induced by spontaneous Rayleigh backscattering in optical systems that are based on self-homodyne detection. Our model includes amplitude and frequency noise of the laser source, random distribution of the scatterers along the fiber, and phase noise induced in fibers due to thermal and mechanical fluctuations. The model shows that at frequencies above about 10 kHz the noise spectrum is determined by the laser white frequency noise. The laser flicker frequency noise becomes the dominant effect at lower frequencies. The noise amplitude depends on the laser polarization. A very good agreement between theory and experiment is obtained for fibers with a length between 500 m to 100 km and for a laser with a linewidth below 5 kHz.
Highlights
Optical fiber sensors and their applications have been intensively studied due to their advantageous attributes such as immunity to electromagnetic interference (EMI), light weight, small size, high sensitivity, and the ability to perform sensing over a very long distance [1]
We present a comprehensive model to describe the intensity noise spectrum that is induced by Rayleigh backscattering in optical fiber systems that use self-homodyne detection
When the laser coherence length is longer than the fiber length, we find a complex dependence of the noise spectrum on the fiber
Summary
Optical fiber sensors and their applications have been intensively studied due to their advantageous attributes such as immunity to electromagnetic interference (EMI), light weight, small size, high sensitivity, and the ability to perform sensing over a very long distance [1]. There is a need for a comprehensive model that is not limited to sources with a short coherence length In this manuscript, we present a comprehensive model to describe the intensity noise spectrum that is induced by Rayleigh backscattering in optical fiber systems that use self-homodyne detection. For shorter fibers with lengths between 500 m to 6 km, we only obtained good agreement at higher frequencies of more than about 500 Hz. We found that the phase noise that is due to mechanical dissipation and thermal fluctuations that is accumulated by waves propagating in the fiber [18,19,20] does not significantly affect the noise spectrum of the self-homodyne detected Rayleigh backscattering. We conclude that stimulated scattering was not an important factor in our experiments
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