Polarization fluctuation caused by mechanical vibration in a high-birefringence fiber system are related to variations of birefringent axes and linear retardance as well as random mode-coupling between orthogonal polarization states. Computer simulation analysis assuming a Gaussian probability distribution for these variables permits us to estimate the origins producing polarization noise. A ratio of a mean value to a standard deviation of time-varying signals resulting from the noise is plotted as a function of angular misalignment and misaligned coupling into a fiber system with joint sections. Experimental results using the test samples of an elliptical-jacket, a bow-tie, and a PANDA fiber are included.
In optical birefringent fiber links with misaligned joint section, forced vibrations by a loudspeaker will cause the polarization state to fluctuate. If the output light from the fiber is detected through an analyzer, the “polarization noise” can be observed. As a quantitative measure, the mean value of intensity fluctuations to standard deviation, that is, the signal‐to‐noise ratio (S/N ratio), is introduced. S/N ratios are measured by varying the incident angle to linearly polarized light (α) and misalignment angle of principal axes of fibers (). If S/N ratios of various birefringent fibers (elliptical jacket, Bow‐Tie and Panda types) with α = 0 and α = 90° are compared, it is confirmed that the latter could be reduced by about 15 dB. As the degradation of the S/N ratio due to polarization noise, the intensity fluctuations of the propagating light are formulated under the assumption that the polarized coupled mode is generated at one place inside the fiber. Computer simulations are carried out to analyze fluctuation of extinction ratio and phase difference of normal modes for Gaussian probability distributions. Consequently, the analytical results are in good agreement with experimental ones of S/N ratio, for proper mean value and standard deviation. Therefore, using this method, it becomes possible to estimate the fluctuation parameters.
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