Scattering Matrix Analysis on the Use of a WideBa

Authors: R J Fredricks

Publish Date: 1982

Volume: , Issue: , Pages: 82-92

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Abstract

Recent results obtained by various laboratories experimenting with passive fiber optic rotation sensors have suggested that a wideband laser source provided it is not so broad that dispersion effects in sensor elements external to the fiber ring such as the inputoutput coupler become significant can appreciably reduce low frequency random noise at the sensor output This lowfrequency noise is due to the time variation of the elements comprising the fiber ring’s scattering matrix model at a given source wavelengthA question has arisen additionally as to whether the use of a fluctuating or random state of polarization SOP at each such source mode may further reduce the lowfrequency noise In this theoretical analysis we show that the use of a random SOP for each mode is not only unnecessary but in general gives rise to a nonreciprocal phase NRP shift between the countertraveling beams in the fiber ring at each mode We find instead that the use of a nonrandom SOP at each source wavelength via suitably oriented polarizers and analyzers eliminates the NRPFinally we show that the resultant intensity signal at the sensor photodetector exhibits a 1/sqrt N suppression of the noise amplitude when a wideband source with N modes is employed This will occur provided there is sufficient spacing between the various modes so that the scattering matrix elements become uncorrelated with each other from one wavelength to the next

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