INTERFEROMETRIC MEASUREMENT OF DISPERSION IN OPTICAL FIBERS

Abstract

An interferometric method for measuring the total dispersion of short lengths of optical single mode fiber has been demonstrated. An analysis of the system in terms of linear system theory has also been carried out. The experiments were performed using a multimode GaAlAs semiconductor laser to measure the total dispersion of a borosilicate single mode optical fiber at a wavelength of approximately .873 μm. The experiments were conducted using various combinations of laser spectral width and fiber length. Changing the drive current to the laser enabled its spectral width to be varied from 2.3 nm to 5.8 nm FWHM. The fiber length was varied from approximately 0.2 m to 1.0 m. An analysis was also carried out to explain the effects on the interferograms of the unequal mode spacing of the multimode GaAlAs laser. Two methods of approximating the amount of variation of the laser mode spacing were also developed based on analysis of the interferograms. Analysis of the auto-correlation interferogram allowed the GaAlAs laser spectral width to be determined. This data was then used to compute a cross-correlation interferogram and then compared with the measured cross-correlation interferogram. The value of the fiber dispersion used in calculating the cross-correlation interferogram was varied until the computed interferogram agreed with the measured interferogram, this determined the value of the dispersion for the fiber that was used in that experiment. The experimentally determined value of the total dispersion of the single mode optical fiber used in these experiments agreed very well with published results.