A novel group delay dispersion (GDD) measurement from a spectral interferogram is presented. Based on the cubic phase function (CPF) of the interference term, the GDD can be directly read from the ridge of CPF without phase retrieval and numerical differentiation operation. The proposed method is applied to measure the GDD and chromatic dispersion difference (CDD) of a polarization-maintaining fiber. The experimental results are unambiguous and insensitive to the filter choice of interference term calculation. GDD measurement can reach a resolution of 1 fs 2 , with a processing time of 25 s for 1001 wavelength points, and CDD measuring deviation is less than 0.5 fs=ðkm Á nmÞ around the center wavelength. The method is expected to be suitable for processing all spectral interferograms with polynomial phases.
Low coherence interferometry (LCI) has been a useful tool to detect distributed polarization coupling (DPC) points in polarization maintaining fiber (PMF). However, due to birefringence dispersion, two close coupling points in long PMF are usually difficult to be distinguished. A novel method in our paper has been presented to tackle the problem. When the product of birefringence dispersion and fiber length called accumulated dispersion (AD) is numerically enough, the coherence envelopes caused by two close coupling points will split into periodic multiple peaks in the overlapping region and the distance of the two coupling points can be further demodulated from the frequency of splitting peaks. An experimental setup based on LCI has been established with two Panda PMFs of 600m and 950m under test. Experimental results show that the measuring errors of two close coupling points distance were less than 5%. When AD reached as high as 29 fs/nm and 46 fs/nm, the spatial resolution was increased by 13-fold and 20-fold, respectively. The constraint conditions to ensure the appearance of peak splitting is also discussed. It indicates that our method may show a potential application of spatial resolution enhancement in high-dispersive LCI without dispersion compensation.
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