Altometer resolution of wavelength shifts using two-mode, elliptical-core fibers

The reduction in the spectral width of laser sources has enabled existing fiber optic links to operate at increasingly higher data rates and hence make optimum use of the available optical bandwidth. The drift in the separating wavelength of these optical sources due to external factors such as temperature fluctuations can lead to degradation in the performance of such systems due to the induced phase noise. We propose a novel technique to detect minute wavelength drifts in small linewidth sources by operating just below the single-mode cutoff wavelength of a highly elliptical-core (e-core) fiber and utilising the resultant modal interference pattern.