Design of high finesse, wideband Fabry-Pe´rot filter based on chirped fiber Bragg grating by numerical method

Abstract

The spectral characteristics of a Fabry-Perot spectrometer (filter) formed by a pair of identical linearly chirped fiber Bragg gratings in optical fiber are studied numerically using the characteristic matrix method. The results indicate that based on available techniques and materials, one can fabricate such filters with a finesse as high as 104 and contrast as high as 109 by inscribing a pair of identical linearly chirped fiber gratings. Achieving such superfinesse and contrast in a conventional Fabry-Perot (FP) is very difficult because of fabrication complexities in achieving superflatness at ultrahigh reflectivities simultaneously and keeping them aligned. Our numerical simulation also indicates that the spectral characteristics of the fiber FP (FFP) filter can be approximated by that of a classical plane mirror FP (PFP) with a mirror separation of L + ?L, where L is the length of any one of the two gratings and ?L is the separation between the two gratings. This analogous characteristic enables one to estimate time domain and other behavior of an FFP from already established PFP analysis. Thus, miniature FFPs can be used not only to achieve ultralow, crosstalk in wavelength division multiplexing (WDM), but they can also be integrated into miniature, hybrid, spectral sensors (such as Brillouin and Raman sensors) where ultrahigh contrast with superresolution is required.