Design of high finesse, wideband Fabry-Perot filter based on chirped fiberBragg grating by numerical method

The spectral characteristics of a Fabry-Perot spectrometer (filter) formed by a pair of identical linearly chirped fiber Bragg gratings in optical fib er are studied numerically using the characteristic matrix method. The resu lts indicate that based on available techniques and materials, one can fabr icate such filters with a finesse as high as 10(4) and contrast as high as 10(9) by inscribing a pair of identical linearly chirped fiber gratings. Ac hieving such superfinesse and contrast in a conventional Fabry-Perot (FP) i s very difficult because of fabrication complexities in achieving superflat ness at ultrahigh reflectivities simultaneously and keeping them aligned. O ur 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+Delta L, where L is the leng th of any one of the two gratings and Delta L is the separation between the two gratings. This analogous characteristic enables one to estimate time d omain and other behavior of an FFP from already established PFP analysis. T hus, miniature FFPs can be used not only to achieve ultralow, crosstalk in wavelength division multiplexing (WDM), hut they can also be integrated int o miniature, hybrid, spectral sensors (such as Brillouin and Raman sensors) where ultrahigh contrast with superresolution is required. (C) 2000 societ y of Photo-Optical Instrumentation Engineers. [S0091-3286(00)02407-7].