In this paper, we propose and experimentally demonstrate a series of new all-fiber, tunable, and highly selective filters based on fiber gratings and Fabry-Perot's. The structures combine high fiber Fabry-Perot (FFP) selectivity and fiber Bragg grating (FBG) bandpass nature and presents high flexibility in the response by using nonuniform gratings. An ultraselective filter (a few MHz in range) is also addressed by cascading two FFP.
Beatriz Ortega, Jose Capmany, and Jose L. Cruz, "Wavelength Division Multiplexing All-Fiber Hybrid Devices Based on Fabry-Perot's and Gratings," J. Lightwave Technol. 17, 1241- (1999)