Realization and Modulation of Fano-Like Lineshape in Fiber Bragg Gratings

Abstract

Optical fiber Bragg gratings (FBGs) featured with narrowband transmission dips (or reflection peaks) have been maturely employed in technologies of optical communications, lasers and sensors. Here, we report a simple strategy to control the lineshapes of FBG's transmission dip by inserting the FBG in one arm of an all-fiber Mach-Zehnder interferometer (MZI). The transmission dip could be modulated into an asymmetric Fano-like lineshape or a transmission peak, which is controlled by the phase difference between the two arms of the MZI. It works for the uniform, chirped, and phase-shifted FBG. We experimentally verify it with a uniform FBG, showing freely modulated asymmetric Fano-like lineshape with the optical delay line, strain and temperature. Due to the modulation, the maximal slope rate is 49.1 dB/nm, and the Fano parameter <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> can be tuned from -∞ to +∞. The tunable lineshapes of the FBGs might open up a new window for the applications of traditional FBGs in lasers, communications and sensors.