Method for fiber Bragg grating control during the fabrication process

Abstract

We present a method for controlling the reflection amplitude and phase of uniform fiber Bragg gratings (FBGs) during their fabrication process. It is done by measuring the spectral interference between the reflections from the FBGs and the fiber end by an optical spectrum analyzer and performing a fast Fourier transform. The method allows correction of the FBGs until obtaining the needed parameters during the writing process, as well as at any time after that. We also demonstrate the use of cascaded uniform FBGs for the generation of periodic optical pulses with arbitrary waveform. It is a significantly simplified structure compared to complex fiber Bragg grating shapes. The pulse shaping is based on splitting of the input pulses by low reflecting FBGs into a number of replicas and their superposition with proper amplitude, time delay and phase shift that depend on the FBG parameters. The reflection amplitude and phase of each grating are unambiguously determined by the needed pulse shape. This method was experimentally verified for converting sinusoidally phase-modulated radiation of CW laser diode into a Gaussian pulse train with a pulse width of 30 ps.