All-optical electrical chirped pulse generation based on nonlinear wavelength-to-time conversion in a chirped fiber Bragg grating

In this paper, we propose and demonstrate a novel approach to optically generating chirped microwave pulse with tunable chirp rate based on spectral shaping and nonlinear wavelength-to-time conversion using a tunable nonlinearly chirped fiber Bragg grating (NL-CFBG). In our approach, the optical power spectrum of a ultrashort pulse from a femtosecond pulsed laser (FSPL) is shaped by a two-tap Sagnac loop filter (SLF) that has a sinusoidal spectral response. The spectrum shaped pulse is then reflected by an appropriately designed NL-CFBG to perform the nonlinear wavelength-to-time mapping. The microwave pulse with a tunable chirp rate is then generated at the output of a high-speed photodector (PD). The NL-CFBG used in the system is produced from a regular linearly chirped fiber Bragg grating (LCFBG) using a new technique based on strain-gradient beam tuning. A simple mathematical model to describe the chirped pulse generation is developed. A proof-of-principle experiment based on the proposed method is carried out.