High resolution chirped pulse lidar with spectral phase modulation for two fold improvement in range resolution

Lidar systems are important for performing many different tasks such as remote sensing, altimetry and imaging. Chirped pulsed lidar systems employing chirped fiber Bragg gratings (CFBGs) for long distance, high resolution ranging and velocimetry have been demonstrated. Broadband CFBGs with dispersions of up to 2 ns/nm across the C-band have recently become commercially available. However, due to imperfections and noise in the grating fabrication process, larger dispersion values come at the price of larger ripple in the group delay. In this paper, we demonstrate a technique that utilizes spectral phase modulation to remove the group delay ripple (GDR) of a CFBG while maintaining a dispersion of 1651 ps/nm across the C-band. The GDR removal is experimentally verified by utilizing the linearly chirped, GDR-free optical pulse train in a chirped pulse lidar setup where a two-fold improvement in the lidar range resolution is observed. In the future, this approach may be used to achieve range resolution of a few hundred micrometers over target distances greater than 10 km, and also for doubling the resolution of chirped pulse Doppler velocity measurements.