Field-programmable gate array-controlled sweep velocity-locked laser pulse generator

This manuscript reports a FPGA-controlled sweep velocity-locked laser pulse generator (SV-LLPG) design based on an all-digital phase-locked loop (ADPLL). A distributed feedback (DFB) laser with modulated injection current was used as a swept-frequency laser source. An open loop pre-distortion modulation waveform was calibrated using a feedback iteration method to initially improve frequency sweep linearity. An ADPLL control system was then implemented using a field programmed gate array (FPGA) to lock the output of a Mach–Zehnder interferometer that was directly proportional to laser sweep velocity to an on-board system clock. Using this system, linearly chirped laser pulses with a sweep bandwidth of 111.16 GHz were demonstrated. Further testing evaluating the sensing utility of the system was conducted. In this test, the SV-LLPG served as the swept laser source of an optical frequency domain reflectometry (OFDR) system was used to interrogate a sub-terahertz range fiber structure (sub-THz-FS) array. A static strain test was then conducted and linear sensor results were observed