A Sweep Velocity-Controlled VCSEL Pulse Laser to Interrogate Sub-THz-Range Fiber Sensors

Abstract

This letter reports an all-digital sweep velocity-controlled pulse laser with enhanced sweep bandwidth. A vertical cavity surface emitting laser was employed as the optical source. An all-digital phase locked loop was designed and implemented using a field programmable logic array chip to lock the laser sweep velocity within each chirped pulse. A laser temperature controller was used to tune the operation temperature to enhance the laser mode-hop-free bandwidth, resulting in a total frequency excursion of 212.12 GHz and a constant sweep velocity of 30.28 GHz/ms. The system was further adopted to interrogate a sub-terahertz-range fiber sensor array. A series of static strain tests were conducted to demonstrate the system sensing capability. Highly linear results with a sensitivity of −0.1426 GHz/ $\mu \varepsilon $ were observed.