Available at: http://digitalcommons.calpoly.edu/theses/1770
Date of Award
MS in Electrical Engineering
Linewidth and Ranging Characterization of a Vernier-Tuned Distributed Bragg Reflector (VT-DBR) All-Semiconductor Tunable Swept Laser System for Lidar in Autonomous Applications
Linewidth and ranging experiments of a Insight packaged Vernier-Tuned Distributed Bragg Reflector (VT-DBR) laser across its wavelength output range of 1522.13 to 1566.18 nm is done in this work to characterize it for lidar applications. The purpose of this paper is to investigate the laser’s potential to combine the advantages of lidar and FMCW radar for autonomous systems.
Linewidth measurements were done by using a Mach-Zehnder interferometer to set up a delayed self-homodyne measurement. The laser was set to output at a fixed wavelength across a range of 1523 to 1566 nm in 1 nm increments, and linewidth was captured each of these increments. For each of the linewidths, coherence time and length along with laser currents were associated. The minimum linewidth found in this test was found to be 50 MHz, leading to a maximum coherence time of 6.366 ns and a maximum coherence length of 129.92 cm. There was a somewhat linear, albeit low correlation, area of low linewidths depending on the front mirror and back mirror currents across the wavelength range.
Initial ranging experiments were performed using interference fringes caused by variable stationary path length differences introduced into a homemade Mach-Zehnder interferometer around the coherence lengths found in the linewidth test. The experimental path length differences indicated by the interference fringes seem to be accurate at very small ruler measured path length differences, but starts to stray away from the ruler measured as the path length differences get larger. Data taken suggests that there is a mathematical relationship in the error between the ruler measured and experimental path length differences leading to the belief that this error can be compensated for.
Keywords: Vernier-Tuned Distributed Bragg Reflector, VT-DBR, FMCW, linewidth, coherence, self-homodyne, Mach-Zehnder Interferometer, interference fringes