A Reconfigurable Architecture for Continuous Double-Sided Swept-Laser Linearization

Abstract

This paper reports a reconfigurable architecture to generate and maintain the linearity of frequency-swept semiconductor lasers for both current rising (up-sweep) and falling (down-sweep) edges, respectively. This method combines both passive and active controls to achieve a high frequency-sweep linearity using an integrated digital architecture. Both the passive and active control utilize the same feedback—the interferometric signal of the laser's output—which has a frequency proportional to laser frequency-sweep velocity. This architecture is highly reconfigurable, allowing key parameters to be changed, including sweep velocity, tuning range, and sweep duration, making it a highly versatile and flexible approach suitable for a range of semiconductor lasers and a variety of applications. This architecture was implemented on an FPGA to validate the concept and evaluate its performance. By precisely tracking the interferometric feedback signal, it was found that this approach allowed a semiconductor laser to generate and maintain a phase error of less than $\frac{\pi }{2}$ within the regions of interest at different sweep velocities for both up-sweep and down-sweep cycles. Given that the delay length of the interferometer is 226 ns, the instantaneous optical frequency error is within 0.12% at 1552 nm.