In-line optical feedback interferometry with 510 nm semiconductor laser and digital post-detection filtering

Abstract

In-line Optical Feedback Interferometry (OFI) is a remote sensing technique that involves reflecting part of a Semiconductor Laser (SL) beam back into its cavity. But frequency-proportional phase noise distorts the signal, resulting in poor measurements of displacement. In this report, we use digital filters [Low Pass, Savitzky Golay (SG), Wiener] to reduce the noise in a simulated OFI setup, and experimentally demonstrate in-line OFI using a visible (nominal wavelength: 510 nm) SL with digital filtering. Interferogram-baseline subtraction using the adaptive iteratively reweighted Penalized Least Squares (airPLS) algorithm is also implemented to correct power amplitude fluctuations due to shot and thermal noise in the photodiode. We report that the SG filter yields the lowest root mean square error, with respect to a noiseless signal. SG filtering and the airPLS algorithm also result in sufficient noise reduction in an in-line OFI setup with a visible light SL.