Phase Shift Measurements Between Intensity and Frequency Modulations of a Self-Mixing Interferometer

Abstract

We present a simple and straightforward method to determine the phase shift between the amplitude modulation (AM) and the frequency modulation (FM) of a laser diode. The approach is based on the measurement of AM and FM signals produced by the dynamical response of a laser diode exposed to weak optical feedback. The AM signal is measured directly on a photodiode detecting the emitted power and the FM signal is demodulated to intensity modulation through the edge filtering techniques using (a) a volumetric Bragg grating or (b) a Mach-Zehnder interferometer as filters prior to the signal detection. In this work, we show experimentally that the phase shift determination unveils the linewidth enhancement factor of semiconductor lasers as predicted by the Lang and Kobayashi theory.

Self-mixing Interferometer: Frequency Modulation Noise Dependence on Laser Source

“…In the last years, there has been an exploration of frequency modulation induced by the self-mixing effect for various measurement applications [4][5][6]. Although the theory of Lang and Kobayashi had predicted the existence of the FM signal [7], the focus had predominantly remained on amplitude modulation (AM) signals for approximately three decades, primarily because it is easier to acquire.…”

“…This level of performance is typically reached by very-high cost instruments, not often available for everyday measurements [3]. In recent years, a new interferometry technique has been proposed, which exploits the frequency modulation of a laser subjected to optical back injection [4][5][6][7][8]. The sensitivity demonstrated by this kind of interferometer is about two orders of magnitude higher than the standard amplitude-modulation self-mixing interferometer [9].…”

Enhanced Vibration Measurement through Frequency Modulated Laser Diode Self-Mixing Interferometry

“…Advancements have explored the use of frequency modulation (FM) signals, which offer higher signalto-noise ratios but present challenges in detection [26][27][28][29][30]. The key advantages of this emerging trend in laser interferometry include an extremely high sensitivity to scattered light, the ability to estimate displacement direction and obtain information from small object surface areas, simple interferometer design, and low implementation cost [31,32]. The main aspects highlighted are the operating principles based on optical feedback and frequency modulation of laser diodes, analysis of the interference signals for various measurement applications, establishing relationships between object motion and signal parameters, and the significant advantages offered by this approach in terms of scattered light sensitivity, directionality information, simplicity, and low cost.…”

Period-One Microwave Photonic Sensing by a Laser Diode With Optical Feedback

“…Various potential applications have been investigated and reported in different dynamic states. In steady state, an LD with EOF can be utilized to detect the Doppler shift, vibration, velocity measurement, and displacement [5][6][7][8]. In P1 state, the optical injection and optical feedback schemes were used to generate microwave [9][10][11].…”