Self-mixing interferometer: analysis of the output signals

Area of Science:

• Optics and Photonics
• Laser Physics
• Interferometry

Background:

• Self-mixing interferometry (SMI) is a technique utilizing laser feedback for sensing.
• Understanding signal characteristics at different outputs is crucial for SMI applications.
• Previous studies noted phase discrepancies but lacked comprehensive theoretical explanations.

Purpose of the Study:

• To theoretically calculate and experimentally validate the amplitude and relative phase of signals at the three distinct outputs of a self-mixing interferometer.
• To explain the observed phase discrepancy between front and rear outputs for different laser sources (He-Ne and diode laser).
• To analyze the phase relationship between the junction voltage output and the rear output for diode lasers.

Main Methods:

• Theoretical calculations of signal amplitude and relative phase for front, rear, and junction voltage outputs.
• Experimental validation using a He-Ne laser and a diode laser.
• Phase comparison analysis between different output signals.

Main Results:

• Front and rear outputs are in phase for He-Ne lasers but in phase opposition for diode lasers.
• The junction voltage output is consistently in phase opposition with the rear output for diode lasers.
• Theoretical calculations accurately predict the observed experimental results.

Conclusions:

• The theoretical framework successfully explains the phase behavior of signals in self-mixing interferometers across different laser types.
• The findings clarify the distinct phase relationships at the front, rear, and junction voltage outputs, crucial for sensor design.
• Experimental validation confirms the theoretical predictions, enhancing the reliability of self-mixing interferometer analysis.