Optical-feedback semiconductor laser Michelson interferometer

Abstract

Industrial applications of displacement measurements require both accuracy and directional discrimination capability which are essential particularly in the motion control of mechanical components along different axes. For versatility, it is also desired that displacement sensors be compact, sturdy, and economical to operate.
Feedback phenomenon in semiconductor laser (SL) diodes has been applied in designs of several displacement-measuring instruments that satisfy the above requirements. These instruments employ self-mixing interference in the SL light source to carry-out small displacement and low-amplitude vibration measurements with high resolution.
In this paper, we demonstrate a new optical-feedback detection scheme for microscopic displacement measurements that uses an 830-nm SL in a Michelson architecture. The instrument which we refer to as the optical-feedback semiconductor laser Michelson interferometer (OSMI) measures displacement of the reflecting target without ambiguity in motion direction. Magnitude and direction of sample displacement are obtained from the periodic and asymmetric variation of the SL output power that results from the change in the path difference between the reference mirror and the reflecting sample. The OSMI has a resolution = 415 nm; dynamic range ≈ 10^-3 m (SL coherence length). A theoretical model is developed to calculate the dependence of SL output power on path difference of the two interforemter arms. Finally, the OSMI performance is evaluated by measuring the vibrational amplitude of voltage-driven piezoelectric transducer (PZT) and audio speaker.