Profile measurement using a self-mixing laser diode

When a fraction of external optical feedback re-enters inside cavity of a laser diode (LD), the laser intensity and its wavelength will thus be altered. The LD in this case is often called as a self-mixing laser diode (SMLD). This paper presents an SMLD for profile measurement. The LD is modulated by the injection current in triangular waveform and a target to be measured is installed on a mechanic scanning device. The reflection light by the target contains its surface profile. The profile information is then carried in the laser intensity and can be pickup by a photodiode packaged in the rear of the LD. We call this modulated laser intensity as self-mixing interferometric (SMI) signal. In this paper, a new algorithm is developed to retrieve the profile from the SMI signal. Results show that the proposed design is able to achieve the measurement of profile with high resolution.