Research On The Key Technology Of Self-mixing Interferometry Based On Vertical Cavity Surface Emitting Laser

With the development of biomedicine,artificial intelligence,military industry and other emerging fields,new requirements and high standards have been put forward for precision measurement technology.The measurement which can realize direct response,non-contact and multi-channel real-time detection has become an important goal in the field of optical measurement.Laser self-mixing interferometry has been widely concerned by scholars at home and abroad because of its simple structure,easy collimation,non-contact and high precision.The traditional laser self-mixing interferometry system needs to cooperate with the external detector to realize the signal detection,this increases the cost of the system and is not conducive to the expansion and integration of the measuring optical path.In view of the above requirements,the main work of this paper includes the following aspects:First,this paper systematically expounds the development of laser self-mixing interference technology and its current research status in vibration measurement and ranging applications.The theoretical model of self-mixing interference based on vertical cavity surface emitting laser(VCSEL)is established,and the physical basis of self-mixing interference signal picked up by PN junction voltage is analyzed.And the output characteristics of VCSEL laser self-mixing depending on the level of external light feedback and the phase of external cavity are simulated.Simultaneously,the optical path of VCSEL self-mixing measurement is built in the experiment,and the external photodetector and junction voltage are used to pick up the signals.The signals of the two show a reverse relationship,which is consistent with the simulation results,and provides a theoretical basis for the subsequent self-mixing interference measurement experiments of VCSEL.Secondly,this paper proposes a dual-channel VCSEL self-mixing interferometric vibration measurement method based on current modulation.A high-precision current source is used to provide working current for two VCSELs working in series.Based on constant current,a sinusoidal current is superimposed to simultaneously modulate the wavelength and power of the two lasers,thereby introducing sinusoidal phase modulation into the self-mixing interference signal.The high-order harmonics of the interference signal carry the target's motion information,and the target's vibration waveform can be reconstructed by extracting the harmonic amplitude.In the experiment,two VCSELs are used to detect the vibration of the speaker and piezoelectric ceramics,and the PN junction voltage of the laser is directly detected to obtain the self-mixed signal.The Fourier transform technology is used to extract the second and third harmonics,and the signal processing program is designed to restore the vibration in real time.This paper presents a new dual-sinusoidal current modulation laser self-mixing ranging method.The double sine current is composed of the superposition of two sine signals of high frequency and low frequency.Among them,the current of the low frequency signal is tuned to the laser wavelength,and a sinusoidal phase dependent on the target distance is generated in the self-mixing interference signal,and the current of the high frequency signal produces fast phase modulation,combined with Fourier analysis method,can demodulate the phase amplitude of low-frequency oscillation,and then accurately measure the distance.In the experiment,the Arb Express software was used to create double sine waveforms to provide double modulation currents for the VCSEL to form a laser self-mixing interference system.An absolute distance measurement experiment was carried out with an external reflection surface as the target.The experimental results show that the minimum distance measurement accuracy can reach 0.2mm in the range of 80mm-240 mm.