Research On Laser Wavelength Stability Of Frequency Modulated Continuous Wave Interferometer

Frequency modulated continuous wave（FMCW）laser interferometer is an optical instrument that uses the principle of FMCW laser interference to measure some physical quantities with high precision.Because FMCW laser interference generates dynamic signals and can calibrate the phase in real time,it has the advantages of strong anti-interference ability and high measurement accuracy.It can be used in aerospace,military equipment and integrated circuit manufacturing and other fields.Aiming at the problem of wavelength drift of semiconductor laser source in the FMCW interferometric system,this paper focuses on the factors affecting the wavelength stability of the laser and measuring the laser central wavelength stability of the FMCW interferometer.The main factors affecting the wavelength stability of the DFB laser: the driving current and the operating temperature are analyzed and measured.The stability of laser current and temperature is realized by laser driver and temperature control detection circuit module.The wavelength-current coefficient of variation is 0.01nm/m A and the wavelength-temperature coefficient of variation is 0.22nm/°C,as measured experimentally.The current stability of the laser is 0.15% and the temperature stability is 0.79%.The results show that the laser under temperature-controlled conditions has good current stability and temperature stability.A method for measuring the wavelength drift of FMCW laser based on fixed interferometric cavity is proposed.Firstly,the theory of FMCW laser interferometry is analyzed,and the optical path structure of fiber Fabry-Pérot（F-P）interferometer is selected.On this basis,the measurement formula of laser wavelength drift is derived.It is concluded that there is a linear relationship between initial phase change-displacement-laser wavelength drift under the condition of constant F-P cavity length;secondly,the F-P fixed cavity is designed and fabricated,and the quartz glass with low coefficient of thermal expansion is selected to reduce the influence of ambient temperature fluctuation on the F-P cavity;then the hardware circuit is designed and made,including power supply and STM32F4 minimum system module,laser driver and temperature control detection module,photoelectric detection and signal conversion module and serial communication module;finally,the wavelength drift demodulation algorithm is written,and the upper computer display interface is designed by Py Qt5.The experimental verification is carried out by building a wavelength stability measurement system.The experimental results show that the "form" displacement of the interferometer is 8nm/℃,the corresponding phase change is 0.06rad/℃,the wavelength drift is 0.096pm/℃,and the wavelength stability is 0.06ppm/℃ under the premise of constant F-P cavity length.The measurement method has the advantages of simple operation,real-time,fast and high resolution.It is of great significance to improve the accuracy of FMCW interferometry.