Research On Phase-shift Grating For Temperature Measurement System Based On Scanning Laser Frequency

In recent years,China has formulated a series of marine development plans in order to promote innovation in marine science and technology and realize the rejuvenation of the country through the sea.Real-time and accurate acquisition of marine physical parameters such as temperature,salinity and depth can provide a multi-directional basic guarantee for the development and utilization of marine resources.At present,the mainstream equipment for the measurement of temperature and salinity parameters in the international still has no place in our country.Sea water temperature is an important index in marine scientific research.It is of great significance to study and master the variation law of sea water temperature in all aspects of marine researchIn this paper,the factors affecting the long-term stability of the system when the ?phase-shift grating is applied to the temperature measurement are studied.The frequency locking of the laser is carried out using the center frequency of the transmission window of the reflection spectrum of the ? phase-shift grating in the gallium fixed point bottle as the frequency reference standard.The reference optical path is relatively stable at the melting point temperature of gallium,which provides a reference frequency standard for the research and measurement systemBased on the above research background.main research content of this paper are as follows:on the basis of the principle of laser frequency sweep and frequency lock,the center frequency of the reflection spectrum transmission window of the ? phase-shift grating placed inside the gallium point bottle is used as the quasi-frequency standard source,the current source is adjusted to achieve laser current tuning so as to lock the laser output frequency above the center frequency of the reflection spectrum transmission window of the ? phase-shift grating.The gallium point bottle provides a temperature stable environment for ? phase-shift grating,reduces the drift of center frequency and enhances the locking stability.The method is verified by experiments.In addition,this paper conducts temperature sensing experiments based on a quasi-frequency standard source.By setting the reference light path and the sensing light path,the sensing ? phase shift grating is placed on the Thermo Electric Cooler(TEC)cooling plate to change its temperature,thereby causing the center frequency drifts of the sensing ? phase-shift grating.The relationship between the temperature change and the frequency drift is demodulated through the cross-correlation algorithm to obtain the temperature sensing empirical formula and the temperature sensing resolution,accuracy and range parameters.The innovation of this paper is that the ? phase-shift grating is placed inside the gallium point bottle as the frequency reference standard needed for laser frequency stabilization and the reference point for temperature measurement.When the grating is applied to temperature sensing,it can theoretically achieve higher resolution and accuracy.The experimental results show that when the triangular wave of 200mHz and 800mV is used to sweep the laser frequency,when 10%of the laser input ? phase-shift grating,the minimum frequency resolution of the system is 3.781 MHz,the sweep range is 30GHz,and the frequency stability fluctuation is 471 MHz within 5 minutes after frequency locking,the system noise was analyzed and optimized based on the Allen variance and Kalman filter.After the filtering,the frequency fluctuation of 3 hours was 158MHz,and the frequency stability calculated by the Allen variance was 6×10-8 at 1s integration time and 2×10-10 at 1000s integration time.When the quasi-frequency standard source is applied to temperature sensing,the final measured temperature resolution is 0.0167?,the temperature measurement accuracy is±0.393?,and the temperature sensing range corresponding to the 30GHz sweep frequency range is 26.4568?.The resolution of the system can be improved by increasing the number of ADC/DAC bits to achieve more accurate temperature sensing.In addition,the instrument parameters used in the experimental system have a great impact on the measurement accuracy.If the instrument with better stability and higher precision can be used,the accuracy of the system can be effectively improved.