Research On Fiber Bragg Grating Demodulation System Based On M-Z Interleaver

Fiber gratings?FBG?have a series of advantages,such as fine diameter,light weight,electrical insulation,low transmission loss,good stability,easy integration,and information transmission,as well as a variety of advantages,such as the drift of the center reflection wavelength and the change of the external environment.Between,for example,temperature,strain,etc.have a certain linear relationship.Therefore,to achieve an accurate measurement using a fiber grating pair,the key is to demodulate the drift of its center wavelength with high accuracy.Among numerous demodulation methods,the Mach-Zehnder?M-Z?interference demodulation method has the advantage of high precision.It is highly valued.The M-Z interference demodulation system based on lithium niobate modulator is studied in this paper.The traditional unbalanced M-Z interference demodulation method is not suitable for static measurement,optical fiber curing package is required,while the internal structure of lithium niobate strength modulator is M-Z type,and considering the flexibility of current optical waveguide fabrication process,the diversity and versatility of waveguide materials,the use of lithium niobate strength modulator instead of optical fiber is used to make M-Z The interferometer can not only greatly improve the demodulation precision,but also can break the limitation of the application of the FBG sensor by the environment interference,so it is of great significance to expand the function and application field of FBG sensor.The demodulation scheme not only maintains the superiority of the traditional M-Z interference demodulation system,but also makes up the defect that the traditional M-Z interference demodulation is easy to be disturbed by the external environment,and is a stable and high-precision M-Z interference demodulation method.The experimental results show that the variance of the experimental data is about 0.15%and the data is less discrete,which shows the stability of the demodulation structure is good.In the study of M-Z interference Demodulation method based on lithium niobate modulator,it is found that the existing lithium niobate modulator arm length difference is too small,it directly leads to the fiber Bragg grating demodulation curve cycle is too large,so that the experimental data can not show a complete cycle,the lithium niobate modulator used in fiber Bragg grating demodulation system has certain limitations,Therefore,the research of comb filter is carried out.In this paper,a M-Z interference demodulation system based on comb filter is designed.The comb filter is composed of a 3x3 coupler,a 2x2 coupler and a mirror,which is simple in structure and small in insertion loss,and can achieve the effect of cascade reflective M-Z comb Filter by the reflection of Mirror,and the use of 3x An idle port in the 3 coupler is used as a monitoring port to maintain the precise control of the coupling coefficient at all times.The comb filter of the structure can not only be used in WDM system,but also applied to the interference demodulation system of fiber Bragg grating.Through theoretical analysis and simulation experiment,this paper obtains:?1?The spectra of the two output ports in this structure have good parity symmetry,unequal bandwidth in frequency domain and steep transmission peaks,that is,when the appropriate coupling coefficient and the interference arm length difference are selected,the structure can realize the unequal bandwidth comb filter,The output waveform is suitable for the staggered use of the spectrum,and when the length difference between the two arms is maintained at a ratio of 1:3,the smaller the arm length difference,the faster the information transmission rate is?2?when the coupling coefficient of coupler and the arm length difference of two coupler are selected,the output curve has a good comb-like spectrum,and in a period of curve,The output intensity and wavelength are monotone change,the curve period is 1.75nm,the reflection peak edge is steep,the curve inclination is higher,the demodulation precision is high,and it is suitable for the demodulation system of fiber Bragg grating.When the change of coupling coefficient k₁ and k₂ is within a certain range?i.e.?k=k×4%?,the deviation between 0.2%⁰.5%and the influence of the experimental results is less.The graph obtained from the experiment accords with the simulation figure.