Research On Optical Fiber Strain Sensors Based On Vernier Effect

In key engineering fields,such as large-scale civil engineering and aerospace engineering,the project investment amount is large and the public pays high attention.Once an accident oc-curs,it will not only cause huge economic losses,but also cause severe social impact.Structure health monitoring,SHM,is one of the important means to evaluate the operation status of the main structure of the project and prevent accidents,and it has received extensive attention from the industry.Deformation and damage in the structure can be transformed into local strain changes,which can be identified through a quasi-distributed system.The sensors are the most front-end and most basic elements of the entire system,and their performance determines the accuracy of the entire system.Optical fiber sensors have become one of the most important choices for strain measurement in engineering due to their advantages in enduring harsh environments,small size,anti-electromagnetic interference,and long-distance measurement.Most of the single optical fiber sensing element used for strain measurement is limited by the material properties,and the sensitivity is difficult to continuously improve.The optical Vernier effect is produced by the superposition of the spectra of two interference elements.Due to the slight difference in the spectra of the two elements,a cyclically undulating envelope is formed,which converts the small-range movement of a single interference spectrum into a large-range movement of the envelope,thereby achieving a multiple increase in sensitivity.This article mainly optimizes the design of the optical fiber strain sensor in parallel config-uration based on the Vernier Effect to achieve better performance.The specific research content is as follows:(1)A fiber optical strain sensor with low temperature crosstalk based on the Vernier Effect is proposed.By improving the optical fiber strain sensor in parallel configuration based on the Vernier Effect,the reference arm is applied to the temperature measurement process to achieve the effect of reducing the temperature sensitivity,thereby suppressing the impact of temperature crosstalk.The test results show that this sensor can effectively reduce the temperature crosstalk without affecting the strain measurement performance,as low as 0.09??/?,which is 84%lower than the original sensor in parallel configuration.(2)A sensitivity enhanced strain sensor based on two-arm Vernier Effect is proposed.A dia-mond frame structure is introduced into the sensor in parallel configuration,and the two arms of this sensor are respectively installed on the two diagonal lines of the diamond.When the sensor senses the strain change,the spectra of the two arms move in opposite directions,thereby obtaining a larger relative offset,which makes the sensor have a larg-er amplification factor than the sensor in parallel configuration.The experimental results show that the magnification factor of the sensor is 26.6,while the magnification factor of the sensor in parallel configuration made with the same Fabry-Perot cavities is 6.8,compared to nearly 4 times Promote.Since the free spectral range of the sensor has not changed,but the amplification factor is increased,this feature is beneficial to effectively improve the sensitivity while controlling the cost of the equipment.(3)A method to realize the vernier effect by software at demodulation terminal is proposed.The artificial periodic signal is used to replace the optical signal of the reference arm to produce the same sensitization effect.By eliminating the need for a reference arm,the fabrication process of the sensor is simplified,thus providing a cost saving effect.And the sensor sensitivity can be adjusted by changing the parameters of the generated signal.