Research On Fiber Laser Refractive Index Sensor In 2 ?m

Refractive index is a very important parameter in many fields such as biology,chemistry,petroleum testing,and food safe.Compared with other types of sensors,optical fiber sensors have the advantages of simple structure,easy manufacturing,light weight,corrosion resistance and electromagnetic interference resistance.Therefore,they are widely used in refractive index measurement research.However,the traditional wide-spectrum fiber sensor has the disadvantages of wider 3 dB bandwidth and lower optical signal to noise ratio(OSNR).Compared with the traditional broad-spectrum sensor system,the proposed fiber laser sensor has a higher OSNR of 40 dB and a narrower 3 dB bandwidth of0.05 nm,which will significantly improve the resolution of sensing.In this paper,we analyze the refractive index laser sensing theories of single-mode fiber dual biconical structure based on mode interference and the single mode-tapered seven core-single mode based on mode coupling.A distinct characteristic of 2 ?m band is the coverage of a strong water absorption band near 1950 nm,which can potentially enable an all-fiber RI sensor.This paper fabricated and tested a single mode fiber dual biconical sensor module and a single mode-tapered seven core-single mode sensor module,and placed these two modules in the fiber ring cavity laser sensor system respectively.By changing the refractive index outside the sensing module,the filtering characteristics of the sensing module change,thereby shifting the output wavelength of the fiber laser sensor.Therefore,the refractive index can be measured by measuring the change of the laser wavelength.In the refractive index range of 1.3325-1.3793,the sensitivity of the fiber laser refractive index sensor based on the dual biconical structure is-90.487 nm / RIU,while the sensitivity of the fiber laser refractive index sensor based on the single mode-tapered seven core-single mode structure is 549.599 nm / RIU.