Study Of The Liquid Refractive Index Measurement Based On Polymer Optical Fiber With Micro-holes Created By Femtosecond Laser

Liquid refractive index is one of important parameters to reflect the internalinformation of objects, and it is closely related to the concentration, the temperature,the dispersion, the density, the stress and the heat ratio of the objects.The measurement of the refractive index distribution of the material has the extremelyimportant significance to the science fair project and production practice. And then,the measurement of the refractive index should not only meet the measurementrequirements of the theory but also realistic operability. Nowadays, there are manykinds of optical measurement method of liquid refractive index, and we can dividethese methods into three categories: geometric optical measurement method, waveoptics measurement method and optical fiber sensor measurement.The technology of fiber optic sensor is a kind of new technology, which emergedwith development of optical fiber communication technology. The optical signaltransmitting in the optical fiber are modulated by external environment, then theintensity, wavelength, frequency, phase and polarization state of which will change.And then, the optical fiber sensor will “perceive” the change of external environment.On the basis of Femtosecond Laser micro-processing technology, a newly liquidrefractive index measurement based on polymer optical fiber with micro-holes ispresented in this article. This optical fiber sensor has many advantages, such as goodlinearity, wide measuring range and high sensitivity. In addition, this optical fibersensor can also work in the case of temperature independence approximately.The main work of this article can be roughly divided into two parts:1) The theoretical simulation and analysis of the polymer optical fiber liquidrefractive index sensor with micro-holes.On the basis of the light ray theory, we have done a lot of effort in the study of thetransmission characteristics of the polymer optical fiber liquid refractive index sensorfrom connection loss and refraction loss two aspects, and we found that the transmission power of the fiber will increase and the refraction loss of the fiber willdecrease with the increase of liquid refractive index in the micro-hole under thecondition of the same aperture of the micro-hole and that the connection loss of thefiber will increase with the increase of the aperture size of the micro-holes under thecondition of the same refractive index of the liquid in the micro-holes.2) The experimental study of the polymer optical fiber liquid refractive indexsensor with micro-holes.In order to study the influence of liquid refractive index in the micro-holes, weproduced a micro-hole with1.00mm depth and0.64mm aperture in the center of thepolymer fiber axis by using Femtosecond Laser machining technologies. We find thatthe power loss of the optical fiber sensor will decrease with the increase of the liquidrefractive index in the micro-hole, and there is a good linear relationship between thetwo aspects; this optical fiber sensor has larger measurement range; the largestsensitivity can reach about18.00dB/RIU. The experimental curve of this part is totallyconsistent with theoretical simulation curve on the trend, but there is certain deviationin the aspect of numerical. For the error analysis in this part, we gave the reasonableexplanation in this article.We reduced polymer fiber sensors with micro-holes of0.32mm,0.44mm and0.64mm respectively in order to explore the influence of aperture ontransmission characteristic of the fiber sensors. From the experimental results we cankwon that the loss value and sensitivity of the optical fiber sensors will increase withthe increase of the aperture when the liquid refractive index is constant, and thepolymer optical fiber liquid refractive index sensor which has the largest aperture willhas the highest sensitivity.3) The data simulation analysis of the polymer optical fiber liquid refractive indexsensor with micro-holes.For the theoretical explanation and numerical simulation to the lossy nature of thispolymer optical fiber sensor, we performed a detailed analysis from connection lossand refraction loss two aspects. In the process of data analysis, we chose threepolymer optical fiber sensors with micro-holes of0.32mm,0.44mm and0.64mm as the research object, the aperture of which are corresponding to the aperture of themicro-holes in the polymer optical fiber used in the experiment. We simulatedthe loss.curves of the connection loss and refraction loss of the three polymer opticalfiber sensors, then getting the total theoretical loss value of the sensors under thecondition of different liquid refractive index. We can know that the loss andsensitivity of the optical fiber sensor will increase with the increase of the aperture ofthe micro-holes; the optical fiber sensors with the largest aperture have the highestsensitivity.At the end of the experiment, we explored the influence of the outer circumstancetemperature on the polymer optical fiber liquid refractive index sensor. Theconclusion is that the influence of the environment’s temperature is small on theoptical fiber sensors when the temperature is between20to70degrees.