Study Of Microscale Dimensional Sensing Based On Fiber Bragg Grating

With the development of modern fabrication industries, the demand formicroscale components with precious structure is increasingly urgent. But thedimension and profile measurement precision of the microstructure is far frommeeting the manufacturing requirement, so it has become the main obstaclerestricting the development of precision manufacturing. At present, the method ofmeasurement of coordinate measuring machine with the probe sensor ofmicro-displacement is considered to be one of the most effective way in thehigh-precision measurements of microstructures. Positioning accuracy of coordinatemeasuring machine has reached the nanoscale, so the performance of themicro-displacement sensor is the key factor that limits to further improve accuracyof microscale measurement.In this paper, the author uses FBG for micro-displacement sensor, establishes acomplete system of fiber grating stress analysis and simulation, analyzes the pitchchanges of FBG and the index distribution of fiber core, designs a correspondingmicro-displacement sensor, and verifies the performance of sensor through theexperiment. Main research contents of the paper are given as follows:1. The basic structure of the micro-displacement sensor based on FBG isproposed according to the principle of FBG sensor. In order to eliminate theinfluence of temperature change on the micro-displacement sensor, temperaturecompensation based on the reference FBG is designed.2. The probe analysis model of sensor is established. Depending on the materialmechanics theory, stress generated by micro-displacement effects on FBG structureparameters are analyzed. According to the stress distribution, dual FBG probe modelwith high resolution is proposed, which is different from traditional probe model.when micro-displacement occurs, the pitch changes of FBG and the indexdistribution of fiber core are analyzed, and the variation of FBG’s center wavelengthis derived. The simulation of center wavelength variation with micro-displacementis carried out. When the resolution of spectrum analyzer is0.01nm, the theoreticalresolution of sensor is15nm. When the resolution of relatively light power is1‰,the theoretical resolution of sensor is5nm.3. By comparing the structure and analyzing the performance of four broadbandlight source, double pass backward broadband light source is selected, which hashigher output power, better stability and greater width of the wavelength. Since thecenter wavelength of the FBG using in sensor is1540nm, double pass backward broadband light source is optimized by changing the length of erbium-doped fiberand the power of pump. When the length of erbium-doped fiber is12m and thepower of pump is100mW, the broadband source’s spectrum nearby1540nm is flatand the power is high.4. Dual FBG probe is fabricated. The test results of sensor’s temperaturestability show that the sensor’s temperature stability is0.052(peak to peak) withouttemperature compensation, and it is0.006with temperature compensation. Itverifies that the temperature compensation have a good inhibitory effect to theinfluence of temperature. The test results of sensor’s static stability show that thecenter wavelength changes24pm within two hour and it changes5pm within twominutes. The test results of sensor’s resolution show that, the sensor’s actualresolution is20nm using the spectrum analyzer for signal demodulation and it is10nm using the optical power meter for signal demodulation.The research achievements of this paper perfect the theory and simulationmethods of FBG’s center wavelength change when the FBG effect by radial externalforce, and enrich the design ideas of fiber grating micro-displacement sensor. Itprovides a new method for microscale dimensional measurement.