Research On Micro-fluidic Sensor Based On Side-hole Fiber

Long period fiber grating(LPFG)is a transmission type passive optical fiber device.Its resonance wavelength and resonance peak amplitude are very sensitive to change in the ex-ternal environment.LPFG is used in communication,sensing,filtering and laser,etc.And it has a wide range of applications in these fields.The side-hole optical fiber has two symmet-rical circular holes beside the core,and the circular hole size is large,which facilitates the in-flow and outflow of the sample solution.Therefore,the side-hole optical fiber is suitable for microfluidic manipulation.In this paper,a CO₂ laser is used to write dual LPFGs on side-hole optical fibers to produce a cascaded fiber grating sensor.The sensor can not only measure the refractive index of dual sample solutions,but also has the advantage of temperature compen-sation during refractive index sensing at the same time.The main research contents of this paper are as follows:First,the coupling mode theory is analyzed,and the transmission spectrum of the LPFG is simulated using the transmission matrix method.The relationship among formant depth,resonance wavelength,bandwidth width,number of cycles,period length,and refractive index modulation depth is studied.In addition,the theory of cascaded long-period fiber gratings is analyzed in detail.Second,the construction of the CO₂ laser writing grid system,the production of long-period fiber gratings,the design and preparation of microfluidic cascade fiber grating sensors are completed.The encapsulation of the grating region by the quartz capillary realizes the real-time replacement of the microfluidic sample and achieves the purpose of measuring the refractive index of the sample solution.Finally,the refractive index and temperature characteristics of the microfluidic sensor are measured experimentally.The experimental results show that the refractive index sensitivity of the two LPFG resonance peaks are-88.724nm/RIU and-79.474nm/RIU respectively,and the temperature sensitivity is 52.0pm/?and 55.7pm/?.Using the refractive index and tem-perature sensitivity to derive the sensing matrix of the microfluidic sensor,and then experi-mentally verify the simultaneous measurement of its two parameters.By comparing the theo-retical and experimental data,the sensor's feasibility of measurement are verified.