The Application Research Of DC-PCF Laser Doppler Technology In Micro Multiphase Flow

Dual-core photonic crystal fiber is a new type of total internal reflection photonic crystal fiber.Because of its unique properties,such as high birefringence,good nonlinearity and single mode transmission,it has been widely used in the fields of curvature,temperature,pressure,torque and speed sensing.In this paper,the coherent characteristic of DC-PCF is identified and utilized to develop a new type of optical fiber laser Doppler velocimetry(LDV)system.Since DC-PCF has a structure that two transmission cores sharing a cladding layer,the LVD system is greatly simplified.The LDV sensing probe is further miniaturized,and is easily embedded into MEMS system to measure the velocity of micro/nano fluid.This paper designed and developed the LDV system based on DC-PCF,including:(1)Transmission and coherence properties of DC-PCF.Experimental results showed that the fiber output of two independent beams,and beam intensity complies with the Gauss distribution and the ratio of intensity about 1:1.About 30?m of the distance to optical fiber ending facet,the two independent beams are superimposed to form 5 interference fringes.As increasing the distance to optical fiber ending facet,the spacing of the interference fringes is gradually increasing.At the distance of 2.0cm,the ratio of the intensity of the second order bright stripe with the zero order and the first order bright stripe is 1:2.4 and 1:3.4 respectively.But the calculation results are 1:4.5 and 1:3.5 respectively.Obviously,the fringe contrast based on experimental has less than the theoretical calculation,resulting from the noise during the experimental process.(2)Probe manufacturinging and system configuration of DC-PCF.By using high voltage discharge technology,the optical fiber end is fused to produce a micro len The micro len can be used to optimize the structure of the DC-PCF.A multi particle emission system was designed and fabricated,the light scattering characteristic of particles was analyzed.The LDV based on DC-PCF was established and improved.(3)Velocity measurement based on DC-PCF LDV.According to the principles of DC-PCF LDV,by collecting the forward scattering signals,the single point,two-point and three point velocity measurements are carried out.For the single point measurement,the average velocity of particle is 0.980m/s and the relative uncertainty is 0.5%.For the two and three particles' average velocity were 1.761?1.769m/s and 2.106?2.084?2.097m/s,respectively.The results show that the LDV based on DC-PCF can carry out the multi point velocity measurement.(4)Velocity measurement of the microfluid based on the DC-PCF LDV embedded MEMS.Designing and manufacturing micro system device,the LDV sensing probing based on DC-PCF is embedded into MEMS.The experimental results showed that the movement velocity of fluid flow is 0.113 m/s,suggesting that the LDV based on DC-PCF can be applied in MEMS.