Monitoring The Deflection of Bridge Span With a Spotreduced Fiber Optics Source

A novel method to increase the measurement range and accuracy of bridge deflection based on the laser datum scheme with reduced spot size of a fiber source is proposed in this paper. To get rid of the problems of non-circular field distribution and changes of the semiconductor laser caused by heating and temperature, the output of a single mode fiber has been used as the light source of the measurement system. By pulling a normal single mode fiber into a smaller diameter, a stable and small spot light source for monitoring the deflection of bridge span can be obtained in our experiment. The FWHM of the spot at 20 meters distance from the fiber output can be reduced from 1.96mm to 1.62mm when the diameter of the fiber core is tapered from 4.04μm to 1.7μm.By using a spot reduced fiber light source, the range and accuracy of the laser deflection detection system can be effectively improved, thus the proposed scheme has prospect in practical applications.