Theoretical Analysis of Object Displacement Sensor using Single Mode and Multimode Fiber Coupler

Abstract

This paper studies object displacement sensor using single mode and multimode fiber coupler based on intensity modulation. A single mode fiber coupler has coupling ratio 0.5, excess loss 0.2 dB, and directivity 60dB and 9μm core diameter. A multimode fiber coupler has coupling ratio 0.5, excess loss1 dB, and directivity 40 dB and 200μm core diameter. Two laser diodes were used. The source in the IR region of wavelength 810 nm, output power of 1 mW and the source in the visible region of wavelength 524 nm(green color), output power of 2 mW. The correlation function between output power and object displacement is analyzed theoretically by Gaussian electromagnetic beam approximation Variation in the output power due to object movement by using MATLAB program within displacement range from0-5 mm. Results show a good sensitivity of the sensor 209.6 μW / mm by using single mode coupler and 119.68μW / mm by using multimode coupler for IR laser source .We got a sensitivity of 419.4 μW / mm by using single mode coupler and 239.4μW / mm by using multimode coupler for green laser source.