Research Of The Measurement Of Temperature And Optical Rotation Angle Based On Laser Beat Frequency

The beat frequency method is a demodulation technique that is not easily affected by the system loss and light source fluctuation.The light passes through the optical fiber grating,erbium-doped optical fiber,core offset optical fiber,magneto optical fiber and circulator,and then the beat frequency is produced,Using the laser beat theory,light signals output from the fiber cavity resonator,then the output signals are measured by spectrum analyzer,and analyzed using digital signal processing module,the DSP module can also calculate and adjust the data,so that the measurement precision can be improved.Using fiber circuit to replace reflection mirror to avoid light insert loss caused by reflection mirror.Core-offset fiber is sensitive to the change of temperature,the system is simple and small,and it can measure the temperature in different circumstances.Using the double reflective effect of fiber,the rotation angle can be measured more precisely.The system is low-cost and the structure is simple thanks to the good attributes of magneto fiber,such as strong magneto-light effect,high sensitivity,strong resistance to interference,and high insulation.The measurement procedure is simple and fast,which overcomes the cumbersome process in the traditional temperature measurement methods.Two methods that measure temperature and optical rotation angle based on the technology of beat frequency are presented in this paper.The measurement of temperature is based on core offset optical fiber sensing method using the technology of beat frequency.The measurement of optical rotation angle is based on the magneto optical fiber sensing method using the technology of beat frequency.The variation of laser beat frequency at different temperature and magnetic field conditions are studied and the performance of the temperature and magnetic sensing system are investigated.The experimental results with different temperature range from 20 ? to 100 ? show that the beat frequency variation of the temperature sensitivity is-39.125 kHz/?.Beat frequency is decreased with the increase of temperature,and the linear fitting degree is 0.99407.The interval of beat frequency is 13.375 MHz when the current is 5A under room temperature.The simulation results show that the sensitivity of the beat frequency variation with the angle of rotation is 1.77MHz/° when the rotation angle ranges from 0° to 90°.Therefore,the laser beat frequency methods based on the core offset fiber and magneto optical fiber with high resolution,high sensitivity,low cost and stable performance advantages can be widely used in power systems,oil exploration,health care and aerospace and other fields.