Research On Laser And Voltage Sensor Based On Random Grating

Recently,random gratings have attracted increasing scientific interests due to their unique properties and potential applications,which have broad application prospects.In this paper,random grating and its applications in areas of fiber laser and sensor are studied.The details are as follows:1.A random fiber laser based on a 25mm long random phase-shift fiber Bragg grating with a ring cavity is experimentally demonstrated.The random phase-shift grating is fabricated in single-mode fiber with the beam-scanning method.The random feedback and light localization are achieved by introducing 20 phase-shift points with random amplitudes along the grating length.The experimental setup is pumped with a 980nm laser,and the threshold power is only 21.8mW.The single-wavelength or dual-wavelength laser emission can be obtained under different pump power.The 3dB bandwidth of 0.44pm and the optical signal-to-noise ratio up to 55dB for the lasing peak near 1549.96nm are realized at the pump power of 130mW.With the random grating exposed to water,mode competition is effectively suppressed and the laser can be operated at more stable single-wavelength mode.2.A random fiber laser based on above-mentioned random phase-shift fiber Bragg grating with a half-open cavity is experimentally demonstrated.Different optical couplers and different monitoring directions are adopted for investigating the output characteristics under multiple conditions.The stable single-wavelength laser operation with the threshold power of25mW is realized using a 980nm pump laser.The optical signal-to-noise ratio up to 67dB and the 3dB bandwidth of 17.7pm are obtained at the pump power of 350mW.It is found that the emitted wavelength varies linearly with the surrounding refractive index within a certain range by immersing the grating in different concentrations of NaCl solutions,which provides a potential method for lasing wavelength tuning and refractive index detection.3.A voltage sensor based on LiNbO₃ random waveguide grating and its voltage detection method are proposed.The random waveguide grating is used as the sensing head of the sensor.When the voltage is applied to the random waveguide grating,the electro-optic effect of the LiNbO₃ crystal makes the effective refractive index of the waveguide grating changed.The cross-correlation operation is performed between the reflection spectrum of the random waveguide grating and the reflection spectrum of the same grating when no voltage is applied.The detection of the voltage is achieved according to the linear relationship between the wavelength shift corresponding to the peak of correlation curve and the applied voltage.The simulation results show that the sensitivity of the voltage detection using the reflection spectrum of the 1550-1600nm band of the random waveguide grating is as high as 16.0pm/V.LiNbO₃ random waveguide gratings are directly fabricated by photolithography and annealed proton exchange.And the experimental research on the proposed voltage sensor is carried out.