Time Domain Sensing Characteristics Of All Fiber Laser Output

As a new type of sensor with high accuracy,stable property and strong tolerance to harsh environment,optical fiber sensor has developed rapidly in recent years.DBR optical fiber sensor is one of the most widely used and simplest structures.It is necessary to analyze the time-domain characteristics of DBR fiber laser sensor by studying the self-Q-switching technology of fiber laser.In this paper,the principle of self-Q-switching in highly doped DBR fiber is studied,and the sensing mechanism of self-Q-switched phenomenon of DBR fiber laser sensor under external disturbance is derived.In the experiment,a research scheme for time-domain sensing measurement of pressure using the self-Q-switched characteristics of fiber-optic DBR sensors is described.The results show that with the increase of external pressure on the DBR fiber sensor,a series of approximately linear variations of the output Q-switched pulse characteristics occur: the peak voltage decreases gradually,the pulse repetition frequency decreases gradually,and the pulse width increases gradually.Therefore,the external pressure can be estimated according to the variation of the output characteristics of DBR self-Q-switched laser pulses.Furthermore,a series of experiments are designed to study the effect of doping concentration on the self-Q-switching of fiber.The method of making DBR fiber laser is described in detail.The self-Q-switching output characteristics of four different doping concentration DBR fiber lasers are compared and summarized.For a fixed 85 cm erbium-doped fiber resonator,four kinds of erbium-doped fiber(11.3 dB/m,22.7 dB/m,30 dB/m,80 dB/m)are used to fabricate DBR fiber lasers.Among them,the most excellent self-Q-switching performance is of the 30 dB/m fiber laser,which has the widest self-Q-switching range,the most stable self-Q-switching phenomenon,and the narrowest self-Q-switching pulse width.Generally speaking,for self-Q-switching,it is not the higher the doping concentration,the better: when the doping concentration is too low,the saturable absorption effect is too weak to produce self-Q-switching phenomenon;when the doping concentration is too high,the absorption loss and pump threshold will increase.