Study On Q-switched Characteristics Of Active Fiber Random Laser

The Q-switched fiber laser has many other advantages,such as good beam quality,high brightness,choosable wavelength and so on.It can be widely used in precision machining,optical fiber communication and medical fields.The random laser without longitudinal mode makes the regulating the output characteristics of this kind of laser a difficulty and a focus of current research.For much previous study on the Q-switched random fiber laser based on the stimulated brillouin scattering,the shape and the repetition frequency of the Q-switched output pulses of the time domain are irregular.The output pulses in the time domain haven't achieved effective control.Therefore,it is of great importance to adjust and control the output pulses in the time domain.According to the present situation,my research is focus on the regulation of the time-domain Q-switched output pulses of the random fiber laser based on active fiber.Firstly,a broadband reflective pulsed random fiber laser is realized.We analyze the characteristics of the time-domain Q-switched output pulses in detail and verify the generation mechanism of the time-domain Q-switched output pulses through the contrast test.Then,by introducing the compound fiber-based optic ring resonator,the pulsed random laser based on the wide-band reflection structure is optimized.A Q-switched random fiber laser with a frequency-fitered feedback is proposed and implemented,which greatly optimizes the continuity of the Q-switched pulses and the shape and the pulse interval of the sub-pulse sequence.A Q-switched random fiber laser with a wide-band reflection sstructure is proposed.One end of the laser cavity is composed of a reflector based on a circulator.And the other end is composed of a segment of Dispersion Compesation Fiber,which is used to provide distributed Rayleigh scattering feedback.By combining random lasing and Q switching,the generation of random Q-switched pulses is demonstrated in the proposed random fiber laser with simple structure.The laser threshold of the proposed structure is relatively low,but the sub-pulses of each Q switching event are not regular.The time-domain output characteristics of the random laser are analyzed when the ring mirror or the Dispersion Compesation Fiber at one end of the laser cavity is removed respectively.The generation mechanism of the random Q-switched pulses is analyzed and verified.We also realize a Q-switched random fiber laser with a frequency-fitered feedback structure to realize the regulation of random pulse from disorder to order.In this case,we use a compound fiber-based optic ring resonator to replace the reflector of the former wide-band reflection structure.The characteristic of the time-domain Q-switched pulses is greatly improved.First,substantially all of the Q-switched pulses are continuous and don't have a long time interval.Second,the amplitude distribution of the Q-switched pulse is more concentrated,which mainly distributed in the range of 0.3 to 0.5.Third,the sub-pulse sequence becomes more regular.Each Q switching event contains multiple sub-pulse sequences with the same pulse shape and the same pulse interval.The energy of the sub-pulse sequences decay in turn as well.