| Tunable femtosecond fiber lasers have become a hot research topic in the laser field in recent years due to their tunable wavelength,high integration,and fast tuning speed.They are widely used in fields such as sensing,industrial processing,national defense,and basic scientific research.The realization of wavelength tunable fiber lasers is mainly divided into three technical methods: adding wavelength selective devices such as optical filters to the laser cavity,using optical nonlinear effects to change the optical transmission mode,and connecting a modulator to change the laser cavity loss.However,conventional tunable fiber lasers are often costly,complex in structure,and difficult to operate.Therefore,it is very meaningful to realize a tunable fiber laser with compact structure,easy operation and excellent stability.Passive mode-locking technology is a technical means to realize femtosecond ultrashort pulse laser,and saturable absorber is the core device among them.The light absorption characteristics of gold nanomaterials are mainly derived from its surface plasmon resonance effect.Because of its excellent fiber compatibility,fast response time and high third-order nonlinear coefficient,it is regarded as a kind of great potential.The saturable absorber.Our research group has realized the pulsed laser output of 1?m,1.5?m and 2?m wavelength based on gold nanorod saturable absorber,but has not studied the tunable fiber laser based on gold nanorod saturable absorber.In response to the above problems,the author conducted a systematic study on the regulation of gold nanorods based on temperature,and proposed a tunable fiber laser based on temperature regulation,and achieved the following research results:(1)Designed and studied the regulating effect of temperature on the saturable absorber of gold nanorods.Through research,it is found that the horizontal and vertical plasmon resonance absorption peaks of gold nanorods are located at 523 nm and 900 nm,respectively,and the absorption spectrum covers 500-3000 nm.Since the temperature can control the plasmon material,increasing the temperature will affect the surface plasmon resonance effect of gold nanoparticles,resulting in changes in the absorption characteristics of the saturable absorber.Therefore,as long as the temperature of the gold nanorods is adjusted,the center wavelength of the output laser of the fiber laser can be tunable.The above results indicate that gold nanorods can be used as a saturable absorber to be used to achieve a tunable ultrashort pulse fiber laser in the 2?m band.(2)Design and develop a tunable pulsed fiber laser based on gold nanorod saturable absorber.In order to design the saturable absorber device to be easy to operate and at the same time reduce the negative impact of the photothermal effect produced by the gold nanorods on the laser,we designed and developed a saturable absorber with a composite structure of gold nanorods and D-shaped fibers based on the evanescent field effect.Device.Not only is it convenient for temperature control and experimental operations,but it can also effectively increase the damage threshold while ensuring the saturable absorption performance of the gold nanorods.It is placed in a ring cavity thulium-doped fiber laser.When the pump power is increased to 700 m W,a modelocked pulse laser output with a center wavelength of 1952.7 nm is realized,and the output pulse full width at half maximum is 370 fs.The laser can maintain at least 90 continuous Stable operation within minutes.During the process of increasing the temperature of the saturable absorber from-5 ? to 45 ?,the center wavelength of the laser output laser was red-shifted from 1962.3 nm to 1965.9 nm,about 3.6 nm.In the process of decreasing the temperature from 45°C to-5°C,the center wavelength of the output laser blue-shifted from 1965.1 nm to 1961.6 nm,about 3.5 nm. |
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