| Ultrafast pulsed lasers are widely used in many applications,such as mechanical cold working,spectroscopy,and laser surgery.Recently,ultrafast fiber laser technology has attracted great attention because of its advantages such as excellent heat dissipation performance,high beam quality,high stability,and compactness.Passively mode-locking operation by using semiconductor saturable absorber mirror(SESAM)is a common method for generating ultrafast pulse in fiber lasers.However,SESAM has many disadvantages such as narrow operating bandwidth(<100 nm),slow response time,and intricate manufacturing process costs.For fiber lasers with a simple structure and easy integration,SESAM compatibility is somewhat flawed.Therefore,we need more advanced saturable absorber devices.This paper focuses on the nonlinear optical characteristics of novel quantum dots saturable absorbers and applies them to ultrashort pulse fiber lasers.The main research results of this article are as follows:1.The erbium-doped ultrafast fiber laser based on a new saturable absorber of sulfur quantum dots is realized by using the prepared sulfur quantum dots.In this paper,the Z-scan system is used to measure the nonlinear optical response of sulfur quantum dots at the wavelength of 800 nm and 1550 nm.The measurement results show that sulfur quantum dots have good saturable absorption effect,the nonlinear coefficient is-5.89×10-2cm/GW,and the third-order nonlinearity coefficient is-10.2×10-14 esu cm.When the pumping power of erbium-doped fiber laser is 298 m W,a stable mode-locked pulse train output is obtained with the output pulse width of 720 fs,the corresponding repetition frequency is 8.32 MHz,the central wavelength is 1530.6 nm with the 3-db bandwidth of 3.9 nm.Under the maximum pumping power of 629 m W,the output power of the laser is 7.71 m W,the single pulse energy is 0.927 n J,and the peak power is 1287.06 W.This research results proposed a single element quantum dot materials with saturable absorption effect and a new type of saturable absorber with great potential.2.The GaTe quantum dots were prepared by liquid exfoliation method,and the erbium-doped ultrafast fiber laser based on GaTe quantum dots was constructed.When the pump power is 144 m W,the mode-locked pulse train output,the average for the laser output power of 1.78 m W,the pulse width of 115 fs which is currently using quantum dots new saturable absorber erbium-doped fiber laser output pulse in the shortest possible,repetition frequency is 8.79 MHz,the center wavelength is 1530.9nm with 3-dB bandwidth is 18.1 nm.In addition,an ytterbium-doped ultrafast fiber laser with pulse width of 752 ps,corresponding repetition frequency of 11.73 MHz,signal-to-noise ratio of 50 dB and central wavelength of 1030.72 nm was also realized.3.The NbSe2 quantum dots were prepared by liquid exfoliation method,and erbium-doped ultrafast fiber laser based on NbSe2 quantum dots was constructed.When the pump power is 15 m W,the mode-locked pulse sequence is obtained,laser output pulse width of 765 fs,repetition frequency is 7.7 MHz,signal-to-noise ratio of 50 dB,pulse period is 130 ns,center wavelength of 1556 nm with 3-dB bandwidth of 2.45 nm.It is worth mentioning that is currently using quantum dots new saturable absorber threshold value of the lowest in mode-locked fiber laser.In addition,a ytterbium-doped ultrafast fiber laser with pulse width of 380 ps,corresponding repetition frequency of 12.3 MHz,central wavelength of 1033 nm with 3-db bandwidth of 0.155 nm was realized by using this passive mode-locking device,which further extended the application of this saturable absorption device. |
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