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Study On Multi-Wavelength Mode-Locked Fiber Laser Based On Nonlinear Effects Of Two-Dimensional Materials

Posted on:2016-03-16Degree:DoctorType:Dissertation
Country:ChinaCandidate:B GuoFull Text:PDF
GTID:1108330503469921Subject:Physical Electronics
Abstract/Summary:PDF Full Text Request
Multi-wavelength mode-locked fiber lasers become a hot topic due to their important applications in many fields, such as optical communication, fiber sensors,biomedical research, laser radar system and nonlinear optics. There are currently two schemes, that is, active mode-locking and passive mode-locking, for realizing the multi-wavelength mode-locked fiber laser. For the active mode-locking method,it usually needs acoustic-optic or electro-optics modulator, which makes the laser structure complex, thus, it is difficult to realize the miniaturization and its pulsewidth obtained is usually picosecond level. Compared with active scheme,passive mode-locking shares more benefits, such as structure compact, narrower pulse output and good stability, which make it obtaining in-depth study and application.Saturable absorber(SA) is one of the key devices for the passively mode-locked fiber lasers. Currently, we usually use semiconductor saturable absorber mirror as the SA. However, it requires output lens for coupling the pump light to the fiber, which makes the structure of fiber lasers complex and has more cavity loss. Thus, it is urgent to explore novel SA. In the recent years, topological insulators(TIs) and two-dimensional(2D) sulfides gain huge attention in physics,chemistry and material fields due to their huge nonlinear refractive index, high modulation depth, and low saturable absorption threshold. Currently, the researchers mainly focus on the study of single-wavelength mode-locked pulse, but it is rarely to use of the high nonlinearity of these 2D materials for the generation of multi-wavelength pulses. Meawhile, the mechanism and theory model of multi-wavelength mode-locked fiber laser are yet not to be established and improved,and it is also an ideal platform for the study of the pulse propagation and nonlinear dynamics evolution.In this paper, we construct a multi-wavelength mode-locked fiber laser by exploiting the dual-function of the TIs and 2D sulfides, that is, saturable absorption and high nonlinearity, and its formation mechanism and dynamic evolution were in-depth analyzed. The main contents are as follows:First of all, we theoretically analyzed the formation mechanism and influence factors of the multi-wavelength mode-locked pulses. Its formation originates from the saturable absorption and high nonlinearity of the TIs and 2D sulfides, and the spectral filtering effect due to the combination of the birefringence of single-mode fiber and the polarization-dependent loss of polarization controller. In experiment,we demonstrated a tunable triple-wavelength and four-wavelength mode-lockedfiber laser by exploiting the TI: Bi2Se3/PVA solution and film, respectively.Secondly, we achieved two kinds of nanosecond pulses with high pulse energy by using the TI polymer film as the mode-locker and analyzed their formation mechanisms. The first one is the dual-wavelength rectangular pulse, its pulsewidth varies tunable from 13.62 ns to 25.16 ns with the pump power increasing,corresponding to its pulse energy of 0.593 n J ~ 2.824 n J, which is far beyond that of the traditional soliton(<0.1n J). In experiment, besides the fundamental frequency operation, we also realized the harmonic mode-locking of the dual-wavelength rectangular pulse. The other one is the dual-wavelength hybrid step-like and dark soliton pulse.Thirdly, we demonstrated firstly the fundamental frequency and high harmonics operation of dual-wavelength bright-dark soliton pair in the nearly zero dispersion region of erbium-doped fiber laser(EDFL) by using the TI polymer film as the mode-locker, and analyzed their formation mechanism and dynamic evolution in the fiber laser. In experiment, the highest repetition rate of the dual-wavelength bright-dark soliton pair obtained is 433.8 MHz, which corresponds to the 280 th harmonic. Furthermore, we firstly obtained the dual-wavelength dark soliton in the fiber laser with the TISA. In addition, we also analyzed the effect of the cavity dispersion on the pulse shape and pulsewidth of dual-wavelength bright-dark soliton pair.Finally, we demonstrated firstly the dual-wavelength femtosecond soliton and dip-sideband soliton in the negative dispersion region of EDFL by using the WS2-based fiber-taper as the mode-locker, and analyzed their formation mechanism and dynamic evolution in the fiber laser. The propagation mechanism of single wavelength femtosecond pulse in single mode fiber is also analyzed by using the coupled nonlinear Schrodinger equation. The study shows that the formation of dual-wavelength solitons in fiber laser is determined by the combination of the cavity dispersion, birefringence, high nonlinearity and saturable absorption.However, the formation of dip-sideband soliton can be attributed to the four-wave mixing of parametric process. For the single-wavelength soliton, we obtain its maximum spectrum width of ~11.48 nm and minimum pulsewidth of ~220 fs reported until now. Meanwhile, we firstly obtained dual-wavelength femtosecond soliton with the spectrum width of ~4.2 nm and ~4.4 nm, which corresponds to pulsewidth of ~605 fs and ~585 fs, respectively.
Keywords/Search Tags:fiber laser, mode-locking, multi-wavelength, topological insulator, WS2
PDF Full Text Request
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