Dissipative soliton evolution in passively mode-locked fiber lasers with large net-normal-dispersion and high nonlinearity is investigated numerically and confirmed experimentally. I have proposed a theoretical model including the nonlinear polarization evolution and spectral filtering effect. This model successfully predicts the pulse behaviors of the proposed laser, such as the multi-soliton evolution, quasi-rectangle-spectrum profile, trapezoid-spectrum profile, and unstable state. Numerical results show that, in contrast to the typical net- or all-normal-dispersion fiber lasers with the slight variation of the pulse breathing, the breathing ratios of the pulse duration and spectral width of our laser are more than three and two during the intra-cavity propagation, respectively. The nonlinear polarization rotation mechanism together with spectral filtering effect plays the key roles on the pulse evolution. The experimental observations confirm the theoretical predictions.

Numerical and experimental investigation of dissipative solitons in passively mode-locked fiber lasers with large net-normal-dispersion and high nonlinearity

We experimentally demonstrate an all-normal-dispersion Yb-doped mode-locked fibre laser with no intentional spectral filter inserted. Pulses with 1.1 nJ pulse energy at a repetition rate of 20.4 MHz are achieved. A theoretical model of the fibre laser is derived, whose coefficients are explicitly dependent on the orientations of the wave plates and the polarizer. Based on the model, stability diagrams of both the mode-locking and the continuous wave regimes of the laser are presented. The influence of group-velocity dispersion (GVD) and cavity length on the stability of mode-locking is also discussed.

https://iopscience.iop.org/article/10.1088/1674-1056/19/7/074212/pdf

All-normal-dispersion Yb-doped mode-locked fibre laser and its stability analysis

A novelty dispersion ultra-flattened Bragg photonic crystal fiber (PCF) has been fabricated in this paper. The fiber is composed of compound cores and periodical claddings with 11 coaxial rings. It has flattened dispersion of 8.5±1.3 ps·(nm·km)−1 in the communication wavelength range of 1460–1625 nm. Its dispersion slope alters from −0.0428 to 0.0392 ps·nm−2·km−1. The low attenuation of 0.52 dB/km and low bending loss of 0.09 dB at 1550 nm of the fiber are also achieved. The Bragg PCF has enormously potential application in the fields of dense wavelength division multiplexing systems because of its superior dispersion properties and easy splicing performances.

Dispersion-flattened Bragg photonic crystal fiber for large capacity optical communication system

The filtering mechanism of a free output coupler mode-locked laser based on large-mode-area photonic-crystal fibre is analysed. A filtering-soliton mode-locked laser with 495 fs pulse width and 21 nJ pulse energy is achieved. Another novel cavity configuration is established to eliminate the filtering effect. Pulses, each 457 fs in width and 16.5 nJ in energy, are obtained in a soliton-like regime. Pulses, each 387 fs in width and 15.8 nJ in energy, are also generated in a stretched pulse regime and could be dechirped to 119 fs externally to the cavity.

Mechanism and elimination of spectrum filtering in a high power mode-locked fibre laser with a free output coupler

In this letter, large-mode-area double-cladding ytterbium-doped photonic crystal fiber was designed in theory and fabricated in practice. This fiber we have fabricated successfully has endless single mode operation performance and large inner-cladding numerical aperture of more than 0.75. The struts width between large air-holes in the outer-cladding is about 0.22 μm. The photonic crystal fiber has a mode-area about 1465.7μm2. Due to the material being pure silica and air, such structures have excellent capacity to with-stand high temperature. The laser light can have very good beam quality, even diffraction-limited beam quality because of the single-mode core. This fabrication technical breakthrough of novelty high performance double-cladding ytterbium-doped photonic crystal fibers will give contributions to the high power fiber lasers and promote the progress of technology in the fields of high power lasers.

https://iopscience.iop.org/article/10.1088/1742-6596/276/1/012002/pdf

High Performance Large Mode-Area Ytterbium-doped Photonic Crystal Fiber for Fiber Lasers

A compact and highly stable high pulse energy passively mode-locked fiber laser is presented. A segment of Yb 3+ -doped double-clad large-mode-area fiber with extremely low nonlinearity is developed as the active medium. The self-starting mode-locked operation is achieved by the cooperation of nonlinear polarization evolution and semiconductor saturable-absorber mirror. The fiber laser generates laser pulses with the average power of 160mW at the repetition rate of 55.9MHz (corresponding to pulse energy of 3nJ), and the pulse duration is 10.6ps.

Li Jin-Yan

Papers

A mode-locked Yb 3+ -doped double-clad large-mode-area fiber laser