Breaking the repetition limit of 2 μm mode-locked fiber laser

The mode-locked fiber laser has the advantages of narrow pulse width, high repetition rate, good tunability, strong anti-interference ability and easy integration. With the increase in the process of integrating fiber optical devices and doped fibers, 1.55 μm and 1 μm conventional band fiber lasers are completely not sufficient for practical applications. Fiber lasers with thulium-doped fiber, thulium-holmium co-doped fiber, holmium-doped fiber as gain media operate at 2 μm range, cover the high transmittance window and high absorption window of the atmosphere. Therefore, 2μm fiber laser has a bright application prospect in such radar, remote sensing, and free space optical communication. In addition, the advantage of active mode-locked fiber laser is that it can achieve super-high repetition frequency and controllable repetition frequency and waveform control, which makes it have important application value in the fields of high-capacity high-speed optical communication, wide-band signal processing, high-speed optical frequency comb generation. However, compared with 1.55 μm and 1μm mode-locked fiber lasers, 2 μm active mode-locked fiber lasers still have poor parameters in terms of repetition frequency, pulse width, tuning range, etc, which is limited by the 2 μm band fiber dispersion and difficult manufacturing process of 2 μm fiber devices. Therefore, it is important to study the 2 μm active mode-locked fiber laser and break through the technical bottleneck of the mode-locked pulse generated at high repetition rate.

    The research team of Professor Wang Tianshu from Changchun University of Science and Technology is devoted to the research of 2 μm ultra-fast fiber laser. A series of key technologies have been developed for the generation of 2 μm all-fiber femtosecond pulse laser, 2 μm high-energy mode-locked pulse and 2 μm ultra-high-repetition-frequency mode-locked pulse. As for the generation of 2 μm all-fiber femtosecond pulsed laser, the related research content of "2 μm mode-locked fiber laser based on nonlinear effect" was published in IEEE Journal of Selected Topics in Quantum Electronics, 2018, 24(3) (Fig. 1). For the generation of 2 μm high-energy mode-locked pulses, the Q-switched mode-locked phenomenon of dissipative soliton resonance pulses in 2 μm passively mode-locked fiber lasers is firstly proposed and discovered. The related research contents are published in Optical Express, 2018, 25(10), an authoritative optical Journal (Fig. 2). Based on this research, research team has broken through the mode-locked pulse laser generation technology in 2.08 μm band up to 10 GHz repetition frequency. At the same time, the number of wavelength channels can be freely switched. The maximum number of channels can reach 27 (Fig. 3). Readers can pay attention to the follow-up reports.

Fig. 1  2 μm multimode fiber laser based on nonlinear effect 

Fig. 2  2 μm Q-switched mode locked dissipative soliton resonance pulse

Fig. 3  2.08 μm multiwavelength active mode locking pulse

About Team
The research group of Professor Wang Tianshu from Changchun University of Science and Technology has been engaged in the research of fiber laser and space laser communication technology for a long time and undertaken more than 10 national and provincial scientific research projects such as the National Natural Science Foundation. More than 40 academic papers have been published in journals such as Optics Letters, Optics Express, IEEE Journal of Selected Topics in Quantum Electronics, and has won the first prize of Jilin's technical invention 1 items. The research achievement of "2 μm broadband tunable fiber laser" has reached the international advanced level after the third party's evaluation. A free space optical communication system based on supercontinuum partially coherent light is proposed for the first time. The research results are of great significance to reduce the bit error rate of space laser communication system in strong atmospheric turbulence environment. In addition, the research group has also carried out a series of in-depth studies in the fields of 2 μm ultrafast fiber laser, Brillouin scattering based fiber sensing and microwave photonics, and in these respects has achieved a number of research results.

Ma Wanzhuo, Wang Tianshu, Wang Furen, et al. Tunable high repetition rate actively mode-locked fiber laser at 2 μm[J]. Opto-Electronic Engineering, 2018, 45(10): 170662.