Approach to high pulse energy emission of the self-starting mode-locked figure-9 fiber laser.

The figure-9 fiber laser exhibits excellent performance, but improvement of its output pulse energy is restricted by the laser structure design that ensures self-starting mode-locking. In this paper, we propose and verify a novel method to increase the pulse energy of the self-starting figure-9 fiber laser. By reducing the linear phase shift step-by-step in a self-starting figure-9 laser and synchronously increasing the pump power, the output pulse energy can be increased while the laser can always operate in the single-pulse mode-locking region. Using a 112-MHz dispersion-managed soliton figure-9 fiber laser, the effectiveness of our proposed method is verified, and the laser output pulse energy has been successfully increased to 1.4 nJ, which is 5.6 times the pulse energy before the boost. The entire self-starting mode-locking of the laser including the program-controlled joint adjustment is less than 1s with 100% success rate of more than 100 tests. This method can in principle solve the limitation on the output pulse energy caused by the self-start of the figure-9 laser.