848 kHz repetition-rate narrowband dissipative soliton ps-pulsed Figure-9 fiber laser.

In this paper, we study the limitations of decreasing the repetition rate for the narrowband dissipative soliton picosecond (ps) pulsed Figure-9 fiber laser with periodically saturable absorber (SA), and demonstrate how to decrease the repetition rate of this kind of fiber laser. By asymmetrically increasing the passive fiber length of nonlinear amplifying loop mirror (NALM) to lower SA saturation power, Q-switching instability can be avoided, thus effectively reducing the repetition rate of ps pulses. To combat noise-like pulse caused by excessive reduction of SA saturation power, we invoke the non-reciprocal output characteristics of periodic SA, and combined with increasing the intracavity fiber length outside the SA, we further reduce the laser repetition rate. Repetition rates for ∼10 and ∼20 ps pulses are reduced to 1.7 MHz and 848 kHz, respectively, which are, to the best of our knowledge, the lowest repetition rates of Figure-9 lasers reported thus far.

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.

Reducing the pulse repetition rate of picosecond dissipative soliton passively mode-locked fiber laser.

This paper proposes and demonstrates a method to reduce the repetition rate of all- polarization-maintaining (PM) linear-cavity picosecond dissipative soliton passively mode-locked fiber lasers. An optical coupler (OC) is inserted into the cavity to extract pulse energy, and the cavity length is increased using a low-nonlinear coefficient large-mode field fiber at the rear end of the OC, where the propagated pulse has lower energy. This enables the nonlinear phase shift to be within the tolerated value of the single pulse mode-locking even with a considerably increased cavity length; this allows reducing the laser repetition rate considerably without substantially changing the pulse characteristics. Using the proposed method, for a 0.3-nm filter bandwidth, the laser repetition rate is successfully reduced to 1.77 MHz with a nearly Fourier-transform limited pulse duration of 10 ps; it can be further reduced by optimizing the OC split ratio. The proposed method can be applied to reduce the repetition rate for a picosecond dissipative soliton passively mode-locked fiber laser with an arbitrary bandwidth filter.