Bound Soliton Fiber Laser Mode-Locking Without Saturable Absorption Effect

Abstract

Stable bound soliton laser mode-locking is experimentally demonstrated in an environmentally stable hybrid mode-locked Er-doped fiber laser without incorporating (equivalent) nonlinear saturable absorption effects. The laser is with a sigma-type cavity and exhibits a higher threshold for single to bound soliton mode-locking state transition. A nonlinear eigenstate analysis based on the master equation model and the concept of steady state lasing gain is developed to more physically explain the observed mode-locking state transition phenomena.

Relative Intensity Noise of Hybrid Mode-Locked Bound Soliton Fiber Laser: Theory and Experiment

“…The phase modulation frequency is set around 10 GHz, with a modulation depth around 1. The cavity linear gain is set to be variable from g 0 = 2.5 to 5 to accord with the lower and higher power level cases according to the relation |u 0 | 2 dt ≈ (g 0 /l 0 − 1)E s [25]. The noise enhancement factor θ is set to be 10.…”

“…The pulse width reduction is extremely sensitive in the single-soliton state; this is because the single-soliton is with a larger peak power to induce larger nonlinearity. Figure 5c shows the required steady-state lasing gain for the considered mode-locking states by analyzing the Master equation as an eigenvalue problem [25,36]. The negative real part of the solved eigenvalue exactly corresponds to the required steady-state lasing gain for the corresponding mode-locking state in the presence of all the cavity effects.…”

“…Notice that in our mode-locked fiber laser, there is no equivalent saturable absorption effect [33,34]. The bound-soliton state can be formed in the higher pump power levels in comparison to the single-soliton state [25]. The RIN noises of both states are measured with a fast photo-detector and a radio frequency (RF) spectrum analyzer (Agilent E4440A, Santa Clara, CA, USA) for detailed comparison.…”

“…In the literature, both passive and active mode-locked lasers have been studied extensively, and the agreement between theoretical and experimental results are reasonable for the considered single-pulse mode-locking cases [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. It is well known that some mode-locked lasers can be operated under a bound-pulse mode-locking state, in which two or more adjacent bound-pulses are formed inside the laser cavity [18][19][20][21][22][23][24][25]. Because of the sophisticated balancing effects among different optical linear/nonlinear processes, bound-pulse mode-locking states can exhibit more interesting appearances.…”

“…As a real example, we investigate an environmentally stable 10 GHz hybrid mode-locked Er-doped fiber laser with active phase modulation. The laser is experimentally built with the interesting property that its mode-locking state can transmit from the single-soliton to the bound-soliton mode-locking state by simply increasing pump power [25,26]. The RIN noises of the laser are experimentally measured under both the bound-and single-soliton states for comparison.…”