Abstract
GHz repetition rate fundamentally mode-locked lasers have attracted great interest for a variety of scientific and practical applications. A passively mode-locked laser in all-fiber format has the advantages of high stability, maintenance-free operation, super compactness, and reliability. In this paper, we present numerical investigation on passive mode-locking of all-fiber lasers operating at repetition rates of 1-20 GHz. Our calculations show that the reflectivity of the output coupler, the small signal gain of the doped fiber, the total net cavity dispersion, and the modulation depth of the saturable absorber are the key parameters for producing stable fundamentally mode-locked pulses at GHz repetition rates in very short all-fiber linear cavities. The instabilities of GHz repetition rate fundamentally mode-locked all-fiber lasers with different parameters were calculated and analyzed. Compared to a regular MHz repetition rate mode-locked all-fiber laser, the pump power range for the mode-locking of a GHz repetition rate all-fiber laser is much larger due to the several orders of magnitude lower accumulated nonlinearity in the fiber cavity. The presented numerical study provides valuable guidance for the design and development of highly stable mode-locked all-fiber lasers operating at GHz repetition rates.
Highlights
Mode-locked laser sources capable of producing ultrashort pulses with femtosecond to picosecond durations have enormous impacts on many disciplines of science and technology
The simulation results show that, when the net cavity dispersion is negative, highly stable Fundamental mode-locking (FML) can be achieved in small specific ranges of modulation depth (MD) of the saturable absorber and the small signal gain of the active fiber and the ranges becomes large as the net cavity dispersion becomes large or the reflectivity of the output coupler becomes small
As the net cavity dispersion is positive, highly stable FML can be obtained in large ranges of MD of the saturable absorber and the small signal gain of the active fiber and the stability of the modelocking doesn’t change much with the net cavity dispersion
Summary
Mode-locked laser sources capable of producing ultrashort pulses with femtosecond (fs) to picosecond (ps) durations have enormous impacts on many disciplines of science and technology. Mode-locked pulses at GHz repetition rates can be achieved with harmonic modelocking of a fiber laser [19]. GHz repetition rate pulses can be obtained from harmonic mode-locking of a long-cavity fiber laser with a fundamental repetition rate of MHz [36,37,38,39], in which multiple pulses are formed within a round trip due to the nonlinear effects [37]. Thorough understanding of the mode-locking of cm-long or sub-cm-long fiber lasers with various parameters is very necessary for us to design and develop GHz repetition rate FML-AFLs. Numerical simulation can essentially help us to understand the experimental results and provide guidelines for optimizing the design and development. Guidelines for the design and development of the GHz repetition rate FMLAFLs are given based on the simulation results
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