The effect of cavity dispersion on the dynamics of bound soliton states in a fiber laser has been studied both experimentally and numerically. The mode-locking mechanism in a laser was provided by the frequency-shifted feedback to avoid the influence of soliton attraction that could be induced by saturable absorption. It was found that phase-locked bound solitons are stable for dispersion below the "threshold" value of 0.2 ps/nm which depends on the other cavity parameters. For higher dispersion the bound states collapse resulting in the multiple weakly-interacting soliton regime, circulating randomly within the cavity.
Mode-locked fibre laser as a dissipative system is characterized by rich forms of soliton interaction, which take place via internal energy exchange through noisy background in the presence of dispersion and nonlinearity. The result of soliton interaction was either stationary-localized or chaotically-oscillated soliton complexes, which have been shown before as stand-alone in the cavity. Here we report on a new form of solitons complex observed in Bi-doped mode-locked fibre laser operated at 1450 nm. The solitons are arranged in two different group types contemporizing in the cavity: one pulse group propagates as bound solitons with fixed phase relation and interpulse position eventuated in 30 dB spectrum modulation depth; while the other pulses form a bunch with continuously and chaotically moving solitons. The article describes both experimental and theoretical considerations of this effect.
We present detailed analysis of the algorithm for adjustment of double resonance in short-length Brillouin ring fiber laser. Adapted laser cavity is simultaneously resonant for the pump and Stokes radiations. Demonstrated approach is equally useful for design of single mode fiber lasers with ultra-narrow optical spectra, Q-switched Brillouin fiber lasers as well as for the applications which required high power fiber resonators free from stimulated Brillouin scattering.Keywords: Brillouin fiber lasers, doubly resonant cavity INTRODUCTIONStimulated Brillouin scattering (SBS) through the resonant interaction of light photons with acoustic phonons is a nonlinear process with the lowest threshold in optical fibers 1 . For a monochromatic pump at 1550 nm, the Brillouin gain factor is almost three orders of magnitude higher than the Raman gain, providing an amplification band of ~35 MHz. Therefore, Brillouin gain is commonly used for narrow-line lasing in fiber configurations enabling a variety of the performance characteristics 2-7 . Lately developed Brillouin fiber lasers with a so-called doubly-resonant cavity (DRC) demonstrate low threshold, high spectral purity and low intensity noise 8-16 , and are very promising for a variety of special uses, such as coherent optical communication, interferometric sensing, coherent radar detection, and microwave photonics. In DRC lasers, a singlefrequency Stokes radiation is generated within a short ring cavity which is simultaneously resonant for pump and Stokes waves. Typically, in order to obtain an established single frequency operation, various forms of active 8-10 or passive 11,12 control systems are used. However, such systems are generally designed for the mode hopping control and cannot provide the adjustment of the resonance conditions itself. In order to achieve double-resonance operation in the ring fiber cavity, we have to provide precise and reliable coincidence of the pump laser frequency with one of the cavity resonant modes. Second, we have to be sure that the Stokes wave generated in the cavity by the resonating pump is also resonant to the cavity, i.e. the peak of the Brillouin gain spectrum induced by the pump in the cavity fiber coincides with one of the cavity resonant modes. Generally, it is not precisely the case, especially, for short cavities of several meters. At the resonance, the Brillouin threshold power is minimal. Therefore, commonly used techniques are based on piece-by-piece cutting of the ring fiber with intention to minimize the Brillouin threshold. Such procedure is boring, time-consuming, and gives rather rough approach to the resonance. Here we report a procedure for precise setting of the ring fiber cavity to the Brillouin resonance for any *vaspir@cicese.mx
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