This report analyses possible mechanisms of conversion of noise-like laser pulses into coherent ones with comparatively high efficiency. It is demonstrated that incoherent or partly coherent pulses can be promising for phase-insensitive pumping in processes where the structure of pumping pulses is not related to the structure of generated/transformed pulses. Among applications that leverage such processes may be mentioned, for example, passively mode-locked pulse generation, supercontinuum generation in a nonlinear amplifier, as well as some others. Efficient conversion of noise-like laser pulses into coherent solitons enables attractive prospects of application of localised noise-like wave objects capable of carrying relatively high energies.
For the first time demonstrated are possibilities of control over the duration of sub-pulses within nanosecond noise-like pulse bunches, from 1.4 ps to 170 fs, through spectral filtering of radiation. The proposed method is implemented on the basis of an actively mode-locked Yb fibre laser. Prospects of electronic control over sub-pulse duration are analysed and practical applications are further discussed, in which sub-pulse duration may be important.
This work studies a fibre laser platform for generation of controllable localised wave structures. It was found out that a figure-8 laser with two independently pumped active media allows precisely controllable generation of solitary-wave bound states of up to the 6th order. Nonlinear shortening of the temporal pulse separation was discovered when 3 or more bound pulses are generated. Shown are the peculiarities of transitions among pre-determined dissipative multi-soliton complexes occurring both with and without Raman wave generation. Provided are distribution maps of peak power and energy of stable bound waves depending on pump powers of the active media.
We report on study of photonic device based on a new spectral Raman converter allowing conversion from incoherent double-scale pumping laser pulses into coherent solitons. The developed photonic device features saturable absorption in the fibre cavity of synchronously pumped Raman laser. Conditions are identified allowing conversion efficiency over 45%. The limitations and advantages of the proposed approach are demonstrated, and also the prospects of its implementation in an all-fibre configuration. Efficient conversion of noise-like laser pulses into coherent solitons through nonlinear Raman shift phenomena enables attractive prospects of application of localised noise-like wave objects capable of carrying relatively high energies.
This work presents for the first time a study of a fibre laser mode-locked due to a carbon-nanotube-based saturable absorber whose parameters could be controlled by a joined action of optical radiation and electric field. Combination of different types of control (optical and electrical) allowed variation of dynamics of the saturable absorber parameters and greater choice of pulsed generation regimes.We demonstrated the possibility of live switching of laser generation between various pulsed regimes through combined electro-optical action on the polymer-free carbon nanotube film.
We demonstrate for the first time a fibre Raman laser delivering record-setting energy (60 nJ) of double-scale picofemtosecond pulses at wavelength of 1270 nm, which is of great interest in bio-medical applications. A Stokes wave was generated in single-stage Raman conversion of amplified radiation from a mode-locked F8 Yb-doped laser passing through a synchronously pumped phosphosilicate fibre ring cavity. The converted radiation at 1270 nm amounting to 47% of the total Raman laser output was maximised by tuning the repetition rate of the pulses generated in the Yb-doped master oscillator to the fundamental inter-mode spacing frequency of the phosphosilicate fibre cavity.
The work reports for the first time on fibre-based Raman conversion with relatively large Stokes shift pumped by double-scale laser pulses having various degree of coherence. It was discovered that the degree of coherence of the pump pulses affects significantly the amount of the wavelength shift, intensity, and spectral width of frequency-downconverted radiation. At lower coherence within double-scale pulses, the magnitude of intra-pulse femtosecond field oscillation grows, leading to stronger nonlinear pulse interaction with the optical medium. This discovery suggests new approaches to nonlinear transformation of partially coherent laser pulses, typical of many mode-locked generation regimes of fibre lasers.
In the current work we demonstrate mode-locked fiber laser with automatic adjustment a coherence degree of the output pulses. As a source of the pulses we used 8-figure fiber laser with two amplifying fibers inside both loops of the laser cavity. Such configuration provides various pulsed regimes that have different degree of coherence from fully mode-locked single scale pulses to partly mode-locked double scale pulses. To search a pulsed regime with defined parameters we applied automatic genetic algorithm. To prove the feasibility of the genetic algorithm we applied it to find double – scale pulsed regimes with a fixed envelope duration of 50 ps and the contrast of the coherence peak in range of 0.02 – 0.5.
The work presents for the first time a comparative study of mode-locked figure-8 laser, in which two independently pumped active media are located either in the same or in different cavity loops. It is shown that the NALM2 configuration (both active media in the same cavity loop) delivers both higher average and peak radiation power. Flexibility of NALM/NALM2 technologies is further demonstrated for implementation of algorithmic electronically driven control over radiation mode-locking regimes. Also discussed are the results of experimental testing of electronic methods relying on NALM/NALM2 technologies for setting desired generation regimes.
The present work proposes and studies approaches for development of new modified non-linear amplifying loop mirror (NALM) allowing flexible and dynamic control of their non-linear properties within a relatively broad range of radiation powers. Using two independently pumped active media in the loop reflector constitutes one of the most promising approaches to development of better NALM with nonlinear properties controllable independently of the intra-cavity radiation power. This work reports on experimental and theoretical studies of the proposed redesigned NALM allowing both a higher level of energy parameters of output generated by mode-locked fibre oscillators and new possibilities of switching among different mode-locked regimes.
In this work, we present our results of RF spectral analysis applied to mode-locked lasers and propose a method of qualitative assessment of mode-locked operation, which allows differentiation of individual generation regimes by a parameter calculated from RF spectra of the fundamental and the n-th radiation harmonics. The proposed parameter is derived both from the signal-to-noise ratio and from width and amount of additional noise present in RF spectrum of inter-mode beats at the fundamental pulse repetition frequency and its harmonic. This work presents analysis of energy fluctuations and temporal instability of pulse train period for different regimes of pulse generation in Yb fibre laser mode locked due to nonlinear polarization evolution. The paper shows that energy fluctuations of single-scale (“conventional”) pulses is about 1.6%, whereas for double-scale pulses energy fluctuations amount to 11.5%. Temporal instability of double-scale pulse train period is 1.5 times higher in comparison with single-scale pulse train period.