In this paper it was investigated the dynamics of frequency-modulated pulses in fiber cascades, consisting of a fibers with sequentially formed refractive index gratings with different periods. It is shown that the proposed scheme can be used to generate picosecond and subpicosecond pulses with peak powers of the order of ~1 MW. In the considered cascade structures, it is shown that it is possible to form stable sequences of pico- and subpicosecond pulses with a subterahertz repetition rate directly from continuous wave signals as a result of a modulation instability regime.
In this work we investigated the possibility of generating subpicosecond pulses as a result of a modulation instability of continuous wave signals with a large modulation depth. In our case a large modulation depth of a continuous wave is achieved by using a cylindrical waveguides with a running refractive index wave (RRIW). Here, the entire cascade fiber system is a cylindrical waveguides RRIW connected in series with a section of passive fiber with anomalous dispersion. To achieve high peak power values in the generated pulse train, it is necessary to add a section of active fiber with normal dispersion to the stage. It is shown that, as a result of the regime of a induce modulation instability, pulses with a peak power that are orders of magnitude higher than the power of the incoming pump wave can be formed.
KEYWORDS: Dispersion, Frequency modulation, Fermium, Optical amplifiers, Fiber amplifiers, Chemical elements, Picosecond phenomena, Modulators, Amplifiers, High power fiber amplifiers
We propose a new all-fiber cascade picosecond pulse amplification scheme based on optical fibers with varying normal group velocity dispersion (GVD). Amplification is performed in the fiber sections with exponential growth of the normal dispersion. Amplification sections are altered by the sections of passive fibers with the decreasing normal GVD. The pulse chirp in dispersion decreasing fibers can be adjusted by the increment of dispersion variation which would allow to control the spectral bandwidth of the pulse to keep it within an amplification band.
In the present work the effects of high-power femtosecond laser irradiation on a functional condition of red blood cells
and neutrophils in vitro have been investigated. The data on parameters of the lipid peroxidation - antioxidants system,
hemoglobin level and rigidity of red blood cell membranes testify destabilization of the membranes under the influence
of the given laser. The study of phagocytic activity, anaerobic and aerobic metabolism of neutrophils, and rigidity of
their membranes allows to suppose the dose-dependent effect to be stimulating.
A method to carry out the compression of parabolic pulse in the nonuniform fibre cascade was proposed. The periodic
modulation of the dispersion along the fibre length can be used to control subpicosecond pulses in time and frequency
domains. Good agreement between simulations and experimental data takes place.
A single-mode fiber with a linear or sinusoidal variation in the group-velocity dispersion is designed and fabricated.
The nonreciprocal effects and pulse compression due to the longitudinal oscillations of the fiber dispersion are
experimentally demonstrated. The periodic modulation of the dispersion can be used to control precisely the
pulse dynamics.
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