The state of a soliton is characterized by the eigenvalues of the Zakharov-Shabat problem.1 Generation of high-intensity pulses through inelastic soliton collisions in dispersion oscillating fibre could be carried out. The inelastic collisions leads to the change amplitudes of solitons, group velocities and even of number of solitons. The generation of giant pulse can be controlled by variation of the modulation period and temporal separation between colliding fundamental solitons. The proposed approach allows to generate rogue waves as result of the inelastic collision of optical solitons.
It is known that eigenvalues of Zakharov-Shabat problem can be used to encode a signal in soliton communication lines. We propose to use dispersion oscillation fiber as a new versalite tool to control the eigenvalues. A fiber with sine-wave variation of the core diameter can be used to manage both real and imaginary parts of the eigenvalues. Change of real part of the eigenvalues results in a splitting of an optical breather into two distinct pulses propagating with the different group velocities. Change of imaginary parts of the eigenvalues allows to realize a reverse process of merge of two solitons into high-intensity pulse. The splitting of optical breather and merge of solitons can be obtained even under the strong effect of stimulated Raman scattering. We believe tools and techniques based on use of dispersion oscillating fiber will grant unprecedented control over soliton eigenstates.
Artificial periodic structures offers an additional degree of freedom in manipulation of nonlinear waves and solitons. It is shown that periodical variation of the coefficients of nonlinear Schrödinger equation allows to change soliton eigenvalues. Pairwise interaction of solitons is demonstrated. The interacting solitons can be selected by appropriate period of the variation of the coefficients of nonlinear Schrödinger equation. The proposed approach for controlling soliton eigenvalues allows to manipulate soliton fission process.
We present an axially tapered large mode area W-fiber for high peak power femtosecond pulse propagation at 1550-nm wavelength. Our numerical simulations show pulse compression with output pulse of 36 kW peak power and 81 fs duration in down-tapered case and nearly undistorted propagation of 20 kW, 150 fs pulse in up-tapered case. Such direction dependent propagation of the pulse in the fiber should find applications in high power laser systems.
The optical pulse evolution in a highly nonlinear normal dispersion increasing fiber has been considered both experimentally and theoretically. It was found that in highly nonlinear fiber with longitudinally increasing normal dispersion large spectral broadening could occur with minimal temporal instabilities. This spectral broadening impose the linear frequency modulation i.e. chirp, required for high-quality pulse compression. The pedestal-free compressed pulses have been demonstrated after de-chirping in a standard single-mode fiber with anomalous dispersion.
Generation of high-intensity pulses through inelastic soliton collisions in dispersion oscillating fibre is discussed. The inelastic collisions leads to the change amplitudes of solitons, group velocities and even of number of solitons. The generation of giant pulse can be controlled by variation of the modulation period and temporal separation between colliding fundamental solitons. Stimulated Raman scattering and third-order dispersion disimprove the formation of high-intensity pulses. The proposed approach allows to generate rogue waves as result of the inelastic collision of optical solitons.
Optical pulse generation and compression have been numerically studied in anomalous dispersion
decreasing fibers (DDF). We show that evolution of modulation instability observed with chirped
wave packets in tapered fibers produces the mechanism for generation of ultra-short pulses with
high repetition rates. The role of modulation instability and Raman self-scattering has been also
discussed. The simulations show that pulse chirping enhances self-Raman scattering at early stages
of pulse propagation and improves compression of the generated pulses. It is also shown that the
presence of amplitude and frequency modulation of the seed wave provide essential impact on the
pulse train formation. The new method for increasing the pulse train repetition rate through
frequency modulation of the seed wave has been proposed.
The study highlights the effect of different modes of in vivo laser irradiation of mice using a PFL8LA laser with λ = 1560 nm, pulse duration of 1,4•10-12 s, peak power of 3,72•103 W and average output power of 20•10-3 W on the lipid peroxidation parameters: conjugated dienes, ketodienes and conjugated trienes, malondialdehyde, Schiff bases and the activity of antioxidant enzymes - catalase, glutathione -S-transferase and superoxide dismutase in erythrocytes and plasma of mice. Two groups of mice received a total dose of 3.8 J/cm2 per group, but the 1st group was irradiated only once, while the 2nd – four times. Significant differences in the parameters of the 1st and 2nd groups indicate different effects of the irradiation modes on redox-dependent processes in red blood cells of mice.
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.
The present work discusses effect of infrared (IR) femtosecond laser irradiation on neoplasm of white
mice with experimental cervical cancer- 5 (CC-5 on the 20th and 30th days after tumor transplantation). Tumor
tissue was irradiated by femtosecond erbium doped fiber laser: the wavelength is 1.55 μm, average and peak
powers are1,25 mW and 6kW, respectively, irradiation trials n=10. The average energy density (energy dose)
on a tissue for two groups of animals was 0,24 J/cm2 and 0,36 J/cm2 for a single trial. Irradiation was
followed by biochemical determination of LPO AOS parameters (“Lipid peroxidation-antioxidants” system):
malondialdehyde (MDA), activity of superoxide dismutase (SOD), catalase and glutathione-reductase (GR),
glutathione-S-transferase (GST). A subsequent morphological study of tumor tissue was performed.
Mathematical analysis of data demonstrates a weak dependence of the studied parameters on energy
dose. The latter implies the trigger effect of IR femtosecond laser irradiation on redox-dependent processes in
neoplasm at experimental cervical cancer.
The cytochemical analysis of the aerobic and anaerobic bactericidal, phagocytic activity, phagocytosis
completeness, as well as membrane topology and rigidity has been performed with the Scanning probe
microscopy (Solver Pro, NT-MDT, Russia) in neutrophils of the patients with cervical carcinoma treated
with the Erbium laser radiation at different intensity. The obtained data reveal a significant effect of the
femtosecond laser radiation on neutrophil morphofunctional state in patients with cervical cancer. The
efficiency of the femtosecond radiation depends on its intensity and clinical stage of the cervical cancer.
The effect of femtosecond laser radiation provided by the Erbium fiber laser with the pulse duration
of 10-13 s, peak and average power of 6,0±0,3 kW and 1,26±0,15 mW, respectively, wavelength λ of 1,55 μm
has been studied in the experiments on rat ascitic ovarian tumor cell in vitro. Irradiation has been performed
at the average intensity of 0,033±0.002 mW/cm2 at two expositions under femtosecond laser radiation of 600
and 900 s. The membrane topology and rigidity of the cancer cells have been estimated with the Scanning
probe microscopy (SolverPro, NT-MDT, Russia). Besides, the viability and apoptosis of the cancer cells have
been estimated. Free-radical processes and antioxidant enzyme activity have been studied in cancer cell
lysate. Femtosecond laser irradiation was established to increases the activity of the
"Lipoperoxidation - antioxidants" system in neoplasm, enhance the apoptosis, decrease the viability, and change cancer cell
membrane topology and rigidity in vitro depending on the energy density of the irradiation.
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.
In this paper, we propose a novel all-fiber laser scheme with the output wavelength of 1565 nm based on a new Er-doped
fiber design. A conventional commercially available pump source at 980nm (D=105μm, NA=0.2) is used for pumping.
A high slope efficiency of 28% comparable with those in Er-Yb lasers was achieved owing to the utilization of the novel
P2O5-Al2O3-SiO2 (PAS) glass as the host for Er3+ ions. A relatively low in-cavity fiber length (~14m) becomes possible
owing to a small outer fiber diameter (80μm) and the use of a fiber taper (105μm to 80μm) for launching the pump.
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.
In this work we experimentally demonstrate the possibility to build up the L-band tunable GHz repetition rate
fiber laser via a dispersion flattened dispersion decreasing fiber. High quality fully synchronized with clock source
0.9 ps pulses are generated.
The possibility to build up an optical source of femtosecond pulses that are smoothly tuned in the telecommunication range using a dispersion-decreasing fiber is demonstrated. The smooth tuning is based on the Raman frequency conversion of ultrashort pulses, which can be effectively tuned due to the compression mechanism for maintaining of a relatively high pulse intensity in the medium with a monotonically decreasing anomalous dispersion. The generation of a 90-fs soliton pulse whose wavelength is smoothly tuned in the wavelength range 1.55 - 1.85 μm is experimentally demonstrated.
A novel method to increase the pulse repetition rate by means of fission of second-order solitons in the fiber with
periodically modulated dispersion is studied. The experiments confirm the results of numerical simulations. The
efficient doubling of the pulse repetition rate takes place in dispersion oscillating fiber (DOF). Good agreement
between theory and experiment was obtained.
KEYWORDS: Optical fibers, Solitons, Dispersion, Optical solitons, Optical signal processing, Digital signal processing, Signal processing, Control systems, Single mode fibers, Fiber optics
The single mode fibers with chromatic dispersion varying along the
length are attracting a considerable attention due to their value for optical soliton processing and applications in stable sources of ultra short optical pulses. In particular, dispersion decreasing fibers (DDF) have been recognized to be useful for high-quality soliton pulse compression and stable against pump noise continuum generation.
The fibers with varying along length dispersion can have a lot of
application in optical signal processing. The method to produce fibers varying along the length from standard preform had been developed. It is possible to draw fibers with a necessary length dependence on the diameter with high accuracy. During the drawing process information about the current diameter is processed by digital control unit and compared with a calculated value. The dispersion deviation from the prearranged value is less than 0.1ps/nm/km. High-quality pulse compression has been obtained in DDF. The compression factor is determined by the ratio of input to output dispersion and typically limited to about 20. Using DDF with optimum dispersion profile it is possible to generate pedestal-free pulses of less than 50fs duration.
In addition, a new DDF design allows to increase the SBS threshold by 7dB over the conventional nonlinear fibers.
The single mode fibers with chromatic dispersion varying along the
length are an attractive medium for nonlinear optics. For optical
soliton, a small dispersion varying perturbs soliton in the same way as an amplification or loss. Such fibers allow to realize both the regime of effective amplification and the effective compression of optical solitons. The method to draw fibers varying along the length from standard preform had been developed. The length of fiber with varying dispersion may be in the range from several meters to several kilometers. The dispersion deviation from the prearranged value is less than 0.1ps/nm/km. In accordance with modern theoretical underground it is possible to develop the DDF (dispersion decreasing fiber) with advanced dispersion
profile to reduce radically the timing jitter and extend the
transmission distance. In addition, one is able to design the
dispersion profile of dispersion varying fiber (DVF) in such way that
it would be possible to apply one and the same DVF both in linear WDM
and soliton communication systems.
A digital control system to draw fibers varying along the length from standard preform had been developed. It is possible to obtain bers with a necessary length dependence on the diameter with high accuracy. During the drawing process information about the current diameter is processed by digital control unit and compared with a calculated value. A control signal produced by the computer is passed to the drawing unit. Ada (ANSI-MIL-STD-1815A) has been choosen as programming language to develop the control system software. In particular the single mode bers with chromatic dispersion decreasing along the length (DDF) had been fabricated. Such bers are an attractive medium for optical signal processing and advanced communication systems. The DDF length may be in the range from several meters to several kilometers. The diameter deviation from the pre-arranged value is less than 0.2%.
The single-mode fibers with chromatic dispersion varying along the length are a novel medium for non-linear optics. For optical soliton, a small dispersion variation perturbs soliton in the same way as an amplification or loss. The fibers with varying dispersion can have a lot of application in the soliton propagation control. Such fibers allow us to realize both the regime of effective amplification and the effective compression of optical solitons. This method needs the precise control of the varying fiber core diameter and for the first time has been implemented.
Metal-coated (Al) tapered all-silica fibers with core diameter up to 1.2 mm, the input/output diameter ratio up to 3:1, the tapered length 1.5 - 2 m, and the core-clad refractive index difference up to 0.017 have been prepared for high energy laser pulses delivery. The increased input diameter allows us to launch higher energy into the fiber keeping the surface power density well below the threshold of radiation-induced surface damage. Using laser radiation with the beam divergence of 3 mrad, the transmission of the fibers has been found to be 85%. Both free running and Q-switched TEM00-mode regimes of Nd:YAG laser have been used to demonstrate stable operation of the fibers for the following set of input parameters: 40 mJ pulse energy, 25 ns pulse duration, and 15 Hz pulse repetition rate.
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