Short pulse propagation in dense dispersion compensated systems

The short Hermite-Gaussian optical pulse transmission over 1440 km in a dense dispersion compensated system is investigated based on numerical simulation. In the simulation, compensation is made not only for the group-velocity dispersion but also for the third order dispersion. It is demonstrated that the pulse with reasonably lower power can propagate steadily in net zero, positive and negative dispersion system.     

Analysis of fiber Bragg grating with exponential–linear and parabolic taper profiles for dispersion slope compensation in optical fiber links

In this paper, the effect of various taper profiles on dispersion slope compensation in optical fiber links is studied. Theoretical and numerical investigation of the linear and nonlinear group delays of tapered fiber Bragg grating's (T-FBG) under strain is made. Calculation is performed using Matlab code based on solving the coupled mode equation using transfer matrix method. Our study shows that the linear tapered FBG profile provide the best result than the linear-exponential profile which can compensate up to 500 km. As result, the spectral characteristics of tapered grating allow them to be used efficiently in high bit rates WDM and long-haul optical communication systems for chromatic dispersion of single-mode fiber.     

A modified split—step fourier method for optical pulse propagation with polarization mode dispersion

A modified split-step Fourier method (SSFM) is presented to solve the coupled nonlinear Schroedinger equation (CNLS) that can be used to model high-speed pulse propagation in optical fibres with polarization mode dispersion (PMD). We compare our approach with the SSFM and demonstrate that our approach is much faster with no loss of pre-chirped RZ(CRZ) formats in the presence of high PMD through this approach. The simulation results show that CRZ pulses are the most tolerant to high PMD values and the extinct ratio has a great impact on the transmission performance.     

Higher-order effects on self-similar parabolic pulse in the microstructured fibre amplifier

By considering higher-order effects, the properties of self-similar parabolic pulses propagating in the microstructured fibre amplifier with a normal group-velocity dispersion have been investigated. The numerical results indicate that the higher-order effects can badly distort self-similar parabolic pulse shape and optical spectrum, and at the same time the peak shift and oscillation appear, while the pulse still reveals highly linear chirp but grows into asymmetry. The influence of different higher-order effects on self-similar parabolic pulse propagation has been analysed. It shows that the self-steepening plays a more important role. We can manipulate the geometrical parameters of the microstructured fibre amplifier to gain a suitable dispersion and nonlinearity coefficient which will keep high-quality self-similar parabolic pulse propagation. These results are significant for the further study of self-similar parabolic pulse propagation.     

Manipulation role of the relative phase and incoherent pumping on a light pulse propagation

In an open A type system with the spontaneously generated coherence (SGC), when the probe and driving fields have different frequencies, the switching of the group velocity of the probe pulse from subluminal to superluminal is realized not only by adjusting values of the relative phase between the probe and driving fields but also by varying values of the incoherent pumping rate. For the subluminal propagation, the system always exhibits the probe absorption, however, the superluminal propagation is always companied with gain of the probe field.     

Pulse–pulse interaction in dispersion-managed fiber systems with nonlinear amplifiers

The pulse–pulse interaction in a dispersion-managed fiber system is studied for the case when a nonlinear gain and spectral filtering are included into the dispersion-gain map. In this system, the pulse of any shape converges quickly to a dispersion-managed soliton. Using the technique of interaction plane, we have found stable bound states of two pulses. The effects we have studied may significantly reduce the chances of pulse coalescence in specially designed optical transmission lines.     

High-order soliton generation in dispersion flattened fiber

By using the amplified 10-GHz, 5.5-ps sech2 pulses with high quality and chirp-free from regeneratively mode-locked fiber laser (RMLFL) as the soliton source, 2-5 order optical soliton phenomena are observed successfully in a 4.28-km dispersion flattened fiber. The experimental results agree well with the theoretical calculation.     

Experimental research on sound pulse propagation and channel match in shallow water

Theoretical and experimental research of low frequency pulse compression and channel match in shallow water sound channel were carried out based on 2000-Winter Yellow Sea experiment. Using pulse compression method, signals with high signal to noise ratio (SNR) were received over range of 110 kilometers in the experiment. The SNR gain in the process is consistent with the theoretical prediction. The experimental measurement indicated that the channel is highly coherent over a length of 500 s. Channel match method was used to compensate the degradation of pulse compression SNR caused by the multi-path propagation. And the SNR gain in the channel match process can be theoretically predicted. Experimental results show that low frequency pulse compression and channel match method can be used in shallow water sound channel to improve the SNR.     

Broadband dispersion compensating fiber using index-guiding photonic crystal fiber with defected core

We present a novel broadband dispersion compensating photonic crystal fiber with defected core in this paper.The small central defect of air hole can flexibly control the chromatic dispersion properties of this kind of photonic crystal fiber.This kind of fiber has broadband large negative chromatic dispersion,and the chromatic dispersion coefficient varies from-440 to-480 ps/(nm·km)in the measured wavelength range of 1500-1625 nm.The calculated chromatic dispersion curve is well matched to the measured chromatic dispersion coefficient in the range of 1500-1625 nm.The proposed photonic crystal fiber can be used to design the dispersion compensating fiber in the desired wavelength range by adjusting its structural parameters.     

Multifilamentation of high-power femtosecond laser pulse in turbulent atmosphere with aerosol

The filamentation of a femtosecond laser pulse in atmosphere under the joint influence of turbulence and aerosol has been numerically studied for the first time. A result of these studies is that the presence of aerosol in a turbulent atmosphere increases the distance to the onset of multifilamentation. We have studied the competition between two factors of aerosol coherent scattering in the process of multiple filamentation of a femtosecond pulse in the atmosphere: generation of light field perturbations and energy losses. Similarity parameters have been determined for different conditions in the problem of multifilamentation in aerosol.     

Influence of Z-pinch evolution on laser pulse duration at 46.9 nm in Ne-like Ar ions

A capillary discharge 46.9 nm Ne-like Ar laser is achieved with peak current of 20–23 kA. The variation of laser pulse duration with initial Ar pressure and rise-time of main current is reported. Measurements show that the laser pulse durations slightly increase with the increased pressure and increased rise-time of current. A comparison of the experimental results with the calculation of snow-plow model indicates that the increase of laser pulse duration is the result of decreased Z-pinch velocity at the pinch time when the radius of plasma is minimal.     

Multiwavelength L-band fiber laser with bismuth-oxide EDF and photonic crystal fiber

A multiwavelength laser comb using a bismuth-based erbium-doped fiber and 50 m photonic crystal fiber is demonstrated in a ring cavity configuration. The fiber laser is solely pumped by a single 1455 nm Raman pump laser to exploit its higher power delivery compared to that of a single-mode laser diode pump. At 264 mW Raman pump power and 1 mW Brillouin pump power, 38 output channels in the L-band have been realized with an optical signal-to-noise ratio above 15 dB and a Stokes line spacing of 0.08 nm. The laser exhibits a tuning range of 12 nm and produces stable Stokes lines across the tuning range between Brillouin pump wavelengths of 1603 nm and 1615 nm.     

Dissipative solitons compounds in a fiber laser. Analogy with the states of the matter

We investigate experimentally ordered and disordered pattern formation of solitons in a double-clad fiber laser. We point out an analogy between the different states of matter and the states of a set of dissipative solitons. In particular, we have identified a gas, a supersonic gas flow, a liquid, a polycrystal and a crystal of solitons. The different states are obtained only by adjustment of the intracavity phase plates.     

Multipath dispersion of pulse signals in a non-line-of-sight optical scattering channel

Multipath-induced pulse broadening in a non-line-of-sight (NLOS) optical scattering channel is investigated. Expressions for impulse response and digital signal-to-noise ratio (DSNR) penalty induced by inter-symbol interference (ISI) of a NLOS ultraviolet (UV) scattering communication are introduced based on a single-scattering model, and simulated results for some typical atmospheric condition and configuration of geometry are given in the paper. It is shown that the multipath dispersion is one of the most important factors limiting the system performances, and return-to-zero (RZ) format is more suitable for the optical scattering communications than non-return-to-zero (NRZ) format. The method proposed here can be used to predict available bandwidth and data rate of the communication system operating in a NLOS optical scattering channel.     

Effect of the ratio of transition dipole moments on few-cycle pulse propagation

Propagation of a few-cycle laser pulses in a dense V-type three-level atomic medium is investigated based on full-wave Maxwell-Bloch equations by taking the near dipole-dipole (NDD) interaction into account. We find that the ratio,γ,of the transition dipole moments has strong influence on the time evolution and split of the pulse:whenγ≤1,the NDD interaction delays propagation and split of the pulse,and this phenomenon is more obvious when the value ofγis smaller;whenγ=2~(1/2),the NDD interaction accelerates propagation and split of the pulse.     

Soliton–like pulse dynamics in add–drop optical filters based on nonlinear fiber grating couplers

The dynamics characteristics of picosecond soliton-like pulses propagating through add–drop optical filters, based on lossless uniform and Gaussian nonlinear fiber grating couplers, are numerically investigated under different power levels. To obtain the temporal profiles, the nonlinear coupled-mode equations, that model these devices, are solved numerically. These devices can perform the extraction (drop) of an optical signal, since there is the reflection of a pulse previously switched between adjacent waveguides. The extraction efficiency, recurrently better at low power levels, is subordinated to the matching between the associated spectra of the input pulses and the hybrid devices analyzed. The switching effects, as well the gratings responsiveness, impact on the outputs profiles, since diverse temporal shapes can be obtained. The results reinforce the importance and the potential of properly engineered structures for all-optical processing requirements.     

980 nm Yb-doped single-mode fiber laser and its frequency-doubling with BIBO

A quasi-three-level Yb-doped single-mode fiber laser at 980 nm by adopting two 0° fiber ends as cavity mirrors generated a total output power of 1.32 W with the slope efficiency of 75.3%. The fiber length was 36.5 cm close to the optimal theoretical fiber length. The corresponding optical conversion efficiency was 66% from the incident pump power at 946 nm to the laser power at 980 nm. Through frequency-doubling with BIBO crystal, a total output power of 15 mW at 490.8 nm was obtained.     

Effects of Lorentz local field correction on propagation properties of few-cycle pulse in dense Λ-type atomic medium

By solving numerically the full Maxwell-Bloch equations without the slowly varying envelope approximation and the rotating-wave approximation, we investigate the effects of Lorentz local field correction (LFC) on the propagation properties of few-cycle laser pulse in a dense Λ-type three-level atomic medium. We find that: when the area of the input pulse is larger, split of pulse occurs and the number of the sub-pulses with LFC is larger than that without LFC; at the same distance, the time interval between the first sub-pulse and the second sub-pulse in the case without LFC is longer than that with LFC, the time of pulse appearing in the case without LFC is later than that in the case with LFC, and the two phenomena are more obvious with propagation distance increasing; time evolution rules of the populations of levels |1>, |2> and |3> in the two cases with and without LFC are much different. When the area of the input pulse is smaller, effects of LFC on time evolutions of the pulse and populations are remarkably smaller than those in the case of larger area pulse.     

The characters of dense dispersion managed soliton in optical fiber transmission systems

The properties of ultra-short dense dispersion-managed soliton (DBMS) in optical fiber links are investigated. They show some excellent characters, such as, reducing pulse's breathing extent greatly, facing fewer mutual interactions and tolerating larger local dispersion. In general, DBMS is more stable than a conventional dispersion-managed soliton in high-capacity systems. Excessively dense dispersion compensation is more suitable for systems with weak nonlinear effect.