Propagation In Optical Fibers Research Articles

Temperature effects on supercontinuum generation using a continuous-wave Raman fiber laser

We describe the effect of temperature variations on supercontinuum (SC) generation in optical fibers using a continuous-wave (CW) Raman fiber laser as a pump. We achieve supercontinuum generation by pumping only ∼2W of power into a 7km-long nonzero dispersion-shifted fiber (NZDSF) in the region of small anomalous dispersion. In these conditions, the supercontinuum builds up basically on modulational instability and Raman. At room temperature, the supercontinuum covers effectively the S, C and L transmission bands defined by the International Telecommunication Union (ITU). Temperature tuning of the fiber environment provides a means of tuning the fiber dispersion, and thus a means of changing the width and shape of the supercontinuum spectrum. We demonstrate a 27% increase in the 10-dB SC width. We believe that the application of this new tuning mechanism to other experimental configurations using pulsed sources might be used to produce extremely broad supercontinuums.

Exact Solutions to Extended Nonlinear SchrödingerEquation in Monomode Optical Fiber

By using the generally projective Riccati equationmethod, more new exact travelling wave solutions to extendednonlinear Schrödinger equation (NLSE), which describes thefemtosecond pulse propagation in monomode optical fiber,are found, which include bright soliton solution, dark solitonsolution, new solitary waves, periodic solutions, and rationalsolutions. The finding of abundant solution structures forextended NLSE helps to study the movement rule of femtosecondpulse propagation in monomode optical fiber.

Computer modelling of tungsten–tellurite photonic crystal optical fibres for parametric fibre devices

Computer modelling of light propagation in optical fibres formed by vacancies in two-dimensional periodic lattices is performed using the MIT Photonic-Bands package to calculate fully vectorial definite-frequency eigenmodes of Maxwell's equations with periodic boundary conditions in a plane-wave basis. The lattices consist of cylindrical holes in bulk glass or of glass tubes with the holes and gaps between the tubes filled with air. Single-site hexagonal and square lattices, often studied both theoretically and experimentally and used in manufacturing silica glass-based photonic crystal optical fibres, are considered. The calculations are carried out for the 80TeO2–20WO3 tungsten–tellurite glass-based fibres with the refractive index frequency dispersion taken into account. The numerical solutions are analysed by the effective mode area approach. The modelled dependences of fundamental mode dispersion on geometrical parameters of the fibres are used to suggest tungsten–tellurite photonic crystal fibres of several types for parametric devices.

Global characterization of optical power propagation in step-index plastic optical fibers

We propose to characterize optical power transmission in stepindex plastic optical fibers by estimating fiber diffusion and attenuation as functions of the propagation angle. We assume that power flow is described by Gloge s differential equation and find a global solution that was fitted to experimental far field patterns registered using a CCD camera as a function of fiber length. The diffusion and attenuation functions obtained describe completely the fiber behavior and thus, along with the power flow equation, can be used to predict the optical power distribution for any condition.

Second-Harmonic Generation in Optical Fibres Induced by aCross-Phase Modulation Effect

When two optical pulses copropagate inside a single-mode fibre,intensity-dependent refractive index couples the pulses through across-phase modulation (XPM). We show that a second-harmonicgeneration (SHG) on a continuous-wave background is possible inthe optical fibre induced by the XPM effect. By means of amulti-scale method the nonlinearly coupled envelope equations forthe SHG are derived and their explicit solutions are provided anddiscussed.

Breaking the limit of maximum effective area for robust single-mode propagation in optical fibers

We propose and demonstrate a novel approach in optical fiber design in which the optical waveguide is formed by a ring of large air holes surrounding a solid silica core. With an appropriate choice of the geometrical configuration, robust single-transverse-mode propagation with a record effective area of 1417 microm2, verified by various methods, was demonstrated. A breakthrough was made toward the development of practical ultra-high-power fiber lasers as we observed negligible loss of the fiber at bending diameters as small as 15 cm.

Germania-based core optical fibers

Germania-glass-based core silica glass cladding single-mode fibers (/spl Delta/n up to 0.143) with a minimum loss of 20 dB/km at 1.9 /spl mu/m were fabricated by the modified chemical vapor deposition (MCVD) method. The fibers exhibit strong photorefractivity with the type-IIa-induced refractive-index modulation of 2/spl times/10/sup -3/. The Raman gain of 300 to 59 dB/(km/spl middot/W) was determined at 1.07 to 1.6 /spl mu/m, respectively, in a 75 mol.% GeO/sub 2/ core fiber. Only 3 m of such fibers are enough for the creation of a 10-W Raman laser at 1.12 /spl mu/m with a 13-W pump at 1.07 /spl mu/m. Raman generation in optical fiber at a wavelength of 2.2 /spl mu/m was obtained for the first time.

Coupled nonlinear Schrödinger systems with potentials

Coupled nonlinear Schrödinger systems describe some physical phenomena such as the propagation in birefringent optical fibers, Kerr-like photorefractive media in optics and Bose–Einstein condensates. In this paper, we study the existence of concentrating solutions of a singularly perturbed coupled nonlinear Schrödinger system, in presence of potentials. We show how the location of the concentration points depends strictly on the potentials.

Numerical simulation of nonuniformly time-sampled pulse propagation in nonlinear fiber

Numerical simulation of pulse propagation in nonlinear optical fiber based on nonlinear Schrodinger equation plays a significant role in the design, analysis, and optimization of optical communication systems. Unconditionally stable operator-splitting techniques such as the split-step Fourier method or the split-step wavelet method have been successfully used for numerical simulation of uniformly time-sampled pulses along nonlinear optical fibers. Even though uniform time sampling is widely used in optical communication systems simulation, nonuniform time sampling is better or even desired for certain applications. For example, a sampling strategy that uses denser sampling points in regions where the signal changes rapidly and sparse sampling in regions where the signal change is gradual would result in a better replica of the signal. In this paper, we report a novel method that extends the standard operator-splitting techniques to handle nonuniformly sampled optical pulse profiles in the time domain. The proposed method relies on using cubic (or higher order) B-splines as a basis set for representing optical pulses in the time domain. We show that resulting operator matrices are banded and sparse due to the compact support of B-splines. Moreover, we use an algorithm based on Krylov subspace to exploit the sparsity of matrices for calculating matrix exponential operators. We present a comprehensive set of analytical and numerical simulation results to demonstrate the validity and accuracy of the proposed method.

Time-Frequency (Wigner) Analysis of Linear and Nonlinear Pulse Propagation in Optical Fibers

Time-frequency analysis, and, in particular, Wigner analysis, is applied to the study of picosecond pulse propagation through optical fibers in both the linear and nonlinear regimes. The effects of first- and second-order group velocity dispersion (GVD) and self-phase modulation (SPM) are first analyzed separately. The phenomena resulting from the interplay between GVD and SPM in fibers (e.g., soliton formation or optical wave breaking) are also investigated in detail. Wigner analysis is demonstrated to be an extremely powerful tool for investigating pulse propagation dynamics in nonlinear dispersive systems (e.g., optical fibers), providing a clearer and deeper insight into the physical phenomena that determine the behavior of these systems.

Exact solutions of the generalized nonlinear Schrödinger equation with distributed coefficients

A broad class of exact self-similar solutions to the nonlinear Schrödinger equation (NLSE) with distributed dispersion, nonlinearity, and gain or loss has been found describing both periodic and solitary waves. Appropriate solitary wave solutions applying to propagation in optical fibers and optical fiber amplifiers with these distributed parameters have also been studied in detail. These solutions exist for physically realistic dispersion and nonlinearity profiles. They correspond either to compressing or spreading solitary pulses which maintain a linear chirp or to chirped oscillatory solutions. The stability of these solutions has been confirmed by numerical simulations of the NLSE with perturbed initial conditions. These self-similar propagation regimes are expected to find practical application in both optical fiber amplifier systems and in fiber compressors.

The application of the extending symmetry group approach in optical soliton communication

A systematic method which is based on the classical Lie group reduction is used to find the novel exact solution of the nonlinear Schrodinger equation (NLS) with distributed dispersion, nonlinearity and gain or loss. We study the transformations between the standard NLS equation and the NLS equations with distributed dispersion, nonlinearity and gain or loss. Appropriate solitary wave solutions can be applied to discuss soliton propagation in optical fibres, and the amplification and compression of pulses in optical fibre amplifiers.

Parallel Split-Step Fourier Methods for the Coupled Nonlinear Schr�dinger Type Equations

The nonlinear Schrodinger type equations are of tremendous interest in both theory and applications. Various regimes of pulse propagation in optical fibers are modeled by some form of the nonlinear Schrodinger equation. In this paper we introduce parallel split-step Fourier methods for the numerical simulations of the coupled nonlinear Schrodinger equation that describes the propagation of two orthogonally polarized pulses in a monomode birefringent fibers. These methods are implemented on the Origin 2000 multiprocessor computer. Our numerical experiments have shown that these methods give accurate results and considerable speedup.

Ultralinear transmission modulation: a new amplitude modulation coding for high efficiency fiber-optic transmissions

A new signal shape modulation which mitigates the effect of self-phase modulation (SPM) is proposed for long-haul amplified transmission systems. This approach aims to reduce the SPM-induced chirp as much as possible by an adapted tailoring of the signal shape. The signal shape is derived in the dispersion-free case. We show that this approach is also valid for nonlinear propagation in dispersive optical fibers.

Fast split-step wavelet collocation method for WDM system parameter optimization

To meet rapidly increasing bandwidth requirements, extensive numerical simulations are an important optimization step for optical networks. Using a basis of cardinal functions with compact support, a new split-step wavelet collocation method (SSWCM) was developed as a general solver for the nonlinear Schro/spl uml/dinger equation describing pulse propagation in nonlinear optical fibers. With N as the number of discretization points, this technique has the optimum complexity O(N) for a fixed accuracy, which is superior to the complexity O(Nlog/sub 2/N) of the standard split-step Fourier method (SSFM). For the simulation of a large 40-Gb/s dense-wavelength-division-multiplexing (DWDM) system with 64 channels, the SSWCM requires less than 40% of computation time compared with the SSFM. This improvement allows a systematic optimization of wavelength-division-multiplexing (WDM) system parameters to achieve a minimum bit-error rate.

Tunable all optical delay via slow and fast light propagation in a Raman assisted fiber optical parametric amplifier: a route to all optical buffering

We propose and demonstrate the use of narrow band optical parametric amplification for tunable slow and fast light propagation in optical fibers. The parametric gain is coupled to the Raman process which changes the gain value moderately but modifies the gain spectral shape. Consequently, the delay is enhanced at short wavelengths while it is moderated at long wavelengths. The maximum delay and tuning range can be optimized with respect to each other considering saturation effects in long fibers. The proposed scheme offers tunable delay in the presence of gain and with a bandwidth which is sufficiently wide to process digital data streams at tens of Gbit/s rates as well as picoseconds pulses.

Enhancing red-shifted white-light continuum generation in optical fibers for applications in nonlinear Raman microscopy

We report an efficient red-shifted continuum generation of picosecond pulses in conventional optical fibers. By using a novel highrepetition rate, high-energy oscillator operating at the fundamental wavelength of 1064 nm, we achieved more than 60% of the output energy in the spectral range from 1150 to 1300 nm, perfectly suitable for broadband coherent anti-Stokes Raman spectroscopy.

Chaos Synchronization in Semiconductor Laser Systems and its Application to Optical Fiber Secure Communications

Chaotic laser synchronization applied to optical fiber secure communications is proposed. A synchronous error equation is achieved to the first order approximation. A model of optical fiber chaotic communication is presented by coupling the chaotic laser synchronous system with optical fiber propagation system. The chaotic synchronous system has been successfully stimulated in a long-haul optical fiber communications. The synchronization is limited by the self-phase modulation in the fiber, and the propagation phase-limited formula and the propagation distance-limited formula are demonstrated. Synchronous errors with optical fiber lengths are calculated. The influences of intensity and phase noises on the synchronous error are also numerically analyzed in detail. Analog and digital optical fiber chaotic secure communications in the system at wavelength of 1.31 μm are studied by numerically simulations. The systems show a good ability of robust security and anti-uncover in time-domain and frequency-domain.

Theoretical studies on optical fiber secure communication using chaotic phase encoding

In this paper, we present the synchronization of chaotic injected semiconductor lasers in an optical fiber system via phase-controllers controlling its lasing p hase shift, and a theoretical model for optical fiber chaotic secure communicati on system via chaos phase shift modulation by coupling a chaotic laser phase con trolled synchronization system and an optical fiber channel. Chaotic synchroniza tion is realized numerically under phase-controllers controlling in a long-haul optical fiber system. Optical fiber chaos propagation formula is demonstrated by analyzing theoretically the effect of optical fiber self-phase modulation on ch aotic signal and synchronization. Chaotic laser phase shift is controlled and it s signal is transmitted via continuous chaos shift keying modulation on end for optical fiber communication encoding. Chaotic laser demodulation is achieved via setting a phase shift of the receiver phase-controllers for optical fiber commu nication decoding. Application of chaotic digital encoding of 50Mbit/s rate is simulated numerically for long-haul optical fiber secure communication. The system parameter mismatch and robustness of anti-noise are analyzed numerically in long-haul optical fiber propagation, in particular.

Properties of soliton solutions on a cw background in optical fibers with higher-order effects

The N-soliton solutions for the integrable Hirota equation describing pulse propagation in optical fibers with higher-order effects are presented by using the Darboux transformation method. As an example, the general one-soliton solution on a cw background is given in its explicit form. Then, two exact analytic solutions that describe (i) modulation instability and (ii) bright pulse propagation on a cw background are discussed in detail. The simulations performed in selected cases show that these soliton solutions can be generated numerically when the involved parameters do not exactly satisfy the required integrability conditions.