光纤中的光孤子

叙述了光纤中光孤子形成的物理机理。即光纤中光孤子的形成是光纤中散射效应和相应调制效应相互制约、平衡的结果。     

Femtosecond second-order solitons in optical fiber transmission

A propagation of the femtosecond second-order solitons in an optical fiber is studied. We show that a generalized nonlinear Schrödinger equation well describes the propagation of the second-order soliton even containing only a few optical cycles. The propagations of a 50 fs and a 10 fs second-order soliton in an optical fiber are numerically simulated. It is found that, for the case of 10 fs second-order soliton, the soliton decay is dominated by the third-order dispersion, in contrast to the case of 50 fs second-order solitons, where the soliton decay is dominated by the delayed Raman response. It is also found that the exact delayed Raman response form must be used for the propagation of the 50 fs or less than 50 fs second-order soliton.     

Dark solitons in optical fiber with inhomogeneous effects

We study the nonlinear wave propagation in an inhomogeneous optical fiber core in the normal dispersive regime. In order to include the inhomogeneous physical effects, the nonlinear Schrödinger equation (NLSE), which governs the solitary pulse propagation in optical fiber, is modified by adding terms for phase modulation and power gain or loss. The modified NLSEs are bilinearized and exact dark soliton solutions are obtained. The results are discussed.     

Dissipative vector Bragg solitons in a birefringent optical fiber

Motionless dissipative vector solitons are found numerically in a birefringent polarization-conserving optical fiber with a longitudinal Bragg grating and nonlinear amplification and absorption in the polarization capture regime. It is shown that dissipative vector Bragg solitons exist and are stable even if the birefringence is comparatively strong.     

Breathing spatial solitons in non-Kerr media

The concept of soliton internal mode is introduced to explain quantitatively the long-lived oscillations of self-guided beams, or breathing spatial solitons. Cubic-quintic nonlinearity is considered in detail, and it is shown that the existence of the internal mode affects strongly the beam propagation in non-Kerr media, leading to oscillatory dependence of the output width of the beam versus its input power.     

Chirped solitons with strong confinement in transmission links with in-line fiber Bragg gratings

We demonstrate that the use of fiber gratings to reverse periodically the pulse chirp in transmission links allows us to produce stable chirped optical solitons with fast-decaying tails. The interaction between neighboring pulses is reduced from that of the usual soliton system as a result of pulse chirping and strong confinement, making possible dense information packing. Such a pulse is an attractive candidate for use as an information carrier in optical transmission systems with ultralarge capacities of approximately 100 Gbits/s.     

Reduced-power optical solitons in fiber lines with short-scale dispersion management

We examine the properties of dispersion-managed (DM) solitons in fiber lines with dispersion-compensation period L much shorter than amplification distance Z(a) . DM solitons in systems with short-scale dispersion compensation have reduced power compared with DM solitons in previously studied regimes with L>/=Z(a) power (for the same local and average dispersion and the same pulse width). As a result, chirped DM soliton transmission with reasonably low power can be realized with shorter pulses when DM solitons in systems with large L/Z(a) ratios have energies that are too high to be used in practice.     

Polarization locked vector solitons and axis instability in optical fiber

We experimentally observe polarization-locked vector solitons in optical fiber. Polarization locked-vector solitons use nonlinearity to preserve their polarization state despite the presence of birefringence. To achieve conditions where the delicate balance between nonlinearity and birefringence can survive, we studied the polarization evolution of the pulses circulating in a laser constructed entirely of optical fiber. We observe two distinct states with fixed polarization. This first state occurs for very small values birefringence and is elliptically polarized. We measure the relative phase between orthogonal components along the two principal axes to be +/-pi/2. The relative amplitude varies linearly with the magnitude of the birefringence. This state is a polarization locked vector soliton. The second, linearly polarized, state occurs for larger values of birefringence. The second state is due to the fast axis instability. We provide complete characterization of these states, and present a physical explanation of both of these states and the stability of the polarization locked vector solitons. (c) 2000 American Institute of Physics.     

Spatial optical solitons in inhomogeneous elliptic core saturating nonlinear fiber

We have investigated the propagation characteristics of spatial optical solitons in saturating nonlinear waveguide employing JWKB and paraxial ray approximation. We have obtained two second-order coupled nonlinear differential equations for transverse soliton widths of solitons. Threshold power for stable propagation of the beam has been calculated from these coupled equations. We have undertaken stability analysis, which predicts robustness of these solitons. Both guiding as well as antiguiding cases have been considered and shown that stable spatial soliton propagation is possible in both cases.     

Gap solitons in a model of a hollow optical fiber

We introduce a model for two coupled waves propagating in a hollow-core fiber: a linear dispersionless core mode and a dispersive nonlinear surface mode. The linear coupling between them may open a bandgap through the mechanism of avoidance of crossing between dispersion curves. The third-order dispersion of the surface mode is necessary for the existence of the gap. Numerical investigation reveals that the entire bandgap is filled with solitons, and they are stable in direct simulations. The gap-soliton (GS) family includes stable pulses moving relative to the given reference frame up to limit values of the corresponding boost delta, beyond which they do not exist. The limit values are asymmetric for delta > or < 0. Recently observed solitons in hollow-core photonic crystal fibers may belong to this GS family.     

Performance of analog optical links employing fiber Raman amplifiers

We present the characterization of an analog optical link employing external modulation and optical carrier in the C-band using a fiber Raman amplifier (FRA). The figures of merit gain and noise figure were characterized from 1 to 9 GHz, whereas the spurious-free dynamic range was measured and compared for both setups for frequencies from 2 to 9 GHz, all with and without the Raman amplifier. Experimental results demonstrate that FRA can simultaneously increase the spurious-free dynamic range, the analog gain and decrease the analog noise figure when compared to the same configuration without optical amplifier.     

High dynamic polarization-OTDR for the PMD mapping in optical fiber links

We describe a new algorithm based on the level-crossing rate analysis of the POTDR trace which enables the distributed measurement of the beat length, the coupling length and the PMD in long optical fiber links. This analysis allows using 500 ns pulses which significantly improves the measurement dynamic compared to classical POTDR.     

The freeze of intrapulse Raman scattering effect of ultrashort solitons in optical fiber

The effect of intrapulse Raman scattering (IRS) for the propagation of the femtosecond solitons in an optical fiber is investigated. To factually simulate its influence, a combination of 27 Lorentian lines to fit experimental Raman gain profile is adopted. By using nonlinear Schrödinger equation and finite-difference time domain method, the propagations of femtosecond fundamental solitons in an optical fiber are numerically calculated. When the initial power is suitably enhanced, it is found that the pulse shape is almost the same as initial pulse and the delay Raman response only makes small pulse shift. In other words, when ultrashort soliton is considered, the IRS effect is similarly frozen under the enhanced initial power.     

On the theory of chirped optical solitons in fiber lines with varying dispersion

We study a soliton solution of a path-averaged (in the spectral domain) propagation equation governing the transmission of a chirped breather pulse in the fiber lines with dispersion compensation. We demonstrate that the averaged Hamiltonian model correctly describes features of the chirped soliton observed in numerical simulations and experiments. We show that the Hamiltonian is bounded from below if the average dispersion is anomalous 〈 d〉>0); that, together with the condition H _sol<0, indicates stability of dispersion-managed solitons in this region. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 11, 791–795 (10 December 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Fractional optical solitons

This Letter shows that soliton propagation can be described by an extended NLS equation which incorporates fractional dispersion and a fractional nonlinearity. The fractional dispersive term is written in terms of Grünwald-Letnikov fractional derivatives (FDs). Forward and backward FDs are introduced in order to satisfy the conservation of energy. It is found that the soliton solutions of this model form a continuous family and are stable. The Vakhitov-Kolokolov criterion is used to confirm the stability of these fractional solitons.     

The evolution of two-frequency solitons in an optical fiber with a longitudinally nonuniform nonlinearity

The evolution of two-frequency solitons in an optical fiber, as well as the practically important special case of absence of the second-harmonic wave, in the presence of a longitudinal nonuniformity of the coefficients characterizing the propagation nonlinearity are considered. The solitons found for media with constant values of the nonlinearity coefficients are used as initial distributions for media with a periodic dependence of the nonlinearity coefficients on the longitudinal coordinate. Modulation of the coefficient of cubic or quadratic nonlinearity is shown to result in oscillations of the peak intensity of the solitons (in both their components if two-color solitons are considered). In the case of a weak modulation of the nonlinearity coefficients, oscillations of the peak intensity occur at the frequency coinciding with the frequency of modulation of the nonlinearity coefficients. Under the weak influence of a periodically modulated cubic nonlinearity, parameters of quadratic solitons also oscillate upon the propagation. Regions of stability of solitons in the space of the modulation parameters are established.     

Comparison of the performance of optical systems in fiber links 4000 km long

This article reports a numerical investigation of the performance of single-channel and WDM optical systems, assuming a fiber link 4000 km long in the presence of the Kerr effect, chromatic dispersion, and the amplifier spontaneous emission noise of the optical amplifiers. Both solitons and NRZ signals are considered, and IM-DD and coherent asynchronous ASK detections are used. Results on the technique of the midpoint spectral inversion are also reported.