Polarization modulational instability in a birefringent optical fiber with fourth order dispersion

We obtain conditions for the occurrence of polarization modulational instability in the anomalous and normal dispersion regimes for the coupled nonlinear Schrödinger equation modelling fourth order dispersion effects when the linearly polarized pump is oriented at arbitrary angles with respect to the slow and fast axes of the birefringent fiber.     

Design of a continuously tunable delay line using vectorial modulational instability and chromatic dispersion in optical fibers

We design an all-optical tunable delay line based on both dispersive and wavelength conversion stages involving modulational instability of a two-frequency pump field propagating in a highly birefringent fiber. More precisely, we numerically show that, by varying the frequency separation between the two orthogonally polarized pump waves, we achieve a controllable and continuous delay of hundreds of picoseconds for signal pulse durations from picoseconds to nanoseconds, without pulse distortion and with only small peak power fluctuations. The proposed method does not require any tunable bandpass filter and can be applied to delay digital data streams at tens of Gbit/s depending on the pump power level.     

Cross-phase modulational instability in an elliptical birefringent fiber with higher order nonlinearity and dispersion

We obtain conditions for the occurrence of cross-phase modulational instability in the normal dispersion regime for the coupled higher order nonlinear Schrödinger equation with higher order dispersion and nonlinear terms.     

Soliton self-frequency shift in a short tapered air-silica microstructure fiber

We report a soliton self-frequency shift of more than 20% of the optical frequency in a tapered air-silica microstructure fiber that exhibits a widely flattened large anomalous dispersion in the near infrared. Remarkably, the large frequency shift was realized in a fiber of length as short as 15 cm, 2 orders of magnitude shorter than those reported previously with similar input pulse duration and pulse energies, owing to the small mode size and the large and uniform dispersion in the tapered fiber. By varying the power of the input pulses, we generated compressed sub-100-fs soliton pulses of ~1-nJ pulse energy tunable from 1.3 to 1.65 mum with greater than 60% conversion efficiency.     

周期色散管理波分复用系统中交叉相位调制边带不稳定性理论分析

色散管理是在波分复用系统中, 周期地使用色散符号相反的光纤，使总的路径平均色散系数接近于零，系统中的色散就得到了补偿的一种技术.研究了波分复用集总放大色散管理系统中交叉相位调制的不稳定性，解析和数值研究表明，当路经平均色散系数表现为反常色散时，存在多阶边带；当路经平均色散系数表现为正常色散时，解析研究表明只存在最低阶边带，数值模拟显示噪声谱中最低阶边带噪声谱功率最强，解析和数值研究得到的结论一致. 关键词： 色散管理 波分复用 边带不稳定性     

Polarization mode dispersion in WDM systems

The coupled nonlinear Schrodinger equations for two wavelength optical pulses in a birefringence fiber are given. The model for treating polarization mode dispersion in two channel (WDM) system is established. Based on this model, optical signal propagation behaviors in two channel WDM with polarization mode dispersion are numerically simulated. The influences of polarization mode dispersion on two channel WDM system are also analyzed.     

Characterizations at high temperatures of long-period gratings written in germanium-free air-silica microstructure fiber

We report what is to our knowledge the first characterization at high temperatures of long-period fiber gratings written in Ge-free air-silica microstructure fiber. The gratings written with the electric-arc technique suffer a low shift of the resonance wavelengths when the temperature is increased from 20 degrees C to 1200 degrees C. This shift is studied and compared with that of a long-period fiber grating written in a standard single-mode fiber by the same technique. Good thermal stability of the grating and of the fiber after annealing at 1200 degrees C for 1 h is demonstrated.     

Self-induced modulational instability laser revisited: normal dispersion and dark-pulse train generation

We study theoretically and experimentally the so-called self-induced modulational instability laser and show that the passive mode-locking mechanism that is at play in this laser relies on a dissipative four-wave mixing process that leads to generation of a dark-pulse train in the normal-dispersion regime.     

有源光放大器链路中交叉相位调制的不稳定性

利用两种方法研究了有源放大器波分复用系统光纤链路中交叉 相位调制的不稳定性．首先利用非线性薛定谔耦合方程，在小幅度扰动下，研究了正常色散 和反常色散光纤中的交叉相位调制不稳定性. 由于相位噪声涨落，利用分裂步长傅里叶 变换法与Monte-Carlo法，模拟了有源放大器链路中反常色散和正常色散情况下的调制不稳定性. 两种方法得到的结论基本一致. 关键词： 调制不稳定性 交叉相位调制 斯托克斯带 反斯托克斯 带     

Low-power high-efficiency wavelength conversion based on modulational instability in high-nonlinearity fiber

Bandwidth and peak efficiency are enhanced for wavelength conversion based on induced modulation instability by use of dispersion-shifted fiber in which the nonlinearity (n(2)/A(eff)) is enhanced by a factor of ~4.5 over that of conventional dispersion-shifted fiber. We experimentally obtain a peak conversion efficiency as high as 28 dB over a 40-nm bandwidth with 600 mW of peak pump power. Considerations for further enhancement of fiber-based wavelength conversion are also discussed.     

Nonlinear phase noise generated in air-silica microstructure fiber and its effect on carrier-envelope phase

We present measurements of the nonlinear phase noise that is due to amplitude-to-phase conversion in air-silica microstructure fiber that is utilized to broaden the frequency comb from a mode-locked femtosecond laser to an optical octave. When the octave of the continuum is employed to phase stabilize the laser-pulse train, this phase noise causes a change in the carrier-envelope phase of 3784-rad/nJ change in pulse energy. As a result, the jitter on the carrier-envelope phase that is due to fiber noise, from 0.03 Hz-55 kHz, is ~0.5rad .     

Polarization dispersion in microstructure fibers with side channels

Polarization dispersion characteristics of microstructure optical fibers were analyzed. A significant difference between the spectral dependences of the phase and group birefringence of microstructure fibers and the polarization characteristics of a standard fiber having birefringence of the same order of magnitude is found. A new method for direct measurement of the phase birefringence is proposed and tested. The applicability of the technique for determining the phase birefringence with the use of the approximation known in the literature is analyzed.     

Visible continuum generation in air-silica microstructure optical fibers with anomalous dispersion at 800 nm

We demonstrate experimentally for what is to our knowledge the first time that air-silica microstructure optical fibers can exhibit anomalous dispersion at visible wavelengths. We exploit this feature to generate an optical continuum 550 THz in width, extending from the violet to the infrared, by propagating pulses of 100-fs duration and kilowatt peak powers through a microstructure fiber near the zero-dispersion wavelength.     

Bragg modulational instability induced by a dynamic grating in an optical fiber

By means of a dynamic Bragg grating obtained through cross-phase modulation with a beating wave in a highly birefringent fiber, we perform a detailed experimental study of Bragg modulational instability.     

Dark-soliton-like pulse-train generation from induced modulational polarization instability in a birefringent fiber

Theory and experiments show that the nonlinear development of the modulational polarization instability of an intense light beam in a normally dispersive, low-birefringence optical fiber leads to ultrashort dark-soliton-like trains with repetition rates in the terahertz range in the polarization orthogonal to the pump.     

Ultrahigh-resolution optical coherence tomography using continuum generation in an air-silica microstructure optical fiber

We demonstrate ultrahigh-resolution optical coherence tomography (OCT) using continuum generation in an air-silica microstructure fiber as a low-coherence light source. A broadband OCT system was developed and imaging was performed with a bandwidth of 370 nm at a 1.3-mu;m center wavelength. Longitudinal resolutions of 2.5 microm in air and ~2 microm in tissue were achieved. Ultrahigh-resolution imaging in biological tissue in vivo was demonstrated.     

Continuous-wave ultrahigh-repetition-rate pulse-train generation through modulational instability in a passive fiber cavity

Thanks to a passive cavity configuration, modulational instability in fibers is successfully observed, for the first time to our knowledge, in the continuous-wave regime. Our technique provides a new means of generating all-optically ultrahigh-repetition-rate pulse trains and opens up new possibilities for the fundamental study of modulational instability and related phenomena.     

Generation of optical domain-wall structures from modulational instability in a bimodal fiber

We study experimentally modulational instability in a normally dispersive bimodal fiber under modal group-velocity-matching conditions. In the strong pump depletion regime, higher order sideband harmonics detected in the output spectra as well as autocorrelation measurements reveal the formation of subpicosecond domain-wall structures. Across these temporal structures the electromagnetic field distribution switches abruptly between the two transverse modes of the fiber. These structures are reminiscent of the so-called domain-wall soliton. Our results constitute therefore an experimental indication of the existence of this fundamental soliton.     

Langmuir turbulence and modulational instability

In this paper we discuss the turbulent state of an unmagnetized, completed ionized hydrogen plasma for the case when the electron temperature is much higher than the ion temperature so that the main modes to be considered are the Langmuir and ion-sound modes, while the transverse, electromagnetic mode can for most purposes be neglected. We give in the introduction a brief discussion of the quasi-linear theory of weak Langmuir turbulence as developed by Tsytovich and coworkers. We discuss why the peak of the resulting spectrum occurs at a finite wavenumber; the reason is that the removal of energy through electron collisions is faster than either thermalization of the ion-component or the transfer to yet lower wavenumbers through scattering by ions. In section 2 we sketch Zakharov's derivation of the basic equations which in the linear form describe the three modes mentioned earlier and which describe the nonlinear modulational instability (M.I.). In section 3 we give the linear analysis of the equations derived in section 2 and show that the decay instability of finite-amplitude Langmuir waves is fully covered by these equations. We also discuss the general dispersion relations for perturbations of such finite-amplitude waves and show that they lead to both the M.I. and the decay instability. We evaluate the growth rates for various kinds of perturbations. It is shown that all our results are valid only provided the energy density of the Langmuir modes W is less than the kinetic energy density nT_e of the electrons. In section 4 we discuss under what circumtances in the linear approximation the M.I. dominates over other dissipative mechanisms and we show that it may well be the dominant mechanism for the case of strong turbulence, when $\text{W/nT}{}_{\mathrm{e}}\text{≡}\text{W}\text{?}\text{> = m}{}_{\mathrm{e}}\text{/m}{}_{\mathrm{i}}$. Section 5 is devoted to a discussion of the one-dimensional variant of our basic equations. We give a brief discussion of various soliton-bearing equations such as the Kortweg-de Vries equation (KdV), the sine-Gordon equation (SG), and the non-linear Schrödinger equation (NLS).We discuss the possible connection between the number of polynomial conserved densities (p.c.d.) which lead to integrals of motion and the number of solitons in the strict sense of the term which can occur in a single exact solution of the equation. We also discuss the evolution of a system of Langmuir solitons in terms of their interactions with one another and with ion-sound. In section 6 we first of all show that in three-dimensions soliton-like structures are unstable against adiabatic collapse. We then discuss the dynamics of such collapsing “cavitons” and show that the theory of collapsing cavitons predicts that the turbulent energy should increase as the $\text{2}\text{3}$ power of the pumping rate. We discuss the fact that it may be difficult to avoid overcrowding of cavitons which would violate their independence. We finally briefly discuss the few relevant experiments and mention some ideas for future research.