单模光纤中三阶色散对超短光脉冲传输的影响

基于超短光脉冲在单模光纤中传输时高阶非线性效应的影响。应用非线性薛定谔方程(HONLS)理论,考虑光纤色散三阶效应,推导出无啁啾的高斯脉冲沿光纤传输时脉冲变化的表达式,并对理论结果进行了数值模拟与分析。结果表明,三阶色散会引起光脉冲形状发生畸变,会在其前沿或后沿附近形成非对称的振荡结构。     

Spatial effects in the linear propagation of drastically ultrashort optical pulses in single-mode waveguides

We analyze the effect of the varying transverse field profile associated to the linear propagation of ultrashort pulses along an optical waveguide. This effect has been systematically ignored in the literature. Based on numerical calculations, we analyze the magnitude of such effect to justify the use of the standard model, at least for pulses larger than about 5–7 optical carrier cycles. Theoretical considerations are presented about the extreme difficulty of even establishing the initial mathematical condition of the propagation problem under such circumstances.     

Theory of polarization mode dispersion with linear birefringence

We derive a compact equation characterizing the polarization property of an optical fiber with linear birefringence. Under particular conditions the solution of this equation gives the differential group delay as a simple functional of the birefringence autocorrelation function.     

Optical-frequency dependent modal birefringence and polarization mode dispersion of birefringent single-mode optical fibers over a broadband optical wavelength range

Optical-frequency dependent polarization mode dispersion as well as modal birefringence of three kinds of specially designed hollow-induced birefringent single-mode fiber are measured over an optical frequency range between 345 and 410 THz by optical frequency-domain interferometry.     

Mathematical modeling of random coupling between polarization modes in single-mode optical fibers: VII. Zero drift in a fiber ring interferometer with a circuit formed by a twisted optical fiber with weak natural linear birefringence

Zero drift and fading of the interference signal determined by polarization nonreciprocity at the exit from a fiber ring interferometer (FRI) of great length designed for recording a number of general relativity (GR) effects and made on the basis of a uniformly twisted single-mode optical fiber (SMF) with weak natural birefringence are considered. The calculations are carried out by numerical simulation using the model of random coupling between orthogonal polarization modes in an SMF, which was proposed in the first part of this work. The so-called minimum arrangement of an FRI with a nonmonochromatic radiation source, including a linear polarizer located between two beam splitters, is considered. Numerical estimates are made. It is shown that the FRI with a circuit on the basis of a twisted SMF has a significantly smaller zero drift and significantly smaller fading of the interference signal than the FRI with a circuit formed by an untwisted SMF. It is shown that the FRI produced on the basis of a twisted SMF provides the polarization sensitivity necessary for detecting the GR effects under study.     

Nonholonomic constraint between the polarization state of light and the twisted angle of a single-mode optical fiber with linear birefringence

The relation between the polarization state of light propagating in a twisted single-mode optical fiber with linear birefringence and the twist angle of the fiber is discussed for the case where the fiber is stretched in a straight line. It is shown that this relation is of the nature of a nonholonomic constraint. Zh. Tekh. Fiz. 68, 128–129 (November 1998)     

Mathematical modeling of random coupling between polarization modes in single-mode optical fibers: Integrated statistical properties of polarization modes of single-mode optical fibers in the presence of random inhomogeneities

Using mathematical modeling, an explicit form is found for the Jones matrix of a segment of a single-mode optical fiber with random inhomogeneities, whose length is considerably greater than the correlation length of random inhomogeneities. It is shown that parameters of this matrix are of a statistical nature. A rational representation of the matrix is proposed. It is shown that, under certain conditions, one of the matrix parameters may be treated as constant, whereas the other parameter is assumed to be continuously distributed on the interval [0, 2π]. As the latter parameter is changed, which corresponds to a change from one random realization of inhomogeneities in a single-mode fiber to another, the ellipticity and the azimuth of the major axis of the polarization ellipse of natural polarization modes of a single-mode fiber simultaneously change.     

Mathematical modeling of random coupling between polarization modes in single-mode optical fibers: XVI. Depolarization and repolarization of polychromatic radiation in single-mode optical fibers with random inhomogeneities

The dependences of the degree of polarization of polychromatic radiation on the length of a single-mode optical fiber (SMF) with random inhomogeneities have been obtained by mathematical modeling. The case is considered where radiation having both polarization modes excited with equal weights of linear polarization is first introduced into a depolarizer of polychromatic radiation (a SMF segment with high linear birefringence) and arrives at an SMF with low linear birefringence. It is shown that the degree of polarization of radiation after transmission through the first segment becomes significantly suppressed and remains almost constant upon propagation through the second segment, after which it begins to sharply increase at some length; i.e., repolarization of radiation occurs. It is shown that repolarization of radiation depends weakly on the angle made by the axes of unperturbed linear birefringence of the first and second segments. The conditions for the length of the first segment (depolarizer) under which the degree of polarization remains minimum throughout the second segment are determined.     

Mathematical simulation of random coupling of polarization modes in single-mode optical fibers: IX. Zero drift in a fiber ring interferometer with a loop made of an optical fiber with strong linear birefringence

Numerical simulation of random inhomogeneities in a strongly anisotropic single-mode optical fiber (SMOF) forming a loop in a fiber ring interferometer (FRI) designed according to the minimal scheme is used to obtain the dependences of an interference signal at the FRI output and the zero shift and drift of an interference pattern of counterpropagating waves on the angles of orientation of the axes of linear birefringence in an SMOF at both inputs of the FRI loop. It is shown that the use of a superluminescent diode as a radiation source makes it possible to increase the sensitivity of fiber-optic gyroscopes fabricated on the basis of FRIs by 1–2 orders of magnitude and to obtain the values of real sensitivity required for navigation purposes.     

Mathematical modeling of random coupling between polarization modes in single-mode optical fibers: XV. Dependence of integral statistical parameters of polarization modes in single-mode optical fibers with random inhomogeneities on the wavelength of light

Spectral dependences of integral statistical elements of the Jones matrix of an extended segment of a single-mode optical fiber (SMOF) with random inhomogeneities, whose length considerably exceeds the correlation length of random inhomogeneities, are found by the method of mathematical modeling. The boundaries of the ranges of optical wavelengths are determined, within the limits of which the parameters under consideration remain quasi-constant. This allows the derivation of analytical expressions for the degree of polarization of nonmonochromatic radiation in an SMOF and for the zero drift in fiber ring interferometers with the help of the approximate method of small perturbations. It is shown that the small-perturbation method leads to adequate results for SMOFs with strong and intermediate linear birefringence.     

Nonlinear polarization evolution of ultrashort pulses in microstructure fiber

We present experimental and numerical results for nonlinear polarization evolution of femtosecond pulses during propagation in microstructure fiber. Numerical modeling shows that fiber dispersion permits a long interaction length between the components polarized along the two principal axes, thereby enhancing the effective nonlinear polarization evolution in microstructure fiber.     

Influence of the irregularity of twisting of the birefringence axes of single-mode optical fibers on the polarization nonreciprocity of fiber ring interferometers

A particular example of the so-called minimum-configuration fiber ring interferometer whose loop comprises two different-length segments of a single-mode optical fiber with the same linear birefringence but different twisting is used to show that even in the case where the birefringence axes at the loop input coincide with the polarizer transmission direction, the phenomenon of polarization nonreciprocity of the fiber ring interferometer can emerge. It is shown that polarization nonreciprocity can be eliminated by the proper adjustment of the axes of a single-mode optical fiber, but the above adjustment should be changed if the waveguide temperature is changed. It is also shown that polarization nonreciprocity is a function of the light wavelength and the polarization nonreciprocity value in a fiber ring interferometer varies quasiperiodically in response to the temperature change in an optical fiber with random irregularities.     

利用声波控制超短脉冲的色散

 声光互作用器件声光可编程色散滤波器（AOPDF）是一种实时的色散补偿器件，它可用于飞秒啁啾脉冲放大系统。通过耦合模理论推导，得到了输出脉冲的群延迟与调制声波的频率、啁啾、带宽等参数的关系，并且对用2.5cm长的LiNbO₃作为声光晶体的AOPDF补偿飞秒光脉冲的色散进行了数值模拟，得到了对中心波长为800 mm的钛宝石飞秒激光色散补偿特性及所需声波的频率和啁啾参数。     

Influence of the birefringence autocorrelation function on the polarization mode dispersion of constantly spun fibers

We show that the polarization mode dispersion of a constantly spun, single-mode fiber is strongly influenced by the autocorrelation function of its birefringence. In particular, under probable conditions, the mean square differential group delay of the spun fiber may even be higher than the delay that the same fiber would have if it were not spun.     

Coupling between elliptic screw polarization modes in single-mode optical waveguides with linear birefringence and regular twist of anisotropy axes in the presence of random axis twist

An analysis is made of single-mode fiber optical waveguides with linear birefringence and regular twist of anisotropy axes in the presence of random twist, which shows that, in this case, the coupling of orthogonal polarization modes having elliptic polarization in the screw coordinate system comoving with twist cannot be characterized by one coupling parameter, as differentiated from the case where constant twist is absent. In this case, the coupling between polarization modes is characterized by three independent parameters, which are different in nature and have different effects on the coupling of polarization modes. An estimate is made of the domain of applicability of the classical formula for the h parameter in single-mode fiber optical waveguides without regular twist of anisotropy axes.     

Soliton-like pulses in nonlinear lightguides with strong birefringence and realizable intermode coupling

The dynamics of a wave packet formed by two unidirectional waves propagating in a nonlinear birefringence lightguide with and without linear coupling between the orthogonal pulse components is investigated. Conditions of forming soliton-like pulses are examined for various polarization angles of input radiation with allowance for the dispersion effects of the first and second orders and of the nonlinear effects caused by phase self-and cross-modulation. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 50–55, March, 2007.     

Beyond the pulse-area theorem: Role of the absorption and the dispersion in the propagation of weak ultrashort resonant pulses

We present here some fundamental but yet underlooked features of the propagation of weak ultrashort pulses (with Δ_dτ << 1, where Δ_d is the Doppler width and τ is the pulse duration) in resonant atomic media. We show that the pulse area behaviour and the pulse spectrum at resonance are governed by the usual optical depth (α₀L, where α₀ is the absorption coefficient at resonance and L the length of the medium), whereas the pertinent parameter that governs the severity of the dispersion effects and the distortion of the pulse is the dispersion parameter e_disp = (α₀L)Δ_dτ that we introduce. Paradoxical effect such as distortionless propagation (e.g. e_disp << 1) with vanishing pulse area (when α₀L >> 1) can then explained within this formalism.     

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.     

Methods for measurement of random coupling of polarized modes in weakly anisotropic single-mode fiber lightguides

Three methods for measurement of the h parameter in single-mode fiber lightguides (SFG) with different degrees of anisotropy are compared experimentally. It is shown that all three methods provide a practically identical result for an SFG with strong anisotropy, while only the method based on excitation of the SFG input by nonmonochromatic radiation of a single polarization mode has an adequate result, provided that the spectral width of the radiation source is comparable with its wavelength.Institute of Applied Physics, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 2, pp. 265–269, February, 1994.