We have studied quantum effects in a system governed by the spatial nonlinear Schrodinger equation derived for a two beams interaction in a quadratic nonlinear material. For a quadratic nonlinear material it has recently been demonstrated [2, 3] that, under suitable conditions, in the interaction between the fundamental and the second harmonic field, the fundamental field propagation can be described as a solution of a nonlinear Schroedinger equation, given in terms of spatial solitons [4,5]. In this work we are interested at the quantum properties of the fundamental beam in this kind of interaction. We use a quantum field description [1] where the spatial variable of propagation z plays the role of time in the standard quantum theory, and we apply it to the case of a strong plane wave that can be described as a classical field propagating through the nonlinear medium in the z-direction. We assume TE polarizations for all the monochromatics fields involved into the interaction in a type I material.
We have studied quantum effects in a system governed by the spatial nonlinear Schrodinger equation derived for a two beams interaction in a quadratic nonlinear material. For a quadratic nonlinear material it has recently been demonstrated [2, 3] that, under suitable conditions, in the interaction between the fundamental and the second harmonic field, the fundamental field propagation can be described as a solution of a nonlinear Schroedinger equation, given in terms of spatial solitons [4,5]. In this work we are interested at the quantum properties of the fundamental beam in this kind of interaction. We use a quantum field description [1] where the spatial variable of propagation z plays the role of time in the standard quantum theory, and we apply it to the case of a strong plane wave that can be described as a classical field propagating through the nonlinear medium in the z-direction. We assume TE polarizations for all the monochromatics fields involved into the interaction in a type I material.
The aim of this work is to study how losses modify quantum effects in a system governed by the spatial nonlinear Schrodinger equation. Quantum effects in space, such as quantum noise, squeezing, and bunching, have been studied in a lossless case.1 We will consider the propagation of a field through a planar nonlinear waveguide,2,3 where confinement is provided in one transverse dimension (y direction) by a linear refractive index and in the orthogonal dimension (x direction) by the intensity dependence of the refractive index.1,4 Attenuation is given to the spatial distribution in the x-z plane. In this work we want to extend the dissipation approach described in Ref. 5 to a system governed by the spatiai-nonlinear Sclirodinger equation (SNLS). We use a quantum-field description1 in which the spatial variable of propagation z plays the role of the time in the standard quantum theory, and we apply it to the case of a strong plane wave that can be described as a classical field propagating through a nonlinear waveguide in the z direction.4 By using both paraxial and slowly-varying-envelope approximations, the propagation of the field in a planar waveguide is described by the NLS.1
A quantum description of the spatial behavior of a field that satisfies a spatial nonlinear Schrödinger equation (e.g., a single-mode field in a nonlinear planar waveguide) is studied with the assumption that quantum effects are small. An analytical expression for dissipation in systems governed by the spatial nonlinear Schrödinger equation is presented. Dissipation is found to have detrimental effects on the behavior of quantum phenomena such as quantum noise, squeezing, and bunching. A detecting scheme for the spatial frequency components of the nonclassical properties is also given.
Summary form only given. The quantum properties of the interaction between an electromagnetic field and a nonlinear media have been widely studied, theoretically and experimentally, but so far these studies concerned mainly measurements performed on the total intensity of light beams, integrated over all the transverse plane. However, the details of the noise distribution inside the transverse plane, as well as the spatial quantum correlation between two different points, can be also very instructive, on a fundamental side in order to understand the propagation of the quantum noise, but also on a practical side to generate special configurations of the field which allow us to increase the spatial resolution of measurements in the transverse plane. We study here the spatial properties of the quantum fluctuations for a field freely propagating in a thick nonlinear medium, and in a case where the interaction distance is not limited by the diffraction : the spatial soliton regime, where diffraction effects are counterbalanced by nonlinearity and which exists in /spl chi//sup (2)/ and /spl chi//sup (3)/ media.
We investigate the spatial behavior of nonclassical light produced by type I second-harmonic generation in the traveling-wave configuration. An input-output transformation for the system of fundamental and second-harmonic field is derived in the framework of a linearization approach and used to investigate the properties of an optical system, which consists of a crystal with a quadratic nonlinearity pumped at frequency $\ensuremath{\omega}$ and enclosed in a two-lens telescopic system. If a faint input image at frequency $2\ensuremath{\omega}$ is injected into this device, for a sufficiently large interaction length, the output displays a pair of symmetric amplified versions of the input image at both fundamental and second-harmonic frequency. The analysis of the quantum fluctuations in the output images shows that under certain conditions, this optical device operates noiselessly with respect to the output at frequency $\ensuremath{\omega},$ whereas the output images at frequency $2\ensuremath{\omega}$ are affected by a slight degradation of the signal-to-noise ratio.
Propagation characteristics of optical soliton in a three level atomic medium are analyzed by treating the material medium quantum mechanically, but the electromagnetic wave classically. Both the cubic and quintic components of the nonlinear polarization of the electromagnetic field are considered along with those generated due to the dipole formation of the material. A numerical simulation is carried out with the help of split-step technique. It is observed that the power of the pulse, distance of propagation and degree of dispersion are intimately related. The role of polarization due to the material is duely compensated by keeping higher order dispersive terms. In this connection we have seen that keeping the higher order dispersive terms, up to the eighth order, which is actually the phenomenon of continuum generation, results in a better form of the pulse. In our paper, we have analyzed the effects in both the cases, that is, including and excluding the quintic terms and in each case we have considered the effects of second-order dispersion (β2) as well as the higher order dispersion terms ( 8 2 j j β =
In the previous chapter we examined nonlinear propagation in a two-level medium, which leads to amplification or absorption of the radiation field. As we will see further on in this volume, when the medium is placed in an optical cavity one realizes a laser in the case of amplification or an optically bistable system in the absorptive configuration. On the other hand, the nonlinear response of the atomic polarization to the electric field leads to further fascinating scenarios [29, 51–60]. For example, a field with central ω 0 can generate harmonic components with central frequencies 2 ω 0 , 3 ω 0 etc., processes that are called second-harmonic generation, third-harmonic generation etc. Furthermore, the interaction of two fields with central frequencies ω 1 and ω 2 , with ω 1 > ω 2 , can generate components with central frequency ω 1 + ω 2 (sum-frequency generation) and ω 1 − ω 2 (difference-frequency generation). Such phenomena have not yet appeared in this volume because we have assumed that the electric field corresponds to a narrow frequency band around a central frequency ω 0 only, whereas to describe them it is necessary to assume that the electric field is the superposition of a number of frequency bands. In this chapter we will provide a description of the basic elements which are necessary to describe these phenomena and we will discuss a small number of them for the case of materials with a quadratic nonlinearity, referring to textbooks in nonlinear optics for the description of other phenomena. The following chapter is devoted, instead, to the case of materials with cubic nonlinearities. The starting point of nonlinear optics is the expansion of the atomic polarization in powers of the electric field, when the electric field is not too intense. In our treatment in Chapter 5 we saw that the expansion of the nonlinear susceptibility contains only even powers of the electric field (see Eq. (5.27)), and therefore the expansion of the polarization includes only odd powers.