Charles H. Papas

On Electromagnetic Waves in Chiral Media.

We analyze the propagation of electromagnetic waves through chiral media, i.e., through composite media consisting of macroscopic chiral objects randomly embedded in a dielectric. The peculiar effects that such media have on the polarization properties of the waves are placed in evidence. To demonstrate the physical basis of these effects, a specific example, chosen for its analytical simplicity, is worked out from first principles.

Electromagnetic wave propagation through a dielectric–chiral interface and through a chiral slab

The reflection from and transmission through a semi-infinite chiral medium are analyzed by obtaining the Fresnel equations in terms of parallel- and perpendicular-polarized modes, and a comparison is made with results reported previously. The chiral medium is described electromagnetically by the constitutive relations D = ∊E + iγB and H = iγE + (1/μ)B. The constants ∊, μ, and γ are real and have values that are fixed by the size, the shape, and the spatial distribution of the elements that collectively compose the medium. The conditions are obtained for the total internal reflection of the incident wave from the interface and for the existence of the Brewster angle. The effects of the chirality on the polarization and the intensity of the reflected wave from the chiral half-space are discussed and illustrated by using the Stokes parameters. The propagation of electromagnetic waves through an infinite slab of chiral medium is formulated for oblique incidence and solved analytically for the case of normal incidence.

Electromagnetic Waveguides and Resonators

Waveguides and cavity resonators play an essential role in microwave physics. They are widely used in physical measurements and special devices. In this article the basic theory of waveguides and cavity resonators is reviewed covering uniform and non-uniform waveguides, slow-wave and surface-wave guiding structures, waveguide junctions, and cavity resonators.

Coupled-mode theory approach to nonlinear pulse propagation in optical fibers

The formalism of coupled-mode theory is adopted for describing nonlinear pulse propagation in optical fibers, the coupling being induced by the nonlinear part of the refractive index. This approach describes in a natural way the influence of the waveguide, and in principle allows of the possibility of investigating soliton propagation when more than one mode is excited.

Theory of time-dependent propagation in multimode lightguides*

A coupled system of equations governing the propagation of a signal in a statistical ensemble of multimode optical fibers is presented. It describes, besides the usual average modal powers, the evolution of the interference terms between the mode amplitudes and of the modal power fluctuations. Our procedure allows us to treat the general nonstationary nonmonochromatic case of an arbitrary signal fed into the lightguide by a source possessing a finite spectral bandwidth. The introduction of modal power fluctuations permits us to establish a theorem connecting the value of the modal power, averaged over the fiber ensemble, with the actual one concerning a single fiber. These two values coincide, in the polychromatic case, for large values of the fiber length, thus providing the main result of the paper, that is the justification of the statistical approach to the problem of propagation. Furthermore, the analysis of the interference terms presents evidence for the difference between the propagation of an amplitude-modulated and a frequency-modulated signal.

On the Application of Symmetrization to the Transmission of Electromagnetic Waves through Small Convex Apertures of Arbitrary Shape.

The transmission of an electromagnetic wave through a small aperture in a perfectly conducting screen is examined from the viewpoint of symmetrization.

On the near-zone inverse Doppler effect

Attention is invited to the recently discovered inverse Doppler effect which occurs in the near-zone field of an antenna emitting a continuous wave. On approaching the antenna, the received signal is blue-shifted in the far zone and then red-shifted in the near zone; and on receding from the antenna, the received signal is blue-shifted in the near zone and then red-shifted in the far zone. Calculations are presented for the ease where the antenna is a simple dipole. It is shown that this effect gives not only the vector velocity of the moving receiver but also its range, i.e., its distance from the antenna.

Role of intensity fluctuations in nonlinear pulse propagation

The effect of intensity fluctuations and the finite coherence time of the field on the propagation of nonlinear optical pulses is discussed. In particular, the statistical properties of the carrier are shown to affect the power level for soliton propagation.

Modal dispersion in lightguides in the presence of strong coupling

The effect of strong mode coupling on modal dispersion in optical fibers has been investigated. The pulse dispersion turns out to be qualitatively different from the one relative to the weak-coupling case, while it exhibits a drastic reduction as compared with that of the uncoupled case. The role of the initial pulse length and of the source coherence time has been elucidated.

Die kapazitive Blende im rechteckigen Hohlleiter

Ein verlustfrei angenommener Hohlleiter mit Rechteckquerschnitt erstrecke sich von z = -∞ nach z = +∞. In der Ebene z = 0 sei eine unendlich dunne metallische Blende symmetrisch in der aus Fig. 12.1 ersichtlichen Weise angebracht. Die Offnung zwischen den beiden metallischen Blendenhalften bezeichnen wir als Apertur.