Waveguide modes of 1D photonic crystals in a transverse magnetic field

We analyze waveguide modes in 1D photonic crystals containing layers magnetized in the plane. It is shown that the magnetooptical nonreciprocity effect emerges in such structures during the propagation of waveguide modes along the layers and perpendicularly to the magnetization. This effect involves a change in the phase velocity of the mode upon reversal of the direction of magnetization. Comparison of the effects in a nonmagnetic photonic crystal with an additional magnetic layer and in a photonic crystal with magnetic layers shows that the magnitude of this effect is several times larger in the former case in spite of the fact that the electromagnetic field of the modes in the latter case is localized in magnetic regions more strongly. This is associated with asymmetry of the dielectric layers contacting with the magnetic layer in the former case. This effect is important for controlling waveguide structure modes with the help of an external magnetic field.     

Conversion of optical modes in an absorbing magnetogyrotropic waveguide

The features of mode conversion in an absorbing magnetogyrotropic waveguide are investigated by a coupled-wave approach. It is shown that absorption leads to an additional contribution to the coupling of both identically and orthogonally polarized modes. A new waveguide regime for mode conversion, in which there is no oscillatory energy exchange between modes, is revealed. The possibility of controlling the damping of the total field in a waveguide by varying the orientation of the magnetization in the waveguide layer is demonstrated. Zh. Tekh. Fiz. 68, 97–104 (June 1998)     

Conversion of waveguide modes in nonuniformly magnetized planar structures

An analysis is made of a planar structure with a nonuniform distribution of magnetization throughout the thickness of a waveguide layer that corresponds to the rotation of magnetic momentum in the plane of the layer. The results of the study show the feasibility of efficiently controlling the conversion of orthogonally polarized modes due to the change of thickness of the transition layer and the angle of magnetization rotation across the waveguide layer.     

Diffraction of light from a stripe domain structure with tilted domain walls

The intensity and polarization parameters of light waves diffracted from a stripe domain structure with tilted domain walls and the magnetic moment in domains oriented parallel to the walls are determined in the approximation of thin layers and linear magnetooptical coupling.     

Collinear light scattering on dipole-exchange spin waves in inhomogeneous ferromagnetic films

A theory is developed for the collinear TE-TM scattering of optical waveguide modes on dipoleexchange spin waves in perpendicularly magnetized ferromagnetic films that are inhomogeneous across their thickness. It is found in homogeneous ferromagnetic films and in films with small deviations from homogeneity that the TE-TM scattering on higher spinwave modes is strongest when the synchronism conditions for the transverse phases and for the longitudinal and transverse wave vectors are satisfied. When the thickness of the planar optical waveguide does not match the thickness of the ferromagnetic film, the phase synchronism condition is violated with the resultant appearance of an oscillating type of dependence of the TE-TM scattering on the spin-wave mode number. The scattering of light on spin-wave modes in films with a magnetization gradient is investigated in the presence of turning points for the magnetostatic potential. It is found that the existence of a turning point in the region of the antinode for the optical modes leads to an increase in the scattering amplitude. The formation of inhomogeneous magnetooptical structures and superlattices based on (Lu,Y,Bi)₃(Fe,Ga)₅O₁₂ is discussed. Zh. Tekh. Fiz. 68, 78–84 (June 1998)     

Magnetooptical Kerr effect in the near field of a nanowire supporting surface plasmons

In terms of Green’s functions, a theory is developed describing the resonant magnetooptical Kerr effect in light scattering by a linear probe that is parallel to the surface of a magnet and placed at a subwavelength distance from it. The probe is supposed to be a metal nanowire supporting long-lived surface plasmons and forming the near field of the “probe + image” complex. The resonant interaction between the probe and the sample is taken into account within a self-consistent approximation of multiple-scattering theory, and the magnetooptical interaction is included in the linear approximation in magnetization. The problem of scanning near-field magnetooptical microscopy with a linear probe is solved analytically in the case where the magnetization is parallel to both the magnet surface and the plane of incidence of light (longitudinal magnetooptical Kerr effect). The polarization, spectral, and angular characteristics of scattered light modulated by magnetization are discussed. It is shown that the magnetooptical modulation of the scattered light intensity is significantly enhanced when surface plasmons are resonantly excited in the nanowire.     

Self-oscillations of spins in a nanodimensional spin waveguide with localized sources of spin-polarized current

Spin oscillations and their phase synchronization are discovered in a spin 1D waveguide (nanowire) after the local injection of a spin-polarized current in the vertical (perpendicular) geometry of magnetization. The mode composition of nonlinear spin self-oscillations is analyzed for a single nano-oscillator using the effect of spin transfer torque with regard to spin wave runaway over the 1D waveguide and synchronized spin self-oscillations at current pumping by two nano-oscillators. It is shown specifically that, along with simple (“nontopological”) oscillation modes, in which singular points in the oscillation amplitude spatial distribution are absent, the 1D waveguide may support modes with pole-type singular points inside the current pumping domain, which are characteristic of the geometry of a precessing 2π-domain boundary. A diagram for frequency- and current-detuning-synchronized spin self-oscillations that are excited by two spin nano-oscillators in the 1D spin waveguide is constructed.     

Reflection and transmission of light by a ferromagnetic structure with a noncollinear orientation of the magnetization of layers

The transmission and reflection of light by a ferromagnetic structure with a noncollinear orientation of the magnetization vectors of layers lying in the plane of the film is considered. The characteristic matrix of the structure that relates the wave amplitudes at the entrance to the system and at the exit from it and that determines the magnetooptical properties of the structure is calculated. The magnetooptical characteristics of this structure are shown to significantly depend on the angle between the magnetization vectors of layers and on the number of layers. Both the magnitude and the character of these dependences are analyzed in relation to the angle of incidence and to the polarization of the incident wave. Such an analysis makes it possible to optimize the magnetooptical properties of this structure.     

组合型TM01-TE11弯形圆波导模式转换器研究

 研究了组合型TM₀₁-TE₁₁弯形圆波导模式转换器（两弯曲段中间加一段直圆波导），在保持其输出与输入端口轴线平行的前提下，分别从理论推导、数值计算、软件模拟三个方面对此结构进行了分析，模拟结果与数值计算结果吻合得很好。结果表明：计及功率损耗，频率为3.75 GHz，铜波导内径为9.0 cm，轴向间距为10.57 m时，模式转换器总的功率转换效率为93.8%。     

Efficiency of Magnetooptical Conversion of Magnetic Fluxes Produced by the High-Temperature Superconductor Matrix

The possibility for using the ferrite-garnet magnetooptical films with a band domain structure has been considered with the aim of visualization of the spatial distribution of a magnetic flux near sensitive elements of a high-temperature superconductor matrix. The methods that enhance the efficiency of magnetooptical conversion have been suggested.     

Hybrid waveguide-surface plasmon polariton modes in a guided-mode resonance grating

We analyze the coupling between surface plasmon polaritons in a metal grating and the guided modes of a dielectric waveguide. Our model structure is a gold wire grating on a slab waveguide made of silicon nitride on silica wafer. The excitation of guided-mode resonances, surface plasmon polariton modes and hybrid waveguide-plasmon modes are observed in numerical simulations. Our experiments verify the existence of the predicted modes. These hybrid modes add significant degrees of freedom in designing structures for plasmonic applications.     

Laser diode integrated with a low radiation loss thickness-tapered beam expander for highly efficient fiber coupling

The optimal structure of a laser diode monolithically integrated with a thickness-tapered beam expander waveguide is demonstrated by analyzing the relationship between fiber coupling efficiencies and radiation losses. It is also found that mode conversion loss is lowered in a ridge waveguide structure than in a buried hetero structure under equivalent fiber coupling. A fabricated ridge waveguide device based on this design shows threshold current as low as 16 mA and narrow beam divergences of 13° and 12°.     

Dynamical regimes of conversion of magnetogyrotropic waveguide modes in the region of ferromagnetic resonance

The dynamical conversion of magnetogyrotropic waveguide modes in the regime of uniform spin precession at large angles is studied. It is shown that the nutation of the magnetization vector due to the precession frequency doubling results in dependence of the light modulation amplitude on the polarization of the microwave field. The contribution of harmonics with frequencies that are multiples of the fundamental precession frequency of ferromagnetic resonance to the total mode-conversion efficiency is analyzed for different lengths of the waveguide and different equilibrium orientations of the magnetization. State University, Ulianovsk, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 5, pp. 651–663, May, 1998.     

Ray-optics analysis of the coupling efficiency from a gaussian beam to a rectangular multimode embedded strip waveguide

Abstract

The modified ray-optics method is used to analyze the coupling efficiency from a Gaussian beam to a rectangular multimode embedded strip waveguide. It is convenient for analyzing the case of a simple waveguide structure because of reduced computation time. The conditions for determining which optical rays can be coupled into the waveguide to become the waveguiding modes, as well as the effective receiving area of the waveguide, are derived in this work. The data obtained by this method are compared with those calculated by the well-known overlap integral theorem and Marcatili's models for investigating the validity of the modified ray-optics method.     

Collinear interaction of optical waveguide modes with an increasing space-charge wave

Collinear interaction of optical modes in a thin-film semiconductor waveguide with a space-charge wave increasing along its propagation direction has been investigated. Analytical solutions to the equations of coupled unidirectional and counterpropagating waveguide modes at their phase matching are obtained for the first time, and the dependence of the mode conversion efficiency on the space-charge wave amplification level, the coupling coefficient, and the length of the interaction region of optical modes is analyzed.     

Wave growth rate in a cylindrical metal waveguide with ion-channel guiding of a relativistic electron beam

This paper addresses the formulae and numerical issues related to the possibility that fast wave may be grown when a relativistic electron beam through an ion channel in a cylindrical metal waveguide.To derive the dispersion equations of the beam-wave interaction,it solves relativistic Lorentz equation and Maxwell’s equations for appropriate boundary conditions.It has been found in this waveguide structure that the TM 0m modes are the rational operating modes of coupling between the electromagnetic modes and the betatron modes.The interaction of the dispersion curves of the electromagnetic TM 0m modes and the upper betatron modes is studied.The growth rates of the wave are obtained,and the effects of the beam radius,the beam energy,the plasma frequency,and the beam plasma frequency on the wave growth rate are numerically calculated and discussed.     

A novel numerical synthetic technique for determination of the TMon dispersion relation in a coaxial corrugated cylindrical waveguide

A novel, highly accurate numerical synthetic technique for determining the complete dispersive characteristics of electromagnetic modes in a spatially periodic structure is presented. The numerical method based on the coupling of the finite difference method in time domain with the discrete fourier transform is applied to calculate the eigenfrequencies and eigenfield distribution of a resonant cavity which is an appropriately shorted periodic slow wave circuit of N periods at both ends. The analytical synthetic technique, which is based on the intrinsic characteristic of spatially periodic structure, is used to derive the complete dispersion relation using the numerically measured resonances. The method was successfully applied for the case of TM_on modes in a coaxial corrugated waveguide and is applicable to slow wave structures of arbitrary geometry.     

Effect of reversible adsorption on the magnetic properties of iron garnet films

The reversible change in the domain structure and the magnetic domain width in bismuth-containing iron garnet films with an easy magnetization axis oriented normal to their surface during adsorption caused by hydrogen bonds is studied by a magnetooptical method. The dependence of the domain width on the vapor pressure of methyl alcohol or water in a cell with a sample is determined, and the time dependence of the domain width induced by the adsorption-desorption processes occurring between methyl alcohol molecules or water molecules on the film surface is studied. A model is proposed to explain the detected effects.     

Pure Reflection and Refraction of a Surface Polariton by a Matched Waveguide Structure

We study the fundamental problem of reflection and refraction of a surface polariton as it strikes the interface between two waveguide structures. By making the two waveguide structures match to each other, coupling of surface polaritons to radiating modes is cancelled, and the reflected and transmitted waves consist of only surface modes. The reflection and transmission coefficients are calculated, and negative refraction of surface polaritons is demonstrated. Finite-difference time-domain numerical simulations are also performed to verify the analytical results. As one of the applications of the matched waveguide structure, a square corner reflector for phase-retardation-free reflection of surface polaritons is proposed.     

Magneto-optical defects in two-dimensional photonic crystals

We analyze the properties of magneto-optical defect states in two-dimensional photonic crystals. With out-of-plane magnetization, the magneto-optical coupling splits doubly-degenerate TE states into two counter-rotating modes at different frequencies. The strength of magneto-optical coupling strongly depends on the spatial overlap of the cavity domain structures and the cross product of the modal fields. The transport property of the resultant nonreciprocal states is demonstrated in a junction circulator structure with a magneto-optical cavity coupled to three waveguides. By a proper matching of the magneto-optical frequency splitting with the cavity decay rate into the waveguide, ideal three-port circulator characteristics with complete isolation and transmission can be achieved, with an operational bandwidth proportional to the magneto-optical constant. The proposed optical circulator in a bismuth-iron-garnet/air photonic crystal is demonstrated with finite-difference time-domain calculations and is compared to an alternative implementation of silicon/air crystal infiltrated with a single bismuth-iron-garnet domain.