One-dimensional Periodic Structure Research Articles

Control method for the tunable ordered structures in magnetic fluid microstrips

Structural evolution along the edges of magnetic fluid microstrips under external magnetic fields is investigated in this article. It was found that when the external magnetic field increased the structure evolves from an originally monodispersed state to a disordered column state, and then to several levels of ordered structures. For the ordered structure state, a one-dimensional periodic structure resulted under lower field strengths, and with an increase in field strength, more columns formed. Hence, a two-dimensional ordered array of columns was achieved. Further experimental results showed that the ordered structure can be manipulated by adjusting control parameters, such as field strength, sweep rate, fluid concentration, strip width, and strip thickness. These results lay the groundwork for utilizing controllable ordered structures in magnetic fluid microstrips to develop potential applications, such as photonic crystals or waveguides.

Flexible mirrorless laser based on a free-standing film of photopolymerized cholesteric liquid crystal

Optically pumped mirrorless laser action has been observed in a dye-doped flexible free-standing film of photopolymerized cholesteric liquid crystal (PCLC). In the PCLC film, self-organized helical structure acts as one-dimensional (1D) photonic crystal. At high excitation intensity above the threshold, a laser action is observed at an edge of the 1D photonic band of the PCLC helical structure. This PCLC film laser possesses an excellent mechanical flexibility, and the laser action is also observed in a bent film of PCLC. This implies that the one-dimensional periodic structure for the laser action is maintained even in the deformed film. Using such flexibility of the PCLC film, a focusing effect of laser emission is demonstrated in a circularly deformed film. Moreover, the helical pitch of the PCLC has no temperature dependence in contrast to that of unpolymerized cholesteric liquid crystal. This means that the operation wavelength of laser action is thermally stable, which is the great advantage for the device application.

Periodic autowave structures in a wide-aperture laser with inertial phase nonlinearity

The formation of a periodic structure of the optical field of a wide-aperture laser with inertial Kerr phase nonlinearity is considered. The conditions for the appearance of one-dimensional periodic wave structures propagating along the aperture are found and their properties are studied.

Structures of a film of the long-chain n-alkane n-C 44H 90 on a Cu [formula omitted] surface

Structures of a film of a long-chain n-alkane, tetratetracontane ( n-C 44H 90; TTC), on a Cu(1 0 0) single-crystal surface were investigated by a combination of infrared reflection absorption spectroscopy (IRRAS) and low energy electron diffraction (LEED). Vacuum vapor deposition was used to prepare epitaxially grown films. Measurements of the step-wise increase in film thickness revealed the structural changes in TTC film during film growth. IRRAS investigations revealed that three phases appear during film growth, as previously observed for TTC deposited on Au(1 1 1) and Ag(1 1 1) surfaces. In the first layer, which consists of TTC molecules directly adsorbed on a Cu(1 0 0) surface, the molecules assume a flat-on structure with the carbon skeleton plane of TTC parallel to the surface (flat-on phase). The next layer consists of slightly disordered molecules including a gauche conformation ( gauche phase). Finally, a film with molecular packing close to that in the crystalline state is formed with further deposition (quasi-crystalline phase). LEED investigations indicated that (1) the first layer forms a regular unit cell with a lamellar structure, (2) the molecular arrangement shows a transition upon the completion of the first layer, which can be ascribed to subdivision of the lamella into antiphase domains, and (3) the surfaces of the gauche and quasi-crystalline phases do not have two-dimensional order. Since the molecule itself has a one-dimensional periodic structure, it is necessary to consider both the intramolecular and intermolecular periodicity for detailed analysis by LEED. Simulation of the LEED pattern by a kinematic theory indicated that the intramolecular rather than the intermolecular periodicity dominates the LEED pattern.

Field transformation approach to photonic band structure calculations

A field transformation method is introduced for the calculation of photonic band structures in periodic lattices of dielectrics. The method has the advantage of avoiding the complications due to matching boundary conditions at the interface of the constituents in a composite medium. The formalism is presented for propagation modes in which the electric field is parallel to the interfaces in both one-dimensional and two-dimensional periodic dielectric structures. Numerical calculations using the present formalism involve typically a matrix of size much smaller than that of using standard plane wave expansions.

Interference of opposing longitudinal acoustic waves in an isotropic absorbing plate and a periodic structure with defects

Interference of longitudinal acoustic waves propagating in opposite directions in a homogeneous isotropic absorbing plate and a periodic structure with a defect is considered theoretically. The periodic structure consists of alternating absorbing solid and transparent liquid layers. The defect is modeled by replacing a solid layer by a liquid layer of the same thickness. The dependences of the transmission spectrum of the energy flux on the amplitude ratio and phase difference of the interacting waves are studied. It is shown that, by varying the parameters of the opposite pressure wave, it is possible to change the transmission spectrum of the direct wave in a wide frequency range. An expression is obtained to determine the extremums of the wave amplitude transmitted through an absorbing plate depending on the amplitude ratio of the interacting waves. The results of studying a one-dimensional periodic structure demonstrate the possibility to considerably change the transmission spectrum of the pressure wave leaving the structure and also to eliminate the invariance of this spectrum under the interchange of the kth and (n−k+1)th layers (where n is the total number of layers in the structure).

Large omnidirectional band gaps and selective transmission in one-dimensional multilayer photonic structures

It has been shown that a one-dimensional periodic structure such as a superlattice can exhibit the property of omnidirectional reflection, which means that any incident wave launched from the vacuum (or from a substrate) will undergo a total reflection at the superlattice boundary, whatever the incident angle or the polarization of light is. In this communication, we show that large omnidirectional band gaps can be obtained by associating two or several superlattices in tandem. We discuss the existence conditions for these gaps as compared to the usual case of a binary superlattice. By introducing a defect layer in the finite layered structure, one can obtain localized modes inside these omnidirectional band gaps, giving rise to the selective transmission through the structure. These modes appear as peaks in the transmission spectrum with a very high quality factor, and therefore may have useful applications in the frame of photonic band-gap materials.

Coupling of impurity modes in one-dimensional periodic systems.

One-dimensional periodic dielectric structures are known to exhibit band gaps because of their symmetry. Defect states can be found in the band gaps if an impurity layer is added to the lattice such that the symmetry of the structure is broken. In this paper, we consider the case where a second impurity layer is added and we discuss the existence of coupling between the two defects. We discuss the possibility of exploiting the coupling of impurity modes in the realization of tunable wavelength emitting devices and dual-wavelength vertical-cavity surface-emitting lasers.

Specular spectroscopic scatterometry

Scatterometry is one of the few metrology candidates that has true in situ/in-line potential for deep submicrometer critical dimension (CD) and profile analysis. Most existing scatterometers are designed to measure multiple incident angles at a single wavelength on periodic gratings. We extend this idea by deploying specular spectroscopic scatterometry. Specular spectroscopic scatterometry (SS) is designed to measure the zeroth-order diffraction response at a fixed angle of incidence and multiple wavelengths. This mechanism allows the use of existing thin-film metrology equipment, such as spectroscopic ellipsometers, to accurately extract topographic profile information from one-dimensional (1-D) periodic structures. In this work, we developed the grating tool-kit (gtk), which implements several variants of rigorous coupled-wave analysis (RCWA) to accurately and efficiently simulate diffraction behavior of 1-D gratings. Theoretical simulations using this package show that specular spectroscopic scatterometry can be applied in the current semiconductor manufacturing technology, and can be easily extended to the 0.07-/spl mu/m generation. We have also applied a library-based profile extraction methodology to resist and poly focus-exposure matrices patterned using 0.25and 0.18-/spl mu/m lithography and etch technology, respectively, to extract their cross-sectional profiles. Discrepancies between CD-SEM, CD-AFM, and SSS measurements are discussed and explained.

Nonlinear Propagation of Light in One-Dimensional Periodic Structures

We consider the nonlinear propagation of light in an optical fiber waveguide as modeled by the anharmonic Maxwell-Lorentz equations (AMLE). The waveguide is assumed to have an index of refraction which varies periodically along its length. The wavelength of light is selected to be in resonance with the periodic structure (Bragg resonance). The AMLE system considered incorporates the effects non-instantaneous response of the medium to the electromagnetic field (chromatic or material dispersion), the periodic structure (photonic band dispersion) and nonlinearity. We present a detailed discussion of the role of these effects individually and in concert. We derive the nonlinear coupled mode equations (NLCME) which govern the envelope of the coupled backward and forward components of the electromagnetic field. We prove the validity of the NLCME description and give explicit estimates for the deviation of the approximation given by NLCME from the {\it exact} dynamics, governed by AMLE. NLCME is known to have gap soliton states. A consequence of our results is the existence of very long-lived {\it gap soliton} states of AMLE. We present numerical simulations which validate as well as illustrate the limits of the theory. Finally, we verify that the assumptions of our model apply to the parameter regimes explored in recent physical experiments in which gap solitons were observed.

Uniplanar one-dimensional photonic-bandgap structures and resonators

This paper presents uniplanar one-dimensional (1-D) periodical structures, so-called photonic-bandgap (PBG) structures, and defect high-Q resonators for coplanar waveguide, coplanar strip line, and slot line. Proposed uniplanar PBG structures consist of 1-D periodically etched slots along a transmission line or alternating characteristic impedance series with wide band-stop filter characteristics. A stop bandwidth obtained is 2.8 GHz with a stopband rejection of 36.5 dB. This PBG performance can be easily improved if the number of cells or the filling factor is modified in a parametric analysis. Using uniplanar 1-D PBG structures, we demonstrate new high-Q defect resonators with full-wave simulation and measured results. These structures based on defect cavity or Fabry-Perot resonators consist of a center resonant line with two sides of PBG reflectors. They achieve a loaded Q of 247.3 and unloaded Q of 299.1. The proposed circuits should have many applications in monolithic and hybrid microwave integrated circuits.

Nondestructive Evaluation of One-Dimensional Periodic Structures by Transmission of Laser-Excited Wide-Band Acoustic Pulses

The propagation of ultrasound in a one-dimensional model and actual periodic structures (PSs) is studied experimentally by the method of optoacoustic spectroscopy based on the laser thermooptical excitation and wide-band piezodetection of short acoustic pulses. It is shown that the ultrasound transmission spectrum of a PS has stop and pass bands, and the greater the number of layers in the PSs, the deeper the stop bands. The case where the thickness, density, and ultrasound velocity of one or several layers in the PS are modified is studied in detail. In this case, a narrow local maximum of ultrasound transmission appears in the stop band, whose location depends considerably on the position of the “defective” layer in the PS. The experimental data obtained coincide well with the theoretical calculation. The nondestructive evaluation of actual PSs consisting of two epoxy-glued identical aluminum plates is carried out by the optoacoustic method. Such materials are widely used in aircraft industry. It is shown that the ultrasound transmission spectrum for these materials depends considerably on the thickness of the epoxy-glue layer.

SLOW BRAGG SOLITONS IN A PERIODIC STRUCTURE WITH KERR NONLINEARITY

On the basis of coupled-mode theory we find a class of solitary solutions for the electromagnetic wave propagating in an infinite one-dimensional periodic structure with an intensity-dependent refractive index. We show that the amplitude of the solitary wave is dependent of the incident frequency and the pulse width. In the Bragg resonance limit, the solitary wave can be simplified to a soliton-like solution which was named as “gap soliton” or “slow Bragg soliton”.

Physicomechanical Properties of One-Dimensional Periodic Structures by Transmission of Laser-Excited Wide-Band Acoustic Pulses

The strength-deformation characteristics of a low-density polyethylene filled with cellulose-containing products, such as microcrystalline cellulose “Thermocell,” pinewood grinding dust and sawdust, and technical Thermocell obtained by a thermocatalytic method from pinewood raw materials are studied. The effect of the type of the filler and its content in the composite on the tensile strength, relative elongation, and work of failure in tension is determined. The water sorption and change in the strength-deformation characteristics of the composites during water sorption and desorption are also studied. It is found that the thermocatalytic treatment of cellulose-containing fillers makes it possible to increase the tensile strength of composites and to decrease the strength drop caused by water sorption.

Interaction induced delocalization for two particles in a periodic potential

We consider two interacting particles evolving in a one-dimensional periodic structure embedded in a magnetic field. We show that the strong localization induced by the magnetic field for particular values of the flux per unit cell is destroyed as soon as the particles interact. We study the spectral and dynamical aspects of this transition.

On vibrations of thin plates with one-dimensional periodic structure

A new approach to problems of thin plates with a periodic structure along one direction in the planes parallel to the plate midplane is proposed. The model is a certain generalisation of the length-scale models for periodic plates, which make it possible to take into account the effect of periodicity cell size on the dynamics of plates with two-dimensional periodic structure [J. Jȩdrysiak, C. Woźniak, J. Theoret. Appl. Mech. 33 (1995) 337–349; J. Jȩdrysiak, Eng. Trans. 46 (1998) 73–87]. In order to describe this effect in stationary processes, e.g., a plate stability, and non-stationary processes for one-dimensional periodic plates the generalised model is presented in this paper. In order to show differences between governing equations of the extended model and the model for plates with two-dimensional periodic structure or the homogenised model vibrations problems of one-dimensional periodic plates will be analysed.

Phase and group synchronization in second-harmonic generation of ultrashort light pulses in one-dimensional photonic crystals

It is shown, on the basis of an analysis of the dispersion relation for an infinite one-dimensional periodic multilayer structure and direct numerical integration of Maxwell’s equations by the finite-difference method, that structures with photonic band gaps (PBGs) make it possible to provide simultaneously conditions for phase and group synchronizations for second-harmonic generation with participation of extremely short light pulses. The phase and group detunings, which arise as a result of the dispersion of the nonlinear medium, are compensated by the dispersion of the PBG structure. The use of this regime of nonlinearly optical interactions opens up the possibility of attaining high frequency conversion efficiencies irrespective of the synchronization length in the interior volume of a nonlinear material.

Controlling dispersion and transmission spectra of hybrid resonant-gas-filled photonic-crystal optical components

Using the model of an infinite one-dimensional periodic layered structure, we consider the possi- bilities of controlling dispersion properties and transmission spectra of hybrid optical components consisting of photonic band-gap structures filled with a resonant gas. It is shown that the combination of resonance- enhanced gas dispersion with the dispersion of a photonic band-gap structure may give rise to new features in the dispersion and transmission of hybrid spectral elements. These effects can be employed to create narrow- band filters and ultrarefractive prisms with controllable parameters. © 2000 MAIK "Nauka/Interperiodica".

Photoacoustic study of the transmission of wide-band ultrasonic signals through periodic one-dimensional structures

The propagation of wide-band acoustic pulses in one-dimensional periodic structures consisting of alternating plexiglas and water layers is studied theoretically and experimentally. The experiment is carried out with the use of the wide-band photoacoustic spectroscopy based on the laser excitation of ultrasound and a wide-band signal detection. The fact that the transmission spectrum of a periodic structure has alternating pass and stop bands is confirmed experimentally. The width and localization of the stop bands strongly depend on the thickness of the layers and on the phase velocity of ultrasound in them. It is demonstrated that defects of the structure periodicity give rise to one or several local transmission maxima in the stop band and to a modification of the pass band. The amplitude and position of a local maximum in the stop band strongly depend on the position of the defective layer. The experimental data agree well with the results of numerical simulation.

Density of states for a dielectric superlattice. II. TM polarization

We present an analysis of the band structure, the equifrequency surfaces, and the density of states (DOS) for the transverse magnetic (TM) polarization mode of the dielectric superlattice, modeled by means of Dirac-delta functions. This complements a recent article [Phys. Rev E 59, 3624 (1999)] that analyzes the case of transverse electric (TE) polarization. Unfortunately, for this simple model, there is no manifestation of the Brewster effect in the band structure for the TM modes. For large values of the frequency or the grating strength, the equifrequency surfaces essentially degenerate into a set of concentric, hollow, and narrow cylinders centered on the superlattice axis. The DOS is enhanced relative to free space for any frequency and it exhibits discontinuities in the slope at the band edges. These results are relevant to the spontaneous emission by an atom or to dipole radiation in one-dimensional periodic structures. The differences between TE and TM modes are discussed. We take the opportunity to correct an error in the DOS calculation for TE polarization in the article referred above.