Strong Light Localization Research Articles

Virtual boundary method for the analysis of elliptically cross-sectional photonic-crystal fibers with elliptical pores

This paper introduces a new semianalytical method for the analysis of propagation characteristics of elliptically cross-sectional photonic-crystal fibers (PCFs) with elliptical pores. This method known as a virtual boundary method (VBM) is based on the equivalency between an actual PCF and a three-layered, transversely inhomogeneous waveguide. The complicated refractive-index profile of the PCF is written as a double Fourier series, and an approximate separable wave equation is found in an elliptical coordinate system for the longitudinal field components. The exact solution to the derived equation is expressed in terms of higher order transcendental functions, such as regular and irregular Coulomb-wave functions and Mathieu functions. After having expressed all the field components, boundary conditions are imposed on the boundaries, and then, a transcendental equation for the propagation constant is derived, which is solved numerically. The validity of the method is ensured by comparing various quantities, such as effective indexes, modal birefringences, and electromagnetic field distributions, with those from an accurate full-vector finite-element method (FEM) simulator, showing relatively good agreement between the results. The method correctly confirms some of the unique PCFs' properties, such as strong localization of light within the fiber and enhancement of modal birefringence as a function of the topology of hole arrangement.

Weak Localization of Light in Ultracold Atomic Gases

We summarize recent experimental and theoretical advances in the physics of coherent multiple light scattering in ultracold atomic gases. Current outstanding problems are reviewed, along with prospects for significant new insights into mesoscopic physics in ultracold atomic samples. The possibility of experimental demonstration of strong localization of light in atomic gases is discussed.

Direct observation of nonlinear effects in a one-dimensional photonic crystal

A total-reflection one-dimensional photonic crystal with a gold nanoparticles dispersed layer as a defect structure is fabricated and defect mode shifts induced by strong localization of light are demonstrated. It is found that the defect mode shift can be attributed to the Kerr effect inside the defect structure. Nonlinear optical effects inside the photonic crystal with the defect structure are also discussed.

Random laser in one dimension.

We present an analytical approach to random lasing in a one-dimensional medium, consistent with transfer matrix numerical simulations. It is demonstrated that the lasing threshold is defined by transmission through the passive medium and thus depends exponentially on the size of the system. Lasing in the most efficient regime of strong three-dimensional localization of light is discussed. We argue that the lasing threshold should have anomalously strong fluctuations from probe to probe, in agreement with recent measurements.

Laser action in strongly scattering rare-earth-metal-doped dielectric nanophosphors

We report continuous-wave laser action in two oxide nanopowders doped with ${\mathrm{Ce}}^{3+}$ and ${\mathrm{Pr}}^{3+}$ ions. To our knowledge, these are the first observations of stimulated emission from electrically pumped random media in which scattering and distributed feedback scale lengths are much shorter than a wavelength. The continuous nature of the laser emission in small volumes (on the order of a cubic wavelength) of these low gain systems, and the absence of coherent speckle, provide compelling evidence that these results are mediated by strong Anderson localization of light.

A Brief Report on Photonic Crystals and Calculations using the Mechanism of Strong Localization of Light

A brief description of a new class of strongly scattering dielectric microstructures, also called photonic material is given. These crystals are speculated to be of fundamental importance in the present day technology like semiconductors. The main theoretical and experimental developments are given. We have also calculated relative width of the Photonic band gap as a function of refractive index and a comparison is given for the close packed and diamond lattice of fcc 3-D structure. The characteristics of liquid crystal as Photonic crystal are re-analyzed. This work may be fruitful for the investigators in the field of Photonic Crystals.

Diffusing wave spectroscopy of uniform translational motion

Diffusing wave spectroscopy (DWS) is used to investigate thestructure and dynamics of opaque (optically dense) media such ascolloidal systems. These systems remain fundamentally importantfrom both scientific and industrial viewpoints. Analyses of DWSsignals from dense systems subject to flow fields have treated onlymotions due to velocity fields. Diffusive and other internal effectsupon the particle motions are ignored. The present work probes theresponse of the DWS signal itself by using a model system in whichthere is no structural dynamics to obscure the motion, in a flowfield where velocity gradients are absent. We observe initial,apparently exponential, components on the Gaussian form of thecorrelation function and compare them to strong localization oflight under conditions of diffusive propagation. For dense systems,DWS displays a time dependence, which is governed by thetranslational motion of the scattering system.

Midinfrared scattering and absorption in Ge powder close to the anderson localization transition

Using a free electron laser we have performed midinfrared transmission and reflection measurements in strongly scattering Ge powder. We have studied the wavelength dependence of the scattering properties and the optical absorption. Results indicate that our samples are close (kl(s) approximately 3) to the Anderson localization transition but still above it. This is in contrast to the recently reported strong localization of light (kl(s)<1) in a similar powder of lower refractive index particles (GaAs).

Strong localization of light and photonic atoms

In the strong localization regime, light confined to a well-defined volume of space by the mutual interference of its countless constituent scattered waves can be expected to acquire unusual characteristics. These include a vanishing momentum, an effective tensorial rest mass, and "photonic atom recoil." Impurity atoms that emit light under these conditions should consist of coupled atom-cavity systems with energy densities extending over regions larger than the atoms, but smaller than a cubic wavelength, in which radiant transport is suppressed by near-field correlated scattering. This unusual regime is now accessible over broad wavelength ranges in random nanoparticle media, opening the way to studies of novel phenomena such as strong localization phase transitions, lasers without cavities, and optical energy storage. PACS Nos.: 78.45+h, 78.60Hk, 42.55Rz, 42.25Fx, 78.35+c, 78.20Dj, 42.50Gy

Strong localization of light and photonic atoms

Strong localization of light and photonic atoms

Localization or classical diffusion of light?

Wiersma et al.1 have reported near-infrared optical transmission and coherent backscattering data from strongly scattering slabs of micrometre-sized semiconductor particles. Their optical transmission was much weaker, and the angular shape of their coherent backscattering more rounded, than would be expected for classical diffusive light propagation without absorption. The authors interpret this as evidence for the onset of strong localization of light, but we find that their data can be explained by classical diffusion combined with reasonable amounts of absorption. Moreover, the turbidities of their samples are much lower than those given in ref. 1 and are comparable to samples with classical transport properties. We therefore question whether their samples are in fact close to the proposed localization transition.

Strong Photon Localization in Mesoscopic Scaled Optical Waveguide

Strong photon localization in mesoscopic-scaled optical waveguide structures has been analyzed through two numerical approaches. The conventional electromagnetic wave analysis and the forced vibrational analysis methods are applied to 2-dimensional mesoscopic-scaled optical waveguide structures. The results indicate that both analysis methods give similar results for the density of states, the photonic band gap and the strong photon localized states according to the introduction of aperiodic structures of the refractive indices in the waveguides. The calculated mode patterns of the midgap states in the photonic band gap indicate that the features of strongly localized states depend on the aperiodicity, and light is localized strongly within a region of several micrometers in the random aperiodic waveguide. We also discuss fabrication techniques for realistic quasi-random aperiodic structures and the smearing out effect by the cladding layer which prevents the strong localization of light.

Strong localization of photons in aperiodic optical waveguides: A numerical realization

Numerical demonstrations of the strong localization of light are presented by illustrating aperiodic two-dimensional waveguides. For this purpose, the correspondence between the discretized form of the wave equation for light and the vibrational equation of motion for lattice dynamics is discussed in a general form. We emphasize that this mapping is useful not only to gain insight into the nature of the strong localization of light, but also to perform large-scale simulations on this phenomenon by employing an accurate numerical technique. The results will serve as a useful guide for the modeling and design of optical waveguides in which one can observe the strong localization of light.

Strong localization of light in two-dimensional disordered dielectric media

By numerically integrating Maxwell's equations in space and time we study the propagation of light of frequency ω emitted radially from a line source in an infinite dielectric medium with transverse disorder, i.e. disorder in only the two directions perpendicular to the line source. We show that such a system displays strong localization of light by demonstrating that the electromagnetic energy stored between consecutive pairs of cylinders, of radii mΔ R and ( m + 1) Δ R, where m=0, 1, 2, …, cente tered on the line source decreases exponentially with increasing m. This behavior contrasts with the lack of exponential decay in the stored electromagnetic energy as a function of mΔ R when the line source is embedded in a dielectric medium that is periodic in each of the two directions perpendicular to it.

Self-consistent treatment for strong localization of light in disordered dielectric superlattices.

Using a self-consistent theory of localization, we investigate the criteria for the localization of electromagnetic waves propagating through a dielectric superlattice with weak disorder. It is shown by calculation that near the band edge the strong localization of photons indeed occurs, irrespective of the strength of the disorder. Diffusion in this system is found by considering the influence of Bragg reflection on the bare diffusion coefficient.

Strong Localization of Light in Spongy Agglimerates of Carbon Grains

Ultraviolet extinction spectra of spongy agglomerates of amorphous carbon grains have been measured in the spectral range 100-300 nm. These spectra present two dips which can be explained in terms of strong localization of light in a disordered medium. The particular spongy structure of the carbon grains samples determines random fluctuations of the refraction index. When a light beam crosses samples having a granular structure, the fluctuatuions of n produce optical resonant modes which are localized along the disordered medium. Therefore, the transmission is enhanced for particular resonant frequences corresponding to the positive interferences of the light within an agglomeration of carbon grains having, in our experiment, a width of about 100 nm.