Waveguiding power of photonic crystal slabs

We consider the waveguiding by thin patterned slabs embedded in a homogeneous medium. In the longwave limit, the wave spectra of slabs are found to be well described by a single frequency-independent parameter, which we call the "guiding power". The guiding power can be evaluated in an effective medium approximation, similar to the Maxwell Garnett theory, but modified for the local field corrections specific to the two-dimensional geometry. The guiding power is different for the transverse magnetic (TM) and transverse electric (TE) polarizations. We show that the confinement factor of TM waves in a porous layer with high index ratio can exceed that for a homogeneous layer. Similarly enhanced confinement of TM waves is demonstrated for a layer of elongated cylinders or elliptic inclusion with a high axis length ratio. The effect originates from the suppression of local field effects and the increasing internal field in the inclusion. It may be useful in the design of far-infrared or THz quantum cascade lasers.Comment: 15 pages, 5 figure

Modal control in semiconductor optical waveguides with uniaxially patterned layers

Uniaxially patterned dielectric layers have an optical anisotropy that can be externally controlled. We study the effects of patterning the cladding or the core layer of a 3-layer optical waveguide on the polarization properties of propagating radiation. Particular attention is paid to the case when the core material is a semiconductor with optical gain. We discuss a number of devices based on incorporating an uniaxially patterned layer in the structure design, such as a polarization-insensitive amplifier, a polarizer, an optically-controlled polarization switch, and an optically controlled modal coupler.Comment: 9 pages 7 figure

Optical Spin Orientation in Strained Superlattices

Optical orientation in the strained semiconductor superlattices is investigated theoretically. The dependence of the features in spin-polarization spectra on the structure parameters is clarified. The value of polarization in the first polarization maximum in the SL structures is shown to grow with the splitting between the hh- and lh- states of the valence band, the joint strain and confinement effects on the hh1- lh1 splitting being strongly influenced by the tunneling in the barriers. In strained structures with high barriers for the holes initial polarization can exceed 95 %. Calculated polarization spectra are close to the experimental spectra of polarized electron emission.Comment: 20 pages, 8 figure

Photon assisted Levy flights of minority carriers in n-InP

We study the photoluminescence spectra of n-doped InP bulk wafers, both in the reflection and the transmission geometries relative to the excitation beam. From the observed spectra we estimate the spatial distribution of minority carriers allowing for the spectral filtering due to re-absorption of luminescence in the wafer. This distribution unambiguously demonstrates a non-exponential drop-off with distance from the excitation region. Such a behavior evidences an anomalous photon-assisted transport of minority carriers enhanced owing to the high quantum efficiency of emission. It is shown that the transport conforms very well to the so-called Levy-flights process corresponding to a peculiar random walk that does not reduce to diffusion. The index gamma of the Levy flights distribution is found to be in the range gamma = 0.64 to 0.79, depending on the doping. Thus, we propose the high-efficiency direct-gap semiconductors as a remarkable laboratory system for studying the anomalous transport.Comment: 12 pages, 9 figure