Armis R. Zakharian

Transmission of light through slit apertures in metallic films

Transmission of polarized light through subwavelength slit apertures is studied based on the electromagnetic field distributions obtained in finite difference time domain computer simulations. The results show the existence of a cutoff for E/sub /spl par// and a strong transmission (with no cutoff) for E/sub /spl perp//, where /spl par/ and /spl perp/ refer to the direction of the incident E-field relative to the long axis of the slit. Interference between the charges and currents induced in the vicinity of two adjacent slits is shown to result in enhanced transmission through both slits when the slits are separated by about one- half of one wavelength.

Design of a compact photonic-crystal-based polarizing beam splitter

A compact polarizing beam splitter based on a photonic crystal (PC) directional coupler with a triangular lattice of air holes is designed and simulated. In the employed PC structure, transverse-electric (TE) light is confined with the photonic bandgap effect, while transverse-magnetic (TM) light is guided through an index-like effect. Due to the different guiding mechanisms, TM and TE light have strikingly different beat lengths, which is utilized to separate the two polarizations in a directional coupler no longer than 24.2 /spl mu/m. The two-dimensional finite-difference time-domain method of computation is used to evaluate the device performance. The extinction ratios are found to be around 20 dB for both TE and TM polarized light.

Plasmonic nano-structures for optical data storage

We propose a method of optical data storage that exploits the small dimensions of metallic nano-particles and/or nano-structures to achieve high storage densities. The resonant behavior of these particles (both individual and in small clusters) in the presence of ultraviolet, visible, and near-infrared light may be used to retrieve pre-recorded information by far-field spectroscopic optical detection. In plasmonic data storage, a femtosecond laser pulse is focused to a diffraction-limited spot over a small region of an optical disk containing metallic nano-structures. The digital information stored in each bit-cell modifies the spectrum of the femtosecond light pulse, which is subsequently detected in transmission (or reflection) using an optical spectrum analyzer. We present theoretical as well as preliminary experimental results that confirm the potential of plasmonic nano-structures for high-density optical storage applications.

Transmission of light through small elliptical apertures

The results of computer simulations based on the Finite Difference Time Domain method with local space and time grid refinement, are presented for an elliptical aperture in a thin metal film illuminated by a normally incident, monochromatic plane wave. Both cases of incident polarization parallel and perpendicular to the long axis of the ellipse are considered. An intuitive description of the behavior of the electromagnetic fields is developed in each case, and simulation results that exhibit patterns similar to those expected from this qualitative analysis are presented. The simulations reveal, in quantitative detail, the amplitude and phase behavior of the E- and B-fields in and around the aperture.

Radiation pressure and the distribution of electromagnetic force in dielectric media

Using the Finite-Difference-Time-Domain (FDTD) method, we compute the electromagnetic field distribution in and around dielectric media of various shapes and optical properties. With the aid of the constitutive relations, we proceed to compute the bound charge and bound current densities, then employ the Lorentz law of force to determine the distribution of force density within the regions of interest. For a few simple cases where analytical solutions exist, these solutions are found to be in complete agreement with our numerical results. We also analyze the distribution of fields and forces in more complex systems, and discuss the relevance of our findings to experimental observations. In particular, we demonstrate the single-beam trapping of a dielectric micro-sphere immersed in a liquid under conditions that are typical of optical tweezers.

Experimental and theoretical analysis of optically pumped semiconductor disk lasers

We describe the experimental cw power scaling of optically pumped semiconductor disk lasers OPS-DLs and give a detailed insight into the physical mechanism of this type of high-power surface-emitting semiconductor laser with external cavity. Minimizing the thermal resistance between active region and heat sink enables improved efficiency and gives access to high power and excellent beam quality of OPS-DL at 1000 nm. Results from initial numerical modeling are in good agreement with the experimental data, and show that thermal management is a critical parameter for the temperature-driven power shutoff in such devices. The computations are based on the macroscopic thermal transport, spatially resolved in both the radial and longitudinal directions, and coupled to the carrier density rate equations. A quantitative microscopic approach is used for the quantum-well gain and absorption dependence on wavelength, carrier density, and lattice temperature. The dependence of the computed output power on the substrate thickness and detuning are discussed.

Multimode interference-based photonic crystal waveguide power splitter

A compact power splitter based on the multimode interference (MMI) effect in photonic crystal waveguides is designed and analyzed. The device size reduction compared with the conventional MMI power splitter can be attributed to the large dispersion of the photonic crystal waveguides. The Massachusetts Institute of Technology Photonic-Bands code is used to calculate the band structures of photonic crystal waveguides. The finite-difference time-domain method is adopted to simulate the relevant structures.

Surface plasmon polaritons on metallic surfaces

A theoretical study of surface plasmon polaritons on flat metallic surfaces and interfaces is undertaken to clarify the nature of these electromagnetic waves, conditions under which they are launched, and the restrictions imposed by Maxwells equations that ultimately determine the strength of the excited plasmons. Finite difference time domain (FDTD) computer simulations are used to provide a clear picture of the electromagnetic field distribution and the energy flow profile in each of the cases studied

Transmission of light through periodic arrays of sub-wavelength slits in metallic hosts

Using Bloch modes to study the extraordinary transmission of light through a periodic array of slits in a metallic host, we discuss the differing roles of surface plasmon polaritons and Woods anomalies in the observed behavior of such structures. Under certain circumstances, the first few excited modes appear to play a decisive role in determining the transmission efficiency of the array. Surface plasmon excitations tend to reduce the transmissivity of a semi-infinitely thick slit array, yet, paradoxically, the same reduction can account for enhanced transmission in an array of finite thickness tau, provided that tau is tuned to a Fabry-Perot-like resonance between the entrance and exit facets of the slit array. At the Wood anomaly, power redistribution produces sharp peaks in the diffraction efficiencies of various reflected and transmitted orders of the semi-infinite structure. With skew incidence, the degenerate states split, resulting in two peaks and two valleys, as observed by Wood in his 1902 experiments.

Electromagnetic-force distribution inside matter

Using the Finite Difference Time Domain method, we solve Maxwells equations numerically and compute the distribution of electromagnetic fields and forces inside material media. The media are generally specified by their dielectric permittivity epsilon(w) and magnetic permeability mu(w), representing small, transparent dielectric and magnetic objects such as platelets and micro-beads. Using two formulations of the electromagnetic force-density, one due to H. A. Lorentz [Collected Papers 2, 164 (1892)], the other due to A. Einstein and J. Laub [Ann, Phys. 331, 541 (1908)], we show that the force-density distribution inside a given object can differ substantially between the two formulations. This is remarkable, considering that the total force experienced by the object is always the same, irrespective of whether the Lorentz or the Einstein-Laub formula is employed. The differences between the two formulations should be accessible to measurement in deformable objects.