A variable optical attenuator employing an electrooptic Kerr material as the functional cladding of a silica waveguide is shown to switch in less than 1 microsecond with an extinction ratio greater than 15 dB. The VOA is designed to operate at 70 C and the electrooptic material has a refractive index that is less than the silica waveguide at that temperature. Methods for achieving low polarization dependent loss are outlined. An electrooptically-induced half-wave plate is shown to provide polarization independent performance with polarization dependent loss less than 0.6 dB at 19 dB of attenuation.
A silica waveguide employing an electrooptic Kerr material as a functioning cladding is shown to modulate light at RF frequencies. The modulator uses a Kerr electrooptic material as the functional cladding on a silica waveguide structure. The modulator is designed to operate at 70 C and the electrooptic material has an index of refraction that is less than the silica waveguide at that temperature. Kerr-based materials have a refractive index that varies as the square of the applied voltage. This quadratic relationship is exploited by combining a DC bias voltage with the RF drive signal in order to reduce the drive voltage of the modulator.
A densely packed bed of alkaline earth fluoride particles percolated by a fluid medium has been investigated as potential index-matched optical limiter in the spirit of a Christiansen-Shelyubskii filter. Marked optical limiting was observed through this transparent medium under conditions where the focused second-harmonic output of a Q-Switched Nd:YAG laser was on the order of about 1 J/cm2. An open- aperture Z-scan technique was used to quantify the limiting behavior. In this case, the mechanism of optical limiting is thought to be a nonlinear shift in the fluid index of refraction, resulting in an index mismatch between the disparate phases at high laser fluence. This induced mismatch appears to be promoted by localized electric field enhancement present near the sharp edges at the crystallite/fluid boundaries. Index mismatch between the two phases leads to multiple reflections, loss of coherence, and a significant transmission decrease due to Mie scattering. The presence of many boundaries significantly amplifies the effect. The role of thermally induced changes in refractive index for this system appears to be relatively small in pulsed-laser experiments. However, cw-laser blocking was achieved by a thermal mechanism when an absorber (iodine) was dissolved in the liquid phase. Fundamental studies of such systems are used to verify theoretical predictions of the limiting effect, and aid in the design and development of improved limiters based upon this optical deflection approach.
Using the LOCALF method, we have examined electric field distributions for high and low dielectric susceptibility cases through systematic variations of defect concentration and orientation. The addition of nonlinear susceptibility terms to the conventional linear contributions in the dielectric formalism incrementally perturbs both the electric field intensities and predicted dielectric constants, having a greater influence on low dielectric materials. These effects are modulate by the relative ratios of the linear and nonlinear susceptibility terms for a material due to polarization-derived changes. Nonlinear effects can have a strong influence on the magnitude of these changes; potentially obscuring predicted changes in dielectric response due to microstructural detail.
The surface and bulk microstructures inherent to the fabrication process of dielectric films, affects both the distribution of the local electric field intensities and its associated dielectric properties. In this paper, we have used a finite element electric field model to examine the effects of a low dielectric surface layer, alignment of a low dielectric component within the dielectric film, and the interaction of these two influences on the local electric fields and dielectric constants. Columnar microstructure and alignment of dielectric components perpendicular to the surface norm are shown to enhance electric intensities and dielectric constants. Predicted dielectric constants are compared against conventional effective medium approximation results.
The microstructure of dielectric films provides a significant influence on the electric field distribution in these materials. In this paper, we focus on the relationship between the electric field distribution and organization of film constituents. Using our self- consistent determination of the local electric field in inhomogeneous media, we have shown that enhanced fields can result from columnar microstructures such as typically generated by CVD-type fabrication processes, and low dielectric components in optical coatings. In addition to the microstructural enhancement, a surface specific enhancement due to presence of low dielectric components is observed.
The complex microstructure of dielectric films alters the local electric fields affecting both the strength by which different sites within a film interact, and the spatial extent. Using our self- consistent lattice element model, we determined the site by site interaction of the local electric fields within a defect ridden dielectric film to determine the effects of microstructure on the interaction of defects sites on its surroundings. Local dielectric properties are compared to currently accepted models of dielectric film properties (such as effective medium methods) determine the local field and polarization.
Using a finite element representation of a dielectric film, we have examined the effects of surface defects on the local electric field and its intensity. Surface defects possess the potential to affect the local electric fields in a dielectric film in a manner similar to those introduced in the bulk solid. Both raised and removed regions tend to focus the electric field vector about the defect, and the interaction of two defects can lead to an enhanced local electric field intensity. In these cases, effective medium methods would approximate the film by an idealized defect-free structure, and thus would not note the sensitivity of the electric field to surface structure.
Inorganic polymers are characterized by both in-plane it''and out-of-plane it bonding interactions in contrast to organic materials where iteffects dominate the optical properties. Involvement of the it'' bonding system results in higher electronic transition energies with the first transition being a it'' ic process. Second hyperpolarizabiities are affected by both it bonding systems and are reduced by higher transition energies and lower transition probabilities. In this paper we present electronic structure calculations of the static hyperpolarizabilities of a series of model compounds for inorganic polymers to illustrate the relationship between their electronic structure and nonlinear optical properties. 1. 0
Different film deposition techniques have been found to generate distinct grain morphologies
and defect distributions, which can result in a wide distribution of local field intensities. We
have developed a lattice element model of an inhomogeneous medium, which we use to selfconsistently
determine the local internal electric field and polarization. We use this method to
show the sensitivity of the polarization to defect shape. The results of this method predict the
local field to have a large range of values within the film and have been used to identify regions
where the local field is a maximum.
Third order hyperpolarizabilities were calculated using the Huckel Hamiltonian and third order perturbation theory for a series of phosphonitrilic compounds, (X2P-N)n, as a function of bond length alternation, ligand substitution and backbone conformation. Phosphonitrilic compounds show hyperpolarizabilities comparable to those reported for organic species, and are modulated by ligand group electronegativity. In contrast to organic polyenes, the difference in it orbital energy between phosphorus and nitrogen is critical to determining the onset of saturation and the magnitude of the hyperpolarizability. Conformation effects are smaller than those seen in polyenes.