Volume 87, Issue 10, 15 May 2000
Index of content:
- LASERS, OPTICS, AND OPTOELECTRONICS (PACS 42)
87(2000); http://dx.doi.org/10.1063/1.372961View Description Hide Description
A differential equation and boundary conditions are derived for the amplitude of the first harmonic of the space-charge field in the case of a lossy thin photorefractive film with anisotropic conductivity that is illuminated by a moving interference pattern. It is shown that for certain values of the anisotropy parameter, detuning, and film thickness, a new resonance phenomenon may occur. This resonance is distinct from and additional to the one that relies on the agreement between the speed of the interference pattern and that of the space charge wave, and has been known for a long time.
Photonic band in two-dimensional lattices of micrometer-sized spheres mechanically arranged under a scanning electron microscope87(2000); http://dx.doi.org/10.1063/1.372962View Description Hide Description
Two-dimensional photonic crystals of dielectric spheres with a 2.1 μm diameter have been fabricated by arranging individual spheres using a micromanipulation technique in a scanning electron microscope. A buildup of photonic bands from whispering gallery modes has been observed as the number of spheres increased, by measuring the transmission spectra for lattices composed of various numbers of spheres. The photonic band dispersion curves were experimentally obtained for a finite system made of 91 spheres from the transmission spectra for oblique incidence in the near-infrared region. They were in good agreement with the results of a numerical calculation for an infinite lattice. Since this mechanical manipulation technique enables us to control the arrangement of individual optical wavelength-sized scatterers, it provides a new way to systematically investigate various photonic band effects.
87(2000); http://dx.doi.org/10.1063/1.372963View Description Hide Description
(NdSB) can be grown as a nonlinear optical crystal having hexagonal (huntite) structure. The crystal has important spectroscopic properties suitable for various applications in photonics. The observed crystal-field splitting of the energy levels of has been identified based on analyses of the fluorescence, absorption, and excitation spectra obtained at 13, 80, and 300 K. A detailed crystal-field splitting calculation in which initial crystal-field parameters are established from lattice–sum calculations gives good agreement to the observed splitting. Experimental branching ratios and fluorescence lifetimes are reported and are compared with calculated values. The spectroscopic properties of in NdSB are also compared with values obtained for as a dopant in the nonlinear crystal
87(2000); http://dx.doi.org/10.1063/1.372964View Description Hide Description
We report calculations of the linewidth enhancement factor for five midinfrared active region materials. The linewidth enhancement factors for two type-I quantum wells based on InAsSb are 2.5 and 5.4, which represent a reduction of up to a factor of 2.6 with respect to bulk However, active region materials based on the type-II, InAs/GaInSb system have linewidth enhancement factors near 1.0, which is a factor of 2–5 reduction compared to the type-I quantum wells. The reduction of the linewidth enhancement factor is associated with both a reduction of the mismatch between the conduction and valence banddensities of states and the presence of conduction band dispersion. We describe an additional optimization that is possible in the type-II materials: Carefully placed intersubband absorption features can be used to further reduce the linewidth enhancement factor. We show that linewidth enhancement values as low as 0.3 can be obtained in the type-II superlattices when fabricated into a distributed feedback structure.
87(2000); http://dx.doi.org/10.1063/1.372965View Description Hide Description
We report the development of high quality, broad-bandwidth, antireflection (AR) coatings using the low index provided by wet thermally oxidized We address the design criteria, fabrication, and characterizations of AR coatings composed of surface and buried oxide layers on GaAs. We show, using native-oxide dispersion data, that surface oxide coatings can be designed to offer a nearly zero minimum of reflectance and a reflectance of <1% over bandwidths as large as 500 nm. Surfacecoatings having a reflectance minimum of 0.4% and a reflectance of <1% over >250 nm have been experimentally demonstrated at a design wavelength of 1 micrometer. Additionally, buried oxide coatings can be designed with an matching layer of any composition to exactly match the admittance of any substrate with effective index between 2.5 and 3.5. We have demonstrated buried oxide coatings, also designed for 1 micrometer, having a reflectance minimum of 0.4% and a reflectance of <1% over 21 nm. The calculated optical scattering loss from measured roughness data indicates that reflectance minima as low as are ultimately achievable with native-oxide antireflection coatings.