The optical properties of two-dimensional (2D) photonic crystal (PhC) slabs based on self-assembled monolayer of
dielectric microspheres are studied. The in-plane transmission spectra of 2D array of dielectric spheres with triangular
lattice are investigated using the finite-difference-time-domain (FDTD) method. The structures studied are monolayer of
dielectric spheres infiltrated with air ('opals') and air spheres infiltrated with dielectric material ('inverse opals'), with
glass substrate sustaining the monolayer of spheres. The transmission spectra are calculated for different values of
refractive index contrasts between the spheres and the infiltrated material and for different values of filling fractions
(compactness of the spheres). As the refractive index is varied, compact spheres are assumed; and as the filling fraction
is varied, the refractive index of the dielectric spheres or the dielectric matrix is fixed to be 2.5. For compact opal
structure on glass substrate, a narrow photonic band gap (PBG) is observed in the transmission spectra for dielectric
spheres with refractive index higher than around 1.9. When the refractive index is fixed at 2.5, the PBG is observed for
more compact spherical arrangement and disappears for more separated spheres. While for inverse opal structure on
glass substrate, using non-compact spheres enlarges the width of PBG which is not observed for compact spherical
arrangement. The application of the study is to realize organic PhC microcavity laser.
Simultaneous two-dimensional nanometric-scale position monitoring can be achieved in a simple interferometric
setup by real-time probing a hexagonal photonic crystal glass substrate. The minimum detectable translational movement
is determined by the period of photonic crystal array, and can be as high as 8 nm in the present work.
A novel technique was proposed to fabricate a three-dimensional photonic crystal by self-assembling microspheres and the autocloning technology. The autocloning thin-film layers were superimposed on the prepared two-dimensional structural substrates using self-assembled microspheres. The thin-film process allows the three-dimensional periodic structure to be easily modified in the thickness dimension to structure as needed. We analyzed the etching effect using the unified process model according to the surface movement and surface velocity of the film to achieve the surface profile of the SiO2 adjusting layer. Finally, 17 layers of Ta2O5/SiO2 multilayers were stacked on the SiO2 adjusting layer successfully.
The authors report on the growth of GaN on AlGaN/(111)Si micropillar array by metal-organic chemical vapor
deposition. Using the substrates with micropillar array, 2 μm-thick GaN films without cracks can be achieved.
Transmission electron microscopy, atomic force microscopy, and micro-Raman studies indicate that the dislocation
density and residual stress of the GaN grown on micropillar array are also reduced. The results reveal the potential of this
type of substrates for growing GaN-based devices as well as preparing GaN freestanding substrates.
Silicon photonic crystal (PhC) waveguide based resonator is designed by introducing a micro-cavity within the line
defect so as to form the resonant band gap structure for PhC. Free-standing silicon beam comprising this nanophotonic
resonator structure is investigated. The output resonant wavelength is sensitive to the shape of air holes and defect length
of the micro-cavity. The resonant wavelength shift in the output spectrum is a function of force loading at the center of a
suspended beam with PhC waveguide resonator. The sensing capability of this new nanomechanical sensor is derived as
that vertical deformation is about 20nm at center and the smallest strain is 0.005% for defect length.
Coupling of a InGaN/GaN multi-quantum well (MQW) and semitransparent metal layer is shown to result in dramatic
enhancement of spontaneous emission rate by the surface plasmon effect in the optical spectral range. A five-pairs
18.5nm InGaN/GaN MQW is positioned 175nm, form various thickness (t=5~50nm) silver layer. And periodic patterns
(p=0.25~0.8μm) are defined in the top semitransparent metal layer by e-beam lithography, which are grating structures
can be incorporated into the metal film to excite surface plasmon between the interference of the metal film and
semiconductor. We have experimentally measured photoluminescence intensity and peak position of spontaneous
emission of the fabricated structures and compared with the unprocessed samples, whilst still ensuring that most of the
emission takes place into the surface plasmon (SP) mode. And the implication of these results for extracting light by
reducing total internal reflection (TIR) from light emission diode is discussed.
We have designed and fabricated a hollow optical waveguide with omnidirectional reflectors (ODRs) on a silicon substrate. The pattern is defined by photolithography on a (100) silicon wafer. The groove is etched by inductive coupled plasma. Plasma-enhanced chemical vapor deposition technology is used to deposit six-pair Si/SiO2 (0.111/0.258 µm) multilayer stacks on the sample. Finally, the top of the sample is covered with an identical ODR. Hence, the light is confined in a hollow waveguide.
Vertical-cavity surface-emitting lasers with variant compressively strained InGaAlAs quantum wells have been investigated. The valence band structures, optical gain spectra, and threshold properties of InGaAlAs/AlGaAs quantum wells are compared and analyzed. The simulation results indicate that the characteristics of InGaAlAs quantum wells can be improved by increasing the amount of compressive strain in quantum well. Furthermore, the properties of VCSELs with these compressively strained InGaAlAs quantum wells are studied numerically. The results of numerical calculations show that the threshold current and maximum output power can be enhanced by using higher compressively strained InGaAlAs quantum well. However, when the compressive strain is larger than about 1.5%, further improvement of the laser performance becomes minimal. The effects of the position and aperture size of the oxide-confinement layers on the laser performance are also investigated. Variation of the oxide layer design is shown to affect the current distribution which makes the temperature in the active region different. It is the main reason for the power roll-off in the VCSEL devices.
In this study, we design and fabricate a hollow optical waveguide with omni-directional reflectors in silicon-based materials. A groove is etched by inductive coupled plasma (ICP) with photolithographic process on (100) silicon wafer. The width of the groove is varied from 3.5 to 5.5 micrometer for different waveguide designs. The depth of the groove is 1.2 micrometers. Plasma enhanced chemical vapor deposition is used to deposit six pairs of Si/SiO2(0.111/0.258micrometers) on the samples. Finally, the top of the sample is covered by another silicon substrate on which the identical omni-directional reflector has been also deposited. By wafer bonding technology, the top omni-directional reflector can be combined with the groove to form a hollow optical waveguide. Light with the wavelength at 1.55 micrometers can be confined by the omni-directional reflectors at single mode operation. Polarization independent hollow optical waveguides can be achieved with this fabrication process.
Photoluminescence (PL) measurement and optical pumping at 25K were studied for high-indium-composition InGaN/GaN multiple quantum well (MQW) structures grown by low-pressure metalorganic chemical vapor deposition. The result show that thermal annealing can reduce the compositional fluctuation of indium content. The optical pumping spectra show 5 stimulated emission (SE) peaks. This phenomenon might be attributed to intersubband transition. The transition between quantized levels for each peak was precisely identified by solving the time-independent Schrodinger equation and finite-difference method. The ratio of conduction- band discontinuities to the valence-band discontinuities of InGaN/GaN QW, (delta) Ec:(delta) Ev=38:62, can be obtained.
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