Volume 89, Issue 20, 13 November 2006
- lasers, optics, and optoelectronics
- plasmas and electrical discharges
- structural, mechanical, thermodynamic, and optical properties of condensed matter
- electronic transport and semiconductors
- magnetism and superconductivity
- dielectrics and ferroelectricity
- nanoscale science and design
- device physics
- applied biophysics
- interdisciplinary and general physics
Index of content:
Several distinctive self-assembledInGaAsquantum dot molecules (QDMs) are studied. The QDMs self-assemble around nanoscale-sized GaAs moundlike templates fabricated by droplethomoepitaxy. Depending on the specific InAsmonolayer coverage, the number of QDs per GaAs mound ranges from two to six (bi-QDMs to hexa-QDMs). The Ga contribution from the mounds is analyzed in determining the morphologies of the QDMs, with respect to the InAs coverages ranging between 0.8 and 2.4 ML. Optical characterization shows that the resulting nanostructures are high-quality nanocrystals.
- LASERS, OPTICS, AND OPTOELECTRONICS
89(2006); http://dx.doi.org/10.1063/1.2388142View Description Hide Description
The authors report on tunable terahertz resonant detection of two cw lasers beating by plasma waves in high electron mobility transistor. The authors show that the fundamental plasma resonant frequency and its odd harmonics can be tuned with the applied gate voltage in the range of . The observed frequency dependence on gate bias is found to be in good agreement with the theoretical plasma wavedispersion law.
Strong resonant luminescence from Ge quantum dots in photonic crystal microcavity at room temperature89(2006); http://dx.doi.org/10.1063/1.2386915View Description Hide Description
Freestanding hexagonal two-dimensional photonic crystal(PhC) microcavities with Geself-assembledquantum dots were fabricated on silicon-on-insulator substrates. Strong photoluminescence associated with Gequantum dots was observed in the wavelength region of at room temperature. Sharp peaks dominated the spectrum, showing strong optical resonance inside the cavity. A resonant peak with a quality factor of 560 was observed at along with a significant enhancement of the luminescence in the microphotoluminescence spectrum. The peaks were also observed to reasonably shift when the structural parameter of PhC was changed.
Single-mode operation in the slow-light regime using oscillatory waves in generalized left-handed heterostructures89(2006); http://dx.doi.org/10.1063/1.2387873View Description Hide Description
The authors present an exact, analytic study of oscillatory modes guided by generalized asymmetric two-dimensional planar heterostructures with negative refractive index in either the core or the cladding. It is shown that, in sharp contrast to normal dielectric configurations, these waveguides always possess a frequency region where the second-order oscillatory mode may exist alone and allow for attaining zero group velocity under weak guidance conditions. In addition the mode has a field distribution that renders it excitable with an end-fire approach, making such structures attractive for applications requiring slow light. Advantages compared to previous methods of slowing or stopping light are discussed.
Improvement of near-ultraviolet nitride-based light emitting diodes with mesh indium tin oxide contact layers89(2006); http://dx.doi.org/10.1063/1.2387941View Description Hide Description
The authors have demonstrated nitride-based near-ultraviolet (NUV) light emitting diodes(LEDs) with mesh indiumtin oxide (ITO) contact layer. With injection current, it was found that forward voltages were 3.94 and while the output powers were 7.54 and for the planar ITO LED and mesh ITO LED, respectively. The larger LED output power should be attributed partially to the reduced absorption of ITO in the NUV region and partially to the better current spreading.
89(2006); http://dx.doi.org/10.1063/1.2387974View Description Hide Description
The authors report on the fabrication and characterization of an organic distributed feedback laser operating in the near infrared. The device, fabricated by room-temperature nanoimprint lithography, is based on an organic dye hosted by a poly(methylmethacrylate) matrix. The laser emission from an imprinted period grating is peaked at with a linewidth of and a pumping threshold of , and it is strongly polarized with a polarization contrast as high as 0.99. The lasing wavelength is tunable in the range of by adjusting the grating period, and the operational lifetime is up to excitation pulses in vacuum environment. These results demonstrate the possibility of realizing imprinted organic-based near-infrared lasers, thus approaching spectral regions relevant for optical communication applications.
Optical probes based on optical fibers and single-walled carbon nanotubes for hydrogen detection at cryogenic temperatures89(2006); http://dx.doi.org/10.1063/1.2370292View Description Hide Description
In this letter, preliminary results on the feasibility to use optical fibersensorscoated by single-walled carbon nanotubes (SWCNTs)-based sensitive materials for hydrogen detection at cryogenic temperatures are presented. The optical probes have been realized by the Langmuir-Blodgett deposition of close-end and open-end SWCNTs on the distal end of standard optical fibers. The results obtained from hydrogen detection testing, carried out at a temperature as low as , demonstrate the excellent potentiality of the proposed configuration to sense very low percentages of gaseous hydrogen , with good recovery and reversibility features as well as fast response times.
89(2006); http://dx.doi.org/10.1063/1.2388943View Description Hide Description
The authors report a micromirror device actuated by electrowetting effect. The micromirror surface is formed by a liquid-metaldroplet jetted on a substrate and then topped with a parylene/Teflon coated indiumtin oxide glass slide. The droplet is deformed by a voltage applied across the parylene/Teflon film. The radius of micromirror is tuned from to , and the normalized area increases from 0.2 to 0.94 accordingly. The switching time ranges from for a diameter droplet to for a one. A micromirror array is demonstrated and switched simultaneously.
89(2006); http://dx.doi.org/10.1063/1.2390644View Description Hide Description
We report on the fabrication of low threshold distributed feedback (DFB)polymer lasers based on a polyfluorene derivative containing statistical binaphthyl units (BN-PFO). First- and second-order feedback lasers have been realized. The emission was tuned in the wavelength range from by varying the grating period and the film thickness. A threshold energy of /pulse was observed in second-order DFB structures, which could be further reduced to /pulse by employing first-order feedback in electron beam lithographically patterned structures with a period of . In these first-order structures, laser oscillation at both edges of the photonic stop band was observed. These very low threshold values render BN-PFO a very promising material for future electrically pumped organic semiconductor laser diodes.
Analysis of defects in an electric and photonic double-layer substrate made by separation-by-implanted-oxygen three-dimensional sculpting89(2006); http://dx.doi.org/10.1063/1.2388882View Description Hide Description
With a view to application to electric-device fabrication, the authors investigated a separation-by-implanted-oxygen (SIMOX) three-dimensional (3D) sculpting method [P. Koonath et al., Appl. Phys. Lett.83, 4909 (2003)] that will integrate in three dimensions electric circuits and photonic circuits on a silicon-on-insulator substrate. The authors analyzed the defects in the first silicon layer for electric circuits and the second silicon layer for optical circuits made by SIMOX 3D sculpting. The authors found that a balance between an acceptable number of defects on the first silicon layer and the formation of a buried optical waveguide is achievable. The defect densities of the first silicon layer and the second silicon layer were and , respectively.
89(2006); http://dx.doi.org/10.1063/1.2388884View Description Hide Description
The authors use high-resolution charge-coupled device based thermoreflectance to derive two dimensional facet temperature maps of a watt-class laser that has a large fundamental optical mode. Recognizing that temperature rise in the laser will lead to refractive index increase, they use the measuredtemperature profiles as an input to a finite-element mode solver, predicting bias-dependent spatial mode behavior that agrees well with experimental observations. These results demonstrate the general usefulness of high-resolution thermal imaging for studying spatial mode dynamics in photonic devices.
89(2006); http://dx.doi.org/10.1063/1.2364876View Description Hide Description
The authors experimentally evidence an increase of light emission efficiency at room temperature in a silicon-on-insulator photonic crystal. The photonic crystal is made of a triangular lattice of silicon rods and operates as a single-mode light extractor. It exhibits a luminescence intensity two orders of magnitude higher than silicon-on-insulator substrate. In light of photoluminescence experiments, emission diagram measurements, and finite difference time domain calculations, they identify the different optical properties of the photonic crystal and they demonstrate the existence of at least a fivefold emission efficiency enhancement per surface unit.
89(2006); http://dx.doi.org/10.1063/1.2369539View Description Hide Description
The authors have investigated laser action in ferroelectric liquid crystal (FLC) sandwiched between dielectricmultilayers composed of and . The single-mode laser action was observed at the band edge of FLC. The lasing threshold was much lower than that of simple FLC because of the double optical confinement caused by the sandwich structure. They have also demonstrated the tuning of lasing wavelength by applying an electric field.
89(2006); http://dx.doi.org/10.1063/1.2390650View Description Hide Description
Compact wavelength detectors that resolve wavelength changes in the subpicometer range over a broad spectral range are presented. A photodiode array or position sensor device is coated with a linear variable filter that converts the wavelength of the incident light into a spatial intensity distribution. The centroid of the spatial distribution is determined by a differential readout of the two elements of the photodiode array or the position sensor device. The device can interrogate any optical sensor that produces a wavelength shift in response to a stimulus. The potential of this device was tested by interrogating fiber-Bragg-grating sensors.
Room-temperature light emitting diodes by liquid phase epitaxy for midinfrared dynamic scene projection89(2006); http://dx.doi.org/10.1063/1.2390655View Description Hide Description
The light emitting diodes(LEDs)grown by liquid phase epitaxy and tuned at several wavelengths inside the band were tested. Light pattern, radiation apparent temperature , thermal resistance, and self-heating details were characterized at in microscale by calibrated infrared cameras operating in the 3–5 and bands. The authors show that LEDs dynamically simulate very hot targets as well as cold objects and low observable. They resume that low cost LEDs enable a platform for photonic scene projection devices able to compete with thermal microemitter technology. Proposals on how to further increase LEDs performance are given.
89(2006); http://dx.doi.org/10.1063/1.2388879View Description Hide Description
Detailed studies are reported on the photoluminescence of multiple quantum wellsgrown by molecular beam epitaxy on InAs substrates with the Sb mole fraction ranging from 0.06 to 0.13. From photoluminescence the band alignment was determined to be staggered type II. By comparing the emission peak energies with a transition energy calculation it was found that both the conduction and valence bands of InAsSb alloy exhibit some bowing. The bowing parameters were determined to be in the ratio of 4:6. For a sample with Sb composition in the quantum well the photoluminescence emission band covers the absorption peak making it suitable for use in sources for detection.
89(2006); http://dx.doi.org/10.1063/1.2388885View Description Hide Description
This work presents an experimental analysis of the sensitivity characteristics to the surrounding refractive index (SRI) in long period gratingscoated with polymeric overlay with high refractive index and thickness values ranging in hundreds of nanometers. The presence of the coating induces the cladding to overlay mode transition depending on the overlay features and the SRI. The immediate consequence is a drastic modification of the sensitivity characteristics from the sublinear monotone behavior to a resonantlike shape. Here, the sensitivity characteristics of coated long period gratings have been investigated to outline their dependence on the overlay thickness and order mode.
High performance InP-based quantum cascade distributed feedback lasers with deeply etched lateral gratings89(2006); http://dx.doi.org/10.1063/1.2388887View Description Hide Description
The fabrication and operating characteristics of lateral grating distributed feedback InP-based quantum cascade lasers emitting at are reported. High performance, room temperature single mode lasers, utilizing double-sided lateral gratings, are achieved in InP-based material grown by metal organic phase epitaxy. These deeply etchedgratings are made possible by the development of a high aspect ratio, multistage, inductively coupled plasmaetch process. A threshold current density of is measured at room temperature and side mode suppression ratio with a tuning coefficient of is observed over a temperature range of .
89(2006); http://dx.doi.org/10.1063/1.2390645View Description Hide Description
The dominant oscillation shown in the laser-excited photoluminescence spectrum of the porous alumina film can be ascribed to the interference within a Fabry-Pérot optical cavity where the separation between two neighboring oscillations is highly sensitive to the film’s thickness and refractive index. The method, designated as photoluminescence oscillation, endows photoluminescence spectrum with another dimension and results in a nondestructive method for the measurement of the thickness and refractive index with a high resolution.
89(2006); http://dx.doi.org/10.1063/1.2390649View Description Hide Description
A compact, solid state optical amplifier based on the conjugated polymer poly[2-methoxy-5-(-ethylhexyloxy)--phenylene vinylene] has been demonstrated. The amplifier was optically pumped. Gratings were used to couple the signal into and out of the film. The transmitted signal was amplified over 100 times in a long waveguide giving gain at . A gain of was observed at 615 and giving a gain bandwidth of . The gain dynamics at pump densities below are described by an exciton-exciton annihilation model. At higher pump intensities, amplified spontaneous emission and photoinduced losses become significant.
Terahertz-wave near-field imaging with subwavelength resolution using surface-wave-assisted bow-tie aperture89(2006); http://dx.doi.org/10.1063/1.2387984View Description Hide Description
We demonstrate the terahertz-wave near-field imaging with subwavelength resolution using a bow-tie shaped aperture surrounded by concentric periodic structures in a metal film. A subwavelength aperture with concentric periodic grooves, which are known as a bull’s eye structure, shows extremely large enhanced transmission beyond the diffraction limit caused by the resonant excitation of surface waves. Additionally, a bow-tie aperture exhibits extraordinary field enhancement at the sharp tips of the metal, which enhances the transmission and the subwavelength spatial resolution. We introduced a bow-tie aperture to the bull’s eye structure and achieved high spatial resolution in the near-field region. The terahertz-wave near-field image of the subwavelength metal pattern (pattern ) was obtained for the wavelength of .