Volume 87, Issue 23, 05 December 2005
- 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:
This letter demonstrates functional enhancements of fiber Bragg gratingsensors powered by in-fiber light. High-power laser light transmitted in double-clad optical fiber was extracted from the fiber core to heat an on-fiber metalcoating. When the power-laser is turned off, the fiber Bragg grating is used as a passive component for temperature sensing. When the laser is turned on, the thermal response of the optically heated grating was used to monitor ambient air pressure. The sensitivity and dynamic range of optically powered fiber sensors can be actively adjusted by in-fiber light to measure vacuumpressures over four orders of magnitude.
- LASERS, OPTICS, AND OPTOELECTRONICS
87(2005); http://dx.doi.org/10.1063/1.2138354View Description Hide Description
A method of characterizing the quantum dot charge buildup in a magnetic field is proposed based on the far-infrared magneto-optical response properties. The inherent topological symmetry of the nanostructure and several optical configurations are analyzed as key factors determining the appropriate use of intraband transitions as a probing tool for the quantum dot charge buildup.
Recovery of time evolving fluorescence spectra via sum-frequency cross-correlation frequency resolved optical gating87(2005); http://dx.doi.org/10.1063/1.2138366View Description Hide Description
Sum-frequency conversion of sample emission with short light pulses has been used for time-resolved fluorescence of chromophores in solution. In contrast to traditional fluorescence upconversion techniques where the time resolved fluorescence signal is approximated from 10 to 15 different sum-frequency gated decays distributed across the fluorescencespectrum, sum-frequency cross-correlation frequency resolved optical gating offers the opportunity to determine the electric field of the sample fluorescence as a function of time. Dynamic quantities associated with changes in the sample emission, such as solvent relaxation, can then be obtained directly from the electric field without assumption of a particular spectral line shape.
87(2005); http://dx.doi.org/10.1063/1.2138787View Description Hide Description
Bias-dependent non-Gaussian dark currentnoise has been observed in -type quantum-well infrared photodetectors. Time domain analysis of the noise revealed two-level telegraphlike fluctuations with exponentially distributed lifetimes that change dramatically with changing bias. The nature of the non-Gaussian fluctuations at intermediate voltages is ascribed to switching between two electric-field distributions corresponding to distinct tunneling probabilities out of the quantum wells. The finite transition time between the levels is identified with the recharging time.
High-resolution differential thermography of integrated circuits with optical feedback laser scanning microscopy87(2005); http://dx.doi.org/10.1063/1.2138794View Description Hide Description
We demonstrate a noninvasive technique for generating differential thermal maps of semiconductor edifices in integrated circuits (IC) at diffraction-limited resolution. An inexpensive optical feedback laser-scanning microscope detects changes in the optical beam-induced currents (OBIC) that are produced in the active layer in response to variations in the IC package temperature. The OBIC yield of a semiconductor normally increases with temperature. A differential thermal map derived from the OBIC output variations, shows locations of high thermal activity in the active layer including anomalous regions where the OBIC outputs decrease with increasing temperature. Anomalous regions are loci of accumulating semiconductorelectrical resistance that are highly susceptible to device failure. They provide the best jump-off points for efficient and accurate IC fault analysis procedure.
87(2005); http://dx.doi.org/10.1063/1.2138809View Description Hide Description
Organic thin-filmstructures, including organic light-emitting diodes, are demonstrated to contain multiple nonvolatile conductance states at low-read voltages. Retention time of states is more than several weeks, and more than 20 000 write-read-rewrite-read cycles have been performed with minimal degradation. The electrical characteristics of these devices are consistent with metal diffusion or filament phenomena found in metal-insulator-metal structures, suggesting a possible mechanism by which the states are stored.
Hole-injecting conducting-polymer compositions for highly efficient and stable organic light-emitting diodes87(2005); http://dx.doi.org/10.1063/1.2132072View Description Hide Description
This letter introduces conducting polymer compositions which can be used for hole-injection layer in organic light-emitting diodes. The compositions are composed of poly (3,4-ethylenedioxythiophene) (PEDOT), polystyrene sulfonic acid (PSS) and a perfluorinated ionomer. The films based on these compositions showed much higher workfunction than conventional PEDOT/PSS . When we fabricated blue polymer light-emitting diodes by using these compositions as a hole-injection layer, the luminescent efficiency was improved and the device lifetime was also enhanced relative to the device using the commercially available PEDOT/PSS. These compositions including perfluorinated ionomers can be one of the promising candidates for a hole-injection layer in organic light-emitting devices.
87(2005); http://dx.doi.org/10.1063/1.2138353View Description Hide Description
A simple method for doubling the laser emission efficiency of pumped cholesteric liquid crystal (CLC) photonic band edge lasers is demonstrated. By adding a mirror or a CLC reflector behind the dye-doped CLC cell, the lasing intensity is nearly doubled. For the mirror reflector, due to the mixing of right-handed and left-handed circular polarizations, the output laser is basically unpolarized. However, for the CLC reflector, a partially coherent laser can be built in which either right-handed or left-handed circularly polarized laser could dominate the output, depending on the handedness of the cholesteric structure.
87(2005); http://dx.doi.org/10.1063/1.2139836View Description Hide Description
Low-loss, quasi-planar ridge waveguide structures have been designed and fabricated in silicon-on-insulator material with waveguide propagation losses of at , and a measured in a ring resonator configuration. These structures offer tight vertical field confinement with scalable bending losses, and should be of interest for integration with both active and passive components. Waveguides were fabricated using optical lithography and processing compatible with siliconelectronics.
87(2005); http://dx.doi.org/10.1063/1.2139837View Description Hide Description
We report the fabrication and the characterization of interdigited metal-germanium on silicon metal photodetectors(metal-semiconductor-metal or MSM) for operation at both optical telecommunication wavelengths: 1.31 and . Femtosecond impulse and frequency experiments have been carried out to characterize those MSM Gephotodetectors. For both wavelengths, the measured bandwidth under bias are close to 10, 18, 20, and for electrode spacings equal to 2000, 1000, 700, and , respectively.
87(2005); http://dx.doi.org/10.1063/1.2139841View Description Hide Description
We demonstrate the growth and fabrication of a semipolar green light emitting diode(LED). The fabricated devices demonstrated a low turn-on voltage of and a series resistance of . Electroluminescencemeasurements on the semipolar LED yielded a reduced blueshifting of the peak emission wavelength with increasing drive current, compared to a reference commercial -plane LED. On-wafer measurements yielded an approximately linear increase in output power with drive current, with measured values of 19.3 and at drive currents of 20 and , respectively. The external quantum efficiency did not decrease appreciably at high currents.Polarizationanisotropy was also observed in the electroluminescence from the semipolar green LED, with the strongest emission intensity parallel to the direction. A polarization ratio of 0.32 was obtained at a drive current of .
87(2005); http://dx.doi.org/10.1063/1.2140092View Description Hide Description
An all-optical switching is demonstrated by use of defect mode in two-dimensional nonlinear photonic crystals made of polystyrene. Transmittance contrast of about 70% is achieved for the probe light. The dynamical shifts of the defect mode induced by pump intensity are measured and analyzed in detail. It is found that the defect mode shifts 5 nm under the excitation of pump intensity, which is in agreement with the theoretical predictions. Time response of the optical switching is smaller than the laser pulse of about 10 ps.
Influence of composition diffusion on the band structures of quantum wells investigated by the band-anticrossing model87(2005); http://dx.doi.org/10.1063/1.2138350View Description Hide Description
We investigate the influence of quantum-well intermixing (QWI) on the electronic band structure of multiquantum wells. The band structures and optical transitions have been calculated based on the band-anticrossing (BAC) model and Fick’s interdiffusion law for both intermixed and nonintermixed samples, respectively. The calculated results are consistent with the true optical transitions observed by photoluminescence excitation spectroscopy and secondary ion mass spectroscopy. Our investigation indicates that BAC model is valid for interdiffused quantum wells and verifies that the QWI process in multiquantum wells is induced mainly by the interdiffusion of In–Ga between the quantum wells and barriers.
87(2005); http://dx.doi.org/10.1063/1.2139620View Description Hide Description
We analyze the performance of a planar lens based on realistic negative index material in a generalized geometry. We demonstrate that the conventional superlens design (where the lens is centered between the object and the image) is not optimal from the resolution point of view, develop an analytical expression for the resolution limit of a generalized lens, use it to find the optimum lens configuration, and calculate the maximum absorption practical nearfield superlenses may have. We demonstrate that in contrast to the conventional superlens picture, planar imaging is typically accompanied by excitation of surface waves at both interfaces of the lens.
Optical properties of self-organized wurtzite quantum dots: A combined atomistic tight-binding and full configuration interaction calculation87(2005); http://dx.doi.org/10.1063/1.2139621View Description Hide Description
In this work, we investigate the electronic and optical properties of self-assembled quantum dots. The one-particle states of the low-dimensional heterostructures are provided by a tight-binding model that fully includes the wurtzite crystal structure on an atomistic level. Optical dipole and Coulomb matrix elements are calculated from these one-particle wave functions and serve as an input for full configuration interaction calculations. We present multiexciton emission spectra and discuss in detail how Coulomb correlations and oscillator strengths are changed by the piezoelectric fields present in the structure. Vanishing exciton and biexciton ground state emission for small lens-shaped dots is predicted.
Index and gain dynamics of optically pumped GaInNAs vertical-cavity semiconductor optical amplifiers87(2005); http://dx.doi.org/10.1063/1.2140068View Description Hide Description
To study the dynamic effects in GaInNAs vertical-cavity semiconductor amplifiers (VCSOAs), we carried out a pump-probe experiment on an optically biased VCSOA, first at antiresonance and then in gain. At antiresonance, the highest absorption region of the amplifier, the carrier-population-depletion-induced shift in the wavelength of the absorption was measured as a function of pump-probe delay. The corresponding index recovery time was measured to be . In the amplification regime, we observed that the carrier depletion induced by the pump pulse decreased the available gain. The recovery time for the device gain in dB under these conditions was measured at . These results indicate that GaInNAs VCSOAs can process data at with no patterning effect.
87(2005); http://dx.doi.org/10.1063/1.2140074View Description Hide Description
Signal amplification at the polymer optical fiber low-loss window of 650 nm is reported in an SU8 rib waveguide coated with Rhodamine-640 doped poly(methyl methacrylate). A signal beam is end-fired into the facet of a waveguide and amplified by top pumping of the -thick cladding region with a pulsed pump source focused into a 9-mm-long stripe. A gain of 14dB and a minimum signal-to-noise ratio of around 2 dB are achieved in a 15-mm-long device with a low threshold pump intensity of , which is an order of magnitude lower than previously reported.
87(2005); http://dx.doi.org/10.1063/1.2140877View Description Hide Description
Recently, a glass composition identified as oxyfluoride glass (OFG™) has stimulated great expectations in terms of creating “athermal” high-energy laser (HEL) windows. A proper evalution of the two thermal lensing coefficients, however, indicates that (a) the intrinsic stress birefringence cannot be ignored , and (b) the evaluation of must include the stress-optic contribution. Strehl-ratio calculations demonstrate that, in the absence of stress-driven failure modes, HEL windows made of OFG outperform fused-silica windows but may not match the capability of windows made of fusion-cast .
Current crowding in graded contact layers of intracavity-contacted oxide-confined vertical-cavity surface-emitting lasers87(2005); http://dx.doi.org/10.1063/1.2140886View Description Hide Description
In this work we present the simulation of the intracavity-contacted oxide-confined vertical-cavity surface-emitting lasers including the thermal effects. We analyze the thermal, electrical, and optical properties of such devices with the different thicknesses of graded layers between the contact and oxide confined layers. Results of simulations for the devices with graded layer thickness of 40–60 Å show a reduced current crowding effect.
All-optical control of the resonant-photon tunneling effect observed in multilayered structures containing quantum dots87(2005); http://dx.doi.org/10.1063/1.2140887View Description Hide Description
We observed the resonant-photon tunneling (RPT) effect at the optical communications waveband in a multilayered structure containing InGaSbquantum dots(QDs) as an active medium by a siliconprism total-reflection measurement. A sharp reflectance dip due to the RPT effect was clearly observed at a resonant-incidence angle in the total reflection region. The resonant-incidence angle clearly shifted when control light was irradiated onto the QDactive layer. We demonstrated that the reflectance around the resonant-incidence angle can be controlled all-optically using the control light irradiation. These results clearly indicate the possibility of creating RPT devices for all-optical signal processing in the optical communication wavebands.
87(2005); http://dx.doi.org/10.1063/1.2140585View Description Hide Description
We studied the location control of a giant grain of polycrystalline silicon produced by Ni-mediated crystallization of amorphous silicon using a cap layer. An organic lens made of acryl was used for the focusing of light for the seed formation and subsequent crystallization. A single grain in diameter was made using an -square cap layer on the . The position of a thin-film transistor(TFT) on a grain can be controlled, so that a single grainTFT can be fabricated at a predetermined position without use of the laser annealing technique.