Volume 88, Issue 12, 20 March 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:
A crossed coplanar waveguide design using polymer insulation layers is developed as a tool to experimentally investigate fast, precessional switching phenomena in view of applications in magnetic random access memory. The photosensitive polymer Cyclotene 4024™ (benzocyclobutene) is used as an electric insulation layer to realize a multilayer sample consisting of several different conducting and insulating layers. We report on the processing of Cyclotene 4024™ multilayers with optimized surface and electric insulating properties after hard cure. The micropatterned impedance matched coplanar waveguides have a bandwidth of according to criterion, and for the criterion the bandwidth exceeds the measurement range of up to . These values allow for short rise and fall times of the pulse for ultrafast magnetization dynamics measurements.
- LASERS, OPTICS, AND OPTOELECTRONICS
88(2006); http://dx.doi.org/10.1063/1.2187438View Description Hide Description
We report the investigation of photonic band-gapproperties of a core-shell simple cubic structure (air core with a dielectric shell) using a two-parameter level-set approach. The proposed structure can be obtained by partially backfilling high refractive indexmaterials into a polymeric template fabricated by multibeam interference lithography. We find that the shell formation in the inverted simple cubic structure increases the complete photonic band-gap width by 10%–20% in comparison to that of a completely filled structure. The band gap between the fifth and sixth bands begins to appear at a refractive index contrast of 2.7. This study suggests the importance to investigate the core-shell formation in three-dimensional photonic crystals through backfilling, which may offer an additional control over their photonic band-gapproperties.
High-detectivity quantum-dot infrared photodetectors grown by metalorganic chemical-vapor deposition88(2006); http://dx.doi.org/10.1063/1.2188056View Description Hide Description
A mid-wavelength infrared photodetector based on quantum dots buried in an matrix and deposited on a substrate was demonstrated. Its photoresponse at was measured to be around with a cutoff at . Due to the high peak responsivity of and low dark-current noise of the device, a specific peak detectivity of was achieved at bias.
Tunable stop-band hollow waveguide Bragg reflectors with tapered air core for adaptive dispersion-compensation88(2006); http://dx.doi.org/10.1063/1.2188592View Description Hide Description
We propose a tunable stop-band hollow waveguideBragg reflector with a variable tapered air core for an adjustable dispersion-compensation device. The tapered air-core structure gives us chirped Bragg reflection. The precise control of tapered air-core thickness and angle enables us to achieve the dynamic tuning of both stop-band width and center wavelength of Bragg reflection. We demonstrate center-wavelength tuning of corresponding to 1.3% of propagation constant change and stop-band expansion up to . Also, we demonstrate dispersion tuning operation either in negative or positive dispersion ranges with delay-time difference of about .
88(2006); http://dx.doi.org/10.1063/1.2186985View Description Hide Description
We present second-harmonic surface emission from distributed feedback quantum-cascade lasers with integrated intersubband nonlinearities. The devices show single mode fundamental and second-harmonic emission at wavelengths of 10.7 and , respectively. Only light is emitted from the surface, as the fundamental light is not coupling to radiating modes for the grating of our choice. The second-harmonic peak optical power via the surface at is for a fundamental peak power of .
Efficient generation of green and UV light in a single PP-KTP waveguide pumped by a compact all-fiber system88(2006); http://dx.doi.org/10.1063/1.2187396View Description Hide Description
We present simultaneous efficient second- (SHG) and third-harmonic generation (THG) in a single periodically-poled KTP waveguided crystal pumped by a compact femtosecond Yb-based laser in a condition of exactly phase-matchedfrequency doubling and nonphase-matched sum-frequency mixing processes. Internal conversion efficiency as high as 33% for SHG and for the cascaded THG is reported. We believe this to be a clear experimental demonstration that strong third-harmonic can be generated in frequency doubling crystals through a nonphase-matched sum-frequency mixing process.
Optical power degradation mechanisms in AlGaN-based deep ultraviolet light-emitting diodes on sapphire88(2006); http://dx.doi.org/10.1063/1.2187429View Description Hide Description
We present a study of reliability of AlGaN-based deep ultraviolet light-emitting diodes on sapphire substrate grown by migration-enhanced metal-organic chemical vapor deposition. Two modes of optical power degradation were observed: catastrophic and gradual. The catastrophic degradation is believed to be due to metal alloying at macroscopic defects in the top layers of the light-emitting diode structure. For the gradual power degradation, two time constants were determined, which were temperature and bias dependent. For the temperature-dependent part, the values of the activation energies and room-temperature degradation rates at dc currents of 10 and were determined to be 0.23 and and , respectively.
Low-temperature-sensitivity heterostructure photonic-crystal wavelength-selective filter based on ultralow-refractive-index metamaterials88(2006); http://dx.doi.org/10.1063/1.2188055View Description Hide Description
We propose and numerically investigate the thermal-insensitive properties of a wavelength-selective filter based on heterostructurephotonic crystals with ultralow-refractive-index metallic nanowires. The operational principle of the proposed device is based on the photon trapping by total external reflections between the ultralow refractive indexmetamaterialcladdings and the guiding air cores. The low propagation losses, the ultracompact size as well as the temperature-insensitive operation are the main advantages of the proposed metamaterial technology, making the proposed de-multiplexer an excellent candidate for applications in nanophotonic-integrated systems operating in the visible frequency spectrum.
Three-dimensional integration of metal-oxide-semiconductor transistor with subterranean photonics in silicon88(2006); http://dx.doi.org/10.1063/1.2184754View Description Hide Description
Monolithic integration of photonics and electronics has been achieved in silicon by three-dimensionally integrating metal-oxide-semiconductor field-effect transistors and waveguide-coupled microdisk resonators.Implantation of oxygen ions into a silicon-on-insulator substrate with a patterned thermal oxide mask followed by a high temperature anneal was utilized to realize the buried photonic structures. This results in the formation of vertically stacked silicon layers separated from each other by an intervening oxide layer. Transistors are fabricated on the surfacesilicon by conventional processing techniques. Optical and electronic functionalities are thus separated into two different layers of silicon, paving the way toward dense three-dimensional optoelectronic integration.
88(2006); http://dx.doi.org/10.1063/1.2188371View Description Hide Description
Midinfrared emission from intersubband superluminescent light-emitting diodes is reported. We have obtained broadband emission spectra at around with a full width at half maximum of , using quantum-cascade-laser active regions designed to emit at 11 different wavelengths simultaneously. By introducing additional mirror loss in the Fabry–Perot resonator using just a single cleaved facet, with the other mirror formed by wet etching, the laser threshold current is significantly increased and superlinear light-current characteristics are observed. Optical peak powers of several tens of are measured at low temperatures.
88(2006); http://dx.doi.org/10.1063/1.2179611View Description Hide Description
We report on a monolithicpolymericmicrocavity laser with all dielectricmirrors realized by low-temperature electron-beam evaporation. The vertical heterostructure was realized by 9.5 pairs evaporated onto an active conjugated polymer, that was previously spincast onto the bottom distributed Bragg reflector (DBR). The cavity supports single-mode lasing at , with a linewidth of , and a lasing threshold of . We also report on the emission properties of the polymer we used, investigated by a pump-probe technique. These results show that low-temperature electron-beam evaporation is a powerful and straightforward fabrication technique for molecular-based fully integrable microcavity resonators.
88(2006); http://dx.doi.org/10.1063/1.2189015View Description Hide Description
A near-field scanning optical microscopy (NSOM) system employing a very-small-aperture laser (VSAL) as an active probe is reported in this Letter. The VSAL in our experiment has an aperture size of and a near-field spot size of about . The resolution of the NSOM system with the VSAL can reach about , and even . Considering the high output power of the VSAL, such a NSOM system is a potentially useful tool for nanodetection, data storage,nanolithography, and nanobiology.
High-quality -superlattice structures for the fabrication of narrow-band 1.4 μm photovoltaic intersubband detectors88(2006); http://dx.doi.org/10.1063/1.2185613View Description Hide Description
We report on high-quality short-period superlattices in the material system. Thanks to significant advances in the epitaxialgrowth, up to 40 superlattice periods with a total layer thickness of could be grown without cracking problems. Given an intersubband transition energy on the order of , these superlattices could be used as room temperature, narrow-band, photovoltaic detectors for wavelengths around . In photovoltaic operation, the full width at half maximum is as narrow as , underlining the high quality of the interfaces and the single layers in our structures.
88(2006); http://dx.doi.org/10.1063/1.2187954View Description Hide Description
We have studied the temperature dependence of exciton localization dynamics in epitaxial films by means of optical Kerr-gate time-resolvedphotoluminescence(PL) spectral measurements. During after laser excitation, the PL dynamics is sensitive to the measurementtemperature. In the temperature range of , the PL rise time decreases and the PL peak energy shifts to higher energy with an increase of temperature. At high temperatures above , the thermal quenching of the PL at shallow localized states occurs. The energy relaxation processes of excitons in localized states of films are discussed.
88(2006); http://dx.doi.org/10.1063/1.2188383View Description Hide Description
We present GaN-based light emitting diodestructures on a Si(001) substrate. The thick, crack-free layers were grown by metalorganic vapor phase epitaxy using a high-temperature AlN seed layer and 4° off-oriented substrates. This allows us to grow a flat, fully coalesced, and single crystalline GaN layer on Si(001). For preventing crack formation, four AlN interlayers were inserted in the buffer structure. The optically active layers consist of five-fold multiple quantum wells showing a bright electroluminescence at at room temperature. The crystallographic structure was analyzed by x-ray diffraction measurements and the optical properties were determined by photo- and electroluminescence.
88(2006); http://dx.doi.org/10.1063/1.2188057View Description Hide Description
We present a simple approach for the fabrication of genuine single quantum-dot light-emitting diodes. A submicron wide bottom contact stripe is formed by focused ion beam implantation doping into a buffer layer. Successive overgrowth with a thin intrinsic layer incorporating self-assembled quantum dots, followed by a top contact layer of complementary doping type and standard photolithographic processing, allows for electrical cross sections in the sub- range. In devices with sufficiently low dot densities, only one single dot is expected to be electrically addressed. Both the observed current versus voltage characteristics and the evolution of the electroluminescence spectra as a function of applied voltage clearly demonstrate that this goal has been achieved.
88(2006); http://dx.doi.org/10.1063/1.2183357View Description Hide Description
We present an all-optical technique that permits sorting within a polydisperse sample of microparticles in the absence of any microfluidicflow. We can sort colloidal samples based on their size and their refractive index. We show experimental and theoretical data for this method. It is based on the specific response of different microparticles to an interference pattern of fringes vibrating with an asymmetric time modulation. The size selectivity arises from the spatial fringe periodicity whereas selection based on refractive index is controlled by the beam power.
88(2006); http://dx.doi.org/10.1063/1.2188599View Description Hide Description
A method of quantum transport between quantum nodes using stationary lights is presented. The quantum transport of a single photon or a quantum state from one node to another is performed by a slow light phenomenon, where the transport time and path between nodes are classically determined. With both no-mirror-cavity characteristics of the stationary light and propagation velocity control of the slow light, the quantum transport has potential applications in quantum information sciences such as type-II quantum computing and quantum communications.
88(2006); http://dx.doi.org/10.1063/1.2187944View Description Hide Description
We report a non-field-applied Solc-type filter constructed by a periodically poled lithium niobate (PPLN). By comparing two types of PPLN Solc filter setup, both theoretically and experimentally, we have proved that without external field applied, it is the photovoltaiceffect that introduces pass peak in the PPLN band filter.
88(2006); http://dx.doi.org/10.1063/1.2187431View Description Hide Description
We have studied the tuning behavior of an external cavity laser in Littrow configuration using antireflection/high-reflection coated quantum dot laserdiodes as the amplifying element. Adding the coatings improves the performance of the setup, and the tunability of the external cavity laser output has been increased up to . Detailed investigations have revealed that laser diode length and width influence the magnitude of the tuning range. Furthermore, the external differential quantum efficiency is systematically increasing as the external cavity laser wavelength is decreasing. These characteristics are discussed in terms of energy levels available in the inhomogeneous broadening of the self-assembledquantum dots.
88(2006); http://dx.doi.org/10.1063/1.2188038View Description Hide Description
In a series of experiments on the Naval Research Laboratory's Electra generator, we have measured the dependence of the laser output in the principal transition of the laser upon both initial gas temperature and Xe concentration. The data show that the laser output is less sensitive to gas temperature when the laser gas contains more Xe. The destruction rate of the molecular ion increases rapidly with gas temperature, but that of does not. Interpreted with a kinetics model, these data indicate that both and contribute to the pumping of the laser.