Volume 87, Issue 24, 12 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:
GaN-based photonic-crystal membrane nanocavities with factors up to 800 have been realized at the wavelength of . The tuning behavior agrees well with numerical calculations using the finite-difference time-domain method. Theoretically, the lowest energy mode of a cavity that consists of seven missing holes in the direction promises a factor as high as with a mode volume of about .
- LASERS, OPTICS, AND OPTOELECTRONICS
87(2005); http://dx.doi.org/10.1063/1.2138348View Description Hide Description
In this letter, we investigate the feasibility of tunable lithium niobatephotonic crystals. The optical response through a photonic structure is theoretically determined in order to obtain a photonic band gap with optimal tunability. We show by means of a finite difference time domain simulation that the optimal lattice parameters can provide a shift in the photonic band gap for a variation of the refractive index with an extinction ratio of . The fabrication process and the optical characterization of these novel photonic crystalstructures are also reported. The extinction ratio of the measured photonic band gap is lower than .
87(2005); http://dx.doi.org/10.1063/1.2138792View Description Hide Description
We demonstrate the coupling of PbSquantum dot emission to photonic crystalcavities at room temperature. The cavities are defined in 33% Al, AlGaAs membranes on top of oxidized AlAs. Quantum dots were dissolved in poly(methylmethacrylate) and spun on top of the cavities.Quantum dot emission is shown to map out the structure resonances. This technique may prove to be viable sources for room temperature cavity coupled single photon generation for quantum information processing applications. Moreover, our results also indicate that such commercially available quantum dots can be used for passive structure characterization. The deposition technique is versatile and allows layers with different dot densities and emission wavelengths to be redeposited on the same chip.
87(2005); http://dx.doi.org/10.1063/1.2140874View Description Hide Description
Distributed Bragg reflectors(DBRs) composed of an superlattice were grown of Si (111) substrates. The first high-reflectance III-nitride DBR on Si was achieved by growing the DBR directly on the Si substrate to enhance the overall reflectance due to the high index of refraction contrast at the interface. For a DBR, the measured peak reflectance of 96.8% actually exceeded the theoretical value of 96.1%. The superlattice served the added purpose of compensating for the large tensile strain developed during the growth of a crack-free DBR/Si structure. This achievement opens the possibility to manufacture high-quality III-nitride optoelectronic devices without optical absorption in the opaque Si substrate.
87(2005); http://dx.doi.org/10.1063/1.2140875View Description Hide Description
Quinternary AlGaInAsSb is introduced as a new barrier material for GaSb-based type-I laser diodes. For wavelengths beyond , this material improves the valence-band offset between GaInAsSb quantum wells and barriers as compared to standard structures. The laser structures, which comprise three compressively strained GaInAsSb quantum wells and AlGaInAsSb barriers and waveguides, show good structural and optical quality. emission has been achieved with ridge waveguide lasers working in pulsed operation up to . With this emission wavelength, a strong absorption line of is accessible for gas absorption measurements.
87(2005); http://dx.doi.org/10.1063/1.2142100View Description Hide Description
Active tuning of photonic crystals can be achieved by filling the porous structures with liquid crystals. Here, the director field in macropores was studied by fluorescence confocal polarizing microscopy. For this purpose, the photonic crystal was infiltrated with a glass-forming liquid crystalline polymer, the sample was cooled below the glass transition temperature and, subsequently, the photonic crystal template was removed. Results on a structure with modulated pores indicate a spatially periodic director field containing a lattice of disclination rings.
87(2005); http://dx.doi.org/10.1063/1.2142096View Description Hide Description
We demonstrate that surface plasmon polaritons can be guided by nanometer-scale dielectricwaveguides on top of a goldfilm. In a test experiment, plasmons were coupled to a curved radius dielectric stripe, which was wide and thick, using a parabolic surface coupler. This experiment demonstrates that using surface plasmon polaritons the scale of optoelectronic devices based on dielectricwaveguides can be shrunk by at least an order of magnitude.
87(2005); http://dx.doi.org/10.1063/1.2142083View Description Hide Description
Smooth voids are achieved in an anisotropic crystal with a high refractive index by use of a femtosecond laser-driven microexplosion method. Due to the anisotropy of the crystal, the maximum fabrication depth and the fabrication power threshold are different in different crystal directions, indicating that the direction perpendicular to the crystal axis is more suitable for thick three-dimensional structure fabrication. The dependence of the threshold power on the illumination wavelength shows that the microexplosion mechanism is caused by a two-photon absorption process. As a result, a near threshold fabrication method can be used to generate quasispherical voids.
87(2005); http://dx.doi.org/10.1063/1.2139846View Description Hide Description
Three-dimensionally periodic structures made of macroporous silicon with varying pore diameter show a photonic stop band in the middle infrared spectral range. A discontinuity of the periodic pore width modulation forms a planar optical resonator with a corresponding transmission peak in the stop band. Infiltration of the porous structure with a nematic liquid crystal and subsequent temperature changing cause a spectral shift of the defect mode. The experimental observations are in good agreement with theoretical calculations.
Highly directional emission via coupled surface-plasmon tunneling from electroluminescence in organic light-emitting devices87(2005); http://dx.doi.org/10.1063/1.2142085View Description Hide Description
We report that highly directional electroluminescence from top-emitting organic light-emitting devices (TEOLEDs) can be achieved by using a two-dimensionally periodically corrugated silverfilm as a cathode and an organic dye with a narrow bandwidth of emission spectrum as an emitting material. The resonant excitation of surface plasmons on the silverfilm interfaces contributes to the light transmission through the silvercathode and to the directional emission. The TEOLEDs with a europium complex as an emissive layer show beam divergence of less than 4° and the beam direction is controlled by periodicity of the corrugation.
Second- and third-harmonic generation in birefringent photonic crystals and microcavities based on anisotropic porous silicon87(2005); http://dx.doi.org/10.1063/1.2133910View Description Hide Description
One-dimensional anisotropicphotonic crystals and microcavities based on birefringent porous silicon are fabricated. The reflectance spectra demonstrate the presence of photonic band gap and microcavity modes with spectral positions tunable upon the sample azimuthal rotation around its normal and/or rotation of polarization plane of incident light. Simultaneous enhancement of second- and third-harmonic generation at the photonic band-gap edge due to the phase matching is observed. The angular positions of the second- and third-harmonic peaks are controllable via the anisotropy of the refractive indices of porous silicon layers.
One-to-many laser fanout generated by single large-size two-dimensional holographic photonic crystal87(2005); http://dx.doi.org/10.1063/1.2143133View Description Hide Description
The phenomenon of one-to-many laser fanout in large-size two-dimensional (2D) holographicphotonic crystals (H-PhCs) is presented. Theoretical analysis demonstrates that the phenomenon is induced by multiple substrate waveguiding effect of 2D H-PhCs, and the orientations of the waveguided beams depend on the lattice structures of 2D H-PhCs. The fanout angle and separations between output spots are determined by , light incident angle and thickness of glass substrate, therefore can be controlled via fabricating special lattice structures. The phenomenon has the potential to enable the application of 2D PhCs as interconnection devices in optical networks.
87(2005); http://dx.doi.org/10.1063/1.2141720View Description Hide Description
A series of organic pure-blue-light-emitting devices based on terflurorenes (TF) compounds are reported. In these double heterojunctions (DHJ) devices, two TF compounds act as a blue emitter, alternatively. Highly efficient pure-blue emissions are obtained from these devices. The maximum luminous efficiency of (corresponding to an external quantum efficiency of 2.7%) with 1931 Commission International De L’Eclairage coordinates of (0.165, 0.072) is obtained. It is indicated that the DHJ device structure is beneficial to the performance of blue devices by means of effective confinement of excitons and carriers in the large energy gap blue emitter.
87(2005); http://dx.doi.org/10.1063/1.2141727View Description Hide Description
87(2005); http://dx.doi.org/10.1063/1.2142294View Description Hide Description
We report a new type of electrically pumped THz source that emits at 9 THz with a maximum operating temperature of 150 K. The mechanism is based on dopant transitions in the 4H-SiC. The two nonequivalent donor sites of nitrogen in SiC were used to give the device a relatively high operating temperature and emission power. At a pumping current of 4.7 A at 4 K, the integrated spectral output power was 0.18 mWatt from the top surface with an area of . These results suggest that high-temperature operating THz devices can be fabricated from dopedSiC.
87(2005); http://dx.doi.org/10.1063/1.2142330View Description Hide Description
Low-energy (18 keV) phosphorus ion implantation and rapid thermal annealing at 650 °C for 120 s were used to create point defects and promote intermixing in quantum stick structures grown by molecular beam epitaxy. With these soft conditions for ion-implantation-induced intermixing, photoluminescence measurements at low temperature show a very large blueshift up to 350 nm and a narrow emission linewidth (down to 30 nm for ion dose equal to ). The band gap tuning limit in this system was evaluated using implantation of phosphorus ions at various doses , at a temperature of 200 °C followed by rapid thermal annealing.
87(2005); http://dx.doi.org/10.1063/1.2142087View Description Hide Description
Room-temperature threshold reduction in vertical-cavity surface-emitting lasers by injection of spin-polarized electrons87(2005); http://dx.doi.org/10.1063/1.2146064View Description Hide Description
We experimentally demonstrate the reduction of the laser threshold of a commercial vertical-cavity surface-emitting laser (VCSEL) by optical injection of spin-polarized electrons at room temperature. Calculations with a rate-equation model reproduce the measured reduction of 2.5% for injected electrons with 50% spin polarization. The model predicts an improved threshold reduction of 50% in otherwise identical VCSELsgrown on a (110) substrate due to the enhanced spin lifetime in such structures.
Short pulse, high-repetition rate, passively -switched Er:yttrium-aluminum-garnet laser at 1.6 microns87(2005); http://dx.doi.org/10.1063/1.2142086View Description Hide Description
We have demonstrated a continuously pumped, passively -switched, 1617 nm Er:yttrium-aluminum-garnet(YAG) laser oscillator with a pulse width of just under 7 ns, a pulse repetition frequency of about 4 kHz, and an output power of 0.9 W. The oscillator was pumped using an Er:fiber laser at 1534 nm, and switched using a saturable absorber. The Er:YAG laser is useful either stand-alone, or as the master oscillator in a master-oscillator-power-amplifier architecture.
Coupled-resonator optical waveguides for biochemical sensing of nanoliter volumes of analyte in the terahertz region87(2005); http://dx.doi.org/10.1063/1.2140479View Description Hide Description
We present a detailed study of coupled-resonator optical waveguide (CROW) based sensors for biochemical sensing. The sensitivity dependence on the CROW structure parameters, such as intercavity distance and cavity type, is investigated for the effects in the THz region of the EM spectrum of introducing small quantities of molecules, such as DNA, in the holes. Introducing the absorptive material into the low-index medium greatly affects the shape of the propagating modes of the CROW and the transmitted E-field. The shift of the resonant frequency also depends linearly on the refractive index changes for off-resonant case (dispersive effect).
Coupled islands of photonic crystal heterostructures implemented with vertical-cavity surface-emitting lasers87(2005); http://dx.doi.org/10.1063/1.2147728View Description Hide Description
Formation of bonding and antibonding states of two coupled photonic crystalheterostructureislands implemented with arrays of vertical-cavity surface-emitting lasers is studied theoretically and experimentally. Coupling of the photonic envelope wave functions confined to each island is brought about by tunneling across the heterobarrier separating the islands. Numerical simulations predict the bonding state to have the lowest modal losses. The experimental observations of lasing supermodes confirm this prediction, showing the island coupling in the bonding state of the coupled envelope functions.