KEYWORDS: Curium, Energy transfer, Energy efficiency, Molecular energy transfer, Optoelectronics, Fluorescence resonance energy transfer, Molecules, Luminescence, Polymethylmethacrylate, Bioalcohols
Aside from salmon DNA, other DNA sources were explored namely, herring and onion, to prepare DNAsurfactant
complex, which will be used as a template for dyes undergoing Forster Resonance Energy
Transfer (FRET). Also, salmon DNA of low and high molecular weight were compared. This study aims to
assess the effect of using different DNA sources and molecular weight on the efficiency of energy transfer
between the dyes, coumarin 480 (Cm 480) and 4-[4-(dimethylamino)styryl]-1-docosyl-pyridinium bromide
(Hemi 22 and to understand the fundamental properties of DNA-CTMA as a supporting matrix for
optoelectronics applications.
Infrared (IR) focal plane arrays (FPAs) with multispectral detector elements promise significant advantages for airborne
threat warning, surveillance, and targeting applications. At present, the use of type II superlattice (T2SL) structures
based on the 6.1Å-family materials (InAs, GaSb, and AlSb) has become an area of interest for developing IR detectors
and their FPAs. The ability to vary the bandgap in the IR range, suppression of Auger processes, prospective reduction
of Shockley-Read-Hall centers by improved material growth capabilities, and the material stability are a few reasons for
the predicted dominance of the T2SL technology over presently leading HgCdTe and quantum well technologies. The
focus of the work reported here is on the development of T2SL based dual-band IR detectors and their applicability for
multispectral imaging. A new NpBPN detector designed for the detection of IR in the 3-5 and 8-12 μm atmospheric
windows is presented; comparing its advantages over other T2SL based approaches. One of the key challenges of the
T2SL dual-band detectors is the spectral crosstalk associated with the LWIR band. The properties of the state-of-the-art
T2SLs (i.e., absorption coefficient, minority carrier lifetime and mobility, etc.) and the present growth limitations that
impact spectral crosstalk are discussed.
We report the influence of bonding temperature on SU-8 to SU-8 bonding and report fabrication of a hybrid microelectromechanical-tunable filter (MEM-TF) using SU-8 bond pads. We demonstrate use of 2-µm-thick 50×50-µm2 SU-8 bond pads to attach 4.92-µm-thick 250×250-µm2 Al0.4Ga0.6As-GaAs distributed Bragg reflectors (DBR) to polysilicon MUMPs® piston actuators. Advantages of this process include compatibility with hydrofluoric-acid-release chemistry, low-temperature/low-pressure bonding, simple bond-pad photolithography, 57% flip-bonded DBR yield, and 30% electrostatically actuatable hybrid MEM-TF yield.
The photoluminescence (PL) and amplified spontaneous emission (ASE) spectra of the conjugated polymer [2-methoxy-5-(2'- ethylhexyloxy)-1, 4-phenylenevinylene] (MEH-PPV) is study under different conditions such as thin film and solution, solvent type and concentration. Experiments indicate that aggregation has a pronounced effect on the measured spectra of both the PL and the ASE. In solution form, the ASE emission bandwidth decreases with the increment on concentration as well as a red shift of the ASE peak. For the thin film samples, the ASE spectra show two emission bands corresponding to the emission of the inner and the outer polymer chains. These two emission bands were associated with the gas to crystal effect, previously reported for PL.
Vertical external cavity surface emitting lasers (VECSELs) have been considered the “ultimate disk-laser” due
to their extremely thin active regions and because they take advantage of the high gain found in semiconductor
material. This paper discusses power scaling limitations, including heating effects, surface roughness losses, and
laterally guided amplified spontaneous emission (ASE).
In this paper, we report on the deposition of nonplanar SiO2 and SiNx dielectric layers using plasma-enhanced chemical vapor deposition (PECVD), radio frequency (rf) sputtering and reactive rf sputtering through metal and dielectric shadow masks. The layers were analyzed for trends in deposition rate and curvature as a function of shadow mask material and geometry, as well as the deposition method. Increasing the top hole diameter, which is the limiting aperture of the shadow mask cavity, increased the rate of deposition inside the cavity, but it also decreased the curvature of the resulting aspheric microlens. As the height of the shadow mask cavity was increased, both the cavity deposition rate and microlens curvature increased. An alumina shadow mask created microlenses with higher deposition rates and more curvature than a nickel shadow mask for the three deposition methods. SiO2 deposited by PECVD produced aspheric microlenses with the most curvature, whereas rf sputtering SiO2 produced microlenses with the highest process efficiency. These results could be exploited to produce single or multilayer dielectric films for use in focal-plane arrays of microlenses, light-emitting diode encapsulations or curved Bragg mirrors for vertical-cavity surface-emitting lasers.
We report and use our micro-electro-mechanically tunable vertical cavity surface emitting laser (MEM-TVCSEL) computer-aided design methodology to investigate the resonant frequency design space for monolithic and hybrid MEM-TVCSELs. For various initial optical air gap thickness, we examine the sensitivity of monolithic or hybrid
MEM-TVCSEL resonant frequency by simulating zero, two, and four percent variations in III-V material growth thickness. As expected, as initial optical airgap increases, tuning range decreases due to less coupling between the active region and the tuning mirror. However, each design has different resonant frequency sensitivity to variations in III-V growth parameters. In particular, since the monolithic design is comprised of III-V material, the shift in all growth thicknesses significantly shifts the resonant frequency response. However, for hybrid MEMTVCSELs, less shift results, since the lower reflector is an Au mirror with reflectivity independent of III-V growth variations. Finally, since the hybrid design is comprised of a MUMPS polysilicon mechanical actuator, pull-in voltage remains independent of the initial optical airgap between the tuning reflector and the III-V material. Conversely, as the initial airgap increases in the monolithic design, the pull-in voltage significantly increases.
A general scheme for the determination of vital operating characteristics of semiconductor lasers from low intensity photo-luminescence spectra is outlined and demonstrated. A fully microscopic model for the optical properties is coupled to a drift-diffusion model for the mesoscopic charge and field distributions to calculate luminescence and gain spectra in barrier-doped laser material. Analyzing experiments on an optically pumped multi quantum-well structure it is shown that the electric fields arising from the charges of ionized dopants lead to strongly excitation dependent optical properties like significant differences between luminescence and gain wavelengths.
We report our progress on the design and fabrication of electrostatically-actuated microelectromechanical (MEM) tunable wavelength filters and vertical cavity surface-emitting lasers (VCSELs). We investigate both an all-semiconductor monolithic approach and a hybrid approach based on the combination of conventional polysilicon microelectromechanical systems (MEMS) and III-V semiconductor thin-film distributed Bragg reflector (DBR) and VCSEL structures. In the tunable hybrid structures the III-V semiconductor layers are flip-bonded onto specially designed polysilicon foundry MEMS structures and separated from their lattice-matched parent substrates by a novel post-bonding lift-off process.
A general scheme for the determination of vital operating characteristics of semiconductor lasers from low intensity photo-luminescence spectra is outlined and demonstrated. A fully microscopic model for the calculation of optical properties is coupled to a drift diffusion model for the mesoscopic charge and electric field distributions to calculate photo-luminescence and gain spectra in barrier-doped semiconductor laser material. Analyzing experiments on an optically pumped multi quantum-well structure it is demonstrated that the electric fields arising from the space charges of ionized dopants contribute to strongly excitation dependent optical properties, such as significant shifts of the luminescence versus peak gain wavelengths.
We describe a multilayered dielectric stack configuration designed specifically for use as a transmissive phase modulator for broadband optical signals. Applications for this device range from full aperture wavefront correction to nonmechanical beam steering arrays for free space optical communication links. Our implementation employs alternating GaAs and AlAs layers of varying thickness on a GaAs substrate to create a bandpass region of high average transmission in the near infrared. Within this transmission bandpass, the phase component of the complex transmission coefficient varies in a near-linear fashion with respect to wavelength. The transmission bandpass is designed to have a bandwidth of 21.0 nm (or 6.3THz frequency bandwidth) and to have an edge-to-edge relative phase change of greater than 4p radians. Modification of the stack materials' optical properties causes the transmission profile to shift spectrally, resulting in a phase modulation for specific bands of transmitted frequencies. Our broadband phase modulator imparts nearly a full-cycle of phase modulation with low loss and low group velocity dispersion. A sample comprising 91 alternating layers has been fabricated to exhibit the bandpass properties required for optical signal phase modulation. We experimentally characterize the sample using an interferometer and spectrometer to measure the spectral transmission and relative phase profiles and to assess the relative phase modulation in response to a variable angle of incidence. We compare the experimental data to computational predictions and discuss the results.
We present an optical delay line structure incorporating InxGa1-xAs quantum wells in the GaAs quarter- wave layers of a GaAs/AlAs distributed Bragg reflector. Applying an electric field across the quantum wells shifts and broadens the e1-hh1 exciton peak via the quantum- confined Stark effect. Resultant changes in the index of refraction thereby provide a means for altering the group delay of an incident laser pulse. Theoretical results predict tunable delays on the order of 50 fs for a 30-period structure incorporating 3 quantum wells per GaAs layer. Structure design, growth and fabrication are detailed. Preliminary group delay measurements on large-area samples with no applied bias are presented.
We describe a design for an agile, electronically- configurable, optical beam steering array to be used in directional free-space transmission of optical signals. The proposed device employs a 1D array of tunable resonant transmissive modulators constructed from customized multi- layered stacks of dielectric materials. Each modulator may be individually configured to transmit an optical signal with a known amount of phase and group velocity modulation. Proper configuration of each individual modulator results in diffractive interactions between multiple modulator outputs, providing a method for directional optical signal transmission. Of particular focus within this paper is the design of the individual modulator. We generate custom transmission functions by varying the parameters describing the modulator's specific construction, such as number of layers within the multi-layer stack, refractive indices of stack materials, layer thickness, and combinations of periodic versus non-periodic layer repetitions. A computational optimization of the variables describing the stack's construction strives to maximize the amount of optical signal modulation obtainable within defined limits. Our optimization is based largely on maximizing transmitted phase delay. We discuss trade-offs between methods of increasing device performance versus practical limitations of fabrication technologies.
A microscopic interpretation of spontaneous and stimulated emission in semiconductor microcavities is developed using Semiconductor Luminescence Equations obtained from a quantum theory for the interacting electron-hole system and microcavity photons. The properties of bare quantum well luminescence as well as nonlinear photoluminescence of microcavity systems showing a threshold-like transition are consistently explained.
The threshold-like growth of the higher energy photoluminescence from a normal-mode-coupling microcavity was previously attributed to exciton polariton lasing (boser) based on Bose condensation into the upper polariton branch. Experimental evidence is presented here showing that this boser crossover occurs just as normal-mode coupling collapses to the perturbative weak coupling, so that boser action is fermionic after all. I.e., it can be understood as electron-hole recombination within a microcavity with density-dependent emission properties.
A single narrow-linewidth quantum-well absorption peak is coupled to the single-mode resonance of a moderately high reflectivity microcavity, resulting in an anticrossing curve as a function of relative detuning. For zero detuning, two cavity peaks and two photoluminescence peaks are seen. Two quantum wells with different resonant energies result in a system of three coupled oscillators. Nonlinear studies include determination of the nonlinearities of the quantum wells, observation of optical bistability, and saturation of the microcavity transmission.
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