An AlGaN Light-emitting diode (LED) emitting with a peak wavelength at 291 nm and a radiant power of 0.5 mW @ 100 mA was fabricated on a sapphire substrate. A compact gated fluorescence detection system was built using this LED as the excitation light source. We demonstrate that it provides sufficient power using Terbium enhanced fluorescence to detect subnanomolar concentrations of dipicolinic acid (DPA, 2, 6-pyridinedicarboxylic acid), a substance uniquely present in bacterial spores such as that from B. anthracis, providing a basis for convenient early warning detectors. We also describe initial results from a novel approach for biological aerosol detection using long lived fluorescence from a Europium tagged dye that binds to proteins.
We present the results of steady state and time dependent photoluminescence measurements on ZnSe/Zn0.83Cd0.17Se multiple quantum wells from which the dominant recombination mechanisms are identified. Our experiments show that excitons rather than free carriers are the players in the recombination dynamics. Exciton localization is found to be an important factor competing with nonradiative recombination and enhancing the radiative efficiency in the multiple quantum wells investigated.
This paper discusses the collaborative optical and electrical characterization of the first photovoltaic (PV) III-nitride based detectors grown and fabricated by the Air Force Research Laboratory (AFRL). These 2.6 micrometer thick, n-type GaN Schottky detector structures doped with Si were grown by molecular beam epitaxy (MBE) on (0001)-oriented sapphire substrates, and incorporated palladium (Pd) as the Schottky metal contact. Working Schottky-barrier detector sizes ranged from 50 micrometer to 1600 micrometer in diameter. Flood- illuminated spectral responsivities of these Schottky detectors were as high as 0.12 A/W (for a 1600 micrometer diameter device biased at -1.5 V) at a peak wavelength of 273 nm. The typical measured frequency response of these detectors was flat from dc to the chopper limit of 700 Hz, and the 1/e response time of a 1600 micrometer diameter Schottky- barrier GaN detector was found to be as low as 50 microsecond(s) at zero bias. Noise characterization of these detectors was also performed, and noise equivalent powers (NEPs) of sample GaN Schottky-barrier detectors are reported.
This paper reviews performance of hybrid and monolithically integrated WDM transmitter arrays based on directly modulated 2.5Gbps lasers, with a focus on the wavelength accuracy and stability under normal operating conditions. We also consider power stability, chromatic dispersion penalties, and the channel cross-talk. Large numbers of four-wavelength devices were obtained and evaluated under a program designed to provide university-based system researchers with advanced WDM components We show that multi-wavelength laser arrays capable of high-performance out-of-the-box operation can be now produced for research-type WDM systems.
A method of propagation functions and transfer amplitudes suitable for the design of integrated optical circuits is presented. The method is based on vectorial formulation of electrodynamics: the distributions and propagation of electromagnetic fields in optical circuits is described by equivalent surface sources. This approach permits a division of complex optical waveguide structures into sets of primitive blocks and to separately calculate the transfer function and the transfer amplitude for each block. The transfer amplitude of the entire optical system is represented by a convolution of transfer amplitudes of its primitive blocks. The eigenvalues and eigenfunctions of arbitrary waveguide structure are obtained in the WKB approximation and compared with other methods. The general approach is illustrated with the transfer amplitude calculations for Dragone's star coupler and router.
Arrays of 8 X 8 of GaAs/AlGaAs vertical cavity surface emitting lasers (VCSELs), which operate at approximately 850 nm, are being fabricated for integration with low power, optoelectronic integrated circuits. These high performance optoelectronic computing modules are being developed for high speed switching and data processing applications. The VCSEL array is a gain-guided, top-surface emitting device. It is fabricated from a GaAs/AlGaAs p-i-n distributed Bragg reflector structure, which is grown by metal organic chemical vapor deposition. The VCSEL fabrication process involves two stages of hydrogen ion implantation and three stages of metallization. A set of five photolithography masks has ben developed for VCSEL fabrication.
Generation and detection of high power short optical pulses are of interest for applications such as high speed switching and optically controlled microwave generation. Such systems based entirely on semiconductor technology are highly desirable. In our experiments significant enhancement in the response of metal-semiconductor-metal photoconductive switches fabricated on Fe doped semi-insulating InP with heavy ion N+3 implantation has been observed. The response tail of the devices was effectively eliminated, resulting in FWHM pulse widths reduction from 200 ps (when unimplanted) to less than 40 ps for 4.5 micrometer gap device. No appreciable decrease in the breakdown field was observed. The dependence of spectral sensitivity on implantation dose was also studied. By proper optimization of the detector circuit, and use of high power semiconductors lasers with saturable absorber, generation of microwave signals in excess of 25 GHz and several volts could be achieved.
The coming of age of wavelength-division-multiplexed (WDM) laser arrays is bringing new challenges in the testing of semiconductor lasers. Because of stringent requirements on the laser linewidths and their frequency stability and because of electrical, optical, and thermal crosstalk problems, a new methodology is required for evaluating the performance of WDM laser arrays. This paper describes techniques that will be used to test WDM laser arrays both cw and under pulsed conditions. The laser arrays for these studies will be procured under a new program called `The WDM Alliance' sponsored by BMDO/AFOSR. Preliminary data on monolithic WDM laser arrays are also presented in this paper.
In the work presented here we study polarization-related dynamic and noise properties of vertical-cavity surface-emitting lasers (VCSELs) and analyze their performance in polarization-selective free-space optical data transmission links.
We describe a novel approach for implementing WDM networks that does not rely on fixed wavelength channels. Rather than tuning to a preassigned fixed wavelength channel any two nodes that require a link select a currently unused portion of the spectrum. Rather than tying to make trnamitters and receivers tune to fixed wavelength channels, the medium access control unit determines the approximate channel wavelength to be used for a given link. The receiver then dynamically locks onto this channel.
We describe the optical design of an optoelectronic 3-D system that is being developed by the Optoelectronic Computing Systems Center at the University of Colorado to prove the utility and viability of 3-D computers that use free-space optical interconnects to achieve a high degree of global connectivity among the PEs of a fine-grained parallel computer. The features of the VCSEL array as a source of coherent emission for hologram reconstruction and the CGH design procedure are discussed. An optical design in paraxial approximation of the 3-D computer with bidirectional 8 x 8 holographic interconnects is presented. The effect of VCSEL wavelength variation on diftraction crosstalk is estimated. The aberration in optical system based on the shelf objective is calculated, and a distortion compensation procedure is proposed.
The vacuum lithography technique has been extended to the nanometer spatial resolution regime by incorporating a 100 keV focused ion beam system which has a beam diameter of 50 nm or less. A portable vacuum transfer chamber is used so that the sample is maintained on vacuum throughout processing without the processing chambers being directly connected. This process employs focused ion beam pattern writing on an ultrathin surface oxide layer which acts as a mask in a subsequent dry etching step. Molecular beam epitaxy is used to overgrow new epitaxial material on the patterned substrates. Examples of patterning and overgrowth applied to InP/InGaAs heterostructures are described.
InGaAs/InP multiquantum well distributed feedback (DFB) lasers with the active layer based on either lattice matched or strained quantum wells are described. The active layer wells are placed in a carefully optimized graded index waveguide structure with very low internal loss. Buried heterostructure Fabry-Perot lasers based on these structures show low threshold current, high quantum efficiency and power output. These characteristics are to a large extent retained in distributed feedback lasers, with the DFB lasers showing mode rejection ratios as high as 50 dB and linewidths as low as 440 kHz. Transmission experiments at 1.7 Gb/s demonstrated dynamic chirp penalty a factor of 8-10 smaller than in conventional lasers.
A vacuum lithographic process for InP-based semiconductors has been developed. It employs a focused Ga ion beam to write patterns on an ultrathin native oxide resist thermally grown on the surface of InP. The pattern is transferred into the substrate by Cl2 etching. Depending on its thickness and composition the oxide is removed by either thermal desorption or by low energy Ar ion bombardment. This lithographic process is compatible with molecular beam epitaxy and has been used to create high quality GaInAsfInP heterostructures on patterned InP substrates. The details of this process are reported with an emphasis on the formation and removal of the oxide resist. Its composition and thickness as a function of oxidation temperature are examined using Auger analysis and a novel in-situ measurement technique respectively.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.