AffiliationEdwards Air Force Base
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AbstractThe Edwards Digital Switch (EDS) provides mission critical voice and time-spaceposition information (TSPI) communication switching capability to the Edwards Test Range. The present system has been in operation for about 10 years. The core of this system is based on widely used commercial-off-the-shelf (COTS) time-slot interchange switches that were designed for a 40-year service life. The application layers of the system, comprising the command/control elements and the communications and user interfaces, were custom developed by the prime contractor to satisfy the performance requirements of the Air Force Flight Test Center (AFFTC). Problems with the current system include difficulty in obtaining replacement items for equipment developed by the prime contractor and higher than expected failure rates for this equipment. Based on experience, the service life for the equipment developed by the prime contractor appears to be about 15 years. Another problem is that lower cost packet switches are taking market share from the more traditional time-slot interchange switches. This factor tends to accelerate the obsolescence of the existing COTS equipment. Solutions are being investigated to update or replace the EDS. One solution is to reuse the existing COTS core equipment and replace the present application layers, preferably with COTS. Another solution is to replace the entire system with COTS or vendormodified COTS hardware and software.
SponsorsInternational Foundation for Telemetering
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ASSESSMENT OF PHOTONIC SWITCHES AS FUTURE REPLACEMENT FOR ELECTRONIC CROSS-CONNECT SWITCHESYoussef, Ahmed H.; TYBRIN Corporation; Edwards Air Force Base (International Foundation for Telemetering, 1999-10)This paper presents the future of optical networking via photonic switches as a potential replacement for the existing electronic cross-connects. Although optical amplifiers are now mainstream and wave division multiplexing (WDM) systems are a commercial reality, the industry’s long-term vision is one of the all-optical network. This will require optical switching equipment such as all-optical or “photonic” cross-connect switches that will provide packet switching at an optical layer. Currently, as voice calls or data traffic are routed throughout Range and commercial networks, the information can travel through many fiber-optic segments which are linked together using electronic cross-connects. However, this electronic portion of the network is the bottleneck that is preventing the ideal network from achieving optimal speeds. Information is converted from light into an electronic signal, routed to the next circuit pathway, then converted back into light as it travels to the next network destination. In an all-optical network, the electronics are removed from the equation, eliminating the need to convert the signals and thereby significantly improving network performance and throughput. Removing the electronics improves network reliability and restoration speeds in the event of an outage, provides greater flexibility in network provisioning, and provides a smooth transition when migrating to future optical transmission technologies. Despite the fact that photonic switching remains uncommercialized, it now seems apparent that the core switches in both the public networks and DoD Range networks of the early 21st century will probably carry ATM cells over a photonic switching fabric.
Ultrafast optical nonlinearities in aluminum phthalocyanine organic thin films and a picosecond all-optical organic etalon switch.Williams, Valorie Sharron (The University of Arizona., 1991)The history of femtosecond laser pulse generation is summarized and a current state-of-the-art femtosecond laser system described. The femtosecond pulses are used to observe coherent coupling effects in a fluoro-aluminum phthalocyanine thin film. The polarization dependency of the coherent coupling indicates that orthogonal polarization states in the phthalocyanine ring are effectively uncoupled. The coherent coupling effect evolves into a nonequilibrium exciton population spectrally coincident with the pump pulse. This population rapidly decays to the bottom of the π- π* absorption band. These singlet excitons exhibit rapid bimolecular decay characteristics. In addition, some singlet excitons relax into the triplet manifold by intersystem crossing. Excited-state triplet-triplet absorption is then observed. The triplet excitons relax to the ground state, apparently via nonradiative decay mechanisms. Femtosecond techniques are also employed to demonstrate a picosecond all-optical organic NOR gate. A dye-doped polymer is used as the nonlinear material inside a Fabry-Perot etalon.
Theory of optical nonlinearities in semiconductors: Applications to nonlinear wavemixing and photonic switching.Richardson, Dean. (The University of Arizona., 1991)Nonlinear optical switching and grating formation/scattering effects in thin semiconductor samples are modeled utilizing a combined microscopic/macroscopic theoretical approach. The microscopic optical nonlinearities of the materials of interest are treated using the semiconductor plasma theory of Banyai and Koch. Computer simulations are used to evaluate the models developed under both steady-state and dynamic conditions. The overall objective of the simulations is to provide a realistic assessment of the potential performance of semiconductor etalon-based nonlinear optical devices for photonic switching and processing applications. To this end, parameter studies are performed with the goal of finding device designs that can operate cascadably, at subnanosecond speeds, with minimum switching energy. Both bistable and two-wavelength operating modes are investigated, with an emphasis on dynamic determination of system characteristics such as contrast, fanout, and differential gain. For bistable semiconductor etalons, the maximum gain achieveable is found to depend in a fundamental way on the relationship between the pulsed-excitation timescale t(p) and the carrier lifetime τ(R). Significant differential gain is shown to disappear for GaAs etalons as t(p)/τ(R) approaches unity, implying that subnanosecond cascading of bistable devices is impractical in this case. For two-wavelength logic gates, several potential solutions to the well-known input/output-wavelength incompatibility problem are proposed. Through the use of a NOR-gate/upconverter etalon pair, picosecond cascadable operation with a fanout of two and contrast of at least five are predicted, requiring a total input energy of 75 picojoules. Utilizing an injected current and stimulated recombination in an active NOR-gate design, the total input energy can be reduced to about 25 picojoules for cascadable, high-contrast operation. The nonlinear semiconductor field-propagation model is also applied to the case of degenerate four-wave mixing in the Raman-Nath regime. The resulting theoretical framework is compared with widely-used small-signal analyses of DFWM in semiconductors for the case of bulk GaAs. The comparison makes clear the inadequacies of such approaches in extracting nonlinear material properties from DFWM experiments performed using moderate to high input intensities. Dynamic simulations of diffraction efficiency spectra in low-temperature CdS are compared with data from corresponding pulsed experiments, producing good qualitative agreement. On the basis of the observed theory-experiment correlation, several drawbacks of DFWM spectroscopy in comparison to pump-probe techniques are discussed.