With the advent of new regulations governing the protection and recovery of sensitive business data, including the Sarbanes-Oxley Act, there has been a renewed interest in business continuity and disaster recovery applications for metropolitan area networks. Specifically, there has been a need for more efficient bandwidth utilization and lower cost per channel to facilitate mirroring of multi-terabit data bases. These applications have further blurred the boundary between metropolitan and wide area networks, with synchronous disaster recovery applications running up to 100 km and asynchronous solutions extending to 300 km or more. In this paper, we discuss recent enhancements in the Nortel Optical Metro 5200 Dense Wavelength Division Multiplexing (DWDM) platform, including features recently qualified for data communication applications such as Metro Mirror, Global Mirror, and Geographically Distributed Parallel Sysplex (GDPS). Using a 10 Gigabit/second (Gbit/s) backbone, this solution transports significantly more Fibre Channel protocol traffic with up to five times greater hardware density in the same physical package. This is also among the first platforms to utilize forward error correction (FEC) on the aggregate signals to improve bit error rate (BER) performance beyond industry standards. When combined with encapsulation into wide area network protocols, the use of FEC can compensate for impairments in BER across a service provider infrastructure without impacting application level performance. Design and implementation of these features will be discussed, including results from experimental test beds which validate these solutions for a number of applications. Future extensions of this environment will also be considered, including ways to provide configurable bandwidth on demand, mitigate Fibre Channel buffer credit management issues, and support for other GDPS protocols.
In recent years, there has been an increasing interest in the design and development of optical waveguides for computer backplanes and intra-card communications. The transition from high speed copper interconnects to optical links is driven by those applications which can most benefit from a greatly increased bandwidth-distance product; this includes rack mounted blade servers, data communication switches and routers, high end enterprise servers, and supercomputers. Typically the candidate applications require hundreds of optical links, each operating at 10 Gigabit per second or higher, for aggregate bandwidths on the order of multi-terabits per second across distances of one to ten meters across a backplane. In this paper, we review some recent developments in polymer-based optical interconnect for these applications. In particular, we report experimental results for arrays of multi-mode acrylate polymer waveguides, fabricated either on the surface of a printed circuit board or embedded within a multi-layer board. Transmission speeds up to 12.5 Gigabit per second have been demonstrated on a single link, with optical attenuation as low as 0.04 dB/cm. Packaging considerations for vertical cavity laser and photodiode arrays will be discussed, including tolerances for passive alignment between waveguides and active components. Finally, we review several recently issued patents for optical backplane connector concepts and their potential applications within the next 3 years.
Recently, there has been increased interest in the use of optical networks for disaster recovery of large computer systems by extending storage area networks (SANs) over hundreds of kilometers or more. These optical datacom networks, which incorporate wavelength division multiplexing (WDM), have several unique requirements. The purpose of this work has been to develop computer simulation tools for optical datacom networks. The models are capable of automatically designing a WDM network configuration based on minimal input; validating the design against any protocol-specific requirements; suggesting alternative configurations; and optimizing the design based on metrics including performance of the network (efficient use of bandwidth to support the attached computing devices), reliability (searching the proposed topology for single points of failure), scalability (based on user input of potential future upgrade paths), and cost of the associated networking equipment. The model incorporates typical computer performance data, which allows the prediction of system performance before the network is implemented. We present simulation results for a variety of MAN topologies, using currently available WDM networking equipment. These results have been validated by comparison with an enterprise optical networking testbed constructed for storage area networks.
Fiber optic data communication networks face unique requirements for applications such as disaster recovery of multiterabyte and petabyte databases. We present experimental results from several enterprise computing testbeds that evaluate dense wavelength-division multiplexing (DWDM) performance in metropolitan area datacom networks. Many networking issues can be addressed through the components used within the DWDM platform; we discuss how current and emerging requirements can be addressed by new packages for 10-Gbit/s links, clock recovery circuits, and wavelength lockers. A comparison of three DWDM platforms evaluated in these testbeds is given, including features such as network bandwidth, scalability, performance over distance, and ease of management. We also report performance of datacom protocols such as enterprise system connection (ESCON), fiber connection (FICON), and FICON Bridge, when extended beyond industry standard distances using DWDM.
Large data processing environments in use today can require multi-gigabyte or terabyte capacity
in the data communication infrastructure; these requirements are being driven by storage area
networks with access to petabyte data bases, new architecture for parallel processing which
require high bandwidth optical links, and rapidly growing network applications such as electronic
commerce over the Internet or virtual private networks. These datacom applications require high
availability, fault tolerance, security, and the capacity to recover from any single point of failure
without relying on traditional SONET-based networking. These requirements, coupled with fiber
exhaust in metropolitan areas, are driving the introduction of dense optical wavelength division
multiplexing (DWDM) in data communication systems, particularly for large enterprise servers
or mainframes. In this paper, we examine the technical requirements for emerging nextgeneration
DWDM systems. Protocols for storage area networks and computer architectures
such as Parallel Sysplex are presented, including their fiber bandwidth requirements. We then
describe two commercially available DWDM solutions, a first generation 10 channel system and
a recently announced next generation 32 channel system. Technical requirements, network
management and security, fault tolerant network designs, new network topologies enabled by
DWDM, and the role of time division multiplexing in the network are all discussed. Finally, we
present a description of testing conducted on these networks and future directions for this
technology.
KEYWORDS: Data communications, Connectors, Standards development, Local area networks, Fiber optics, Interfaces, Asynchronous transfer mode, Copper, Transmitters, Transceivers
Isaac Kim, Ron Stieger, Joseph Koontz, Carter Moursund, Micah Barclay, Prasanna Adhikari, John Schuster, Eric Korevaar, Richard Ruigrok, Casimer DeCusatis
KEYWORDS: Visibility, Signal attenuation, Laser communications, Scintillation, Visibility through fog, Telecommunications, Transmittance, Laser systems engineering, Local area networks, Data communications
Wavelet transforms have found many practical applications in signal processing, including image processing, pattern recognition, and feature extraction. Since the wavelet transform is fundamentally given by the correlation of an input signal with a family of daughter wavelets, any real- time correlator can be used to implement the wavelet transform. Optical correlators are particularly well suited to this application, since the wavelet transform of a 1D signal produces a 2D wavelet transform. In this paper,w e discuss implementations of the wavelet transform using acousto-optic correlators and smart pixels as spatial light modulators. Smart pixels integrate both electronic processing and optical devices in a 2D array, which takes full advantage of the programmability of electronics and the parallel processing of optical devices. We describe a specific smart pixel implementation consisting of analog liquid crystal integrated on silicon 2.0-micrometers CMOS circuitry; and present experimental results of the wavelet transform implementation. An acousto-optic architecture for real-time wavelet correlators using this device will also be presented.
In conventional acousto-optic devices ultrasound signals are generated in a solid medium by applying an RF electrical signal to a piezoelectric transducer, which is bonded to the optical medium. However, it is well known that ultrasound can be generated in solids by sing high power optical pulses incident on the medium. This offers the potential to perform acousto-optic modulation without the piezoelectric transducers and associated electronics. This method can be utilized to modulate a lower power laser beam using a second higher power laser source. Using femtosecond optical pulses, acousto-optic interaction in the terahertz regime becomes feasible. In this paper, these all-optical acousto-optic devices are utilized for signal processing applications. Some preliminary experimental results using laser generated ultrasound in different substrates will be given.
In this paper, we describe how a photorefractive holographic interferometer may be modified to implement the wavelet transform. By placing phase-only spatial light modulators, such as acousto-optic devices, in the optical path of the sample and reference beams, it is possible to perform correlations on the phase modulated signals and then convert them into intensity modulated signals for detection and signal processing. We discuss a potential application of this architecture known as progressive pattern recognition using the wavelet transform.
This paper discusses a new method for performing wavelet-based pattern recognition and feature extraction. Known as 'progressive pattern recognition,' this approach is based on performing a subband transform of a target image and then performing partial correlations with different subband resolutions; it is possible to recognize the image without correlating against the complete wavelet transform, thereby realizing considerable savings in computational time. Computer simulations of palm print recognition are presented, and extensions to both scale and rotation invariant systems and optical implementations are discussed.
Recently there has been a great deal of interest in the optical implementation of wavelet transforms for image processing. In this paper, we discuss applications of the wavelet transform to image analysis, rotation and scale invariance, and pattern recognition in the presence of background noise. We describe a method for scale and rotation invariant pattern recognition based on wavelet features of an image. Finally, we give an example of using discrete wavelet filters to extract information from an image.
Recently there has been a great deal of interest in the use of wavelets and implementation of wavelet transforms. We discuss applications of the wavelet transform to image analysis, including target recognition, rotation and scale invariance, and pattern recognition in the presence of background noise. We propose a method for both scale and rotation invariant pattern recognition based on wavelet features of an image. Wavelets offer advantages in these applications because of their improved ability to discriminate signals in the presence of noise. Performance can be improved by careful selection of the mother wavelet for a given application; we have chosen a two-dimensional Gaussian mother wavelet. Computer simulations of wavelet transform based pattern recognition are discussed, which illustrate scale and rotation invariant target recognition in the presence of noise. Because the wavelet transform is essentially a correlation between the input signal and the family of daughter wavelets, it may be implemented by any type of programmable correlator. In particular, acousto-optic devices offer several advantages; they are programmable and capable of changing their input functions in real time, and commercial devices are available which offer large time-bandwidth products. Acousto-optic image correlators are discussed as a potential implementation of the wavelet transform; by encoding a 1 dimensional wavelet filter bank as a 2 dimensional image, we can implement the wavelet transform image processor without requiring a 2 dimensional spatial light modulator. An alternative implementation utilizes a 2 dimensional array of acousto-optic correlators for a hybrid implementation of a quadrature mirror filter bank.
In recent years there has been a great deal of interest in the use of wavelets to supplement or replace conventional Fourier transform signal processing. This paper provides a review of wavelet transforms for signal processing applications, and discusses several emerging applications which benefit from the advantages of wavelets. The wavelet transform can be implemented as an acousto-optic correlator; perfect reconstruction of digital signals may also be achieved using acousto-optic finite impulse response filter banks. Acousto-optic image correlators are discussed as a potential implementation of the wavelet transform, since a 1D wavelet filter bank may be encoded as a 2D image. We discuss applications of the wavelet transform including nondestructive testing of materials, biomedical applications in the analysis of EEG signals, and interference excision in spread spectrum communication systems. Computer simulations and experimental results for these applications are also provided.
The use of acousto-optic (AO), electro-optic (EO), and acousto-electro-optic (AEO) effects has been demonstrated as an effective means of performing wide-band signal processing operations such as convolution, correlation, and matrix processing. In this paper, we present experimental results using a new integrated optic AEO device fabricated on a y-cut, z- propagating lithium niobate substrate with a titanium in-diffused surface waveguide. Incident and diffracted light is coupled through the device by use of optical fibers. Device fabrication and performance are discussed, as well as potential future directions of this work.
The acousto-optic correlator is a well developed tool for performing pattern recognition. By cascading several one-dimensional correlators in parallel, it is possible to implement two- dimensional image correlation using only one acousto-optic device. We review the development of acousto-optic correlation and pattern recognition systems, and describe recent developments which have made image correlation practical. Computer simulations of image correlation and modifications to the existing architectures are discussed.
Binary holographic phase gratings, also known as Dammann gratings, can be electronically synthesized by using the acousto-optic effect. We review the field of digital phase grating optics, and discuss some of their modern applications. We present the underlying grating theory and describe an approach to realizing these gratings in an acousto-optic device. Potential applications include Fourier domain signal processing, matched filtering, optical interconnects, and switches for digital optical computing.
Hybrid optical/electronic nonlinear optical devices are presented that have bistable and hysteresis properties. These devices are based on linear optical modulators and nonlinear electronic feedback that controls the modulators. Because the nonlinearity is contained entirely in the feedback electronics, the nonlinearity is electronically and optically tunable. An experimental implementation of a hybrid device using a linear acousto-optic modulator and a nonlinear electronic Schmitt trigger is discussed. A conceptual electro-optical device, which may be implemented in arrays, is described.
An analog optical signal processor has been developed to implement the function of
antenna sidelobe interference cancellation. The architecture, which includes optical correlators
with Bragg cell input, an optical time modulator, and an optical spatial integrator, performs an
operation which is equivalent to the multiple-loop Howells-Applebaum Least Mean Square (LMS)
algorithm. This implementation offers the potential for cancelling multiple correlated interference
signals (i.e. direct path and multipath interference signals) with an appropriate number of auxiliary
antennas. A previous report described single frequency CW tests of such a processor. Preliminary
tests with wide-band waveforms and the special test instrumentation developed to perform these
tests are described in this paper.
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