Paul R. Prucnal

Ultrafast All-Optical Synchronous Multiple Access Fiber Networks

Two synchronous multiple access schemes, TDMA and CDMA, are proposed for fiber optic networks using optical signal processing. Network synchronization is achieved by using a central modelocked laser which also serves as the source for each station. The data are converted into a high-bandwidth optical signal using electrooptic modulators. The accessing schemes use optical fiber delay lines. The feasibility of these schemes is discussed.

Multiplication noise in the human visual system at threshold: 1. Quantum fluctuations and minimum detectable energy

We have carried out a series of frequency-of-seeing experiments similar to those performed by Hecht, Shlaer, and Pirenne [ J. Gen. Physiol.25, 819– 840 ( 1942)], using an Ar+ laser operated at 514.5 nm as the source of light. In certain blocks of trials, our subjects were encouraged to report as seen those trials in which the stimulus might have been present. It was determined that sensitivity and reliability were traded against each other over a broad range: for our four subjects, the detection of 147 photons at the cornea with 60% frequency of seeing entailed, on the average, a 1% false-positive rate (FPR), whereas the detection of 34 photons at the cornea with 60% frequency of seeing was accompanied by a 33% FPR. A new neural-counting model has been developed in the framework of signal-detection theory. It combines Poisson stimulus fluctuations with additive and multiplicative neural noise, both of which are known to be present in the visual system at threshold. The resulting probability-of-detection curves, derived from the Neyman Type-A counting distribution, are in good accord with our experimental frequency-of-seeing data for sensible values of the model parameters. We deduce that, on the average, our four subjects are able to detect a single photon at the retina with 60% frequency of seeing, at the expense of a 55% FPR. In Part 2 of this set of papers [ PrucnalP. R.TeichM. C., Biol. Cybern.43, 87– 96 ( 1982)], we use the normalizing transform, together with probit analysis, to provide improved estimates of threshold parameters, whereas in Part 3 [ TeichM. C.PrucnalP. R.VannucciG.BretonM. E.McGillW. J., submitted to Biol. Cybern.], we consider the effects of non-Poisson quantum fluctuations.

Photonic switch with optically self-routed bit switching

hotonic switches capable of routing wideband optical signals will be an important element of ultrahigh-capacity fiber-optic networks of the future [ 1,2]. A photonic switch generally consists of a multistage connecting network-each stage comprising switching devices and controllers-which routes optical information between input and output ports. We restrict our attention here to photonic switching devices which maintain signals in optical form as they traverse the switch. The controllers process address information supplied by the source. This processing can be performed either electronically or optically. The controller output sets u p the appropriate switch permutation to route the signal to its destination. This control signal may be either electrical or optical, depending upon whether switching is accomplished by an electro-optic or opto-optic effect. Photonic switching devices which have been previously demonstrated include 2x2 integrated-optic wave-guide switches, controlled electrically [3-51. Arrays of these 2x2 switching devices have been organized in NXN crossbar configurations [6-91. Crossbar switch arrays can be further cascaded into photonic switching networks [ 101. Recently, optically-controlled photonic switching devices have also been developed [11,12] and are expected to ultimately switch at speeds in excess of 1 THz [ 131. Whatever photonic switching device is used, the speed of future photonic switches will be limited not only by the device switching speed, but by the speed of the controller. A severe data flow bottleneck will occur at the controller if electronic processing is used. This bottleneck can be eliminated with optical processing. In switches requiring electro-optic control, the output of the optical processor must be converted to an electrical signal to activate the switch. In future photonic switches employing opto-optic control, this conversion would not be necessary. T h e speed of such a switch would then be limited by the speed of the optical decision-making process or the speed of the photonic switching device itself. There have been few proposals of photonic switches with optically-processed control. Haque and Arozullah [14] have proposed that some of the electronic functions in a conventional electronic switch be replaced by their optical or electro-optic counterparts. We propose to improve the performance of photonic switches by developing a novel optical architecture with optically-processed control which could not be implemented with electronic components. Distinguishing characteristics of optical processing include its inherent parallelism and non-interfering nature as well as its high speed [ 151. We report the experimental demonstration of a photonic switch using optically self-routed …

Self-Routing Photonic Switching Demonstration With Optical Control

The self-routing of optical information through a photonic switch using optically processed control is reported. Routing decisions are made on a bit-by-bit basis. Destination information is encoded in each data bit using optical spread spectrum techniques. Switching of 3.125 Mbits/s data is experimentally demonstrated. Extension of this Technique to a self-routing N x N switch is discussed.

Transformation of image-signal-dependent noise into image-signal-independent noise

A point transformation, the normalizing transform, is presented, which, when applied to a measured noisy image, renders its noise signal independent. The transform is suitable for arbitary noise-to-signal dependence. We demonstrate its applicability and its limitations by using, as an example, noisy signals that belong to a family of gamma-distributed random variables with power-law variance-to-mean dependence. Its normalizing and variance-stabilizing properties are studied.

Multiplication noise in the human visual system at threshold

Several kinds of light used in vision experiments produce photon statistics that are distinctly non-Poisson. Representative examples are light from a cathode-ray tube and an image-intensifier device. For the class of vision experiments in which the photon statistics play an important role, excess fluctuations produced by such light sources can alter the observed results and obscure the visual mechanisms being studied. They must therefore be accounted for in a proper way. We use the results of a Hecht-Shlaer-Pirenne type experiment, carried out with modulated Poisson light, to illustrate the point. Sensitivity and modulation depth, as well as sensitivity and reliability, are shown to be traded against each other. Finally, we demonstrate that number-state light, which is comprised of photons of an ideal kind, provides the ultimate tool for extracting information about the intrinsic noise distribution in the visual system at threshold. The state of the art in producing such light is discussed.

Multiplication noise in the human visual system at threshold: 2. Probit estimation of parameters

A mathematical technique is described that relates detection model parameters to stimulus magnitude and experimental probability of detection. The normalizing transform is used to make the response statistics approximately Gaussian. Conventional probit analysis is then applied. From measurements at M stimulus levels, a system of M equations is solved and estimates of M unknown parameters of the detection model are obtained. The technique is applied to a threshold vision model based on additive and multiplicative Poisson noise. Results are obtained for the parameter estimates for individual subjects, and for the standard deviation of the estimates, for various values of the stimulus energy and number of trials. A frequency-of-seeing experiment is performed using a point-source stimulus that randomly assumes 3 energy levels with 200 trials per level. With a central efficiency of 50%, the estimated ocular quantum efficiency for our four subjects lies between 12% and 23%, the average dark count at the retina lies between 8 and 36 counts, and the threshold count for our (low falsereport rate) data lies between 11 and 32. The theoretical results reduce to those obtained by Barlow (J. Physiol. London 160, 155–168, 1962), in the absence of dark light and multiplication noise.

Statistical properties of counting distributions for intensity-modulated sources

Statistical properties such as the cumulants, and the central, factorial, and ordinary moments are obtained for photocounting distributions when the incident radiation is intensity-modulated with arbitrary statistics. The results are applied in some detail to the cases of triangular, sinusoidal, and square-wave modulation of multimode superposed coherent and chaotic radiation. The coefficient of variation, skewness, and kurtosis are obtained as a function of modulation depth. Comparison is made with experimental data in the cases of triangular and sinusoidal modulation of a laser source.

Integrated fiber-optic coupler for very large scale integration interconnects

A new optical interconnect technique, suitable for high packing densities, is demonstrated for implementation in very-large-scale integration circuits. The approach permits vertical bonding.

Refractory effects in neural counting processes with exponentially decaying rates

The effect of nonparalyzable dead time on Poisson point processes with random integrated rates is studied. The case of exponentially decreasing rate, plus background (pedestal), with a uniformly uncertain starting time is explicitly presented. The decay time is considered to be slow compared to the refractory time. No constraints on the sampling time are imposed for calculating the mean and variance, though for the counting distribution, the sampling time must be short compared to the decay time. The results are expected to be useful in neurobiology, neural counting, psychophysics, photon counting, nuclear counting, and radiochemistry.