Abstract: Chromatic dispersion is efficiently compensated in a compact device by combining a spatial mode converter with a dispersive waveguide having a dispersion characteristic of substantially equivalent magnitude, and opposite sign, to the desired amount of dispersion to be compensated. The spatial mode converter exchange the optical energy from one propagating spatial mode to another spatial mode whose propagation is supported by the multimode or dual-mode fiber. This apparatus is applicable to lightwave repeaters, regenerators, transmitters, and receivers.

Abstract: A novel process is disclosed for fabricating semiconductor devices with self-aligned contacts. Characteristic of the resulting structure is a digitated electrode and a contiguous conductive region that contact first semiconductor regions and second semiconductor regions, respectively. The first semiconductor regions and the second semiconductor regions are formed in a semiconductor substrate, with each second semiconductor region underlying a finger of the digitated electrode. Advantageously, by forming a contiguous conductive region over the first semiconductor regions located between the fingers of the digitated electrode, it is not only possible to contact second semiconductor regions with a common electrode, but also to self-align the common electrode with the digitated electrode. Ohmic shorting between the digitated electrode and the contiguous conductive region is prevented by interposing an insulating region therebetween.

Abstract: A time delay neural network is defined having feature detection layers which are constrained for extracting features and subsampling a sequence of feature vectors input to the particular feature detection layer. Output from the network for both digit and uppercase letters is provided by an output classification layer which is fully connected to the final feature detection layer. Each feature vector relates to coordinate information about the original character preserved in a temporal order together with additional information related to the original character at the particular coordinate point. Such additional information may include local geometric information, local pen information, and phantom stroke coordinate information relating to connecting segments between the end point of one stroke and the beginning point of another stroke.The network is also defined to increase the number of feature elements in each feature vector from one feature detection layer to the next.

Abstract: An optical apparatus for generating an optical frequency comb from an optical input signal is realized by transmitting the optical signal through an optical circuit comprising an optical amplifier and a Bragg cell configured in an optical cavity. By aligning the cavity such that the incident light is deflected by the Bragg cell and recirculated therein, on each pass within the cavity the incident light is frequency shifted by a predetermined frequency, producing a comb of optical frequencies, each a time-delayed replica of the incident light. Importantly, the optical amplifier positioned within the cavity substantially compensates for any cavity loss, enhancing the output uniformity of each generated carrier.

Abstract: Timing restrictions for coincidence of control and data signal pulses to a soliton-based optical logic device are significantly relaxed by predistorting a characteristic of data signal pulses input to the device. Predistortion in the form of normal dispersion is sufficient to cause each predistorted data signal pulse to change shape subsequently in the optical logic device and thereby permit effective interaction between the data signal pulses and the control pulses to achieve the desired result of the logic operation. The temporal separation between control and data signal pulses has been extended to cover a total range of up to four pulse widths without degrading the operation of the optical logic device.

Abstract: Realization of a reconfigurable neuron for use in a neural network has been achieved using analog techniques. In the reconfigurable neuron, digital input data are multiplied by programmable digital weights in a novel connection structure whose output permits straightforward summation of the products thereby forming a sum signal. The sum signal is multiplied by a programmable scalar, in general, 1, when the input data and the digital weights are binary. When the digital input data and the digital weights are multilevel, the scalar in each reconfigurable neuron is programmed to be a fraction which corresponds to the bit position in the digital data representation, that is, a programmable scalar of 1/2, 1/4, 1/8, and so on. The signal formed by scalar multiplication is passed through a programmable build out circuit which permits neural network reconfiguration by interconnection of one neuron to one or more other neurons.

Abstract: In a semiconductor optical modulator, two semiconductor materials having different refractive indices are grown in an alternating sequence of layers to form a semiconductor mirror wherein each layer has approximately a quarter wave thickness for a predetermined wavelength. Delta doping is performed at each heterointerface. The delta doping conductivity type alternates from one heterointerface to the next. Lateral surface contacts are selectively made to the n-type heterointerfaces on one edge of the mirror and to the p-type heterointerfaces on the other edge of the mirror. An interleaved ohmic contact structure results within the modulator. By applying a nominally low voltage to the lateral surface contacts, it is possible to effect refractive index changes in the layers so that the mirror performs reflection or transmission of an impinging light beam.

Abstract: A polarization independent guided wave semiconductor device is realized wherein the waveguide region of the device includes one or more strained quantum well layers wherein strain is designed to be tensile in nature so that energy subbands in the quantum well or wells are displaced by a predetermined amount in a direction opposite to that for the quantum size effect. Polarization independence is achieved when, for a lightwave signal having an incident mean photon energy below the absorption bandedge of the strained quantum well layer or layers, the ratio of the oscillator strengths versus the wavelength detuning for heavy and light holes in a first polarization (TE) is substantially equal to a similar ratio computed in a second polarization (TM). Wavelength detuning is understood to be the difference between the wavelength of operation and the wavelength of an exciton resonance peak. Passive and active or actively controllable waveguides and waveguide devices are described.

Abstract: Improved side mode suppression with significantly reduced side mode suppression ratio fluctuation during laser tuning is realized in a distributed Bragg reflector laser structure by incorporating at least one reflector element which exhibits an asymmetric reflection characteristic versus wavelength over a band of wavelengths wide enough to include at least two longitudinal modes of the laser. That is, the asymmetric characteristic is wider than the mode separation for adjacent longitudinal modes of the laser. In one embodiment, a distributed Bragg reflector laser is shown wherein the Bragg reflector includes a corrugated waveguides with corrugations having a period which varies nonlinearly from .LAMBDA..sub.O at one end of the reflector to .LAMBDA.hd L at the opposite end of the reflector, where .LAMBDA..sub.O is greater than .LAMBDA..sub.L. Integrated and extended cavity or hybrid structures are described in both semiconductor and fiber laser structures.

Abstract: An optical logic device based on the time-shift-keying architecture is described in which digital logic functions are realized by applying appropriate signal pulses to a nonlinear shift or "chirp" element whose output is supplied to a dispersive element capable of supporting soliton propagation. In an optical fiber realization of the optical logic device, two orthogonally polarized pulses are supplied to the combination of a moderately birefringent fiber acting as the nonlinear chirp element and a polarization maintaining fiber acting as the soliton dispersive delay element having a anomolous group velocity dispersion at the signal wavelengths of interest. A nonlinear frequency shift is created in one of the pulses in the former element through cross-phase modulation and, in turn, the frequency shift is translated into a temporal shift of the affected pulse in the latter element. These devices operate at switching energies approaching 1pJ.

Abstract: An optical interconnection arrangement having a high degree of connectivity and bandwidth is obtained by a non-collinear arrangement of lenses. In a preferred embodiment, the optical system comprises a first pupil lens, a second pupil lens and an array of fanout lenslets wherein the optical axes of the first and second pupil lenses are collinear. The first and second pupil lenses form an afocal system with the array of fanout lenslets situated between and at the focal planes of the first and second pupil lenses. Light beams from arrays of light emitting devices are collimated by input probe lenses that have their optical axes non-collinear with the optical axis of the first lens. The first pupil lens forms a coincident pattern of the arrays of light emitting devices. Additionally, the array of fanout lenslets fans out exiting beamlets comprising the coincident pattern such that each exiting beamlet substantially fills the aperture of the second pupil lens.

Abstract: Optimized synchronization planning and clock distribution for a network of interconnected digital equipment is achieved by designating a network node at the highest stratum level as the master clock node, forming a group of all unassigned nodes connected to the assigned node or nodes, selecting subgroup of all nodes from the group wherein the subgroup includes all nodes having the highest stratum level of the group, limiting the subgroup to the nodes which have a desired characteristic when such nodes are included in the subgroup, determining the synchronization performance of each node in the subgroup according to a predetermined criterion, assigning one node from the subgroup as a clock timing receiver wherein the one node exhibits the best performance for nodes in the subgroup, and iterating the method at the forming step.

Abstract: Highly accurate, reliable optical character recognition is afforded by a layered network having several layers of constrained feature detection wherein each layer of constrained feature detection includes a plurality of constrained feature maps and a corresponding plurality of feature reduction maps. Each feature reduction map is connected to only one constrained feature map in the same layer for undersampling that constrained feature map. Units in each constrained feature map of the first constrained feature detection layer respond as a function of a corresponding kernel and of different portions of the pixel image of the character captured in a receptive field associated with the unit.

Abstract: Unwanted, monotonic growth of sideband energy is avoided in wavelength-division-multiplexed and frequency-division-multiplexed lightwave communication systems by transmitting adjacent channels approximately 2 nm to 3 nm apart in the normal dispersion regime of the optical fiber for the system and by transmitting each channel more than 0.4 nm below a mean zero dispersion wavelength, .lambda..sub.0, of the optical fiber. Interchannel spacing and individual channel separation from the zero dispersion wavelength are measured with respect to a nominal carrier wavelength for each channel.

Abstract: A monolithic integrated photoreceiver comprising a p-i-n photodiode and a heterojunction bipolar transistor is realized in a structural configuration that allows the photonics and electronics to be separately optimized in addition to maintaining materials compatibility. These desirable features are accomplished by growing the epilayers of the photodiode and heterojunction bipolar transistor in a single epitaxial growth run. The p-i-n epilayers of the photodiode are grown first on a non-patterned substrate, followed by the direct epitaxial growth of the heterostructure bipolar transistor over the photodiode structure. Selective wet chemical etching over a portion of the entire structure was used in order to delineate the mesa structures of the p-i-n photodiode and transistor such that no contiguous conductive semiconductor layer exists therebetween.

Abstract: Bidirectional lightwave transmission is restored and uniform amplification of lightwave signals over long spans of optical fiber is achieved by employing distributed amplification over the spans. Distributed amplification is achieved with an amplifying optical fiber which includes a long length of optical fiber having a dilute rare-earth dopant concentration substantially in the fiber core region, and a corresponding pump signal generator at at least one end of the doped fiber having the appropriate wavelength and power to cause amplification of optical signals by both Raman effects and stimulated emission from the rare-earth dopants. Dilute concentrations are understood as the range of concentrations substantially satisfying the condition that the gain from the rare-earth dopant, when near saturation, is substantially equal to the fiber loss.

Abstract: Reproducible doped optical fiber preforms having a predetermined dopant concentration level are fabricated by inserting a doped filament into a completed preform prior to consolidation and final collapse so that the filament and dopant materials are centrally located in the core region upon formation of the preform. Doped fiber is drawn from the doped preform using standard fiber drawing techniques.

Abstract: Highly accurate, reliable optical character recognition is afforded by a hierarchically layered network having several layers of parallel constrained feature detection for localized feature extraction followed by several fully connected layers for dimensionality reduction. Character classification is also performed in the ultimate fully connected layer. Each layer of parallel constrained feature detection comprises a plurality of constrained feature maps and a corresponding plurality of kernels wherein a predetermined kernel is directly related to a single constrained feature map. Undersampling is performed from layer to layer.

Abstract: Accurate mode partition data from a laser are collected simply and rapidly in accordance with the principles of the invention wherein the laser output is directed to a filter which separates a central longitudinal mode from the side modes. The filter operates to present all side modes in a predetermined wavelength range simultaneously and continuously at the output of the filter. By subsequently comparing the intensity or power in the side modes delivered to the filter output with a predetermined threshold, it is possible to determine the frequency of occurrence and magnitude of mode partition events for side modes in the predetermined wavelength range.

Abstract: Resonant tunneling devices having an improved device switching speed are realized by including an optical control element rather than an electrical control element for switching the device from one stable state to the other. The resulting optoelectronic device including at least one double barrier quantum well semiconductor heterostructure is controllably switched from an active state to an inactive state and vice versa by impinging optical signals from an optical control element having a mean photon energy less than the bandgap energy of the double barrier quantum well semiconductor heterostructure, wherein the active state of the device exhibits conduction of charge carriers by resonant tunneling. Improvement in the switching speed occurs because the optical processes initiated by the optical control element are condsiderably faster than the electronic processes induced by prior art electrical control elements.