Abstract: Input values are data encoded for improved signal characteristics (e.g., limited maximum run length and limited cumulative DC-offset) so as to form "data codewords," and then a number of the data codewords, collectively referred to as a block, are error protection encoded, preferably using a conventional linear and systematic forward error control ("FEC") code, to yield an FEC code block. Preferably, an FEC code block is formed by generating a number of check bits or FEC bits equal to the number of data codewords in the block, and then concatenating one FEC bit and its binary complement with each data codeword, so that one FEC bit and its complement is interposed between each successive codeword.

Abstract: A network interconnection architecture for a plurality of nodes uses sets of grouped node connections which form a plurality of node groups. A central electrically passive interconnection hub is coupled via a signal transmission path to each node group to establish a full mesh coupling between each of the plurality of node groups. An input and output matrix switch along with a pair of 1.times.N multiplexers are also coupled to each of the plurality of node groups and the hub multiplexer via the signal transmission path. The architecture can be further extended to encompass other networks with electrically passive hubs using a sandwich coupling of a matrix switch between two wavelength multiplexers.

Abstract: An image to be smoothed is represented by a matrix of pixels arranged in a plurality of adjacent scan lines. Each pixel under examination is changed to the value of a predetermined number of pixels in a 3.times.3 pixel neighborhood surrounding the pixel under examination. The image pixels are represented by a sequence of 16 bit digital words, each bit representing a corresponding pixel. The bits of three adjacent words on three adjacent scan lines are accumulated in 16 counters, respectively, with the words shifted so that the 9 bits of each of sixteen 3.times.3 neighborhoods are simultaneously accumulated in the sixteen counters. Each counter is constructed so that when a predetermined number of ONEs is accumulated from the 3.times.3 neighborhoods, the most significant counter stage goes to ONE and remains at ONE irrespective of further accumulation. One of the three words is the word to be smoothed.

Abstract: Input values are data encoded for improved signal characteristics (e.g., limited maximum run length and limited cumulative DC-offset) so as to form "data codewords, " and then a number of the data codewords, collectively referred to as a block, are error protection encoded, preferably using a conventional linear and sytematic forward error control ("FEC") code, to yield an FEC code block. Preferably, an FEC code block is formed by generating a number of check bits or FEC bits equal to the number of data codewords in the block, and then concatenating one FEC bit and its binary complement with each data codeword, so that one FEC bit and its complement is interposed between each successive codeword.

Abstract: An optical multiplexing/demultiplexing device combines an etalon and weak diffraction grating along with temperature control to finely tune local resonant stations along the etalon to separate and/or combine a plurality of optical signals that are finely spaced in wavelength.

Abstract: A network interconnection architecture for a plurality of nodes uses sets of grouped node connections which form a plurality of node groups. A central electrically passive interconnection hub is coupled via a signal transmission path to each node group to establish a full mesh coupling between each of the plurality of node groups. An input and output matrix switch along with a pair of 1.times.N multiplexers are also coupled to each of the plurality of node groups and the hub multiplexer via the signal transmission path. The architecture can be further extended to encompass other networks with electrically passive hubs using a sandwich coupling of a matrix switch between two wavelength multiplexers.

Abstract: An optical time domain reflectometer comprises a detector device for detecting optical energy received at an end of a fiber under test, an amplifier having an input terminal connected to the detector device, and a photoconductive switch connected between the amplifier input terminal and a reference potential level. The photoconductive switch is selectively illuminated.

Abstract: A system for the thermal control of optical devices includes an optical device having at least one coating of an electrically conductive material formed on a surface in a heat conducting relationship with the material and connected to a controllable current source which passes varying amounts of electrical current through the layer to vary the amount of thermal energy introduced into the device to control its optical response characteristics. The electrically conductive layer or layers can be optically active, that is, function to affect the light energy transmitted into or through the device as well as acting as an electrically conductive thermal element.

Abstract: An optical communications system for providing wavelength division multiplexed communications with high spectral channel density and increased sensitivity and selectivity through coherent detection utilizes a fixed frequency source for introducing at least one fixed frequency carrier for system-wide propagation through a system bus. Terminal devices coupled to the system bus functioning as transmitters remove a portion of the system-wide carrier energy and effect a frequency translation and modulation of the translated carrier energy for return to the system bus as a modulated, frequency shifted information bearing signal. Terminal devices functioning as a receiver effect either synchronous homodyne or heterodyne coherent detection by removing a portion of the system-wide carrier energy, optionally effecting a frequency translation, and combining the frequency shifted carrier energy with that of the frequency shifted information bearing signal to effect coherent detection.

Abstract: Bulk optic echelon gratings suitable for use in multi/demultiplexing optical signals carried on sets of optical fibers. The gratings can be either reflective or transmissive and may be either curved with self-focusing properties or planar requiring the use of auxiliary collimating optics. All versions have the property of being simultaneously blazed at at least two different wavelengths whose ratio is in the range between 0.8 and 0.9. This property of the gratings enables their operation over preferred multiple wavelength bands using a limited set of fibers which are fixed in place. Preferred wavelengths at which the gratings are simultaneously blazed include 1.3 and 1.55 micrometers. Devices incorporating the gratings can be used singly or in groups in inverted tree arrangements for tandem or hierarchical multiplexing purposes.

Abstract: An optical fiber communications system includes a closed loop birefringent optical fiber bus for supporting optical energy propagated in a first and a second orthogonal polarization state. An optical energy source introduces a fixed frequency system wide carrier onto the optical fiber bus in a first polarization state for propagation in a first direction. Terminal devices coupled to the optical fiber bus include a bus tap resonator for removing a portion of the system wide carrier light and, in addition to modulating the removed light, effecting a frequency shift to a side frequency and effecting a state shift from the first to the other polarization state, and returning the information bearing optical energy to the optical fiber bus for propagation in a direction opposite to the first direction. A receiving device includes a bus tap resonator for removing a portion of the light from the bus and effecting demodulation to recover the information bearing signal.

Abstract: An optical communications system includes an optical bus and a plurality of terminal devices coupled to the bus and a reference signal generator for propagating a reference signal through the bus for use by all terminal devices in selecting one of a predetermined number of frequency distinct communications channels. The reference signal is frequency swept in a recurring manner between two fixed frequencies and is introduced onto the system bus, along with a system synchronization signal, for propagation to bus tap resonators associated with the terminal devices in the system. Each terminal device detects the moment at which the swept reference frequency passes through one of the resonant modes of its bus tap resonator and determines the elapsed time thereof from the system synchronization signal.

Abstract: Integrated optic devices incorporating echelon gratings suitable for use in performing multi/demultiplexing functions in optical communications systems. The echelon gratings can be either reflection or transmissive types and are conveniently formed using conventional photolithographic techniques.

Abstract: An optical communications system with terminal devices connected to an optical pathway for communications with one another. A system wide reference signal is introduced into the optical pathway by a reference signal generator for propagation throughout the system. Each terminal device includes a resonant cavity to support one of a plurality of available sets of resonant modes, each set having an associated free spectral range between resonant modes, and controls the resonant cavity structure to lock one of the resonant modes of the resonant cavity to the system wide reference signal. The resonant characteristics of the resonant cavity at each terminal device can be changed to vary the number of integral wavelengths supported in the resonant cavity. Plural terminal devices can communicate with one another to support a set of resonant modes common to one another with one mode of the common set locked to the system wide frequency reference.

Abstract: Integrated optic resonant structures for use in optical communications and sensing applications requiring control or detection of electromagnetic radiation in the optical region of the spectrum. Preferably of planar form, the structures comprise a substrate made of a ferroelectric crystalline material in which there is formed by selectively exchanging protons for an ionic constituent of the substrate at least one optically continuous waveguiding region having predetermined resonant characteristics. At least one other waveguiding region is similarly formed in the substrate to optically couple with the resonant region and includes at least one port by which radiation can be coupled in and out of the substrate. The substrate material is preferably lithium niobate (LiNbO.sub.3) or lithium tantalate (LiTaO.sub.3) in which lithium ions are selectively exchanged for protons supplied by diffusion from a hydrogen rich acid.

Abstract: A battery powered optical sensor, capable of functioning for a period of time approximately equal to the shelf life of the battery, utilizes an LED driven by an optical transducer and biased by the battery at a level that exceeds the shot noise level of the LED by the dynamic range of the sensor.

Abstract: An apparatus for sensing acceleration utilizes a multimode input optical fiber to provide an output of light which passes through a grating, and is collimated by a grinrod lens. The collimated light is reflected from a double faceted reflecting surface in two beams. Absent acceleration, the two beams are focussed by the grinrod lens onto portions of the grating covering, respectively, the input faces of two multimode output optical fibers, and provide 1/2 the maximum possible amount of light to each of the output optical fibers, with a balanced output. In response to acceleration, the reflection surface tilts, the beams move, and the outputs of the output optical fibers change, representing the acceleration.

Abstract: An acoustic sensor with ambient pressure and temperature compensation having a photoelastic element positioned between a diaphragm and a support beam. Thin layers of oil between the photoelastic material and both the diaphragm and support beam prevent surface stress of the photoelastic element due to slowly varying pressures while surface stresses are caused thereon by relatively rapid pressure variations.

Abstract: A pressure and temperature compensated acoustic transducer utilizing a pressure sensitive birefringent element coupled between a flexible diaphragm sealing the transducer and an internal variable rigid diaphragm that forms two internal chambers. Relatively rapid variation in pressure applied to the birefrigent element cause fluctuations in the phase difference between orthogonal components of a polarized light beam traversing the photo-elastic material. Detections of this phase difference variation provides signals representative of incident acoustic signals. Provision for the transfer of liquid filling the chambers permits the equalization between the two chambers of slowly varying internal pressures caused by changes in external ambient pressure and temperature.

Abstract: An optical 1.times.N switch uses a polarizing beam splitter cube and a reflector to separate an arbitrarily polarized incident light beam into polarized components which propagate along parallel paths. A polarization rotator is positioned in the path of the reflected component to rotate the plane of polarization of the light beam component propagating therealong to be coplanar with that of the undeviated light beam in the parallel path. The two beams are simultaneously or individually deflected by selectively activating the electrodes of a liquid crystal nematic reflector/transmitter array confined between prismatic bodies to emerge at one or more of a plurality of desired outputs. In a second embodiment, a second polarization rotator and polarizing beam combiner assembly re-establishes the initial polarization and the beams are thereby combined to emerge from one or more selected output terminals as an arbitrarily polarized light beam.