Abstract: A technique is disclosed for improving the recovery of data signals transmitted on orthogonally polarized carrier signals by creating redundancy with respect to timing and carrier information. In the receiver, the carrier and timing recovery circuitry, which controls the recovery of the data signals from the incoming orthogonally polarized carrier signals, operate in response to a selected one of the carrier signals or at least one data signal recovered from this selected carrier signal. This selection is based on an examination of the data signals recovered from each of the orthogonally polarized carrier signals. Use of the described technique advantageously lessens the possibility of the carrier and timing recovery circuits losing synchronous operation during fading as it is less likely that a fade will simultaneously affect both orthogonally polarized carrier signals. As a result, data signal recovery is improved.

Abstract: The performance of carrier and/or timing recovery circuits which control the recovery of data signals from modulated quadrature-related carrier signals is improved by the use of a phase detector which correlates the two most significant bits of the data signals. This correlation significantly reduces the acquisition time, i.e., the time required for these circuits to acquire synchronous operation. Moreover, this correlation can be advantageously combined with correlations of the most and least significant bits of the data signals to reduce phase jitter as well as reduce the acquisition time.

Abstract: A technique for converging the tap-weight coefficients of an automatic or adaptive equalizer. The technique utilizes a training period during which time a plurality of identical signal sequences is transmitted. In the equalizer, during a training period, corresponding signal samples from the transmitted sequences are combined and used to generate the equalizer output and revise the tap-weight coefficients to their optimal values. Each combination of corresponding signal samples is an average or is a function which approximates an average.

Abstract: The present invention relates to a wireless PBX network wherein direct sequence spread spectrum multiple access is used for voice and data communications to support a plurality of local-local and local-external calls. The present wireless PBX arrangement comprises a plurality of local user transceivers using a first separate unique chip sequence patterns for information communication and a second common chip sequence pattern for call-set up; and a central PBX comprising (a) a plurality of PBX transceivers, each of which uses a separate first chip sequence pattern which is matched to a corresponding local user transceiver; (b) a switching means for interconnecting local users to each other or to an external network via the associated PBX transceivers; and (c) a call set-up receiver responsive solely to initial call set-up information sent by any user using the second common chip sequence pattern.

Abstract: The invention relates to a hand-held device for detecting whether or not an optical fiber is carrying a light signal. The device includes a spring loaded hook for grabbing an exposed optical fiber anywhere along its length, thereby introducing microbending, a photodetector for responding to the presence of light emitted in the proximity of the microbend, and a light emitting diode connected by way of an amplifier to the photodetector for indicating when a light signal has been detected. Upon release of the spring loaded hook, the fiber returns to its normal state. The device can be easily modified to indicate not only the presence of a light signal, but also the strength of the signal and the direction in which the signal is being transmitted.

Abstract: A technique for reducing the average fade duration of signals in a radio system by simulating motion of a plurality of transmitting antennas is disclosed. This simulation is accomplished by slowly and continuously varying a characteristic of the modulated carrier signal supplied to the antennas. The altered characteristic can either be the power of the modulated carrier signal supplied to each of the antennas or the phase between modulated carrier signals coupled to the antennas. This technique can also be applied at a receiver to reduce the average fade duration of signals arriving thereat by simulating motion of a plurality of receiving antennas.

Abstract: A carrier recovery circuit which phase aligns receiver-generated, quadrature-related carrier signals to incoming modulated, quadrature-related carrier signals is disclosed. The amplitudes of these modulated carriers determine data points in a signal-space diagram. In the carrier recovery circuit, the amplitude of each of said modulated carrier signals is sensed relative to thresholds which pass through the outermost data points in the signal-space diagram. These outermost data points form a periphery when interconnected by straight lines which encompass all of the data points. A phase error signal is generated which maintains phase alignment of the receiver-generated carriers to the incoming carriers when the sensed amplitudes fall in selected regions of the signal-space diagram lying outside of the aforementioned periphery.

Abstract: A Fresnel lens is fabricated by depositing concentric layers of first and second materials in alternation on a substrate surface. The substrate and deposited layers are then drawn down to provide a predetermined Fresnel lens zone structure.

Abstract: A Fresnel lens is fabricated by depositing concentric layers of first and second materials in alternation on a substrate surface. The substrate and deposited layers are then drawn down to provide a predetermined Fresnel lens zone structure.

Abstract: Equalizers, which provide distortion compensation for a modulated carrier signal having a time-varying signal envelope, are adjusted at selected times in response to the signal envelope and the data signals regenerated therefrom. Each selected time corresponds to a time when the signal envelope has a preselected value. Advantageously, the disclosed equalizer adjustment is unaffected by loss of receiver synchronization to the modulated carrier signal and is applicable to a variety of communications systems and modulation formats.

Abstract: An adaptive timing technique is disclosed for adjusting the sampling times of a received digital signal for fewer regeneration errors. In accordance with the disclosed technique, a sequence of digital signal samples is formed and an error signal is generated by comparing a selected sample in the sequence to a threshold. The sampling times of subsequently formed samples are then altered in response to the sample sequence and error signal only when the sample values in the sequence are successively increasing or decreasing.

Abstract: A canceller for eliminating the cross-polarization interference in incoming signals having polarizations which are orthogonal to one another is proposed. Each incoming signal is coupled to an associated adaptive filter. Each filter output is then summed with an associated one of the incoming signals which has a polarization orthogonal to that of the filter input signal. The signal sums formed are the canceller output signals. Adjustment of the adaptive filters so as to cancel the cross-polarization interference in each received signal is made in response to the incoming signals and the canceller output signals at selected times. During these times, circuitry for adjusting the adaptive filters examines spectral tones formed by the incoming signals and the canceller output signals.

Abstract: Compensation for arbitrary combinations of linear and nonlinear distortion is provided by altering a received symbol value by a preselected amount. This amount is based on an estimate of the sequence of transmitted symbol values represented by the received symbol value at a sampling time and a number of received symbol values at other sampling times. The altered symbol value is then compared with the closest one of the possible transmitted symbol values to determine the difference, if any, therebetween. The closest one of the possible transmitted symbol values is then outputted if the difference meets a prescribed criterion. If not, the received symbol value is altered by a different amount in response to another estimate until the recited difference meets the prescribed criterion. In the disclosed embodiments, the foregoing technique is incorporated in a memory-based canceler or transversal filter.

Abstract: The dispersion in an optical fiber is determined using an intensity or optical signal envelope cross-correlation. Light from an optical source is injected into two transmission paths in which the relative delay can be varied. At least one path comprises the optical fiber whose dispersion is to be determined. Each path provides an output signal having a signal envelope. These envelopes are then cross-correlated for a number of wavelengths to provide a measurement of group delay from which the dispersion is determined.

Abstract: A digital processor (16) is disclosed for improving the statistical characteristics of nondeterministic random-like binary sequence. The basic elements of the digital processor are a feedback loop comprising a delay (17) and a signal combiner (18) and a subsampler (19). Maximum performance of the digital processor is achieved when a relatively prime relationship exists between number of cells in the delay (17) and ratio of the original signaling rate to the output signaling rate of the subsampler (19). Mathematical analysis is presented for showing that the digital processor improves both the equidistribution of the binary variable and autocorrelation statistic of output signal over the nondeterministic random-like binary signal. A further improvement in statistical properties is obtained by using two digital processors (116 and 121) in serial fashion.

Abstract: An improved wavelength tunable TE to TM optical mode converter is provided by confining the electric fields for mode conversion and wavelength tuning to non-overlapping regions of a bi-refringent waveguide. Several electrode configurations for providing this spatial separation are disclosed.

Abstract: Amplifier-produced distortion known as amplitude modulation to phase modulation (AM/PM) conversion is reduced through the use of GaAs FETs which are biased to generate AM/PM having an algebraic sign opposite to that generated by the amplifier. This algebraic sign reversal is accomplished by biasing the GaAs FETs so that a DC drain current .ltoreq.75% and .gtoreq.10% of the short-circuit drain current is established. In the disclosed embodiment, several GaAs FETs are cascaded in alternation with attenuators to increase the magnitude of the compensating AM/PM conversion without generating substantial amplitude modulation to amplitude modulation (AM/PM) conversion.

Abstract: Continuously variable attenuation between the substantially abutting ends of two optical fibers is provided by varying the angle formed between the fiber ends. In the disclosed embodiment, the ends of two optical fibers are abutted and biased against a fiber receiving member. The varying angle is then formed by displacement of the receiving member.

Abstract: A track and hold circuit comprising an electronic switch and a signal storing device. During a tracking interval, the switch couples a varying input signal from an input node to the storing device in response to at least one track control signal. In a holding interval, the switch isolates the input node in response to at least one hold control signal. An input-signal-independent and substantially constant track-to-hold offset is provided by the use of selected track and hold control signals. Specifically, the track and hold control signals respectively vary with input signal during each tracking and each holding interval and have a substantially constant difference therebetween. In the disclosed embodiments, the track and hold circuit can be easily modified to reduce the effects of feedthrough and droop.

Abstract: In a disconnectable low-loss optical connection for optical fibers, each fiber in a pair of optical fibers is surrounded by a connector body to the conical frustum mating end of which is applied a tiny, transparent, flexible index matching dome of silicone rubber or equivalent material. The connector bodies are held together by mating to each other or to a common alignment receptacle having conically hollow receiving surfaces, so that the fiber ends are aligned and the domes touch and flex completing the optical connection.