Abstract: An optical, wavelet-based fractal modulation of ultra-short light pulses is used as part of a high-bandwidth communications system. The preferred embodiment utilizes the scheme as part of a hybrid wireless optical and RF transmission system for broadband communications among fixed and/or mobile platforms. An ultra-short pulse laser, high-power WDM-ARRAY laser or high-power incoherent light sources may be used. Computer-generated hologram techniques are employed in designing the optical transceiver subsystems for spectral encoding and decoding of wavelet patterns. Part of the design goal is to select a diversity receiver Field-of-View (FOV) in a way that the effects of scintillation are reduced by as much as possible. Compared to existing optical wireless systems, the invention offers a much higher average transmission bit rate and a much smaller bit error rate outage value, thus enabling highly available FSO links.

Abstract: An infrared communications system includes a multi-beam transmitter for producing an array of diffusing spots upon a reflecting surface, and a receiver comprising a plurality of receiving elements, where each receiving element has an independent field of view that is in line of sight of at least one of said diffusing spots. The array may be in the form of a regular grid, and the grid of diffusing spots may be formed via the emission from the transmitter of a plurality of collimated beams of equal intensity. The transmitter may include a light source, collimating optics, and a spot array generator, and each of the receiving elements may include a band-pass filter, a concentrator and a photodetector.

Abstract: Bidirectional WDM transmission at 2.5 Gb/s using a bidirectional erbium-doped fiber amplifier (EDFA) is demonstrated over a distance of 300 km. A symmetrical EDFA configuration with a frequency tunable reflection attenuator is used as a bidirectional amplifier. Experimental results show that the allowable gain of the EDFA can be increased significantly while the associated bit error rate BER penalty remains negligible.

Abstract: In N.times.N optical couplers, such as are used in local area networks and backplanes of telecommunications and computer equipment, which use BRAGG volume diffraction means to couple light beams between the inputs and outputs, the number of gratings is reduced by means of so-called "grating degeneration" one grating can be shared by at least two wave pairs at the same time. In order to achieve this reduction, the directions of light waves in the dielectric slab (or the lateral positions of fibre ends) are suitable arranged. In other embodiments, a reduced number of gratings is achieved by using a "sandwiched" structure which uses multi-layered dielectric slabs. Both embodiments may be combined in the one coupler.

Abstract: An optical receiver includes a photodiode having a surface area of suitable dimensions to permit reception of a signal at a high bit rate. Also, the optical receiver includes an optical taper having a head and a tail. The head is of greater diameter than the tail, and co-axial with the tail. The tail is aligned with the photodiode.

Abstract: An optical homodyne differential phase shift keying (DPSK) receiver for receiving and demodulating optical input signals, is provided with a power splitter for splitting the input signal into first and second signals, a delay is applied to the second signal, an optical amplifier optically amplifies the delayed second signal, and a balanced noise reduction circuit combines the first signal and the delayed amplified second signal to produce a demodulated output signal.

Abstract: The present invention relates to packet switched interconnection protocols for use in high-speed optical Star-configured Local Area Networks (LANs). In the present Star LAN, a plurality of N+1 wavelength division multiplexed (WDM) channels are provided for use by M transceivers connected to the Star coupler, where preferably M>N. N of the N+1 WDM channels are used for transmission of data packets, and the remaining WDM channel is used by all transceivers for transmitting control packets only. In the present protocols, a transmitter in an active transceiver first send a control packet over the control channel using a first protocol such as, for example, ALOHA or CSMA. The control packet includes (1) the transmitter's unique address, (2) the destined receiver's address, and (3) the address of the data channel to be used in transmitting the associated data packet.

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 present invention relates to a collision detection technique for an optical Star LAN using CSMA/CD. The present technique is implemented by preferably adding two or more fixed Hamming weight sequences, e.g., a fixed even or odd number of 1's in each unique cyclic error correcting code word, to the preamble section of each packet of information to be transmitted. These collision detection sequences have a length which is beyond the vulnerable time period of the CSMA/CD protocol (maximum round-trip propagation delay for each packet) by at least one code word length in order to prevent any misdetection, or false detection, of a collision. Each receiver in the listening period, looks for a code pattern with a fixed Hamming weight. When code patterns collide, the Hamming weight of the resulting code word in the collision period will exceed the nominal sequence weight (will include more 1's than the fixed Hamming weight) and a sequence weight violation is detected.

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: Data-aided equalization and cancellation in digital data transmission over dually polarized fading radio channels is disclosed. The present invention uses decision feedback structures with finite-tap transversal filters. Subject to the assumption that some past and/or future data symbols are correctly detected, formulas and algorithms for evaluating the least mean-square error for different structures are disclosed. In a sequence of curves, the performance of various structures for a particular propagation model and several fading events are evaluated and compared.

Abstract: The present invention relates to a cross-polarization cancellation arrangement for digital radio channels wherein the cancellation arrangement comprises a canceller section and an equalizer section in cascade which operate at baseband. The canceller section includes both a main lobe estimator and detection circuits. The estimator provides a preliminary estimate of the main lobe of the pulse response in each of the two received orthogonally polarized signals. The detection circuits take each of the estimator means output signals, relating to each received polarized signal, and generates therefrom error control signals for adaptively updating the main lobe estimate signals from the estimator and also to provide an output signal which is used to cancel the interferer main lobe in the received oppositely polarized signal. The equalizer section then mitigates intersymbol and cross-rail interference in each of the orthogonally received signals.