Abstract: The synchronous digital communications system according to the invention serves to transmit electric signals optically. The electric signals to be transmitted are converted from electrical to optical form (E/O1, E/O2, E/On) and are transmitted using wavelength division multiplexing (WDM) or dense wavelength division multiplexing (DWDM). At least one optical connection is configured as a nonswitched connection using at least one wavelength per transmission section between optical network elements or optical and electrical network elements, and serves to transmit synchronization and information signals. This has the advantage that independently of the switched communication links, synchronization is constantly ensured throughout the network. Each network element (NE1, NE2, NE3) has at least one interface unit that is reserved for synchronization and that continuously receives signals at the wavelength (&lgr;1) reserved for synchronization.

Abstract: A transmitter terminal in an ultra-long haul optical transmission system receives separate channel input signals in separate ones of a plurality of return-to-zero transmitters (RZTX). Each RZTX generates a corresponding forward error correction (FEC) modulated output signal in a separate channel frequency sub-band including predetermined channel separations from adjacent channel frequency bands. A multiplexing arrangement multiplexes the plurality of channel frequency bands from the RZTXs into separate groups of frequency bands. The groups of frequency bands have predetermined band-gap separations therebetween, and each group of frequency bands has a predetermined separate pre-chirp introduced therein before being multiplexed with all other groups of frequency bands into a single multiplexed output signal. An optical transmission line (OTL) is subdivided into predetermined sections and receives the single multiplexed output signal.

Abstract: A free space communication system includes first and second terminals, and the first terminal includes a transmitter to transmit an input signal. The transmitter has plural laser sources, at least one optical delay line and a telescope. Each laser source modulates the input signal onto a wavelength that is distinct from a wavelength of each other laser source. The plural laser sources include a first laser source and at least one other laser source, and the at least one optical delay line is coupled to a respective output of the at least one other laser source. The telescope projects an output of the first laser source and an output of each of the at least one optical delay line toward the second terminal. Alternatively, a free space communication system includes first and second terminals, and the first terminal includes a transmitter to transmit an input signal. The transmitter has at least one electrical delay line, plural laser sources and a telescope.

Abstract: A communication system includes plural nodes interconnected with an optical transmission medium capable of carrying plural bands of optical channels. A device at each node is coupled to the medium for dropping one or more bands, adding one or more bands, and passively transmitting other bands such that a pair of nodes can communicate directly using a band common to the respective bands. One band of the bands associated with each of a first set of nodes overlaps with one band of the bands associated with each of a second set of nodes. Multiple overlapping bands provide a high level of wavelength termination diversity. An optical management bus system and method connects plural hybrid optical/electrical cables between transmission equipment and optical modules which connect to network fibers to provide a set of electrical connections that can be used to determine optical interconnections in an optical shelf configuration.

Abstract: A method and apparatus for preparing groups of low duty cycle WDM transmission channels such that each group can be demultiplexed either via conventional WDM (e.g., by optically filtering each channel and receiving that channel at its line rate) or via TDM (e.g., directing an entire group of WDM channels onto a signal higher speed detector, receiving them all and demultiplexing the channels in a temporal (electronic) domain).

Abstract: The invention aims to provide an optical transmission system that specifies such a transmission condition so as to obtain high spectrum efficiency and a large transmission distance-capacity product at the same time, and uses low cost and small sized optical senders and optical receivers, to realize a high density wavelength multiplexing optical transmission. For this purpose, a WDM optical transmission system of the invention has a system structure that specifies by calculation the spectrum efficiency at which transmission distance-capacity product becomes a maximum value based on the determination of the type of signal light modulation and the assumption of an equation model expressing transmission characteristics of an optical multiplexer and an optical demultiplexer, and optimizes a bit rate and frequency spacing of signal light output from each optical sender, and the transmission characteristics of the optical multiplexer and the optical demultiplexer, so as to approach the spectrum efficiency.

Abstract: In a method of controlling a switching operation of an optical network for use in connection between an optical transmitter and an optical receiver through an optical switch is controlled by a switch controller, the optical receiver is given through the optical switch a sequence of combined optical signals which is formed by combining a sequence of optical signals with an additional sequence of optical signals. The additional sequence of the optical signals may be either a sequence of optical signals sent to another optical receiver or a sequence of dummy optical signals. The combined optical signal sequence has a time interval which is defined between two adjacent ones of the combined optical signals and which is shorter than a predetermined time interval of, for example, 1 millisecond. Such a combined optical signal sequence serves to avoid occurrence of an optical surge appearing when the time interval is longer than the predetermined time interval.

Abstract: An optical transmission system includes a number of corresponding modular multiplexing and demultiplexing units used in transmitting and receiving an optical signal respectively. Additionally, compensation components compensate for optical dispersion experienced by the optical signal. The modular multiplexing and demultiplexing units are assembled in a cascade fashion at the transmit side and the receive side of the optical transmission system, respectively. The dispersion compensation components share dispersion compensation fiber across the cascaded units.

Abstract: A wavelength division multiplex optical system includes a WDM combiner to provide a source signal, at least one transmitter coupled to an input of the WDM combiner, a broadband noise source, and a filter coupled between the broadband noise source and another input of the WDM combiner. In one embodiment, the filter is an optical notch filter. In an alternative embodiment, the filter includes a WDM demultiplexer coupled through plural filters to provide a plurality of noise signals and a WDM multiplexer coupled through at least one filter of the plural filters to respective noise signals.

Abstract: A method and apparatus are provided for transmitting and receiving multiple RF/microwave subcarriers on a single optical wavelength over an optical link. The method includes the steps of modulating a plurality of RF/microwave subcarrier frequencies with a respective communication signal and modulating an optical carrier wave with the plurality of modulated RF/microwave subcarrier frequencies.

Abstract: A tuning system for use in a receiver of an optical transmission system. The receiver includes a data channel transporting a data signal and a monitoring channel transporting a copy of the data signal. The tuning system includes a processing module for processing the copy of the data signal to generate a control signal conveying tuning information. This tuning information is used by the receiver to alter an operating point of the receiver on the data channel. The operating point of the receiver that is susceptible to be altered by the control signal is a decision threshold applied on the data signal to discriminate one binary value from another binary value on the data channel of the receiver. This approach allows, when required or desired, tuning of the system while the system is in service. This is possible since the tuning of the system is performed using the monitoring channel, and does not disturb nor corrupt the actual data being transported on the data channel.

Abstract: The present invention provides a remodulating channel selector for a wavelength division multiplexed optical communication system. The remodulating selector receives a WDM input signal, selects a particular optical channel from the WDM signal and places the information from the selected signal onto a newly-generated optical output signal. The wavelength of the output optical signal can be the same as or different from one of the optical channels which comprises the WDM input signal. When used in a WDM optical communication system with remodulators at the transmission input, the remodulating selectors provide complete control over the interfaces with optical transmitters and receivers, permitting use with a broad range of optical equipment.

Abstract: A two-optical signal generator is provided for generating two optical signals, where a difference between optical frequencies or optical wavelength of the two optical signals can be adjusted. A first optical modulator modulates a single-mode optical signal generated by a first light source according to an inputted signal, and outputs a modulated optical signal including predetermined specific two optical signals having a predetermined optical frequency difference, while a second light source generates a multi-mode optical signal including predetermined two further optical signals having substantially the same wavelengths as those of the predetermined specific two optical signals of the modulated optical signal, respectively.

Abstract: An optical transmitter having a function which compensates for wavelength dispersion is provided with a plurality of light sources for outputting light having wavelengths that differ from one another. Before the optical transmission system begins operating, the wavelength of light output to an optical transmission line is varied by changing over the light sources in order to detect a wavelength whose transmission characteristic is optimum with regard to wavelength dispersion exhibited by this optical transmission line. During system operation, the light having the detected optimum wavelength is output to the optical transmission line.

Abstract: An optical transmission system of the present invention includes at least one transmitter configured to receive information from a plurality of optical receivers and transmit the information in a plurality of information carrying optical signal wavelengths. At least one optical receiver is configured to receive a plurality of information carrying optical signal wavelengths and a local oscillator signal. The optical receiver converts a plurality of optical signal wavelengths into a corresponding number of electrical signal frequencies. The optical systems reduce the number of transmitters and receivers required interconnecting various optical systems, as well as providing multiple wavelength regenerators and converters and add/drop devices with increased capacity and system flexibility.

Abstract: A bidirectional optical link has a plurality of wavelengths to carry information in first and second differing transmission directions to optimize system performance. First and second sets of wavelengths of the plurality of wavelengths are determined wherein the wavelengths of the first set alternate with the wavelengths of the second set. Transmitting is performed in the first transmission direction by way of the first set of wavelengths and in the second transmission direction by way of the second set of wavelengths whereby the transmission directions of adjacent wavelengths of the plurality of wavelengths differ. The wavelengths of the plurality of wavelengths are wavelength division multiplexed within the optical link and the wavelengths transmitted in the same direction are multiplexed with each other. The wavelengths of the plurality of wavelengths can be substantially evenly spaced apart from each other or adjacent wavelengths transmitted in different directions may overlap.

Abstract: A communication system between head-ends and end-users is provided which expands bandwidth and reliability. A concentrator receives communication signals from a head-end and forwards the received communication signals to one or more fiber nodes and/or one or more mini-fiber nodes. The concentrator demultiplexes/splits received signals for the mini-fiber nodes and the fiber nodes and forwards demultiplexed/split signals respectively. The mini-fiber nodes may combine signals received from the head-end with loop-back signals used for local medium access control prior to forwarding the signals to the end-users. Upstream data are received by the mini-fiber nodes and/or fiber node and transmitted to the concentrator. The concentrator multiplexes/couples the mini-fiber node and the fiber node upstream signals and forwards multiplexed/coupled signals to the head-end.

Abstract: The invention provides an optical communication system, an optical transmitting apparatus, an optical receiving apparatus, an optical communication method, and a storage medium, in which a large-capacity transmission can be performed at high speed and multiplexing efficiency can be improved. The optical communication system includes an optical transmitting apparatus and an optical receiving apparatus connected via a transmitting medium having anomalous dispersion characteristics. In this system, the optical transmitting apparatus converts a plurality of information signals output from a plurality of signal sources into light signals having amplitudes different according to the respective information signals to output the light signals LP, by providing an individual specified optical intensity capable of performing an optical soliton transmission.

Abstract: A wavelength division multiplexing ring network is constructed using a simple architecture and a fewer number of hardwares between the nodes compared with the conventional ring network. Each node is structured so that any number of multiple waves can be processed, and a fault in the network or within a node is resolved by providing a path-based protection so that switching can be performed without disrupting other nodes or even within one node.

Abstract: Four optical interferometers are arranged in parallel. Optical path length differences of the optical interferometers are set to L, r×L, r×r×L, and r×r×r×L, respectively, where L is a unit optical path length difference (constant). A coefficient r by which the unit optical path length difference L is multiplied is any non-integer real number for example an irrational number. An irrational number is for example a surd ({square root}2, {square root}3, etc.), ratio of circumference D, or base e of a natural logarithm. When such optical path length differences are set in such a manner, a chaotic dynamical system, an addition theorem, and a chaotic map are not satisfied with respect to the intensities of light which is output from the optical interferometers. In other words, a thoroughly unpredictable sequence can be generated. The sequence is spectrum spread as spread codes.

Abstract: An optical module according to the present invention includes: a light-emitting device that outputs laser light; a temperature adjustment unit that adjusts a wavelength of the laser light outputted from the light-emitting device so as to be locked at a predetermined wavelength; a wavelength monitor unit that receives laser light outputted from the light-emitting device by allowing the laser light to pass through an optical filter provided above the temperature adjustment unit and monitors the wavelength thereof; a package for sealing the light-emitting device, the temperature adjustment unit, and the wavelength monitor unit into the inside thereof; and a package temperature detection unit for detecting a temperature of the package, in which the temperature adjustment unit adjusts an oscillation wavelength of the laser light outputted from the light-emitting device to the predetermined lock wavelength based on a signal outputted from the wavelength monitor unit, and a signal from the package temperature detect