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: When a branching unit combines a first optical signal transmitted from a branch station with a second optical signal which is different in power level from the first optical signal and is transmitted from a terminal station A or B in an optical add-drop system, the S/N ratio of the lower power level of the two different power levels decreases, thereby deteriorating the system performance. Therefore, a dummy light is transmitted together with an optical signal to adjust the power level of the optical signal. Otherwise, an optical attenuator or an active optical signal level adjustment unit is provided for the branching unit so that both optical signals to be combined can be equal in level.

Abstract: A self-adjusting optical add-drop multiplexer monitors the power in a drop signal and attenuates the power in an add signal to match the power in express WDM channels (signals). When used in a fiber network, and more particularly, in a metro network, the deleterious effects of optical amplification are reduced. Power attenuation is also used in an optical switching assembly particularly useful in two-fiber ring network. The optical switching assembly monitors drop channels from the two rings of the network and attenuates the add channel(s) accordingly. An optical switch operates to direct the drop signal from one of the two rings to a receiver in accordance with a control signal based on the monitored drop channels. The self-adjusting optical add-drop multiplexer also monitors the power in the drop signals and issues an alarm if the drop signal is of a power level above or below predetermined levels.

Abstract: An optical transmission system formed from a plurality of nodes interconnected in a ring configuration via at least two transmission media provides protection capacity for each optical channel. If a channel signal does not meet predetermined criteria, then a loss of signal indication is declared for the channel and one of a plurality of protection switching states is invoked to re-route service traffic carried by the impaired channel to its destination via corresponding protection capacity. The switching states include particular transmission states and at least “keep-alive” and “protection access” states.

Abstract: An optical transmission line allows optical signals to be transmitted with higher stability over longer distances. According to a first aspect, an optical NRZ signal is split in two, one half is presented to a clock extraction circuit, and the other half is presented to an EA modulator. An optical RZ signal is obtained as an output because the EA modulator is energized by the provided clock component. According to a second aspect, a nonlinear phase shift based on cross-phase modulation is induced in an RZ pulse train by an optical NRZ signal, and only the RZ pulses corresponding to the optical NRZ signal are extracted. According to a third aspect, first dispersion compensator is provided to a preceding stage of an optical fiber transmission line for transmitting optical pulses, and second dispersion compensation compensator is provided to a subsequent stage. Pulse widening in the optical fiber transmission line is controlled by a nonlinear chirp induced in the first dispersion compensator.

Abstract: An optical fiber ring network includes a plurality of interconnected nodes, each pair of neighboring nodes being interconnected by a pair of optical links. Using coarse wavelength division multiplexing, data is transmitted in both directions over each link, using a first wavelength &lgr;1 to transmit data in a first direction over the link and a second wavelength &lgr;2 to transmit data in a second, opposite direction over the link. The two wavelengths &lgr;1 and &lgr;2 differ by at least 10 nm. Each of the data streams transmitted over the optical link has a bandwidth of at least 2.5 Gbps. Further, each data stream has at least two logical streams embedded therein. A link multiplexer at each node of the network includes one or more link cards for coupling the link multiplexer to client devices, and one or more multiplexer units for coupling the link multiplexer to the optical links.

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: Methods and systems for implementing polarization division multiplexing to allow recovery of data in different multiplexed channels at a receiving end without recovering multiplexed polarizations used in the transmitting stage.

Abstract: An optical apparatus comprises a phase grating, an input-ring array, an output-ring array and an optical interconnect. The phase grating produces a modulated light beam for each of a plurality of processing elements. The modulated light beams have a plurality of light wavelengths. An input-ring array receives the plurality of data modulated light beams. An output-ring array outputs a light beam to each processing element. An optical interconnect transfers light from the input-ring array to the output ring array and uniquely rotates each wavelength of the transferred light.

Abstract: In one embodiment, the present invention provides a method of transmitting an optical signal. This signal is transmitted through an optical fiber 12 (24) and is amplified by an optical amplifier 14 (22). The signal is then provided to an arrayed waveguide grating 16 (20). The arrayed waveguide grating 16 (20) has a wavelength-dependent optical amplitude response characterized in that the wavelength having the peak optical amplitude is different than the center channel wavelength of the signal. In some instances, this may result in a situation where the total tilt effect for the optical fiber 12 (24), the optical amplifier 14 (22) and the arrayed waveguide grating 16 (20) is less than the total tilt effect for the optical fiber 12 (24), the optical amplifier 14 (22) and an arrayed waveguide grating with a standard wavelength-dependent optical amplitude response where a signal at the center channel wavelength corresponds to the peak optical amplitude of the arrayed waveguide grating.

Abstract: An embodiment includes an optical source, an optical receiver, and an interconnecting optical fiber. A data sequence is received and encoded or formatted as an IP packet using an encoding format capable of returning a signal representing the IP packet to a predetermined value at the beginning of each bit period of the IP packet at a physical layer of the network. The encoded IP packet is then transmitted directly over an optical layer of the network without adapting the IP packet to another encoding format or using an adaptation layer in the network (e.g., at a data link layer or higher). The optical receiver receives the IP packet and then a clock signal is extracted without the overhead and costs associated with additional adaptation or encoding of the IP packet.

Abstract: A fiber optic communications link having PMD characterization across multiple optical channels to identify PMD problems. The communications link has adaptive PMD controls employed along the optical link, whereby PMD phenomena detected by instruments, such as PMD compensators, are interpreted as being either attributable to perturbation of fiber characteristics at large, or by failure of PMD equipment along the link. The present invention avoids taking unnecessary control or maintenance actions upon PMD related controllers and compensators. PMD notifications from various PMD compensators are correlated to identify which portion of the link has undergone a change in polarization characteristics to further identify PMD related errors and problems.

Abstract: An arbitrary signal is converted to IP packets, which are routed by an IP packet routing part to Optical path signal conversion parts. Optical path signals from the Optical path signal conversion parts are provided directly to an optical path route switching part of an IP packet transmission equipment. By the optical path route switching part, optical path signals, obtained by wavelength-demultiplexing of OTM signals from optical backbone transmission lines by OTM/optical path signal conversion parts, and optical path signals from the Optical path signal conversion parts are cross-connected to output routes according to their destinations.

Abstract: A monitoring system useful for monitoring the state of a fiber communication channel in which a portion of the fiber signal is tapped and detected by a photodiode. The dark current of the photodiode and other DC offsets of the system may be compensated by passing a known signal through the photodiode and extracting the component due to the known signal. The known signal may be a locally generated optical signal having a predetermined harmonic signature. Optionally, the fiber signal may be selectively attenuated before being combined with the known signal so only the known signal is detected. The known signal may also be a dark signal induced by selectively attenuating the fiber signal. The system may include a temperature sensor which allows the compensation to be performed against stored temperature dependent compensation values while the fiber signal is not attenuated.

Abstract: A system for managing signal power levels in an optical network. The optical network comprises a plurality of nodes having logic to receive and transmit optical signals over a plurality of network interconnections. The system includes a method wherein each of the nodes is provided configuration parameters, each of the nodes is configured based on the configuration parameters, power parameter information is exchanged between the nodes, at least some of the nodes are re-configured based on the power parameter information and the steps of exchanging power parameter information and re-configuring at least some of the nodes are repeated until the optical network is fully configured so that the optical signals have selected signal power levels.

Abstract: In an amplified wavelength division multiplexes (WDM) fiber optic communication system, each channel experiences a different optical gain, dispersion and noise. Also, the evolution of WDM fiber optic systems to higher density channel spacing has further aggravated multi-channel non-linear distortions such as four-wave mixing (FWM) and cross-phase modulation (XPM). The standard method for controlling these nonlinearities is the peak power control method. The performance of the channels can be equalized by adjusting the transmission powers of the optical transmitters. However, just equalization of a performance indication factor (PIF) such as BER or Q is not the optimum approach when peak power control mode of operation dominates. This invention is directed towards improving the margins of performance of WDM fiber optic channels.

Abstract: A point-to-multipoint bi-directional wide area telecommunications network employing atmospheric optical communication. The network comprises a primary transceiver unit, a plurality of subscriber transceiver units and an optical router. The primary transceiver unit may send data destined for the subscriber transceiver units through the optical router, and the subscriber transceiver units may send data destined for the primary transceiver unit through the optical router. The primary transceiver unit and optical router communicate by means of light beams which are transmitted through the atmosphere. Similarly, the optical router and the subscriber transceiver units communicate by means of light beams which are transmitted through the atmosphere.

Abstract: A method of increasing capacity on a long-haul undersea cable system having at least one optical fiber, said method comprising interleaving counter-propagating forward-propagating and backward-propagating signals in forward and backward channels on a common optical fiber, wherein the wavelength offset between said forward and backward channels is typically half of the channel spacing of co-propagating signals.

Abstract: An angle modulating portion 1 converts an inputted electrical signal into a predetermined angle-modulated signal. An optical modulating portion 2 converts the angle-modulated signal outputted from the angle modulating portion 1 into an optical-modulated signal and sends the optical-modulated signal to an optical waveguide portion 3. An interference portion 6 separates the optical-modulated signal transmitted through the optical waveguide portion 3 into two optical signals having predetermined difference in propagation delay and then combines the optical signals. An optical/electrical converting portion 4 subjects the combined optical signal to homodyne detection, to acquire a demodulated signal of the original electrical signal and output the electrical signal.

Abstract: A method for synchronizing optical signals conducted via different optical waveguides to an optical network node, wherein the variations in propagation time of the optical signals are compensated by adjustable optical delay circuits of a synchronizing device. To set a new delay for one of the optical waveguides, one of the adjustable delay circuits, already switched into the passive state, is set at the desired delay. This delay circuit is then switched into the active state by means of a high-speed optical switch, and the previously active delay circuit is switched into a passive state.