Abstract: A reconfigurable WDM add/drop multiplexer and its method of operation at an add/drop node on an optical fiber carrying a plurality of WDM signals is described. The WDM add/drop multiplexer has a coupler and a demultiplexer element dropping WDM signals from the optical fiber to a plurality of drop terminals, and a wavelength-selective switch adding WDM signals from a plurality of add terminals onto the optical fiber. The coupler splits the WDM signals received from the optical fiber and passes the split WDM signals to the first and second output terminals. The demultiplexer element separates the split WDM signals at the plurality of drop terminals. The wavelength-selective switch, which has an input terminal for connection to the second coupler output terminal and an output terminal for connection to the optical fiber, selectively adds WDM signals on the plurality of add terminals to the optical fiber responsive to control signals.

Abstract: Information about optical amplifier ASE power is propagated down a link. Each amplifier along the link can learn of the ASE power at its input and take this input ASE power into account in controlling its own per channel output power. Each amplifier can also pass along to the next amplifier an indicator that represents its output ASE power taking into account both its input ASE power and own generated ASE power. Intermediate optical add/drop multiplexers (OADMs) adjust the ASE power indicator to account for losses and the spectral characteristics of each filter.

Abstract: A mesh optical network node has switch cards which carry active components, such as wavelength routers to switch the paths of optical signals through the node and a fiber organizer handles the numerous optical fiber interconnections among the switch cards. The fiber organizer has no active components and can include optical paths to verify not only that a switch card connection to the fiber organizer has been made but that the connection is properly made.

Abstract: In one embodiment, first optical signal can be generated at a first end of an optical fiber segment at a first time. The first optical signal can be detected at a second end of the optical fiber segment at a second time. A second optical signal can be generated at a second end of the optical fiber segment at a third time in response to the detection of the first optical signal. The second optical signal can be detected at the first end of the optical fiber segment at a fourth time. A length of the optical fiber segment can be determined based on a difference between the second time and the first time, a difference between the third time and the second time, and a difference between the fourth time and the third time.

Abstract: An economic way of determining the chromatic dispersion along a link of a DWDM network is provided. A transmitter modulates the output signals of two lasers operating at two different wavelengths and the modulated output signals are sent into the link. Detectors at each one of a plurality of detection sites along the link determine a phase difference in modulation between the output signals of the two lasers. The chromatic dispersion for each detection site can be calculated from the modulation frequency and determined phase differences at that site.

Abstract: A mesh optical network node has switch cards which carry active components, such as wavelength routers to switch the paths of optical signals through the node and a fiber organizer handles the numerous optical fiber interconnections among the switch cards. The fiber organizer has no active components and can include optical paths to verify not only that a switch card connection to the fiber organizer has been made but that the connection is properly made.

Abstract: In one embodiment, techniques provide a mechanism for tracking wavelengths in a DWDM network. In particular, embodiments of the present invention also provide for connection tracking using a fast pilot tone in a DWDM network without dedicated hardware for the generation and the diction of the tone.

Abstract: Switching architectures for WDM mesh and ring network nodes are presented. In mesh networks, the switching architectures have multiple levels - a network level having wavelength routers for add, drop and pass-through functions, an intermediate level having device units which handle add and drop signals, and a local level having port units for receiving signals dropped from the network and transmitting signals to be added to the network. The intermediate level device units are selected and arranged for performance and cost considerations. The multilevel architecture also permits the design of reconfigurable optical add/drop multiplexers for ring network nodes, the easy expansion of ring networks into mesh networks, and the accommodation of protection mechanisms in ring networks.

Abstract: A efficient and inexpensive optical WDM network architecture with add and drop couplers. Add couplers and drop couplers connected to a network optical fiber with wavelength blocker units which filter out optical signals at selected wavelengths on the optical fiber. The wavelength blocker units are distributed among the add and drop couplers so that each segment of the optical fiber between pairs of neighboring wavelength blocker units has at least three add and drop couplers. More specifically, each segment has the following relationship: THRU+ADD+DROP+LOCAL?TOTAL where THRU is the number of channels passing through the segment; ADD is the number of channels added within the segment; DROP the number of channels dropped within the segment; LOCAL the number of channels confined within the segment; and TOTAL is the total capacity of the optical fiber.

Abstract: A reconfigurable WDM add/drop multiplexer and its method of operation at an add/drop node on an optical fiber carrying a plurality of WDM signals is described. The WDM add/drop multiplexer has a coupler and a demultiplexer element dropping WDM signals from the optical fiber to a plurality of drop terminals, and a wavelength-selective switch adding WDM signals from a plurality of add terminals onto the optical fiber. The coupler splits the WDM signals received from the optical fiber and passes the split WDM signals to the first and second output terminals. The demultiplexer element separates the split WDM signals at the plurality of drop terminals. The wavelength-selective switch, which has an input terminal for connection to the second coupler output terminal and an output terminal for connection to the optical fiber, selectively adds WDM signals on the plurality of add terminals to the optical fiber responsive to control signals.

Abstract: Systems and methods for controlling power of WDM channels in a WDM receiver. A preamplifier is provided prior to a demultiplexer in the WDM receiver chain. The gain of the preamplifier may be controlled based on power measurements made on individual WDM channels. A filter with controllable tilt may be employed to compensate for amplifier gain tilt and assure that all of the WDM channels remain within the dynamic range of the photodetector and receiver electronics. This provides improved bit error rate performance.

Abstract: An optical transmission system has been designed to optimize the use of the spectral emission range of rare-earth-doped fiber amplifiers. The system includes a wide band of channels in the spectral emission range of erbium-doped fiber amplifiers, which is split into two sub-bands, a low sub-band corresponding to the low end of the range and a high sub-band corresponding to the high end of the range. The two sub-bands are separately amplified and optimized, and then recombined without significant competition between the two sub-bands. In addition, an equalizing filter, such as a specialized Bragg filter or interferential filter, is applied to the low sub-band instead of the entire band of channels, thus greatly reducing any equalization need or unequalization effects.

Abstract: An optical fiber amplifier and filtering apparatus and method for a bidirectional wavelength-division-multiplexing (WDM) system having odd and even interleaved channels is disclosed. The apparatus uses optical circulators, in-fiber Bragg gratings, and erbium-doped fiber amplifiers to amplify channels traveling in opposite directions in a WDM system and to filter unwanted ASE and back reflection noise between the channels. Interface circulators positioned at opposite ends of the apparatus respectively receive odd and even channels traveling in opposite directions in the WDM system and pass the channels through an erbium-doped fiber amplifier. Other circulators direct the amplified channels to two series of Bragg gratings that respectively reflect only the odd channels and pass only the even channels or vice versa, thereby filtering ASE and other noise located between the channels. An additional amplifier may boost the channels before they exit the apparatus via the interface circulators.

Abstract: An optical telecommunication system including a transmitting station and a receiving station for optical signals, connected with each other by an optical fiber line including optical line amplifiers having a rare-earth-doped active fiber and connected in series, in which the transmitting station includes signal generator for generating signals at several wavelengths, and connections for conveying the signals to a single optical fiber line. The optical signal receiving station includes apparatus for separating the signals. At least one of the optical line amplifiers has dopants, fiber length and pumping power capable of determining, at the input of the receiving station, an optical signal/noise ratio which for the different wavelengths has a difference less than 2 dB, and for each signal is greater than 15 dB.

Abstract: An optical telecommunication system including a transmitting station and a receiving station for optical signals, connected with each other by an optical fiber line including optical line amplifiers having a rare-earth-doped active fiber and connected in series, in which the transmitting station includes signal generator for generating signals at several wavelengths, and connections for conveying the signals to a single optical fiber line. The optical signal receiving station includes apparatus for separating the signals. At least one of the optical line amplifiers has dopants, fiber length and pumping power capable of determining, at the input of the receiving station, an optical signal/noise ratio which for the different wavelengths has a difference less than 2 dB, and for each signal is greater than 15 dB.

Abstract: An optical telecommunication system includes means for generating optical signals of different wavelengths, an optical-fibre line with amplifying means, a pre-amplifer, and receiving means. The the pre-amplifier comprises an optical waveguide doped with a rare earth material, differential-attenuation means located at a first position along the doped waveguide and capable of causing an attenuation in the signal band which is greater than the attenuation caused at the pumping wavelength, and filtering means located at a second position and adapted to attenuate by a value higher than a predetermined minimum, the spontaneous emission in a wavelength band contiguous with the signal band.The position and attenuation of the differential-attenuation means and filtering means and the wavelength band are selected in a functional relation with respect to each other in order to limit the output power variations from the pre-amplifier.