Abstract: The invention provides a method and system for selectively canceling a specified frequency band in the payload of an optical communication system. This selected frequency band is to be used for launching pilot tones for power measurement and identification. The method controls the intensity of the optical payload signal through an intensity modulator that is included in the optical communication system. The frequency band in payload to be cancelled is removed where as the other frequency components of the payload are passed without attenuation. An embodiment that uses a feed-forward unit, a feedback unit and a control unit for generating a cancellation signal for the intensity modulator is described. An advantage of the method is that it removes a continuum of payload tones in the specified frequency band to be cancelled.

Abstract: Channels in an optical WDM network are each identified by at least two dither tones with which the channel is modulated, the dither tones alternating with a predetermined periodicity so that at any instant each channel is modulated by only one dither tone. The dither tones are continuously generated at precise frequencies. Channel detection by detecting the dither tones, for channels having optical powers over a wide dynamic range, makes use of an FFT process which can detect dither tones for high power channels in a single operation. Coherent averaging of FFT results over time is used to detect dither tones for low power channels over multiple FFT operations.

Abstract: Signals in an optical communications network, such as optical channels in an optical WDM network for example, are each identified by at least two low frequency dither tones with which the signal is modulated. The dither tones alternate with a predetermined periodicity to produce a cyclically repeated sequence of dither tones. A network parameter, such as a channel identifier for example, is obtained by the detection of the particular combination of dither tones in the sequence. To detect a number of network parameters a signal is modulated with a number of cyclically repeated sequences of dither tones each uniquely identifying a respective network parameter. In some implementations each dither tone in a cyclically repeated sequence of dither tones is repeated with substantially the same phase and coherent averaging is performed over a number of periods to detect dither tones on low power signals.

Abstract: Channels in an optical WDM network are each identified by at least two dither tones with which the channel is modulated, the dither tones alternating with a predetermined periodicity so that at any instant each channel is modulated by only one dither tone. The dither tones are continuously generated at precise frequencies. Channel detection by detecting the dither tones, for channels having optical powers over a wide dynamic range, makes use of an FFT process which can detect dither tones for high power channels in a single operation. Coherent averaging of FFT results over time is used to detect dither tones for low power channels over multiple FFT operations.

Abstract: A method and system for identification of a channel in an optical network is provided. The channel is identified by the use of unique combinations of two or more low frequencies, or tones, modulated onto the channel and optionally, a network parameter associated with the channel.

Abstract: An optical add/drop multiplexing (OADM) apparatus and method are disclosed for detecting pilot tones, removing ghost tones, and re-inserting pilot tones on WDM signals in an optical network. The OADM apparatus comprises a smart processing and control unit (PCU) for detecting pilot tones used for channel identifications, including identifying and removing ghost tones associated with respective optical channels, and re-inserting the processed pilot tones into the respective optical channels. The OADM apparatus and method may incorporate digital PCU or analog PCU for processing pilot tones and removing ghost tones.

Abstract: A method and system for multi-level power management in an optical network is provided. They include three levels of power management. The first level of power management dynamically changes equipment settings in each module of equipment so that required module setpoint values in each module are achieved. The second level of power management determines module setpoint values for each module of equipment within each node in the optical link so that required node setpoint values are achieved. The third level of power management determines node setpoint values at each node in the optical link so that the optical link meets predetermined power specifications. If any of the three levels cannot achieve the required setpoint values, an error signal is generated by that level of power management and sent to the level of power management above it, thus initiating a higher level of power management.

Abstract: A multi-stage method and apparatus for determining a faulty component location along an optical path through an optical fiber in an optical network are disclosed. A total power of the optical fiber, and a total wavelength power as a sum of powers of the individual wavelengths at a plurality of local detection points are measured and compared at the local detection points, followed by determining whether or not a faulty detection point exists along the optical path. If a fault is identified, the method provides a multi-stage fault detection procedure, including measuring a total wavelength power loss between a local detection point and an adjacent detection point, between the local detection point and multiple non-adjacent detection points, and a correlation of the measured total wavelength power losses between the various detection points. A corresponding apparatus for determining the faulty component location in the optical network is also provided.

Abstract: A method and system for compensating for side effects of cross gain modulation in amplified optical networks, which allows reliable identification of expected and unexpected channels in the network is provided. Each optical channel traveling in the optical network is marked with a unique channel signature (expected channel signature), having one or more dither tone modulated onto the optical channel; followed by detecting a spectrum of tones, including said modulated dither tones and ghost tones thereof produced by the cross gain modulation in the optical network, at various locations in the optical network. Amplitudes of the spectrum tones, which belong to the expected channel signature, are compared with a first threshold, while amplitudes of the remaining spectrum tones, which are not the valid tones, are compared with a second threshold, which is lower than the first threshold.

Abstract: A method for automatic initialization of an optical network is provided. A network management system (NMS) performs remote determination of span losses and sets the operating points of network components. The initialization method comprises remotely and automatically setting target gains of optical amplifiers and signal power levels at transmitters and receivers to required operating values. The methods for initialization of the optical network of the embodiments include gain excursion minimization (GEM) for individual channels passing through amplifiers and/or pre-emphasis of the optical link, where channel powers at the transmitters are biased to compensate for the effects of optical amplifiers gain ripple.

Abstract: Channels in an optical WDM network are each identified by at least two dither tones with which the channel is modulated, the dither tones alternating with a predetermined periodicity so that at any instant each channel is modulated by only one dither tone. The dither tones are continuously generated at precise frequencies. Channel detection by detecting the dither tones, for channels having optical powers over a wide dynamic range, makes use of an FFT process which can detect dither tones for high power channels in a single operation. Coherent averaging of FFT results over time is used to detect dither tones for low power channels over multiple FFT operations.

Abstract: Ethernet packets are transmitted in full duplex mode over a single coaxial cable, such as RG6 and RG59. Symmetrical full duplex operation is achieved by separating the upstream and downstream signals in the frequency domain whereby a 100BaseT signal is transmitted unmodified in one direction while the other is modulated upon a high frequency carrier to be transmitted in the other direction. In a second embodiment, the separation is in the time domain whereby the signals are sampled in blocks, each block compressed in time and transmitted at a higher rate, thus allowing for the interleaving of upstream and downstream blocks on the same coaxial cable. In a third embodiment, different rate upstream and downstream signals are separated in the frequency domain, but without modulation. The resulting asymmetrical 1000/100 Mb/s Ethernet over coax link is valuable in network architectures where asymmetry in the up and down traffic loads is expected.

Abstract: This invention provides a method for commissioning an optical network using internal Automatic Spontaneous Emission (ASE) light inherently present in the optical network as a light source (the ASE light source) for measuring losses inside and between nodes in the network. A modular segmented approach is adopted and the network is commissioned segment by segment. The method uses techniques for the correction of the Optical Signal to Noise Ratio induced error as well as the Spectral Filtering Error during the loss computation required for adjusting the gains of the amplifiers at each network node to an appropriate value. Since the method does not require an external laser source that needs to be moved manually from node to node, it greatly reduces the commissioning time. Since it uses only the existing components of the network nodes it also leads to a significant saving in cost.

Abstract: A multi-stage method and apparatus for determining a faulty component location along an optical path through an optical fiber in an optical network are disclosed. The optical fiber carries a plurality of wavelengths, which may or may not be modulated by low frequency dither tones that are utilized for identification purposes and performance monitoring in the optical network. First, the method comprises measuring a total power of the optical fiber and a total wavelength power as a sum of powers of the individual wavelengths at a plurality of local detection points; comparing the measured powers at the local detection points; and determining whether or not a faulty detection point exists along the optical path. If a fault is identified, the method further provides a multi-stage fault detection procedure, which comprises measuring a total wavelength power loss between a local detection point and an adjacent detection point, between the local detection point and multiple non-adjacent detection points.

Abstract: An apparatus and method for minimizing channel gain excursion in an optical system with automatic gain control is provided. The apparatus includes a feedback control loop which dynamically regulates the target gain of an automatic gain controlled (AGC) amplifier so as to compensate for the action of the AGC amplifier to maintain a constant linear average gain without accounting for the distribution of channels that carry signals across the amplifier spectral gain profile, which causes gain excursion of individual channels. The feedback control loop measures gain of individual channels and uses these measurements to regulate the target gain of the amplifier so as to minimize gain excursion of individual channels. If required, the apparatus may be integrated into a package. In one embodiment, the method for regulating the target gain is to maintain constant gain for all channels irrespective of the number of channels that carry a signal. This method is simple and guarantees no gain excursion.

Abstract: A method and system for multi-level power management in an optical network is provided. They include three levels of power management. The first level of power management dynamically changes equipment settings in each module of equipment so that required module setpoint values in each module are achieved. The second level of power management determines module setpoint values for each module of equipment within each node in the optical link so that required node setpoint values are achieved. The third level of power management determines node setpoint values at each node in the optical link so that the optical link meets predetermined power specifications. If any of the three levels cannot achieve the required setpoint values, an error signal is generated by that level of power management and sent to the level of power management above it, thus initiating a higher level of power management.

Abstract: In a WDM optical network, optical components of optical add/drop multiplexers (OADMs) at different nodes are made independent of the optical channel wavelengths to be dropped and added. Groups of optical channels each comprise a respective channel in each of a plurality of optical bands of channels having adjacent wavelengths, and the OADMs use tunable optical filters to drop and add channels in a selected group. A remote source supplies unmodulated optical carriers at channel wavelengths via an optical carrier fiber to each node, and at least one, conveniently all, of the optical carriers in a respective optical band is/are modulated with a signal to be transmitted via the add filter.

Abstract: A method and system for compensating for side effects of cross gain modulation in amplified optical networks, which allows reliable identification of expected and unexpected channels in the network is provided. Each optical channel traveling in the optical network is marked with a unique channel signature (expected channel signature), having one or more dither tone modulated onto the optical channel; followed by detecting a spectrum of tones, including said modulated dither tones and ghost tones thereof produced by the cross gain modulation in the optical network, at various locations in the optical network. Amplitudes of the spectrum tones, which belong to the expected channel signature, are compared with a first threshold, while amplitudes of the remaining spectrum tones, which are not the valid tones, are compared with a second threshold, which is lower than the first threshold.

Abstract: An optical add/drop multiplexing (OADM) apparatus and method are disclosed for detecting pilot tones, removing ghost tones, and re-inserting pilot tones on WDM signals in an optical network. The OADM apparatus comprises a smart processing and control unit (PCU) for detecting pilot tones used for channel identifications, including identifying and removing ghost tones associated with respective optical channels, and re-inserting the processed pilot tones into the respective optical channels. The OADM apparatus and method may incorporate digital PCU or analog PCU for processing pilot tones and removing ghost tones.

Abstract: A method for automatic initialization of an optical network is provided. A network management system (NMS) performs remote determination of span losses and sets the operating points of network components. The initialization method comprises remotely and automatically setting target gains of optical amplifiers and signal power levels at transmitters and receivers to required operating values. The methods for initialization of the optical network of the embodiments include gain excursion minimization (GEM) for individual channels passing through amplifiers and/or pre-emphasis of the optical link, where channel powers at the transmitters are biased to compensate for the effects of optical amplifiers gain ripple.