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 and apparatus are disclosed for operating an eVOA by modulating its attenuation. If an optical signal power is below a loss of signal (LOS) power threshold the eVOA attenuation is set to a maximum attenuation and then, periodically and quickly decreased and increased in steps while checking for the presence of optical signals above the LOS power threshold. The method is also used for operating a multiplicity of eVOAs while minimizing the risk of damage to optical network equipment.

Abstract: A system and method for operating a plurality of eVOAs in an optical network is provided. The system comprises a number of eVOAs, each eVOA coupled to one or more optical taps and connected to a microcontroller. The microcontroller comprises a monitor signal processing controller for measuring the power of the optical signal at the eVOAs; a scheduler for continuously cycling and checking the eVOAs operating attenuations; a microprocessing controller for determining, setting, adjusting and updating the eVOA operating attenuation and a means for communications between the microprocessor and the other controller within the system. The microcontroller cycles through the plurality of eVOAs and controls one eVOA at a time according to a predetermined method of the eVOA operation. Individual eVOAs may be controlled according to the same or different methods of controlling operations thereof as required.

Abstract: This invention describes a method for controlling attenuation for a variable optical attenuator (VOA) inserted in an optical path of an optical signal propagating in an optical network, comprising the steps of measuring power of the optical signal at the VOA; comparing the measured power with a target power; and if the measured power differs from the target power, changing the attenuation of the VOA in one or more variable size intervals (VSI) so that the power of the optical signal substantially equals to the target power, wherein the VSI being a function of the measured power and target power.

Abstract: In an optical WDM network, each optical channel is modulated with a respective channel identity. Detectors, conveniently at multiplex ports of optical band filters, detect the channel identities of all of the optical channels in an optical signal at the respective points to produce respective channel lists. A network management system determines channel lists for through ports of the optical band filters, identifies matching pairs of channel lists to determine a topology of each node and to identify optical paths entering or leaving each node, and identifies matching pairs of channel lists for these paths to determine an inter-node topology of the network. The channel identity detector points can alternatively be at the optical paths entering or leaving each node.

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 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 system and method for operating a plurality of eVOAs in an optical network is provided. The system comprises a number of eVOAs, each eVOA coupled to one or more optical taps and connected to a microcontroller. The microcontroller comprises a monitor signal processing controller for measuring the power of the optical signal at the eVOAs; a scheduler for continuously cycling and checking the eVOAs operating attenuations; a microprocessing controller for determining, setting, adjusting and updating the eVOA operating attenuation and a means for communications between the microprocessor and the other controller within the system. The microcontroller cycles through the plurality of eVOAs and controls one eVOA at a time according to a predetermined method of the eVOA operation.

Abstract: This invention describes a method for controlling attenuation for a variable optical attenuator (VOA) inserted in an optical path of an optical signal propagating in an optical network, comprising the steps of measuring power of the optical signal at the VOA; comparing the measured power with a target power; and if the measured power differs from the target power, changing the attenuation of the VOA in one or more variable size intervals (VSI) so that the power of the optical signal substantially equals to the target power, wherein the VSI being a function of the measured power and target power.

Abstract: An optical connection arrangement is provided in an optical path to facilitate changing optical add/drop multiplexer (OADM) and other optical component modules while optical traffic is present on the optical path, with minimal interruption to such traffic. The connection arrangement has a plurality of optical ports to each of which an optical component can be coupled, and one or more optical switches which can be controlled to selectively include in the optical path or bypass each optical port. Such connection arrangements can be coupled in series and/or in parallel for convenient modular add/drop configurations and for opposite directions of transmission of optical traffic on respective optical paths.

Abstract: A method and system for multi-level power management in an optical network is provided. They include three levels of control of an amplifier. The first level of control maintains the gain of the amplifier operating in automatic gain control (AGC) mode at a target amplifier gain. The second level of control eliminates channel gain excursion by dynamically changing the amplifier target gain so as to provide that the gain for each channel is within a gain ripple of the amplifier. The third level of control sets the target gains of amplifiers according to fiber span losses. The third level of control also performs pre-emphasis of channel powers by changing the power of one or more channels passing through the amplifier so as to compensate for gain ripple of the amplifier. As a result, this multi-level control of the amplifiers in the network provides an increased level of optical signal to noise ratio (OSNR), protection of network components, and stabilization of channel power in the network.

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: In an optical WDM network, each optical channel is modulated with a respective channel identity. Detectors, conveniently at multiplex ports of optical band filters, detect the channel identities of all of the optical channels in an optical signal at the respective points to produce respective channel lists. A network management system determines channel lists for through ports of the optical band filters, identifies matching pairs of channel lists to determine a topology of each node and to identify optical paths entering or leaving each node, and identifies matching pairs of channel lists for these paths to determine an inter-node topology of the network. The channel identity detector points can alternatively be at the optical paths entering or leaving each node.

Abstract: An optical connection arrangement is provided in an optical path to facilitate changing optical add/drop multiplexer (OADM) and other optical component modules while optical traffic is present on the optical path, with minimal interruption to such traffic. The connection arrangement has a plurality of optical ports to each of which an optical component can be coupled, and one or more optical switches which can be controlled to selectively include in the optical path or bypass each optical port. Such connection arrangements can be coupled in series and/or in parallel for convenient modular add/drop configurations and for opposite directions of transmission of optical traffic on respective optical paths.