Abstract: Various methods and apparatuses are provided for performing a radix-M FFT (Fast Fourier Transform) upon N time domain samples to produce N/S frequency domain samples for detecting tones of dithers impressed on channels of a WDM (wavelength Division Multiplexed) optical signal. Successive tones have a tone frequency spacing, &Dgr;fta, and a sampling frequency, fs, is chosen so that fs=N&Dgr;fta/S. S is a spacing given by S=Mw with w being an integer. The radix-M FFT is performed in k=logm(N) stages and within the stages a reduced number of radix-M computations, when compared to the number of radix-M computations of a conventional radix-M FFT, are performed on data points associated with the N time domain samples. This is possible because successive frequency domain samples of the N/S frequency domain samples differ by &Dgr;fta=S&Dgr;f where &Dgr;f is a frequency bandwidth.

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: 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: 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: Various methods and apparatuses are provided for performing a radix-M FFT (Fast Fourier Transform) upon N time domain samples to produce N/S frequency domain samples for detecting tones of dithers impressed on channels of a WDM (wavelength Division Multiplexed) optical signal. Successive tones have a tone frequency spacing, &Dgr;fta, and a sampling frequency, fs, is chosen so that fs=N&Dgr;fta/S. S is a spacing given by S=Mw with w being an integer. The radix-M FFT is performed in k=logm(N) stages and within the stages a reduced number of radix-M computations, when compared to the number of radix-M computations of a conventional radix-M FFT, are performed on data points associated with the N time domain samples. This is possible because successive frequency domain samples of the N/S frequency domain samples differ by &Dgr;fta=S&Dgr;f where &Dgr;f is a frequency bandwidth.

Abstract: Provided is a signal detector and method for spectrum analysis and for measuring power of one or more channels of an electrical or optical signal. Each channel may carry a unique modulation tone. A DSP (digital-signal processor) performs DFTs (discrete Fourier transforms) on the signal. Frequency bands of interest which contain a tone that requires detection are processed. Higher layers of coherent integrations are performed on bands which have not detected a tone with a resolution that is suitable for power measurement. The higher layers of coherent integrations are performed by collecting additional data and performing a coherent integration. Further higher layer coherent integrations are performed until all modulation tones have been detected with a suitable resolution or up to a maximum detection latency.

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: Provided is a signal detector and method for spectrum analysis and for measuring power of one or more channels of an electrical or optical signal. Each channel may carry a unique modulation tone. A DSP (digital-signal processor) performs DFTs (discrete Fourier transforms) on the signal. Frequency bands of interest which contain a tone that requires detection are processed. Higher layers of coherent integrations are performed on bands which have not detected a tone with a resolution that is suitable for power measurement. The higher layers of coherent integrations are performed by collecting additional data and performing a coherent integration. Further higher layer coherent integrations are performed until all modulation tones have been detected with a suitable resolution or up to a maximum detection latency.

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: 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: 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: 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.