Abstract: The present invention includes a fast algorithm to compute the pre-equalized waveform for simultaneous compensation of the self-phase modulation and chromatic dispersion experienced by a high-speed optical signal, e.g., at 10 Gb/s, and shows that it is used for an automatic self-adapting pre-equalization when the knowledge on transmission link details is inaccurate or incomplete.

Abstract: A method and apparatus for mitigating intersymbol interference (ISI) from narrow-band optical filtering and improving transmission performance by filtering multichannel optical signals using an optical filter device that exhibits a desired loss ripple in the transmittance profile of the filter passband.

Abstract: An optical add/drop multiplexer (OADM) adapted to route optical signals having at least two different bit rates. The OADM has at least two sets of DWDM channels, e.g., with channels in a first set having a first bandwidth value suitable for the transmission of 10-Gb/s signals and channels in a second set having a second bandwidth value suitable for the transmission of 40-Gb/s signals. The first and second sets occupy two different spectral bands and the first set has two subsets of interleaved channels. In one embodiment, the OADM has first and second optical branches adapted to process optical signals corresponding to first and second groups of channels, respectively. The first group includes a first subset from the first set while the second group includes the second set and a second subset from the first set. Advantageously, OADMs of the invention may be used to create independent processing paths for different groups of channels. As a result, a communication system having those OADMs can be upgraded, e.g.

Abstract: A method and apparatus for transmitting optical pulses in a dispersion-managed optical transmission system comprises determining the pulse width of optical pulses in a optical transmission channel in accordance with the path-average dispersion (PAD) experienced by that channel.

Abstract: A repeater node for an optical transmission system provides amplification of optical signals and uses a modulated pump signal to transfer status information about the repeater node to a control system via an optical supervisory signal. The pump signal supplied by a pump source to an optical amplifier is modulated with one or more tones that are indicative of status in the repeater node. In a transmission fiber coupled to the output of the optical amplifier, the modulation of the pump signal is transferred to the supervisory signal of the optical transmission system as a result of Raman effect. More specifically, the pump wavelength and the supervisory signal wavelength are such that the modulated tone on the shorter wavelength pump signal is transferred to the longer wavelength supervisory signal. The tone can then be extracted from the supervisory signal and processed at another node in the system.

Abstract: A method, apparatus and system for reducing gain ripple in a Raman-amplified WDM system includes determining a gain profile of an optical signal transported via a first Raman amplification span in a Raman-amplified WDM system, comparing the determined gain profile to a gain profile of an optical signal transported via a second Raman amplification span, determining, from the comparison, an amount of wavelength adjustment required for a plurality of Raman pumps comprising at least one Raman pump block of the second Raman amplification span to alter the gain profile of an optical signal transported via the second Raman amplification span, such that a cumulative gain profile of an optical signal transported via the first and the second Raman amplification spans approaches a desired gain profile, and generating a control signal suitable for adjusting the wavelengths of the plurality of Raman pumps of the at least one Raman pump block an amount consistent with the determined amount.

Abstract: A repeater node for an optical transmission system provides amplification of optical signals and uses a modulated pump signal to transfer status information about the repeater node to a control system via an optical supervisory signal. The pump signal supplied by a pump source to an optical amplifier is modulated with one or more tones that are indicative of status in the repeater node. In a transmission fiber coupled to the output of the optical amplifier, the modulation of the pump signal is transferred to the supervisory signal of the optical transmission system as a result of Raman effect. More specifically, the pump wavelength and the supervisory signal wavelength are such that the modulated tone on the shorter wavelength pump signal is transferred to the longer wavelength supervisory signal.

Abstract: A method and apparatus for transmitting optical pulses in a dispersion-managed optical transmission system comprises determining the pulse width of optical pulses in a optical transmission channel in accordance with the path-average dispersion (PAD) experienced by that channel.

Abstract: A method, apparatus and system for reducing gain ripple in a Raman-amplified WDM system includes determining a gain profile of an optical signal transported via a first Raman amplification span in a Raman-amplified WDM system, comparing the determined gain profile to a gain profile of an optical signal transported via a second Raman amplification span, determining, from the comparison, an amount of wavelength adjustment required for a plurality of Raman pumps comprising at least one Raman pump block of the second Raman amplification span to alter the gain profile of an optical signal transported via the second Raman amplification span, such that a cumulative gain profile of an optical signal transported via the first and the second Raman amplification spans approaches a desired gain profile, and generating a control signal suitable for adjusting the wavelengths of the plurality of Raman pumps of the at least one Raman pump block an amount consistent with the determined amount.

Abstract: A distortion analyzer for generating a distortion signal based on an input signal. For example, the distortion signal may be generated by adding a first signal corresponding to the entire spectrum of the input signal to a second signal corresponding to a low-frequency component of the input signal and then subtracting from the result of addition a third signal corresponding to a specific frequency band of the input signal. The effect of polarization mode dispersion that an optical signal experiences as it propagates through an optical transmission fiber may be compensated for at a receiver using a birefringent compensator, in which the distortion analyzer continuously examines the signal outputted by the compensator and supplies the distortion signal to the compensator, which causes the compensator to reduce the effect of such polarization mode dispersion based on the level of the distortion signal.

Abstract: A distortion analyzer for generating a distortion signal based on an input signal. For example, the distortion signal may be generated by adding a first signal corresponding to the entire spectrum of the input signal to a second signal corresponding to a low-frequency component of the input signal and then subtracting from the result of addition a third signal corresponding to a specific frequency band of the input signal. The effect of polarization mode dispersion that an optical signal experiences as it propagates through an optical transmission fiber may be compensated for at a receiver using a birefringent compensator, in which the distortion analyzer continuously examines the signal outputted by the compensator and supplies the distortion signal to the compensator, which causes the compensator to reduce the effect of such polarization mode dispersion based on the level of the distortion signal.

Abstract: The effect of polarization mode dispersion that an optical signal experiences as it propagates through an optical transmission fiber is compensated for at a receiver using a birefringent compensator, in which a distortion analyzer repeatedly examines the signal outputted by the compensator and causes the compensator to reduce the effect of such polarization mode dispersion based on the results of such examination.

Abstract: A protection facility is provided for use in an optical communications node that communicates with another optical communications node via first and second bidirectional communications paths respectively serving as a service path and protection path, in which a filter filters signals respectively received over the service and protection paths and generates a main signal and a complementary signal for each of the paths. A control unit then generates a Loss of Signal (LOS_A) indication for the service path if a SUM signal or DIFF signal respectively derived as a function of a sum of the main and complementary signals generated for the service path and difference between the main and complementary signals generated for the service path is less than a respective threshold value. A switch then invokes protection switching responsive to the presence of the LOS_A indication.

Abstract: An optical amplifier is adapted to cancel the Raman gain of an optical transmission path that degrades those optical signals occupying the low end of the bandwidth such that the power is transferred from the latter signals to the optical signals occupying the high end of the bandwidth. More specifically, the optical amplifier adjusts the gain that it applies to the optical signals so that it favors the signal components at the low end of the bandwidth.

Abstract: The invention is directed to an optical transmission system employing an electro-absorption modulator operative that absorbs energy from light received from a source of light and modulates the received light with information signals received from a source of information and outputs the modulated light signal to an optical transmission line, and employing apparatus that controls the level of light signals provided by the source as a function of a control signal having a level proportional to the level of the absorbed energy.

Abstract: The effect of polarization mode dispersion that an optical signal experiences as it propagates through an optical transmission fiber is compensated for at a receiver using a birefringent compensator, in which the compensator automatically and adaptively generates a level of differential time delay that substantially equals the differential time delay that the optical signal experiences, but of different sign, and, therefore, essentially cancels out the undesired delay.

Abstract: A facility in a communication system associates a unique identification signal with each currently active communications channel and then transmits the unique identification signal and associated information signals within the respective channel. In this way, apparatus that receives the transmitted signals may determine the number of channels that are active based on the number of the identification signals it receives and then output the received signals at a power level determined as a function of that number.

Abstract: Monitoring of optical amplifiers is accomplished, in accordance with the invention, by an apparatus and method for detecting a power level of a tone modulated upon a signal input to the amplifier, detecting an output power level of the amplifier, and comparing the power level of the tone to the output power level of the amplifier to determine an indication of the performance of the amplifier. In illustrative embodiments of the invention, each of the individual channels within a multiplexed optical signal are modulated with a specific low-frequency tone. The modulating is performed at the transmission site of the optical signal, and the specific tone frequencies are chosen to be lower than the low-frequency cut-off of any other information encoded upon the optical signal. The channel power of each channel is determined after each stage of optical amplification in the network by measuring the power of its respective unique low-frequency tone using a low-cost monitor.

Abstract: A technique for reducing the power threshold at which stimulated brillouin scattering ("SBS") occurs within an optical fiber by directly modulating a conventional laser generating an optical signal propagated along that fiber. The modulation is accomplished by employing an alternating waveform to induce a dither upon the laser output. The specific frequency of the alternating waveform is chosen to be very much lower than the low frequency cut-off of any receiver coupled to the optical fiber, but sufficiently high enough to efficiently suppress the Brillouin gain. This dithering causes the laser to be frequency modulated, thereby broadening the effective linewidth of the laser output and increasing the SBS power threshold.