Abstract: An exemplary technique is provided for a scalable architecture for a network node that allows a very high switching capacity. The network node has a number of packet optical add drop multiplexers (POADMs), a number of dual line cards, respectively associated with the POADMs, and an optical switch matrix. Each POADM has an input and an output line interface and serves to selectively add and drop optical packets into and from packet timeslots of output and input wavelength-multiplexed optical signals transmitted and received at said output and input line interfaces, respectively. The dual line cards serve to electrically process and buffer packets to be added and dropped. The optical switch matrix configurably interconnects internal optical interfaces contained within the dual line cards on a packet by packet basis.

Abstract: An exemplary apparatus is provided for a high capacity switching system for use in a transport network, which contains a number of input and output subsystems and a central interconnection means configurably interconnecting the input and output subsystems. The subsystems have input and output line modules for receiving and transmitting data signals to and from transmission lines of the network, one or more link modules connecting the subsystems to the interconnection means, and local switching means switching data signals in time and space domain between the input and output modules and the one or more link modules within one subsystems. The link modules are adapted to aggregate data signals from different input and output line modules of the same input and output subsystems and destined to input and output line modules of another one of the input and output subsystems into signal bursts and add a payload gap to each signal burst.

Abstract: An exemplary technique is provided for a scalable architecture for a network node that allows a very high switching capacity. The network node has a number of packet optical add drop multiplexers (POADMs), a number of dual line cards, respectively associated with the POADMs, and an optical switch matrix. Each POADM has an input and an output line interface and serves to selectively add and drop optical packets into and from packet timeslots of output and input wavelength-multiplexed optical signals transmitted and received at said output and input line interfaces, respectively. The dual line cards serve to electrically process and buffer packets to be added and dropped. The optical switch matrix configurably interconnects internal optical interfaces contained within the dual line cards on a packet by packet basis.

Abstract: The present invention relates to optical transmission systems. In particular, the present invention relates to a method and system for estimating the spectral efficiency which may be achievable in an optical transmission network and for adapting the parameters of the transmission network to the achievable spectral efficiency. A method and system for controlling an optical transmission system comprising a first and a second optical transmission channel is described. The first optical transmission channel is affected by the second optical transmission channel. The method comprises the steps of measuring the inverse signal-to-noise ratio of the first channel for a plurality of input power levels used by the first and second channel; determining a contribution of the second channel to the inverse signal-to-noise ratio; and determining the input power to the second channel, such that an overall throughput of the first and second channel is maximized.

Abstract: The present invention provides a high capacity switching system for use in a transport network, which contains a number of input/output subsystems and a central interconnection means configurably interconnecting the input/output subsystems. The subsystems have input/output line modules for receiving and transmitting data signals to and from transmission lines of the network, one or more link modules connecting the subsystems to the interconnection means, and local switching means switching data signals in time and space domain between the input/output modules and the one or more link modules within one subsystems. The link modules are adapted to aggregate data signals from different input/output line modules of the same input/output subsystems and destined to input/output line modules of another one of said input/output subsystems into signal bursts and add a payload gap to each signal burst.

Abstract: The present invention relates to optical transmission systems. In particular, the present invention relates to a method and system for estimating the spectral efficiency which may be achievable in an optical transmission network and for adapting the parameters of the transmission network to the achievable spectral efficiency. A method and system for controlling an optical transmission system comprising a first and a second optical transmission channel is described. The first optical transmission channel is affected by the second optical transmission channel. The method comprises the steps of measuring the inverse signal-to-noise ratio of the first channel for a plurality of input power levels used by the first and second channel; determining a contribution of the second channel to the inverse signal-to-noise ratio; and determining the input power to the second channel, such that an overall throughput of the first and second channel is maximized.

Abstract: A method for selecting an optimum delay length in a polarization mode dispersion (PMD) compensator configured with a constant-length delay line and deployed in an optical communication system. The optimum delay length depends on the data modulation format, bit rate, and/or signal bandwidth and is preferably selected such that outage probability in the communication system is at a minimum. System performance of a PMD compensator configured with a constant-length delay line having the optimum length approaches that of a PMD compensator configured with a variable-length delay line. The method extends the application range of constant-length delay line PMD compensators while reducing the cost of implementing high-performance PMD compensation.

Abstract: The delay setting of an optical delay line interferometer (DLI) used to decode differentially encoded phase shift keyed signals (DPSK or DQPSK) is controlled using a control signal representative of the ratio Perr2/Perr1 of the rate of occurrence of double errors and the rate of occurrence of errors. The ratio Perr2/Perr1, as the delay setting of the DLI is varied, exhibits a characteristic W-shaped structure consisting of a local maximum at the optimum value and two minima adjacent to the maximum, one on each side of it. This structure is present over a wide range of signal to noise ratio and residual dispersion.

Abstract: A decision feedback structure for recovering a bit stream out of received signals is disclosed, wherein the sampling instant may be tuned in dependence of the sequence or pattern of the preceding bits so as to follow the bit sequence dependent instant of the maximum eye opening. The decision-feedback equalizer structure includes decision means for making a bit value decision at a sampling instant, a feedback path to feed back bit values to said decision means and means for adapting the sampling instant for a bit value decision made by said decision means with respect to the sampling phase depending on the bit values of preceding bits, in particular depending on the bit value of the previous bit.

Abstract: A method of adjusting equalization parameters in a receiver wherein a bit error rate (BER) in a data stream is measured from the number of corrected bits in data blocks which have an information section and an error correction section. A predetermined equalization parameter is changed, and the bit error rate (BER) after change is again measured to find out how to change the predetermined equalization parameter until an optimum is reached. When adjusting the threshold value of the receiver, the history of occurring bits preceding the actual sampled bit is taken into consideration in that the amount and direction of adjustment is derived from a look-up table.

Abstract: A method of signal equalization of a transmitted bit stream by means of a feed forward equalizer is provided, whereby the signal is decomposed into at least two components and the components are multiplied with equalization parameters to form equalized components, which are superposed to form an equalized signal, and whereby conditional bit error rates by counting faulty transmitted bits in dependence of preceding and succeeding bits are determined and the equalization parameters are tuned dependent on the determined conditional bit error rates.

Abstract: In accordance with the invention, an optical fiber communication system is provided with a tunable linearly chirped Bragg grating in high birefringence fiber for reduction of polarization mode dispersion without increasing chromatic dispersion. A first embodiment using a single grating can be tuned for optimal PMD compensation, optimal chromatic compensation or optimal simultaneous compensation. Alternative embodiments using a plurality of gratings permit simultaneous compensation of both PMD and chromatic dispersion.

Abstract: A method for correcting the phase of a clock in a data receiver which receives a data flow representing different signal levels with logical high and low signal values and signal transitions positioned therebetween, wherein the positions of such signal transitions between respective two adjacent logical signal values are evaluated for correcting the phase of the clock. The position of a signal transition between a first pair of signal values on one level (11) or a second pair of signal values on the other level (00) is weighted stronger in the evaluation then the positions of signal transitions between adjacent single signal values (1,0) of different signal levels.

Abstract: The delay setting of an optical delay line interferometer (DLI) used to decode differentially encoded phase shift keyed signals (DPSK or DQPSK) is controlled using a control signal representative of the ratio Perr2/Perr1 of the rate of occurrence of double errors and the rate of occurrence of errors. The ratio Perr2/Perr1, as the delay setting of the DLI is varied, exhibits a characteristic W-shaped structure consisting of a local maximum at the optimum value and two minima adjacent to the maximum, one on each side of it. This structure is present over a wide range of signal to noise ratio and residual dispersion.

Abstract: A method for reducing deleterious effects of higher-order polarization mode dispersion (PMD) on the quality of data transmission in a long-haul optical communication system. An optical bandpass filter (OBF) designed for spectral bandwidth reduction of a received data-modulated optical signal is placed at the receiver end of the communication system next to a first-order PMD compensator. The OBF may be, e.g., a Mach-Zehnder filter having a bandwidth approximately equal to a modulation frequency of the optical signal. A center frequency of the OBF may be detuned from that of the optical signal. Using the OBF at the receiver may decrease a number of optical bit errors associated with the effects of higher-order PMD.

Abstract: In accordance with the invention, an optical fiber communication system is provided with a tunable linearly chirped Bragg grating in high birefringence fiber for reduction of polarization mode dispersion without increasing chromatic dispersion. A first embodiment using a single grating can be tuned for optimal PMD compensation, optimal chromatic compensation or optimal simultaneous compensation. Alternative embodiments using a plurality of gratings permit simultaneous compensation of both PMD and chromatic dispersion.

Abstract: A method for selecting an optimum delay length in a polarization mode dispersion (PMD) compensator configured with a constant-length delay line and deployed in an optical communication system. The optimum delay length depends on the data modulation format, bit rate, and/or signal bandwidth and is preferably selected such that outage probability in the communication system is at a minimum. System performance of a PMD compensator configured with a constant-length delay line having the optimum length approaches that of a PMD compensator configured with a variable-length delay line. The method extends the application range of constant-length delay line PMD compensators while reducing the cost of implementing high-performance PMD compensation.

Abstract: A decision feedback structure for recovering a bit stream out of received signals is disclosed, wherein the sampling instant may be tuned in dependence of the sequence or pattern of the preceding bits so as to follow the bit sequence dependent instant of the maximum eye opening. The decision-feedback equalizer structure includes decision means for making a bit value decision at a sampling instant, a feedback path to feed back bit values to said decision means and means for adapting the sampling instant for a bit value decision made by said decision means with respect to the sampling phase depending on the bit values of preceding bits, in particular depending on the bit value of the previous bit.

Abstract: A method for correcting the phase of a clock in a data receiver which receives a data flow representing different signal levels with logical high and low signal values and signal transitions positioned therebetween, wherein the positions of such signal transitions between respective two adjacent logical signal values are evaluated for correcting the phase of the clock. The position of a signal transition between a first pair of signal values on one level (11) or a second pair of signal values on the other level (00) is weighted stronger in the evaluation then the positions of signal transitions between adjacent single signal values (1,0) of different signal levels.

Abstract: A method of signal equalization of a transmitted bit stream by means of a feed forward equalizer is provided, whereby the signal is decomposed into at least two components and the components are multiplied with equalization parameters to form equalized components, which are superposed to form an equalized signal, and whereby conditional bit error rates by counting faulty transmitted bits in dependence of preceding and succeeding bits are determined and the equalization parameters are tuned dependent on the determined conditional bit error rates.