Abstract: The invention relates to a method of generating a feedback signal for adjusting a polarization mode dispersion compensator (PMDC, 21) in a transmission system with alternate-polarization. A first signal (37) is determined by measuring a spectral component of the radio frequency modulation of an optical signal (33) at a particular radio frequency. Preferably, the radio frequency essentially corresponds to half the symbol rate of the optical signal (33). Also a second signal (35) is determined by coupling the optical signal (33) into a delay line interferometer (DLI, 50) having a delay essentially corresponding to the symbol period or an odd multiple of the symbol period between its arms (51, 54). Downstream of the DLI (50), the signal is optical-to-electrically converted. Downstream of the optical-to-electrical conversion, an intensity measurement is performed. The first (37) and second (35) signals are then combined to generate the feedback signal (28).

Abstract: An optical receiver has an adaptive optical compensator and/or an adaptive electrical equalizer for compensating signal distortion in a received optical signal. In order to achieve a very fast adaptation of the receiver to the actual signal distortion, which is important for example for bursts mode optical signals in a packet-switched optical transmission network, at least one predetermined trainings sequence is provided in the optical signal, which is known at the receiver and thus enables fast adaptation of the compensator and/or equalizer to the actual signal distortion.

Abstract: The invention relates to a method of generating a feedback signal for adjusting a polarization mode dispersion compensator (PMDC, 21) in a transmission system with alternate-polarization. A first signal (37) is determined by measuring a spectral component of the radio frequency modulation of an optical signal (33) at a particular radio frequency. Preferably, the radio frequency essentially corresponds to half the symbol rate of the optical signal (33). Also a second signal (35) is determined by coupling the optical signal (33) into a delay line interferometer (DLI, 50) having a delay essentially corresponding to the symbol period or an odd multiple of the symbol period between its arms (51, 54). Downstream of the DLI (50), the signal is optical-to-electrically converted. Downstream of the optical-to-electrical conversion, an intensity measurement is performed. The first (37) and second (35) signals are then combined to generate the feedback signal (28).

Abstract: The invention relates to optical communication, in particular to compensation of non-linear distortions incurred in high bit-rate optical communication systems. A method and system for compensating self-phase modulation at an optical receiver of an optical transmission system using polarization division multiplexing and a modulation scheme with constant amplitude is proposed. The method comprises the step of performing a phase modulation on a received signal, wherein the received signal comprises two signal components associated with two orthogonal polarizations, each component comprising an in-phase sub-component and a quadrature-phase sub-component, thereby spanning a four-dimensional space. The phase modulation is determined by evaluating an error signal which depends on the distance in the four-dimensional space between the received signal after the phase modulation and a four-dimensional sphere defined by target constellation points of the optical transmission system.

Abstract: A fiber optical system (10) for transmitting an optical signal comprises an optical fiber line (1) with a plurality of successively arranged polarization scramblers (6a to 6c) for polarization modulation of the optical signal transmitted through the optical fiber line (1) and a reference frequency signal (11) which synchronizes scrambling frequencies of all of the polarization scramblers (6a to 6c) to a common reference frequency.

Abstract: A receiver (10) for an optical signal containing a time jitter and a time-varying distortion caused by a periodic polarization scrambled signal comprises at least one decision gate (11) and a clock recovery module (13) providing a clock signal (C) recovered from the optical signal to the at least one decision gate (11). The receiver (10) further comprises a scrambling frequency generator (16) synchronized to the scrambling frequency and phase of the polarization scrambled signal, a jitter function generator (17) generating a clock phase control signal (??b) reproducing the time jitter, and at least one clock phase modulator (14) modulating the phase of the clock signal (C) according to the clock phase control signal (??b).

Abstract: A method for estimating at least one optical link parameter using a Viterbi equalizer (1) generating averaged values (M) of signal amplitudes of a distorted optical signal transmitted through an optical link (2) for a set of decided bit patterns (a, b, c, d, . . . ), the method comprising the following steps: forming a first parameter set (S) characteristic of a distorted signal sequence using the averaged values (M(a), M(b), M(d), M(g)) for a given sequence (abdg) of bit patterns (a, b, c, d, . . . ), comparing the first parameter set (S) to a plurality of reference parameter sets (R1, R2, . . . ) characteristic for reference signal sequences of the same sequence (abdg) of bit patterns (a, b, c, d, . . . ), each of the reference parameter sets (R1, R2, . . .

Abstract: A polarization mode dispersion (PMD) controller device for controlling the state of polarization of an optical light wave comprising a dispersion compensation unit (2; 25; 40) and an adaptation control unit (6; 28; 44), wherein the dispersion compensation unit (2; 25; 40) comprises a multitude of compensation stages processing the optical light wave, and wherein the adaptation control unit (6; 28; 44) controls the dispersion compensation unit (2; 25; 40) is characterized in that at least one feed-forward signal tap (4; 26a-26c, 73a-73c) is provided tapping the optical light wave inserted into one of the compensation stages, that the feed-forward signal(s) is(are) fed into a distortion analyzer unit (5; 27; 66) and that the distortion analyzer unit (5; 27; 66) provides the adaptation control unit (6; 28; 44) with information about the incoming optical light wave. It accelerates the adaptation speed and lowers the costs of a high-speed PMD controller device.

Abstract: The present invention concerns a method for performing optical dispersion compensation of wavelength division multiplexed (WDM) optical signals. The method comprises the steps of providing a compensation stage with an optical transmission medium to be used as parallel operating cascade of polarization controllers and optical birefringent elements to compensate dispersion of the WDM optical signals when being transmitted spectrally dispersed into the different wavelength channels in parallel through the parallel cascades. The method is being characterized by determining the chromatic dispersion of the optical signals at one or few different wavelength channels possibly allowing an extrapolation of the chromatic dispersion to the other wavelength channels for defining accordingly an additional feedback signal to be used for the polarization controller setting.

Abstract: A clock recovery circuit (1a) for a digital signal (DS) comprising a clock signal and a high-frequency jitter component due to polarisation scrambling in the optical domain.

Abstract: An optical time multiplexer for generating an N Gbits/s output signal (36) from n data modulated input pulse streams (21, 22) with a pulse frequency of N/n GHz, where n?IN and n?2, with a combiner device for passively interleaving the n input pulse streams (21, 22) is characterized by at least n?1 first phase shifting elements (25) tuning the optical phases of at least n?1 input pulse streams (22) and being connected to a controller device (32), which derives at least n?1 control signals from a comparison of the optical phases of the n input pulse streams (21, 22) and controls the at least n?1 first phase shifting elements (25) such that the optical phases of all n input pulse streams (21, 22) are locked with respect to each other. This optical time multuplexer reduces the drifting penalty of ODTM signals due to multiplexer instability, it prohibits the broadening of RZ pulses, and it grants the possibility to easily generate carrier-suppressed RZ signals or similar modulation formats.

Abstract: A receiver (1?) for a polarization scrambled optical signal comprising an adaptive equalizer (3?) and a feedback signal generating means (12) for generating a feedback signal serving to adjust the equalizer (3?) characterized by a filtering means (11) for filtering the feedback signal by selecting minimum or maximum values of the feedback signal at the scrambling frequency or a beat frequency of different scrambling frequencies of the optical signal, a fiber optical system comprising an optical fiber line (14) with at least one polarization scrambler (17) for polarization modulation of the optical signal transmitted through the optical fiber line (14) having such a receiver (1?), and a method for performing adaptive equalization therewith.

Abstract: A method for operating a switched optical network, in particular an automatically switched optical network (=ASON), wherein the method allocates a transparent physical path out of a multitude of candidate paths to an optical data signal, is characterized in that the method takes into account the polarisation mode dispersion (=PMD) on each candidate path, wherein the PMD of the candidate paths is determined for each wavelength channel individually, taking into account the wavelength (?) dependence of the PMD. The method allows the operation of the ASON with high reliability of the data transmission and increased data transfer capacity and the exploitation of the network resources.

Abstract: A method for estimating at least one optical link parameter using a Viterbi equalizer (1) generating averaged values (M) of signal amplitudes of a distorted optical signal transmitted through an optical link (2) for a set of decided bit patterns (a, b, c, d, . . . ), the method comprising the following steps: forming a first parameter set (S) characteristic of a distorted signal sequence using the averaged values (M(a), M(b), M(d), M(g)) for a given sequence (abdg) of bit patterns (a, b, c, d, . . . ), comparing the first parameter set (S) to a plurality of reference parameter sets (R1, R2, . . . ) characteristic for reference signal sequences of the same sequence (abdg) of bit patterns (a, b, c, d, . . . ), each of the reference parameter sets (R1, R2, . . .

Abstract: A fiber optical system (10) for transmitting an optical signal comprises an optical fiber line (1) with a plurality of successively arranged polarization scramblers (6a to 6c) for polarization modulation of the optical signal transmitted through the optical fiber line (1) and a reference frequency signal (11) which synchronizes scrambling frequencies of all of the polarization scramblers (6a to 6c) to a common reference frequency.

Abstract: A receiver (10) for an optical signal containing a time jitter and a time-varying distortion caused by a periodic polarization scrambled signal comprises at least one decision gate (11) and a clock recovery module (13) providing a clock signal (C) recovered from the optical signal to the at least one decision gate (11). The receiver (10) further comprises a scrambling frequency generator (16) synchronized to the scrambling frequency and phase of the polarization scrambled signal, a jitter function generator (17) generating a clock phase control signal (??b) reproducing the time jitter, and at least one clock phase modulator (14) modulating the phase of the clock signal (C) according to the clock phase control signal (??b).

Abstract: A device for receiving a distorted signal, in particular an optical signal converted by an opto/electrical converter, comprises an analog/digital converter (1) with adjustable thresholds and a Viterbi equalizer (10). The device further comprises a histogram estimator (13) for determining a probability density function of the distorted signal and a threshold estimator (4) for dynamically adjusting at least one threshold of the analog/digital converter (1) in an overlap region of a first signal amplitude attributed to a first symbol (?10, X10) and a second signal amplitude attributed to a second symbol (?11, X11) of the probability density function.

Abstract: A device (1) for receiving a distorted signal, in particular an optical signal converted by an opto/electrical converter (2), comprises an electrical low-pass filter (3), an analog/digital converter (4), and a Viterbi equalizer (5). The bandwidth of the electrical low-pass filter (3) and the sampling rate of the device (1) are set such that a noise sample at an actual sampling time is correlated to one or more noise samples at one or more adjacent sampling times and the Viterbi equalizer (5) comprises a means (5a) for mitigating inter-symbol interference by taking into account correlation of the different noise samples at the actual sampling time and one or more adjacent sampling times.

Abstract: A process is proposed for recovering disturbed digital signals, wherein the electrical signals pass through a feedback equalizer and an analogue control of the setting parameters of the equalizers is performed. A pseudo-error monitor, which facilitates a high-speed adjustment of decision element thresholds, is also provided.

Abstract: The present invention concerns a method for performing optical dispersion compensation of wavelength division multiplexed (WDM) optical signals. The method comprises the steps of providing a compensation stage with an optical transmission medium to be used as parallel operating cascade of polarization controllers and optical birefringent elements to compensate dispersion of the WDM optical signals when being transmitted spectrally dispersed into the different wavelength channels in parallel through the parallel cascades. The method is being characterized by determining the chromatic dispersion of the optical signals at one or few different wavelength channels possibly allowing an extrapolation of the chromatic dispersion to the other wavelength channels for defining accordingly an additional feedback signal to be used for the polarization controller setting.