A skew adjustment method and a digital coherent receiver which can achieve skew adjustment without using a fixed pattern for skew detection are provided. A digital coherent receiver (100) includes: a chromatic dispersion adder (103) that adds chromatic dispersion to the optical multiplexed signal; a skew adjuster (201) that sets a quantity of skew adjustment for each of the plurality of channel signals obtained by detecting the optical multiplexed signal; and a skew controller (204) that is configured to, while monitoring signal quality of a reception signal obtained from the plurality of channel signals skew-adjusted, search for a quantity of skew adjustment at which the signal quality is made better.

The present disclosure provides signal management with unequal eye spacing by: sending, from a local transmitter, first and second signals with different first and second known eye patterns to a remote receiver over a channel; sending temperature data of the local transmitter and operating wavelength data of the first and second signals to the remote receiver over the channel; receiving, from the remote receiver, tuning parameters based on a dispersion of the channel based on a first difference between the first known eye pattern as transmitted and as received and a second difference between the second known eye pattern as transmitted and as received; and adjusting transmission rail values used to encode data for transmission over the channel by the local transmitter based on the tuning parameters to produce a conditioned signal for transmission with an unequally spaced eye pattern.

A method and apparatus for determining in-band OSNR in optical information signals, e.g. in polarization-multiplexed QPSK and higher-order M-ary QAM signals, are disclosed. A correlation measurement of the signal amplitude or power at two distinct optical frequencies of the signal may be used to determine the in-band optical noise in the signal. A measurement of the signal power may be used to determine the OSNR based on the determined in-band noise.

A transmission device includes a memory, and a processor coupled to the memory and configured to acquire a polarization mode dispersion value of each of wavelengths of a polarization-multiplexed optical signal having a wavelength, multiply a mean value of the polarization mode dispersion values of the wavelengths by a prescribed ratio, to thereby calculate a maximum value of the polarization mode dispersion value that is temporally varied, and select a multi-level modulation scheme of the polarization-multiplexed optical signal based on an index value of transmission quality of the polarization-multiplexed optical signal depending on the maximum value.

A method for compensating the distortions introduced by impairments of MZMz implementing an optical transmitter, according to which the level of total amplitude and phase distortions caused by the optical transmitter is measured and all impairments in the constellation domain are compensated by pre-distorting the input signal to be transmitted by symmetrically adding imbalance to the voltage applied to the MZM arms. The imbalance is determined by introducing a phase rotation in either I or in the Q path of the optical transmitter, which compensates the total amplitude distortion, and also introducing a phase rotation to both I and Q paths of the optical transmitter, which compensate the total phase distortion and the phase shift caused by compensating the amplitude distortion, until reaching a desired operating point, which corresponds to the level of pre-distortion.

A skew compensation system for a coherent optical communication network includes a transmitter modulator having a first driver input for receiving a first signal from a first channel, a second driver input for receiving a second signal from a second channel, a source input for receiving a continuous wave source signal, and a modulation output in communication with an optical transport medium of the network. The system further includes a tunable delay line disposed between the second channel and the second driver input for inserting a pre-determined training sequence onto the second signal prior to the second driver input, and a processor for determining a skew amount between the second signal at the second driver input and the first signal at the first driver input, calculating a pre-compensation value corresponding to the skew amount, and reducing the skew amount at the modulation output according to the pre-compensation value.

Systems and methods for optical fiber characterization using a nonlinear measurement of shaped Amplified Spontaneous Emission (ASE) transmitted over the optical fiber are provided. A method includes receiving an ASE signal on an optical fiber, wherein the ASE signal is transmitted from an ASE source connected to the optical fiber and the ASE signal includes a spectral shape at an input of the optical fiber; measuring a broadened spectral shape of the received ASE signal where the broadened spectral shape is different from the spectral shape at the input and broadened due to propagation of the ASE signal over the optical fiber; and determining one or more parameters of the optical fiber based on the broadened spectral shape of the received ASE signal.

A band division timing adjustment unit (10) aligns timings of a plurality of signals, which are generated by dividing a received signal according to a plurality of frequency bands, in a time domain and combines the plurality of signals for which the timings have been aligned. A chromatic dispersion compensation unit (17) compensates chromatic dispersion of an output signal of the band division timing adjustment unit (10) for each of the plurality of frequency bands.

Generation of data streams for two dimensions comprises compensation for a nonideal response of a signal path in an optical communications signal. The data streams are converted to analog electrical signals which drive two dimensions of an electrical-to-optical converter. Output of the electrical-to-optical converter is coupled through an optical link to an optical-to-electrical converter.

A skew adjustment method and a digital coherent receiver which can achieve skew adjustment without using a fixed pattern for skew detection are provided. A digital coherent receiver (100) includes: a chromatic dispersion adder (103) that adds chromatic dispersion to the optical multiplexed signal; a skew adjuster (201) that sets a quantity of skew adjustment for each of the plurality of channel signals obtained by detecting the optical multiplexed signal; and a skew controller (204) that is configured to, while monitoring signal quality of a reception signal obtained from the plurality of channel signals skew-adjusted, search for a quantity of skew adjustment at which the signal quality is made better.