An optical transmission system includes: a transmission unit configured to co-propagate a signal light in which data is modulated and an idler light having complex amplitude that is phase conjugate with the signal light via an optical transmission medium; at least one optical amplifier configured to perform a phase sensitive amplification operation through an action among the signal light, the idler light, and an excitation light in a nonlinear medium; and a reception unit configured to receive the signal light that has been amplified by the optical amplifier, coherently detect the signal light and the idler light individually, and conduct a diversity synthesis to demodulate the data.

A coherent optical data receiver having a digital signal processor (DSP) capable of mitigating equalization-enhanced phase noise (EEPN). In an example embodiment, the DSP mitigates EEPN by applying individual phase adjustments to different spectral slices of a digital stream carrying CD-compensated digital samples of the received optical data signal. In different embodiments, the individual phase adjustments can be dynamically selected based on symbol decisions taken prior to EEPN mitigation, based on transmitted pilot symbols, and/or using moving averages computed for different spectral slices. Some embodiments are suitable for handling polarization-division-multiplexed optical data signals. Some embodiments are advantageously capable of producing an effective SNR gain of approximately 1 dB.

A system for laser phase noise compensation for a fibered communication path, the system being configured for connection with a node of the fibered communication path, including at least one signal splitter optically coupled to a laser source of the fibered communication path, the at least one signal splitter having two output communication path, the communication paths having a path difference therebetween; an integrated coherent receiver (ICR) optically coupled to the first output communication path and the second output communication path; and a digital signal processor (DSP) communicatively connected to the ICR, the ICR being configured to determine, based signals received from the first and second output communication paths, at least one phase noise indication related to phase noise of the laser source, the DSP being configured to determine an estimated laser phase noise based on at least the at least one phase noise indication.

A plurality of digital processors may be used to adjust phases in a plurality of phase modulators. The plurality of digital processors may receive a periodic pulse, or heartbeat signal, from a synchronization controller in order to control the digital processors. The synchronization controller may output an additional signal used to determine and to control the phase of the signals output from the plurality of phase modulators.

When a frequency deviation compensation amount is compensated for by use of frequency shift, a phase offset occurs between adjacent input blocks included in a plurality of input blocks as divided, with the result that an error occurs in a reconstructed bit sequence. A frequency deviation compensation system of the invention is characterized by comprising: a frequency deviation compensation means for compensating for a frequency deviation occurring in a signal by use of frequency shift; and a phase offset compensation means for compensating for a phase offset occurring, in the signal, due to the frequency shift.

An apparatus includes an optical source of an optical wavelength carrier, an optical modulator to receive the optical wavelength carrier, and an optical data receiver. The optical data modulator is configured to produce, from the optical wavelength carrier, an optical signal to carry separate data on different first and second components thereof in individual modulation periods during data transmission and to carry a training sequence on one of the components during time slots for calibration. The first component is relatively phase offset from the second component in the optical signal. The optical data modulator alternates the one of the components between the first and second components over the time slots for calibration. The optical receiver is connected to receive a portion of the optical signal and to temporally interleave a measurement of a characteristic of the first component and a measurement of a characteristic of the second component over the time slots for calibration. The optical receiver is configured to feedback information to the optical data modulator based on the measured characteristics. The optical data modulator is configured to reduce an imbalance between the two components of the optical carrier during data transmission based on the information.

The invention presents an equalizing device, a corresponding method and an optical signal with a frame structure for enabling the method. The equalizing device includes a first 2×2 MIMO equalizer configured to perform a first equalization on the digital signal, supported by a 2×2 MIMO channel estimation of the channel based on the digital signal. Further, the device includes a second 2×2 MIMO equalizer, arranged after the first equalizer and configured to perform a second equalization on the digital signal, supported by a State of Polarization (SOP) estimation of the optical signal based on the digital signal.

A receiver system is provided for receiving a coherent Pulse Amplitude Modulation (PAM) encoded signal. The receiver system may include an optical polarization component configured to modulate a polarization of the received coherent PAM encoded signal. The receiver system may further include a digital signal processor (DSP) configured to perform polarization recovery between the received coherent PAM encoded signal and the LO signal using a first control loop, and to perform phase recovery between the received coherent PAM encoded signal and the LO signal using a second control loop.

An optical coherent transceiver includes a transmitter and a receiver that share laser light. The transmitter includes a pair of parent MZIs in a modulator, which are parent MZIs configured to perform quadrature modulation on the laser light according to a bias voltage, and two pairs of child MZIs in the modulator, which are child MZIs configured to perform phase modulation on the laser light according to the bias voltage. The transmitter includes a control circuit configured to control the bias voltage to be applied to the parent MZIs and the child MZIs. The control circuit is configured to, when turning light output of the transmitter off, with input of a data signal being set off, control the bias voltage such that a phase difference between the parent MZIs is around 90 degrees and a phase difference between the child MZIs in each of the pairs is 180 degrees.

Methods, systems, and apparatus, including computer programs encoded on computer storage media, for performing asymmetric pulse-shaping filtering. In some implementations, a receiver comprises a detector circuit operable to receive optical signal data from an optical link. The receiver comprises a filter circuit, coupled to the detector circuit, operable to (i) filter the optical signal data according to an asymmetric filtering scheme and (ii) output the filtered optical signal data, wherein the asymmetric filtering scheme comprises utilizing a shaping filter with first criteria, the first criteria including one or more values greater than one or more values of second criteria utilized by a shaping filter at a transmitter, the transmitter communicating with the receiver.