A transmitter can include a laser operable to output an optical signal; a digital signal processor operable to receive data and provide a plurality of electrical signals based on the data; and a modulator operable to modulate the optical signal to provide a plurality of optical subcarriers based on the plurality of electrical signals. One of the plurality of subcarriers carries first information indicative of a first portion of the data in a first time slot and second information indicative of a second portion of the data in a second time slot. The first information is associated with a first node remote from the transmitter and the second information is associated with a second node remote from the transmitter. A receiver as well as a system also are described.

Disclosed are a chromatic dispersion estimation method and device in optical coherent communication, wherein, the method includes: performing a fast Fourier transform on IQ-imbalance compensated data to obtain frequency-domain data in two polarization directions; calculating autocorrelation sequences of the frequency-domain data and performing an inverse fast Fourier transform on the values of the autocorrelation sequences; calculating modulus squares of the results of the inverse fast Fourier transform, and adding the results in the two polarization directions to obtain; determining a mean value of s of a plurality of data sets; calculating an index of the maximum value of, and estimating a dispersion value of the optical fiber link according to the index of the maximum value of. The abovementioned technical solution allows a significantly accurate and rapid estimation of dispersion values.

In a receiver of Quadrature Amplitude Modulation (QAM) signal, the received QAM signal is divided into multiple Quadrature Phase Shift Keying (QPSK) symbol streams. A Maximum Likelihood Symbol Estimation (MLSE) is performed on each QPSK symbol stream to recover information bits in the received QAM signal. In one advantageous aspect, complexity of implementation can be reduced by performing MLSE on QPSK signals instead of QAM signals.

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.

A frame synchronization apparatus (10) according to this invention includes a multiplication unit (11) configured to multiply a received signal by an inverse complex number of a predetermined synchronization pattern with respect to a predetermined signal point on a complex space diagram for each of a plurality of symbols of the received signal, an addition average unit (12) configured to perform addition averaging of outputs from the multiplication unit for the plurality of symbols of the received signal, and a synchronization determination unit (13) configured to perform coincidence determination of whether an output from the addition average unit (12) falls within a predetermined coincidence determination range of the predetermined signal point, and determine a synchronization state of the frame synchronization based on a result of the coincidence determination. According to this invention, it is possible to provide a frame synchronization apparatus that correctly determines a synchronization state even if an error rate of received symbols is high.

Disclosed are the method and system to derive the wavelength/frequency information covering wide wavelength or frequency range. Its practical applications include both fixed wavelength optical signal and wide bandwidth tunable or non-tunable optical signal, where the wavelength/frequency information is necessary for optical signal calibration, control, and monitoring, optical communications, and data processing. The approach has a “self-compensation” feature which is preferred to improve the accuracy of the extracted wavelength or frequency information even though there are components in the system having strong wavelength or frequency dependence in the wide wavelength or frequency range. The method is generic which can be realized in free space, fiber, or photonic integrated circuit (PIC).

To provide an optical 90-degree hybrid formed of a silicon waveguide capable of suppressing an optical loss and a phase error, and facilitating electronic packaging and optical packaging. In the optical 90-degree hybrid circuit including two optical branching units facing each other and two optical coupling units facing away from each other, four arm waveguides are arranged including bent waveguides each of which guides an output light of the optical branching unit to the optical coupling unit, and is formed in a curved shape.

An optical modulator includes first and second waveguides; a first phase shifter provided in at least one of the first and second waveguides and configured to control a phase of the laser beam; a first optical element configured to combine the laser beam propagating through the first waveguide and the laser beam propagating through the second waveguide and separate the combined laser beam into two laser beams; a third (fourth) waveguide on which one (the other) of the laser beams separated by the first optical element is incident; a second phase shifter provided in at least one of the third and fourth waveguides and configured to control a phase of the laser beam; and a second optical element configured to combine the laser beam propagating through the third waveguide and the laser beam propagating through the fourth waveguide and emit the laser beam in the superposition state.

Amplitude-modulated (AM) signals spanning a spatial wide area can be efficiently detected using a slowly scanning optical system. The system decouples the AM carrier from the AM signal bandwidth (or carrier uncertainty), enabling Nyquist sampling of only the information-bearing AM signal (or the known frequency bandwidth). The system includes a staring sensor with N pixels (e.g., N>10.sup.6) that searches for a sinusoidal frequency of unknown phase and frequency, perhaps constrained to a particular band by a priori information about the signal. Counters in the sensor pixels mix the detected signals with local oscillators to down-convert the signal of interest, e.g., to a baseband frequency. The counters store the down-converted signal for read out at a rate lower than the Nyquist rate of AM signal. The counts can be shifted among pixels synchronously with the optical line-of-sight for scanning operation.

A transmission/reception device is configured to convert an optical signal based on a plurality of first optical signals having frequency bands different from each other into an electric signal and output the electric signal as a plurality of first electric signals; receive the plurality of first electric signals, change frequency bands of some or all of a plurality of second electric signals to narrow an interval between frequency bands of two second electric signals having frequency bands adjacent to each other, and output, as third electric signals, electric signals; to receive a plurality of the third electric signals, combine and output the plurality of third electric signals as a fourth electric signal; and receive the fourth electric signal, convert the fourth electric signal into an optical signal, and output the optical signal as a second optical signal.