An heterodyne apparatus and method for measuring performance parameters of a coherent optical receiver at RF frequencies is disclosed. Two coherent lights are launched into signal and LO ports of the receiver with an optical frequency offset f. One of the lights is modulated in amplitude at a test modulation frequency F. COR performance parameters are determined by comparing two frequency components of the COR output. CMRR is determined based on a strength of a direct detection spectral line at the modulation frequency relative to that of spectrally-shifted lines at (Ff). GDV information is obtained by modulating one of the lights at two phase-locked frequencies, such as F and 2F, and comparing phases of two time-domain traces corresponding to frequency components of the COR output signal at the two frequencies.

A frequency characteristic adjustment circuit is disclosed. The frequency characteristic adjustment circuit is disposed between an optical circuit element and a drive circuit for driving the optical circuit element. A capacitor is connected to an output of the drive circuit. A current supply circuit is controlled by a voltage generated by the drive circuit. The current supply circuit supplies a different current value depending on a voltage received from the drive circuit to the optical circuit element.

A signal processing device includes: a filter configured to perform an adaptive equalization process of a signal, on a basis of a filter coefficient; an updater configured to update the filter coefficient, on a basis of amplitude of the signal and a target value of the amplitude; and a corrector configured to correct the target value, on a basis of the amplitude of the signal.

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.

A transmitting apparatus includes an optical modulator configured to modulate input light from a light source into a light signal including a carrier signal and a sideband signal based on a radio frequency (RF) signal, having polarization characteristics crossing each other, an optical power splitter configured to split the light signal into a plurality of light signals, a plurality of light phase shifters configured to respectively shift phases of the plurality of light signals, a plurality of polarization controllers configured to perform control so that a carrier signal and a sideband signal included in each of the phase-shifted plurality of light signals have the same polarization characteristic, and a plurality of photodetectors configured to convert the plurality of light signals, having polarization characteristics controlled by the plurality of polarization controllers, into a plurality of electrical signals and to transfer the electrical signals to a plurality of antenna elements.

A method includes distributing payload data among a master sub-band and a plurality of slave sub-bands. The master sub-band and the plurality of slave sub-bands collectively extend over an allocated frequency spectrum; the master sub-band and the plurality of slave sub-bands are associated with different carrier frequencies; and the master sub-band has a center frequency that corresponds to a center frequency of the allocated frequency spectrum. The method includes generating modulated data for the master sub-band and the plurality of slave sub-bands based on the distributed payload data; and transmitting an optical signal to an optical medium representing the modulated data.

The present invention relates to communication systems, devices, and methods for providing for a wide bandwidth optical receiver including amplification through optical beating from a local oscillator laser operating without a phase-locked loop at frequency near the receiver optical signal and decreasing the system-performances dependence on optical polarization alignment between the signal and the local oscillator. Systems, devices, and methods including a local oscillator providing a local oscillator signal having a local oscillator frequency that may be controlled based on a frequency offset from the signal center frequency through the use of monitoring signals representative of the frequency offset. A combiner/splitter couples the optical data signal with light from the local oscillator to provide first and second coupled optical signals with orthogonal polarization. Two opto-electrical converters for converting first and second coupled signals into first and second electrical signals. The first and second electrical signals are individually rectified and then combined to provide the electrical data signal. The opto-electronic converters and rectifiers may have a bandwidth substantially similar the wavelength channel bandwidth to enable the optical receiver to receive optical signal with different center frequencies within the wavelength channel.

An optical transmitter, an optical receiver, and an optical transmission method are disclosed. The optical transmitter includes an optical signal generator, N spreaders, N pairs of data modulators, and a combiner, where the optical signal generator generates N optical carriers; an i.sup.th spreader spreads an i.sup.th optical carrier, to obtain a spread optical signal having two subcarriers; splits the spread optical signal into a first optical signal and a second optical signal; and delays the second optical signal to obtain a third optical signal; an i.sup.th pair of data modulators modulate the first optical signal and the third optical signal to obtain a pair of modulated optical signals, transmit the pair of modulated optical signals to the combiner, where the pair of modulated optical signals reaching the combiner differ by 1/(4 fsi) in time domain; and the combiner combines, into one optical signal, N pairs of modulated optical signals.

A method and apparatus for estimating a burst error. A burst error estimation method includes measuring a frequency of a spectrum null for an optical signal received through an optical receiver; determining whether the measured frequency of the spectrum null corresponds to an intermediate frequency of a baud rate; and estimating that a burst error occurrence condition is met when the frequency of the spectrum null is determined to correspond to the intermediate frequency of the baud rate.

Embodiments herein disclose receiver of coherent optical communication link and method of compensating carrier phase offset in receiver. 90 optical hybrid is configured to receive input of reference optical carrier (LO) signal and modulated optical signal (S) and carrier phase offset detection block is configured to generate output signal representing average of the phase offset at the input of the carrier phase offset detection block. Electronic control unit configured to receive output signals from the carrier phase offset detection block for generating control signals and tunable phase delay block configured to receive the control signals from the electronic control unit. 90 optical hybrid, carrier phase offset detection block, electronic control unit and the tunable phase delay block are configured in feedback loop, such that outputs of the carrier phase offset detection block are used for tuning the phase delay of the tunable phase delay block to achieve carrier phase synchronization.