There is provided a method of determining at least one linear-crosstalk-related parameter of an optical signal-under-test having, within an optical channel bandwidth, at least a data-carrying signal contribution and a wavelength-dependent linear-crosstalk contribution arising from a data-carrying signal contribution of an adjacent optical signal associated with an adjacent channel to the optical signal-under-test, the method comprising: acquiring at least one optical spectrum trace encompassing a quasi-continuum of closely-spaced wavelengths over a spectral range extending to at least part of both the signal under test and the adjacent optical signal; and estimating said linear-crosstalk contribution using at least spectral properties of said at least one optical spectrum trace; wherein one of said at least one linear-crosstalk-related parameter is the linear-crosstalk contribution and is determined from said estimating.

A first transceiver and a method performed by the first transceiver for monitoring a fibre cable. The first transceiver is connectable to a second transceiver by the fibre cable. The transceivers employ SCM analogue modulation where baseband is dedicated for monitoring and the subcarriers are dedicated for data transmission. The method comprises receiving, from a device, at least one electromagnetic data signal to be transmitted towards the second transceiver on the fibre cable, and shifting the at least one data signal in the frequency domain. The method further comprises generating an electromagnetic test signal in a base band, combining the at least one data signal and the generated test signal, and modulating the combined data signal and test signal to respective optical carrier. The method further comprises transmitting the modulated data signal and generated test signal on the fibre cable towards the second transceiver.

A method of controlling a multiple sub-carrier optical channel of an optical communications system. The multiple sub-carrier optical channel includes at least two sub-carriers modulated with respective sub-channel data streams within a spectral range allocated to a single optical channel of the optical communications system. A transmitter modem of the optical communications system applies a respective dither signal to each sub-carrier. A receiver modem of the optical communications system detects a respective quality metric of each sub-carrier. A respective optimum power level of each sub-carrier is estimated based on the applied dither signals and the detected quality metrics. A respective power level of each sub-carrier is then adjusted in accordance with the estimated respective optimum power level of each sub-carrier.

A method and system for measuring chromatic dispersion, experienced by ASK/PSK modulated optical signals, are provided. Dispersion measurement is enabled either by encoding an additional overhead at lower baud rate or by monitoring signal SOP or RF spectrum of signal SOP. The bulk chromatic dispersion of the link is measured by analyzing the dispersion broadening of the overhead constellation or signal temporal diagram, or time-overlapped signal diagram, or overhead spectrum. This information is used to reduce the computation time required for electronic recovery of a highly dispersed signal.

An imaging receiver comprising an antenna array to receive RF signals from at least one RF source, a plurality of electro-optic modulators to modulate an optical carrier with a received RF signal to generate modulated optical signals, a first and second set of optical fibers configured to transmit the modulated optical signals into an interference region to cause interference among the modulated optical signals to generate optical signal interference; a lens to perform a Fourier transform of the optical signal interference to spatial positions on an image plane, a photodetector array to record the optical signal interference on the image plane, and a processor to computationally reconstruct the at least one RF source in k-space from the recorded optical signal interference. The optical fibers included in the first set of optical fibers have varying lengths, and the optical fibers included in the second set of optical have the same length.