Abstract: The present document relates to an optical communication system. In particular, the present document relates to the alignment of the laser frequency at a transmitter of the optical communication system and the local oscillator frequency at a coherent receiver of the optical communication system. A coherent optical receiver (222) is described. The receiver (222) comprises a reception unit adapted to convert a received optical signal at a carrier frequency into a digital signal using a local oscillator, referred to as LO, having an LO frequency; a spectral analysis unit adapted to estimate a degree of asymmetry of a spectrum of the received optical signal, based on the digital signal; and a transmission unit adapted to transmit an indication of the degree of asymmetry to a near-end transponder (210) comprising a transmitter (211) of the received optical signal.

Abstract: An optical receiver (20) for multimode communications comprises: a mode demultiplexer (21) having an input connected to a multimode link (22) and a plurality of output lines (231-234), wherein the mode demultiplexer is adapted to couple each of the modal components of the optical signal substantially into a selected one of the output lines, a plurality of coherent optical detectors (251-254) respectively connected to the output lines to produce a set of electrical digital signals each comprising an in-phase component and a quadrature-phase component, a plurality of independently adjustable optical delay devices (241-244) arranged on the output lines to impart a selected delay to each of the corresponding modal components, and a signal processing device (26) adapted to process the digital signals to recover the independent modulations of the respective modal components by inverting a mode-mixing characteristic of the multimode link.

Abstract: A modulator with polarization marking comprising two input ports for receiving two optical signals at one wavelength, and exhibiting essentially perpendicular optical polarization states, capable of phase-modulating those signals with data signals and of combining them with polarization, characterized in that it comprises a source of phase overmodulation for overmodulating the phase of one of said two optical signals, said phase overmodulation exhibiting a modulation frequency substantially lower than the modulation frequency of said data signals. A method and a coherent receiver are also disclosed.

Abstract: The present invention refers to a method for operating a coherent optical packet receiver comprising at least one linear physical impairment compensation filter wherein the settings of at least one linear physical impairment compensation filter applied on a received optical packet having at least one given travelling parameter are determined in function of previous settings determination of said at least one linear physical impairment compensation filter achieved on at least one optical packet having a similar at least one travelling parameter as said received optical packet.