Optical communication system employing a multidimensional constellation with an increased minimum distance

An apparatus, comprising a coherent optical data receiver including:

• an optical hybrid configured to mix an optical data signal and an optical local-oscillator signal to generate a respective plurality of mixed optical signals for each of first and second mutually orthogonal polarizations of the optical data signal;
• a plurality of photodetectors connected to the optical hybrid to convert the mixed optical signals into separate streams of measurements of in-phase and quadrature components of each of said first and second mutually orthogonal polarizations;
• and
• a digital signal processor configured to process said separate streams to recover data modulated onto the optical data signal in which a multidimensional modulation symbol spans three or more consecutive modulation time slots, different ones of said consecutive modulation time slots having different parts of the multidimensional modulation symbol;
• wherein the digital signal processor is further configured to identify a multidimensional constellation symbol corresponding to the multidimensional modulation symbol by comparing the measurements in said consecutive modulation time slots and corresponding sets of values of a constellation;
• wherein paired in-phase and quadrature coordinates of each of first and second parts of each multidimensional constellation symbol of the constellation have values corresponding to first and second circles in a corresponding complex plane;
• and
• wherein at least some sets of the paired in-phase and quadrature coordinates determined based on the multidimensional modulation symbol in said consecutive modulation time slots are different.

An apparatus, comprising an optical data transmitter including:

• a plurality of in-phase and quadrature-phase (IQ) optical modulators;
• and
• an electronic controller configured to operate the IQ optical modulators to optically output a sequence of multidimensional constellation symbols to an end of an optical fiber such that, near the end, each of the multidimensional constellation symbols has separate parts thereof primarily carried by different respective guided modes of the optical fiber, said separate parts forming two or more respective optical signal streams in the optical fiber;
• wherein the electronic controller is configured to cause the two or more optical signal streams to be different in at least some modulation time slots;
• and
• wherein each of the multidimensional constellation symbols spans three or more consecutive modulation time slots.

An apparatus, comprising a coherent optical data receiver including:

• an optical front-end configured to output a plurality of parallel sequences of measurements of different phase and polarization components of two or more optical signal streams each received primarily from a corresponding guided mode of an optical fiber end-coupled to the coherent optical data-receiver;
• and
• a digital signal processor configured to determine, from the measurements, a stream of multidimensional constellation symbols having separate parts thereof in the two or more of the optical signal streams;
• wherein each of the two or more of the optical signal streams corresponds to a different independent linear combination of the separate parts;
• and
• wherein each of the multidimensional constellation symbols spans three or more consecutive modulation time slots.