Tetrahedral Coding and Non-Unitary Resilience in Polarization-Multiplexed Lightwave Transmissions

This paper deals with polarization-multiplexed optical transmissions. It addresses the challenge of designing optimal yet practical modulation codes for the 2×2 MIMO fiber channel. This specific use case diverges from classical MIMO models encountered, e.g., in the wireless literature as, here, non-ergodicity and low-complexity are key. While rather simple from a fundamental viewpoint, the proposed modulation schemes appears to be optimal and geometrically pleasing as the second minimum distance turns out to be the object of interest and the associated vectors encode the basis of a regular tetrahedron in the affine space. From an operational viewpoint, these new schemes for single channel use form polarization codes that achieve unit dB gains while exhibiting low implementation complexity.