Patent ID: 8743984

Claim:
A method for optical communications, the method comprising a. using a 2(M+2)-dimensional signal-space for single-mode fiber applications, with two phase coordinates (I and Q) and M pulse-position like coordinates per single polarization; and b. alternatively using a D=2(2+M)N-dimensional space for few-mode fiber (FMF)/multimode fiber (MMF) applications, where the factor 2 originates from two polarizations, and N represents the number of orbital angular momentum (OAM)states used in FMF/MMF applications, wherein spectral efficiency improvement to pulse position modulation (PPM) can be expressed as S E , D - dim . S E , PPM = log 2 ⁢ L D / ( M / T s ) log 2 ⁢ M PPM / ( M PPM ⁢ / T s ) = D ⁢ ⁢ log 2 ⁢ L / M log 2 ⁢ M PPM ⁢ / M PPM , Where S E,D-dim is spectral efficiency for the D-dimensional space, S E,PPM is spectral efficiency for the PPM, L is the number of amplitude levels per dimension, M PPM is the number of pulse-position like coordinates per polarization, and T s is a symbol duration, and wherein M and N are integers, M≧1, and N≧1.