COMPLEX MODULATION COMES TO OPTICAL FIBER.

The article deals complex modulation schemes necessary for managing long-distance transmissions of data. An illustration on how a 100 gigabyte per second (Gbps) transmitter divides a laser into two polarizations and modulates four 25-Gbps data streams onto a single fiber at a single wavelength is presented. It explains how noise and nonlinear phase distortion affects Quadrature-phase-shift-keying (QPSK) signals more than nonreturn-to-zero (NRZ) signals. INSET: WHAT'S IN A G?.