Real-Time Demonstration of Augmented-Spectral-Efficiency DMT Transmitter Using a Single IFFT

Increasing the power and spectral efficiency in intensity-modulated direct-detection short-haul fiber-optic links enables higher data rates in power- and bandwidth-limited optical communication systems. Augmented spectral efficiency discrete multi-tone (ASE-DMT) can improve the spectral efficiency of pulse-amplitude-modulated DMT while maintaining its power advantage over dc-biased DMT, whose transmitter requires only one inverse fast Fourier transform (IFFT) with Hermitian symmetric inputs. Although the ASE-DMT transmitter requires multiple IFFTs, we show how these can be mapped onto a single IFFT, by using both the real and imaginary outputs of the IFFT and by extracting some signals from within the IFFT's structure. Using only one IFFT, we first demonstrate a real-time PAM4-encoded optical ASE-DMT transmitter with a net data rate of 18.4 Gb/s. When implemented in a FPGA, using a single IFFT saves 30% of logic resources, compared with a four-IFFT ASE-DMT transmitter. Finally, a 1550-nm directly modulated laser is used to evaluate its optical transmission performance with offline signal processing in the receiver. Without using any optical amplifiers, the ASE-DMT signal can be successfully transmitted over 10-km standard single-mode fiber (SSMF), but fails over 20-km SSMF due to the influence of fiber dispersion and laser chirp.