Single-Carrier 2.5-Tbps Transmission Using CSRZ-OTDM with 8×4 Digital Calibrator

We demonstrate a technique for generating high-quality optical signals at a symbol rate twice the sampling rate of digital-to-analog converters (DACs). Optical time-division multiplexing (OTDM) with a carrier-suppressed return-to-zero (CSRZ) wave doubles the symbol rate in a spectrally efficient manner. An 8×4 digital calibrator effectively compensates for the spurious spectral components in the CSRZ waveform, relaxing the required accuracy of the pulse generator and enhancing the signal integrity. We implemented a 224-GBaud CSRZ-OTDM transmitter with a single Mach-Zehnder modulator as the CSRZ carver and an integrated delayed dual in-phase-and-quadrature modulator as the data modulator, both fabricated using an InP n-i-p-n platform, and achieved single-carrier net bit rates of 2.59 Tbps at back to back and 2.52 Tbps after 80-km transmission.