In this paper, we propose and experimentally demonstrate the direct-detection optical orthogonal-frequency-division-multiplexing superchannel (DDO-OFDM-S) and optical multiband receiving method (OMBR) to support >100-Gb/s data rate and a longer distance for direct-detection systems. For the new OMBR, we discuss the optimum carrier-to-sideband power ratio (CSPR) both in the cases of back-to-back and after transmission, and derive the analytical form for CSPR which is verified with numerical results. An overhead-efficient training method for in-phase/quadrature-phase imbalance estimation is also introduced in order to obtain a better performance while maintaining the high throughput of the system. With experimental setups, we evaluate the two systems with 1) 16-QAM, 214-Gb/s (190 Gb/s without overhead) and 2) 4-QAM, 117-Gb/s (100 Gb/s without overhead) systems. The new proposals enable the record data rate per wavelength (214 Gb/s) and record distance of 720-km standard single-mode fiber (SSMF) for the >100-Gb/s DDO-OFDM systems, and achieve the record optical signal-to-noise ratio sensitivity of 21.2 dB and record distance of 1200-km SSMF (~1 dB penalty) for the 100-Gb/s class DDO-OFDM systems.
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