A Survey on OFDM-Based Elastic Core Optical Networking <s> 2) Coherent Detection (CO-OFDM) <s> Coherent optical orthogonal frequency division multiplexing is proposed to combat dispersion in optical media. It is shown that optical-signal-to-noise ratio penalty at 10 Gbit/s is maintained below 2 dB for 3000 km transmission of standard-singlemode fibre without dispersion compensation. <s> BIB001 </s> A Survey on OFDM-Based Elastic Core Optical Networking <s> 2) Coherent Detection (CO-OFDM) <s> This paper describes coherent optical orthogonal frequency division multiplexing (CO-OFDM) techniques for the long-haul transmission of 100-Gb/s-class channels. First, we discuss the configurations of the transmitter and receiver that implement the optical multiplexing/demultiplexing techniques for high-speed CO-OFDM transmission. Next, we review the no-guard-interval (No-GI) CO-OFDM transmission scheme which utilizes optical multiplexing for OFDM signal generation and the intradyne receiver configuration with digital signal processing (DSP). We examine the transmission characteristics of the proposed scheme, and show that No-GI CO-OFDM offers compact signal spectra and superior performance with regard to tolerance against optical amplifier noise and polarization-mode dispersion (PMD). We then introduce long-haul high-capacity transmission experiments employing No-GI CO-OFDM; 13.4 Tb/s (134 times 111 Gb/s) transmission is successfully demonstrated over 3600 km of ITU-T G.652 single-mode fiber without using optical dispersion compensation. <s> BIB002
Coherent detection, also referred to as coherent demodulation, is a technique of phase locking to the carrier wave to improve detection. The concept of CO-OFDM was originally proposed in BIB001 . Recently, more proposals and demonstrations of CO-OFDM have been made BIB002  . In this approach, a local phase reference or oscillator is mixed with the incoming signal. In this way, the optical analog signals contain all the amplitude, phase, and polarization information before they are received by the photo-detectors and converted into digital streams. Subsequently, the data is recovered by means of DSP where the functions of clock recovery, equalization, carrier phase estimation, and recovery are performed. When compared to DDO-OFDM, CO-OFDM improves performance in receiver sensitivity, spectral efficiency, and robustness against polarization dispersion BIB001 [44], but it requires higher complexity in transceiver design. The superior performance of CO-OFDM makes it an excellent candidate for long-haul transmission systems, whereas DDO-OFDM is more suitable for cost-effective short-reach applications.