A Survey on OFDM-Based Elastic Core Optical Networking <s> c) Super-Wavelength Signal Generation <s> We show the first experiment of bit and power loading for coherent optical orthogonal frequency-division-multiplexing (CO-OFDM) systems. The data rate of CO-OFDM systems can be dynamically adjusted according to the channel condition. The system performance can be further improved through optimal power loading into each modulation band. <s> BIB001 </s> A Survey on OFDM-Based Elastic Core Optical Networking <s> c) Super-Wavelength Signal Generation <s> We propose and experimentally demonstrate optical path aggregation in a spectrum-sliced elastic optical path network (SLICE). Multiple optical orthogonal frequency-division-multiplexed (OFDM) 100-Gb/s optical paths are aggregated in the optical domain to form a spectrally continuous 1-Tb/s super-wavelength optical path and transmitted over a network of bandwidth-variable wavelength cross-connects. We evaluate the potential implementation issues and conclude that the OFDM paths can be optically aggregated with optical signal-to-noise ratio penalty of less than 1 dB. <s> BIB002 </s> A Survey on OFDM-Based Elastic Core Optical Networking <s> c) Super-Wavelength Signal Generation <s> We propose a spectrally-efficient super-wavelength-path routing in SLICE by selecting a set of subcarrier numbers and modulation levels according to path distances. We demonstrate 420 Gb/s path routing using short-reach 14-subcarrier 8-APSK and long-reach 21-subcarrier QPSK. <s> BIB003 </s> A Survey on OFDM-Based Elastic Core Optical Networking <s> c) Super-Wavelength Signal Generation <s> This paper experimentally demonstrates flexible-bandwidth networking by splitting a 500-GHz waveform generated by optical arbitrary waveform generation into its two tributary spectral slices using a liquid-crystal spatial light phase modulator as a wavelength selective switch. <s> BIB004 </s> A Survey on OFDM-Based Elastic Core Optical Networking <s> c) Super-Wavelength Signal Generation <s> This paper presents a bandwidth-scalable, coherent optical transmitter based on the parallel synthesis of multiple spectral slices. As a proof-of-principle, two spectral slice, 6-ns DPSK and QPSK waveforms at 12 Gsymbols/s are generated and measured. <s> BIB005 </s> A Survey on OFDM-Based Elastic Core Optical Networking <s> c) Super-Wavelength Signal Generation <s> We demonstrate a multi-flow/multi-rate/multi-reach optical transmitter and spectral routing of total 400 Gb/s optical flows. The number of optical flows, bit rate, and optical reach can be adjusted to enable efficient elastic spectral routing. <s> BIB006
For super-wavelength services, several OFDM channels can be merged together into a super-channel, transporting a multiple of the capacity of an individual OFDM channel. The data stream is first divided into several channels using layer-2 link aggregation, and then modulated onto continuous OFDM optical paths without guard bands in between. This optically-aggregated super-wavelength path occupies less spectral resources than the corresponding WDM multiplexing method, thereby leaving room for additional traffic. In BIB002 , an aggregation of seven optical paths into a single spectrallycontinuous super-wavelength optical path with a bandwidth of 1 Tb/s was achieved. The individual channels are aggregated into one spectrally-continuous super-wavelength optical path, which can be transmitted through the core network consisting of bandwidth-variable wavelength cross-connects (WXCs). In BIB003 , a 420 Gb/s distance-adaptive super-channel with DQPSK and 8-APSK modulation was also demonstrated. A cost comparison between OFDM data-rate variable transponder and 10/40 Gb/s single-carrier transponder was given [82] , showing the appropriate cost of the OFDM datarate variable transponder will lead to total network cost reduction. One of the issues of data-rate/bandwidth-variable transponder technology is that, when it is used to provide transmission for sub-wavelength services, the remaining capacity of the transponder might be wasted. To address this issue, a flexible-bandwidth and format-agile transmitter based on optical arbitrary waveform generation technology BIB004 BIB005 [84] was proposed to provide parallel synthesis of multiple spectral slices inside a transponder, thereby supporting multiple virtual transponders to make full use of the physical transponder. Recently, a multi-flow, multi-rate, and multi-reach transponder was demonstrated to support flexible point-tomulti-point optical connections BIB006 . Furthermore, the optical power control of the transponder is a challenging problem, when the number of subcarriers or modulation scheme varies dynamically BIB001 . Table III summarizes recent research work related to datarate/bandwidth-variable transponders, although we note that research is still ongoing and the appropriate scheme that best fits the requirement of the elastic optical network is an open issue.