Investigation of the Impact of Ultra-Narrow Carrier Spacing on the Transmission of a 10-Carrier 1Tb/s Superchannel

Single- and multi-carrier techniques to build up Tb/s per channel transmission systems

“…Channel separation at the receiver is performed using a matched filter (in this case an ideal rectangular filter) to ensure that ISI does not occur at the optimum sampling instant [22]. Recently, the appropriate matched filters were implemented optically at the transmitter, and electronically, after coherent detection, at the receiver [14]. The ideal frequency response for OFDM, a sinc function, may be approximated using a single asymmetric Mach-Zehnder interferometer (AMZI) and an optical band-pass filter [12,21], or by an optical implementation of a discrete Fourier transform in a single compact monolithic circuit, or using a cascade of AMZIs.…”

“…Such optical multiplexing techniques may clearly be employed using conventional modulation of subcarriers either in the time [9,10] or frequency domain [11][12][13][14]. With appropriate care, ideal information spectral densities may be achieved.…”

“…Whilst analog electronic techniques, such as Kineplex [1] and the related DSP implementation OFDM [3] may theoretically achieve the theoretical maximum capacity of a channel, these techniques themselves do not overcome the electronic bottleneck, and must be combined with ultra-dense WDM, where optical comb generation is often employed to provide a stable channel spacing [4][5][6][7][8], to create Tb/s superchannels with high spectral efficiency. Such optical multiplexing techniques may clearly be employed using conventional modulation of subcarriers either in the time [9,10] or frequency domain [11][12][13][14]. With appropriate care, ideal information spectral densities may be achieved.…”

“…In the frequency domain, such all-optical techniques may closely approach the capacity limits using matched filtering. This can be achieved by either using Nyquist filtering [13,14] or approximations to the channel orthogonality condition [1] using a one [11,12] or more [7,8] tap optical implementation of the discrete Fourier transform required for OFDM. Inevitably, the filters will not be perfectly matched, and in this case, control of the relative phases of adjacent subcarriers may alleviate any residual penalties [12].…”

Next Generation Flexible and Cognitive Heterogeneous Optical Networks

“…Operators provide connections with capacity that fulfils the highest (worst case) demand (over-provisioning), while these connections remain underutilised for most of the time. To this account, the recent advances in coherent technology, softwaredefined optics and multicarrier transmission tecniques, such as Orthogonal Frequency Division Multiplexing (OFDM) [4]- [5] and Nyquist WDM (N-WDM) [6], have introduced the possibility to achieve a significantly high spectrum-efficiency providing a fractional bandwidth feature. In fact, thanks to these technologies it is possible to dynamically tune the required bit-rate and the optical reachability by appropriately choosing the allocation of the spectrum and the modulation format.…”