A Survey on OFDM-Based Elastic Core Optical Networking <s> c) Guard Band and Filtering Characteristics <s> We present a high-resolution blocking filter, which seamlessly supports data rates from 2.5 Gbit/s to 160 Gbit/s with a granularity of 13.2 GHz. The filter consists of a linear array of 64 MEMS micromirrors and a high-dispersion echelle grating. <s> BIB001 </s> A Survey on OFDM-Based Elastic Core Optical Networking <s> c) Guard Band and Filtering Characteristics <s> We present a novel wavelength selective switch (WSS) based on a liquid crystal on silicon (LCOS) switching element. The unit operates simultaneously at both 50 and 100 GHz channel spacing and is compatible with 40 G transmission requirements. <s> BIB002 </s> A Survey on OFDM-Based Elastic Core Optical Networking <s> c) Guard Band and Filtering Characteristics <s> We demonstrated, for the first time, a novel spectrum-efficient elastic optical path network for 100 Gb/s services and beyond, based on flexible rate transceivers and variable-bandwidth wavelength crossconnects. <s> BIB003 </s> A Survey on OFDM-Based Elastic Core Optical Networking <s> c) Guard Band and Filtering Characteristics <s> We investigate the performance of OFDM-modulated signals in spectrum-sliced elastic optical path network. We analyze the filtering characteristics and the guard band for multi-node transmission. The architecture increases spectral efficiency over the current WDM systems. <s> BIB004 </s> A Survey on OFDM-Based Elastic Core Optical Networking <s> c) Guard Band and Filtering Characteristics <s> We demonstrate a bit rate variable add- and drop function performed on an optical OFDM superchannel signal by optical filtering and superposition of OFDM subbands and the application of different modulation formats for dynamic networks. <s> BIB005 </s> A Survey on OFDM-Based Elastic Core Optical Networking <s> c) Guard Band and Filtering Characteristics <s> The increasing spectral efficiency of Optical Transmission systems is constrained by the limitations of wavelength switching and is driving a requirement for significantly more flexible approaches to routing of the optical traffic. We present the intrinsic Grid-free capabilities of LCOS and show how it can be used practically in a flexible Grid architecture to maximize total fiber capacity. <s> BIB006 </s> A Survey on OFDM-Based Elastic Core Optical Networking <s> c) Guard Band and Filtering Characteristics <s> A gridless dynamic multi-granular optical network supporting flexible spectrum allocation is proposed and experimentally demonstrated to efficiently accommodate high-speed traffic and increase channel density for lower speed traffic leading to improved network efficiency and scalability. <s> BIB007
Theoretically, a continuous-spectrum signal based on OFDM does not have a guard band requirement in the frequency domain between the respective OFDM channels or subbands. However, when an OFDM spectrum signal travels through multiple bandwidth-variable WXCs, the subcarriers on the edge of the spectrum will experience a larger penalty because of the imperfect shape of WSS filters. A guard band between adjacent optical paths can alleviate this problem at the cost of reducing the spectrum efficiency. Furthermore, if WSS filtering is required to perform add/drop functions in a BV-WXC, some residual signal of adjacent channels besides the added or dropped channels will remain due to the finite slope of the filter edges. To avoid BIB003 LCoS-based WSS Multiple of 50 GHz Baxter et al. BIB002 LCoS-based WSS Multiple of 50 GHz or 100 GHz Frisken et al. BIB006 LCoS-based WSS Multiple of 12.5 GHz Amaya et al. BIB007 LCoS-based WSS Multiple of 12.5 GHz Ryf et al. BIB001 [92] Free-space diffraction grating combined with MEMS Multiple of 13.2 GHz high penalties because of the cross talk, a spectral gap (guard band) must be added between adjacent channels BIB005 . The guard band size depends on the number of filters (WXC nodes) to cascade, and the filtering characteristics of the WSS. The trade-off between the filter shape and the guard bandwidth was numerically analyzed in BIB004 . Results show that, for the case of transmission over 10 cascaded filtering stages with second-order Gaussian shape, the optimum guard band for OFDM channels with 10 Gb/s subcarriers is 30 GHz. Further narrowing of the guard band size could be expected in the future, for instance by increasing the filter order.