A Survey on OFDM-Based Elastic Core Optical Networking <s> 2) Bandwidth-Variable Optical Switching <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> BIB001 </s> A Survey on OFDM-Based Elastic Core Optical Networking <s> 2) Bandwidth-Variable Optical Switching <s> The trends, architecture, and performance of wavelength-selective switches (WSS) are analyzed in the context of their application to reconfigurable optical add/drop multiplexer (ROADM)-based optical networks. The resulting analyses define the requirements for the latest generation of ROADM systems and provide insight into the critical specifications of this technology. In addition, the current trends for WSS technology are reviewed in the context of synergies with the strengths of different switching technologies. <s> BIB002 </s> A Survey on OFDM-Based Elastic Core Optical Networking <s> 2) Bandwidth-Variable Optical Switching <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> BIB003 </s> A Survey on OFDM-Based Elastic Core Optical Networking <s> 2) Bandwidth-Variable Optical Switching <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> BIB004
To support an end-to-end elastic optical path, every bandwidth-variable WXC (BV-WXC) along the path should allocate an appropriate-sized cross-connection with the corresponding spectrum bandwidth. Therefore, the BV-WXC needs to configure its switching window in a flexible manner according to the spectral width of the incoming optical signal. The traditional wavelength-selective switch (WSS) is designed for a fixed channel spacing, as there is usually a oneto-one relationship between the WDM channels and switching granularity BIB002 . In contrast, the novel bandwidth-variable WSS is designed to group more adjacent switching granularities, accommodating a flexible channel width, as shown in Fig. 14 . Furthermore, finer switching granularity (smaller than the typical channel spacing of 50 GHz or 100 GHz) is required to fit the subcarrier-level spectrum. Liquid crystal or MEMS-based bandwidth-variable WSSs can be employed as switching elements to realize an optical cross-connect with flexible bandwidth and center frequency. In BIB001 , a BV-WSS based on LCoS was reported with the switching granularity of a multiple of 50 GHz or 100 GHz. In BIB003 , a LCoS-based variable bandwidth filter was implemented, supporting 12.5 GHz resolution for setting the channel bandwidth. In BIB004 , an experimental demonstration was performed using a LCoS-based flexible spectrum optical switch, supporting 1 GHz resolution with a minimum 12.5 GHz spectrum width.