In conventional wavelength division multiplexing (WDM) optical networks, a connection is supported by a wavelength channel occupying a 50 GHz spectrum. Dynamic Survivable Multipath Routing and Spectrum Allocation in OFDMBased Flexible Optical Networks This rigid and coarse granularity leads to waste of spectrum when the traffic between the end nodes is less than the capacity of a wavelength channel. To address this issue, optical networks capable of flexible bandwidth allocation with fine granularity are needed. Orthogonal frequency division multiplexing (OFDM) is a promising modulation Dynamic Survivable Multipath Routing and Spectrum Allocation in OFDMBased Flexible Optical Networks technology for optical communications because of its good spectral efficiency, flexibility, and tolerance to impairments . In optical OFDM, a data stream is split into multiple lower rate data streams, each modulated onto a separate subcarrier. By allocating an appropriate number of subcarriers, optical OFDM can use just enough bandwidth to serve a connection request. A novel OFDM-based optical transport network architecture called a spectrum-sliced elastic optical path network (SLICE) is proposed in . The SLICE network can efficiently accommodate subwavelength and superwavelength traffic by allocating just Dynamic Survivable Multipath Routing and Spectrum Allocation in OFDMBased Flexible Optical Networks enough spectral resource to an end-to-end optical path according to the user demand. The performance superiority of OFDM-based flexible optical networks over conventional WDM optical networks has been demonstrated in . An important problem in the design and operation of OFDM-based flexible optical networks is the routing and spectrum allocation (RSA) problem. The RSA problem for static demands is studied in , dynamic RSA algorithms are proposed to efficiently accommodate Dynamic Survivable Multipath Routing and Spectrum Allocation in OFDMBased Flexible Optical Networks connection requests as they arrive at the network. In , the authors propose a split spectrum approach that splits a bulky demand into multiple spectrum channels, all of which are routed over the same path. This approach relaxes the constraint of transmission impairment over long distance and also makes more efficient use of discontinued spectrum fragments. A similar approach called lightpath fragmentation is proposed in. Dynamic Survivable Multipath Routing and Spectrum Allocation in OFDMBased Flexible Optical Networks A dynamic multipath provisioning (MPP) algorithm with differential delay constraints for OFDM-based elastic optical networks is proposed in . Here a demand is split over multiple routing paths. In , the authors propose several dynamic routing, modulation, and spectrum assignment algorithms in elastic optical networks with hybrid single-/multipath routing. These algorithms achieve lower bandwidth blocking probability (BBP) than the conventional single-path routing and the split spectrum approaches.