Emerging services, such as high-definition Internet Protocol TV (IP-TV) or data center migration, are going to increase the amount of multicast traffic in the Internet. The support of multicast directly in the optical domain, instead of at the IP layer, is a target for reducing the amount of optical–electronic–optical conversions (thus, the network operational and capital expenditure) and energy consumption. In parallel, flex-grid technology (e.g., bandwidth variable wavelength selective switches) is emerging as a candidate solution to be adopted in future optical transport networks given its capacity of improving spectrum efficiency. This paper is focused on optical multicast in flex-grid optical networks and on its control through the Path Computation Element (PCE). First, we present two node architectures supporting optical multicast. The first node architecture achieves optical multicast through passive light split and requires that the multicast connection satisfies the spectrum continuity constraint. The second node architecture achieves optical multicast with frequency conversion. In particular, a specific implementation of the second architecture is proposed in this paper exploiting a periodically poled lithium niobate (PPLN) waveguide. Then, a PCE architecture to control optical multicast (with and without frequency conversion) is proposed. Optical multicasting, based on the proposed node architectures, at 100 and is experimentally demonstrated in a flex-grid network testbed. In particular, multicasting is demonstrated with polarization multiplexing 16 quadrature amplitude modulation (PM-16QAM) and polarization multiplexing quadrature phase shift keying (PM-QPSK), and with PM-16QAM considering the light-split node architecture. Moreover, optical multicast with two frequency conversions, achieved in a single PPLN device, is demonstrated for the first time with a PM-16QAM signal. The testbed also includes the PCE, which is extended to control optical multicast in flex-grid optical networks.
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