Abstract-Wavelength-striped optical packet multicasting comprises a potentially important functionality for future energy-efficient network applications. We report on two multicast-capable architectures to experimentally demonstrate multiwavelength packet multicasting in an optical switching fabric testbed. The first design uses programmable packet-splitter-and-delivery that simultaneously supports the nonblocking unicast, multicast, and broadcast of high-bandwidth optical packets with parallel switches. This realization achieves the error-free multicasting of optical messages with 8 10 Gb/s payloads, with confirmed bit-error rates less than , and scalability of per-channel data rates to 40 Gb/s. We then introduce a second multistage multicasting architecture with lower hardware and energy costs, with the design trade-off of more complex routing logic; the experimental demonstration shows the successful switching and error-free multicasting of 8 10 Gb/s optical packets. The energy costs in terms of the capital and operational expenditures are then compared for the two designs, showing the benefits of the second multicast architecture.Index Terms-Future internet, multicast networks, optical communication, photonic switching systems, routing, wavelength-division multiplexing (WDM).