Optical space switches are key elements for the next generation of switching fabrics in backbone routers, high performance computing systems, and large data processing and storage systems. A number of architectures and alternative options for gating elements have been proposed, assessed, and implemented for a limited port count. The challenge is to further enhance the scalability and energy efficiency of space switches to support future traffic loads. This paper proposes a heterogeneous implementation of the space switches based on two different types of gating elements, namely semiconductor optical amplifiers (SOA) and Mach-Zehnder Interferometers (MZI). With respect to the existing homogeneous implementations, a higher energy efficiency can be achieved by minimizing the number of SOAs, but crosstalk is introduced by MZI. To reduce the power consumption while still guaranteeing adequate physical layer performance, the design of both Spanke and multi-stage architectures is optimized by strategically placing the different gating and amplification elements, and a physical layer analysis is carried out to validate the performance. The proposed heterogeneous implementation is able to achieve power savings up to 10% and 50% in the Spanke and multi-stage Beneš architectures, respectively, with respect to SOA-based space-switch implementations. Moreover, an improvement of the physical layer performance is achievable in the Spanke architecture thanks to the different placement of the SOAs.
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