With the rapidly increasing aggregate bandwidth requirements of data centers there is a growing interest in the insertion of optically interconnected networks with high-radix transparent optical switch fabrics. Silicon photonics is a particularly promising and applicable technology due to its small footprint, CMOS compatibility, high bandwidth density, and the potential for nanosecond scale dynamic connectivity. In this paper we analyze the feasibility of building silicon photonic microring based switch fabrics for data center scale optical interconnection networks. We evaluate the scalability of a microring based switch fabric for WDM signals. Critical parameters including crosstalk, insertion loss and switching speed are analyzed, and their sensitivity with respect to device parameters is examined. We show that optimization of physical layer parameters can reduce crosstalk and increase switch fabric scalability. Our analysis indicates that with current state-of-the-art devices, a high radix 128 × 128 silicon photonic single chip switch fabric with tolerable power penalty is feasible. The applicability of silicon photonic microrings for data center switching is further supported via review of microring operations and control demonstrations. The challenges and opportunities for this technology platform are discussed.
Integrated photonics offers the possibility of compact, low energy, bandwidth-dense interconnects for large port count spatial optical switches, facilitating flexible and energy efficient data movement in future data communications systems. To achieve widespread adoption, intimate integration with electronics has to be possible, requiring switch design using standard microelectronic foundry processes and available devices. We report on the feasibility of a switch fabric comprised of ubiquitous silicon photonic building blocks, opening the possibility to combine technologies, and materials towards a new path for switch fabric design. Rather than focus on integrating all devices on a single silicon chip die to achieve large port count optical switching, this work shifts the focus towards innovative packaging and integration schemes. In this work, we demonstrate 1 × 8 and 8 × 1 microring-based silicon photonic switch building blocks with software control, providing the feasibility of a full 8 × 8 architecture composed of silicon photonic building blocks. The proposed switch is fully non-blocking, has path-independent insertion loss, low crosstalk, and is straightforward to control. We further analyze this architecture and compare it with other common switching architectures for varying underlying technologies and radices, showing that the proposed architecture favorably scales to very large port counts when considering both crosstalk and architectural footprint. Separating a switch fabric into functional building blocks via multiple photonic integrated circuits offers the advantage of piece-wise manufacturing, packaging, and assembly, potentially reducing the number of optical I/O and electrical contacts on a single die.
The dynamic orientational order-disorder transition of clusters consisting of octahedral AF6 molecules is formulated in terms of symmetry-adapted rotator functions. The transition from a higher-temperature body-centered-cubic phase whose molecules are orientationally disordered at their sites to lower-temperature, monoclinic, orientationally-ordered phase is a two-step process: first, at temperatures well below the limit of stability for the liquid, a transition occurs to a partially ordered monoclinic phase driven by the rotational-vibrational coupling. This transition has two local minima in the free energy, and hence behaves like a finite-system counterpart of a first-order transition. Further lowering of the temperature initiates another transition, to an orientationally-ordered base-centered monoclinic structure. This last transition is dominated by rotational-rotational interaction and is found from simulations to be continuous. The temperature of this transition predicted by the analytic theory presented here for a 59-molecule cluster of T eF6, 27K, is in good agreement with the 30K result of canonical Monte Carlo calculations.
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