We analytically study roughness-induced scattering loss in a photonic crystal waveguide ͑PCW͒. A crosssectional eigenmode orthogonality relation is derived for a one-dimensional ͑1D͒-periodic system, which allows us to significantly simplify the coupled mode theory in the fixed eigenmode basis. Assisted by this simplification, analytic loss formulas can be obtained with reasonable assumptions despite the complexity of PCW mode fields. We introduce the radiation and backscattering loss factors ␣ 1 and ␣ 2 such that the loss coefficient ␣ can be written as ␣ = ␣ 1 n g + ␣ 2 n g 2 ͑n g is the group index͒. By finding analytic formulas for ␣ 1 and ␣ 2 , and examining their ratio, we show why the backscattering loss generally dominates the radiation loss for n g Ͼ 10. The interplay between certain mode-field characteristics, such as the spatial phase, and structure roughness is found crucial in the loss-generation process. The loss contribution from each row of holes is analyzed. The theoretical loss results agree well with experiments. Combined with systematic simulations of loss dependences on key structure parameters, the insight gained in this analytic study helps identify promising pathways to reducing the slow light loss. The cross-sectional eigenmode orthogonality may be applicable to other 1D-periodic systems such as electrons in a polymer chain or a nanowire.
Abstract-This paper presents a resource-aware and link quality based (RLQ) routing metric to address energy limitations, link quality variations, and node heterogeneities in wireless sensor and actor networks (WSANs). The RLQ metric is a combined link cost metric, which is based on both energy efficiency and link quality statistics. The primary objective of the proposed metric is to adapt to varying wireless channel conditions, while exploiting the heterogeneous capabilities in WSANs. Different from most of the existing simulation based studies, this research effort is guided by extensive field experiments of link quality dynamics at various locations over a long period of time using recent sensor platforms, which realistically addresses the real-world wireless communication challenges in WSANs. Performance evaluations, via test-bed experiments, show that the RLQ routing metric achieves high performance in terms of packet reception rate, network throughput and network lifetime.
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