Chern Ruey-Lin, Hong Wei-Ting
Institute of Applied Mechanics, National Taiwan University, Taipei, Taiwan.
Opt Express. 2011 Apr 25;19(9):8962-72. doi: 10.1364/OE.19.008962.
The feature of enhanced absorption in two-layered grating structures is theoretically investigated. The underlying structures make the most use of resonance mechanism to achieve a nearly perfect absorption in an intrinsically low-loss medium. For standalone gratings, the maximum absorption efficiency is shown to be 50%, which is attributed to the coupling of short range (bonding) or long range (antibonding) surface plasmons with cavity resonances. By attaching a dielectric slab on top or bottom to the metallic grating, the maximum absorption efficiency can be raised to nearly 100%. The presence of guided waves in the dielectric slab causes the strong concentration of fields and reinforces the absorption to its extreme value. The efficient absorption mechanism is illustrated with the pattern of resonance fields and the distribution of power loss density. A phenomenological theory is also used to characterize the absorption anomaly in terms of complex pole and zero.
对双层光栅结构中增强吸收特性进行了理论研究。其底层结构充分利用共振机制，在本质上低损耗的介质中实现近乎完美的吸收。对于独立光栅，最大吸收效率显示为50%，这归因于短程（键合）或长程（反键合）表面等离子体与腔共振的耦合。通过在金属光栅顶部或底部附着一个介质平板，最大吸收效率可提高到近100%。介质平板中导波的存在导致场的强烈集中，并将吸收增强到极值。通过共振场模式和功率损耗密度分布来说明高效吸收机制。还使用了唯象理论，根据复极点和零点来表征吸收异常。
