亚波长波导能够控制光在亚波长的尺寸中以很小损耗传输，在集成光学中有广泛的应用。利用二维时域有限差分(FDTD)法，研究了光波在金属层中亚波长两狭缝之间的耦合过程。分别在较厚的金属层前表面和后表面刻上两个狭缝，纵向错开一定距离(间距)，横向重叠一定长度(耦合长度)，两个狭缝能够将光波从金属层的前表面耦合到后表面。改变两个狭缝长度、间距和耦合长度等参数，耦合波长和效率发生明显变化。结合振幅分布，认为光波在两狭缝形成波导共振，前表面狭缝的共振将入射波能量耦合进入狭缝中，后表面狭缝的共振将能量耦合出去，两个狭缝之间通过隧穿效应耦合。

Transmission losses are very little for optial wave in subwavelengh structure, which have wide applications in integration optics. By using two-dimensional finite difference of time domain, the coupling between two subwavelengh slits is investigated. Two slits are located on the front surface and back surface of a metal layer, displacing a certainty distance in longitudinal direction and overlap a certainty length (coupling length) in transverse direction. Optical wave transmit the metallic layer through the coupling between two slits. Varying the parameters, such as the slits length, separation distance and coupling length and so on, coupling wavelength and efficiency will change. Combining with the amplitude distributions,the optical wave forms a waveguide resonance between two slits, the resonance at the front surface couples the incident energy into the slit, but the resonance at the back surface will couple the energy away from the metal layer. The energy coupling between the two slits is achieved by a tunneling effect coupling.