Anatomical analysis of the light transmission through a single subwavelength metal slit by the FDTD method

Transverse-magnetic (TM) polarized light transmission through a single subwavelength metal slit is re-examined with finite-difference time-domain (FDTD) simulations. In contrast to previous studies, we derive an anatomical view of the electromagnetic field distribution in different cross-sections and emphasize the generation of a field coupling mode in the slit. Numerical modeling reveals that both peak and dip transmissions are features of the field interference in the slit. The slit width and depth are mainly responsible for establishing the amplitude and phase, respectively, of the coupled mode. Moreover, it is found that the output energy dispensation between the radiative and surface components is actually determined by the slit width. Analysis of the physical properties of the slit, including the coupled mode structure in the transverse plane, the effective refractive index and Ohmic absorption losses, provides new insights into the light transmission processes.