Very Small Aperture Laser (VSAL) system is a near field optical data storage system that utilizes a nano-aperture fabricated at the front facet of a semiconductor laser to define a nano-sized spot and hence to achieve ultra-high density storage. However, these nano-apertures typically have very poor power throughput behavior when the sizes of the apertures are much smaller than the wavelength of the incident light. In this paper, we use numerical simulation tool XFDTD, which is a three-dimensional vector electro-magnetic field simulator based on the finite difference time domain (FDTD) method, to study the behavior of the nano-apertures. We show that for square apertures, the power throughput decays as r4 (r is the size of the aperture) when the aperture size r is less than lamda/4 (lamda is the incident light wavelength). To solve the power throughput shortage problem, we present our novel nano-aperture design -'C'-aperture. Compared with a conventional 100nm square aperture, the 'C'-aperture provides 1000x higher power throughput while maintaining a comparable near field spot size. We show that the greatly enhanced power throughput is due to both the polarization and resonance effects.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.