Design analysis of a beam splitter based on the frustrated total internal reflection

In this work, a theoretical analysis on the design of the beam splitter (BS) based on the frustrated total internal reflection (FTIR) is made. We consider a model structure made of a low-index gap layer bounded by two high-index layers. In the design of a 50/50 BS, we find that there exists a critical gap thickness which is a decreasing function of the angle of incidence for both TE and TM waves. There also exists a critical wavelength for the incident wave, and it increases with increasing angle of incidence. Finally, at a fixed gap thickness and wavelength of incident wave, the critical angle in TE wave is slightly larger than that of TM wave. The analysis provides some fundamental information that is of particular use to the design of a BS within the framework of FTIR.