Shigeto OMORI^*

Osaka Science and Technology Center, 2-7-1, Ayumino, Izumi, Osaka, 594-1157 Japan

(Received December 18, 2000; Accepted June 29, 2001)

A data projector using three liquid crystal display panels has a complex optical system. The illuminating optics separate the beam from a light source into three primary colors and separate those into opposite polarizations using multi-layer films and prisms. A reflection grating with the period of subwavelength has high diffraction efficiency for p polarized light and high regularly reflectance for s polarized light. The diffraction angle of a grating largely depends on the wavelength, because a diffractive optical element (DOE) has large chromatic dispersion. The grating with the period of subwavelength can separate the unpolarized light into polarization components effectively using its polarization dependency and can separate white light into color components using its chromatic dispersion simultaneously. The grating makes the optical system simpler and smaller than those with conventional devices. In this paper the efficiency of polarization separation for the grating is calculated by a rigorous analytical method. Next, the condition for color separation is calculated by Snell’s law, and an optical system using a grating that performs polarization and color separation is proposed. Experimental results of the DOE fabricated are well matched with those of this simulation.

Key words : subwavelength grating, reflection grating, polarization separation, color separation, polarization conversion

omori@coeosaka.gr.jp