1. Field of the Invention
The present invention relates to a light modulation device that has a resonator structure.
2. Description of the Related Art
In recent years, as a recording method for large volumes, digital information recording systems that use the principle of holograms have become known (for example, Patent Document 1).
As a material for a spatial light modulator of a hologram recording device, a material having electro-optical effects such as, for example, lead lanthanum zirconate titanate (referred to below as PLZT) or the like, can be used. PLZT is a transparent ceramic having a composition of (Pb1-yLay) (Zr1-xTix)O3. An electro-optical effect is a phenomenon in which, if an electrical field is applied to a material, polarization is produced in the material so that the refractive index changes. If an electro-optical effect is used, by switching an applied voltage on and off, it is possible to switch the phase of the light. As a result, it is possible to apply a light modulating material, which has an electro-optical effect, to an optical shutter of the spatial light modulator or the like.
Conventionally, bulk PLZT has been widely used for application to devices such as the optical shutter or the like (Patent Document 2). However, with the optical shutter using the bulk PLZT, it is difficult to respond to demand for miniaturization and integration, and to demand for reduction in operating voltage and lowering of costs. Furthermore, since the bulk method includes processing at a high temperature of 1000° C. or more, after mixing metal-oxide that is raw material, when applied to a device formation process, many constraints on selection of material, device structure, and the like, are added.
From this situation, instead of the bulk PLZT, tests are being considered in which thin film PLZT formed on a substrate is applied to an optical control element. Patent Document 3 describes a display device in which a PLZT film is formed on a transparent substrate, such as glass or the like, and a comb-shaped electrode is provided thereon. This display device has a configuration in which a polarizing plate is provided on both faces of a display board on which the PLZT film is formed. Here, by electrode terminals of each pixel being connected to an external drive circuit, a desired pixel can be driven, and a desired display can be made by transmitted light from a light source provided on one face of the display board.
Patent Document 1: Japanese Patent Application, Laid Open No. 2002-297008
Patent Document 2: Japanese Patent Application, Laid Open No. Hei5-257103
Patent Document 3: Japanese Patent Application, Laid Open No. Hei7-146657
The inventors of the present invention carried out investigation concerning a light modulation device using PLZT film as a light modulating film, as an example of applying a thin film of PLZT to an optical control device. This light modulation device is provided with a Fabry-Perot type of resonator in which the light modulating film is formed on a first reflective layer, and a second reflective layer is formed on the light modulating film. Reflected light from the resonator is controlled by applying an electrical field to the light modulating film to change its refractive index, so as to shift resonance wavelength of the resonator.
However, the inventors of the present invention found that in cases in which the formed light modulating film is used as it is, the intensity of the reflected light decreases with respect to the intensity of incident light in the light modulation device, that is, that the utilization efficiency of the light cannot easily be raised. In particular, it was found that when a light source of short-wavelength blue light (approximately 450 nm) or violet-blue (approximately 400 nm) is used, the utilization efficiency of the light deteriorates significantly.