Display device with a transparent optical filter

Abstract

Optical filter which is adapted to prevent the reflection of external light and improve a signal level of a signal sent from a display device by preventing attenuation thereof, and which is further adapted to prevent a change in hue of an image and to improve the hue, contrast and brightness of an image, thereby enhancing visibility. First, a liquid crystal display device () outputs light which is linearly polarized light. First linearly polarizing plate () is mounted in the filter in such a manner as to be adjusted to an axis of polarization of the linearly polarized light. Namely, the light outputted from the liquid crystal display device () passes through the first linearly polarizing plate () without being changed. The light passing through the first linearly polarizing plate () is then changed by a first quarter-wave phase difference plate () into circularly polarized light so that the phase difference between extraordinary light and ordinary light is (1/4) of the wavelength. Subsequently, light passes through a transparent touch panel () and further propagates through a second quarter-wave phase difference plate (). At that time, a phase difference therebetween is caused by (−1/4) of the wavelength of the light in which the phase difference of (1/4) of the wavelength has been caused. Thus, when passing through the touch panel(), the light is changed into linearly polarized light. Then, the light, which has propagated through the transparent touch panel () and the second quarter-wave phase difference plate (), passes through the second linearly polarizing plate ().