Optical unit and projection-type image display apparatus using the same

A projection type image display apparatus which forms optical images according to an image signal by irradiating image display devices with the associated light fluxes and enlarges and projects an optical image, comprising:

• polarization changing means for producing P-polarized light or S-polarized light;
• separating means for producing a red light component from the polarized light, a green light component from the polarized light, and a blue light component from the polarized light;
• a polarization split device for each of the red, green, and blue light components, each polarization device arranged to receive one of the light components and to produce a polarized color light component;
• a light valve for each of the polarized color light components, each light valve modulating the polarized color light component incident upon one of its surfaces according to an image signal;
• color-composing element arranged to receive light that emanates from each of the light valves to produce composed multi-color light;
• a projection lens unit to enlarge and project the composed multi-color light;
• and
• a drive circuit to produce image signals to drive the light valves,
• each polarization split device comprising:
• an amount of translucent material;
• a first surface disposed within the amount of translucent material;
• a diffractive grating formed on the first surface;
• and
• a second surface disposed within the amount of translucent material and spaced apart from the first surface thereby defining a space therebetween,
• the space between the first surface and the second surface being absent of the translucent material,
• the space between the first surface and the second surface having an index of refraction that is different from an index of refraction of the translucent material.

An optical unit which receives light flux from a light source and forms optical images by irradiating light valves with polarized light flux and modulating the light valves according to an image signal, and enlarging and projecting a resulting optical image, the optical unit comprising:

• a first polarization split device having a red light flux incident thereon and configured to emit polarized red light;
• a second polarization split device having a green light flux incident thereon and configured to emit polarized green light;
• a third polarization split device having a blue light flux incident thereon and configured to emit polarized blue light;
• a first light valve arranged such that the red polarized light is incident on one of its surfaces, the first light valve operative to produce a modulated red polarized light;
• a second light valve arranged such that the green polarized light is incident on one of its surfaces, the second light valve operative to produce a modulated green polarized light;
• a third light valve arranged such that the blue polarized light is incident on one of its surfaces, the third light valve operative to produce a modulated blue polarized light;
• a light flux combiner arranged to receive the modulated red, green, and blue polarized light to produce a composed multi-color light;
• and
• a projection lens unit arranged to receive the composed multi-color light to enlarge and project it,
• each of the polarization split devices comprising:
• an amount of translucent material;
• a first surface disposed within the amount of translucent material;
• a diffractive grating formed the first surface;
• and
• a second surface disposed within the amount of translucent material and spaced apart from the first surface thereby defining a space therebetween,
• the space between the first surface and the second surface being absent of the translucent material,
• the space between the first surface and the second surface having an index of refraction that is different from an index of refraction of the translucent material.