Light source device and projection display apparatus including plural light sources, and a lens condensing light from the plural light sources into one spot

1. A light source device comprising:

a solid-state light source;

a first retardation plate that changes a polarization direction of light from the solid-state light source to make a ratio of p-polarization and s-polarization components of the light constant under control, the first retardation plate having a normalized transmittance of polarized light greater than 0.9 for incidence angles between negative 30 degrees to positive 30 degrees;

a dichroic mirror that separates the light from the first retardation plate according to the polarization direction;

a condenser element that collects light transmitted through the dichroic mirror;

a second retardation plate that converts linearly polarized light into circularly polarized light, the second retardation plate having a normalized transmittance of polarized light greater than 0.9 for incidence angles between negative 30 degrees to positive 30 degrees; and

a reflection plate, wherein

the first retardation plate is disposed at a point of incidence of one of collected light and divergent light between the solid-state light source and the dichroic mirror, the collected light being collected at a single light collection spot, the divergent light diverging from a single light collection spot, and

the second retardation plate is between the condenser element and the reflection plate.

2. The light source device according to claim 1 , wherein

each of the first and the second retardation plates is a thin-film retardation plate that uses birefringence due to oblique vapor deposition and includes an inorganic material.

3. The light source device according to claim 1 , wherein

each of the first and the second retardation plates is a microstructural retardation plate that uses birefringence due to a microstructure.

4. A projection display apparatus comprising:

a light source;

an illumination optical system that collects light from the light source and illuminates a to-be-illuminated region with the light;

an image forming element that forms an image according to a video signal; and

a projection lens that magnifies and projects the image formed by the image forming element, wherein

the light source is the light source device according to claim 1 .

5. The light source device according to claim 1 , further comprising a collimating lens between the first retardation plate and the dichroic mirror, the collimating lens being configured to collimate light from the solid-state light source.

6. The light source device according to claim 5 , further comprising a first diffusion plate between the collimating lens and the dichroic mirror, the first diffusion plate being configured to diffuse the light collimated by the collimating lens.

7. The light source device according to claim 6 , wherein a width of the first retardation plate is less than a width of the first diffusion plate.

8. The light source device according to claim 1 , further comprising a second diffusion plate between the condenser element and the second retardation plate, the second diffusion plate being configured to diffuse the light collected by the condenser element.

9. The light source device according to claim 8 , wherein a width of the second retardation plate is less than a width of the second diffusion plate.

10. The light source device according to claim 1 , further comprising a mirror configured to reflect light from the solid-state light source toward the first retardation plate.

11. The light source device according to claim 10 , wherein the mirror is configured such that the reflected light focuses between the mirror and the first retardation plate.