Light source apparatus, and information display system and head-up display apparatus using the same

A light source apparatus, wherein the light source apparatus includes:

• a point or planar light source;
• an optical element configured to reduce a divergence angle of light output from the light source;
• a light guide configured to have a reflection surface that reflects the light output from the light source and propagates the light to the image display apparatus;
• and
• a retardation plate and a reflection surface configured to face the other surface of the light guide in an order from the light guide,
• the reflection surface provided on the light guide is arranged so as to reflect the light output from the light source and propagate the light to the image display apparatus facing the light guide,
• a reflection type polarizing plate is arranged between the reflection surface of the light guide and the image display apparatus,
• light having a specific polarization direction reflected by the reflection type polarizing plate is reflected by the reflection surface close to and face the other surface of the light guide, passes through the retardation plate arranged between the light guide and the reflection surface twice to undergo polarization conversion, and passes through the reflection type polarizing plate to propagate the light having the specific polarization direction to the image display apparatus, and
• a part or all of a divergence angle of a light flux entering the image display apparatus from the light source is controlled by a shape and surface roughness of the reflection surface provided in the light source apparatus.