Prism device for use in two-plate video projector apparatus capable of reducing internal stray light of prism device

The prism device as claimed in 1,

• wherein an angle θx of the sixth side face with respect to the reference surface satisfies:
• θ
• ⁢
• ⁢
• x
• >
• 90
• -
• 2
• ·
• θ
• ⁢
• ⁢
• p
• +
• sin
• -
• 1
• ⁡
• (
• 1
• 2
• ·
• np
• ·
• F
• )
• -
• sin
• -
• 1
• ⁡
• (
• 1
• np
• )
• ,
• wherein “F” denotes an F value of a modulated light incident from the first optical modulator element to the first prism element, “np” denotes a refractive index of the first and second prism elements, and “θp” denotes an angle between the second and third side faces.

A video projector apparatus comprising:

• a prism device, and first and second optical modulator elements,
• wherein the prism device comprises first and second prism elements;
• wherein the first prism element has first to third side faces in parallel with a reference axis, the first side face is opposing the first optical modulator element, and any two planes among three planes respectively including the first to third side faces intersect with each other;
• wherein the second prism element has fourth to sixth side faces in parallel with the reference axis, the fourth side face is provided to be in contact with the third side face via a dichroic coating layer and in parallel with the third side face, the fifth side face is opposing the second optical modulator element and in parallel with the second side face, the sixth side face is provided on an opposite side of the first optical modulator element with respect to an optical axis of the second optical modulator element;
• wherein the sixth side face is formed to be inclined at an angle larger than 0 degrees and smaller than 90 degrees with respect to a reference surface passing through an intersection line of a plane including the second side face and a plane including the third side face, the reference surface being perpendicular to the plane including the second side face, such that a light beam incident from the first optical modulator element to the first prism element via the first side face, then reflected by the second side face, and then incident from the first prism element to the second prism element via the third and fourth side faces is not totally reflected by the sixth side face.