Patent ID: 8764197

Claim:
A polarization conversion element that has a light incident face and alight outgoing face that are approximately parallel to each other, the polarization conversion element comprising: a plurality of light transmitting substrates that are joined together through an adhesive layer by a joining face having a predetermined tilt angle with respect to the light incident face or the light outgoing face; an optical element that is alternately disposed in boundary portions between the plurality of light transmitting substrates and includes polarization splitting portions that split light incident to the light incident face into two mutually-different types of linearly-polarized light beams of which polarization directions are perpendicular to each other, transmit one linearly-polarized light beam, and reflect the other linearly-polarized light beam and reflective portions that change a direction of an optical path by reflecting the other linearly-polarized light beam that is reflected; and a phase difference plate that is arranged on the light outgoing face, converts any one of the two types of linearly-polarized light beams into a linearly-polarized light beam parallel to a polarization plane of the other linearly-polarized light beam by rotating a polarization plane of the one linearly-polarized light beam, and outputs the converted linearly-polarized light beam, wherein the adhesive layer is an ultraviolet-curing type adhesive having a thickness equal to or larger than 5 μm and equal to or less than 10 μm, wherein the phase difference plate is a phase difference plate that is arranged in an area located above the polarization splitting portion or an area located above the reflective portion on the light outgoing face, is formed by stacking a first wave plate of a phase difference Γ 1 for light of wavelength λ and a second wave plate of a phase difference Γ 2 for light of a wavelength λ such that optical axes of the first and second wave plates intersect each other, converts an incident linearly-polarized light beam into a linearly-polarized light beam acquired by rotating the polarization plane of the incident linearly-polarized light beam by a rotation angle θ=90 (degrees), and outputs the converted linearly-polarized light beam, wherein a relationship between the phase difference Γ 1 and the phase difference Γ 2 satisfies “|Γ 1 −ΓF 2 |=180 (degrees)”, and wherein an azimuth θ 1 of the optical axis of the first wave plate and an azimuth θ 2 of the optical axis of the second wave plate are perpendicular to each other and satisfy θ 1 =45 (degrees) and θ 2 =135 (degrees) or θ 1 =135 (degrees) and θ 2 =45 (degrees).