OPTICAL ELEMENT, OPTICAL UNIT, AND PROJECTION DISPLAY APPARATUS FOR SWITCHING POLARIZATION DIRECTION
Each of a first polarization separation element and a second polarization separation element reflects one of two polarization components perpendicular to each other included in incident light and transmits the other polarization component. A switching element is placed between the first polarization separation element and second polarization separation element and switches between a first state of transmitting an incident polarization component as it is and a second state of converting an incident polarization component to the other polarization component perpendicular to the incident polarization component and transmitting the converted component.
1 . An optical unit, comprising:
a first polarization separation element and a second polarization separation element which each are configured to reflect one of two polarization components perpendicular to each other included in incident light and transmit the other polarization component; and
a switching element placed between the first polarization separation element and the second polarization separation element and configured to be switchable between a first state of transmitting an incident polarization component as it is and a second state of converting an incident polarization component to the other polarization component perpendicular thereto and transmitting the converted component.
2 . A projection display apparatus, comprising:
the optical unit of claim 1 ; and
a control unit configured to switch between a two-dimensional mode for displaying a two-dimensional image and a three-dimensional mode for displaying a three-dimensional image, the control unit providing control such that the switching element is placed in the first state or the second state in accordance with switching between the two-dimensional mode and the three-dimensional mode.
3 . The projection display apparatus of claim 2 , further comprising:
a imager configured to modulate light reflected by the optical unit in accordance with an image signal;
a projection lens configured to project light modulated by the imager onto a projection surface; and
a time-division polarization switching element placed between the imager and the projection lens and configured to switch the polarization direction of light modulated by the imager in a time-division manner, wherein
the control unit allows the time-division polarization switching element to switch the polarization direction in a time-division manner in the three-dimensional mode.
4 . The projection display apparatus of claim 2 , wherein:
the switching element functions as a mode switching element configured to switch between the two-dimensional mode and the three-dimensional mode;
the optical unit further comprises a time-division polarization switching element configured to switch the polarization direction of a polarization component reflected by the first polarization separation element in a time-division manner;
the second polarization separation element, the mode switching element, the first polarization separation element, and the time-division polarization switching element are placed in this order in the optical unit; and
the control unit allows the time-division polarization switching element to switch the polarization direction in a time-division manner in the three-dimensional mode.
5 . An optical element of wire grid type including metal wires and half-wave plates inserted between the metal wires.