Beam diameter expanding device and display device

A beam diameter expanding device comprising:

• a first optical element including a first incident face provided at one end of the first optical element and a first emission face provided at another end of the first optical element, the first emission face and the first incident face being separate from and opposed to each other, the first optical element expanding a beam diameter of a light beam that has entered through the first incident face by expanding in a first direction, and emitting the light beam from the first emission face;
• and
• a second optical element including a second incident face provided at one end of the second optical element and a second emission face provided at another end of the second optical element, the second emission face and the second incident face being separate from and opposed to each other, the second optical element expanding a beam diameter of the light beam that has entered through the second incident face in a state in which the beam diameter has been expanded in the first direction by the first optical element, by expanding in a second direction intersecting with the first direction, and emitting the light beam from the second emission face;
• and
• the beam diameter expanding device configured such that a width of the first incident face in the second direction is narrower than a width of the second incident face in the first direction, wherein
• the first optical element includes a first partially reflective layer having a first end and a second end that are separate from and opposed to each other in a length direction of the first optical element;
• the first end of the first partially reflective layer intersects the first incident face;
• the second end of the first partially reflective layer intersects the first emission face;
• the second optical element includes a second partially reflective layer having a third end and a fourth end that are separate from and opposed to each other in a length direction of the second optical element;
• the third end of the second reflective layer intersects the second incident face;
• the fourth end of the second partially reflective layer intersects the second emission face;
• when viewed from a direction parallel with the first partially reflective layer, the first incident face overlaps the first emission face;
• and
• when viewed from a direction parallel with the second partially reflective layer, the second incident face overlaps the second emission face.