Patent ID: 7706049

Claim:
A mirror device with a mirror system having (i) a movable mirror which reflects incoming light and is capable of switching the direction of the reflect light by a reflect surface angle and (ii) a flat-shaped crystal member which is provided for the mirror system in a united form and lets incoming light from outside pass therethrough to let the light enter a reflect surface of the movable mirror and lets light reflected by the movable mirror pass therethrough to output the light outside as output light, in which mirror device it is possible to combine light bi-directionally and mutually, via the movable mirror whose reflect surface angle is switchable and the crystal member, between a single first optical path and a plurality of second optical paths arranged on the same plane as that of the first optical path with the first optical path at the end thereof, wherein the crystal member is arranged in such a manner that a first angle is not larger than a second angle, said first angle and said second angle being defined as angles made by the crystal member with respect to the first optical path and one of the second optical paths, respectively, which are a pair of paths in which, out of the first optical path and the second optical paths, an input angle and an output angle to the movable mirror become the maximum at the both sides thereof by means of switching the reflect surface angle of the movable mirror, and wherein the crystal member is constructed in such a manner that a third angle is substantially equal to a half of a fourth angle, said third angle being defined as an angle made between the first optical path and axis C of the crystal member, and said fourth angle being an angle made between the first optical path and the second optical path, which is made of the pair of optical paths passing through the crystal member in which an input angle and an output angle to the movable mirror become the maximum at the both end thereof by means of switching the reflect surface angle of the movable mirror.