Patent ID: 7340128

Claim:
A wavelength selection device, comprising: an optical port; a spectroscopic element for applying spectroscopy to an input light from the optical port; a collection optical system, comprising a lens, for collecting the spectroscopically split light; mirrors, mounted on mirror holders which are made from materials having different linear expansion coefficients, for folding a light path in the front and rear of the lens; an optical element for receiving the collected light; and a housing for supporting the optical port, spectroscopic element, collection optical system and optical element on a plane approximately perpendicular to the spectroscopic plane of the spectroscopic element, wherein said housing has a rectangular shape within which said optical port, spectroscopic element, collection optical system and optical element are fixed, and wherein said lens is adapted to rotate according to a variation of environmental temperature and to compensate for a displacement of an optical path formed by optical members fixed onto said housing due to an environmental temperature variation by rotation of mirrors caused by temperature deformation of mirror holders which differs for materials of different expansion coefficients.