Patent ID: 8285088

Claim:
A wavelength selective switch, comprising: a spectroscopic element to separate input light and providing angular dispersion depending on wavelengths; a collective lens to gather light output from the spectroscopic element; a fixture member to fix one end of the collective lens; and a movable reflection block which comprises a plurality of mirrors arranged in a direction of the angular dispersion made by the spectroscopic element, changes the angles of the mirrors in a direction differing from the direction of angular dispersion, and reflects light output from the collective lens; wherein the collective lens is fixed at one end by the fixture member with respect to the direction of angular dispersion of the light output from the spectroscopic element, wherein the collective lens is fixed at an end in a direction in which the angle of the light output from the spectroscopic element changes in accordance with the spectroscopic element's temperature characteristics when the temperature rises, and wherein the collective lens expands with heat in a direction in which the collective lens is not fixed when the temperature changes, and the angle of the light output from the collective lens is changed in a direction opposite to the direction in which the angle of the light output from the spectroscopic element changes so as to correct a deviation in light gathering positions on the mirrors, of the light output from the spectroscopic element, depending on the temperature characteristics.