Patent ID: 7636503

Claim:
A wavelength selective switch comprising: an input-output optical system in which at least one input port and at least one output port are arranged in a first direction; a spectral element which separates a light output from the at least one input port of the input-output optical system according to wavelengths, to angularly disperse the separated lights in a second direction different from the first direction; a condenser lens which condenses the separated lights output from the spectral element; and a mirror array including a plurality of movable mirrors whose angularly variable reflecting surfaces are arranged on condensing positions of the separated lights of respective wavelengths condensed by the condenser lens, in which angles of the reflecting surfaces of the movable mirrors are controlled so that the lights of respective wavelengths reflected by the respective movable mirrors are led, via the condenser lens and the spectral element, to the at least one output port which is set as an output destination of the input-output optical system, wherein the condenser lens is arranged so that a center axis thereof is shifted in the second direction relative to an axis passing through a center of a spreading angle in the second direction of the separated lights output from the spectral element, and in the mirror array, at a non-operating time when the movable mirrors are not driven, the lights of respective wavelengths condensed by the condenser lens are incident on the movable mirrors by being tilted in the second direction by an offset angle corresponding to a shift amount of the center axis of the condenser lens in the second direction, whereas at an operating time when the movable mirrors are driven, the angles of the reflecting surfaces of the movable mirrors are controlled in the second direction according to the offset angle so that the lights of respective wavelengths condensed by the condenser lens are normally incident on the movable mirrors.