The technology described herein relates to a wavelength selective switch (WSS). An output port arrangement solution of an optical fiber array of the WSS includes: centers of output ports are arranged along a curve or along a combination line that includes a line segment, and a straight line connecting centers of any two output ports on the curve or the combination line does not pass through an input port. A light beam received from the input port is diffracted to the output ports through an LCoS panel, and a straight line that all diffraction orders that are generated after the diffraction pass through intersects with the curve or the line segment, and there is only one intersection point.