A wavelength selective switch includes an optical fiber array, a multiplexing/demultiplexing component, and a transmission direction adjustment component. The optical fiber array includes a first optical fiber and at least one second optical fiber. The first offset is used to compensate for a second offset of a diffraction spectrum generated when a plurality of single-wavelength optical signals obtained after an optical input signal is processed by the multiplexing/demultiplexing component arrive at the transmission direction adjustment component, so that the second offset of the diffraction spectrum of the plurality of single-wavelength optical signals arriving at the transmission direction adjustment component is 0 or may be ignored. An optical system has a simple structure, and no optical element needs to be added. This increases optical design freedom, facilitates optical path system commissioning, and reduces reliability risks and costs of subsequent products.