The invention discloses a C and L waveband 
wavelength selecting switch, as well as an implementation method and a 
processing unit thereof, wherein the 
processing unit comprises an input-output 
fiber array, a 
polarization diversity element, a cylindrical surface reflector, a collimating 
lens array, a 
grating array and a programmable 
spatial light modulator; and a C waveband input 
light signal and an L waveband input 
light signal enter respectively the 
polarization diversity element through the input-output 
fiber array for polarization state adjustment, are reflected by the cylindrical surface reflector, collimated by the collimating 
lens array, expanded by the 
grating array according to different wavelengths, reflected to the programmable 
spatial light modulator for adjustment on magnitude and phase through the collimating 
lens array and the cylindrical surface reflector, and then returned to the 
grating array to be synthesized into a C waveband output 
light signal and an L waveband output light 
signal through the cylindrical surface reflector and the collimating lens array, and the C waveband output light 
signal and the L waveband output light 
signal are output through a designated output 
optical fiber port after the polarization state is restored. According to the C and L waveband 
wavelength selecting switch, as well as the implementation method and the 
processing unit, only one programmable 
spatial light modulator is used for realizing dynamic allocation of a C waveband 
wavelength resource and an L waveband wavelength resource through a skillful design of a light path, the structure is simple and the 
system cost is greatly reduced.