Wavelength selective switch with multiple deflector arrays

A dual grism comprising:

• first and second in-coupling prisms for receiving and propagating therein first and second spaced apart sub-beams, respectively, of a light beam;
• and
• first and second diffraction gratings coupled to the first and second in-coupling prisms respectively, for dispersing the first and second sub-beams respectively into first and second wavelength components respectively, wherein the first and second diffraction gratings are disposed in different planes separated by a non-zero distance therebetween;
• wherein the first and second in-coupling prisms are disposed parallel one another and optically joined by an interface layer therebetween extending along parallel paths of propagation of the first and second sub-beams in the first and second in-coupling prisms respectively.

A method for aligning a wavelength selective switch comprising a polarizing collimator for splitting an input light beam into polarized collimated first and second sub-beams, the method comprising:

• aligning the polarizing collimator to provide the first and second sub-beams propagating along non-overlapping optical paths;
• aligning a first portion of a dispersive element for dispersing the first sub-beam into first wavelength components impinging onto a first angle-to-offset element independently of alignment of the second sub-beam, for the first angle-to-offset element to focus the first wavelength components onto a first deflector array;
• and
• aligning a second, different portion of the dispersive element for dispersing the second sub-beam into second wavelength components impinging onto a second angle-to-offset element independently of alignment of the first sub-beam, for the second angle-to-offset element to focus the second wavelength components onto a second, separate deflector array.