Reduction of crosstalk in a colourless multicasting LCOS-based wavelength selective switch by the application of wavefront encoding

To optimise the design of a wavelength selective switch based on a phase-only liquid crystal on silicon spatial light modulator and mitigate crosstalk, we propose using a technique referred to as wavefront encoding that involves purposefully building a wavefront error into the optical system. Experimental results taken at 674nm are presented that show wavefront encoding based on defocus can reduce the worst case crosstalk by >10dB compared to a standard Fourier transform set-up. In the case of the WSS we propose using wavefront encoding based on astigmatism.