G02F 1/17

Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on variable-absorption elements not provided for in groups [CPC: G02F1/015] - [CPC: G02F1/169]