Abstract: An optical associative learning element (200) comprising a first waveguide (202), a second waveguide (204) and a modulating element (206), wherein: a cascaded first (208) and second (210) directional coupler are formed from a portion (212) of the first (202) and second (204) waveguides in which the first (202) and second (204) waveguides are substantially parallel, evanescently coupled and separated by a gap; the modulating element (206) is evanescently coupled to the second waveguide (204) in the second directional coupler (210) and is arranged to modify a transmission or absorption characteristic of the second waveguide (204) dependent on the state of the modulating element (206); and the state of the modulating element (206) is adjustable between a first and second state by an optical field carried by the first (202) and/or second (204) waveguide.