a resonator having an enclosed geometric structure;

a first injection optical waveguide and at least one further injection optical waveguides, each of said optical waveguides comprising an input port and a second end, the optical waveguides passing the resonator at respective approach points;

coupling regions between said resonator and said injecting waveguides at said approach points respectively, the coupling regions providing optical coupling between said resonator and said injecting waveguides; and

an output port at a second end of said first injection optical waveguide configured to provide a plurality of shapes of frequency or time or phase or intensity responses according to parameters of said injecting waveguides or of said coupling regions and further according to a power of an optical control signal injected at said at least one further optical waveguide;

at least two input ports;

at least two output ports; and

electrodes at ones of said coupling regions, said electrodes each being configured to separately vary a respective coupling coefficient, thereby to provide a programmable matrix function.