An optical device is presented for use in modulation of light and/or in sensing an external field, by at least partially, directly or indirectly exposing the device to the controllable or unknown external field. The device comprises a waveguide structure configured to define at least a first light channel having a light input and a light output, and having a first deformable resonating structure. The device thereby allows exposure of said at least first channel to the external field of the kind affecting a deformation of the first resonant structure thus causing a change in the first resonant wavelength, resulting in a corresponding change in at least one parameter of light output from said first channel, said change in the output light parameter being indicative of the external field.