Abstract: A wavelength selective optical waveguide coupler (1) comprises a first undulatory optical D-fiber (2) and a second optical D-fiber (4) embedded in respective substrates (4,8). The fibers (2,6) are located adjacent one another, the undulations of the fiber (2) defining a set of regularly spaced optical coupling regions. This provides a readily formed coupler able to be accurately set to selectively couple a pre-selected wavelength by relatively coarse macroscopic adjustment.

Abstract: An optical switch which selectively transmits or does not transmit light from an input optical fibre (10) to an output optical waveguide (11,12) has one of the input (10) and output (11,12) optical waveguides an optical fibre which is flexible and mounted to be capable of movement towards and away from the other, and an electrode (14) arranged to subject the one optical waveguide to an electrostatic field. In use, application of an electrical potential to the electrode (14) causes the one optical waveguide to move in a direction to enable or prevent optical coupling between the waveguides and hence operation of the switch. The optical fibre is a D-fibre so that it is more flexible in that direction is providing the fibre with a degree of self-alignement. It is preferred that the one optical waveguide is entirely electrically non-conducting and that the optical switch includes more than one electrode (14) to provide a non-uniform electrostatic field.