Patent ID: 6973240
Filing Date: 2005-12-06
Classification: G02B

Abstract:
1. An optical filter comprising (a) a multimode waveguide; and (b) first and second coupling waveguides which communicate with the multimode waveguide at respective ends thereof and which are arranged centrally of the multimode waveguide's transverse cross-section; wherein the length of the multimode waveguide is such that an optical field distribution, being lowest order transverse mode of the coupling waveguides, introduced into the multimode waveguide via the first coupling waveguide is substantially reproduced on the multimode waveguide's central longitudinal axis at the end of the multimode waveguide remote from the first coupling waveguide, and coupled into the second coupling waveguide, for radiation of a wavelength to be passed by the filter in preference to radiation of other wavelengths by virtue of modal dispersion and inter-modal interference within the multimode waveguide, characterised in that the filter further comprises means presenting N apertures at a longitudinal position within the multimode waveguide at which 1-to-N way intensity division of said optical field occurs, the centre of each aperture being located at a lateral position within the multimode waveguide at which a local optical intensity maximum occurs when said division occurs.