Apparatus for launching or detecting waves of selected modes in an optical dielectric waveguide

Claim 1

Apparatus for launching or detecting radiation in selected modes of propagation in an optical dielectric fibre waveguide having a core surrounded by cladding, said apparatus including a tapered section of waveguide in which the transverse dimension of at least the core of the waveguide is progressively reduced relative to that of the main length of the waveguide to such an extent that radiation propagating in a selected tightly bound mode in the main length of the waveguide would lose a significant amount of energy into the cladding of the waveguide as a result of the tapering of the tapered section, the tapered section being long compared with the wavelength of the radiation, and a prism of refractive index greater than that of the cladding of the waveguide having first and second surfaces, the first surface being located alongside the waveguide, adjacent the narrow end of the tapered section and optically coupled to the waveguide, and the second surface being such that a light beam can pass through it towards the waveguide to induce in the main length of the waveguide radiation propagating away from the tapered section in the selected mode, and can pass through it away from the waveguide due to radiation propagating towards the tapered section in the selected mode in the main length of the waveguide, at least part of the tapered section lying between the point of incidence and emergence of the light beam on the waveguide and the broad end of the tapered section.

Claim 8

A method of launching radiation in selected modes of propagation in a main part of an optical dielectric fibre waveguide having a core surrounded by cladding, the method including generating light radiation, passing the radiation through the cladding of the waveguide so that the radiation propagates in the core in a first, weakly bound, mode of propagation by means of a prism adjacent to the waveguide into a first part of the waveguide and transforming the mode of propagation of the radiation from the first mode into a selected and more strongly bound mode by passing the radiation in the waveguide through an outwardly tapering section of the waveguide in which the transverse dimension of at least the core is progressively increased from that at the first part of the waveguide to that in the main part of the waveguide.

Claim 9

A method of launching radiation in selected modes of propagation in a main part of an optical dielectric fibre waveguide having a core surrounded by cladding, the method including generating light radiation, passing the radiation through the cladding of the waveguide so that the radiation propagates in the core in a first, weakly bound, mode of propagation by means of a prism adjacent to the waveguide into a first part of the waveguide and transforming the mode of propagation of the radiation from the first mode into a selected and more strongly bound mode by passing the radiation in the waveguide through an outwardly tapering section of the waveguide in which the transverse dimension of at least the core is progressively increased from that at the first part of the waveguide to that in the main part of the waveguide.

Claim 12

A method of detecting radiation in selected modes of propagation in a main part of an optical dielectric fibre waveguide having a core surrounded by cladding, the method including transforming the mode of propagation of radiation in the waveguide from a selected mode to a second and weakly bound mode by passing the radiation in the waveguide through an inwardly tapering section of the waveguide in which the transverse dimension of at least the core of the waveguide is progressively reduced from that in the main part of the waveguide, and detecting radiation passing from the core through the cladding of the waveguide at a position in a relatively narrow part of the waveguide by means including a prism adjacent to the waveguide and a light radiation detector located so that radiation passing through the prism from the cladding of the waveguide will impinge on the detector.

Claim 13

A method of detecting radiation in selected modes of propagation in a main part of an optical dielectric fibre waveguide having a core surrounded by cladding, the method including transforming the mode of propagation of radiation in the waveguide from a selected mode to a second and weakly bound mode by passing the radiation in the waveguide through an inwardly tapering section of the waveguide in which the transverse dimension of at least the core of the waveguide is progressively reduced from that in the main part of the waveguide, and detecting radiation passing from the core through the cladding of the waveguide at a position in a relatively narrow part of the waveguide by means including a prism adjacent to the waveguide and a light radiation detector located so that radiation passing through the prism from the cladding of the waveguide will impinge on the detector.