APPARATUS FOR LAUNCHING OR DETECTING WAVES OF SELECTED MODES IN AN OPTICAL DIELECTRIC WAVEGUIDE

摘要

1527228 Light guides POST OFFICE 10 Dec 1975 [18 Dec 1974] 54764/74 Heading G2J Apparatus for launching, Fig. 1 or detecting, Fig. 2 radiation in selected modes in a core/cladding waveguide comprises a tapered section 3, 20 of waveguide, long compared to the wavelength, and a prism 6, 21 of R.I. greater than that of the cladding positioned adjacent the waveguide either at, but not overlapping, the tapered section 3, 20 or at least partially overlapping it. To launch radiation, Fig. 1, light from laser 10 passes through prism 16 and enters the waveguide core in a weakly bound mode which is transformed to a selected, strongly bound mode by travelling in the outwardly tapering section 4 before reaching the main waveguide part 5. To detect radiation, Fig. 2, radiation in a selected mode in waveguide 5 is transformed to a weakly bound mode by travelling in the inwardly tapering section 20 and is then extracted by prism 21 so as to impinge on defector 23. An index matching liquid 8 may be present between the prism and the waveguide. The waveguide may be of sodium borosilicate glass having an external diameter tapering from 70-100Ám down to 12-15Ám and a core diameter which tapers from 12Ám to 3Ám.