GB1525985A - Arrangements for tapping signal power from optical fibre waveguides - Google Patents

Abstract

1525985 Tapping an optical fibre WESTERN ELECTRIC CO Inc 10 Nov 1975 [11 Nov 1974(3)] 46437/75 Heading G1A [Also in Division G2] An arrangement for tapping signal power from an intermediate portion without breaking optical fibre 22 (Fig. 2B) comprises a coupling material 28 disposed in coupling relationship with and laterally offset from the portion to couple power therefrom and having a refractive index such that optical power is coupled out of the core of the fibre, and a photo-cell 24 serving to intercept such coupled out power. Cladding is stripped from fibre 22 for a limited length. Body 28 is an optically transparent cement, e.g. an epoxy, and should be within three optical wavelengths of the fibre. Photo-cell 22 may be a p-i-n photodiode or an avalanche photodiode. In the embodiment of Fig. 3B, fibre 32 is between respectively hard and compliant discs 37, 38 with refractive indices respectively equal to or lower than and equal to or higher than that of the cladding. Brass holder 39 comprises rectangular cross-bar 39À2 soldered diametrically across annular base 39À1. Disc 37 is a tight fit in hole 41 or may be glued. The embodiment of Fig. 5A (not shown) is similar to that of Fig. 2A but the fibre is bent into a curve to obviate cladding removal. The embodiment of Fig. 6 also uses this principle and has a compliant coupling disc 68 of PVC and a hard disc 67 with a curved lower surface. An arrangement for adjusting the pressure of disc 67 and thus the amount of power tapped off is described in Fig. 7 (not shown). Fig. 8A shows another embodiment using this principle. Holder 89 is a rectangular block of refractive index lower than that of the cladding and contains a coupling region 93 of refractive index equal to or greater than that of the cladding and of thickness equal to that of curved groove 91, which may be smeared with index matching fluid. Fig. 11A shows a mode coupling means combined with a fibre tap 140. Mode coupling plates 144, 145, one or both corrugated, are adjustably pressed against fibre 142 to provide a deformation with a spatial periodicity equal to the heat wavelength between a pair of modes, thereby increasing the proportion of power in the higher order modes, thus increasing the power from tap 140. Power can also be coupled by the mode coupling means from the core to the cladding, which thus need not be removed for the tap.