GB1559765A

GB1559765A - Method of preparing the ends of optical fubres

Info

Publication number: GB1559765A
Application number: GB1244878A
Authority: GB
Original assignee: International Standard Electric Corp
Current assignee: International Standard Electric Corp
Priority date: 1977-04-04
Filing date: 1978-03-30
Publication date: 1980-01-23
Also published as: FR2386829A1; FR2386829B1

Description

(54) METHOD OF PREPARING THE ENDS OF OPTICAL FIBRES (71) We, INTERNATIONAL STAN DARD ELECTRIC CORPORATION a Corporation organised and existing under the Laws of the State of Delaware, UN ITED States of America, of 320 Park Avenue, New York 22, State of New York, United States of America do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to optical fibre transmission and especially to a process for the preparation of optical fibre ends.

In most applications of optical conductors, light is injected, conducted from one section of fibres to another connected endto-end and recovered through plane facets perpendicular to the axis. Light losses at these facets are manly due to boundary reflections caused by the difference in index of the media on each side of this boundary and to diffusion by bondary imperfections.

Several methods are used to obtain fibre ends having satisfactory optical qualities.

These methods include mechanical grinding and polishing of the ends; fracturing the fibre, previously scratched by a diamond tool and then subjected to bending and tensile stresses; and thermal shock in which the fibre is subjected to a very localized heating usually induced by an electric spark.

These processes are often difficult to implement and are not always suitable for application in question. In fact, when the fibres are already mounted, for example in a connector, only the first method can be used.

So, one object of this invention is a method of preparing the ends of optical fibres which is simpler and quicker than those known in the art.

According to the invention there is provided a process for preparing the ends of an optical fibre, a bundle of optical fibres or an optical mixer, mounted in a support, which includes the steps: a) the fibre, fibre bundle or mixer are severed by a jet of compressed gas carrying abrasive particles so as to obtain an unpolished surface slightly recessed from the corresponding face of said support; b) the unpolished surface produced by step a) is coated with a transparent glue or the like hardenable by a physical agent and whose refractive index is as close as possible to that of the core of the fibre, bundle or mixer; c) a film whose surface is as flat as possible is then applied over the said coated suface; and d) the physical agent referred to in step b) is activated to harden the glue.

Embodiments of the invention will now be described with reference to the attached drawings in which: Figure 1 is a cross-section of a fibre mounted in a support; Figure 2 shows the first step of the process embodying the invention; Figure 3 shows another step of the above process, consisting in repairing the surface condition of the end of the fibre; Figure 4 is an enlarged cross-sectional view of the end of the fibre obtained by the process embodying the invention: Figure 5 shows a variant of the above process embodying the invention; and Figure 6 shows the process used in the case of a multi-fibre bundle.

Figure 1 shows a fibre mounted in a support. This support consists, for example, of a hollow body or ferrule 1 into one end of which is seated a ring 2 (e.g. a jeweller's ruby) whose inside diameter is approximately equal to the diameter of the optical fibre to be mounted. The optical fibre is inserted through the hole in the ruby 2 and bonded by a drop of glue 5. The protective shea thing 4 is also bonded to the body 1 by a drop of glue 6. Such a support is for example described in Patent Specification No.

1479575 (Standard Tele hones and Cables Limited, J.D. Archer 2.

After the glue has hardened, the end of the fibre is prepared in accordance to the present process, of which the two main steps are illustrated in Figures 2 and 3. These represent respectively the grinding operation (Figure 2) and the end-repairing operation (Figure 3).

Figure 2 shows the process used to sever and grind the fibre. The end of the fibre 3 which extends past the support is subjected to the action of a compressed air jet containing fine abrasive particles. A nozzle 7 is used to direct the jet stream parallel to the front face of the said support. Machines known as "microsanders" may be used for this, and particles such as alumina or silicon carbide can be used as abrasives. During the operation, we observe successively the narrowing and severing of the fibre, the erosion and disappearance of excess glue 9, and then the wearing of the fibre 3 which should be very slightly recessed with respect to the front face of the ruby 2. When using alumina abrasive particles, the ruby is hardly worn away at all. The surface of the fibre end is then very rough.

Figure 3 shows how this surface condition is repaired. A drop of glue is placed on the end face of the support when the latter is mounted vertically. A membrane 10 is then applied on this end face and stretched while exerting a downward pull around the edges so that the excess of glue 11 is driven out at the edges. The membrane 10 is a material which does not adhere to the glue and which has the smoothest possible surface. After the glue hardens, the membrane 10 is withdrawn and the excess glue 11 is removed. In a preferred method, the glue used is one which hardens under the action of ultraviolet rays, e.g. The glue sold under the trademark "VITRALIT", and the membrane is a plastics sheet, e.g. that sold under the trademark "MYLAR". When the membrane is stretched out, its end is subjected to ultraviolet light until the glue hardens.

The result obtained by the above process is shown in Figure 4. The end of the fibre is capped by a film of glue 12 which adopts the form of the rough surface left by the grinding operation and presents on the top a surface as uniform as that of the membrane.

The diffusion of light due to the unevenness of the end of the fibre core 31 is as low as the refractive indices of the core and glue approach the same value.

A varient of the process is shown in Figure 5, in which the glue hardens under the action of pressure, e.g. cyanoacrylate glues, and the membrane is a very thin leaf of glass 16 (only a few microns thick.) The assembly is then pressed by a pad 17 until the glue hardens The excess glue 15 as well as that part of the glass leaf which extends past the support are then removed. Clearly the refractive indices of the glue and the glass leaf should meet the same require- ments as above. The glass leaf can also be bonded with "VITRALIT" glue, but then the pad must be transparent to ultraviolet rays. The product thus obtained has the advantage, over the first method, of having a less fragile surface.

Although in the above description we have only considered the example of a single fibre mounted in a support, the same process can be used advantageously for a fibre bundle or for a tubular mixer, e.g. one described in our Application No. 15530/77 Serial No. 1558643 (G.R.Antell 10) when this bundle or this mixer is mounted in a support. Figure 6 shows how to carry out the grinding operation for a multi-fibre bundle 30 arranged in a ring, around a core 18, in the bore of a ruby 2. Uniform abrasion of the fibres is obtained by rotating the support 1 and stopping the action of the microsander 7 before the central core 18 is severed. The core 18 does not exist in the case of a compact, rather than annular, bundle. In the case of a compact bundle, the number of fibres must not be too great so that the outer fibres do not develop too much of a recess from the. face of the support.

WHAT WE CLAIM IS: 1. A process for preparing the ends of an optical fibre, a bundle of optical fibres or an optical mixer, mounted in a support, which includes the steps: a) the fibre, fibre bundle or mixer are severed by a jet of compressed gas carrying abrasive particles so as to obtain an unpolished surface slightly recessed from the corresponding face of said support: b) the unpolished surface produced by step a) is coated with a transparent glue or the like hardenable by a physical agent and whose refractive index is as close as possible to that of the core of the fibre, bundle or mixer: c) a film, whose surface is as flat as possible, is then applied over the said coated suface; and d) the physical agent referred to in step b) is activated to harden the glue.

2. A process according to claim 1, and in which the abrasive particles are alumina particles.

3. A process according to claim 1, and in which the abrasive particles are silicon carbide particles.

4. A process according to claim 1, 2 or 3, in which the glue is hardenable by exposure to ultraviolet rays, and in which the said film is of a material transparent to

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

thing 4 is also bonded to the body 1 by a drop of glue 6. Such a support is for example described in Patent Specification No.

1479575 (Standard Tele hones and Cables Limited, J.D. Archer 2.

After the glue has hardened, the end of the fibre is prepared in accordance to the present process, of which the two main steps are illustrated in Figures 2 and 3. These represent respectively the grinding operation (Figure 2) and the end-repairing operation (Figure 3).

Figure 2 shows the process used to sever and grind the fibre. The end of the fibre 3 which extends past the support is subjected to the action of a compressed air jet containing fine abrasive particles. A nozzle 7 is used to direct the jet stream parallel to the front face of the said support. Machines known as "microsanders" may be used for this, and particles such as alumina or silicon carbide can be used as abrasives. During the operation, we observe successively the narrowing and severing of the fibre, the erosion and disappearance of excess glue 9, and then the wearing of the fibre 3 which should be very slightly recessed with respect to the front face of the ruby 2. When using alumina abrasive particles, the ruby is hardly worn away at all. The surface of the fibre end is then very rough.

Figure 3 shows how this surface condition is repaired. A drop of glue is placed on the end face of the support when the latter is mounted vertically. A membrane 10 is then applied on this end face and stretched while exerting a downward pull around the edges so that the excess of glue 11 is driven out at the edges. The membrane 10 is a material which does not adhere to the glue and which has the smoothest possible surface. After the glue hardens, the membrane 10 is withdrawn and the excess glue 11 is removed. In a preferred method, the glue used is one which hardens under the action of ultraviolet rays, e.g. The glue sold under the trademark "VITRALIT", and the membrane is a plastics sheet, e.g. that sold under the trademark "MYLAR". When the membrane is stretched out, its end is subjected to ultraviolet light until the glue hardens.

The result obtained by the above process is shown in Figure 4. The end of the fibre is capped by a film of glue 12 which adopts the form of the rough surface left by the grinding operation and presents on the top a surface as uniform as that of the membrane.

The diffusion of light due to the unevenness of the end of the fibre core 31 is as low as the refractive indices of the core and glue approach the same value.

A varient of the process is shown in Figure 5, in which the glue hardens under the action of pressure, e.g. cyanoacrylate glues, and the membrane is a very thin leaf of glass 16 (only a few microns thick.) The assembly is then pressed by a pad 17 until the glue hardens The excess glue 15 as well as that part of the glass leaf which extends past the support are then removed. Clearly the refractive indices of the glue and the glass leaf should meet the same require- ments as above. The glass leaf can also be bonded with "VITRALIT" glue, but then the pad must be transparent to ultraviolet rays. The product thus obtained has the advantage, over the first method, of having a less fragile surface.

Although in the above description we have only considered the example of a single fibre mounted in a support, the same process can be used advantageously for a fibre bundle or for a tubular mixer, e.g. one described in our Application No. 15530/77 Serial No. 1558643 (G.R.Antell 10) when this bundle or this mixer is mounted in a support. Figure 6 shows how to carry out the grinding operation for a multi-fibre bundle 30 arranged in a ring, around a core 18, in the bore of a ruby 2. Uniform abrasion of the fibres is obtained by rotating the support 1 and stopping the action of the microsander 7 before the central core 18 is severed. The core 18 does not exist in the case of a compact, rather than annular, bundle. In the case of a compact bundle, the number of fibres must not be too great so that the outer fibres do not develop too much of a recess from the. face of the support.

WHAT WE CLAIM IS: 1. A process for preparing the ends of an optical fibre, a bundle of optical fibres or an optical mixer, mounted in a support, which includes the steps: a) the fibre, fibre bundle or mixer are severed by a jet of compressed gas carrying abrasive particles so as to obtain an unpolished surface slightly recessed from the corresponding face of said support: b) the unpolished surface produced by step a) is coated with a transparent glue or the like hardenable by a physical agent and whose refractive index is as close as possible to that of the core of the fibre, bundle or mixer: c) a film, whose surface is as flat as possible, is then applied over the said coated suface; and d) the physical agent referred to in step b) is activated to harden the glue.
2. A process according to claim 1, and in which the abrasive particles are alumina particles.
3. A process according to claim 1, and in which the abrasive particles are silicon carbide particles.
4. A process according to claim 1, 2 or 3, in which the glue is hardenable by exposure to ultraviolet rays, and in which the said film is of a material transparent to

ultraviolet rays which does not adhere to the glue and the physical agent is ultraviolet radiation.
5. A process according to claim 1, 2 or 3, in which the glue can be hardened under the action of pressure, and in which the film is of a transparent material whose refractive index is as close as possible to that of the core of the fibre, bundle or mixer, and the said physical agent is a pressure exerted on the said film.
6. A process for preparing the ends of an optical fibre, substantially as described with reference to Figures 2, 3 and 4, or Figure 5, or Figure 6, of the accompanying drawings.
7. A product obtained by a process in accordance with any one of claim 1, 2, 3, 4, 5 or 6.