METHOD TO OPTICALLY CONNECT AN OPTICAL FIBRE END TO AN OPTICAL ELEMENT

Abstract: In a method of optically connecting an end portion of an optical fibre with an other optical element the end portion of the optical fibre is connected with a lense. The connection is provided by fixing the lense in a connector element, the optical axis of the lense and the axis of a surface of revolu­ tion constituting a reference surface of the connector ele­ ment being thereby provided in a coinciding position. The end portion of the optical fibre is fixed in a sleeve shaped element with the end portion of the fibre in a centered position in relation to a surface of revolution constituting a reference surface of the sleeve shaped element. The sleeve shaped element and the optical fibre fixed therein are then connected with the connector element while said reference surfaces are moved into engagement with each other. Thereby the lense and the end portion of the optical fibre are optically centered in a correct position in relation to each other.

Description: The present invention relates to a method of optically connecting an end portion of an optical fibre with another optical element, for example an end portion of another optical fibre. From certain points of view it is advantageous to include a lens system in an arrangement for connecting an end portion of an optical fibre with another optical element, for example another optical fibre, Thereby the most important advantage is that the sensitivity to dirt at the point of connection is substantially reduced because of the fact that the magnification of the cross-sectional size of the optical signals provides that the dirt will occupy a smaller portion of the connection surface. Thereby, it is of great importance for providing a connection having as small losses as possible that the lenses are connected with the end portions of the optical fibres in a correct way. According to the previously known technique this connection is provided by fixing the fibre ends to the surfaces of the lenses by means of an adhesive. This technique is accompanied by several drawbacks as it does not provide the desired accuracy with regard to the requirement that the optical axis of the lens shall coincide with the optical axis of the fibre and is a technique which can not be used by the customer at the place where the connection shall be provided. In a known improved method of optically connecting an end portion of an optical fibre with another optical element (cf. EP-A-0 053 914), the end portion of the optical fibre is first optically connected with a lens by the following steps: fixing the lens in a tubular connector element, said tubular connector element being provided with a surface of revolution constituting a reference surface whose axis coincides with the optical axis of the lens, fixing the end portion of the optical fibre in a sleeve shaped element, with the fibre end portion centered in relation to a surface of revolution constituting a reference surface of the sleeve shaped element, and connecting the sleeve shaped element having the optical fibre fixed therein with the tubular connector element having the lens fixed therein by positioning said reference surfaces in engagement with each other so that the lens and the end portion of the optical fibre are optically centered in relation to each other; and the lens is thereafter optically connected with the other optical element, for example the end portion of another optical fibre, through another lens. The object of the invention is to provide an improved, simplified and more accurate method of such an optical connection of an end portion of an optical fibre with another optical element, for example an end portion of another optical fibre, in which the connection arrangement comprises a lens. The method according to the present invention is characterized in that said surface of revolution constituting the reference surface of the connector element is formed on said connector element after the lens has been fixed therein, by mounting the connector element having the lens fixed therein in a rotating machine part by transversally adjusting the position of the connector element with respect to the axis of rotation of said rotating machine part so as to bring the optical axis of the lens in coincidence with said axis of rotation, and by then forming said reference surface on the connector element by machining, preferably turning, the connector element while the connector element is rotated about said axis of rotation, which coincides with the optical axis of the lens. In a preferred embodiment of the invention the coincidence of the optical axis of the lens with the axis of rotation of the rotating machine part is obtained by transmitting light through the lens and transversally adjusting the position of the connector element until the light beam leaving the lens forms a stationary image when the connector element and the lens fixed therein are rotated. It is realized that the positioning of the optical axis of the lens so that it coincides with the axis of the rotational reference surface of the connector element is conducted in a factory, whereupon the connection of the end portion of the optical fibre with another optical element can be provided according to principles known per se by fixing the end portion of the optical fibre in the sleeve shaped element and connecting the sleeve shaped element with the optical fibre fixed therein with the connector element provided with the lens, whereupon the lens is optically connected with said second optical element. It is also realized that the steps last mentioned can be conducted at the place where the connection shall be provided. Thus, the working steps which have to be conducted at the work place can be conducted without special equipment or special education. In spite of this, there is according to the method of the invention provided an optical connection in which the losses are substantially less than in connections prepared by means of previously known technique. The invention is described in the following with reference to the accompanying drawings. Fig. 1 is an axial section of a connector assembly for optical fibres provided according to the principals of the method of the invention. Fig. 2 is an axial section on an enlarged scale of a portion of the connector assembly according to Fig. 1. Fig. 3 is an axial section of a portion of the connector assembly according to Fig. 1 and also including the portion thereof shown in Fig. 2 illustrating the conducting of the method according to the invention. In Fig. 1 there is shown a connector assembly by means of which an end portion of a first optical fibre is connected with an end portion of a second optical fibre. The connector assembly shown in Fig. 1 comprises a first connector element 2 and a second connector element 4. The connector elements 2 and 4 are connected with each other by means of a conventional collar nut 6 which is rotatably connected with the connector element 4 and is threaded onto an outer thread of the connector element 2. A fibre cable 8 is connected with the connector element 2 and a fibre cable 10 is connected with the connector element 4. The fibre cables 8 and 10 constitute the two end portions of said first and said second optical fibres which are connected with each other by means of the connector assembly shown in Fig. 1. The connector assembly shown in Fig. 1 provide the connection of only one pair of end portions of optical fibres, but it is realized that the connector assembly can be constructed so as to provide connection of two or several pairs of end portions of optical fibres. The first optical fibre extends from the fibre cable 8 in a way not shown, to a sleeve shaped element 12 of the first connector element 2, while the second optical fibre extends from the fibre cable 10 in a way which is not shown in the drawing, to a sleeve shaped element 14 of the second connector element 4. The sleeve shaped elements 12 and 14 are of the kind shown and described in the Swedish patent No 426 882. Thus, each of the sleeve shaped elements 12 and 14 has an outer conical reference surface 16 and 18, respectively, the end portions of the optical fibres being centered in relation to the reference surfaces of the sleeve shaped elements 12 and 14. The conical reference surfaces 16 and 18 engage complementary, conical inner surfaces 20 and 22, respectively, of the connector element 24 and 26, respectively. In each connector element 24 and 26 there is positioned a lense 28 and 30, respectively. The lenses 28 and 30 are connected with each of the connector elements 24 and 26 in such a way that the optical axes of the lenses are positioned exactly on the axes of the conical inner surfaces 20 and 22. Because of the fact that each of the conical reference surfaces 16 and 18 engages one of the conical inner surfaces 20 and 22 and the end portions of the optical fibres and the lenses are centered in relation to said surfaces there is also provided a correct mutual relationship between the end portions of the optical fibres and the adjacent lens. On the side of the lenses 28 and 30 opposite from the sleeve shaped elements 12 and 14 the connector elements 24 and 26 are provided with transparent protecting elements 32 and 34. The connector elements 24 and 26 have substantially cylindrical outer surfaces 36 and 38 which are concentric with each of the conical inner surfaces 20 and 22 and each of the lenses 28 and 30. The cylindrical outer surfaces 36 and 38 engage with pressfit bores in insert portions 40 and 42. The insert portions 40 and 42 are correctly positioned in relation to each other by means of guide pins of which only one guide pin 44 is visible in Fig. 1. The guide pin 44 is fixed in the insert element 40 and engages a bore in the insert element 42 in order to provide the correct mutual relationship between the insert portions 40 and 42. The guide pin 44 has a conical end portion 46 engaging a complementary conical recess in a resilient engagement element of the insert portion 42. When the connector elements 2 and 4 are connected with each other according to Fig. 1 there is, as described above, provided such a positioning of the end portions of the optical fibres and the lenses between themselves and in relation to each other that there is provided a connection between the fibre end portions, which has very small losses. Thus, the light signal from one of the fibre end portions is transferred to the other fibre end portion through the lenses 28 and 30 and because of the fact that there is transferred a light signal having a magnified cross-section there is provided a reduction of the detrimental effects of dirt in the connection. In Fig. 2 there is shown a cross-section on an enlarged scale of the insert portions 40 and 42 and the elements thereof described with reference to Fig. 1. In order to obviate the transfer of such forces, for example bending forces, to which the outer surfaces of the connector elements 2 and 4 are subjected to the inner portions of the connector assembly the insert elements 40 and 42 are resiliently or in a floating way suspended in the connector elements 2 and 4 by means of O-rings 50 and corrugated springs 52. Fig. 3 illustrates the method according to the invention for providing the correct position of the lens 28 in the connector element 24 in relation to the conical inner surface 20 and the cylindrical outer surface 36 of the connector element. The method of providing the correct positioning is valid also in respect of the connector element 26 and the lens 30 thereof. Before the method according to the invention is initiated the connector element 24 is defined by the cylindrical inner surface 54 shown in broken lines instead of by the conical inner surface 20 and by the cylindrical outer surface 56 also shown in broken lines instead of the cylindrical outer surface 36. After the lens 28 has been fixed in the connector element 24 the connector element is connected with a retainer element 58. The retainer element 58 is rotatably supported in a working machine. The retainer element is supported in the working machine in such a way that the retainer element and thereby the connector element 24 are movable long two axes extending transversely of the rotation axis of the working machine so that the retainer element 58 and the connector element 24 can be adjusted to desired position in relation to said axis of rotation. Light is supplied to the lens 28 from the right in Fig. 3, the light beam leaving the lens from the left end surface 60 thereof in Fig. 3. The focus of the lense 28 is thereby positioned outside the lens to the left of the end surface 60. The light beam from the lens 28 is projected on a surface, for example the surface of a sensing device. Thereupon the retainer element and therewith the connector element 24 are rotated, whereby it is possible to establish if the optical axis of the lens coincides with the rotational axis. If this is not the case the projection of the light beam will conduct a circular motion. The retainer element 58 with the connector element 24 is adjusted along the axes extending transversely of the rotational axis until the projection of the light beam is stationary, which means that the optical axis of the lens 28 coincides with the rotational axis. The surfaces 54 and 56 are thereupon machined while the retainer element 58 and the connector element 24 are rotated using the same rotational axis as previously used by means of turning. Thereby the conical inner surface 20 and the outer cylindrical surface 36 are formed in such a way that the axes of said surfaces will exactly coincide with the optical axis of the lens 28. When using the conical inner surface 20 and the cylindrical outer surface 36 for connecting the connecting element 24 with the sleeve shaped element 12 and the insert element 40 there is provided an exactly correct positioning of the lens in relation to the end portion of an optical fibre fixed in the sleeve shaped element 12.

Claims: A method of optically connecting an end portion of an optical fibre with another optical element, for example an end portion of another optical fibre, in which the end portion of the optical fibre is first optically connected with a lens (28, 30) by the following steps: fixing the lens (28, 30) in a tubular connector element (24, 26), said tubular connector element being provided with a surface of revolution constituting a reference surface (20, 22) whose axis coincides with the optical axis of the lens; fixing the end portion of the optical fibre in a sleeve shaped element (12, 14), with the fibre end portion centered in relation to a surface of revolution constituting a reference surface (16, 18) of the sleeve shaped element; and connecting the sleeve shaped element having the optical fibre fixed therein with the tubular connector element having the lens fixed therein by positioning said reference surfaces (20, 22; 16, 18) in engagement with each other so that the lens and the end portion of the optical fibre are optically centered in relation to each other, and in which the lens is thereafter optically connected with the other optical element, for example the end portion of another optical fibre, through another lens (30, 28), characterized in that said surface of revolution constituting the reference surface (20, 22) of the connector element (24, 26) is formed on said connector element after the lens has been fixed therein, by mounting the connector element (24, 26) having the lens (28, 30) fixed therein in a rotating machine part by transversally adjusting the position of the connector element with respect to the axis of rotation of said rotating machine part so as to bring the optical axis of the lens in coincidence with said axis of rotation, and by then forming said reference surface on the connector element by machining, preferably turning, the connector element while the connector element is rotated about said axis of rotation, which coincides with the optical axis of the lens. A method as claimed in claim 1, characterized in that the coincidence of the optical axis of the lens with the axis of rotation of the rotating machine part is obtained by transmitting light through the lens and transversally adjusting the position of the connector element until the light beam leaving the lens forms a stationary image when the connector element and the lens fixed therein are rotated. A method as claimed in claim 1 or 2, characterized in that the reference surface of the connector element (24, 26) is formed as an inner conical surface (20, 22). A method as claimed in any of the preceding claim, characterized in that the lens (28, 30) is positioned in the connector element (24, 26) so that the focus thereof is positioned on the optical axis of the optical fibre and on the end surface of the end portion of the optical fibre, after said connector element has been connected to said sleeve shaped element (12, 14) having the end portion of the optical fibre fixed therein.

Inventors: NODFELT, INGVAR
Applicants: AB STRATOS CONNECTORS
Application year: 1986
Main classification: G02B6
IPC codes: G02B6