EP0636253A1

EP0636253A1 - Optical connector

Info

Publication number: EP0636253A1
Application number: EP94906337A
Authority: EP
Inventors: Simon George Preston Meadowcroft
Original assignee: BT&D Technologies Ltd; Hewlett Packard Ltd
Current assignee: Hewlett Packard Ltd
Priority date: 1993-02-17
Filing date: 1994-02-16
Publication date: 1995-02-01
Also published as: JPH08500195A; WO1994019718A1; AU6008794A; GB9303169D0

Abstract

An optical connector includes a sleeve (14) extending from a flange. The sleeve has a wide zone adjacent to the flange (10) and a deformable zone, of smaller cross-sectional area, further from the flange. The deformable zone is conveniently constituted as a plurality of spring segments (16a, 16b) separated by a plurality of longitudinally extending slits (17a, 17b). The optical system is attached to the flange on the opposite side to the collar (15). During use, the ferrule of a terminated optical fiber is located in the sleeve for communication with the optical system. The connector is based on the theory that the sleeve repeatable locates a ferrule inserted therein and the optical member is adjusted to this repeatable position using an active technique which monitors the performance of a test optical system until optimal performance indicates that the optical system is located in the best position. The connector with a fibre ferrule (60) is located in the sleeve. The ferrule contains a fibre (61) and the ferrule (60) is part of the termination of this fibre which extends to whatever location is appropriate. The termination also includes a cap (62) which is spring loaded to the ferrule (60) by spring (63). The cap (62) includes a retaining lip (64) which is located in a retaining groove (43) of the tubular protective member (41). Because of this engagement of the cap (62) the spring (63) is compressed which urges the ferrule (60) into contact with the flange (10). This locates the flange in the longitudinal direction. Because the flange has a wider diameter than the deformable zone of the component (40) the spring members (16a) and (16b) are forced apart. Because they are springy they grip the ferrule and hold it in a reproducible location. Thus the insertion of the ferrule (60) into the component (40) produces a reproducible location of the tip of the fibre (61). The component is machined from a resilient material such as phosphor-bronze.

Description

OPTICAL CONNECTOR

This invention relates to an optical connector and, in particular, to an optical connector which is adapted to receive a terminated fibre and to locate said fibre for optical interaction with an optical device contained in the connector. A complete optical connector can be regarded as comprising two major items, namely a plug and a socket. Connection clearly involves bringing together the two separate items so as to establish optical communication between them. In the context of the present invention, the plug comprises a waveguiding structure, especially an optical fibre which has been suitably terminated. The termination usually comprises a ferrule, eg a brass ferrule, which is mounted on the end of the optical fibre. In many cases the termination also includes a cap which is spring loaded to the ferrule. The cap and spring serve to hold the ferrule in place after its insertion into the socket.

This invention relates to the socket part of the connector and this part usually includes an optical device which maybe an active device or a passive device^ Active devices include signal generators, eg a semiconductor device which converts electric power into an optical signal. Examples of such semiconductor devices include light emitting diodes (LEDs), edge light emitting diodes (ELEDs), and a wide variety of semiconductor lasers. A signal generator often provides a divergent beam which is inconvenient for forming optical connections. In such circumstances it is usual for the source component to include lenses which either collimate the beam or cause it to converge to a focus.

Alternatively, the active device may be an optical detector, eg a semiconductor device which converts an optical signal into an electrical signal. Examples of such devices include photodiodes and PIN diodes. As mentioned above, the optical component may be a passive device such as a waveguiding structure, eg a fibre which is permanently located in the connector.

The purpose of a connector is to provide optical inter-connection between a (terminated) fibre temporarily inserted into the socket of the connector and another optical device which is permanently comprised in the connector. In order to achieve optical inter-connection it is important that the two optical components are accurately located so that a beam provided by one is captured by the other. For example, it may be important that a beam from a signal generator is accurately focused onto the end of a fibre temporarily located within the connector. Thus accurate relative position is an important requirement for an optical connector. One of the reasons for using a connector rather than a permanent connection is the necessity to make, break and remake the connection. It is important that the accurate location be achieved every time a new connection is made.

It has been proposed to achieve the necessary accuracy by using components which are accurately machined. In some cases it is necessary to impose tolerances as low as ±500 nm and it will be appreciated that the achievement of such tight tolerances is very difficult and very expensive. It is an object of this invention to achieve satisfactory optical inter-connection without imposing very high tolerances.

This invention is based upon the recognition of certain features of optical inter- connection and it takes advantage of these features to provide an effective connector of simple structure. More specifically, the invention is based upon the recognition of two features and their interaction. The two features are

(a) reproducibility, and

(b) method of assembly of the connector. Each of these features will now be described.

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Reproducibility means that a particular socket will accurately and repeatedly return an inserted ferrule to the same position, that is to its own arbitrarily selected position rather than a predetermined position. The accurate machining mentioned above is necessary if it is intended to place a ferrule at a predetermined point. However, simpler structures with much looser tolerances are effective if it is only necessary for accurate repeatability for location at the same arbitrary location.

Method of Assembly

Many connectors are assembled using an active technique. According to this technique a fibre ferrule is located in the socket while the other component is permanently assembled into the connector. During this course of this assembly the optical system is made operational. Under these circumstances optical interaction through the connector is possible during the course of assembly and the permanent optical device is moved and located for optimum interaction; this usually means maximum signal transfer. Once the permanent device has achieved its optimal location it is secured at this position and a good connection is achieved because the experimental technique is designed to ensure this. This good connection is established between the permanently located device and the arbitrary point of the socket. However, the socket is repeatable so that every re-connection returns a fibre to the same arbitrary point with adequate accuracy. Thus it can be seen that active assembly has the effect that repeatability is sufficient to achieve good re-connection without the need to impose the additional requirement that the repeatability is to a predetermined point. According to this invention an optical connector comprises an optical device, eg active and passive devices as described above, directly or indirectly mounted on the first side of a flange and a sleeve extending from the second side of the flange said sleeve being adapted to receive and reproducibly locate a fibre ferrule containing the end of an optical fibre, said location being suitable for optical interaction between the fibre and the optical device via an aperture in the flange, wherein said sleeve has a larger cross sectional area in an innermost zone adjacent to said second side of said flange than in a deformable zone further from said flange whereby the insertion of a fibre ferrule to abut the flange for reproducible longitudinal location expands the sleeve in its deformable zone whereby the deformable zone grips the ferrule for reproducible location within the cross sectional area of the sleeve.

Preferably the deformable zone is divided into a plurality of spring segments by a plurality of longitudinally extending slits. It will be appreciated that the number of slits is equal to the number of segments and that the segments are organised in diametrically opposed pairs so that the number is even, eg 2, 4, or 6. In a particularly convenient configuration the innermost zone takes the form of an undivided collar having a diameter greater than that of the tip of the ferrule to be inserted and the deformable zone takes the form of a plurality of spring members, eg spring members arranged as described above, extending from said collar.

The connector described above is included in conventional connector configurations. For example the sleeve may be located inside a tubular protective member which is also connected to the flange. The tubular protective member may include attachment means for holding the cap of a fibre termination whereby the spring loading between the cap and the ferrule urges the ferrule into abutment with the flange for more precise location. As specified above, the first side of the flange is connected directly or indirectly to an optical member and this assembly will be well known to persons skilled in the art. In addition the protective tubular member may provide attachment to an operational panel.

The invention includes the assembly of the optical connector and this is preferably achieved by the active technique described above. A particularly convenient form of attachment for the optical device to the flange and the active technique for assembly are both described in our co-pending UK patent application number 9217732.8.

A connector according to the invention will now be described by way of example with reference to the accompanying drawings in which: - Figure 1 is a pair of perspective drawings which show the general appearance of the key component of the connector;

Figure 2 is an end view of the component shown in Figure 1 ,

Figure 3 is a longitudinal cross section of the component shown in Figures 1 and 2; and Figure 4 is a longitudinal cross section showing the component of Figures 1-3 mounted into a complete connector having a fibre termination located therein.

The key component of the connector is shown in Figures 1, 2 and 3 and the same parts have the same reference numeral in all three figures.

The key component has a flange 10 which has a first face 11 which, in the completed device as shown in Figure 4, supports an optical component. The flange 10 has a second face 12 from which a sleeve 14 extends. The sleeve 14 has a collar 15 and a deformable zone formed of two spring members 16a and 16b which are separated from one another by longitudinally extending slits 17a and 17b. The flange 10 has a central aperture 13 for the passage of optical signals. As can be seen most clearly in Figure 3, the diameter of the deformable zone is defined by the distance between the spring segments 16a and 16b and this diameter is smaller than the diameter in the collar 15.

To give some idea of the size of the connector typical dimensions will be given as an indication: - Total length 5.5 mm

Diameter of aperture 1.0 mm

Diameter of deformable zone 2.5 mm

Diameter of collar 2.8 mm

Ferrules are usually between 2.7 mm and 2.6 mm in diameter so a ferrule will force apart spring segments 16a and 16b but it is small enough to be contained within the collar 15. Thus an inserted ferrule is gripped, and located, by the spring members 16a and 16b and the end face of the ferrule can be placed in abutment with the second face 12 of the flange 10 whereby the inserted ferrule is placed in a reproducible location.

The component illustrated in Figures 1 , 2 and 3 is machined from a resilient material such as phosphor-bronze. This is a convenient operation for the mass production of items at a reasonably low price. Since the items are intended for mass production it is important to compare one with another. Each item will have its own individual point for locating an inserted ferrule but this will vary substantially from item to item. In other words, it is not necessary to define a predetermined locational point and to ensure that each item brings a ferrule to this predetermined point. To this extent each item is its own individual. Nevertheless each single item is reproducible in that it will accurately replace an inserted ferrule to its own individual point. Therefore, as will be explained below, mounting an optical device in relationship to this individual point will enable accurate relocation of the ferrule for optical interaction every time.

A fully assembled connector in accordance with the invention is shown in Figure 4. This Figure includes a fibre ferrule which is temporarily inserted for optical communication.

In Figure 4, which is a longitudinal cross section, the component of Figures 1, 2 and 3 is generally indicated by the numeral 40. Since this component has been fully described it is not necessary to repeat this description. The left hand portion of Figure 4 illustrates the optical package 42 which is attached to the first face of the flange 10. The right hand portion illustrates the socket arrangements.

The sleeve 14 of the component 40 is surrounded by a tubular protective member 41 (which is also attached to the second face of the flange 10). This protective member enables the completed connector to be attached, for example, to a panel 44. Figure 4 shows the connector with a fibre ferrule 60 located in the sleeve. The ferrule contains a fibre 61 and the ferrule 60 is part of the termination of this fibre which extends to whatever location is appropriate. The termination also includes a cap 62 which is spring loaded to the ferrule 60 by spring 63. The cap 62 includes a retaining lip 64 which is located in a retaining groove 43 of the tubular protective member 41. Because of this engagement of the cap 62 the spring 63 is compressed which urges the ferrule 60 into contact with the flange 10. This locates the flange in the longitudinal direction. Because the flange has a wider diameter than the deformable zone of the component 40 the spring members 16a and 16b are forced apart. Because they are springy the grip the ferrule and hold it in a reproducible location. Thus the insertion of the ferrule 60 into the component 40 produces a reproducible location of the tip of the fibre 61. The optical package 42, which is located on the left hand side of the flange 10, comprises an active component, eg an LED 50 which is positioned to provide optical signals to the fibre 61 via the aperture 13. These signals are acquired by the fibre 61 for onward transmission. The LED 50 is contained inside encapsulation 51 (which is the conventional way of mounting an active optical device). The encapsulation 51 is located inside an intermediary component 52 one face of which is in contact with the first face 11 of the flange 10. It will be appreciated that this arrangement makes it possible, during the assembly of the connector, to move LED 50 to its optimum position for interaction with the fibre 51. The intermediary component 52 provides freedom of movement in cross sectional directions so that the LED 50 can be moved onto, for example, the optical axis of the fibre 61. In addition the encapsulation 51 can be slid in or out of the intermediary component 52 so that the distance between LED 50 and the end of the fibre can also be optimised. When the LED 50 is in its optimum location glue is applied to the various surfaces so that the optimum location is made permanent.

Conveniently, the optical package 42 is enclosed in a protective cover 45 which also engages with the flange 10 and the panel 44.

From the previous description it will be appreciated that whenever ferrule 60 is removed and replaced the ferrule (whether it is the same or a different one) is brought back to the same reproducible location so that good optical interaction is established between the fibre 61 and the LED 50.

As indicated briefly above, the connector is assembled as follows. Ferrule 60 is located in the sleeve 14 which is clamped. The fibre 61 is connected to an optical detector for measuring the strength of signals acquired by the fibre. The component 40 including the inserted ferrule is clamped during the assembly process. The encapsulation 51 is placed inside the intermediary component 52 and this is moved into approximately the correct position with the component 52 in contact with the flange 10. At this stage electric power is supplied by the leads 53 so that LED 50 produces its optical signal which is acquired by the fibre 61. The encapsulation 51 is moved until maximum transmission is obtained. This is possible because the intermediary component 52 permits free movement of the encapsulation 51 in three dimensions (at least over the required distances). When the optimum location of the LED 50 has been established a small amount of glue is introduced into the space between the encapsulation 51 and the flange 10. Surface tension draws the glue into the space and it also draws the intermediary member 52 into close proximity of the flange 10. Glue is also introduced into the annular space between the encapsulation 51 and the intermediary component 52. Surface tension also draws glue into this gap and, since the signal generator 50 is clamped in its optimum location during this procedure, when the glue sets the optimum configuration is made permanent. Whenever the ferrule in the sleeve 14 is replaced it goes back to the same reproducible location which is therefore the optimum configuration established when the connector was assembled. Because the connector is adjusted for optimal signal transfer it is only necessary to have a reproducible sleeve and there is no value in having a sleeve which locates a ferrule at a predetermined position.

Claims

1. An optical connector comprising an optical device directly or indirectly mounted on the first side of a flange and a sleeve extending from the second side of the flange, said sleeve being adapted to receive and reproducibly locate a fibre ferrule containing the end of an optical fibre said location being suitable for optical interaction between the fibre and the optical device via an aperture in the flange, wherein said sleeve has a larger cross sectional area in an innermost zone adjacent to said second side of said flange than in a deformable zone further from said flange whereby the insertion of a fibre ferrule to abut the flange for reproducible longitudinal location expands the sleeve in its deformable zone whereby the deformable zone grips the ferrule whereby the ferrule is reproducibly located within the cross sectional area of the sleeve.

2. An optical connector according to Claim 1, wherein the sleeve, in its deformable zone, is divided into a plurality of spring segments by a plurality of longitudinally extending slits.

3. An optical connector according to Claim 2, wherein the number of spring segments is even and the spring segments are arranged in diametrically opposed pairs for gripping an inserted ferrule.

4. A connector according to Claim 3, wherein the number of segments equals the number of slits and said number is either 2, 4 or 6.

5. A connector according to any one of Claims 2-4, wherein the innermost zone takes the form of an undivided collar having a diameter greater than that of the tip of a ferrule to be inserted and the deformable zone takes the form of a plurality of spring members extending from said collar.

6. A connector according to any of the preceding claims wherein the optical device is either an active device selected from signal generators and optical detectors or a passive device comprising a waveguide connected or adapted for connection outside the connector.

7. A connector according to any of the preceding claims which also includes a tubular member which surrounds the sleeve whereby the sleeve is protected by the tubular member.

8. A connector according to Claim 7, which includes a fibre termination located for optical interaction with the optical device wherein said termination includes a ferrule, a cap and a spring located between the cap and the ferrule, wherein said ferrule is located within the sleeve, and also wherein the tubular member has a lip portion releasably engaged with said cap whereby the spring is compressed so that it urges the ferrule into abutment with the flange whereby the fibre located within the ferrule is repeatably located for interaction with said optical device.

9. A method for making a connector according to any one of the preceding claims, which method includes positioning the optical member by an active technique, wherein said active technique comprises: (i) inserting a fibre ferrule into the sleeve to establish an operable optical system which includes the fibre in the ferrule, the optical device and a monitor for measuring the optical performance of said optical system;

(ii) adjusting the position of said optical device to achieve an optimal position indicated by optimal performance of the system as indicated by the monitor; and

(iii) securing said optical device in said optimal position.

10 A method according to Qaim 9, wherein the optimal performance is taken as maximum transmission of optical signals through the assembled connector as indicated by the monitor.