GB2282898A - Optical connector having flexible material for transverse movement - Google Patents

Abstract

An optical connector device comprises a support 36 formed with an aperture 422, and engaging portion 421 extending at least partially within the aperture 422 for engaging with a corresponding optical connector 402, 406, and flexible material 423 sandwiched between the support 36 and the engaging portion 421 to secure the engaging portion to the support so as to permit limited movement of the engaging portion transverse to the direction of engagement of the connectors. Such connector devices are used for optical plug-in modules in rack mounting upto - electronic equipment. Connector mounting portion 401 may be secured to printed circuit board 29. Epoxy resin 425 is shown. <IMAGE>

Description

RACK-MOUNTING OPTO-ELECTRONIC EOUIPMENT The present invention relates to rack-mounting opto-electronic equipment, in particular to making optical connections to such equipment, and also relates to optical connectors suitable for use in such equipment.

Optical fibres are being increasingly used to connect together items of opto-electronic equipment, particularly in the field of telecommunications where, for example as shown in Figure 1 of the accompanying drawings, copper cable connections previously used between customer premises 1 and local distribution nodes 2 of a communications network and also between such distribution nodes 2 and main network nodes 3 of such a network, are being replaced by optical fibres 4.

As more optical fibres are provided, and the data processing capabilities of the individual items of equipment rise, so it is increasingly required to connect multiple optical fibres to a single item of equipment.

The opto-electronic equipment used in the telecommunications field is commonly provided in the form of many individual plug-in modules which are designed to be mounted, when in use, in equipment racks which provide power to the modules and serve to connect the modules together to allow data and control signals to pass between them. For example, such an equipment rack could be located at the distribution node 2 in Figure 1. The rack commonly provides one or more shelves, in each of which a set of the plug-in modules can be housed side-by-side, the modules having respective printed circuit board cards and being located in their respective housing positions in a shelf by guides that extend in the forward/backward direction of the shelf and hold the top and bottom edges of the cards.The top and bottom edges of each card can slide in the guides so as to permit the modules to be inserted into and removed from the shelf individually.

As shown in Figure 2 of the accompanying drawings, which shows a schematic cut-away side view of a conventional equipment rack 10, each plug-in module 12 has at its rear edge an electrical connector which, when the module is in place in its housing position, plugs into a corresponding connector 16, referred to as a backplane connector, on a rear panel (backplane connection panel) 18 of the rack. In this way, the connectors 14 and 16 provide electrical connections between the module 12 and the rack 10, for example power supply connections and data and control signal connections.

In the rack of Figure 2 any optical connections to the modules 12 are conventionally made by connecting optical fibres 20 directly to respective optical connectors 22 mounted on the front and/or top edges of the modules.

When there are only a few optical fibres 20 to be connected to each module, the connection arrangement shown in Figure 2 is satisfactory. However, as the number of optical fibre connections required increases, two problems arise. Firstly, the size of the printed circuit board card of each module imposes a limit upon the maximum number of optical connections that can be made to a module, particularly since it is often not convenient to miniaturize the optical connectors 22 or to place them in very high densities because manual manipulation of the connectors is required to connect/disconnect the individual fibres 20.Secondly, if a module 12 is to be replaced, for example because it develops a fault, it is necessary to disconnect all the optical fibres individually from the module before removal thereof can be carried out, which can take a significant amount of time when there are a large number of fibres, leading to an unacceptably long "down time".

If the optical connectors on a module are all of the same type, there is also the possibility that the optical fibres 20 will be reconnected to the replacement module in the wrong order.

According to a first aspect of the present invention there is provided apparatus comprising a rack, for housing a plurality of optical plug-in modules in respective positions in the rack, and such an optical plug-in module, the rack having at a rear portion thereof a plurality of first optical connector devices arranged so that, when the said optical plug-in module is brought into one of the said housing position in the rack, one of those first optical connector devices is engaged with a corresponding optical connector device of the module so as to permit an optical signal to pass between the rack and the module via the mutually-engaged optical connector devices, and also having, at a fibre interface portion thereof accessible from outside the rack when the modules are housed therein, further optical connector devices, coupled optically within the rack to the said first optical connector devices, for connection to respective optical fibres extending to the rack from further equipment external thereto; one or both of the pair of optical connector devices, made up of the said one first optical connector device of the rack and the said corresponding optical connector device of the module, extending through an aperture in a support member and having flexible material, sandwiched between the support member and the device concerned, securing the device to the support member in such a way as to permit limited movement of the device in a direction transverse to the direction in which the two connector devices are brought into mutual engagement.

In such a rack, the optical fibres are not connected directly to the modules, but are instead connected to the rack, at the fibre interface portion thereof, and the shelf provides optical connections between the fibres and the modules when the modules are in place in the rack. As a result, each module can "service" a larger number of optical fibres than was possible in the conventional connection arrangement discussed above with reference to Figure 2, because the backplane optical connector devices of the rack and the corresponding optical connector devices of the modules are not required to be manipulated manually, or even connected/disconnected to/from one another individually, and accordingly can be of a small size and be mounted very close together.

In the fibre interface portion of the rack, space is not restricted, and the optical connectors there can be made conveniently large and spaced apart appropriately to facilitate manual manipulation thereof for individual disconnection/connection of the optical fibres.

Furthermore, each module can be replaced quickly without disconnecting the optical fibres which it services. Because the fibre connections can be left alone during replacement of a module there is no possibility of fibres being reconnected in the wrong order to the replacement module, as was the case heretofore.

The rack may also have electrical connectors, adjacent to its optical connectors, which engage respectively with corresponding electrical connectors of the modules when the modules are in their respective housing positions to permit the rack to supply power to the modules and/or to enable electrical signals to pass between the modules via electrical connection lines within the rack.

Heretofore, it has not been considered practicable to connect the modules optically to the rack, using optical connectors at the backplane of the rack, because of difficulties in aligning the optical connectors of the modules with those of the rack, particularly when large numbers of connectors must be connected together in mutually-corresponding pairs at the same time. This arises partly because the guides and locking mechanisms traditionally used in the rack to locate the modules in their housing positions in the rack have provided only a relatively coarse alignment between the modules and the rack which, although sufficient for engaging electrical connectors, is not adequate for the purposes of aligning optical connectors, particularly optical connectors used to terminate monomode optical fibres for which the alignment tolerances are much tighter than for multimode fibres.

By virtue of the limited movement or play, in the transverse direction, of the or each connector device of the pair, the optical connector devices of the pair can engage accurately with one another even though, when initially brought together, they are only relatively coarsely aligned by the guides/locking mechanisms of the rack. In this way it is possible to use the optical connectors to connect monomode fibres.

Preferably, one of the devices of the pair has a light-transmitting plug portion which is adapted to be inserted into a light-transmitting socket portion of the other device of the pair.

In a preferred embodiment the said support member is a backplane connection panel of the rack and serves to support all of the said first optical connector devices at different respective positions thereon.

The flexible material is preferably an elastomeric material.

To promote precise final alignment of the connector devices of a pair, whilst requiring only coarse initial alignment such as can be achieved by the guides/locking mechanisms of the rack, the plug portion and/or socket portion should preferably be tapered in the insertion direction. Also, to promote precise final alignment it is preferable that one or each device of the pair has means for urging the plug and socket portions together as the connector devices of the pair are brought together.

According to a second aspect of the present invention there is provided an optical connector device including: a support member formed with an aperture; an engaging portion extending at least partially within the said aperture and adapted for engaging with a corresponding portion of another optical connector device; and flexible material sandwiched between the support member and the said engaging portion for securing the engaging portion to the support member in such a way as to permit limited movement of the engaging portion in a direction transverse to the direction in which the said engaging portion and the said corresponding portion are brought into mutual engagement.

Reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1, discussed hereinbefore, shows a block diagram of parts of a communications network employing optical fibres; Figure 2, also discussed hereinbefore, shows a schematic cut-away side view of a conventional equipment housing rack and a plug-in module therefor housed in the rack; Figure 3 shows a schematic cut-away side view of an equipment housing rack and a plug-in module therefor embodying the present invention; Figure 4 shows a front view of the rack and plugin module of Figure 3; and Figure 5 shows in more detail a partiallysectional side view of optical connectors used to connect the module optically to the rack in Figure 3.

Figure 6 shows a schematic view, of parts of the Figure 5 optical connectors, for use in explaining the forces thereon during use.

The equipment housing rack 25 shown in Figures 3 and 4 has a shelf 26 in which a plurality of plug-in modules 27 can be removably fitted in respective housing positions of the shelf, the modules 27 each having a front face 28 and a printed circuit board 29 which can slide forwardly and backwardly within guides (not shown) provided on the top and bottom interior surfaces 30 and 31 of the shelf 26 to permit the modules 27 to be withdrawn from or inserted into the shelf individually. Locking mechanisms 32 serve to secure the modules 27 to the shelf when the modules are in place in the shelf.

Each module 27 has at its rear edge an electrical connector 33, for example a multipole plug connector, which engages with a corresponding electrical backplane connector 34 of the shelf mounted on a backplane connection panel 36 of the rack which extends vertically, perpendicularly to the printed circuit boards 29 of the modules 27. The different backplane connectors 34 for the modules are connected electrically together by wires behind the backplane connection panel 36 or by printed circuit tracks formed on the panel 36 itself.

Each module 27 also has a set of optical connectors 40 at its rear edge which, when the module is in its housing position, engage with respective optical connectors 42 mounted on the backplane connection panel 36 of the rack. The structure of the optical connectors 40 and 42 will be described later with reference to Figure 5.

The rack 25 also has, at an upper portion thereof, a fibre interface panel 50 which extends above, and parallel to, the backplane connection panel 36. The two panels 36 and 50 can be formed integrally if desired. The fibre interface panel 50 carries an array of further optical connectors 52 which are connected to respective ones of the optical connectors 42 by respective optical fibre links 54 passing therebetween behind the panels 36 and 50. It is possible for the connections between the optical connectors 52 and 42 to be made by "freespace" optics, that is by using light redirecting mirrors etc. to cause light beams to pass through the free space between the connectors behind the panels 36 and 50. The optical fibre links 54 can be provided by multimode or monomode optical fibres.

Optical fibres 56 (not shown in Figure 4), which can also be multimode or monomode fibres, are connected respectively to the optical connectors 52 mounted on the fibre interface panel 50. As shown in Figure 4, the connectors 52 are spaced apart so as to permit the fibres 56 to be connected and disconnected individually by manual manipulation.

Figure 5 shows the optical connectors 40 and 42 in more detail.

The optical connector 40 is a male connector and has a mounting portion 401 secured to the printed circuit board 29 of the module 27. The male connector 40 also has a plug portion 402 that has a tube 403, one end of which passes into a bore (not shown) in the mounting portion 401 and is slidable axially within the bore to permit movement of the plug portion 402, relative to the mounting portion 401, in the forward/backward direction of the rack.

The other end of the tube 403 is fixed to a spring mounting 404, and a helical spring 405 extends around the outside of the tube 403 between the spring mounting 404 and the mounting portion 401 so that the plug portion 402 is urged by the spring 405 in the rearward direction of the rack, away from the mounting portion 401.

The plug portion 402 also has, connected to the rear end of the spring mounting 404, a ferrule 406. An optical fibre (not shown) extends within the plug portion 402 from the free end of the ferrule 406 via the tube 403 into the mounting portion 401, through which fibre light can pass between the free end of the ferrule 406 and the mounting portion 401. The ferrule 406 surrounds and protects the optical fibre therewithin.

The ferrule 406 may be tapered in the rearward direction.

The optical connector 42 is a female connector and includes a sleeve 421 which is fitted in an aperture 422 in the backplane connection panel 36 by a mounting 423 made of flexible material. The sleeve 421 serves as a socket portion of the female connector 42 and provides an orifice 424 in which the ferrule 406 of the plug portion 402 of the male connector 40 is received, the spring 405 in the male connector 40 serving to promote penetration of the ferrule 406 into the orifice 424. The inside diameter of the sleeve 421 is preferably decreased in the rearward direction, so that the orifice 424, like the ferrule 406, is tapered in the rearward direction.

The sleeve 421 has inserted into its rear end one of the optical fibre links 54 used to connect the optical connector 42 to its associated optical connector in the fibre interface panel 50. The optical fibre link 54 is held in place by epoxy resin 425 for example.

When the ferrule 406 of the plug portion 402 of the male connector 40 is pushed fully home inside the orifice 424 of the female connector 42, the end of the optical fibre within the ferrule 406 is in close opposition to the end of the optical fibre link 54 so that light can pass between the two opposed ends with acceptably low attenuation.

The flexible mounting 423 used to secure the sleeve 421 to the backplane connection panel 36 permits limited movement of the sleeve relative to the panel as the two optical connectors 40 and 42 are brought together, so as to make insertion of the ferrule 406 into the orifice 424 consistently possible despite inevitable positioning tolerances of the connectors.

Similar limited movement of the plug portion 402 relative to the module 27 can be achieved, for example, by having a flexible mounting between the mounting portion 401 and the tube 403, in which case there is no need to employ a sleeve that is flexible to receive the ferrule.

The tapering of the orifice 424 in the rearward direction also serves to enable consistent insertion despite positioning tolerances. If the ferrule 406 is also tapered, initial alignment of the fibre end in the ferrule with the fibre end in the sleeve 421 is eased whilst accurate final alignment of the fibre ends is obtained when the ferrule 406 is pushed fully home into the orifice 424 by the action of the spring 405.

The flexible mounting 423 is preferably formed from an elastomeric material. The selection and dimensions of such an elastomeric material are discussed below with reference to Figure 6.

In Figure 6, L represents the length of the tapered portion of the sleeve 421 and D is the maximum mismatch (offset) between the centre of the ferrule 406 and the centre of the aperture 422 in which the flexible mounting 423 is fitted. Thus, D is a measure of the amount of limited movement, or play, which is required between the male and female connectors 40 and 42. 8 is the angle of the taper to the horizontal.

F represents the insertion force (assumed to be in the horizontal direction) required to insert the ferrule 406 into the sleeve 421. G represents the component of this insertion force F in the direction normal to the inner surface of the tapered portion of the sleeve 421. H represents this force G resolved in the vertical direction.

G = F Cos (900 - 8) N (N = newtons) H = G Cos 8 N H = F Cos 8 x Sin e N H is the maximum force required to produce the deflection D.

do is the elasticity coefficient of the flexible material mounting 423 in mm/N.

D = H x do mm do = D / (F Cos 8 x Sin 8) mm/N If some typical values are substituted a value of do can be calculated.

For example, the force to insert the connector should be less than 20N. The maximum offset of the connector halves should be less than 0.5mm. 8 can be calculated from D and L. L will be approximately 20mm.

Therefore: tan 8 = 1/20 For small angles sin 8 5 tan 8 and cos 8 Z 1 Thus: do > 0.5 / (20 x 1 x l/20)mm/N > O.Smm/N The required elasticity of the material is a function of outer thickness, e.g. a more flexible material can have narrower outer diameter. The material and its thickness can be selected to give the required value of do.

Because individual manual connection/disconnection of the optical connectors 40 and 42 is not required when they are employed in a rack as shown in Figures 3 and 4, the connectors can be smaller, and mounted more closely together, than the connectors 52 in the fibre interface panel 50. For example, the outside diameter of the flexible mounting 423 may be 7mm or less, the outside diameter of the sleeve 421 may be 4mm or less, and the outside diameter of the ferrule 406 may be 2mm or less.

It will be understood that the connectors 40 and 42 can use different structures than those shown in Figure 5 to facilitate the desired limited movement or play therebetween when the connectors are brought together.

Furthermore it is not essential that the connectors in the backplane connection panel 36 be female connectors whilst those on the modules are male connectors. Male connectors could be provided on the shelf, and female connectors on the modules, if desired.

It is not essential for the fibre interface panel to be parallel to the backplane connection panel. The fibre interface panel could, for example, be mounted horizontally in the rack.

Claims (12)

CLAIMS:

1. Apparatus comprising a rack, for housing a plurality of optical plug-in modules in respective positions in the rack, and such an optical plug-in module, the rack having at a rear portion thereof a plurality of first optical connector devices arranged so that, when the said optical plug-in module is brought into one of the said housing position in the rack, one of those first optical connector devices is engaged with a corresponding optical connector device of the module so as to permit an optical signal to pass between the rack and the module via the mutuallyengaged optical connector devices, and also having, at a fibre interface portion thereof accessible from outside the rack when the modules are housed therein, further optical connector devices, coupled optically within the rack to the said first optical connector devices, for connection to respective optical fibres extending to the rack from further equipment external thereto; one or both of the pair of optical connector devices, made up of the said one first optical connector device of the rack and the said corresponding optical connector device of the module, extending through an aperture in a support member and having flexible material, sandwiched between the support member and the device concerned, securing the device to the support member in such a way as to permit limited movement of the device in a direction transverse to the direction in which the two connector devices are brought into mutual engagement.

2. Apparatus as claimed in claim 1, wherein the rack also has at its said rear portion a plurality of electrical connector devices arranged so that when the said optical plug-in module is brought into one of the said housing positions in the rack, one of those electrical connector devices is engaged with a corresponding electrical connector device of the module so as to permit electrical signals and/or electrical power to pass between the rack and the module via the mutually-engaged electrical connector devices.

3. Apparatus as claimed in claim 1 or 2, wherein one of the devices of the pair has a light-transmitting plug portion which is adapted to be inserted into a light-transmitting socket portion of the other device of the pair.

4. Apparatus as claimed in claim 3, wherein one or each of the devices of the pair has means for urging the plug portion and socket portion together during insertion of the plug portion into the socket portion.

5. Apparatus as claimed in claim 3 or 4, wherein, in one or each of the devices of the pair, the plug or socket portion, as the case may be, of the device is tapered in the insertion direction.

6. Apparatus as claimed in any one of claims 3 to 5, wherein the said socket portion comprises a sleeve in one end of which the said plug portion is received when the devices of the pair are connected together, and in the other end of which an optical fibre is fitted, which fibre serves to couple the device having the socket portion to one of the said further optical connector devices of the rack.

7. Apparatus as claimed in any one of claims 3 to 6, wherein the said plug portion includes an optical fibre, an end portion of which is surrounded by a ferrule that is received within the said socket portion when the two devices of the pair are connected together.

8. Apparatus as claimed in any preceding claim, wherein the said support member is a backplane connection panel of the rack and serves to support all of the said first optical connector devices at different respective positions thereon.

9. An optical connector device including: a support member formed with an aperture; an engaging portion extending at least partially within the said aperture and adapted for engaging with a corresponding portion of another optical connector device; and flexible material sandwiched between the support member and the said engaging portion for securing the engaging portion to the support member in such a way as to permit limited movement of the engaging portion in a direction transverse to the direction in which the said engaging portion and the said corresponding portion are brought into mutual engagement.

10. A rack, for housing a plurality of optical plug-in modules in respective positions in the rack, substantially as hereinbefore described with reference to Figures 3 to 6 of the accompanying drawings.

11. Apparatus, comprising a rack and an optical plugin module for use with the rack, substantially as hereinbefore described with reference to Figures 3 to 6 of the accompanying drawings.

12. An optical connector device substantially as hereinbefore described with reference to Figures 5 and 6 of the accompanying drawings.