WO2000033118A1

WO2000033118A1 - Fibre optic management

Info

Publication number: WO2000033118A1
Application number: PCT/GB1999/004002
Authority: WO
Inventors: Alain Wambeke; Bart Herremans; Etienne Robert Laeremans
Original assignee: Tyco Elctronics Raychem Nv; Raychem Limited
Priority date: 1998-12-02
Filing date: 1999-11-30
Publication date: 2000-06-08
Also published as: AU1398700A

Abstract

A guide unit (31) for the transition region between primary and secondary clad optical fibres, has at least one channel (53) for receiving at least the transition region of a single optical fibre, and retainer means (64) for retaining at least the transition region of the optical fibre within the channel. Some of the walls defining the channels (53) have notches or recesses in a surface thereof to receive the retainer means (64).

Description

FIBRE OPTIC MANAGEMENT

The present invention relates to fibre optic management systems, and in particular systems for retaining and guiding optical fibres which are to be joined end-to-end in a so-called splice.

The management of optical fibres in networks for communication purposes is becoming

increasingly complex with the need to be able quickly and easily to install networks leading

from trunk transmission cables or bundles of optical fibres through secondary racks or

cabinets at the interface between the main communication trunk and a local area such as a building, and further subsidiary splice trays where optical fibres are spliced or divided in order

to route the communications information stream appropriately.

Because of the possibility of future changes to the communication routes optical fibre

infrastructure systems must be capable of modification at a later date, and for this purpose

splice organiser technology must allow for the possibility of individual fibres being handled to

make new splices, and/or reposition them within the tray or cabinet within which they are

originally located. Optical fibres, however, are not very robust and, in particular, must not be

subject to a bend radius tighter than a critical minimum radius in order to avoid damage

resulting in loss of transmission. Partly to accommodate this, and in order to leave sufficient

freedom to future users, it is known to form splices in organiser trays or cabinets in which

surplus lengths of fibre are held in loops or coils which will allow future changes to the connections to be made. Considerable attention has been given to means for handling and

accommodating spare loops or coils of fibre in order to avoid bending these at less than the

critical radius, usually in separate storage units forming part of the overall assembly. Such means usually involve providing external guidance to the loops, so that the curvature of spare loops of optical fibre is defined by the position of guide surfaces on the radially outer side of

the path followed by the loop.

Because access to fibres after initial installation is often required to allow changes such as

reassignment to be made to connectors or fibres, and in particular because in many cases

reconfiguration, testing and expansion are regularly required, a system in which access to the

fibres is easily available for the operator such as by relatively loose guidance for the loops has many advantages.

Although such an arrangement is satisfactory for the main length of the spare loops of optical

fibres, it has been appreciated by the present inventors that there is a particular problem in the

region close to a splice. This occurs because the optical fibre, which as is known comprises a

central core of optically transmissive material (typically of 9 microns in diameter) clad with an

inner or primary cladding which, together with the core defines the optical path for light

within the fibre. The primary cladding of multimade optical fibres is usually 250 microns in

diameter. An outer layer, for the purpose of providing adequate physical support is provided

in the form of a secondary cladding which may be 900 microns or above in diameter. The

fibre has to be stripped of these outer, or secondary claddings in the region of the splice in

order properly to form the splice. The central core of a conventional optical fibre with its

primary cladding, typically of the order of 250 microns in diameter, is referred to hereinafter

as primary fibre, and clad fibre, typically up to 900 microns in diameter is referred to

hereinafter as secondary fibre. The region from which the coating is stripped to bare the

primary fibre is referred to as the transition region since, in this region the fibre exhibits a transition from the smaller diameter of the primary fibre, to the larger diameter of the

secondary fibre.

The stiffness of primary optical fibre is less than that of secondary fibre and, therefore, at the

transition there is a singularity which, it has been determined by the present inventors, requires special attention in order to give reliable performance.

In many optical fibre splice organisers the splices themselves together with short sections of

the primary fibre to either side, are held in a rectilinear configuration, with the splices being

located in splice holders in order properly to protect the region of the splice which is less

strong than the remainder of the optical fibre. Because of space restrictions the spare lengths

of optical fibre must then be coiled or looped within the organiser tray or cabinet and

although the length of stripped primary optical fibre is kept, for obvious reasons, to a

minimum, there is a certain risk that a bending stress will be exerted in the transition region.

Tests conducted by the applicants have established that splice organiser trays subject to

impact or vibration, which happens from time to time in a real life environment, can be

subject to variations in transient transmission losses in excess of ldB and this is entirely

unacceptable. It has been determined that such transient transmission losses can be

minimised or eliminated by supporting the optical fibres at the transition regions where the

strength singularity is located.

The present invention seeks, therefore to provide a guide unit for optical fibre transitions

which will overcome the above-described problem. In particular, the present invention seeks

to provide a device which will secure optical fibres in the transition region and protect the fibres from excessive bending either in static or dynamic (i.e. vibration-induced or impact- induced) conditions. Such a device is not known from the Prior Art.

British Patent Application GB 2 250 105 discloses a splice tray provided with a groove for retaining a splice. The problem of transient regions is however not addressed.

European Patent Application EP 0 581 306 discloses another type of splice tray in which a

strain relief device is arranged near the transition region of a fibre cable but the transition

region itself is not supported, nor are the primary fibres restrained.

Other examples of Prior Art optical fibre splice trays are disclosed in United States Patents

US 5 353 366, US 5 530 787, and US 5 071 211. However, none of these US Patents deals

with the transition region between primary and secondary clad optical fibres.

According, therefore, to one aspect of the present invention there is provided a guide unit for

the transition region between primary and secondary clad optical fibres, having at least one

channel for receiving at least the transition region of a single optical fibre, and retainer means

for retaining at least the transition region of the said optical fibre within the channel.

In a preferred embodiment of the invention the said retainer means comprise a cover

extending over at least part of the or each channel.

In a practical embodiment the said retainer means are removable to allow access to the fibre

for manipulation thereof subsequent to installation. Of course, for most practical applications a guide unit of the invention should have a plurality of channels, and in embodiments of the

invention formed with a plurality of channels these are preferably defined between adjacent upstanding walls of the unit.

Preferably, at least some of the walls have notches or recesses in a surface thereof to receive

the said retainer means. When installed, therefore, the guide unit with the retainer means has

a smooth and relatively uninterrupted outer profile to avoid the risk of snagging or catching

of other fibres within an optical fibre splice organiser tray or cabinet.

In a particularly preferred embodiment the said retainer means are provided with snap-

enagageable connectors receivable in respective openings in the guide unit whereby to hold the retainer means in place thereon. Such a configuration allows the ready removal of the

retainer means at a subsequent time to allow changes to be made.

In embodiments of the invention having a plurality of channels it is particularly convenient if

each channel is curved along its length. This, then, allows the guide unit to limit the

minimum bending radius of the fibres guided thereby as well as securing the transition region

against movement induced by impact or vibration and thereby preventing transient losses in

use of the system. Practically, of course, splice organiser trays are made of limited

dimensions in order to make the maximum use of available space, which means that it is

sometimes not possible for the bend radius of adjacent fibres to be centred at the same point.

This is especially true of the situation in which a relatively large number of splices are located

side-by-side, occupying a significant width, whereas the spare loops of fibre must overlie one

another after having been turned through an angle, typically at 90°, to position the spare optical fibre loops along the side of the organiser tray. A particularly preferred embodiment

of the invention is, therefore, provided with an individual centre of curvature for each channel

different from that of at least some of other channels. In the specific embodiment to be

described hereinafter in more detail the centre of curvature of each channel is in fact different from that of all of the other channels.

The channels of a guide unit of the invention are typically separated by ribs which separate

adjacent channels. Facing walls of each channel are preferably substantially parallel to one another to provide a regularly spaced guide for an optical fibre, whereas opposite walls of

each rib preferably converge from one end of the rib to the other in order to achieve the

configuration in which adjacent channels have different centres of curvature. A corollary to

this is that the lengths of the guide channels are not necessarily all the same although, for

obvious reasons, it is preferable for the guide channels to have a region which is at least a

certain distance from the splice in the optical fibres so that it is not necessary for the operator to know in advance which channel of the guide unit will be occupied by a given fibre when

stripping the primary fibre and consequently determining the distance between the splice and the transition.

The retainer means which, as mentioned above, are preferably in the form of a cover, do not

have to extend over the entire length of every channel although it does have to cover a part

of each channel in order to retain the optical fibre located within the channel in position and

prevent escape even in the event of severe impacts. It has been found that by forming at least

one edge portion of the cover to project beyond the boundary of the unit it is possible to

provide additional guidance for the optical fibres of the spare loop. A guide unit formed as an embodiment of the invention may also be provided with a

projecting limb for locating the unit in position on an optical fibre organiser frame or tray.

The present invention also comprehends an optical fibre splice organiser, in the form of a

frame or tray or the like, having means for retaining one or a plurality of optical fibre splices

in position thereon, means for guiding primary clad optical fibres stripped of their secondary

cladding to the splice, and at least one fibre transition guide unit located in the region of the fibre transition or transitions.

The present invention also comprehends an optical fibre splice organiser having means for

locating and retaining at least the transition region of a spliced fibre against displacement,

comprising opposite guide surfaces for constraining the fibre to follow a predetermined path

at least over the transition region.

Various embodiments of the present invention will now be more particularly described, by

way of example, with reference to the accompanying drawings, in which:

Figure 1 is a schematic view of the splice and transition region of a set of optical

fibres;

Figure 2 is a diagrammatic schematic view of the relative positioning of a splice

holder and a transition guide formed in accordance with the present invention;

Figure 3 is a schematic plan view of a splice organiser tray showing a transition guide

unit formed as an embodiment of the invention located in position; Figure 4 is a perspective view of a transition guide unit of the invention used in conjunction with a cover of the invention;

Figure 5 is a diagrammatic perspective view of a guide unit formed as an embodiment of the invention;

Figures 6 and 7 are plan views of symmetrical left and right handed guide units, with a plan and side view of an associated cover;

Figure 8 is a view on a larger scale of a part of a splice organiser tray with a guide

unit of the invention located in position, particularly showing the shape and position of the

retainer cover;

Figure 9 is a perspective view of an alternative configuration of retainer cover; and

Figure 10 is a partial perspective view of a splice tray showing the retainer cover of

Figure 9 in position.

Referring now to the drawings, and particularly to Figure 1, there is schematically shown an

arrangement 10 consisting of a set of three primary optical fibres 11, 12, 13 joined at splices

14, 15, 16 to the primary fibres 17, 18, 19.

The splices 14, 15, 16 are supported in a splice protection region to either side of the

individual splice itself by respective splice protectors 20, 21, 22. These may be of any appropriate type and will not be described in more detail hereinbelow.

In order to expose the primary fibres 11, 12, 13 the secondary cladding of the fibres identified

as 23, 24, 25 respectively has been stripped off and, as will be seen from Figure 1, a portion

of each of the primary fibres 11, 12, 13 extends beyond the fibre protection region defined by the protective housings 20, 21, 22 up to the transition regions 26, 27, 28 between the primary

fibres 11, 12, 13 and the secondary fibres 23, 24, 25. Typically, the primary fibre may be a loose tube primary fibre of 250 microns diameter and the secondary may be a semi-tight clad fibre of about 900 micron diameter.

It has been established by the applicant that such transitions are the cause of significant

variation in losses, that is greater than 1 dB, when subject to verification and vibration testing of a fibre splice organiser tray having a splice configuration such as that described in relation

to Figure 1, and simulating real life requirements. Such transitions are also subject to stresses

when handling the connectors in the patch panel of the tray.

Figure 2 illustrates in schematic form the position of a splice holder and protector

assembly 30 (corresponding to the housings 20-22 of Fig. 1) in relation to an optical fibre

transition guide formed as an embodiment of the invention and generally indicated 31. The

transition guide 31 acts to locate the transition region of each optical fibre laterally and to

guide the optical fibres 32 (corresponding to the optical fibres 11-13 in Fig. 1) in a curved

path which, at least in the transition region, does not exceed the critical bend radius. Because

the splice holder 30 retains the optical fibres 32 (shown in Figure 2 as comprising twelve

fibres 32a-321) in a side by side array these fibres occupy a width generally indicated D in

Figure 2. The available space for the secondary optical fibres, however, is frequently less

than D and, as shown in Figure 2, may for example be in the region of d. In order to

accommodate this the curved line to which each fibre 32 is guided, comprises here an arcuate

section having a different centre of curvature indicated 43a-431 respectively to identify the centre of curvature of the curved path of each optical fibre 32. The radius of curvature is

chosen so as to be at least equal to the minimum bend radius of the fibres.

The embodiments of the transition guide 31 shown in Fig. 2 has curved fibre trajectories in

order to minimise the surface area required for accommodating the splice holder 30 and at

least one transition guide 31 in a single tray. It will be understood that the transition guide of

the present invention can equally well be provided with substantially straight trajectories.

Figure 3 shows a configuration of use of the transition guide 31 of the present invention. A

splice organiser tray 45 of known type has a splice holder and protector assembly 30 located

adjacent one end thereof. One secondary fibre transition guide unit formed as an embodiment

of the invention is shown in position to one side of the splice holder 30 to retain the transition

region of the secondary fibres and guide the path of the fibres into loops, generally indicated 48, guided within a tray 49 in a known way. It will be appreciated that, although only one

transition guide 31 is shown in Figure 3, positioned to one side of the splice holder 30, such

guide units may be located symmetrically to both sides of the splice holder and, in practice,

would be so provided.

In Fig. 4, a transition guide unit 31 and an associated cover 64 of the present invention are

shown when assembled. The transition guide unit 31, which will be discussed in more detail

later with reference to Fig. 5, is provided with channels or slots 53 which define fibre

trajectories. The cover 64 constitutes the restraining member which prevents the fibres (not

shown in Fig. 4) from leaving the slots 53. In the particular embodiment shown, the cover 64 is provided with wings 71 and 73, as will be discussed in more detail later with reference to

Fig. 9.

Referring now to Figure 5 an exemplary transition guide unit 31 is shown in perspective. The

guide unit 31 is formed as an integrally moulded unitary body suitably of a hard plastics

material such as PC/ABS-NO having a generally planar base 51 with a plurality of arcuately

curved upstanding ribs 52 defining between them respective arcuately curved channels 53.

As will be seen from the drawings, and in particular Figure 5, the channels 53 are each

defined by opposite facing wall surfaces of adjacent ribs 52 which are substantially parallel to one another such that each channel 53 is of substantially the same lateral width throughout its

length. Opposite faces of the same rib, however, are not parallel to one another such that each rib tapers from end to end. This results in each adjacent channel 53 having a different

centre of curvature as particularly illustrated in Figure 2. The locus of the centres of

curvature is plotted in Figure 2. The height of each channel 53 is substantially greater (in this

embodiment between two and three times greater) than the width of the channel such that a

secondary fibre placed in and guided by the channel can be pressed down to a lower region

and be securely located therein. The upper faces 54 of the ribs 52 are provided with aligned

notches or recesses 55 to receive a retainer or cover 64 (see Figure 9) which acts to hold the

optical fibres in position in the channels 53. The notches or recesses 55 are aligned with one

another to form an interrupted groove extending between two lugs 56, 57 on opposite sides

of the guide element, and each having a respective transverse opening 58, 59 into which a snap-engageable connector (see Figure 9) of the retainer cover can be fitted to retain the cover in position on the unit. Various different possible configurations of the retainer cover are shown in Figures 6, 7 and 8 in addition to the exemplary embodiment of Figure 9.

The proposed lugs 56, 57 of the unit 31 aid in locating it in position on an organiser tray such

as the tray 45 of Figures 3 and 4. To aid positioning the lug 57 has an associated secondary lug 60 adjacent thereto defining between them a bight 61 which can be engaged over a pin or

peg (not illustrated) on the organiser tray 45 in order to locate the guide unit 31 accurately in

the tray 45.

Figure 6 shows symmetrical left and right guide units 3 IL and 3 IR in which the two openings

58, 59 for receiving the connectors 62, 63 of a retainer cover 64 are aligned parallel to one

edge of the unit 31 and the retainer cover 64 has a generally triangular shape lying to one side

of a line joining the two connectors 62, 63. These connectors 62, 63 are formed as split pegs

to allow a frictional or snap-engagement contact between themselves and the openings 58, 59

when the cover is located in position.

In the embodiment of Figure 7 the guide units 3 IL, 3 IR are of substantially the same

configuration as in the embodiment of Figure 6, but the cover 64 is configured as a

"butterfly" shape with two opposite lobes or wings 66, 67 extending in opposite directions

from the line joining the connectors 62, 63. Moreover the connectors 62, 62 are formed as

pins projecting to both sides of the general plane of the retainer cover 64 to allow it to be

positioned on the guide unit 3 IL or 3 IR in either of two orientations with one of the lobes

66, 67 overlying the unit 31 itself and covering at least part of each channel and the other lobe overlying the path followed by the optical fibres where they extend from one end of the channels in the guide unit.

The particular embodiment of the cover is chosen to optimise the area of the transmission

guide covered while providing symmetry (and thus exchangeability between two mirror-

imaged transition guides) and avoiding interference with other parts of the tray 45, such as

the lid latch 39. It will be understood that other shapes of the cover 64 may be chosen if other requirements apply. Thus, a cover 64 extending over the entire transition guide 31 may

be used, or a cover 64 which does not extend beyond the recesses 55 (Fig. 5).

Figure 8 shows a further alternative configuration in which the retainer cover 64 likewise has

two oppositely directed lobes 66, 67, but the position of the holes 58, 59 for receiving the

connectors 62, 63 is such that the line joining them does not lie parallel to one side of the unit

such that each lobe partly overlies some of the channels with relatively little overlap beyond

the edge of the unit 31.

Figure 9 illustrates a retainer cover of different form having a central "spine" 70 extending

between the two connectors 62, 63 and two pairs of oppositely directed wings 71, 72 and 73,

74 separated from one another by a section 75 of the "spine" 70. An arcuately curved

transversely extending rib 76 projects from a nose portion 77 of the spine 70 beyond the

wings 71, 72 and adjacent the connector 62 to assist in locating this into the hole 56 by

contact with the outer curved cylindrical surface of the boss 56 of the unit 31 illustrated in Figure 5. Figure 10 illustrates a splice tray 45 fitted with a guide unit 31 over which is a retainer cover

64 of the form illustrated in Figure 9. The relative orientation of the guide unit 31 and the

retainer cover 64 can be seen from Figure 10, which also shows how the wings 73, 74 of the

cover project beyond the ends of the channels of the guide unit 31 in use so as to help retain

in place any spare loops of optical fibre which may be stored in the tray, for example as

shown in Figures 3 and 4. It can also be seen from Fig. 10 that the wings 73, 74 of the cover 64 stay clear of the lid fastening means 89 of tray 45.

It will be understood by those skilled in the art that the the embodiments described above

are provided by way of example only and that many additions and modifications are

possible without departing from the scope of the present invention as defined in the

appending claims

Claims

1. A guide unit (31) for the transition region between primary and secondary clad optical

fibres, having at least one channel (53) for receiving at least the transition region of a single optical fibre (32), and retainer means (64) for retaining at least the transition

region of the said optical fibre (32) within the channel (53).

2. A guide unit as claimed in Claim 1, in which the retainer means (64) comprise a cover

extending over at least part of the or each channel (53).

3. A guide unit as claimed in Claim 1 or 2, in which the retainer means (64) are

removable to allow access to the fibre (32) for manipulation subsequent to

installation.

4. A guide unit as claimed in any of Claims 1 to 3, in which there are a plurality of

channels (53) defined between adjacent upstanding walls (52) of the guide unit (31),

and at least some of the walls (52) have notches or recesses (55) in a surface (54)

thereof to receive the retainer means (64).

5. A guide unit as claimed in Claim 3 or 4, in which the retainer means (64) have

snap-engageable connectors (62, 63) receivable in respective openings (58, 59) in the guide unit (31) whereby to hold the retainer means in place thereon.

6. A guide unit as claimed in any preceding claim having a plurality of channels (53) with

each channel being curved along its length.

7. A guide unit as claimed in Claim 6, in which at least some of the curved channels (53) have different centres (43) of curvature.

8. A guide unit as claimed in Claim 7, in which each channel (53) has an individual

centre of curvature (43) different from that of at least some of the other channels.

9. A guide unit as claimed in Claim 7 or 8, in which the centre of curvature (43) of each

channel (53) is different from that of all the other channels.

10. A guide unit as claimed in any preceding claim, in which there are a plurality of

channels (53) separated by ribs (52), facing walls of each channel being substantially

parallel to one another and opposite walls of each rib converging towards one another

from one end to the other.

11. A guide unit as claimed in any preceding Claim, in which the depth of the or each

channel (53) is substantially greater than the width thereof.

12. A guide unit as claimed in any preceding claim, in which the retainer means (64)

comprise a cover extending over the or each channel (53) and at least one edge

portion of the cover projects beyond the boundary of the unit (31).

13. A guide unit as claimed in Claim 12, in which the said at least one portion (73, 74) of

the cover (64) projects beyond the boundary of the unit (31) in the region of the exit ends of at least some of the channels (53) whereby further to guide the path of optical

fibres in the channels.

14. A guide unit as claimed in any preceding claim, further having a projecting limb (76)

for locating the unit in position on an optical fibre organiser frame or tray (45).

15. An optical fibre splice organiser having means (30) for retaining one or a plurality of

optical fibre splices in position and at least one fibre transition guide unit (31) located in the region of the fibre transition or transitions.