GB2191604A - Optical repeater having resilient coiled optical fibre carrier - Google Patents

Abstract

An optical repeater comprises a tubular pressure resistant housing (1, Figure 1), a pressure resistant bulkhead 2 removably secured to the housing, a tail cable 167 sealed in a gland 164 removably secured in the bulkhead 2, and a resilient coiled carrier 161 carrying optical fibres connected between the cable 167 and optical-electronic components of the repeater. <IMAGE>

Description

SPECIFICATION Optical repeaters This invention relates to repeaters suitable for regenerating the signal in a digital undersea transmission system.

With the advent of high speed digital optical systems it is important to ensure that the opto-electronic components are adequately protected from the hostile underwater enviroment. It is importantto prevent ingress of gas and moisture and and to maintain adequate screening between channels in the repeater.

It is an object of the present invention to provide a constructional arrangement which lends itselfto good screening, hermetic sealing and flexibility of requirements in system design.

According to the present invention there is provided an optical repeater for a submerged optical transmission system comprising a tubular pressure resistant housing, a pressure resistant bulkhead removably secured to the housing, and a tail cable sealed in a gland removably secured in the bulkhead, there being a resilient coiled carrier carrying the optical fibres connected between the cable on the one hand and the optical-electronic components of the repeater on the other hand whereby the gland or bulkhead can be removed from or assembled into the housing, the carrier stretching or closing like a spring during these manouvers.

In one embodiment the repeater comprising a pressure resistant bulkhead at each end removably secured to the housing, a pressure resiliant cable gland removably secured in each bulkhead, and a chassis located inside the housing, the chassis being electrically and optically connected to both cables in the cable glands, and being physically connected to one ofthe bulkheads, the optical and power feeds between the chassis and the cable in the other bulk head being held in the resilient coiled carrier.

Figures 7A and iB show details of Figure 1, not necessarily on the same scale; Figure 2 shows in perspective part of Figure 1 on an enlarged scale; Figure2A shows a detail of Figure 2.

Figure3 shows schematically part ofthe assembly procedure; Figure 3A shows a detail of Figures 3,4,5 and 6 on a larger scale; Figure4showsschematicallyanotheraspectof the assembly/test procedure; Figure5shows schematicaliy and on a largerscale one end of the repeater of Figure 1, and Figure 6shows schematically partofthe assembly/test procedure associated with the sea cable gland.

Referring to Figure 1 the undersea repeatercom prises a pressure resistant metal housing 1 made of steel sealed by bulkheads 2 and 3 at each end.

Through the bulkheads are sealed and secured re spectivefibre optic cables 4 and 5 which also have a power conductor e.g. 4a (Figure 3A) for providing el ectrical power to the repeater to power the circuitry.

The technique by which the cable, power conductor and fibres are sealed through the bulkhead together with other aspects of the repeater are described in ourco-pending British PatentApplications2058484 (Parfree 10-7-2) and 8401447 (D.A.Gunn et all 0-6-1 - 1) and 8401432 (A.A. Davis-R.Eady 3-2).

The bulkheads 2 and 3 each contain a sealed chamber (not shown), in which the optical fibres 6 and 7 are spliced and the fibres extend from the chamber on a carrier 161 (Figure 5)through the bulkhead radially or radially and circumferentially and followagentlycurved pathintoalongitudinaldirec- tion towards the semiconductor injection laser in its package 8 and the PIN FET diode Sa and receive amplifier package 9b in an assembly 9. Both packages and assemblies are hermetically sealed. The laser package 8 is sealed into an aperture 10 inclined towards the longitudinal axis of the repeater and more easily seen in Figure 2, and the assembly 9 has interconnection leads 9c extending between the receive amplifier package 9b and casing 21, and her meticallysealed in both.

Referring to Figure 2 there is shown a transmit and receive module 20 comprising a metal casing 21 having eight sides around its circumference. Four of the sides 22,23,24 and 25 provide for electrical and optical connections, either interconnections between this module and the adjacent or co-operating module, or input and output power and optical signal connections to and from the sea cable 4 or 5.

The otherfour sides 26,27,28 and 29 support electrically insulating thermally conductive resilient heat transfer devices 30,31,32 and 33 which provide a good heat transfer path between the module and the metal housing 1.

Each heat transfer device such as 30 comprises a box-like part 40 made of heat conductive electrically insulating material such as alumina, the underside of part 40 being secured e.g. by heat-conductive glue, to face 26. Inside the box-like part 40 is seated a channel shaped part 41 of brass with slots 42 in the side walls 43 ofthechannel 41. The part41 is in good heat transfer connection with the base of box 40. A number of transverse metal slats such as 44 have two lugs45 and 46 which locate in the opposed slot 42 and metal springs 47 urgetheslats44outwards.

The surface of the slats 44 will bear against the inside surface of the housing 1 when the module is located in the housing 1, slightly compressing the springs 47.

Thefunction of the heattransfer devices such as 30 is to ensure that the temperature of the electronic components and particularly the laser diode rises as little as possible above the ambient temperature of the repeater housing 1 which on the seabed will nor mally be close to 4"C except in tropical areas or where strong currents flow. The heat transfer dev ices are more fully described in our co-pending app lication 8401432 (A.A. Davis-R.Eady3-2).

The interior of the casing 21 is divided into two re gions by an integral wall 50. Thus on the side ofthe module 20 hidden from view is a circular chamber corresponding to the one which is visible but over twice as deep. The visible chamber houses the transmit circuitry; the hidden chamber houses the receive circuitry and supervisory circuitry. The in tegral wall ensures good screening between the transmit and receive parts of the circuitry. The module is closed and sealed hermetically by welding orsoldering a metal lid on each sidetoa rim such as 51 on the module casing 21 with an inertclean atmosphere locked inside.

On theface 24 ofthe module casing, diametrically opposite the laser package 8, will be mounted a PIN FET diode and receive amplifier assembly similarto the assembly 9 shown in Figure 1. This will receive the signal from the direction B to A in fibre 7a and the laser package8transmits the regenerated signal in the same direction via fibre 6. The arrows on thefibre indicate the signal direction.

The regenerator module 60 shown in Figure 1 is similar two module 20 in all respects exceptthat it receives and transmits in the direction Ato B via fibres 7 and 6a respectively and the supervisory circuitwill respond to provide a loop back condition in response to a different signal compared with module 20.

In between the two modules 20 and 60 is a power module 70 which receives powerfrom the cable 4 and zener diodes are used to pick off a voltage for powering the adjacent modules 20 and 60. In other respects the structure of module 70 is the same as 60 and 20.

The three modules 20,60 and 70 are clamped togethertoforma modular assembly by bolts (not shown) passing through holes such as 48 (Figure 2) and cylindrical spacers on the bolts and between the modules. At each end there is clamped (Figure 1 B) an insulating plastics plate 80 with holes 81 corresponding to holes 48. Plate 80-has a hole 82 which at one end (right hand) co-operates with an annular projec- tion 83 on a second insulating plastics or glass fibre plate 84to hold a resilient '0' ring 85 between them.

Projection 83 has an annular recess 83a in which the '0' ring 85 partially sits. Screws secured in holes such as 86 in plate 84 locate in holes 86a in plate 80to secure this plate to plate 80 but with freedom for limited radial but not axial relative movement between the plates against the resilience of the '0' ring 85 and such thatthe resilient heattransfer devices are not damaged byovercompression during shock loading on the housing. The plate 84 is a sliding fit inside the repeater housing 1 whereas plate 80 has a smaiier overall diameter, and the '0' ring 85 acts as a resilient radial supportforthe modular assembly 20,60,70 at the right hand end.Furtherthe assembly is locked to the end flange 90 ofthe bulkhead 2 by a rubber ring 91 having two internal grooves 92,93 into which fit the peripheries of flange 90 and the flange 94 of module 20 (flange 94 is not shown in Figure 2 but is secured to the casing 21). An annular metal clamping ring 95 is secured overthe rubber ring 91 to resili ently lock the modular assembly to the bulkhead in an axial direction and in the rasdial direction.

The modular assembly described provides regeneration for a fibre pair in the cable 4 and 5for both directions. A second modular assembly indicated generally by reference numeral 100 is similartothe one just described and provides regeneration for a second fibre pair in the cable. The two modular assemblies are locked together by a rubber ring 91 and clamp 95 in the sameway asthefirst modular assembly is locked to the bulkhead 2 and as shown in Figure 1A.

In the embodiment shown in Figure 1 there are illustrated just two modular assembliosfortwo fibre pairs. In practice the repeater housing 1 could accommodate more such assemblies depending on the numberoffibre pairs in the system and the length ofthe housing 1. In assembling the regenera torthe left hand bulkhead 2 is pre-assembled with the modular assemblies joined together and then inserted into the housing. The right hand end is then completed by making the necessary splices between tail fibres and power feed connections, and the right hand bulkhead is then secured and sealed in place.In repairing a regenerator the left hand bulkhead can be removed complete with modular assemblies and there is enough coiled length in the fibres and power feed atthe right-hand end to enable the left hand bulkhead with assemblies attached to be completely withdrawn.

The embodiment described has the advantage of three distinct levels of sealing the opto-electronics from the hostile environment of the ocean bed; there aretwosealsthroughthe bulkhead and afurtherseal through the individual regenerator module or power module. Afurther advantage is the flexibility in de- sign -an additional modular assembly can simply be added for each fibre pair of the system without the need to design a different regenerator for each system. It also has the distinct advantage of enabling individual pressure testing of each seal and of electrically and optically testing each module priorto assembly. The individual modules are inherently self screening so that electronics of each module are well screened from other modules.

The embodiment described also facilitates assembly and repair and in particular splices between the sea cable and the repeater.

Figure 3 of the drawings showes this somewhat schematically and Figure 3A shows a detail of Figure 3.

Referring to Figure 3 the repeater housing 1 is shown housingthetwo bulkheads2and3. Bulkhead 2 is in position in the housing together with the two modular assemblies of Figure 1 designated generally by the reference numeral 150 and secured to the bulkhead 2 by the clamping ring 95 as described earlier.

Between the pressure chamber of bulkhead 3 and the end of the modular assembly 150 is a 'U'-section resilient fibre carrier 151 part of which is shown in greater detail and on an enlarged scale in Figure 3A, which in this embodiment is moulded from plastics e.g. Nylon (Trade Mark). Referring to Figure3Athe U-channel 152 opens outwardly and contains the four (or more) fibres. On the radially inner surface of the carrier is defined a second channel 153 for the powerfeed conductor4a and there are chip-like elements 154 which retain the power conductor 4a within the channel 153.

The carrier 161 is exactly the same as the carrier 151 except 161 is smaller in overall diameter and is shorter because it only needs to open over the distance "z" shown in Figure 6which is similarto the distance "x" but much shorter than the distance y In the U-section channel 152 of the carrier 151 are located four optical fibres, two of which (6a and 7a) are shown in Figure 1 for modular assemblies 20,60 and 70, the other two (not shown in Figure 1) serving to carry the transmission signals to and from the modular assembly 100.

The U-section carrier 151 enables the modular assemblies attached to the bulkhead 2 to be mounted within the casing 1 as shown in Figure3whilethe bulkhead 3 is out ofthe casing. The fibres from the 'B' end of the modular assemblies can be withdrawn from the casing and secured via the glands into the 'B' end bulkhead pressure chamber. This carrier 151 can stretch over the distance "x" to allowthis procedure. Furthermore afterthe basic assembly has taken place and the bulkhead 3 is sealed to the casing 1, it may be desired to remove bulkhead 2 and ex- posethewholemodularassemblyfromthe'A'end as illustrated in Figure 4, for e.g. testing purposes.

The U-section carrier will enable this to be done by stretching elastically overthe distance "y" whilst allowing full optical and power connection through bulkhead 3 to be maintained, therebey enabling test ingto be carried out.

In addition within each pressure chamber at the "A" and at the "B" end are located respective second and third U-section carriers ofsmaller diameterthan the carrier 151. One of these is shown in Figure 5 and designated 161 located in the pressure chamber 162 ofthe bulkhead 2. This carrier is secured at one end of a splicing chamber 163 carried on the back ofthe cable gland 164. The gland 164 is removably secured in the central aperture 165 of the bulkhead 2 by screws such as 166. The diameter of the aperture 165 is slightly larger than the outer diameter of the carrier 162 so that the gland with the carrier attached can be assembled or removed and fibre splicing can be carried out to splice e.g. at 168 the fibres ofthotail cable 167 to the fibres 6 and 7 coupled to the laser and the photodiode. Thus the carrier 161 extends el astically so that the splice chamber can be with- drawn through the aperture 165 to a location outside the bulkhead as shown in Figure 6. When splicing is complete the gland is returned and the coils ofthe spring-like carrier 161 close up. The diameter of the aperture 165 is large enough to allowthe minimum bending radius ofthe fibre in the carrier 161 not to be exceeded (in the negative sense).

Claims (4)

1. An optical repeater for a submerged optical transmission system comprising a tubular pressure resistant housing, a pressure resistant bulkhead removably secured to the housing, and a tail cable sealed in a gland removably secured in the bulkhead there being a resilient coiled carrier carrying the optical fibres connected between the cable on one hand and the optical-electronic components of the repeater on the other hand whereby the gland can be removed from or assembled into the housing, the carrier stretching or ciosing like a spring during these manouvers.

2. An optical repeater as claimed in claim 1 comprising a pressure resistant bulkhead at each end removably secured to the housing, a pressure resistant cable gland removably secured in each bulkhead, and a chassis located inside the housing, the chassis being electrically and optically connected to both cables in the cable glands, and being physically con- nected to one of the bulkheads, the optical and powerfeeds between the chassis and the cable in the other bulkhead being held in the resilient coiled carrier.

3. Arepeater as claimed in claim 1 or claim 2, wherein said carrier has a u-section channel in which said optical fibres are located.

4. A repeater substantially as hereinbefore described with reference to Figures 3 to 6 of the accompanying drawings.