GB2053784A

GB2053784A - Apparatus for and method of production of optical branching element and its components

Info

Publication number: GB2053784A
Application number: GB8020902A
Authority: GB
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1979-06-27
Filing date: 1980-06-26
Publication date: 1981-02-11
Also published as: FR2459987B1; DE2926003A1; FR2459987A1; GB2053784B

Abstract

A moulding body 1 is provided with a precision recess 2 to be filled with a casting compound, and with guide grooves 4,6 for light waveguides 9,10. One of the guide grooves, 6, is shaped to allow adjustment of the waveguide by means of a member 7. The light waveguides 9,10 intersect at an edge A9' of the recess 2 at an angle of 45 DEG . At least in the region of this intersection point the moulding body is provided with a hollow 5. Moulding pins 3a, 3b may be used to form recesses adjacent the waveguides so that supportive glass capillary tubes can be inserted into the recesses over the waveguides. Following the hardening of the casting compound and the ejection of the element half at least that side surface F9' whose surface normal forms an angle of 45 DEG with the light waveguides 9,10 is polished so as to be optically flat. Two halves of this kind, one of which is provided with a transmissive/reflective interface, are assembled to form a branching element. <IMAGE>

Description

SPECIFICATION Apparatus for and method of production of optical branching element and its components This invention relates to apparatus for and method of production of optical branching element and its components where the branching element is to operate in accordance with the beam divider principle.

Optical branching elements which operate in accordance with the beam divider principle are known for example from the IEEE Catalogue No. 79, CH 1431 - 6 QUE 1979, pages 80,82 and 83. In a precisely shaped, right-angled and equilateral component, one light waveguide is enclosed as the bisector of the right angle. The two side surfaces which enclose the right angle are subsequently polished together with the tip of the enclosed light waveguide. A branching element is formed by the precise assembly of several such components interposing a partially transm issive/reflective interface, for example a thin metal layer of a dielectric interface. The polishing or grinding of the optical bevels at the tips of the individual components gives rise to substantial difficulties.The tips of the light waveguides can easily break during the polishing or grinding procedure with the outcome that these components can no longer be used in a low-loss junction.

Other optical branching elements which operate in accordance with the beam divider principle have also been proposed, wherein a plurality of light waveguides abut against one throughgoing light waveguide. The light waveguides run in guide grooves, formed for example in a silicon plate or other substrate, and are fixed with the substrate to a cover by cementing. This "sandwich" is subsequently split at an angle of 45" to the light waveguides through the point of intersection of these light waveguides. Then the cut surfaces are polished so as to be optically flat, one of the cut surfaces is rendered partially reflective, and the two components are precisely reassembled and cemented.

There can be no question of the ends of the light waveguides breaking off during grinding and consequently optical branching elements exhibiting very low transfer losses can be produced with a high success yield.

According to a first aspect of this invention there is provided apparatus for the production of a component part of an optical branching element which is to operate in accordance with the beam divider principle, said apparatus comprising a mould body in which is provided a precision recess in the shape of at least part of the component to be produced, said shape including a side surface the normal to which forms an angle of substantially 45" with the path of at least one light waveguide to be included in the component so as to intersect said side surface intermediate its ends, said mould body including a guide groove for the or each said light waveguide, the longitudinal axis ofthe guide groove extending in the desired direction of said light waveguide to intersect an edge of the precision recess that corresponds to said side surface.

According to a second aspect of this invention there is provided a method of producing a component part of an optical branching element which is to operate in accordance with the beam divider principle, said method including the steps of forming a block of casting compound around at least one light waveguide so that the latter intersects a side surface of the block intermediate the ends of the side surface and so that the light waveguide forms an angle of substantially 450 with a normal to said side surface.

According to a third aspect of this invention there is provided a method of producing an optical branching element which is to operate in accordance with the beam divider principle, said method including the step of securing together the side surfaces of component parts produced by a method according to said second aspect.

According to a fourth aspect of this invention there is provided a component part of an optical branching element which is to operate in accordance with the beam-divider principle, said component part comprising a block of casting compound around at least one light waveguide so that the latter intersects a side surface of the block intermediate the ends of the side surface and forms an angle of substantially 45" with a normal to said side surface.

Embodiments of this invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure lisa plan view of one form of the lower portion of apparatus for the production of a component comprising one half of an optical branching element; Figure la is a section on a larger scale through part of both portions of the apparatus shown in Figure 1; Figures 2, 2a to 2c are plan views illustrating further steps in the processing of moulded component of a branching element; Figure 3 is a plan view of a branching element comprising two halves each in the form of a component as shown in Figure 2b; Figure 4 is a plan view of another embodiment of one half of an optical branching element which can be produced by the apparatus shown in Figure 1;; Figures 5 and 6 are plan views (Figure 6 partial) of respective modified forms of complete branching element with housing and plugs; and Figure 7 is a plan view corresponding to Figure 1 of the lower half of apparatus for the simultaneous production of two halves of an optical branching element.

Figure lisa plan view of the lower part 1 of the moulding body of apparatus for the production of one half of a branching element and is provided with a precision recess 2. The base of this recess is provided by an ejection ram (not shown here) which possesses a flat surface parallel to the drawing plane. Guide grooves 4 and 6 serve to accommodate - lightwaveguides 9 and 10 respectively.

The finished component must be polished so as to be optically flat together with the enclosed light waveguides at least along one surface. In order to simplify the necessary grinding operation and to enable adherence to the precise angle within narrow tolerances, the moulding body possesses one or more hollows along the edge of the precision recess which intersects the axes of the guide grooves at 45 .

In particular one of these hollows lies in the region of the intersection point of the axes of the guide grooves and the edge. These hollows can each consist of a quarter-sphere so that during the casting procedure, when a cover is used which for example is of similar form to the moulding body, modular like projections are formed on the surface which isto be ground. During grinding it is then merely necessary to polish away these projections.

Furthermore the hollow in the region ofthe coupling point of two light waveguides can be used to ensure that initially only the hollow is filled with a hardening adhesive and consequently the light waveguides are fixed in position relative to one another in the region of their coupling point. For this purpose an additional dispensing device should be provided for example in the moulding body. It is particularly advisable to use an optical adhesive which hardens rapidly under UV light When a cover is used, at least part of the cover must be suitable for transmission of UV light. When the optical cement has hardened the entire precision process is filled with a casting compound. Here it is important that the casting compound should form an intimate connection with the surface of the light waveguides and with the optical adhesive in the hollow.In the event that the light waveguides abut against one another at their meeting point, at least in this region the casting compound must be optically transparent so that at the coupling from one light waveguide to the other light is not lost between the light waveguides.

In the region of the points of intersection of two light waveguides the moulding body possesses a small hollow 5 in the form of a quarter-sphere so that during the casting procedure, when the upper part (Figure la) of the moulding body is in position, a nodular elevation is formed on the edge Ag'. Two further such hollows, which further facilitate angular accuracy during grinding, are indicated by dashdotted lines.

In order that circular-cylindrical recesses may be formed in the case components in the region of the light waveguides 9 and 10, the moulding body is provided with moulding pins 3a and 3b respectively.

In order that the component which is to be produced should possess a defined surface it is advantageous for the moulding body to be sealed by a cover. This cover simultaneously serves to fix the light waveguides in position. Under the simplest circumstances, this can consist of a flat cover or can also consist of a cover which has a similar form to the moulding body to complement the latter.

Figure la is a sectional view of part of the lower half 1 of the moulding body and the upper half of cover I of the moulding body in the region of one of the moulding pins, the halves being shown as spaced apart by a small interval b. As can be seen from this drawing, the two halves 3b and Illb of the moulding pin are provided with the guide grooves4 and 4' respectively which serve to accommodate the light waveguide 9. When the halves of the branching element are cast, the two components of the moulding body are pressed together so that the spacing 5 = zero.

As can also be seen from Figure 1, the guide groove 6 diverges conically from the precision recess 2 in order to facilitate precise adjustment of the lightwaveguide 10 at the coupling with the throughgoing light waveguide 9 by means of an adjusting member 7 provided with a guide groove 8.

Only one such adjustment is carried out on the casting device after which the member 7 is firmly secured to the moulding body 1. The adjustment serves to ensure that the intersection point of the axes of the light waveguides 9 and 10 lies precisely in the centre of the hollow 5, i.e. on the extension of the edge Ag'.

One half of an optical branching element is now produced in that firstly the light waveguide 9 is inserted into the guide groove 4 of the lower half 1 of the moulding body. At this point, in the region of the moulding body, at least in the region of the hollow 5, the light waveguide 9 must be free of any synthetic coating. The lightwaveguide 10 is brought towards the light waveguide 9. The end surface of the light waveguide 10 must be flat and fault-free. Then the upper component I of the moulding body is firmly secured to the lower component 1 and the precision recess 2 is filled with the casting compound. Following hardening of the latter the moulded element half can be ejected. It is advantageous to use an optically transparent material for the casting compound particularly in the region of the hollow 5 at the waveguide coupling.The casting compound should also have rapid hardening properties.

However it is also conceivable that prior to the total filling of the precision recess 2 with casting compound, the light waveguides 9 and 10 should be caused to adhere together by means of an optical cement or adhesive initially only in the region of the hollow. For this purpose an additional dispensing device should be provided in the moulding body. It can be particularly advisable to use an optical adhesive which hardens rapidly under UV light.

When such an adhesive is used the UV lamp must be able to illuminate the region of the hollow 5 which for example is facilitated by providing the upper half I of the moulding body with a removable portion.

When the optical adhesive has hardened the entire precision recess 2 is filled with a casting compound.

It is important that the casting compound should form an intimate connection with the surfaces ofthe light waveguides and the optical adhesive. - In Figure 2a is shown the ejected half 111 of the branching element that consists of cast component 11 and the light waveguides 9 and 10. In the two circular-cylindrical recesses formed by the moulding pins 3a and 3b, glass capillary tubes 12a and 12b have already been inserted over the light waveguides and these must be cemented to the light waveguides and to the cast component 11.The element half 111 is now polished so as to become flat over the three outer surfaces Fg,Fg' and F10 at right angles to the light waveguides so that optical surfaces are formed in the region of the glass capillary tubes 12a and 1 2b and at the optical coupling point of the light waveguides 9 and 10. As it is merely necessary to polish away nodule 13 in the region of the coupling point, the large base area Fg' provided for the polishing ensures that the critical surface position (intersection point of the fibre waveguide axes precisely at the 45Q end surface Fg') can be adhered to within narrow tolerances. Figure 2b illustrates the polished element half. Figure 2c illustrates on a larger scale an area around the coupling point.

The end surface F97 is now provided with a beam divider transmissive/reflective interface 15 in known manner and subsequently optically cemented to a transmissive, non-reflective, but otherwise identical element half 112 corresponding to Figure 3, to form a branching element 110. Here it must be ensured that the axes of the four light waveguide sections are precisely in appropriate alignment. The assembly is greatly simplified in the surfaces Fg and F10 are used as reference surfaces and the assembly of the two element halves 111 and 112 is carried out on a flat assembly board provided with edge portions which serve as stop means.

Another embodiment of an element half corresponding to Figure 2a is illustrated in Figure 4.

Identical integers have again been provided with like references. In this case, in place of the glass capillary tubes, lightwaveguide cable sheaths 14a and 14b have been inserted over the exposed ends of the light waveguides and cemented to the cast component 11. The polishing of the 45" end surface Fg' is carried out as before. Then two element halves, one of which has been provided with a transmissive/ reflective interface similarly to the embodiment illustrated in Figure 3, are cemented to one another.

In orderto increase the mechanical stability of the cemented surface, and in order to afford it protection this cemented branching element can finally be provided with an external coating so that only the four cable ends are exposed.

Figure 5 illustrates the manner in which a branching element 110 corresponding to Figure 3 is installed in a housing 16 provided with four bores 17a to 17d. In the region of these bores, flanges 18a to 18dare adjusted relative to the axes of the light waveguides on the exterior of the housing, and are subsequently fixed in position. Precision bores in these flanges later permit the end surfaces of external light waveguide plugs to be directly coupled to the end surfaces of the branching element 110.

The function of the glass capillary tubes 1 2a to 1 2d is to receive the pressure of these plugs and distribute the pressure over a large area of the casting compound in order that the sensitive end surfaces of the light waveguides of the branching element should not be damaged.

Figure 6 illustrates another embodiment with a branching element 110' in which longer glass capillary tubes 1 2a' to 1 2d' have been cemented into the recesses of the cast components. Threaded flanges can be directly positioned on to these glass capillary tubes and rigidly joined to the branching element 110' for example by means of a housing casting 21.

Precision sleeves 20a to 20dwhich are centred relative to the axes of the light waveguides are positioned on to the threaded flanges. The plugs formed in this way can be joined in conventional manner to external matching plugs.

Figure 7 illustrates apparatus for the simultaneous production of the two halves of an optical branching element. Identical integers have again been provided with references which are similar to those used in Figure 1. The components of the second element half have been characterised by such references being provided with an apostrophe. In this embodiment of the casting apparatus, the hollow 5 corresponding to the exemplary embodiment shown in Figure 1 has been replaced by a gap between the two arms 5a' and 5,". Here it is advantageous to produce merely one circular-cylindrical bridge in place of the previously used nodules as a means for joining the two halves. All the other steps required to produce a branching element correspond to those previously described.

Claims

1. Apparatus for the production of a component part of an optical branching element which is to operate in accordance with the beam divider principle, said apparatus comprising a mould body in which is provided a precision recess in the shape of at least part of the component to be produced, said shape including a side surface the normal to which forms an angle of substantially 45" with the path of at least one light waveguide to be included in the component so as to intersect said side surface intermediate its ends, said mould body including a guide groove for the or each said light waveguide, the longitudinal axis of the guide groove extending in the desired direction of said light waveguide to intersect an edge of the precision recess that corresponds to said side surface.

2. Apparatus according to claim 1 wherein two of said guide grooves are provided so that their longitudinal axes extend at 45" to the normal of, and intersect at, the edge of the precision recess corresponding to said side surface.

3. Apparatus according to claim 2 wherein one of the two guide grooves diverges conically away from said edge, an adjusting member having an auxiliary guide groove being provided adjacent the outlet of the conical groove portion from the mould body, said adjusting member enabling adjustment of the relevant light waveguide to achieve said intersection of the two guide grooves at said edge prior to moulding.

4. Apparatus according to any one of the preceding claims wherein the mould body has a cover for sealing the precision recess.

5. Apparatus according to claim 4 wherein the cover is capable of allowing the transmission through it of ultraviolet light so that the latter can impinge on the region of said intersection of the guide groove with said edge of the precision recess.

6. Apparatus according to claim 4 or claim 5 wherein the cover is shaped similarly to the mould body so as to have complemental precision recesses and guide grooves.

7. Apparatus according to any one of the preceding claims wherein one or more identation are provided in said edge of the precision recess corresponding to said side surface.

8. Apparatus according to claim 7 wherein the or one of the indentations is in the region of the point of intersection of said guide groove(s) and said edge of the precision recess.

9. Apparatus according to any one of the preceding claims wherein a moulding pin, coaxial with the guide groove or each respective guide groove, projects into the precision recess.

10. Apparatus according to any one of the preceding claims wherein an ejection ram is provided in the precision recess.

11. Apparatus according to any one of the preceding claims wherein two of said precision recesses are provided in the same mould body.

12. Apparatus according to claim 11 wherein said precision recesses are identical.

13. Apparatus according to claim 11 or claim 12 wherein said precision recesses have their respective intersections of the guide grooves with said edges corresponding to said side surfaces interconnected by means of a channel.

14. Apparatus for the production of components of an optical branching element which operates in accordance with the beam divider principle, wherein each of these components contains at least one light waveguide which forms an angle of approximately 45" at least with the normal of one side surface, said apparatus comprising a moulding body which is provided with at least one precision recess which serves to accommodate a casting compound to form the component and with a guide groove for the or each light waveguide which is to be provided.

15. Apparatusforthe production of a component part of an optical branching element which is to operate in accordance with the beam divider principle, said apparatus being substantially as described herein with reference to Figures 1 and la orto Figure 7 of the accompanying drawings.

16. A method of producing a component part of an optical branching element which is to operate in accordance with the beam divider principle, said method including the steps of forming a block of casting compound around at least one light waveguide so that the latter intersects a side surface of the block intermediate the ends of the side surface and so that the light waveguide forms an angle of substantially 45" with a normal to said side surface.

17. A method according to claim 16 and including the further step of polishing said side surface.

18. A method according to claim 16 or claim 17 and using apparatus according to any one of claims 1 to 15.

19. A method according to claim 18 as appendent to claim 9 wherein after moulding of the block of casting compound the moulding pin or pins are removed and replaced by glass capillaries around the light waveguides.

20. A method according to any one of claims 16 to 19 wherein prior to formation of said block two of said light waveguides are positioned so as to meet at the side surface intermediate the ends of the latter.

21. A method according to claim 20 wherein said light waveguides are secured together at their mutual meeting point by means of optical cement prior to formation of said block.

22. A method according to claim 21 wherein said optical cement is hardened by means of radiation.

23. A method according to claim 22 wherein said radiation is ultraviolet light.

24. A method according to any one of claims 16 to 23 wherein said casting compound is optically transparent.

25. A method according to any one of claims 16 to 24 wherein said side surface of said block is provided with at least one nodule of casting compound.

26. A method according to claim 25 as appendentto claim 20 wherein the or one of the nodules is adjacent the meeting point of the light waveguides.

27. A method according to claim 26 wherein said casting compound is optically transparent in the region of said nodule at the meeting point of the light waveguides.

28. A method according to any one of claims 16 to 27 wherein two of said components are produced in the same operation, by means of which also the respective blocks of casting compound are simul taneouslyjoined by a bridge of the casting compound at the intersections of the light waveguides with said side surfaces.

29. A method of producing a component part of an optical branching element which is to operate in accordance with the beam divider principle, said method being substantially as described herein with reference to Figures 1 and la alone or in combination with Figure 2 or Figure 4 or to Figure 7 of the accompanying drawings.

30. A method of producing an optical branching elementwhich is to operate in accordance with the beam divider principle, the step of securing together the side surfaces of component parts produced by a method according to any one of claims 16to 29.

31. A method according to claim 30 wherein the side surface of one of the component parts is provided with a partlytransmissive/reflective layer prior to being secured to the other component part.

32. A method according to claim 31 wherein the branching element is mounted in a housing providing lightwaveguide communicating means for external light waveguides to the light waveguides of the branching element.

33. A method of producing an optical branching element which is to operate in accordance with the beam divider principle, said method being substantially as described herein with reference to Figure 3 or Figure 5 or Figure 6 of the accompanying drawings.

34. A component part of an optical branching element which is to operate in accordance with the beam-divider principle, said component part comprising a block of casting compound around at least one light waveguide so that the latter intersects a side surface of the block intermediate the ends of the side surface and forms an angle of substantially 45" with a normal to said side surface.

35. A component part of an optical branching element which is to operate in accordance with the beam divider principle, said component part being produced by a method according to any one of claims 16 to 29.

36. An optical branching element which is to operate in accordance with the beam divider princi ple, said branching element being produced by a method according to any one of claims 30 to 33.