GB2321971A - Method for manufacturing an integrated optical switch - Google Patents

Abstract

The invention relates to a method for manufacturing an integrated optical switch. A support plate (1), which comprises for example an electrode (11), serves as cover for a nickel mould (17) which forms by means of an edge (31) a hollow space sealed towards the outside. A substrate is poured into the hollow space through filing holes (9), wherein surfaces covered by elevations (29) are exposed. After setting of this substrate the nickel mould is removed, wherein a waveguide trench has been formed by the elevation (25). A material with a higher refractive index is poured into this trench, so that a waveguide core is formed. After this a cover foil (43) is stuck to the substrate surface.

Description

Method for Manufacturing an Integrated Optical Switch Prior art The invention is based on a method for manufacturing an integrated optical switch.

An integrated optical switch and a method for manufacturing a cover for an integrated optical switch is already known from patent application DE P 42 40 950. This cover consists of a polymer which surrounds an optical component essentially completely, for example with an electrode. This cover is manufactured by the casting method, in which the optical component is placed on a male mould and adjusted and the polymer is then poured on. The male mould comprises, in addition to adjusting means for the optical component, guide lugs, which form guide grooves in the cover.

The cover is then bonded with a substrate, which is likewise manufactured by means of the casting method. Trenches for the waveguide cores together with adjusting means are introduced into this substrate. The optically transparent and higher-refractive index adhesive used for the bonding fills up these trenches and thus forms the waveguide cores. In order to prevent a reduction in the quality of the integrated optical switch, close contact of the cover with the substrate over the whole substrate surface, but at least in the vicinity of the waveguide cores, is necessary. Uneven areas in the cover surface, however, which can occur for example through shrinkage of the polymer on setting or for example through differing thermal expansion of the polymer and the optical component cast around, affect the close contact and hence the quality of the switch. The contacting of the electrical leads furthermore causes problems in the optical component, since the latter is cast around completely. In addition, an unnecessarily large amount of material of high optical quality has to be consumed for the cover. The substrate has also to be constructed relatively thick on stability grounds.

The present invention provides a method for manufacturing an integrated optical switch, with a casting mould which comprises at least two guide lugs and an elevation connecting the two guide lugs, wherein the casting mould is closed in a sealing manner by a support plate provided with at least two guide grooves, and optically transparent substrate material is poured into the hollow space formed between casting mould and support plate.

Advantages of the invention The integrated optical switch manufactured according to the invention has conversely the advantage that the use of a support plate leads to a strengthening of the substrate. Furthermore, the material of the support plate can be optimized more easily in mechanical and thermal terms, since it does not necessarily have to be optically transparent. It can be regarded as a further advantage that the substrate is mounted on the support plate only at the required points and preferably has a thickness of approx. 20 llm. Since the cover foil also does not cover the whole area of the support plate and also possesses a thickness of preferably only some 30 clam, a further saving on material can also be achieved here.

Preferably an overflow trench is constructed in the substrate, which lies adjacent to the contacting points of the electrodes and protects the latter against adhesive during the bonding.

The method according to the invention has the advantage compared with the prior art that uneven areas no longer occur on the substrate surface. Because of the fact that the substrate material is injected into the casting area formed by a male mould and the support plate preferably through filling holes in the support plate, shrinkage during the setting of the substrate can be compensated very simply by refilling with substrate material.

Since the use of a cover in the conventional sense with adjusting indentations, guide grooves etc. is also not involved, manufacture is simplified considerably. In particular the quality of the coupling of fibre and integrated optical switch now depends more on the accuracy of a component, namely the male mould.

Preferably a cover foil is stuck onto the substrate, wherein an adjustment by means of guide lugs, as is required between cover and substrate in the prior art, is not involved. In particular the cover foil can be made very thin, so that savings on material are possible.

In a development the support plate is not covered completely by the cover foil, but only in the region of the waveguides. In addition to a further saving on material, the advantage of improved contacting of the electrodes results from this.

Advantageous developments and improvements of the method described in claim 1 are possible through the measures given in the sub-claims.

Attention is directed to co-pending Application 9700126.7 (publication no. 2 309 540) from which this application is divided.

Drawing Examples of integrated optical switches which may be manufactured using the method according to the invention are shown in the drawing and explained in detail in the following description, where Figure 1 shows a diagrammatic representation of the support plate and the casting mould, Figure 2 a diagrammatic cross-section of the support plate with superimposed casting mould, Figure 3 an integrated optical switch in cross-section, Figure 4 a diagrammatic representation of a support plate with a casting mould according to a further example, Figure 5 the support plate shown in Figure 4 with superimposed casting mould and Figure 6 a diagrammatic representation of an integrated optical switch according to a further example.

Description of the embodiments Figure 1 shows in perspective a support plate 1 which is manufactured for example by means of a casting technique from a polymer. The material used for this is mechanically stable, but not necessarily optically transparent. V-shaped guide grooves 5.1, 5.2, 7.1 and 7.2 are introduced into the surface 3 of the support plate 1. All four guide grooves 5, 7 are constructed with open edges, wherein the two guide grooves 5.1 and 5.2 become fibre guide trenches which accommodate the fibres to be coupled.

Filling holes 9 are provided over the entire surface of the support plate 1, which completely penetrate the support plate. Electrical conductor tracks are likewise placed on the surface 3 of the support plate 1, which form a heating electrode in the example shown. The current feed takes place by means of two contact surfaces 15.1 and 15.2, which are disposed close to the edge of the support plate 1. The heating electrode 13 lies in the vicinity of the waveguide core still to be constructed.

A nickel mould serving as a male mould is also shown in Figure 1. This nickel mould has roughly the same dimensions as the support plate and comprises various elevations on its side 19 facing the support plate.

Thus four guide lugs 21 and 23 are provided. Their alignment relative to one another and their form are selected in such a way that they fit into the guide grooves 5 and 7. This means that the guide lug 21.1 engages with the guide groove 5.1, the guide lug 21.2 with the guide groove 5.2 and the guide lugs 23.1 and 23.2 with the guide grooves 7.1 and 7.2 when the nickel mould is placed on the support plate. An exact adjustment of nickel mould 17 relative to support plate 1 is ensured in this way.

The two guide lugs 21.1 and 21.2 are connected to one another by an elevation 25 of trapezoidal cross-section, wherein the ends of this lengthwise elevation 25 are disposed centrally relative to the respective base side of the guide lug. The dimensions of this elevation, in particular its height, are determined by the desired waveguide cross-section.

A further elevation 27 serves for the formation of an overflow trench.

Next to this elevation 27 there extend vertically to the longitudinal axis two cuboid-shaped elevations 29 disposed parallel to one another, whose spacing from one another corresponds to the spacing of the two contact surfaces 15. The positioning and the height of the two elevations 29 on the side 19 of the nickel mould itself is selected so that they cover the two contact surfaces 15 when the nickel mould is superimposed.

There extends parallel to the lateral edges of the nickel mould 17 on the side 19 a cuboid-shaped edge 31, which surrounds the elevations 25, 27 and 29. The edge 31 is interrupted only by the guide lugs 21 and 23. The height of this edge 31 is selected as a function of the desired substrate thickness. Conventionally some 20 ,um are calculated for this. The height of the elevations 29 is then adapted to the height of the edge 31. The layout of the individual elevations and of the guide lugs 21, 23 must guarantee that, when the nickel mould is superimposed, the edge 31 is supported uniformly on the support plate 1 and seals in an outward direction the hollow space formed between nickel mould and support plate. This edge 31 acting as a seal can naturally also be disposed on the support plate. The outline of the edge 31 can also be so arranged that the contact surfaces 15 lie outside. The elevations 29 are then omitted.

In the sectional view, shown in Figure 2, of a nickel mould superimposed on the support plate it can be seen clearly that the height of the elevation 25 is less than the height of the edge 31. Furthermore it can be seen from Figure 2 that the guide lugs 21 and 23 fit exactly into the V-shaped guide grooves 5.

The conductor tracks 11 and in particular the contact surface 15 can be seen as embedded in the support plate 1, with the elevation 29 covering the contact surface 15.

In order to manufacture the integrated optical switch, the nickel mould 17 is first of all placed on the support plate 1, so that the guide lugs 21 and 23 engage with the corresponding V-shaped guide grooves 5 and 7 and the edge 31 seals off the hollow space formed on the inside.

There is now charged into this hollow space through the filling holes 9 a curable optically transparent liquid until such time as the hollow space is completely filled. The charged liquid is given the reference symbol 33 in Figure 2. The shrinkage which generally occurs during the curing is compensated by means of the holes 9. Should the guide lugs 21 or 23 not engage exactly with the corresponding guide grooves, the hollow spaces thereby formed are likewise filled with the liquid. It is consequently always ensured that an exact reproduction of the nickel mould 17 is obtained.

As soon as the liquid has cured into a substrate, the nickel mould 17 can be removed.

The result can be seen in Figure 3. Thus the contact surface 15 is because of the covering elevation 29 not covered by a substrate 33, so that easy contacting is ensured. The elevation 27 has exposed an overflow trench during the pouring out, the function of which will be explained later. The elevation 25 has created a trench 37 for the waveguide core. On the two edges of the support plate 1 the guide lugs 21 and 23 have created V-shaped fibre guide trenches 39 and 41, into which the fibre ends can be introduced.

In the next step a cover foil 43 is then applied to the essentially plane surface of the substrate 33. An adjustment of this cover foil, which is obtained for example by grooves and lugs when the conventional cover is used, is not required. The cover foil 43 has a thickness of some 30 Fm and is made of a high-quality optical material. An optical adhesive with a higher refractive index is used for joining this cover foil 43 with the substrate 33. This adhesive in addition fills the trench 37, so that a waveguide core is obtained The fibre ends introduced into the fibre guide trenches 39 are also fixed with this adhesive.

When the cover foil is pressed onto the substrate, adhesive escapes laterally. In order to protect the contact surface 15, the overflow trench 35 is provided, into which the laterally escaping adhesive runs.

A further simplification with respect to the contacting of the contact surfaces 15 consists in the fact that the cover foil 43 does not cover the whole substrate surface, but simply the region of the optical waveguides, as can be seen clearly in Figure 3.

A heat sink 45 is then applied to the cover foil 43 in the last step.

Figures 4 and 5 show a further example of a nickel mould and a support plate, wherein the discussion below will deal only with the differences from the first example.

In contrast with the example shown in Figure 1, the nickel mould 117 does not possess an edge 31 constructed as an elevation. Instead the lateral surfaces 119 of the nickel mould 117 are prolonged in form, so that they project significantly beyond the tips of the guide lugs 21, 23. This prolongation of the lateral surfaces can be seen clearly in Figure 5. The shape of the nickel mould 117 is selected so that the lateral surfaces 119 form a peripheral seal around the support plate 1, so that the hollow space obtained is likewise sealed off laterally. The depression in the nickel mould. into which the support plate 1 is introduced, can be produced very easily by KOH etching of the silicone master mould and subsequent electrolytic casting in nickel.

In addition the contact surfaces 15 are formed as raised contact surfaces 115, wherein their height matches the substrate height. The elevations 29 for covering the contact surfaces 15 can therefore be omitted. The actual manufacture of the integrated optical switch corresponds however to the manufacture carried out in accordance with Figures 1 and 2, so that a renewed explanation will not be given.

A further example is shown in Figure 6, the difference consisting in the fact that the position of the heat sink has been interchanged with that of the support plate.

During the manufacture of the substrate 33, therefore, the support plate 1 does not serve as closure of the nickel mould 17, but rather the heat sink 45.

The heat sink 145 shown in Figure 6 comprises in turn V-shaped guide trenches 121 and 123, with which the guide lugs 21 and 23 of the nickel mould 17 can engage. The desired substrate 33 is obtained by the introduction of a substrate liquid 33 through the filling holes 109 into the hollow space formed between nickel mould 17 and heat sink 145, wherein the elevation 25 exposes a trench 37 for the waveguide core on the substrate surface. This trench 37 is after removal of the nickel mould 117 filled with a material with a higher-refractive index before a cover foil 143 is applied. The support plate 1 is then superimposed on the cover foil, wherein the guide grooves 5.1 and 7.1 are aligned with the corresponding grooves 121 and 123. This is quite possible if circular glass fibres of defined thickness are placed in the grooves 121 or 5.1. A width of the heat sink 145 is selected such that the section of the support plate 1 comprising the contact surfaces 15 juts out when heat sink and support plate 1 are combined. The contact surfaces can thus be contacted without difficulty.

It is naturally also possible, in addition to the optical structure, for electronic components (e.g. drivers, amplifiers etc.) to be accommodated on the support plate 1. In addition, the material of the support plate 1 can be selected at will. The stipulation of specific optical properties is not necessary.

Claims (9)

1. Method for manufacturing an integrated optical switch, with a casting mould which comprises at least two guide lugs and an elevation connecting the two guide lugs, wherein the casting mould is closed in a sealing manner by a support plate provided with at least two guide grooves, and optically transparent substrate material is poured into the hollow space formed between casting mould and support plate.

2. Method according to claim 1, wherein a cover foil is stuck onto the substrate surface and an adhesive fills up a waveguide trench formed by the elevation of the casting mould.

3. Method according to claim 1 or 2, wherein only waveguide regions are provided with a cover foil.

4. Method according to one of claims 1 to 3, wherein a heat sink is applied to the cover foil.

5. Method according to one of claims 1 to 4, wherein an electrode is introduced into the support plate prior to the application of a substrate.

6. Method according to one of claims 1 to 5 wherein the support plate is provided with filling holes penetrating the latter.

7. Method according to claim 5, wherein the two contact surfaces of the electrode are covered by elevations on the casting mould during the pouring in of the substrate material.

8. Method according to one of the preceding claims, wherein an overflow trench is formed in the substrate during the casting.

9. Any of the methods of manufacturing integrated optical switches substantially as hereinbefore described with reference to the accompanying drawings.