GB2312527A

GB2312527A - Arrangement for coupling a transmitting or receiving element to an optical waveguide

Info

Publication number: GB2312527A
Application number: GB9708044A
Authority: GB
Inventors: Nikolaus Schunk
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1996-04-23
Filing date: 1997-04-21
Publication date: 1997-10-29
Anticipated expiration: 2017-04-21
Also published as: JPH1054928A; GB2312527B; DE19616015C1; GB9708044D0

Description

2312527 Arrang=ent for cmWling Qptical transmittin- n! elements to an

optcal wavemide

The invention relates to an arrangement for coupling optical transmitting or receiving elements to an optical waveguide according to the preamble of Claim 1 and to a method of producing it according to Claim 20.

Prior The coupling of optical transmitting and receiving elements to an optical waveguide is known. In said coupling, very narrow coupling tolerances have to be maintained in order to be able to inject as much power as possible into the optical waveguide or to receive as much power as possible at the receiving diode. In addition, the coupling arrangement has to be mechanically fixed in position, which is possible only at considerable expense with axial alignment of the individual components. DE-A 143 13 493 therefore describes an arrangement for coupling in which the transmitting or receiving element is mounted on a planar carrier plate and the coupling is carried out by moving the carrier plate towards the optical waveguide. The beam deflection is carded out according to this disclosure at V-grooves. At the one side of the V-groove, the beam deflection is caffied out by total deflection. while the other side of the V-groove is provided with an antireflection layer in order to reduce the reflection losses. Such arrangements are, however, still capable of improvement in regard to the coupling losses encountered and the mechanical fixing of the individual components.

2 Advantages of the invention By way of contrast, the arrangement having the features of the main claim has the advantage that the passive arrangement of optical fibre, waveguide and insertable parts, which arrangement is fixed in position by the structures provided, makes possible a better coupling to transmitting or receiving elements. For this purpose, the optical transmitting or receiving elements are advantageously aligned on the film which at least partly covers the base plate. The alignment of the optical transmitting or receiving elements on the fihn has, m addition to the high coupling efficiency, made possible thereon, to the passively aligned components in the base plate, also the advantage that electrical supply leads to said elements can be arranged in a simple manner and do not have to be introduced into the base plate, which is necessary, for example, if the optical elements are mounted theremi. The insertable components used according to the invention, such as deflection mirrors, wavelength- selective mirrors, lenses or optical insulators are therefore passively aligned, that is to say they are substantially aligned automatically because of their dimensions and of the corresponding structures of the base plate. Advantageously, therefore, no active alignment, requiring for example micromanipulators, of the insertable components is necessary. The passive alignment has production advantages since it is easier to carry out than active alignment. Finally, the production of the arrangements according to the invention is extremely inexpensive because of the polymer moulding technology used.

Further advantageous developments of the invention are to be found in the subclaims.

In a particularly advantageous manner, the structure prefabricated in the base plate for receiving the insertable component has a depth T which is less than the height H of the misertable component. This has the consequence that the upper edge of 3 a deflection mirror present for example, on an insertable component can be situated above the upper edge of the optical waveguide. Since, in particular, a clearance is present between deflection mirror and end of the optical waveguide, a fanwise spreading of the light beam leaving the optical waveguide occurs. In order to deflect said fanwise-spread light beam as completely as possible, it is therefore advantageous that the upper edge of the mirror does not exactly terminate with the upper edge of the waveguide, but, on the contrary, is situated above it.

In a further embodiment, the invention also relates to a method for producing the arrangements according to the invention, in which the structures present in the base plate for the waveguide, the fibre guidance and the at least one insertable component are applied to a silicon wafer, said structures are transferred by electroforming to a nickel die plate, the at least one insertable component is inserted in the nickel die plate, the base plate is produced, the optical waveguide is produced from polymeric material, the film is pressed on and the transmitting or receiving elements are aligned on the film. As a result of casting components having precise dimensions, the desired optical fimctions, such as for example beam deflection, can be easily and exactly produced.

The method according to the invention therefore comprises the production of structures in a silicon wafer which serves as master wafer. The structures to be provided on the silicon wafer are formed, for example, by means of reactive ion etching (RIE) or anisotropic etching. In a particularly advantageous manner, the invention also provides an embodiment of said method according to which elevations are provided on the silicon wafer serving as master wafer. For this purpose, a structure is first produced in the silicon wafer for an insertable part, for example, by means of reactive ion etching or anisotropic etching. A precisely fitting silicon piece of defined height is introduced into this structure, said defined 4 height H being greater than the depth T of the structure etched in. Accordingly, an elevation is formed on the wafer. The precisely fitted silicon piece is then joined to the wafer, preferably welded on. Disposed on the surface of the silicon master wafer, there are accordingly elevations of height H minus T, which are encountered again as depressions in the nickel die plate. The recess formed in this manner serves to receive the upper region of the insertable component so that the latter does not terminate by means of its upper edge with the optical waveguide disposed in the surface of the base plate but projects above it by the height H minus T. The method according to the invention for producing elevations in structured, planar silicon wafers therefore makes it possible to produce a particularly advantageous embodiment of the invention and is, of course, not limited to the production of elevations mi silicon wafers, but on the contrary, can also be applied to other compositions such as InP or GaAs wafers.

Drawing The invention is explained in greater detail by reference to the following figures.

In the figures:

Figure 1 diagrammatically shows a longitudinal section through a receiving module; Figure 2 diagrammatically shows a longitudinal section through a transmitting module having an edge-emitting laser diode; Figure 3 diagrammatically shows a longitudinal section through a transmitting module having a surface-emitting laser diode; Figures 4 to 6 diagrammatically show representations of various elements of a transceiver module; Figure 7 shows the production of a base plate; Figure 8 shows the structuring of a master silicon wafer; Figure 9 shows an alternative embodiment for structuring the master silicon wafer and Figure 10 shows the production of beam deflection elements.

Figure 1 shows an arrangement 1, formed as receiving module, having a base plate made of PMMA (polyniethyl methacrylate) and a polymer film 3 which partially covers the latter. The base plate 2 has a waveguide structure 4 for receiving a polymeric optical waveguide 5. The waveguide 5 can be cured with UV light or thermally. The base plate 2 has, in addition, a fibre guidance groove 6 for receiving an optical fibre 7. The optical fibre 7 is disposed in the fibre guidance groove 6 in such a way that its end aperture 8 is aligned with the waveguide aperture 9. Disposed in the same plane at a distance from that aperture 10 of the optical waveguide which is remote from the optical fibre 7 is a structure 11 for receiving an insertable component 12, which has a deflection mirror, formed as a concave mirror 13, at its bevelled end face 3 8 adjacent to the aperture 10 of the waveguide 5. The insertable part 12 made, for example, of PMMA or PC (polycarbonate) accordingly has a bevelled end face 38 (preferably 45 to the longitudinal axis of the waveguide 5) on which end face 38 a concave mirror 13 is formed for the purpose of beam focusing. Said mirror can be produced by vapour deposition with gold or dielectric layers. Figure 1 makes clear that the 6 depth T of the structure 11 in the base plate 2 Is less than the height H of the insertable component 12. The upper edge 14 of the concave mirror 13 therefore projects above the surface 15 of the base plate 2 and consequently, also the upper edge of the waveguide 5 disposed in the surface 15 of the base plate 2. The waveguide 5 and the insertable component 12 are covered by a polymeric film 3 on which the photodiode 16 is fixed in position by passive, supported alignment with the vertically emerging light by means of two-dimensional movement. With a photodiode 16 having exact dimensions, the alignment can be facilitated by coloured maffings 29 (insertable parts) (not shown here) in the base plate 2. The photodiode 16 is fixed in position by briefly heating and impressing in the fihn 3. The photodiode 16 is provided with an antireflection coating 17 (AR coating) with respect to the polymer and with a bonding agent, and is firmly joined to the polymer fihn 3 by means of a UV adhesive 18. Figure 1 furthermore shows electrical connections 19 which are connected to the photodiode 16 and which are disposed outside of the base plate 2 and the polymer film 3.

Light emerging from the optical fibre 7 is passed through the optical waveguide 5 onto the concave mirror 13 and is deflected there in the direction of the photodiode 16. Of course, other elements can also be used for beam deflection. Particularly preferred are metallic or dielectric mirrors. Since, in addition, the concave mirror 13 projects above the surface 15 of the base plate 2, the light leaving the aperture 10 of the waveguide 5 is coupled with particularly low losses.

The reference numerals used in Figure 1 are used below for components having the same fimetion even if there are structural differences.

Figure 2 shows an arrangement 20 formed as transmitting module and having a base plate 2 and a polymer film 3 partially covering the latter. The arrangement and design of the base plate 2 and of the elements and structures contained therein 7 correspond to that of Figure 1. In contrast to Figure 1, however, an edge- emitting laser diode 21 which has an antireflection layer 17 and which is rotated through 90 and placed on the surface of the film 3 by active alignment and fixed in position by an adhesive 18 is mounted on the polymer film 3. The laser diode 21 is mounted on a heat sink (submount) 22 to dissipate heat. An electrical connection 19 disposed outside the base plate 2 and the polymer film 3 is fluthermore shown.

The fight leaving the laser diode 21 is coupled via the concave mirror 13 into the waveguide 5, which is formed as a strip waveguide, and can therefore enter the fibre 7.

The transmitting module according to Figure J3 essentially corresponds to that of Figure 2, but instead of the edge-emitting laser diode 2 1, a surface-emitting laser diode 23 is shown on the film 3. The mounting of a surface-emitting laser'diode 23 is substantially easier than that of the edge-emitting laser diode 21 since it can be carried out in exactly the same way as the mounting of a photodiode 16, that is to say a passive alignment can be carried out by briefly heating and impress g in the polymer film 3. The laser diode 23 has an antireflection layer 17 and is joined by means of a metal ring 24 for rear contacting and a UV adhesive 18 to the polymer film 3. The laser diode 23 and the metal ring 24 have electrical connections 19 situated outside the base plate 2 and the polymer film 3. To match the greater beam divergence of the laser diode 23, the concave mirror 13 on the insertable component 12 is of larger design so that the laser field is imaged better onto the field of the waveguide 5, which is formed as a strip waveguide.

In a further embodiment, a reflection- insensitive transmitting module can be produced by introducing graded-index lenses and optical insulators. To match the greater diameter of these components, a thicker polymer film has to be used into 8 which the component structures of the graded-index lens and of the optical insulator are pre-impressed. As a result of the passive alignment of the lenses and of the optical insulator, a very inexpensive transmitting module can be produced.

Figures 4 to 6 diagrammatically show the elements of a transceiver module. A transceiver module 25 shown diagrammatically in plan view in Figure 6 can be produced by combining the receiving module 1, for example, according to Figure 1 (Figure 4) and the transmitting module 20, for example, according to Figure 2 (Figure 5). The transceiver module 25 has a wavelength-selective component 26, with strip waveguide design, for example an array demultiplexer or a "grating assisted coupler", which is coupled to the optical waveguide 5. Any desired combination of transmitting and receiving modules is possible in accordance with the wavelength selection and the number of waveguide outputs on the array demultiplexer. Figure 6 shows an embodiment in which any number of receiving modules 1 (photodiode array) is combined with only one transmitting module 20, a receiving module Fformed as monitor module being provided, in addition, for monitoring the transmitting power. Of course, any other combinations of transmitting and receiving modules according to the invention are also possible.

Figure 7 shows the production of a base plate 2 from PMMA. An insertable component 12 for beam deflection is inserted in the nickel die plate 27, to be exact in a recess 28, which nickel die plate 27 is produced as explained below. The insertable component 12, which has a concave mirror 13, is inserted in the recess 28 of the nickel die plate 27 in such a way that the upper edge 14 of the concave mirror is adjacent to the nickel die plate 27. The structures of the insertable component 12 and the structures formed as elevations on the nickel die plate 27 for the waveguide rib 4 and the fibre guide groove 6 are produced by filling with PNEVIA on the base plate 2 produced in this way. The nickel die plate 27 is then removed. The waveguide 5 is produced by applying the core polymer to the 9 structure 4 for the waveguide 5 and also by pressing it on with the fibn 3. An optical transmitting or receiving element is then passively aligned on the film.

Figure 7 shows segment-wise in a detailed plan view of the nickel die plate a coloured insertable part 29 for aligning the optical transmitting or receiving element. Said insertable part 29 is fixed in its position on the base plate 2 by a holding structure 30.

Figure 8 shows the structuring of the silicon master wafer structure necessary for producing the nickel die plate 27. The structures 4', 6, 11' are produced in a silicon wafer 31 by reactive ion etching (RIE). In accordance with the geometry of the waveguide 5, the etched trenches for the said structures are formed about 5 to 6 micrometres deep. This is done by reactive ion etching (Figure 8a). The structure 4' for the waveguide and the structure 6' ultimately produced in a subsequent method step for the fibre guidance groove are sealed with resist so that the structure 11' for the insertable component 12 can be formed more deeply by subsequent reactive ion etching (Figure 8a) or anisotropic etching. The structure 6' for the fibre guidance groove is converted to its final shape by anisotropic etching. A vertical edge 32 between structure 4' for the waveguide and structure 6for the fibre guidance groove is produced with a wafer saw. A precisely fitting silicon piece -3)3 is inserted in the structure 1 V, which silicon piece 33 has the shapes required for passively aligning the insertable component 12 used later. The silicon piece 33 is firmly joined to the silicon wafer 3 1 by welding. The depth T' of the structure 11' is less than the height H' of the silicon piece 3 3. The silicon wafer 31 therefore has an elevation of height H' minus T above its surface. This elevation is encountered again as a depression in the nickel die plate 27 into which the insertable component 12 is inserted and therefore projects above the surface of the base plate 2 after the latter has been formed.

The structures, that is to say depressions and elevations, are then transferred from the silicon wafer 31 to a nickel die plate 27 by electroforming and then used to produce according to Figure 7 the base plate 2 and the arrangement according to the invention.

Figure 9 shows an alternative to reactive ion etching for forming the structure 11, for receiving the silicon piece 3 3. According to this, the structure 11' can be etched anisotropically in the form of a V-groove having a certain width in the silicon wafer 3 1. A precisely fitting silicon piece 33' which is anisotropically etched and broken along the etched edges is then inserted into the recess 11' produced in this way. Of course, other silicon pieces 3Y, for example having etched surface structures, can also be used.

Figure 10 explains the production of components for beam deflection. A movable in ection-moulding tool 34 having an injection-moulding aperture 35 is shown. j Mounted on a base plate 36 is a block 37 with a bevelled end face (preferably 45') 38. Between the movable injection-moulding tool 34 and the block 37 and the base plate 36 there remains a cavity which has the shape of the insertable component 12. It may, however, also comprise a multiplicity of insertable components 12. The insertable part 12 is produced by the injection-moulding method. Suitable as material is a lowattenuation polymer, for example PMMA or PC, so that a beam splitting for the application as transceiver is possible (Figure 10a). If only a beam deflection is necessary, the insertable component can be produced from any material. In an embodiment which is likewise preferred, the bevelled end face 38 can be machined as a concave mirror (Figure 10b) for the purpose of beam focusing so that a better field matching between the active component and the waveguide can be achieved. The mirror layer is applied by vapour deposition.

Claims

1. Arrangement for coupling optical transmitting or receiving elements to an optical waveguide which has a base plate and a film which at least partly covers the latter, characterized in that the optical transmitting or receiving elements (16, 21, 23) are aligned on the film (3) and the base plate (2) has structures (4, 11) for the optical waveguide (5) and for receiving at least one insertable component (12).

2. Arrangement according to Claim 1, characterized in that an optical waveguide (5) composed of a polymer is disposed in the structure (4) and covered by the film (3).

3. Arrangement according to one of Clauns 1 or 2, characterized in that the optical transmitting or receiving element (16, 21, 23) is aligned passively, preferably by means of an adhesive (18), on the film (3).

4. Arrangement according to one of Claims 1 or 2, characterized in that the optical transmitting or receiving element (16, 21. 23) is actively aligned on the flhn (3).

5. Arrangement according to one of Claims 1 to 4, characterized in that the base plate (2) additionally has structures (6) for guiding an optical fibre (7).

6. Arrangement according to one of Claims 1 to 5, characterized in that at least one insertable component (12) which is preferably passively aligned is disposed on the base plate (2).

7. Arrangement according to one of Claims 1 to 6, characterized in that 12 the insertable component (12) has a wavelength-selective mirror or a deflection mirror (13), preferably a concave mirror.

8. Arrangement according to one of Claims 1 to 7, characterized in that the insertable component (12) is a lens or optical insulator.

9. Arrangement according to one of Claims 1 to 8, characterized in that the insertable component (12) is disposed at a distance from the end aperture (10) of the waveguide (5) so that a coupling of the waveguide (5) to the transmitting or receiving element (16, 21, 23) is ensured.

10. Arrangement according to one of Claims 1 to 9, characterized in that the end face (38) of the insertable component (12) is disposed at an angle of 45' to the longitudinal axis of the waveguide (5).

11. Arrangement according to one of Claims 1 to 10, characterized in that the structure (11) for receiving the insertable component (12) has a depth (T) in the base plate (2) which is less than the height (H) of the insertable component (12).

12. Arrangement according to one of Claims 1 to 11, characterized in that the upper edge (14) of the deflection mirror (13) disposed on the insertable component (12) is disposed above the surface (15) of the base plate (2).

13. Arrangement according to one of Claims 1 to 12, characterized in that the optical transnuitting element is a laser diode, preferably an edgeemitting or surface-emitting laser diode (21, 23).

14. Arrangement according to one of Claims 1 to 12, characterized in 13 that the optical receiving element is a photodiode ( 16).

15. Arrangement according to one of Claims 1 to 14, characterized in that the base plate (2) and the flilm (3) are formed from a polymeric material, preferably PMMA (polymethyl methacrylate).

16. Arrangement according to one of Claims 1 to 15, characterized in that the base plate (2) has at least one coloured insertable part (29) for aligning the optical transmitting or receiving element.

17. Transceiver module containing at least one arrangement according to one of Claims 1 to 16.

18. Method for producing elevations in structured, planar wafers (3 1), in which a structure (1 F) having the depth (T) for a wafer piece (33, 33', 33,') having the height (H) is etched in the wafer (3 1), and the precisely fitting wafer piece (3 3, 3 Y, 33 ") is inserted in said structure and joined, preferably welded, to the wafer (3 1), H'being > T'.

19. Method according to Claim 18. characterized in that the structure (1 F) is produced by means of reactive ion etching or anisotropic etching.

20. Method for producing an arrangement for coupling optical transmitting or receiving elements (16, 21, 23) to an optical waveguide (25), which arrangement has a base plate (2) having structures (4, 6, 11) and a film (3) which at least partly covers the latter, in which method the structures (4, 6, 11), present in the base plate (2), for the waveguide (5), the optical fibre (7) and the at least one insertable component (12) are applied to a silicon wafer (3 1), said structures are transferred to a nickel die plate (27) by electroforming, the at least one 14 insertable component (12) is inserted in the nickel- die plate (27), the base plate (2) is produced, the waveguide (5) is formed, the film (3) is pressed on and the transmitting or receiving elements (16, 21, 23) are passively aligned.

21. Any of the arrangements for coupling optical transmitting or receiving elements to an optical waveguide, substantially as hereinbefore described with reference to the accompanying drawings.

22. Method for producing elevations 'm structured planar wafers substantially as hereinbefore described with reference to the accompanying drawings.

23. Method for producing an arrangement for coupling optical transmitting or receiving elements substantially as hereinbefore described with reference to the accompanying drawings.