| WO1995001580A1 | 1995-01-12 |
| 1. | A method of making an optical component comprising a plurality of integrated, optical waveguides (7) on a sub¬ strate (4) , with a coupling device which is restrictive in three dimensions and has holding and guide grooves for coupling the waveguides to optical fibres, wherein the integrated waveguides (7) are formed in a manner known per se by depositing/growing and etching on a plane side of the substrate (4), and wherein the holding and guide grooves (14) of the coupling device are provided by etching channelshaped depressions in the surface of the plane substrate as a termination on the integrated optical waveguides (7) which are to be coupled to optical fibres (1), said waveguides (7) terminating in the wall of the depression, c h a r a c t e r i z e d by providing a separate element (8) having a guide groove (18) which corresponds to the holding and guide grooves (11) in the plane side of the substrate, which guide groove (18) of the element (8), when the element (8) en¬ gages the substrate side provided with holding and guide grooves (11), diverges from the facet of the integrated optical waveguide (7) in the holding and guide grooves (11) of the substrate wafer, and attaching the element (8) to the plane side of the substrate wafer having holding and guide grooves (11) prior to the mounting of the fibres (1), so that the holding and guide grooves (11) are substantially covered by the element (8) in their longitudinal direction. |
| 2. | A method according to claim 1, c h a r a c t e r ¬ i z e d by preparing a large number of component sub¬ strates on a substrate wafer (4), and separating said component substrates after bonding to a corresponding substrate wafer which serves as the separate element (8). |
| 3. | A method according to claim 1 or 2, c h a r a c ¬ t e r i z e d by fusing the fibres (1) and glass in the waveguide layer (57) together by means of eletromagnetic energy transferred through the element (8) attached to the plane substrate side. |
| 4. | An optical component comprising a first substrate wa¬ fer (4) having a plurality of optical waveguides (7) in tegrated therein, and a coupling device, which is re¬ strictive in three dimensions, for coupling the waveguides in the substrate wafer to one or more optical fibres, said coupling device comprising holding and guide grooves (11) in the form of depressions provided in one of the sides of the substrate wafer in extension of the integrated waveguides (7) to receive and retain respec¬ tive optical fibres (1), c h a r a c t e r i z e d in that the coupling device moreover comprises an element (8) which is attached to the side of the substrate wafer having holding and guide grooves (11), so that the hold¬ ing and guide grooves (11) of the substrate are substan¬ tially covered by the element (8) in their longitudinal direction, and that the element (8) is likewise formed with a guide groove (18) which, when the element (8) is mounted, diverges from the facet of the integrated opti¬ cal waveguide (7) in the holding and guide grooves (11) of the first substrate wafer. |
| 5. | An optical component according to claim 4, c h a r a c t e r i z e d in that the element (8) is wafer shaped and is made of the same material as the first sub strate wafer (4) with the integrated optical waveguides (7), and that the guide groove (18) of the wafershaped element is made by etching. |
| 6. | An optical component according to claim 4, c h a r ¬ a c t e r i z e d in that the wafershaped element (8) is formed as a second substrate wafer, which is likewise formed with integrated, optical waveguides (7), in exten¬ sion of which holding and guide grooves (11) are formed, and that the associated coupling device comprises diverg¬ ing holding and guide grooves (18) provided in an adja¬ cent part of the first substrate wafer (4). |
| 7. | An optical component according to claims 46, c h a r a c t e r i z e d in that the holding and guide groove (11) on the plane substrate side comprises an in¬ ner channel section (II) of constant crosssection at the facet of the waveguide and an outer channel section (III) having a constant depth and a width which converges with the inner channel section (II). |
| 8. | An optical component according to claim 7, c h a r ¬ a c t e r i z e d in that the guide groove (18) in the element (8) likewise comprises an inner channel section (II) of constant crosssection at the facet of the waveguide and has an outer channel section (III) having an increasing depth as well as width in a direction away from the inner channel section (II). |
| 9. | A coupling device, which is restrictive in three di¬ mensions, for receiving and mechanical retention of opti¬ cal fibres (1) with respect to a plurality of optical waveguides (7) integrated in a substrate wafer (4) and comprising holding and guide grooves (11) in the form of depressions provided in one of the sides of the substrate wafer in extension of the integrated waveguides (7) to receive and retain respective optical fibres (1), c h a r a c t e r i z e d in that it moreover comprises an element (8) which is attached to the substrate wafer side having holding and guide groves (11), so that the holding and guide grooves (11) are substantially covered by the element (8) in their longitudinal direction, and that the element (8) is likewise formed with a guide groove (18) which, when the element (8) is mounted, di¬ verges away from the facet of the integrated optical waveguide (7) in the holding and guide grooves (11) of the first substrate wafer. |
The invention concerns a method of making an optical com¬ ponent which comprises a substrate having a plurality of integrated optical waveguides, and which has a coupling device which is restrictive in three dimensions and has holding and guide grooves for coupling the waveguides to optical fibres, said method being defined by the features which are stated in the introductory portion of claim 1. The invention also concerns an optical component of the type defined in the introductory portion of claim 4 and a coupling device of the type defined in the introductory portion of claim 9.
Optical fibres have been widely used as a transmission medium for many years, because they possess a number of properties which are essential to high speed transmission of huge data amounts over long distances.
With a view to minimizing coupling loss, component sizes, component costs, etc., intensive efforts have been de¬ voted for a number of years on manufacturing optical com- ponents based on a substrate, primarily a silicon sub¬ strate, on the surface of which glass layers are depos¬ ited to form optical elements; examples of such elements include optical couplers and power splitters.
These components have now reached a stage where they can advantageously be implemented in new installations. Now, there are great expectations that the communications sys¬ tem based on optical fibres will become even more wide¬ spread. The transition from discrete optical elements to elements integrated on a substrate will probably involve a development similar to the one which was brought about
by occurrence of the first chips with integrated electric circuits.
One of the remaining problems is to couple optical fibres to the waveguides on the substrate. The problems are that the optical energy is transmitted in the core of the fibre and in the waveguide of the substrate, and that the transmitting parts have diameters or transverse dimen¬ sions of the order of 6-8 μm. Though the cladded fibre has a considerably larger diameter, about 125 μm, it will be extremely difficult to ensure correct coupling between fibres and waveguides, since the perspectives of the technology are that each component will have many input and output fibres.
It has previously been attempted to solve these problems in various ways, but so far the solutions proposed have not enabled easy mounting of the optical fibres on the substrate in the assembly. The optical components are supplied by the manufacturer as a substrate with protruding fibres (pigtails), which are subsequently spliced to transmission fibres by an operator.
JP-A-62-94805 discloses a method wherein an optical fibre is placed and fixed in a wedge-shaped depression on a substrate, whose surface is polished, thereby exposing a portion of the fibre core. A glass layer can hereby be placed on top of the polished surface, and coupling and decoupling of optical energy between the fibre core and discrete, optical elements on top of the glass layer can take place therethrough.
US 5 150 440 discloses a coupling structure where the waveguide layer is formed with a channel into which the fibre may be inserted and be fixed. Reference is made to
fig. 12B in particular, which shows a structure in which a fibre may be retained in two dimensions.
US 5 239 601 shows a substrate structure in which the substrate surface, on which the waveguides are provided, is formed with channels to receive the fibres.
Finally, WO 95/01580 shows a substrate with grooves in which fibres are mounted, and a cover substrate with grooves which is succeedingly attached over the fibres for mechanical retention.
The two US patents disclose approaches whereby a fibre core and an integrated waveguide can be aligned to obtain small coupling losses, but it will still be almost impos¬ sible for a mounting robot, when mounting fibres on the integrated optical waveguides, to mount several fibres side by side in a substrate, because the fibre ends are flexible.
Accordingly, the object of the invention is to provide a method of making optical components so that these compo¬ nents comprise a coupling device which is restrictive in three dimensions and serves to guide the fibres into po- sition during the insertion into the channels, in which, after fixing, they are correctly positioned with respect to the waveguide, thereby providing an optimum optical coupling.
This object is achieved by a method of the type defined in the opening paragraph which is characterized by the features defined in the characterizing portion of claim 1.
Hereby, it is possible to provide a funnel-shaped opening of the substrate channel to receive and retain fibres, thereby facilitating their insertion into the channel.
The invention moreover concerns an optical component hav¬ ing the characteristics defined in claim 5, it being hereby ensured that the fibres are guided into position during the insertion, as well as a coupling device having the features defined in the characterizing portion of claim 10, wherein the covering element serves as a cover or a side in the funnel-shaped channel.
It will hereby be possible to create a clearance for the insertion of the fibres, e.g. corresponding to 2-5 the external fibre diameter, and this will be sufficient to ensure correct insertion and positioning.
The invention will be described more fully below in con¬ nection with preferred embodiments and with reference to the drawing, in which:
fig. 1 is a schematic view in vertical longitudinal sec¬ tion of a preferred embodiment of a coupling structure according to the invention for retention of an optical fibre;
fig. 2 shows the coupling structure of fig. 1 before separation;
fig. 3 is a schematic end view showing how the waveguide is provided on the substrate wafer;
fig. 4 is a schematic top view showing how the holding and guide groove in the substrate wafer is etched in a preferred embodiment of the invention;
figs. 5 and 6 are sectional views schematically illus¬ trating how the holding and guide groove in the substrate wafer is etched in a preferred embodiment of the inven¬ tion;
figs. 7-10 are vertical longitudinal sections schemati¬ cally illustrating how the guide groove in the covering element is etched in a preferred embodiment of the inven¬ tion;
fig. 11 is a detailed, cross-sectional view showing a preferred embodiment of a fibre coupling device of the invention;
fig. 12 is a lateral longitudinal section showing the fibre coupling device, shown in fig. 11, of the inven¬ tion; and
fig. 13 is a top longitudinal section showing the fibre coupling device, shown in fig. 11, of the invention.
As will appear, the figures are not to scale for better illustration of the principles of the structures. The ac¬ tual sizes appear from the numerical examples.
Fig. 1 shows a preferred embodiment of an optical compo¬ nent having a coupling device of the invention for coup¬ ling to any optical fibre adapted for the purpose. The optical component is generally designated by 9 and com- prises a wafer-shaped substrate 4, e.g. of crystalline silicon. An oxide layer having a plurality of waveguides 7 with a refractive index Ώ.2 is provided on this sub¬ strate wafer 4 between cladding layers 5 and 6 with a re¬ fractive index n j _. These refractive indices have been se- lected such that the greater part of the optical energy propagates within the waveguides 7.
The waveguide layer 5-7 has mounted thereon a separate element 8, e.g. in the form of another silicon wafer whose size corresponds to the substrate wafer 4. The ele¬ ment 8 is attached by means of a suitable adhesive, and one side of the component is formed with a funnel-shaped coupling device 10. The wafer-shaped substrate 4 and the wafer-shaped element 8 are formed with holding and guide grooves which diverge away from the facet of the waveguide 7, thereby forming a funnel to facilitate the insertion of the fibre 1. The fibre 1 comprise a core 3 and a cladding 2 in a known manner.
The substrate wafer 4 is shown in a vertical end section in fig. 3 prior to etching of the holding and guide grooves. Etching provides a channel 11 in the surface of the substrate wafer, which is shown in fig. 4. It will be seen that the channel 11, which preferably has a uniform depth, is divided into three sections, I, II and III.
The first channel section I comprises a portion in which the waveguide layer 5-7 is underetched, i.e. silicon ma¬ terial is removed to a certain degree below the facet of the waveguide. This ensures a good optical connection, since the waveguide facet is the part that first gets into mechanical contact with the inserted fibre. As also appears from fig. 1, it is ensured in the mounting of the element 8 that a cavity exists also above the waveguide facet. The length of the channel section I is about 5 μm in the preferred embodiment.
The channel 11 is formed by placing a mask 12 (fig. 5), following which the substrate wafer is subjected to a suitable etch, e.g. RIE. Figs. 5 and 6 are sectional views through the channel section II, and it will be seen that the waveguide layer 5-7 is also underetched along
the side edges of the channel. When subjected to etching, the depth of the channel 11 is controlled by means of the etching time, so that the fibre core, when the fibre en¬ gages the bottom of the channel, is flush with the facet of the waveguide 7. The width of the channel 11 is deter¬ mined by the mask 12 and is selected to be slightly larger than the diameter of the fibre, which may e.g. be 125 μm, so that this is retained loosely when inserted into the channel, until final fixing takes place.
The length of the channel section II is about 3 mm in the preferred embodiment, while the third channel section III may e.g. be about 1 mm. Here, the width of the channel 11 diverges to 2-5 times the width of the channel 11 in the second channel section II, which means in the shown ex¬ ample that the width of the channel facet will be about 0.25-0.6 mm.
Figs. 7-10 are longitudinal sections through the element 8 during the etching and masking steps which are neces¬ sary to form the guide groove in the element 8. It is noted in this connection that the optical components may advantageously be manufactured by bonding two etched wa¬ fers together and then separating the components, e.g. by sawing, which may be illustrated by the formation of cavities having the shape shown in fig. 2, since separa¬ tion by sawing along the line 17 results in the formation of two funnel-shaped coupling devices A and B, respec¬ tively.
In fig. 7, the element 8 is provided with a mask 13 which exposes the areas to be etched. Suitable etching creates a depression 15, which is shown in fig. 8. The mask 13 is removed, and a new mask 14 (fig. 9) is applied, exposing an even larger area, since the originally exposed area is etched deeper than the areas exposed last, so that the
etched depression will be deepest in the centre where the element was exposed originally. The mask 14 is subse¬ quently removed.
After attachment to the substrate 4 with the waveguide layer 5-7, the channels 11 and 16 form the funnel-shaped holding and guide groove for the optical fibre. The height of the funnel-shaped holding and guide groove in the second channel section II is slightly greater than the fibre diameter, while the height in the third channel section is increased to 1.5-5 times the fibre diameter or is about 0.2-0.6 mm.
Figs. 11-13 show that, prior to being assembled with the substrate wafer 4, the element 8 is provided with an ad¬ hesive 16. This adhesive 16 may e.g. be a hydrophilic glass layer containing water (spin-on glass), if the glass layer 7 is hydrophilic. Alternatively, it may have a great light absorbing capacity at a wavelength at which the other glass types are transparent. In this case, the wafers may be welded together by means of a laser. Elec¬ trostatic bonding might also be used. When a glass layer 16 is used as a "glue layer", this may be quite thin, e.g. 50 nm.
After mounting of the fibres, they are welded together with their respective waveguides by means of an FIR light source, e.g. a CO2 laser which emits optical energy through the element 8 at a wavelength of 10.6 μm. Fibre and waveguide are hereby fused together. Alternatively, the fibres may be attached using gluing with epoxy.