DE4208278A1 - Integrated optical component eg modulator or switch - provides polymer optical conductor running on polymer material filling positioning slanted trench at connection with glass fibre - Google Patents

Abstract

The component includes an optical conductor (17) on a silicon substrate having an optical buffer layer with low refractive index. An anisotropic etching is carried out into the substrate, aligned to the light wave conductor aligned positioning trench (12). The positioning trench is filled in with a synthetic material (15) at the connecting side end area. The conductor stretches out on the synthetic material as far as a perpendicular to the axial direction fo the conductor running in the plane of the connecting end surface lying end surface (18) of the synthetic material. This end surface is outside a slanting end area (13) of the positioning trench. USE/ADVANTAGE - Eg for directional coupler, polariser or distributor. Enables self adjusting coupling of glass fibres or fibre arrangement on light wave conductor of optical polymer to be realised in simple way.

Description

State of the art

The invention relates to an integrated optical component, in particular a modulator, directional coupler, switch, polar sator, distributor or the like. According to the genus of the main claim and a method for producing such a construction elements.

The increasing use of integrated optical components for optical communication technology, for sensors and the computer area (optical data bus) leaves the optical Connection technology (chip-fiber coupling) an ever larger Importance. Even smaller private agencies with around 1000 subscriber lines several thousand optical connections, for example between the individual sub-switching stages, since number and com complexity of the optical integrated on individual substrates Components due to the extreme aspect ratio in the optics is severely limited. In such application cases determines feasibility and reliability (mechanical and thermal stability) of the optical an last technology and the required connection effort last Lich the achievable level of expansion of an optical communication system.

The light coupling efficiency when coupling glass fibers and integrated waveguides of the components depends very much from the distance of the end faces, a lateral one  Shift and an angular tilt of the optical Axes against each other. The glass fiber has the Coupling accordingly five degrees of freedom, which are independent must be optimized from each other: an axial freedom degrees, two lateral degrees of freedom and two angular degrees of freedom straight. With the field distributions typical for glass fibers leads z. B. already a lateral offset of only a few microns coupling losses in the dB range. An effective coupling procedure requires a reduction in degrees of freedom as well a way of positioning everyone at the same time Fibers of a bundle. From appl. Opt. 17 (1978), 895, "Opti cal coupling from fibers to channel waveguides formed on silicon ", J. T. Boyd and S. Sriram, it is known to have V-grooves as positioning trenches for the glass fibers in a silicon etch substrate. The anisotropically etched V-grooves are bounded on all sides by slowly etching (111) planes, which includes an angle of 54.7 ° to the wafer surface eat. The integrated are aligned with these V-grooves Waveguide arranged, the width of the grooves so can be optimized that by the resulting groove shape the fiber core in the same horizontal plane as the Optical fiber comes to rest. The Kopp end face to the optical waveguide the V-groove is also ge at an angle of 54.7 ° tends so that the fiber does not quite reach the waveguide can be pushed up. As a solution to this problem is proposed by Boyd and Sriram to use fiber optics to provide an end surface that is also inclined by 54.7 °, so that the fiber core except for butt coupling to the inte push in the optical fiber. This method has the disadvantage, however, that complex end faces processing of the fiber is necessary and the fiber only in a certain position may be inserted into the groove. When coupling, there is also the risk that  or at least slide the two end faces together the end region of the fiber is therefore pushed out of the groove becomes. An additional difficulty arises from the Need not only the fiber, but also the inte grated waveguide with a correspondingly inclined End surface.

Furthermore, it is known from the cited literature reference to be held in etched V-grooves glass fibers and by closing filling of liquid polymer (polyurethane) a connection to the organic optical fiber put out in the extended V-grooves and through this is defined. Because the size of the grooves on the paddock However, the point is determined by the glass fiber cladding diameter is, such waveguides are extremely fashionable and for monomode systems of telecommunications not to be used chen. Taping of the channel waveguide is also provided beat, the width and thus the depth of the V-groove gradually reduced in size to make the transition to usual thin film waves to realize ladders. But since in this case too Transition from the fiber core of the glass fiber to the channel waveguide a big jump in the diameter of the waveguide structures , higher modes are unavoidable and thus a high coupling efficiency in single-mode Operation not expected.

Advantages of the invention

The integrated optical component and have the inventive method for its manufacture in contrast the advantage that a self-adjusting coupling development of glass fibers or fiber arrangements on light waves conductor made of an optical polymer in a simple way reali is sizable. The end face processing of the optical fibers is simple and preferably carried out by laser ablation  bar. The production of the holding grooves for the glass fibers can easily by anisotropic etching after a established technology. In doing so, a high Accuracy of the relative position of the fiber and waveguide end surfaces reached. With easily realizable field adaptations solutions using exposure processes can be a high coupling efficiency can be achieved. Furthermore, a big one thermal and mechanical stability through common Potting of waveguide and fiber can be achieved. The Component according to the invention is particularly suitable for single-mode waveguide structures.

By the measures listed in the subclaims are advantageous developments and improvements of component specified in the main claim possible.

A particularly simple and mechanically stable production of the optical waveguide can be caused in that a buffer layer carrying the optical waveguide and the plastic material in the V trench to the level of the end surface covering layer from an optical, through Exposure in its refractive index changeable polymer is provided, with the optical waveguide by de Exposure of this layer formed as part of the same is. This allows the optical fiber to be more variable Way after mechanical application of the polymer layer be formed. The trained as an optical fiber The area of the layer has a higher refractive index on.

The plastic material for filling the positioning trench is expediently also an optical polymer, this in particular with that of the one covering the buffer layer Layer is identical. An optimal field adjustment can done here in that the glass fiber end of  Optical fiber adiabatic to the diameter of the Glass fiber core is expanded. This is not just one lateral, but additionally or alternatively also one vertical expansion possible, which is reflected in the optical Polymer that fills the V-groove.

For field adaptation of the optical fiber to the glass fiber in addition to the geometric Adaptation of the area of the optical waveguide optical polymer an adiabatic, the refractive index difference between optical fiber and the surrounding Index to the fiber index-reducing area point.

Another advantageous way to adapt and Coupling is that the glass fiber end of the optical fiber tapered to a point and in another Optical fiber with a lower refractive index opens which extends to the fiberglass core. Here is also even with a relatively strong leader compared to the glass fiber core Optical fibers with small cross-sectional dimensions high coupling efficiency possible. The further light waves ladder can have a larger extension in width and / or have depth and dimensioning of the glass fiber core to be adapted to the coupling end surface.

In an advantageous embodiment of the method according to the invention can apply the layer and fill in the Posi trench in one operation with the same optical Polymer are carried out. This allows the manufacture be carried out easily and inexpensively.

The formation of the optical waveguide is more expedient wise over a sheet placed on the polymer layer tion mask, with a refraction by photopolymerization  index increase in the fiber optic range becomes. Furthermore, for example, in the case of non-linear optical polymers an exposure mask on the polymer layered and through a UV photo fading process a refractive index reduction of areas is carried out that limit the optical fiber.

To optimize the field adjustment between fiber optics and fiber optic adiabatic expansion of the Fiber optic in front of the glass fiber core, is expediently for lateral expansion up to the diameter of the glass fiber core an exposure mask used with widening mask opening. Alternatively or in addition to vertical expansion up to the diameter of the glass fiber core the exposure intensity and / or the exposure time towards the glass fiber is ramp-like enlarged. To further optimize the field a second mask can be used to make adjustments used with variable transparency for post-exposure on the fiber side are more transparent and light has less transparency on the waveguide side.

A second taper concept is used to manufacture and Coupling of a tapered optical waveguide next in a first exposure step with a first Exposure mask a first pointed towards the glass fiber running optical fiber is formed, and then in a second exposure step a second, the first Optical fiber connecting with the coupling end face Optical fibers with a lower refractive index are formed, the second optical fiber in diameter is adapted to the fiberglass core.

With the method according to the invention can be advantageous Way a variety of adjacent light waves  conductors or connections are made at the same time.

drawing

Embodiments of the invention are in the drawing shown and in the description below explained. Show it:

Fig. 1, an integrated optical device having a coupled optical fiber in a V-groove in a plan view as a first embodiment,

The component shown in Fig. 1 Fig. 2 in a vertical sectional representation,

Fig. 3 is a similar arrangement of an optical Bauele ment with a getaperten structure in a plan view as a second embodiment,

Fig. 4, the device shown in Fig. 3 in a vertical sectional representation,

Fig. 5 is a similar optical component with a cusped optical waveguide in a plan view as a third embodiment,

Fig. 6, shown in Fig. 5 third execution example, in vertical section,

Fig. 7, the vertical in FIGS. 5 and 6 component illustrated in a vertical section to the section plane of FIG. 6 and

Fig. 8 is the same device in a perspective view towards the waveguide.

Description of the embodiments

The integrated optical component shown in FIGS. 1 and 2 consists essentially of a silicon substrate 10 , in which a positioning trench 12 with a V-shaped cross section is etched anisotropically to accommodate a glass fiber 11 . The known anisotropic etching technology has a high level of development and is also used in the state of the art at the beginning. With the help of the window opening in an etching mask, the width a of the positioning trench 12 and thus the depth j of the etched groove is determined. With the help of alkaline etching media, such as. B. Potassium hydroxide, V-shaped recesses are formed, which enclose a very precise angle of 54.7 ° to the surface. Such an angle also forms on an inclined end surface 13 of the positioning trench 12 , which extends over a length c into the trench.

After the etching of the preprocessed silicon substrate 10 (wafer), which in addition to the positioning trench 12 can also carry active and / or passive optical components (not shown) and electronic arrangements, an optical buffer layer 14 with a low refractive index and a thickness k is applied. This can be silicon dioxide, but an organic film can also be used. The buffer layer thickness must be taken into account as a mask when etching the positioning trench 12 .

An optical polymer such as PMMA with photoinitiator is then applied over the entire surface, which leads to a filling 15 of this trench in the region of the positioning trench 12 and to the formation of a layer 16 covering the surface in the remaining region.

An optical waveguide 17 with the width f is now produced in the layer 16 by UV exposure. Local photo polymerization leads to an increase in the refractive index in the exposed area. The exposure mask, not shown, is aligned with the etched V-grooves of the positioning trench 12 or by additional adjustment aids.

The optical waveguide 17 then forms in accordance with the shape of the elongated mask opening.

Instead of the photopolymerization described, the optical waveguide 17 can in principle also be equivalent when using some nonlinear optical polymers by local thermal polishing and / or by a UV photo bleaching process.

The lateral light guidance is realized by an index difference between the exposed (optical waveguide 17 ) and the unexposed area (weak guidance), which is generally small for monomodal waveguides. The vertical extension of the optical waveguide 17 is given in the case of thin layers (approximately 2 μm) by the thickness m of the polymer layer 16 , the vertical waveguide being determined by the index jump on the one hand to the buffer layer ( 14 ) and on the other hand to air or an upper cover layer will (strong leadership). The corresponding field distributions can usually be well adapted to the field distributions of active optical semiconductor components on the integrated optical chip with small layer thicknesses.

In the area of greater layer thicknesses, that is in the area of the filling 15 , the vertical extension of the optical waveguide 17 is limited by the effective depth of the photopolymerization process. With strong UV absorption of the photopolymerizable materials, this depth depends on the exposure parameters and the material composition (e.g. proportion of the photoinitiator), so that the channel waveguide can be specifically expanded to an adjustable depth q below the surface. At the same time, the light wave is also guided downwards weakly in these areas, as is the case in the lateral direction, which facilitates the field adaptation to the radially symmetrical distribution of the fiber.

Up to this manufacturing step, the positioning trench 12 is filled with the optical polymer. For the chip-fiber coupling, the positioning trench 12 must now be exposed to accommodate the glass fiber 11 with the diameter h. This can be done by laser ablation using an excimer laser. The resulting, sufficiently smooth cut edge 18 through the optical waveguide 17 and the filling 15 makes further processing of the optical fiber end surface unnecessary. The cut is made at a distance b from the upper end edge of the positioning trench 12 , this distance b exceeding the extent c of the oblique end surface and thus allowing a butt coupling between glass fiber 11 and optical waveguide 17 , which is only limited by the residual roughness of the optical fiber end surface. The relative vertical position n of the optical axes of optical waveguide 17 and fiber 11 can be optimized overall over the depth of the V-groove so that the optical fields overlap as well as possible. The glass fiber core 19 with the diameter i is then aligned precisely enough with the optical waveguide 17 . In the case of a strong top layer, e.g. B. air, the glass fiber 11 can also be placed slightly lower, so that the glass fiber core 19 is flush with the optical fiber 17 , as shown in Fig. 2.

If the buffer layer 14 is an organic buffer layer, this is also removed by laser ablation, which is to be taken into account in the mask layout over the width of the structures to be etched.

In the manufacturing process described, with only one lithography / etching step for the positioning trench 12 and one UV exposure for the optical waveguide 17, all degrees of freedom of the chip-fiber coupling are determined with sufficient precision by the mask processes. A thermal baking process for stabilizing the photopolymerized waveguide structures can then take place before the end surfaces are created by the laser treatment and the positioning trench 12 is exposed. The fiber can then be inserted and fixed directly into the positioning trench 12 without active adjustment. It should be noted that, for simplification in FIGS. 1 and 2 and also in the other figures to be described, only a single positioning trench 12 with a glass fiber 11 and an optical waveguide 17 is shown. In practice, however, a plurality of parallel positioning trenches 12 are created, and a corresponding number of optical waveguides 17 is generated by exposure before a corresponding number of glass fibers 11 are again inserted and fixed.

To increase the thermal and mechanical stability, a common upper cover layer can be created by jointly encapsulating the inserted glass fibers 11 and the optical waveguide 17 , which is not shown in the figures. A UV-curable optical liquid polymer can be used for this purpose, for example. If the index jump to this upper cover layer is kept low, the field distributions can be approximated further by a vertically weak guide.

It is of course also possible to use a different plastic material with lower optical damping and suitable refractive indices for the filling 15 than for the layer 16 and the optical waveguide 17 , provided that strong guidance in the optical waveguide 17 in the connection area to the glass fiber 11 is of particular value is placed.

In the second embodiment shown in FIGS . 3 and 4, the same or equivalent parts and areas are provided with the same reference numerals and are not described again.

A tapered structure is used here to optimize the field adaptation between the glass fiber 11 and the optical waveguide 17 . The glass fiber end portion 17 a of the optical waveguide 17 is expanded adiabatically to the diameter of the glass fiber core 19 . This is done laterally by a corresponding expansion of the mask opening of the exposure mask, the longitudinal edges of which have a small opening angle α. In a typical example, α is 1 ° and the taper length is approximately 500 µm. With an optical fiber width of 4 µm and a fiber core diameter of approx. 10 µm.

The vertical extent of the end region 17 a of the optical waveguide 17 depends on the material composition and the exposure. For example, in the case of a PMMA material with a photoinitiator, the maximum index increase that can be achieved by UV exposure is a function of the concentration of the photoinitiator. This saturation effect can be exploited in vertical taping in such a way that when the optical waveguide is strongly overexposed, on the one hand its refractive index remains constant at the saturation value, but on the other hand the depth expansion increases with the exposure dose (intensity · time). As a result, the end region 17 a can be vertically widened towards the filling 15 , as shown in FIG. 4. The increasing widening towards the glass fiber core can be generated by a so-called gray wedge, which has a high transparency on the fiber side and a lower transparency on the fiber optic side. This widening to a width q compared to the thickness in the layer 16 can of course also be carried out in the first embodiment in which the lateral width remains constant.

By UV post-exposure of the layer 16 in the area of the tapered structure, the refractive index outside the optical waveguide 17 can subsequently be raised, so that the light guidance becomes weaker as the difference in refractive index becomes smaller and the field adaptation to the glass fiber 11 can be further optimized. This post-exposure can also produce an adiabatic index curve if a mask with variable transparency is used again ("gray wedge"). In Fig. 3, the region 20 to be post-illuminated is identified by a border. The exposure for fiber arrays arranged in parallel can be done in strips over all positioning trenches 12 by simple mask adjustment.

In the third exemplary embodiment shown in FIGS . 5 to 8, the glass fiber-side end region 17 b of the optical waveguide 17 is formed to be tapered and opens before the cutting edge 18 . This end region 17 b is surrounded by a further optical waveguide 21 , which provides the connection to the glass fiber 11 or to the glass fiber core 19 . As a result, even very thin optical waveguides 17 can be optimally coupled to a relatively thick glass fiber core 19 . The compared to the optical waveguide 17 having a slightly lower refractive index further optical waveguide 21 is generated by a second exposure process with its own exposure mask. With a larger cross-section and with a suitable index profile with a correspondingly greater depth expansion of the optical fields in the area of the filling 15 , the field distribution of the glass fiber 11 (typical glass fiber core diameter i approximately = 8-10 μm) can then be approximated in order to achieve high coupling efficiencies. Due to the tapered shape of the end region 17 b, the light wave guided therein is coupled into the further optical waveguide 21 with a lower refractive index. The field distribution in the very narrow optical waveguide 17 is adapted, for example, to optoelectronic semiconductor components, and then an adjustment to the field distribution of the glass fiber 11 is achieved via the optical waveguide 21 .

In Figs. 7 and 8 yet a top cover layer 22 is shown overlying the layer 16 and the optical waveguide 17 and may also mitüberdecken the optical fiber 11. FIG. 7 shows a cross section through the arrangement perpendicular to the longitudinal direction of the optical waveguide outside of the positioning trench 12 .

In the perspective view according to FIG. 8, the buffer layer 14 has been left to simplify the illustration. The glass fiber 11 and the cover layer 22 have also not been shown.

Instead of the structuring technique described (UV-Be radiation) to form the optical waveguide can prince other structuring techniques, such as an ion implantation or the formation of a rib wave head z. B. by dry etching. Through such a structure techniques, including the UV radiation described or the UV photo fading process can also be used the manufacture of the optical fiber also other Line structures, switches or the like in uniform techno generate logic on the integrated optical chip.

Depending on the requirements for the coupling efficiency between fiber and waveguide, the measures described can be carried out in a more or less pronounced manner. If the requirements are not quite as high, the simpler embodiment according to FIG. 1 can suffice for example.

Claims (22)

1. Integrated optical component, in particular modulator, directional coupler, switch, polarizer, distributor or the like., With an arranged on at least one optical buffer layer with a low refractive index silicon substrate arranged optical waveguide made of an optical polymer and with an anisotropic in the substrate etched positioning trench with a V-shaped cross-section, aligned essentially with the optical waveguide, for receiving a glass fiber to be coupled to the coupling end face of the optical waveguide, characterized in that the positioning trench ( 12 ) is filled with a plastic material ( 15 ) at the coupling-side end region, wherein the optical waveguide ( 17 ) on the plastic material ( 15 ) extends to an end surface ( 18 ) of the plastic material ( 15 ), which runs perpendicular to the axial direction of the optical waveguide ( 17 ) and lies in the plane of the coupling end face, and d ate this end surface ( 18 ) outside of a sloping ver end region ( 13 ) of the positioning trench ( 12 ) is arranged. 2. Component according to claim 1, characterized in that one of the optical waveguide ( 17 ) carrying buffer layer ( 14 ) and the plastic material ( 15 ) to the level of the end face ( 18 ) covering layer ( 16 ) of an optical, by exposure in its refractive index changeable polymer is provided, the optical waveguide ( 17 ) being formed as part of the same by appropriate exposure of this layer ( 16 ). 3. Component according to claim 2, characterized in that the region of the layer ( 16 ) formed as an optical waveguide ( 17 ) has a higher refractive index. 4. Component according to one of the preceding claims, characterized in that the positioning trench ( 12 ) has a dimension through which the glass fiber core ( 19 ) of the inserted glass fiber ( 11 ) is aligned with the optical waveguide ( 17 ). 5. Component according to one of claims 2 to 4, characterized in that the plastic material ( 15 ) for filling the positioning trench ( 12 ) is an optical polymer. 6. The component according to claim 5, characterized in that the plastic material ( 15 ) with the optical polymer of the buffer layer ( 14 ) covering layer ( 16 ) is identical. 7. Component according to one of claims 2 to 6, characterized in that the glass fiber-side end region ( 17 a) of the optical waveguide ( 17 ) is expanded adiabatically to the diameter of the glass fiber core ( 19 ). 8. The component according to claim 7, characterized in that a lateral and / or vertical expansion is provided is. 9. The component according to one of claims 2 to 6, characterized in that the glass fiber-side end region ( 17 b) of the optical waveguide ( 17 ) tapers and ends in a further optical waveguide ( 21 ) with a lower refractive index, which extends up to the glass fiber core ( 19 ) extends. 10. The component according to claim 9, characterized in that the further optical waveguide ( 21 ) has a greater expansion in width and / or depth and the dimensioning of the glass fiber core ( 19 ) is adapted to the coupling end face. 11. The component according to one of claims 2 to 10, characterized in that for the field adaptation of the optical waveguide ( 17 ) to the glass fiber ( 11 ) towards the optical waveguide ( 17 ) surrounding area of the optical polymer layer ( 16 ) an adiabatic, the refractive index difference between Optical waveguide ( 17 ) and this surrounding area towards the glass fiber reducing index course. 12. A method for producing an integrated optical component, such as a modulator, directional coupler, switch, polarizer, distributor or the like, which has an optical waveguide made of an optical polymer which is arranged on a silicon substrate provided with at least one optical buffer layer with a low refractive index, wherein for Inclusion of a glass fiber to be coupled to the optical waveguide, a positioning trench with a V-shaped cross section, essentially in alignment with the optical waveguide, is anisotropically etched into the silicon substrate by means of an elongated mask opening on the exposure mask, in particular according to one of the preceding claims, characterized in that after the etching of the Positioning trench ( 12 )

• a) the optical buffer layer ( 14 ) is applied,
• b) a layer ( 16 ) of an optical polymer is applied over it, the positioning trench ( 12 ) being filled beforehand or simultaneously with a plastic material ( 15 ),
• c) is formed by appropriate local exposure or thermo polarity of this layer ( 16 ) of the optical waveguide ( 17 ) and
• d) the positioning trench ( 12 ) is exposed up to a plane ( 18 ) which runs vertically to the axial direction of the optical waveguide ( 17 ) and forms a coupling end face.

13. The method according to claim 12, characterized in that the application of the layer ( 16 ) and the filling of the positioning trench ( 12 ) is carried out in one operation with the same optical polymer. 14. The method according to claim 12 or 13, characterized in that an exposure mask is placed on the polymer layer ( 16 ) and a refractive index increase is carried out in a region which is to serve as an optical waveguide ( 17 ) by photopolymerization. 15. The method according to claim 12 or 13, characterized in that an exposure mask placed on the polymer layer ( 16 ) and a refractive index reduction of areas is carried out by a UV photo bleaching process, which limit the optical waveguide ( 17 ). 16. The method according to claim 14 or 15, characterized in that in order to optimize the field adaptation between glass fiber ( 11 ) and optical waveguide ( 17 ), an adiabatic expansion of the optical waveguide ( 17 ) in front of the glass fiber core ( 19 ) is carried out. 17. The method according to claim 16, characterized in that an exposure mask is used with a widening mask opening for lateral expansion to the diameter of the glass fiber core ( 19 ). 18. The method according to claim 16 or 17, characterized in that for the vertical expansion up to the diameter of the glass fiber core ( 19 ), the exposure intensity and / or the exposure time to the glass fiber is increased like a ramp. 19. The method according to claim 14 or 15, characterized in that in a first exposure step with a first exposure mask, a first, to the glass fiber ( 11 ) tapered optical waveguide ( 17 ) is formed, and that in a second exposure step with a second exposure mask second, the first optical waveguide ( 17 ) with the coupling end face connecting optical waveguide ( 21 ) with a lower refractive index is formed, the second optical waveguide ( 21 ) being adapted in its diameter to the glass fiber core. 20. The method according to any one of claims 16 to 19, characterized in that an exposure mask with variable transparency is used for post-exposure of the layer ( 16 ), which has a higher transparency on the fiber side and a lower transparency on the optical fiber side. 21. The method according to any one of claims 12 to 20, characterized characterized in that the exposure of the positioning trench is carried out by means of a laser (laser ablation). 22. The method according to any one of claims 12 to 21, characterized in that a plurality of juxtaposed the connections, positioning trenches ( 12 ) and optical fibers ( 17 ) is produced simultaneously.