KR100240079B1 - Integrated optical component - Google Patents

Abstract

An integrated optical component consisting of at least one waveguide connected to an end of an optical fiber and integrated in a substrate, each bonded by a first and a second adhesive drop to a substrate in an area spaced from the fiber end, the adhesive forming the first drop Has a glass transition temperature that is within the predetermined operating temperature of the part, and the adhesive forming the second drop typically has a glass transition temperature that is above the operating temperature range, thus ensuring absorption of other thermal expansions, thereby ensuring optical continuity of the fiber / waveguide connection. And mechanical strength of the fiber / substrate connection.

Description

Integrated optical components

Figure 1 shows a partial cross-sectional view of an integrated optical component in accordance with the present invention, showing the connection between the fiber and the waveguide integrated into the substrate and the connection between the fiber and the component substrate.

FIG. 2 shows a cross-sectional view similar to that of FIG. 1 as a second embodiment of an integrated optical component according to the invention.

3 is a third embodiment of an integrated optical component in accordance with the present invention, showing a cross section similar to FIGS. 1 and 2.

4 is a fourth embodiment of an integrated optical component in accordance with the present invention, showing a cross section similar to FIGS. 1, 2 and 3;

The present invention relates to an integrated optical component consisting of at least one waveguide integrated into a substrate and coupled to an end of a monomode or multimode optical fiber. More particularly, the present invention relates to the component on which the fiber is bonded to the substrate, on the one hand facing the output of the integrated waveguide and away from the output on the other.

Such integrated optical components are known, for example, from US Pat. No. 4,943,130 to Dannoux et al., Assigned to Corning Glass Works on March 12, 1987. In a preface to the TWNWT 000442 paper published in November 1990 by Bellcore (US A), the optical component must undergo a pre-determined test to ensure the mechanical strength of the fiber / substrate connection and the transmission performance of the optical signal. do. The mechanical strength is tested by the tensile force applied on the fiber / substrate connection, which is aged over a temperature range of -40 ° C to + 85 ° C and aged at 60 ° C for 93 hours at a relative humidity of 93% and also at 85 ° C for 2000 hours. It must withstand a force of 5N during the process. Furthermore, the excess signal loss observed in the transmitted optical signal shall not exceed 0.8 dB for pre-determined limits, for example components with one input and two outputs.

The use of the integrated optical components cited above creates one problem with respect to the different thermal expansions of the materials forming the substrate, the optical fiber and the adhesive of the device. The substrate is readily made of glass having a coefficient of thermal expansion of approximately 80 × 10 ⁻⁷ K ⁻¹ . The integrated optical waveguide is formed on the glass by, for example, a photolithographic mask process and an ion exchange method. Monomode or multimode optical fibers consist of, for example, very pure silica and doped silica with a coefficient of thermal expansion of less than 6 × 10 ⁻⁷ K ⁻¹ . Thus, when increasing to the same temperature, the substrate expands more than the fibers so that the fibers are joined at two separate points to the substrate. The substrate therefore exerts a tensile stress on the fiber site located between the two points. This stretching force may cause fission, change of optical properties of the silica constituting the fiber, or damage of the fiber junction. The coefficient of thermal expansion of the adhesive may also play a big role in other observed expansions. This phenomenon can change or in some cases destroy the coherent properties of the connection between the fiber and waveguide of the integrated optical component, resulting in an incidental change or complete loss of the optical signal transmitted through this connection. Another factor of the change in the connection is the influence of the environment, in particular the humid atmosphere and the maturation of the materials constituting the part, especially in the case of rapid changes when the temperature decreases from room temperature to a low temperature (eg -40 ° C). Severe.

Accordingly, the present invention aims to produce an integrated optical component having the above-described structure and designed to ensure satisfactory mechanical and optical properties in a predetermined wide temperature range.

The present invention also aims to produce such components with satisfactory resistance to the effects of high humidity atmosphere and ripening.

The object of the present invention is achieved by an integrated optical component designed for use in a predetermined temperature range, which component is formed on a substrate and at least respectively the first and second adhesive drops in the area separated from the substrate at the output region. and at least one integrated optical waveguide coupled to the connected optical fiber by drop.

Each adhesive constituting the drop has a glass transition temperature. According to the invention the glass transition temperature of the first drop of the adhesive is in a predetermined temperature range, the glass transition temperature of the second drop is usually in a second temperature range that is above the predetermined range, the lower limit of the second category is the predetermined It is +/- 10 degreeC of an upper limit.

Thus, the mechanical difference of the fiber / substrate connection is improved so that the expansion difference does not change the optical continuity of the fiber / waveguide connection or harm the optical fiber.

According to another embodiment of manufacturing the integrated optical component according to the present invention, the third drop of the adhesive is applied farther from the fiber endface than the second drop to fix the fiber to the substrate. The glass transition temperature is usually above the predetermined temperature range. Therefore, as will be described later, the amount of adhesive used can be reduced, and the expansion of these adhesives in the humid atmosphere can reduce the influence of the optical performance of the fiber / waveguide connection.

According to another embodiment of manufacturing the integrated optical component according to the invention, the fourth drop of the adhesive is used to connect the fibers located between the second and third drops to the substrate, wherein the glass transition temperature of the adhesive is It is within the predetermined temperature range. Thus, as will be described later, the strength of the fiber region between the second and third drops of adhesive is increased.

Other features and advantages of the invention are set forth in the description which follows and in the accompanying drawings.

Referring to FIG. 1, this shows an integrated optical component according to the invention consisting of a substrate 1 made of glass, for example, and an optical fiber 2 protected by a coated portion 3. The fiber 2 is partially peeled off and placed on a step 4 formed on the substrate, the end face of which is coupled to the output of the conduit 5 formed on the substrate, for example, by an ion exchange method. Be sure to In accordance with the method and design described in Dannoux et al., U.S. Patent No. 4,943,130 (hereinafter referred to), the transverse exit groove 6, groove (e.g. 1 to 2 mm wide) is provided with the exit and the fiber ( It may be provided between the junction of 2) and step 4. This mechanical and optical bonding is made by the first drop of adhesive 7 with adequate optical performance, preferably the first drop being a small amount. A positive second adhesive drop 8 is applied on the fiber and the substrate to connect the fiber and the substrate, as shown in Figure 1. The drop 8 covers both the stripped and coated portions of the optical fiber. The second drop is separated from the first by the transverse exit groove 6. The method for manufacturing the part according to the invention is described in detail in Dannoux et al. In US Pat. No. 4,943,130.

The connection between the fiber and the substrate is required at two points separated from each other. As discussed above, thermal expansion differences are likely to cause mechanical stress that can be harmful to the connection.

When these stresses reach certain thresholds, a drop in the optical continuity of the fiber / waveguide connection, drop of the fiber or deformation of the optical properties is observed. All these phenomena seriously affect the optical signal transmission between the fiber 2 and the waveguide 5 with the mechanical strength of the fiber / substrate connection and the partial or total attenuation of the optical signal.

According to the invention, this problem can be avoided, which is within the predetermined operating temperature range (eg -40 ° C to + 85 ° C as described above) for the part in dry state to produce the drop 7. This is accomplished by using an adhesive with a glass transition temperature (Tg). Within this temperature range, when the temperature of the drop becomes higher than the Tg of the drop, the adhesive constituting the drop passes through the visco-elastic phase.

The fluid connection produced between the fiber and the substrate by the adhesive in this state causes the fiber to creep in the drop somewhat due to the observed thermal expansion differences. This somewhat crawling prevents the stress on the fibers from reaching the limits that can affect the integration or optical continuity of the fiber / waveguide connections. In selecting the adhesive constituting the drop 7, the optical performance of the final product should be taken into account so as not to cause significant changes in the optical signal in the passage between the fiber end section and the integrated waveguide output. In all cases the temperature (Tg) of the adhesive within the temperature range considered should be chosen such that the difference in thermal expansion occurring below that Tg does not significantly affect the function or structure of the integrated light component according to the invention.

At the same time an adhesive drop 8 can be used, the glass transition temperature of which is usually in the second temperature range above the predetermined range, the lower limit of which is +/- 10 ° C (typically the upper limit of the above-mentioned operating temperature range). Ideal temperature range).

The mechanical connection stability between the fiber and the support thus depends on the adhesion of the drop 8 over the whole temperature range considered, in particular at the upper end of the range.

The adhesive selected as the drop 7 has a glass transition temperature (Tg) within the operating temperature range to reliably absorb thermal expansion differences that are harmful to the component and the fiber / waveguide connection ensures optical continuity. With the drop 7 it is necessary to choose a transparent adhesive which has a refractive index similar to that of the glass, ie close to 1.5.

The integrated optical component produced according to the invention thus makes it possible to meet the conditions of the strength requirements of the fiber / substrate connection under the above mentioned basic conditions, in particular the stretching force carried out at + 85 ° C. However, it was difficult to satisfy the conditions by the preceding standards on operation in a humidified atmosphere.

Another manufacturing method modified to overcome this problem is shown in FIG. In this figure, the same numbers used in FIG. 1 as in FIGS. 3 and 4 correspond to the same or similar parts.

The manufacturing method of FIG. 2 can be distinguished from the method of FIG. 1, which is composed of a thin film of adhesive drop 8 placed on the fibers 2 at the edge of step 4, The drop is composed of an adhesive having a temperature above the considered glass transition temperature. This drop 8 is overlapped and covered by an overlapping drop 9 of adhesive whose glass transition temperature is within the above temperature range. The drop 8 establishes the mechanical integration of the connection between the fiber and the substrate within this temperature range. The drop 9 protects the drop 8 and the fibers 2 against mechanical attack and significant humidity of the ambient atmosphere. As shown in FIG. 2, the overlapping drop 9 strengthens the connection formed by the drop 8 between the substrate and the fiber, strips off the optical fiber 2, and the drop 8 and adjacent areas of the coating site. Covering. In the embodiment of the invention shown in FIG. 2, the drop 8 covers only the stripped portion of the optical fiber and does not cover the coated portion, while the drop 9 overlaps the portion of the coated portion. . This manufacturing method separates the role of mechanical coupling and optical continuity. The mechanical connection is first secured by drop 8 and second by drop 9, and the optical continuity is secured by drop 7.

In general, the thermal expansion difference is absorbed by the drop 7, so that a space of about 15 to 25 μm, preferably 18 to 20 μm, is arranged between the fiber end face on the substrate and the waveguide output area during installation. It is good, thereby providing transparency between the fiber and the waveguide.

The optical parts manufactured in accordance with FIG. 2 can satisfy all of the conditions described by the above-described preliminary reference values. However, it has been satisfied that under the high humidity environment, the expansion of the drop 9 may cause bowing of the optical fiber 2 onto the cross-out groove 6 under the influence of this humidity. This bending is the result of misalignment of the fibers with respect to the waveguide, resulting in attenuation of the transmitted optical signal.

According to the present invention, the bending phenomenon can be reduced or eliminated with the integrated optical component manufactured as shown in FIG. The drop 8 of the component shown in FIG. 2 is separated into two drops 8 'and 8 "in the component of FIG. 3, which are separated from each other, and the drop 8' is a step 4 of the substrate. ) And the drop 8 "is placed on the unpeeled coated part 3 of the fiber 2). Adhesives used for both drops typically have a glass transition temperature above the operating temperature range. The combined amount of the two drops 8 'and 8 "is significantly less than the amount of the drop 9 in FIG. 2. Thus, the bending of the fiber caused by the expansion of the drop 9 by water molecules is considerably Thus, the performance of the part in the humid atmosphere is significantly improved The effect of fiber bending at the end due to the expansion of the adhesive no longer causes an unacceptable misalignment of the fiber to the waveguide.

As shown in Figure 3, the lateral groove 10 separates the drops 8 'and 8 ". The intersection of the surface at the edge of the transverse groove is caused by the surface tension of the drop 8' and ( 8 ") to prevent outflow and eventually they are separated by the groove 10.

3 is another embodiment shown in FIG. Due to this difference, the drop (8 ') and (8 ") separated into spaces (usually an adhesive with a glass transition temperature (Tg) above the component's operating temperature range) are those with a glass transition temperature within the above temperature range. The drop 11 improves the mechanical performance of the fiber / substrate connection In the embodiment of Figure 3 two of the adhesives with glass transition temperatures are typically above the operating temperature range of the part. It is necessary to take into account the fact that the drops 8 'and 8 "define a fixed point of engagement throughout the operating temperature range.

Increasing the temperature in the temperature range under consideration increases the stress due to other thermal expansion, although the increased stress drops even though the increased tension is defined by the coated area 3 between the drop 8 "and the fiber 2. It is applied in the fiber between (8 ') and (8 "). The interposed drop 11 in the embodiment of FIG. 4 increases the resistance of the fiber to the stress, thereby improving the mechanical performance of the assembly.

Substantially in the third embodiment, the assembly of the fibers 2 and the substrate is carried out as follows. Initially the fibers and substrate are assembled by dropping drops 11, 8 'and 8 "on them, as shown in FIG. 4, and the drop 8' is carried out as low as possible. The output portions of the fiber 2 and the waveguide 5 are connected by a drop of the adhesive 7 as done in the above embodiment.

Adhesives that have a particular glass transition temperature and are suitable for the present invention, as described above, are ultimately easily useful as a function of the optical properties desired and the particular application desired, by virtue of being within or typically above the operating temperature range. It can be selected by the expert belonging to the present invention from the adhesive. From this point of view the adhesive is solid when below the glass transition temperature of the adhesive, whereas if it is above the temperature they soften, and this result increases as the temperature deviates from the glass transition temperature (Tg). The same is true of the coefficient of thermal expansion of the adhesive, which is more important than the temperature Tg rather than the temperature. The glass transition temperature starts by applying heat at a temperature below the glass transition temperature (Tg) and then scans the dried product with a temperature gradient of 5 to 10 ° C per minute and then by differential thermal analysis or fission analysis. It is a characteristic of each adhesive that can be measured. This has been edited in the Academic press and published at RCMckenzie's Volume 2, page 392 under the heading "Differential Thermal Analysis" and at the assembly of the society of Technical Analysis and Characterization of Macro-molecular Material in Paris, France, 1986. See the publication "Annales des Composite" (L. Monnerie), 157ff.

Particularly suitable are adhesives made of acrylic or vinyl resin by free radical polymerization. Thus, for this effect, monomers or oligomers in the form of acrylic or vinyl having one or more double bonds which cause free radical polymerization initiated by photoinitiators which cause free radicals in the presence of light (e.g. visible or ultraviolet) are used. Can be.

It is also possible to use an inorganic filler consisting of silica powder or the above resin with a hard organic material, for example, to reduce the sensitivity of the adhesive to humidity except for the drop which firms the fiber / waveguide connections which should optionally have good transparency. have.

As mentioned above, the choice of a particular resin is a function of where the glass transition temperature is within and beyond the operating temperature range. In this respect, the change in the glass transition temperature should be considered as a function of the humidity placed on the resin and of the Young-Modulus in the viscoelastic state as a function of the humidity. The choices made on the basis of the above considerations are typical for the expert belonging to the present invention.

Various resins may be suitable for preparing the adhesives used in the present invention. Thus, adhesives having a glass transition temperature in the temperature range (-40 ° C., + 85 ° C.) specified by way of example only include the trade names Virtralit 612B (Tg = 55 ° C.), or Vitralit 7104, 7105 and 7106, etc. by Elosor. have.

Adhesives having a glass transition temperature above the above temperature range are NOA 81 (Tg = 120 ° C.) or NOA 61 (Tg = 130 ° C.) from EPOTECHNY, France, and LCR 000 and LCR 070 (Tg = 106, from Imperial Chemical Industries, UK). The CCR or 117 degreeC and the hardening process are used), LCR 050 (Tg = 106 degreeC), LCR 000V (Tg = 100 degreeC), LCR 000 / 1.52 (Tg = 100 degreeC), etc. are mentioned.

Of course, the present invention is not limited to the above-described manufacturing process, which is merely shown as an example similar to the above-described preliminary standard. The present invention can be broadly applied to all integrated optical components, multiplexing couplers, amplifiers, which are connected to one or more optical fibers by an adhesive, in particular with respect to the adhesive which can pass in a viscoelastic state. It must be absorbed without damage by other thermal expansions of the parts that are clearly present between the various parts. The present invention is not limited to components containing glass substrates in which one or several waveguides are integrated (integrated) by ion exchange, on the contrary, the present invention is directed to silica or silicon having waveguides integrated by vapor deposition, for example. It can be extended to the component and the substrate of lithium niobate or indium phosphide.

Claims (15)

Bonded by a first drop of adhesive to a substrate of an optical fiber, bonded by a second drop of adhesive to the substrate in an area separate from the fiber, the adhesive forming a drop with a glass transition temperature, and Wherein the glass transition temperature of the adhesive forming is within a predetermined temperature range, the glass transition temperature of the adhesive forming the second drop is within a second temperature category, and the second glass transition temperature is above the upper limit of the predetermined temperature range. An integrated optical component for use in a predetermined temperature range consisting of at least one waveguide having an output portion coupled to a substrate and coupled to the end of the optical fiber within +/- 10 ° C. 2. The integrated optical component of claim 1, wherein the fiber has one stripped and coated portion, and wherein the adhesive of the second drop covers only the stripped portion but not the coated portion. 2. The integrated optical component of claim 1 wherein the fiber has one stripped and coated portion, and wherein the adhesive of the second drop covers both the stripped portion and the coated portion. 3. The method of claim 2, further comprising an overlapped drop having a glass transition temperature within the predetermined temperature range, wherein the overlapping drop reinforces the connection formed by the second drop between the substrate and the fiber, And an overrambling drop covering said deth drop and said stripped and coated fiber portion. The temperature range of claim 1, further comprising a third drop further spaced apart from the fiber end than the second drop to connect the fiber to the substrate, wherein the glass transition temperature of the adhesive forming the third drop is the predetermined temperature range. Integrated optical component, characterized in that it is within the range of + / -10 ℃ of the upper limit and more. 6. The integrated optical component according to claim 5, wherein the fiber contains one stripped portion and a coated portion, and wherein the third drop adhesive covers the coated portion. 6. The integrated optical component of claim 5, further comprising a cross groove formed in the substrate and separated from the second drop and the third drop. 6. The method of claim 5, further comprising a fourth adhesive drop connecting a portion of the fiber between the second and third drops to the substrate, wherein the glass transition temperature forming the fourth drop is within the predetermined temperature range. Integrated optical component, characterized in that. 6. The integrated optical component of claim 5, further comprising a cross-out groove formed in the substrate separating the first and second drops. The integrated optical component according to claim 1, wherein the adhesive is acrylic or vinyl resin by free radical polymerization. 11. The integrated optical component according to claim 10, wherein said polymerization is photocuring polymerization. 12. The integrated optical component of claim 10, wherein the one or more adhesives used to secure the fibers on the substrate contain fillers. 13. The integrated optical component of claim 12, wherein the adhesive is filled with an inorganic material or a hard organic material. 2. The integrated optical component according to claim 1, wherein said fiber end and said waveguide output portion are separated during assembly into a space of about 15 to 25 mu m. 2. The apparatus of claim 1, wherein the substrate comprises: a substrate having a waveguide integrated by ion exchange; Silica or silicon substrates having waveguides integrated by vapor deposition; Lithium niobate substrates; And an indium phosphide substrate.