JPH11271561A - Method for joining optical fiber array and optical waveguide chip - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical waveguide chip which can shorten the time of irradiation with ultraviolet rays when joined and has small deterioration in a joining loss and small deterioration in a reliability test at a high temperature and high humidity. SOLUTION: In this joining method, the optical axes of an optical waveguide chip 14 and a 1st array 16 are aligned with each other (<=0.2 μm optical axis deviation) and the width L of a gap between the both is set to about 8 μm. The gap is filled with a resin for adhesion and the gap is irradiated in the two top and bottom directions with ultraviolet rays under irradiation conditions of 150 mW/cm<2> irradiation intensity and a 9,000 mJ/cm<2> irradiation quantity by using ultraviolet-ray irradiating devices 40a and 40b. The difference between the irradiation quantities from the two directions is set to <=6000 mJ/cm<2> .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for joining an optical fiber array provided with optical fibers to an optical waveguide chip using an adhesive resin.

[0002]

2. Description of the Related Art An optical fiber array is generally used to connect an optical waveguide chip and an optical fiber.
This optical waveguide chip includes a GaAs-based or InP-based semiconductor waveguide chip, an oxide film formed on Si, a dielectric (glass) waveguide chip using a glass substrate, LiNb.
There are many types such as a ferroelectric crystal waveguide chip composed of O ₃ or LiTaO ₃ crystal.
An optical waveguide in which a metal such as i is diffused is formed. For these optical waveguide chips, for example, sensor / measurement relations such as optical fiber gyros, optical fiber communication relations such as high-speed modulators, optical information processing relations such as A / D converters, and light source / light conversion such as diode arrays A wide variety of uses in relationships are being considered.

For example, when manufacturing an optical fiber gyro as described above, two ends of an optical fiber derived from a fiber coil formed by winding a long optical fiber around a cylindrical object and a phase modulator are used. A polarization-maintaining optical fiber array is used to connect the built-in optical waveguide chip while maintaining the polarization plane of the optical axis in a fixed direction.

The polarization-maintaining optical fiber array includes, for example, two substrates, one of which has a groove formed therein, and an optical fiber embedded in the groove to hold the polarization plane in a predetermined direction. After that, the two substrates are overlapped, and a gap between the groove and the optical fiber is filled with an ultraviolet-curable adhesive resin such as epoxy to form an adhesive resin layer. It is formed by curing and fixing the optical fibers in the grooves of the array.

Since the substrate of the optical fiber array on which the optical fibers are disposed and the substrate of the optical waveguide chip on which the optical waveguides are disposed have different coefficients of thermal expansion, the temperature at the time of using a finished product in which the two are joined is used. There is a problem that the optical axis shifts due to thermal expansion caused by the cycle.

As a countermeasure, when joining the optical fiber array and the optical waveguide chip, a gap having a predetermined width is provided on the joining surface of the two.

Specifically, first, while observing the polished joint surface of the optical fiber array and the optical waveguide chip from the side thereof using a microscope, the two are once pressed using a positioning jig so as to eliminate the gap. To secure the parallelism of the joining surface (hereinafter, referred to as “planarization”). Next, the two are separated from each other by using the positioning jig to secure a gap having a predetermined width. Thereafter, as shown in FIG.
The gap between the bonding surfaces 2a and 4a of the optical waveguide chip 4 and the optical waveguide chip 4 is filled with an ultraviolet-curing adhesive resin 6, and the adhesive resin 6 is cured by irradiating ultraviolet rays using an ultraviolet irradiating device 8, thereby curing the light. The bonding between the fiber array 2 and the optical waveguide chip 4 is completed.

[0008]

However, according to such a bonding method of the optical fiber array and the optical waveguide chip, the optical axis at the bonding surface between the optical fiber array and the optical waveguide chip is also caused due to various causes. The problem that the displacement occurs and the coupling loss increases as a result has not been solved.

One of the causes is that when the bonding resin layer filled in the gap is cured by irradiating ultraviolet rays, the amount of shrinkage of the bonding resin layer varies, and as a result, the optical fiber array and the It is known that the degree of parallelism of the bonding surface with the optical waveguide chip is deviated, causing a shift of the optical axis.

The present invention has been made in view of such a problem, and it is possible to greatly reduce a deviation of an optical axis at a joint surface between an optical fiber array and an optical waveguide chip when a finished product is used. It is another object of the present invention to provide a method for joining an optical fiber array and an optical waveguide chip having excellent light propagation characteristics.

[0011]

According to the present invention, there is provided a method for joining an optical fiber array and an optical waveguide chip, comprising the steps of: A gap having a predetermined width is provided, the gap is filled with an adhesive resin, and the resin is cured by irradiating ultraviolet rays to join the optical fiber array and the optical waveguide chip, at least including a facing direction. Irradiation of ultraviolet rays from two or more directions, and a difference in irradiation amount of the ultraviolet rays irradiated from the two or more directions is 600 mJ / cm ^2.
It is characterized as follows. Here, the irradiation amount of ultraviolet rays (mJ / cm ² ) means irradiation energy per unit area (unit mJ / cm ² ) represented by the following equation.

Irradiation energy per unit area (unit: mJ
/ Cm ² ) = irradiation intensity per unit area (mW / c)
m ² ) × irradiation time (sec) By this, curing and shrinkage are uniformly performed in each part of the adhesive resin layer filled in the gap, so that the parallelism at the joint surface between the optical fiber array and the optical waveguide chip is maintained. Thus, it is possible to obtain an optical waveguide chip with less deterioration of coupling loss and less deterioration in a reliability test under high temperature and high humidity. Further, the irradiation intensity of the ultraviolet light from each direction can be increased, and the irradiation time of the ultraviolet light can be shortened. In this case, it is more preferable that the difference between the irradiation intensities of the ultraviolet rays irradiated from the two or more directions is 10 mW / cm ² or less. Here, the irradiation intensity of ultraviolet rays (mW / cm ² ) refers to the irradiation intensity per unit area (mW / c).
m ² ).

Further, in the method for bonding an optical fiber array and an optical waveguide chip according to the present invention, a deviation of an optical axis at a bonding surface between the optical fiber array and the optical waveguide chip is set to 0.2 μm or less and the gap of the gap is set to 0.2 μm or less. 6 ~
After the thickness is set within the range of 10 μm, the above-described effect of the present invention can be further exhibited by filling the gap with the adhesive resin.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method for joining an optical fiber array and an optical waveguide chip according to the present invention, for example, a polarization method for connecting an optical waveguide chip and an optical fiber while maintaining the polarization plane in a fixed direction. An embodiment applied to a wavefront preserving optical fiber array will be described below with reference to FIGS.

As shown in FIG. 1, the optical fiber array according to the present embodiment has first and second arrays 16 in which optical fibers 10, 12 and optical waveguide chip 14 are fixed so as to regulate the joining direction. , 18.

Here, the optical waveguide chip 14 is, for example,
An optical waveguide having a predetermined shape (for example, a LiNbO ₃ substrate 20)
A Y-shaped optical waveguide 22 is formed and the metal electrode 2
4 and a polarizer 26 are provided.

As shown in FIG. 2, the two ends of the optical fiber 10 (for example, the start end 10a and the end 10b connected to the fiber coil of the optical fiber gyro) are connected to the optical waveguide chip 14 in the joining direction. First array 16 to regulate
And the optical fiber 12 as shown in FIG.
At one end (eg, an optical fiber 1 connected to a light source).
The second end 12a) is fixed to a second array 18 that regulates the bonding direction with the optical waveguide chip 14, and the optical fibers 1 are passed through the first and second arrays 16 and 18.
The ends 10a, 10b and 12a of the optical waveguide chips 14 and 10 are optically coupled to the optical waveguide chip 14.

More specifically, as shown in FIG. 2, the first array 16 has two V-shaped grooves 30a, 30b extending on one main surface toward one end surface and facing the other end surface. 16A on which a wide counterbore portion (escape groove for adhesion) 32 extending continuously is formed, and each groove 30a, 30 of the substrate 16A is formed.
b and 32 for closing the lid substrate. The interval between the two V-shaped grooves 30a and 30b is the same as the interval that matches the optical axis of the two branch paths in the optical waveguide 22 shown in FIG.

When assembling the first array 16, first, as shown in FIG. 2, the two ends 1 of the optical fiber 10 are inserted into the V-shaped grooves 30a and 30b of the substrate 16A.
After crawling 0a and 10b, the polarization preserving surface of the optical fiber 10 is adjusted to the direction of the polarization plane of the light propagating through the optical waveguide 22. Thereafter, the lid substrate 16B is covered from above, and the room temperature curing type adhesive resin is filled in the gap between the V-shaped grooves 30a and 30b and the optical fiber 10, and the two are left at room temperature to bond and fix them. By polishing the free end side end face 16a of the optical fiber 10 in the end face of the first array 16, the fixing work of the first array 16 to the optical fiber 10 is completed.

The second array 18, as shown in FIG.
One V-shaped groove 3 extending on one principal surface toward one end surface
4 and a substrate 18A in which a wide counterbore (an escape groove for bonding) 36 extending toward the other end surface is continuously formed;
Lid substrate 18 for closing each groove 34, 36 of substrate 18A
B.

When assembling the second array 18, first, one end 12a of the optical fiber 12 is laid in the V-shaped groove 34 of the substrate 18A, and then the polarization of the optical fiber 12 is adjusted. The wave preserving surface is aligned with the direction of the plane of polarization of light propagating through the optical waveguide 22. Then, from above, the lid substrate 1
8B, and adhered with an adhesive resin.
By polishing the free end face 18a of the optical fiber 12 in the end face of the optical fiber 12, the second array 18
Is completed.

On the other hand, the optical waveguide chip 14 is manufactured as follows. First, for example, an optical waveguide 22 having a predetermined shape is formed on one main surface (functional surface) of, for example, a _3- inch wafer (for example, a LiNbO ₃ substrate) by, for example, vacuum evaporation, and a polarizer 26 and a metal electrode are formed on the optical waveguide 22. 24 are formed to form a number of optical IC patterns on one wafer (not shown). Next, the optical IC patterns are cut out from the wafer in sets by using, for example, a dicing apparatus having a diamond cutter.
And polishing the surface to which the second arrays 16 and 18 are bonded. Thereafter, each of the optical IC patterns is cut from each group by using the same dicing device to separate the optical IC patterns into a number of optical waveguide chips.
Is obtained (see FIG. 1).

Then, the first and second arrays 16 and 18 to which the optical fibers 10 and 12 are already fixed are bonded to one optical waveguide chip 14, respectively. Of the two end faces of the optical waveguide chip 14, the second array 18 is joined to the end face near the polarizer 26, and the first array 16 is joined to the end face near the metal electrode 24 with their optical axes aligned. At this time, the bonding with the bonding resin is performed while the optical axis is adjusted so that the light output becomes the strongest.

Specifically, first, the optical fiber 1 fixed to the first array 16 is measured while measuring the light from the light source propagated through the optical waveguide 22 with a photodetector (not shown).
In FIG. 1, the three orthogonal XYZ directions and the optical fiber 10 in FIG.
The optical axis is adjusted with respect to the rotation direction of the two cores (start end 10a and end 10b). In parallel with this, the optical waveguide 22
A photodetector is arranged on the other end surface side (not shown) of the second array while measuring the light from the light source output through the two branch paths of the optical waveguide 22 with the photodetector. The polarization preserving surface of the optical fiber 12 fixed to the
In FIG. 1, XYZ orthogonal 3
The optical axis is adjusted in the axial direction. When the respective optical axis adjustments are completed, the first array 16 and the optical waveguide chip 14 and the second array 18 and the optical waveguide chip 14
Are simultaneously performed with the bonding resin.

The optical axis adjustment and the bonding operation are performed using a positioning jig to which a CCD camera having an optical magnification of 4 to 8 times is connected.

First, a free end face 16a of the optical fiber 10 in the end face of the optical waveguide chip 14 having two branch paths and the end face of the first array 16 using a positioning jig.
The parallel alignment (see FIG. 2) is performed within a range of about ± 0.1 deg, and they are brought into close contact with each other without any gap. Thereby, the joining surface is flattened. Next, the CCD
The first array 16 and the optical waveguide chip 14 are separated from each other by using a positioning jig while observing the gap between the joining surfaces using a camera, and a gap having a predetermined width is secured. At this stage, the optical axis of the optical waveguide chip 14 and the first array 16 is adjusted. In parallel with this, the same method is used to make the joint surface between the second array 18 and the optical waveguide chip 14 flat, adjust the gap, and adjust the optical axis. Thereafter, the optical waveguide chip 14
The gap between the bonding surfaces of the optical waveguide chip 14 and the array 16 and the second array 18 and the optical waveguide chip 14 is filled with an ultraviolet-curing adhesive resin, and then the XY axes are finely adjusted. After confirming that the gap is maintained at a predetermined width, the bonding resin is cured by irradiating ultraviolet rays to complete the joining operation.

The bonding step using the adhesive resin in the above operation will be described in more detail by taking the bonding step between the first array 16 and the optical waveguide chip 14 as an example.

As shown in FIG. 4, two of the first arrays 16
Of the substrates 16A and 16B, a V-shaped groove 30b is formed in the substrate 16A, and the optical fiber 1 is inserted into the groove 30b.
The lower end of the optical fiber 10 and the lower end of the V-shaped groove 30b are separated from each other, and the room-temperature-curable adhesive resin layer 31 is interposed therebetween. End face 1 of the substrate 16A
The height of the optical fiber 6a (vertical direction in FIG. 4) is about 3 mm, the diameter of the optical fiber 10 provided is about 80 μm at the core, and about 200 μm including the clad covering the core.
It is.

On the other hand, the optical waveguide chip 14 is
The height (vertical direction in FIG. 4) of the end face 14a in the direction of the polarization plane of the light propagating through 2 is about 1 mm, and the height of the optical waveguide 22 formed on the surface layer of the optical waveguide chip 14 by diffusion of Ti ( The vertical direction in FIG. 4 is several μm. The width of the optical waveguide chip 14 (in the direction perpendicular to the paper of FIG. 4) is about 2 mm.
The width of the optical waveguide 22 (in the direction perpendicular to the paper surface in FIG. 4) is several μm. Optical waveguide chip 14 and first array 16
4 means that the cross-sectional center line of the optical waveguide 22 and the cross-sectional center line of the optical fiber 10 are coaxial, that is, positioned in the vertical direction and the paper vertical direction in FIG. 4 so that the deviation of the optical axis is 0.2 μm or less. I have. In the present embodiment, even if the variation in the width W of the true gap occurs about ± 2 μm, the deviation of the optical axis falls within the allowable range of about ± 0.1 degrees, so that a problem of an increase in coupling loss occurs. Without deteriorating the temperature characteristics and the optical waveguide chip 14 and the first array 16
In consideration of the dimensional variation in the fabrication of the device, it is desirable to set the width W of the true gap to about 8 μm.

In the gap, an ultraviolet-curing adhesive resin layer 3
No. 8 is filled with a pigtail resin (trade name “UV-3000” manufactured by Daikin Industries, Ltd.) in consideration of ensuring moisture resistance when using the product and suppressing thermal expansion. Next, in FIG. 4, a high-pressure mercury lamp (300 to 400
nm) as the light source using ultraviolet irradiation devices 40a and 40b. The UV irradiation conditions at this time are as follows:
In each of the ultraviolet irradiation devices 40a and 40b, irradiation is performed for 60 seconds with the irradiation intensity of the ultraviolet light set to 150 mW / cm ² .
At this time, the irradiation amount is 9000 mJ / cm ² . Note that when irradiating ultraviolet rays from three or more directions, angles divided equally around the joint surface between the first array 16 and the optical waveguide chip 14 (for example, 120 degrees when viewed from three directions) Angle).

The ultraviolet irradiation conditions are set based on the following examination results.

First, FIGS. 5 and 6 show variations in deterioration of coupling loss when ultraviolet rays are irradiated from one direction and two opposite directions. FIG. 5 shows 1
It shows the appearance frequency (number) of each of the coupling loss deterioration levels for 29 samples irradiated for 180 seconds at an irradiation output of 50 mW from the direction. On the other hand, FIG. 6 shows, as a method according to the present embodiment, about 400 samples irradiated for 60 seconds at an irradiation power of 150 mW from two opposite directions, respectively, as in FIG. Shows the appearance frequency (number) of.

The deterioration of the coupling loss is such that the median value when irradiating ultraviolet rays from one direction is 0.6 dB, while the median value when irradiating ultraviolet rays from two opposing directions is 0 dB.
B, and it was found that the deterioration of the coupling loss was significantly improved by irradiating ultraviolet rays from two opposing directions.

FIG. 7 shows the relationship between the difference between the irradiation amounts of the ultraviolet rays from the two directions and the deterioration of the coupling loss when the irradiation is performed while changing the irradiation amounts of the ultraviolet rays from the two opposite directions. In particular,
The irradiation time was fixed at 60 seconds, and the irradiation power was fixed at 50 mW on one side and gradually increased from 0 mW on the other side. Deterioration of the coupling loss is caused by the difference in the irradiation amount of ultraviolet rays being 0 m.
There was a tendency to increase almost in a quadratic curve with the peak of the deterioration of the coupling loss at J / cm ^{2 being} 0.08 dB. The practically allowable upper limit of the deterioration of the coupling loss is about 0.1 dB, and therefore, it has been found that it is desirable that the difference between the irradiation amounts of ultraviolet rays from different directions be 600 mJ / cm ² or less. Further, the difference in the irradiation intensity of the ultraviolet rays is 10 mW / c.
If m ^{2 is} exceeded, the deterioration of the coupling loss exceeds 0.1 dB, so it was also found that the difference in the irradiation intensity of ultraviolet rays was desirably 10 mW / cm ² or less (see FIG. 8).

FIG. 9 shows the relationship between the deterioration of the coupling loss and the maximum value of the loss during the temperature characteristic test when the irradiation amount of the ultraviolet light from the two opposite directions is changed, and FIG.
The relationship between the deterioration of the coupling loss and the variation of the branching ratio during the temperature characteristic test will be described. This data shows that the difference in UV irradiation dose is 60
0 mJ / cm ² and also contain in excess of that in FIG. 9 and FIG. 10, deterioration 0dB and near the coupling loss,
In the case of 0.15 dB, the difference in the irradiation amount of ultraviolet rays is 600 mJ.
/ Cm ² or less, and those having a deterioration of the coupling loss of 0.55 dB and 1.22 dB are irradiated under the condition that the difference in the irradiation amount of the ultraviolet rays exceeds 600 mJ / cm ² . Here, in the temperature characteristic test, as shown in FIG. 11, a constant temperature change pattern between 85 ° C. and −40 ° C. is repeated three times in an 8-hour cycle, and the loss of the waveguide is increased or decreased in real time even during the test. And the variation of the branching ratio of the waveguide. In the optical waveguide chip according to the present embodiment, the maximum value of the increase or decrease of the waveguide loss is 0.7 dB or less,
The variation in the branching ratio of the waveguide was 3% or less, which proved to be good.

Thus, the optical waveguide chip 14 and the optical fiber arrays 16 and 18 joined by the method according to the present embodiment are completed.

[0037]

As described above, in the method for joining an optical fiber array and an optical waveguide chip according to the present invention, the method for joining the optical fiber array and the optical waveguide chip in alignment with the optical axes of the two includes: A gap having a predetermined width is provided on the surface, and the gap is filled with an adhesive resin, and the resin is cured by irradiating ultraviolet rays to join the optical fiber array and the optical waveguide chip, at least in a facing direction. Irradiation from two or more directions including ultraviolet rays, and the difference of the irradiation amount of the ultraviolet rays irradiated from the two or more directions is 600 mJ.
/ Cm ² or less.

From this, it is possible to maintain and secure the parallelism at the joint surface between the optical fiber array and the optical waveguide chip, and to obtain an optical waveguide chip with less deterioration in coupling loss and temperature characteristic test. The effect is obtained. In addition, the irradiation intensity of ultraviolet rays from two or more directions can be increased, and the irradiation time of ultraviolet rays can be shortened. In this case, the effect of the present invention can be further exhibited by setting the difference between the irradiation intensities of the ultraviolet rays irradiated from two or more directions to 10 mW / cm ² or less.

Further, the displacement of the optical axis at the joint surface between the optical fiber array and the optical waveguide chip is set to 0.2 μm or less, and the width of the gap is set within a range of 6 to 10 μm. The effect of the present invention described above can be further exhibited by filling the adhesive resin.

[Brief description of the drawings]

FIG. 1 is a perspective view of an optical fiber and an optical waveguide chip connected by an optical fiber array according to the present embodiment.

FIG. 2 is an exploded perspective view showing a state where an optical fiber whose end is branched is fixed to the optical fiber array.

FIG. 3 is an exploded perspective view showing a state where an optical fiber having one end is fixed to the optical fiber array.

FIG. 4 is a partially enlarged cross-sectional view of a joint between the optical fiber array and the optical waveguide chip according to the present embodiment.

FIG. 5 is a diagram showing the frequency of occurrence of variation in deterioration of coupling loss between an optical fiber array and an optical waveguide chip joined by using a conventional joining method of irradiating ultraviolet rays from one direction.

FIG. 6 is a diagram showing the frequency of occurrence of variation in deterioration of coupling loss between an optical fiber array and an optical waveguide chip joined using the joining method according to the present embodiment in which ultraviolet light is irradiated under predetermined conditions from two opposite directions. It is.

FIG. 7 is a diagram illustrating a relationship between a difference in irradiation amount and a deterioration in coupling loss when irradiation is performed while changing irradiation amounts of ultraviolet rays from two opposing directions.

FIG. 8 is a diagram showing a relationship between a difference in irradiation intensity and a deterioration in coupling loss when irradiation is performed while changing the irradiation amount of ultraviolet rays from two opposite directions.

FIG. 9 is a diagram showing a relationship between deterioration of coupling loss when irradiation is performed while changing the irradiation amount of ultraviolet rays from two opposing directions and a maximum value of increase and decrease of loss of a waveguide in a deterioration test evaluation under a high temperature environment. .

FIG. 10 is a graph showing the relationship between the deterioration of coupling loss when irradiation is performed while changing the irradiation amount of ultraviolet light from two opposing directions, and the change in the branching ratio of the waveguide in the deterioration test evaluation under a high temperature environment.

FIG. 11 is a diagram showing a temperature change pattern in one cycle in a temperature characteristic test.

FIG. 12 is a view for explaining a conventional bonding method of irradiating a bonding surface with ultraviolet light from one direction.

[Explanation of symbols]

10 and 12 ... optical fiber 14 ... optical waveguide chip 14a, 16a ... end surface 16, 18 ... the array 20 ... LiNbO ₃ substrate 22 ... optical waveguide 24 ... metal electrodes 26 ... polarizer 30a, 30b, 34 ... grooves 32, 36 ... seat Rolling portion 38: Adhesive resin layer 40a, 40b: UV irradiation device L: Width of gap

Claims (3)

[Claims] 1. A method of joining an optical fiber array and an optical waveguide chip with an optical axis aligned, wherein a gap having a predetermined width is provided on a joining surface between the optical fiber array and the optical waveguide chip, and the gap is used for bonding. When the resin is filled and the bonding resin is cured by irradiating ultraviolet rays to join the optical fiber array and the optical waveguide chip, ultraviolet rays are irradiated from at least two directions including at least opposing directions. The difference between the irradiation amounts of the ultraviolet rays irradiated from two or more directions is 6
A method for joining an optical fiber array and an optical waveguide chip, wherein the method is not more than 00 mJ / cm ² . 2. The method of joining an optical fiber array and an optical waveguide chip according to claim 1, wherein the difference in irradiation intensity between the ultraviolet rays irradiated from the two or more directions is 10 mW / cm ² or less. A method for joining a fiber array and an optical waveguide chip. 3. The method for bonding an optical fiber array and an optical waveguide chip according to claim 1 or 2, wherein a deviation of an optical axis at a bonding surface between the optical fiber array and the optical waveguide chip is set to 0.2 μm or less. A method for bonding an optical fiber array and an optical waveguide chip, wherein the gap is filled with the adhesive resin after setting the width of the gap within a range of 6 to 10 μm.