JP2682208B2 - Waveguide type optical device - Google Patents

Description

The present invention relates to a waveguide type optical device, and more particularly to a waveguide type optical device in which an airtight structure of an optical fiber take-out portion of a housing accommodating a waveguide substrate is improved. Regarding the device.

[Conventional technology]

Generally, a waveguide type optical device is formed by forming a waveguide having a high refractive index for confining and guiding light in a substrate made of a strong dielectric material or a semiconductor material. An electrode for applying a voltage is formed on or near the waveguide. By externally applying a voltage to this electrode, the refractive index of the waveguide in the substrate is changed to modulate the phase and intensity of light or switch the optical path.

Conventionally, as such a waveguide type optical device, an optical device using a lithium niobate substrate (LiNbO ₃ substrate) having a relatively high electro-optical effect among ferroelectric materials is known. In this optical device, as shown in FIGS. 3 and 4, a titanium film (Ti film) is formed on a LiNbO ₃ substrate 1,
After patterning into a desired waveguide pattern, heat diffusion is performed at a high temperature of around 1000 ° C. for several hours to form a waveguide 2, and a silicon dioxide buffer layer (SiO ₂ layer) 3 is formed on this, and a metal is formed on the upper surface thereof. This is an optical device in which an electrode 4 is formed of a film and the electrode is used as a functional element.

The optical waveguide device thus manufactured is cut into a wafer, polished on the end faces to be made into chips, and after adjusting the optical axes of the optical waveguide and the optical fiber and fixing them, the optical waveguide device is mounted in a housing. Then, the signal terminals provided on the housing and the electrode pads of the optical waveguide device are connected by wire bonding.

The optical waveguide device shown in FIGS. 3 and 4 is
This is a directional coupling type optical switch, and its operating principle will be briefly described. As described above, the two waveguides 2 each having a portion that is close to the LiNbO ₃ substrate 1 at a constant length are formed, and the SiO ₂ buffer layer 3 is provided above the two waveguides 2 via the SiO ₂ buffer layer 3. An electrode 4 made of a metal film is formed. In the state where no voltage is applied to the electrode 4, mode coupling occurs between the two adjacent waveguides 2, and the light input from one waveguide 2A moves to the other waveguide 2B. If the length of the proximity portion is appropriately selected according to the manufacturing conditions of the waveguide 2, almost 100% of the light from the waveguide 2A can be transferred to the waveguide 2B (the length of the proximity portion in this case is Called the "full bond length"). On the other hand, if one of the two electrodes 4 provided on the waveguide 2 is grounded and a voltage is applied to the other,
As shown in FIG. 4, an electric field C is generated in the waveguide 2 in the substrate 1 in the vertical direction, the refractive index of the waveguide 2 is changed by the electro-optic effect of the LiNbO ₃ substrate, and the two waveguides 2 When the coupling state of the is changed and the applied voltage is set to an appropriate voltage value, the waveguide
The light input from 2A can be directly output from the waveguide 2A. In this way, the switching function can be realized using the waveguide 2.

Since such a waveguide type optical device can integrate the above-mentioned switching function on a substrate, development is being promoted as a matrix optical switch for optical switching system and an optical path switching optical switch for OTDR. Further, since light can be modulated at high speed, it is expected to be put into practical use as an external modulator for large capacity communication.

5 and 6 show structures of different waveguide type optical devices.

Usually, in a waveguide type device, an optical fiber is fixed to both end faces of the chip for inputting into the waveguide. Therefore, in the structure shown in FIG. 5, when the waveguide substrate 1 having the optical fibers 5 fixed to both end surfaces is mounted in the housing 6, the U groove 7 is provided in advance from the upper side on the side surface of the housing 5, The optical fiber 5 is placed on the U-groove 7 and fixed by the resin 8, and the housing 6 is covered with the cover 9. In addition, 10 is upper yatoy.

Further, in the structure shown in FIG. 6, the optical fiber 5 metallized into a strand is inserted through a hole 11 provided in the side surface of the housing 6 in advance to adjust the optical axis of the waveguide, and then to the housing 6. The gap between the wires is fixed with solder 12 to achieve airtightness.

[Problems to be solved by the invention]

By the way, in practical use of the waveguide type optical device, it is necessary to sufficiently study the moisture resistance in order to obtain high reliability. That is, in the waveguide device, as described above, an electrode having a width of several μm, which is similar to the waveguide, is formed on the upper part of the waveguide having a width of several μm formed in the substrate. A voltage of about V to 100 V is applied to this electrode. Then, especially in high humidity, electrolysis occurs due to moisture in the air in the vicinity of the electrode, and the electrode is significantly deteriorated. Also, the fixation of the waveguide and the optical fiber is
Since the two are directly contacted with each other, the adhesive is often used, but the adhesive is generally weak against humidity, and it is necessary to improve the moisture resistance also in this respect. Furthermore, wire bonding is generally used for the connection between the waveguide element and the signal terminal, and moisture resistance is also important.

In the conventional waveguide optical switch shown in FIG. 5, since the U groove 7 is provided on the side surface of the housing 6 and the optical fiber 5 is fixed to the U groove 7 with the resin 8, sufficient airtightness is not achieved. The reliability decreases under high humidity. Further, in the one shown in FIG. 6, since the gap between the optical fiber 5 and the housing 6 is filled with the solder 12, the moisture resistance is excellent as compared with the one in FIG. It is necessary to insert a terminal at the tip through the hole 11 on the side surface of the optical fiber, and to metalize the optical fiber strand to attach the terminal at the tip in a bare state, which is very difficult. Further, the optical axis adjustment and the fixing work with the waveguide have to be performed inside the housing 6 with the hole fiber 5 being passed through the hole 11 on the side surface of the housing 6, and the workability is extremely poor. .

The present invention has been made in view of such circumstances, and it is possible to easily and reliably realize airtightness inside the housing, improve the reliability of the waveguide element and the electrode, and fix the waveguide and the optical fiber to each other or to fix the wire. An object of the present invention is to provide a waveguide type optical device capable of improving the reliability of the bonding portion.

[Means for solving the problem]

In the present invention, a waveguide substrate on which a waveguide is formed, a first optical fiber optically coupled to the waveguide at an end face of the waveguide substrate, and the waveguide substrate and the first optical fiber are accommodated. And a second optical fiber optically coupled to the first optical fiber on the outside of the housing, wherein (a) the end face side of the waveguide substrate is The flange-side end surface of the flanged metal fitting is fixed, and the optical fiber terminal is attached to the other end surface of the flanged metal fitting. One end of the first optical fiber passes through the hole formed in the flanged metal fitting. The optical axis is adjusted and fixed to the end face of the waveguide substrate.
And a capillary having an inner diameter slightly larger than the outer diameter of the strands of the second optical fiber is provided, and the tip ends of the strands of the first and second optical fibers are inserted into the capillaries to optically contact each other. It is characterized by being connected. And thereby, airtightness is improved and the above-mentioned object is achieved.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to FIG. 1 and FIG. In addition, this embodiment relates to a waveguide type optical switch, and by applying a voltage from the outside,
It has a function of turning on / off the light.

In this embodiment, a waveguide substrate 21 in which a waveguide is formed,
A first optical fiber 22 optically coupled to the waveguide at the end face of the waveguide substrate 21, the waveguide substrate 21 and the first optical fiber 22.
And a second optical fiber 24 that is optically coupled to the first optical fiber 22 outside the housing 23. The housing 23 accommodates the optical fiber 22 of FIG. A capillary 25 having an inner diameter slightly larger than the outer diameters of the strands 22a, 24a of the first and second optical fibers 22, 24 is provided, and the strands of the first and second optical fibers are provided in this capillary 25. twenty two
The tips of a and 24a are inserted and abutted against each other for optical connection. In addition, on the peripheral wall of the portion of the capillary 25 protruding inward of the housing 23, the outer peripheral surface and the capillary 25
A horizontal hole 27 communicating with the inner hole 26 is opened, and the wire 22a of the first optical fiber and the wire 24a of the second optical fiber 24 are brought into contact with each other at the portion of the horizontal hole 27, and the capillary 25 Side hole 27
Resin 28 is filled in the vicinity. In addition, the element wire 24a of the second optical fiber 24 is metallized, the capillary 25 is housed in the metal pipe 29, and the gap between the metal pipe 29 and the metallized portion of the second optical fiber 24 is filled with the solder 30. Has been done.

The waveguide substrate 21 is supposed to be a LiNbO ₃ substrate, and a Ti film is formed to form a directional coupling pattern, and after thermal diffusion, SiO _{2 is used.}
A Cr-Au electrode is formed via a buffer layer and formed into a chip to form a waveguide element. Further, the waveguide substrate 21 is provided with a holding glass 31 and an upper glass 32, which are adhered after the cutting of the waveguide substrate 21 and end-polished. An optical fiber terminal 33 is attached to one end of the first optical fiber 22, and the optical axis of the optical fiber is adjusted to the waveguide substrate 21 by using a metal fitting 34 with a flange, and then fixed by an adhesive.

When mounting the waveguide substrate 21, first, the capillary 25 is fixed to the side surface of the housing 23 with the low-melting glass 35, and the metal pipe 29 made of kovar contained therein is fixed by brazing. Then, the waveguide substrate 21 is fixed to the housing 23, and one optical fiber
The tip wire 22a of 22 is inserted into the capillary 25. Also, a second optical fiber 24, which is the pigtail of the device.
Inserts the tip end wire 24a into the capillary 25 from the outside of the housing 23. Then, in the portion of the lateral hole 27 of the portion of the capillary 25 that protrudes inside the housing 23, the element wire 22 of the two optical fibers 22 and 24 is
The tips of a and 24a are brought into contact with each other, and the resin 28 is injected from here to fill the inside of the capillary 25. In this embodiment,
An ultraviolet curable adhesive was used for the resin 28. Further, here, a single mode fiber is used for the optical fibers 22 and 24, and since the outer diameter thereof is 126 μm, the capillaries having an inner diameter of 127 μm are used.
25 was used. Excess loss due to connection at this time is input / output 2
It was 0.3 dB at the point. Next, the metal pipe 29 accommodating the capillary 25 and the strand 24 a of the second optical fiber 24.
The gap between the metallized portion and the gap is filled with the solder 30, and the wire portion and the core portion are reinforced with the resin 36. Finally, the electrode of the waveguide substrate 23 and the signal input terminal are connected by a bonding wire, and the cover 37 is fixed to the housing by the seam weld 38.

According to the waveguide type optical switch of the present embodiment, the first optical fiber 22 fixed to the optical axis in the waveguide and the second optical fiber 24 serving as the pigtail of the device are separated, and these are housed in the housing 23. The optical fibers 22 and 24 inside and outside the housing 23 can be easily connected because they can be inserted and fixed in a capillary 25 having an inner diameter slightly larger than the outer diameter of the optical fiber provided on the side surface of the housing. Therefore, the strand 24a of the second optical fiber 24 on the outside of the housing 23 can be metalized, the capillary 25 is housed in the metal pipe 29, and the capillary metal portion and the optical fiber metallized portion are separated from each other. By filling the gap with the solder 30, it is possible to realize the airtightness of the optical fiber extraction portion of the housing 23.

The waveguide type optical switch of this example was subjected to a high temperature and high humidity test as a humidity resistance evaluation, and the following results were obtained. The waveguide type optical switch of this example was compared with the conventional waveguide type optical switch using resin shown in FIG. The test conditions were 60 ° C and 95%, and in the conventional waveguide type optical switch, the switching characteristics deteriorated after continuous use for about 200 hours, and the sufficient switching function was not achieved. Especially, when the voltage is applied, the light is not completely turned off. Therefore, it is presumed that the humidity entered the inside of the housing through the resin part and partially destroyed the electrode. Also, after about 600 hours, some of the samples were not working at all. When the cover was removed and the inside was observed, the bonding wire connecting the electrode of the waveguide substrate and the verification input terminal was detached from the electrode film due to corrosion, which is considered to be caused by moisture.

On the other hand, in the waveguide type optical switch of this embodiment,
After 1500 hours, no characteristic deterioration was observed, and the normal operation was maintained without any problems as in the conventional example. Therefore, according to this example, it was confirmed that complete airtightness could be achieved and the moisture resistance of the entire device could be dramatically improved.

In addition, in the above-mentioned embodiment, the 2 × 2 optical switch having a simple structure among the waveguide type optical devices is applied, but it is needless to say that the present invention can be applied to the waveguide type optical devices having various structures. For example, when applied to an optical fiber having a plurality of optical fibers on one side such as an 8 × 8 optical switch, the number of sleeves may be provided on the side surface of the housing.

〔The invention's effect〕

As described above, according to the present invention, a capillary having an inner diameter slightly larger than the outer diameter of the optical fiber strand is provided on the side surface of the housing, and the tip of the optical fiber inside the housing and the pigtail cord of the device are formed. The tip of the external optical fiber is inserted into and brought into contact with the capillary, so that the optical fiber extraction portion of the housing can be easily hermetically sealed. Therefore, it is possible to prevent the characteristic change of the waveguide element, improve the reliability of the electrode, and further improve the reliability of the fixed portion between the waveguide and the optical fiber, the reliability of the wire bonding portion, and the like. .

Further, in the present invention, a waveguide type optical device is provided, a waveguide substrate on which a waveguide is formed, a first optical fiber optically coupled to the waveguide at an end face of the waveguide substrate, and these waveguide substrates. Since the housing is configured to include the housing for housing the first optical fiber and the second optical fiber that is optically coupled to the first optical fiber on the outside of the housing, only the airtightness is good. In addition, it is possible to realize a waveguide type optical device having good workability. Moreover, since the flange side of the flanged metal fitting is fixed to the end face side of the waveguide substrate, the fixing area is secured, whereby the optical fiber terminal is firmly fixed, and the end of the first optical fiber is fixed. This has the effect of stabilizing optical coupling with the end face of the waveguide substrate.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing an embodiment of the present invention, FIG. 2 is an enlarged view of a main part of FIG. 1, and FIG. 3 shows an operating principle of a directional coupling type switch element which is a waveguide type optical device. Top view, 4th
FIG. 4 is a sectional view taken along the line IV-IV in FIG. 3, FIG. 5 is a perspective view showing a conventional example, and FIG. 6 is a perspective view showing another conventional example. 21 ... Waveguide substrate, 22 ... First optical fiber, 22a ... Elemental wire, 23 ... Housing, 24 ... Second optical fiber, 24a ... Elemental wire, 25 ... Capillary.

Claims (3)

(57) [Claims] 1. A waveguide substrate having a waveguide formed therein, and a first optical substrate optically coupled to the waveguide at an end face of the waveguide substrate.
Optical fiber, a housing for accommodating the waveguide substrate and the first optical fiber, and a second optical fiber optically coupled to the first optical fiber outside the housing. In the waveguide type optical device, a flange-side end surface of a flanged metal fitting is fixed to the end surface side of the waveguide substrate, and an optical fiber terminal is attached to the other end surface of the flanged metal fitting. Has one end penetrating through a hole formed in the flanged metal fitting and fixed to the end face of the waveguide substrate by adjusting the optical axis, and is attached to the side face of the casing of the first and second optical fibers. A capillary having an inner diameter slightly larger than the outer diameter of the wire is provided, and the tip ends of the wire strands of the first and second optical fibers are inserted into the capillary and abutted against each other to be optically connected. Guided wave Type optical devices. 2. A side wall of a portion of the capillary projecting inwardly of the housing is provided with a lateral hole that connects the outer peripheral surface thereof with a hole in the capillary, and the portion of the lateral hole forms the first optical fiber strand. 2. The waveguide type optical device according to claim 1, wherein the second optical fiber and the elemental wire of the second optical fiber are brought into contact with each other, and resin is filled in the vicinity of the lateral hole of the capillary. 3. An element wire of a second optical fiber is metallized, a capillary is housed in a metal pipe, and a solder is filled in a gap between the metal pipe and the metallized portion of the second optical fiber. The waveguide type optical device according to claim 2.