JPS6086529A - Manufacture of optical wave guide switch - Google Patents

Abstract

PURPOSE:To easily obtain an optical wave guide switch prevented from excitation of a light of high-order mode by simultaneously forming a buffer layer and a filter layer through partial anodic oxidation of a vapor deposited aluminum film after forming the optical wave guide. CONSTITUTION:An optical wave guide 33 made of Ti is formed on a substrate 31, and an aluminum film 34 is vapor deposited on all the surface of the substrate 31. Then, a pattern 35 for forming a desired filter film is formed with a photoresist on the film 34, this film 34 is anodically oxidized to convert the aluminum film 34 not protected with the resist film 35 into an alumina film 36, and the resist film 35 remaining on the film 34 is etched off with hydrofluoric acid or the like. As a result, the filter film 34 for absorbing unnecessary light and a buffer layer 36 made of the alumina film for preventing light absorption are formed at the same time. An objective optical wave guide switch can be obtained by forming an optical switch electrode, etc. by the conventional method.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to optical circuit elements, particularly optical switches, optical modulators, etc. using optical waveguides (hereinafter collectively referred to as 1 optical waveguide switch 1
). More specifically, the present invention includes:
The present invention relates to an improved method for manufacturing an optical waveguide switch that prevents light absorption and crosstalk between waveguides and electrodes.

Background of the Technology With the spread of optical communication technology, miniaturization and mass production of optical circuit elements are required, and optical waveguide technology is attracting attention as a device form that satisfies these demands. like this,
As a basic optical circuit element using a leading waveguide, there is a leading waveguide switch that will be discussed here.

As is well known, an optical switch is a means for switching an optical path. Such a switch has at least one pair each of an optical input terminal, an optical path, and an optical output terminal, and the pair of optical paths can be switched midway. ◇Furthermore, a switching mechanism for the optical path is provided. One of these is one that is constructed using electro-optic effects. For example, lithium niobate (Li
NbO3), lithium tantalate) C'LIThO3
) A high refractive index linear region that can function as a waveguide is formed in a partial region of a plate-like member (substrate) manufactured using an electro-optic crystal that exhibits an electro-optic effect 2 such as This is an optical waveguide switch in which an optical switch electrode is further formed and the optical path can be switched depending on whether a voltage is applied to the optical switch electrode or not.

PRIOR ART AND PROBLEMS Several important problems remain unsolved in conventional guided waveway switches of the type described above.

The first problem is that directly on the surface of the formed optical waveguide,
The cause was that the optical switch electrode was formed across it. That is, in this case, the guided light was partially absorbed between the waveguide and the electrode, resulting in light attenuation. The second problem is that excitation of higher-order mode light tends to occur near the optical input terminal, and
The problem is that light is undesirably emitted at curved portions of the waveguide (light leakage). The second and third problems tend to cause so-called crosstalk.

In order to avoid the first problem mentioned above, a buffer layer that prevents light absorption is placed between the waveguide and the electrode, and a second layer is placed between the waveguide and the electrode.
In order to avoid the third problem, it has been proposed to directly attach a filter film made of a light-absorbing substance such as metal onto the substrate where the problem is expected to occur. This proposal was revolutionary and could fully solve the problems mentioned above. However, in the case of this proposal, problems remained in the formation of the buffer layer and the filter membrane. That is, conventionally, after forming the waveguide, alumina (At205) was coated on the entire surface of the substrate.
, one layer of transparent buff such as silicon dioxide (Sin2) is formed by vapor deposition, and a part of it is processed.

Aluminum (At) is removed by
Although a filter film was formed by adhering a light-transmitting gold film such as (2), etching of the middle At203 was required, and (li) annealing treatment was required to improve the insulation of At20s. It remained as a new defect.

OBJECTS OF THE INVENTION An object of the present invention is to provide an improved method for manufacturing an optical waveguide switch of the type described above, which simplifies the process and does not require etching or annealing.

According to the present invention, in the vicinity of the surface of a plate-like member made of a crystal exhibiting an electro-optic effect, there are at least linear regions of high refractive index that are close to each other or intersect with each other. One end of the linear region is an optical input terminal, the other end is an optical output terminal, and a low refractive index material is formed on the region where the linear regions are adjacent to or intersect with each other. An optical switch electrode is formed through a single buffer layer, and at least a region surrounding the linear region near the optical input terminal and a region facing a convex portion of a curved portion of the linear region, A method for manufacturing a guided wave path switch in which a filter film made of a light-absorbing substance is formed on the surface of the plate member, the method comprising: after forming the linear region and before forming the optical switch electrode; Aluminum as a light-absorbing substance is vapor-deposited on the entire surface of the plate member, a desired pattern for forming a filter film is formed on the vapor-deposited surface with 7-otoresist, and a buffer layer made of alumina and aluminum are partially anodized. This can be achieved by a method for manufacturing a leading wavepath switch, which is characterized by simultaneously forming a filter film consisting of:

DESCRIPTION OF THE PREFERRED EMBODIMENTS The implementation of the present invention will now be described in detail with reference to the accompanying drawings.

FIG. 1 is a plan view of an example of a conventional optical waveguide switch. In the figure, 1 is lithium niobe)
(LiNbO3) crystal plate-like member (substrate), and 2 and 2' are waveguides consisting of linear regions whose refractive index is increased by a titanium (T1) diffusion layer, etc. In this example, the central part It intersects at. 3 and 3' are optical switch electrodes, and 4 and 4' are optical switch electrode wiring pads.

5 and 5' are optical input terminals, and 6 and 6' are optical output terminals, each of which is in contact with an optical transmission means 7 such as an optical fiber.

In the conventional optical waveguide switch having such a structure, excitation of higher-order mode light is likely to occur near the optical input terminals 5 and 5', and in the curved portion of the waveguide, as shown by the broken line A in the figure. In addition, it is difficult to avoid a certain amount of light leaking out of the waveguide, and when the optical output terminal is located in the traveling direction of this leaked light A, it is likely to cause a four-stroke.

As mentioned earlier, with the purpose of eliminating the above drawbacks,
A buffer layer that prevents light absorption is provided between the waveguide and the electrode, and a filter film made of metal or the like that easily absorbs TM mode light is provided in a specific region (TM mode light is extremely easily absorbed by metals, etc.). (Using natural laws) has been proposed in the past. This prior art will be explained in detail with reference to FIGS. 2 to 6.

Refer to Figure 2: Wafer 11 is manufactured by cutting a lithium niobate (LiNbO3) crystal parallel to a plane perpendicular to the two axes to a thickness of approximately 0.5 mm, and then the wafer 11 is manufactured using a sputtering method or the like. A titanium (T1) film 12 with a thickness of 400 to 800
It is formed to a thickness of about 0A.

After that, a photoresist mask (not shown) is formed in the shape of the desired waveguide using a photolithography method, and titanium (T1) is removed from the area not covered by the photoresist mask using an ion milling method or the like. The film 12 is removed and the titanium (T1) film 12 is patterned into the shape of a desired waveguide.

Refer to Figure 3: By heating at about 1,000 t:' for 5 to 10 hours, titanium (T1) is formed in the substrate 11 in the upper region of the titanium (T1) film 12.
A titanium (T1) diffusion region 16 is formed by diffusing the titanium (T1) to a depth of about several μm. FIG. 3 is a sectional view taken along line BB in FIG. 2, and its plan view is almost the same as FIG. 2. In this diffusion process, the remaining titanium (T1) film 12 has already been oxidized and there is no optical problem. Since the refractive index of the titanium (T1) diffusion region 16 is greater than the refractive index of the lithium niobate (TJ1Nbo3) crystal substrate 11, the titanium (T1) diffusion region 13 functions as an optical waveguide.

See FIG. 4: A film 14 of silicon dioxide (S10□) or alumina (At203) is formed on the entire surface of the substrate 11 to a thickness of about 2,000A. This step is easily possible using the OVD method or the like.A region 15 surrounding one end of the titanium (T1) diffusion region 13 (one end that becomes an optical input terminal) and a curved portion of the titanium (T1) diffusion region 13 Silicon dioxide (SiO2) or alumina (At20.) [1
After forming a photoresist film (not shown) on the entire surface of the substrate 4, the film 14 is dissolved and removed using hydrofluoric acid (IP) or the like to expose the substrate 11 in regions 15 and 16. In FIG. 4, titanium (T1) diffusion region 13 is indicated by a broken line.
There is also a film 14 made of silicon dioxide (S102) on top.

Refer to FIG. 5: After coating the entire surface of the substrate 11 with the photoresist, the photoresist film is removed from the areas 15 and 16 and the area where the optical switch electrode is to be formed, exposing the substrate 11 in the above areas. Next, a metal such as aluminum (At) is formed to a thickness of about 5.000× over the entire surface of the substrate 11 using a vacuum evaporation method or the like, and then the photoresist film is dissolved and removed. In this way, linear aluminum (At) films 17 and 18 are formed on the upper surface of the lithium niobe (LiNbO3) substrate 11 in regions 15 and 16, and silicon dioxide is formed near the intersection of the titanium (T1) diffusion layer 16. Optical switch electrodes 19 and 19' are formed via films such as (8102).

See Figure 6: Complete the optical waveguide switch by scribing to a size of approximately 5mi+X10mm. In this way, titanium (Ti)
Aluminum (At)It! of the pair of ml & region 13. l
! A portion 20 surrounded by 17 is an optical input terminal,
An end 21 in the opposite direction across the intersection is used as a light output terminal. 22 is an optical switch wiring pad.

In the waveguide optical switch having the structure described above, in the region 15 surrounding the optical input terminal, an aluminum (At) film 17 is directly formed on the substrate 11 exhibiting an electro-optic effect.
is formed, so excitation of higher-order mode light is prevented, and as a result, leakage of light at the curved portion of the waveguide is prevented. The substrate 1 exhibiting an electro-optic effect also in the region 16
Since the aluminum (At) film 18 is directly formed on the curved part, the TM mode light is absorbed by the aluminum (At) #18, and the leaked light becomes light. This effectively prevents the light from entering the output terminal 21 and causing p-stoke.

When viewed structurally, the optical waveguide switch according to the present invention has the following features:
It is basically the same as that shown in FIG. 6 above.

However, the optical switch according to the present invention is applied after the waveguide is formed (the fourth
The manufacturing process in Figures ~) is different from the conventional one.

This example will be explained step by step with reference to FIGS. 7 to 10.

See FIG. 7: After forming the optical waveguide 33 as shown in FIG. 6, aluminum (At) [34] is vapor-deposited on the entire surface of the substrate 61. The thickness of this At film 34 is about 1000 to 2000A.

See FIG. 8: After the Jkt film 34 is deposited, a desired filter film forming resist pattern 35 is formed above it.

Here, for example, Microposi, ) 1350 (product name)
A photoresist such as can be used.

Refer to FIG. 9; After forming the resist pattern 35, positive W4 oxidation is performed according to a conventional method to remove the At that is not protected by the resist film 35.
The film 34 is an At203 film 35.

See FIG. 10: Subsequently, the resist #35 remaining on the A4 film 34 is removed. For example, when removing the resist film, use Fu! (HP
) etc. In this way, the filter film (At film) 34 absorbs unnecessary light.
and buffer i (At203 film) that prevents light absorption36
can be formed poetically.

The subsequent formation of the optical switch electrode can be carried out according to a conventional method, for example, as shown in FIG. Finally, an optical waveguide switch similar to that shown in FIG. 6 can be manufactured.

Effects of the Invention According to the present invention, excitation of higher-order mode light is prevented, and light that inevitably leaks out of the waveguide at the curved portion of the waveguide is prevented from causing crosstalk. In order to improve the insulation properties of the At205 film, an optical waveguide switch is made without etching the formed At film, and annealing is performed to improve the insulation properties of the At205 film.
The 1 ink drawer II (because of its good 11 ink drawability) can be manufactured using an extremely simple process.

[Brief explanation of the drawing]

FIG. 1 is a plan view of an example of a conventional waveguide switch. 2.3.4 and 5 are respectively a plan view or a cross-sectional view of the substrate after the main manufacturing process of an optical waveguide switch according to an embodiment of the prior art is completed;
The figure is a plan view of the board in its completed state. Further, FIGS. 7, 8, 9, and 10 are cross-sectional views sequentially showing the main manufacturing steps of the optical waveguide switch according to the present invention. 1.11... Substrate, 2,16... Waveguide (titanium diffusion region), 5. 5', 19. 19'...Hikari Sui,
blood'? a pole, 4.4', 22... light switch, chi'IrL
Polar wiring pa, de, 5°5', 20... optical input terminal, 6
．． 6', 21... optical output terminal, 7... optical transmission means,
A... Traveling direction of leaked light, 12... Titanium film, 14
...Silicon dioxide or aluminum oxide film, 1
5...A region surrounding one end (optical input terminal) of the 4 wave paths, 16
...Region facing the convex part of the curved part of the waveguide, 17.1
8... Aluminum film, 31... Substrate, 33...
Waveguide (titanium diffusion region), 34...aluminum film, 55...resist film, and 36...aluminum oxide film. Patent Applicant Fujitsu Limited Patent Application Agent Akira Aoki Patent Attorney Kazuyuki Nishidate Patent Attorney Yukio Uchida Patent Attorney Akiyuki Yamaguchi #81 Figure fs2 Figure ts3 Figure ts4 Figure 6 fsS Figure fsG Figure 7 @ Figure 10

Claims (1)

[Claims] t11 At least one pair of linear regions with a high refractive index that are close to each other or intersect with each other are formed near the surface of a plate-like member made of crystal that exhibits an aero-optic effect. , one end of the linear region is an optical input terminal and the other end is an optical output terminal, and a buffer layer made of a low refractive index material is provided on the region where the linear regions are adjacent to each other or intersect with each other. An optical switch electrode is formed, and the surface of the plate member is formed at least in a region surrounding the linear region near the optical input terminal and in a region facing a convex portion of a curved portion of the linear region. An optical waveguide switch on which a filter film made of a light-absorbing material is formed. After the linear region is formed and before the optical switch electrode is formed, aluminum as the light-absorbing substance is vapor-deposited on the entire surface of the plate-like member, and the method comprises: 7. A method for manufacturing an optical waveguide switch, which comprises forming a desired pattern for forming a filter film using photoresist, and simultaneously forming a buffer layer made of alumina and a filter film made of aluminum by partial anodic fermentation.