JP2000081521A - Fixing structure of waveguide type element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a waveguide type element to obtain a stable high frequency characteristic without being affected by the strength of electrical connection with a casing due to the width of a ground electrode. SOLUTION: A notched part 12 is formed in a casing 11 and a modulation electrode and a optical waveguide 2 composed of a signal electrode 3 and the ground electrode 4 are formed in the part of the notched part 12. Here, a substrate 1 is installed and fixed on the casing 11 so that the area where a high frequency electric signal applied on a waveguide type element from the modulation electrode and a light wave guided in the optical waveguide 2 substantially interact each other, is positioned, that is, so that the area of the substantial interaction is not brought in contact with the casing 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveguide type device fixing structure, and more particularly, to a waveguide type optical intensity modulator, a phase modulator, and a polarization type used in a high-speed and large-capacity optical fiber communication system. The present invention relates to a waveguide element fixing structure that can be suitably used for a scrambler or the like.

[0002]

2. Description of the Related Art In recent years, with the progress of high-speed, large-capacity optical fiber communication systems, lithium niobate (hereinafter, sometimes abbreviated as LN) having an electro-optical effect is used as a substrate, as represented by an external modulator. The high-speed modulator used for (1) has been put to practical use and widely used. As shown in FIG. 1, such a high-speed modulator includes an optical waveguide 2 for guiding a light wave on a substrate 1 having the above-described electro-optic effect, and a high-speed modulation signal of a microwave band applied to the light wave. A modulation electrode composed of a signal electrode 3 and a ground electrode 4 for applying an electric current is formed, and the substrate 1 on which such a modulation electrode and the like are formed is placed on a casing 5 made of brass or stainless steel. After fixing and mounting, it is used as an actual device.

In the element as shown in FIG. 1, it is necessary to make the electrical connection between the ground electrode 4 and the housing 5 strong and to apply a high-speed modulation signal in the microwave band stably. The width a of the electrode 4 is set to about 200 to 3000 μ.
In general, the width is set to several tens to several hundreds times the width b of the signal electrode 3.

On the other hand, attempts have been made to lower the drive voltage of a waveguide element in order to reduce power consumption. As a method of lowering the driving voltage, as described in Japanese Patent Application Laid-Open No. 5-196902,
For example, the width a of the ground electrode 4 in FIG.
There is a method of reducing the width so as to be approximately three times or less with respect to the width b.

[0005]

However, it is possible to reduce the drive voltage by reducing the width a of the ground electrode 4 as described above. However, when the device is mounted and actually used as an element, This makes it impossible to make an electrical connection with the housing 5 firmly. For this reason, when a high-speed modulation signal in the microwave band is applied, in addition to the waveguide mode guided as the modulation signal, a leakage mode that leaks into the substrate and a radiation mode that is radiated into the air This causes a problem that stable high-frequency characteristics cannot be obtained.

On the other hand, even when the width a of the ground electrode 4 is relatively large as described above without lowering the drive voltage, the electrical contact between the contact portion 6 between the ground electrode 4 and the housing 5 and the vicinity thereof is maintained. High-frequency characteristics are affected by subtle effects such as a difference in connection state, and stable high-frequency characteristics cannot be obtained in some cases.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a waveguide-type device fixing structure capable of obtaining stable high-frequency characteristics without being affected by the strength of electrical connection due to the width of a ground electrode.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a waveguide-type element fixing structure for mounting a waveguide-type element by fixing a waveguide-type element having a modulation electrode and an optical waveguide to a housing. A region where a high-frequency electric signal applied to the waveguide element by the modulation electrode and a light wave guided through the optical waveguide substantially interact is fixed so as not to substantially touch the housing. This is a fixed structure of the waveguide element, characterized in that:

FIG. 2 is a perspective view showing an example of a fixing structure of the waveguide element of the present invention, and FIG. 3 is a cross-sectional view of the fixing structure shown in FIG. 2 taken along line II. . Note that FIG.
In FIGS. 3 and 3 and the following drawings, the size of the signal electrode, the optical waveguide, and the like are drawn differently from actual ones for clarity of explanation.

In FIGS. 2 and 3, a notch 12 is formed in a housing 11, and the substrate 1 is placed on the notch 12.
The signal electrode 3, the ground electrode 4 and the optical waveguide 2 are formed substantially parallel to each other, so that the light wave guided through the optical waveguide 2 of the waveguide element and the high-frequency electric signal applied to the signal electrode 3 substantially cross each other. The substrate 1 is placed and fixed on the housing 11 so that a region where the operation is performed (a portion corresponding to the length c, the width d, and the thickness e in FIG. 2) is located. That is, the substrate 1 is fixed to the housing 11 so that the region where the light wave guided through the optical waveguide 2 and the high-frequency electric signal applied by the signal electrode 3 substantially interact does not touch the housing 11. I have.

On the other hand, FIG. 7 is a view showing high-frequency characteristics in the conventional structure for fixing the waveguide element shown in FIG.
4 is a drawing showing the high-frequency characteristics of the fixed structure of the waveguide element of the present invention shown in FIGS. 7 and 8, the vertical axis indicates the amount of propagation of the high-frequency electric signal, and the horizontal axis indicates the frequency of the high-frequency electric signal applied to the signal electrode 3.

As is apparent from FIGS. 7 and 8, when the conventional waveguide element fixing structure shown in FIG. 1 is used, the leakage mode and the radiation mode as shown by A in the figure at a specific frequency are obtained. Although loss dip occurs due to this, when the waveguide element fixing structure of the present invention shown in FIGS. 2 and 3 is used, the above-described loss dip does not occur, and a smooth and stable high-frequency characteristic is exhibited. That is, it is understood that stable high-frequency characteristics can be obtained by the fixing structure of the present invention.

The cause can be considered as follows. In the fixed structure of the waveguide element according to the present invention, since the substantial interaction region as described above does not touch the housing, the relative dielectric constant in the peripheral portion of the interaction region of the waveguide element is set. The rate becomes 1. As described above, when a high-frequency electric signal is applied,
When the high frequency characteristics due to the electric signal become unstable, a leakage mode and a radiation mode occur in addition to the waveguide mode,
When the relative dielectric constant around the substantial interaction region is 1, as described above, the electric field distribution of the high-frequency electric signal applied from the modulation electrode does not leak outside the waveguide element, and Focus on the interaction area. Therefore,
The leakage mode and the radiation mode are inevitably reduced, and as a result only the guided mode remains and becomes dominant, so that stable high-frequency characteristics can be obtained.

The "substantially interacting region" referred to in the present invention is, for example, in the case of a waveguide type device as shown in FIG. 2, a modulation comprising the optical waveguide 2, the signal electrode 3 and the ground electrode 4. And a region defined by a length c, a width d, and a thickness e where a high-frequency electric signal is applied from a signal electrode 3 to a light wave guided through the optical waveguide 2. .

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments of the invention with reference to the drawings. The fixed structure of the waveguide element according to the present invention includes a high-frequency electric signal applied from the modulation electrode in the waveguide element in which the modulation electrode including the signal electrode and the ground electrode and the optical waveguide are formed. It is necessary that a region where light waves guided through the optical waveguide substantially interact with each other does not effectively touch a housing for fixing the waveguide type element. As long as the above conditions are satisfied, the specific form is not particularly limited.

FIGS. 2 and 3 show, as an example of the fixing structure of the waveguide element of the present invention, a rectangular cutout 12 formed on the surface of the housing 11 to which the waveguide element is fixed, as described above. The substantially interacting region as described above is located on the notch 12.

In order to satisfy the above condition, the length h of the notch 12 should be substantially equal to the length c of the substantially interacting region, and preferably, h / c = 0. 8 ~
The notch 12 is formed so as to be 1.2. Thereby, the object of the present invention can be achieved.

In an actual waveguide type device such as a waveguide type optical intensity modulator, the length c of the substantially interacting region is 10 to 40 mm, so that the notch 12 has a length h. 8 to 48 mm. Further, the depth i of the cutout portion 12 is formed so as to be 0.1 to 0.5 mm so that the substrate 1 does not substantially contact the housing 11. The notch 12 can be formed using a means such as milling. Further, the housing 11 and the substrate 1 constituting the waveguide element are fixed using an adhesive such as an epoxy resin. 2 and 3, a rectangular notch is formed, but the shape of the notch is not particularly limited, and any shape may be used as long as the object of the present invention can be achieved. Can be used.

FIG. 4 is a cross-sectional view showing another example of the fixing structure of the waveguide element according to the present invention. 4 is a drawing corresponding to FIG. 3 showing a cross section taken along line II in the fixed structure of the waveguide element of FIG. That is, FIG.
Then, instead of forming the notch 12 on almost the entire surface of the housing 11 as shown in FIGS. 2 and 3, a rectangular groove 22 having a width j smaller than the width f of the substrate 1 constituting the waveguide element is used. Is formed in the housing 21, and the substrate 1 is installed on the housing 21 so as to cover the entire groove 22 so that the region where the interaction substantially occurs is located on the groove 22.

By adopting such a configuration, almost the entire surface of the housing as shown in FIGS. 2 and 3 is cut out, so that there is a cutout portion other than the portion where the waveguide element is fixed. It is possible to obtain an effect that a highly reliable fixing structure that is strong against vibration, impact, and the like can be obtained.

In the example shown in FIG. 4, the width j of the groove 22 needs to be larger than the width d of the substantially interacting region and smaller than the width f of the substrate, and preferably j /
It is formed so that d = 1-8. Specifically, when the width f of the substrate is set to a typical value of 800 μm, the width f is formed to 90 to 700 μm. Further, regarding the length and depth of the groove 22, the notch 12 shown in FIGS.
Formed in the same manner as the length h and the depth i. Groove 2 shown in FIG.
2 can also be formed by means such as milling as in the case of FIGS. 2 and 3, and the housing 21 and the substrate 1 can be fixed to the same epoxy resin as in the example shown in FIGS. Can be performed by using an adhesive. Although FIG. 4 shows the case where the rectangular groove 22 is formed, any shape can be adopted as long as the object of the present invention can be achieved.

FIG. 5 is a view showing still another example of a fixing structure of a waveguide element according to the present invention. In FIG. 5, FIG.
7 shows a cross section of the fixing structure of the waveguide element as in the cases of FIGS. In FIG. 5, instead of providing notches or grooves in the housing as described above, an uneven structure 32 is formed on the housing 31 and a substrate constituting a waveguide element is formed on the structure 32. 1 is set.

When the waveguide element is installed and fixed on the housing via such an uneven structure, as shown in FIG. 5, a large amount of air layer 3 is formed in the concave portion of the uneven structure 32.
3 intervenes, the substantial interaction area is
1 is substantially the same as not touching. Accordingly, the relative effect of the area around the substantially interacting region becomes substantially 1 due to the above-described operation and effect, so that stable high-frequency characteristics can be obtained.

The uneven structure 32 can be formed from a material such as an epoxy resin. The height k of the uneven structure 32 is not particularly limited, but is preferably in the range of 50 to 300 μm from the viewpoint of easy fixing of the element. Further, the depth l of the concave portion and the opening width m of the concave portion of the uneven structure 32 are set to about 0.1 mm and m to about 0.5 mm in order to effectively achieve the effects of the present invention. Is preferred. In addition, the housing 31 and the uneven structure 32 can be fixed using an epoxy resin adhesive as described above.

FIG. 6 is a view showing another example of the fixing structure of the waveguide element of the present invention. That is, in the fixed structure of the waveguide element shown in FIG.
Has a metal layer 13 formed on the back surface thereof. The technology for forming a metal layer on the back surface of the substrate 1 in this manner is known as a microwave strip line, but by forming the metal layer on the back surface of the waveguide-type element in this manner, the conductor fixed to the housing is formed. The modulation characteristics of the waveguide element can be further improved.

As the metal layer 13, materials such as nickel and chromium can be used. Further, it is preferable that the thickness n is formed to a thickness of 0.05 to 0.2 μm. FIG. 6 shows the fixing structure of the waveguide element in which the cutout portion 12 is provided in the housing 11 shown in FIGS. 2 and 3, but it may be used for the fixing structure shown in FIGS. It can be used for fixing structures of the present invention other than those shown in the present specification.

Further, in the above specific example, an L-shaped housing is used as the housing. However, the housing can be formed in an arbitrary form according to the application of the waveguide device. Furthermore, the size of the housing can be set to any size according to the application.

The fixed structure of the waveguide element according to the present invention has a structure in which the width a of the ground electrode is three times as large as the width b of the signal electrode in order to reduce the driving voltage, as described in "Prior Art". In the case where it is relatively small so that the electrical connection of the waveguide type element cannot be made firmly, it has a remarkable effect on the stability of the high frequency characteristics. However, even when the width of the ground electrode is increased and the electrical connection of the waveguide element is firmly secured, it is possible to obtain more stable high-frequency characteristics by using the waveguide element fixing structure of the present invention. Can be.

[0029]

The present invention will be specifically described below with reference to examples. Example In this example, the fixing structure of the waveguide element shown in FIGS. 2 and 3 was manufactured. As the substrate 1, the thickness e is 1 mm,
Using an X plate of LN having a width f of 2 mm and a length g of 60 mm,
An optical waveguide 2 having a width of 9 μm was formed by a Ti thermal diffusion method, and a modulation electrode composed of a signal electrode 3 having a width of 7 μm and a ground electrode 4 having a width of 18 μm was formed by using both a plating method and an evaporation method. In this case, the length c of the substantially interacting region is 40 mm, and the width d is about 100 μm.
And the thickness e was 1 mm.

Next, a notch 12 having a length h of 35 mm and a depth i of 0.1 mm is formed in the housing 11 by milling, and the substantially interacting region is formed on the housing 11. The substrate 1 was set so that the substrate 1 was located in the cutout portion 12 and fixed using an epoxy adhesive, thereby producing a waveguide element fixing structure as shown in FIGS.
In this fixed structure, the electrode inlet 7 formed on the side wall of the housing 11
Then, the electrical connector terminal 8 is introduced and connected to the signal electrode 3 by bonding, and a high-frequency electric signal is applied to the signal electrode 3 from an external high-frequency power supply (not shown) to form the fixed structure of the waveguide element. The high frequency characteristics were examined. FIG. 8 shows the results.

Comparative Example In this comparative example, a conventional waveguide-type element fixing structure as shown in FIG. 1 was manufactured. After forming the optical waveguide 2, the signal electrode 3, and the ground electrode 4 in the same manner as in the embodiment, the substrate 1 constituting the waveguide element is set on the housing 1 and fixed with the same adhesive as in the embodiment. . Next, the electrical connector terminal 8 was connected to the signal electrode 3 in the same manner as in the example, and the high-frequency characteristics in the fixed structure of the waveguide element were examined. FIG. 7 shows the results.

7 and 8, the vertical axis indicates the propagation amount of the high-frequency electric signal, and the horizontal axis indicates the high-frequency electric signal applied to the signal electrode 3, as described in "Means for Solving the Problems". Is shown. As is clear from FIGS. 7 and 8, when the waveguide-type element fixing structure of the present invention is employed, as shown in FIG. 8, as the frequency of the applied high-frequency electric signal increases, the propagation of the high-frequency electric signal increases. Although the amount is reduced, the high-frequency characteristics are smooth, and no loss dip due to the leakage mode or the radiation mode is observed.

On the other hand, in a fixed structure in which the interacting region substantially touches the housing, as in the conventional fixed structure of the waveguide element, the A at a specific frequency in FIG.
The loss dip caused by the leakage mode and the radiation mode indicated by (1) is seen, and stable high-frequency characteristics cannot be obtained.

[0034]

As described above, according to the waveguide element fixing structure of the present invention, even when a high-frequency electric signal is applied, the electrical connection with the housing due to the width of the ground electrode is made smaller. It is possible to obtain a stable high-frequency characteristic in which the guided mode is dominant without depending on the strength.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a conventional waveguide element fixing structure.

FIG. 2 is a perspective view showing an example of a fixing structure of the waveguide element of the present invention.

FIG. 3 is a cross-sectional view of the fixing structure of FIG. 2 taken along line II.

FIG. 4 is a cross-sectional view showing another example of the fixing structure of the waveguide element of the present invention.

FIG. 5 is a cross-sectional view showing still another example of the fixing structure of the waveguide element of the present invention.

FIG. 6 is a cross-sectional view showing another example of the waveguide structure fixing structure of the present invention.

FIG. 7 is a diagram illustrating high-frequency characteristics of a conventional structure for fixing a waveguide element.

FIG. 8 is a diagram showing high-frequency characteristics of a fixed structure of a waveguide element according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Substrate 2 Optical waveguide 3 Signal electrode 4 Ground electrode 5, 11, 21, 31 Housing 6 Contact part between ground electrode and housing 7 Electrode inlet 8 Electrical connector terminal 12 Notch 13 Metal layer 22 Groove 32 Irregular structure Body 33 Air layer a Width of the ground electrode b Width of the signal electrode c Length of the region where the light wave guided in the waveguide substantially interacts with the high-frequency electric signal applied to the waveguide type element d The width of the region where the light wave guided in the wave path and the high-frequency electric signal applied to the waveguide element substantially interact e The thickness of the substrate (waveguide element) f The substrate (waveguide element) G The length of the substrate (waveguide type element) h The length of the notch portion i The depth of the notch portion j The width of the groove k The height of the uneven structure l The depth of the concave portion of the uneven structure M Opening width of concave part of uneven structure n Thickness of metal layer A Yip

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yoshihiro Hashimoto 585 Tomicho, Funabashi-shi, Chiba Sumitomo Osaka Cement Co., Ltd. F-Term in Opto-Electronics Division, Cement Co., Ltd. (Reference) 2H047 AA04 BB00 HH08

Claims (5)

[Claims] 1. A waveguide element fixing structure for mounting a waveguide element by fixing a waveguide element on which a modulation electrode and an optical waveguide are formed to a housing, wherein: A region in which a high-frequency electric signal applied to the waveguide element and a light wave guided through the optical waveguide substantially interact with each other is fixed so as not to substantially touch the housing. Fixed structure of waveguide element. 2. A notch portion is formed in the housing, and the waveguide element is disposed such that the substantially interacting region is located above the notch portion. A fixing structure for the waveguide element according to claim 1. 3. A groove having a width smaller than a width of the waveguide element is formed in the housing, and the substantially interacting region of the waveguide element is located on the groove. 2. The device according to claim 1, wherein the waveguide element is provided.
3. The fixing structure for a waveguide element according to item 1. 4. An uneven structure is formed in the housing, and the waveguide element is disposed on the structure via an air layer in a concave portion of the structure, and the substantial part of the waveguide element is provided. The fixing structure for a waveguide-type element according to claim 1, wherein a region that interacts substantially does not substantially touch the housing. 5. The waveguide type device according to claim 1, wherein a width of a ground electrode constituting the modulation electrode is reduced to reduce a driving voltage. Fixed structure.