JP2000275586A - Fixing structure for optical waveguide element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing structure for an optical waveguide element which has sable high-frequency characteristics without being affected by the strength of an electric connection depending upon the width of a ground electrode. SOLUTION: On the reverse surface 11B of a substrate 11, a cut part 12 is formed over the area where a signal electrode 3 and the ground electrode 4 are present. Consequently, the optical waveguide element 15 is fixed to a housing 5 so that the area where a high-frequency electric signal applied to the signal electrode 3 having length C, width (d), and thickness (e) and a light wave guided in an optical waveguide 2 interact with each other is not in direct contact with a housing 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide device fixing structure, and more particularly, to a waveguide type optical intensity modulator, a phase modulator, and a polarization scrambler used in a high-speed and large-capacity optical fiber communication system. The present invention relates to an optical waveguide element fixing structure that can be suitably used for a bra and 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 an electro-optic effect, and a high-speed modulation signal in a microwave band applied to the light wave. And a modulation electrode composed of the signal electrode 3 and the ground electrode 4. Then, the substrate 1 on which the modulation electrodes and the like are formed is fixed and mounted on a housing 5 made of brass, stainless steel, or the like, and then used as an actual element.

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 μm.
In general, the width is set to several tens to several hundreds times the width b of the signal electrode 3.

Further, in order to reduce power consumption, attempts have been made to lower the drive voltage of the optical waveguide device.
As a method for lowering the driving voltage, Japanese Patent Application Laid-Open No. 5-196
As described in Japanese Patent Application Publication No. 902, for example, FIG.
The width a of the ground electrode 4 may be reduced to be about three times or less the width b of the signal electrode 3.

[0005]

However, it is possible to reduce the drive voltage by reducing the width a of the ground electrode 4 as described above, but when mounting and actually using it as a device, The electrical connection with the body 5 cannot be made firmly. That is, the reduction in the drive voltage and the strong electrical connection of the ground electrode 4 to the housing 5 are in a mutually contradictory relationship. Therefore, when the width a of the ground electrode 4 is reduced as described above in order to reduce the driving voltage, when a high-speed modulation signal in the microwave band is applied, in addition to the waveguide mode guided as the modulation signal, the inside of the substrate is increased. There is a problem that a leaky mode that leaks out into the air and a radiation mode that radiates into the air occur, and 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 fixing structure of an optical waveguide device 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]

According to the present invention, an optical waveguide device having an optical waveguide and a modulation electrode is fixed to a housing having an electro-optic effect in a housing, and an optical waveguide for mounting the optical waveguide device is mounted. A fixing structure of a waveguide element, wherein
A notch is formed on the back surface opposite to the main surface on which the modulation electrode and the optical waveguide are formed, and a high-frequency electric signal applied to the optical waveguide by the modulation electrode and the optical waveguide is guided. Wherein at least a part of the region where light waves interact substantially does not substantially touch the housing, wherein the optical waveguide element and the housing are fixed, It is a fixed structure.

FIG. 2 is a perspective view showing an example of a fixing structure of the optical waveguide device of the present invention, and FIG. 3 is a plan view of the optical waveguide device shown in FIG. In FIGS. 2 and 3 and the following drawings, the size of the signal electrodes, the optical waveguides, and the like are drawn so as to be different from actual ones for clarity of description. Further, the same parts as those in FIG. 1 are denoted by the same reference numerals.

In FIGS. 2 and 3, the main surface 1 of the substrate 11 is shown.
An optical waveguide 2, a signal electrode 3, and a ground electrode 4 are formed on 1A, and constitute an optical waveguide element 15. A cutout portion 12 having a length L over the entire width f of the substrate 11 is formed on the entire surface of the rear surface 11B of the substrate 11 where the signal electrode 3 and the ground electrode 4 are present. And
A region where the light wave guided through the optical waveguide 2 substantially interacts with the high-frequency electric signal applied between the signal electrode 3 and the ground electrode 4 (the length c, width d, and thickness e in FIG. 2). (Corresponding portion) fixes the optical waveguide element 15 and the housing 5 so as not to substantially touch the housing 5.

On the other hand, FIG. 9 is a diagram showing high-frequency characteristics in the fixed structure of the conventional optical waveguide element shown in FIG.
0 is a diagram showing high-frequency characteristics in the fixed structure of the optical waveguide device of the present invention shown in FIGS. 9 and 10, 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. 9 and 10, when the conventional structure for fixing an optical waveguide element shown in FIG. 1 is used, at a specific frequency, a leakage mode and a radiation mode as shown in FIG. Loss dip occurs. However, when the fixing structure of the optical waveguide element 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, stable high-frequency characteristics can be obtained by the fixing structure of the present invention.

The cause can be considered as follows. In the fixing structure of the optical waveguide device of the present invention, since the above-described substantial interaction region does not touch the housing, the relative permittivity in the peripheral portion of the interaction region of the optical waveguide device is reduced. It becomes 1. As described above, when the high-frequency characteristics due to the electric signal become unstable when the high-frequency electrode is applied, the leakage mode and the radiation mode occur in addition to the waveguide mode. When the relative permittivity around the region is 1, the electric field distribution of the high-frequency electric signal applied from the modulation electrode concentrates on the substantial interaction region without leaking to the outside of the optical waveguide element. . Therefore, the leakage mode and the radiation mode are inevitably reduced. As a result, only the waveguide mode remains and becomes dominant, so that stable high-frequency characteristics can be obtained.

The "region in which the high-frequency electric signal applied to the optical waveguide by the modulation electrode and the light wave guided through the optical waveguide substantially interact" in the present invention is, for example, the one shown in FIG. In the case of the optical waveguide device as shown in FIG. 1, the optical waveguide 2 and the modulation electrode composed of the signal electrode 3 and the ground electrode 4 are formed substantially in parallel, and the lightwave guided in the optical waveguide 2 is transmitted from the signal electrode 3 to the modulation electrode. The length c to which the high-frequency electric signal is applied,
It refers to a region represented by width d and thickness e.

Further, "at least a part of the substantially interacting region does not substantially touch the housing" means that the substantially interacting region of the optical waveguide element does not directly contact the housing. Say when For example, as shown in FIGS. 2 and 3, by forming a notch 12 on the back surface 11 </ b> B of the substrate 11, the substantially interacting regions (length c, width d, and thickness) of the optical waveguide element 15 are formed. e) is fixed to the housing 5 via the air layer 16.

[0016]

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 notch in the optical waveguide device fixing structure of the present invention guides the high-frequency electric signal applied to the optical waveguide by the modulation electrode and the optical waveguide when the optical waveguide device and the housing are fixed. It is necessary that at least a part of the region where the light wave substantially interacts is formed on the back surface of the substrate without substantially touching the housing. As long as the above condition is satisfied, the specific form of the cutout is not particularly limited.

2 and 3, a notch 12 is formed on the back surface of the substrate 11 over the entire area where the signal electrode 3 and the ground electrode 4 as modulation electrodes are formed. Accordingly, the electric field distribution of the high-frequency electric signal applied between the signal electrode 3 and the ground electrode 4 is concentrated on the substantial interaction region without leaking to the outside of the optical waveguide device. Therefore, the leakage mode and the radiation mode can be more effectively reduced, and extremely stable high-frequency characteristics can be obtained. In order to more effectively achieve the object of the present invention, the depth D of the notch 12 is preferably 10 to 200 μm, and more preferably 50 to 100 μm.

FIG. 4 is a plan view showing another example of the fixing structure of the optical waveguide element of the present invention. In FIG. 4, a notch 22 having a width H including a substantially interacting region indicated by a length C and a width d is formed on the back surface of the substrate 21 over the entire length of the substrate 21 in the longitudinal direction. . Even in such a form, the object of the present invention can be sufficiently achieved.

FIG. 5 is a plan view showing still another example of the optical waveguide element fixing structure of the present invention. In FIG. 5, a cutout portion 32 having a width R is formed on the back surface of the substrate 31 so as to include the entire ground electrode 4 in a region where the length C and the width d substantially interact with each other. This ensures that at least a portion of the substantially interacting region does not substantially contact the housing. By employing the fixing structure having the configuration as shown in FIG. 5, the electrical connection area can be reduced as compared with the related art, and the manufacturing time can be shortened. Furthermore, mounting can be performed even if the width W of the ground electrode 4 is reduced in order to reduce the drive voltage.

In the configuration as shown in FIG. 5, the width R of the notch 32 is set to be R / W = 1 to 1 with respect to the width W of the ground electrode 4.
00, more preferably 2 to 50. Further, the cutout portion may be formed so as to include the entire signal electrode 3 instead of the ground electrode 4. Furthermore, the notch may be formed so as to include the entirety of the signal electrode 3 and the ground electrode 4.

FIG. 6 is a plan view showing another example of the fixing structure of the optical waveguide element of the present invention. In FIG. 6, in a substantially interacting region having a length C and a width d, the cutout 42 is formed so as to include the entire ground electrode 4 so as to include the entirety of the substrate 4.
1 is formed on the back surface. Also in this case, the same effect as in the case of FIG. 5 can be obtained, and the notch can be formed continuously from the end of the substrate, so that the notch can be easily formed.

FIG. 7 is a perspective view showing an example of a different mode of the fixing structure of the optical waveguide element of the present invention. FIG.
FIG. 2 is a cross-sectional view of the fixing structure of the optical waveguide element shown in FIG. In the fixing structure shown in FIGS. 7 and 8, plate members 52-1 and 52-2 are formed over the entire width f of the substrate 51 on the back surface 51B of the substrate 51 instead of the cutout portion 12. Then, by mounting the substrate on which the plate-like member is formed on the main surface 5A of the housing 5,
The length C, width d, and thickness j of the optical waveguide element 55 do not come into direct contact with the housing 5 so that substantially interacting areas do not directly contact the housing 5.
Substantially interacting regions can be substantially non-touching the housing 5.

A plate member 52-1 as shown in FIGS.
And 52-2 are formed on the back surface 51B of the substrate 51,
The height h of the member is preferably from 10 to 500 μm. In addition, the number and size of the plate-shaped members formed on the back surface of the substrate are not limited as long as the region that substantially interacts with the case 5 can be substantially prevented from touching. The plate members 52-1 and 52-2 can be formed from any material such as lithium niobate, glass, and metal.

The notch can be formed by means such as milling. The housing 5 and the optical waveguide elements 15 and 55 are fixed using an adhesive such as an epoxy resin.

Although not an essential element in the present invention,
A metal layer may be formed on the back surface of the substrate on which the notch or the plate member is formed. Thereby, the modulation characteristics of the optical waveguide element fixed and mounted on the housing can be further improved. The metal layer can be formed from materials such as nickel and chromium. Further, the thickness is preferably formed to a thickness of 0.05 to 0.2 μm.

Further, in the above-mentioned specific examples, an L-shaped housing is used, but any shape can be adopted according to the application of the optical waveguide device. Further, as for the size of the housing, any size can be used according to the application.

According to the fixing structure of the optical waveguide element of the present invention, the width a of the ground electrode is three times or less than 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 not possible to make the electrical connection of the optical waveguide element 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 optical waveguide element is firmly secured, more stable high-frequency characteristics can be obtained by using the optical waveguide element fixing structure of the present invention. .

[0028]

The present invention will be specifically described below with reference to examples. Example In this example, the fixing structure of the optical waveguide device shown in FIGS. 2 and 3 was manufactured. The thickness e is 1 m as the substrate 11
An X plate of LN having m, width f of 2 mm and length g of 60 mm was used. Next, an optical waveguide 2 having a width of 9 μm is formed on the main surface 11A of the substrate 11 by a Ti thermal diffusion method, and is composed of a signal electrode 3 having a width of 7 μm and a ground electrode 4 having a width of 18 μm by using both a plating method and an evaporation method. A modulation electrode was formed. The length c of the substantially interacting region in this case is about 4
The width d was about 100 μm, and the thickness e was about 1 mm.

Next, the width f is set to 2 by milling.
A notch 12 having a length L of 37.8 mm and a depth D of 0.1 mm was formed so that the substantially interacting region was included on the back surface of the substrate 11. Thereafter, the substrate 11 and the housing 5 were adhered and fixed using an epoxy adhesive, thereby producing an optical waveguide element fixing structure as shown in FIGS.

An electric connector terminal 8 was introduced from the electrode introduction port 7 formed on the side wall of the housing 5 to the fixed structure, and the signal electrode 3 was connected by bonding. Next, a high-frequency electric signal was applied to the signal electrode 3 from an external high-frequency power supply (not shown), and high-frequency characteristics in the fixed structure of the optical waveguide element were examined. The results are shown in FIG.

Comparative Example In this comparative example, a conventional optical waveguide 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 example, the substrate 1 and the housing 5 were fixed with the same adhesive as in the example. 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 optical waveguide element were examined. FIG. 9 shows the results.

9 and 10, the vertical axis indicates the amount of propagation 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. 9 and 10, when the fixing structure of the optical waveguide element of the present invention is adopted, as shown in FIG. 10, as the frequency of the applied high-frequency electric signal increases, the propagation amount of the high-frequency electric signal increases. Decreases, but its high frequency characteristics are smooth,
No loss dip caused by leakage mode or 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 optical waveguide element, at a specific frequency in FIG. Loss dip is observed, and stable high-frequency characteristics cannot be obtained.

As described above, the present invention has been specifically described based on the embodiments of the present invention with specific examples, but the present invention is not limited to the above contents and does not depart from the scope of the present invention. All changes and modifications are possible as far as possible.

[0034]

According to the fixing structure of the optical waveguide element of the present invention, even when a high-frequency electric signal is applied, the electric conduction is not dependent on the strength of the electrical connection with the housing due to the width of the ground electrode. It is possible to obtain stable high-frequency characteristics in which the wave mode is dominant.

[Brief description of the drawings]

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

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

FIG. 3 is a plan view of a fixing structure of the optical waveguide element shown in FIG.

FIG. 4 is a plan view showing another example of the fixing structure of the optical waveguide element of the present invention.

FIG. 5 is a plan view showing still another example of the fixing structure of the optical waveguide element of the present invention.

FIG. 6 is a plan view showing another example of the fixing structure of the optical waveguide element of the present invention.

FIG. 7 is a perspective view showing an example of a different mode of the fixing structure of the optical waveguide element of the present invention.

8 is a cross-sectional view of the fixing structure shown in FIG. 7 taken along the line II.

FIG. 9 is a diagram showing high-frequency characteristics in a conventional optical waveguide element fixing structure.

FIG. 10 is a diagram showing high-frequency characteristics in the fixed structure of the optical waveguide element of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1, 11, 21, 31, 41, 51 Substrate 2 Optical waveguide 3 Signal electrode 4 Ground electrode 5 Housing 6 Contact part between a ground electrode and a housing 7 Electrode inlet 8 Electrical connector terminal 12, 22, 32, 42 Notch 15, 55 Optical waveguide element 16 Air layer 52-1, 52-2 Plate-like member 11B, 51B Back surface of substrate c High-frequency electric signal applied to modulation electrode and light wave guided through optical waveguide are substantially formed The length of the interacting region d The high-frequency electric signal applied to the modulating electrode and the width of the region where the light wave guided through the optical waveguide substantially interacts e The high-frequency electric signal applied to the modulating electrode The thickness of the region (substrate thickness) where the light wave guided through the optical waveguide substantially interacts; f the width of the substrate; j the high-frequency electric signal applied to the modulation electrode; and the light wave guided through the optical waveguide. And interworking virtually The thickness D notch depth L cutout length H of the region, the height A loss dip width h-shaped member of R notch

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yoshihiro Hashimoto 585 Tomicho, Funabashi-shi, Chiba Sumitomo Osaka Cement Co., Ltd. F-term in the New Technology Research Laboratories of Cement Corporation (reference) 2H079 AA02 AA12 BA01 BA02 BA03 CA05 DA03 DA22 EA03 EA33 EB05 HA12 HA14 HA15

Claims (4)

[Claims] An optical waveguide device having an optical waveguide and a modulation electrode on a substrate having an electro-optic effect is fixed to a housing,
A fixing structure of an optical waveguide element for mounting the optical waveguide element, wherein a cutout portion is formed on a back surface of the substrate opposite to a main surface on which the modulation electrode and the optical waveguide are formed, A high-frequency electric signal applied to the optical waveguide by the modulation electrode, and at least a part of a region where light waves guided through the optical waveguide substantially interact with each other so as not to substantially touch the housing. A fixing structure of the optical waveguide element, wherein the optical waveguide element and the housing are fixed. 2. The fixing of the optical waveguide element according to claim 1, wherein the notch is formed over the entire area of the back surface of the substrate where the modulation electrode is present. Construction. 3. The modulation electrode includes a signal electrode and a ground electrode, and the cutout portion is formed in a region where at least one of the signal electrode and the ground electrode exists in the substantially interacting region. The fixing structure for an optical waveguide element according to claim 1, wherein the fixing structure is formed over the entirety. 4. An optical waveguide device having an optical waveguide and a modulation electrode on a substrate having an electro-optical effect is fixed to a housing,
A fixing structure of an optical waveguide element for mounting the optical waveguide element, wherein a plate-shaped member is formed on a back surface of the substrate opposite to a main surface on which the modulation electrode and the optical waveguide are formed, At least a part of a region where a high-frequency electric signal applied to the optical waveguide by the modulation electrode and a light wave guided through the optical waveguide substantially interact does not substantially touch the housing. A fixing structure of the optical waveguide element, wherein the optical waveguide element and the housing are fixed.