JP3366777B2 - Optical waveguide device - Google Patents

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 comprising an optical waveguide chip having electrodes provided on a substrate on which an optical waveguide is formed, and a metal casing for housing the optical waveguide chip.

In recent years, the spread of optical communication has been remarkable in response to demands for high speed, large capacity, long distance and high quality of data transmission. Moreover, further speeding up of optical communication is being promoted, and practical application of, for example, about 10 Gbps is being promoted. There is a demand for an optical waveguide device applicable to such high speed.

[0003]

2. Description of the Related Art A schematic structure of a general optical waveguide device will be described with reference to FIG. 1 showing the appearance of an optical waveguide device 1 according to the present invention.

In FIG. 1, an optical waveguide device 1 comprises a metal casing 11, an optical waveguide chip 12, and a connector 1.
It is composed of 3,13. The optical waveguide chip 12 is
An optical waveguide is formed near the surface of a substrate 31 having a cross section of about 1 × 1 mm and a length of about several cm, and a traveling wave electrode 34 for controlling light passing through the optical waveguide is further formed on the surface. It is provided and configured.

FIG. 10 is a sectional view showing a state in which a housing 81 and an optical waveguide chip 82 in a conventional optical waveguide device 80 are attached. In FIG. 10, the housing 81 has a bottom surface portion 91 and a side surface portion 92 that is orthogonal to and continuous with the bottom surface portion 91. Since the housing 81 is formed by cutting a metal material of a small size by cutting, the bottom surface 9
In the corner portion 93, which is the boundary portion between 1 and the side surface portion 92, the rounded surface remains without being cut. An adhesive is applied to the bottom surface 82a of the optical waveguide chip 82, and the optical waveguide chip 82 is attached by being adhered to the inner surface (bottom surface) 91a of the bottom surface portion 91.

[0006]

As shown in FIG. 10, in the conventional case, the rounded surface and the optical waveguide chip 8 are used.
The side surface 82b of the optical waveguide 82 due to interference with the corner edge of
The surface (side surface) 92a of the side surface portion 92 of the housing 81 could not be brought into close contact with each other, and a gap 94 was formed between them. In addition, the adhesive AH applied to the bottom surface 82a protruded on both sides, and the protruding adhesive AH also formed a gap 94.

Therefore, a standing wave is generated by the gap 94, which disturbs the microwave characteristics of the optical waveguide device 80. Further, the excess adhesive AH attached to the bottom surface 82a and the protruding adhesive AH have an influence on the microwave characteristics.

Therefore, the upper limit of the operating frequency of the optical waveguide device 80 is limited, and it is not possible to use it at a high speed of several Gbps or more. The present invention has been made in view of the above problems, and provides an optical waveguide device capable of further increasing the upper limit of the operating frequency by improving the characteristics of microwaves and further increasing the speed. The purpose is to

[0009]

According to a first aspect of the present invention, there is provided an optical waveguide device, wherein a refractive index of the optical waveguide is changed by applying a microwave drive voltage to a substrate on which the optical waveguide is formed. An optical waveguide chip provided with an electrode for controlling light passing through the optical waveguide,
An optical waveguide device comprising a metal casing for accommodating the optical waveguide chip, wherein the casing is provided with the optical waveguide at a corner portion which is a boundary portion between the inner bottom surface and one side surface continuous with the bottom surface. A groove is provided to avoid interference with the corner edge of the waveguide chip, and the optical waveguide device has a bottom surface and one side surface with respect to the bottom surface and one side surface continuous with the bottom surface of the optical waveguide chip. Are attached in close contact with each other, with respect to the optical waveguide of the optical waveguide chip by the standing wave generated by the presence of the groove
The dimensions of the groove are selected so that the resonance frequency in the vertical cross section is on the higher frequency side of the microwave use frequency band of the optical waveguide device.

[0010]

In the optical waveguide device according to a second aspect of the present invention, the concave groove is substantially 45 with respect to the bottom surface of the housing.
It is formed by electrical discharge machining so as to form an angle of degrees. In the optical waveguide device according to the invention of claim 3, the optical waveguide chip is attached to the housing by bonding the bottom surface of the housing and the bottom surface of the optical waveguide chip with an adhesive. It becomes.

[0012]

With the groove formed in the corner portion, interference between the housing and the corner edge portion of the optical waveguide chip can be avoided, and the bottom surface and side surface of the optical waveguide chip can be brought into close contact with the bottom surface and side surface of the housing. . Excess adhesive applied to the surface of the optical waveguide chip flows into the groove, and the adhesiveness of the adhesive surface is not impaired.

The resonance frequency in the cross section of the optical waveguide chip is lowered by the standing wave due to the presence of the groove, but the resonance frequency is lower than the operating frequency band by properly selecting the width or depth dimension. It becomes the high frequency side, and the required frequency band is secured.

[0014]

1 is a perspective view showing the appearance of an optical waveguide device 1 according to the present invention, and FIG. 2 is a sectional view of the optical waveguide device 1.
3 is an enlarged view showing a part of the cross section of the optical waveguide device 1, FIG. 4 is a further enlarged view showing a part of the cross section of the optical waveguide device 1, and FIG. 5 is a part of the optical waveguide device 1. It is a top view which expands and shows. The cover is omitted in FIG. Also, the description of FIG. 1 has been given in the section of the prior art, and therefore will be simplified here.

The optical waveguide device 1 of this embodiment is an optical modulator used for optical communication. As shown in FIG. 2, the housing 11 includes a bottom surface portion 21, side surface portions 22, 23,
It has a box-like shape including the end surfaces 24 and 25, and the cover 14 is attached to the upper surface. The housing 11
The cover 14 and the cover 14 are made of a metal material having the same linear expansion coefficient as that of the substrate 31 of the optical waveguide chip 12.

2 to 5, one side surface portion 2
On the inner surface of 2, a step portion 51 for connecting the optical waveguide chip 12 to the electrode 34 is provided. The optical waveguide chip 12 is provided in the corner portion 26 which is a boundary portion between the inner surface (bottom surface) 21a of the bottom surface portion 21 and the inner surface (side surface) 22a of the step portion 51 of the side surface portion 22 continuous with the bottom surface portion 21. A concave groove 27 is provided to avoid interference with the corner edge of the.

The concave groove 27 is formed so as to cover the entire length of the optical waveguide chip 12, and has a width of about 300 μm and a depth so that the angle θ of the bottom surface portion 21 with respect to the surface 21a is 45 degrees. It is formed by electrical discharge machining so as to have a thickness of about 500 μm. By setting the angle θ to 45 degrees, the standing wave becomes simple, the characteristic is less affected, and the processing is easy. The concave groove 27 is formed by the adhesive A.
It also serves as an escape groove for H.

As best shown in FIGS. 4 and 5,
The optical waveguide chip 12 includes a substrate 31 and Mach-Zehnder type optical waveguides 32 a and 32 formed on the surface layer of the substrate 31.
b, the buffer layer 33, and electrodes 34a and 34b arranged above the optical waveguides 32a and 32b.

The substrate 31 is made of a Z plate LiNbO ₃ crystal. The size of the substrate 31 is, for example, 10 in the vertical and horizontal sections.
The size is mm × 11 mm and the length is 60 mm. Optical waveguide 32
The a and 32b are formed by thermal diffusion of titanium. That is, a titanium film having a thickness of about 1000 Å is provided on the surface of the substrate 31 and patterned into a strip shape having a width of about several μm. Then, the substrate 31 is removed in a wet oxygen atmosphere.
Heat to 0 ° C. and hold for 10 hours. The optical waveguides 32a and 32b are formed by this series of processes.

The buffer layer 33 is a silicon dioxide layer having a thickness of about 0.5 μm, and is provided mainly for preventing light absorption by the electrodes 34a and 34b. Electrodes 34a, 3
4b is formed by a thin film process of depositing and patterning gold after providing the buffer layer 33. In order to supply power to the optical waveguide chip 12, the electrode 34b and the step 5
The stress relief contact and the Au ribbon 35 are connected to the upper surface of the No. 1 unit. Electrode 34a is A
It is connected to the center pin of the connectors 13, 13 by the u ribbon 36. The ground side of the connectors 13 and 13 is connected to the housing 11, that is, the step portion 51.

The bottom surface 12a of the optical waveguide chip 12 is coated with an epoxy adhesive AH, and the bottom surface 12a and the side surface 12b are in close contact with the front surface 21a and the front surface 22a of the housing 11, respectively. It is glued and attached. The excess of the applied adhesive AH is
The excess adhesive AH is prevented from remaining in the adhesive surface or protruding from the adhesive surface to the side surface by flowing into the concave groove 27.

In the optical waveguide device 1 configured as described above, the resonance frequency due to the standing wave (see FIG. 3) in the cross section of the optical waveguide chip 12 is higher than the operating frequency band. . Next, the relationship between the size of the groove 27 and the resonance frequency will be described.

FIG. 7 is a graph showing the frequency dependence with respect to the width w of the groove 27, and FIG. 8 is a graph showing the microwave transmission characteristic S ₂₁ of the optical waveguide device 1. In FIG. 7, each plotted point is an actual measurement value of the frequency drop point (resonance frequency) of the microwave transmission characteristic S ₂₁ with respect to the width w when the depth of the concave groove 27 is 500 μm.

As can be seen from FIG. 7, the resonance frequency is inversely proportional to the size of the width w of the groove 27. When the width w is increased, the influence of the concave groove 27 becomes stronger and the resonance frequency is lowered, so that the width w cannot be increased so much. In the concave groove 27 of the present embodiment, the width w was set to 300 μm as described above, so the measured value of the resonance frequency was 13.8 GHz.

As shown in FIG. 8, the gain is drastically reduced at the first resonance frequency of 13.8 GHz, but the characteristics are gentle until then. Therefore, it can be said that the optical waveguide device 1 can be used up to about 13 GHz.

Incidentally, in the conventional optical waveguide device, as shown in an example in FIG. 9, there was the first resonance frequency in the vicinity of 8.5 GHz, and the upper limit of the used frequency was low, but the optical waveguide device of the present embodiment. It is understood that in No. 1, it is improved.

When using the optical waveguide device 1, 2
A microwave drive voltage is applied between the two electrodes 34a and 34b. By applying the drive voltage, the optical waveguides 32a, 3a
An electric field is applied to 2b, the refractive index changes, and the polarization plane of the light propagating in the optical waveguides 32a and 32b rotates.

According to the above-described embodiment, the presence of the concave groove 27 eliminates the interference between the rounded surface of the housing 11 and the corner edge of the optical waveguide chip 12 unlike the conventional case, and the bottom surface 1
The surface 2a and the side surface 12b can be brought into close contact with the surfaces 21a and 22a of the housing 11. Moreover, since the excess adhesive AH does not remain on the adhesive surface and does not protrude to the side surface of the optical waveguide chip 12, the adhesiveness of the adhesive surface is not impaired.

Further, the width w of the concave groove 27 is appropriately selected,
As shown in FIG. 3, the resonance frequency due to the standing wave in the cross section of the optical waveguide chip 12 is prevented from being greatly reduced. For example, when the operating frequency is 10 GHz, the width w of the concave groove 27 is selected so that the resonance frequency is sufficiently higher than 10 GHz.

By thus improving the microwave characteristics, the upper limit of the operating frequency of the optical waveguide device 1 is raised, and the communication speed can be further increased.

In the above-mentioned embodiment, the housing 11 is formed by cutting from the material of 尨, but it may be constructed by joining a plurality of members by silver brazing or the like. FIG. 6 is a partial sectional view of a housing 11a according to another embodiment.

In FIG. 6, the housing 11a is a bottom member 6
1, the side surface member 62 and the like are joined by silver brazing 68. A groove 67 is formed in the corner portion 65, which is a joining portion of the bottom member 61 and the side member 62, by cutting each member, and silver brazing 68 is performed inside the groove 67. In addition, the surplus of the adhesive AH applied to the bottom surface of the optical waveguide chip 12 flows into the concave groove 67.

Even when such a casing 11a is used,
The interference between the housing 11 and the optical waveguide chip 12 is eliminated, the optical waveguide chip 12 can be brought into close contact with the surfaces 61a and 62a of the housing 11a, and the width w and the depth of the concave groove 67 are appropriately selected. As a result, the resonance frequency is prevented from being greatly reduced, and the microwave characteristics can be improved.

In the above embodiment, the depth of the groove 27 can be changed. It is also possible to supply power to the optical waveguide chip 12 via a strip line. Various types can be applied as the optical waveguide chip 12. In addition, the configuration, dimensions, shape, material, etc. of the entire or each part of the optical waveguide device 1 can be appropriately changed in accordance with the gist of the present invention.

[0035]

According to the inventions of claims 1 to 3 ,
By improving the characteristics of the microwave, the upper limit of the used frequency can be further raised, and the communication speed can be further increased.

[Brief description of drawings]

FIG. 1 is a perspective view showing an appearance of an optical waveguide device according to the present invention.

FIG. 2 is a sectional view of an optical waveguide device.

FIG. 3 is an enlarged view showing a part of the cross section of the optical waveguide device.

FIG. 4 is a view further enlarging a part of the cross section of the optical waveguide device.

FIG. 5 is a plan view showing an enlarged part of the optical waveguide device.

FIG. 6 is a partial cross-sectional view of a housing of another embodiment.

FIG. 7 is a graph showing frequency dependence with respect to the width w of the groove.

FIG. 8 is a diagram showing microwave transmission characteristics of the optical waveguide device according to the present invention.

FIG. 9 is a diagram showing an example of microwave transmission characteristics of a conventional optical waveguide device.

FIG. 10 is a cross-sectional view showing a mounting state of a housing and an optical waveguide chip in a conventional optical waveguide device.

[Explanation of symbols]

1 Optical waveguide device 11,11a housing 12 Optical waveguide chip 21a, 61a Surface (bottom surface) 22a, 62a Surface (side surface) 26,65 Corner 27,67 concave groove 31 substrate 32a, 32b optical waveguide 34a, 34b electrodes

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Claims (3)

(57) [Claims] 1. An electrode for controlling light passing through the optical waveguide by changing a refractive index of the optical waveguide by applying a driving voltage by a microwave to a substrate on which the optical waveguide is formed. An optical waveguide device comprising an optical waveguide chip formed by: and a metal housing for accommodating the optical waveguide chip, wherein the housing has a boundary portion between the inner bottom surface and one side surface continuous with the bottom surface. A certain corner portion is provided with a concave groove for avoiding interference with a corner edge portion of the optical waveguide chip, and the optical waveguide device has the optical waveguide chip with respect to the bottom surface and the one side surface. bottom and one side continuous to it, mounted in close contact each resonance in the cross section perpendicular to the optical waveguide of the optical waveguide chip according to the standing wave occurring in the presence of the groove Optical waveguide device wave number so that a high-frequency side than the frequency band of the microwave of the optical waveguide device, the size of the concave groove is formed by selecting, characterized in that. 2. The optical waveguide device according to claim 1, wherein the groove is formed by electrical discharge machining so as to form an angle of about 45 degrees with the bottom surface of the housing. 3. The adhesive is applied between the bottom surface of the housing and the bottom surface of the optical waveguide chip,
The optical waveguide device according to claim 1, wherein the optical waveguide chip is attached to the housing.