JP4056545B2 - High frequency line connection structure - Google Patents

Description

  The present invention relates to a high-frequency line connection structure, and more particularly to a connection structure between a coaxial line and a planar line used in an optical device such as an optical modulator.

In recent years, with the advancement of high-speed, large-capacity optical fiber communication systems, there has been a demand for optical devices for electro-optical conversion or optical-electric conversion having high-frequency response characteristics, for example, as represented by optical modulators. An optical modulator capable of high-speed operation using a material having an electro-optic effect such as lithium niobate as a substrate has been put into practical use.
Many of these optical devices are often formed on a planar substrate having an electro-optic effect, and therefore, planar lines are frequently used for wiring of signal electrodes and ground electrodes in the optical devices. On the other hand, the electrical signal introduced into or derived from the optical device uses a high-frequency microwave reflecting the recent increase in communication speed, and the microwave signal is outside the optical device. Generally, it is transmitted using a coaxial cable.

For this reason, for example, it is necessary to smoothly transmit a microwave propagating through a coaxial line such as a coaxial cable to a planar line in an optical device. A connecting member 10 as shown in FIG. 1 is used.
The connecting member 10 is provided with an electrical signal input / output connector 20 for attaching a coaxial cable on one side, and the other connected to each of the signal electrode 2 and the ground electrode 3 of the planar line formed on the substrate 1. The connecting member 12 for grounding and the connecting member for grounding (in FIG. 1, the housing of the connecting member 10 also serves as the connecting member for grounding) are provided. The signal line in the connector 20 is electrically connected to the signal connection member 12 in the connection member 10, and the ground portion of the connector 20 is connected to the ground connection member (the housing itself of the connection member 10 in FIG. 1). It is connected.
Note that the connection member for grounding is not limited to the example in which the casing of the connection member 10 itself is used as shown in FIG. In addition, a conductive cylindrical member configured to surround the signal line in the connector 20 may be provided, and the cylindrical member may be used as a ground connection member.

Further, for connection between the signal line in the connector 20 and the signal connection member 12, a signal connection member 12 composed of a plane portion a and a substantially cylindrical portion b as shown in FIG. The cylindrical part b is put on the signal line and fixed by tightening.
For joining the signal connection member 12 and the signal electrode 2, a method of ultrasonically pressing the planar portion a (joint portion with the signal electrode) to the signal electrode 2 is used.
Regarding the connection structure of the ground portion, in particular, in the connection between the ground connection member (connection member 10 in FIG. 1) and the ground electrode 3, a method of bonding both with a gold wire 4 or a ribbon-like lead wire, or the connection member 10 For example, a method of joining the substrate 1 and the substrate 1 with solder or a conductive adhesive is used.

  When good response is required even at a high frequency of several tens of GHz or more due to an increase in communication speed or the like, the width of the signal electrode 2 on the planar line, particularly the connection position of the signal electrode 2 (generally referred to as a pad portion). As shown in FIG. 3, the width of the signal electrode 2 becomes smaller than the width of the flat portion a of the signal connection member 12. For this reason, there was a problem that the high frequency characteristics deteriorated.

In the structure as shown in FIG. 1, bonding means cannot be used for connection of the ground portion, and therefore it is necessary to connect using a conductive adhesive or the like. In such a case, the bonded portion may be damaged due to a difference in thermal expansion between the bonding member 10 and the substrate 1.
Furthermore, since these connecting portions have a small space, workability is also difficult.
For this reason, as shown in FIG. 4, the notch 11 is provided so that the cross-section of the connecting member 10 'is substantially L-shaped, a surface substantially parallel to the substrate 1 is formed, and a wire such as a wire or ribbon Is configured to be bonded.
However, since the impedance of the coaxial line is not maintained at the notch portion 11, there is a problem that electrical characteristics particularly at high frequencies deteriorate.

  The problem to be solved by the present invention is to solve the above-mentioned problems, suppress propagation loss due to reflection or leakage of microwaves at the connection part between the coaxial line and the planar line, and improve the connection workability. It is to provide an excellent high-frequency line connection structure.

In order to solve the above-described problem, the invention according to claim 1 is to electrically connect the grounding portion of the coaxial line and the ground electrode of the planar line in the connection structure of the high-frequency line that connects the coaxial line and the planar line. A grounding connection member , wherein a through hole corresponding to the shape of the grounding portion of the coaxial line is formed from the coaxial line side to the plane line side of the ground connection member, and the plane line side of the ground connection member a ground connection member in which a surface substantially parallel to the cutout of the ground electrode of the plane line is formed, a lid member that is mounted in the missing portion Ri 該切, mounted in the missing portion Ri該切the lid member and having a lid member provided with recesses corresponding to the through hole to form a coaxial shape corresponding to the coaxial line in.

  According to a second aspect of the present invention, in the high frequency line connection structure according to the first aspect, the ground connection member and the ground electrode of the planar line are connected by bonding means, and the bonding means is connected to the lid member. It is characterized by providing a cutout portion that avoids the above.

The invention according to claim 3, in the connection structure for a high-frequency line according to claim 1 or 2, the lid member in accordance with proximity to the planar line side from the coaxial line side, an upper portion of the coaxial shape gradually An inclined surface is formed so that the height of the lid member decreases toward the planar line side so as to be opened.

  According to a fourth aspect of the present invention, in the high frequency line connection structure according to any one of the first to third aspects, a part of the lid member is configured to protrude on the planar line. Features.

The invention according to claim 5 is the high-frequency line connection structure according to any one of claims 1 to 4, wherein the planar line is a coplanar line.
Further, the invention according to claim 6 is the high-frequency line connection structure according to claim 5, wherein a width between GND and GND of the coplanar line is equal to or less than a GND conductor diameter of the coaxial line.
The invention according to claim 7 is the high-frequency line connection structure according to any one of claims 1 to 6, wherein the planar line is provided in an optical device for electrical-optical conversion or optical-electrical conversion. It is characterized by being.
In particular, the invention according to claim 8 is the high-frequency line connection structure according to claim 7, wherein the optical device is an optical modulator.

  According to the first aspect of the present invention, by providing a lid member that complements the notch portion, the impedance of the coaxial line is maintained in the same manner as when the notch portion is not provided in terms of electrical characteristics. It becomes possible to prevent deterioration of characteristics.

  According to the invention of claim 2, even when the grounding portion is connected using a bonding means such as a wire, the notch is formed in the lid member so as to avoid the position where the bonding means is applied. The lid member can be brought into close contact with the ground connection member, and the impedance of the coaxial line can be maintained better.

  According to the invention of claim 3, the radial electric field between the signal line and the grounding portion surrounding the signal line on the coaxial line is gradually converted into a lateral electric field state formed on the planar line. Therefore, conversion between the coaxial line and the planar line can be performed smoothly.

  According to the invention of claim 4, by providing a lid member that straddles both the coaxial line and the planar line, the change in the state of electrical characteristics between the coaxial line and the planar line is alleviated, and smooth conversion is enabled. .

  The invention according to claims 5 to 8 has an effect of improving high-frequency characteristics with respect to an optical device using a high-frequency microwave such as an optical modulator, particularly a device using a planar line such as a coplanar line. .

Hereinafter, the present invention will be described in detail using preferred examples. Here, the description will focus on the optical modulator.
As a substrate constituting the optical modulator, a material having an electro-optic effect, such as lithium niobate (LiNbO ₃ ; hereinafter referred to as LN), lithium tantalate (LiTaO ₃ ), PLZT (lead lanthanum zirconate titanate), In particular, LiNbO ₃ crystal, LiTaO ₃ crystal, or a solid solution crystal composed of LiNbO ₃ and LiTaO ₃ is used because it is easy to configure as an optical waveguide device and has high anisotropy. Is preferred.

As a method of manufacturing an optical modulator, an optical waveguide is formed by thermally diffusing Ti on an LN substrate, and then an LN substrate is used for reducing propagation loss in the optical waveguide and for speed matching between the microwave and the optical wave. A dielectric buffer layer such as SiO ₂ is provided thereon. Further, it is common to construct a coplanar structure electrode having a height of several tens of μm by a gold plating method or the like.

  As a method for driving the optical modulator, a high-frequency microwave is applied to the signal electrode and the ground electrode formed on the substrate, and the refractive index of the optical waveguide is changed by an electric field generated between the signal electrode and the ground electrode. The phase of the light passing through the optical waveguide is changed. Further, if necessary, it is possible to multiplex a plurality of lights having a phase change and perform light intensity modulation.

A feature of the present invention is a connection structure between a planar line such as a signal electrode and a ground electrode provided on a substrate such as an optical modulator and a coaxial line that transmits microwaves.
As the signal line connection structure, the signal connection member 12 shown in FIG. 2 is used, but the shape of the joint portion with the signal electrode on the substrate, which is the flat portion a, has a tip as shown in FIG. It is formed in a tapered shape and is joined to the signal electrode 2 by ultrasonic pressure bonding or the like.
Specifically, the width w1 on the coaxial line side of the joint is wider than the width w1 ′ of the signal electrode, and the width w2 of the tip of the joint is configured to be equal to or smaller than the width w2 ′ of the signal electrode at the same position. Has been.
For this reason, compared to the conventional example as shown in FIG. 3, the width of the electrode in the planar state continuously changes from the coaxial line to the planar line, so that the conversion between both lines can be performed smoothly. It becomes.
In addition, although the shape of the plane part a illustrated the trapezoidal shape in FIG. 5, it can also be made into the triangular shape which sharpened the front-end | tip part.

FIG. 6 shows the result of measuring the electric reflection characteristics using the signal line connection method shown in FIG. 5 for the high-speed LN optical modulator. According to this, the improvement of the frequency characteristic was seen especially at 15 GHz or more.
In the present invention, both the width on the coaxial line side and the width on the front end portion on the plane line side are defined in the joint portion of the signal connection member. Needless to say, improvement in characteristics can be seen.

Next, the connection structure of the ground part will be described.
As shown in FIG. 4, a notch 11 is provided in the ground connection member (the housing itself of the connection member 10 'carries the ground connection member), and the ground connection member and the ground electrode on the substrate are connected to each other. Bonding is performed with a wire or the like.
A conductive lid member 13 as shown in FIG. 7 is placed on the ground connection member 10 ′, and the ground connection member 10 ′ and the lid member 13 are joined and electrically integrated.
The lid member 13 is formed with a recess 14 corresponding to the coaxial line, and is configured to have the same effect as when the coaxial line extends to the vicinity of the substrate 1.

  Further, the lid member 13 is formed with a notch 15 corresponding to an electrical connection means such as wire bonding, and the lid member is closely attached to the ground connection member 10 ′ while avoiding the electrical connection means. be able to.

  FIG. 8 shows the result of measuring the electric reflection characteristics of the high-speed LN optical modulator using the lid member shown in FIG. According to this, the improvement of the frequency characteristic was seen especially at 15 GHz or more.

Further, as shown in FIG. 9, by inclining the planar line side of the lid member 16, the concave portion 17 forming a part of the coaxial line is moved closer to the planar line side from the coaxial line side. Is formed to be gradually opened.
This makes it possible to gradually change the electric field generated radially around the signal line in the coaxial line into a horizontal electric field like a plane line, and smoothly convert between the coaxial line and the plane line. Can be realized.

  In addition, as shown in FIG. 10, by providing a cover member straddling between the ground connection member 10 ′ and the substrate 1, the state change between the coaxial line and the planar line can be changed with respect to the ground connection member 10 ′ and the substrate. Since the distinction at the boundary with 1 is suppressed, the line state can be changed more smoothly.

  When a coplanar line is used as a planar line, the width between GND and GND of the coplanar line (the inner width between the ground electrodes sandwiching the signal electrode) at the connection portion between the coplanar line and the coaxial line By making the GND conductor diameter (inner diameter) or less, leakage of high-frequency microwaves to the substrate can be further prevented. In the case of using the ground connection member or the cover member described above, the GND conductor diameter of the coaxial line is the GND conductor surrounding the signal line of the ground connection member or the cover member at the connection portion between these members and the coplanar line. It means the inner diameter of the (grounded conductor part).

  The present invention is not limited to the technical matters described above. For example, various combinations of the above technologies, such as a connection structure having both a technology related to a signal line and a technology related to a grounding part, can convert a coaxial line and a planar line. This includes things that are performed more smoothly.

  As described above, according to the present invention, by providing the shape of the joint portion of the signal connection member, the lid member or the like related to the connection member for grounding, the connection work of the grounding portion is maintained in a simple state. In addition, it is possible to suppress propagation loss due to reflection or leakage of microwaves at the connection portion between the coaxial line and the planar line.

The figure which shows the conventional connection structure. The figure which shows the conventional connection member for signals. The figure which shows the connection state of the conventional signal connection member and a signal electrode. The figure which shows the connection structure which has the conventional notch part. The figure which shows the connection state of the signal connection member of this invention, and a signal electrode. The figure which shows the measurement result at the time of employ | adopting the connection structure which concerns on the signal wire | line of this invention. The figure which shows the connection structure using the cover member of this invention. The figure which shows the measurement result at the time of employ | adopting the connection structure which concerns on the grounding part of this invention. The figure which shows the application example which concerns on the cover member of this invention. The figure which shows the other application example which concerns on the cover member of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Board | substrate 2 Signal electrode 3 Ground electrode 4 Connection parts, such as a wire 5 Connection parts, such as a ribbon 10 Connection member (connection member for grounding)
12 signal connection member 13 lid member 20 connector

Claims (8)

In the connection structure of the high-frequency line that connects the coaxial line and the planar line,
A grounding connection member for electrically connecting a grounding portion of a coaxial line and a grounding electrode of a planar line , and the shape of the grounding portion of the coaxial line from the coaxial line side to the planar line side of the grounding connection member A grounding connection member in which a corresponding through hole is formed and a notch portion substantially parallel to the surface of the ground electrode of the planar line is formed on the plane line side of the grounding connection member, and attached to the notch portion a lid member that is, characterized by comprising a lid member provided with recesses corresponding to the through hole to form a coaxial shape corresponding to the coaxial line when mounted in the missing portion Ri該切the lid member A high-frequency line connection structure.   The high-frequency line connection structure according to claim 1, wherein the ground connection member and the ground electrode of the planar line are connected by bonding means, and a notch portion for avoiding the bonding means is provided in the lid member. A high-frequency line connection structure. In the connection structure of the high-frequency line according to claim 1 or 2, the lid member in accordance with proximity to the planar line side from the coaxial line side, so that the top of the coaxial shape is gradually opened, the plane trackside A connecting structure for a high-frequency line, characterized in that an inclined surface in which the height of the lid member decreases toward the surface is formed.   4. The high frequency line connection structure according to claim 1, wherein a part of the lid member is configured to protrude on the planar line. 5.   5. The high-frequency line connection structure according to claim 1, wherein the planar line is a coplanar line.   6. The high frequency line connection structure according to claim 5, wherein a width between GND and GND of the coplanar line is equal to or less than a GND conductor diameter of the coaxial line.   7. The high-frequency line connection structure according to claim 1, wherein the planar line is a line provided in an optical device for electrical-optical conversion or optical-electrical conversion. Connection structure.   8. The high frequency line connection structure according to claim 7, wherein the optical device is an optical modulator.

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