JP3731622B2 - Optical waveguide device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical waveguide device that performs guided light control using an electro-optic effect.
[0002]
Optical waveguide devices are attracting attention as key devices indispensable for speeding up and increasing the capacity of optical communications. In order to expand the high-speed communication network, an optical waveguide device having excellent response characteristics for high-frequency signals exceeding 10 GHz and an inexpensive cost is required.
[0003]
[Prior art]
In optical communication, an optical waveguide device such as a modulator or a switch is inserted into a transmission line made of an optical fiber as necessary. An optical waveguide device is an optical functional device in which an optical waveguide having a width of several μm is formed on a surface layer portion of a substrate of an electro-optic material, and then an insulating layer and an electrode made of a conductive film are sequentially provided on the substrate. Used in a state of being housed in a housing.
[0004]
In an optical waveguide device, a coplanar waveguide electrode structure (CPW: CoPlanar Waveguide) or an asymmetric coplanar strip electrode structure (CPS: CoPlanar Strip) is adopted as an electrode structure in order to realize a wide band and low voltage drive. . In both of these structures, a first traveling wave electrode (signal electrode) having a small width and a second traveling wave electrode (ground electrode) having a large width are arranged on the same plane. In the CPW, ground electrodes are provided on both sides of the signal electrode, and in the CPS, a ground electrode is provided on one side of the signal electrode.
[0005]
Optical fibers are connected to both ends of the substrate in the extending direction of the optical waveguide (light propagation direction). For this reason, the connection between the signal electrode and the ground electrode and the external circuit is performed on one end side of the substrate in the width direction of the optical waveguide. In other words, the signal electrode is patterned in a concave shape consisting of a main portion extending along the optical waveguide and a lead portion extending from both ends thereof to the end portion of the substrate in the width direction. And conductively connected. The ground electrode is also extended from the vicinity of the main part of the signal electrode to the end of the substrate for conductive connection with the housing side.
[0006]
[Problems to be solved by the invention]
In the conventional optical waveguide device, when the frequency dependence (frequency characteristic) of the optical response characteristic (S ₂₁ ) is measured, a remarkable deterioration (ripple) of the characteristic is observed at a specific frequency within the range of 10 GHz to 20 GHz.
[0007]
An object of the present invention is to provide an inexpensive optical waveguide device having good frequency characteristics.
[0008]
[Means for Solving the Problems]
As a cause of the ripple, power loss due to resonance can be considered. In order to prevent resonance, it is effective to strengthen the setting of the reference potential (so-called grounding), that is, to increase the size of the grounding conductor. In a general printed circuit, a method is used in which grounding is strengthened by providing a solid electrode on the back surface of a substrate and connecting the front wiring pattern with a through-hole. However, in an optical waveguide device, it is extremely difficult to form a through hole in a substrate made of an electro-optic material, and providing a solid electrode on the back surface also causes a significant increase in cost. From these things, in order to reduce a ripple, grounding is strengthened by connecting the ground electrode on a board | substrate with an external conductor.
[0009]
As a connection method, a crimping (bonding) of a jumper conductor such as a ribbon or a wire is preferable in terms of cost. In order to obtain a sufficient grounding state with less crimping of the jumper conductor, the crimping part was searched. Thereby, it was found that the vicinity of the bent portion of the signal electrode (both ends of the main portion) is optimal. In order to minimize the length of the jumper conductor, it is desirable to place the outer conductor as close as possible to the crimping position on the ground electrode.
[0010]
If the ground electrode is connected to the external conductor in the vicinity of either one of both ends of the main portion of the signal electrode, desired characteristics may be obtained. However, in terms of mass productivity, it is more advantageous to connect the ground electrode to the external conductor in the vicinity of both ends of the main part than to check whether one of the connections is effective. In addition, it is possible to connect a wide area over the entire length of the main part of the ground electrode and the external conductor using a wide jumper conductor.
[0011]
The device of the invention of claim 1 is a substrate of an electro-optic material having an optical waveguide formed on a surface layer portion, an insulating layer covering the surface of the substrate, a main portion along the optical waveguide, and one end of the main portion; A signal electrode layer comprising a lead portion extending from each of the other ends to the external connection side which is one end side in the width direction of the optical waveguide, and a ground electrode layer having a concave shape in plan view surrounding the signal electrode layer, An optical waveguide device in which a signal electrode layer and a ground electrode layer are formed on the insulating layer, wherein the ground electrode layer is electrically connected to an external conductor by a jumper conductor on a side opposite to the external connection side with respect to the optical waveguide. The jumper conductors are pressure-bonded to the surface of only a total of two bent regions adjacent to one end and the other end of the main portion of the signal electrode layer in the ground electrode layer. It is.
[0012]
In the optical waveguide device according to a second aspect of the present invention, the outer conductor is a housing that houses the substrate.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is an external view of a modulator unit U according to the present invention.
The modulator unit U is composed of a modulator 1 which is an optical waveguide device, a long rectangular pillar-shaped metal casing 2 having a length of several centimeters, and the like, and is included in an optical transmission path composed of optical fibers 3A and 3B. Used when inserted in Two connectors 21 and 22 are attached to the side surface of the housing 2. In use, the modulator 1 and the high-frequency signal source 7 are connected via one connector 21, and the modulator 1 and a termination resistor 8 of about 50Ω are connected via the other connector 21.
[0016]
FIG. 2 is a schematic diagram of the modulator 1. 2A shows the planar shape of the electrode, and FIG. 2B shows the structure of the cross section taken along the line bb in FIG. 2A. FIG. 3 is a cross-sectional view of a main part of the modulator unit U.
[0017]
The modulator 1 includes a substrate 11 made of an electro-optic material, an optical waveguide 12, a signal electrode layer 13, ground electrode layers 14 and 15, and a buffer layer 16. The substrate 11 is a Z-cut LiNbO ₃ crystal. The external dimensions of the substrate 11 are, for example, 1 mm (X) × 60 mm (Y) × 1 mm (Z).
[0018]
The optical waveguide 12 is a Mach-Zehnder type waveguide having a pair of parallel waveguides 121 and 122, and is formed by thermally diffusing titanium in the surface layer portion of the substrate 11. The width of the optical waveguide 12 is about 7 μm. The signal electrode layer 13 and the ground electrode layers 14 and 15 are thick gold films having a thickness of 20 to 30 μm, and are formed by an electrolytic plating method using a gold deposited film (thickness of about 0.2 μm) as a base. . The buffer layer 16 is an insulating layer (thickness of about 1.3 μm) for preventing light absorption by the electrode metal, and is provided so as to cover almost the entire surface of the substrate. The material of the buffer layer 16 is silicon dioxide. In the Mach-Zehnder type waveguide, when an electric field is applied to one of the branch waveguides 1 2 1, the phase of the guided light shifts, and a phase difference is generated between the waveguide light propagating through the other branch waveguide 1 2 2. By combining the guided light beams having different phases, output light having an intensity corresponding to the phase difference can be obtained. The amount of phase shift depends on the applied voltage and the length (electrode length) L of the signal electrode layer 13 in the propagation direction M1.
[0019]
The electrode pattern of the modulator 1 in this embodiment is a coplanar waveguide type in which the ground electrode layers 14 and 15 are arranged on both sides of the signal electrode layer 13, and the substrate in the arrangement direction (width direction) M <b> 2 of the splitters 121 and 122. 11 is patterned so as to be connected to an external circuit on one end side (external connection side). That is, the signal electrode layer 13 includes a linear main portion 131 that extends along the branch 121 and a lead-out portion 132 that extends from one end and the other end of the main portion 131 to the end on the external connection side of the substrate 11. Become. The leading end portion of each drawer portion 132 is enlarged to be a connection terminal. The ground electrode layer 14 extends from the vicinity of the main portion 131 to the end on the external connection side, and both end portions of the ground electrode layer 15 are extended to the end on the external connection side. The ground electrode layer 14 is surrounded on three sides by the signal electrode layer 13, and the signal electrode layer 13 is surrounded on the three sides by the ground electrode layer 15.
[0020]
The length L of the main portion 131 of the signal electrode 13 is about 4 mm, and the width w13 is 5 μm. The gap dimension between the main part 131 and each ground electrode layer 14 and 15 is 20 μm. The maximum width w14 of the ground electrode 14 is 655 μm, and the minimum width w15 of the ground electrode 15 is 300 μm. Further, the width of the enormous portion of the lead-out portion 132 is about 200 μm, and the distance between the electrodes at the end of the substrate 11 on the external connection side is about 600 μm.
[0021]
The modulator 1 having the above configuration is housed in the housing 2 and the back surface of the substrate 11 and the inner bottom surface of the housing 2 are joined by an adhesive 90 (see FIG. 3). The optical waveguide 12 is optically joined to an optical fiber (not shown) at both ends, and the signal electrode layer 13 and the ground electrode layers 14 and 15 are electrically connected to external connection terminals (not shown) provided in the housing 2. External connection terminals of the housing 2 are connected to predetermined terminals of the connectors 21 and 22 described above. Connection between the modulator 1 and the external connection terminal of the housing 2 is performed by crimping the gold ribbons 31 to 36. One lead portion 132 of the signal electrode layer 13 is connected to the high-frequency signal source 7 via the gold ribbon 31, and the other lead portion 132 is connected to the termination resistor 8 via the gold ribbon 32. The ground electrode layer 14 is connected to an external ground line via gold ribbons 33 and 34, and the ground electrode layer 15 is connected to an external ground line via gold ribbons 35 and 36, respectively.
[0022]
In order to improve the frequency characteristics in addition to the wiring connection indispensable in such an operation, the modulator 1 includes the ground electrode layer 15 and the housing 2 on the side opposite to the external connection side in the width direction M2. The gold ribbons 37 and 38 are electrically connected by crimping. The gold ribbons 37 and 38 have a width of 500 μm and a thickness of 30 μm.
[0023]
The crimping positions of the gold ribbons 37 and 38 in the ground electrode layer 15 are selected in the bent regions E1 and E2 close to the one end and the other end of the main portion 131 of the signal electrode layer 13, respectively. The size of the crimping surface is about 500 μm × 200 μm. Further, in order to minimize the length of the gold ribbons 37 and 38, the facing distance (see FIG. 3) between the side surface 11s of the substrate 11 and the housing 2 is set to 100 μm or less. As shown in FIG. 3, the housing 2 is composed of a main body 2 a having a step on the inner surface and a lid 2 b that closes the opening. The gold ribbons 37 and 38 are joined to the upper surface of the step portion of the main body 2a.
[0024]
FIG. 4 is a graph showing the frequency characteristics of the modulator 1.
As shown by the solid line in the figure, by connecting the bent regions E1 and E2 of the ground electrode layer 15 to the housing 2, the grounding is strengthened and resonance is suppressed, and the characteristics are gentle in the range of 0 to 20 GHz. Obtained. On the other hand, as indicated by the broken line in the figure, when the connection with the external conductor (housing 2) by the gold ribbons 37 and 38 is omitted, a ripple occurs.
[0025]
According to the above embodiment, since the grounding is strengthened by the same crimping as the wiring for connection to the external circuit, a special process for improving the characteristics is unnecessary, and the cost increase due to the characteristics improvement is minimized. It can be.
[0026]
In the above-described embodiment, the ground electrode 14 may be omitted and an asymmetric coplanar strip electrode structure may be used. When good characteristics are obtained, only one of the bent regions E1 and E2 may be connected to the housing 2. Further, when the reliability of the crimping can be ensured, a wide area extending over the bent shape region E1 and the bent shape region E2 is connected to the housing 2 using a wide jumper conductor (gold ribbon or the like). May be. The present invention can be applied not only to the modulator 1 but also to other optical waveguide devices such as a switch. The substrate material, the shape of each part, dimensional conditions, and the like can be variously changed in accordance with the gist of the present invention.
[0027]
【The invention's effect】
According to the invention of claim 1 or claim 2, it is possible to frequency characteristics can be obtained an optical waveguide device suitable for improved and mass production and low cost good guided light control of the frequency characteristic.
[Brief description of the drawings]
FIG. 1 is an external view of a modulator unit according to the present invention.
FIG. 2 is a schematic diagram of a modulator.
FIG. 3 is a cross-sectional view of a main part of a modulator unit.
FIG. 4 is a graph showing frequency characteristics of a modulator.
[Explanation of symbols]
1 Modulator (optical waveguide device)
2 Housing (outer conductor)
11 Substrate 13 Signal electrode layer 15 Ground electrode layer 16 Buffer layer (insulating layer)
37,38 Gold ribbon (jumper conductor)
121 splitter (optical waveguide)
131 Main part 132 Drawer part E1, E2 Bending shape area

Claims (2)

The substrate of the electro-optic material in which the optical waveguide is formed in the surface layer portion, the insulating layer covering the surface of the substrate, the main portion along the optical waveguide, and one end and the other end of the main portion of the optical waveguide A signal electrode layer including a lead portion extending to the external connection side, which is one end side in the width direction, and a ground electrode layer having a concave shape in plan view surrounding the signal electrode layer, and the signal electrode layer and the ground electrode layer are An optical waveguide device formed on an insulating layer,
The ground electrode layer is electrically connected to the external conductor by a jumper conductor on the side opposite to the external connection side with respect to the optical waveguide,
The optical waveguide is characterized in that the jumper conductor is crimped to the surface of only a total of two bent regions adjacent to one end and the other end of the main part of the signal electrode layer in the ground electrode layer. device. The optical waveguide device according to claim 1 , wherein the outer conductor is a housing that houses the substrate .

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