JPH10239648A - Waveguide type optical element and optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the wettability to solder to realize stable grounding and to eliminate the occurrence of higher modes by coating proper areas on side faces and the rear face of an electrooptic crystal substrate, whose principal face an optical waveguide is formed, with a metallic film. SOLUTION: With respect to a waveguide-type optical element provided with an optical waveguide 2 formed on a principal face 1a of a substrate 1 consisting of electro-optic crystal and an exciting electrode 33 and an grounding electrode 34 which are provided in the vicinity of this optical waveguide 2, the substrate surface 1a except light input/output end faces of the substrate 1, a part corresponding to a tapered part 33a of the exciting electrode 33 on the opposite face of the principal face 1a, and a part in the vicinity of a feeder part 33b at the edge of this taper part on side faces of the substrate is coated with a metallic film which is to be an extension part 34a of the grounding electrode 34.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveguide type optical element and an optical device used for an optical modulator in optical communication.

[0002]

2. Description of the Related Art A Mach-Zehnder type optical modulator using a lithium niobate (LiNbO ₃ ) crystal substrate, for example, is known as this type of waveguide type optical device.

[0003] In recent years, this device comprising an optical waveguide and a control electrode formed on a lithium niobate crystal substrate has excellent modulation characteristics such as broadband characteristics and small chirping (pulse waveform is hardly distorted). From what you get,
It is widely used in optical communication systems.

FIG. 6 shows a waveguide type optical element used as a conventional Mach-Zehnder type optical modulator, and FIG. 7 shows a waveguide type optical device in which the waveguide type optical element is mounted on a metal housing. In these figures, 1 is a lithium niobate crystal substrate as an electro-optic crystal substrate having pyroelectricity, 2 is an optical waveguide formed on the main surface of the substrate, and a plurality of optical waveguides are formed on the main surface near the optical waveguide. The excitation electrode 3 and the ground electrode 4 which constitute the control electrodes are provided as planar electrodes. Here, a portion near both ends of the excitation electrode 3, which is one control electrode, is a tapered portion 3a, and an edge of the tapered portion 3a is a feeder portion 3b for applying a high-frequency signal.

[0005] A waveguide type optical device 10 as shown in FIG.
A waveguide type optical device is constructed by mounting the device on the metal housing 20 as shown in FIG. The mounting of the optical element 10 on the metal housing 20 is performed by connecting the ground electrode 4 of the flat electrode as the other control electrode.
Is fixed to the metal housing 20 by soldering at the side edge portions. The excitation electrode 3 is connected to the center pin 21a of the RF connector 21 by soldering.

[0006]

The optical modulation at a high frequency of 1 GHz or higher is based on the premise that good electrical frequency characteristics are obtained. Therefore, pure electric modulation such as impedance matching and grounding stability is required. It is necessary to take an optical element configuration and a mounting method thereof in consideration of specific characteristics.

In order to stabilize the ground, it is preferable to connect the ground electrode of the planar electrode formed on the substrate of the waveguide type optical element and the metal housing with as large an area as possible. In the case where the size is reduced, wire bonding is difficult in terms of size, and the resistance of the conductive resin increases at a high frequency due to its resistance, and there is a problem of reliability.

In connection with solder as in the conventional example shown in FIGS. 6 and 7, the portions (crystal surfaces) of the optical element 10 other than the electrodes 3 and 4 have extremely low solder wettability and poor workability. As can be seen from the enlarged sectional view in the circle P of FIG. 7, the solder fusion portion 22 connecting the ground electrode 4 of the flat electrode and the metal housing 20 cannot go around the side surface of the substrate, and the ground electrode 4 and the metal housing There is a problem that reproducibility of the connection of the ground to the ground 20 cannot be obtained. Further, there is a problem that a dip occurs in the transmission characteristic as shown in the high-frequency electric characteristic (frequency characteristic of the transmission power (S ₂₁ )) in FIG. 8 due to the instability of the ground.

Japanese Patent Application Laid-Open No. 5-158002 proposes a structure in which almost the entire optical element is coated with a conductive material to enhance grounding (earth).
Although the problem of the connection workability between the optical element and the metal housing is improved, there is a problem that a high-order mode of microwaves is generated in the feeder portion of the control electrode, and the high-frequency characteristics are significantly deteriorated.

In view of the foregoing, an object of the present invention is to increase the wettability to solder by coating an appropriate region on the side surface and the back surface of an electro-optic crystal substrate having an optical waveguide on the main surface with a metal film. It is another object of the present invention to provide a waveguide-type optical element and an optical device that enable stable grounding and do not generate higher-order modes.

Other objects and novel features of the present invention will be clarified in embodiments described later.

[0012]

In order to achieve the above object, a waveguide type optical device according to the present invention comprises an optical waveguide formed on a main surface of a substrate made of an electro-optic crystal, and an optical waveguide provided near the optical waveguide. Having a plurality of control electrodes, the light input / output end surface of the substrate, and a portion corresponding to the tapered portion of the control electrode on the opposite surface of the main surface of the substrate,
Except for a portion of the side surface of the substrate near the feeder portion at the edge of the tapered portion, the surface of the substrate is covered with a metal film.

Further, a waveguide type optical device according to the present invention is a waveguide having an optical waveguide formed on a main surface of a substrate made of an electro-optic crystal, and a plurality of control electrodes provided near the optical waveguide. In a configuration in which the optical element is mounted on a metal housing, the waveguide-type optical element corresponds to a light input / output end surface of the substrate and a tapered portion of the control electrode on a surface opposite to the main surface of the substrate. Except for the portion and the side surface of the substrate, except for a portion near the feeder portion at the edge of the tapered portion, the substrate surface is coated with a metal film, and the metal film is soldered to the metal housing. A waveguide-type optical element is fixed to the metal housing.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the waveguide type optical device and optical device according to the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view of an embodiment of a waveguide type optical device according to the present invention, in which a main surface (upper surface) and a right side surface of a substrate are viewed, and FIG. 3) is a perspective view of the main surface and the left side of the substrate.
The waveguide type optical element 30 shown in these figures has a structure as a Mach-Zehnder type optical modulator, 1 is a lithium niobate crystal substrate as an electro-optic crystal substrate having pyroelectricity, and 2 is a main component of the substrate. An excitation electrode 33 and a ground electrode 34 that constitute a plurality of control electrodes are provided on a main surface near the optical waveguide, which is an optical waveguide formed on the surface 1a.
Here, a portion near both ends of the excitation electrode 33 which is one control electrode is a tapered portion 33a, and an edge of the tapered portion 33a is a feeder portion 33 for applying a high frequency signal.
b.

The extension 34a of the ground electrode 34 is
Extend as a metal film on the left side surface 1b, the right side surface 1c, and the back surface 1d, and cover the substrate surface. However, the optical input / output end faces 1e and 1f, which are both end faces of the substrate 1, are not provided with the extension 34a. Further, the extension 34a is not provided in the region A on each surface of the substrate near the light input / output end surfaces 1e and 1f.
The region A without the metal film also extends to a portion corresponding to the tapered portion 33a on the back surface 1d as shown in the perspective view showing the back surface of the substrate in FIG. That is, no metal film is present on the back surface of the substrate facing the tapered portion 33a with the substrate 1 interposed therebetween. Further, as shown in FIG. 3, the extension portion 34a is not provided in a region B of the left side surface 1b which is a portion near the feeder portion 33b at the edge of the tapered portion.

In the main surface 1a of the substrate 1, a gap G between the excitation electrode 33 and the ground electrode 34 is an inter-electrode gap G, which is a portion having no metal film.

The method of manufacturing the optical waveguide 2, the excitation electrode 33, the ground electrode 34 and the extension 34a thereof is carried out, for example, by the following steps.

First, a Ti film having a thickness of 800 angstroms and a width of 6 μm is formed on a main surface of a z-cut LiNbO ₃ substrate (for example, a diameter of 3 inches and a thickness of 0.5 mm) by vacuum evaporation and lift-off for 7.5 hours 1050. The optical waveguide 2 is formed by thermal diffusion in dry -O ₂ at ° C.

Next, after depositing SiO ₂ on the main surface of the substrate at a thickness of 1 μm, an undercoat film is formed in the order of 50 nm for Cr and 50 nm for Au, and then a guide resist (coated on a portion not requiring electrolytic plating) is formed. Then, an Au electrode having a thickness of 15 μm is formed in a portion where the guide resist is not provided.

After removing the guide resist and the underlying film underlying the guide resist by etching, the guide resist is cut into a predetermined substrate 1 shape.
Polish the end face.

Then, the light input / output end faces 1e, 1f of the substrate 1
Polished end surface, the main surface 1a on which the electrodes are formed, the region A (the back surface portion corresponding to the tapered portion, etc.), and the region B
After applying a photoresist (applied to the unnecessary portion of the electroless plating) with a brush (a portion near the feeder portion at the tapered edge of the left side surface 1b), the resist is immersed in an electrolytic solution to perform electroless Ni plating. By peeling off, the waveguide type optical device of FIGS. 1 to 3 can be manufactured.

According to this waveguide type optical device, the extension 34a of the ground electrode 34 formed on the substrate 1 extends as a metal film on the left side 1b, the right side 1c, and the back 1d of the substrate 1 so as to extend to the surface of the substrate. And stable grounding can be performed in a wide area using the metal film portions on the left and right side surfaces, and unnecessary coupling can be avoided.

Further, a portion (that is, region A) of the back surface 1d of the substrate (opposite main surface) corresponding to the tapered portion 33a of the excitation electrode 33, and a portion of the side surface of the substrate near the feeder portion 33b at the edge of the tapered portion. Since the metal film is not formed in (that is, in the region B), generation of a high-order mode of microwaves can be eliminated, and high-frequency characteristics can be maintained well.

FIG. 4 shows an embodiment of a waveguide type optical device in which the waveguide type optical element shown in FIGS. 1 to 3 is mounted on a metal housing. The mounting of the waveguide type optical element 30 on the metal housing 20 is performed by fixing the ground electrode 34 and both side portions of the extension 34a to the metal housing 20 by soldering. The excitation electrode 33 is directly connected to the center pin 21a of the RF connector 21 by soldering.

The soldering of the waveguide type optical element 30 is as follows.
For example, the metal housing 20 may be made of brass, paste solder may be applied to an element fixing portion of the housing 20, and then the element 30 may be placed and heated.

According to this structure, most of both side surfaces of the optical element 30 shown in FIGS. 1 to 3 are covered with the extension portions 34a as the metal film, and the surface of the optical element 30 and the fixing surface of the metal housing 20 are fixed. 4 means that the solder has good wettability. As can be seen from the enlarged sectional view in the circle Q in FIG. And stable grounding properties can be easily obtained. In other words, the workability of the soldering is improved, and the soldering area for connecting the ground electrode 34 and the extension 34a to the metal housing 20 is sufficiently large, and the connection area between the two is sufficiently large, resulting in grounding instability. Inconvenience can be eliminated.

After mounting and fixing the waveguide type optical element 30 to the metal housing 20, high-frequency characteristics as an optical modulator were measured.
Good characteristics with almost no variation (dip) in the transmission characteristics as in ( ₂₁ ) frequency characteristics) were obtained.

Although the embodiments of the present invention have been described above, it is obvious to those skilled in the art that the present invention is not limited to the embodiments and various modifications and changes can be made within the scope of the claims. There will be.

[0030]

As described above, according to the present invention,
It is possible to obtain a waveguide type optical element and an optical device which are excellent in the workability of the mounting and have good high frequency characteristics.

[Brief description of the drawings]

FIG. 1 is a perspective view of an embodiment of a waveguide type optical element according to the present invention, showing a main surface and a right side surface of a substrate.

FIG. 2 is a perspective view of the back surface of the substrate (an opposite surface of the main surface).

FIG. 3 is a perspective view of a main surface and a left side surface of the substrate.

FIG. 4 is a cross-sectional view showing an embodiment of a waveguide optical device according to the present invention.

FIG. 5 is a high-frequency electrical characteristic diagram in the case of an embodiment of a waveguide optical device according to the present invention.

FIG. 6 is a perspective view showing a conventional waveguide type optical element.

FIG. 7 is a cross-sectional view showing a conventional waveguide type optical device.

FIG. 8 is a graph showing high-frequency electric characteristics in a conventional case.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Optical waveguide 3, 33 Excitation electrode 3a, 33a Taper part 3b, 33b Feeder part 4, 34 Ground electrode 10, 30 Waveguide type optical element 20 Metal housing 21 RF connector 22, 32 Solder fusion part 34a Extension part

Claims (2)

[Claims] 1. A waveguide type optical device comprising: an optical waveguide formed on a main surface of a substrate made of an electro-optic crystal; and a plurality of control electrodes provided in the vicinity of the optical waveguide. An output end surface, a portion of the substrate opposite to the main surface corresponding to a tapered portion of the control electrode, and a portion of the substrate side surface except for a portion near a feeder portion at an edge of the tapered portion. A waveguide-type optical element having a surface coated with a metal film. 2. A waveguide type optical element having an optical waveguide formed on a main surface of a substrate made of an electro-optic crystal and a plurality of control electrodes provided near the optical waveguide is mounted on a metal housing. In the waveguide type optical device, the waveguide type optical element includes an optical input / output end face of the substrate and a portion corresponding to a tapered portion of the control electrode on a surface of the substrate opposite to the main surface, Except for a portion near the feeder portion of the tapered portion edge of the substrate side surface,
A waveguide-type optical device, wherein the surface of the substrate is covered with a metal film, and the metal film is soldered to the metal housing to fix the waveguide-type optical element to the metal housing.