JP2002196295A - Optical waveguide element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical waveguide element which has broad band frequency characteristics, and a bonding defect and a break of the element which can be caused in a wire bonding job are prevented. SOLUTION: On the back face 1B of a substrate 1 which has an electrooptic effect, for an example, a substrate composed of LiNbO3, a groove 17 of which vertical cross section has an inversed V-shape is formed with, preferably, a sandblast method in a way that the bottom part 17B of the groove is opposed to a signal electrode 4.

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, and more particularly, to a waveguide type optical intensity modulator, phase modulator, and the like used in a high-speed and large-capacity optical fiber communication system.
And an optical waveguide element that can be suitably used for a polarization scrambler and the like.

[0002]

In recent years, with the progress of high-speed, large-capacity optical fiber communication system, as typified by an external modulator, a high speed modulator comprising a LiNbO ₃ having an electro-optical effect from the optical waveguide device employing the substrate Has been commercialized and widely used.

FIG. 1 is a cross-sectional view showing an example of a conventional optical waveguide device used for the above high-speed optical modulator.
The optical waveguide device 10 shown in FIG. 1 includes a substrate 1 having an electro-optical effect, for example, a Z-cut plate of LiNbO _{3 or} the like, and an optical waveguide 2 formed on the main surface 1A side of the substrate 1. Further, a buffer layer 3 is provided on the main surface 1 of the substrate 1, and a signal electrode 4 and a ground electrode 5-1 and 5-2 constituting a modulation electrode are provided on the buffer layer 3.

A groove 7 having a rectangular cross section perpendicular to the length direction is formed on the back surface 1B side of the substrate 1. The inside of the groove 7 is hollow, and has a dielectric constant substantially equal to that of air. This dielectric constant is determined by the LiN
Since the dielectric constant of bO ₃ is smaller than that of bO _3, the high frequency modulation signal applied to the optical waveguide 2 from the signal electrode 4 does not leak to the groove 7 when passing through the substrate 1.

As a result, the high-frequency modulation signal is concentrated on the optical waveguide 2, and even when a high-frequency modulation signal is applied at a high voltage, the signal is efficiently applied to the optical waveguide 2. Therefore, the frequency characteristic of the optical waveguide element 10 is broadened.

[0006]

When the optical waveguide device 10 as shown in FIG. 1 is put to practical use, the optical waveguide device is fixed to a predetermined case, and the high-frequency modulation signal is supplied from an external power source to the signal electrode. Is bonded to the end of the signal electrode. This bonding is generally performed using ultrasonic bonding. However, when bonding is performed using this method, it is necessary to efficiently apply ultrasonic waves to a portion to be bonded.

However, as shown in FIG. 1, in the optical waveguide device 10 having the groove 7 having a rectangular cross section, since the cavity in the groove 7 is relatively large, ultrasonic waves leak into the cavity. In some cases, ultrasonic waves cannot be efficiently applied to a portion to be bonded. For this reason, sufficient bonding strength cannot be obtained,
In some cases, the wire was broken during use.
Also, the applied ultrasonic waves may concentrate on the remaining portion of the substrate, causing cracks in the substrate and causing breakage.

[0008] It is an object of the present invention to provide an optical waveguide device which avoids the above-mentioned problems associated with the wire bonding that occurs in the casing of the optical waveguide device.

[0009]

In order to achieve the above object,
The optical waveguide element of the present invention is made of a material having an electro-optical effect, and has a substrate having a pair of main surfaces facing each other, an optical waveguide formed on one main surface side of the substrate, and the one of the substrates. A dielectric buffer layer and a modulation electrode for controlling a light wave guided in the optical waveguide, and the light wave and the modulation on the other main surface side of the substrate. A groove having an inverted V-shaped cross section perpendicular to the length direction is formed in at least a part of a region where the high frequency modulation signal from the application electrode substantially interacts.

The present inventors have conducted intensive studies in order to have a frequency characteristic that has been broadened as in the prior art and to avoid problems such as damage to the substrate during wire bonding due to the casing.

As a result, in accordance with the present invention, the length of the region on the back surface of the substrate where the light wave guided in the optical waveguide and the high-frequency modulation signal from the signal electrode constituting the modulation electrode substantially interact with each other. By forming a groove having an inverted V-shaped cross section perpendicular to the vertical direction, the high frequency modulation signal does not leak into the cavity of the groove as in the related art, so that the high frequency modulation signal can be concentrated on the optical waveguide. Become like

Further, unlike the conventional groove having a rectangular cross section, the groove has an inverted V-shaped cross section. Therefore, the volume of the hollow portion of the groove decreases, and contradictoryly, the remaining portion of the substrate increases. Therefore, at the time of the above-described ultrasonic bonding, the ratio of the ultrasonic wave leaking into the cavity of the groove decreases, and the ultrasonic wave does not concentrate on a predetermined portion of the substrate. Therefore, wire bonding to the signal electrode can be performed firmly, and breakage of the substrate due to the wire bonding can be effectively prevented.

Since the inverted V-shaped groove of the present invention has a smaller number of hollow portions as compared with the conventional rectangular groove portion, a high-frequency modulated signal is prevented from leaking into the hollow portion to the optical waveguide. The degree of concentration may decrease. In this case, by appropriately adjusting the formation position and the size of the inverted V-shaped groove, the high-frequency modulation signal can be concentrated on the optical waveguide as in the case of forming the conventional rectangular groove. Can be. As a result, high-frequency characteristics equivalent to those of the conventional optical waveguide device can be obtained.

For example, when the modulation electrode constituting the optical waveguide element is composed of a signal electrode and a ground electrode, the bottom corresponding to the top of the inverted V-shaped groove is formed so as to face the signal electrode. Is preferred. The distance between the bottom of the groove and the one main surface of the substrate is 300 μm.
It is preferable to form it as follows.

[0015]

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. FIG. 2 is a perspective view showing an example of the optical waveguide device of the present invention, and FIG. 3 is a cross-sectional view of the optical waveguide device shown in FIG. 2 taken along line II. The same components as those in FIG. 1 are denoted by the same reference numerals.

The optical waveguide device 20 shown in FIGS. 2 and 3 includes a substrate 1 having an electro-optical effect, for example, a Z-cut plate of LiNbO ₃ , and an optical waveguide 2 formed on the main surface 1A side of the substrate 1. It has. Further, the main surface 1 of the substrate 1
The buffer layer 3 is provided on the
A signal electrode 4 and a ground electrode 5 constituting a modulation electrode are provided thereon.
-1, 5-2. An electrode pad 4A for wire bonding is provided at an end of the signal electrode 4.

On the back surface 1B side of the substrate 1, a groove 17 having an inverted V-shaped cross section perpendicular to the length direction is formed. The inside of the groove 17 is hollow, and has a dielectric constant substantially equal to that of air. Therefore, similarly to the conventional optical waveguide device shown in FIG. 1, when the high-frequency modulation signal applied from the signal electrode 4 to the optical waveguide 2 passes through the inside of the substrate 1, it does not leak to the groove 17, and as a result, The high-frequency modulation signal is concentrated on the optical waveguide 2, and the frequency characteristic of the optical waveguide device 20 is broadened.

In FIG. 3, an inverted V-shaped groove 17 is formed.
Are formed such that the bottom 17A corresponding to the apex thereof is opposed to the signal electrode 4. Thereby, the optical waveguide device 20 of the present invention has an inverted V-shaped groove portion having a smaller number of hollow portions as compared with a conventional optical waveguide device having a rectangular cross-sectional groove portion as shown in FIG. Also in this case, it is possible to prevent the leakage of the high-frequency modulation signal to the hollow portion in the groove, concentrate the high-frequency modulation signal on the optical waveguide, and effectively achieve a wider frequency characteristic in the optical waveguide element 20. .

The distance d between the bottom 17A of the groove 17 and the main surface 1A of the substrate 1 is preferably not more than 300 μm, and more preferably not more than 250 μm. This effectively prevents the high-frequency modulation signal from leaking into the cavity of the groove 17 as described above, and
Frequency characteristics can be broadened.

The lower limit of the distance d is preferably 50 μm, and more preferably 100 μm, in consideration of the strength at the time of handling the optical waveguide element.

The above-described inverted V-shaped groove 17 can be formed by a known processing method such as micro-controlled mechanical turning, etching and laser processing. However, it is preferably formed using a sandblast method. According to this sandblasting method, the inverted V-shaped groove can be stably formed with good reproducibility.

FIGS. 4 and 5 schematically show an example of the steps in the case of forming the inverted V-shaped groove 17 by sandblasting. First, as shown in FIG. 4, the optical waveguide 2 is formed on the main surface 1A side of the substrate 1, and the main surface 1A is formed.
After the buffer layer 3 is formed on A, a sheet resist mask 18 having, for example, a thickness of about 100 μm and having an opening 18A at a portion where a groove is to be formed is attached to the back surface 1B where the groove 17 is to be formed.

Next, as shown in FIG. 5, SiC abrasive grains 19 having a diameter of several tens to several hundreds of μm are sprayed, and
Physically scrape the exposed part in. In this case, if the abrasive density in the central portion is increased, this portion is intensively shaved off, so that an inverted V-shaped groove portion 17 as shown in FIGS. 2 and 3 can be formed.

When increasing the abrasive grain density, besides simply increasing the supply amount of the abrasive grains, it is possible to form a state in which the abrasive grain density is increased by spraying fine abrasive grains. Further, the abrasive density can also be increased by increasing the abrasive pressure.

Thereafter, the signal electrode 4 and the ground electrode 5-1,
By forming 5-2, an optical waveguide device 20 as shown in FIGS. 2 and 3 can be obtained.

The substrate 1 is made of LNbO ₃ and L
Examples thereof include iTaO ₃ and PLZT (lanthanum lead titanate zirconate). The optical waveguide 2 can be formed by a Ti diffusion method, a proton exchange method, an ion implantation method, an epitaxial growth method, or the like. Further, for the signal electrodes 3 and 4 and the ground electrodes 5, 6, and 7, A
It can be formed from a metal such as u, Ag, or Cu by a vapor deposition method or a plating method, or by using these in combination.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments. (Example) In this example, an optical waveguide device 20 as shown in FIGS. 2 and 3 was manufactured. The substrate 1 has a width of 2 mm
A Z cut plate of LiNbO ₃ was used. Then, an optical waveguide 2 having a width of about 7 μm was formed on the main surface 1A side of the substrate 1 by a Ti thermal diffusion method. Next, a buffer layer 3 made of SiO ₂ was formed to a thickness of 1.3 μm. Next, as shown in FIG. 4, a sheet resist mask having a thickness of about 100 μm was attached on the back surface 1B of the substrate 1.

Thereafter, SiC abrasive grains having a diameter of 20 μm are sprayed in a beam at a pressure of 245 kPa to form an inverted V-shaped groove 1.
7 was formed. At this time, the supply amount of the SiC abrasive grains at the center is increased, and the main surface 1A of the substrate 1 and the bottom 1 of the groove 17 are increased.
The distance d from 7A was set to 300 μm. Also,
The width W of the opening was about 900 μm, and the length was about 40 mm corresponding to the working length of the electrode.

Next, the plating method and the vapor deposition method are used
The signal electrode 4 and the ground electrodes 5-1 and 5-2 made of u were formed to a thickness of 25 μm to complete the optical waveguide device 20. The frequency characteristics of the thus optical waveguide element 20 was fabricated, and voted transmission attenuation S ₂₁ of the microwave is a high frequency modulated signal, the measurement results for each frequency shown in the curve A in FIG.

Since the groove 17 having a width of about 900 μm is formed, the minimum width of the remaining portion of the substrate is about 50 μm.
Although it was reduced to 0 μm, no bonding failure and no breakage of the element occurred during wire bonding using ultrasonic waves.

(Comparative Example) In this comparative example, an optical waveguide device having the same shape and the same dimensions was formed in the same manner as described above except that the groove was not formed in the above embodiment. The frequency characteristics of the optical waveguide device fabricated in this manner, the similarly voted transmission attenuation S ₂₁ of the microwave, the measurement results for each frequency shown in curve B of Figure 6.

As is clear from the examples and comparative examples, the optical waveguide device of the present invention having an inverted V-shaped groove has the following features.
Compared with an optical waveguide device having no groove, especially at 35 GHz
In the above frequency z difference can be seen in the growth of S _21. Therefore, it can be seen that the optical waveguide device having the inverted V-shaped groove portion of the present invention has a wider frequency characteristic and can prevent breakage and bonding failure during wire bonding.

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 optical waveguide device of the present invention, since an inverted V-shaped groove is formed on the back surface opposite to the main surface of the substrate on which the signal electrode and the ground electrode are formed, unlike the conventional case, the frequency is reduced. Along with widening the characteristics,
It is possible to effectively prevent bonding failure and element damage during wire bonding.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a conventional optical waveguide device.

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

FIG. 3 is a cross-sectional view of the optical waveguide device shown in FIG.

FIG. 4 is a process diagram in the case of forming an inverted V-shaped groove by a sandblast method.

FIG. 5 is a view showing a step subsequent to the step shown in FIG. 4;

6 is a graph showing frequency dependence of microwave transmission attenuation S _21.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Optical waveguide 3 Buffer layer 4 Signal electrode 5-1 and 5-2 Ground electrode 7, 17 Groove part 10, 20 Optical waveguide element 18 Sheet resist mask 19 Abrasive grain

 ──────────────────────────────────────────────────の Continuing from the front page (72) Inventor Yuji Yamane 585 Tomimachi, Funabashi-shi, Chiba F-term in the New Technology Research Laboratory, Sumitomo Osaka Cement Co., Ltd. 2H047 KA04 NA02 QA03 RA08 TA13 TA42 2H079 AA02 AA12 BA01 BA02 BA03 CA05 DA03 DA22 EA03 EA08 EB05 HA12

Claims (4)

[Claims] 1. A substrate made of a material having an electro-optic effect and having a pair of main surfaces facing each other, an optical waveguide formed on one main surface side of the substrate, and the one main surface of the substrate Formed thereon, comprising a dielectric buffer layer and a modulation electrode for controlling a light wave guided in the optical waveguide, on the other main surface side of the substrate, the light wave and the modulation electrode An optical waveguide device, wherein a groove having an inverted V-shaped cross section perpendicular to the length direction is formed in at least a part of a region where the high frequency modulation signal substantially interacts. 2. The modulation electrode includes a signal electrode and a ground electrode, and the groove is formed such that a bottom of the groove corresponding to a vertex of the V-shaped cross section faces the signal electrode. The optical waveguide device according to claim 1, wherein: 3. The optical waveguide device according to claim 1, wherein a distance between a bottom of the groove and the one main surface of the substrate is 300 μm or less. 4. The optical waveguide device according to claim 1, wherein said groove is formed by a sand blast method.