JPH06214264A - Waveguide type electrooptical element - Google Patents

Abstract

PURPOSE:To separate buffer layers by each electrode and and to suppress DC drift by forming a thin-film optical waveguide by a proton exchange and heat treatment. CONSTITUTION:This waveguide type electrooptical element has the thin-film optical waveguide 11 formed on an LiNbO3 substrate 10, the buffer layer consisting of an SiO2 film formed thereon, EOG electrodes 13 formed on the buffer layer 12, a linear diffraction grating (LGC) for light input and LGC for light output formed on the surface of the optical waveguide 11 in the state of separating these EOG electrodes 13 from each other with spaces therebetween and a driving circuit for applying a prescribed voltage to the EOG electrodes 13. The thin-film optical waveguide 11 is formed by executing the heat treatment after the proton exchange. The buffer layer 12 is separated by each electrode of the EOG electrodes 13. As a result, the generation of the DC drift is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a thin film optical waveguide having an electro-optic effect and a grid electrode formed on the thin film optical waveguide. The grid light is selectively diffracted according to the voltage applied to the grid electrode. The present invention relates to a waveguide-type electro-optical element configured to do so.

[0002]

2. Description of the Related Art As disclosed in, for example, Japanese Patent Application Laid-Open No. 2-931, a thin-film optical waveguide having an electro-optical effect and an electro-optical diffraction grating (Elec grating) formed on the thin-film optical waveguide are provided.
Lattice-like electrodes that form tro-Optic Gratigs (hereinafter EOG)
(Referred to as an electrode) and a drive circuit that applies a voltage to the EOG electrode, and guides light guided through the optical waveguide,
A waveguide type electro-optical element is known which is configured to selectively diffract according to a voltage applied state to an EOG electrode.

When such a waveguide type electro-optical element is used, when either the diffracted light or the non-diffracted light (0th order light) is used, the used light depends on the presence or absence of diffraction or the degree thereof. Can be modulated. Further, it is possible to configure an optical switch that switches the optical path of the guided light depending on the presence or absence of the diffraction.

By the way, in the above-mentioned waveguide type electro-optical element, a buffer layer made of SiO ₂ or the like is formed between the EOG electrode and the optical waveguide in order to avoid light scattering and light absorption by the EOG electrode. It is necessary.

[0005]

However, in the above-described waveguide type electro-optical element provided with the buffer layer, so-called DC drift, that is, a phenomenon in which the characteristics of the applied voltage and the diffraction efficiency change as the voltage is applied. It is recognized that

As a structure for preventing such DC drift, there has been a conventional Japanese JOURNAL OF APPLIED PHYS.
ICS (Japanese Journal of Applied
Physics) Vol.20, No.4, April, 1981 pp.733〜73
As shown in 7, an optical waveguide type coupler optical modulator in which COBRA type electrodes are formed on two Ti diffusion type channel optical waveguides, and a buffer layer disposed between the COBRA type electrodes and the optical waveguide. There is known a structure in which the buffer layer is separated for each electrode by removing the portion between the electrodes.

This structure is formed on the above-mentioned thin film optical waveguide by E
Although the structure of the optical waveguide and the electrode structure are completely different from the waveguide type electro-optical element in which the OG electrode is formed, a thin film optical waveguide is formed by the Ti diffusion method similarly to the above, and it is tried on it. Although an EOG electrode was formed through a buffer layer separated for each electrode, the effect of suppressing DC drift was not obtained in the waveguide type electro-optical element thus obtained.

The present invention has been made in view of the above circumstances, and an object thereof is to prevent the occurrence of DC drift in a waveguide type electro-optical element formed by forming an EOG electrode on a thin film optical waveguide. It is what

[0009]

A waveguide type electro-optical element according to the present invention comprises a thin film optical waveguide as described above and an EO.
In a waveguide-type electro-optical element including a G electrode and a drive circuit for applying a voltage thereto, the thin film optical waveguide formed by proton exchange and heat treatment is used, while the EOG electrode and the thin film optical waveguide are used. A separate buffer layer is formed between the electrodes.

[0010]

As described above, when the EOG electrode is formed on the Ti diffusion type thin film optical waveguide, even if the buffer layer disposed between the two is separated for each electrode, D
Although the effect of suppressing the C drift cannot be obtained, when the thin film optical waveguide is formed by the proton exchange and the heat treatment as in the above-mentioned configuration, the reason is unknown, but the DC drift is caused by separating the buffer layer for each electrode. Will be suppressed.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on the embodiments shown in the drawings. 2 and 3 are plan and side views, respectively, of a waveguide type electro-optical element according to an embodiment of the present invention. This waveguide type electro-optical element is configured as an optical modulator, and is made of LiNbO ₃
The thin film optical waveguide 11 formed on the substrate 10, the buffer layer 12 formed on the SiO ₂ film, the EOG electrode 13 formed on the buffer layer 12, and the EOG electrode 13 are interposed between the thin film optical waveguide 11 and the buffer layer 12. At a distance from each other, a linear diffraction grating for optical input (Linear Gratig Co
upler: hereinafter referred to as LGC) 14 and light output LGC
15 and a drive circuit 16 for applying a predetermined voltage to the EOG electrode 13.

A modulated light beam 20 is emitted, for example He
A laser light source 21, such as a Ne laser, is provided with an end face 10a of the substrate 10 in which this light beam 20 which is parallel light is obliquely cut.
Through the optical waveguide 11 and is incident on the portion of the LGC 14. As a result, the light beam 20 is diffracted by the LGC 14 and enters the optical waveguide 11, and travels in the optical waveguide 11 in the waveguide mode in the direction of arrow A.

The light beam (guided light) 20 is emitted from the EOG electrode.
Although guided through the portion corresponding to 13, the guided light 20 travels straight when no voltage is applied to the EOG electrode 13. On the other hand, when a predetermined voltage is applied to the EOG electrode 13 from the drive circuit 16, the refractive index of the optical waveguide 11 having the electro-optical effect is changed and a diffraction grating is formed in the optical waveguide 11, and the guided light 20 is diffracted. Diffract by the grating. The light beam 20A diffracted as described above and the non-diffracted light beam 20B
Is diffracted to the substrate 10 side in the LGC 15 and emitted from the obliquely cut end face 10b of the substrate 10 to the outside of the element.

Therefore, if, for example, the light beam 20A emitted outside the device is used as light, the light beam 20A can be modulated according to the presence or absence of voltage application by the drive circuit 16. For example, the light beam 20 is generated based on a predetermined image signal.
When A is modulated, the drive circuit is based on the image signal.
The voltage application by 16 may be controlled.

In this embodiment, an X plate or a Y plate is used as the LiNbO ₃ substrate 10, and the propagation direction of the guided light 20 is the Y axis direction (when the X plate is used) or the X axis direction (Y plate).
When using a board). The guided light 20 is guided in the TE mode. Further, the LiNbO ₃ substrate 10 includes
In order to reduce optical damage, it is preferable to use one doped with MgO or one having a peak at 2.87 μm in terms of OH absorption spectrum.

On the other hand, as the EOG electrode 13, the electrode period Λ is 6.9 μm and 13.8 μm, and the number of electrodes is 20 pairs and 40.
Pair, 80 pairs, electrode length 100 Λ (= 690 μm and 138
0 μm) was prepared in total of 6 ways.

As is apparent from the above description, according to this configuration, it is possible to form an optical switch that switches the optical path of the light beam 20 between two ways.

Here, in the waveguide type electro-optical element of this embodiment, as shown in FIG. 1 which is a sectional view taken along the line BB of FIG. 2, the buffer layer 12 is separated for each electrode of the EOG electrode 13. ing. The thin film optical waveguide 11 is formed by heat treatment after proton exchange. Hereinafter, a method of creating a portion having the above configuration will be described with reference to FIG.

First, the optical waveguide 11 is formed. Pyrophosphoric acid is stored in a platinum crucible and kept at a temperature of 150 ° C., and a LiNbO ₃ substrate is immersed therein for 64 minutes to carry out H ⁺ (proton) exchange (see (1) in FIG. 4). Next, the substrate is washed with water to remove the acid, dried and then heat-treated at 350 ° C. for 1 hour to diffuse H ⁺ to obtain a thin film optical waveguide 11 (see (2) in FIG. 4).

The results of measuring the characteristics of the thin film optical waveguide 11 produced as described above are shown below. The profile of the guided light was measured using a He-Ne laser with a wavelength of 633 nm, and was 1 / e ² diameter was 1.6 μm thick.
Optimal for G. The optical propagation loss is 1 dB / cm
When it is less than 1, the loss is extremely low.

Next, the buffer layer 12 and the EOG electrode 13 are formed. A resist is applied to the surface of the thin film optical waveguide 11 formed as described above, and EO is drawn by electron beam (EB) drawing.
The pattern of the G electrode 13 is formed (see (3) in FIG. 4). Next, development is performed (see (4) in FIG. 4), then SiO ₂ is sputtered to a thickness of 50 to 100 nm (see (5) in the same figure), and Al is vapor-deposited to a thickness of 100 to 500 nm (see FIG. 5). (6) in the figure), and then lift-off is performed to obtain a buffer layer made of SiO ₂ as shown in (7) in the figure.
An EOG electrode 13 made of Al is formed on the surface 12. By doing so, the buffer layer 12 is separated for each electrode of the EOG electrode 13. The buffer layer 12 may be formed of Al ₂ O ₃ , SiNx, or the like in addition to SiO ₂ described above.

The results of measuring whether or not DC drift occurs in the waveguide type electro-optical element of the present embodiment having the above-mentioned structure will be described below. The waveguide type electro-optical element used for this measurement is one of the above-mentioned six types, that is, the electrode period Λ is 13.8 μm and the number of electrodes is 20 pairs. The measurement is performed by applying a pulse voltage having a pulse width of 50 seconds shown in FIG. 5 (1) to the EOG electrode 13 at a cycle of 100 seconds from the drive circuit 16 and detecting the intensity of the light beam 20A at that time. It was In this case, as shown in (2) of FIG. 5, it was confirmed that the intensity of the light beam 20A changed with the same waveform as the pulse voltage, and no DC drift occurred.

On the other hand, as a comparative example, a Ti diffusion optical waveguide is formed in place of the optical waveguide 11 by the above-mentioned proton exchange,
On top of that, the buffer layer 12 and EOG similar to those in the above-mentioned embodiment are provided.
A waveguide-type electro-optical element formed by layering the electrodes 13 was prepared. In the device of this comparative example, the buffer layer 12 made of SiO ₂ has a thickness of 50 nm and the EOG electrode 13 made of Al.
Has a thickness of 140 nm, and the buffer layer 12 is an EOG electrode
It is separated for each of the 13 electrodes.

The result of the same measurement as described above for the device of this comparative example is shown in FIG. 5 (3). As shown in the figure, in the device of this comparative example, the intensity of the light beam 20A should be maintained in a pulse-like state while the drive voltage is being applied to the EOG electrode 13, but the intensity sharply decreases after the rise. It can be seen that when the drive voltage is turned off, the intensity of the light beam 20A should be instantly reduced to zero, but there is a response delay, and the effect of preventing DC drift is not obtained.

[Brief description of drawings]

FIG. 1 is a sectional view showing a main part of a waveguide type electro-optical element according to an embodiment of the present invention.

FIG. 2 is a plan view of the waveguide type electro-optical element.

FIG. 3 is a side view of the waveguide type electro-optical element.

FIG. 4 is a schematic diagram illustrating a method for manufacturing the above-mentioned waveguide type electro-optical element.

FIG. 5 is a graph showing the results of examining the DC drift occurrence state of the above-mentioned waveguide type electro-optical element together with the element of the comparative example.

[Explanation of symbols] 10 LiNbO ₃ substrate 11 thin film optical waveguide 12 buffer layer 13 EOG electrode 16 drive circuit 20 light beam 20A diffracted light beam 20B non-diffracted light beam

Claims (1)

[Claims] 1. A thin film optical waveguide having an electro-optical effect,
The thin film optical waveguide has a grid electrode formed on the optical waveguide and a drive circuit for applying a voltage to the grid electrode, and guides light guided in a portion corresponding to the grid electrode of the thin film optical waveguide. In a waveguide type electro-optical element that selectively diffracts according to a voltage applied state to a grid electrode, a thin film optical waveguide formed by proton exchange and heat treatment is used. A waveguide type electro-optical element characterized in that a buffer layer separated for each electrode is formed between the waveguide and the waveguide.