JPS60144704A - Thin film type optical element and its manufacture - Google Patents

Abstract

PURPOSE:To obtain high diffracting efficiency with large interaction between a surface acoustic wave and guided light and small RF power by forming a thermally diffused metal layer on the surface of a substrate consisting of a waveguide crystal and implanting proton into the diffused layer thereby forming an optical waveguide layer. CONSTITUTION:The (y) plane or (x) plane of an LiNbO3 crystal substrate 1 which is a (y) plate or (x) plate is polished to the degree of flatness within several Newton rings and is then ultrasonically cleaned by using acetone then pure water. Said plate is dried by the gaseous nitrogen blown thereto. A thin Ti film is deposited by electron beam evaporation on the (y) plane or (x) plane and is thermally diffused in an oxygen a atmosphere to form a thermally diffused Ti layer 8. V, Ni, Au, Ag, Co, Nb, Ge, etc. may be used as the metal to be thermally diffused. Benzoic acid and lithium benzoate are then uniformly mixed and are put into a crucible consisting of alumina. The LiNbO3 crystal substrate having the layer 8 is put into the crucible contg. the benzoic acid and lithium benzoate and is thereafter put into a heating furnace. A proton exchange layer 9 is formed in the layer 8 as a result of an ion exchange treatment.

Description

[Detailed description of the invention] 〔Technical field〕 The present invention relates to a 71 film type optical element.

[Prior art]

An electro-optic (EO) device or an acousto-optic (AO) device of the ie Ifg type optical waveguide type is used in an optical polarizer, an optical modulator, a spectrum analyzer, a correlator, and the like.

As the optical waveguide substrate of the above KO element or AO element,
Lithium niobate (hereinafter referred to as LiNbO3) crystal and lithium tantalate (hereinafter referred to as LiT
pO5) crystals are widely used. A typical method for manufacturing a thin film optical waveguide using one such crystal group is to thermally diffuse titanium (hereinafter referred to as Ti) onto the surface of the crystal substrate at a high temperature. There is a method of completely forming an optical waveguide having a refractive index M slightly larger than the refractive index of the substrate on the surface.

On the other hand, the interaction between the surface acoustic wave excited on the optical waveguide or the electric field on the optical waveguide and the guided light propagating in the optical waveguide increases as the energy distribution of the guided light is confined near the substrate surface. It is said [C,S,
T8ml, IgEg TRANSACTIONSON
CIRCUITS AND SYSTEMS, VOL
CAS-26, 12, 1979].

Therefore, from the viewpoint of the interaction between surface acoustic waves or waveguides and guided light, in the case of an optical waveguide fabricated by thermally diffusing Ti as shown above, the 4-wave light energy is absorbed by the substrate. Since the wave is distributed relatively far from the surface, the interaction between the surface acoustic wave or the electric field and the guided light is weak.In order to achieve highly efficient diffraction of the guided light by the surface acoustic wave, it is necessary to use a surface acoustic wave generation comb. However, in order to strengthen the interaction between the electric field and the guided light, the voltage applied to the EO effect practical electrode must be increased. Was. That is, for example, a Ti film with a thickness of 200X is formed on the surface of a y-plate LINb03 crystal substrate by electron beam evaporation, and
A comb-shaped electrode with a center frequency of 400 M) fz was formed on the optical waveguide which was thermally diffused for 2.5 hours in an oxygen atmosphere at 5°C.
The diffracted light intensity of the first-order diffracted light of the guided light when a 400 MHz RpA power is applied is as shown in Figure 1, and the R1i' i9 power required to reach the maximum total diffracted light intensity is 350. It is large at mW.

However, the wavelength of the guided light is 6328X.

In addition, Ti diffused NbO3 optical waveguide or T
The I-diffused L i TaO5 optical waveguide has the disadvantage that it is easy to receive optical loss + IA, and only a very small amount of light can be introduced. Here, optical damage is defined as [when the intensity of light input to an optical waveguide is increased, the intensity of the light propagated within the optical waveguide and taken out to the outside is proportional to the input light intensity due to scattering. ``a phenomenon in which the growth of a substance ceases to increase.''

[Object of the present invention]

The present invention is based on the above-mentioned conventional technology, and when used as an acousto-optic device, the interaction between surface acoustic waves and guided light is large, and high diffraction assistance can be obtained with a small RF power, and also as an electro-optic device. To provide a thin i13γ type optical transponder which is not only fragile but also has a high optical damage threshold, which can obtain high modulation efficiency with a small voltage applied to the electrodes to obtain the above effect when used as a thermo-optical element. That's true.

The above objects are achieved by forming a gold spider thermal diffusion layer on the surface of a waveguide crystal substrate and injecting 10 tons into the diffusion layer to form an optical waveguide layer.

[Example of the present invention]

Embodiment 'f' of the present invention will be described below with reference to the drawings.

FIG. 2 is a perspective view showing an embodiment of a thin film type AO element according to the present invention. In the figure, l is X plate or y plate ■, 1
A Nb03 crystal substrate, 2 an optical waveguide layer consisting of a titanium diffusion and proton exchange layer, 3 and 4 a grating optical coupler, and 5 a comb-shaped electrode. He Ne with wavelength 6328X
The laser beam 6 is guided into the optical waveguide layer 2 from the grating optical coupler 3, and is diffracted by the elastic surface wave 7 generated by applying RF power to the comb M electrode 5. The light is taken out to the outside by the optical coupler 4.

FIG. 3 is an explanatory diagram of a method for manufacturing the above-mentioned tO film type AO element. First, as shown in FIG. 3(,), after grinding the y-plane or the X-plane of the LiNbO3 crystal substrate 1 of the y-plate or After carrying out the usual ultra-cleaning process, I sprayed it with chlorine gas and dried it. Next, electron beam evaporation is applied to the above y-plane or
1 thin film was completely deposited and thermally diffused at 965° C. for 2.5 hours in an oxygen atmosphere to form a Ti thermally diffused matrix 8 as shown in FIG. 3(b).

Metals to be thermally diffused include V, Ni r Au
tAgrCo, Nb, Ge, etc. may also be used. Next, benzoic acid (C6H5COOH) 94.77
g and lithium benzoate 5.2311 are mixed until homogeneous, and the alumina is mixed. I put it in. Figure 3 (b) is placed in a crucible containing benzoic acid and lithium benzoate.
A LiNbO3 crystal substrate having a Ti diffusion layer 8 of
These were placed in a heat furnace and held at a temperature of 250° C. for 5 hours for ion exchange treatment. As a result, a proton exchange layer 9 was formed in the Ti diffusion layer 8, as shown in FIG. 3(c). .

In forming the proton exchange layer, in addition to the mixed solution of benzoic acid and lithium benzoate, a phase material having a dissociation degree of 10-6 to 10-3 in carbic acid and hydrogen in the carboxyl group of this carbic acid are used to convert lithium into 11! For example, 74 rumitic acid (CH, (C
H2), 4COOH) and lumitin enemy lithium [CH
3 (CI(2), 4COOLi) and a mixture of stearic acid [CH, (CH2), 6COOF() and lithium stearate [OH5(CH2), 60OOLi].

In addition, the molar ratio of the material substituted with lithium is from 1% to 1
Perform within the range of 0%. Ultrasonic cleaning was performed with ethanol, and nitrogen gas was blown to dry.

Next, using normal photolithography techniques, a third
As shown in Figure (d), a comb-shaped city @10 was formed on the proton exchange layer 9.

In the above manufacturing process, the infrared absorption spectrum was measured for the substrate after Ti diffusion shown in Figure 3 (bl).
5 (The absorption of OH groups in the vicinity of 10 cm-' is 0.01.) When the infrared absorption rate was determined for the substrate after the proton exchange treatment shown in Figure 3 (c), 3500
The absorption of the OH group near cm-' was 0.15', confirming that zoloton had entered the crystal.

Next, using the device shown in Fig. 2, we measured the relationship between the It F-power applied to the comb-shaped electrodes N and 4 and the intensity of the V1 light. As in the case, center Jr.
jj i1M number 400 MHz, applied RF
'The power frequency was also set to 400 MHz. The results are shown in FIG. However, the wavelength of the guided light is 6328X. As can be seen from Figure 4, the RF power to obtain the maximum diffraction efficiency is 150 mW, and the T1 diffused LiN
b0. 350 mW when using optical waveguide (Figure 10 Ill@
) is quite small compared to

On the other hand, for optical damage threshold measurement, Ti diffusion L + N
The test was carried out for both the bOs optical waveguide and the L I NbO5 optical waveguide subjected to the proton exchange treatment after Ti diffusion according to the present invention. Laser light guide used for measurement, wavelength 6328X
This is a HeNe laser. In the case of the Ti-diffused LtNbo5 optical waveguide, the i4 power of the output light shown in FIG. 2 is Q,
When the voltage exceeded 1 mV4, an optical damage phenomenon occurred. However, L
In the case of INbO3 optical waveguide, the output light power is 0.5 m
A second embodiment of the present invention will be described with reference to FIG. 5, in which the optical loss phenomenon does not occur up to W/W.

FIG. 5 shows the actual EO element h1! i
It is a perspective view showing an example. In the figure, 1 is an X plate or a Y&LiNbO3 crystal substrate, 2 is an optical waveguide layer consisting of a titanium diffusion and Groton cross layer, 3 and 4 are grating optical couplers, and 11 is a W effect agent comb type '1 model. It is. The laser beam 6 is guided from the grating optical coupler 3 into the optical waveguide layer 2, and the voltage applied to the comb-shaped electrode 11 is ? The diffracted light is diffracted by one round grating formed by adding the light, and the diffracted light is taken out to the outside by the grating optical coupler 4.

The method for manufacturing the thin-rib EO element as described above is the same as that for the Ao element of the first embodiment. It was set in 80 tones and 350 logarithmic pairs. In the case of an optical waveguide layer consisting only of a Tl diffusion layer, the above-mentioned EO effect is put into practice, and the diffraction efficiency is 95 when the voltage applied to the mold electrode is 5V.
% were killed. On the other hand, in the case of the optical waveguide layer in which a proton-pattern layer is formed on the Ti expansion layer of the present invention, the above-mentioned EO effect is put to practical use, and a diffraction efficiency of 95- is obtained when the voltage applied to the mold electrode is 3.6V. It was found that Akane diffraction efficiency can be obtained with low applied voltage.

In addition, the optical waveguide cypress made by Meiji Honto has the above-mentioned A0 element,
It has been found that high modulation efficiency can be obtained with a low applied voltage even for optical elements that utilize the thermo-optical (To) effect, rather than the EO effect.

[Effects of the present invention]

According to the present invention as described above, in the tough film type optical element,
The interaction due to effects such as AO, EO, and To of guided light can be enhanced, the applied frost, pressure, or lζF power may be small, and the threshold of optical damage in the optical waveguide can be increased.

[Brief explanation of drawings]

FIG. 1 and FIG. 4 show the RF A? of the conventional AO element and the present invention, respectively. It is a graph of the relationship between mulberry and diffraction efficiency. Figure 2 is a diagram of the present invention AO Seiko, and Figure 3 (
a) to (d) are congratulatory drawings of the manufacturing process. FIG. 5 is a perspective view of the EO transponder of the present invention. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Optical waveguide, :(, 4... Grating optical coupler, 5, 10.11... Comb-shaped electrode, 8... Ti diffusion layer, 9... Proton Exchange) Zeng.箪・1Figure RF8＞-(mVV) 52Figure 63 Figure

Claims (2)

[Claims] (1) A lithium niobate crystal substrate or a lithium tantalate crystal substrate has an optical waveguide layer in which metal is thermally diffused on the surface thereof, and protons are injected into the optical waveguide layer. Thin film optical element. (2) After thermally diffusing metal onto the surface of a lithium niobate crystal substrate or a lithium tantalate crystal substrate, the crystal substrate is heated to a degree of dissociation of 10-6 to 10 in calginic acid.
The optical waveguide layer is formed on the substrate coating 1n1 by heat-treating the material I in which the hydrogen of the carboxyl group of the carboxylic acid is replaced with lithium on the material 3. A method for manufacturing a thin film optical element.