JPH09197152A - Optical waveguide and optical information detecting device using that - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical waveguide which has less restriction on conditions for the production and acts as a single mode for the one side of linearly polarized light and as a double mode for the other side of linearly polarized light by diffusing a metal in a lithium niobate substrate which is subjected to proton desorption treatment. SOLUTION: A lithium niobate substrate 1 is preliminarily treated to decrease the amt. of proton, namely, subjected to proton desorption treatment to prepare the substrate 1. The crystal direction of the substrate 1 is selected to give a z-cut plane (which means the principal plane is perpendicular to the z-axis of the crystal axis). A Ti film is formed in the form of an optical waveguide on the lithium niobate substrate 1 thus prepared and is patterned by a lift-off method or etching. Then, the lithium niobate substrate 1 with the patterned Ti film is heated in an electric furnace. By heating, Ti atoms in the Ti film is diffused into the lithium niobate substrate, the refractive index in the region 8 where Ti is diffused, is increased higher than the refractive index of lithium niobate, and thus the region 8 is made as an optical waveguide. Then, the end faces of the optical waveguide are polished to complete the optical waveguide.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a single-mode optical waveguide for one linearly polarized light and a double-mode optical waveguide for the other linearly polarized light of two linearly polarized lights having different polarization directions. It relates to a working optical waveguide. The present invention also relates to an optical information detection device that detects information by using such an optical waveguide.

[0002]

2. Description of the Related Art In recent years, optical waveguides have attracted attention in various fields. The reason is that the use of the optical waveguide has the advantages that the size and weight of the optical system can be reduced and the adjustment of the optical axis becomes unnecessary.

Lithium niobate (LiNbO ₃ ) single crystal is widely used as a substrate for producing an optical waveguide.
A Ti diffusion method is widely used as a method for producing an optical waveguide on a lithium niobate substrate. For example, it is described in detail in "Optical integrated circuit" (Nishihara et al., Ohmsha). Specifically, a Ti film is patterned and formed in the shape of an optical waveguide on a lithium niobate substrate, and then the substrate is heated in an electric furnace to diffuse Ti into lithium niobate. T
The region where i is diffused becomes an optical waveguide by increasing the refractive index of the region where Ti is not diffused. The lithium niobate single crystal is a uniaxial crystal and has a refractive index anisotropy depending on the axial direction of the crystal. In the Ti diffused region, the refractive indices of both ordinary rays and extraordinary rays increase.

The optical waveguide is a single-mode optical waveguide in which only zero-order mode light is excited (propagates light in a single mode) due to the difference in refractive index between the optical waveguide and the substrate, the width of the optical waveguide, or the refractive index distribution. And, two mode light of 0th order and 1st order can be excited (propagating light in double mode)
Double-mode optical waveguide and 0th, 1st and 2nd or higher order 3
It is classified as a multimode optical waveguide in which two or more mode lights can be excited (propagating light in multimode). At this time, the double-mode optical waveguide and the multi-mode optical waveguide are not always excited by a plurality of mode lights, but are classified by the maximum number of mode lights excited. For example, only 0th-order mode light may be excited depending on the position and state of light incident on the optical waveguide.

As an application of such an optical waveguide to a completely new field, there is an optical information detecting device utilizing the mode interference phenomenon in the double mode optical waveguide, and it is useful as a useful device in various fields. It is getting attention. Regarding its basic principle and its application to a mode interference type laser scanning microscope, see H. 0oki and J. Iw
asaki, 0pt. Commun. 85 (1991) 177-1
82 and JP-A-4-208913 and JP-A-4-208913.
-296810. Regarding application to an optical pickup, JP-A-4-252444
The details are described in Japanese Patent Publication No.

The above-mentioned mode interference type laser scanning microscope is
An optical waveguide device in which three single-mode optical waveguides are connected to a double-mode optical waveguide via a branching portion is used to detect the tilt and reflectance distribution of an object to be inspected. The illumination light is made incident on the central single-mode optical waveguide among the three single-mode optical waveguides, and is made incident on the double-mode optical waveguide via the branching portion. When the center lines of the central single-mode optical waveguide and the double-mode optical waveguide are aligned, only the zero-order mode of the double-mode optical waveguide is excited. The double-mode optical waveguide irradiates the object to be inspected with the illumination light propagated only in the 0th mode.

Light propagated only in the 0th mode exits from the optical waveguide in the single mode state. Therefore, if there is a step or a distribution of reflectance in the object to be illuminated by such illumination light, the object to be inspected The reflected light from A has an asymmetry that reflects a step or a reflectance distribution. When the reflected light from the object to be inspected is made incident on the double-mode optical waveguide, when the phase distribution of the reflected light is inclined or the intensity distribution is asymmetric, the 0th-order mode and the 1st-order mode are separated. When excited, the interference light of both modes propagates while meandering and is distributed to the three single-mode optical waveguides. By detecting the intensity difference of the light distributed to the single mode optical waveguides on both sides of the three single mode optical waveguides, the symmetry of the reflected light from the object to be inspected can be detected.

Here, 0 which propagates through the double mode optical waveguide
Let Lc be the length at which the phase difference between the second-order mode light and the first-order mode light is 180 ° (complete coupling length), and let L be the length of the region where light can propagate in the double mode in the optical waveguide.

[0009]

When L = Lc (2m + 1) / 2 (m = 0, 1, 2, ...) (1), the information of the phase distribution of the reflected light due to the step of the object to be inspected (phase Information) only detected,

[0010]

## EQU00002 ## When L = mLc (m = 1, 2, 3, ...) (2), information on the amplitude distribution of the reflected light due to the transmittance or reflectance of the object to be measured (amplitude information ) Is detected, and when the length of the double mode region is set to an arbitrary length other than equations (1) and (2), the information of the phase distribution (phase information) and the information of the amplitude distribution (amplitude information) are obtained. Both can be detected at any ratio. This configuration becomes a mode interference system.

Here, the length of the region in which light can propagate in the double mode means the double mode optical waveguide, the branch portion and
In the single-mode waveguide of the book, this is a substantial length that allows light to propagate in a double mode. For example, in a region where three single-mode optical waveguides are close to each other, coupling may occur between the three single-mode optical waveguides, and light may propagate in a double mode in this region. Therefore, the length L of the double mode region described above is defined as the length of light that propagates substantially in the double mode.

Further, a material having an electro-optical effect such as lithium niobate is used for a substrate for forming an optical waveguide, an electrode is arranged in the vicinity of the double mode optical waveguide via a buffer layer, and an electric field is applied from this electrode. By doing so, the length of the above-mentioned perfect bond length is changed. By controlling the voltage applied to the electrodes, the phase information, the amplitude information, and the phase information and the amplitude information of the object to be inspected can be arbitrarily obtained even if the geometric length of the double mode region is constant.

In the mode interference type laser scanning microscope described above, the optical waveguide device is formed so that the center line of the central single mode optical waveguide and the center line of the double mode optical waveguide coincide with each other. The light entering the double mode optical waveguide from the optical waveguide is configured to excite only the 0th mode light in the double mode optical waveguide.

However, it is difficult in the manufacturing process to manufacture an optical waveguide device so that the center line of the central single-mode optical waveguide and the center line of the double-mode optical waveguide completely coincide with each other.

When the optical waveguide is manufactured, if the center line is deviated, the branching region is not symmetrical with respect to the center, or the refractive index distribution of the double mode optical waveguide is deviated, the double In addition to the 0th-order mode light, the 1st-order mode light may be excited in the mode region.
When the first-order mode light is excited, the light emitted from the optical waveguide is not in the single mode state, and therefore it becomes impossible to detect the microscopic tilt of the object to be inspected from the reflected light of the object to be inspected. . Therefore, the optical waveguide device must be manufactured with high accuracy, and the device becomes expensive.

To solve this problem, Japanese Patent Laid-Open No. 6-16
The mode interference laser scanning microscope described in Japanese Patent No. 0718 has a double-mode optical waveguide formed of a material having anisotropy in refractive index, and is a single-mode optical waveguide for polarization of illumination light. For the polarization of the reflected light, it has been proposed to construct a double-mode optical waveguide. Thereby, even if the center line of the single-mode optical waveguide does not completely coincide with the center line of the double-mode optical waveguide, the illumination light can be propagated only in the 0th mode and emitted from the end face.

[0017]

However, the configuration described in Japanese Patent Laid-Open No. 6-160718 described above is a light guide which is single mode for the polarization of the illumination light and double mode for the polarization of the reflected light orthogonal thereto. There are problems that the manufacturing process for manufacturing the waveguide is complicated, the manufacturing conditions are strict, and the manufacturing cost is high.

In the present invention, of two predetermined linearly polarized lights having different polarization directions, one linearly polarized light serves as a single-mode optical waveguide, and the other linearly polarized light serves as a double-mode optical waveguide. An object of the present invention is to provide an optical waveguide which is a waveguide and whose manufacturing conditions are gentle, and an optical information detecting device using such an optical waveguide.

[0019]

In order to achieve the above object, according to the present invention, linearly polarized illumination light having a predetermined polarization azimuth a is propagated only in the 0th mode to an object whose information is to be detected. The linearly polarized light having a predetermined polarization azimuth b different from the polarization azimuth a, which is reflected light from the object to be inspected, is irradiated only toward the 0th mode or 0
An optical waveguide for propagating in a second mode and a first mode,
And a detection means for detecting the symmetry of the reflected light that has propagated through the optical waveguide, wherein the optical waveguide is formed by diffusing a metal into a proton desorption treated lithium niobate substrate. An optical information detecting device is provided.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described.

First, a method of manufacturing the optical waveguide according to the first embodiment of the present invention will be described.

The inventors of the present invention used Ti on a lithium niobate substrate.
In the optical waveguide formed by diffusing light, by using a substrate that has undergone a proton desorption process as the substrate, a double mode waveguide and a single mode waveguide can be produced depending on the polarization azimuth of the incident light under manufacturing conditions that are gentler than before. It has been found that an optical waveguide acting as a waveguide can be obtained.

The manufacturing method will be specifically described below.

As the lithium niobate substrate 1, there is prepared a lithium niobate substrate 1 which has been previously subjected to a treatment for reducing the amount of protons in the substrate 1, that is, a proton desorption treatment.
As the proton desorption treatment, for example, a method of heating the substrate in an atmosphere free of hydrogen ions and hydrogen atoms can be used. In the present embodiment, a lithium niobate substrate (manufactured by Nippon Crystal Optical Co., Ltd.) that has been subjected to a proton desorption treatment in advance is used. It is known that the concentration of protons in the substrate and the absorption coefficient of light are in a proportional relationship, but the above-mentioned substrate used in the present embodiment has an absorption coefficient of light of 0.8 in the wavelength of 2.87 μm. It is 0476 cm ^-1 .

The crystal orientation of the substrate 1 is Z-cut (the main plane is perpendicular to the Z-axis of crystal axes). As shown in FIG. 1, a Ti film 2 is formed in the shape of an optical waveguide on the lithium niobate substrate 1 and patterned by a lift-off method or an etching method. In the present embodiment, since the shape of the optical waveguide to be formed is a straight line and the light propagation direction is the X axis (X propagation) of the crystal axis, the strip-shaped Ti film 2 has the longitudinal direction as the X axis. Form to match.

After that, the lithium niobate substrate 1 on which the Ti film 2 is patterned is heated in an electric furnace. In FIG.
The schematic block diagram of an electric furnace is shown. A heater 4 and a heat insulating material (not shown) are arranged around the quartz tube 3. The lithium niobate substrate 1 on which the Ti film 2 is formed is placed in the quartz tube 3 of this electric furnace and heated at 1000 ° C. for 6 hours. During this heating, dry O ₂ gas is introduced into the quartz tube 3 from the tube 7.

The dry O ₂ gas was used as the atmosphere during heating because the substrate in which the amount of protons in the lithium niobate crystal was small as in the present embodiment, the O ₂ gas containing moisture in the diffusion atmosphere was used. This is because it is known that Li ₂ O does not diffuse out even without using. The details are J
apanese Jounal of Applied Physics Vol. 33 (1
994) pp.L957-L958 Part2, No. 7A A. Koi
de, H. Shimizu and T. Saito.

By heating, as shown in FIG.
Ti of the film 2 diffuses into the lithium niobate substrate,
The refractive index of the region 8 in which Ti is diffused is higher than the refractive index of lithium niobate to form an optical waveguide. Then, the end face of the optical waveguide is polished to complete the optical waveguide.

In the present embodiment, the T arranged on the substrate 1
The thickness of the i-film 2 was set to 200 angstroms, and the width thereof was changed from 0.5 μm to 8.0 μm in increments of 0.5 μm to prepare 10 types of samples (Table 1). The Ti film 2 was diffused by the above method to form the optical waveguide 8.

The wavelengths of the completed 10 kinds of optical waveguides 8 are 0.
The mode order for light of 6328 μm was measured. The measurement was performed by the following procedure. First, a helium neon laser beam is made incident from one end face of the optical waveguide 8 and a near-field image of light emitted from another end face is photographed by a camera. Then, the incident position of light is shifted in the width direction of the optical waveguide 8 and the change in the pattern of the near-field image is observed to confirm the mode of the maximum order to be excited. Therefore, the mode order confirmed using this method is the mode order in the width direction of the waveguide. Table 1 shows the measurement results of the mode orders. Further, when the mode order in the depth direction of the waveguide was separately investigated, it was found that the maximum mode orders were all single-mode waveguides with the 0th-order mode regardless of the polarization direction.

[0031]

[Table 1]

As shown in Table 1, when the width of the Ti film 2 before diffusion is 5.0 μm, 5.5 μm and 6.0 μm, the completed optical waveguide 8 excites the primary mode with respect to the ordinary ray. It was found that a double-mode optical waveguide was formed, and only an 0th-order mode was excited with respect to an extraordinary ray to become a single-mode optical waveguide, and the desired optical waveguide was obtained.

On the other hand, as a comparative example, an optical waveguide prepared by using a substrate not subjected to proton desorption treatment under the same conditions as in the first embodiment except that the width of the Ti film before diffusion was 5 Only in the case of 0.5 μm, the first-order mode is excited for the ordinary ray and becomes the double-mode optical waveguide, and only the zero-order mode is excited for the extraordinary ray and becomes the single-mode optical waveguide.

[0034]

[Table 2]

From the above, according to the manufacturing method of the first embodiment of the present invention using the proton desorption treated lithium niobate substrate, the width of the Ti film 2 before diffusion is 5.0 μm or more and 6.0 μm or less. Of at least 1 μm, the target optical waveguide can be obtained, but in the comparative example using the substrate not subjected to the proton desorption treatment, the T
It can be seen that the target optical waveguide can be obtained only when the width of the i film is 5.5 μm, and the target optical waveguide cannot be obtained when the i film has a deviation of ± 0.5 μm from 5.5 μm. Therefore, when an optical waveguide functioning as a single-mode optical waveguide or a double-mode optical waveguide is to be produced depending on the polarization direction of incident light, by using the lithium niobate substrate that has undergone the proton desorption treatment as in the present invention, Ti An error of at least ± 0.5 μm can be allowed as the width of the film, and the manufacturing conditions can be made gentle.

Next, in the second to fourth embodiments of the present invention, the thickness of the Ti film 2 is changed to form an optical waveguide in the same manner as in the first embodiment, whereby the polarized light of the incident light is polarized. Ti film 2 capable of forming an optical waveguide functioning as a single mode optical waveguide or a double mode optical waveguide depending on the orientation
I investigated the range of width.

In the second embodiment, the Ti film thickness is set to 220 Å, and other optical waveguide manufacturing conditions are the first.
The same as the embodiment.

Table 3 shows the measurement results of the mode orders of the optical waveguide obtained in the second embodiment.

[0039]

[Table 3]

From Table 3, the width of the Ti film 2 before diffusion is 4.5 μm.
m, 5.0 μm, 5.5 μm, 6.0 μm, the obtained optical waveguide becomes a double mode optical waveguide due to the excitation of the first-order mode for ordinary rays and the zero-order mode for extraordinary rays. It can be seen that only the light is excited and becomes the single-mode optical waveguide, which is the desired optical waveguide.

In the third embodiment, the Ti film thickness is set to 240 Å, and the other optical waveguide manufacturing conditions are the same as those in the first embodiment.

Table 4 shows the measurement results of the mode orders of the optical waveguide obtained in the third embodiment.

[0043]

[Table 4]

From Table 4, the width of the Ti film 2 before diffusion is 4.5 μm.
In the case of m, 5.0 μm and 5.5 μm, the obtained optical waveguide excites the first-order mode for ordinary rays and becomes a double-mode optical waveguide, and only the zero-order mode for extraordinary rays. It can be seen that it becomes a single-mode optical waveguide, and the target optical waveguide.

In the fourth embodiment of the present invention, the Ti film thickness is set to 260 Å, and the other optical waveguide manufacturing conditions are the same as those in the first embodiment.

Table 5 shows the measurement results of the mode orders of the optical waveguide obtained in the fourth embodiment.

[0047]

[Table 5]

From Table 5, the width of the Ti film 2 before diffusion is 4.0 μm.
In the case of m, 4.5 μm and 5.0 μm, the obtained optical waveguide excites the first-order mode for ordinary rays and becomes a double-mode optical waveguide, and only the zero-order mode for extraordinary rays. It can be seen that it becomes a single-mode optical waveguide, and the target optical waveguide.

In the above-described first to fourth embodiments and comparative examples, the width of the Ti film in which the intended optical waveguide is obtained and other manufacturing conditions are shown together in FIG. As can be seen from FIG. 8, in the present invention using the substrate subjected to the proton desorption treatment, the target optical waveguide can be obtained with a Ti film width of at least 1 μm even if the thickness of the Ti film is changed. be able to. Therefore, as for the Ti film width, under the manufacturing conditions gentler than the conventional one, the first-order mode is excited for the ordinary ray and becomes the double-mode optical waveguide, and only the zero-order mode is excited for the extraordinary ray and the single-mode is excited. An optical waveguide that becomes an optical waveguide can be manufactured.

As the fifth, sixth, and seventh embodiments, a substrate on which a proton desorption process is performed is used as in the first embodiment, and the main plane of the substrate is perpendicular to the X axis of the crystal axis. Then, the case where the optical waveguide is manufactured so as to propagate light in the Y-axis direction (X-cut Y-propagation) will be described. Fifth,
FIG. 9 shows the manufacturing conditions of the sixth and seventh embodiments and the width of the Ti film on which the desired optical waveguide is obtained.

In the fifth embodiment, the crystal orientation of the lithium niobate substrate is X-cut Y-propagation, and the Ti film thickness is 30.
The thickness was set to 0 Å, and the other optical waveguide manufacturing conditions were the same as those in the first embodiment.

Table 6 shows the measurement results of the mode order of the obtained optical waveguide. In Table 6, the symbol-indicates that no light was guided.

[0053]

[Table 6]

From Table 6, the width of the Ti film 2 before diffusion is 5.5.
In the case of μm, 6.0 μm, and 6.5 μm, the optical waveguide becomes a double-mode optical waveguide by exciting the first-order mode with respect to the ordinary ray, and only the zero-order mode is excited with respect to the extraordinary ray by the single-mode light guide. It turns out that it becomes a waveguide, and it becomes a target optical waveguide.

In the sixth embodiment, the crystal orientation of the lithium niobate substrate is X-cut Y-propagation, and the Ti film thickness is 320.
The thickness is set to angstrom, and the other optical waveguide manufacturing conditions are the same as those in the first embodiment.

Table 7 shows the measurement results of the mode orders of the obtained optical waveguide.

[0057]

[Table 7]

From Table 7, the width of the Ti film 2 before diffusion is 5.5.
In the case of μm, 6.0 μm, and 6.5 μm, the optical waveguide becomes a double-mode optical waveguide by exciting the first-order mode with respect to the ordinary ray, and only the zero-order mode is excited with respect to the extraordinary ray by the single-mode light guide. It turns out that it becomes a waveguide, and it becomes a target optical waveguide.

In the seventh embodiment, the crystal orientation of the lithium niobate substrate is X-cut Y-propagation, and the Ti film thickness is 400.
The temperature was set to angstrom and the heat treatment temperature was set to 1050 ° C. The other optical waveguide manufacturing conditions were the same as those in the first embodiment.

Table 8 shows the measurement results of the mode order of the obtained optical waveguide. However, in this embodiment, the mode order is measured using a semiconductor laser having a wavelength of 0.830 μm.

[0061]

[Table 8]

From Table 8, the width of the Ti film 2 before diffusion is 5.1.
In the case of μm, 5.4 μm, 6.2 μm, and 6.9 μm, the optical waveguide excites the first-order mode for ordinary rays and becomes the double-mode optical waveguide, and excites only the zero-order mode for extraordinary rays. However, it turns out that it becomes a single-mode optical waveguide, and the target optical waveguide.

As can be seen from FIG. 9, in the present invention using the substrate subjected to the proton desorption treatment, even if the thickness of the Ti film or the crystal axis direction of the substrate is changed, the T in the range of at least 1 μm is obtained.
The target optical waveguide can be obtained with the i film width. Therefore, as for the Ti film width, under the manufacturing conditions gentler than the conventional one, the first-order mode is excited for the ordinary ray and becomes the double-mode optical waveguide, and only the zero-order mode is excited for the extraordinary ray and the single-mode is excited. It becomes an optical waveguide, and the desired optical waveguide can be manufactured.

Next, a method of manufacturing an optical waveguide according to another embodiment of the present invention will be described.

The inventors of the present invention used the lithium niobate substrate not subjected to the proton desorption treatment as the optical waveguides functioning as the single mode optical waveguide and the double mode optical waveguide depending on the polarization direction of the incident light, while using the width of the Ti film. We searched for manufacturing conditions that can make the conditions of (4) relatively mild.

As a result, in the lithium niobate substrate not subjected to the proton desorption treatment, at least under the manufacturing conditions of the eighth to eleventh embodiments described in detail below,
It has been found that by keeping the Ti concentration of the optical waveguide as low as possible, the conditions for the Ti width with which the desired optical waveguide can be manufactured tend to become gentle. In the Ti diffusion step, the diffusion depth of Ti depends on the heating time, and the Ti concentration of the optical waveguide depends on the Ti film thickness. Therefore, by reducing the Ti film thickness, the manufacturing accuracy of the width of the Ti film can be moderated. . However, if the Ti film thickness is made too thin, the amount of increase in the refractive index becomes small and the optical waveguide cannot be formed. Therefore, it is necessary to set the thickness appropriately.

First, in the eighth embodiment of the present invention, a lithium niobate substrate not subjected to a proton desorption treatment was used as the substrate 1, and the main plane of the substrate 1 was made perpendicular to the X axis of the crystal axis. A Ti film 2 is formed on the substrate 1 so as to propagate light in the Y axis direction of the crystal axis (X cut Y propagation). The thickness of the Ti film was 400 Å. Then, 11 kinds of samples were prepared in which the width of the Ti film 2 was changed in the range of 2.6 μm or more and 8.5 μm or less as shown in Table 9.

Then, these samples were heated in an electric furnace to diffuse Ti. FIG. 3 is a schematic configuration diagram of an electric furnace used for heating. A heater 4 and a heat insulating material (not shown) are arranged around the quartz tube 3. Quartz tube 3 of this electric furnace
The above sample is put therein and heated at 1000 ° C. for 6 hours.
During this heating, dry O ₂ gas was introduced into the bubbler 5, and about 6
Steam is introduced through warm water 6 at 0 ° C. and introduced into the quartz tube 3 through the tube 7. Thus, the reason why the gas is made to contain water vapor is to prevent out diffusion of Li ₂ O. As a result, the Ti film 2 diffuses into the substrate 1, and the refractive index of the Ti-diffused portion 8 becomes higher than that of lithium niobate as shown in FIG. 2 to form an optical waveguide. afterwards,
The end face of the optical waveguide was polished to complete the optical waveguide.

The maximum mode order excited in the completed optical waveguide was measured. The measurement of the mode order is the same as that of the first embodiment, but the incident light has a wavelength of 0.83.
The semiconductor laser light was 0 μm. Table 9 shows the measured mode orders.

[0070]

[Table 9]

From Table 9, the width of the Ti film before diffusion is 4.1 μm.
m, 4.6 μm, 5.1 μm, 5.4 μm, the first-order mode is excited for extraordinary rays and becomes a double-mode optical waveguide, and only the zero-order mode is excited for ordinary rays and single-mode optical It can be seen that it becomes a waveguide and the desired mode order is obtained.

Further, as the ninth embodiment, the thickness of the Ti film is set to 450 Å, and other manufacturing conditions are as follows.
Table 10 shows the mode orders of the optical waveguide when the same as in the eighth embodiment.

[0073]

[Table 10]

Further, as a tenth embodiment, Ti
Table 11 shows the mode order of the optical waveguide when the film thickness is set to 500 Å and the other manufacturing conditions are the same as those in the eighth embodiment.

[0075]

[Table 11]

FIG. 10 shows the manufacturing conditions of the eighth to tenth embodiments described above and the width of the Ti film from which the optical waveguide of the desired mode order is obtained. Further, FIG. 12 shows a graph showing the relationship between the Ti film width and the permissible range of the Ti film width (the number of types of Ti film width) at which the target mode order is obtained. As is clear from FIGS. 10 and 12, the allowable range of the Ti film width becomes narrower as the Ti film thickness becomes thicker.

Specifically, under the manufacturing conditions of the eighth to tenth embodiments, by setting the Ti film thickness to 500 angstroms or less, an allowable range of the Ti film width of at least 0.4 μm can be obtained. Further, by setting the Ti film thickness to 450 angstroms or less, an allowable range of the Ti film width of at least 1 μm or more can be obtained.

As described above, in the case of using the substrate which has not been subjected to the proton desorption treatment, the allowable range of the width of the Ti film can be made gentler than the conventional one by suppressing the thickness of the Ti film.

Next, as an eleventh embodiment, Ti
Figure 1 shows another manufacturing condition when the film thickness is kept small.
1 will be described.

In the present embodiment, the main plane of the substrate 1 is perpendicular to the Z axis of the crystal axis, and the light propagation direction is parallel to the X axis of the crystal axis (Z cut X propagation). Then, the Ti film thickness is set to 2
I kept it at 20 Å. Ti film width is 3.0μ
Ten kinds of samples as shown in Table 12 were prepared by changing the thickness in the range of m to 8.5 μm. Then, an optical waveguide was prepared in the same manner as in the eighth embodiment, and the mode order was measured. Table 12 shows the results.

[0081]

[Table 12]

As is clear from FIG. 11 and Table 12,
It can be seen that by suppressing the Ti film thickness to 220 Å, the target mode order can be obtained with the Ti film width of 4.5 μm, 5.0 μm, and 5.5 μm, and the allowable range of at least 1 μm can be obtained.

Next, as a twelfth embodiment of the present invention, a mode interference type laser scanning microscope using the optical waveguide manufactured in the above embodiment will be described with reference to FIG.

The mode interference type laser scanning microscope of the twelfth embodiment, as shown in FIG. 5, detects the laser light source 101 for irradiating the object 109 with light and the reflected light from the object 109. The optical waveguide device provided with the photodetectors 114 and 115 is used. In the optical waveguide device, an optical waveguide for propagating the illumination light emitted from the laser light source 101 and the reflected light from the object to be measured 109 is formed on the lithium niobate substrate 103.
Specifically, the main optical waveguide 104 and the main optical waveguide 10
A branch part 113 for branching 4 into three optical waveguides, and three branch optical waveguides 110, 102 connected to the branch part 113,
111 are formed.

The laser light source 101 is a light source for emitting linearly polarized light in the polarization direction a (polarization in the depth direction of the optical waveguide), and is arranged on the end face of the central branch optical waveguide 102.
In the present embodiment, the laser light source 101 has a wavelength of 0.
A 6328 μm semiconductor laser was used. The central branch optical waveguide 102 is formed to be a single mode for linearly polarized light in the polarization direction a emitted from the laser light source 101. The light emitted from the laser light source 101 propagates through the central branch optical waveguide 102 and the main optical waveguide 104, and is irradiated onto the object to be inspected 109 from the end surface 105 of the main optical waveguide.

Between the substrate 103 and the test object 109,
The quarter-wave plate 106, the XY two-dimensional scanning means 107, and the objective lens 108 are arranged in this order, and the linearly polarized light of the illumination light is converted into circularly polarized light and scanned to scan the object 1 to be inspected.
Focus on 09. These optical systems are used for the object 109 to be inspected.
The circularly polarized reflected light from the polarization direction b orthogonal to the illumination light
It also serves as an optical system that converts the light (polarized light in the width direction of the optical waveguide) into linearly polarized light and focuses it on the end surface 105 of the main optical waveguide 104.

The reflected light from the object 109 to be inspected enters from the end face 105 of the main optical waveguide 104, and the main optical waveguide 1
After guiding 04, it is branched into three branch optical waveguides 11
0, 102, 111 are propagated. Branch optical waveguides 110, 1
Reference numeral 11 is configured to serve as a single mode waveguide for light in the polarization direction b. Photodetectors 114, 11
Reference numeral 5 is arranged on the end faces of the branch optical waveguides 110 and 111 on both sides and detects the intensity of light propagating through the branch optical waveguides 110 and 111.

The main optical waveguide 104 is a single-mode optical waveguide for linearly polarized light in the polarization direction a (polarization in the depth direction of the optical waveguide) as described above, but is polarized in the polarization direction b (in the polarization direction of the optical waveguide). For the reflected light that is linearly polarized light of (polarized light), a double-mode optical waveguide is formed. The photodetectors 114 and 115 are connected to a differential detection means 116 for obtaining a difference in light amount. The output signal 117 of the differential detector 116 is input to the control means 118. Further, an XY two-dimensional scanning means 107 is connected to the control means 118 and inputs the position of the light spot to the control means 118. The control means 118 synthesizes the differential signal image of the object 109 to be inspected and displays it on the monitor 119.

Next, the structure of each optical waveguide 104, 110, 102, 111 formed on the substrate 103 will be described in detail.

As the substrate 103, Z-cut X-propagation lithium niobate which had been subjected to a proton desorption treatment was used. The main optical waveguide 104 and the branch optical waveguides 110, 102 and 111 are manufactured by the Ti diffusion method.

The branch optical waveguides 102, 110 and 111 are single mode optical waveguides for both the polarization direction a (extraordinary ray) and the polarization direction b (ordinary ray). Main optical waveguide 1
Reference numeral 04 is a single-mode optical waveguide for the polarization direction a (extraordinary ray), but is a double-mode optical waveguide for the polarization direction b (ordinary ray). Main optical waveguide 10
4 and the branch optical waveguides 102, 110, and 111 can be simultaneously formed by using the manufacturing method of the first embodiment. However, the branch optical waveguide is a single mode optical waveguide for both the polarization direction a (extraordinary ray) and the polarization direction b (ordinary ray) by setting the width of the Ti film 2 to be 2.5 μm or more and 4.5 μm or less. So that

Further, on the substrate 103, the optical waveguide 104,
A manufacturing method for manufacturing 110, 102, and 111 will be specifically described. First, on the lithium niobate substrate 103, a Ti film having a width of 5.5 μm is formed in the region 104 of the main optical waveguide, and in the regions of the branch optical waveguides 110, 102 and 111, a width of 3.
A Ti film of 5 μm is patterned and deposited to a thickness of 200 Å. A well-known lift-off method is used as the patterning method. In this embodiment, since the manufacturing method of the first embodiment is used, the main optical waveguide 10
As a Ti film width for No. 4, an error of ± 0.5 μm can be allowed. Therefore, it can be easily formed by the lift-off method. Next, the lithium niobate substrate is put into the quartz tube 3 in the electric furnace shown in FIG. 4 and heated at a temperature of 1000 ° C. for 6 hours. Dry O ₂ gas is introduced into the quartz tube 3 during this heating.

After that, as a buffer layer, S was formed by the EB vapor deposition method.
An optical waveguide device is completed by depositing an iO ₂ film at 2000 angstroms, depositing Al as an electrode material at 5000 angstroms by the EB vapor deposition method, patterning the shape of the electrodes 112 by the etching method, and polishing both end surfaces of the optical waveguide.

By using such an optical waveguide, both the branch optical waveguide 102 and the main optical waveguide 104 are in the single mode with respect to the illumination light, so that the amount of light can be transferred efficiently. It is sufficient to connect to the branch portion 113 on the substrate 103.
Can be easily formed.

Further, the main optical waveguide 104 is the object 1 to be inspected.
Since it is a double-mode optical waveguide for the reflected light from 09, the differential information of the object to be inspected can be extracted from the reflected light by branching the propagated light to the technical optical waveguides 110 and 111.

Here, the principle by which the differential information of the object to be inspected from the reflected light can be extracted by the mode interference scanning laser microscope of the present embodiment will be further described.

The illumination light emitted from the end surface 105 of the main optical waveguide 104 is linearly polarized light in the depth direction of the optical waveguide as described above, and is converted into circularly polarized light by passing through the quarter wavelength plate 106. , The XY two-dimensional scanning means 107, and then enters the objective lens 108,
9 is focused. Object 109 illuminated by spotlight
If there is an inclination or a gradient of reflectance at one point above, the reflected light of the spot light will have an asymmetric phase distribution inclination or intensity distribution. The reflected light is again reflected by the objective lens 108 and X.
-By passing through the quarter-wave plate 106 again via the Y two-dimensional scanning means 107, the polarized light changes from circularly polarized light to linearly polarized light in the width direction of the optical waveguide orthogonal to the polarization direction at the time of emission of the optical waveguide. Converted and main optical waveguide 1
It is condensed on the end surface 105 of 04.

Here, since the incident end of the optical waveguide 104 behaves like a pinhole, this structure constitutes a confocal laser scanning microscope. When the reflected light of the spot light has a gradient of the phase distribution or an asymmetry of the intensity distribution, the 0th order in the double mode optical waveguide 104 with respect to the extraordinary ray,
When the primary both modes are excited and reach the branch region 113 due to the interference of both modes, the two branch optical waveguides 110, 11
The amount of light distributed to 1 is different. Therefore, the ratio of the optical power reaching the two photodetectors 114, 115 changes.
Therefore, the differential detector 116 causes the two detectors 11 to
By taking the difference signal of the outputs of
It is possible to detect a minute step above or a change in reflectance.

At this time, the length L of the double mode optical waveguide for extraordinary rays is L = Lc (2m + 1) / 2 (m = 0, 1, 2, ...
..) Similarly, when observing the intensity distribution of the object, L = mLc (m = 1, 2, ...). Further, when the length L of the double mode optical waveguide is other than the above, the phase distribution and the intensity distribution of the object can be simultaneously observed at a rate corresponding to the length. This configuration becomes a modal interference system. These matters are described in detail in JP-A-4-208913.

At this time, the above-mentioned length L of the double-mode optical waveguide is determined by adding the length of the main optical waveguide 104 and the length of the portion of the branch 113 where the light propagates in the double mode. It is the length. I mean,
This is because even in the branching portion 113, light can propagate in the double mode in the portion where the waveguides are close to each other.

Further, since the lithium niobate substrate 103 has an electro-optical effect, an electric field is applied from the electrode 112 by using the electrode 112 arranged in the vicinity of the main waveguide 104 with a buffer layer (not shown) interposed therebetween. By doing so, the complete bond length Lc can be changed. Therefore, the above two conditions are satisfied for the same length L of the double mode region by adjusting the voltage applied to the electrode 112. That is, the phase information and the intensity distribution of the object can be independently detected by one optical waveguide device.

By using the optical waveguide as described above, the illumination light always propagates in the main optical waveguide 104 only in the 0th mode. Conventionally, since the first-order mode is not excited, the branch optical waveguide 102 is mechanically highly accurate.
It was necessary to manufacture a connection part between the main optical waveguide 104 and the main optical waveguide 104, but in the ninth embodiment, since both are single mode optical waveguides with respect to the illumination light, there is no fear of excitation of the primary mode, It is sufficient that the amount of light is efficiently delivered. As a result, the branch portion 113 on the substrate 103
Since it can be easily manufactured, the manufacturing cost can be reduced, and an inexpensive mode interference type laser scanning microscope including an optical waveguide capable of propagating illumination light only in the 0th mode can be realized.

Next, as a thirteenth embodiment of the present invention, another configuration of the optical waveguide device which can be used in the mode interference type laser scanning microscope of the twelfth embodiment will be described with reference to FIG. .

In the optical waveguide device of FIG. 6, parts common to those of the optical waveguide device of FIG. 5 have the same numbers. The main optical waveguide 104 of the thirteenth embodiment is the fifth optical waveguide.
The optical waveguide is manufactured by the method for manufacturing an optical waveguide according to the embodiment.

Next, a method of manufacturing the optical waveguides 104, 110, 102 and 111 on the lithium niobate substrate 103 will be described. First, the width of 6.0 μm is formed in the region 104 of the main optical waveguide on the crystal orientation X-cut Y-propagation lithium niobate substrate 103 subjected to the proton desorption treatment.
A Ti film having a width of 4.5 μm is patterned and deposited in the regions of the branch optical waveguides 110, 102, and 111 with a film thickness of 300 angstroms. A well-known lift-off method was used as the patterning method. Next, the lithium niobate substrate is placed in the quartz tube 3 of the electric furnace shown in FIG. 4 and heated at a temperature of 1000 ° C. for 6 hours. Dry O ₂ gas is introduced into the quartz tube 3 during this heating.

After that, as a buffer layer, S was formed by the EB vapor deposition method.
An optical waveguide device is completed by depositing an io ₂ film of 2000 angstrom, depositing 5000 angstrom of Al as an electrode material by EB vapor deposition method, patterning the shape of the electrode by etching method, and polishing both end surfaces of the optical waveguide.

Next, as a fourteenth embodiment of the present invention, an optical waveguide device which can be used in the mode interference type laser scanning microscope of the twelfth embodiment will be described. The optical waveguide device according to the fourteenth embodiment is shown in FIG.
Since the optical waveguide device has the same configuration as that of the optical waveguide device of FIG. The same numbers are used for the parts common to the optical waveguide device of FIG.

The main optical waveguide 104 of the optical waveguide device of the fourteenth embodiment is composed of the optical waveguide manufactured by the optical waveguide manufacturing method of the eighth embodiment.

A method of manufacturing the optical waveguides 104, 110, 102 and 111 on the lithium niobate substrate 103 will be described. First, in the X-cut Y-propagation lithium niobate substrate, which is not subjected to the proton desorption treatment, in the region 104 of the main optical waveguide on the substrate 103, the width is 4.7 μm.
The Ti film is deposited in the regions of the branch optical waveguides 109, 102 and 111 by patterning a Ti film having a width of 3.0 μm with a film thickness of 400 Å. A well-known lift-off method was used as the patterning method. Next, the lithium niobate substrate is placed in the quartz tube 3 of the electric furnace shown in FIG. 3 and heated at a temperature of 1000 ° C. for 6 hours. Dry O ₂ during this heating
The gas is introduced into the bubbler 5, water vapor is introduced through warm water 6 at about 60 ° C., and introduced into the quartz tube 3 from the tube 7.

Since the subsequent manufacturing method is the same as that of the twelfth embodiment, its explanation is omitted.

Next, as a fifteenth embodiment of the present invention, an optical waveguide device which can be used in the mode interference type laser scanning microscope of the twelfth embodiment will be described with reference to FIG.
This will be described with reference to FIG. The same numbers are used for the parts common to the optical waveguide device of FIG.

Main optical waveguide 104 of the fifteenth embodiment
Comprises an optical waveguide manufactured by the optical waveguide manufacturing method of the eleventh embodiment.

A method of manufacturing the optical waveguides 104, 110, 102 and 111 on the lithium niobate substrate 103 will be described. First, a Ti film with a width of 4.5 μm is formed in a region 104 of the main optical waveguide on a substrate 103 of a crystal orientation Z-cut X-propagation lithium niobate substrate not subjected to a proton desorption treatment, and a branch optical waveguide 109, 102, 1
A Ti film having a width of 3.0 μm is patterned and deposited in a thickness of 260 angstroms on the region 11 of FIG. A well-known lift-off method was used as the patterning method. Next, FIG.
The lithium niobate substrate is placed in the quartz tube 3 of the electric furnace shown in, and heated at 1000 ° C. for 6 hours. During this heating, dry O ₂ gas was introduced into the bubbler 5 and was passed through warm water 6 at about 60 ° C. to contain water vapor, and the tube 7 to the quartz tube 3
To be introduced.

Other than that, the configuration, operation, and the like are the same as those of the ninth embodiment, and the description thereof will be omitted.

As described above, according to the present invention, when the optical waveguide is formed on the lithium niobate substrate by the Ti diffusion method, the manufacturing conditions are limited so that the condition of the Ti film width is relaxed and the polarization of light is reduced. It is possible to easily manufacture an optical waveguide that becomes a single mode optical waveguide or a double mode optical waveguide depending on the direction. For example, as in the first to seventh embodiments described above, by using a lithium niobate substrate that has undergone a proton desorption process as the substrate, the conditions for the Ti film width can be made gentle. In addition, for example,
By reducing the Ti film thickness as in the eleventh embodiment, the condition of the Ti film width can be made gentle.

Further, by using the optical waveguide manufactured by such a manufacturing method, as in the twelfth to fifteenth embodiments, in the optical information detecting device for detecting the optical information by using the mode interference, Since light can be propagated and emitted only in the 0th-order mode and reflected light can be propagated in the 0th-order mode and the 1st-order mode, an optical waveguide device that can be easily manufactured can be provided. In the twelfth to fifteenth embodiments described above, specific examples in which some of the first to eleventh optical waveguides are applied to the mode interference laser scanning microscope have been described. It is of course possible to use the other optical waveguides of the embodiment in a mode interference type laser scanning microscope.

In the twelfth embodiment described above, the example in which the optical information detecting device is used in the mode interference type laser scanning microscope has been described, but the optical information detecting device of the present invention is not limited to the microscope. The present invention can be applied to other devices as long as they are devices that detect the phase distribution and amplitude distribution of light using mode interference.

Further, in each of the above embodiments, the light spot is scanned on the object to be inspected by an XY two-dimensional scanner such as a vibrating mirror or a rotating mirror. It is only necessary to move the spot relative to the light spot. Therefore, it is possible to fix the light spot and scan the stage on which the object to be inspected is placed.

[0119]

As described above, according to the present invention, of the two linearly polarized lights having different polarization directions, one linearly polarized light acts as a single mode optical waveguide and the other linearly polarized light acts as a double mode optical waveguide. It is possible to provide an optical waveguide for which the manufacturing conditions are gentle, and an optical information detecting device using such an optical waveguide.

[Brief description of drawings]

FIG. 1 is a perspective view showing one step of a method for manufacturing an optical waveguide of the present invention.

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

FIG. 3 is an explanatory view of an electric furnace used in the method for manufacturing an optical waveguide of the present invention.

FIG. 4 is an explanatory diagram of an electric furnace used in the method for manufacturing an optical waveguide of the present invention.

FIG. 5 is an explanatory diagram showing a configuration of a mode interference type laser scanning microscope according to a twelfth embodiment of the present invention.

FIG. 6 is an explanatory diagram showing a configuration of an optical waveguide device according to a thirteenth to fourteenth embodiments of the present invention.

FIG. 7 is an explanatory diagram showing a configuration of an optical waveguide device according to a fifteenth embodiment of the present invention.

FIG. 8 is an explanatory view showing a method for manufacturing an optical waveguide according to the first to fourth embodiments of the present invention.

FIG. 9 is an explanatory view showing a method for manufacturing an optical waveguide according to fifth to seventh embodiments of the present invention.

FIG. 10 is an explanatory view showing the manufacturing method of the optical waveguide according to the eighth to tenth embodiments of the present invention.

FIG. 11 is an explanatory view showing the manufacturing method of the optical waveguide according to the eleventh embodiment of the present invention.

FIG. 12 shows the number of target optical waveguides (Ti) obtained by the optical waveguide manufacturing methods according to the eighth to tenth embodiments of the present invention.
The kind of width | variety) and the graph which shows the relationship between Ti film thickness.

[Explanation of symbols]

 1, 103 ... Lithium niobate substrate 2 ... Ti film 8 ... Optical waveguide 104 ... Main optical waveguide 102, 110, 111 ... Branch optical waveguide 113 ... Branch portion 112 ... Electrode 101 ... Laser light source 114, 115 ... Photodetector 106 ... Quarter wave plate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masaaki Toi 3 2-3 Marunouchi, Chiyoda-ku, Tokyo Inside Nikon Corporation

Claims (12)

[Claims] 1. A linearly polarized illumination light having a predetermined polarization azimuth a propagates only in the 0th mode and illuminates an object whose information is to be detected, and is reflected light from the object to be inspected. An optical waveguide for propagating linearly polarized light having a predetermined polarization azimuth b, which is different from the polarization azimuth a, only in the 0th-order mode or in the 0th-order mode and the 1st-order mode, and has propagated through the optical waveguide. A detecting means for detecting the symmetry of the reflected light, wherein the optical waveguide is formed by diffusing a metal into a lithium niobate substrate which has been subjected to a proton desorption treatment. Optical information detection device. 2. The substrate according to claim 1, wherein the substrate has a wavelength of 2.
An optical information detection device having an absorption coefficient of 87 μm of 0.05 cm ⁻¹ or less. 3. The optical information detecting device according to claim 1, wherein the metal is Ti. 4. A predetermined polarization direction b different from the polarization direction a in that the maximum mode order that can be excited by linearly polarized light having a predetermined polarization direction a is the 0th mode.
Is an optical waveguide in which the maximum mode order that can be excited by the linearly polarized light is a first-order mode, and is formed by diffusing a metal into a lithium-niobate substrate that has undergone a proton desorption process. Waveguide. 5. A predetermined polarization azimuth b different from the polarization azimuth a in which the maximum mode order that can be excited by linearly polarized light having a predetermined polarization azimuth a is the 0th mode.
Is a method of manufacturing an optical waveguide in which the maximum mode order that can be excited by linearly polarized light is the first-order mode, a Ti film is formed on a proton desorption treated lithium niobate substrate, and the substrate is heat-treated. By so doing, the Ti is diffused into the substrate. 6. The substrate according to claim 5, wherein the main plane of the substrate is perpendicular to the Z axis of the crystal axis, and the Ti film is formed such that the light propagation direction coincides with the X axis of the crystal axis. The heat treatment is performed at 1000 ° C. for 6 hours, and the Ti film has a thickness of 200 Å or more.
A method for manufacturing an optical waveguide, which is 60 angstroms or less and has a width of more than 3.5 μm and less than 6.5 μm. 7. The substrate according to claim 5, wherein the main plane is perpendicular to the X axis of the crystal axis, and the Ti film is formed so that the light propagation direction coincides with the Y axis of the crystal axis. The heat treatment is performed at 1000 ° C. or more and 1050 ° C. or less for 6 hours, and the Ti film has a thickness of 300 Å or more 4
A method for manufacturing an optical waveguide, which has a thickness of 00 Å and a width of more than 5.0 μm and less than 7.0 μm. 8. A predetermined polarization azimuth b different from the polarization azimuth a in that the maximum mode order that can be excited by linearly polarized light of the predetermined polarization azimuth a is the 0th mode.
Is a method for manufacturing an optical waveguide in which the maximum mode order that can be excited by linearly polarized light is the first mode, the thickness of which is 500 angstroms or less on a lithium niobate substrate whose main plane is perpendicular to the X axis of the crystal axis. A band-shaped Ti film is formed so that the longitudinal direction thereof coincides with the Y axis of the crystal axis, and the substrate is heat-treated at 1000 ° C. for 6 hours to diffuse the Ti into the substrate. Method. 9. The method of manufacturing an optical waveguide according to claim 8, wherein the Ti film has a thickness of 500 Å and a width of more than 2.6 μm and less than 4.6 μm. 10. The method of manufacturing an optical waveguide according to claim 8, wherein the Ti film has a thickness of 450 Å and a width of more than 3.7 μm and less than 5.4 μm. 11. The method of manufacturing an optical waveguide according to claim 8, wherein the Ti film has a thickness of 400 Å and a width of more than 3.7 μm and less than 6.2 μm. 12. A predetermined polarization azimuth b different from the polarization azimuth a in that the maximum mode order that can be excited by linearly polarized light of the predetermined polarization azimuth a is the 0th mode.
Is a method for manufacturing an optical waveguide in which the maximum mode order that can be excited by linearly polarized light is a first-order mode, the main plane of which is 220 angstroms thick on a lithium niobate substrate whose crystal plane is perpendicular to the Z axis of the crystal axis. Width is 4.0 μm
A band-shaped Ti film having a size larger than 6.0 μm and having a longitudinal direction aligned with the X-axis direction of the crystal axis is formed, and the substrate is heat-treated at 1000 ° C. for 6 hours to diffuse the Ti into the substrate. A method for manufacturing an optical waveguide, which is characterized by the above.