JPH10132513A - Optical waveguide type displacement detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical waveguide type displacement detecting device which can accurately measure displacement without being affected by the inclination of a testpiece even in the case where the testpiece is inclined to an incident light. SOLUTION: Light emitted from a light source 1 is converged on a testpiece surface 4 by a converging optical system 3. Light reflected from the testpiece surface 4 is guided into the first and the second double mode channel waveguides 6, 7. The size of a deviation in the distribution of the electric field strength of the light severally propagated in the first and the second double mode channel waveguides 6, 7 is detected by detecting means 14-19. A difference between the size of the deviation of a propagated light in the first double mode channel waveguide 6 and the size of the deviation of the propagated light in the second double mode channel waveguide 7 is obtained by a subtracting means 20. In this case, the optical axis of the reflected light is arranged so that it may be located between the incident end face of the first double mode channel waveguide 6 and the incident end face of the second double mode channel waveguide 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a displacement detecting device for measuring a vertical displacement of a surface of a sample such as an optical pickup. The present invention particularly relates to a displacement detection device utilizing a mode interference phenomenon of a double mode optical waveguide.

[0002]

2. Description of the Related Art A laser scanning mode interference microscope has been proposed which observes a step on a sample surface and a change in reflectivity by utilizing mode interference in a double mode optical waveguide (for example, Japanese Patent Application Laid-Open No. H11-163, 1988).
H. OKI and J.M. Iwasaki, Opt
ics communications 85 (199
1) 177). Also, by injecting the light from the condensing optical system at a position slightly deviated from the center of the input end face of the double mode optical fiber, the inclination of the wavefront of the light generated by the condensing optical system is detected, and the There has been proposed a method for measuring a change in the distance of the object. (For example, R. Ju
skaitisand T. Wilson, Appl
ied Optics 31 (1992) 4569).

[0003] In these cases, the length L of the double mode waveguide (fiber) is determined by the perfect coupling length between the even mode and the odd mode (the phase difference between the even mode and the odd mode). Lc = Lc (2m + 1) / 2 (m = 0, 1, 2, 2)
…) It is known that the displacement can be efficiently detected when the length can be expressed by: A mode interference device formed on a substrate for the purpose of measuring the amount of displacement is disclosed in, for example, Japanese Patent Laid-Open No. 4-208.
913 publication.

[0004] FIG. 4 is a diagram showing a double mode waveguide device proposed in Japanese Patent Application Laid-Open No. 4-208913.
FIG. 3 is a schematic diagram of an apparatus that detects a tilt of a wavefront of light generated by a converging optical system and measures a vertical displacement of a sample surface.

As shown in FIG. 4, light emitted from a light source 24 is reflected by a half mirror 25 and condensed on a sample surface 27 by a lens 26. The reflected return light from the sample surface 27 passes through the lens 26 and the half mirror 25 again, and is incident on a position slightly shifted from the center of the incident end face of the double mode channel waveguide 29 formed on the substrate 28. The light of the even mode and the odd mode excited in the double mode channel waveguide 29 by this incident light propagates in the double mode channel waveguide 29 while causing mode interference, and the two channel waveguides 31 in the waveguide branching section 30. , 32,
The two channel waveguides 31 and 32 are excited and propagated. The two photodetectors 33 and 34 disposed at the emission ends of the two channel waveguides 31 and 32 respectively detect the intensity of the light propagating through the two channel waveguides 31 and 32 and convert them into electric signals. Convert. The difference signal between the outputs of the two photodetectors 33 and 34 is obtained by the subtraction circuit 35.

The length L of the double mode channel waveguide 29
Is Lc = Lc (2m + 1) / 2 (m = 0,1,2,2) where Lc is the complete coupling length between the even mode and the odd mode guided in the double mode channel waveguide 29.
…) Is set to the length represented by. Such a length L
In the case where the length of the double mode channel waveguide 29 is set, the asymmetry of the phase of the incident light on the incident end face of the double mode channel waveguide 29 is determined by the branch 30
Can be selectively detected as the asymmetry of the intensity distribution of the propagated light at. That is, the double mode channel waveguide 29
When the phase of the incident light at the incident end surface of the optical waveguide is symmetric with respect to the central axis of the double mode channel waveguide 29,
Since the intensity distribution of the propagating light becomes symmetric in the branching section 30, the intensity of the light distributed to the two channel waveguides 31 and 32 is equal. On the other hand, the double mode channel waveguide 29
When the phase of the incident light at the incident end face of the optical waveguide is asymmetric, the intensity distribution of the propagating light at the branching section 30 becomes asymmetric, so that the intensity of light distributed to the two channel waveguides 31 and 32 is A difference corresponding to the phase asymmetry is generated.

FIGS. 6 (a), 6 (b) and 6 (c) show the reflected return light 3 near the incident end face of the double mode channel waveguide 29. FIG.
FIG. 9 is an explanatory diagram schematically illustrating a state in which a light beam 9 is incident. FIG.
In (a), (b) and (c), the curve in the reflected return light 39 represents the wavefront at that position. Sample surface 27
Is at the focal position, the wavefront 4 of the reflected return light 39 at the time of reaching the incident end face of the double mode channel waveguide 29
0 is parallel to the width direction of the incident end face (FIG. 6B).
Therefore, the light intensity distributed to the channel waveguides 31 and 32 at the branch part 30 is equal. The output of the subtraction circuit 35 becomes 0.

On the other hand, when the sample surface 27 is closer to the double mode channel waveguide 29 than the focal position, the wavefront 40 at the time when the sample surface 27 reaches the incident end face of the double mode channel waveguide 29 is reached.
Becomes a curved surface and is inclined with respect to the width direction of the double mode channel waveguide 29 (FIG. 6A). Therefore, the light intensity distributed to the channel waveguides 31 and 32 at the branching unit 30 is not equal, and the output of the subtraction circuit 35 does not become zero.

When the sample surface is farther from the focal position than the double mode channel waveguide 29, the wavefront 40 at the time of reaching the incident end face of the double mode channel waveguide 29 is
6A is inclined in a direction opposite to that in the case of FIG.
(C)). Therefore, the channel waveguide 31,
The light intensity distributed to 32 is not equal, the output of the subtraction circuit 35 does not become 0, and the output of the subtraction circuit 35 has a polarity opposite to that in the case of FIG.

When the output signal of the subtraction circuit 35 is plotted on the vertical axis and the displacement of the sample surface 27 at this time is plotted on the horizontal axis, as shown in FIG. , A curve 38 is obtained which passes through the point where the output signal becomes zero. Therefore, the vertical displacement of the sample surface 27 can be known from the difference signal.

[0011]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Laid-Open No. 4-20
In the configuration of the displacement detection device disclosed in JP-A-8913 or the like, not only when the sample is displaced from the focal position but also when the sample is inclined with respect to the incident light, the wavefront of the reflected light is inclined. However, the conventional displacement detection device cannot distinguish between the inclination of the wavefront of the reflected light due to the displacement of the sample from the focal position and the inclination of the wavefront of the reflected light due to the inclination of the sample itself. Therefore, when the sample is inclined with respect to the incident light, the output of the subtraction circuit includes an output component due to the displacement of the sample surface and an output component due to the inclination of the sample surface, and the displacement is accurately detected. There was a problem that it was not possible.

SUMMARY OF THE INVENTION The present invention solves such a problem, and enables an optical waveguide type displacement to accurately measure the displacement amount without being affected by the inclination of the sample even when the sample is inclined with respect to the incident light. It is an object to provide a detection device.

[0013]

In order to solve the above problems, the present invention provides the following displacement detecting device. That is, a light source, a condensing optical system for condensing light emitted from the light source on a sample surface, and first and second double-mode channel waveguides for transmitting light reflected on the sample surface, respectively. Detecting means for detecting the magnitude of the deviation of the electric field intensity distribution of the light propagating through the first and second double mode channel waveguides; and detecting the magnitude of the deviation of the first double mode channel waveguide detected by the detecting means. Subtraction means for calculating a difference between the magnitude of the bias of the propagating light and the magnitude of the bias of the propagating light of the second double-mode channel waveguide, wherein the first and second double-mode channel waveguides each include: An incident end face for allowing the reflected light to enter, and an optical axis of the reflected light, the incident end face of the first double mode channel waveguide, and the incident end face of the second double mode channel waveguide. It is an optical waveguide type displacement detector, characterized in that located between.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical waveguide type displacement detecting device according to an embodiment of the present invention will be described with reference to the drawings.

As shown in FIG. 1, first and second double-mode channel waveguides 6 and 7 are formed on a Si substrate 5 in parallel at a predetermined interval. The incident ends of the double mode channel waveguides 6 and 7 are exposed on the side surface of the substrate 5. The other ends of the double mode channel waveguides 6 and 7 are connected to branch portions 8 and 9 for branching the propagated light into two, respectively. In the branch part 8,
Channel waveguides 10 and 11 are connected. Branch 9
Are connected to channel waveguides 12 and 13. The emission ends of the channel waveguides 10, 11, 12, and 13 are arranged so as to be exposed on the side surfaces of the substrate 5, and silicon photodiodes 14, 15, 16, and 17 are attached thereto.

The double mode channel waveguides 6, 7, the branch portions 8, 9, and the channel waveguides 10, 11, 12,.
Reference numeral 13 is formed by patterning the SiO ₂ layer to which Ge is added into these shapes. They are,
As shown in FIG. 7, a lower clad layer 101 composed of SiO ₂ formed on the substrate 5, it is disposed between the upper cladding layer 102 made of SiO _2.

In the double mode channel waveguides 6 and 7 and the branch portions 8 and 9, the length L in which light is substantially propagated in the double mode is equal to the double mode channel waveguides 6 and 7.
Lc is the complete coupling length between the even mode and the odd mode
L = Lc (2m + 1) / 2 (m = 0, 1, 2,
…) The length is set to satisfy. The double mode channel waveguides 6 and 7 are formed in the same shape. As already known, by setting the lengths of the double mode channel waveguides 6 and 7 to such a length L, asymmetry of the phase of the incident light on the incident end faces of the double mode channel waveguides 6 and 7 is obtained. Characteristic can be selectively detected as the asymmetry of the light intensity in the branch portions 8 and 9, that is, the bias of the electric field intensity distribution of the propagating light.

The substrate 5 is arranged so that the end faces of the double mode channel waveguides 6 and 7 face the sample 4 to be measured. A laser diode 1 having a wavelength of 670 nm, a half mirror 2, an objective lens 3 are provided between the substrate 5 and the sample 4.
Is arranged. The light emitted from the laser diode 1 is reflected by the half mirror 2 and condensed by the objective lens 3 and then radiated to the sample 4 so that the reflected light is
The alignment is performed such that the light passes through the objective lens 3 and the half mirror 2 in order and is irradiated on the center of the region between the double mode channel waveguides 6 and 7 on the side surface of the substrate 5.

The silicon photodiodes 14, 1
5 is connected to a subtraction circuit 18 for obtaining the difference between these output signals. Silicon photodiode 1
A subtraction circuit 19 for obtaining the difference between these output signals is also connected to 6 and 17. To the subtraction circuits 18 and 19, a subtraction circuit 20 for further obtaining the difference between these output signals is connected.

Next, the operation of the optical waveguide type displacement detecting device according to the present embodiment will be described.

The light emitted from the laser diode 1 is
The light is reflected by the half mirror 2, and the sample surface 4 is reflected by the objective lens 3.
Is collected. The reflected return light from the sample surface 4 passes through the objective lens 3 and the half mirror 2 in order, and is incident on the center of the region between the first and second double mode channel waveguides 6 and 7. Thus, the reflected light from the sample surface 4 is incident on the end faces of the first and second double mode channel waveguides 6 and 7, respectively, and excites the double mode waveguides 6 and 7. Light that has propagated through the double mode waveguides 6 and 7 is transmitted to two channel waveguides 10 and 1 at waveguide branch portions 8 and 9 respectively.
1 and the channel waveguides 12, 13 to excite these channel waveguides 10, 11 and 12, 13.

Four channel waveguides 10, 11 and 1
The light propagating through the light emitting elements 2 and 13 is applied to four silicon photodiodes 14, 15 and 1 disposed at the light emitting ends, respectively.
The light intensities are converted into electric signals by the devices 6 and 17.

The first subtraction circuit 18 obtains a difference signal between the outputs of the silicon photodiodes 14 and 15. Further, the second subtraction circuit 19 obtains a difference signal between the outputs of the two silicon photodiodes 16 and 17. Then, the first and second subtraction circuits 18,
The difference signal of the output from 19 is determined.

Here, the change in the magnitude of the output of the subtraction circuit 20 due to the displacement and inclination of the sample surface 4 is shown in FIG.
This will be described with reference to FIG. FIG. 2 shows that reflected return light 21 from the sample surface 4 inclined with respect to the double mode channel waveguides 6 and 7 is incident on the incident end faces of the first and second double mode channel waveguides 6 and 7. It is explanatory drawing which showed the situation. The curve in the reflected return light 21 represents the wavefront at that position.

In FIG. 2B, the sample surface 4 is at the focal position of the objective 3. If the sample surface 4 is not inclined, FIG.
As in (b), the wavefront of the reflected return light 21 at the time of reaching the incident end face is parallel to the width direction of the double mode channel waveguides 6 and 7. Therefore, in the branch portions 8 and 9, the electric field intensity distribution of the propagating light becomes symmetric with respect to the width direction of the waveguide. However, in the case of FIG.
Is inclined, the wavefront 22 of the reflected return light 21 at the time of reaching the incident end face is inclined with respect to the double mode channel waveguides 6 and 7. Therefore, the electric field intensity distribution of the propagation light reaching the branch portions 6 and 7 of the double mode optical waveguides 6 and 7 has asymmetry according to the inclination of the wavefront of the reflected return light due to the inclination of the sample surface 4.

The intensity of the light distributed to the channel waveguides 10 and 11 corresponds to the bias of the electric field distribution of the light when the light propagated through the first double-mode channel waveguide 6 reaches the branch portion 8. I do. The intensity of the light distributed to the channel waveguides 12 and 13 corresponds to the bias of the electric field distribution of the light when the light propagated through the second double-mode channel waveguide 7 reaches the branch portion 9. . Therefore, in FIG. 2B, the light intensity distributed to the channel waveguide 10 is not equal to the light intensity distributed to the channel waveguide 11. Further, the light intensity distributed to the channel waveguide 12 is not equal to the light intensity distributed to the channel waveguide 13. Therefore, the outputs of the subtraction circuits 18 and 19 are not 0.

However, as can be seen from FIG. 2B, the direction and amount of inclination of the wavefront 22 are different for the first double mode channel waveguide 6 and the second double mode channel waveguide 7. The same is true for Therefore, the magnitude of the bias of the electric field distribution of the propagation light reaching the branch portion 8 of the first double mode channel waveguide 6 depends on the electric field of the propagation light reaching the branch portion 9 of the second double mode channel waveguide 7. It is the same as the magnitude of the distribution bias. Therefore, the subtraction circuit 1
The outputs of 8 and 19 are not 0, but the polarities and magnitudes of the outputs are the same.

Accordingly, the output of the subtraction circuit 20, which determines the difference between the outputs of the subtraction circuits 18 and 19, is determined when the sample surface 4 is at the focal position of the objective lens 3 as shown in FIG. It becomes 0 even if 4 is inclined.

When the sample surface 4 is at the focal position of the objective lens 3 and the sample surface 4 is not inclined, the first
The outputs of the subtraction circuit 18 and the second subtraction circuit 19 of FIG.
Since each of them is 0 as in the case of (b), the output of the subtraction circuit 20 is also 0.

Therefore, in the displacement detecting device of FIG. 1 according to the present embodiment, when the sample surface 4 is at the focal position of the objective lens 3, the subtraction circuit can be used whether the sample surface 4 is inclined or not. The output of 20 is zero.

Next, a case where the sample surface 4 is displaced from the focal position to a position closer to the double mode channel waveguide 29 while the sample surface 4 is inclined will be described. At this time, the wavefront 22 of the reflected return light at the time of reaching the incident end faces of the double mode channel waveguides 6 and 7 becomes a curved surface as shown in FIG. Tilts. Therefore, the deviation of the electric field intensity distribution of the propagating light in the branching portions 8 and 9 is obtained by adding the inclination of the wavefront 22 due to the curved surface of the wavefront 22 and the inclination of the entire wavefront 22 due to the inclination of the sample surface 4. Corresponding to things.

At this time, since the direction and magnitude of the inclination of the wavefront 22 caused by the inclination of the sample surface 4 are the same with respect to the double mode channel waveguides 6 and 7, FIG.
As in the case of (b), the polarity and magnitude of the output of the subtraction circuit 18 caused by the inclination of the sample surface 4 are the same as the polarity and magnitude of the output of the subtraction circuit 19.

On the other hand, when the sample surface 4 is shifted from the focal point of the objective lens 3, the inclination of the wavefront 22 due to the wavefront 22 being curved is opposite in the double mode channel waveguides 6 and 7. Become inclined. This is because the optical axis of the reflected return light is aligned so as to be at the center of the region between the double mode channel waveguides 6 and 7. Therefore, the polarity of the subtraction circuit 18 caused by the displacement of the sample surface 4 from the focal point is opposite to the polarity of the output of the subtraction circuit 19.

Therefore, the subtraction circuit 1
When the difference between the output of the sample surface 4 and the output of the subtraction circuit 19 is obtained, the output components due to the inclination of the sample surface 4 cancel each other out to become 0, but the output component due to the displacement of the sample surface 4 from the focal point has a polarity. Are added because they are different.
Output from

Therefore, in the displacement detecting device shown in FIG. 1, when the sample surface 4 is displaced closer to the double mode channel waveguides 6 and 7 than the focal position of the objective lens 3,
Whether the sample surface 4 is inclined or not, the subtraction circuit 2
From 0, an output corresponding to the amount of displacement of the sample surface 4 from the focal point is obtained.

As shown in FIG. 2C, when the sample surface 4 is displaced to the side farther than the focal position of the objective lens 3 from the double mode channel waveguides 6 and 7 while the sample surface 4 is inclined. The wavefront 22 at the time of reaching the incident ends of the double mode channel waveguides 6 and 7 has a curved surface in the opposite direction to the case of FIG. 2A, and the entire wavefront 22 is inclined due to the inclination of the sample surface 4. Also in this case, as in FIG. 2A, the output components of the subtraction circuits 18 and 19 based on the inclination of the sample surface 4 have the same polarity and the same magnitude as each other, but subtraction due to the displacement of the sample surface 4 from the focal point. The output components of the circuits 18 and 19 have opposite polarities. Therefore, the subtraction circuit 20
By calculating the difference between the outputs of the subtraction circuits 18 and 19, the output components due to the inclination of the sample surface 4 cancel each other to become 0, and the output components due to the displacement of the sample surface 4 from the focal point are added to each other. Thus, it is output from the subtraction circuit 20.

Therefore, in the displacement detecting device of FIG. 1, when the sample surface 4 is displaced farther from the double mode channel waveguides 6 and 7 than the focal position of the objective lens 3, the sample surface 4 is inclined. Even when the sample surface 4 is not tilted, an output corresponding to the amount of displacement of the sample surface 4 from the focal point is obtained from the subtraction circuit 20.

The direction of the curved surface of the wavefront 22 in the case of FIG. 2C is opposite to the direction of the curved surface of the wavefront 22 in the case of FIG. Subtraction circuit 20
Is opposite to the polarity of the output of the subtraction circuit 20 in the case of FIG. Thus, similarly to the curve 38 in FIG. 5, a curve is obtained in which the output of the subtraction circuit, the displacement amount, and the direction of the displacement uniquely correspond regardless of the inclination of the sample surface 4.

Furthermore, the above-described displacement detection apparatus can be used to detect the displacement of the sample surface 4 from the focal point even when the amount of inclination of the sample surface 4 is unknown or when the amount of inclination of the sample surface changes during measurement. Only the amount can be accurately detected.

Further, in the displacement detection apparatus of the present embodiment, the output component due to the displacement of the sample among the outputs of the subtraction circuits 18 and 19 is added by the subtraction circuit 20, so that the slope of the curve 38 in FIG. There is also the advantage of becoming.

In this embodiment, since the first and second double mode channel waveguides are arranged close to each other, the first and second double mode channel waveguides 6 are arranged depending on the configuration of the waveguide. , 7 and the channel waveguide 1
Between 1 and 12, there may be cases where optical coupling cannot be ignored. In such a case, grooves are formed in the substrate 5 between the first and second double mode channel waveguides 6 and 7 and between the channel waveguides 10 and 11 along the longitudinal direction of the waveguide. By doing so, it is possible to eliminate optical coupling between the waveguides by the gap formed by the groove.

Next, a second embodiment of the optical waveguide type displacement detecting apparatus according to the present invention will be described with reference to FIG.
In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

In the embodiment shown in FIG. 3, the double mode channel waveguide 6 and the double mode channel waveguide 7 are mounted on independent substrates 5a and 5b, respectively. Then, a half prism 23 for dividing the reflected return light passing through the half mirror 2 into two optical paths is provided. Substrate 5
a and 5b are arranged at positions where the split light enters the double mode channel waveguides 6 and 7, respectively. The optical axes of the divided optical paths are aligned so as to be slightly deviated from the central axes of the double mode channel waveguides 6 and 7, respectively. The direction and amount of shift of the optical axis are such that the shift with respect to the first double-mode channel waveguide 6 and the shift with respect to the second double-mode channel waveguide 7 have opposite shift directions, and the shift amounts are equal. To That is, when the optical axes of the divided optical paths are overlapped, the double mode channel waveguides 6 and 7 are arranged so as to be symmetrical with respect to the overlapped optical axis. This is because the outputs of the subtraction circuits 18 and 19 due to the inclination of the sample surface 4 have the same polarity.

In this configuration, the reflected return light transmitted through the half prism 23 enters a position slightly deviated from the center of the first double mode channel waveguide 6 formed on the substrate 5a. The light reflected by the half prism 23 enters a position slightly deviated from the center of the second double mode channel waveguide 7 formed on another substrate 5b. As a result, as in the first embodiment, the output due to the tilt of the sample is canceled by the subtraction circuit 20, and only the displacement can be measured. Also, in the configuration of FIG.
And the second double mode channel waveguides 6 and 7 are spatially separated from each other, so that the space between the first and second double mode channel waveguides 6 and 7 and the channel waveguide 1
There is no possibility that optical coupling occurs between 1 and 12. Therefore, the range of selection of the substrate and the waveguide material and the range of design values such as the size of the waveguide can be expanded.

The double mode channel waveguides 6, 7
In order to prevent optical coupling between the channel waveguides 11 and 12 from occurring, in the configuration of FIG.
The double mode channel waveguides 6 and 7 are formed on the same substrate 5 with a wide interval, and the optical path of the reflected return light that has passed through the half mirror 2 is divided into two, and one of the optical paths is a double mode channel waveguide. It is also possible to use a deflecting member that causes the light to enter the wave path 6 and the other to enter the double mode channel waveguide 7. In this case as well, the optical axes of the respective optical paths are shifted from the centers of the double mode channel waveguides 6 and 7 as shown in FIG.

Since each of the above-described displacement detection devices can detect the amount of displacement regardless of the inclination of the sample surface, the displacement detection device of the present embodiment measures the deformation of the surface of a semiconductor wafer, for example. Can be used for In a conventional displacement detection device using only one double mode channel waveguide, the tilt direction and tilt amount change complicatedly depending on the sample portion, as in the case where the wafer is wavy and deformed. When measuring an unknown sample, the tilt is detected by adding it to the displacement,
Displacement cannot be measured accurately. However, by using the displacement detection device of the present embodiment,
Since the displacement amount can be detected regardless of the inclination, the wavy deformation of the wafer can be detected with high accuracy. This allows, for example,
The photomask used when exposing the photoresist formed on the semiconductor wafer can be set at an accurate interval in parallel with the semiconductor wafer in consideration of the inclination of the semiconductor wafer. Therefore, a pattern can be formed with high accuracy even when the semiconductor wafer is deformed.

[0047]

As described above, according to the present invention, even when the sample is inclined with respect to the incident light, the displacement amount can be measured accurately without being affected by the inclination of the sample. It is possible to provide a device.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an optical waveguide displacement detection device according to a first embodiment of the present invention.

FIGS. 2A, 2B, and 2C are explanatory diagrams showing wavefronts of reflected return light from a sample surface to double mode channel waveguides 6 and 7 of the optical waveguide type displacement detection device of FIG.

FIG. 3 is a block diagram showing a configuration of an optical waveguide type displacement detection device according to a second embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration of a conventional optical waveguide type displacement detection device.

5 is a graph showing the relationship between the displacement of the sample surface obtained by the optical waveguide displacement detector shown in FIG. 4 and the signal of a subtraction circuit.

6 (a), (b), (c) are explanatory diagrams showing the wavefront of reflected light returning from the sample surface to the double mode waveguide of the optical waveguide displacement detection device shown in FIG.

FIG. 7 is a cross-sectional view taken along the line AA ′ showing a structure of a double mode channel waveguide of the optical waveguide displacement detection device shown in FIG. 1;

[Explanation of symbols]

1 ... Laser diode, 2 ... Half mirror, 3
... Objective lens, 4 ... Sample surface, 5 ... Silicon substrate, 6, 7 ... Double mode channel waveguide,
8, 9 ... branch part, 10, 11, 12, 13 ... channel waveguide, 14, 15, 16, 17 ... silicon photodiode, 18, 19, 20 ... subtraction circuit,
21 ... reflection return light, 22 ... wavefront, 23 ... half prism, 24 ... light source, 25 ... half mirror, 26 ... lens, 27 ... sample surface, 28 ...
.Substrate, 29... Double mode channel waveguide, 30
... branch part, 31, 32 ... channel waveguide, 3
3, 34 photodetector, 35 subtraction circuit, 101
... lower cladding layer, 102 ... upper cladding layer.

Claims (9)

[Claims] 1. A light source, a condensing optical system for condensing light emitted from the light source on a sample surface, and first and second double mode channels for transmitting light reflected on the sample surface, respectively. A waveguide; detection means for detecting the magnitude of the deviation of the electric field intensity distribution of the light propagating through the first and second double mode channel waveguides; and a first double mode channel detected by the detection means Subtraction means for calculating a difference between the magnitude of the deviation of the propagation light of the waveguide and the magnitude of the deviation of the propagation light of the second double mode channel waveguide, wherein the first and second double mode channel waveguides ,
Each has an incident end face for allowing the reflected light to enter, and an optical axis of the reflected light is defined by an incident end face of the first double mode channel waveguide and an incident end face of the second double mode channel waveguide. An optical waveguide type displacement detecting device, which is located between the optical waveguide type displacement detecting devices. 2. An incident end face of the first double mode channel waveguide and an incident end face of the second double mode channel waveguide which are symmetrical with respect to an optical axis of the reflected light. An optical waveguide-type displacement detecting device, wherein 3. The optical waveguide type displacement detecting device according to claim 1, wherein said first and second double mode channel waveguides are formed on the same substrate. 4. The optical waveguide type displacement detecting device according to claim 3, wherein the first double mode channel waveguide is formed in parallel with the second double mode channel waveguide. 5. An optical waveguide according to claim 3, wherein a groove is formed in said substrate between said first double mode channel waveguide and said second double mode channel waveguide. Mold displacement detector. 6. The optical waveguide type displacement detecting device according to claim 1, wherein the first double mode channel waveguide and the second double mode channel waveguide are formed on different substrates, respectively. . 7. The optical system according to claim 1, further comprising a splitting optical system for splitting the reflected light in two directions, wherein an incident end face of the first double mode channel waveguide is:
The split reflected light is disposed at a position where one of the reflected light is incident, and the incident end face of the second double mode channel waveguide is disposed at a position where the other of the divided reflected light is incident and the second The incident end face of the double mode channel waveguide and the incident end face of the second double mode channel waveguide are arranged such that the centers of the respective incident end faces are outside the optical axes of the reflected light divided in the two directions. An optical waveguide type displacement detecting device, which is disposed so as to be positioned. 8. The apparatus according to claim 1, wherein said detecting means comprises: first and second branch portions for branching light propagating through said first and second double mode channel waveguides in two directions, respectively. A photodetector that detects the intensity of light branched in two directions by the first and second branching units, and an output difference between the photodetectors is obtained, so that the light is branched by the first and second branching units. An optical waveguide type displacement detecting device, comprising: a subtraction means for subtracting an intensity difference of the applied light. 9. The structure according to claim 1, wherein the length L of the first double mode channel waveguide is a total coupling length Lc between an even mode and an odd mode guided in the double mode waveguide.
L = Lc (2m + 1) / 2 (m = 0, 1, 2,
..), And the length L of the second double-mode channel waveguide is represented by Lc, where Lc is the perfect coupling length between the even mode and the odd mode guided in the double-mode channel waveguide. Lc (2n + 1) / 2 (n = 0, 1, 2,
…) An optical waveguide type displacement detection device characterized by the following.