JP2000065525A - Displacement detecting device and focus detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a displacement detecting device which is constituted by using a double-mode waveguide and able to detect precisely a displacement quantity even if the body to be detected is inclined. SOLUTION: The light from a light source 1 is converged by a convergence optical system 4 on the body 5 to be detected. The light which is reflected by the body 5 to be detected and passes through the convergence optical system 4 is split by a splitting means 6 into 1st and 2nd pieces 105 and 106 of luminous flux. The 1st luminous flux 105 is made incident on a position slightly off the center of a 1st double-mode waveguide 12. The 2nd luminous flux 106 is made incident on the center of a 2nd double-mode waveguide 22. Then 1st and 2nd detecting means 102, 13, 14, 15, 16, 103, 23, 24, 25, and 26 detect the symmetry of intensity distributions of lights propagated through the 1st and 2nd double- mode waveguides 12 and 22.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a focus detection device and a displacement detection device using an optical waveguide.

[0002]

2. Description of the Related Art In recent years, optical waveguides have attracted attention in the fields of optical communication and optical measurement. 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 is not required.

[0003] As one of measuring instruments using an optical waveguide,
A focus detection device has been proposed (JP-A-6-33184).
No. 1). In Japanese Patent Application Laid-Open No. 6-331841, FIG.
As described above, a double mode waveguide is used as an optical waveguide.
When a laser beam is made incident on a double mode waveguide, the zero-order mode and the
The next mode is excited and these two modes interfere in the double mode waveguide. This causes asymmetry in the light intensity distribution at the exit end of the double mode waveguide. JP-A-6-331841 discloses a focus detection device.
By utilizing this property, the positional shift of the focal point is detected by detecting the asymmetry of the light intensity distribution at the end face of the double mode waveguide.

There are two factors that cause the asymmetry of the light intensity distribution in the double mode waveguide, one is the asymmetry of the intensity distribution of the incident laser light, and the other is the asymmetry of the incident laser light. Is the phase asymmetry. By setting the length of the double mode region to an appropriate length, asymmetry due to two elements can be selectively detected (H. Oki and J. Iwasaki, Opt.
ics Communications 85 (199
1) 177). In the focus detection device as shown in FIG. 3, the focus can be detected by setting the length of the double mode region so as to observe the phase distribution of the object.

[0005] The configuration of FIG. 3 will be specifically described. In FIG. 3, a light 302 emitted from a light source 101 is converted into a parallel light by a collimator lens 102, and then becomes a half mirror 10
3 and reflected by the objective lens 104
5 is collected. Light 300 reflected on the test object 105
Passes through the objective lens 104 again and passes through the half mirror 103
And is condensed by the condenser lens 106 on the incident end 107 of the double mode waveguide 111 formed on the substrate 110. The incident end 107 is disposed at the focal position of the condenser lens 106, and furthermore, the optical axis 301 of the reflected light 300.
Are arranged at positions slightly shifted in the width direction from the central axis of the double mode waveguide 111.

When the test object 105 is at the focal position of the objective lens 104, the reflected light 300 is most converged and enters the incident end 107 (FIG. 4B). Therefore, the equal phase plane 401 of the light of the reflected light 300 is parallel to the width direction of the double mode waveguide 111 at the incident end 107, and the phase distribution is symmetrical in the width direction from the center of the double mode waveguide 111. On the other hand, when the test object 105 is shifted from the focal position of the objective lens 104, the reflected light 30
The convergence point of 0 is shifted toward the near side or the far side from the incident end 107 (FIGS. 4A and 4C). Therefore, the incident end 10
7, an equal phase plane 401 of the light spot of the reflected light 300
Is a curved surface, and the phase distribution is asymmetric with respect to the center of the incident end 107.

The length L of the double mode waveguide 111 is a condition for observing the phase distribution of an object. L = L _c (2m + 1) / 2 (m = 0, 1, 2, 2
... However, L _c is set so as to satisfy the perfect coupling length (the length at which the phase difference between the zero-order mode and the first-order mode becomes π). Accordingly, the light propagating through the double mode waveguide 111 is branched into the waveguides 112 and 113, and the intensity distribution thereof is detected by the photodetectors 114 and 115, and the difference is obtained by the differential amplifier 116. The asymmetry at 107 can be detected. The output signal 117 of the differential amplifier 116 has a curve as shown in FIG. 5 with respect to the focal position shift amount.
The position shift of the objective lens 104 from the focal point can be known.

[0008]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Application Laid-Open No. Hei 6-3
The focus detection device described in Japanese Patent No. 31841 obtains a focus error signal by detecting the inclination of the equal phase surface of the reflected light 300 at the incident end 107. However, when the test object 105 itself is tilted as shown in FIG. 6, the reflected light 300 is incident on the incident end 107 from an oblique direction.
For this reason, even if the test object 105 is located at the focal position of the objective lens 104, the equiphase plane at the entrance end 107 is inclined and asymmetric with respect to the center of the entrance end 107, and the output of the differential amplifier 117 does not become 0. For this reason, the relationship between the output 117 of the differential amplifier 116 and the focal position shift amount does not become as shown in FIG. As described above, when the test object 105 is inclined, there is a problem that accurate focus detection and displacement detection cannot be performed.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a displacement detecting device having a configuration using a double mode waveguide and capable of accurately detecting a displacement amount even when an object to be measured is inclined.

[0010]

According to the present invention, there is provided the following displacement detecting apparatus.

That is, a light source, a condensing optical system for condensing light from the light source on a test object, and light reflected by the test object and passed through the condensing optical system again to first and second light sources. 2
Splitting means for splitting the first and second light fluxes into first and second double-mode waveguides, and the first and second double-mode waveguides for causing the first and second light fluxes to enter and propagate, respectively. First and second detecting means for detecting the symmetry of the intensity distribution of the propagated light, respectively, wherein the first double-mode waveguide is configured such that the first light flux is the first double-mode waveguide. The second double mode waveguide is disposed at a position where it is incident on a position slightly deviated from the center of the mode waveguide, and the second double mode waveguide is located at a position where the second light flux enters the center of the second double mode waveguide. It is a displacement detection device characterized by being arranged.

[0012]

An embodiment of the present invention will be described with reference to the drawings.

First, a displacement detecting device according to a first embodiment will be described with reference to FIG. The substrate 10 is formed with two double mode waveguides 12 and 22 of a double mode in the width direction. Input ends 1 of two double mode waveguides
Both 1 and 21 are arranged on the side surface 101 of the substrate 10. On the substrate 10, a branch portion 102 for branching the light propagating through the double mode waveguide 12 into two directions, and waveguides 13 and 14 for respectively propagating the branched light are formed. Further, a branch portion 103 for branching the light propagating through the double mode waveguide 22 in two directions, and waveguides 23 and 24 for respectively propagating the branched light are formed.

A condenser lens 8, a half mirror 6, a mirror 7, a half mirror 3,
The objective lens 4, the collimator lens 2, and the laser light source 1
They are arranged as shown in FIG.

Light detectors 15, 16, 25, and 26 are attached to the emission ends of the waveguides 13, 14, 23, and 24, respectively. The photodetectors 15 and 16 are connected to a differential amplifier 17 for obtaining a difference between these outputs.
A differential amplifier 27 is connected to the photodetectors 25 and 26. A processing circuit 30 is connected to the differential amplifiers 17 and 27.

Note that the length L ₁ of the double mode region of the double mode waveguide 12 and the branch portion 102 and the length L ₂ of the double mode region of the double mode waveguide 22 and the branch portion 103 are respectively the phase of the object. Conditions for observing distribution L ₁ = L _c1 (2m + 1) / 2 (m = 0,1,2,2
...) L ₂ = L _c2 (2n + 1) / 2 (n = 0, 1, 2,
...) Where L _c1 : perfect coupling length (0 in double mode waveguide 12)
L _c2 : perfect coupling length (0 in the double mode waveguide 22)
(The length at which the phase difference between the next mode and the first mode is π).

The substrate 10 is positioned so that the incident ends 11 and 21 are located at the focal length of the condenser lens 8 in the y direction in FIG. The distance between the optical axes of the light 105 and the light 106 is set to be slightly wider than the distance between the double mode waveguides 12 and 22 on the substrate 10. The optical axis 108 of the light 105 is incident on a position slightly shifted from the central axis of the double mode waveguide 12, and the optical axis 109 of the light 106 is positioned such that it enters the central axis of the double mode waveguide 22. It has been aligned.

Here, the operation of the displacement detecting device shown in FIG. 1 when the test object 5 is not inclined will be described.

The light 104 emitted from the laser light source 1 is
After being converted into parallel light by the collimator lens 2, the light is reflected by the half mirror 3 and condensed on the test object 5 by the objective lens 4. The light 107 reflected by the test object 5 passes through the objective lens 4 again, passes through the half mirror 3, and reaches another half mirror 6. Here, a part of the light 105 is transmitted through the half mirror 6 and the remaining light 106 is a half mirror 6
Is reflected by Light 106 reflected by half mirror 6
Is deflected by the mirror 7 and becomes parallel to the light 105. The light 105 and the light 106 are both condensed by the condenser lens 8, the light 105 is incident on the incident end 11 of the double mode waveguide 12, and the light 106 is incident on the incident end 21 of another double mode waveguide 22. Incident.

As described above, since the light 105 is positioned so as to enter a position slightly shifted from the center of the incident end 11 of the double mode waveguide 12, the incident end 1
The phase 105 of the light 105 at 1 has asymmetry according to the amount of deviation of the test object 5 from the focal position of the objective lens 4.

More specifically, when the test object 5 is at the focal position of the objective lens 4, the light 105 is most converged and is incident on the incident end 11 (FIG. 4B). The phase plane 401 is parallel to the width direction of the double mode waveguide 12. Therefore, the phase distribution is symmetric in the width direction from the center of the double mode waveguide 12. The length L ₁ of the double mode region of the double mode waveguide 12 is set to a length that satisfies the condition for observing the phase distribution described above. As a result of the interference with the light, light having the same intensity is distributed to the waveguides 13 and 14 in the branch portion 102. On the other hand, when the test object 5 is displaced from the focal position of the objective lens 4, the convergence point of the light 105 is shifted to the near side or the far side from the incident end 11 (FIGS. 4A and 4C).
Equal phase plane 4 of light spot of light 105 at incident end 11
01 is a curved surface, and the phase distribution is asymmetric with respect to the center of the incident end 11. Therefore, the double mode waveguide 12
In this case, the 0th-order mode light and the 1st-order mode light are excited, and the light in which the two-mode light interferes propagates in the double-mode waveguide 12 while meandering. Since the length L ₁ of the double mode region of the double mode waveguide 12 is set under the conditions for observing the phase distribution described above, in the branch portion 102, the length L ₁ according to the asymmetry of the equal phase plane at the incidence end 11. Light of high intensity is distributed to the waveguides 13 and 14 and propagates through the waveguides 13 and 14. The intensity of the light propagating through the waveguides 13 and 14 is detected by photodetectors 15 and 16, and the difference is obtained by a differential amplifier 17. Therefore, the magnitude of the output of the output signal 18 of the differential amplifier 17 has a relationship like the focus error curve in FIG. 5 with respect to the amount of deviation of the test object 5 from the focal position of the objective lens 4.

On the other hand, the double mode waveguide 22 on which the light 106 is incident is positioned so that the light 106 is incident on the center of the incident end 21. For this reason, in the state of FIG. 1 in which the test object 5 is not tilted, the light at the incident end 21 is always maintained regardless of whether the test object 5 is at the focal position of the objective lens 4 or is shifted from the focal position. The equal phase plane 106 is symmetric with respect to the center of the double mode waveguide 22. Therefore, only the zero-order mode light is excited in the double mode waveguide 22, and the light having the same intensity is branched into the waveguides 23 and 24 at the branching unit 103. The intensity of the light propagating through the waveguides 23 and 24 is detected by photodetectors 25 and 26, and the difference is obtained by a differential amplifier 27. in this case,
Since the light intensities of the waveguides 23 and 24 are equal, the output signal 28 of the differential amplifier is always 0.

Next, a case where the test object 5 is inclined by θ will be described with reference to FIG.

When the object 5 is tilted, the object 5
The reflected light 107 of the double mode waveguide 12,
Lights 105 and 106 incident on 22 also tilt. The light 105 incident on the double mode waveguide 12 is in the same state as in FIG. 6 of the conventional example. Therefore, the output signal 18 of the differential amplifier 17 includes information on both the asymmetry of the phase distribution due to the inclination θ of the test object 5 and the asymmetry of the phase distribution due to the amount of deviation from the focal point. Therefore, the differential amplifier 1
The output signal 18 of 7 does not become 0 even when the test object 5 is at the focal position, and does not become a curve passing through the origin as shown in FIG.

On the other hand, since the light 106 incident on the double mode waveguide 22 is incident on the center of the incident end 21, the phase distribution becomes asymmetric due to the inclination of the equiphase plane due to the inclination θ of the test object 5. Therefore, the output signal 28 of the differential amplifier 27 is an output representing only the information on the inclination θ of the test object 5.

Therefore, in the displacement detecting apparatus of the present embodiment, the processing circuit 30 detects the inclination θ of the object 5 based on the signal 28, thereby detecting the accurate focal position shift of the object 5 to be detected. Enable. The processing circuit 30 includes a storage unit 130 and a selection unit 131 as shown in FIG. The storage unit 130 has a table indicating the relationship between the magnitude of the signal 18 and the amount of focal position shift measured in advance by tilting the sample of the test object 5 by θ, and the magnitude of the signal 28 at that θ. Is stored. This table is
It is prepared for each value of θ in the range of θ ₁ ≦ θ ≦ θ ₂ .
However, the range of θ ₁ ≦ θ ≦ θ _{2 is} a range in which the test object 5 may be inclined. The selection unit 131 receives the signal 28 and the signal 18 measured on the actual test object 5,
The table corresponding to the magnitude of the signal 28 is selected. Further, the selecting unit 131 reads out the focal position shift amount corresponding to the magnitude of the signal 18 from the table, and outputs the signal 31 corresponding to the focal position shift amount. The signal 31 may be a digital signal representing a numerical value of the focal position deviation amount, or a current or voltage signal having a magnitude proportional to the focal position deviation amount.

As described above, in the displacement detecting device of the present embodiment, two double mode waveguides 12 and 22 are used, one of which detects only the tilt information of the test object 5. Thus, the displacement can be accurately detected even when the test object 5 is tilted.

The processing circuit 30 can have a configuration other than the configuration described above. For example, the storage unit 130
Alternatively, a configuration may be employed in which a correction mathematical expression predetermined for each magnitude of the signal 28 is stored. This correction formula is a formula for removing the output of the tilt information of the test object 5 included in the output of the signal 18. When the sample of the test object 5 is tilted in advance, the correction It is determined by measuring the relationship with the amount. When obtaining the actual displacement of the test object 5, the selection unit 131 sets the measured signal 28
Is read from the storage unit 130 and the output of the signal 18 is substituted into this formula, thereby correcting the signal 18 and outputting the correction result as a signal 31. Thereby, it is possible to output an accurate defocus amount that does not include the tilt information of the test object 5.

In this case, even if θ changes, only the coefficients and constants of the mathematical expression change, and the skeleton of the mathematical expression itself does not change. It can also be stored. Selector 13
1 reads out a coefficient or a constant corresponding to the signal 28,
A formula is created by applying the coefficients and constants, and the signal 18 is corrected by substituting the output of the signal 18 into the formula. Even by such a method, it is possible to output an accurate focal position shift amount that does not include the tilt information of the test object 5.

Next, a displacement measuring apparatus according to another embodiment will be described with reference to FIG.

In the displacement measuring device shown in FIG.
It is mounted on a stage 701 for correcting inclination. The stage 701 changes the inclination of the test object 5 in the width direction of the double mode waveguides 12 and 22. When the output signal 28 of the differential amplifier 27 is not 0, the control circuit 307 determines that the test object 5 is tilted,
The signal 702 is output while monitoring the change in the value of the signal 28, and the stage 701 is tilted so that the signal 28 approaches 0. As a result, the object 5 is no longer tilted, and the signal 28 becomes 0 (the state shown in FIG. 1). When the signal 28 becomes 0, the control circuit 307 outputs the signal 1
8 is output as a focal position shift signal. In FIG.
1 and FIG. 3 are the same as those in the embodiment described with reference to FIG. 1 and FIG.

Since the displacement measuring apparatus shown in FIG. 7 is configured to output the signal 18 after setting the inclination of the test object to 0, the light 104 from the light source 1 can always be vertically incident on the test object 5. it can. Therefore, the signal 18 includes the test object 5
, And only the focal position shift information can be output.

In the configuration shown in FIG. 7, the inclination of the test object 5 is changed by the stage 701. However, the tilt of some test objects 5 cannot be changed. In such a case, the optical system from the substrate 10 to the objective lens 4 is
, And the inclination of the stage can be changed so that the signal 28 becomes zero.
As a result, the light 104 from the light source 1 can always be vertically incident on the test object 5 as in FIG. 7, and the signal 18 including only the focal position shift information can be obtained.

In each of the embodiments described above, the displacement measuring device is used. However, since this configuration outputs the displacement amount of the objective lens 4 from the focal point as a displacement,
It can also be used as a focus detection device that detects a position where the focus position shift amount becomes 0 as a focus position.

[0035]

As described above, according to the present invention,
It is possible to provide a displacement detection device having a configuration using a double mode waveguide and capable of accurately detecting a displacement amount even when a test object is inclined.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a displacement measuring device according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a state where a test object 5 is tilted in the displacement measuring device of FIG. 1;

FIG. 3 is a block diagram showing a configuration of a conventional displacement measuring device using a double mode waveguide.

FIGS. 4A, 4B, and 4C are explanatory diagrams showing the relationship between the double-mode waveguide shown in FIGS. 1 and 3 and an equal phase plane of reflected light from a test object.

FIG. 5 is a graph showing a focus error curve obtained by the apparatus shown in FIGS. 1 and 3;

FIG. 6 is a block diagram showing a state in which a test object is inclined in the apparatus shown in FIG. 3;

FIG. 7 is a block diagram showing a configuration of a displacement measuring device according to a second embodiment of the present invention.

[Explanation of symbols]

1 ... laser light source, 2 ... collimator lens, 3 ...
..Half mirror, 4 ... objective lens, 5 ... test object, 6 ... half mirror, 7 ... mirror, 8 ...
・ Condenser lens, 10 ・ ・ ・ substrate, 11, 21 ・ ・ ・ incident end, 12, 22 ・ ・ ・ double mode waveguide, 15, 1
6, 25, 26: photodetector, 17, 27: differential amplifier, 30: processing circuit.

Claims (5)

[Claims] 1. A light source, a condensing optical system for condensing light from the light source on a test object, and a light reflected by the test object and passed through the condensing optical system again to first and second light sources. Splitting means for splitting into two light beams, first and second double-mode waveguides for causing the first and second light beams to enter and propagate, respectively, and the first and second double-mode waveguides And first and second detection means for respectively detecting the symmetry of the intensity distribution of the light that has propagated through the first double-mode waveguide. The second double-mode waveguide is disposed at a position slightly incident from a center of the double-mode waveguide, and the second double-mode waveguide is located at a position where the second light flux enters the center of the second double-mode waveguide. Displacement detection device characterized by being disposed at . 2. The displacement detecting device according to claim 1, wherein
A displacement detection apparatus, comprising: a processing unit configured to remove inclination information of the test object included in an output of the first detection unit using a detection result of the second detection unit. 3. The displacement detecting device according to claim 2, wherein
The processing unit has a storage unit and a selection unit. The storage unit has an output of the first detection unit, an output of the second detection unit, and an output of the object to be detected, which are obtained in advance. A table indicating a relationship with the displacement amount is stored, and the selecting unit reads the displacement amount of the test object corresponding to the output of the first and second detection means from the table, and outputs this. Characteristic displacement detection device. 4. The displacement detecting device according to claim 2, wherein
Wherein said processing means performs a calculation for correcting an output of said first detecting means by using a correction value obtained in advance and corresponding to a detection result of said second detecting means. apparatus. 5. A light source, a condensing optical system for condensing light from the light source on a test object, and a light reflected by the test object and passed through the condensing optical system again, to first and second light sources. Splitting means for splitting into two light beams, first and second double-mode waveguides for causing the first and second light beams to enter and propagate, respectively, and the first and second double-mode waveguides And first and second detection means for respectively detecting the symmetry of the intensity distribution of the light that has propagated through the first double-mode waveguide. The second double-mode waveguide is disposed at a position slightly incident from a center of the double-mode waveguide, and the second double-mode waveguide is located at a position where the second light flux enters the center of the second double-mode waveguide. Focus detection device characterized by being arranged at .