JP2001241913A - White light interferometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a white light interferometer dispensing with a moving device for a movable mirror and a displacement measuring instrument. SOLUTION: The white light interferometer has a first optical system for forming light path difference in the light from a white light source and a second optical system for detecting the light path difference of the light from the first optical system and the second optical system has a branch means for branching light into two lights and a photodetector for detecting the interference fringe formed by the light from the branch means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a white light interferometer for measuring displacement by detecting an optical path difference. More particularly, it relates to a white light interferometer that measures displacement using a low coherence or white light source.

[0002]

2. Description of the Related Art An example of a conventional Michelson-type white light interferometer will be described with reference to FIG. The white light interferometer of this example includes a white light source 11 and two optical systems that generate an optical path difference. First
The optical system includes a collimator lens 12, a first beam splitter 21, a first fixed mirror 22, and a first movable mirror 2.
4 is included. The second optical system is a second beam splitter 3
It includes a first and second fixed mirror 32, a second movable mirror 34, and a light receiver 36.

The light from the white light source 11 is collimated by a collimator lens 12 and split into two lights by a first beam splitter 21. The first light is reflected by the first fixed mirror 22, returns to the first beam splitter 21, passes through the first beam splitter 21, and is guided to the second beam splitter 31. The second light is the first
After being reflected by the movable mirror 24, the beam returns to the first beam splitter 21, and is reflected by the first beam splitter 21 to be guided to the second beam splitter 31.

[0004] The distance between the first beam splitter 21 and the first fixed mirror 22 is L1, and the distance between the first beam splitter 21 and the first movable mirror 24 is L2. If there is a difference between the two distances L1 and L2, an optical path difference occurs between the optical path of the first light and the optical path of the second light. The optical path difference ΔL1 is an optical path difference generated by the first optical system, and is represented by the following equation.

[0005]

Equation 1 ΔL1 = 2 | L2-L1 |

[0006] Light from the first optical system is guided to the second optical system. Light from the first beam splitter 21 is split by the second beam splitter 31. The first light is reflected by the second fixed mirror 32, returns to the second beam splitter 31, passes through the second beam splitter 31, and is guided to the light receiver 36. The second light reflects on the second movable mirror 34 and then returns to the second beam splitter 31, and reflects on the second beam splitter 31 to
It is led to.

[0007] The distance between the second beam splitter 31 and the second fixed mirror 32 is L3, and the distance between the second beam splitter 31 and the second movable mirror 34 is L4. If there is a difference between the two distances L3 and L4, an optical path difference occurs between the optical path of the first light and the optical path of the second light. This optical path difference ΔL2 is an optical path difference generated by the second optical system, and is represented by the following equation.

[0008]

L2 = 2 | L4-L3 |

A description will be given with reference to FIG. FIG. 7 schematically shows light from two optical systems of the white light interferometer of FIG. FIG. 7A shows light from the first optical system, and FIGS. 7B, 7C and 7D show light from the second optical system. As described above, the light from the first optical system includes two lights having an optical path difference ΔL1, that is, light F that has passed through a short optical path length (L1) and light S that has passed through a long optical path length (L2).

[0010] Of the two lights F and S from the first optical system, the light F that has passed through the short optical path length (L1) after passing through the second optical system has two lights having an optical path difference ΔL2, ie, two lights. , The light FF that has passed through the short optical path length (L3) and the long optical path length (L4)
Is divided into the light FS that has passed. Of the two lights F and S from the first optical system, the light S that has passed through the long optical path length (L2)
After passing through the second optical system, is separated into two lights having an optical path difference ΔL2, that is, light SF having passed through a short optical path length (L3) and light SS having passed through a long optical path length (L4).

FIG. 7B shows a case where the second optical path difference ΔL2 is smaller than the first optical path difference ΔL1, and FIG. 7C shows a case where the first optical path difference ΔL1 and the second optical path difference ΔL2 are the same.
D is a case where the second optical path difference ΔL2 is larger than the first optical path difference ΔL1.

The first movable mirror 22 is mounted on the object to be measured, and is displaced correspondingly when the object to be measured is displaced. Therefore, the first optical path difference ΔL1 represents the displacement or position of the measurement target. The second movable mirror 32 can be freely displaced by the measurer. Therefore, the measurer can freely change the second optical path difference ΔL2.

While displacing the second movable mirror 32,
The output of the light receiver 36 is monitored. FIG. 7 shows the output of the light receiver 36.
When the waveform shown in C is reached, the displacement of the second movable mirror 32 or the second optical path difference ΔL2 is read. At this time, the second
Since the optical path difference ΔL2 is equal to the first optical path difference ΔL1, the first optical path difference ΔL1 is detected. Thus, the displacement or position of the first movable mirror 22 is detected.

An example of a conventional Fabry-Perot white light interferometer will be described with reference to FIG. Comparing the white light interferometer of the present example with the white light interferometer shown in FIG.
Is a half mirror, and is different in that it is arranged along the same optical path as the optical path of the first movable mirror 24. The second optical system of the white light interferometer of this example is the same as the second optical system of the white light interferometer shown in FIG.

The light from the white light source 11 is collimated by the collimator lens 12, passes through the first beam splitter 21, and is split into two lights by the half mirror 23. The first light returns to the first beam splitter 21 after being reflected by the half mirror 23, is reflected by the first beam splitter 21, and is guided to the second beam splitter 31. The second light passes through the half mirror 23 and reflects on the first movable mirror 24, and then the first beam splitter 2
1 and reflects the first beam splitter 21 to
To the beam splitter 31.

Light from the first optical system is guided to the second optical system. The first optical path difference ΔL1 generated by the first optical system is represented by Expression 1, and the second optical path difference ΔL2 generated by the second optical system is represented by Expression 2. The method for detecting the displacement or the position of the measurement target mounted on the first movable mirror 24 is the same as in the case of the white light interferometer in FIG.

[0017]

In the conventional white light interferometer, by moving the second movable mirror 34, FIG.
Is configured to detect the interference position shown in FIG. Therefore, a mechanical moving device for moving the second movable mirror 34 and a displacement detecting device for detecting the displacement of the second movable mirror are required.

An object of the present invention is to provide a white light interferometer that does not require a moving device and a displacement detecting device for a movable mirror.

[0019]

According to the present invention, there is provided a white light interferometer comprising: a white light source; a first optical system for generating an optical path difference in light from the white light source; A second optical system for detecting an optical path difference of the light of
The optical system includes a branching unit that splits light into two, and a light detection device that detects interference fringes generated by the light from the branching unit.

According to the present invention, since the second optical system has no movable mirror, there is no need to provide a mechanical device for moving the movable mirror and a displacement detecting device for detecting the displacement of the movable mirror. .

According to the present invention, the above-described photodetector has photodetectors composed of photoelectric conversion elements arranged in a line.
The second optical system includes an optical integrated circuit, and the branching unit is a Y-branch formed in the optical integrated circuit.

According to the white light interferometer of the present invention, the first
And the second optical system are connected by an optical fiber, and the first optical system includes a white light source and a beam splitter that generates an optical path difference between the light from the white light source, a fixed mirror, a movable mirror, and an optical path difference. And a coupler for guiding the generated light to the optical fiber, the second optical system includes an optical integrated circuit for guiding the light passing through the optical fiber, and the branching unit is formed on the optical integrated circuit. Y branch.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first example of a white light interferometer of the present invention will be described with reference to FIG. The white light interferometer of this example includes a low coherence light source, that is, a first optical system that generates an optical path difference with the white light source 11, and a second optical system that detects the optical path difference. The first optical system includes a collimator lens 12, a first beam splitter 21, a first fixed mirror 22, and a first movable mirror 24. The second optical system has a reflecting mirror 21, a condenser lens 42, an optical integrated circuit 43, and a photodetector 45. The optical integrated circuit 43 includes a Y branch 44 composed of an optical waveguide.
Having.

The white light source 11 and the first optical system may have the same configuration as the white light source 11 and the first optical system of the conventional white light interferometer described with reference to FIG. In the second optical system, by providing the reflecting mirror 41, the overall size of the white light interferometer can be reduced.
It is not mandatory to use 1.

The light from the white light source 11 is collimated by the collimator lens 12 and split into two lights by the first beam splitter 21. The first light reflects off the first fixed mirror 22 and then returns to the first beam splitter 21, and the second light reflects off the first movable mirror 24 and returns to the first beam splitter 21.

An optical path difference ΔL1 is generated by the first optical system. The distance between the first beam splitter 21 and the first fixed mirror 22 is L1, and the distance between the first beam splitter 21 and the first movable mirror 24 is L2.
The optical path difference ΔL1 is expressed by the above equation (1).

Light having the optical path difference ΔL1 is guided from the first optical system to the second optical system. That is, it reflects the reflecting mirror 41,
The light is guided to the optical integrated circuit 43 via the condenser lens 42.

This will be described with reference to FIG. The X-axis and the Y-axis are taken along the main surface of the optical integrated circuit 43 so that the Y-axis is along the optical axis of the light entering the optical integrated circuit 43, and the Z-axis is taken vertically above the main surface. The light guided to the optical integrated circuit 43 is branched into two by the Y branch 44. The two lights exit from the optical integrated circuit 43 and are detected by the light detection device 45.

The two lights emitted from the optical integrated circuit 43 form interference fringes at the position where the photodetector 45 is disposed. The interference fringes appear as light and dark repetitions on a line along the X axis on the XZ plane. Therefore, at a position separated from the optical integrated circuit by an appropriate distance, a row of photodetectors, such as photoelectric conversion elements, are arranged along a line in the X-axis direction on the XZ plane. The half graph in FIG. 2 is an example of the output of the photodetector 45 and shows the contrast of the interference fringes.

A description will be given with reference to FIG. FIG. 3 is an example of an output signal of the photodetector 45. The horizontal axis is the distance in the X-axis direction,
The vertical axis is the output of the photodetector 45. In the bright portion of the interference fringe, the output amplitude of the photodetector 45 is large, and in the dark portion of the interference fringe, the output amplitude of the photodetector 45 is small.
The distance between the central light and the adjacent light, that is, the distance x between the peak position of the central waveform and the peak position of the adjacent waveform is proportional to the optical path difference ΔL1 represented by the equation (1). Therefore, when the optical path difference ΔL1 changes, the distance x between the peak positions of the two waveforms changes accordingly.

For example, FIG. 3A shows the output of the photodetector 45 when the optical path difference has an initial value, and FIG. 3B shows the output of the photodetector 45 after the optical path difference has changed from the initial value. FIG. 3A
3B, the distance between the peak positions of the two waveforms changes from x to x ′. The change amount Δx = x′−x of the distance between the peak positions corresponds to the change amount of the optical path difference.

[0032]

## EQU3 ## Δx = kΔL1

This corresponds to the displacement or position of the first movable mirror 24. Therefore, by detecting a change in the distance between the peak positions of the two waveforms, the displacement of the measurement target mounted on the first movable mirror 24 is detected.

As described above, according to the present embodiment, since the movable mirror is not used in the second optical system, a mechanical drive for driving the movable mirror and a displacement detector for detecting the displacement of the movable mirror are not required. .

A second example of the present invention will be described with reference to FIG. The white light interferometer of this embodiment includes a low coherence light source or white light source 11, a first optical system for generating an optical path difference, and a second optical system for detecting the optical path difference. The first optical system may have the same configuration as the first optical system of the conventional white light interferometer described with reference to FIG. The second optical system may have the same configuration as the second optical system of the first example of the present invention described with reference to FIG.

The first optical system generates an optical path difference represented by the equation (1), and the second optical system detects the optical path difference. The detection of the optical path difference is performed by the light detection device 45 as described with reference to FIGS.

A third example of the present invention will be described with reference to FIG. The white light interferometer of the present example includes a low coherence light source, that is, a white light source 11, a first optical system that generates an optical path difference, and a second optical system that detects the optical path difference. The first optical system has a condenser lens 13, a coupler 26, a collimator lens 25, a fixed mirror 23, and a movable mirror 24. The second optical system has an optical integrated circuit 44 and a photodetector 45. In this example, the first optical system and the second optical system are connected by an optical fiber 27. The fixed mirror 23 is a half mirror.

The light from the white light source 11 is condensed by the condensing lens 13, and an optical fiber end (pig tail) at one end of the coupler 26 and an optical fiber end (pig tail) at the other end.
Through the collimator lens 25. Light from the collimator lens 25 is split into two by a fixed mirror 23, that is, a half mirror. One is fixed mirror 23
And the other passes through the fixed mirror 23 and reflects the movable mirror 24.

The two lights are guided to the optical integrated circuit 43 via the optical fiber end (pig tail) at one end of the coupler 26 and the optical fiber end (pig tail) at the other end, and further via the optical fiber 27.

Similarly, an optical path difference represented by the equation (1) is generated by the first optical system, and the optical path difference is detected by the second optical system. The detection of the optical path difference is shown in FIGS.
Is performed by the photodetector 45 as described with reference to FIG.

Although the embodiments of the present invention have been described in detail above, it will be apparent to those skilled in the art that the present invention is not limited to the above-described embodiments and can adopt various other configurations without departing from the gist of the present invention. It will be easily understood.

[0042]

According to the present invention, the white light interferometer has an advantage that a moving device and a displacement measuring device for the movable mirror are not required since the movable mirror is not used in the optical system for detecting the optical path difference.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first example of a white light interferometer of the present invention.

FIG. 2 is an explanatory diagram for explaining a light detection device of the white light interferometer of the present invention.

FIG. 3 is a diagram illustrating an example of an output of the light detection device of the white light interferometer of the present invention.

FIG. 4 is a diagram showing a second example of the white light interferometer of the present invention.

FIG. 5 is a diagram showing a third example of the white light interferometer of the present invention.

FIG. 6 is a diagram showing an example of a conventional Michelson-type white light interferometer.

FIG. 7 is an explanatory diagram for explaining a measurement principle of a conventional white light interferometer.

FIG. 8 is a diagram showing an example of a conventional Fabry-Perot white light interferometer.

[Explanation of symbols]

11 white light source 12 collimator lens 13 condensing lens 21 beam splitter 22, 23
Fixed mirror, 24: movable mirror, 25: collimator lens, 26: coupler, 27: optical fiber, 31
… Beam splitter, 32, 33… Fixed mirror, 3
4: movable mirror, 36: light receiver, 41: reflecting mirror,
42: condenser lens, 43: optical integrated circuit, 44: Y branch, 45: photodetector,

Claims (4)

[Claims] 1. A white light source, a first optical system for generating an optical path difference in light from the white light source, and a second optical system for detecting an optical path difference of light from the first optical system. An optical system, wherein the second optical system includes a branching unit that splits the light into two, and a light detection device that detects an interference fringe generated by the light from the branching unit. White light interferometer. 2. The white light interferometer according to claim 1, wherein
The white light interferometer, wherein the light detection device includes a light detection element including photoelectric conversion elements arranged in a line. 3. The white light interferometer according to claim 1, wherein
The second optical system includes an optical integrated circuit, and the branching unit is a Y-branch formed in the optical integrated circuit. 4. The white light interferometer according to claim 1, wherein
The first optical system and the second optical system are connected by an optical fiber, and the first optical system includes a white light source and a beam splitter that generates an optical path difference between the light from the white light source, a fixed mirror, and a movable mirror. And a coupler for guiding the light having the generated optical path difference to the optical fiber, the second optical system includes an optical integrated circuit for guiding the light passing through the optical fiber, and the branching unit includes the optical integrated circuit. A white light interferometer having a Y-branch formed in a circuit.