JPH11118446A - Two-dimensional array type cofocal optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To irradiate the illuminating light from a light source to an object without enhancing coherence by projecting the image of an incoherent light source imaged by a microlens array to the object, branching the reflected light from the illuminating light, and forming the image of the microlens array on a two-dimensional detector. SOLUTION: The illuminating light emitted from an incoherent light source 1 is made into a parallel light by a collimator lens 4, and the illuminating light emitted from the collimator lens 4 is converged by a microlens array 6 to project the image of the light source 1 to an object A through an objective lens 8. An optical path branching optical element 5 branches the reflected light reflected by the object and passed again through the objective lens 8 and the microlens array 6 from the optical path of the illuminating light. An imaging lens 12 forms the image of the microlens array 6 on a two-dimensional detector 14, and a diaphragm 13 is set in the local position on the rear side. The formed image of the microlens array 6 is photoelectrically converted by the two-dimensional detector 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical device for obtaining a confocal image mainly for the purpose of three-dimensional measurement.

[0002]

2. Description of the Related Art An optical system for obtaining an image by a confocal optical system is called a confocal imaging system, and an image obtained by the confocal imaging system is called a confocal image. As a general confocal imaging system, there are a laser scanning microscope and a Nippow disk scanning microscope. A two-dimensional array type confocal imaging system which does not have a scanning mechanism as described above, and two-dimensionally arranges confocal pinholes and simultaneously exposes each pixel of a confocal image is suitable because of its high speed. It is disclosed in JP-A-4-265918 and JP-A-7-181223. Also, the same inventor as the present invention has filed an application as Japanese Patent Application No. 8-94682. These prior arts are disclosed in Japanese Patent Application No. 8-94.
682 will be described as an example.

An apparatus according to Japanese Patent Application No. 8-94682 will be described with reference to FIG. Illumination light from light source 3 is pinhole 2
, And are collimated by the collimator lens 4 to be emitted. The optical path branching optical element 5 is a polarizing beam splitter, and passes illumination light as linearly polarized light. The illumination light passing through the optical path branching optical element 5 enters the microlens array 6 and is collected at the focal point of each microlens. A pinhole array 7 is provided at the focal position of the microlens array 6.
Are provided, and each pinhole exists at the position of the focal point of the illumination light condensed by each microlens. The pinhole array 7 converts the illumination light into a so-called point light source array. The illumination light having passed through the pinhole enters the objective lens 8, is converted into circularly polarized light by the 波長 wavelength plate 10 provided inside the objective lens 8, and projects the image of the pinhole onto the object A. The objective lens 8 is a double-sided telecentric lens having a telecentric stop 9 and lenses 8a and 8b inside, so that a change in magnification does not occur even if the object A or the optical system is moved in the optical axis direction. The reflected light from the object A again enters the objective lens 8, becomes linearly polarized light orthogonal to the illumination light by the 波長 wavelength plate 10, is collected, and is again focused on the pinhole array 7.
To reach. The reflected light passing through the pinholes of the pinhole array 7 is emitted by the microlens array 6 as a parallel light flux. Since the reflected light is linearly polarized light orthogonal to the illumination light, the reflected light is deflected by the optical path branching optical element 5 which is a polarization beam splitter and enters the imaging lens 12. The reflected light incident on the imaging lens 12 passes through the stop 13 and reaches the two-dimensional detector 14. In the imaging lens 12, the surface of the microlens array 6 and the surface of the two-dimensional detector 14 are conjugate. As a result, a confocal image is obtained on the two-dimensional detector 14, is photoelectrically converted by the two-dimensional detector 14, and is output as an electric signal.

[0004]

The two-dimensional array type confocal optical device has been described by taking the device of Japanese Patent Application No. 8-94682 as an example, but the problem to be solved by the present invention is that of Japanese Patent Application No. 8-9.
4682 as well as the apparatuses disclosed in JP-A-4-265918 and JP-A-7-181023. Each device has a pinhole array for the purpose of producing a two-dimensional array of point light sources, and a problem occurs in this portion.

[0005] In the case of a two-dimensional array type confocal imaging system, illumination light is required to be light having as low coherence as possible. This is to obtain an image in which granular noise (hereinafter, referred to as speckle) generated by local light interference is minimized. In the scanning type confocal imaging system, the spot projected on the object moves even during the exposure time of the two-dimensional detector, so even if speckle occurs, the state of the speckle changes due to the movement and is averaged. . However, in the two-dimensional array confocal imaging system, the spot does not move at all during the exposure time of the two-dimensional detector. Therefore, when speckles occur in the spot, they directly affect the image. This is particularly remarkable in the case of observation of a rough surface with a large spot size when an objective lens having a low magnification and a low numerical aperture is used. For this reason, in the two-dimensional array type confocal imaging system, an incoherent light source is used, or coherent light is made incoherent by a phase randomizer and used. But,
Even if an incoherent light source is used, passing through the pinholes of the pinhole array will eventually increase the coherence and cause speckles.

Further, it is technically difficult to prepare hundreds of thousands of pinhole arrays. In particular, when a microlens is arranged coaxially with a pinhole to increase the amount of light, a special device is required for positioning. Become. It is also necessary to take measures to prevent the light reflected by the light-shielding film portion of the pinhole from reaching the two-dimensional detector. (In the conventional device, a polarizing beam splitter, a polarizing optical element such as a quarter-wave plate, etc. is a countermeasure. is there).

Accordingly, the present invention provides a two-dimensional array confocal imaging system which has a simple structure and is easy to manufacture, and which can project illumination light from an incoherent light source onto an object without increasing coherence. It is intended for.

[0008]

In order to achieve the object, an incoherent light source 1, a collimator lens 4 for collimating the illumination light emitted from the incoherent light source 1, and an collimator lens 4 emitted from the collimator lens 4. A microlens array 6 for condensing the illumination light thus formed and forming an image of the incoherent light source 1 for each microlens, and an image of the incoherent light source 1 formed by the microlens array 6 on an object A Objective lens 8 for projecting and object A
Reflected by the objective lens 8 and the micro lens array 6 again.
An optical path branching optical element 5 for branching the reflected light passing through the optical path of the illumination light, an imaging lens 12 for imaging the image of the microlens array 6 on the two-dimensional detector 14, and a rear side of the imaging lens 12. The diaphragm 13 is provided at the focal position, and the two-dimensional detector 14 photoelectrically converts the formed image of the microlens array 6. This configuration eliminates the need for a pinhole array and does not increase coherence. Moreover, the structure is simpler. There is no need to perform alignment with the microlens, and there is no reflection from the light-shielding film.

Further, the focal length of the collimator lens 4 is configured to be at least 100 times the focal length of each micro lens of the micro lens array 6. With this configuration, the light source may be somewhat large, and a high-output incoherent light source can be obtained.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of an embodiment of the present invention. Hereinafter, the configuration of the present invention will be described according to the path of illumination light. The illumination light from the incoherent light source 1 is emitted by the collimator lens 4 as substantially parallel light. This illumination light passes through the optical path branching optical element 5, enters the microlens array 6, and is collected at the focal point of each microlens. An image of the incoherent light source 1 is formed on each microlens at the focal point. The imaging magnification is the focal length f1 of the collimator lens 4 and the focal length f2 of the microlens.
Is determined by the ratio f2 / f1. In this embodiment, the imaging magnification is set to several hundredths. In this case, even if the incoherent light source 1 has a size of about several mm, its image is at most about 10 μm, and can be regarded as a sufficient point. The focused illumination light becomes divergent light again, enters the objective lens 8, and projects the image of the light spot obtained by the microlens array 6 onto the object A. Objective lens 8
Has a telecentric aperture 9 and lenses 8a and 8b inside
A telecentric lens with
Alternatively, even if the optical system is moved in the optical axis direction, no change in magnification occurs. The reflected light from the object A again enters the objective lens 8 and reaches the microlens array 6. The reflected light that has passed through the microlens array 6 is deflected by the optical path branching optical element 5 to form the imaging lens 1.
2, the luminous flux is restricted by the stop 13 and reaches the two-dimensional detector 14. At this time, a confocal image has been obtained on the two-dimensional detector 14.

The illumination system (incoherent light source 1,
The collimator lens 4 and the micro lens array 6) will be described in detail. In a two-dimensional array type confocal imaging system, it is necessary to project an image of a point light source onto an object using an objective lens. Therefore, as described in the description of the related art, a pinhole (pinhole array) is required in an illumination system to create a point light source. ) Is common. However, light emitted from the pinhole has high coherence, is non-scanning type (two-dimensional array type) and has low magnification,
In a confocal imaging system with a low numerical aperture, speckles occur during rough surface observation, resulting in deterioration of image quality and reduction of three-dimensional measurement accuracy.
Even if the light source is, for example, a white incoherent light source such as a halogen lamp, passing through a pinhole increases coherence. In view of this, the present invention proposes a point light source without passing through a pinhole and reducing the coherence of the light source by reducing and projecting the light source using a lens. This will be specifically described below.

The collimator lens 4 and the microlens array 6 form an image of the incoherent light source 1 at the focal position of each microlens at a magnification f2 / f1. The image of the incoherent light source 1 is formed for each micro lens by the image duplication ability of the micro lens array 6. If f2 = 0.5 mm and f1 = 100 mm, the imaging magnification is 1/200. For example, even if the size of the incoherent light source 1 is φ2 mm, the image is φ1
0 μm. (Of course, an image spread occurs due to diffraction of light determined by the numerical aperture of the microlens and the wavelength of the incoherent light source 1.) If the objective lens 8 has a magnification of 5 and a numerical aperture of 0.1, the object The size of the spot projected on the incoherent light source 1 is geometrically optically φ2 μm, and the diameter of the point spread function (PSF) of the astigmatic lens having a numerical aperture of 0.1 is 6 μm or more. That is negligible. In other words, even if the incoherent light source 1 having a size is used, such an optical arrangement can sufficiently function as illumination of a confocal optical system, and a pinhole conventionally required to be used as a point light source can be obtained by the present invention. It can be said that this is not necessary for the lighting system. Since there is no pinhole, the low coherence of the incoherent light source 1 is kept as it is, so that the occurrence of speckle is suppressed.

Further, the absence of a pinhole means that there is no light-shielding film, so that reflection on the light-shielding film, which is a problem in the conventional device, does not need to be considered. The light shielding film uses three layers of chromium oxide / chromium / chromium oxide,
Even with chromium oxide, reflection of about 5% occurs. When there is no light-shielding film, reflection can be reduced to about 0.2% by applying a multilayer AR coat. For this reason, in the conventional device, measures are taken using a polarizing element such as a polarizing beam splitter or a quarter-wave plate so that the reflected light of the illuminating light from the light shielding film does not enter the two-dimensional detector. Such measures are not always necessary. Of course, noise light can be cut more by taking the same countermeasures. Therefore, the same configuration as the conventional device may be adopted.

Next, the operation of the imaging lens 12 and the aperture 13 will be described. In this optical arrangement, the microlens array 6
The focal position of each microlens and the rear focal position of the imaging lens 12 are in a conjugate relationship, and the microlens array 6
All the light passing through the focal position of each microlens is focused on the rear focal position on the optical axis of the imaging lens 12. By placing the aperture 13 here, it is possible to obtain the same effect as the presence of a pinhole at the focal point of each microlens. That is, assuming that there is a pinhole at the focal point of each microlens, the light passing through the pinhole forms an imaging lens at a magnification f3 / f2 determined by the ratio of the focal length f2 of the microlens to the focal length f3 of the imaging lens 7. Although the light passes through the aperture 13 to reach the vicinity of the rear focal point of the lens 12, the light passing through the light-shielded portion when there is a pinhole at the focal point of each microlens is transmitted from the vicinity of the rear focal point of the imaging lens 12. Since the light reaches the deviated position, the light is blocked by the aperture 13.

When this structure is compared with the conventional device shown in FIG. 2, the essential difference is only the pinhole array 7 (the polarizing element such as the quarter-wave plate 10 and the pinhole 2 are used in the present invention). (It is not a minimum component.) In the conventional apparatus, the aperture 13 is provided as a countermeasure against stray light and is not used in the sense of a confocal pinhole for obtaining a confocal effect, but in the present invention, the aperture 13 also plays a role of a confocal pinhole. . This eliminates the need for a pinhole array and greatly facilitates manufacturing compared to conventional devices.

The above embodiment is merely an example of the present invention.
However, it is not limited to this. For example, the incoherent light source 1 has been described assuming that it has a considerable size because it is incoherent.
Or a phase randomizer that applies a beam emitted from a laser light source to a diffuser, rotates the diffuser, and randomizes the phase to produce incoherent light. A coherent light source may be used. In this case, the collimator lens 2 is more appropriately called a beam expander. Anything can be used as long as it produces an incoherent light output. It does not matter whether it is monochromatic or white.

For example, if an incoherent light source 1 is a mercury lamp or an ultraviolet laser made incoherent by a phase randomizer, and a dichroic beam splitter is used as an optical path branching optical element 5, an optical system capable of obtaining a fluorescent image can be obtained. Becomes

[0018]

The two-dimensional array type confocal optical device of the present invention is characterized in that speckles do not occur during rough surface observation even when an objective lens having a low magnification and a low numerical aperture is used. In applications such as three-dimensional measurement on an automatic inspection line in automation, rough surface and low magnification measurement are often required, which is considered to be remarkably effective. Structurally, there are no parts that require delicate alignment or adjustment, so it can be manufactured only by assembling and adjusting general optical systems, and there is no need to provide any more technical and manufacturing equipment. Therefore, it is thought that the cost will be remarkably improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an embodiment of the present invention.

FIG. 2 is a diagram for explaining a conventional device. 0

[Explanation of symbols]

 Reference Signs List 1 incoherent light source 2 pinhole 3 light source 4 collimator lens 5 optical path branching optical element 6 microlens array 7 pinhole array 8 objective lens 8a lens 8b lens 9 telecentric aperture 10 1/4 wavelength plate 12 imaging lens 13 aperture 14 2 Dimension detector 1

Claims (2)

[Claims] 1. An incoherent light source 1, a collimator lens 4 that converts illumination light emitted from the incoherent light source 1 into parallel light, and an illumination light emitted from the collimator lens 4 is collected and focused. Coherent light source 1
A microlens array 6 that forms an image of each microlens, an objective lens 8 that projects the image of the incoherent light source 1 formed by the microlens array 6 onto an object A, The optical path branching optical element 5 for branching the reflected light passing through the objective lens 8 and the microlens array 6 again to the optical path of the illumination light, and the imaging lens 12 for forming an image of the microlens array 6 on the two-dimensional detector 14. A diaphragm 13 placed at a focal position behind the imaging lens 12 and a two-dimensional detector 14 for photoelectrically converting the formed image of the microlens array 6. Array type confocal optical device. 2. The two-dimensional array type confocal optical device according to claim 1, wherein the focal length of the collimator lens is at least 100 times the focal length of each micro lens of the micro lens array.