JP3350918B2 - Two-dimensional array confocal optical device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical device used for measuring a three-dimensional shape of an object, and more particularly to an optical device using a confocal optical system.

[0002]

2. Description of the Related Art It is known that a three-dimensional shape of an object can be measured by using a confocal optical system. Prior to the description of the prior art, a general three-dimensional shape measurement method using a confocal optical system will be described. FIG. 10 shows the basic configuration of the confocal optical system. Light emitted from the point light source 101 is condensed by the objective lens 103 through the half mirror 102, and is projected on an object. The light reflected from the object enters the objective lens 103 again, enters the pinhole 104 located at the same optical position as the point light source 101 via the half mirror 102, and the amount of light passing through the pinhole 104 is detected by the detector 105. Is measured by This is the basic configuration of the confocal optical system. Using such an optical system, the position of a point on the object surface in the z direction can be measured as follows. When the object surface is at a position conjugate to the point light source 101, the reflected light converges on the pinhole 104 surface, which is also at the conjugate position, and most of the reflected light passes through the pinhole 104. However, when the object surface moves away from a position conjugate to the point light source, the amount of light passing through the pinhole 104 rapidly decreases (the optical path is shown by a broken line in the figure). From this, if the distance between the object and the objective lens 103 is changed and the detector 105 finds a point showing the maximum output, the z position of the object surface can be specified. If such z-position measurement is performed by scanning the object or the confocal optical system two-dimensionally (in the xy directions), the three-dimensional shape of the object can be measured. This is the principle of three-dimensional shape measurement using a confocal optical system.

A two-dimensional (xy direction) scan is performed to
When measuring a dimensional shape, an object and an objective lens 1
Instead of changing the distance of the object 03 and measuring the z position, two-dimensional scanning is performed in the xy direction at a position where the distance between the object and the objective lens 103 is constant to obtain planar light amount data (hereinafter, such as The planar light quantity data is referred to as a confocal image), and the distance between the object and the objective lens 103 is changed to obtain a confocal image in the same manner.
From these many confocal images with different distances from each other,
The three-dimensional shape of the object can also be obtained by performing a process of finding an image that gives the maximum amount of light for each point of the image. This is faster than the principle method. When three-dimensional measurement is performed using a confocal image as described above, as a method of obtaining a confocal image, a method of scanning a laser beam with an optical deflection element (AO element, EO element, galvanometer mirror, polygon mirror, or the like) is used. Generally, a confocal image is obtained without optical scanning by arranging a confocal optical system two-dimensionally in order to obtain a confocal image faster or to have a simpler structure. An optical system (hereinafter, such an optical system is referred to as a two-dimensional confocal optical system) is disclosed in JP-A-4-265918 and JP-A-Hei-7.
No. -181023. These conventional techniques will be described below.

FIG. 7 shows an apparatus disclosed in Japanese Patent Application Laid-Open No. 4-265918 (hereinafter referred to as prior art A). Light emitted from the white light source 1 is radiated to the pinhole array unit 7 as parallel light by the collimating lens 4. Here, the pinhole array section 7 has a large number of pinholes arranged on the same plane. Light that has passed through each pinhole of the pinhole array unit 7 is regarded as a point light source, which is equivalent to the arrangement of point light sources. The light that has passed through the pinhole passes through the half mirror 71 and is projected onto the object A by the objective lens 8 including the lenses 8a and 8b and the stop 9. Object A
The light reflected from the CCD sensor 72 is condensed by the objective lens 8 and deflected in the optical path by the half mirror 71.
Reach the top. The above configuration is equivalent to a configuration in which confocal optical systems are arranged in parallel. Generally, when arranging a plurality of confocal optical systems, the distance between the confocal optical systems is required to be 5 to 10 times the pinhole diameter. By arranging confocal optical systems in parallel with no size and using a CCD sensor 72 with a low aperture ratio (a small ratio of photoelectric conversion elements to pixels) for a pinhole generally required in a detector portion. It is unnecessary.

FIG. 8 shows an apparatus according to Japanese Patent Application Laid-Open No. 7-181023 (hereinafter referred to as prior art B). The light source is a laser light source 81, and a beam expander 82 is used to obtain parallel light having a large diameter. In this device, the pinhole array unit 7 originally required separately for the light source side and the detector side is shared, the half mirror is eliminated, and the detector array unit 83 is placed on the substantially same plane as the pinhole array unit 7. Therefore, it is more compact than the prior art A. FIG. 9 shows details of the vicinity of the pinhole array section 7 and will be described in more detail. From above, a mask section 61, a reflection type hologram section 62,
It is divided into a micro lens array section 6, a detector array section 83, and a pinhole array section 7. The parallel light that has passed through the mask part 61 is incident on the reflection type hologram part 62, and the zero-order diffracted light is incident on the microlens array part 6, is collected, and passes through the pinhole array part 7. When the reflected light from the object returns and passes through the pinhole array section 7 again, it is collected by the microlens array section 6 to become parallel light, and enters the reflection type hologram section 62. The reflection hologram unit 62 reflects the first-order diffracted light in an oblique direction, is condensed by the microlens array unit 6 three times, and converges on the detector array unit 83.

[0006]

In the prior art A, the position of the photoelectric conversion element of the CCD sensor 72 is accurately determined with respect to the pinhole position of the pinhole array section 7 and the corresponding imaging position of the reflected light. There is a problem that they need to be aligned, and their alignment is difficult. CCD sensor 7
It is necessary that the photoelectric conversion elements in the two pixels themselves function as pinholes on the detector side, and a very high level of positioning (submicron order) is required. In addition, the pinhole diameter and the pinhole pitch of the pinhole array section 7 need to be the same as the photoelectric conversion element (about 2 μm) and the pixel pitch (about 10 μm) of the CCD sensor 72. The ratio of passing through the pinhole (illumination light rate) is significantly deteriorated, and it is difficult to obtain the amount of light required for measurement. Japanese Patent Application Laid-Open No. 4-265918 describes that a microlens is arranged coaxially with a pinhole in order to improve the illumination light rate. However, a microlens having a diameter of 10 μm condenses light having a spot diameter of about 2 μm. Considering diffraction, it is practically impossible, and a large spot diameter does not provide a sufficient improvement.

In the prior art B, since the pinholes on the light source side and the detector side are shared, there is no problem of alignment between the pinhole and the photoelectric conversion element as in the prior art A.
In addition, since there is no restriction on the size of the micro lens by the CCD sensor, the problem of insufficient light quantity can be avoided. However, since the structure is very complicated, there is a problem that large-scale equipment is required for manufacturing (the technology for integrally manufacturing a pinhole array, a detector array, and their readout circuit is a semiconductor process technology. Laminating micro lens arrays and reflection holograms that require a dedicated production line,
The process of performing precise alignment with the pinhole array and bonding them together cannot be manufactured without dedicated manufacturing equipment.) In addition, since the effect of the reflection hologram needs to be sufficiently exhibited, the light source is basically limited to a laser, so that interference is likely to occur, which is inconvenient for three-dimensional shape measurement. For example, if the surface of the object has irregularities on the order of wavelength, just 1
There is a problem that where there is unevenness with a wavelength of / 2, the reflected light is erased due to interference and measurement becomes impossible. Also, color observation is not possible. Furthermore, for use in fluorescence observation in the field of biotechnology, it is necessary to separate illumination light and reflected light with a dichroic mirror, but this is not possible with this configuration.

Therefore, the present invention has a simple structure, is easy to manufacture, has a high illumination light rate, can use white light (light other than monochromatic light) as a light source, and can perform color observation and fluorescence observation. It is an object of the present invention to provide a dimensional array type confocal optical system.

[0009]

In order to achieve the object, a light source for emitting illumination light, an optical path splitting optical element for splitting an optical path between the illumination light and the reflected light, and an illumination having passed through the optical path splitting optical element. A microlens array unit including a plurality of two-dimensionally arrayed microlenses for condensing light as a plurality of light spots, and a focal plane of the microlens array unit having the same array as the microlens array unit And an objective lens that condenses the illumination light passing through the pinhole array portion and projects it on an object, condenses reflected light from the object, and guides the reflected light from the object to the pinhole array portion. A two-dimensional photoelectric sensor that receives reflected light from an object that has passed through the pinhole array unit and is branched by the optical path branching optical element, and converts the reflected light into an electric signal; Serial configured by an imaging optical unit for imaging the position to the image of the microlens array portion in the two-dimensional photoelectric on the sensor between the two-dimensional photoelectric sensor. With this configuration, the problem of alignment of the pinhole array for projecting and receiving light is eliminated, the object can be efficiently illuminated with illumination light, the light source may be white light, and the structure is relatively simple and realizable. Easy.

Further, the spatial frequency of the image of the microlens array section formed on the two-dimensional photoelectric sensor by the imaging optical system is を of the spatial frequency of the pixel array of the two-dimensional photoelectric sensor.
With the following means, it is not necessary to strictly correspond the microlenses to the pixels of the two-dimensional photoelectric sensor.

Further, by making the shape of the microlenses in the microlens portion hexagonal or quadrangular, illumination light can be transmitted more efficiently and the reflection of illumination light from the substrate glass in the microlens array portion is reduced. can do.

A polarizer positioned between the light source unit and the microlens array unit and configured to linearly polarize the illumination light emitted from the light source unit, and a light path between the microlens array unit and the object in the optical path of the objective lens. And a analyzer located between the microlens array unit and the two-dimensional photoelectric sensor and arranged so as to be orthogonal to the polarizer. Thus, stray light due to reflection of illumination light from the pinhole array or the microlens array can be reduced.

Further, if the optical path branching optical element is a dichroic mirror, fluorescence observation becomes possible.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a first 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. Illumination light from the light source unit 1 becomes a point light source at the pinhole 2, becomes parallel light by the collimator lens 4, and is emitted as linearly polarized light at the polarizer 3. The optical path branching optical element 5 is a polarizing beam splitter and passes linearly polarized illumination light as it is. The illumination light passing through the optical path branching optical element 5 enters the microlens array unit 6 and is collected at the focal point of each microlens. A pinhole array section 7 is provided at the focal position of the microlens array section 6, and each pinhole is present at the position of the focal point of the illumination light collected by each microlens. 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 has a telecentric stop 9 and lenses 8a and 8 inside.
b), so that the magnification does not change even if the object A or the optical system is moved in the optical axis direction. The reflected light from the object A is
The light 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 reaches the pinhole array unit 7 again. The reflected light that has passed through the pinholes of the pinhole array unit 7 is emitted as a parallel light beam by the microlens array unit 6. 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 polarizing beam splitter and enters the imaging optical unit 16. The reflected light that has entered the imaging optical unit 16 forms an image of the surface of the microlens array unit 6 on the two-dimensional photoelectric sensor 15 by the imaging lens 12 including the lenses 12a, 12b, and the aperture 13. The light is condensed and the spatial frequency of the image of the microlens array unit 6 is reduced by the low-pass filter 14 to the two-dimensional photoelectric sensor 15.
The band is limited to の of the spatial frequency of the pixel array described above and reaches the two-dimensional photoelectric sensor 15. As a result, a confocal image is obtained on the two-dimensional photoelectric sensor 15, photoelectrically converted by the two-dimensional photoelectric sensor 15, and output as an electric signal. Here, the aperture 13 cuts stray light such as light reflected on the surface of the microlens, light scattered near the edge of the pinhole, and light that could not pass through the pinhole due to a processing error of the microlens by limiting the NA. Is provided.

Next, the configurations of the microlens array section 6 and the pinhole array section 7 will be described in detail with reference to FIGS. 2 is a side view and FIG. 3 is a top view. As shown in FIG. 2, a large number of microlenses are formed on the upper surface of a glass substrate, and the antireflection coating optimized for illumination light is formed on the surface of the microlenses. A light-shielding film is deposited on the lower surface of the glass substrate, and a pinhole pattern is formed by photolithography. The lower surface as well as the upper surface is provided with an anti-reflection coating. As shown in FIG. 3, each microlens has a hexagonal shape, and a pinhole is formed so as to be located at the center of each microlens. In this example, the microlens array section 6 and the pinhole array section 7 are formed integrally on the upper and lower surfaces of the glass substrate, but need not necessarily be integrated. Hereinafter, characteristic portions of the operation in the first embodiment of the present invention will be described in detail.

First, in the present invention, the optical path branching optical element 5
Is brought behind the pinhole array 7 when viewed from the objective lens 8 (the front side in the prior art A). For this reason,
The pinholes of the pinhole array section 7 serve as shared pinholes for the illumination light and the reflected light, and the positioning between the pinhole array and the photoelectric conversion element section of the CCD sensor is not required unlike the related art A. Further, since there is no need to use the optical path branching optical element 5 that assumes monochromatic light as in the reflection hologram of the prior art B, a white light source can be used as a light source and color observation is possible. Further, in the present invention, since most of the light incident on the microlens can pass through the pinhole, high illumination efficiency can be obtained. Most of the light incident on the microlens can pass through the pinhole without the restriction of the size and pitch of the pinhole as in the prior art A (the size of the image can be freely adjusted by the magnification of the imaging lens 12 in FIG. 1). It can be changed to). For example, imaging lens 1
If the magnification of 2 is 1/5, the microlens diameter (pinhole pitch) may be about 50 μm, and the pinhole diameter may be about 10 μm (the pixel pitch of the two-dimensional photoelectric sensor 15 is 10 μm).
In this case, when the pinhole diameter is considered to be 1/5 of the pinhole pitch), then (when the microlens diameter is 50 μm)
Obtaining a spot of 0 μm is sufficiently possible even in consideration of diffraction. When laser light (linearly polarized light) is used as the light source of the present invention in the same manner as in the prior art B, the loss of light in each optical component is ignored, and the object A is an ideal mirror surface and has a high reflectance. Prior art B assuming 100%
In comparison with the conventional technology B, in the light incident on the reflection hologram part, the light that can reach the detector array part is 24%.
% (When the diffraction efficiency of the reflection hologram is 40%), whereas in the present invention it is almost 100%, which is a very high illumination efficiency.

The reason why the shape of the microlens is hexagonal is to substantially eliminate the glass substrate surface other than the microlens. As a result, the amount of light that does not enter the microlens is reduced as much as possible to enhance the illumination efficiency. The same effect can be obtained with a square. For example, in the case of a circular microlens, there is a considerable glass substrate surface between the microlenses. Since the light applied to this portion does not pass through the pinhole, the illumination efficiency is lower than that of a hexagonal or square microlens.

In the case where the optical path branching optical element 5 is located behind the pinhole array section 7 when viewed from the objective lens 8,
A common problem is stray light. As can be seen from FIG. 1, when the illumination light is reflected by the microlens array section 6, the reflected light becomes stray light and reaches the two-dimensional photoelectric sensor 15 to deteriorate the image. Hexagonal microlenses also have the effect of preventing this stray light. That is, since most of the illumination light incident on the microlens passes through the pinhole, the hexagonal microlens has no reflection components other than the surface reflection light on the microlens surface in principle. Surface reflection can be reduced to a degree that is not problematic by the anti-reflection coating. The same applies to a square. If there are many glass substrate surfaces other than microlenses like circular microlenses, it is necessary to mask this part with a light shielding film,
The reflection component from the light-shielding film is another problem.

As described above, a hexagonal or quadrangular microlens is very effective in principle, but in practice, light incident on the microlens does not converge on the pinhole due to a processing error, and the periphery of the pinhole May be reflected by the light-shielding film and become stray light. Further, there is a possibility that the reflection at the boundary between the microlenses or the illumination light branched by the optical path branching optical element 5 is reflected to something and becomes stray light to deteriorate the image. In particular, when the reflectance of the object A is low, such stray light cannot be ignored and must be removed. In the example of the present embodiment, the illumination light is converted into linearly polarized light by the polarizer 3 as shown in FIG.
1/4 wavelength plate 1 using a polarizing beam splitter
By 0, the plane of polarization between the illumination light and the reflected light from the object A is 90.
They are different. Thus, the stray light generated before the light enters the quarter-wave plate 10 is not polarized by the optical path branching optical element 5 and does not enter the two-dimensional photoelectric sensor 15 . In this case, the polarizing beam splitter functions as an analyzer . Of course, the same effect can be obtained even if an analyzer is provided separately from the polarizing beam splitter. If the reflectance of the object A is high, such measures are not necessary. That is, the polarizer 3, the quarter-wave plate 10,
Is not necessary, and the optical path branching optical element 5 may be a non-polarizing beam splitter.

Next, the imaging optical section 16 will be described in detail with reference to FIG. In FIG. 4, 90-degree deflection by the optical path branching optical element 5 is omitted. In the drawing, fa is the focal length of the lens 12a, and fb is the focal length of the lens 12b. In this optical system, the surface of the microlens array 6 and the sensor surface of the two-dimensional photoelectric sensor 15 are conjugate. The reflected light from the object A emitted from the microlens is parallel light if the pinhole is considered to be an ideal point, but actually the pinhole has an area and therefore has an angle with respect to the optical axis. Light exists. There is also diffracted light due to the aperture of the microlens, which is also light having an angle with respect to the optical axis. The imaging lens 12 forms an image of the microlens array 6 on the sensor surface of the two-dimensional photoelectric sensor 15 including all these lights. The diaphragm 13 controls light having an angle with respect to the optical axis. If the size is too small, the diffracted light cannot pass through, and only the parallel light component emitted from the microlens reaches the two-dimensional photoelectric sensor 15, so that the resolution is reduced. Conversely, if it is too large, light having an angle larger than necessary with respect to the optical axis is likely to be stray light, and this also degrades the image.

FIG. 5 shows the intensity distribution of the image on the two-dimensional photoelectric sensor 15. The broken line in the figure is the intensity distribution when the low-pass filter 14 is not provided. In this case, it is necessary to exactly match the position of the image of the microlens (the peak) with the pixel of the two-dimensional photoelectric sensor 15. If they do not match, aliasing will occur and correct results will not be obtained. As a method of avoiding such strict alignment, a method of passing through a low-pass filter 14 is considered. By passing through the low-pass filter 14, the spatial frequency is band-limited, resulting in a smooth waveform as shown by the solid line in FIG. 5, eliminating the need for precise alignment between the microlens image and the pixel.
The band limitation is based on the sampling theorem.
At least one half of the spatial frequency formed by the pixel interval of 5 is cut. In this example, the band is limited using the low-pass filter 14, but the MTF of the imaging lens 12 itself is limited.
Can be designed to satisfy the condition,
It can also be realized by stopping down the stop 13 to lower the NA of the imaging optical unit 16.

FIG. 6 shows a second embodiment of the present invention. The difference from the first example is that the light source unit 1 is a mercury lamp,
There is no polarizing component (polarizer 3, quarter-wave plate 10), the only difference is that the optical path branching optical element 5 is a dichroic mirror, and the rest is exactly the same as the first example. The optical path branching optical element 5 that is a dichroic mirror transmits ultraviolet light that is illumination light and reflects fluorescence from the object A. In this way, fluorescence observation of the object A is possible.

The above embodiment is merely an example of the present invention.
However, it is not limited to this. For example, the microlens array section 6 and the pinhole array section 7 may be formed on separate glass substrates, or may not be glass substrates. For example, an optical resin may be used. Also, the shape of the microlens does not necessarily have to be hexagonal or quadrangular, and even a circular or triangular shape is within the scope of the present invention. Also,
Even if the positional relationship between the illumination system optical system and the imaging system optical system branched by the optical path branching optical element 5 is reversed, they are optically equivalent. The illumination light can use not only white light but also laser light.

[0024]

The two-dimensional array type confocal optical device of the present invention can be manufactured only by assembling and adjusting a general optical system because there is no portion requiring fine positioning and adjustment.
Since there is no need to prepare any more technical and manufacturing equipment, the manufacturing and assembly becomes very simple. In addition, since the illumination efficiency is very high and there is no need to use optical components that assume monochromatic light, white light can be used as illumination light, and color observation is possible. If a dichroic mirror is used, fluorescence observation becomes possible. In addition, 3
The problem of interference of reflected light due to the state of the object surface in dimension measurement can also be avoided.

[Brief description of the drawings]

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

FIG. 2 is a side view of a microlens array section and a pinhole array section of the present invention.

FIG. 3 is a top view of a microlens array section and a pinhole array section of the present invention.

FIG. 4 is a diagram for explaining an imaging optical system of the present invention.

FIG. 5 is a diagram for explaining a correspondence between an image of a microlens of the present invention and a pixel of a two-dimensional photoelectric sensor.

FIG. 6 is a diagram showing a second example of the embodiment of the present invention.

FIG. 7 is a diagram for explaining the prior art A.

FIG. 8 is a diagram for explaining a conventional technique B;

FIG. 9 is a diagram for explaining the vicinity of a pinhole array section according to a conventional technique B;

FIG. 10 is a diagram showing a basic configuration of a confocal optical system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light source part 2 Pinhole 3 Polarizer 5 Optical path branching optical element 6 Micro lens array part 7 Pinhole array part 8a lens 8b lens 9 Telecentric diaphragm 10 1/4 wavelength plate 12a lens 12b lens 13 diaphragm 14 low-pass filter 15 two-dimensional photoelectric Sensor

Claims (5)

(57) [Claims] A light source for emitting illumination light; an optical path branching optical element for branching an optical path between the illumination light and the reflected light; and an illumination light passing through the optical path branching optical element is collected as a plurality of light spots. A microlens array unit including a plurality of two-dimensionally arranged microlenses, a pinhole array unit having the same arrangement as the microlens array unit, and a pinhole array unit positioned on a focal plane of the microlens array unit;
The objective lens that condenses the illumination light passing through the pinhole array portion and projects it on an object, condenses reflected light from the object and guides the reflected light to the pinhole array portion, passes through the pinhole array portion, A two-dimensional photoelectric sensor that receives reflected light from an object branched by the optical path branching optical element and converts the reflected light into an electric signal; and a microlens array unit located between the optical path branching optical element and the two-dimensional photoelectric sensor. A two-dimensional array type confocal optical device, comprising: an image forming optical unit that forms the image of the image on the two-dimensional photoelectric sensor. 2. A spatial frequency of an image of a microlens array portion formed on a two-dimensional photoelectric sensor by an image forming optical system,
2. The device according to claim 1, further comprising means for reducing the spatial frequency of the pixel array of the two-dimensional photoelectric sensor to 1/2 or less.
Dimensional array type confocal optical device. 3. The two-dimensional array type confocal optical device according to claim 1, wherein the shape of the microlenses in the microlens array section is hexagonal or quadrangular. 4. A polarizer positioned between a light source unit and a microlens array unit and configured to linearly polarize illumination light emitted from the light source unit, and between a microlens array unit and an object in an optical path of an objective lens. A quarter-wave plate arranged at the position of
4. The analyzer according to claim 1, further comprising an analyzer located between the microlens array unit and the two-dimensional photoelectric sensor, wherein the analyzer is arranged so as to be orthogonal to the polarizer. Two-dimensional array type confocal optical device. 5. The two-dimensional array type confocal optical device according to claim 1, wherein the optical path branching optical element is a dichroic mirror.