JP2002311388A - Optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical system which is free from the occurrence of the unevenness of the luminosity of a surface to be irradiated and the brightness of an image and which uses a polarization beam splitter. SOLUTION: Light emitted from a light source 1 is incident on PBS and only an S polarization component is reflected by a splitting surface and passes through a λ/4 plate 5 through a lens 3 and lens 4 to irradiate the surface 6 with it. Reflected light from the surface 6 moves back along the route of irradiation light and is incident on PBS 2 through the plate 5, the lens 4 and the lens 3. This light passes through the split surface of the PBS 2 and an analyzer 7 transmitting only P polarization and forms the image of the surface 6 on an image surface 8. Since the light source 1 is placed within a telecentric part 10, light emitted from the light source 1 to be incident on the PBS 2 is incident at the same incident angle at any position of the split surface of the PBS 2. Thus, the S polarization component is reflected by the same reflectance with respect to incident light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical system, and more particularly to an optical system for a surface such as an observation optical system.

[0002]

2. Description of the Related Art A method of illuminating a surface to be observed or a surface to be measured with light from a light source and forming an image on an imaging surface for observation and measurement includes a microscope, a shape measuring device, and optical information recording / reproduction. It is used in a wide range of fields such as equipment.

At this time, a problem is noise called flare. Flare occurs when light unrelated to the object to be measured, such as light reflected on the surface of a lens provided in the optical system, enters the measurement system and becomes background noise. In order to eliminate such flare, observation and measurement have been conventionally performed using polarized light, and a basic optical system has been established.

An example is shown in FIG. This example is used for an optical pickup of an optical information recording / reproducing apparatus, and divides output light of a semiconductor laser 21 into three beams by a diffraction grating 22. And these are collimated lens 23
Is converted into parallel light by the polarization beam splitter 24 (hereinafter, referred to as a parallel beam).
PBS), through the λ / 4 plate 25,
The light is condensed on the surface of the optical disk 27 by the objective lens 26.
When the reflected light from the optical disk 27 passes through the λ / 4 plate 25 again, it becomes linearly polarized light whose polarization plane is rotated by 90 °, is reflected by the polarization beam splitter 24, passes through the cylindrical lens 28, and passes through the 6-division PIN diode 29. Incident.
A focusing signal is read out by the zero-order light, and tracking is performed by ± first-order light.

In such a measuring system, a λ / 4 plate 2
Only the light that has passed twice through 5 is reflected by the polarization beam splitter 24 and detected by the 6-division PIN diode 29. Therefore, light or the like that does not pass through the λ / 4 plate 25 twice but is reflected by an intermediate lens is a six-division PIN diode 2 serving as a detector.
9, the flare can be greatly reduced.

[0006] Such an optical system is widely used, for example, Japanese Patent Publication No. 6-52168, Japanese Patent No.
No. 43,674, Japanese Patent No. 256513, Japanese Patent No. 31
No. 42251, and the like.

[0007]

However, in the optical systems described in the above patent publications, including the conventional example shown in FIG. 3, the PBS is a parallel optical system part of the optical system, that is, a certain point. All the rays emanating from are placed in the part of the optics that travels in parallel. In these examples, the light source is a point light source, and the light is condensed and illuminated on the object to be measured, and the reflected light from that point is incident on the PBS as a parallel light flux. No problem.

However, in an optical system such as a microscope in which the observation surface is a surface and the irradiation light must be irradiated on the surface, if the PBS is provided in the parallel optical system portion,
There is a problem that the transmittance and the reflectance of the PBS vary depending on the position where light enters the PBS.

FIG. 4 shows this state. The light emitted from the light source 31 enters the PBS 32, and only the S-polarized light component is reflected on the split surface, passes through the lens 33, and further passes through the λ / 4.
The light is irradiated on the irradiation surface 35 through the plate 34.

The reflected light from the irradiated surface 35 reverses the path of the irradiated light, passes through the λ / 4 plate 34 and the lens 33, and
It is incident on BS32. This light becomes P-polarized light by passing through the λ / 4 plate 34 twice. Therefore, PB
The light passes through the split surface of S32, passes through the lens 36, and
After passing through an analyzer 37 that transmits only polarized light,
An image of the illuminated surface 35 is formed.

The lens 3 is closer to the irradiation surface 35 than the lens 33.
6 is closer to the image plane 38 than the telecentric unit 3
9 and 40, so that even if the positions of the irradiation surface 35 and the image surface 38 change, the illumination uniformity is maintained and the image blur is reduced. Between the lens 33 and the lens 36 is a parallel system part 41 in which light travels in parallel.

In such an optical system, PBS 32
Are provided in the parallel system part 41. Parallel optical system section 41
As shown in the figure, as shown in the drawing, the light irradiated to different points on the irradiated surface 35 has different angles with respect to the optical axis, so if the PBS 32 is provided therein, the light enters the split surface of the PBS 32. The incident angle of the irradiation light or the light reflected from the irradiated surface 35 differs depending on the position of the split surface of the PBS 32. For this reason, a phenomenon occurs in which the luminous intensity on the irradiated surface and the brightness of the image become uneven depending on the location.

The present invention has been made in view of such circumstances, and even when irradiating light on a surface or capturing an image of a surface, the luminous intensity of the surface to be irradiated and the brightness of the image can be improved. An object of the present invention is to provide an optical system using a polarizing beam splitter, which does not cause unevenness.

[0014]

Means for Solving the Problems A first method for solving the above problems is described below.
Means, wherein the polarizing beam splitter is provided in the telecentric optical unit (claim 1).
It is.

In this means, since the polarization beam splitter is provided in the telecentric optical section, the angle of incidence of light incident on the split surface of the polarization beam splitter is the same at any position on the split surface. Therefore, the intensity of light illuminating the surface to be illuminated is the same at any point. Also, the light reflected from the observation surface and the reflected light from any point are reflected or transmitted by the polarizing beam splitter with the same reflectance and transmittance.

A second means for solving the above-mentioned problem is the first means, further comprising a light source, and irradiating the object surface with light from the light source via the polarizing beam splitter. (Claim 2).

A third means for solving the above-mentioned problem is as follows.
In the second means, reflected light from the object surface,
An image forming means for forming an image on an imaging surface is provided (claim 3).

A fourth means for solving the above problem is as follows.
The third means, wherein the imaging plane is on one optical path separated by the polarizing beam splitter, and the light source is on the other optical path separated by the polarizing beam splitter. (Claim 4).

A fifth means for solving the above-mentioned problem is:
The third means or the fourth means, wherein a λ / 4 plate is arranged in an optical path between the polarization beam splitter and the object, through which light from the light source and reflected light from the object pass together. (Claim 5).

A sixth means for solving the above-mentioned problem is as follows.
The optical system of any one of the third to fifth means, which is provided on the object side of the polarizing beam splitter, irradiates the object with light, and receives reflected light from the object, It is characterized by having a telecentric optical system (claim 6).

Each of the second to sixth means is an embodiment of the first means, and the functions and effects of the first means are exhibited in these means.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing an observation optical system which is an example of an embodiment of the present invention. Light emitted from the light source 1 is incident on the PBS 2, and only the S-polarized light component is reflected on the split surface and passes through the lenses 3 and 4,
Further, the light is irradiated on the irradiation surface 6 through the λ / 4 plate 5.

The reflected light from the irradiated surface 6 reverses the path of the irradiated light and passes through the λ / 4 plate 5, the lens 4 and the lens 3 and enters the PBS 2. This light becomes P-polarized light by passing through the λ / 4 plate 5 twice. Therefore, PB
An image of the illuminated surface 6 is formed on the image plane 8 through the analyzer 7 which transmits through the split surface of S2 and transmits only P-polarized light.

In the figure, a portion below the lens 4 (that is, a portion closer to the irradiated surface 6 than the lens 4) and a portion above the lens 3 (that is, a portion closer to the image plane 8 or the light source 1 than the lens 3) are telecentric. It is a system,
The telecentric units 9 and 10 are respectively formed.
The space between the lens 3 and the lens 4 is a parallel optical system, and constitutes a parallel system section 11. Although the actual optical system is formed by a large number of optical elements such as lenses and diaphragms, these are omitted in the drawings, and only the optical elements necessary for the description are representatively shown.

Since the light source 1 is placed in the telecentric section 10, light emitted from the light source 1 and incident on the PBS 2 is incident at the same incident angle at any position on the split surface of the PBS 2. Therefore, the S-polarized light component is reflected at the same reflectance with respect to the incident light. The P-polarized light reflected from the irradiated surface 6 also transmits through the PBS 2 at the same transmittance at all portions of the split surface.

In this optical system, the irradiated surface 6
The telecentric part 9 is provided on the side. This is to prevent the illumination state from changing even if the position of the irradiated surface changes. In this optical system, the analyzer 7
Is provided to cut off light other than P-polarized light. However, since light transmitted through the PBS 2 is originally P-polarized light, the analyzer 7 is not necessarily provided.

In an optical system as shown in FIG. 1, an image of an irradiated surface is formed on an image surface while reducing flare by the mechanism described in the description of the prior art, and observation and imaging are performed. be able to. At that time, as described above, the illumination uniformity of the illuminated surface and the uniformity of the image forming intensity are maintained.

FIG. 2 is a diagram showing an outline of an optical system according to another embodiment of the present invention. In this embodiment, the arrangement of the light source 1, the PBS 2, the lenses 3, 4, the λ / 4 plate 5, the irradiated surface 6, the analyzer 7, and the image plane 8 is the same as that of the embodiment shown in FIG. The operation is the same, and the operation is the same as the operation described in the description of FIG.

In the embodiment shown in FIG. 2, a zoom unit 12 is provided behind the image plane 8 (above the figure).
The image on the image plane 8 is enlarged and formed on the imaging surface of the imaging element 13. Therefore, the portion between the lens 3 and the image plane 8 is telecentric, but the portion above the image plane 8 (the part on the imaging element 13 side) is not telecentric. However, there is no problem since the PBS is not provided in the non-telecentric system.

In the embodiment shown in FIG.
The positions of the analyzer 7 and the image plane 8 and the position of the light source 1 may be interchanged. That is, in FIG. 1, among the light from the light source 1, the S-polarized light component reflected on the split surface of the PBS 2 goes to the irradiated surface 6, but the light source 1 is connected to the analyzer 7 in FIG.
It may be arranged at the position of the image plane 8 so that the P-polarized light component of the light from the light source that has passed through the split plane of the PBS 2 is directed to the irradiated surface 6. In this case, the reflected light from the irradiated surface 6 becomes S-polarized light and returns to the PBS 2. Therefore, FIG.
If the analyzer 7 and the image plane 8 are arranged at the position of the light source 1 in the above, the S-polarized light component (reflected light from the irradiated surface 6) reflected on the split plane of the PBS 2 can be imaged on the image plane 8. .

Similarly, in the embodiment shown in FIG. 2, the position of the optical unit including the analyzer 7, the image plane 8, the zoom unit 12, and the image pickup device 13 may be interchanged with the position of the light source 1. In this case, of the light from the light source, the P-polarized light component transmitted through the split surface of the PBS 2 goes to the irradiated surface 6, but the reflected light from the irradiated surface 6 becomes S-polarized light and becomes PB light.
It returns to S2. This S-polarized reflected light is reflected by the split surface of the PBS 2 and forms an image on the image plane 8. Then, the image on the image plane 8 is enlarged by the zoom unit 12 behind the image plane 8 and formed on the imaging surface of the imaging element 13.

[0032]

As described above, in the present invention, the intensity of the light illuminating the surface to be illuminated is the same at any point, and the light reflected from the observation surface is also the reflected light from any point. Can also be transmitted through the polarizing beam splitter with the same reflectance and transmittance.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an observation optical system as an example of an embodiment of the present invention.

FIG. 2 is a diagram showing an outline of an optical system according to another embodiment of the present invention.

FIG. 3 is a diagram showing an example of a conventional optical system used for an optical pickup of an optical information recording / reproducing apparatus.

FIG. 4 is a diagram showing a problem of an optical system provided with a polarization beam splitter in a parallel optical system unit.

[Explanation of symbols]

1 ... light source, 2 ... PBS, 3 ... lens, 4 ... lens, 5 ...
λ / 4 plate, 6: irradiated surface, 7: analyzer, 8: image surface, 9:
Telecentric part, 10 ... Telecentric part, 11 ... Parallel system part, 12 ... Zoom unit, 1
3. Image sensor

 ──────────────────────────────────────────────────続 き Continued on front page F term (reference) 2H042 CA06 CA14 CA17 2H052 AA01 AB05 AB24 AC04 AC27 AF14 2H087 KA09 NA02 RA41 RA43 RA44 2H099 AA05 BA09 CA02 CA07 5D119 AA43 BA01 JA25 JA32

Claims (6)

[Claims] 1. An optical system, wherein a polarizing beam splitter is provided in a telecentric optical unit. 2. The optical system according to claim 1, further comprising a light source, and irradiating the object surface with light from the light source via the polarizing beam splitter. 3. The optical system according to claim 2, further comprising an imaging unit that forms an image of the reflected light from the object surface on an imaging surface. 4. The image forming apparatus according to claim 3, wherein the image plane is located on one optical path separated by the polarizing beam splitter, and the light source is located on the other optical path split by the polarizing beam splitter. An optical system according to item 1. 5. A λ / 4 plate is disposed between the polarization beam splitter and the object in an optical path through which light from the light source and light reflected from the object pass together. Item 5. The optical system according to Item 4. 6. An optical system provided on the object side of the polarizing beam splitter, for irradiating the object with light and receiving reflected light from the object, has a telecentric optical system. The optical system according to any one of claims 3 to 5.