JPH01121782A - Photodetecting device - Google Patents

Abstract

PURPOSE:To reduce the size and manufacture cost of the title photodetecting device by selecting the size of photodetection without being restrained by the photodetection visual field of the photodetecting device. CONSTITUTION:A diaphragm 2 is arranged at a distance f0 from the objective lens 1 of the photodetecting device used for a distance measuring instrument which utilizes a laser light beam, the aperture diameter of the diaphragm 2 is denoted as D, and the angle of the photodetection visual field is tan<-1>[(D/2)/ f0]. Further, an exit pupil based upon the lens 1 and a collimator lens 3 is positioned at a distance delta behind the collimator lens 3 by setting the effective diameter of the lens 1 to D0, the focal length f0 of the collimator lens 3 to (f0/D)/(1/D-1/D0), and the interval between the diaphragm 2 and collimator lens 3 to fC. When an image forming lens 4 with focal length (f) is placed at the position of this exit pupil, a real image of the diaphragm 2 is formed at a distance (f) behind the lens 4, and its size DS of the image is reduced by decreasing f/fC; and a photodetecting element 5 of size larger than DS is arranged at the position of the image and then light passed through the diaphragm 2 is all photodetected.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a distance measuring device using a laser beam.
The present invention relates to a light receiving device that receives reflected laser light from a distance measurement target.

[Conventional technology]

Conventionally, as this type of light receiving device, those shown in FIGS. 2 and 3 have been used. FIG. 2 is a diagram showing a light receiving device in which the field of light reception is limited by an objective lens and an diaphragm, and FIG. 3 is a diagram showing a light receiving device in which the field of light reception is limited by an objective lens and a photodetector element.

In FIG. 2, (11 is an objective lens, and (2) is an aperture.

(51 is the photodetection element, (6) is the case of the photodetection element, (
7) is the window of the case, (81ti electrode).

In FIG. 3, (1) is an objective lens, (5) is a photodetecting element, (6) is a case of the photodetecting element, and (7) is a window of the case.

(8) is an electrode.

Next, the operation will be explained. In Figure 2, incident light passing through the objective lens (1) enters the photodetector element (5) via the aperture (2) and window (7), and an electrical signal corresponding to the incident light can be extracted from the electrode (8). . In laser distance measuring equipment,
It is necessary to exclude laser reflected light from sources other than the distance measurement target, so the aperture (2) is placed at the focal point of the objective lens (1) and limits the field of view of the light receiving device by the aperture (21K). 2), and the focal length of the objective lens (1) is 'tfo, the viewing angle is 2 tan-'' ((D/2
)/f0).

In Fig. 3, the incident light passing through the objective lens (1) is
) and enters the photodetector element (5), and an electrical signal corresponding to the incident light is obtained from the electrode (8). The photodetecting element (5) is placed at the focal point of the objective lens (1), and the field of view of the light receiving device is set at the focal point of the objective lens (1), with the diameter of the photodetecting element (5) being D3.
), then 2tan-”((Ds/
2)/fo).

[Problem that the invention seeks to solve]

In the conventional device shown in FIG. 2, in which the light receiving field f is limited by an objective lens (1) and an aperture (2), a photodetector element (5) is placed behind the aperture (2).

At the position where the photodetection element (5) is placed, the photodetection element (5) necessary to receive all the light passing through the objective lens (1) and the aperture +21't - that is, the light within the field of view.
) is the diameter 'k D6 of the objective lens (1)
Assuming that the -aperture of the +diaphragm (2) is taken and the focal length of the objective lens (υ is IO+the distance tL between the aperture (2) and the photodetector element (5)), -(L/7'0)D0+D is obtained. If the F value of the objective lens (υ is F), then F=fcy'Do, so DB-L/F+D.Generally, in laser distance measuring devices, the aperture of the objective lens is made thicker in order to increase the distance measuring ability. In order to reduce the size of the optical system, the focal length of the objective lens is shortened.In other words, it is preferable to reduce the F number, but in consideration of lens aberrations, cost, etc., an objective lens of around F-4 is often used. The photodetecting element (5) is housed in a case (6), and the window (7) and the photodetecting element (5)
) intervals are usually in numerical order. For this reason, the aperture (2)
The distance between the photodetecting element (5) and the photodetecting element (5) is also several orders of magnitude or more. - Taking L-4 proverb as an example, Ds = 474 + D -1
+D.

The photodetecting element (5) is larger than the aperture diameter of the aperture (2).
1 is required.

The photodetecting element (5) is preferably one with a high acid content.

Avalanche photodiodes are often used.

Its price largely depends on the dimensions.

However, in the arrangement shown in Figure 2, due to the structure of the photodetector, it is not possible to reduce the distance between the aperture (2) and the photodetecting element (5), and a large photodetecting element (5) must be used. was there.

It is shown in Figure 3. Objective lens (1) and photodetection element (5)
A conventional device that limits the light-receiving field of view is an example of a device devised to eliminate the disadvantage that the photodetector element (5) in FIG. 2 must be made large.

In Figure 3, the photodetecting element (5) is connected to the objective lens (1).
It is placed at the focal point of the diaphragm and determines the field of view with the same function as an aperture.
) is equivalent to setting the interval between the lines to O, and there is no need to add anything to the dimensions of the photodetecting element (5) other than the dimensions corresponding to the light receiving field of view.

However, in the conventional device shown in FIG. 3, the dimensions of the photodetecting element (5) corresponding to the light receiving field of view are as follows.

The size is still larger than that of an inexpensive avalanche photodiode, and the peripheral area of the photodetector has large sensitivity irregularities, making it impossible to clearly define the receiving field of view as in the case of an aperture, and because there is no aperture, the person shown in Figure 3 In such an optical path, there were problems such as light from outside the field of view entering the photodetector element.

The present invention has been made to solve these conventional problems, and it is an object of the present invention to provide a light receiving device in which the dimensions of the photodetecting element can be selected without being restricted by the light receiving viewing angle.

[Means for solving problems]

The light receiving device according to the present invention includes an objective lens, a diaphragm provided at the focal point of the objective lens, and a diaphragm located on the opposite side of the diaphragm to the objective lens, the diaphragm being arranged such that its focal length matches the distance between the diaphragm and the diaphragm. an imaging lens provided at the exit pupil formed by the objective lens and the collimator lens on the opposite side of the aperture of the collimator lens; and a collimator lens of the imaging lens. and a photodetecting element provided at the focal position on the opposite side.

[Effect]

- In this invention, the field of view is limited by the aperture.

The light that has passed through the aperture is guided to a photodetector element by a collimator lens and an imaging lens.

〔Example〕

An embodiment of this invention will be described below. FIG. 1 is a diagram showing a light receiving device according to the present invention.

In Fig. 1, (1) is the objective lens, and (2) is the aperture.

(31it collimator lens, (41Vi imaging lens,
(5) is a photodetecting element.

Next, the operation will be explained. In FIG.

The aperture (21tl) is placed at a distance of focal length f0 from the objective lens (1), and if the aperture diameter of the aperture (2) is D, the reception viewing angle is 2 tan-" ((D/2)/fo). .The effective diameter of the objective lens il+.The focal length fc of the collimator (3) is fc-(fo/D)/(1/D I/Do) ---
---lit, aperture (2) and collimator lens (3)
), the exit pupil of the objective lens (1) and the collimator lens (3) can be positioned a distance a behind the collimator lens (3).

δ−f. Cfo+fc)/fo ・・・・・・・・・・・・
−・・・・・・・・・・・・・・・・・・・・・・・・
・It is +21. When an imaging lens (4) with a focal length f is placed at the position of the exit pupil, a real image of the aperture (21) is created at a distance f behind the imaging lens (4).The image size Ds is -(f /fc)n・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・
...-(31), which can be reduced by decreasing the ratio of le/fc.If a photodetector element (5) of the above size is placed at the image position, all the light passing through the aperture (2) will be received. can do.

Note that in FIG. 1, the case of the photodetecting element is omitted and not drawn. Furthermore, in order to show the basic optical configuration of the present invention, each lens is simplified and shown as a single lens in FIG. ), but in reality, it is possible to arrange the imaging lens (4) as a set of lenses by lengthening the pack focus.

〔Effect of the invention〕

As described above, according to the present invention, the dimensions of the photodetecting element can be selected without being restricted by the viewing angle of light reception, so that it is possible to use a small and inexpensive photodetecting element.

[Brief explanation of the drawing]

Fig. 1 shows a light receiving device according to the present invention, Fig. 2 shows a conventional light receiving device in which the field of view is limited by an objective lens and an aperture, and Fig. 3 shows a field of view limited by the dimensions of the objective lens and photodetector element. FIG. 2 is a diagram showing a light receiving device according to the prior art. In the figure, (1) is the objective lens, (2) is the aperture, and (3
) is a collimator lens, (4) is an imaging lens, (5) is a photodetecting element, (6) is a case, and (7) is a window. Note that the same reference numerals in Figure 9 indicate the same or corresponding parts.

Claims (1)

[Claims] an objective lens; a diaphragm provided at the focal position of the objective lens; a collimator lens located on the opposite side of the diaphragm from the objective lens and provided so that its focal length matches the distance between the diaphragm and the diaphragm; an imaging lens provided at a position of the exit pupil formed by the objective lens and the collimator lens on the opposite side of the aperture of the collimator lens; and an imaging lens provided at a focal position of the imaging lens on the opposite side of the collimator lens. A light receiving device characterized by comprising a photodetecting element.