JPH0567419A - Light receiving device - Google Patents

Abstract

PURPOSE:To eliminate influence of disturbance light by providing a light shielding part having a small aperture in the vicinity of a focal plane between a lens and a light receiving element. CONSTITUTION:A light shielding part 4 having an aperture equivalent to a light converging spot is provided in the vicinity of a focal plane of a lens 1. With this constitution, only light within a narrow angular range can reach a light receiving element 5 so that malfunction due to disturbance light can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light receiving device for detecting external light.

[0002]

2. Description of the Related Art Conventionally, for example, a state in which a light receiving device receives light transmitted from a light emitting device and the light is blocked when an obstacle arrives during this period to detect a change in state A change detection device is used.

[0003]

However, in the light receiving device used in such a device, the condenser lens is arranged in front of the light receiving element, and the periphery of the lens and the light receiving element is formed of a light-shielding material. Despite the use of a condenser lens, the large light receiving angle also detects unnecessary extraneous light, and diffuse reflection inside the lens or case becomes noise light, making it difficult to detect low-level regular light. Had a problem.

The present invention has been made in view of the above circumstances, and provides a light-receiving device having a small light-receiving angle and not affected by diffused reflection in a lens or a case.

[0005]

In order to solve such a problem, a first invention comprises at least a lens and a light receiving element, and a lens aperture is provided between the lens and the light receiving element and near the focal plane of the lens. Is provided with a light-shielding portion having a sufficiently small opening. According to a second aspect of the present invention, in the first aspect of the invention, the lens is a diffraction grating provided on a transparent flat plate and having unequal intervals. According to a third invention, in the first invention, the lens is a gradient index lens having a refractive index distribution in a transparent flat plate. A fourth invention is the lens according to the second invention or the third invention, wherein the lens reaches the light-shielding portion and is in close contact with the light-shielding portion. 5th invention is 1st invention thru | or 4th invention,
It has a plurality of combinations of a lens, a light shielding portion, and a light receiving element. A sixth aspect of the invention is the same as the first to fifth aspects of the invention, in which the light shielding portion and the light receiving element are connected by an optical fiber cable.

[0006]

In the light receiving device having the above structure, the light of the unnecessary portion is eliminated by the light shielding portion having the opening sufficiently smaller than the lens aperture.

[0007]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a view showing an embodiment of a light receiving device of the present invention, in which 1 is a condenser lens attached to the opening of the case 2, 3 is a light receiving element attached to the bottom of the case 2,
Reference numeral 4 denotes a light shielding portion which is provided between the lens 1 and the light receiving element 3 in the vicinity of the focal plane of the lens 1 and has an opening 4a which is sufficiently smaller than the opening of the lens.

Here, assuming that the aperture size of the light shielding part 4 is 2w, the center wavelength of incident light is λ, and NA is the lens numerical aperture, the aperture size is determined by the following criteria. 2w = 1.75 × λ / NA

Since the light-shielding portion 4 having the opening of the above-mentioned size is provided near the focal plane position of the lens 1, the grounds for calculation are omitted, but the lens diameter and the focal length are 4 respectively. When it is set to 0.6 mm, the focused spot diameter 2w becomes 2.1 μm. Assuming that the thickness of the light shielding portion 4 is ignored and the aperture diameter is 2w, assuming that the amount of light reaching the light receiving element 5 is halved when the focal position of the lens deviates by w on the focal plane, the light receiving relative sensitivity The light receiving angle θ at which 50% becomes 50% is 0.013 °.

Therefore, by providing such a light-shielding portion 4, only the input light in an extremely narrow range can be received, so that the directivity becomes sharp and the disturbance light is less likely to be disturbed.
Moreover, even if diffuse reflection occurs in the lens 1 and the casing 2,
Since the probability that the light will pass through the opening of the light shielding portion 4 is very low, the light due to irregular reflection rarely becomes noise light, and it becomes possible to detect even low level regular light. Therefore, the detectable distance can be increased.

FIG. 1 shows an example in which the optical axis of the lens 1 and the center of the aperture of the light-shielding portion 4 coincide with each other. However, as shown in FIG. 2, this is the same when detecting the light off the optical axis. It doesn't matter if you don't.

FIG. 3 shows a lens 1a constructed by providing diffraction gratings on the light receiving element 3 side of a transparent plate at unequal intervals. The diffraction gratings should be arranged at equal intervals to diffract incident light in only one direction. However, if the distances are made unequal and the amount of diffraction increases toward the outside, the input light will be focused on the same point, that is, will have a focus, and the same effect as the lens can be obtained. With such a configuration, the lens can be made thin, so that a lightweight lens having a large aperture can be realized.

FIG. 4 shows an example in which the gradient index lens 1b is used, and FIG. 5 shows a lens 1c in which a surface on the side of the light receiving element 3 reaches the light shielding portion 4 by forming diffraction gratings with unequal intervals on the outside. The surface of the lens 1c on the side of the light shielding portion 4 is brought into close contact with the light shielding portion 4. FIG. 6 shows the lens 1c in FIG. 5 located outside the case 2.

FIG. 7 shows a case in which a lens 1e having a plurality of lenses integrally formed, a light shielding portion 4e having a plurality of light shielding portions integrally formed, and a plurality of light receiving elements 3 are also used. An arrangement example, FIG. 8 shows an example in which a part of the light receiving element is arranged at a position off the optical axis.

In FIG. 9, for example, diffraction gratings having unequal intervals are provided,
The light shielding portion 4f is brought into close contact with the back surface of the lens 1f having a thickness reaching the focal plane, and the light passing through the light shielding portion 4f is guided by the optical fiber cable 5 to the light receiving element 3 provided inside the light shielding case 2e. However, this structure increases the degree of freedom in the mounting place.

[0016]

As described above, since the light receiving device according to the present invention has the light shielding portion having the small opening between the lens and the light receiving element, the light receiving angle becomes small and the light is interfered by the external light from an unnecessary angle. In addition to that, the optical noise due to diffused reflection in the lens and the case can be reduced, so that even low-level light can be detected.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a configuration of a second exemplary embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of a third exemplary embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of a fourth exemplary embodiment of the present invention.

FIG. 5 is a diagram showing a configuration of a fifth exemplary embodiment of the present invention.

FIG. 6 is a diagram showing a configuration of a sixth exemplary embodiment of the present invention.

FIG. 7 is a diagram showing a configuration of a seventh exemplary embodiment of the present invention.

FIG. 8 is a diagram showing a configuration of an eighth embodiment of the present invention.

FIG. 9 is a diagram showing a configuration of a ninth embodiment of the present invention.

[Explanation of symbols]

 1 lens 2 case 3 light receiving element 4 light shield 5 optical fiber cable

Claims (6)

[Claims] 1. A light-shielding portion having at least a lens and a light-receiving element, and provided between the lens and the light-receiving element and near a focal plane of the lens, the light-shielding portion having an opening sufficiently smaller than a lens aperture. Light receiving device. 2. The light receiving device according to claim 1, wherein the lens is composed of a diffraction grating provided on a transparent flat plate at unequal intervals. 3. The light receiving device according to claim 1, wherein the lens is a gradient index lens in which a transparent flat plate has a refractive index distribution. 4. The light receiving device according to claim 2 or 3, wherein the lens has a thickness reaching the light shielding portion and is in close contact with the light shielding portion. 5. The lens according to any one of claims 1 to 4,
A light-receiving device having a plurality of combinations of a light-shielding portion and a light-receiving element 6. The light receiving device according to claim 1, wherein the light shielding portion and the light receiving element are connected by an optical fiber cable.