JPH04366905A - Light projection device using optical fiber, and collimation and convergence optical system - Google Patents

Abstract

PURPOSE:To obtain thin collimated light and reduce the size and weight. CONSTITUTION:A conic reflection body 20 which has a conic reflecting surface 21 is fixed to the tip part of the optical fiber 10. The projection light of the optical fiber 10 enters the conic reflection body 20 from an opening 22 for light incidence and is reflected by the reflecting surface 21 and projected from an opening 23 for light projection. The opening 23 for light projection is regarded as a spot light source and the light projected from the opening 23 is collimated by a lens 26 and projected to the outside.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light projection device using an optical fiber, and a collimating optical system and a focusing optical system using an optical fiber.

0002

2. Description of the Related Art Light projecting devices using optical fibers are used in many optical application fields. One of them is an optical fiber type photoelectric switch.

FIG. 6 shows an example of a transmission type photoelectric switch using an optical fiber, and FIG. 7 shows an example of a reflection type photoelectric switch using an optical fiber.

In FIG. 6, a light-emitting optical fiber 41 and a light-receiving optical fiber 42 are arranged facing each other, and the projected light emitted from the light-emitting optical fiber 41 is transmitted to the light-receiving optical fiber 42.
incident on . When an object Ob enters between these two optical fibers 41 and 42, the projection light emitted from the light emitting optical fiber 41 is blocked by this object Ob and does not enter the light receiving optical fiber 42. The presence or absence of the object Ob is detected based on the presence or absence of light incident on the light-receiving optical fiber 42. The light emitting end of the light emitting optical fiber 41 has an optical system for projecting light, as will be described later, and the light receiving end of the light receiving optical fiber 42 has an optical system for introducing incident light into the optical fiber. Needless to say, each system has its own system.

In FIG. 7, a light emitting optical fiber 41 and a light receiving optical fiber 42 are arranged in parallel. If an object Ob exists in front of these optical fibers 41 and 42 for projection and reception, the projection light emitted from the optical fiber 41 for projection will be reflected by the object Ob, and a part of the reflected light will enter the optical fiber 42 for reception. incident. If the object Ob does not exist, the reflected light does not enter the light receiving optical fiber 42. The presence or absence of the object Ob is detected based on the presence or absence of reflected light incident on the light-receiving optical fiber 42.

The following requirements are required for such an optical fiber type photoelectric switch.

(1) In order to increase the detection distance, the light projected from the light projecting optical fiber 41 needs to be collimated. If this projected light is not collimated, it propagates while spreading, so the distance from the light output end of the light projection optical fiber 41 to the light input end of the light reception optical fiber 42 (in the case of the reflective type shown in FIG. 7) , the projected light is the object O
If the distance (distance from reflection at b to input into the light receiving optical fiber 42) is long, hardly any light will enter the light receiving optical fiber 42, or even if it does, it will be extremely difficult to detect. This is because the amount of light received by the light receiving optical fiber 42 decreases in proportion to the square of the distance.

(2) When the diameter of the projection light beam emitted from the projection optical fiber 41 is larger than the object Ob to be detected, especially in a transmission type, all the projection light is directed toward the object O.
The light is not blocked by b. A part of the projected light passes around the object Ob and enters the light receiving optical fiber 42. Therefore, it becomes difficult or impossible to detect the object Ob. Even in the case of a reflective type, if the object Ob is small, the amount of reflected light decreases, and a similar problem occurs. Therefore, the projected light beam needs to be thinner than the size of the detection object Ob.

(3) It is preferable that the device be inexpensive, small, and lightweight.

FIG. 8 shows how light is emitted from the end face of an optical fiber. As is well known, the optical fiber 50 basically consists of a core 52 at the center and a cladding 51 surrounding the core. The refractive index of the cladding 51 is smaller than the refractive index of the core 52, and light is confined within the core 52 and propagates within the core 52 by total reflection at the interface between the core 52 and the cladding 51. Therefore, the light emitted from the end face of the optical fiber 50 spreads in various directions. The light emitted from the end face of the optical fiber is as shown above (
It is impossible to satisfy requirements 1) and (2).

FIG. 9 shows a conventional light projecting optical fiber in which the emitted light is made as thin as possible by providing a collimating optical system on the end face of the optical fiber.

A cylinder 44 is attached and fixed to the tip of the optical fiber 50 (the attachment structure is not shown). A collimating lens 46 is provided inside the cylindrical body 44, and a cover glass 45 is attached to a light exit window at the tip of the cylindrical body 44.

[0013]

However, even with such a configuration, the projected light cannot be sufficiently collimated, and it is inevitable that the emitted light will have a certain degree of spread.

That is, as shown in FIG. 10, when a collimating lens 46A having a focal length f is placed at a distance f from the output end face of the optical fiber 50, the spread angle of the light emitted from the collimating lens 46A is θ is expressed by the following formula.

[0015]

[Equation 1] θ=2 tan-1 (d/2f) ‥‥Formula 1

Here, d is the diameter of the core 52 of the optical fiber 50.

The divergence angle θ can be determined by reducing the diameter d of the optical fiber core or by reducing the focal length f of the collimating lens.
It can be made smaller by making it longer.

Since it is not possible to reduce the diameter d of the optical fiber core, if a collimating lens with a long focal length is used, as shown by reference numeral 46B, the divergence angle will become smaller, as shown by the broken line.

When the focal length of the collimating lens is increased, the collimating lens 46B must be placed at a position farther from the output end face of the optical fiber 50. As mentioned above, the light emitted from the optical fiber 50 has a spread, so if you try to make all the light emitted from the optical fiber 50 enter the collimating lens 46B (to ensure the amount of light), the collimating lens 46B will The lens diameter must be increased.

As a result, the collimating optical system provided at the output end of the optical fiber becomes large, and the above requirement (3) is no longer satisfied.

[0021] This invention satisfies the above requirements (1) and (2).
The present invention provides an optical system that satisfies (3) as much as possible.

[0022]

[Means for Solving the Problems] A light projection device using an optical fiber according to the first invention includes an optical fiber having a light output end face for outputting light introduced into the inside, and an inner surface having a conical reflecting surface. , a conical reflector having a light output side aperture formed smaller than a light input side aperture, and a conical reflector arranged such that the light input side aperture receives the light emitted from the light output end face of the optical fiber; A collimating lens is provided so as to be located approximately at the light exit side aperture of the conical reflector, and collimates the light emitted from the light exit side aperture.

A light projection device using an optical fiber according to the second invention includes an optical fiber having a light output end face for outputting the light introduced therein, an opening on the light output side being formed smaller than an opening on the light input side, The light-incidence-side opening is arranged to receive light emitted from the light-output end face of the optical fiber, and the light introduced into the light-input-side opening is totally reflected on the peripheral side of the light-output-side opening. a conical reflector that guides the light to the conical reflector, and a collimating lens that is arranged so that the focal point is located approximately at the light exit side aperture of the conical reflector, and that collimates the light emitted from the light exit side aperture. It is.

In the collimating optical system using an optical fiber according to the present invention, the light exit side aperture is formed smaller than the light input side aperture, and the light input side aperture receives the light emitted from the end face of the optical fiber. a conical reflector that guides the light introduced into the interior from the light input side opening to the light output side opening by reflection; and a conical reflector such that the focal point is approximately located at the light output side opening of the conical reflector. A collimating lens is arranged to collimate the light emitted from the light emitting side aperture.

In the condensing optical system using an optical fiber according to the present invention, the light exit side aperture is formed smaller than the light input side aperture, and the light input side aperture receives the light emitted from the end face of the optical fiber. a conical reflector that guides the light introduced into the interior from the light input side opening to the light output side opening by reflection; and a conical reflector that collects the light emitted from the light output side opening of the conical reflector. It is equipped with a condensing lens placed at a position where light is emitted.

[0026]

[Operation] In any of the light projection devices, collimating optical systems, and condensing optical systems that use optical fibers, the light emitted from the optical fiber enters the conical reflector through the light input side opening of the conical reflector, and then The light is guided to the light emitting side opening by specular reflection or total reflection, and is emitted from this light emitting side aperture. The light emitted from the light exit side aperture is collimated by a collimating lens or condensed by a condensing lens.

The light incident on the collimating lens or the condensing lens exits from the light exit side opening of the conical reflector. In other words, the light exit side aperture can be considered as a type of light source. In Equation 1 above, the diameter of the light exit side aperture of the conical reflector corresponds to d. The light exit side aperture can be made smaller than the core diameter of the optical fiber.
Therefore, the spread angle θ can be reduced without increasing the focal length f.

[0028]

[Effects of the Invention] As mentioned above, since it is possible to make the diameter of the light exit side aperture of the conical reflector sufficiently smaller than the core diameter of the optical fiber, the light exit side aperture can be regarded as a point light source. Can be done. This makes it possible to keep the spread angle of the light emitted from the lens small without increasing the focal length of the collimating lens or condensing lens.

Therefore, it is possible to create a strongly collimated, narrow light beam, and to construct an optical system that is small, lightweight, and inexpensive.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of a light projecting device using an optical fiber according to the first invention.

The optical fiber 10 is composed of a core 12 at the center and a cladding 11 surrounding the core.

A conical reflector 20 is attached and fixed to the light emitting end of the optical fiber 10. The conical reflector 20 has cylindrical portions 20a and 20b at both ends thereof, and a conical space is formed in the center. The conical reflector 20 is fixed by fitting one cylindrical portion 20a into the end of the optical fiber 10. For fixing the conical reflector 20 to the optical fiber 10, adhesives or suitable fasteners are used, if necessary.

A specular reflective surface 21 is formed on the inner surface of the central conical space of the conical reflector 20 by vapor deposition or sputtering of aluminum or other metal. This conical space has a light input side opening 22 facing the light output end face of the optical fiber 10 and a light output side opening 23 on the opposite side. The size of the light input side aperture 22 is the same as or larger than the cross section of the core 12 of the optical fiber 10, and the light output side aperture 23 is formed much smaller than the light input side aperture 22.

The light emitted from the core 12 of the optical fiber 10 enters the conical space through the light-incidence side aperture 22, is reflected by the reflective surface 21, and exits from the light-emission side aperture 23. Preferably, in order to prevent the generation of return light due to reflection on the reflective surface 21, the light entering the conical space is configured such that it is reflected only once on the reflective surface 21 and exits from the light exit side opening 23. It is preferable to determine the shape of the conical reflector 20. Further, the internal space of the conical reflector 20 is not limited to a conical shape, but may of course be pyramid-shaped.

A collimating lens 26 is disposed and fixed within the other cylindrical portion 20b of the conical reflector 20 so that its focal point is located at the light exit side aperture 23. This cylindrical portion 20b is covered with a cylindrical cover 24, and a cover glass 25 is attached and fixed to an opening (light exit window) in the end face of this cylindrical cover 24.

Since the light exit side aperture 23 of the conical reflector 20 is small, it can be regarded as if it were a point light source. Light emitted from a point light source placed at the focal point of the condenser lens is collimated by the condenser lens.

Therefore, the light emitted from the light exit side aperture 23 is collimated by the lens 26 and
It is emitted to the outside through. In other words, since the diameter d in equation 1 can be made sufficiently small, the lens 26
The spread angle θ of the emitted light can be made small without increasing the focal length f.

FIG. 2 shows a modification, and the basic configuration is the same as that shown in FIG. 1, so the same components are given the same reference numerals and their explanation will be omitted.

A ball lens 27 is used as a collimating lens. In this way, any shape of lens can be used as the collimating lens. The cylindrical cover 24 has an annular protrusion 24a projecting inward on its inner surface, and when this annular protrusion 24a fits into an annular groove formed on the outer peripheral surface of the cylindrical portion 20b of the conical reflector 20, Fixed.

FIGS. 3 and 4 show an embodiment of a light projecting device using an optical fiber according to the second invention.

A support cylinder 34 is attached and fixed to the tip of the optical fiber 10. A conical reflector 30 and a Fresnel lens 36 are fixed inside the support cylinder 34. Further, a cover glass 35 is attached to the light exit window at the tip of the support cylinder 34.

The conical reflector 30 and Fresnel lens 36 are integrally formed of synthetic resin or the like. conical reflector 3
0 is a conical transparent block whose large-diameter end surface serves as a light incident side opening 32 and is in contact with the end surface of the core 12 of the optical fiber 10. The tip of the conical reflector 30 is cut to have an end surface with a small area, and this end surface becomes the light exit side opening 33. The light exit side aperture 33 is much smaller than the light input side aperture 32.

The focal point of the Fresnel lens 36 is located at the light exit side aperture 33.

The light emitted from the core 12 of the optical fiber 10 enters the conical reflector 30 through the light-incidence side aperture 32, and is totally reflected on the circumferential side 31 of the conical reflector 30, thereby passing through the light-output side aperture 33.
guided by. The light emitted from the light exit side aperture 33 then enters the Fresnel lens 36, is collimated, and passes through the cover glass 35.
is projected to the outside through.

The conical reflector 30 is also designed such that the incident light is totally reflected only once and then exits from the light output side aperture 33.
Preferably, its shape is defined.

The conical reflector 30 is not limited to a conical shape, but may be a pyramidal shape. Further, if necessary, a specular reflection film may be formed on the outer peripheral surface 31 of the reflector 30.

Collimating lens is also Fresnel lens 3
6, a plano-convex lens 3 as shown in FIG.
7 can also be used. It goes without saying that the conical reflector and collimating lens may be separate bodies.

In the above embodiment, in place of the collimating lens, a condenser lens is placed at a position to condense the light emitted from the light output side aperture of the conical reflector, so that condensing light using an optical fiber can be achieved. Optical system is realized.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of a light projecting device using an optical fiber according to a first invention.

FIG. 2 is a partially cutaway perspective view showing a modification.

FIG. 3 is an assembled perspective view showing an embodiment of a light projecting device using an optical fiber according to a second invention.

FIG. 4 is a sectional view of the light projection device of FIG. 3;

FIG. 5 is a sectional view showing another example of a collimating lens.

FIG. 6 shows a conventional transmission type optical fiber photoelectric switch.

FIG. 7 shows a conventional reflective optical fiber photoelectric switch.

FIG. 8 shows how light emitted from an optical fiber spreads.

FIG. 9 is a partially cutaway perspective view showing a conventional light projection device.

FIG. 10 shows how light emitted from an optical fiber is spread even when a collimating lens is used.

[Explanation of symbols]

10 Optical fiber 11 Clad 12 Core 20 Conical reflector 20a, 20b Cylindrical portion 21 Specular reflective surface 22 Light entrance side opening 23 Light output side opening 24 Tube cover 25 Cover glass 26 Collimating lens 27 Ball lens (collimating lens) lens) 30
Conical reflector 31 Circumferential side (total reflection surface) 32 Light entrance side opening 33 Light exit side opening 34 Support cylinder 35 Cover glass

Claims (14)

[Claims] [Claim 1] An optical fiber having a light output end face for outputting light introduced therein, the inner surface being a conical reflecting surface, the light output side aperture being formed smaller than the light input side aperture,
a conical reflector arranged such that the light incident side opening receives light emitted from the light output end face of the optical fiber;
and a collimating lens that is arranged so that its focal point is substantially located at the light exit side aperture of the conical reflector and that collimates the light emitted from the light exit side aperture, using an optical fiber. . 2. The optical fiber according to claim 1, wherein a support cylinder is attached to the light output side end of the optical fiber, and the conical reflector and the collimating lens are fixed to the support cylinder. A floodlight device using 3. The light projecting device using an optical fiber according to claim 2, wherein the conical reflector constitutes a part of the support cylinder. 4. The light projecting device using an optical fiber according to claim 2, wherein a light exit window is formed on the distal end surface of the support cylinder, and a transparent cover is attached to the light exit window. 5. An optical fiber having a light output end face for outputting the light introduced into the optical fiber, the light output side opening being formed smaller than the light input side opening, and the light input side opening being the light output end face of the optical fiber. a conical reflector arranged to receive the light emitted from the end face and guiding the light introduced into the interior from the light input side opening to the light output side opening by total reflection on the circumferential side; A light projection device using an optical fiber, including a collimating lens that is disposed substantially at the light exit side opening of the reflector and collimates the light emitted from the light exit side opening. 6. The optical fiber according to claim 5, wherein a support cylinder is attached to the light output side end of the optical fiber, and the conical reflector and the collimating lens are fixed to the support cylinder. A floodlight device using 7. The light projection device using an optical fiber according to claim 5, wherein the conical reflector and the collimating lens are integrally formed. 8. The light projecting device using an optical fiber according to claim 6, wherein a light exit window is formed on the distal end surface of the support cylinder, and a transparent cover is attached to the light exit window. 9. A light exit side aperture is formed smaller than a light input side aperture, the light input side opening is arranged to receive light emitted from the end face of the optical fiber, and the light input side opening is arranged to receive light emitted from the end face of the optical fiber. A conical reflector that guides the introduced light to the light output side opening by reflection, and a conical reflector arranged such that the focal point is approximately located at the light output side opening of the conical reflector, and the light is emitted from the light output side opening. A collimating optical system that uses an optical fiber and is equipped with a collimating lens that collimates light. 10. The collimating optical system using an optical fiber according to claim 9, wherein the conical reflector has a conical mirror surface, and the incident light is guided to the light exit side opening by reflection by the mirror surface. 11. The collimating optical system using an optical fiber according to claim 9, wherein the conical reflector guides the light introduced into the interior to the light exit side opening by total reflection on a peripheral surface. 12. A light exit side aperture is formed smaller than a light input side aperture, the light input side opening is arranged to receive light emitted from an end face of the optical fiber, and the light input side opening is arranged to receive light emitted from the end face of the optical fiber. A conical reflector that guides the introduced light to the light output side opening by reflection, and a condenser lens arranged at a position to condense the light emitted from the light output side opening of the conical reflector. A condensing optical system using an optical fiber. 13. The condensing optical system using an optical fiber according to claim 12, wherein the conical reflector has a conical mirror surface, and the incident light is guided to the light exit side opening by reflection by the mirror surface. . 14. The condensing optical system using an optical fiber according to claim 12, wherein the conical reflector guides the light introduced into the interior to the light exit side opening by total reflection on a peripheral surface.