JPS6337366B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a light splitter that uses a diffraction grating to split a light beam for use in camera photometry, etc.

A light splitter using a diffraction grating was published in 1973.
82355 JP-A-50-86356, JP-A-51-144634~
No. 144652 has already been filed by the applicant.

Hereinafter, the light splitter filed above and the light splitter related to the present invention will be explained using the drawings.

FIG. 1 is a diagram illustrating the light splitter shown in the above-mentioned patent application. In this light splitter 1, a diffraction grating 3 having substantially the same refractive index as the parallel plane glass plate 2 is bonded to a parallel plane glass plate 2 with an adhesive or the like. Note that it is desirable that this adhesive has substantially the same refractive index as that of the parallel plane glass plate 2. 4 and 5 are boundary surfaces, and these boundary surfaces 4 and 5 are usually in contact with air. 6 is a light flux passing through one boundary. 7 is the undiffracted light from the diffraction grating 3. 8 is diffracted light. The diffraction grating 3 is the undiffracted light 7
The structure is such that the diffracted light 8 is diffracted at a diffraction angle such that the diffracted light 8 is totally reflected by the boundary surface 4 so that it is transmitted through the boundary surface 4. Therefore, the diffracted light 8 is totally reflected by the boundary surface 4 and directed toward the boundary surface 5 . The light totally reflected by the boundary surface 5 passes through the output end surface 9 and is directed toward the photodetector P.

Such a light splitter is most suitable for the photometry device of a single-lens reflex camera. An example of this application is shown in FIG. 2 below.

10 is a photographing lens, 11 is an aperture, 12 is a quick return mirror, 13 is an imaging plane, 14 is a shutter, 15 is a focusing glass, 16 is a light splitter, 1
7 is a condenser lens, 18 is a pentaprism, 19 is an eyepiece, 20 is an eye, and 21 is a photodetector. Light from the outside world is imaged on a focusing glass 15 by a photographing lens 10, the light from the focusing glass enters a light splitter 16, the diffracted light reaches a photodetector 21 by total reflection, and the undiffracted light reaches a condenser lens 17. , pentaprism 18, eyepiece 1
It reaches the eye through 9.

Further, FIGS. 3 and 4 show a light splitter having a different configuration from that in FIG. 1.

The difference between the light splitter shown in FIG. 1 and the light splitter shown in FIG.
This is the point held by 2. The light splitter shown in FIG. 4 differs from the light splitter shown in FIG. 3 in that the angle of the diffraction grating is made larger with respect to the incident light. Therefore, the diffracted light is first reflected by the surface 5'.

FIG. 5 is a diagram showing the most preferable method for producing a diffraction material used in the light splitter of the present invention.

30 is a coherent light source such as a laser tube. 31 is a beam expander, 32 is a beam splitter, 33 and 34 are coherent light beams split into two by the beam splitter,
35 is a reflecting mirror.

36 and 37 are prisms having approximately the same refractive index. A photosensitive agent 39 coated on a glass substrate 38 is sandwiched between the prisms 36 and 37.

The glass substrate 38 is preferably one that can be used as the parallel plane glass plate 2 described above, and
This refractive index is approximately equal to that of the prisms 36 and 37.
Further, it is desirable that the photosensitive material 39 be applied sufficiently thickly so that a volume hologram can be created.
Further, as the photosensitizer, it is desirable to use a material capable of producing a phase-type hologram, such as dichromated gelatin or a photopolymer. Furthermore, in order to eliminate the formation of an air layer between the prisms 36 and 37, it is desirable to immerse a liquid having the same refractive index as each optical glass or the like between the two prisms 36 and 37.

One coherent beam 33 split by the beam splitter 32 is directed so as to pass through the glass substrate 38, and the other coherent beam 34 is directed by the mirror 35 at a total reflection angle with respect to the upper surface of the glass substrate 38. Directed by. In this way, a holographically diffractive body is created.

Further, FIG. 6 shows a method for creating a diffraction grating that is different from that in FIG. 5. The difference in this method is the fifth
Compared to the method shown in the figure, this method includes a cylindrical lens 140 in the optical path of the coherent light beam 34. With this cylindrical lens 140, the light beam 34 is transmitted to the future photodetector P as shown in FIG.
is focused at the position where it is placed, and then diverges. Therefore, when a diffraction grating made using such a cylindrical lens is used as a light splitter, it has the advantage that diffracted light can be focused to a certain extent on a light receiver without a condensing lens. Note that 141 is a light-absorbing substance.

However, the above-mentioned light splitter has disadvantages as explained below. That is, as shown in FIG. 8, the light incident on the diffraction grating 40 is diffracted at an angle α with respect to the diffraction grating surface according to Bragg's diffraction conditions. (For simplicity, the angle change due to the difference in diffraction index between the diffraction grating and the glass plate is ignored.) This angle α
Most of the light diffracted by the glass plate reaches the end face 9 while undergoing total reflection on the surface of the glass plate, where it is refracted and exits at an angle θ.

Therefore, the light split by the diffraction grating 40 having a constant area is split into two symmetrical emitted light beams 45 and 46 at the exit end 9. In that case, it is sufficient that the photodetector P is close to the exit end face 9 as shown in FIG. 1, but if they are arranged at regular intervals as shown in FIG. If the light is not incident, the situation described above will occur. In devices such as general cameras, it is often necessary to place the photodetector in the position shown in Figure 8 due to the structural relationship with other parts. This method has the disadvantage that the divided luminous flux cannot be detected effectively.

In view of the above, the present invention aims to provide a light splitter that can effectively guide split light to a photodetector even when the distance between the exit end face of the light splitter and the photodetector becomes large. purpose.

FIG. 9 shows the first embodiment. 44 in Figure 9
is a transparent body whose surface facing the photodetector P has a V-shaped notch shape. This transparent body 44 has a refractive index substantially the same as the refractive index n ₁ of the parallel flat glass 2, and is bonded to the end surface of the parallel flat glass 2 via the antireflection film 43. Furthermore, the V-shaped notches have an apex angle β as shown in Fig. 9, and this apex angle β is preferably n ₁ sin (90° − β − α) = sin (90° − β). has a value to be determined. In a light splitter having such a transparent body, among the split light that is diffracted by the diffraction grating and transmitted through the flat glass while being totally reflected, it is reflected at the upper surface 41 and is reflected at the V-shaped upper end surface 48 as shown in FIG. The light emitted from the V
The light refracted and emitted from the character-shaped end surface 49 is emitted in a direction substantially parallel to the flat glass, and is incident on a photodetector placed quite apart from the exit end surface.
In this embodiment, the transparent body 44 may be placed a little apart from the end surface of the flat glass without being bonded to it, or V-shaped notches may be formed directly on the end surface of the parallel flat glass 2. In addition, in general cameras, etc., the incident light 6 is not only perpendicular to the diffraction grating surface, but is also distributed within a certain angular range, so the apex angle β of the V-shaped increments completely satisfies the above conditional expression. Further, the optimum value can be changed depending on the position of the photodetector.

In this way, a light splitter whose exit end face has a refracting surface formed by an inclined plane forming an angle β different from a right angle to the total reflection surface can effectively emit light even if the distance between the photodetector and the exit end face is long. Split light can be guided to the detector.

In the embodiment shown in FIG. 9, a V-shaped notch formed by two symmetrical slopes was used as the exit end face of the light splitter. It is possible to form an injection end surface that achieves the following. FIG. 10 is a diagram showing an embodiment of the invention, in which a light splitter is formed by a plurality of slopes 50 forming a predetermined angle β with a total reflection surface 41 or 42 parallel to the diffraction grating surface and a plurality of surfaces 51 parallel to the total reflection surface. The end face is formed.

Also in this light splitter, the emitted light that spreads in the thickness direction of the light splitter is totally reflected at the surface 51 and the slope 50
Due to the refraction effect at , the light is effectively directed toward the photodetector.

FIG. 11 shows the embodiment shown in FIG. 9, in which a cylindrical lens 52 is further inserted between the exit end face and the photodetector to condense the emitted light that spreads in the direction perpendicular to the thickness of the light splitter. This shows an example with added effects.

Further, FIG. 12 shows that a member 53 having V-shaped increments that effectively directs the emitted light that spreads in the thickness direction of the light splitter toward the photodetector has a curvature in the direction perpendicular to the member 53, as shown in FIG. Cylindrical lens 5
An embodiment that also has the effects of the second example will be shown.

In this embodiment, it is possible to effectively guide the emitted light that spreads in two directions to the photodetector using a single exit surface.

Although FIGS. 11 and 12 show only an example in which there is one V-shaped notch, the same effect can be obtained using a plurality of V-shaped notches.

In addition, in an embodiment in which a member having an exit surface with an oblique refracting surface is installed apart from the parallel flat glass 2, the oblique jetting surface may be placed opposite to the exit surface of the parallel flat glass. .

As described above, the light splitter of the present invention is an extremely highly usable light splitter that can effectively guide split light in the direction of the light detection means with a simple mechanism even if the light detection means is far away. I can do things.

[Brief explanation of the drawing]

Figure 1 is a diagram explaining a conventional light splitter, Figure 2 is a diagram explaining the application of the light splitter in Figure 1 to a photometric device for a single-lens reflex camera, Figures 3 and 4. Figure 5 is a diagram explaining a light splitter different from Figure 1.
Figures 6 and 7 are diagrams explaining the most preferable method for making a diffraction material used in a light splitter, Figure 8 is a diagram explaining the drawbacks of a conventional light splitter, and Figure 9 is a diagram explaining the method used in the book. Figure 10 is a diagram explaining the first embodiment of the invention, Figure 10 is a diagram explaining the second embodiment, and Figures 11 and 12 show that the light splitter also has light condensing properties in the direction perpendicular to the thickness direction. It is a figure showing an example. In the figure, 1 is a light splitter, 2 is a parallel flat glass,
4, 5, 41, 42 are boundary surfaces, 40 is a diffraction grating,
Reference numeral 9 indicates an exit surface, P a photodetector, 48, 49, and 50 oblique surfaces, and 52 a cylindrical lens.

Claims (1)

[Claims] 1. A diffraction grating is disposed between two boundary surfaces, a light flux incident from one boundary surface is split into undiffracted light and diffracted light by the diffraction grating, and the undiffracted light is split between two boundary surfaces. In the light splitter that transmits the diffracted light through the surface, totally reflects the diffracted light by the one or the other boundary surface, and emits the diffracted light toward the photodetector from the output end surface, the output end surface of the light splitter has the boundary surface. A plurality of refractive surfaces having mutually different inclination directions are provided obliquely to the boundary surface, or an optical element having a plurality of refractive surfaces having mutually different inclination directions obliquely provided to the boundary surface is provided. Features a light splitter. 2. The light splitter according to claim 1, wherein the refraction surface is composed of a plurality of oblique surfaces. 3. The light splitter according to claim 1, wherein the refracting surface has a curvature for condensing light.