JPS583202B2 - Hikari Bun Katsuki - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a light splitter that splits a light beam using a diffraction grating.

A light splitter using a diffraction grating was filed as Patent Application No. 124196 on December 11, 1970, and as Patent Application No. 13478 on November 29, 1978.
This application has been filed by the applicant as No. 2.

These applications were then combined and filed in West Germany.

This West German application was published as West German Patent Publication No. 2,361,623 on July 12, 1971.

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 this adhesive desirably has approximately the same refractive index as 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 configured such that the undiffracted light passes through the boundary surface 4 and the diffracted light 8 is diffracted at a diffraction angle such that it is totally reflected by the boundary surface 4.

Therefore, the diffracted light 8 is totally reflected by the boundary surface 4 and directed toward the boundary surface 5 .

Therefore, the diffracted light 8 enters the diffraction grating 3 again and is diffracted again.

However, if this diffraction grating 3 has narrow angular characteristics, the diffracted light 8 will pass through this diffraction grating 3,
It is totally reflected by the boundary surface 5.

The light further reflected by this boundary surface 5 naturally enters the diffraction grating 3.

Since this light has little difference in incidence angle from the incident light 6, re-diffracted light 9 is generated.

This re-diffracted light 9 may be emitted from the boundary surface 4 as shown in Figure 2.

Such re-diffracted light 9 becomes noise light when used in a photometry device of a single-lens reflex camera, as shown in FIG. 3, for example.

To explain Fig. 3, 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 ivy, 20 is an eye, and 21 is a photodetector.

Light from the outside world is focused by a photographic lens 10 through a focusing glass 15
The light from the focusing glass enters the light splitter 16, the diffracted light reaches the photodetector 21 by total reflection, and the undiffracted light passes through the condenser lens, pentaprism, and eye bead and reaches the eye.

In this case, the fundamental diffracted light 9 is naturally also condensed by the condenser lens 17,
The light reaches the eye 20 via the pentaprism 18 and the eye bead 19, forming a ghost image.

Further, this re-diffracted light 9 is generated in the same manner in a light splitter configured as shown in FIG.

The difference between the light splitter of FIG. 1 and the light splitter of FIG. 4 is that the diffraction grating 3 is sandwiched between two substantially identical plane parallel plates 2, 22.

The light splitter shown in FIG. 5 differs from the light splitter shown in FIG. 4 in that the angle of the diffraction grating is made larger and steeper with respect to the incident light.

Therefore, the diffracted light is first reflected by the surface 5.

FIG. 6 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 divided into two by the beam splitter, and 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.

Note that the glass substrate 38 is the parallel plane glass plate 2 described earlier.
It is preferable that the prisms be used as prisms 36 and 37, and their refractive index is approximately equal to that of the prisms 36 and 37.

Further, it is desirable that the photosensitive material 24 is coated sufficiently thickly so that a volume hologram can be created, and the photosensitive material 24 is preferably one that can create a phase hologram, such as dichromated gelatin or a photopolymer. desirable.

Moreover, in order to eliminate the formation of an air layer between the prisms 36, 37, a liquid having the same refractive index as each optical glass, etc. is applied to the two prisms 36, 36, 37. It is desirable to soak the water between 37 and 37 hours.

One coherent light beam 33 split by the beam splitter 32 is directed so as to pass through a glass substrate 38, and the other coherent light beam 34 is directed by a mirror 35 at an angle of total reflection to the upper surface of the glass substrate 38.

In this way, a holographic diffractive body is created.

Further, FIG. 7 shows a method for creating a diffraction grating that is different from that in FIG. 6.

This method differs from the method shown in FIG. 6 in that a cylindrical lens 40 is included in the optical path of the coherent light beam 34.

As shown in FIG. 8, the cylindrical lens 40 focuses the light beam 34 on a position where the light receiving element 21 will be placed in the future, 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 on a light receiver without a condensing lens.

Note that 41 is a light absorbing substance.

The light splitter described above generates re-diffracted light as previously explained with reference to FIG.

The present invention relates to a light splitter that prevents the generation of this re-diffracted light.

This prevention of re-diffracted light can be achieved by changing the structure of the diffraction grating at the position where re-diffraction would occur, that is, by changing the angle selection characteristics.

SUMMARY OF THE INVENTION An object of the present invention is to provide a light splitter in which the above-mentioned drawbacks are eliminated. and the first part of the diffraction grating.
The second part of the diffraction grating on which the first diffracted light beam diffracted by the second part re-enters has different angle selection characteristics to prevent re-diffraction.

First, an example in which a volume type phase hologram is used as the diffraction grating structure will be described.

As shown in FIG. 9, the volume type hologram diffraction grating has interference fringes formed primarily in the thickness direction of the photosensitive material.

(In the case of a phase hologram, these interference fringes are formed by changes in the refractive index.

) The characteristic of such a diffraction grating is that it has a Gragg diffraction condition, and for a light beam of wavelength λ, θ Bragg = cos-1 (λ/2d) d is the incident light beam that satisfies the grating line spacing condition. It diffracts most efficiently against
As the condition deviates from this condition, the diffraction efficiency decreases.

The situation is shown in FIG. In this figure, the angular width Δθ is related to the thickness of the diffraction grating, and the thicker the grating, the smaller the width.

Therefore, if the first diffracted light re-enters the second part of the diffraction grating, the angular characteristics of the second part of the diffraction grating should be changed so that the first diffracted light does not fall within its angular width Δθ. By setting such characteristics, re-diffraction of the first diffracted light by the second portion of the diffraction grating can be prevented.

A first method of changing the angle selection characteristics of the second portion B of the diffraction grating is to partially change the inclination angle in the thickness direction of the diffraction grating, as shown in FIG.

For example, the dichromated gelatin method using a Kodak 649F dry plate (Reference: Appl. Ont. 9, No. 7,
1651 (1970)), the thickness of the sensitive material is about 15μ, the inclination angle of the first portion A of the diffraction grating is α=35°, and the pitch is d=0. The angular width for λ = 5500 Å when 48 μm is approximately 1°, and the second portion B of the diffraction grating
It is sufficient to tilt it by about 1°.

Incidentally, such a diffraction grating can be obtained by changing the cutting angles of the coherent beams 33 and 34 shown in FIG. 6 between the first portion and the second portion.

A second way to change the angular properties of the second portion B of the grating is to change the spacing d of the grating lines shown in FIG.

For example, by setting the interval d from 0.48 μm to 0.51 μm, the θ Bragg angle can be shifted by 1°, and re-diffraction can be prevented as in the case of using the diffraction grating of the first method.

Moreover, re-diffraction can be prevented even if the directions of the grating lines of the first portion A of the diffraction grating and the second portion B of the diffraction grating are made different.

In particular, it is effective to make the directions of the grating lines of the first portion A of the diffraction grating and the second portion B of the diffraction grating different by 90 degrees as shown in FIG.

In this example, when obtaining a "rice ball-shaped" condensing photometric distribution, we focus the light on the head of the rice ball and change the direction of the diffraction grating by 90 degrees in the area where ghosts are likely to occur due to re-diffraction to avoid re-diffraction. At the same time, since the sky part of the subject is usually located at the head of this rice ball, we divided the metering for this part,
The other light-receiving element B can be used for photometry.

Although the above example prevents re-diffraction between diffraction gratings in the same plane, the present invention is not limited to such an arrangement. For example, a three-dimensional arrangement as shown in FIG. It can also be applied to re-diffraction release between diffraction gratings.

Further, the diffraction grating having the angular characteristics of the present invention can be produced not only by a volume type phase hologram but also by an ion implantation method.

[Brief explanation of drawings]

Figure 1 is a diagram showing a conventional light splitter, Figures 2 and 3 are diagrams explaining the drawbacks when the light splitter in Figure 1 is used in a single-lens reflex camera, and Figures 4 and 5 The figure shows a light splitter having a different configuration from that in FIG. 1. 6, 7, and 8 are diagrams showing the most preferable method for creating a diffraction grating. Figures 9 and 10 are diagrams for explaining Bragg's conditions, Figure 11 is a diagram for explaining the first embodiment of the present invention, Figure 12 is a diagram for explaining the second embodiment, and Figure 13 is a diagram for explaining the third embodiment. FIG. In the figure, 1 is a light splitter, 2 is a parallel plane glass plate, 3 is a diffraction grating, 4 and 5 are boundary surfaces, 6 is incident light, 21 is a light receiver, and A
is the first part of the grating and B is the second part of the grating.

Claims (1)

[Claims] 1 A diffraction grating is arranged between two boundary surfaces, and the light flux incident from one boundary surface is split into undiffracted light and diffracted light by the first part of the diffraction grating, and the undiffracted light is transmitted to the other boundary surface. At the same time, the diffracted light is totally reflected by the one and/or the other boundary surface, and is again incident on the second part of the diffraction grating in substantially the same direction of incidence as the direction of incidence on the first part. In the light splitter directed to the photodetector through the rear exit surface, the grating is a volume grating, the first part and the second part having different angular selection characteristics;
A light splitter characterized in that when light diffracted by one part is incident on the other part, re-diffraction does not occur.