JPS583201B2 - 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 introduced on December 11, 1971.
Japan as Patent Application No. 124196, dated November 29, 1972, and Patent Application No. 13478, filed on November 29, 1972.
This application has been filed by the applicant as No. 2.

The present invention relates to an improvement of such a light splitter, and its feature is that a diffraction grating is arranged at the interface between two optical members having substantially the same refractive index as the diffraction grating.

Here, the boundary surface is the boundary surface between two substances having different refractive indexes, and is usually the boundary surface between glass and air.

These structural features have the advantage that the light splitter of the present invention allows the use of a large diffraction grating and prevents the quality of the diffraction grating from deteriorating.

Examples of the present invention will be described below in comparison with a light splitter that does not have the configuration of the present invention.

FIG. 1 is the light splitter shown in the above-mentioned application.

This light splitter 1 has a diffraction grating 3 on the surface of a parallel plane glass plate 2.
are attached with adhesive or the like.

It is desirable that the parallel plane glass plate 2, the diffraction grating 3, and the adhesive have substantially the same refractive index.

Further, the diffraction grating is preferably a volume type diffraction grating having a three-dimensional grating structure.

4 and 5 are boundary surfaces in contact with air, respectively.

6 is an exit surface. 7 is a light receiving element.

Incoming light 8 from one boundary surface 5 is split by the diffraction grating 3 into undiffracted light 9 and diffracted light 10.

The undiffracted light passes through the boundary surface 5, but the diffracted light 10 is configured so that the diffraction body 3 diffracts the diffracted light 10 to another boundary surface 4 at an angle that satisfies the condition for total reflection. Therefore, it is totally reflected by the boundary surface 4.

The diffracted light 10 reflected by this surface 4 is further totally reflected by the boundary surface 5, emitted from the exit surface 6, and received by the light receiving element 7.

As is clear from this figure, when the size of the light splitter 1 is a dog, the diffracted light 10 further enters the diffraction grating 3 at a position of 11.12.

Therefore, the diffracted light is diffracted again at these positions 11 and 12, and part of it becomes stray light.

If the diffraction grating has narrow angular characteristics, the diffraction index of the re-diffracted light generated at position 11 will be good.

However, the re-diffracted light generated at position 12 is the incident light 8
The diffraction index of the re-diffracted light is large because the angle of incidence is close to that of .

Therefore, it is necessary to remove the re-diffracted light at these 12 positions.

Furthermore, in the configuration shown in Figure 1, the diffraction grating is in direct contact with the outside air, so if the diffraction grating is made of dichromated gelatin, which is easily affected by humidity, quality deterioration may occur. There was a risk that it would occur.

The present invention was invented taking these points into consideration, and the second
As shown in Figure 3, the diffractive body 3 is held between glass plates.

That is, the parallel plane glass plate 13 is bonded to the boundary surface 5 of the diffractive body 3 using the adhesive as described above.

It is desirable to use glass having almost the same refractive index as the diffraction grating 5 for the glass plate 13.

Further, although the glass plates 2 and 13 are shown as parallel plane glass plates, the present invention is not limited to this, and may have curved surfaces.

As is clear from the figure, the position 12 is far away and no re-diffraction occurs, so no stray light occurs.

Furthermore, since the diffraction grating 3 is not directly exposed to air, there is no risk of quality deterioration.

In this embodiment, the case where the diffraction grating 3 is sandwiched between two parallel plane glass plates has been described, but the same effect can be obtained even if the diffraction grating 3 is enclosed in almost the same glass plate as the diffraction grating 3. be.

Further, in this embodiment, the diffracted light 10 is described as traveling in the direction of the boundary surface 4 on the exit side, but it may be made to travel in the direction of the boundary surface 5' on the incident surface side.

To achieve this, the inclination angle of the grating structure of the diffraction grating 3 with respect to the incident light 8 may be increased as shown in FIG.

The third embodiment shown in FIG. 4 is the most preferred embodiment of the invention.

In this embodiment, the adhesive 14 of the diffraction grating 3 completely seals the diffraction grating 3 so that it is not exposed to the outside air, and further strengthens the bonding state between the glass plates 2 and 3.

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

15 is a coherent light source such as a laser tube.

16 is a beam expander, 17 is a beam splitter, 18 and 19 are coherent light beams divided into two by the beam splitter, and 20 is a reflecting mirror.

21 and 22 are prisms having approximately the same refractive index.

A photosensitive agent 24 coated on a glass substrate 23 is sandwiched between the prisms 21 and 22.

Note that the glass substrate 23 is the parallel plane glass plate 2 described earlier.
It is desirable that the prism can be used as the prism 21. Almost equal to 22.

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

Furthermore, in order to eliminate the formation of an air layer between the prisms 21 and 22, it is desirable to immerse a liquid having the same refractive index as each optical glass or the like between the two prisms 21 and 22.

One coherent light beam 18 split by the beam splitter 17 is directed so as to pass through the glass substrate 23, and the other coherent light beam 19 is directed by the mirror 20 at an angle of total reflection to the upper surface of the glass substrate 23.

In this way, a holographic diffractive material is created.

Also, Figure 6 shows Figure 5 and . Different methods of making diffraction gratings are shown.

This method differs from the method shown in FIG. 5 in that a cylindrical lens 25 is included in the optical path of the coherent light beam 19.

As shown in FIG. 7, the cylindrical lens 25 focuses the light beam 19 on a position where the light receiving element 7 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 focusing lens.

Note that 26 is a light absorbing substance.

[Brief explanation of drawings]

FIG. 1 shows a prior art light splitter, FIG. 2 shows a first embodiment of a light splitter according to the present invention, FIG. 3 shows a second embodiment, and FIG. A diagram showing the third embodiment, FIG. 5 is a diagram showing the best method for producing the diffraction material used in the present invention,
FIGS. 6 and 7 are diagrams showing a production method different from that in FIG. 5. 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 an output surface, 7 is a light receiving element, 8
9 is a light beam, 9 is a undiffracted light, 10 is a diffracted light, 11 and 12 are positions where re-diffraction occurs, and 13 is a parallel plane glass.

Claims (1)

[Claims] 1 A diffraction grating is sandwiched between two plate-shaped optical members in a state of optical close contact with an adhesive having a refractive index that has an index matching effect, one side is used as an incident surface, the other side is used as an output surface, and the above-mentioned Separating the light beam incident from the incident surface into undiffracted light and diffracted light by the diffraction grating, emitting the undiffracted light from the exit surface, and totally reflecting the diffracted light by the entrance surface or the exit surface and guiding it to the light receiver. A light splitter featuring: