JPH02262602A - Optical element - Google Patents

Abstract

PURPOSE:To obtain the optical element which hardly generates reflected light beam to be a cause for flares, ghosts, etc., by providing antireflecting films between the surfaces excluding joint surfaces and light incident/emitting surfaces and light absorptive layers. CONSTITUTION:The antireflecting films C1, C2 are provided between the surfaces excluding the joint surfaces and the light incident/emitting surfaces 1, 2 and the light absorbing layers B. The light quantity lost by the reflection on the joint surfaces is thereby extremely lessened and, therefore, the problem of the unbalance of the light quantity is substantially eliminated and since the reflected light on the joint surfaces is slight, the light to be the cause for the flares, ghosts, etc., decreases. Further, the antireflecting films C2 are provided between the surfaces excluding the light incident/emitting surfaces and the light absorbing layers B as well and, therefore, the reflection of the light on the side faces of the optical element is extremely little and the greater part arrives at the right absorbing layers B. The reflected light which is the cause for the flares, ghosts, etc., is hardly generated and the good-quality images which are uniform and bright are obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical element provided with an antireflection film that can be used in various optical devices.

[Conventional technology]

ill! BACKGROUND OF THE INVENTION Optical devices such as microscopes and endoscopes often use optical elements in which two prisms are bonded together with an adhesive. An example of such an optical element is shown in FIG. 10, which includes two triangular prisms PI, P! are joined on the slope via adhesive layer A, and the surfaces other than the entrance surface 1 and the exit surface 2 are coated with black material such as ink, which absorbs and prevents light from passing through, in order to prevent unnecessary light from entering from the outside. A light absorbing layer B made of paint is provided.

[Problem to be solved by the invention]

When light is incident in such a way that it passes obliquely through the cemented surface of such an optical element, if the light beam is not parallel but convergent as shown in Figure 10, the right and left sides of the optical axis O will be Since the angle of incidence θ1 and θf with respect to the bonding surface are significantly different,
There is a large difference in their Fresnel reflectance. For this reason,
There is a problem in that the amount of light transmitted through the cemented surface becomes non-uniform across the optical axis O.

Also, some of the light reflected from this bonded surface is reflected again from the side of the optical element, as shown by the broken line in the figure, and observed.

Another problem is that the light enters the optical path for shadows and the like, causing flare, ghost, and the like.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to provide an optical element that is less likely to cause imbalance in the amount of light and that is capable of producing reflected light that causes flare, ghost, and the like.

[Means and effects for solving the problems] The present invention provides an optical element including a bonded surface inclined with respect to the incident surface and a light absorption layer covering a surface other than the incident/exit surface. An antireflection film is provided between a surface other than the light input/output surface and the light absorption layer.

According to this configuration, the amount of light lost due to reflection at the bonding surface is extremely small, so the problem of unbalanced light amount is almost eliminated. Furthermore, since the light reflected from the joint surface is weak, the amount of light that causes flare, ghost, etc. is reduced. Moreover, since an anti-reflection film is provided between the light absorption layer and the surface other than the input/output surface, the reflection of light on the side surfaces of the optical element is extremely reduced, and most of the light reaches the light absorption layer and is absorbed. As a result, the occurrence of flare, ghost, etc. is further reduced.

〔Example〕

Hereinafter, the present invention will be described in detail based on an illustrated embodiment. FIG. 1 shows an embodiment of the optical element according to the present invention, the basic configuration of which is the same as that of FIG. An antireflection film C1 is provided on the incident surface 1. An antireflection film C8 is provided between the surface other than the exit surface 2 and the light absorption layer B.
is provided. FIG. 2 is a diagram showing the structure of the first embodiment of the antireflection film C+ provided on the bonding surface. This has four antireflection films deposited between the prisms P+P and the adhesive layer A, respectively, in order to significantly reduce Fresnel reflection occurring at the joint surface of the prisms P1 and P8.

In this example, the two triangular prisms Pt and Px are both made of glass. Then, the divergence angle (θ
, -01) is 8° (therefore, the difference between θ and θ is 16°)
In this case, the following configuration of the antireflection film CI is suitable.

The structure of this antireflection film CI is shown below, however, all thicknesses are expressed in terms of optical thickness (Nd - refractive index x thickness), and the unit is rho.

Layer Material Refractive index (N) Optical thickness (Nd) P+
Glass 1.7859 - A Adhesive 1.56±0.01 1560~560G Pg glass 1.7859 ``In addition, the incident angle θ of the light ray with respect to the bonding surface in the glass is 35° ~ 55°
Fig. 3 shows a reflectance curve when the incident angle θ is -55°.

Further, FIG. 4 shows a reflectance curve for the same incident angle in the case of the following configuration without an antireflection film.

Layer Material Refractive index (N) Optical thickness (Nd) P
+ Glass 1.7859 -A Adhesive 1.56±0.01 1560P, Glass 1.
7859 ``If you compare Figure 3 with Figure 4,
It is clear that in this example, the loss in the amount of light within the visual field due to Fresnel reflection and the amount of ghost light are reduced to approximately one-twentieth. Therefore, an imbalance in the amount of light is less likely to occur, and reflected light that causes flare, ghost, etc. is less likely to occur.

In addition, the feature of this example is that since it is made of extremely stable materials such as ZT and CeFs, the refractive index of the evaporated material changes during evaporation, and the refractive index value varies each time evaporation is performed. As a result, a coating with stable characteristics can be obtained. Additionally, since the same material is repeatedly deposited, the coating process can be simplified. Furthermore, the film structure may be composed of CeF s, which has a refractive index between that of glass and adhesive, and ZT, which has a refractive index higher than that of glass, or may include a very thin film. .

After further consideration, the following conditions were met! It has become clear that good results can be obtained if these conditions are satisfied.

Condition ■ +11 Refractive index of glass>Refractive index of first layer (2)
Refractive index of the 1st layer × Refractive index of the 2nd layer (3) Refractive index of the 2nd layer > Refractive index of the 3rd layer (4) Refractive index of the 3rd layer <4th layer
Refractive index of layer (5) Refractive index of 4th layer>Refractive index of adhesive layer (6) Film thickness of 1st layer Nd1-71±20171
Second layer thickness Nd! -39±15(8) 3rd
Layer thickness Na, -195±45 (91 4th layer thickness
Nd4-11±4 Also, as shown in condition (2) below, if materials with the same refractive index are used frequently, the same material can be used for manufacturing, which is advantageous in terms of cost.

Condition ■ In Condition I, 0 1st layer and 3rd layer have the same refractive index 00 2nd layer and 431st layer have the same refractive index @ Adhesive layer thickness (Nd) is 100 On- or more Figure 5 is reflective Prevention M
It is a figure which shows the structure of 2nd Example of e. This is a single layer anti-reflection film deposited between the prisms P+, Pg and the adhesive layer A. The configuration of this antireflection MCI is shown below.

Layer Material Refractive index (N) Optical thickness (Nd) P
, glass 1.7859 o.

CI CeFs 1.6±0.05 339±
60A Adhesive 1.56±0.01 1560~C
I CePx 1.6±0.05 339±6
0pg Glass 1.7859 - Incidentally, the angle of incidence θ of the light beam in the glass with respect to the joint surface is 35' to 55
6, and FIG. 6 shows a reflectance curve when the incident angle θe is 55'.

Comparing FIG. 6 with FIG. 4, it is clear that this embodiment can reduce the Fresnel reflectance to about one-fifth, and is effective against light loss and ghosting.

Although the first embodiment has a better anti-reflection effect, this embodiment has a very simple structure and has great manufacturing advantages, and is suitable for use only when there are very strict requirements regarding non-uniform brightness. This level is sufficient for practical use.

Further, it goes without saying that the antireflection Hc + may be provided on at least one bonding surface of the adhesive layer A.

FIG. 7 is a diagram showing the structure of antireflection Hc z provided between the light absorption layer B and a surface other than the entrance/exit surface of the prisms P, , P, that is, the side surface. This is the prism P1. P! In order to reduce Fresnel reflection occurring between the side surface of the prism P+ and the light absorption layer B, three antireflection films are deposited between the prism P+, Pt, and the light absorption layer B.

The configuration of this anti-reflection 11ci is shown below.

Layer Material Refractive index (N) Optical thickness (Nd
)P+, Pg glass 1.7859 cX1
Sunlight absorption layer 1.56 g of carbon mixed into a transparent body.11 gF is provided to prevent total reflection on the glass surface.

This embodiment may be considered to have a three-layer structure including MgP, or it may be considered that a single layer coating is applied between glass, M, F, MgF, and a light absorption layer, respectively.

FIG. 8 shows a reflectance curve when the ghost incident angle is θ'-65°.

Moreover, FIG. 9 shows a reflectance curve for the same ghost incident angle in the case where there is no antireflection film in the following configuration.

Layer Material Refractive index (N) Optical thickness (Nd)
P,,P wealth glass 1.7859 Marshal H mountain 1
．． 38 1380 B Light absorption layer 1.52 (To) Comparing FIG. 8 and FIG. 9, this example has nothing to do with visual light loss, but it does have a problem with the decrease in the light amount of ghost rays. It is clear that the effect is sufficient and the amount of light is reduced to about 115.

〔Effect of the invention〕

As described above, the optical element according to the present invention is less likely to cause an imbalance in the amount of light, and is less likely to cause reflected light that causes flare, ghost, etc., and therefore can obtain high-quality images with uniform brightness. .

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of one embodiment of the optical element according to the present invention, and FIG.
FIG. 3 is a graph showing the reflectance curve when the first embodiment is used; FIG. 4 is a graph showing the reflectance curve when the first embodiment is not used. FIG. 5 is a diagram showing the structure of a second embodiment of the antireflection film provided on the joint surface of the optical element, FIG. 6 is a graph showing the reflectance curve when the second embodiment is used, and FIG. The figure shows the structure of the anti-reflection film provided between the light absorption layer and the surface other than the entrance plane of the optical element, and Fig. 8 shows the reflectance curve when the anti-reflection film shown in Fig. 7 is used. Figure 9 is a graph showing the reflectance curve when the anti-reflection film in Figure 7 is not used.
Figure 0 is a sectional view of a conventional example. Pt, Ps...prism, A...adhesive layer, B
...Light absorption layer, C+, C snow...Anti-reflection film, l
...Incidence surface, 2...Emission surface. Figure 3 Figure 2 Figure 5 Figure 4 Off Figure Figure 10 Figure 16 Figure O Rishi J4Ps Figure 19 Figure 6. Contents of amendment fll rZT on page 6, line 11 and line 20 of the specification is corrected to ``Z T (Zr Ox) J. (2) Between line 9 and line 21O on page 11 of the specification Insert the following sentence: ``In addition, Ta is used instead of 2.0 as the material for the anti-reflection film.
Even if a mixture of xes or Z-Os and Taxes is used, almost the same results are obtained. In addition, Al or Os may be used in place of C6F3, 1 procedural amendment (spontaneous) July 1, 1985 Director-General of the Japan Patent Office 1, Indication of Case Patent Application No. 1983-27170 2, Title of the Invention Optical Element 4, Agent: 5-19 Shinbashi, Minato-ku, Tokyo 105 Phone: Tokyo (432) 4576 <6582) Yasushi Shinohara, Patent Attorney 5, Column for detailed explanation of the invention in the specification to be amended.

Claims (1)

[Claims] In an optical element comprising a bonded surface inclined with respect to the incident surface and a light absorption layer covering a surface other than the incident/exit surface, between the bonded surface and the surface other than the input/output surface and the light absorption layer. An optical element characterized in that an antireflection film is provided on the surface of the optical element.