JP2011095310A - Optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical element having high transmittance in the optical element in which light entering and outgoing surfaces forming a light reflecting suppression film include a plurality of light entering and outgoing surface parts which are arranged by centering an optical axis, are mutually different in angles for the optical axis and discontinuously installed. <P>SOLUTION: The light reflecting suppression film 20 is composed so that each of light wavelength regions Δλ<SB>1</SB>, Δλ<SB>2</SB>includes a use wavelength region Δλ<SB>0</SB>. The light wavelength region Δλ<SB>1</SB>is a light wavelength region suppressing reflection in the light entering and outgoing surface 10a when film thickness of the light reflecting suppression film 20 is the maximum film thickness d<SB>0</SB>. The light wavelength region Δλ<SB>2</SB>is a light wavelength region suppressing reflection in the light entering and outgoing surface 10a when the film thickness of the light reflecting suppression film 20 is the minimum film thickness d<SB>1</SB>. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical element.

  Conventionally, for example, in an optical device such as a liquid crystal display device, a Fresnel lens sheet having a Fresnel lens surface is used as a lens used for condensing and diffusing light. The Fresnel lens sheet has a large optical power despite its thin sheet thickness. For this reason, by using a Fresnel lens sheet, it becomes possible to achieve high functionality and downsizing of the optical device.

  By the way, the Fresnel lens sheet is also required to have a high transmittance as in the case of a normal optical element. For this reason, for example, the following Patent Document 1 proposes to provide an antireflection film on the light entrance / exit surface of the Fresnel lens sheet.

JP 2007-86774 A

  Patent Document 1 describes that by providing an antireflection film on at least one entrance / exit surface of a Fresnel lens sheet, the reflectance can be reduced and the transmittance can be increased. However, as a result of intensive studies by the inventors, it has been found that, for example, when an antireflection film is simply formed as in the case of forming an antireflection film on a glass substrate, reflection may not be sufficiently suppressed.

  The present invention has been made in view of such a point, and an object of the present invention is to arrange the light incident / exit surfaces on which the light reflection suppressing film is formed around the optical axis, and the angles with respect to the optical axis are mutually different. It is an optical element including a plurality of light entrance / exit surfaces provided differently and discontinuously, and an optical element having high transmittance.

The optical element according to the present invention includes an element body and a light reflection suppressing film. The element body has a pair of light entrance / exit surfaces. The light reflection suppression film is a film that suppresses reflection of light on the light entrance / exit surface. The optical element according to the present invention is an optical element that is used for light in the used wavelength range Δλ ₀ . The light entrance / exit surface on which the light reflection suppressing film is formed includes a plurality of light entrance / exit portions. The plurality of light entrance / exit surfaces are arranged around the optical axis. The plurality of light entrance / exit surfaces have different angles with respect to the optical axis and are provided discontinuously. The light reflection suppression film is formed on the plurality of light entrance / exit surfaces. In the optical element according to the present invention, the light reflection suppressing film is configured such that each of the light wavelength region Δλ ₁ and the light wavelength region Δλ ₂ includes the use wavelength region Δλ ₀ . Here, the light wavelength region Δλ ₁ is a light wavelength region in which reflection is suppressed at the light incident / exit surface when the thickness of the light reflection suppressing film is d ₀ . d ₀ is the film thickness of the light reflection suppressing film in the portion where the film thickness of the light reflection suppressing film is maximum in the normal direction of the light entrance / exit surface portion. The light wavelength region Δλ ₂ is a light wavelength region in which reflection is suppressed at the light incident / exit surface when the thickness of the light reflection suppressing film is d ₁ . d ₁ is the film thickness of the light reflection suppressing film in the portion where the film thickness of the light reflection suppressing film is minimum in the normal direction of the light incident / exit surface portion.

  In the present invention, the film thickness of the light reflection suppressing film in the normal direction of the light incident / exit surface portion is the normal direction of the light incident / exit surface portion in the portion of the light reflection suppressing film located on a certain light incident / exit surface portion. Is the film thickness of the light reflection suppressing film. That is, the measurement direction of the film thickness is different between the portions of the light reflection suppressing film that are located on different light entrance / exit surfaces.

Further, in the present invention, when the film thickness of the light reflection suppressing film is d ₀ , the light wavelength range Δλ ₁ in which reflection is suppressed on the light entrance / exit surface is the light reflection when the light reflection suppressing film is not formed. It refers to the wavelength region of light where the light reflectance is lower than the rate.

Similarly, the wavelength range Δλ _{2 of the} light whose reflection is suppressed at the light incident / exit surface when the film thickness of the light reflection suppressing film is d ₁ is also higher than the light reflectance when the light reflection suppressing film is not formed. It refers to the wavelength range of light where the light reflectance is low.

The light wavelength range Δλ ₁ in the optical element is, for example, between the light reflection suppression film and the flat plate when the light reflection suppression film having a film thickness of d ₀ is formed on a flat plate made of the same material as the element body. Can be obtained by directly or indirectly measuring the reflection of light at the boundary surface.

Similarly, the wavelength range Δλ ₂ of the light in the optical element is, for example, between the light reflection suppressing film and the flat plate when the light reflection suppressing film having a film thickness d ₁ is formed on the flat plate made of the same material as the element body. It can be determined by directly or indirectly measuring the reflection of light at the interface between them.

  In the present invention, as described above, the light input / output surface on which the light reflection suppressing film is formed includes a plurality of light input / output surface portions. The plurality of light entrance / exit surfaces have discontinuous angles with respect to the optical axis. That is, in the present invention, the light incident / exit surface on which the light reflection suppressing film is formed is a Fresnel lens surface (also referred to as a discontinuous refractive surface) or a phase step surface, and a surface having a plurality of steps. Thus, even if a light reflection suppressing film is formed on a light incident / exit surface having a plurality of steps, a sufficient light reflection suppressing effect may not be obtained.

  As a result of intensive studies by the present inventors, the cause of this is that when a light reflection suppressing film is formed on a surface having a plurality of steps (hereinafter, also referred to as “step surface”), the thickness of the light reflection suppressing film is It turned out that it was not uniform. That is, when the light reflection suppressing film is formed on the step surface, a light reflection suppressing film having a non-uniform film thickness is formed, and a portion thinner than the desired film thickness is partially formed. Here, the wavelength region in which the light reflection suppressing film can suppress light reflection (hereinafter referred to as “reflection suppressing wavelength region”) varies depending on the film thickness of the light reflection suppressing film. Specifically, the reflection suppression wavelength region of the light reflection suppression film shifts to the lower wavelength side as the light reflection suppression film becomes thinner. For this reason, for example, if the film thickness of the light reflection suppression film becomes too thin, and the reflection suppression wavelength range of the light reflection suppression film is greatly shifted to the lower wavelength side, the maximum wavelength of the reflection suppression wavelength range of the light reflection suppression film However, it becomes smaller than the maximum wavelength of the used wavelength range. As a result, the reflectance in the portion on the long wavelength side of the used wavelength range increases, and the transmittance decreases.

For example, as shown in FIG. 1, when the wavelength region Δλ ₁ is substantially the same as the used wavelength region Δλ ₀ , the light reflection suppression wavelength region Δλ _ref in the portion where the film thickness is thinner than d ₀ is Since it is located on the lower wavelength region side than the wavelength region Δλ _1, the portion Δλ ₃ on the higher wavelength region side of the used wavelength region Δλ ₀ is not included. Therefore, reflection of light in the portion Δλ ₃ on the high wavelength region side of the used wavelength region Δλ ₀ cannot be sufficiently suppressed. Therefore, the transmittance in the wavelength region Δλ ₃ is lowered.

On the other hand, in the present invention, when the film thickness of the light reflection suppressing film is d ₀ , the light reflection suppressing wavelength region Δλ ₁ where reflection is suppressed at the light incident / exit surface and the film thickness of the light reflection suppressing film are d. _The light reflection suppressing film is configured so that each of the reflection suppression wavelength regions Δλ _{2 of} which reflection is suppressed at the light incident / exit surface when it is ₁ , includes the use wavelength region Δλ ₀ . That is, even when the film thickness of the light reflection suppression film is reduced to d ₁ , the light reflection suppression film is configured such that the wavelength range in which light reflection is suppressed includes the use wavelength range Δλ ₀ . .

Specifically, for example,
Use wavelength range Δλ ₀ : λ _{min0 to} λ _max0 ,
Reflection suppression wavelength region Δλ ₁ : λ _{min1 to} λ _max1 ,
Reflection suppression wavelength region Δλ ₂ : λ _{min2 to} λ _max2 ,
((Film thickness d ₁ ) / (film thickness d ₀ )): x,
((Thickness _d 1) / (film thickness _d 0)) = when x, the magnitude of the maximum wavelength lambda _max2 reflection-inhibiting wavelength range [Delta] [lambda] ₂ with respect to the maximum wavelength lambda _max1 reflection-inhibiting wavelength range [Delta] [lambda] ₁ (lambda _max2 / Λ _max1 ): y,
Then, the light reflection suppressing film is designed so as to have a relationship as shown in FIG.

In other words, in the present invention, the minimum wavelength λ _{min1 of the} reflection suppression wavelength region Δλ ₁ is used in anticipation of a portion where the film thickness of the light reflection suppression film becomes y times thinner than the target film thickness d _0. The light reflection suppressing film is smaller than the minimum wavelength λ _min0 of the wavelength region Δλ ₀ and the maximum wavelength λ _max1 is not less than λ _max0 / y (that is, λ _max1 × y is not less than λ _max0 ). Is configured. Therefore, the minimum wavelength λ _min2 of the reflection suppression wavelength region Δλ ₂ that is shorter than the minimum wavelength λ _{min1 of} the reflection suppression wavelength region Δλ ₁ is smaller than the minimum wavelength λ _min0 of the use wavelength region Δλ ₀ . Further, since λ _max1 ≧ λ _max0 / y, λ _max2 = λ _max1 × y ≧ λ _max0 . Therefore, the use wavelength range Δλ ₀ is also included in the reflection suppression wavelength range Δλ ₂ . Therefore, even in a portion of the light reflection suppressing film that is thinner than the target film thickness d _0, it is possible to suppress the reflection of light in the used wavelength range Δλ ₀ . Therefore, in the present invention, it is possible to effectively suppress the reflection of light on the light entrance / exit surface in the entire use wavelength range Δλ ₀ . As a result, high transmittance can be realized in the entire use wavelength range Δλ ₀ .

Here, the inventors of the present inventors have intensively studied, the maximum wavelength lambda _max2 reflection-inhibiting wavelength range [Delta] [lambda] ₂ is substantially a value obtained by multiplying the d _{1 /} d ₀ to the maximum wavelength lambda _max1 reflection-inhibiting wavelength range [Delta] [lambda] ₁ It turns out that they match. That is, in the above example, it was found that x (= ((film thickness d ₁ ) / (film thickness d ₀ ))) _≈y (= λ _max2 / λ _max1 ). Therefore, by designing the light reflection suppression film such that the value obtained by multiplying the maximum wavelength λ _max1 of the reflection suppression wavelength region Δλ ₁ by d ₁ / d ₀ is _equal to or greater than the maximum wavelength λ _max0 of the use wavelength region Δλ ₀ . , Λ _max1 ≧ λ _max0 and λ _max2 ≧ λ _max0 .

Therefore, in the present invention, the value obtained by multiplying the maximum wavelength λ _max1 of the reflection suppression wavelength region Δλ ₁ by d ₁ / d ₀ is _equal to or greater than the maximum wavelength λ _max0 of the use wavelength region Δλ ₀ , and the reflection suppression wavelength region Δλ as the _first minimum wavelength lambda _min1 is less than the minimum wavelength lambda _min0 used wavelength range [Delta] [lambda] _0, it is preferable that the light reflection suppression film is formed. By doing so, it is possible to reliably increase the light transmittance in the use wavelength region Δλ ₀ .

In addition, the design of the light reflection suppressing film in the present invention is greatly different from the design of the light reflection suppressing film conventionally performed. Conventionally, for example, when it is desired to suppress the reflection of light having a wavelength of 405 nm, it is designed to suppress the reflection of only light having a wavelength of 405 nm, and the reflection of light of other wavelengths is suppressed in a permissible direction. Membrane design has been done. This is because, in order to suppress reflection of light in a wider wavelength range, it is necessary to make the light reflection suppression film a multilayer film having a larger number of layers, or it becomes difficult to produce the light reflection suppression film. It is. Therefore, as in the present invention, designing a light reflection suppression film so that the reflection suppression wavelength region Δλ ₁ is significantly wider than the use wavelength region Δλ ₀ can be easily conceived from the conventional design concept. It was not.

In the present invention, in order to design the light reflection suppressing film, at least one of data such as the film thickness d ₀ , the film thickness d ₁ , the wavelength region Δλ ₁ , and the wavelength region Δλ ₂ is required. The method for obtaining these data is not particularly limited. These data may be obtained experimentally, for example, or may be obtained by experiments and simulations.

When determining the ratio (film thickness d ₁ ) / (film thickness d ₀ ) between the film thickness d ₀ and the film thickness d ₁ , it is ideal to measure the film thickness in the entire region of the light reflection suppressing film. However, the light reflection suppression film is usually very thin and it may be difficult to measure the film thickness, and it is actually difficult to measure the film thickness in the entire region of the light reflection suppression film.

When a light reflection suppression film is formed using a normal thin film formation method such as sputtering or vapor deposition, the thickness of the light reflection suppression film is the angle between the surface on which the light reflection suppression film is formed and the optical axis. Correlates with size. Specifically, the smaller the angle between the surface on which the light reflection suppression film is formed and the optical axis is, the larger the film thickness of the light reflection suppression film formed is. On the other hand, the greater the angle between the surface on which the light reflection suppression film is formed and the optical axis, the smaller the film thickness of the light reflection suppression film formed. Further, in an optical element that collects and diffuses light, the angle formed between the light input / output surface and the optical axis is the smallest in the portion of the plurality of light input / output surface portions that is located closest to the optical axis. This is because the required optical power is minimized in this portion. On the other hand, the angle formed between the light input / output surface and the optical axis is the largest in the portion of the plurality of light input / output surfaces that is located farthest from the optical axis. This is because the required optical power is maximized in this portion. Accordingly, the film thickness d ₀ is the film thickness of the light reflection suppressing film on the portion of the plurality of light entrance / exit surfaces that is closest to the optical axis, and the film thickness d ₁ is the thickness of the plurality of light entrance / exit surfaces. The film thickness of the light reflection suppressing film on the portion farthest from the optical axis of the film is measured, and the film thickness is measured or simulated at these two locations, whereby the ratio of the film thickness d ₀ to the film thickness d ₁ ( thickness _d 1) / (may be obtained a film thickness _{d 0).}

The design of the light reflection suppressing film satisfying the determined reflection suppressing wavelength region Δλ ₁ can be performed using a known design method. Depending on the reflection suppression wavelength region Δλ ₁ , the light reflection suppression film may be composed of a single film or a multilayer film. However, in general, tends to give a broader reflection suppressing wavelength range [Delta] [lambda] ₁ better to configure the antireflection film of a multilayer film. For this reason, the light reflection suppressing film is preferably a multilayer film. However, the multilayer film formation process is complicated and the film formation cost is high. Therefore, from the viewpoints of film formation ease and film formation cost, the antireflection film is preferably a single film.

  In the present invention, “Fresnel lens surface” and “phase step surface” refer to surfaces in which a plurality of light input / output surfaces and a plurality of light non-transparent surfaces are alternately arranged around the optical axis. . The light non-transmission surface portion is a surface arranged in parallel with the optical axis. The light non-transmission surface portion is located between the adjacent light entrance / exit surface portions. Of the surfaces in which a plurality of light entrance / exit surface portions and a plurality of light non-transparent surface portions are alternately arranged with the optical axis as the center, the Fresnel lens surface has optical power realized mainly by light refraction. The phase step surface is a surface on which optical power is realized mainly by diffraction of light. Whether light refraction or diffraction occurs predominantly is determined by the wavelength of the incident light and the pitch of the light entrance / exit surface.

  In each of the Fresnel lens surface and the phase difference step surface, since the light passes through the light entrance / exit surface portion, it is sufficient that the light reflection suppression film is formed only on the light entrance / exit surface portion. It may be formed on the light non-transmission surface part.

  Each of the light entrance / exit surface portion and the light non-transmission surface portion may be a flat surface or a curved surface. When the light input / output surface portion is a curved surface, the normal line of the light input / output surface portion is a normal line of the approximate plane of the light input / output surface portion.

  According to the present invention, the light incident / exit surfaces on which the light reflection suppressing films are formed are arranged with the optical axis as the center, and the angles with respect to the optical axis are different from each other and are provided discontinuously. An optical element including a light entrance / exit surface portion and having high transmittance is provided.

It is a schematic diagram which shows the relationship of the wavelength range at the time of designing wavelength range (lambda) 1 substantially equal to use wavelength range (lambda) 0. It is a schematic diagram which shows the relationship of the wavelength range in this invention. It is a schematic sectional drawing of the optical element which concerns on one Embodiment which implemented this invention. FIG. 4 is a schematic cross-sectional view of a portion IV in FIG. 3. FIG. 4 is a schematic cross-sectional view of a V portion in FIG. 3. It is a graph showing the transmittance | permeability of the Fresnel lens and glass substrate which have not formed the light reflection suppression film | membrane, and the Fresnel lens and glass substrate which formed the light reflection suppression film | membrane. 3 is a graph showing the transmittance of a Fresnel lens with a light reflection suppressing film manufactured in Example 1. FIG. When the light reflection suppressing film of Example 1 is formed with a film thickness d ₀ , it is negative rough representing the reflectance of light. A light reflection suppression film of Example 1, a negative rough representing the reflectivity of light at the time of forming a film thickness d _1. 6 is a graph showing the transmittance of a Fresnel lens with a light reflection suppression film produced in Example 2. 6 is a graph showing the transmittance at a wavelength of 405 nm of a Fresnel lens with a light reflection suppression film produced in Example 2. FIG. When the light reflection suppressing film of Example 2 is formed with a film thickness d ₀ , this is a negative rough representing the reflectance of light. A light reflection suppression film of Example 2, a negative rough representing the reflectivity of light at the time of forming a film thickness d _1. 6 is a graph showing the transmittance of a Fresnel lens with a light reflection suppressing film produced in Example 3. 6 is a graph showing the transmittance at a wavelength of 405 nm of a Fresnel lens with a light reflection suppressing film produced in Example 3. A light reflection suppression film of Example 3, a negative rough representing the reflectivity of light at the time of forming a film thickness d _0. A light reflection suppression film of Example 3, a negative rough representing the reflectivity of light at the time of forming a film thickness d _1.

  Hereinafter, a preferred embodiment in which the present invention is implemented will be described taking the optical element 1 shown in FIG. 3 as an example. The optical element 1 is merely an example. The optical element according to the present invention is not limited to the optical element 1.

The optical element 1 shown in FIG. 3 is an element used for light in a use wavelength range Δλ ₀ of a minimum wavelength λ _min0 or more and a maximum wavelength λ _max0 or less. As shown in FIG. 3, the optical element 1 includes an element body 10. The element body 10 is not particularly limited as long as it is a member that transmits light in the use wavelength range of the optical element 1. The element body 10 may be made of resin or glass, for example.

  The element body 10 includes a pair of light entrance / exit surfaces 10a and 10b. That is, light incident from one of the light incident / exit surfaces 10a and 10b is emitted from the other of the light incident / exit surfaces 10a and 10b. In the present embodiment, the light entrance / exit surface 10b constitutes a light incident surface. The light entrance / exit surface 10a constitutes a light exit surface.

  The light entrance / exit surface 10b is formed in a planar shape. On the other hand, the light entrance / exit surface 10a is formed on the Fresnel lens surface. Specifically, the light entrance / exit surface 10a includes a plurality of planar light entrance / exit surfaces 10a1 and a plurality of planar light non-transmission surface portions 10a2. The plurality of light entrance / exit surfaces 10 a 1 and the plurality of light non-transmission surfaces 10 a 2 are alternately arranged in the radial direction with the optical axis A as the center. For this reason, the light non-transmissive surface portion 10a2 is located between the adjacent light entrance / exit surface portions 10a1. Therefore, the plurality of light entrance / exit surfaces 10a1 are provided discontinuously.

  Since the light non-transmissive surface portion 10a2 is disposed in parallel with the optical axis A, light is not substantially emitted from the light non-transmissive surface portion 10a2. The light incident on the optical element 1 is substantially emitted from the light incident / exit surface portion 10a1.

  The plurality of light entrance / exit surfaces 10a1 have different angles with respect to the optical axis A. Specifically, the closer to the optical axis A, the smaller the angle formed between the normal line of the light entrance / exit surface portion 10a1 and the optical axis A. The further away from the optical axis A, the larger the angle between the normal line of the light entrance / exit surface portion 10a1 and the optical axis A.

  A light reflection suppressing film 20 is formed on the light entrance / exit surface 10a. Specifically, the light reflection suppressing film 20 is formed on the plurality of light entrance / exit surfaces 10a1 of the light entrance / exit surfaces 10a.

  In the present embodiment, an example in which a light reflection suppression film is not substantially formed on the light entrance / exit surface portion 10b will be described. However, the present invention is not limited to this configuration. For example, a light reflection suppressing film may be formed on both of the pair of light entrance / exit surfaces.

In the present embodiment, the light reflection suppressing film 20 is formed by a thin film forming method such as a sputtering method or a vapor deposition method. For this reason, as shown in FIG.4 and FIG.5, the film thickness of the light reflection suppression film | membrane 20 is non-uniform | heterogenous. Specifically, the film thickness of the portion of the light reflection suppressing film 20 formed on the portion where the angle between the normal line of the light incident / exit surface portion 10a1 and the optical axis A is small among the plural light incident / exit surfaces 10a1 is as follows. Is relatively large. Of the plurality of light entrance / exit surfaces 10a1, the thickness of the portion of the light reflection suppression film 20 formed on the portion where the angle between the normal line of the light entrance / exit surface 10a1 and the optical axis A is large is relatively small. Further, even on the same light entrance / exit surface portion 10a1, the apex side is thick and the bottom side is thin. The thickest part of the light reflection suppression film 20 is the part closest to the optical axis A. In the present embodiment, since the light reflection suppressing film 20 is formed on the optical axis A, the thickness along the normal line of the portion 20a located on the optical axis A of the light reflection suppressing film 20 shown in FIG. d ₀ . On the other hand, the thinnest portion of the light reflection suppression film 20 is a portion 20b farthest from the optical axis A in the light reflection suppression film 20 shown in FIG. Therefore, the thickness along the normal direction of the portion 20b is _{d 1.}

The light reflection suppression film 20 is a film for suppressing reflection of light in the use wavelength range Δλ ₀ on the light input / output surface 10a. The light reflection suppressing film 20 includes a light reflection suppressing wavelength region Δλ ₁ in which reflection is suppressed on the light entrance / exit surface 10 a when the film thickness of the light reflection suppressing film 20 is d ₀ , and a film thickness of the light reflection suppressing film 20. Each of the reflection suppression wavelength regions Δλ _{2 of} which reflection is suppressed at the light entrance / exit surface 10 a when d ₁ is d ₁ is configured to include the use wavelength region Δλ ₀ .

Specifically, in this embodiment, the value obtained by multiplying the maximum wavelength λ _max1 of the reflection suppression wavelength region Δλ ₁ by d ₁ / d ₀ is _equal to or greater than the maximum wavelength λ _max0 of the use wavelength region Δλ ₀ , and the reflection suppression is performed. as minimum wavelength lambda _min1 wavelength range [Delta] [lambda] ₁ is equal to or less than the minimum wavelength lambda _min0 used wavelength range [Delta] [lambda] _0, the light reflection suppression film 20 is formed.

Therefore, as described above, it is possible to suppress the reflection of light in the used wavelength range Δλ ₀ and increase the light transmittance.

In addition, the structure of the light reflection suppression film | membrane 20 can be suitably selected as long as the said conditions are satisfy | filled. The light reflection suppressing film 20 may be constituted by a single film, for example, or may be constituted by a multilayer film. The material of the light reflection suppression film 20 is not particularly limited, for _example, can be constituted by TiO _{2, Nb} 2 O 5, an oxide such as SiO ₂ or CaF ₂ and the like fluoride. Typically, the light reflection suppressing film 20 can be formed of a laminated film in which low refractive index films and high refractive index films are alternately laminated.

In addition, the light reflection suppressing film 20 is formed of a structure in which a large number of minute protrusions or recesses having a minimum wavelength λ _min0 or less in the use wavelength range Δλ ₀ are formed, and the apparent refractive index gradually changes in the thickness direction. May be.

(Experimental example)
As described above, as a result of earnest research, the present inventor has found that even if a light reflection suppressing film is formed on a light incident / exit surface having a plurality of steps, a sufficient light reflection suppressing effect may not be obtained. . Here, the experiment conducted at that time will be described.

  First, a Fresnel lens under the following conditions and a flat glass substrate were prepared. And the transmittance | permeability was measured about each of these Fresnel lenses and a glass substrate.

Thereafter, a light reflection suppressing film was formed under the same conditions on the Fresnel lens surface of the Fresnel lens and one surface of the flat glass substrate. The formed light reflection suppressing film was assumed to be able to reduce the light reflectance at about 400 nm to 700 nm when formed on a flat glass substrate. Specifically, a condition that a laminated film of an Nb ₂ O ₅ film (film thickness: 13.4 nm) and an SiO ₂ film (film thickness: 93.6 nm) is formed on the surface of the glass substrate from the element body side. Then, a light reflection suppressing film was formed. And the transmittance | permeability was measured also about each of the Fresnel lens and glass substrate which formed the light reflection suppression film | membrane. The results are shown in FIG.

(Fresnel lens)
Fresnel lens planar shape: rectangular shape Fresnel lens dimension: effective radius 350 mm
Fresnel lens material: Polyethylene terephthalate (PET)
Maximum thickness of Fresnel lens: 0.4mm
Fresnel lens pitch: 31.8 μm
Focal length of Fresnel lens: 643mm

  As shown in FIG. 6, by forming the light reflection suppressing film on the glass substrate, it was possible to improve the transmittance in a wavelength range of about 400 nm to 700 nm as estimated. From this result, it can be seen that the reflection of light in the wavelength region of about 400 nm to 700 nm can be reduced as expected by forming the light reflection suppressing film on the glass substrate.

  On the other hand, when the light reflection suppression film was formed on the Fresnel lens, the light transmittance was substantially the same as when the light reflection suppression film was not formed on the Fresnel lens. From this result, even if the light reflection suppression film designed by the same design method as the case of forming the light reflection suppression film on the flat glass substrate is formed on the Fresnel lens, the reflection of light cannot actually be suppressed. I understood that.

Example 1
In Experimental Example 1, a Fresnel lens used for light having a wavelength of 750 nm was designed, manufactured, and evaluated.

First, the film thickness ratio (d ₁ / d ₀ ) when the light reflection suppression film 20 was formed on the Fresnel lens surface of the Fresnel lens used in the above experimental example was obtained by simulation. In the simulation, it is assumed that the diffusion of particles scattered from the target follows the cosine law. From the shape of the Fresnel lens surface and the distance between the Fresnel lens surface and the target, from which region of the target to each part of the Fresnel lens surface It was calculated whether the particles were scattered. Then, the film thickness ratio (d ₁ / d ₀ ) is calculated from the area of the target that scatters particles on the optical axis of the Fresnel lens surface and the area of the target that scatters particles farthest from the optical axis of the Fresnel lens surface. Was calculated. As a result, in this experimental example, the film thickness ratio (d ₁ / d ₀ ) was calculated to be 0.3.

For this reason, the value obtained by dividing the used wavelength: 750 nm by the film thickness ratio (d ₁ / d ₀ ): 0.3 is 2500 nm. Therefore, by setting the wavelength region Δλ _{1 of} light whose reflection is suppressed at the light entrance / exit surface when the film thickness of the light reflection suppressing film is d ₀ to 750 nm to 2500 nm, the wavelength region Δλ ₂ seems to include 750 nm. Will be able to. Based on this result, the light reflection suppression film was designed using a known design method. As a result, it was calculated that the wavelength region Δλ ₁ can be set to 750 nm to 2500 nm by forming a light reflection suppressing film having the configuration shown in Table 1 below.

Next, it was confirmed that each of the wavelength region Δλ ₁ and the wavelength region Δλ ₂ includes a use wavelength of 750 nm. Specifically, the light reflectance was obtained when the light reflection suppressing film having the structure shown in Table 1 was formed on a glass plate made of the same material as the Fresnel lens. The result is shown in FIG. The light reflectance when a light reflection suppressing film having a film thickness obtained by multiplying the film thickness shown in Table 1 by (d ₁ / d ₀ ) = 0.3 on a glass plate made of the same material as the Fresnel lens is shown. Obtained. The result is shown in FIG.

From the results shown in FIG. 8, in this embodiment, [Delta] [lambda] ₁ is 590Nm～2510nm, it can be seen that include the use wavelength 750nm to [Delta] [lambda] _1.

Further, from FIG. 9, it can be seen that Δλ ₂ includes at least a use wavelength of 750 nm in the present embodiment.

  Next, a light reflection suppressing film having the configuration shown in Table 1 was formed on the Fresnel lens surface of the Fresnel lens by a sputtering method. Thereafter, the transmittance of the Fresnel lens was measured. The result is shown in FIG. 7 together with the transmittance data of the Fresnel lens alone.

  As shown in FIG. 7, in Experimental Example 1, by forming the light reflection suppressing film, not only the transmittance at 750 nm but also the light transmittance increased in a wide wavelength region of about 370 nm or more.

(Example 2)
In Example 2, when the wavelength used is 405 nm and the film thickness of the light reflection suppressing film is d ₀ , the wavelength range Δλ _{1 of} light whose reflection is suppressed on the light incident / exit surface is 405 nm to 1350 (= 405 nm / 0). .3) A light reflection suppressing film having a thickness of nm was designed. Table 2 below shows the film configuration of the light reflection suppressing film in Example 2.

Next, it was confirmed that each of the wavelength region Δλ ₁ and the wavelength region Δλ ₂ includes a use wavelength of 405 nm. Specifically, the light reflectance was obtained when the light reflection suppressing film having the structure shown in Table 2 was formed on a glass plate made of the same material as the Fresnel lens. The result is shown in FIG. The light reflectance when a light reflection suppressing film having a film thickness obtained by multiplying the film thickness shown in Table 2 by (d ₁ / d ₀ ) = 0.3 on a glass plate made of the same material as the Fresnel lens is shown. Obtained. The result is shown in FIG.

From the results shown in FIG. 12, in this embodiment, [Delta] [lambda] ₁ is 400Nm～1430nm, it can be seen that include the use wavelength 405nm to [Delta] [lambda] _1.

From FIG. 13, it can be seen that Δλ ₂ includes at least a use wavelength of 405 nm in this embodiment.

  Next, the transmittance of the Fresnel lens when the light reflection suppression film shown in Table 2 below was formed on the Fresnel lens surface in the same manner as in Example 1 was obtained. The results are shown in FIGS. 10 and 11 together with the transmittance data of the Fresnel lens alone.

  As shown in FIG. 10, also in the present Example 2, the transmittance in the used wavelength band of 405 nm was increased by forming the light reflection suppressing film.

  Further, as shown in FIG. 11, in Example 2 in which the light reflection suppressing film is formed, it is understood that the transmittance of light having a wavelength of 405 nm is improved in the entire Fresnel lens.

(Example 3)
In the third embodiment, similarly to the second embodiment, when the film thickness of the light reflection suppressing film is d ₀ , the wavelength range Δλ _{1 of} light in which reflection is suppressed on the light incident / exit surface is 405 nm to 1350 nm. A light reflection suppressing film having a configuration different from that of Example 2 was designed. Table 3 below shows the film configuration of the light reflection suppressing film in Example 3.

Next, it was confirmed that each of the wavelength region Δλ ₁ and the wavelength region Δλ ₂ includes a use wavelength of 405 nm. Specifically, the light reflectance was obtained when the light reflection suppressing film having the structure shown in Table 3 was formed on a glass plate made of the same material as the Fresnel lens. The result is shown in FIG. Further, the light reflectance when a light reflection suppressing film having a film thickness obtained by multiplying the film thickness shown in Table 3 by (d ₁ / d ₀ ) = 0.3 on a glass plate made of the same material as the Fresnel lens is shown. Obtained. The result is shown in FIG.

From the results shown in FIG. 16, in this example, Δλ ₁ is 400 nm to 1430 nm, and Δλ ₁ includes the use wavelength of 405 nm.

FIG. 17 also shows that Δλ ₂ includes at least a use wavelength of 405 nm in the present embodiment.

  Next, the transmittance of the Fresnel lens when the light reflection suppressing film shown in Table 3 below was formed on the Fresnel lens surface in the same manner as in Example 2 was obtained. The results are shown in FIGS. 14 and 15 together with the transmittance data of the Fresnel lens alone.

  As shown in FIG. 14, also in Example 2, the transmittance in the used wavelength band of 405 nm was increased by forming the light reflection suppressing film.

  Further, as shown in FIG. 15, in Example 3 in which the light reflection suppressing film is formed, it is understood that the transmittance of light having a wavelength of 405 nm is improved in the entire Fresnel lens.

  From the results of Examples 1 to 3, it can be seen that by using the light reflection suppressing film designed according to the present invention, the reflection of light on the light entrance / exit surface can be effectively suppressed and a high transmittance can be obtained.

DESCRIPTION OF SYMBOLS 1 ... Optical element 10 ... Element main body 10a, 10b ... Light entrance / exit surface 10a1 ... Light entrance / exit surface part 10a2 ... Light non-transmission surface part 20 ... Light reflection suppression film 20a ... Light reflection suppression film part 20b with the largest film thickness ... Light reflection suppression The smallest part of the film

Claims (7)

An element body having a pair of light entrance and exit surfaces;
A light reflection suppressing film that suppresses reflection of light on the light incident / exit surface;
An optical element used for light having a used wavelength range of Δλ ₀ ,
The light entrance / exit surface on which the light reflection suppressing film is formed is arranged around the optical axis, and includes a plurality of light entrance / exit portions that are discontinuously provided with different angles with respect to the optical axis. ,
The light reflection suppressing film is formed on the plurality of light entrance / exit surfaces.
In the normal direction of the light incident / exit surface portion, the thickness of the light reflection suppression film at the portion where the film thickness of the light reflection suppression film is maximum is d ₀ , and in the normal direction of the light incident / exit surface portion, the light reflection suppression the thickness of the light reflection suppression film in a portion where the thickness of the film is minimized when the d _1,
When the film thickness of the light reflection suppression film is d ₀ , the wavelength region Δλ _{1 of} light whose reflection is suppressed at the light entrance / exit surface, and the light when the film thickness of the light reflection suppression film is d ₁ An optical element in which the light reflection suppression film is configured such that each of the light wavelength ranges Δλ _{2 of} which reflection is suppressed on the entrance / exit surface includes the use wavelength range Δλ ₀ . A value obtained by multiplying the maximum wavelength λ _max1 of the wavelength range Δλ ₁ by d ₁ / d ₀ is not less than the maximum wavelength λ _max0 of the use wavelength range Δλ ₀ , and the minimum wavelength λ _min1 of the wavelength range Δλ ₁ is 2. The optical element according to claim 1, wherein the light reflection suppression film is configured to be equal to or less than a minimum wavelength λ _min0 of a usable wavelength range Δλ ₀ . The film thickness d ₀ is a film thickness of the light reflection suppressing film on a portion of the plurality of light entrance / exit surfaces that is closest to the optical axis,
3. The optical element according to claim ₁ , wherein the film thickness d ₁ is a film thickness of the light reflection suppressing film on a portion of the plurality of light entrance / exit surfaces that is farthest from the optical axis.   The optical element according to claim 1, wherein the light reflection suppressing film is a multilayer film.   The optical element according to claim 1, wherein the light incident / exit surface on which the light reflection suppressing film is formed is a Fresnel lens surface.   The light incident / exit surface on which the light reflection suppressing film is formed is located between the adjacent light incident / exit surfaces, and has a light non-transmitting surface portion arranged in parallel with the optical axis. The optical element as described in any one of these.   The optical element according to claim 1, wherein the light reflection suppressing film is a film formed by a sputtering method or a vapor deposition method.

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