JP2016045415A - Diffusion plate and optical device having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a diffusion plate which provides a desired diffusion angle and uniform diffuse light intensity and can be used with coherent light.SOLUTION: A diffusion plate has a diffusion surface obtained by two-dimensionally arranging a number of microlens surfaces L1-L4 of two or more types, where effective diameters D and focal lengths f of the arranged microlens surfaces L1-L4 are randomly different on the diffusion surface. An effective diameter D and focal length f of each microlens surface are set such that tanθ=D/(2|f|) is satisfied for a desired diffusion angle 2θ, and an F-number, defined as Fn=|f|/D, is approximately the same for each microlens surface.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a diffusion plate and an optical apparatus using the diffusion plate.

  A “diffusing plate” that diffuses light incident from one side and emits it as diffused light from the other side is used in various optical devices such as a single-lens reflex camera.

  Conventionally known diffusion plates have a fine cross-sectional uneven shape such as a random structure such as ground glass or a structure in which microlenses are regularly arranged.

  Recently, a diffusion plate having “desired diffusion characteristics” according to the purpose of use has been demanded and proposed (Patent Documents 1 and 2).

  There is also a need for a diffusion plate that has a predetermined diffusion range defined as a design condition, and that the intensity of light diffused within the diffusion range is uniform.

  Conventionally, it has been difficult to realize a predetermined diffusion range and uniform intensity of diffused light.

FIG. 3 is a view for explaining a conventionally known general diffusion plate.
In the upper diagram of FIG. 3, reference numeral 10 denotes a “general diffusion plate known from the past”.

  The upper diagram of FIG. 3 shows a state of diffusion when the incident light beam IL is incident as a “thin parallel light beam” so as to be orthogonal to the diffusion plate 10 as an explanatory diagram.

  The diffusing plate 10 is designed and manufactured so as to diffuse the incident light beam IL with the angle 2θ shown in the upper diagram of FIG. 3 as a “diffusion angle”.

  The incident light beam IL is diffused by the diffusion plate 10 and is emitted as the diffused light DL.

  If the diffusion plate 10 has a “function as designed”, the diffusion angle of the diffused light DL is 2θ. However, in the case of the conventionally known diffusion plate 10, the actual diffusion angle is the designed diffusion angle. : Not 2θ but slightly larger than 2θ.

  The diffused light also exists in the areas DM1 and DM2 outside the designed diffusion angle: 2θ. Further, the intensity of diffused light (indicated by “the length of the arrow” in the figure) is not uniform.

  That is, the intensity of the diffused light is not uniform in the area DM0.

  In FIG. 3B, the horizontal axis represents the angle of the diffused light, and the vertical axis represents the light intensity. The angle dependency of the intensity of the diffused light is represented.

  The diffused light is also present in the regions DM1 and DM2 outside the designed diffusion angle: 2θ, and the intensity of the diffused light is nonuniform in the region DM0. By diffracting by the diffusion plate 10.

  A phenomenon in which diffracted light having an intensity other than 0 is generated in the regions DM0, DM1, and DM2 in FIG. 3A is referred to as “bleeding” of diffracted light.

  Some conventionally known diffusion plates have a “structure in which micro lenses and the like are regularly arranged”.

  Recently, as a light source used in various optical devices, a laser light source or the like that emits “coherent light” has been widely used.

  When a “diffuser plate having a structure in which micro lenses and the like are regularly arranged” is used for coherent light, the regular array structure acts as a diffraction grating, and a diffraction pattern is generated in the diffused light.

  This invention makes it a subject to implement | achieve the diffusion plate which can implement | achieve a desired diffusion angle and uniform diffused light intensity | strength, and can be used also with respect to coherent light in view of the situation mentioned above.

The diffusing plate of the present invention is a diffusing plate having a diffusing surface by diffusing a large number of two or more kinds of micro lens surfaces two-dimensionally and having a diffusion angle of 2θ. The effective diameter of the micro lens surface: D and the focal length: f are randomly different on the diffusion surface,
Effective diameter: D and focal length: f of each microlens surface are as follows: diffusion angle: 2θ
tan θ = D / (2 | f |)
And satisfy
Fn = | f | / D
The F number defined by is set to be substantially the same for each microlens surface.

  According to the diffusion plate of the present invention, a desired diffusion angle: 2θ and a uniform diffused light intensity can be realized.

  Further, even when this diffuser plate is used for coherent light, generation of a “diffraction pattern” can be effectively reduced or prevented.

It is a figure for demonstrating one Embodiment of a diffuser plate. It is a figure for demonstrating three typical examples of a diffusion surface. It is a figure for demonstrating a diffusion plate and its problem. It is a figure which shows one example of the arrangement | sequence of a micro lens surface.

  Hereinafter, embodiments will be described.

  FIG. 1A shows an example of the usage state of the diffusion plate 1.

  The coherent light emitted from the semiconductor laser light source 3 is converted into a parallel light beam by the collimator lens 5, and this parallel light beam is made incident on the diffusion plate 1 as an incident light beam IL.

  The diffusing plate 1 diffuses the incident light beam IL and converts it into diffused light DL with a uniform light intensity having a diffusion angle: 2θ.

  The diffusing surface formed on the diffusing plate 1 is “a surface in which a large number of two or more kinds of micro lens surfaces are two-dimensionally arranged” as described above, and is configured to realize “diffusion angle: 2θ”. .

  The shape of the two or more types of microlens surfaces constituting the diffusing surface is “convex surface (having positive focal length: f (> 0))” and “concave surface (non-focal length: f <0)”. It can be either.

  Further, the diffusing surface can be formed by “two-dimensional array of only convex microlens surfaces” or “two-dimensional array of only concave microlens surfaces”.

  Furthermore, “a convex microlens surface and a concave microlens surface can coexist” on the same diffusion surface.

The effective diameter: D and focal length: f of each microlens surface are randomly different on the diffusion surface, but the effective diameter: D and focal length: f of each microlens surface are different from each other with respect to the diffusion angle: 2θ.
tan θ = D / (2 | f |)
Satisfied.

  Accordingly, the parallel light beam incident on the minute lens surface is converted into a divergent light beam having an opening angle of 2θ by all the minute lens surfaces.

Further, although the effective diameter of the microlens surface differs for each type, the effective diameter: D and the focal length: f
The ratio of | f | / D is common to all the microlens surfaces.

  “| F | / D” is a definition of F number: Fn, and means “brightness” of the microlens surface, and therefore, all microlens surfaces that share Fn have the same brightness.

  That is, the incident parallel light beam IL is converted into a divergent light beam having an opening angle of 2θ on all of two or more kinds of minute lens surfaces forming the diffusing surface, and the converted divergent light beams have the same brightness.

  Accordingly, as shown in FIG. 1B, a diffused light DL having a diffusion angle: 2θ (−θ to + θ) and having a uniform light intensity within the range of the diffusion angle is obtained.

FIG. 2 shows three types of diffusion plates 1A, 1B, and 1C having different diffusion surfaces.
In the diffusing plate 1A shown in FIG. 2A, the diffusing surface is formed by a two-dimensional arrangement of four types of micro lens surfaces L1, L2, L3, and L4.

  The four types of micro lens surfaces L1, L2, L3, and L4 are all convex surfaces, and therefore their focal length: f is positive.

  Therefore, when the incident light beam IL, which is a parallel light beam, is incident, it is converted into a condensed light beam by each microlens surface and becomes a divergent light beam after being condensed.

These micro lens surfaces L1, L2, L3, and L4 have different effective diameters: D and focal lengths: f (> 0), but effective diameters: D and focal lengths: f have a relationship:
tan2θ = D / f
Therefore, the light beams diverged by the minute lens surfaces have a common opening angle: 2θ. Further, since f / D is common to all types of microlens surfaces, all the divergent light beams have the same brightness.

  Therefore, the diffused light DL having a uniform light intensity with a diffusion angle of 2θ can be obtained by the diffusion plate 1A.

  In the diffusing plate 1B shown in FIG. 2B, the diffusing surface is formed by a two-dimensional array of four types of micro lens surfaces L21, L22, L23, and L24.

  The four types of micro lens surfaces L21, L22, L23, and L24 are all concave surfaces, and therefore their focal length: f is negative.

  Therefore, when the incident light beam IL, which is a parallel light beam, is incident, it is diverged by each minute lens surface.

These micro lens surfaces L21, L22, L23, and L24 have different effective diameters: D and focal lengths: f (<0), but the effective diameters: D and focal lengths: f have a relationship:
tan2θ = D / | f |
Therefore, the light beams diverged by the minute lens surfaces have a common opening angle: 2θ. Further, since | f | / D is common to all types of microlens surfaces, all the divergent light beams have the same brightness.

  Therefore, the diffused light DL having a uniform light intensity at a diffusion angle of 2θ can be obtained by the diffusion plate 1B.

  In the diffusing plate 1C shown in FIG. 2C, the diffusing surface is formed by a two-dimensional arrangement of four types of micro lens surfaces L31, L32, L33, and L34.

  Among the four types of micro lens surfaces, the micro lens surfaces L31 and L33 are convex and have a positive focal length: f (> 0), the micro lens surfaces L32 and L34 are concave, and a negative focal length: f (< 0).

  When the incident light beam IL, which is a parallel light beam, is incident, the light beam incident on the minute lens surfaces L31 and L33 is once converted into a condensed light beam, and after being condensed, becomes a divergent light beam.

  The light beam incident on the minute lens surfaces L32 and L34 is converted into a divergent light beam.

These micro lens surfaces L31, L32, L33, and L34 have different effective diameters: D and focal lengths: f, but effective diameters: D and focal lengths: f have a relationship:
tan2θ = D / | f |
Therefore, the light beams diverged by the minute lens surfaces have a common opening angle: 2θ. Further, since | f | / D is common to all types of microlens surfaces, all the divergent light beams have the same brightness.

  Therefore, the diffused light DL having a uniform light intensity with a diffusion angle of 2θ can be obtained by the diffusion plate 1C.

  All of the diffusion plates 1A, 1B, and 1C illustrated in FIG. 2 are formed with a two-dimensional arrangement of four types of microlens surfaces. It does not mean that the microlens surfaces are limited to four types.

  The type of microlens surface constituting the diffusion surface may be “two or more types, and three or five types”.

  The diffusion surface is formed as a surface shape made of a material that is transparent to the used light (IL). The form of the transparent material is not limited to “plate shape” but may be “film shape”.

  What is important is that the arrangement of the microlens surfaces is not regular but random. The plurality of types of microlens surfaces form a two-dimensional diffusion surface depending on the arrangement.

As described above, the diffusion plate has a “diffusion surface” by “many two or more kinds of minute lens surfaces are randomly arranged two-dimensionally”.
In other words, the effective diameter: D and focal length: f of these plural types of microlens surfaces are randomly distributed on the diffusion surface. That is, the structure of the diffusion surface does not act as a diffraction grating.

  Therefore, even when the diffusing plate is used for coherent light such as laser light, generation of diffracted light and a diffraction pattern can be effectively reduced or prevented.

  Each microlens surface differs in effective diameter: D and focal length: f depending on the type, but these D and f are “tan θ = D / (2 | f |)” for a desired diffusion angle: 2θ. Satisfied.

  Therefore, as shown in FIG. 1B, the diffusion angle 2θ of the diffused light DL diffused by each microlens surface is constant regardless of the type of microlens surface.

  Further, since the F number: Fn (= | f | / D) of the minute lens surface is substantially constant regardless of the type of the minute lens surface, all the minute lens surfaces have “same brightness”.

  And since arrangement | positioning of a micro lens surface is random, the light quantity of diffused light is averaged to the whole diffused light.

  That is, different types of microlens surfaces have different effective diameters: D and focal lengths: f, but these are not completely independent.

  Diffusion angle: D and f are set so that tan θ = D / (2 | f |) is satisfied according to 2θ, and | f | / D is substantially constant regardless of the type of the microlens surface. It has been established.

  Therefore, the diffusion range of the diffused light DL is limited to the diffusion angle: 2θ, and the intensity of the diffused light diffused within the diffusion angle is constant.

  Therefore, it is possible to realize a diffusion plate having a desired diffusion angle: 2θ and characteristics as described with reference to FIG.

  A diffusion plate as described above, in which a plurality of types of minute lens surfaces are randomly arranged in a two-dimensional manner to form a diffusion surface, is known as a “lens diffusion plate”, and its manufacturing method has also been established.

  Therefore, if the diffusion angle: 2θ, the type of microlens surface, the effective diameter: D, and the focal length: f are designated, the diffusion plate of the present invention can be manufactured using these as specifications.

  This diffusing plate functions in the same way for light of the same wavelength regardless of the presence or absence of coherence, and thus can be used as a diffusing plate for a light beam obtained by combining a plurality of light beams.

  In that case, it also functions as a “homogenizer for each beam”, and the intensity of diffused light within the diffusion angle is made uniform.

FIG. 4 shows a specific example of a two-dimensional array of minute lens surfaces.
In this example, four types of small and large lens surfaces having different effective diameters D are arranged two-dimensionally.

  The microlens surface having the smallest effective diameter has a lens diameter of 0.1 mm, and is arranged at a pitch of 0.1 mm in the horizontal direction and 0.0866 mm in the vertical direction.

  These four types of micro lens surfaces can be “all convex surfaces”, “all concave surfaces”, or “mixed convex and concave surfaces”.

  Hereinafter, the specifications of the diffusion plate will be described.

  Various optical materials can be used as the material constituting the diffusion plate of the present invention. For example, normal optical glass and optical crystals such as quartz are suitable as materials.

  A plastic mold can also be used as a material. When the light to be diffused (electromagnetic wave) is far infrared, a metal crystal such as Ge can also be used.

  The form of the diffuser plate is most commonly “flat plate”, but is not limited thereto, and may be a form “compositely formed on the lens surface”. It may be a film as well as a flat plate.

  Moreover, although the "light transmissive" thing was demonstrated above, it is good also as a form of a reflective surface.

  The form of the “micro lens surface” may be various forms such as a spherical surface, an axially symmetric aspherical surface, an anamorphic surface (cylinder surface, toroidal surface, etc.), a Fresnel surface, a DOE surface, etc.

  The arrangement of the micro lens surfaces can be a rectangular arrangement, a hexagonal close-packed arrangement, a circular arrangement, or the like. Of course, in this easy arrangement, various micro lens surfaces are randomly arranged.

  In addition, the combination of the microlens surfaces is arranged such that at least two types of microlens surfaces are arranged on the basis of 50:50, and the amount of the compound having the strong influence of diffracted light is reduced.

  The diameters of the two types of microlens surfaces are also preferably set so that the least common multiple is large. Three or more types of micro lens surfaces are preferable.

  The effective diameter of the micro lens surface can be set to “several μm to several mm”. The focal length can be set to “several μm to several tens of mm”, and the F number can be set to “around 0 to several hundreds”.

  The diffusion plate of the present invention can be used for various purposes. For example, it can be used as “an optical element that diffuses a light source image or performs uniform illumination”.

  Alternatively, it can be used to reduce speckle noise in a display image in a projector or a head-up display using laser light.

  When the diffuser plate is used to generate “diffused light that is incident on the lens”, it is preferable to set sin θ for the diffusion angle: 2θ to be larger than the NA of the lens to reduce the influence.

  Thus, various optical devices such as a projector and a head-up display can be implemented by mounting the diffusion plate of the present invention.

  As described above, according to the first aspect, the following diffusion plate can be realized.

[1]
A diffusion plate (1, 1A, etc.) having two or more kinds of micro lens surfaces (L1, L2, etc.) arranged two-dimensionally to form a diffusion surface, and a diffusion angle by the diffusion surface: 2θ, The effective diameter: D and the focal length: f of the microlens surfaces arranged two-dimensionally differ randomly on the diffusion surface,
Effective diameter: D and focal length: f of each microlens surface are as follows: diffusion angle: 2θ
tan θ = D / (2 | f |)
And satisfy
Fn = | f | / D
The diffusion plate is set so that the F number defined in (1) is substantially the same for each microlens surface.

[2]
[1] The diffusing plate (1A) according to [1], wherein two or more kinds of micro lens surfaces that are two-dimensionally arranged to form a diffusing surface are convex surfaces.

[3]
[1] The diffusion plate (1B) according to [1], wherein two or more kinds of micro lens surfaces that are two-dimensionally arranged to form a diffusion surface are concave surfaces.

[4]
[1] The diffusion plate (1C) according to [1], wherein a minute lens surface forming a convex surface and a minute lens surface forming a concave surface are mixed to form a diffusion surface.

[5]
The diffusion plate according to any one of [1] to [4], wherein the diffusion plate is used to generate diffused light to be incident on the lens, and a diffusion angle: sin θ with respect to 2θ is set larger than the NA of the lens. Board.

[6]
[1] An optical apparatus equipped with the diffusion plate according to any one of [5].

1 Diffuser L1, L2, L3, l4 Micro lens surface formed as a convex surface
L21, L22, L23, L24 Micro lens surface formed as a concave surface
L31, L33 Micro lens surface formed as a convex surface
L32, L34 Micro lens surface formed as a concave surface
IL Incident light flux
DL diffused light

JP-A-8-129205 JP-A-6-167602

Claims (6)

A diffusing plate having a number of two or more kinds of micro lens surfaces arranged two-dimensionally to form a diffusing surface, and a diffusion angle by the diffusing surface: 2θ,
The effective diameter: D and the focal length: f of the microlens surfaces arranged two-dimensionally differ randomly on the diffusion surface,
Effective diameter: D and focal length: f of each microlens surface are as follows: diffusion angle: 2θ
tan θ = D / (2 | f |)
And satisfy
Fn = | f | / D
The diffusion plate is set so that the F number defined in (1) is substantially the same for each microlens surface. The diffusion plate according to claim 1,
A diffusion plate in which two or more kinds of microlens surfaces that are two-dimensionally arranged to form a diffusion surface are convex surfaces. The diffusion plate according to claim 1,
A diffusing plate in which two or more kinds of minute lens surfaces that are two-dimensionally arranged to form a diffusing surface are concave. The diffusion plate according to claim 1,
A diffusion plate in which a minute lens surface forming a convex surface and a minute lens surface forming a concave surface are mixed to form a diffusion surface. The diffusing plate according to any one of claims 1 to 4,
A diffusing plate, which is used for generating diffused light to be incident on a lens, wherein a diffusing angle: sin θ with respect to 2θ is set larger than an NA of the lens.   An optical apparatus on which the diffusion plate according to any one of claims 1 to 5 is mounted.

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