Compound diffractive optical element

Abstract

To provide a composite type diffraction optical element of which performance is less likely to be changed or degraded by a usage environment and can be prevented from a forgery or a copying.SOLUTION: A fine structure pattern P is formed in a projection side of a parallel flat board G made of glass, a coating structure M is formed to cover the fine structure P, and the fine structure pattern P and the coating structure M are formed of energy cured resin, and the flat board G, the fine structure pattern P, and the coating target structure M each have an index of refraction that satisfies a predetermined condition.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a diffractive optical element (DOE) that converts light emitted from a laser light source or an LED light source into a specific pattern.

Background Art

[0002] In recent years, an optical projection module that combines a diffractive optical element with fine uneven shapes formed on a flat plate and an LED, a solid-state laser, or a vertical cavity surface emitting laser (VCSEL) to project a specific pattern and can be used for three-dimensional measurement, face recognition, guidance display, laser processing, etc. has been widely spread.

[0003] A composite diffractive optical element that forms fine uneven shapes using a transparent resin that cures with UV light or thermal energy on a glass lens is disclosed in Patent Document 1.

[0004] As an example of a diffractive optical element used in these optical projection modules, a composite diffractive optical element that suppresses performance degradation due to resin expansion caused by humidity and peeling and cracking of fine structure parts due to temperature changes is disclosed in Patent Document 2.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] Diffractive optical elements can project complex optical patterns with a small number of components, such as a light source and the element itself, and are thus widely used in various fields including face recognition and three-dimensional measurement. As described above, in order to suppress changes due to temperature and humidity and improve performance, proposals have been made for composite diffractive optical elements that combine different materials, and structures that protect the fine structure parts, etc., and a certain degree of improvement effect has been obtained.

[0007] Diffractive optical elements are created by forming fine uneven shapes on a substrate. There are cases where diffractive optical elements are formed from a single material such as glass or resin, and there are also composite diffractive optical elements in which a resin layer with a fine shape is formed on a glass substrate.

[0008] Diffractive optical elements utilize the diffraction phenomenon. When light passes through a fine uneven shape designed to form a specific projection pattern, light diffraction occurs, and the incident light is emitted so as to form the designed projection pattern. Since diffractive optical elements utilize the diffraction phenomenon, if the designed fine structure, for example, the height or period changes, problems such as the designed projection pattern collapsing, or flare occurring around the projection pattern and the contrast decreasing are known to occur.

[0009] Resin materials are known to change more significantly due to temperature and humidity compared to glass materials. When a diffractive optical element is made of only a resin material, expansion and contraction occur in the material depending on the temperature and humidity environment during use, the fine structure collapses, and the performance deteriorates.

[0010] Furthermore, when expansion and contraction occur in the resin material, the positional relationship from the light source to the fine structure pattern also changes, resulting in performance degradation.

[0011] Also, when damage to the pattern part due to scratches or burying of the uneven parts due to dirt occurs in the fine structure pattern part, light diffraction does not occur and the performance deteriorates.

[0012] Furthermore, when assuming use in a liquid, it is necessary to adopt a structure such that the liquid does not penetrate into the fine structure pattern portion of the diffractive optical element, or to perform an individual pattern design in consideration of the refractive index of the target liquid, and it is necessary to perform design and manufacturing for each liquid, which results in an increase in the number of parts and an increase in the product variety.

[0013] The above is an issue when assuming use in a liquid. However, even when used in air, when placed in a high-humidity environment, condensation may occur and the fine structure pattern portion may be covered with moisture. When the fine structure pattern is covered with condensed water, light diffraction does not occur and the performance deteriorates extremely. Therefore, a high-level waterproof structure is required so that condensation does not occur in the fine structure pattern portion of the diffractive optical element.

[0014] Furthermore, in recent years, the performance of measuring devices has also improved, and it has become possible to precisely measure the fine structure pattern and perform reverse engineering. A general diffractive optical element can be observed for its shape from the side of the fine structure pattern with a laser microscope or an electron microscope, and based on this measurement result, a diffractive optical element having the same performance can be replicated.

[0015] In addition, the number of resin materials that can form complex patterns with high precision has increased, and since the product can be directly replicated by molding the fine structure pattern of the diffractive optical element with resin or the like, there is a risk that the product itself will be copied.

[0016] The present invention has been made to solve such problems, and an object thereof is to provide a diffractive optical element that has little performance change or performance deterioration with respect to the use environment and can prevent forgery and replication.

Means for Solving the Problems

[0017] To solve the above problems, the diffractive optical element according to the present invention is configured such that a fine structure pattern P is formed on the projected side surface G2 of a parallel flat plate G made of glass, a coating structure M is formed so as to cover the fine structure P, the fine structure pattern P and the coating structure M are formed of an energy-curable resin, and the following conditions (1) to (4) are satisfied.

[0018] (Equation 1) |NG - NP| ≤ 0.1 ··· (1) |NP - NM| ≥ 0.3 ··· (2) 1.25 ≤ NM ≤ 1.5 ··· (3) NP > NM ··· (4) NG Refractive index of the parallel flat plate glass at the wavelength of use NP Refractive index of the resin material of the fine structure portion at the wavelength of use NM Refractive index of the resin material of the coating structure portion at the wavelength of use

[0019] Here, the energy-curable resin used refers to a material in which a crosslinking reaction or a polymerization reaction proceeds by receiving energy from the outside. Examples of the external energy include heat, ultraviolet rays, electron beams, etc. Such energy-curable resins include thermosetting types, ultraviolet-curing types, electron beam-curing types, etc. depending on the type of energy, and silicone-based, epoxy-based, and acrylic-based are generally known as the material system types. Thus, although the types of energy-curable resins are diverse, as long as they are optically sufficiently transparent, they can be used as the resin lens material of the present invention. The limitation of transparency here means that the light absorption and scattering of the material are small enough to withstand use within the wavelength range of use.

[0020] Since the composite diffractive optical element of the present invention has a fine structure M formed on a parallel flat plate glass G, it can suppress changes with respect to temperature and humidity more than when a diffractive optical element is made of resin alone.

[0021] Generally, the coefficient of linear expansion of resin materials is more than one order of magnitude larger than that of glass. When incorporating a diffractive optical element as a component into a lens barrel or the like, a thickness that can be incorporated is required. When forming a diffractive optical element from resin alone, the distance from the light source changes by the amount of expansion of the thickness due to temperature changes. However, in the present invention, since the fixing to the lens barrel or the like can be borne by the glass part, it is possible to suppress the positional change due to temperature.

[0022] Furthermore, in the composite diffractive grating of the present invention, since the fine structure M is fixed on the parallel flat glass, changes in the fine structure due to temperature can be suppressed. In a diffractive optical element formed of resin alone, expansion occurs not only in the thickness direction but also in the radial direction, so the structural pattern collapses. However, in the present invention in which the structural pattern is fixed on the glass, deformation of the structural pattern can be suppressed, and deterioration of performance due to temperature can be suppressed.

[0023] Also, except for some resin materials, it is known that resin materials absorb moisture in the air. The amount of moisture absorbed is proportional to the water absorption rate and volume of the resin material. Since the composite diffractive optical element of the present invention is formed mostly of glass in terms of volume, performance changes due to humidity can be suppressed.

[0024] The light emitted from the light source is incident in the order of the parallel flat glass G, the fine structure P, and the coating structure M. Here, an interface GP between glass and resin exists on the projection side surface G2 of the parallel flat glass G and the light source side surface P1 of the fine structure P. By satisfying equation (1), interface reflection at this glass-resin interface can be suppressed. When exceeding the range of equation (1), interface reflection at the glass-resin interface GP increases, and in addition to the problem that light returns to the light source side, the amount of light decreases by the amount of reflection and the projection pattern becomes dark.

[0025] The design of a projection pattern using light diffraction is defined by the refractive index of the medium and the step distance of the microstructure. When forming a structural pattern using two types of materials, the greater the refractive index difference between the materials used, the smaller the step required to form the microstructure. When a precise projection pattern is required to form the microstructure, the structure must be created with a fine pitch. When forming a structure with a fine pitch, if the step is large, it becomes difficult to transfer during resin molding, and it also becomes difficult to release the mold during molding, resulting in problems such as damage to the structural pattern during mold release. By satisfying equation (2), it is possible to set the step within the manufacturable range at the resin interface between the microstructure portion P and the coating structure M. To obtain sufficient light diffraction with a refractive index difference below equation (2), a large step is required, and a manufacturable microstructure cannot be obtained.

[0026] When creating a composite diffraction element using glass and resin, the refractive index of each material is important. It is known that the glass material corresponds to a wide range of refractive indices, while the resin material has a narrower selection range of refractive indices compared to the glass material. To realize a manufacturable microstructure, it is necessary to satisfy equation (2), and to maintain the light quantity and prevent stray light, it is necessary to satisfy equation (1). Therefore, the resin refractive index NP used for the microstructure P and the resin refractive index NP used for the coating structure M are limited. Furthermore, in order to suppress performance degradation when used in a liquid or when dew condensation occurs, it is desirable that the refractive index difference between the refractive index NM of the coating structure M and the refractive index of the liquid is within 0.1. If the refractive index difference is 0.1 or less, reflection occurring at the interface between the liquid and the resin can be suppressed, and refraction at the interface can also be suppressed. Since the refractive index of the liquid is about 1.3 to 1.5 except for some special solutions, the refractive index NM of the coating structure M may be determined within the range of equation (3) considering the solution used. Furthermore, considering the refractive index region of the glass material, in order to satisfy equations (1), (2), and (3), it is preferable to satisfy the condition that the refractive index NP of the microstructure P in equation (4) is smaller than the coating structure NM.

[0027] Furthermore, in this structure, since the fine structure P is covered by the covering structure M, the fine structure pattern is protected, and the composite diffraction grating is imparted with scratch resistance and antifouling properties. In addition, it is possible to prevent the direct measurement of the fine structure pattern.

Advantages of the Invention

[0028] According to the composite diffractive optical element of the present invention, by forming a fine structure on a parallel flat glass with a resin material, covering the fine structure with a different resin material, and appropriately controlling the refractive indices of the resin and the glass, while suppressing interface reflection, sufficient light diffraction can be generated, the protection of the formed fine structure can be realized while suppressing performance changes due to temperature and humidity, and it is possible to use it in a liquid. In addition, performance changes due to dew condensation can be suppressed.

Brief Description of the Drawings

[0029]

Figure 1

Figure 2

Figure 3

Figure 4

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Figure 8

Modes for Carrying Out the Invention

[0030] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that each drawing illustrates a configuration example according to the present invention, and only schematically shows the cross-sectional shape, arrangement relationship, etc. of each component to the extent that the present invention can be understood, and the present invention is not limited to the illustrated examples. In addition, in the following description, specific conditions, etc. may be used, but these materials and conditions are only one of the preferred examples, and therefore, the present invention is not limited to these in any way.

[0031] Figure 1 is a configuration diagram of the composite diffractive optical element of the present invention. A fine structure P is formed on the projection side surface of the parallel flat glass G with an energy-curable resin, and a coating structure M is formed thereon with a different energy-curable resin.

[0032] Here, for the following drawings, when the light source side is the light source side and the light ray exit side is the projection side with the composite diffractive optical element in between, the light source side surface of the parallel flat glass G is G1, the projection side surface is G2, and similarly, the light source side of the fine structure P is P1, the projection side is P2, the light source side of the coating structure M is M1, and the projection side is M2. Also, the joint surface between the parallel flat glass G and the fine structure P is GP, and the joint surface between the fine structure P and the coating structure M is PM.

Example

[0033] Figure 2 is a configuration diagram of the composite diffractive optical element in the first embodiment. A laser light source RS, a parallel flat glass G, a fine structure P, and a coating structure M are arranged in order from the light source side. The structure pattern of the fine structure M is shown enlarged for convenience, but originally it has a pitch and step of about several tens of nm to several μm. The projection side surface M2 of the coating structure M has a planar shape. Although not shown, a silane coupling treatment is performed on the joint surface between the glass and the resin to strengthen the interfacial adhesion. The silane coupling agent is a material that can bind to both the resin and the glass and is widely used to strengthen the interfacial adhesion between the glass and the resin in hybrid lenses.

[0034] The refractive index NG of the parallel flat glass G is 1.72, the refractive index NP of the fine structure P is 1.62, and the refractive index NM of the coating structure M is 1.29. As a resin material with a refractive index of 1.5 or less, fluorine-based resins or silicone-based resins can be applied. As a resin material with a refractive index of 1.5 or more, epoxy or acrylic resins can be applied. These are one of the examples, and as long as it is an energy-curable resin that is cured by external energy, the material system is not limited.

[0035] In this embodiment, the refractive index difference between the parallel flat glass G and the microstructure P is 0.1, satisfying equation (1). Also, the refractive index difference between the microstructure P and the coating structure M is 0.33, satisfying equation (2). Furthermore, the refractive index of the coating structure M is 1.29, satisfying equation (3), and the refractive index of the microstructure P is greater than that of the coating structure M, also satisfying equation (4).

[0036] By configuring in this way, the reflected light is suppressed, the performance changes with respect to temperature and humidity are suppressed, and since the coating structure protects the microstructure, it is resistant to scratches and dirt and can also be used in liquids.

[0037] Figure 3 is a configuration diagram of the composite diffractive optical element in the second embodiment. The order of the configuration is the same as in the first embodiment, but the projected side surface M2 of the coating structure M has a curved surface shape. In the present invention, the shape of the projected side surface of the coating structure M is not particularly limited, and in addition to a plane, it may be a curved surface or a prism surface according to the intended use.

[0038] The refractive index NG of the parallel flat glass G is 1.61, the refractive index NP of the microstructure P is 1.66, and the refractive index NM of the coating structure M is 1.34.

[0039] In this embodiment, the refractive index difference between the parallel flat glass G and the microstructure P is 0.05, satisfying equation (1). Also, the refractive index difference between the microstructure P and the coating structure M is 0.32, satisfying equation (2). Furthermore, the refractive index of the coating structure M is 1.34, satisfying equation (3), and the refractive index of the microstructure P is greater than that of the coating structure M, also satisfying equation (4).

[0040] By configuring in this way, in addition to obtaining the same effects as in the first embodiment, since the projected side surface M2 of the coating structure M can be used as a lens surface, it is also possible to change the pattern projection position in a liquid and in air as shown in Figure 4.

[0041] Figure 5 is a configuration diagram of the composite diffractive optical element in the third embodiment. The order of the configuration is the same as in the first embodiment, but the projected side surface M2 of the coating structure M has a prism shape.

[0042] The refractive index NG of the parallel flat glass G is 1.80, the refractive index NP of the fine structure P is 1.72, and the refractive index NM of the coating structure M is 1.41.

[0043] In this embodiment, the refractive index difference between the parallel flat glass G and the fine structure P is 0.08, satisfying equation (1). Also, the refractive index difference between the fine structure P and the coating structure M is 0.31, satisfying equation (2). Furthermore, the refractive index of the coating structure M is 1.41, satisfying equation (3), and the refractive index of the fine structure P is greater than that of the coating structure M, also satisfying equation (4).

[0044] By configuring it in this way, not only can the same effects as in Example 1 be obtained, but since the projection side surface M2 of the coating structure M can be used as a prism surface, as shown in FIG. 6, the projection pattern travels straight in the liquid and can also be folded back in the air.

[0045] FIG. 7 is a configuration diagram of the composite diffractive optical element in the fourth embodiment. The order of the configuration is the same as in Example 1, and the refractive indices of each material are the same as in Example 3, but the projection side surface M2 of the coating structure M has a fine prism shape.

[0046] By configuring it in this way, not only can the same effects as in Example 1 be obtained, but since the projection side surface M2 of the coating structure M can be used as a fine prism surface, as shown in FIG. 8, the projection pattern travels straight in the liquid and can be made such that the projection pattern does not exit to the projection surface side in the air.

Explanation of Reference Numerals

[0047] G Parallel flat glass P Fine structure joined on the parallel flat glass M Coating structure for sealing on the fine structure G1 Light source side surface of the parallel flat glass G2 Projection side surface of the parallel flat glass P1 Light source side surface of the fine structure P2 Projection side surface of the fine structure M1 Light source side surface of the coating structure M2 Projection side surface of the coating structure Bonding surface between GP parallel flat glass and microstructures Bonding surface between PM microstructures and coating structures

Claims

1. A fine structure pattern having a pitch and a step with a diffraction function is formed on the projection side surface of a parallel flat plate made of glass, and a coating structure (excluding those with light diffusing properties) is formed so as to cover the entire surface of the fine structure pattern. The fine structure pattern and the coating structure are formed of an energy-curing resin. The surface shape on the projection side of the coating structure is a curved surface shape or a prism shape. When the refractive index of the parallel flat plate made of glass at the use wavelength is NG, the refractive index of the energy-curing resin constituting the fine structure pattern at the use wavelength is NP, and the refractive index of the energy-curing resin constituting the coating structure at the use wavelength is NM, it is configured to satisfy the following conditions (1) to (4). The difference in refractive index between NM and the liquid is within 0.1, and the projection position of the projection pattern is different in the liquid and in the air. A composite diffractive optical element that can be used in both the liquid and the air. |NG - NP| ≤ 0.1...(1) |NP - NM| ≥ 0.3...(2) 1.25 ≤ NM ≤ 1.5...(3) NP > NM...(4)

2. The surface shape on the projection side of the coating structure is a prism shape, The prism shape is an inclined surface shape, and when used in air, total reflection occurs at the use wavelength and no light returns to the light source side. The composite diffractive optical element according to Claim 1.

3. The surface shape on the projection side of the coating structure is a prism shape, The prism shape is a fine shape, and when used in air, total reflection occurs at the use wavelength and light returns to the light source side. The composite diffractive optical element according to Claim 1.

4. The light of the projection pattern travels straight in the liquid. The composite diffractive optical element according to Claim 2 or 3.

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