JP6981074B2 - Optical element - Google Patents

Description

The present invention relates to an optical element that generates a predetermined phase difference.

Various optics that generate a predetermined phase difference in incident light, such as a diffractive optical element that generates a predetermined pattern of light spots with respect to incident light, a lens element that has a refraction action, and a diffuser element that diffuses light to a predetermined emission angle. The element is used.

Such an optical element is, for example, a diffractive optical element that generates a predetermined light to irradiate a measurement target in an irradiation optical system of a measuring device, or light that propagates communication information in a communication information propagation optical system of a communication device. Examples thereof include a lens and a microlens that guide the optical path to a predetermined optical path.

For example, Patent Document 1 exemplifies an optical element which is composed of a substrate having a fine structure distribution that expresses dispersion (diffusion or scattering) having a controllable intensity change with respect to an incident beam and functions as a diffusion element or a display screen. Has been done.

Optical devices provided with the above optical elements handle not only visible light but also near-infrared light. However, some of these optical devices are required to have an action of diffracting, diffusing, and refracting at emission angles that are significantly different from the traveling direction of the incident light. When dealing with near-infrared light, such an optical element has a problem that the concave-convex structure is physically restricted due to the length of the wavelength. In particular, when considering an optical element having a concavo-convex structure having a relatively large maximum emission angle with respect to light incident in the visible region or near-infrared region having a wavelength of 600 nm or more (up to 1200 nm or less), it is necessary to form the concavo-convex structure. It is necessary to use a high refractive index material or to deepen the uneven part.

In particular, as the depth of the uneven portion increases, the aspect ratio (for example, "height of the convex portion / width of the convex portion") also increases accordingly, and the problem that the processing accuracy cannot be improved becomes remarkable. Therefore, it may be difficult for the optical element to generate a desired phase difference with high accuracy. For example, in the case of a diffractive optical element that generates a predetermined light spot at a wide angle with respect to incident light, the uneven structure becomes finer and the aspect ratio becomes larger. For this reason, it becomes difficult to process the uneven structure as designed in the processing process such as etching, and there is a problem that the controllability of the diffraction efficiency distribution is lowered. Further, even in the case of an optical element such as a diffusion element or a microlens array that exhibits a refraction action, in order to obtain a large refraction angle, the inclination angle formed by the lens portion (more specifically, the uneven portion having a curved surface shape) is increased. There is a need to.

In order to reduce such restrictions on the shape, a configuration in which a high refractive index material is used for the uneven portion and the difference in the refractive index from the peripheral medium is increased to reduce the aspect ratio can be mentioned. For example, the use of a semiconductor material such as amorphous silicon, which has a large absorption for visible light and a high refractive index for near-infrared light, can be mentioned. For example, Patent Document 2 discloses a diffractive optical element in which a multilayer structure including a plurality of amorphous silicon phase shift layers is formed so that a desired phase difference can be generated with respect to infrared light.

U.S. Pat. No. 70333736 Japanese Unexamined Patent Publication No. 2004-62200

The diffractive optical element of Patent Document 2 has an etch stop layer of silicon dioxide in order to adjust the uneven shape, and the layer is exposed to air as a peripheral medium. However, when a high-refractive index material is used as the uneven portion, the reflection (hereinafter referred to as interfacial reflection) generated at the entrance side interface and the exit side interface of the uneven portion becomes large, causing reflection loss and reducing the light utilization efficiency. Another problem arises. The etch stop layer described in Patent Document 2 describes that silicon dioxide exhibiting its function has a thickness of less than 5 nm, but it is configured to include a material suitable for etch stop to the last, and is generated there. No consideration is given to the reflection loss.

Therefore, an object of the present invention is to provide an optical element having a high light utilization efficiency having a concavo-convex structure that generates a predetermined phase difference with respect to incident light, and an optical element having ease of processing in addition to the optical element.

The optical element according to the present invention includes a transparent base material and a concavo-convex portion provided on the transparent base material and generating a predetermined phase difference with respect to a predetermined polarization component of the incident light or the incident light. The uneven portion is composed of two or more different materials, and when one of the materials constituting the uneven portion has a complex refractive index in the wavelength band of the incident light as n−k, n ≧ 2. 5 and the first material with k <0.01, the forward transmittance in at least the effective region is 80% or more, or at least, with respect to the incident light incident from the normal direction of the plane of the transparent substrate. The transmittance in the effective region is 10% or less, and the uneven portion has one or more curved surfaces that are non-parallel to the transparent substrate or one or more inclined surfaces that are non-parallel to the transparent substrate. An antireflection layer is provided at the interface between the concavo-convex structure of a single layer and a predetermined medium that covers the interface with the transparent substrate and / or the surface of the concavo-convex portion on the side where the curved surface or the inclined surface is formed. It is characterized by including.

According to the present invention, it is possible to provide an optical element having a high light utilization efficiency having a concavo-convex structure that generates a predetermined phase difference with respect to incident light, and an optical element having ease of processing in addition to the optical element.

The cross-sectional schematic diagram of the optical element 10 of 1st Embodiment. FIG. 6 is a schematic cross-sectional view showing another example of the optical element 10. FIG. 6 is a schematic cross-sectional view showing another example of the optical element 10. FIG. 6 is a schematic cross-sectional view showing another example of the optical element 10. FIG. 6 is a schematic cross-sectional view showing another example of the optical element 10. Explanatory drawing which shows an example of the pattern of light generated by an optical element 10. The figure which shows typically the example of the concavo-convex portion 12 of an optical element 10. FIG. 6 is a schematic cross-sectional view showing an example of propagation of diffracted light in the optical element 10. A schematic plan view and a schematic cross-sectional view of the optical element 40 of the second embodiment. FIG. 6 is a schematic cross-sectional view showing another example of the optical element 40. FIG. 6 is a schematic cross-sectional view showing another example of the optical element 40. Schematic diagram of a cross section showing an example of the refraction action of light emitted from an inclined surface having an inclination of α. Calculation result of reflectance in light of wavelength 800-1000 nm of Example 1 and its comparative example. Calculation result of reflectance in light of wavelength 800-1200 nm of Example 2. Schematic diagram of a main part of the optical element 10 of Examples 3 to 6. Calculation result of reflectance in light of wavelength 800-900 nm of Example 3. Calculation result of reflectance in light of wavelength 800-900 nm of Example 4. Calculation result of reflectance in light of wavelength 800-900 nm of Example 5. Calculation result of reflectance in light of wavelength 800-900 nm of Example 6. The explanatory view of the manufacturing method of the optical element 40 of Example 7. Calculation result of reflectance in light of wavelength 800-1000 nm of Example 7. FIG. 6 is a schematic cross-sectional view of a main part of the optical element 40 of Example 8. The explanatory view of the manufacturing method of the optical element 10 of Example 9. Calculation result of reflectance in light of wavelength 800-1000 nm of Example 9.

Embodiment 1.
FIG. 1 is a schematic cross-sectional view of the optical element 10 of the first embodiment. The optical element 10 includes a transparent base material 11 and an uneven portion 12 provided on the transparent base material. Reference numeral 13 in the figure indicates a medium that covers the uneven portion 12.

The uneven portion 12 is a multilayer structure composed of two or more different materials and having two or more layers. Further, the uneven portion 12 includes at least a portion of incident light or incident light that causes a predetermined phase difference with respect to a predetermined polarization component. Although FIG. 1 illustrates the two-layer uneven portion 12, the uneven portion 12 may have three or more layers.

In the present embodiment, with respect to the uneven portion 12 having a multi-layer structure, the one at a position higher than the lowest portion of the surface where the uneven portion 12 and the medium 13 are in contact is also referred to as the convex portion 121 of the uneven portion 12. Further, a recessed portion surrounded by the convex portion 121 and lower than the uppermost surface of the convex portion 121 is also referred to as a concave portion 122 of the concave-convex portion 12. Hereinafter, the direction toward the transparent base material 11 as viewed from the uneven portion 12 is downward, and the direction away from the transparent base material 11 is upward. Therefore, the interface between the transparent base material 11 and the uneven portion 12 is the lowermost surface of the uneven portion 12, and the surface of the upper surface of each stage of the uneven portion 12 that is farthest from the transparent base material 11 is the uppermost surface. Further, the layer located between the highest portion and the lowest portion of the surface where the uneven portion 12 and the medium 13 are in contact with each other is also referred to as a retardation layer 123.

As the transparent base material 11, a member such as glass or resin that is transparent to the wavelength of light used can be used.

Further, the uneven portion 12 uses a material satisfying the formula (1) in at least one or more layers when the complex refractive index at the wavelength used by the layer is n-ik. Hereinafter, the material satisfying the formula (1) is also referred to as a first material. The "complex refractive index" referred to here corresponds to the refractive index at the wavelength having the highest light intensity among the wavelengths used, and is set in the range of ± 20 nm or ± 10 nm with respect to the wavelength, for example. May be good. Hereinafter, the same applies to the “refractive index”.

n ≧ 2.5, k <0.01 ... (1)

The wavelength used is the wavelength band of the incident light on the optical element 10. Hereinafter, it will be described that near-infrared light having a wavelength of 700 to 1200 nm is incident on the optical element 10. As will be described later, the wavelength band is not particularly limited because the incident light of 520 nm can also be targeted. For example, when handling light having a longer wavelength than visible light, such as near-infrared light, the unevenness tends to be high in order to increase the optical path length difference, so that the configuration of the optical element of the present embodiment is effective. be.

As the first material, a material having amorphous silicon or an amorphous silicon compound as a base material can be exemplified. When the material is used, k can be sufficiently reduced at a wavelength of 700 to 1200 nm. In particular, from the viewpoint of chemical stability, hydrogenated ones such as hydrogenated amorphous silicon or hydrogenated amorphous silicon compounds are preferable. Vacuum vapor deposition, sputtering, plasma CVD, or the like can be used for film formation of a material using amorphous silicon or an amorphous silicon compound as a base material. Hereinafter, amorphous silicon is also referred to as “a—Si”.

Materials using a-Si or a-Si compound as a base material include hydrogenated a-Si and compounds of a-Si and carbon or germanium (described as a-SiC and a-SiGe, respectively). In addition, these materials may be hydrogenated. For example, hydrogenated compounds of carbon and germanium with respect to a-Si and a-Si are described as a-Si: H, a-SiC: H, a-SiGe: H, etc., respectively. .. Further, each of these may be partially doped with oxygen or nitrogen.

The advantage of using the a-Si compound is that it absorbs less in the near infrared light. The bandgap of crystallized silicon is about 1.1 eV, which is about 1130 nm in terms of wavelength. Therefore, in the case of crystallized silicon, light having a wavelength of 1130 nm or less cannot be transmitted. On the other hand, as the compound of a-Si, a-SiC: H is 1.8 to 2.4 eV (wavelength of about 520 to 690 nm), and a-Si: H is 1.7 to 1.9 eV (wavelength of about 650). ~ 730 nm), a-SiGe: has a hand gap of 1.0 to 1.7 eV (about 730 to 1240 nm in wavelength) at H. According to these, light having a wavelength of 520 nm or more can be transmitted with a small absorption.

Further, some of these a-Si compounds have a refractive index in the range of 2.3 to 4. In particular, it is preferable to use a material having a refractive index of 2.5 or more because the refractive index becomes larger than that of an optical material such _{as TiO 2 used in the visible region.} The refractive index is more preferably 2.8 or more, and even more preferably 3 or more. Further, if the refractive index is too high, absorption is likely to occur, so that the upper limit of the refractive index is preferably 5 or less, more preferably 4 or less.

When the above material is used, the wavelength range of the optical element can be set to 520 nm or more. However, since absorption may remain in the vicinity of the absorption edge where the transmittance is higher than the transmittance, the wavelength of the light used is preferably 600 nm or more, more preferably 700 nm or more. Even with crystallized silicon, since absorption is small when the wavelength is 1130 nm or more, particularly 1200 nm or more, crystallized silicon can be used when the wavelength range is used. However, when the wavelength of the light used is 1200 nm or less, it is preferable to use the a-Si compound from the viewpoint of material selectivity.

Further, since the base material is required to be transparent to light of the wavelength used, when light of 1200 nm or less is used, a material such as crystallized silicon cannot be used as the base material. Therefore, it is necessary to use transparent materials such as glass, resin, and ceramics. Further, since the general refractive index of optical glass is about 1.5, and even if it is high, it is about 2.1, a large difference in refractive index occurs at the interface between the base material and a-Si, and a large reflected light is generated. .. From this point of view, it is necessary to prevent reflection at the interface by using a refractive index adjusting layer and an antireflection layer, which will be described later.

Further, when an a-Si or a-Si compound having a thickness of 0.5 μm or more is provided on the base material, peeling may occur due to stress between these members and the base material. The difference should be small. The absolute value of the difference in the coefficient of linear expansion between the substrate and the a-Si or a-Si compound ^{is preferably 4 × 10 -6} / K or less, and more preferably ^{2 × 10 -6 / K or less.} The coefficient of linear expansion of a-Si is 1.5 to 4.0 × 10 ⁻⁶ / K. Therefore, as an example of the coefficient of linear expansion of the base material, 8 × 10 ^-6 / K or less is preferable, and 6 × 10 ^-6 / K or less is more preferable. Here, when glass is used as the base material, the coefficient of linear expansion can be compared with the average coefficient of linear expansion of 20 ° C to 300 ° C. The coefficient of linear expansion ^{is preferably -2 × 10 -6} / K or more, and more preferably 0 × 10 ^-6 / K or more.

By using such a material, the height of the uneven portion 12 can be reduced, and the machining can be completed before an unintended structure such as a taper is generated when machining by etching, for example, and a shape closer to the design can be obtained. .. This facilitates control of the optical function of the optical element 10.

Although FIG. 1 illustrates a two-step uneven portion 12, the uneven portion 12 may have a stepped pseudo-blaze structure having three or more steps. Here, the number of steps of the uneven portion 12 is counted as one step for each surface constituting the step that causes a phase difference with respect to the incident light, as in the case of a general diffraction grating.

For example, the optical element 10 may be provided with three or more steps of uneven portions 12 as shown in FIG. 2A, and at least all of the uneven portions 12 on the optical path are transparent as shown in FIG. 2B. The configuration may be such that the third medium 13 is in contact with the base material 11 and is not in contact with the transparent base material 11. Hereinafter, in such a configuration, the layer constituting the first stage of the uneven portion 12, that is, the layer covering the surface of the transparent base material 11 at least in the effective region of the incident light is also referred to as the base layer 124. In the configuration of FIG. 2B, the upper surface of the base layer 124 is the first stage of the uneven portion 12. The base layer 124 may be a single layer or a multilayer. Here, the effective area of the incident light and the light intensity is 1 / e ² or more regions of the incident light, that is, when the highest (position) the light intensity of the incident light is 100%, more than 13% The area to be irradiated with light indicating the light intensity.

When the optical element 10 is a diffractive optical element and the uneven portion 12 has an N-step stepped pseudo-blaze shape, the optical path generated by the convex portion 121 and the concave portion 122 (medium 13) when the equation (2) is satisfied. It is preferable that the length difference can be approximated to the wavefront for one wavelength and high diffraction efficiency can be obtained. Here, N is an integer of 3 or more.

{(N-1) / N} × λ = Δnd ・ ・ ・ (2)

Here, Δn is the difference in the refractive index between the uneven portion 12 and the medium 13, and d is the difference between the highest portion and the lowest portion of the surface in which the uneven portion 12 and the medium 13 are in contact, that is, the height of the retardation layer 123.

For example, in the case of near-infrared light where the quartz glass having a refractive index of 1.455 has an air atmosphere, {(N-1) / N} × λ = 0.455d. From this, it is preferable that the height d of the retardation layer 123 satisfies d <{(N-1) / N} × λ / 0.455. Further, when the wavelength of the light used is 700 to 1200 nm, the height d of the retardation layer 123 is preferably 750 nm or less, particularly in the case of the two-stage uneven portion 12. The height d is preferably 1150 nm or less when the height is 4 or more, and preferably 1350 nm or less when the height is 8 or more.

Further, the uneven portion 12 may have an antireflection function. For example, the concavo-convex portion 12 itself may have a concavo-convex structure that generates a predetermined phase difference and may have a multi-layered concavo-convex structure having an antireflection structure.

Here, the incident light at an incident angle theta ₀ from a medium M1 having a refractive index n _0, refractive index of each layer thickness at n _r is transmitted through the multilayer film M2 formed of q layer is d _r, the refractive index n Consider the case where light is incident on the medium M3 of _m. The reflectance at this time can be calculated by the equation (3). Note that η ₀ , η _m , and η _r are the effective refractive indexes of the medium M1, the multilayer film M2, and the medium M3 in consideration of oblique incident, respectively. Hereinafter, the reflectance R represented by the equation (3) is also referred to as a theoretical reflectance due to the multilayer structure. Further, unless otherwise specified, θ ₀ = 0, but when the incident surface is inclined, the incident angle may be defined by the average inclination of the inclination.

Therefore, by designing the multi-layer structure of the uneven portion 12, when Y is _{brought close to η 0} , interfacial reflection with other media can be reduced. Especially in the case of vertical incident, η ₀ , η _m and η _r are equivalent to the refractive index. In this case, the uneven portion 12, the refractive index of each layer n _r, a multilayer film consisting of a thick was d _r q layer. Further, the refractive index of the member (transparent base material 11 or medium 13) constituting the incident side interface when viewed from the uneven portion 12 is n ₀ , and the member (medium 13 or transparent group) constituting the exit side interface when viewed from the uneven portion 12 is set. The refractive index of the material 11) may be _nm.

For example, it is preferable that the uneven portion 12 satisfies the theoretical reflectance R ≦ 4% due to the multilayer structure, more preferably R ≦ 2%, and further preferably R ≦ 1%.

As an example, as shown in FIG. 3A, the uneven portion 12 has a refractive index adjusting layer 14a at the interface with the lowermost layer, that is, the transparent base material 11, and at the interface with the uppermost layer, that is, the medium 13. A configuration having a refractive index adjusting layer 14b may be used. Here, the refractive index adjusting layers 14a and 14b emit the refractive index of the medium (for example, the transparent base material 11) forming the interface on the incident side in the uneven portion 12 of the multilayer structure including the refractive index adjusting layer 14a by _nm . medium forming the side surface (e.g., air or medium 13) when the refractive index n _{0 of,} n _r of each of the concavo-convex portion _12, the thickness was set to d _r, with respect to both interfaces of the concavo-convex portion 12, The theoretical refractive index R may satisfy the above condition by the single-layer or multi-layer structure satisfying the formula (4).

(N ₀ × n _m ) ^{0.5 −} α <n _r <(n ₀ × n _m ) ^0.5 + α, and (1-β) × λ / 4 <n _r × _dr <(1 + β) × λ / 4
However, α = 0.25 and β = 0.6
... (4)

Here, α is preferably 0.25, more preferably 0.2, and even more preferably 0.1. Further, β is preferably 0.6, more preferably 0.4. Further, the intermediate layer 14c shown in FIG. 3A may be one layer or two or more layers. Further, the refractive index adjusting layer 14a does not have to be the lowest layer, and the refractive index adjusting layer 14b does not have to be the uppermost layer either. Further, the uneven portion 12 may be configured to include only one of the refractive index adjusting layers 14a and 14b. That is, for convenience of explanation, the layers constituting the uneven portion 12 are given names such as the refractive index adjusting layers 14a, 14b, and the intermediate layer 14c, but in any of the configurations, the unevenness of the multilayer structure including at least the first material is given. The unit 12 may be configured such that the equation (4) or the theoretical reflectance R satisfies the above conditions.

Further, when the uneven portion 12 has three or more stages, each stage of the uneven portion 12 (provided that the stage has a height) may be a multi-layer structure having two or more thin film structures as a basic block. That is, the step having a height among the steps of the uneven portion may be configured by stacking one or more basic blocks which are two or more layers of multilayer films having a predetermined refractive index and thickness. The basic block is not limited to one type, and may be a plurality of types. In that case, the theoretical reflectance R due to the multi-layer structure of the basic block is configured to satisfy the above conditions.

Further, as shown in FIGS. 3 (b) and 3 (c), the uneven portion 12 has an interface in contact with at least the transparent base material 11 in the effective region of the incident light, in addition to the retardation layer 123 and the base layer 124. The antireflection layers 15a and 15b may be provided at the interface in contact with the medium 13 and the medium 13. In this case, the retardation layer 123 and the antireflection layers 15a and 15b are included and referred to as an uneven portion 12. The uneven portion 12 may include at least the antireflection layer 15a. Further, in FIG. 3B, the antireflection layers 15a and 15b are laminated in the recess 122, and the antireflection layer 15a has at least a layer formed by the first material in the effective region of the incident light. It may be provided between the included retardation layer 123 (if the base layer 124 is present, the base layer 124) and the transparent base material 11. Further, the antireflection layer 15b may be provided between the retardation layer 123 and the medium 13 at least in the effective region of the incident light.

The antireflection layers 15a and 15b may be a single layer or may be a multilayer film having two or more layers. Various metals, semiconductor oxides, nitrides, oxynitrides, and fluorides can be used as the material for forming the antireflection layer, but if it is a single-layer film or a multilayer film made of a silicon compound containing silicon, for example, etching. It is preferable because it is not necessary to change the processing conditions significantly when processing.

As an example, in the antireflection layers 15a and 15b, the refractive index of the medium forming the incident side interface is _nm , the refractive index of the medium forming the exit side interface is n ₀ , and the refractive index of the antireflection layer or each layer thereof is n. _r, when the thickness was set to d _r, with respect to both interfaces of the anti-reflection layer, the theoretical reflectivity R by the antireflection-layer or multi-layer structure of a single layer satisfying the expression (4) may satisfy the above conditions. For example, when light is incident from the transparent base material 11 side in FIG. 3 (b), the medium forming the incident side interface is the transparent base material 11 and the medium forming the exit side interface is the retardation layer with respect to the antireflection layer 15a. It is a member of 123. Further, with respect to the antireflection layer 15b, the medium forming the interface on the incident side is a member of the retardation layer 123, and the medium forming the interface on the exit side is the medium 13.

Further, the retardation layer 123 may be a single layer or a multilayer layer. The thickness of each layer of the uneven portion 12 is preferably 5 nm or more from the viewpoint of generating a desired phase difference and contributing as an optical layer for reducing the reflectance. The reason is that, for example, when the uneven portion 12 has an etching stop layer having a thickness of about 5 nm as in the conventional configuration, the multilayer structure is not optically controlled as compared with the configuration without the layer. This is because there is a large variation in the interference state that occurs. Even if the thickness of each layer is about 5 nm, the reflectance of the entire uneven portion 12 may satisfy the above condition, and in that case, the lower limit condition of the thickness of each layer may be ignored.

Further, the medium 13 may be air or other than air. That is, as shown in FIG. 4, the optical element 10 may include a filling portion 16 that covers and flattens the surface of the uneven portion 12 on the side facing the transparent base material 11. In this case, the material of the filling portion 16 is the medium 13.

Examples of the medium 13 other than air include resins and inorganic substances. In this case, the refractive index difference Δn between the uneven portion 12 (more specifically, the convex portion 121) and the filling portion 16 with respect to light of a predetermined wavelength (range) in order to generate a desired phase difference is 0.45 or more. Is preferable, and 0.6 or more is more preferable. The optical element 10 is not limited to the example in which the filling portion 16 is exposed (FIG. 4), and as shown in FIG. 5A, the uneven portion 12 and the filling portion 16 are formed by the transparent base materials 11-1 and 11-2. It may be configured to cover the main surface, or may have a plurality of uneven portions 12. In this case, two optical elements 10 having one uneven portion 12 may be stacked, or as shown in FIG. 5 (b), two uneven portions 12 (12-1 and 12-2) are interposed via the medium 13. ) May be bonded together.

Further, the reflectance of the optical element 10 as a whole may be 10% or less, preferably 6% or less, more preferably 4% or less, still more preferably 3% or less. At this time, the reflectance due to the laminated structure of the transparent base material 11, the uneven portion 12, and the medium 13 may be 8% or less, preferably 4% or less, more preferably 2% or less, still more preferably 1% or less. Here, the reflectance due to the laminated structure of the transparent base material 11, the uneven portion 12, and the medium 13 can also be evaluated by the theoretical reflectance due to the multilayer structure represented by the equation (3).

Next, the optical element 10 will be described in more detail assuming that it is a diffractive optical element. In this case, the uneven portion 12 may have a structure capable of exhibiting a diffraction action. As shown in FIG. 1, for example, the uneven portion 12 may have two or more steps on one surface of the transparent base material 11, and the upper surfaces of the steps may be parallel to each other.

Next, the diffraction action exhibited by the optical element 10 will be described with reference to an example of the light pattern generated by the optical element 10 of FIG. The optical element 10 is formed so that the diffracted light group 22 emitted with respect to the incident light flux 21 with the optical axis direction as the Z axis is distributed two-dimensionally. When the optical element 10 has an intersection with the Z axis and the axes perpendicular to the Z axis are the X axis and the Y axis, the minimum angle θ x _min on the X axis to the maximum angle _{θ x max} and the minimum angle θ y _{min on the Y axis} The light beam group is distributed within the angle range of the maximum angle θy _{max (not shown).}

Here, the X-axis is substantially parallel to the long side of the light spot pattern, and the Y-axis is substantially parallel to the short side of the light spot pattern. The irradiated range of the diffracted light group 22 formed by the minimum angle θx _min to the maximum angle θx _{max in} the X-axis direction and the maximum angle θy _{max from the minimum angle θy min} in the Y-axis direction is the same as that of the optical element 10. The range is substantially the same as the light detection range of the photodetector used. In this example, in the light spot pattern, the straight line parallel to the Y axis passing through the light spot whose angle in the X direction with respect to the Z axis is θx _max is the short side, and the angle in the Y direction with respect to the Z axis is θy _max . The straight line parallel to the X-axis passing through a certain light spot is the long side. Hereinafter, the angle formed by the Z axis and the straight line connecting the intersection of the short side and the long side and the diffractive optical element is _{defined as θ d,} and this angle is referred to as a diagonal angle. The diagonal angle θ _d corresponds to the maximum emission angle of the optical element 10.

The number of light spots generated by the optical element 10 is preferably 10 points or more, more preferably 100 points or more, still more preferably 1000 points or more. The upper limit of the number of light spots is not particularly limited, but may be, for example, 10 million points.

In addition, the concave-convex structure of the diffractive optical element usually has a binary shape, a blaze shape, or the like in a cross section. If there is a variation in the light, stray light may be generated in addition to the desired diffracted light. However, since such stray light is not intended at the design stage, it is not included in the light spots distributed within the above angle range.

Further, in FIG. 6, _Rij indicates a divided region of the projection plane. For example, in the optical element 10, when the transparent surface is divided into a _{plurality of regions R ij} , the distribution density of the light spots 23 by the diffracted light group 22 irradiated to _{each region R ij is ± 50 with respect to the average value of all regions.} It may be configured to be within%. The distribution density may be within ± 25% of the average value of all regions. With such a configuration, the distribution of the light spots 23 can be made uniform in the projection plane, which is suitable for measurement applications and the like. Here, the projection plane may be a curved surface as well as a plane. Further, in the case of a flat surface, a plane inclined other than the plane perpendicular to the optical axis of the optical system may be used.

Each diffracted light included in the diffracted light group 22 shown in FIG. 6 is diffracted into an angle θ _{xo in} the X direction and an angle θ _{yo in the Y direction with respect to the Z-axis direction in the grating equation shown in the equation (5).} It becomes light. In the formula (5), m _x is the diffraction order in the X direction, m _y is the diffraction order of the Y-direction, lambda is the wavelength of the light beam _21, P x, P _y is the basic unit of the optical element to be described later Is the pitch in the X-axis direction and the Y-axis direction, θ _xi is the angle of incidence on the optical element in the X direction, and θ _yi is the angle of incidence on the optical element in the Y direction. By irradiating the projected surface of the screen or the object to be measured with the diffracted light group 22, a plurality of light spots 23 are generated in the irradiated area.

sinθ _xo = sinθ _xi + m _x λ / P _{x
sinθ yo = sinθ yi + m y} λ / P y
... (5)

As the optical element 10 that emits the diffracted light group 22 satisfying such a predetermined condition, an optical element designed by an iterative Fourier transform method or the like can be used. More specifically, an optical element in which basic units that generate a predetermined phase distribution are periodically, for example, two-dimensionally arranged can be used. In such an optical element, the distribution of the diffraction order of the diffracted light in the distance is obtained by the Fourier transform in the basic unit.

As shown in FIG. 7A, the optical element 10 has a basic unit 31 constituting the uneven portion 12 on the transparent base material 11 having a pitch P _{x in} the X-axis direction and a pitch P _y in the Y-axis direction. It may be arranged dimensionally and periodically. The basic unit 31 has, for example, a phase distribution as shown in FIG. 7 (b). In the example shown in FIG. 7B, the uneven pattern is formed so that the black-painted area is the convex portion 121 and the white area is the concave portion 122. The uneven portion 12 only needs to be able to generate a phase distribution, and includes a structure in which an uneven pattern is formed on the surface of a member (transparent base material 11) that transmits light such as glass or a resin material. In addition to this, as the optical element 10, a member (filling portion 16) having a refractive index different from that of this member is attached onto a transparent member (transparent base material 11) on which an uneven pattern is formed. A structure having a flat surface or a structure in which the refractive index is changed in a transparent member may be used. That is, the uneven pattern does not mean only when the surface shape is uneven, but also includes a structure in which a phase difference can be given to the incident light.

Further, when the basic units 31 are two-dimensionally arranged on the optical element 10, the number of basic units does not have to be an integer number, and if one or more basic units are included in the uneven pattern, the uneven pattern and the uneven pattern are provided. The boundaries of the non-existent areas do not necessarily have to match the boundaries of the base unit. Further, the basic unit 31 is not limited to one type, and may be a plurality of types.

Further, the optical element 10 includes a diffraction optical element that exhibits a diffusion function by having a plurality of basic units in addition to the above-mentioned diffraction optical element, and a Frenel lens element that imparts a phase to an incident wave surface such as a lens action. It may be a phaser that gives a phase difference for each polarized light by structural double refraction, a polarizing element that transmits only specific polarized light, or the like.

For example, the uneven portion 12 may have an aperiodic uneven structure that exhibits a two-dimensional light diffusion function. Further, the concavo-convex portion 12 has a concavo-convex structure that diffracts light in a one-dimensional direction, a concavo-convex structure having a Fresnel lens structure that imparts a phase to an incident wavefront such as a lens action, and a position with respect to a predetermined polarization component of the incident light. Structure that gives a phase difference An uneven structure that exhibits a double refraction action may be used.

Based on the equation (5), the pitch of the lattice becomes shorter as the diffraction angle becomes larger. Further, in general, if an attempt is made to increase the number of light spots to be emitted, the uneven shape of the basic unit becomes complicated. Then, the width of the uneven shape becomes fine and it becomes difficult to process the shape according to the ideal shape, so that it tends to be difficult to control the diffracted light. Therefore, the optical element 10 of the present embodiment is particularly effective when obtaining a relatively wide-angle diffraction angle.

Generally, a planar pattern having an uneven shape of a diffractive optical element that emits light in two dimensions is a complicated two-dimensional pattern. Therefore, it is difficult to obtain an index of the shape such as a simple aspect ratio, but in order to discuss the processability of the shape, the spatial period P _p and the height d of the unevenness are used to form a formal aspect ratio. _RA is defined by the equation (6).

_RA = d / (P _p / 2) ・ ・ ・ (6)

The order m _x, m _y of formula (5) obtained a two-dimensional shape of the concave-convex portion 12 and the Fourier transform, but can be interpreted as also seeking spatial frequency components included in the two-dimensional shape by the Fourier transform. In this case, when x, the maximum degree in the y direction _{m xmax,} and _{m ymax,} spatial period _P px corresponding _{thereto, P py} is _{P px = P x / m xmax} , P py = P y / m ymax Will be. These values are used as the above spatial period P _p. The preferred range of the formal aspect ratio _RA is preferably 3 or less in both the x and y directions, preferably 2 or less, and more preferably 1 or less.

The above configuration has, for example, a diffraction angle, specifically, a diagonal formed by each of a plurality of diffracted lights (light spots) generated when the incident light is incident from the normal direction of one surface of the transparent substrate 11. It is preferable to apply it when the angle θ _{d in the} direction is 7.5 ° or more, preferably 15 ° or more, and more preferably 25 ° or more. This can be applied not only to a diffractive optical element that expresses a two-dimensional light spot, but also to a diffraction grating, a Fresnel lens element, a diffuser plate, a splitter, and the like that express one-dimensional diffracted light. In this case, the diagonal angle θ _d may be read as the spread angle of the lens, the spread angle of the diffuser plate, the maximum emission angle of the polarizing element, and the like. In addition, as an expression including these, there is a case where it is simply referred to as "the maximum emission angle of the optical element 10."

Further, in the above, the configuration based on the reflectance of the interface between the uneven portion 12 and the other medium has been described, but in an actual optical element, the reflected light is also branched into a plurality of reflected light by the action of the uneven structure, so that the reflected light is reflected. It may be difficult to measure the amount of light. In this case, the evaluation of the amount of reflected light may be evaluated by the amount of transmitted light. The amount of transmitted light can be evaluated by having a light receiving element such as an integrating sphere adjacent to the element receive light emitted from an emitting surface facing the incident surface of the optical element and measuring the amount of light. For example, the amount of transmitted light may be evaluated by the forward transmittance, which is the ratio of the amount of received light to the amount of incident light. At this time, the amount of transmitted light is not only the reflection generated at the interface of the transparent base material 11, the uneven portion 12, and the medium 13 from the light amount of the incident light, but also the absorption of the element, the reflection generated at the interface of the incident side element, and the emission side element. It is the one excluding the reflection generated at the interface.

When the optical element 10 is a diffractive optical element, for example, the amount of transmitted light may be evaluated using a theoretical value using a grating equation (Equation (5)) for each diffracted light. Also in this case, it is assumed that in the optical element, absorption in the element and reflection at the element interface do not occur in addition to the reflection by the interface of the transparent base material 11, the uneven portion 12, and the medium 13.

Here, in the case where the optical element 10 is a diffractive optical element having a structure in which the filling portion 16 is sealed with two transparent base materials 11 as shown in FIG. 5A, the forward transmittance is (A) from the incident light. (C) Diffracted light is emitted from the element interface in addition to the two factors of (B) reflection by the interface between the base material, the uneven portion and the filling portion, and (B) absorption of the base material, the uneven portion and the member constituting the filling portion. It is necessary to consider the components that propagate in the element. This component is, for example, a light beam that is totally reflected at any interface in the element, as shown by the solid arrow in FIG. 8, and can be calculated using, for example, equation (5). In equation (5), the vector component of the light ray in the Z direction is (1-sin ² θ _xo ^{− sin 2} θ _yo ) ^0.5 , but when the value in parentheses is a negative value, the propagation vector component of the Z component. May be determined as a component that becomes an imaginary number and is not emitted into the air. Strictly speaking, the diffracted light propagating in the device may be totally reflected at the device interface, re-incidented in the uneven portion, and diffracted again in the device. Suppose there is no disturbance.

The forward transmittance can be evaluated by a light receiving element such as an integrating sphere, but the component propagating in the element due to total reflection at the interface of the emitting side element as described above is also measured by the light receiving device by measuring the light emitted from the side surface of the element. Can be evaluated. When the optical element has no absorption, the reflectance of the optical element may be evaluated by the difference between the front transmittance and the amount of light emitted from the side surface of the optical element from the amount of incident light.

As described above, the front transmittance of the optical element may change depending on the design of the maximum emission angle, and the change tends to be remarkable especially when a wide-angle light is emitted. Further, when the reflectance due to the interface between the uneven portion and another medium is low, the front transmittance can be relatively increased. Therefore, the forward transmittance, which is an index for evaluating the amount of reflected light, may be 80% or more, preferably 85% or more, more preferably 90% or more, still more preferably 95% or more. Further, although the optical element may include other functional layers, the above-mentioned front transmittance assumes a simple structure including only one uneven portion. On the other hand, in the case of an optical element having another functional layer, the loss due to absorption or reflection by the other functional layer may be calculated and removed, and the forward transmittance may be evaluated. Further, the loss due to reflection and absorption generated at a place other than the interface between the uneven portion and the other medium may be calculated and evaluated, and the loss may be removed.

Embodiment 2.
9 (a) and 9 (b) are a schematic plan view and a schematic cross-sectional view of the optical element 40 of the second embodiment, respectively. The optical element 40 of the present embodiment includes an uneven portion 42 having one or more curved surfaces that are non-parallel to the main surface of the transparent base material 41 and are continuous on one surface of the transparent base material 41. Reference numeral 43 in the drawing indicates a medium that covers the surface of the uneven portion 42 on the side facing the transparent base material 41.

As shown in FIG. 9B, the optical element 40 has a concave-convex structure 44 that forms one or more continuous curved surfaces that are non-parallel to the main surface of the transparent base material 41 on the main surface of the transparent base material 41. A concavo-convex portion 42 including an antireflection layer 45a provided between the concavo-convex structure 44 and the transparent base material 41 and an antireflection layer 45b provided between the concavo-convex structure 44 and the medium 43 is provided. As described above, the uneven portion 42 is a multilayer structure of the antireflection layer 45a, the uneven structure 44, and the antireflection layer 45b. The uneven portion 42 may be configured to include only one of the antireflection layer 45a and the antireflection layer 45b.

Hereinafter, the portion constituting each curved surface in the concave-convex structure 44 is also referred to as a curved surface portion 421.

In the concave-convex structure 44, as shown in FIGS. 9A and 9B, the curved surface portion 421 forming a continuous curved surface non-parallel to the transparent base material 41 has no gap at least in the effective region of the incident light. The arranged structure can be mentioned. At this time, a portion of the curved surface portion 421 whose boundaries between two adjacent curved surfaces are discontinuous (corresponding to a ridge) may be formed. As described above, the curved surface portion 421 has a shape in which there is no gap (no flat portion) due to the plurality of curved surfaces, so that the straight-through component of the incident light is reduced and the light utilization efficiency is enhanced.

The optical element 40 in FIGS. 9 (a) and 9 (b) exemplifies, but is not limited to, a diffuser plate. The optical element 40 includes a blaze-type diffractive optical element having a diffraction action in a one-dimensional direction or a two-dimensional direction, a lens element or a microlens array that causes a lens action, and a blaze-type Frenel lens element that imparts a phase to an incident wave surface. , A blaze-type phaser or the like that exerts a structural double-refractive action by giving a phase difference to a predetermined polarization component of the incident light. At this time, the concave-convex structure 44 may be a structure that replaces a continuous curved surface that is non-parallel to the transparent base material 41, or has one or more inclined surfaces that are non-parallel to the transparent base material in addition to the curved surface.

Hereinafter, even in this embodiment, it is assumed that near-infrared light having a wavelength of 700 to 1200 nm is incident on the optical element 40.

Similar to the transparent base material 11, the transparent base material 41 can be made of a member that is transparent to the wavelength of light used, such as glass and resin.

Also in this embodiment, the uneven portion 42 is a multilayer structure composed of two or more different materials and having two or more layers. The uneven portion 42 uses a material (first material) satisfying the formula (1) in at least one or more layers, where the complex refractive index at the wavelength used by the layer is n-ik.

The antireflection layers 45a and 45b are basically the same as the antireflection layers 15a and 15b, and the first embodiment. The antireflection layers 15a and 15b described in the above can be configured as a single layer or a multi-layer structure, or the same material may be used, or the same can be followed.

Further, the first embodiment. As with the anti-reflection layer 15a, 15b in the anti-reflection layer 45a, respectively 45b also the refractive index n _m of the medium constituting the incident side _interface, the refractive index of the medium forming the exit-side interface n _0, the anti-reflective layer or the refractive index of each layer n _r, when the thickness was set to d _r, with respect to both interfaces of the anti-reflection layer, the theoretical reflectivity R by the antireflection-layer or multi-layer structure of a single layer satisfying the expression (4) One or more antireflection layers satisfying the above conditions may be used.

Further, the medium 43 may be air or other than air such as a resin or an inorganic substance. That is, as shown in FIG. 10A, the optical element 40 may include a filling portion 46 that covers and flattens the surface of the uneven portion 42 on the side facing the transparent base material 41. In this case, the material of the filling portion 46 is the medium 43. Further, the optical element 40 may include a second transparent base material 41-2 that seals the filling portion 46. That is, the optical element 40 may have a configuration in which the uneven portion 42 and the filling portion 46 are sealed by the first transparent base material 41-1 and the second transparent base material 41-2.

Also in this embodiment, the refractive index difference Δn between the uneven portion 42 (particularly, corresponding to the convex portion of the concave-convex structure 44) and the filling portion 46 in the light of a predetermined wavelength (range) is preferably 0.45 or more, and 0. 6 or more is more preferable.

Further, as shown in FIG. 11, the optical element 10 may include two or more uneven structures 44 having a surface that causes a refraction action or the like. In this case, two optical elements 40 including a concavo-convex portion 42 having one concavo-convex structure 44 may be stacked, or as shown in FIGS. 11 (a) and 11 (b), on one transparent base material 41. In addition, two uneven structures 44 may be laminated. At this time, as shown in FIG. 11A, the first concavo-convex structure 44-1 of the two concavo-convex structures 44 may be integrated with the transparent base material 41. In that case, the second uneven structure 44-2 of the two uneven structures 44 is laminated on the first uneven structure 44-1, and the antireflection layer 45a is the first uneven structure 44-1 (transparent base material 41). It is provided between the concavo-convex structure formed by the material of 1) and the second concavo-convex structure 44-2 (concave and convex structure formed by the first material). Further, the antireflection layer 45b is provided between the second uneven structure 44-2 (the uneven structure formed by the first material) and the medium 43. In this case, the uneven portion 42 includes four functional layers (first uneven structure 44-1, antireflection layer 45a, second uneven structure 44-2, antireflection layer 45b).

Further, as shown in FIG. 11B, the first uneven structure 44-1 may be provided by another member on the surface of the transparent base material 41. In that case, the antireflection layer 45a may be provided between the transparent base material 41 and the first concavo-convex structure 44-1 (particularly, in the case of the concavo-convex structure formed by the first material). Further, the antireflection layer 45b may be provided between the second concavo-convex structure 44-2 (particularly, in the case of the concavo-convex structure formed of the first material) and the medium 43. Further, an antireflection layer 45c may be provided between the first uneven structure 44-1 and the second uneven structure 44-2. In this case, the uneven portion 42 includes five functional layers (antireflection layer 45a, first uneven structure 44-1, antireflection layer 45c, second uneven structure 44-2, antireflection layer 45b). As described above, it is preferable that the antireflection layer is provided at all the interfaces between the medium forming the uneven structure and the other medium.

Like the antireflection layers 45a and 45b, the antireflection layer 45c has a single-layer or multilayer structure satisfying the formula (4) with respect to both interfaces of the antireflection layer, and is designed so that the theoretical reflectance R satisfies the above conditions. All you need is. For example, when near-infrared light is incident from the transparent substrate 41 side in FIG. 11B, the medium forming the incident side interface with respect to the antireflection layer 45c is the first concave-convex structure 44-1 and the emission side interface. The medium forming the surface is the second uneven structure 44-2.

Further, when the surface of the transparent base material 41 is cut to obtain the concavo-convex structure 44 as shown in FIG. 11A, the lowest surface of the surface of the concavo-convex structure 44 is referred to as the transparent base material. It may be a boundary (that is, the lowermost surface of the uneven structure 44 and the surface of the transparent base material 41).

Further, as shown in FIG. 11C, the optical element 40 may have a configuration in which the first concavo-convex structure 44-1 and the second concavo-convex structure 44-2 are adjacent to each other. In the case of FIG. 11C, the antireflection layer 45a has a first concavo-convex structure 44-1 (concave-convex structure formed of the material of the transparent base material 41) and a second concavo-convex structure 44-2 (first material). It is provided between the uneven structure formed by the above. Further, the antireflection layer 45b is provided between the second uneven structure 44-2 (the uneven structure formed by the first material) and the medium 43. In this case, the uneven portion 42 includes four functional layers (first uneven structure 44-1, antireflection layer 45a, second uneven structure 44-2, antireflection layer 45b).

Here, using FIG. 12, the refraction action of light incident on the concave-convex structure 44 having a refractive index n from the normal direction of the transparent base material 41 and emitted from a surface inclined at an angle α to air (refractive index = 1). To explain. First, according to Snell's law, nsinα = sinβ is established. For example, when quartz glass (refractive index 1.455) is used as a material when α = 10 °, the emission angle (β-α) = 4.6 °. Will be. On the other hand, when a material having a refractive index of 2.8 is used for the uneven structure 44, the emission angle is 19 °. Therefore, by using a material having such a large refractive index for the uneven structure 44, a large emission angle can be obtained even with a small inclination angle. Here, the inclined surface may be regarded as an approximation of a part of the curved surface of the concave-convex structure 44. Therefore, if a material having a relatively large refractive index is used, the inclination angle of the inclined surface or the curved surface of the uneven structure can be reduced, and the height of the portion forming the inclined surface or the curved surface of the uneven structure 44 can be reduced. Since it can be formed, it becomes easy to process an uneven structure (particularly, a boundary region where an inclined surface or a curved surface is adjacent). Therefore, also in this embodiment, the above configuration of the optical element 40 may be applied when the maximum emission angle is 7.5 ° or more. The maximum emission angle may be 15 ° or more, or 25 ° or more.

From the same viewpoint, when the concave-convex structure 44 has one or more curved surfaces, the sag amount of each curved surface of the concave-convex structure 44 is preferably 20 μm or less, more preferably 5 μm or less.

Further, the optical element of each embodiment is also used for a three-dimensional measuring device and a projection device such as an authentication device that irradiates light and irradiates (inspection) light scattered by an object into a predetermined projection range. can. Further, the optical element of each embodiment can also be used as a lens or a microlens in an optical system for propagating communication information included in a communication device.

In each of these devices, the ratio of the amount of light emitted from the optical element to the amount of light emitted from the light source is preferably 50% or more due to the effect of reducing the reflectance of the optical element.

Further, the optical element of each embodiment may generate a predetermined phase difference that causes a predetermined wavefront modulation with respect to a predetermined polarization component of the incident light or the incident light. For example, when the amount of aberration corrected by a predetermined wavefront modulation is 1λrms or less, it is more effective to apply the optical element of each of the above embodiments. Here, it is possible to correct the amount of aberration of 1λrms or more, but in general, the aberration is suppressed to 1λrms or less by the optical system, and stray light due to diffraction may occur in order to approximate a large wavefront. 1λrms or less is preferable.

(Example 1)
This example is an example of the optical element 10 of the first embodiment shown in FIG. In this example, a glass substrate is used as a member of the transparent base material 11. Further, a—Si: H and SiO ₂ are used as the material of the uneven portion 12. Here, a—Si: H corresponds to the first material.

The complex refractive index of a—Si: H used in this example at a wavelength of 950 nm is 3.82-ik (k = 0.001 or less). The refractive indexes of the glass substrate and SiO _{2 at} a wavelength of 950 nm are 1.513 and 1.457, respectively. Further, the medium 13 is air.

First, a—Si: H is formed on a glass substrate with a thickness of 130 nm, and then SiO ₂ is formed with a thickness of 228 nm. Then, the a-Si: H film and the SiO ₂ film are processed into a two-stage uneven structure by photolithography and etching to obtain an uneven portion 12 having a two-layer structure on a glass substrate. Here, the pitches Px and Py of the basic unit are 1056 μm (X direction) and 1003 μm (Y direction), and the maximum orders m _xmax and _mymax are 640 (X direction) and 480 (Y direction). Thus, X-direction spatial period _P px = 1.65 .mu.m, a spatial period _P py = _2.09μm in the Y direction. From here, the aspect ratio R _AX = 0.434 in the X direction and the aspect ratio R _AY = 0.343 in the Y direction. The maximum emission angle of the diffracted light emitted to the light having a wavelength of 950 nm is 34.7 ° in the X direction and 26.7 ° in the Y direction.

FIG. 13 shows the calculation result of the reflectance for the vertical incident of the optical path passing through the convex portion 121 of this example in the light having a wavelength of 800 to 1000 nm. The reflectance was calculated using the equation (3). Here, the optical path passing through the convex portion 121 of this example in the figure is specifically an optical path passing through the glass substrate, a—Si: H, SiO ₂ and air as the medium 13. As shown in FIG. 13, the reflectance of this example in light of 950 nm is 0.1%, which is sufficiently small. It should be noted that it is 0.1% or less at 950 ± 10 nm and 1.1% or less at 950 ± 20 nm. At this time, the phase difference Δnd / λ generated by the uneven portion 12 and the medium 13 is 0.5, which is suitable as a two-stage diffraction optical element.

Further, as a comparative example, FIG. 13 also shows the calculation result of the reflectance with respect to the vertical incident of the optical path passing through the convex portion when the concave-convex portion is configured only with a—Si: H in the above configuration. The thickness of the a—Si: H film of the comparative example is 167 nm, and Δnd / λ = 0.5. Here, the optical path of the comparative example in the figure is specifically an optical path passing through a glass substrate, a-Si: H, and air. As shown in FIG. 13, the reflectance of the comparative example is 60.2% in the light of 950 nm, which is larger than the reflectance of this example, and the loss due to the reflection is large.

(Example 2)
This example is an example of the optical element 10 of the first embodiment shown in FIG. 3 (c). In this example, a glass substrate is used as a member of the transparent base material 11. _{Further, a—Si: H, SiO 2} and SiN are used as the material of the antireflection layer 15a of the uneven portion 12. Further, a—Si: H is used as the material of the base layer 124 and the retardation layer 123. Further, SiN is used as the material of the antireflection layer 15b.

The complex refractive index of a—Si: H light having a wavelength of 950 nm used in this example is 3.82-ik (k = 0.001 or less). The refractive indexes of the glass substrate, SiO ₂ , and SiN at wavelengths of 950 nm are 1.513, 1.457, and 1.9, respectively. Further, the medium 13 is air (refractive index = 1).

First, an antireflection layer 15a having a three-layer structure composed of a-Si: H, SiO _{2, and SiN is formed on a glass substrate.} The film thickness of each layer is 130 nm, 230 nm, and 120 nm, respectively. Then, an a—Si: H film to be the base layer 124 and the retardation layer 123 is formed with a thickness of 400 nm. After the film formation, the a—Si: H film is processed into a four-stage uneven structure. In the uneven structure, the height of one step of the retardation layer 123 is 85 nm. After processing into an uneven structure, SiN as the antireflection layer 15b is formed into a film having a thickness of 125 nm. As a result, the uneven portion 12 having a five-layer structure is obtained on the transparent base material 11. Here, the pitch and the maximum degree of the basic unit in the x and y directions are Px = 1056 μm, Py = 1003 μm, m _xmax = 640, and _mymax = 480. Therefore, x, y-direction spatial period _P px = 1.65 _.mu.m, a P py = 2.09μm. From here, the aspect ratios in the x and y directions are R _AX = 0.309 and R _AY = 0.244.

Table 1 summarizes the members and heights of each layer of the uneven portion 12 in the configuration of this example.

FIG. 14 shows the calculation result of the reflectance for the vertical incident of each optical path (more specifically, the region corresponding to each stage of the uneven portion) of this example in the light having a wavelength of 800 to 1200 nm. As shown in FIG. 14, the maximum reflectance of this example in light of 950 nm is 0.9%, and the average reflectance of each optical path is 0.6%, which is sufficiently small. At this time, the phase difference Δnd / λ generated by the uneven portion and the medium is 0.75 (4 stages), which is suitable as a 4-stage diffraction optical element.

(Example 3)
This example is an example (comparative example) in which the antireflection layer 15a is not provided as compared with the optical element 10 of the first embodiment shown in FIG. 3 (b). The optical element of this example includes a transparent base material 11, a retardation layer 123, and an antireflection layer 15b provided between the retardation layer 123 and the medium 13. In this example, a glass substrate is used as a member of the transparent base material 11. Further, a—Si: H is used as the material of the retardation layer 123 of the uneven portion 12. Further, SiN is used as the material of the antireflection layer 15b. The complex refractive index of a—Si: H light having a wavelength of 850 nm used in this example is 3.5-ik (k = 0.001 or less). The refractive indexes of the glass substrate and SiN at a wavelength of 850 nm are 1.514 and 1.87, respectively. In addition, SiN is calculated assuming that the refractive index is 1.87 regardless of the wavelength.

First, a—Si: H is formed on a glass substrate with a thickness of 297.5 nm, and then SiO ₂ is formed with a thickness of 228 nm. After that, the a—Si: H film is processed into an eight-stage uneven structure by photolithography and etching. In the uneven structure, the height of one step of the retardation layer 123 is 42.5 nm. After processing into an uneven structure, SiN _x as the antireflection layer 15b is formed into a film having a thickness of 114 nm. As a result, the uneven portion 12 having a two-layer structure is obtained on the transparent base material 11. Here, the pitch and the maximum degree of the basic unit in the x and y directions are Px = 1056 μm, Py = 1003 μm, m _xmax = 640, and _mymax = 480. Therefore, x, y-direction spatial period _P px = 1.65 _.mu.m, a P py = 2.09μm. Here, x, y direction of the aspect ratio _R AX = _0.361, the R AY = 0.285.

FIG. 15A is a schematic cross-sectional view of a main part of the optical element of this example. In addition, Table 2 summarizes the members and heights of each layer of the uneven portion 12 in the configuration of this example.

FIG. 16 shows the calculation result of the reflectance for the vertical incident of each optical path of this example in the light having a wavelength of 800 to 900 nm. As shown in FIG. 16, the maximum reflectance of this example in light of 850 nm is 17.0%, and the average reflectance of each optical path is 17.0%. At this time, the phase difference Δnd / λ generated by the uneven portion and the medium is 0.875 (8 steps).

(Example 4)
This example is an example (comparative example) in which a stop etch layer 17 made _{of SiO 2} is further provided between each stage of the retardation layer 123 in the configuration of Example 3. FIG. 15B is a schematic cross-sectional view of a main part of the optical element of this example. The thickness of each of the stop etch layers 17 of this example was 5 nm. Other configurations are the same as in Example 3. Table 3 summarizes the members and heights of each layer of the uneven portion 12 in the configuration of this example.

FIG. 17 shows the calculation result of the reflectance for the vertical incident of each optical path of this example in the light having a wavelength of 800 to 900 nm. As shown in FIG. 17, the maximum reflectance of this example in light of 850 nm is 18.0%, and the average reflectance of each optical path is 15.9%. At this time, the phase difference Δnd / λ generated by the uneven portion and the medium is 0.883 (8 steps).

(Example 5)
This example shows an example in which the thickness of the stop etch layer 17 is 2 nm as another example (comparative example) of the configuration shown in Example 4. Table 4 summarizes the members and heights of each layer of the uneven portion 12 in the configuration of this example.

FIG. 18 shows the calculation result of the reflectance for the vertical incident of each optical path of this example in the light having a wavelength of 800 to 900 nm. As shown in FIG. 18, the maximum reflectance of this example in light of 850 nm is 17.4%, and the average reflectance of each optical path is 16.6%. At this time, the phase difference Δnd / λ generated by the uneven portion and the medium is 0.894 (8 steps).

(Example 6)
This example is an example in which the antireflection layer 15a is further provided with respect to the configuration of Example 4, and is a configuration for suppressing the reflection generated in the stop etch layer 17. This example is an example of the optical element 10 of the first embodiment shown in FIG. 3 (b). FIG. 15C is a schematic cross-sectional view of a main part of the optical element of this example. The thickness of each of the stop etch layers 17 of this example was 5 nm. Further, as the material of the antireflection layer 15a, TiO ₂ having a refractive index of 2.3 at a wavelength of 850 nm was used. Other configurations are the same as in Example 4.

Table 5 summarizes the members and heights of each layer of the uneven portion 12 in the configuration of this example.

FIG. 19 shows the calculation result of the reflectance for the vertical incident of each optical path of this example in the light having a wavelength of 800 to 900 nm. As shown in FIG. 19, the maximum reflectance of this example in light of 850 nm is 0.5%, and the average reflectance of each optical path is 0.2%. At this time, the phase difference Δnd / λ generated by the uneven portion and the medium is 0.883 (8 steps).

(Example 7)
This example is an example of the optical element 40 of the second embodiment shown in FIG. 11 (c). In this example, a glass substrate is used as the material of the transparent base material 41 and the first uneven structure 44-1, and a-Si: H is used as the material of the second uneven structure 44-2. Further, as the antireflection layer 45a, a three-layer multilayer film composed _{of Ta 2} O ₅ , SiO ₂ and Ta ₂ O _{5 is used.} Further, as the antireflection layer 45b, a two-layer multilayer film composed _{of SiO 2} and Ta ₂ O _{5 is used.} The complex refractive index of a—Si: H light having a wavelength of 950 nm used in this example is 3.68-ik (k = 0.001 or less). The refractive indexes of the glass substrate, SiO ₂ , and Ta ₂ O _{5 at} a wavelength of 950 nm are 1.513, 1.47, and 2.158, respectively. Further, the medium 43 is air.

First, the first uneven structure 44-1 having an irregular concave curved surface portion 421 group having an average pitch in the X direction of 30 μm and an average pitch in the Y direction of 24 μm by photolithography and etching on the surface of the glass substrate. (Fig. 20 (a)). The X direction and the Y direction are two directions orthogonal to each other in the element plane. Here, the average radius of curvature of the curved surface portion 421 is 70 μm, and the average inclination of the end portion of the curved surface portion 421 is 12.4 ° in the X direction and 9.9 ° in the Y direction. The height difference between the highest surface and the lowest surface in the uneven structure 44-1 is 3 μm. The size of the element is 3 mm square, and the processing region of the uneven structure covers the entire surface of the element. Further, the effective area of the incident light is 2 mmφ.

Next, on the first uneven structure 44-1, a three-layer antireflection layer 45a composed _{of Ta 2} O _{5 having a thickness of 112 nm, SiO 2 having} a thickness of 171 _{nm and Ta 2} O _{5 having} a thickness of 224 nm is produced by sputtering. Membrane (FIG. 20 (b)). Then, by plasma CVD, a-Si: H to be the second uneven structure 44-2 can be covered on the antireflection layer 45a with the curved surface portion 421 of the first uneven structure 44-1. The film is formed as described above (FIG. 20 (c)). Then, the surface of the a-Si: H film is polished and flattened to obtain a second uneven structure 44-2. _{Further, a two-layer antireflection film 45b made of SiO 2 having a} thickness of 55 nm and Ta ₂ O having a thickness of 55 nm is formed on the flat surface of the second uneven structure 44-2, and the optical element 40 of this example is formed. Obtain (FIG. 20 (d)).

FIG. 21 is a calculation result of the reflectance for light having a wavelength of 800 to 1000 nm, which is vertically incident at the interface between the incident side and the exit side of the concave-convex structure 44-2 of this example. The reflectance of the incident side interface of the uneven structure 44-2 is specifically determined from the transparent base material 41 (first uneven structure 44-1) side via the antireflection layer 45a to the second uneven structure 44-. It is the reflectance when light is vertically incident on 2. Further, the reflectance of the emission side interface of the uneven structure 44-2 is specifically when light is vertically incident on the air (medium 43) from the second uneven structure 44-2 via the antireflection layer 45b. The reflectance of. As shown in FIG. 21, the reflectance at the interface between the incident side and the exit side of the concave-convex structure 44-2 of this example is 1% or less in the wavelength band of 950 nm ± 50 nm, respectively, and the wavelength band of 950 nm ± 20 nm. It is 0.5% or less.

When light having a wavelength of 950 nm is vertically incident on the main surface of the glass substrate before processing with respect to the optical element 40 of this example, the first concave-convex structure 44-1 and the second concave-convex structure 44-2 The average emission angle of the light refracted at the end of each curved surface portion 421 of the uneven portion 42 after bonding is 28 ° in the X direction, 22 ° in the Y direction, and 39 ° in the diagonal direction. Therefore, the maximum emission angle is 39 °. As a comparison, if such an emission angle is realized only by the uneven structure obtained by surface processing of a glass substrate having a refractive index of 1.51, the inclination angle of the end of the curved surface portion 421 is 52.5 ° in the X direction and 52.5 ° in the Y direction. 42 ° is required. Therefore, by providing the second uneven structure 44-2 formed by a-Si: H, the inclination angle is reduced, and the curved surface portion 421 of the uneven portion 42 has a shape that can be easily processed. Here, the average emission angle of each of the curved surface portions 421 ends may be regarded as the maximum emission angle of the optical element 40 of this example.

(Example 8)
This example is another example of the optical element 40 of the second embodiment. FIG. 22 is a schematic cross-sectional view of a main part of the optical element 40 of this example, and includes a concavo-convex portion 42 including a convex curved surface portion 421. In this example, a glass substrate is used as a member of the transparent base material 41. Further, a—Si: H is used as the material of the concave-convex structure 44. Further, a three-layer multilayer film composed _{of Ta 2} O ₅ , SiO ₂ and Ta 2 O _{5 is used} as the antireflection layer 45a, _{and a two- layer multilayer film composed of SiO 2} and Ta ₂ O ₅ is used as the antireflection layer 45b. The complex refractive index of a—Si: H light having a wavelength of 950 nm used in this example is 3.68-ik (k = 0.001 or less). Further, the refractive index of the glass substrate, SiO ₂ , and Ta ₂ O _{5 at} a wavelength of 950 nm is the same as that of Example 7.

First, a three-layer antireflection layer 45a composed _{of Ta 2} O _{5 having a thickness of 112 nm, SiO 2 having} a thickness of 171 _{nm and Ta 2} O _{5 having} a thickness of 224 nm is formed on a glass substrate by sputtering. The antireflection layer 45a may be provided at least at a position where the concave-convex structure 44 (more specifically, the convex curved surface portion 421) is formed later. Then, by plasma CVD, a—Si: H having an uneven structure 44 is formed on a glass substrate provided with the antireflection layer 45a to a thickness of 4.5 μm. After that, the a-Si: H film is processed into a lens array having an outer diameter of 120 μm, a radius of curvature of 400 μm, and a pitch of 240 μm by photolithography and etching, and unevenness having a convex curved surface portion 421 laminated on the antireflection layer 45a. Obtain structure 44. _{After that, a two-layer antireflection film 45b made of SiO 2 having a} thickness of 55 nm and Ta ₂ O ₅ having a thickness of 55 nm was formed on a glass substrate provided with the uneven structure 44, and the optical element 40 of this example was formed. obtain.

When light having a wavelength of 950 nm is vertically incident on the main surface of the glass substrate with respect to the optical element 40 of this example, the emission angle of the light refracted at the end of each curved surface portion 421 forming the lens array is 23.7. It becomes °. The central thickness of each curved surface portion 421 is 4.5 μm. As a comparison, if such an emission angle is to be realized only by the uneven structure obtained by surface processing of a glass substrate having a refractive index of 1.51, 41.4 ° is required as the inclination angle of the end portion of the curved surface portion 421, and The central thickness of the curved surface portion 421 needs to be 23 μm. Therefore, by using a—Si: H as the material of the lens array, the curved surface portion 421 of the uneven portion 42 (each lens forming the lens array) has a shape that can be easily processed.

(Example 9)
This example is an example of the optical element 10 of the first embodiment shown in FIG. 4, and a glass substrate is used as a member of the transparent base material 11. Further, a—Si: H and SiO ₂ are used as the material of the uneven portion 12. Here, a—Si: H corresponds to the first material. _{Further, SiO 2} is used as the material of the filling portion 16 which is the medium 13 of this example.

The complex refractive index of a—Si: H used in this example at a wavelength of 950 nm is 3.82-ik (k = 0.001 or less). The refractive indexes of the glass substrate and SiO _{2 at} a wavelength of 950 nm are 1.513 and 1.47, respectively. The refractive index of SiO ₂ is different from that of other examples, but it is different depending on the film forming conditions and the like.

First, on a glass substrate, a three-layer multilayer film _{composed of a—Si: H having a thickness of 107 nm, SiO 2} having a thickness of 239 nm, and a—Si: H having a thickness of 107 nm, which finally becomes a retardation layer 123. Is formed (FIG. 23 (a)). After that, the multilayer film is processed into a concavo-convex shape in which rectangular convex portions 121 are lined up at a predetermined pitch by photolithography and etching, and a two-stage concavo-convex portion 12 including a retardation layer 123 having a three-layer structure is formed on a glass substrate. Obtain (FIG. 23 (b)). Then, on the glass substrate on which the uneven portion 12 is formed, the SiO ₂ to be the filling portion 16 is formed into a film having a thickness of 453 nm or more that can cover the concave portion 122 of the uneven portion 12 (FIG. 23 (c)). ). Then, _{the surface of the SiO 2} film is polished and flattened to obtain the optical element 10 of this example having the filling portion 16.

FIG. 24 is a calculation result of the reflectance for light having a wavelength of 800 to 1000 nm, which is vertically incident in the optical path passing through the convex portion 121 of this example. Specifically, the reflectance was calculated as the reflectance generated by the transparent base material 11, the convex portion 121 of the three-layer structure, and the filling portion 16. As shown in FIG. 24, the reflectance in the wavelength band of 950 nm ± 10 nm is 1% or less. Further, the phase difference generated by the convex portion 121 having the three-layer structure and the concave portion 122 due to the filling member has a half wavelength with respect to the wavelength of 950 nm, and the optical element 10 of this example is suitable as a binary lattice.

Any optical element or device having a concavo-convex structure that generates a predetermined phase difference such as diffraction, diffusion, and refraction at different emission angles with respect to incident light can be suitably applied.

10, 40 Optical elements 11, 41 Transparent base material 11-1, 41-1 First transparent base material 11-2, 41-2 Second transparent base material 12, 42 Concavo-convex part 121 Convex part 122 Concave part 123 Phase difference Layer 124 Underlayer 13, 43 Medium 14a, 14b Refractive index adjustment layer 14c Intermediate layer 15a, 15b Antireflection layer 16, 46 Filling part 17 Stop etch layer 21 Light beam 22 Diffraction light group 23 Light spot 31 Basic unit 421 Curved surface part 44 Concavo-convex Structure 44-1 First uneven structure 44-2 Second uneven structure 45a, 45b, 45c Antireflection layer

Claims (4)

With a transparent base material
It is provided on the transparent substrate and is provided with an uneven portion that generates a predetermined phase difference with respect to a predetermined polarization component of the incident light or the incident light.
The uneven portion is composed of two or more different materials.
One of the materials constituting the uneven portion is the first material in which n ≧ 2.5 and k <0.01 when the complex refractive index in the wavelength band of the incident light is n−k. ,
With respect to the incident light incident from the normal direction of the plane of the transparent substrate, the front transmittance at least in the effective region is 80% or more, or at least the reflectance in the effective region is 10% or less.
The uneven portion is
A single-layer concavo-convex structure having one or more curved surfaces that are non-parallel to the transparent substrate or having one or more inclined surfaces that are non-parallel to the transparent substrate.
Optics characterized by including an antireflection layer at the interface with the transparent substrate and / or with a predetermined medium covering the surface of the uneven portion on the curved surface or the surface on which the inclined surface is formed. element. The optical element according to claim 1 , wherein the uneven structure is a structure in which curved surfaces that are non-parallel to the transparent substrate and are continuous are arranged without gaps at least in the effective region of the incident light. The optical element according to claim 2 , wherein the sag amount of each curved surface of the uneven structure is 20 μm or less. The concavo-convex portion comprises two single-layer concavo-convex structures having one or more curved surfaces that are non-parallel to the transparent substrate or having one or more inclined surfaces that are non-parallel to the transparent substrate.
The first concavo-convex structure of the two concavo-convex structures is integrated with the transparent base material or provided on the surface of the transparent base material.
The second concavo-convex structure of the two concavo-convex structures is laminated on the first concavo-convex structure.
The optical element according to claim 2 or 3 , wherein the uneven portion further includes an antireflection layer provided between the first uneven structure and the second uneven structure.

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