Optical element, imaging optical system, and optical apparatus

Abstract

To provide an optical element that has a multilayer film in which a variation in reflectance characteristics hardly occurs even if the multilayer film is formed on an optical surface having a curvature and has a film thickness distribution.SOLUTION: An optical element has a multilayer film 100 formed on a curved surface of a substrate 200. The multilayer film includes a first film formed of first material and a second film formed of second material laminated alternately. When the maximum value of a half-open angle in an optical effective region of the curved surface is defined as φ; the total film thickness of the multilayer film at a position of the half-open angle of 0° as DC; the total film thickness of the multilayer film at a position of the half-open angle of φ as DQ; the refractive index at a wavelength λ [nm] of the first material as nL(λ); and the refractive index at a wavelength λ [nm] of the second material as nH(λ), conditions of φ≥20°, 0.75≤DQ / DC≤0.95, 1.4≤nL(587.56)≤1.6, 1.9≤nH(587.56)≤2.4, nH(587.56)-nL(587.56)≥0.40, and 1 / (nH(420)-nH(680))≥4.5 are satisfied.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an optical element having a multilayer film that reflects and transmits light. [Background technology]

[0002] In optical devices such as head mounted displays (HMDs), a half mirror (reflective / transmissive surface) and polarized light are used to fold the optical path, thereby achieving a reduction in size and weight while ensuring the required optical path length. Patent Document 1 discloses an optical system using a reflective refractive element with a half-mirror coating applied to its convex surface and a circularly polarized light selective semi-transparent mirror. Patent Document 2 discloses an optical system using a transmissive refractive element with a half-mirror coating applied to its concave surface and a circularly polarized light selective semi-transparent mirror attached to an aspherical resin lens.

[0003] Half-mirror coatings are often formed by depositing a metal film or a dielectric multilayer film by vapor deposition on the optical surface of a substrate such as a lens. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 3295583 [Patent Document 2] Patent No. 4419281 Summary of the Invention [Problem to be solved by the invention]

[0005] When a half-mirror coating is formed on a curved optical surface by vapor deposition, the film thickness varies (film thickness distribution), which results in a variation in the reflectance of the half-mirror coating, making it difficult to obtain good reflectance characteristics.

[0006] The present invention provides an optical element having a multilayer film that is unlikely to suffer from variations in reflectance characteristics even when formed on an optical surface having curvature and has a film thickness distribution. [Means for solving the problem]

[0007] The optical element according to one aspect of the present invention is used in an imaging optical system, and has a substrate including a curved surface and a multilayer film formed on the curved surface. The multilayer film includes a first film made of a first material and a second film made of a second material that are alternately laminated. The maximum value of the half aperture angle within the optically effective area of ​​the curved surface is φ, and the total thickness of the multilayer film at the position of the half aperture angle of 0° is D. C The total thickness of the multilayer film at the half-angle φ is D Q The refractive index of the first material at a wavelength λ [nm] is n L (λ), the refractive index of the second material at wavelength λ [nm] is n H (λ), φ≧20° 0.75≦D Q / D C ≦0.95 1.4≦n L (587.56)≦1.6 1.9≦n H (587.56)≦2.4 n H (587.56)-n L (587.56)≧0.40 1 / (n H (420)-n H (680))≧4.5 The optical element is characterized in that it satisfies the following conditions: Note that an image-forming optical system or an optical device having the optical element constitutes another aspect of the present invention. Effect of the Invention

[0008] According to the present invention, it is possible to provide an optical element having a multilayer film that is unlikely to produce variations in reflectance characteristics even when formed on an optical surface having a curvature with a half open angle of 20° or more and has a film thickness distribution. [Brief description of the drawings]

[0009] [Figure 1] FIG. 2 is a schematic diagram showing an optical element according to an embodiment. [Diagram 2]FIG. 2 is a schematic diagram showing the film configurations of Example 1 and Comparative Examples 1 and 2. [Diagram 3] 1A to 1C are schematic cross-sectional views of optical elements in Examples 1 and 2 and Comparative Examples 1 and 2. [Figure 4] FIG. 4 is a graph showing refractive index characteristics of a deposition material in Example 1. [Diagram 5] FIG. 4 is a graph showing reflectance characteristics for 0° incident light in Example 1. [Figure 6] FIG. 5 is a schematic diagram showing a film configuration of Example 2. [Figure 7] FIG. 11 is a graph showing refractive index characteristics of a deposition material in Example 2. [Figure 8] FIG. 11 is a graph showing reflectance characteristics for 0° incident light in Example 2. [Figure 9] 4 is a schematic cross-sectional view of an optical element according to a third and fourth embodiment. FIG. [Figure 10] FIG. 11 is a schematic diagram showing a film configuration in Example 3. [Figure 11] FIG. 11 is a graph showing refractive index characteristics of a deposition material in Example 3. [Figure 12] FIG. 11 is a graph showing reflectance characteristics for 0° incident light in Example 3. [Figure 13] FIG. 13 is a schematic diagram showing a film configuration in Example 4. [Figure 14] FIG. 13 is a graph showing refractive index characteristics of a deposition material in Example 4. [Figure 15] FIG. 13 is a graph showing reflectance characteristics for 0° incident light in Example 4. [Figure 16] FIG. 1 is a diagram showing an optical system using the optical elements according to Examples 1 to 4. [Figure 17] FIG. 3 is a cross-sectional view of an optical device including the optical system. [Figure 18] FIG. [Figure 19] FIG. 13 is a graph showing the refractive index characteristics of a deposition material in Comparative Example 1. [Figure 20] FIG. 13 is a graph showing reflectance characteristics for 0° incident light in Comparative Example 1. [Figure 21] FIG. 11 is a graph showing reflectance characteristics for 0° incident light in Comparative Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0011] 1(a) and (b) show schematic diagrams of optical elements 301 and 302 as representative embodiments of the present invention. The optical elements 301 and 302 are used in imaging optical systems such as the observation optical system of an optical device such as an HMD or the imaging optical system of an imaging device such as a camera.

[0012] The optical element 301 shown in FIG. 1(a) has a transparent substrate 201 and a half mirror 101 which is a dielectric multilayer film in which a plurality of thin films are laminated. The half mirror here means a transmissive and reflective surface which is responsible for both transmission and reflection. In other words, the ratio of the transmittance and reflectance of the half mirror is not limited to 1:1. The optical element 302 shown in FIG. 1(b) has a transparent substrate 202 and a half mirror 102 which is a dielectric multilayer film. In FIGS. 1(a) and 1(b), the lens surfaces to which the half mirrors 101 and 102 are not applied are omitted. FIG. 1(a) shows a case where the lens surface forming the half mirror 101 on the transparent substrate 201 has a concave shape, and FIG. 1(b) shows a case where the lens surface forming the half mirror 102 on the transparent substrate 202 has a convex shape.

[0013] The lens surfaces of the optical elements 301 and 302 have a curved shape having an axis of rotational symmetry, i.e., a rotationally symmetric curved shape. The curved shape may be spherical or aspherical. In FIG. 1(a), position C is the center of the lens surface of the transparent substrate 201 to which the half mirror 101 is attached, and is the position where the axis of rotational symmetry (hereinafter referred to as the optical axis) L of the lens surface intersects with the lens surface of the transparent substrate 201. C indicates the total film thickness of the half mirror 101 at position C. Position Q is the outermost position within the optically effective area (area through which light rays pass to form an image in an image circle in an optical system) on the lens surface of the transparent substrate 201. If the angle between the optical axis L and the normal to position Q (hereinafter referred to as the half aperture angle) is φ, the half aperture angle φ is the maximum value of the half aperture angle within the optically effective area. D Qindicates the total film thickness of the half mirror 101 at the position Q. D shown in FIG. C , D Q , C, Q and φ are the same as those in FIG. 1(a).

[0014] Generally, in dry methods such as sputtering and deposition, the evaporation source is placed facing the center of the lens (position C in this embodiment) to form a film. In this case, when a film is formed by a dry method on a lens surface with a small radius of curvature (i.e., a lens surface with a large half-angle), the incidence angle of the deposition material becomes larger toward the periphery, so the film thickness decreases compared to the center. If the film thickness of the deposition material at the center is D, the film thickness at a half-angle ψ is approximately D × cos(ψ). In other words, the film thickness at a half-angle of 40° is about 75% of the film thickness at the center. Therefore, the larger the half-angle of the lens surface, the greater the film thickness distribution within the lens surface.

[0015] In this embodiment, the half-open angle φ (°) at the position Q is φ≧20° (1) In a lens with φ<20°, the film thickness distribution within the optical surface of the half mirror 100 is small, and the variation in reflectance is also small, so that the change in reflectance characteristics does not pose a problem.

[0016] In addition, φ≧25° (1)′ It is more preferable that the following condition is satisfied.

[0017] Also, φ≧30° (1)″ It is more preferable that the following condition is satisfied:

[0018] In this embodiment, the total thickness D of the half mirror 100 at the position Q is Q but, 0.75≦D Q / D C ≦0.95 (2) The following conditions are satisfied. D Q / D C If D is greater than 0.95, the problem of in-plane variation in anti-reflection performance does not occur. Q / DC If is smaller than 0.75, the difference in film thickness is too large, making it difficult to form a high-performance half mirror.

[0019] 2 shows the film configuration at position C of the half mirror 100 of this embodiment. The half mirror 100 is composed of thin films 11, 12, 13, 14, 15, 16, 17, and 18, in that order from the transparent substrate 200 side. The thin films 12, 14, 16, and 18 are made of a first material, and the thin films 11, 13, 15, and 17 are made of a second material. That is, the half mirror 100 is composed of thin films of the first material and thin films of the second material alternately laminated.

[0020] The half mirror 100 has a wavelength of light incident on the half mirror 100 of λ (here, 587.56 nm of the d-line) and a refractive index of the first material at the wavelength λ of n L (λ), the refractive index of the second material is n H (λ), 1.4≦n L (587.56)≦1.6 (3) 1.9≦n H (587.56)≦2.5 (4) Specific examples of the first and second materials will be described later.

[0021] In addition, 1.4≦n L (587.56)≦1.5 (3)′ 2.1≦n H (587.56)≦2.5 (4)′ It is more preferable that the following condition is satisfied.

[0022] In addition, the half mirror 100 of this embodiment has the following features: n H (587.56)-n L (587.56)≧0.40 (5) The first material and the second material are both dielectric materials, and the greater the difference in refractive index between these materials, the more improved the performance of the half mirror.

[0023] In addition, n H (587.56)-n L (587.56)≧0.50 (5)′ It is more preferable that the following condition is satisfied.

[0024] Also, n H (587.56)-n L (587.56)≧0.70 (5)″ It is more preferable that the following condition is satisfied:

[0025] Furthermore, the half mirror 100 of this embodiment has the following features: 1 / (n H (420)-n H (680))≧4.5 (6) The following conditions are satisfied.

[0026] In addition, 1 / (n H (420)-n H (680))≧5.0 (6)′ It is more preferable that the following condition is satisfied.

[0027] In general, a dielectric material has a large energy gap between the visible region of wavelengths 400 to 700 nm. Due to this energy gap, the dielectric material exhibits normal dispersion in which the refractive index gradually decreases from the short wavelength side to the long wavelength side of the visible region. A dielectric material with a high refractive index that satisfies the condition of formula (4), such as the second material, has a refractive index that changes more rapidly in the visible region than the first material that satisfies the condition of formula (3). In other words, the refractive index dispersion is large. The reflectance R is expressed as n×d / λ, where d is the film thickness, n is the refractive index, and λ is the wavelength. In film design, the film thickness d is determined so that the reflectance characteristics fall within a certain range in a certain wavelength band. When the wavelength λ changes, the refractive index n also changes, so the larger the refractive index dispersion of the second material, the greater the change in the reflectance characteristics. In this embodiment, the refractive index dispersion of the second material is specified in order to keep the change in the reflectance characteristics as small as possible even if the film thickness d changes.

[0028] By satisfying the condition of formula (6), the half mirror 100 of this embodiment has a large half aperture angle and a film thickness distribution along the lens surface, but the variation in reflectance due to position is small. In other words, the reflectance at position C (position of half aperture 0°) when the incident angle at the wavelength λ nm is 0° (hereinafter referred to as 0° incidence) is R C (λ), the reflectance at position Q (position of half aperture angle φ) is R Q (λ) in the entire wavelength range of 420 to 680 nm 45%≦R C <=55% (7) and 45%≦R Q <=55% (8) It is desirable to satisfy the following conditions.

[0029] The thicknesses of the thin films (hereinafter also referred to as layers) 11, 12, 13, 14, 15, 16, 17 and 18 are respectively represented by d 11 , d 12 , d 13 , d 14 , d 15 , d 16 , d 17 , and d 18 (nm), the total film thickness at position C is D C teeth, D C =d 11 +d 12 +d 13 +d 14 +d 15 +d 16 +d 17 +d 18 (9) The total thickness of the layer made of the first material at the position C can be expressed as D CL , the total thickness of the layers of the second material is D CH When D CL =d 12 +d 14 +d 16 +d 18 (10) D CH =d 11 +d13 +d 15 +d 17 (11) D C =D CL +D CH (12) At this time, 0.20≦D CH / D C ≦0.40 (13) It is desirable to satisfy the following conditions.

[0030] In addition, 0.22≦D CH / D C ≦0.40 (13)′ It is more preferable that the following condition is satisfied.

[0031] In the half mirror 100 of this embodiment, the layer 18 farthest from the transparent substrate 200 is made of the first material, the layer made of the first material next farthest from the transparent substrate 200 after the layer 18 is the layer 16, and the layer next farthest after that is the layer 14. In this case, the film thickness d 14 teeth, 100≦d 14 <= 180 (14) It is desirable to satisfy the following condition. 16 teeth, 100≦d 16 <= 180 (15) It is more desirable to satisfy the following condition.

[0032] The number of layers (films) of the half mirror 100 is m, and the film thickness of the mth layer from the substrate side is d m Then, equations (14) and (15) can be rewritten as equations (16) and (17).

[0033] 100≦d m-4 <= 180 (16) 100≦d m-2 <= 180 (17) The number of layers m of the half mirror 100 is 8≦m≦11 (18) It is preferable that the thickness of the (m-4)th layer and the (m-2)th layer made of the first material is a parameter related to the wavelength band in which the half mirror 100 achieves a desired target. If the thicknesses of these two layers satisfy the condition of formula (16), and more preferably the condition of formula (17), the wavelength band in which the desired target can be achieved becomes wider, and the characteristics become less susceptible to the influence of changes in the thickness.

[0034] The thermal expansion coefficient α(10 -5 / ℃), 1.5≦α≦30.0 (19) It is desirable that the following conditions be satisfied. The transparent substrate 200 is made of a resin material. As described above, since the optical element of this embodiment is used in the optical system of an optical device such as an HMD, it is desirable that it be small and lightweight. The transparent substrate 200 used in the half mirror 100 is desirably made of a lightweight resin material.

[0035] The first material is preferably a material containing silicon oxide. More preferably, the first material is a material containing silicon oxide containing a small amount of aluminum. Furthermore, the first material preferably contains aluminum at a weight ratio of 0.001% to 10% and silicon oxide at a weight ratio of 90% or more. When the transparent substrate 200 is made of a resin material, it is easy to expand. For this reason, forming a film with a large compressive stress on the resin substrate makes it less likely for the film to crack or peel off. A film containing silicon oxide has a large compressive stress. Furthermore, the compressive stress can be increased by containing a small amount of aluminum. The aluminum content is effective for compressive stress even if it is a small amount of about 0.001% by weight.

[0036] The second material is preferably a material containing at least one of titanium oxide and niobium oxide. When the transparent substrate 200 is made of a resin material, it will deform or crack if heated. For this reason, the half mirror 100 must be formed by deposition without heating (or low-temperature heating at 80°C or less). Titanium oxide and niobium oxide can satisfy the conditions of formulas (4) to (6) even when a deposition method without heating is used. As titanium oxide, TiO2, in which the number of titanium atoms is 1 and the number of oxygen atoms is 2, is preferable. When the number of oxygen atoms is smaller than twice the number of titanium atoms (for example, Ti4O7), if a film is formed by deposition without heating, the dispersion becomes large and the condition of formula (8) is often not satisfied. More preferably, the second material is TiO2 or Nb2O5. In particular, Nb2O5 has a relatively small radiant heat and has a small thermal effect on resin, so that deformation and cracking of the transparent substrate 200 can be prevented. In addition, Nb2O5 has a smaller refractive index dispersion than TiO2 and satisfies the condition of formula (9), so that the change in reflectance characteristics due to the variation in film thickness can be further suppressed.

[0037] The method for forming the film of the half mirror 100 is not particularly limited as long as it is a physical vapor deposition method such as a deposition method, a sputtering method, or an ion plating method. In particular, the deposition method is preferable because it is easy to adjust the film thickness and the refractive index. In the deposition method, the method for heating the deposition material includes a resistance heating method, an electron beam deposition method, a laser deposition method, and an ion beam assisted method. The electron beam deposition method is a preferable heating method because it can directly heat the film material, so that the film can be formed on the substrate without heating, and there is little contamination and the quality of the film is relatively high.

[0038] In addition, the ion beam assisted method is a preferred heating method because an independent ion source plays the role of assisting the deposition, which allows the formation of a dense film with high strength and little absorption and scattering. In deposition using the ion beam assisted method, the magnitude and dispersion of the refractive index vary depending on the flow rate of the assist gas during deposition (deposition pressure), the ion current density, and the deposition rate. In this embodiment, the second material must satisfy the conditions of formula (4) or formula (6) and formula (8). In order to satisfy these conditions, it is desirable to deposit the deposition material in a single layer and confirm in advance that these conditions are satisfied.

[0039] Specific examples (experimental examples) are given below. EXAMPLES

[0040] FIG. 3 shows a cross section of the optical element (lens) in Example 1. Positions C, Q, L and the maximum value φ of the half angle in FIG. 3 are the same as those in FIG. 1. The R1 surface of the transparent substrate 200 is the surface to which the half mirror 100 in Example 1 is attached. Note that the half mirror 100 is not shown in FIG. 3. Position P is a position corresponding to the half angle θ, and is a position on a plane including the optical axis L, position C, and position Q. FIG. 2 shows the eight-layer film configuration of the half mirror 100 at position C.

[0041] In Example 1, APEL (manufactured by Mitsui Chemicals) with a refractive index of 1.54 at the d-line was used as the material of the substrate 200. The R1 surface forming the half mirror 100 has a concave shape. The half aperture angle φ at the position Q is 40°, which satisfies the condition of formula (1). As the layer materials, SiO2 (containing Al: 4.5% by weight) was used for the thin films 12, 14, 16, and 18, and Nb2O5 was used for the thin films 11, 13, 15, and 17.

[0042] In Example 1, the half mirror 100 was formed by deposition. An electron beam was used to heat the deposition materials SiO2 and Nb2O5. In addition, an ion beam assisted deposition method was used to form a denser film. The inside of the vacuum chamber of the deposition device was filled with 2×10 -3The vacuum chamber was evacuated to a high vacuum region of approximately 1000 MPa (Pa). After confirming that the inside of the vacuum chamber had reached a high vacuum state, Ar was introduced as an inert gas into the ion gun, and the ion gun was discharged. The deposition conditions for each deposition material are shown in Table 1.

[0043] The refractive index dispersion of each deposition material formed under the conditions in Table 1 is shown in Figure 4. The refractive index of SiO2 (containing 4.5% Al by weight) at the d line is 1.47, and the refractive index of Nb2O5 at the d line is 2.31, which satisfies the conditions of formulas (3), (4), and (5). The refractive index of Nb2O5 at a wavelength of 420 nm is 2.43, and the refractive index at a wavelength of 680 nm is 2.28. Therefore, 1 / (n H (420)-n H (680)) is 6.47, which satisfies the condition of equation (6).

[0044] Table 2 shows the total film thickness of the half mirror 100, the total film thickness of Nb2O5, and the film thicknesses of the thin films 11 to 18 at position C where the half angle is 0°, position P where the half angle θ is 26°, and position Q where the half angle is 40°. It can be seen from Table 2 that Example 1 satisfies the condition of formula (2). In addition, at position C, it satisfies the condition of formula (13). Furthermore, it also satisfies the conditions of formulas (16) and (17).

[0045] 5 shows the reflectance characteristics for 0° incident light at positions C, P, and Q of the half mirror 100 of Example 1. The film thickness of the half mirror 100 varies depending on the position of the half aperture on the transparent substrate 200, but the reflectance is between 45% and 55% at wavelengths from 420 nm to 680 nm, and good reflectance characteristics are achieved.

[0046] [Table 1]

[0047] [Table 2] EXAMPLES

[0048] In Example 2, a half mirror 100 having a 10-layer film configuration as shown in Fig. 6 was formed on the R1 surface of a transparent substrate similar to that of Example 1. As the layer material, thin films 12, 14, 16, 18, and 20 were made of SiO2, and thin films 11, 13, 15, 17, and 19 were made of Nb2O5, the same as in Example 1.

[0049] The half mirror 100 of Example 2 was also formed by the deposition method in the same manner as in Example 1. The deposition conditions for each deposition material are shown in Table 3. The refractive index dispersion of each deposition material formed under the conditions in Table 3 is shown in FIG.

[0050] The refractive index of SiO2 at the d line is 1.46, and the refractive index of Nb2O5 at the d line is 2.31. Nb2O5 is the same material as in Example 1. Therefore, the conditions of formulas (3), (4), (5), and (6) are satisfied.

[0051] Table 4 shows the total film thickness of the half mirror 100, the total film thickness of Nb2O5, and the film thicknesses of the thin films 11 to 20 at position C where the half angle is 0°, position P where the half angle θ is 26°, and position Q where the half angle is 40°. It can be seen from Table 4 that Example 2 satisfies the condition of formula (2). Furthermore, at position C, it satisfies the condition of formula (13). Furthermore, it also satisfies the conditions of formulas (16) and (17).

[0052] 8 shows the reflectance characteristics for 0° incident light at positions C, P, and Q of the half mirror 100 of Example 2. The film thickness of the half mirror 100 varies depending on the half-angle position on the transparent substrate 200, but the reflectance is between 45% and 55% at wavelengths from 420 nm to 680 nm, and good reflectance characteristics are achieved.

[0053] [Table 3]

[0054] [Table 4] EXAMPLES

[0055] Fig. 9 shows a cross section of the optical element in Example 3. Positions C, Q, L, maximum half-angle φ, and R1 in Fig. 9 are the same as those in Fig. 3. Fig. 10 shows the film configuration of 11 layers of the half mirror 100 at position C.

[0056] In Example 3, APEL (manufactured by Mitsui Chemicals) with a refractive index of 1.54 at the d-line was used as the material of the substrate 200. The R1 surface forming the half mirror 100 has a convex shape. The half aperture angle φ at the position Q is 40°, which satisfies the condition of formula (1). As the layer material, SiO2 (containing Al: 4.5% by weight) was used for the thin films 11, 13, 15, 17, 19, and 21, and Nb2O5 was used for the thin films 12, 14, 16, 18, and 20.

[0057] In Example 3, the half mirror 100 was also formed by the deposition method. The deposition conditions for each deposition material are shown in Table 5. The ion current density during deposition of the Nb2O5 film was set lower than in Examples 1 and 2. This resulted in a smaller refractive index.

[0058] The refractive index dispersion of each deposition material formed under the conditions in Table 5 is shown in Figure 11. The refractive index at the d line of SiO2 (containing 4.5% Al by weight) is 1.47, and the refractive index at the d line of Nb2O5 is 2.21, which satisfies the conditions of formulas (3), (4), and (5). The refractive index at a wavelength of 420 nm of Nb2O5 is 2.29, and the refractive index at a wavelength of 680 nm is 2.18. Therefore, 1 / (n H (420)-n H (680)) is 9.47, which satisfies the condition of equation (6).

[0059] Table 6 shows the total film thickness of the half mirror 100, the total film thickness of Nb2O5, and the film thicknesses of the thin films 11 to 21 at position C where the half angle is 0°, position P where the half angle θ is 26°, and position Q where the half angle is 40°. It can be seen from Table 6 that Example 3 satisfies the condition of formula (2). In addition, at position C, it satisfies the condition of formula (13). Furthermore, it also satisfies the conditions of formulas (16) and (17).

[0060] 12 shows the reflectance characteristics for 0° incident light at positions C, P, and Q of the half mirror 100 of Example 3. The film thickness of the half mirror 100 varies depending on the half angle position on the transparent substrate 200, but the reflectance is between 45% and 55% at wavelengths from 420 nm to 680 nm, and good reflectance characteristics are achieved.

[0061] [Table 5]

[0062] [Table 6] EXAMPLES

[0063] The optical element of Example 4 has a cross section shown in Fig. 9, similarly to Example 3. Fig. 13 shows the nine-layer film configuration of the half mirror 100 at position C.

[0064] In Example 4, the substrate 200 is APEL (manufactured by Mitsui Chemicals) with a refractive index of 1.54 at the d-line. The R1 surface forming the half mirror 100 has a convex shape. The half aperture angle φ at the position Q is 40°, which satisfies the condition of formula (1). As the layer materials, SiO2 (containing Al: 4.5% by weight) was used for the thin films 11, 13, 15, 17, and 19, and TiO2 was used for the thin films 12, 14, 16, and 18.

[0065] The half mirror 100 of Example 4 was also formed by ion beam assisted deposition in the same manner as in Example 1. The deposition conditions for each deposition material are shown in Table 7. The refractive index dispersion of each deposition material formed under the conditions in Table 7 is shown in FIG. 11. The refractive index at the d line of SiO2 (containing Al: 4.5% by weight) is 1.47, and the refractive index at the d line of TiO2 is 2.35, which satisfies the conditions of formulas (3), (4), and (5). The refractive index at a wavelength of 420 nm of TiO2 is 2.51, and the refractive index at a wavelength of 680 nm is 2.31, so that 1 / (n H (420)-n H (680)) is 5.30, which satisfies the condition of equation (6).

[0066] Table 8 shows the total film thickness of the half mirror 100, the total film thickness of TiO2, and the film thicknesses of the thin films 11 to 19 at position C where the half angle is 0°, position P where the half angle θ is 26°, and position Q where the half angle is 40°. It can be seen from Table 8 that Example 3 satisfies the condition of formula (2). Furthermore, at position C, it satisfies the condition of formula (13). Furthermore, it also satisfies the conditions of formulas (16) and (17).

[0067] 15 shows the reflectance characteristics for 0° incident light at positions C, P, and Q of the half mirror 100 of Example 4. The film thickness of the half mirror 100 varies depending on the half angle position on the transparent substrate 200, but the reflectance is between 45% and 55% at wavelengths from 420 nm to 680 nm, and good reflectance characteristics are achieved.

[0068] [Table 7]

[0069] [Table 8]

[0070] Fig. 16(a) shows an optical system 401 including the optical element of Example 1 or Example 2. Fig. 16(b) shows an optical system 402 including the optical element of Example 3 or Example 4. These optical systems 401 and 402 are used as observation optical systems in optical instruments such as HMDs.

[0071] The optical system 401 is made up of a plurality of optical elements G51 to G54, and the optical system 402 is made up of a plurality of optical elements G61 to G64.

[0072] The optical elements G51 and G61 are lenses having circular polarization selective reflecting and transmitting mirrors on their respective surfaces 55 and 65. The optical element G52 is a lens having the half mirror 100 described in the first or second embodiment provided on its surface 56, and the optical element G62 is a lens having the half mirror 100 described in the third or fourth embodiment provided on its surface 66. The optical elements G53 and G63 are polarization conversion elements, and the optical elements G54 and G64 are display elements such as liquid crystal displays.

[0073] Light from the display elements G54, G64 that display images is incident on the optical elements G53, G63 and converted into circularly polarized light. 50% of the light (circularly polarized light) emitted from the optical elements G53, G63 passes through the half mirror 100 provided on the surfaces 56, 66, and is then reflected by the circularly polarized light selective reflecting transmission mirrors on the surfaces 55, 65. This reflected light again passes through the half mirror 100 provided on the surfaces 56, 66, where 50% is reflected. The reflected light from the half mirror 100 passes through the circularly polarized light selective reflecting transmission mirrors on the surfaces 55, 65, and reaches the eyes 57, 67 of the user (observer).

[0074] By disposing refractive optical elements G52 and G62 having optical power in the optical systems 401 and 402, the images displayed on the display elements G34 and G44 are magnified and observed by the user.

[0075] It should be noted that the optical systems 401 and 402 are merely examples, and the optical elements of each embodiment may be used in other optical systems.

[0076] Fig. 17 is a schematic cross-sectional view of an optical device, an HMD 500. Fig. 18 shows the external appearance of the HMD 500. The HMD 500 is used by being worn on the user's head.

[0077] The HMD 500 has left and right optical systems 403, 404 including the optical element according to any one of the first to fourth embodiments. The optical systems 403, 404 have the same optical configuration. The optical systems 403, 404 are housed in a goggle-type case 73 and guide light from display elements 74, 75 to the left eye 71 and right eye 72 of the user, respectively. This allows the user to see an enlarged image of the image displayed on the display elements 74, 75. The display elements 74, 75 display a left eye image and a right eye image having a parallax with each other, allowing the user to see a stereoscopic image.

[0078] Comparative examples in comparison with Examples 1 to 4 will now be described.

[0079] Comparative Example 1 In Comparative Example 1, a half mirror 100' having the film configuration shown in Fig. 2 was formed on the same lens as in Example 1. As the layer material, thin films 12, 14, 16, and 18 were made of SiO2, and thin films 11, 13, 15, and 17 were made of Ti4O7.

[0080] The half mirror 100' of Comparative Example 1 was also formed by the deposition method in the same manner as in Example 1. The deposition conditions for each deposition material are shown in Table 9. The refractive index dispersion of each deposition material formed under the conditions in Table 9 is shown in FIG. 19. The refractive index of SiO2 at the d line is 1.46, and the refractive index of Ti4O7 at the d line is 2.33, which satisfies the conditions of formulas (3), (4), and (5). However, the refractive index of Ti4O7 at a wavelength of 420 nm is 2.54, and the refractive index at a wavelength of 680 nm is 2.28, so that 1 / (n H (420)-n H (680)) is 3.91. In other words, it does not satisfy the condition of equation (6).

[0081] Table 10 shows the total film thickness of the half mirror 100', the total film thickness of Ti4O7, and the film thicknesses of the thin films 11 to 18 at position C where the half angle is 0°, position P where the half angle θ is 26°, and position Q where the half angle is 40°. It can be seen from Table 10 that Comparative Example 1 satisfies the condition of formula (2). In addition, at position C, it satisfies the condition of formula (13). Furthermore, it also satisfies the conditions of formulas (16) and (17).

[0082] FIG. 20 shows the reflectance characteristics for 0° incident light at positions C, P, and Q of the half mirror 100′ of Comparative Example 1. The film thickness of the half mirror 100′ varies depending on the position of the half angle on the transparent substrate 200. The reflectance characteristics at position P are between 45% and 55% at wavelengths from 420 nm to 680 nm. However, the reflectance characteristics at position C are reduced near wavelengths from 420 nm to 450 nm, and at position Q are reduced near wavelengths from 420 nm to 460 nm and near wavelengths of 670 nm. In other words, when the condition of formula (6) is not satisfied, the reflectance characteristics are significantly reduced due to the change in film thickness.

[0083] [Table 9]

[0084] [Table 10]

[0085] Comparative Example 2 In Comparative Example 2, a half mirror 100' having the film configuration shown in FIG. 2 was formed on a lens similar to that of Example 1 using the same layer materials and deposition method as in Example 1. Therefore, Comparative Example 2 satisfies the conditions of formulas (3), (4), (5), and (6). Comparative Example 2 differs from Example 1 in the film thickness of each layer.

[0086] Table 11 shows the total film thickness of the half mirror 100', the total film thickness of Nb2O5, and the film thicknesses of the thin films 11 to 18 at position C where the half angle is 0°, position P where the half angle θ is 26°, and position Q where the half angle is 40°. It can be seen from Table 11 that Comparative Example 2 satisfies the condition of formula (2). However, at position C, it does not satisfy the conditions of formulas (13), (16), and (17).

[0087] 21 shows the reflectance characteristics for 0° incident light at positions C, P, and Q of the half mirror 100′ of Comparative Example 2. The film thickness of the half mirror 100′ varies depending on the position of the half angle on the transparent substrate 200. The reflectance characteristics at position P are between 45% and 55% at wavelengths from 420 nm to 680 nm. However, the reflectance characteristics at position C are reduced near the wavelength of 420 nm, and at position Q are reduced near the wavelength of 610 nm to 680 nm. In other words, when the conditions of formulas (13), (16), and (17) are not satisfied, the reflectance characteristics are significantly reduced due to the change in film thickness.

[0088] [Table 11]

[0089] The above embodiment includes the following configurations.

[0090] (Configuration 1) An optical element for use in an imaging optical system, the optical element having a substrate including a curved surface and a multilayer film formed on the curved surface, the multilayer film includes a first film made of a first material and a second film made of a second material that are alternately laminated; The maximum value of the half aperture angle within the optically effective area of ​​the curved surface is φ, and the total thickness of the multilayer film at the half aperture angle of 0° is D. C The total thickness of the multilayer film at the half-angle φ is D Q year, The refractive index of the first material at a wavelength λ [nm] is n L (λ), the refractive index of the second material at a wavelength λ [nm] is n H (λ), φ≧20° 0.75≦D Q / D C ≦0.95 1.4≦n L (587.56)≦1.6 1.9≦n H (587.56)≦2.4 n H (587.56)-n L (587.56)≧0.40 1 / (n H (420)-n H (680))≧4.5 An optical element characterized by satisfying the following conditions. (Configuration 2) 1 / (n H (420)-n H (680))≧4.5 2. The optical element according to configuration 1, which satisfies the following conditions: (Configuration 3) The reflectance of the multilayer film with respect to light of wavelength λ incident at an incident angle of 0° at the position of the half aperture angle of 0° is defined as R C (λ), and the reflectance of the multilayer film for light of wavelength λ incident at the position of the half aperture angle φ at an incident angle of 0° is R Q (λ), In the range of 420≦λ≦680, 45%≦R C ≦55% 45%≦R Q ≦55% 3. The optical element according to configuration 1 or 2, which satisfies the following conditions: (Configuration 4) The total thickness of the second film at the half-open angle of 0° is defined as D CH When 0.20≦D CH / D C ≦0.40 4. The optical element according to any one of configurations 1 to 3, which satisfies the following condition: (Configuration 5) The total number of films constituting the multilayer film is m, The thickness of the (m-4)th film counting from the substrate side is d m-4When 100≦d m-4 <= 180 5. The optical element according to any one of configurations 1 to 4, which satisfies the following condition: (Configuration 6) The total number of films constituting the multilayer film is m, The thickness of the (m-2)th film counted from the substrate side is d m-2 When 100≦d m-2 <= 180 6. The optical element according to any one of configurations 1 to 5, which satisfies the following conditions: (Configuration 7) When the total number of films constituting the multilayer film is m, 8≦m≦11 7. The optical element according to any one of configurations 1 to 6, which satisfies the following condition: (Configuration 8) The thermal expansion coefficient of the substrate is α[10 -5 / ℃], 1.5≦α≦30.0 8. The optical element according to any one of configurations 1 to 7, which satisfies the following condition: (Configuration 9) 9. The optical element according to any one of configurations 1 to 8, wherein the first material contains aluminum in a weight ratio of 0.001% to 10% both inclusive, and silicon oxide in a weight ratio of 90% or more. (Configuration 10) 10. The optical element of any one of configurations 1 to 9, wherein the second material includes at least one of titanium oxide and niobium oxide. (Configuration 11) 11. The optical element of any one of configurations 1 to 10, wherein the second material includes TiO2. (Configuration 12) 12. The optical element of any one of configurations 1 to 11, wherein the second material includes Nb2O5. (Configuration 13) 13. An imaging optical system comprising the optical element according to any one of configurations 1 to 12. (Configuration 14) 14. An optical instrument comprising the imaging optical system according to aspect 13. (Configuration 15) A display element for displaying an image is provided. 15. The optical apparatus according to configuration 14, wherein the imaging optical system guides light from the display element to an observer's eye.

[0091] The embodiments described above are merely representative examples, and various modifications and alterations are possible for each embodiment when implementing the present invention. [Explanation of symbols]

[0092] 100 Half mirror (multilayer film) 200 Transparent substrate

Claims

1. An optical element used in an imaging optical system, comprising a substrate including a curved surface and a multilayer film formed on the curved surface, the multilayer film includes a first film made of a first material and a second film made of a second material that are alternately stacked; The maximum value of the half angle within the optically effective area of ​​the curved surface is φ, and the total thickness of the multilayer film at the half angle of 0° is D Ｃ , the total thickness of the multilayer film at the position of the half-open angle φ is D Ｑ year, The refractive index of the first material at a wavelength λ [nm] is n Ｌ (λ), the refractive index of the second material at wavelength λ [nm] is n Ｈ When (λ) is used, φ≧20° 0.75≦D Ｑ / D Ｃ ≦0.95 1.4≦n Ｌ (587.56)≦1.6 1.9≦n Ｈ (587.56)≦2.5 n Ｈ (587.56)-n Ｌ (587.56)≧0.40 1 / (n Ｈ (420)-n Ｈ (680))≧4.5 An optical element characterized by satisfying the following conditions.

2. 1 / (n Ｈ (420)-n Ｈ (680))≧5.0 2. The optical element according to claim 1, wherein the following condition is satisfied:

3. The reflectance of the multilayer film with respect to light of wavelength λ incident at an incident angle of 0° at the position of the half aperture angle of 0° is defined as R Ｃ (λ), the reflectance of the multilayer film for light of wavelength λ incident at the position of the half aperture angle φ at an incident angle of 0° is R Ｑ When (λ) is used, In the range of 420≦λ≦680, 45%≦R Ｃ ≦55% 45%≦R Ｑ ≦55% 2. The optical element according to claim 1, wherein the following condition is satisfied:

4. The total thickness of the second film at the half-open angle of 0° is defined as D ＣＨ When 0.20≦D ＣＨ / D Ｃ ≦0.40 2. The optical element according to claim 1, wherein the following condition is satisfied:

5. The total number of films constituting the multilayer film is defined as m, The thickness of the (m-4)th film counted from the substrate side is defined as d ｍ－４ When 100≦d ｍ－４ ≦180 2. The optical element according to claim 1, wherein the following condition is satisfied:

6. The total number of films constituting the multilayer film is defined as m, The thickness of the (m-2)th film counted from the substrate side is defined as d ｍ－２ When 100≦d ｍ－２ ≦180 2. The optical element according to claim 1, wherein the following condition is satisfied:

7. When the total number of films constituting the multilayer film is m, 8≦m≦11 2. The optical element according to claim 1, wherein the following condition is satisfied:

8. The thermal expansion coefficient of the substrate is α[10 －５ / ℃], １．５≦α≦３０．０ 2. The optical element according to claim 1, wherein the following condition is satisfied:

9. 2. The optical element according to claim 1, wherein the first material contains aluminum in a weight ratio of 0.001% to 10% and silicon oxide in a weight ratio of 90% or more.

10. 2. The optical element according to claim 1, wherein the second material includes at least one of titanium oxide and niobium oxide.

11. The second material is TiO ２ The optical element according to claim 1 , comprising:

12. The second material is Nb ２ O ５ The optical element according to claim 1 , comprising:

13. An imaging optical system comprising the optical element according to claim 1 .

14. An optical instrument comprising the imaging optical system according to claim 13.

15. a display element for displaying an image; 15. The optical apparatus according to claim 14, wherein the imaging optical system guides light from the display element to the observer's eye.

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