JP2010128343A - Diffraction optical element, optical system, and optical apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a diffractive optical element with little performance deterioration due to a phase mismatch portion and high diffraction efficiency over a wide wavelength band, and an optical system and optical apparatus having the diffractive optical element.
A diffractive optical element having a first optical member having a first diffractive optical surface and a second optical member having a second diffractive optical surface arranged so as to be in contact with the first diffractive optical surface. In the element 10, the refractive index of the first optical material constituting the first optical member 11 is higher than the refractive index of the second optical material constituting the second optical member 12. The cross-sectional area of the phase mismatch portion of the peak of the diffractive optical surface 13 is configured to be smaller than the cross-sectional area of the phase mismatch portion of the valley of the first diffractive optical surface 13.
[Selection] Figure 1

Description

  The present invention relates to a diffractive optical element, and more particularly to a diffractive optical element in which a decrease in diffraction efficiency during manufacturing is reduced, an optical system having the diffractive optical element, and an optical apparatus.

Conventionally, a method using a diffractive optical element is known as one of methods for reducing chromatic aberration of an optical system. In recent years, a diffractive optical element called a multilayer type has been proposed. This type of diffractive optical element has a structure in which optical members (for example, diffraction gratings) made of a plurality of types of materials are stacked and their diffractive optical surfaces (hereinafter also referred to as grating surfaces) are in close contact with each other. High diffraction efficiency is maintained in almost the entire wavelength region (for example, visible light region), that is, the wavelength characteristic is good. Such a diffractive optical element is manufactured by a method such as injection molding or glass molding. These methods have the advantage that manufacturing costs can be reduced because a large number of elements can be mass-produced using the mold once manufactured (see, for example, Patent Document 1).
JP 2004-157404 A

  When the diffractive optical element is manufactured by a molding method, a molding die having a mold surface having a shape reversed from the design-shaped grating surface is produced. For example, the mold surface is formed by cutting with a cutting tool having a small tip diameter. For this reason, at least the shape of the valley on the mold surface of the mold is rounded depending on the diameter of the tip of the cutting tool. Then, the peak of the grating surface of the manufactured diffractive optical element is rounded by transferring the roundness of the valley of the mold surface of the mold, and the grating surface shape of the molded diffraction grating is different from the ideal shape. . In a diffractive optical element having such a diffraction grating, a portion where the ideal shape of the grating surface is different from the shape of the actually formed grating surface is a so-called “phase mismatched portion” in which the phase of the light is different from the desired value. (See FIG. 9). The light passing through the phase mismatching portion proceeds in an unintended direction to become flare light, so that there is a problem that the diffraction efficiency is lowered and the optical performance of the diffractive optical element is lowered.

  The present invention has been made in view of such problems, and provides a diffractive optical element that has little performance deterioration due to a phase mismatch portion and has high diffraction efficiency over a wide wavelength band, and an optical system and optical apparatus having the diffractive optical element. The purpose is to do.

  According to the first aspect of the present invention, the first optical member having the first diffractive optical surface and the second optical member having the second diffractive optical surface arranged to contact the first diffractive optical surface. The refractive index of the first optical material constituting the first optical member is higher than the refractive index of the second optical material constituting the second optical member, and in the first optical member, A diffractive optical element is provided in which a cross-sectional area of a phase mismatch portion of a peak of the diffractive optical surface is smaller than a cross-sectional area of a phase mismatch portion of a valley of the first diffractive optical surface.

  According to the 2nd aspect which illustrates this invention, the optical system characterized by having the diffractive optical element of the said aspect is provided.

  According to a third aspect illustrating the present invention, there is provided an optical apparatus having the diffractive optical element according to the above aspect.

  According to the present invention, it is possible to provide a diffractive optical element with little performance deterioration due to a phase mismatch portion and high diffraction efficiency over a wide wavelength band, an optical system and an optical apparatus having the diffractive optical element.

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

  Conventionally, various attempts have been made to incorporate a diffractive optical surface into an optical system such as a pickup lens for an optical disk, in order to achieve high performance and miniaturization that cannot be achieved by a refractive optical system or a reflective optical system. However, in a single-layer type diffractive optical element having such a diffractive optical surface, there is a problem that flare occurs due to light in a wavelength region deviated from the design wavelength, and the image quality and imaging performance are impaired. It was limited to use in a single wavelength such as a laser light source or a narrow wavelength range.

  Therefore, in recent years, a diffractive optical element called a multilayer type (or laminated type) has been proposed. This type of diffractive optical element has, for example, a diffractive optical surface (relief pattern) formed in a sawtooth shape, and a plurality of optical element elements having different refractive indexes and dispersions are laminated in a separated or closely contacted manner. Thus, high diffraction efficiency is maintained in almost the entire desired wide wavelength range (for example, visible light range). That is, the wavelength characteristic of the diffraction efficiency is good.

Here, the structure of the multi-layered diffractive optical element will be described. Generally, as shown in FIGS. 10A and 10B, the first optical element element 111 made of the first material and the refractive element are refracted. A second optical element element 112 made of a second material having a different rate and dispersion value is formed, and sawtooth diffractive optical surfaces 111a and 112a are formed on opposing surfaces of the respective optical element elements. Then, the grating height (groove height) h1 of the first optical element element 111 is determined to be a predetermined value so as to satisfy the achromatic condition for specific two wavelengths, and the second optical element element 112 The grid height h2 is determined to another predetermined value. As a result, the diffraction efficiency is 1.0 for specific two wavelengths, and a considerably high diffraction efficiency can be obtained for other wavelengths. Thus, by making the diffractive optical element a multilayer type, the diffractive optical element can be applied to almost all wavelengths. The diffraction efficiency is a ratio η between the intensity I _{0 of} light incident on the diffractive optical element and the intensity I ₁ of first-order diffracted light included in the light transmitted through the diffractive optical element in the transmission type diffractive optical element. (= I ₁ / I ₀ ).

  In addition, by satisfying the predetermined condition, as shown in FIG. 10B, the lattice height h1 of the first optical element element 111 and the lattice height h2 of the second optical element element 112 are matched. It becomes possible to achieve a contact multilayer type diffractive optical element. In this close-contact multi-layer diffractive optical element, the error sensitivity (tolerance) of the grating height becomes loose or the error sensitivity (tolerance) of the surface roughness of the grating surface, compared to the separated multi-layer type shown in FIG. ) Is easy to manufacture, and has advantages such as excellent productivity, high mass productivity, and favorable cost reduction of optical products.

  Also, in the case of the adhesion multilayer type compared to the separation multilayer type, since the difference in refractive index at the interface is small, the error sensitivity such as surface roughness is small, and the tip diameter of the tool for tooling can be increased. It is advantageous in processing. In addition, when the tip diameter of the tool is large, not only can the number of processing steps be reduced, but there is also an advantage that the tool life can be extended. Therefore, it is preferable to set the tip diameter of the cutting tool as large as possible while ensuring the performance as a diffractive optical element.

  Further, in the case of the contact multilayer type as compared with the separated multilayer type, either one of the first optical element element 111 and the second optical element element 112 is first precisely formed, and then The other optical element element can be poured into a UV curable resin and molded. In this case, there is an advantage that the previously formed lattice can be used as a mold, and the lattice to be formed later can be precisely formed, and the eccentricity of both does not occur at all. Here, in the case of molding using a UV curable resin, since the tip shape of the tool that has processed the die is transferred almost as it is, the peak side of the optical member made of a material having a low refractive index as in this embodiment. It is preferable to make the crest side of the optical member made of a material having a high refractive index sharp so that the tip of the cutting tool comes to the end.

  The present embodiment relates to a technique for reducing the reduction in diffraction efficiency during the manufacture of the above-described contact multilayer diffractive optical element. More specifically, this embodiment relates to a technique for forming an optical member with a precision mold and stably producing a replica of the optical member at low cost.

  By the way, when calculating the diffraction efficiency of the diffractive optical element, in the range of the scalar theoretical calculation, the grating thickness is assumed to be 0, so that the phase distribution on the grating surface has the same amount of dimension defect (phase error) in the diffraction grating. If it is a matching portion (see FIG. 9), the change in diffraction efficiency is considered to be the same. However, as in the present embodiment, the contact multilayer type or laminated type diffractive optical element has a thick grating structure, so that the scalar calculation is not sufficient, and strict electromagnetic field analysis calculation is required. Therefore, in this embodiment, when calculating the diffraction efficiency of the diffractive optical element, the RCWA method (strict coupling wave analysis), which is one method of electromagnetic field analysis calculation, is used. In the present embodiment, the blaze order is set to -1. This is because when the blaze order is set to 1 to −1, the grating height can be kept low, so that the optical characteristics with respect to obliquely incident light become favorable, which is preferable.

  In the present embodiment, which will be described in detail below, as a result of calculating the numerical value of diffraction efficiency using the RCWA method, the phase mismatching portion of the peak and the trough phase mismatching of the optical member made of a relatively high refractive index material It has been demonstrated that the effect is different with the part even with the same amount of dimensional defects. That is, in an optical member made of a material having a relatively high refractive index and low dispersion, the peak phase mismatched portion has a higher error sensitivity than the valley phase mismatched portion. Therefore, in an optical member made of a material having a relatively high refractive index and low dispersion, if the cross-sectional area of the phase mismatch portion of the valley is made smaller than the cross-sectional area of the phase mismatch portion of the valley, the diffraction efficiency is reduced. Found that it can be reduced.

  As an example, the diffractive optical element has a concentric periodic structure (sawtooth relief pattern, blazed shape, etc.) centered on the optical axis. The cross-sectional shape cut by a plane including the optical axis of the diffractive optical element has, for example, a cross-sectional shape as shown in FIG. FIG. 1 shows only a part of the sectional shape of the diffractive optical element.

  As shown in FIG. 1, the diffractive optical element 10 of this embodiment is a so-called contact multilayer type diffractive optical element in which two optical members (for example, a diffraction grating) are stacked. That is, it has the 1st optical member 11 which has the 1st diffractive optical surface 13, and the 2nd optical member 12 which has the 2nd diffractive optical surface 14 arrange | positioned so that the 1st diffractive optical surface 13 may be contact | connected. Here, the refractive index of the first optical material constituting the first optical member 11 is configured to be higher than the refractive index of the second optical material constituting the second optical member 12. Further, in the first optical member 11, the cross-sectional area (the cross-sectional area cut by the plane including the optical axis) ΔSH of the peak phase mismatch portion of the first diffractive optical surface 13 is the valley of the first diffractive optical surface 13. The cross-sectional area of the phase mismatching portion (the area of the cross section cut by the plane including the optical axis) ΔSL is configured.

  In the present specification, a mountain is a relative value of two adjacent vertices A and B of the ideal shape of the diffractive optical surface 13 (a shape indicated by a one-dot chain line in FIG. 1 with no roundness at each vertex). An area on the apex A side having a small interior angle α. Further, the valley means an area on the apex B side having a relatively large inner angle β.

  Further, in this specification, the phase mismatched portion means an ideal shape of the diffractive optical surface 13 (shown by a one-dot chain line in FIG. 1 and a shape in which each vertex is not rounded) and an actual shape (solid line in FIG. 1). The shape which is different from (the shape with roundness at each vertex) is indicated. In the phase mismatched portion, the phase of the actual light passing therethrough is different from the phase of the light passing through the ideally shaped diffractive optical surface, that is, the phase of the actual light and the phase of the ideal light. Are not consistent. In this way, in the phase mismatch portion where the phase of the light passing through the diffractive optical surface 13 is mismatched, the passing light proceeds in an unintended direction to become flare light, and the diffraction efficiency is lowered.

  In this embodiment, when the difference in refractive index at the d-line at the interfaces (diffractive optical surfaces) 13 and 14 where the two optical members 11 and 12 are in close contact with each other is Δnd, You may make it satisfy the conditional expression (1).

  0.005 <Δnd <0.45 (1)

  The conditional expression (1) defines an appropriate range of the refractive index difference Δnd in the d-line at the interfaces (diffractive optical surfaces) 13 and 14 where the two optical members 11 and 12 are in close contact. In order to configure the close contact type diffractive optical element as in the present embodiment, the optical material forming the two optical members 11 and 12 (at the interface) is composed of an optical material having a relatively high refractive index and a low refractive index. One important condition is that the optical material has a refractive index. However, either material may be located on the object side. In consideration of this, if the upper limit value of conditional expression (1) is exceeded, the refractive index difference Δnd becomes excessively large, and the manufacturing error sensitivity of the grating increases, which is not preferable. On the other hand, if the lower limit value of conditional expression (1) is not reached, the height of the cliff becomes too large, which is disadvantageous in manufacturing, as well as the first diffraction having a cliff (shown in FIG. 2 having peaks and valleys). On the optical surface 13, a shadow is generated with respect to the progress of light due to the top of the adjacent mountain (vertex A) and the bottom of the valley (vertex B)), and the diffraction efficiency of blazed light is reduced or hits a cliff. The stray light due to light scattering and reflection becomes large, which causes a deterioration in image quality. In order to further suppress the error sensitivity in manufacturing, the upper limit value of conditional expression (1) can be set to 0.2. In order to further suppress the error sensitivity in manufacturing, the lower limit value of conditional expression (1) can be set to 0.01.

  Further, as shown in FIG. 1, in the diffractive optical element 10 of the present embodiment, in the first optical member 11, the approximate radius of the phase mismatch portion of the peak of the first diffractive optical surface 13 is set to r1, and the first diffractive optical element 10 is used. When the height of the cliff of the surface 13 is h, the condition of the following equation (2) may be satisfied.

  r1 / h <0.6 (2)

  Conditional expression (2) appropriately defines the ratio between the approximate radius r1 of the phase mismatch portion of the peak of the first diffractive optical surface 13 and the height h of the cliff in the first optical member 11. Here, the approximate radius r1 of the phase mismatch portion of the mountain is assumed to be obtained by the least square method when the shape is irregular. In addition, the height h of the cliff refers to the distance (the length along the first diffractive optical surface 13) from the top of the adjacent mountain (vertex A) to the bottom of the valley (vertex B). Therefore, when the cliff is formed to be inclined with respect to the optical axis, the direction of the height h of the cliff is inclined with respect to the optical axis. In order to prevent a decrease in diffraction efficiency in the diffractive optical element, it is preferable that the peaks of the first optical member 11 are sharp. However, exceeding the upper limit value of conditional expression (2) is not preferable because the sharpness of the peaks of the first optical member 11 becomes dull and the reduction in diffraction efficiency increases. In addition, in order to fully demonstrate the effect of this embodiment, the upper limit of conditional expression (2) can be set to 0.25.

  Further, in the diffractive optical element 10 of the present embodiment, as shown in FIG. 1, the minimum value of the grating pitch of the first diffractive optical surface 13 is p, the thickness along the optical axis of the first optical member 13 and the first Of the thicknesses along the optical axis of the two optical members 12, the smaller thickness is d (in FIG. 1, for the sake of explanation, the thickness along the optical axis of the second optical member 12 is shown as d. The condition of the following equation (3) may be satisfied.

  p / d> 0.03 (3)

  Conditional expression (3) appropriately defines the ratio between the minimum grating pitch p of the first optical member 11 and the thickness d of the two optical members 11 and 12 having the smaller thickness along the optical axis. To do. If the lower limit value of conditional expression (3) is not reached, the minimum grating pitch p becomes too fine, which not only lowers the diffraction efficiency, but also makes it difficult to manufacture, and the tip diameter is the same. However, the reduction in the diffraction efficiency when cutting is increased. In addition, in order to fully demonstrate the effect of this embodiment, the lower limit of conditional expression (3) can be set to 0.05. Moreover, in order to fully demonstrate the effect of this embodiment, the lower limit value of conditional expression (3) can be set to 0.10.

  Further, in the diffractive optical element 10 of the present embodiment, the difference in refractive index at the C line between the first optical material and the second optical material is ΔnC, and the refractive index at the F line between the first optical material and the second optical material. If the difference of ΔnF is ΔnF, the condition of the following equation (4) may be satisfied.

  ΔnF−ΔnC <0 (4)

  The above conditional expression (4) is that the diffractive optical element 10 is configured when the design center wavelength is d-line, the C-line is set as the long-wavelength side beam, and the F-line is set as the short-wavelength beam. An appropriate magnitude relationship between the refractive index difference ΔnC on the long wavelength side of the first optical material and the second optical material and the refractive index difference ΔnF on the short wavelength side is defined. Since the optical path difference (cliff height × refractive index difference) of the light passing through the diffractive optical surface is proportional to each wavelength, satisfying conditional expression (4) is sufficiently high diffraction efficiency over a wide wavelength band. It is a condition for obtaining. In addition, when the conditional expression (4) is not satisfied, the diffraction efficiency on the long wavelength side and the short wavelength side is significantly reduced, and sufficient optical performance cannot be obtained.

  Further, in the diffractive optical element 10 of the present embodiment, the diffraction efficiency at the d-line with respect to the light ray incident along the height direction of the cliff of the first diffractive optical surface 13 is Ed, and the diffraction efficiency at the g-line is Eg. When the diffraction efficiency at the C-line is EC, the condition of the following equation (5) may be satisfied.

  (Eg + EC) / (2 × Ed)> 0.80 (5)

  Conditional expression (5) defines an appropriate range for the balance of diffraction efficiency with respect to the used light having a wide wavelength range. When falling below the lower limit value of the conditional expression (5), at least one of the g-line having a relatively short wavelength and the C-line having a long wavelength with respect to the d-line that is the dominant wavelength (design center wavelength). The diffraction efficiency is too low at the wavelength, the diffraction flare becomes large, and the image quality is impaired. That is, light having a wavelength or angle of view other than the blazed light becomes unnecessary diffracted light, and the occurrence of flare increases, so that good image quality cannot be obtained. In order to secure the effect of conditional expression (5), the lower limit can be set to 0.90. Moreover, the upper limit of conditional expression (5) can be set to 0.95 according to the use of a diffractive optical element. The calculation of diffraction efficiency is based on the RCWA method (strict coupling wave analysis) described above. In the present embodiment, the blazing is performed with respect to the d line. However, the present invention is not limited to this, and the blazing may be performed with respect to other wavelengths.

  In the diffractive optical element 10 of the present embodiment, the difference in refractive index at the d-line between the first optical material and the second optical material is Δnd, and the main dispersion (nF−) between the first optical material and the second optical material. When the difference of nC) is Δ (nF−nC), the condition of the following equation (6) may be satisfied.

  −20.0 <Δnd / Δ (nF−nC) <− 2.0 (6)

  The conditional expression (6) is an appropriate value between the refractive index difference Δnd of the first optical material and the second optical material constituting the diffractive optical element 10 and the difference Δ (nF−nC) of the main dispersion. Define the relationship. Conditional expression (6) is an important condition for obtaining a high diffraction efficiency over a wide wavelength region in the multi-contact diffractive optical element as in the present embodiment. If it deviates from the range of the conditional expression (6), high diffraction efficiency over the entire use wavelength range cannot be obtained, and there is a disadvantage that the light use efficiency is lowered. In addition, in order to fully exhibit the effect of the conditional expression (6), the upper limit value can be set to −3.5. Moreover, in order to fully exhibit the effect of the conditional expression (6), the lower limit value can be set to −10.0.

  3A and 3B, when the diffractive optical element 10 of the present embodiment is disposed in the optical system 1 having the diaphragm S, the first optical member 11 is located on the diaphragm S side. It may be arranged. 3A shows a case where the diffractive optical element 10 is arranged on the image plane I side from the stop S, and FIG. 3B shows a case where the diffractive optical element 10 is arranged on the object side from the stop S. Show. With such a configuration, it is possible to obtain the effects of reducing flare and increasing the diffraction efficiency of blazed light. Note that the diffractive optical element of the present embodiment is preferably applied to an optical system having a front diaphragm such as a laser scanning optical system.

  In the diffractive optical element 10 of the present embodiment, the cliff of the first diffractive optical surface 13 may be formed to be inclined with respect to the optical axis, and the inclination may be such that the center of the surface is smaller than the periphery of the surface. Or you may make it the inclination the surface center part become larger than a surface peripheral part. More specifically, as shown in FIGS. 4A and 4B, the cliff of the diffractive optical surface 13 is inclined toward the center of the pupil (incidence pupil or exit pupil), that is, substantially follows the principal ray. To give a tilt. In FIG. 4, (a) shows a case where an inclination is given toward the center of the entrance pupil, and (b) shows a case where an inclination is given so as to be emitted from the center of the exit pupil. In FIG. 4, the cliff is emphasized to make the inclination easier to understand. According to this configuration, the scattering by the cliff of the diffractive optical surface 13 and the decrease in the diffraction efficiency of the blazed light can be reduced. Furthermore, such a tilt is preferable because a resin molding method using a mold can be used as a method for forming the diffractive optical element, which increases productivity and reduces costs.

  Further, in the diffractive optical element 10 of this embodiment, in the region where the grating pitch of the first diffractive optical surface 13 is minimum, the cross-sectional area of the phase mismatched portion of the valley of the first diffractive optical surface 13 is ΔSL, and the phase error If the sectional area of one lattice when there is no matching portion is ΔSA, the condition of the following equation (7) may be satisfied (see FIG. 2).

  ΔSL / ΔSA ≦ 0.06 (7)

  Conditional expression (7) has a cross-sectional area (area of the cross section including the optical axis) ΔSL of the valley phase mismatch portion of the first diffractive optical surface 13 and no peak phase mismatch portion (that is, an ideal shape). ) To define an appropriate relationship with the cross-sectional area ΔSA for one lattice. If the upper limit value of the conditional expression (7) is exceeded, the diffraction efficiency is drastically lowered, and flare due to high-order diffracted light becomes large. In addition, in order to fully exhibit the effect of the conditional expression (7), the upper limit value can be set to 0.05.

  In the diffractive optical element 10 of the present embodiment, in the first optical member 11, the cross-sectional area of the phase mismatch portion of the peak of the first diffractive optical surface 13 is ΔSH, and the cross-sectional area of the phase mismatch portion of the valley is ΔSL. In this case, the condition of the following expression (8) may be satisfied (see FIG. 1).

  ΔSH / ΔSL <0.9 (8)

  In the first optical member 11, the conditional expression (8) indicates that the cross-sectional area of the phase mismatched portion of the peak (area of the cross section cut by the plane including the optical axis) ΔSH and the cross-sectional area of the phase mismatched portion of the valley ( An appropriate relationship of ΔSL, the cross-sectional area cut by the plane including the optical axis, is defined. In the first optical member 11, the peak phase mismatch portion has higher error sensitivity than the valley phase mismatch portion. For this reason, if it exceeds the upper limit of conditional expression (8), the phase mismatch part of a mountain will become large and the diffraction efficiency of the diffractive optical element 10 will fall. In addition, in order to fully exhibit the effect of the conditional expression (8), the upper limit value can be set to 0.8. Moreover, in order to fully exhibit the effect of the conditional expression (8), the upper limit value can be set to 0.5. Furthermore, in order to sufficiently exhibit the effect of the conditional expression (8), the upper limit value can be set to 0.3.

  Furthermore, in order to achieve better performance and specifications, the following conditional expressions may be satisfied.

  In the diffractive optical element 10 of the present embodiment, when the length of the straight portion of the cliff of the first diffractive optical surface 13 is s and the height of the cliff of the first diffractive optical surface 13 is h, the following equation (9) The condition may be satisfied (see FIG. 1).

  s / h> 0.3 (9)

  Conditional expression (9) defines an optimum ratio between the length s of the straight portion of the first diffractive optical surface 13 and the height h of the cliff. Here, the length s of the straight portion of the cliff region is, as shown in FIG. 1, from the contact point of a circle whose radius is the approximate radius r 2 of the phase mismatch portion of the valley of the first diffractive optical surface 13. The distance (the length along the first diffractive optical surface 13) to the contact point of a circle whose radius is the approximate radius r1 of the phase mismatch portion is assumed. If the lower limit of conditional expression (9) is not reached, the reduction in diffraction efficiency due to the peaks of the first diffractive optical surface 13 becomes too large, which is inconvenient. In addition, in order to fully demonstrate the effect of this embodiment, a lower limit can be 0.5. Furthermore, in order to fully demonstrate the effect of this embodiment, the lower limit can be set to 0.9. Moreover, in order to fully demonstrate the effect of this embodiment, the length s of the straight portion of the cliff can be set to 7.0 μm or more. The straight portion of the cliff has no phase mismatching portion with respect to the wavefront that travels in that direction, and the wavefront in the vicinity of the cliff becomes a smooth plane, so that high diffraction efficiency can be obtained.

  Further, the diffractive optical element 10 of the present embodiment may satisfy the condition of the following formula (10) when the height of the cliff of the first diffractive optical surface 13 is set to the design reference wavelength λ ( (See FIG. 1).

  h / λ <70.0 (10)

  The conditional expression (10) defines an appropriate ratio between the height h of the cliff of the first diffractive optical surface 13 and the design reference wavelength λ. If the upper limit of conditional expression (10) is not reached, the height h of the cliff of the first diffractive optical surface 13 becomes too large, the diffraction efficiency for oblique incident light is reduced, and unnecessary flare light is generated. It is inconvenient. Here, the height h of the cliff is the distance (the length along the first diffractive optical surface 13) from the top of the adjacent mountain (vertex A) to the bottom of the valley (vertex B) shown in FIG. However, the height is not limited to the height in the optical axis direction. The height h of the cliff is usually the height in the optical axis direction, and is the blaze height according to the scalar theory defined by h = (difference in refractive index at the interface where two optical members are in close contact) × (design reference wavelength). In many cases, however, the incident light from a direction different from the optical axis direction does not result in an optimum blaze, and the diffraction efficiency is lowered. For this reason, it is necessary to set the height h of the cliff to the distance (the length along the first diffractive optical surface 13) from the top of the adjacent mountain (vertex A) to the bottom of the valley (vertex B). is there. In addition, in order to fully demonstrate the effect of this embodiment, an upper limit can be set to 40.0.

  In addition, the diffractive optical element 10 of the present embodiment may have a structure that prevents specular reflection and reduces stray light by using the cliff of the first diffractive optical surface 13 as a stepped step or rough surface.

  Further, in the diffractive optical element 10 of this embodiment, the approximate radius of the phase mismatch portion of the peak of the first diffractive optical surface 13 is r1, and the length of the straight portion of the cliff of the first diffractive optical surface 13 is s. At this time, the condition of the following expression (11) may be satisfied (see FIG. 1).

  r1 / s <1.0 (11)

  The conditional expression (11) defines an appropriate ratio of the approximate radius r1 (the so-called approximate radius of the edge portion) of the mountain phase mismatch portion of the first diffractive optical surface 13 and the length s of the straight portion of the cliff. . If the upper limit value of the conditional expression (11) is exceeded, the approximate radius r1 of the phase mismatch portion of the peak of the first diffractive optical surface 13 becomes too large, and the diffraction efficiency of the diffracted light of the order that forms a desired image is formed. In addition, the diffracted light of unnecessary order is generated, resulting in harmful flare. In addition, in order to fully demonstrate the effect of this embodiment, an upper limit can be 0.3.

  Further, in the diffractive optical element 10 of the present embodiment, the minimum value of the grating pitch of the first diffractive optical surface 13 is set to p and the cliff of the first diffractive optical surface 13 is formed in order to facilitate processing and prevent a decrease in diffraction efficiency. If the height of h is h, the condition of the following equation (12) may be satisfied (see FIG. 2).

  p / h> 0.4 (12)

  Furthermore, when the diffractive optical element 10 is actually configured, the following requirements may be satisfied.

  In the diffractive optical element 10 of the present embodiment, the material constituting the two optical members 11 and 12 has a viscosity (uncured product viscosity) of the optical material in order to maintain good moldability and ensure excellent mass productivity. May be 5 mPa · s or more and 50000 mPa · s or less. When a resin having a viscosity of 5 mPa · s or less is used as the optical material, the resin easily flows during molding, and workability may be deteriorated. In addition, when a resin of 50000 mPa · s or more is used, the resin is difficult to flow and workability is deteriorated, and bubbles are easily mixed. In addition, in order to fully demonstrate the effect of this embodiment, a lower limit can be 40 mPa * s. Furthermore, in order to fully exhibit the effect of the present embodiment, the lower limit value can be set to 2000 mPa · s.

  Further, in the diffractive optical element 10 of the present embodiment, the optical materials constituting the two optical members 11 and 12 may both be UV curable resins. This configuration is preferable because production efficiency is improved. In addition, the number of man-hours can be reduced, leading to cost reduction.

  In the diffractive optical element 10 of the present embodiment, the optical material constituting the two optical members 11 and 12 may be a resin material having a specific gravity of 2.0 or less. This is effective in reducing the weight of the optical system 1 having the diffractive optical element 10 because the specific gravity of the resin is smaller than that of glass. In addition, in order to exhibit the effect more fully, it can be set as the resin material whose specific gravity is 1.6 or less.

  Further, the diffractive optical element 10 of the present embodiment is not necessarily formed on a flat surface, and may be formed on a spherical surface or an aspherical surface of a lens or a mirror. In such a case, it can be approximated as a flat diffractive optical surface in the vicinity of the target diffractive optical surface.

  An optical system composed of a plurality of components obtained by incorporating the diffractive optical element 10 of the present embodiment does not depart from the scope of the present embodiment. The same applies to an optical system obtained by incorporating a gradient index lens, a crystal material lens, or the like.

  The diffractive optical element 10 (see FIG. 1) according to the first to fourth examples will be described below. The table of FIG. 11 shows [optical material data] and [constituent conditions and values corresponding to conditional expressions] in the respective examples.

  [Optical material data] shows the refractive indexes of two materials constituting the optical members 11 and 12, that is, the first optical material having a high refractive index and low dispersion and the second optical material having a low refractive index and high dispersion. Here, nd is the refractive index for the d-line (wavelength 587.562 nm), nC is the refractive index for the C-line (wavelength 656.273 nm), nF is the refractive index for the F-line (wavelength 486.133 nm), and ng is the g-line (wavelength). Refractive index for 435.835 nm) is shown respectively. Further, in each embodiment, the materials constituting the optical members 11 and 12 are common, and as shown in the table of FIG. 11, the first optical material having a high refractive index and low dispersion is d-line, C-line, F-line, A material having a refractive index of 1.5569, 1.5537, 1.5648, and 1.5711 for the g-line, and a refractive index of 1.5276, 1.5233, d-line, C-line, F-line, and g-line, respectively, as the second optical material having a low refractive index and high dispersion. The materials 1.5385 and 1.5477 were used, respectively.

  In [Configuration Condition and Conditional Expression Corresponding Value], the configuration condition of the diffractive optical element 10 and the value corresponding to the conditional expressions (1) to (12) are shown (however, the incident direction of light is the second optical member). The calculation was made assuming that the direction from the 12th side toward the first optical member 11 side). Here, h is the height of the cliff of the first diffractive optical surface 13 (unit: [μm]), α is the slope of the cliff with respect to the optical axis (unit: [°]), and d is the light of the first optical member 11. The smaller one of the thickness along the axis and the thickness along the optical axis of the second optical member 12 (unit: [μm]), p is the minimum of the grating pitch of the first diffractive optical surface 13 The value (unit: [μm]), r1 is the approximate radius of the phase mismatch portion of the peak of the first diffractive optical surface 13, and r2 is the approximate radius of the phase mismatch portion of the valley of the first diffractive optical surface 13. Show.

(First embodiment)
In the diffractive optical element 10 according to the first example, as shown in the table of FIG. 11, the first optical material having a high refractive index and low dispersion (the refractive indexes of the d-line, C-line, F-line, and g-line are 1.5569, respectively. 1.5537, 1.5648, 1.5711) and a second optical material having a low refractive index and high dispersion (the refractive indices of d-line, C-line, F-line, and g-line are 1.5276, 1.5233, 1.5385, and 1.5477, respectively) The height h of the cliff of the first diffractive optical surface 13 is 20 μm, the slope α of the cliff of the first diffractive optical surface 13 is 5 °, the thickness along the optical axis of the first optical member 11 and the second optical member 12. The thickness d of the thinner one of the thicknesses along the optical axis was set to 100 μm, and the minimum value p of the grating pitch of the first diffractive optical surface 13 was set to 50 [μm]. Based on such a configuration condition, the combination of the approximate radius r1 of the peak phase mismatch portion of the first diffractive optical surface 13 and the approximate radius r2 of the valley phase mismatch portion is (r1, r2) = ( The cases of (0, 0), (0.2, 1), (0.2, 5), (0.2, 10) were examined.

  In the case of (r1, r2) = (0.2,10), an example in which the conditional expression (7) ΔSL / ΔSA ≦ 0.06 (ΔSL / ΔSA = 0.09 in this embodiment) was not satisfied (comparative example) It is posted as.

  From the table of FIG. 11, in the diffractive optical element 10 according to the first example, the above conditional expression is obtained when (r1, r2) = (0, 0), (0.2, 1), (0.2, 5). It can be seen that (1) to (12) are all satisfied.

  FIG. 5 is a diagram showing the diffraction efficiency when the angle of the incident light beam is changed between −40 degrees and 20 degrees in the diffractive optical element 10 according to the first example, and FIG. In the case of d-line, (b) shows the diffraction efficiency when the incident light is C-line, (c) shows the diffraction efficiency when the incident light is F-line, and (d) shows the diffraction efficiency when the incident light is g-line. 5A to 5D, the incident angle of incident light is positive in the counterclockwise direction with respect to the optical axis and negative in the clockwise direction. 5A to 5D, the combination of the approximate radius r1 of the peak phase mismatch portion of the first diffractive optical surface 13 and the approximate radius r2 of the valley phase mismatch portion is (r1, r2). = (0, 0) is a solid line, (r1, r2) = (0.2, 1) is a dotted line, (r1, r2) = (0.2, 5) is a dashed line, (r1, The case of r2) = (0.2,10) is indicated by a two-dot chain line.

  5A to 5D, in the diffractive optical element 10 of the first example, the cases of (r1, r2) = (0, 0), (0.2, 1), (0.2, 5) It was found that high diffraction efficiency (diffracted light intensity) can be obtained over a wide wavelength region from g-line to d-line. In particular, it was found that high diffraction efficiency can be obtained when the slope of the cliff of the first diffractive optical surface 13 and the incident angle of the incident light beam substantially coincide. Further, it was found that when the conditional expression (7) ΔSL / ΔSA ≦ 0.06 cannot be satisfied as in the case of (r1, r2) = (0.2, 10), the diffraction efficiency is deteriorated.

(Second embodiment)
In the diffractive optical element 10 according to the second example, as shown in the table of FIG. 11, the first optical material having a high refractive index and low dispersion (the refractive indexes of the d-line, C-line, F-line, and g-line are 1.5569, respectively. 1.5537, 1.5648, 1.5711) and a second optical material having a low refractive index and high dispersion (the refractive indices of d-line, C-line, F-line, and g-line are 1.5276, 1.5233, 1.5385, and 1.5477, respectively) The height h of the cliff of the first diffractive optical surface 13 is 20 μm, the slope α of the cliff of the first diffractive optical surface 13 is 10 °, the thickness along the optical axis of the first optical member 11 and the second optical member 12. The thickness d of the thinner one along the optical axis was set to 200 μm, and the minimum value p of the grating pitch of the first diffractive optical surface 13 was set to 50 [μm]. Based on such a configuration condition, the combination of the approximate radius r1 of the peak phase mismatch portion of the first diffractive optical surface 13 and the approximate radius r2 of the valley phase mismatch portion is (r1, r2) = ( The cases of (0, 0), (0.2, 1), (0.2, 5), (0.2, 10) were examined.

  In the case of (r1, r2) = (0.2,10), an example in which the conditional expression (7) ΔSL / ΔSA ≦ 0.06 (ΔSL / ΔSA = 0.07 in this embodiment) was not satisfied (comparative example) It is posted as.

  From the table of FIG. 11, in the diffractive optical element 10 according to the second embodiment, the above conditional expression is obtained when (r1, r2) = (0, 0), (0.2, 1), (0.2, 5). It can be seen that (1) to (12) are all satisfied.

  FIG. 6 is a diagram showing diffraction efficiency when the angle of incident light is changed between −45 degrees and 15 degrees in the diffractive optical element 10 according to the second example, and FIG. In the case of d-line, (b) shows the diffraction efficiency when the incident light is C-line, (c) shows the diffraction efficiency when the incident light is F-line, and (d) shows the diffraction efficiency when the incident light is g-line. 6A to 6D, the incident angle of incident light is positive in the counterclockwise direction with respect to the optical axis and negative in the clockwise direction. 6A to 6D, the combination of the approximate radius r1 of the peak phase mismatched portion of the first diffractive optical surface 13 and the approximate radius r2 of the phase mismatched portion of the valley is (r1, r2). = (0, 0) is a solid line, (r1, r2) = (0.2, 1) is a dotted line, (r1, r2) = (0.2, 5) is a dashed line, (r1, The case of r2) = (0.2,10) is indicated by a two-dot chain line.

  6 (a) to 6 (d), in the diffractive optical element 10 of the second embodiment, the case of (r1, r2) = (0, 0), (0.2, 1), (0.2, 5) It was found that high diffraction efficiency (diffracted light intensity) can be obtained over a wide wavelength region from g-line to d-line. In particular, it was found that high diffraction efficiency can be obtained when the slope of the cliff of the first diffractive optical surface 13 and the incident angle of the incident light beam substantially coincide. Further, it was found that when the conditional expression (7) ΔSL / ΔSA ≦ 0.06 cannot be satisfied as in the case of (r1, r2) = (0.2, 10), the diffraction efficiency is deteriorated.

(Third embodiment)
In the diffractive optical element 10 according to the third example, as shown in the table of FIG. 11, the first optical material having a high refractive index and low dispersion (the refractive indexes of the d-line, C-line, F-line, and g-line are 1.5569, respectively. 1.5537, 1.5648, 1.5711) and a second optical material having a low refractive index and high dispersion (the refractive indices of d-line, C-line, F-line, and g-line are 1.5276, 1.5233, 1.5385, and 1.5477, respectively) The height h of the cliff of the first diffractive optical surface 13 is 20 μm, the slope α of the cliff of the first diffractive optical surface 13 is 0 °, the thickness along the optical axis of the first optical member 11, and the second optical member 12. The thickness d of the thinner one along the optical axis was set to 300 μm, and the minimum value p of the grating pitch of the first diffractive optical surface 13 was set to 20 [μm]. Based on such a configuration condition, the combination of the approximate radius r1 of the peak phase mismatch portion of the first diffractive optical surface 13 and the approximate radius r2 of the valley phase mismatch portion is (r1, r2) = ( The cases of (0, 0), (0.2, 1), (0.2, 3), (0.2, 5) were examined.

  In the case of (r1, r2) = (0.2, 5), an example in which the conditional expression (7) ΔSL / ΔSA ≦ 0.06 (ΔSL / ΔSA = 0.15 in this embodiment) was not satisfied (comparative example) It is posted as.

  From the table of FIG. 11, in the diffractive optical element 10 according to the third example, the above conditional expression is obtained when (r1, r2) = (0, 0), (0.2, 1), (0.2, 3). It can be seen that (1) to (12) are all satisfied.

  FIG. 7 is a diagram showing diffraction efficiency when the angle of the incident light beam is changed between −20 degrees and 20 degrees in the diffractive optical element 10 according to the third example. In the case of d-line, (b) shows the diffraction efficiency when the incident light is C-line, (c) shows the diffraction efficiency when the incident light is F-line, and (d) shows the diffraction efficiency when the incident light is g-line. In FIGS. 7A to 7D, the incident angle of incident light is positive in the counterclockwise direction and negative in the clockwise direction with respect to the optical axis. 7A to 7D, the combination of the approximate radius r1 of the peak phase mismatched portion of the first diffractive optical surface 13 and the approximate radius r2 of the valley phase mismatched portion is (r1, r2). = (0, 0) is a solid line, (r1, r2) = (0.2, 1) is a dotted line, (r1, r2) = (0.2, 3) is a dashed line, (r1, The case of r2) = (0.2,5) is indicated by a two-dot chain line.

  7A to 7D, in the diffractive optical element 10 according to the third example, the case of (r1, r2) = (0, 0), (0.2, 1), (0.2, 3) is used. It was found that high diffraction efficiency (diffracted light intensity) can be obtained over a wide wavelength region from g-line to d-line. In particular, it was found that high diffraction efficiency can be obtained when the slope of the cliff of the first diffractive optical surface 13 and the incident angle of the incident light beam substantially coincide. Further, it was found that when the conditional expression (7) ΔSL / ΔSA ≦ 0.06 cannot be satisfied as in the case of (r1, r2) = (0.2, 5), the diffraction efficiency is deteriorated.

(Fourth embodiment)
In the diffractive optical element 10 according to the fourth example, as shown in the table of FIG. 11, the first optical material having a high refractive index and low dispersion (the refractive indexes of the d-line, C-line, F-line, and g-line are 1.5569, respectively. 1.5537, 1.5648, 1.5711) and a second optical material having a low refractive index and high dispersion (the refractive indices of d-line, C-line, F-line, and g-line are 1.5276, 1.5233, 1.5385, and 1.5477, respectively) The height h of the cliff of the first diffractive optical surface 13 is 20 μm, the slope α of the cliff of the first diffractive optical surface 13 is 5 °, the thickness along the optical axis of the first optical member 11 and the second optical member 12. The thickness d of the thinner one along the optical axis was set to 60 μm, and the minimum value p of the grating pitch of the first diffractive optical surface 13 was set to 50 [μm]. Based on such a configuration condition, the combination of the approximate radius r1 of the peak phase mismatch portion of the first diffractive optical surface 13 and the approximate radius r2 of the valley phase mismatch portion is (r1, r2) = ( The cases of (0, 0), (2.75, 5), (3.53, 5), (4.47, 5) were examined.

  From the table in FIG. 11, it can be seen that in the diffractive optical element 10 according to the fourth example, all the conditional expressions (1) to (12) are satisfied.

  FIG. 8 is a diagram showing diffraction efficiency when the angle of incident light is changed between −40 degrees and 20 degrees in the diffractive optical element 10 according to the fourth example. FIG. In the case of d-line, (b) shows the diffraction efficiency when the incident light is C-line, (c) shows the diffraction efficiency when the incident light is F-line, and (d) shows the diffraction efficiency when the incident light is g-line. 8A to 8D, the incident angle of incident light is positive in the counterclockwise direction with respect to the optical axis and negative in the clockwise direction. 8A to 8D, the combination of the approximate radius r1 of the peak phase mismatch portion of the first diffractive optical surface 13 and the approximate radius r2 of the valley phase mismatch portion is (r1, r2). = (0, 0) is a solid line, (r1, r2) = (2.75, 5) is a dotted line, (r1, r2) = (3.53, 5) is a dashed line, (r1, The case of r2) = (4.47,5) is indicated by a two-dot chain line.

  8A to 8D, in the diffractive optical element 10 according to the fourth example, high diffraction efficiency (diffracted light intensity) can be obtained over a wide wavelength region from the g-line to the d-line. I understood. In particular, it was found that high diffraction efficiency can be obtained when the slope of the cliff of the first diffractive optical surface 13 and the incident angle of the incident light beam substantially coincide.

  As described above, as can be seen from the first to fourth embodiments, the cross-sectional area of the phase-mismatched portion of the peak (the cross-sectional area cut by the plane including the optical axis) ΔSL of the trough phase-mismatched portion ( High diffraction efficiency can be obtained by configuring the diffractive optical element so that (the area of the cross section cut by a plane including the optical axis) ΔSH becomes smaller. More preferably, higher diffraction efficiency can be obtained by satisfying conditional expression (7) ΔSL / ΔSA ≦ 0.06.

  Next, an optical apparatus using the diffractive optical element of the above embodiment will be briefly described. FIG. 12 is a schematic configuration diagram of a head-mounted display using the diffractive optical element of the above embodiment. The head mounted display is a system that is mounted on a user's head and provides video and audio to the user. The head-mounted head mounting unit 40 and a display unit unit that can be attached to the head mounting unit 40 50 and a playback device 60 that supplies an audio signal and a video signal to the display unit 50 and supplies power to each member.

  The head mounting unit 40 provides a pair of speaker units 41 located in the vicinity of the left and right ears of the user and a biasing force for clamping the user's head via the speaker unit 41 when mounted on the user. The arm portion 42 and an ear hooking member 43 that extends in an arch shape from each of the pair of speaker portions 41 and hooks on the user's ear. Each of the speaker parts 41 has a shape that can be fitted to the coupling part 51 of the display unit part 50, and an electrical contact 44 with the display unit part 50 is provided on the outside. When the display unit unit 50 is not attached to the speaker unit 41, the dummy cap 55 is attached to improve the appearance.

  Next, the display unit unit 50 includes a coupling unit 51 that can be fitted to the outside of the speaker unit 41, a storage unit 52 that includes a space that is attached to the coupling unit 51 and stores a display arm 53 described later, and a storage unit. The display arm 53 can be stored in and pulled out from the display 52, and a display arm 53 to which a display unit 54 incorporating the liquid crystal display element, the diffractive optical element 10 of the above-described embodiment, or the like is attached. The display unit unit 50 is connected to the playback device unit 60, supplies power and video signals supplied from the playback device unit 60 to the display unit 54, and supplies audio signals to the combining unit 51. Wiring is built in.

  The coupling unit 51 has an electrical contact (not shown) that can be connected to the electrical contact 44 of the speaker unit 41, and supplies an audio signal to the speaker unit 41 through this electrical contact (not shown).

  The display arm 53 can be stored in the storage unit 52 as described above. When the head mounted display is mounted, the display arm 53 is removed from the storage unit 52 so that the display unit 54 is positioned in front of the user's eyes. Extend and use. Further, when not attached, the display arm 53 can be stored in the storage portion 52.

  As shown in FIG. 12, the display unit 54 is supported by a cantilever structure with a display arm 53. The optical system provided in the display unit 54 includes a liquid crystal display element, a diffractive optical element 10 that forms a virtual image of an image of the liquid crystal display element, a backlight that illuminates the liquid crystal display element, and a backlight light. An illumination optical element that diffuses light. In the illumination optical element, the backlight side is a lens surface for condensing the light of the backlight, and the liquid crystal display element side is a diffusing surface in the form of a ground glass or a microlens array. The illumination distribution of the element is made uniform. The lens surface may be a Fresnel lens shape.

  Here, the diffractive optical element 10 has both a condensing action and a diffractive action by a refracting action, and cancels chromatic aberration caused by the refracting action by the diffractive action. Therefore, even when a full color image is projected using the eyepiece lens of the head mounted display as described above, a high quality image can be provided to the user.

  In the above embodiment, the head mounted display is shown as an example of the optical device, but the optical device using the diffractive optical element of the present embodiment is not limited to these, and the other is not deviated from the gist of the invention. It can be applied to various optical systems and optical devices (for example, microscopes, binoculars, telescopes, cameras, projectors, etc.), and good optical performance can be obtained.

  In addition, in order to make the present invention easy to understand, the configuration requirements of the embodiment have been described as described above, but it goes without saying that the present invention is not limited to this.

FIG. 5 is a diagram for illustrating a cross-sectional configuration of the diffractive optical element according to the present embodiment and for explaining a cross-sectional area ΔSL of a trough phase mismatch portion and a cross-sectional area ΔSH of a crest phase mismatch portion in the first diffractive optical surface. . While showing the cross-sectional structure of the diffractive optical element according to the present embodiment, the cross-sectional area ΔSL of the phase mismatched portion of the valley on the first diffractive optical surface and the cross-sectional area ΔSA of one grating when there is no phase mismatched portion It is a figure for demonstrating. It is a figure for demonstrating the optical system which concerns on this embodiment, (a) is a case where a diffractive optical element is arrange | positioned on the image side with respect to a stop, (b) is a diffractive optical element on the object side with respect to a stop. Each case is shown. It is a figure for demonstrating the inclination of the cliff of the diffractive optical element which concerns on this embodiment, (a) gives inclination with respect to the center of an entrance pupil, (b) is inclination with respect to the center of an exit pupil Are given respectively. In the diffractive optical element according to the first embodiment, it is a diagram showing the diffraction efficiency when the angle of the incident light is changed between -40 degrees and 20 degrees, (a) when the incident light is a d-line, (B) shows the case where the incident light is C-line, (c) shows the case where the incident light is F-line, and (d) shows the case where the incident light is g-line. In the diffractive optical element according to the second embodiment, it is a diagram showing the diffraction efficiency when the angle of incident light is changed between -45 degrees and 15 degrees, (a) when the incident light is a d-line, (B) shows the case where the incident light is C-line, (c) shows the case where the incident light is F-line, and (d) shows the case where the incident light is g-line. In the diffractive optical element according to the third example, it is a diagram showing the diffraction efficiency when the angle of the incident light is changed between -20 degrees and 20 degrees, (a) when the incident light is d-line, (B) shows the case where the incident light is C-line, (c) shows the case where the incident light is F-line, and (d) shows the case where the incident light is g-line. In the diffractive optical element according to the fourth example, it is a diagram showing the diffraction efficiency when the angle of the incident light is changed between -40 degrees ~ 20 degrees, (a) when the incident light is d-line, (B) shows the case where the incident light is C-line, (c) shows the case where the incident light is F-line, and (d) shows the case where the incident light is g-line. It is a figure explaining a phase mismatching part. It is a schematic cross-sectional view of a multilayer diffractive optical element, (a) is a schematic cross-sectional view of a separated multi-layer diffractive optical element, and (b) is a schematic cross-sectional view of a contact multilayer diffractive optical element. is there. It is a table | surface which shows [Optical material data] and [Structural condition and conditional expression corresponding value] in each Example. It is a schematic block diagram of the head mounted display using the said diffractive optical element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical system 10 Diffractive optical element 11 1st optical member 12 2nd optical member 13 1st diffractive optical surface 14 2nd diffractive optical surface

Claims (13)

A first optical member having a first diffractive optical surface; and a second optical member having a second diffractive optical surface disposed so as to contact the first diffractive optical surface;
The refractive index of the first optical material constituting the first optical member is higher than the refractive index of the second optical material constituting the second optical member,
In the first optical member, the cross-sectional area of the phase mismatch portion of the peak of the first diffractive optical surface is smaller than the cross-sectional area of the phase mismatch portion of the valley of the first diffractive optical surface. element. In the first optical member, when the approximate radius of the phase mismatch portion of the peak of the first diffractive optical surface is r1, and the height of the cliff of the first diffractive optical surface is h, the following formula r1 / h < 0.6
The diffractive optical element according to claim 1, wherein the following condition is satisfied. The minimum value of the grating pitch of the first diffractive optical surface is p, and the smaller one of the thickness along the optical axis of the first optical member and the thickness along the optical axis of the second optical member. Where d is the following formula: p / d> 0.03
The diffractive optical element according to claim 1, wherein the following condition is satisfied. When the difference in refractive index at the C line between the first optical material and the second optical material is ΔnC, and the difference in refractive index at the F line between the first optical material and the second optical material is ΔnF, ΔnF−ΔnC <0
The diffractive optical element according to claim 1, wherein the following condition is satisfied. With respect to light incident along the height direction of the cliff of the first diffractive optical surface, the diffraction efficiency at the d-line is Ed, the diffraction efficiency at the g-line is Eg, and the diffraction efficiency at the C-line is EC. Then, the following formula (Eg + EC) / (2 × Ed)> 0.80
The diffractive optical element according to claim 1, wherein the following condition is satisfied. The difference in refractive index at the d-line between the first optical material and the second optical material is denoted by Δnd, and the difference in main dispersion (nF−nC) between the first optical material and the second optical material is denoted by Δ (nF −nC), the following formula −20.0 <Δnd / Δ (nF−nC) <− 2.0
The diffractive optical element according to claim 1, wherein the following condition is satisfied. The cliff of the first diffractive optical surface is formed inclined with respect to the optical axis,
The diffractive optical element according to claim 1, wherein the inclination is smaller in the center of the surface than in the periphery of the surface. The cliff of the first diffractive optical surface is formed inclined with respect to the optical axis,
The diffractive optical element according to any one of claims 1 to 6, wherein the inclination is greater in the center of the surface than in the periphery of the surface. In the region where the grating pitch of the first diffractive optical surface is the smallest, the cross-sectional area of the phase mismatched portion of the valley of the first diffractive optical surface is ΔSL, and the section corresponding to one grating when there is no phase mismatched portion When the area is ΔSA, the following formula ΔSL / ΔSA ≦ 0.06
The diffractive optical element according to claim 1, wherein the following condition is satisfied. In the first optical member, when the cross-sectional area of the phase mismatching portion of the peak of the first diffractive optical surface is ΔSH and the cross-sectional area of the phase mismatching portion of the valley is ΔSL, the following expression ΔSH / ΔSL <0. 9
The diffractive optical element according to claim 1, wherein the following condition is satisfied.   An optical system comprising the diffractive optical element according to claim 1. The diffractive optical element and a diaphragm;
The optical system according to claim 11, wherein the first optical member is disposed on the diaphragm side.   An optical apparatus comprising the diffractive optical element according to claim 1.

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