JP6536718B2 - Method of designing optical material of diffractive optical element and method of manufacturing diffractive optical element - Google Patents

Description

  The present invention relates to an optical material used for a diffractive optical element.

Diffractive optical elements (DOEs) are often used in optical instruments because they can obtain predetermined optical characteristics while being thin. As an example, a contact multi-layer diffractive optical element configured by laminating a low refractive index high dispersion optical material and a high refractive index low dispersion optical material with a diffraction grating groove is used. In the adhesive multilayer type diffractive optical element, the larger the difference between the refractive index and the dispersion value of the low refractive index / high dispersion optical material constituting this and the high refractive index / low dispersion optical material, the more the diffractive optical element It is easy to get the performance as Therefore, there is a demand for an optical material in which the difference in refractive index and the difference in dispersion value are large. In order to increase the difference between the refractive index and the dispersion value, it has been proposed to use a resin in which inorganic fine particles are dispersed as an optical material (see, for example, Patent Document 1).

JP, 2006-342254, A

  However, it is difficult to completely disperse inorganic fine particles in a resin composition completely, and it is difficult to stably mold a diffractive optical element using a resin in which inorganic fine particles are dispersed.

  The present invention has been made in view of such problems, and it is a diffractive optical element formed of an optical material using a resin component made of an organic compound without using an inorganic fine particle dispersion type resin. Finding a combination of low refractive index, high dispersion optical material and high refractive index, low dispersion optical material with excellent performance as an optical grating, and high performance diffractive optics using the combination of optical materials found The task is to obtain an element.

An optical material design method for a diffractive optical element that solves the above-mentioned problems comprises a first optical material having a low refractive index and a high dispersion, and a first optical material having a high refractive index and a low dispersion. 2. A method of designing an optical material of a contact multi-layer type diffractive optical element comprising a plurality of optical materials and a grating groove provided and stacked, wherein the wavelength of light for which the diffractive optical element is used is λ [nm] The lower limit of the wavelength is λ1 nm, the upper limit of the wavelength is λ2 nm, and the difference in refractive index between the first optical material and the second optical material as candidates for use in the diffractive optical element is Assuming that n ₂₁ (λ) is a function indicating the spectral sensitivity characteristic of the image sensor standardized to have a maximum value of 1 as g (λ), the condition represented by the equation (3) described later is satisfied. To determine whether or not to be selected, and the above-mentioned An optical material and the second optical material, so as to determine an optical material that can be used for the diffractive optical element.

The manufacturing method of the diffractive optical element which solves the above-mentioned subject is the 1st optical material of low refractive index and high dispersion, and the second optical of high refractive index and low dispersion, each of which is mainly composed of resin consisting of organic compound and does not contain inorganic fine particles. It is a manufacturing method of a contact multi-layer type diffractive optical element constituted by laminating a material and a diffraction grating groove provided, wherein the wavelength of light for which the diffractive optical element is used is λ [nm], and the wavelength And the upper limit of the wavelength is λ2 nm, and the difference in refractive index between the candidate first optical material and the second optical material used for the diffractive optical element is n ₂₁ (λ Whether or not the condition represented by the equation (3) described later is satisfied, where g (λ) is a function that indicates the spectral sensitivity characteristic of the image sensor normalized so that the maximum value is 1. And the first optical material of the candidate that satisfies the condition and The serial second optical material, includes determining an optical material that can be used for the diffractive optical element.

It is a graph of the grating height and the amount of flares which are obtained according to the combination of the optical material of a diffractive optical element. FIG. 2 is a cross-sectional view showing a configuration of a contact multi-layer type diffractive optical element. FIG. 2 is a cross-sectional view of a lens configured to include a contact multi-layer diffractive optical element. (A) is a graph showing the relationship between the flare ratio and the wavelength in the diffractive optical element of which the blaze wavelength is d-line, and (a) shows the relationship between the flare ratio and the wavelength in the diffractive optical element of which e-line is blazed It is a graph. (A) is a graph showing the relationship between the wave front step difference and the wavelength in the diffractive optical element of which the blaze wavelength is d line, and (a) shows the relationship between the wave front step difference and the wavelength in the diffractive optical element of which the blaze wavelength is e line It is a graph. It is a graph which shows the relationship between a refractive index difference and a wavelength. It is a graph which shows the relationship between a flare ratio and a wavelength. It is a graph which shows the relationship between the flare ratio and the wavelength according to the change of grating | lattice height. It is a graph which shows the relationship between the amount of flares, and lattice height. It is a flowchart which shows the optical material design method of a diffractive optical element. It is a graph which shows a relative visibility curve. It is a figure which shows the imaging device using a diffractive optical element.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. First, an example of the diffractive optical element (DOE) of the present embodiment and an optical lens using the same will be described. FIG. 2 shows the structure (cross-sectional structure) of the contact multi-layer diffractive optical element DOE. The diffractive optical element DOE includes a first diffractive optical element 1 made of a first optical material of low refractive index and high dispersion containing an inorganic compound and a resin made of an organic compound as a main component, and a high refractive index and low dispersion first A sawtooth-shaped relief pattern 5 (a groove pattern forming a diffraction grating) is formed between the first and second diffractive optical elements 1 and 2 and is formed of a second diffractive optical element 2 made of two optical materials. .

  FIG. 3 shows an example of an optical lens (hereinafter referred to as a PF lens 10) using the above-described diffractive optical element DOE. The PF lens 10 is configured by sandwiching the diffractive optical element DOE between the first lens element 11 and the second lens element 12. The first and second lens elements 11 and 12 are formed of general glass, resin or the like into a predetermined lens shape.

In the above-described diffractive optical element DOE, the difference in refractive index between the first optical material and the second optical material each containing a resin composed of an organic compound as a main component and containing no inorganic fine particle is n ₂₁ (λ) Assuming that the wavelength of light for which DOE is used is λ (λ1 ≦ λ ≦ λ2) and the predetermined weighting function is g (λ), the condition of the following equation (1) is satisfied.

Formula (1) shows the range of an appropriate combination from the viewpoint of diffraction efficiency in the first optical material and the second optical material defined by the difference in refractive index n ₂₁ (λ), and In the combination with the second optical material, the total flare amount Fm in the case where the total flare amount F is minimized is defined. The value of the total amount of flare Fm = 0.23 as the upper limit value of the equation (1) is a value at which the flare is sufficiently suppressed. However, in some cases, it may be necessary to adjust the grating height in order to realize a flare color (a color of flare generated by diffracted light) according to the application of the optical system on which the diffractive optical element is mounted. By selecting the material so that the first optical material and the second optical material constituting the diffractive optical element satisfy the condition of the equation (1), the grating height is slightly increased in order to adjust the color tone of the flare color. Even when corrected, it is possible to provide a diffractive optical element with excellent diffractive flare imaging performance while minimizing the increase in flare.

In the above-described diffractive optical element DOE, the difference in refractive index between the first optical material and the second optical material each containing a resin composed of an organic compound as a main component and containing no inorganic fine particle is n ₂₁ (λ) Assuming that the wavelength of light for which DOE is used is λ (λ1 ≦ λ ≦ λ2) and the predetermined weighting function is g (λ), the condition of the following equation (2) is satisfied.

Formula (2) shows the range of a proper combination from the viewpoint of the grating height in the first optical material and the second optical material defined by the difference in refractive index n ₂₁ (λ). When the value exceeds the upper limit value of the formula (2), when forming the diffractive optical element DOE, air bubbles are likely to be mixed in when the optical material is spread, so that the forming becomes difficult. In addition, when the mold (molding die) is peeled, chipping or the like of the pattern is likely to occur.

Furthermore, in the above-described diffractive optical element DOE, the difference in refractive index between the first optical material and the second optical material each containing a resin made of an organic compound as a main component and containing no inorganic fine particles is n ₂₁ (λ). Assuming that the wavelength of light for which the optical element DOE is used is λ (λ1 ≦ λ ≦ λ2) and the predetermined weighting function is g (λ), the condition of the following equation (3) is satisfied.

Formula (3) shows the range of a more appropriate combination from the viewpoint of diffraction efficiency in the first optical material and the second optical material defined by the refractive index difference n ₂₁ (λ), and the first optical material In the combination of the second optical material and the second optical material, a further preferable total flare amount Fm is defined when the total flare amount F is minimized.

  The first optical material and the second optical material to be used for the diffractive optical element DOE can be determined by using the above formulas (1) to (3).

Hereinafter, derivation of the equations (1) to (3) and an optical material design method using this equation will be described. First, the flare ratio used in the optical material design method of the present embodiment will be described. According to the scalar theory in the field of optics, the diffraction efficiency _{m m} (λ) of _m- order diffracted light (m: integer)
Is expressed by the following equations (4) to (6).

Here, n ₁ (λ) is the refractive index of the first optical material for light of wavelength λ, and n ₂ (λ) is the refractive index of the second optical material for light of wavelength λ. Also, d is the height of the relief pattern 5 (hereinafter referred to as the grating height), and φ (λ) represents the wavefront step in wavelength units. Ideally, for φ (λ), the following equation (7) is required for all the wavelengths used.

At this time, the diffraction efficiency η ₁ (λ) of the _first- order diffracted light is expressed by the following equation (8).

At this time, the diffraction efficiency η ₀ (λ) of the _zeroth- order diffracted light is expressed by the following equation (9).

At this time, the diffraction efficiency η ₂ (λ) of the _second- order diffracted light is expressed by the following equation (10).

In this embodiment, it is assumed that φ (λ) slightly deviates from the ideal. In this case, φ (λ) is expressed by the following equations (11) and (12).

Here, Δn (λ) is a deviation amount from the ideal refractive index difference at the wavelength λ, and is expressed by the following equation (13).

When Δφ (λ) is sufficiently small compared to 1, the diffraction efficiency η ₁ (λ) of the _first- order diffracted light is given by
It is represented by 14).

At this time, the diffraction efficiency η ₀ (λ) of the _zeroth- order diffracted light is expressed by the following equation (15).

At this time, the diffraction efficiency η ₂ (λ) of the _second order diffracted light is expressed by the following equation (16).

Here, the flare ratio f _R (λ) is defined as the following equation (17) as the ratio of the zeroth order diffracted light and the second order diffracted light to the first order diffracted light.

Substituting the equations (14) to (16) into the equation (17), the flare ratio f _R (λ) is expressed by the following equation (18).

Furthermore, if it approximates that Δφ (λ) is sufficiently small compared to 1, then the flare ratio f _R (λ
Can be expressed as in the following equation (19).

  As an example, as a first optical material having a low refractive index and a high dispersion, one obtained by curing a composition containing a mixture of a fluorine-based acrylic acid ester and a fluorene-based acrylic acid ester as a main component is used. The result of scalar calculation of the flare ratio using a cured product of an oligomer obtained by reacting an acrylic ester having a tricyclodecane skeleton as a second optical material to be dispersed (corresponding to the eighth group described later) A graph comparing the result of approximate calculation according to (19) is shown in FIG. FIG. 4 (a) shows the calculation result in the diffractive optical element having the blaze wavelength of d line (587.56 nm), and FIG. 4 (b) shows the calculation in the diffractive optical element having the blaze wavelength of e line (546.07 nm). It is a result. As shown in FIG. 4, it can be seen that the approximation accuracy by the equation (19) is high.

  Note that Δφ (λ) can be calculated using Equations (12) and (13), if the refractive index difference between the first optical material and the second optical material and the grating height are known. The calculation result of Δφ (λ) is shown in FIG. FIG. 5 (a) shows the calculation result in the diffractive optical element of which the blaze wavelength is d-line, and FIG. 5 (b) shows the calculation result in the diffractive optical element of which the blaze wavelength is e-line.

Next, a grid height optimization method using the flare ratio approximated by equation (19) will be described. The relationship between the refractive index difference between the first optical material and the second optical material in the conventional diffractive optical element used in FIGS. 4 and 5 and the wavelength is shown in FIG. The relationship between the flare ratio and the wavelength in the conventional diffractive optical element is shown in FIG. In FIG. 6, the inclination of the ideal straight line indicating the refractive index difference between the first optical material and the second optical material is the reciprocal (1 / d) of the grating height, as can be understood from the equation (13). Therefore, the shift amount Δn (λ) from the ideal refractive index difference depends on the grating height d. Further, the same can be said for the flare ratio from equation (19). That is, the wavelength characteristics of the flare (the zero-order diffracted light and the second-order diffracted light unnecessary when using the diffractive optical element DOE) are the refractive index n ₁ (λ) of the first optical material and the refractive index of the second optical material It is determined by n ₂ (λ) and the grating height d. Therefore, to reduce the flare ratio, it is necessary to optimize the grid height d. The flare ratio f _R (λ) can be re-expressed as f _R as in the following equation (20).

The sum of flare ratios (hereinafter referred to as the total amount of flares) F occurring in the wavelength λ ranging from λ1 (for example, 400 nm) to λ2 (for example, 700 nm) is an integral value of flare ratio f _R (λ) It can be expressed as 21).
In the present embodiment, when the diffractive optical element is used as an imaging optical system using visible light, such as a digital still camera, a digital video camera, an interchangeable lens of a single-lens reflex camera, etc. Is set to 400 nm, and the upper limit λ2 of the wavelength is set to 700 nm.

Here, g (λ) is the spectral distribution of the optical system, the transmittance of the optical system, the sensitivity of the imaging system, or the like, or a weighting function (a function of the wavelength λ) represented by the product of these. When Formula (21) is expanded using Formula (20), the flare total amount F is represented by following Formula (22).

Here, each term A, B, C, D of Formula (22) is respectively represented by following Formula (23)-(26).

  The condition for minimizing the total amount of flare F is expressed by the following equation (27).

From equation (27), the grid height dm when the total amount of flare F is minimized is expressed by the following equation (28).

Further, from the equation (28), the total amount of flare Fm when the total amount of flare F is minimum is expressed by the following equation (29).

The equations (28) and (29) are conditional equations for optimizing the grating height d so that the total amount of flare F is minimized. When the spectral distribution of the optical system, the transmittance of the optical system, the sensitivity of the imaging system, and the like are not considered, that is, when g (λ) = 1, the grating height dm when the total amount of flare F becomes minimum is It is expressed by the following equation (30).

Further, when g (λ) = 1, the total flare amount Fm in the case where the total flare amount F is minimized is expressed by the following equation (31).

As an example, as a first optical material having a low refractive index and a high dispersion, one obtained by curing a composition containing a mixture of a fluorine-based acrylic acid ester and a fluorene-based acrylic acid ester as a main component is used. A cured product of an oligomer obtained by reacting an acrylic acid ester having a tricyclodecane skeleton as a second optical material to be dispersed (corresponding to an eighth group described later) is used, and the lattice height d is 22.8 μm to 24. FIG. 8 shows flare ratios f _R (λ) calculated with changing to 8 μm. Further, FIG. 9 shows the relationship between the total amount of flare F calculated in the wavelength range of 400 nm to 700 nm and the grating height d. In FIG. 9, g (λ) = 1. As shown in FIG. 9, it can be seen that the total amount of flare F is minimized under the condition that the grating height d is around 23.8 μm. Also, as shown in FIG. 8, when the grating height d at which the total amount of flare F becomes minimum is 23.8, the wavelength distribution in visible light becomes most uniform, and the color of the flare is red, blue, green, etc. You can prevent extreme bias.

Thus, if the difference in refractive index between the low refractive index high dispersion first optical material and the high refractive index low dispersion second optical material is known, formulas (28) to (29) (or formulas (30) to The grid height d can be optimized so as to minimize the total amount of flare F using (31). For the total flare amount Fm when the total flare amount F is minimum, the low refractive index high dispersion first optical material and the high refractive index low dispersion second optical material satisfy the condition of the following equation (32) Is preferred.

  That is, it is preferable to satisfy the condition of Formula (1) described above. As described below, when the total amount of flare Fm to be minimized is 0.23 or less, the flare generated from the diffractive optical element DOE can be suppressed, so that the optical performance of the diffractive optical element DOE can be maintained well. Essentially, the value of the total amount of flare Fm = 0.23 as the upper limit value of the equation (32) is a value at which the flare is sufficiently suppressed. However, depending on the application of the optical system on which the diffractive optical element is mounted, it may be necessary to adjust the color tone of the slightly remaining flare light. As shown in FIG. 8, when the lattice height deviates from dm expressed by equation (30) to the plus side or the minus side, the color tone of flare light changes. The color tone of flare light can be adjusted by adjusting the grid height using this change. The range of grating height to be adjusted is usually in the range of about ± 0.05 μm to ± about 0.5 μm for adjusting the color tone of flare light.

  FIG. 9 is a diagram showing the relationship between the grating height and the total amount of flare when the result of FIG. 8 is multiplied by the relative visual sensitivity. For example, in FIG. 9, Fm = 0.102 is the minimum value, and the total amount of flare Fm is 0.23 or less even when the lattice height at that time changes over a range of about ± 0.5 μm. Therefore, the color tone of the flare light can be freely adjusted according to the usage within the range of the lattice height. That is, by satisfying the condition of Formula (32), it is possible to provide a diffractive optical element that maintains sufficient optical performance even when the color tone is adjusted. Furthermore, since the color tone adjustment is performed based on the minimum value Fm of the total flare amount of the low refractive index high dispersion first optical material and the high refractive low dispersion second optical material, the total flare amount relative to the change in grating height is It is possible to minimize the rate of change. Thus, if the difference in refractive index between the low refractive index high dispersion first optical material and the high refractive index low dispersion second optical material is known, the equations (28) to (29) (or the equation (30)) (31) can be used to select the optimum combination of the first optical material and the second optical material so as to minimize the total amount of flare F.

Furthermore, it is preferable to satisfy the condition of equation (33) for the grid height dm when the total amount of flare F is minimum.

That is, it is preferable to satisfy the condition of Formula (2) described above. If the grating height dm satisfies the condition of Formula (33), the diffractive optical element DOE can be easily shaped. When the value exceeds the upper limit value of the expression (33), when the diffractive optical element DOE is molded, air bubbles are likely to be mixed in when the optical material is spread, and the molding becomes difficult. In addition, since problems such as chipping of a pattern are likely to occur when peeling a mold (molding die), restrictions such as molding conditions become large.

Furthermore, for the total flare amount Fm when the total flare amount F is minimum, the low refractive index high dispersion first optical material and the high refractive index low dispersion second optical material satisfy the condition of the following equation (34) It is preferable to do.

Formula (34) shows the range of a more appropriate combination from the viewpoint of diffraction efficiency in the first optical material and the second optical material defined by the difference in refractive index n ₂₁ (λ), and the first optical material In the combination of the second optical material and the second optical material, a further preferable total flare amount Fm is defined when the total flare amount F is minimized. By selecting the first optical material and the second optical material which satisfy the conditional expression of the equation (34), the total amount of flare F can be further suppressed, and also the degree of freedom in adjusting the color tone of flare light and the degree of freedom in manufacturing conditions Can be increased.

  Subsequently, a design flow of an optical material using the equations (1) and (2) will be described with reference to the flowchart of FIG. First, candidates for combinations of the low refractive index high dispersion first optical material and the high refractive index low dispersion second optical material are determined (step ST101). As a candidate combination, both the first optical material and the second optical material may be newly created optical materials, and one of the first optical material and the second optical material may be newly created optical The other of the materials may be an existing optical material. Also, both the first optical material and the second optical material may be existing optical materials.

Next, the difference between the refractive index and the refractive index of the first optical material and the second optical material determined in the previous step ST101 is determined (step ST102). At this time, the refractive index n ₁ (λ) of the first optical material
For the h-line (405 nm), g-line (436 nm), f-line (486.1 nm), e-line (546.07 nm), d-line (587.56 nm), c-line (656.3 nm), etc. The refractive index for each wavelength is measured, and the coefficients A _{0 to} A ₅ of each term in the dispersion curve of refractive index represented by the following equation (35) are calculated to determine the refractive index for each wavelength.

Also, the refractive index of the second optical material n ₂ (lambda), the refractive index for a plurality of wavelengths as well as the refractive index n ₁ (lambda) of the first optical material were measured, Table by the following formula (36) The coefficients B _{0 to} B ₅ of each term in the dispersion curve of the refractive index to be calculated are calculated to determine the refractive index for each wavelength.

Then, using the equations (35) and (36), the difference in refractive index (n ₂₁ (λ): see equation (6)) for each wavelength is determined. Although the coefficient B ₀ .about.B ₅ coefficients A ₀ to A ₅ and of the formula (35) (36) are as defined, in this embodiment, it is stated separately for explanation easier.

Hereinafter, with respect to a plurality of resins synthesized as candidates for the low refractive index high dispersion first optical material and the high refractive index low dispersion second optical material, the following 14 combinations of resins are selected, and the above measurement is performed to obtain flare The total amount Fm and the optimal grid height dm were calculated. Table 1 shows combinations of resins. The combination of resins is conveniently referred to as first to fourteenth groups. In the following, a resin which is a first optical material of low refractive index and high dispersion is denoted by symbol A, and a resin which is a second optical material of high refractive index and low dispersion is denoted by symbol B. It has a number according to. Furthermore, hyphens (−) 1 to hyphens (−) 3 are added to distinguish one having a different composition ratio even if the resins of the composition are the same.

(Table 1)
Group name First optical material Second optical material First group Resin A1 Resin B1
Second Group Resin A2 Resin B2
Third Group Resin A3 Resin B3
Fourth Group Resin A1-1 Resin B2-1
Fifth Group Resin A1-1 Resin B2-2
Sixth Group Resin A1-2 Resin B2-3
Seventh Group Resin A1-2 Resin B3-1
Eighth group resin A1-2 resin B4
Ninth Group Resin A4 Resin B1
Tenth group resin A4 resin B4-1
Eleventh Group Resin A2 Resin B5
The 12th group resin A2 resin B5-1
The 13th group resin A4 resin B4-2
Fourteenth group resin A2 resin B1

In the first group, the low refractive index and high dispersion first optical material is a resin obtained by curing a composition containing as a main component a mixture of a fluorine-based acrylic acid ester and a fluorene-based acrylic acid ester. The second optical material of high refractive index and low dispersion is a resin obtained by curing an oligomer obtained by reacting a thiol and an acrylic ester having a tricyclodecane skeleton.
In the second group, the low refractive index and high dispersion first optical material is a resin having a bisphenol skeleton. The second optical material of high refractive index and low dispersion is a resin obtained by curing an oligomer obtained by reacting a thiol and an acrylic ester having a tricyclodecane skeleton.
In the third group, the low refractive index and high dispersion first optical material is a resin having a bisphenol skeleton. The second optical material of high refractive index and low dispersion is a resin obtained by curing an oligomer obtained by reacting two types of thiol and an acrylic ester having a tricyclodecane skeleton.
In the fourth group, the low-refractive-index high-dispersion first optical material is the same as the first optical material in the first group, and the compounding ratio is changed. Further, the second optical material of high refractive index and low dispersion is the same as the second optical material in the second group, and the compounding ratio is changed.

In the fifth group, the low refractive index and high dispersion first optical material is the same as the first optical material in the fourth group. Further, the second optical material of high refractive index and low dispersion is the same as the second optical material in the second group, and the compounding ratio is changed.
In the sixth group, the low-refractive-index high-dispersion first optical material is the same as the first optical material in the first group, and has a different blending ratio. Further, the second optical material of high refractive index and low dispersion is the same as the second optical material in the second group, and the compounding ratio is changed.
In the seventh group, the low refractive index and high dispersion first optical material is the same as the first optical material in the sixth group. Further, the second optical material of high refractive index and low dispersion is the same as the second optical material in the third group, and the compounding ratio is changed.
In the eighth group, the low refractive index and high dispersion first optical material is the same as the first optical material in the sixth group. Further, the second optical material of high refractive index and low dispersion comprises an oligomer obtained by reacting two types of thiol (one is a thiol having a tricyclodecane skeleton) with an acrylic ester having a tricyclodecane skeleton. It is a cured resin.

In the ninth group, the low refractive index and high dispersion first optical material is a resin obtained by curing a mixture of an acrylic ester having a bisphenol skeleton and a fluorine-based acrylic ester. In addition, the second optical material of high refractive index and low dispersion is the same as the second optical material in the first group.
In the tenth group, the low refractive index and high dispersion first optical material is the same as the first optical material in the ninth group. In addition, the second optical material of high refractive index and low dispersion is the same as the second optical material in the eighth group, and the compounding ratio is changed.
In the eleventh group, the low refractive index and high dispersion first optical material is the same as the first optical material in the second group. The second optical material of high refractive index and low dispersion is a resin obtained by curing an oligomer obtained by reacting a thiol having a tricyclodecane skeleton with an acrylic ester having a tricyclodecane skeleton.
In the twelfth group, the low refractive index and high dispersion first optical material is the same as the first optical material in the second group. In addition, the second optical material of high refractive index and low dispersion is the same as the second optical material in the eleventh group, and the compounding ratio is changed.
In the thirteenth group, the low refractive index and high dispersion first optical material is the same as the first optical material in the ninth group. Further, the second optical material of high refractive index and low dispersion is the same as the second optical material in the tenth group, and the compounding ratio is changed.
In the fourteenth group, the low refractive index and high dispersion first optical material is the same as the first optical material in the second group. In addition, the second optical material of high refractive index and low dispersion is the same as the second optical material in the first group.

  In addition, resin of the 1st-14th group mentioned above contains 0.1-0.5 weight% of photoinitiators, respectively.

Next, the refractive index (coefficient A _{0 to} A ₅ and coefficient B _{0 to} B ₅ ) calculated for the diffractive optical element DOE made of the combination of the first optical material and the second optical material shown in Table 1 is shown in Table 2 below. Shown in.

(Table 2)
Group name A ₀ / B ₀ A ₁ / B ₁ A ₂ / B ₂ A ₃ / B ₃ A ₄ / B ₄ A ₅ / B ₅
First group 2.277981-0.00464 0.01461 2 0.00261-0.00036 0.0000342
2.367936 0.002708 0.02193-0.00162 0.000288-0.000016
The second group 2.275591 -0.00316 0.016172 0.002251 -0.00039 0.0000322
2.376195 -0.00692 -0.00014 0.005781 -0.00083 0.0000462
The third group 2.275591 -0.00316 0.016172 0.002251 -0.00039 0.0000322
2.319678 0.038251 0.045709-0.00671 0.000793-0.000035
The fourth group 2.265189-0.0138 0.009935 0.001919-0.0000018-0.0000007
2.379781-0.00406 0.003001 0.005383 -0.00083 0.000047
The fifth group 2.265189-0.0138 0.009935 0.001919-0.0000018-0.0000007
2.317441 0.027186 0.054526-0.01405 0.002489-0.0001
Sixth group 2.29366 0.00071 0.019114 0.001897 -0.00028 0.0000304
2.329237 0.037535 0.063875-0.01449 0.002227-0.00013
The seventh group 2.286323 -0.00444 0.036998 -0.00791 0.001758 -0.000111
2.333714 0.04042 0.068656-0.01621 0.002526-0.00015
The eighth group 2.29366 0.00071 0.019114 0.001897 -0.00028 0.0000304
2.435204 -0.02572-0.01407 0.009837-0.0014 0.0000783
The ninth group 2.365574-0.03098-0.0153 0.011076-0.00151 0.0000853
2.367936 0.002708 0.02193-0.00162 0.000288-0.000016
The tenth group 2.365574-0.03098-0.0153 0.011076-0.00151 0.0000853
2.343431 0.019152 0.04043 -0.00727 0.001102 -0.00006
The eleventh group 2.277563 -0.0031 0.016484 0.001416 -0.00014 0.0000013
2.314673 0.027899 0.049493-0.00998 0.001438-0.000076
The twelfth group 2.277563-0.0031 0.016484 0.001416-0.0001 4 0.0000013
2.347063 0.002701 0.023477 -0.00291 0.000549 -0.000034
The thirteenth group 2.365574-0.03098-0.0153 0.011076-0.00151 0.0000853
2.370312 0.004577 0.023047-0.00194 0.000333-0.000018
The 14th group 2.277563 -0.0031 0.016484 0.001416 -0.00014 0.0000013
2.367936 0.002708 0.02193-0.00162 0.000288-0.000016

  Next, from the difference in refractive index determined in the previous step ST102, the grating height dm and the total flare amount Fm in the case where the total flare amount F is minimized are determined using Equations (28) to (29) Step ST103). Here, an example of calculation of the grid height dm and the total amount of flare Fm when the total amount of flare F is minimized is shown in the following Table 3 and FIG. Each group shown in Table 3 and FIG. 1 is the same as each group in Table 1. In addition, when calculating the grid height dm and the total amount of flare Fm, as shown in FIG. 11 as the weighting function g (λ), the relative luminosity curve at a bright place standardized so that the maximum value is 1 The formula of is used.

(Table 3)
Group name dm [μm] Fm
First group 19.6 0.224
The second group 24.57 0.259
The third group 19.32 0.276
The fourth group 15.82 0.489
The fifth group 15.75 0.436
The sixth group 19.87 0.183
Seventh group 17.61 0.282
The eighth group 22.85 0.102
The ninth group 34.64 0.111
The tenth group 32.11 0.135
The eleventh group 22.1 0.26
The twelfth group 25.78 0.16
The thirteenth group 31.81 0.138
The 14th group 19.26 0.421

  Next, whether or not the grating height dm and the total flare amount Fm in the case where the total amount of flare F obtained in the previous step ST103 is minimum satisfy the conditions of the above-mentioned equations (32) and (33) That is, it is determined whether the conditions of Formula (1) and Formula (2) are satisfied (step ST104). If the determination is Yes, the candidate first optical material and second optical material are determined as optical materials usable (suitable) for the diffractive optical element DOE (step ST105). On the other hand, if the determination is No, the candidate first optical material and second optical material are determined as optical materials unsuitable for the diffractive optical element DOE (step ST106). For example, in the example of Table 3 and FIG. 1 described above, an optical material which can be used for the diffractive optical element DOE in which the combination of the first optical material and the second optical material of the first, sixth, eighth and twelfth groups is used. It is determined as By using a combination of these four sets of resins, the amount of flare light can be suppressed to a sufficiently small value with only the resin composed of an organic compound without using the inorganic fine particle dispersion type resin. Furthermore, the diffractive optical element made of a combination of these resins can suppress the increase in the amount of flare light to a sufficiently small value even when the color tone of the flare light is adjusted according to the application of the diffractive optical element.

  In the example of Table 3 and FIG. 1 described above, also for the ninth, tenth, and thirteenth groups, the formula is used as a combination of the first optical material of low refractive index and high dispersion and the second optical material of high refractive index and low dispersion. The condition of (1) is satisfied. As described above, when only the condition of the equation (1) is satisfied, although the molding condition is restricted, the flare light amount can be sufficiently suppressed, and the color tone of the flare light is adjusted according to the application of the diffractive optical element Even in this case, it is possible to realize a diffractive optical element in which the increase in the amount of flare light is suppressed to a sufficiently small value.

  Further, in step ST104 described above, the grid height dm and the total amount of flare Fm in the case where the total amount of flare F obtained in the previous step ST103 is minimum satisfy the conditions of the above-described equations (34) and (33). It may be determined whether the conditions of Equation (3) and Equation (2) are satisfied. In this way, it is possible to further suppress the flare light quantity, and to significantly improve the adjustment freedom of the color tone of flare light and the manufacturing condition according to the application of the diffractive optical element. For example, in the example of Table 3 and FIG. 1 described above, the combination of the first optical material and the second optical material of the sixth, eighth and twelfth groups is determined as an optical material that can be used for the diffractive optical element DOE Ru.

  Of course, the combination of the first optical material with low refractive index and high dispersion and the second optical material with high refractive index and low dispersion may be selected based on the condition that only the condition of equation (3) is satisfied. . In this way, although the molding conditions are restricted, it is possible to further suppress the flare light quantity, and even if the color tone of the flare light is adjusted according to the application of the diffractive optical element, the flare light quantity is further increased. A diffractive optical element suppressed to a small value can be realized.

  FIG. 12 shows an imaging device 51 as an example of an optical apparatus on which the contact multi-layer diffractive optical element (DOE) of the present embodiment is mounted. The imaging device 51 is a so-called digital single-lens reflex camera, and a lens barrel 53 is detachably attached to a lens mount (not shown) of the camera body 52. Then, light passing through the imaging lens 54 of the lens barrel 53 is imaged on the sensor chip (solid-state imaging device) 55 of the multi-chip module disposed on the back side of the camera body 52. At least one lens group 56 constituting the imaging lens 54 includes the above-described contact multilayer diffractive optical element (DOE).

  As described above, according to the present embodiment, on the left side of the above-mentioned equation (1), the difference between the refractive indices of the low refractive index high dispersion first optical material and the high refractive index low dispersion second optical material The total flare amount Fm can be obtained when the total flare amount F is minimum. Further, in the left side of the above-mentioned equation (2), a grating in the case where the total amount of flare F is minimized, due to the difference in refractive index between the low refractive index high dispersion first optical material and the high refractive index low dispersion second optical material The height dm can be determined. Then, if a combination of the first optical material and the second optical material in which the total amount of flare Fm satisfies the condition of the equation (1) is found, a low refractive index and a high height suitable for the diffractive optical element DOE by a simple method. A first optical material of dispersion and a second optical material of high refractive index and low dispersion can be obtained. Further, if a combination of the first optical material and the second optical material in which the grating height dm satisfies the condition of the equation (2) is found, the diffractive optical element DOE with few processing restrictions can be obtained by a simple method. A suitable low refractive index high dispersion first optical material and a high refractive index low dispersion second optical material can be obtained.

  Further, by using the diffractive optical element created according to this embodiment for an imaging optical system such as a digital still camera, digital video camera, interchangeable lens of single-lens reflex camera, microscope, etc., the amount of flare light is small and chromatic aberration is reduced. It is possible to obtain a suppressed optical image.

The weighting function g (λ) is used as an observation optical system for visual observation such as a microscope or binoculars by setting it as a function indicating a relative luminosity characteristic standardized so that the maximum value is 1. Low refractive index and high dispersion first optical material and high refractive index and low dispersion second suitable for the diffractive optical element DOE
Optical materials can be obtained. Further, as shown in FIG. 11, there are relative luminosity in the bright place and relative luminosity in the dark place in the relative visual sensitivity, and it is possible to design a flexible optical material by using properly according to the application. .

  In the above-described embodiment, as the weighting function g (λ), a function showing relative luminosity characteristics standardized so that the maximum value is 1 is exemplified, but it is not limited to this. For example, A function indicating spectral sensitivity characteristics of an image sensor (not shown) standardized so that the maximum value is 1 may be used. Thereby, a low-refractive-index, high-dispersion first optical material and a high-refractive-index low-dispersion suitable for a diffractive optical element DOE used for an imaging optical system such as a digital still camera, a digital video camera, or an interchangeable lens of a single lens reflex camera And the second optical material of

  In the above-described embodiment, the cross-sectional structure of the diffractive optical element DOE is a sawtooth shape, but is not limited to this. For example, it may be a rectangular shape, as long as a diffraction grating groove is formed.

  In the above embodiment, the first optical material and the second optical material of the first, sixth, eighth and twelfth groups are exemplified as a combination of optical materials satisfying the conditions of the equations (1) and (2). However, the present invention is not limited to this, and any combination of resin materials satisfying the conditions of formulas (1) and (2) may be used.

  In the above embodiment, the visible wavelength range of 400 nm to 700 nm is exemplified as the working wavelength range of the optical material, but the present invention is not limited thereto. For example, an ultraviolet range or infrared range such as an infrared imaging device or a fluorescence microscope It is also possible to design an optical material corresponding to the wavelength range of

DOE diffractive optical element 1 first diffractive optical element 2 second diffractive optical element 5 relief pattern (diffraction grating groove)
51 Imaging device (optical equipment)

Claims (4)

A low-refractive-index, high-dispersion first optical material and a high-refractive-index, low-dispersion second optical material, each of which is mainly composed of a resin composed of an organic compound and does not contain inorganic fine particles It is an optical material design method of a contact multi-layer type diffractive optical element,
The wavelength of light for which the diffractive optical element is used is λ [nm], the lower limit of the wavelength is λ 1 [nm], the upper limit of the wavelength is λ 2 [nm], and The function representing the spectral sensitivity characteristic of the image sensor standardized to have a difference of the refractive index between the one optical material and the second optical material as n ₂₁ (λ) and the maximum value being 1 is g (λ) When you

To determine whether the condition of
An optical material design method for a diffractive optical element, wherein the candidate first optical material and the second optical material satisfying the conditions are determined as optical materials that can be used for the diffractive optical element. The diffractive optical element according to claim 1, wherein the candidate first optical material and the second optical material are determined as optical materials that can be used for the diffractive optical element so as to satisfy the following condition: Optical material design method.

A low-refractive-index, high-dispersion first optical material and a high-refractive-index, low-dispersion second optical material, each of which is mainly composed of a resin composed of an organic compound and does not contain inorganic fine particles A method of manufacturing a contact multi-layer diffractive optical element
The wavelength of light for which the diffractive optical element is used is λ [nm], the lower limit of the wavelength is λ 1 [nm], the upper limit of the wavelength is λ 2 [nm], and The function representing the spectral sensitivity characteristic of the image sensor standardized to have a difference of the refractive index between the one optical material and the second optical material as n ₂₁ (λ) and the maximum value being 1 is g (λ) When you

To determine whether the condition of
A method of manufacturing a diffractive optical element, comprising determining the candidate first optical material and the second optical material satisfying the conditions as optical materials that can be used for the diffractive optical element. The method according to claim 3, further comprising determining the candidate first optical material and the second optical material as optical materials that can be used for the diffractive optical element so as to satisfy the following condition: Method of manufacturing a diffractive optical element

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