JP2019148666A - Optical element and optical device having the same - Google Patents

Abstract

To provide an optical element which offers high diffraction efficiency over a wide wavelength range, and an optical device having the same.SOLUTION: An optical element is configured to be switchable between a first state, in which the optical element exhibits first optical power, and a second state, in which the optical element exhibits second optical power that is greater than the first optical power, and comprises a substrate with a diffraction surface and an electroactive material disposed in the vicinity of the substrate and configured to change the refractive index according to a voltage applied thereto. In one of the first and second states, a diffraction order corresponding to the maximum diffraction efficiency for incident rays is zero and, in the other of the first and second states, a diffraction order corresponding to the maximum diffraction efficiency for incident rays is one. The birefringence of the electroactive material is set appropriately.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical element having a variable focus function and an optical apparatus including the same.

  Conventionally, reading glasses using a single focus lens, a progressive lens for both perspective and a bifocal lens are known. In elderly people with normal vision, presbyopia is resolved by using reading glasses with a single-focus lens when focusing on near points such as reading. On the other hand, elderly with non-sightedness are lenses that are adjusted to focus on far points such as infinity, and are equipped with a progressive lens and a bifocal lens, some of which are processed for presbyopia. It is necessary to use glasses.

  However, in spectacles equipped with a progressive lens for both perspective and a bifocal lens, regions having different optical power (focal length) are mixed in the lens. For this reason, when viewing from a distance using such glasses, the scenery looks distorted, or a portion out of focus is generated and the image is blurred. Further, in the bifocal lens, the small lens of the power unit for presbyopia is added to a part of the lens, and the appearance of the glasses themselves is not preferable.

  Patent Document 1 discloses an electroactive device capable of adding optical power to a presbyopia power unit when the user looks far away without adding optical power to the presbyopia power unit when viewing a distance. Glasses using a (liquid crystal diffractive lens) are disclosed.

Special table 2015-529845 gazette

  However, in the liquid crystal diffractive lens of Patent Document 1, the diffraction efficiency in the short wavelength region is low in the inactivated state and the activated state, and it is difficult to obtain high diffraction efficiency in a wide wavelength region. Thereby, unnecessary diffracted light becomes a flare and deteriorates visibility.

  An object of the present invention is to provide an optical element and an optical apparatus having sufficiently high diffraction efficiency in a wide wavelength range.

An optical element according to one aspect of the present invention switches between a first state having a first optical power and a second state having a second optical power greater than the first optical power. A possible optical element comprising: a substrate having a diffractive surface; and an electroactive material that is close to the substrate and changes a refractive index in accordance with an applied voltage, and is in the first or second state. The diffraction order at which the diffraction efficiency with respect to the incident light beam is maximum in one state is 0, and the diffraction order with the maximum diffraction efficiency with respect to the incident light beam is 1 in the other state of the first or second state. And when the birefringence of the electroactive material is Δn,
0.03 <Δn <0.20
The following conditional expression is satisfied.

  According to the present invention, it is possible to provide an optical element and an optical apparatus having sufficiently high diffraction efficiency in a wide wavelength range.

It is sectional drawing of the optical element which concerns on embodiment of this invention. It is a figure which shows the refractive index of the material required in order to satisfy diffraction conditions. It is a figure which shows the refractive index and refractive index dispersion | distribution of the material which comprise the optical element of Example 1. FIG. It is a figure which shows the refractive index for every wavelength of the material which comprises the optical element of Example 1. FIG. FIG. 3 is a diagram showing the diffraction efficiency of the optical element of Example 1. It is a figure which shows the refractive index and refractive index dispersion | distribution of the material which comprise the optical element of Example 2. FIG. It is a figure which shows the refractive index for every wavelength of the material which comprises the optical element of Example 2. FIG. FIG. 6 is a diagram showing the diffraction efficiency of the optical element of Example 2. It is a figure which shows the refractive index and refractive index dispersion | distribution of the material which comprise the optical element of Example 3. It is a figure which shows the refractive index for every wavelength of the material which comprises the optical element of Example 3. FIG. FIG. 6 is a diagram showing the diffraction efficiency of the optical element of Example 3. FIG. 10 is a diagram illustrating eyeglasses as an example of an optical apparatus including the optical element of Example 4. It is a figure which shows the refractive index for every wavelength of the material which comprises the optical element of a prior art example. It is a figure which shows the diffraction efficiency of the optical element of a prior art example.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In each figure, the same members are denoted by the same reference numerals, and redundant description is omitted.

  With reference to FIG. 13 and FIG. 14, problems of the conventional optical element (liquid crystal diffractive lens or electroactive lens) will be described. The conventional optical element includes a substrate having a diffractive structure and an electroactive material. By applying a voltage to the electroactive material, the refractive index of the electroactive material changes and the optical power of the optical element changes.

  FIG. 13 shows the refractive index for each wavelength of a substrate material MR-10 (registered trademark) manufactured by Mitsui Chemicals, Inc. and a high birefringence nematic liquid crystal which is an electroactive material. By applying a voltage to the electroactive material, the refractive index of the electroactive material changes from the average refractive index nave to the ordinary light refractive index no, and additional power is generated by diffraction according to the refractive index difference between the substrate material and the electroactive material. To do. Further, the refractive index of the substrate material and the average refractive index “nave” of the electroactive material coincide at a wavelength of 550 nm.

  FIG. 14 shows the diffraction efficiency of an optical element as a conventional example. The diffraction efficiency is defined as the ratio of the light beam propagating in each diffraction direction to the incident light beam. In FIGS. 14A and 14B, a state where a voltage higher than a predetermined value is not applied to the electroactive material (inactivated state) and a voltage higher than a predetermined value is applied to the electroactive material, respectively. The diffraction efficiency of the optical element in the state (activated state) is shown. In the inactivated state, the diffraction efficiency of the 0th order diffracted light is remarkably reduced in the short wavelength region, and the −1st order diffracted light is generated in the short wavelength region. Even in the activated state, the diffraction efficiency of the first-order diffracted light is reduced in the short wavelength region, and the 0th-order diffracted light and the second-order diffracted light are generated in the short wavelength region. Thus, when diffracted light of a plurality of diffraction orders is mixed, unnecessary diffracted light becomes flare and deteriorates the visibility of an object to be observed.

  Hereinafter, the configuration of the optical element (liquid crystal diffraction lens or electroactive lens) 100 according to the embodiment of the present invention will be described. FIG. 1 is a cross-sectional view of an optical element 100 according to an embodiment of the present invention.

  The optical element 100 includes a first substrate 110, a second substrate 120, a liquid crystal layer (electroactive material) 130, electrodes 140 and 150, and alignment films 160 and 170. The optical element 100 has a variable focus function. When used in reading glasses (optical equipment), the optical element 100 does not add optical power to the presbyopia power portion when looking far away such as infinity, and is close to reading. The optical power can be added to the presbyopia power section only when viewing the image.

  The first substrate 110 has both flat surfaces. The second substrate 120 has a relief surface (diffraction surface) on the liquid crystal layer 130 side. The relief shape (periodic unevenness shape) of the relief surface can be formed by machining, transfer by a mold, etching or the like. The liquid crystal layer 130 is provided between the first substrate 110 and the second substrate 120 so as to be close to the first substrate 110 and the second substrate 120.

  The electrodes 140 and 150 are a pair of transparent electrodes provided so as to sandwich the liquid crystal layer 130, and a voltage can be applied to the liquid crystal layer 130 in accordance with an instruction from a control unit (not shown). The electrodes 140 and 150 are made of, for example, a transmissive conductive oxide (such as ITO) or a conductive organic material (PEDOT: PSS or carbon nanotube). The thickness of the electrodes 140 and 150 can be set to 1 μm, for example, but is preferably 0.1 μm. When a voltage is applied to the liquid crystal layer 130, an electric field is generated between the electrodes 140 and 150, and the alignment direction of the liquid crystal molecules in the liquid crystal layer 130 changes. With such a configuration, the refractive index and refractive index dispersion of the liquid crystal layer 130 change.

  The alignment films 160 and 170 are thin films provided in contact with the liquid crystal layer 130 and are made of a polyimide material or the like. The thickness of the alignment films 160 and 170 is preferably 0.1 μm or less. The alignment films 160 and 170 are subjected to a rubbing process or a photo-alignment process in which ultraviolet rays are irradiated with linearly polarized light. With such a configuration, the initial alignment of the liquid crystal molecules in the liquid crystal layer 130 can be controlled.

  The optical element 100 is configured to be switchable between at least two states in accordance with the voltage applied to the liquid crystal layer 130. As described above, when a voltage is applied to the liquid crystal layer 130, the refractive index of the liquid crystal layer 130 changes. In the present embodiment, the optical element 100 enters an inactivated state (first state) when a voltage equal to or higher than a predetermined value is not applied to the liquid crystal layer 130, and the first optical power (focal length) is set. Have. The optical element 100 is activated (second state) when a voltage of a predetermined value or higher is applied to the liquid crystal layer 130, and has a second optical power greater than the first optical power. Have. That is, the optical element 100 has different optical powers in the inactivated state and the activated state. As a representative example, the optical element 100 has substantially no optical power in the inactivated state and has a desired optical power (for example, + 2D) in the activated state. In addition, when the voltage more than predetermined value is not applied, the case where the voltage smaller than predetermined value is applied and the case where the voltage is not applied substantially are included.

  In the optical element 100, in order to maximize the diffraction efficiency with respect to an incident light beam incident vertically (incident along the vertical direction in FIG. 1), the optical path length difference between the crest and the groove of the relief surface is an integral multiple of the wavelength. And it is sufficient. At this time, the following conditional expression (1) is satisfied.

(N2 (λ0) −n1 (λ0)) d = mλ0 (1)
In equation (1), λ0 is the design wavelength, d is the height of the relief shape, n1 (λ) is the refractive index of the liquid crystal layer 130 corresponding to the wavelength λ, and n2 (λ) is the second substrate corresponding to the wavelength λ. The refractive index of 120, m is the diffraction order.

  The diffraction efficiency η of the m-th order diffracted light of the wavelength λ that does not hold the formula (1) is expressed by the following formula (2).

η (λ) = [sin {π (φ (λ) −m)} / {π (φ (λ) −m)}] ² (2)
In the equation (2), φ (λ) = (n2 (λ) −n1 (λ)) d / λ. When equation (1) holds for all wavelengths λ, the wavelength dependence of the diffraction efficiency η is eliminated. When Expression (1) is established for the d line, C line, and F line, the following Expression (3) is derived.

(N2 (λd) −n1 (λd)) / {(n2 (λF) −n2 (λC)) − (n1 (λF) −n1 (λC))} = λd / (λF−λC) (3)
In Expression (3), λd, λC, and λF are the wavelengths of the d-line, C-line, and F-line, respectively. The right side of Expression (3) is a constant, which is −3.45. For this reason, if the numerator is a positive value on the left side of the expression (3), the denominator needs to be a negative value. That is, in order to realize high diffraction efficiency in a wide wavelength range, it is necessary to configure the optical element 100 by combining a high refractive index / low dispersion material and a low refractive index / high dispersion material.

  As an example, conditions for maximizing diffraction efficiency are obtained at three wavelengths of 450 nm, 550 nm, and 650 nm.

  When the optical element 100 is in the activated state, the m1-order diffracted light of each wavelength of light satisfies the following conditional expressions (4) to (6).

Δn1 (λ550) d = m1λ550 (4)
Δn1 (λ450) d = m1λ450 (5)
Δn1 (λ650) d = m1λ650 (6)
In Expressions (4) to (6), Δn1 is a refractive index difference between the second substrate 120 and the liquid crystal layer 130 in the activated state, and m1 is a diffraction order (design diffraction) that maximizes the diffraction efficiency in the activated state. Order).

  When the optical element 100 is in an inactivated state, the m2 order diffracted light of each wavelength of light satisfies the following formulas (7) to (9).

Δn2 (λ550) d = m2λ550 (7)
Δn2 (λ450) d = m2λ450 (8)
Δn2 (λ650) d = m2λ650 (9)
In Expressions (7) to (9), Δn2 is the refractive index difference between the second substrate 120 and the liquid crystal layer 130 in the inactivated state, and m2 is the diffraction order (design) that maximizes the diffraction efficiency in the inactivated state. Diffraction order).

  Expression (4) can be transformed into the following expression (4 ′).

d = m1λ550 / Δn1 (λ550) (4 ′)
In the equation (4 ′), the height d of the relief shape can be determined by determining the design diffraction order m1 in the activated state and the refractive index difference Δn1 in the activated state. Expressions (5) and (6) can be transformed into the following expressions (5 ′) and (6 ′) by Expression (4 ′), respectively.

Δn1 (λ450) = Δn1 (λ550) λ450 / λ550 (5 ′)
Δn1 (λ650) = Δn1 (λ550) λ650 / λ550 (6 ′)
Moreover, Formula (7)-Formula (9) can be deform | transformed into the following formula | equation (7 ')-Formula (9') by Formula (4 ')-Formula (6'), respectively.

Δn2 (λ550) = Δn1 (λ550) m2 / m1 (7 ′)
Δn2 (λ450) = Δn1 (λ450) m2 / m1 (8 ′)
Δn2 (λ650) = Δn1 (λ650) m2 / m1 (9 ′)
The right side of the equations (5 ′) to (9 ′) includes the refractive index difference at a wavelength of 550 nm in the activated state, and the rest is a constant. That is, by determining the refractive index difference at a wavelength of 550 nm in the activated state, a condition that the refractive index difference at each wavelength in the inactivated state and the activated state should be satisfied is derived.

  FIG. 2 shows the refractive indexes of the substrate and the liquid crystal layer that satisfy the diffraction conditions described above. In FIG. 2A, the designed diffraction order m1 in the activated state is 1, and the designed diffraction order m2 in the deactivated state is -1. In this configuration, from the equations (5 ′) and (6 ′), in the activated state, the refractive index difference at a wavelength of 450 nm is smaller than the refractive index difference at a wavelength of 550 nm, and the refractive index difference at a wavelength of 650 nm is growing. Further, from the equations (7 ') to (9'), in the inactivated state, the refractive index difference at each wavelength is opposite to the refractive index difference in the activated state. In the liquid crystal layer, the refractive index dispersion decreases as the refractive index increases (the value of the refractive index dispersion changes from positive to negative). However, in a general liquid crystal, the refractive index dispersion is small when the refractive index is low, and the refractive index dispersion is large when the refractive index is high. Therefore, the condition (refractive index difference) for increasing the diffraction efficiency in a wide wavelength region in the inactivated state and the activated state required in the configuration of FIG. 2A is the refractive index difference obtained from a realistic material. Departs greatly from the relationship.

  In FIG. 2B, the designed diffraction order m1 in the active state is 1, and the designed diffraction order m2 in the inactivated state is 0. In this configuration, from the equations (5 ′) and (6 ′), in the activated state, the refractive index difference at a wavelength of 450 nm is smaller than the refractive index difference at a wavelength of 550 nm, and the refractive index difference at a wavelength of 650 nm is growing. Further, from the formulas (7 ') to (9'), the refractive index difference at each wavelength is 0 in the inactivated state. By setting the design diffraction order in one state of the inactivated state or the activated state to 0, the refractive indexes of the substrate and the liquid crystal layer match in one state. Thus, the conditions (refractive index difference) for increasing the diffraction efficiency in a wide wavelength region in the inactivated state and the activated state required in the configuration of FIG. Deviation from the relationship can be reduced. Therefore, sufficiently high diffraction efficiency can be obtained in a wide wavelength region in the inactivated state and the activated state.

  In the present invention, as described above, the design diffraction order is 0 in one state of the inactivated state or the activated state, and the design diffraction order is 1 in the other state of the inactivated state or the activated state. do it. In this embodiment, as a typical example, the design diffraction order in the inactivated state is set to 0, and the design diffraction order in the activated state is set to 1. With such a configuration, an optical element having sufficiently high diffraction efficiency in a wide wavelength region in the inactivated state and the activated state can be realized.

  The birefringence Δn (= 2 (nave−no)) of the liquid crystal layer 130 satisfies the following conditional expression (10) in order to obtain diffraction efficiency in a wide wavelength region in the inactivated state and the activated state. It is preferable.

0.03 <Δn <0.20 (10)
More preferably, the birefringence Δn of the liquid crystal layer 130 satisfies the following conditional expression (10 ′).

0.05 <Δn <0.18 (10 ′)
In general liquid crystals, as the birefringence increases, the difference in refractive index dispersion between the inactivated state and the activated state increases. Therefore, when the birefringence Δn is larger than the upper limit value of the conditional expression (10), the condition for increasing the diffraction efficiency in a wide wavelength range in the inactivated state and the activated state is a refractive index obtained from a realistic material. It will deviate greatly from the relationship of the difference. On the other hand, when the birefringence Δn is smaller than the lower limit value of the conditional expression (10), the height d of the relief shape becomes too large, and it becomes difficult to process the relief shape.

  The refractive index difference nsub-no between the refractive index nsub of the second substrate 120 and the refractive index no in the activated state of the liquid crystal layer 130 preferably satisfies the following formula (11).

0.03 ≦ nsub-no ≦ 0.10 (11)
In the activated state, in order to maximize the diffraction efficiency with respect to the vertically incident incident light beam, it is necessary to set the optical path length difference between the peak and groove of the relief surface to an integral multiple of the wavelength. The human vision system does not respond uniformly to light of all wavelengths in the visible light spectrum. Specifically, the human visual system shows a large response near the center of the visible light spectrum, but the response is small for the red and blue wavelengths at both ends. Since the response peak under the light adaptation condition is in the vicinity of the wavelength of 550 nm, the design wavelength is generally set to be in the vicinity of 550 nm. For example, when the design wavelength is 550 nm and the design diffraction order is 1, the refractive index difference nsub-no is calculated as 550 nm / d from Equation (1). When the refractive index difference nsub-no is larger than the upper limit value of the expression (11), the height d of the relief shape becomes too small, and it becomes difficult to process the relief shape. The relief shape can be formed using a number of techniques including machining, transfer by mold, or etching, but ideally the height of the relief shape is preferably 5 to 20 μm. On the other hand, if the difference in refractive index (nsub-no) is smaller than the lower limit value of the expression (11), the height d of the relief shape becomes too large, and it becomes difficult to process the relief shape. When the aspect ratio d / p between the height d of the relief shape and the width p of the relief shape is greater than 1, it becomes difficult to process the relief shape.

  The refractive index difference nsub-nave between the refractive index nsub of the second substrate 120 and the refractive index nave in the inactivated state of the liquid crystal layer 130 preferably satisfies the following formula (12).

0.001 ≦ nsub-nave ≦ 0.003 (12)
In the inactivated state, if the design diffraction order is 0, the right side of Equation (1) is 0. Since the height d of the relief shape is determined by conditions for increasing the diffraction efficiency of the first-order diffracted light in the activated state, the refractive index difference nsub-nave needs to be a value close to zero. When the refractive index difference nsub-nave is larger than the upper limit value of the expression (12), the refractive index difference nsub-nave is greatly deviated from 0, and it is difficult to increase the diffraction efficiency of the 0th-order diffracted light. When the refractive index difference nsub-nave becomes smaller than the lower limit value of the expression (12), the combination of the second substrate 120 and the liquid crystal layer 130 becomes a combination of a high refractive index / low dispersion material and a low refractive index / high dispersion material. Therefore, it becomes difficult to obtain high diffraction efficiency in a wide wavelength range.

  The Abbe number νave in the inactivated state and the Abbe number νo in the activated state of the liquid crystal layer 130 preferably satisfy the following formula (13).

1 / νave−1 / νo ≦ 0.02 (13)
When the value on the left side is larger than the value on the right side, the difference in refractive index between the inactivated state and the activated state of the liquid crystal layer 130 varies greatly depending on the wavelength. This makes it difficult to simultaneously increase the diffraction efficiency of the 0th-order diffracted light in the inactivated state and the diffraction efficiency of the 1st-order diffracted light in the activated state.

  The liquid crystal material of the liquid crystal layer 130 is preferably cholesteric liquid crystal or nematic liquid crystal to which a chiral twist agent is added. A cholesteric liquid crystal is optically uniaxial and birefringent like a nematic liquid crystal. However, with respect to cholesteric liquid crystals, the director of the liquid crystal molecules rotates in a spiral manner across the thickness direction of the liquid crystal material. The length along the rotation axis until the director of the liquid crystal molecules rotates 360 ° is called a twist pitch. A cholesteric liquid crystal has an average refractive index nave (= (no + ne) / 2) with respect to a light wave having a wavelength corresponding to a twist pitch and propagating perpendicularly to a director of liquid crystal molecules. When a sufficiently strong voltage is applied, the director of the liquid crystal molecules is parallel to the direction of the electric field. For this reason, the cholesteric liquid crystal has an ordinary refractive index no with respect to the light wave propagating in the direction of the electric field. Therefore, the cholesteric liquid crystal changes the orientation of the liquid crystal molecules according to the applied electric field strength, and changes the refractive index value between the average refractive index nave and the ordinary refractive index no for the light wave propagating along the rotation axis of the director. Have.

  Further, by adding a chiral twist agent to the nematic liquid crystal, it is possible to obtain the same characteristics as the cholesteric liquid crystal. The nematic liquid crystal to which the chiral twist agent is added has the same ordinary refractive index no and extraordinary refractive index ne as the original nematic liquid crystal, and the twist pitch is adjusted to a desired value by the helical twist force of the added chiral twist agent. Is possible.

  Since the average refractive index nave of the nematic liquid crystal to which the cholesteric liquid crystal or the chiral twist agent is added becomes a constant value independent of the polarization state of the incident light beam, the nematic liquid crystal to which the cholesteric liquid crystal or the chiral twist agent is added has polarization insensitivity. Therefore, by using a cholesteric liquid crystal or a nematic liquid crystal to which a chiral twisting agent is added as the liquid crystal material of the liquid crystal layer 130, it is possible to uniformly apply a convergence power to a randomly polarized light beam. .

  FIG. 3 shows an example of the refractive index and refractive index dispersion (reciprocal of the Abbe number) of the material constituting the optical element 100 of the present embodiment. However, the refractive index is a value with respect to the d-line, and the Abbe number is a value with the d-line as a reference wavelength. FIG. 4 shows the refractive index for each wavelength of each material. As shown in FIG. 3, the refractive index and refractive index dispersion of the substrate material A forming the first substrate 110 and the second substrate 120 do not change between the inactivated state and the activated state. The refractive index and refractive index dispersion of the liquid crystal material A forming the liquid crystal layer 130 change between an inactivated state and an activated state. Therefore, the difference in refractive index between the substrate material A and the liquid crystal material A varies between the inactivated state and the activated state. Specifically, the refractive index difference is small in the inactivated state, but the refractive index difference is large in the activated state. In FIG. 3, the refractive index nsub and Abbe number νsub of the substrate material A are 1.594 and 47.00, respectively. The refractive index (average refractive index) nave and Abbe number νave in the inactivated state of the liquid crystal material A are 1.583 and 25.70, respectively. The refractive index (ordinary refractive index) no and the Abbe number νo in the activated state of the liquid crystal material A are 1.504 and 32.00, respectively. The refractive index difference between the substrate material A and the liquid crystal material A is 0.011 in the inactivated state and 0.090 in the activated state. With such a configuration, it is possible to increase the diffraction efficiency of the 0th-order diffracted light in the inactivated state and the diffraction efficiency of the 1st-order diffracted light in the activated state. The power can be changed. In the activated state and inactivated state, the substrate material A and the liquid crystal material A are a combination of a high refractive index / low dispersion material and a low refractive index / high dispersion material. With such a configuration, high diffraction efficiency can be obtained in a wide wavelength range in the inactivated state and the activated state.

  FIG. 5 is a diagram showing the diffraction efficiency of the optical element 100 of the present embodiment. FIGS. 5A and 5B show diffraction efficiencies in the inactivated state and the activated state, respectively. In the inactivated state, the diffraction efficiency of the 0th-order diffracted light with a wavelength of 550 nm is 95% or more, and almost no unnecessary diffracted light is generated near the wavelength of 550 nm. In the activated state, the diffraction efficiency of the first-order diffracted light of the light having a wavelength of 550 nm is 95% or more, and almost no unnecessary diffracted light is generated near the wavelength of 550 nm. Further, in the inactivated state and the activated state, sufficiently high diffraction efficiency is obtained in a wide wavelength range from 400 nm to 700 nm. In the inactivated state, the diffraction efficiency of the 0th-order diffracted light of the light having a wavelength of 400 nm is 90% or more, and the diffraction efficiency of the 0th-order diffracted light of the light having a wavelength of 700 nm is 90% or more. In the activated state, the diffraction efficiency of the first-order diffracted light with a wavelength of 400 nm is 80% or more, and the diffraction efficiency of the first-order diffracted light with a wavelength of 700 nm is 80% or more. Therefore, by using the optical element 100 of this embodiment for an optical instrument, it is possible to obtain a good field of view with less flare in the inactivated state and the activated state. In this embodiment, the wavelength at which the diffraction efficiency of the first-order diffracted light is maximized in the activated state may be 500 nm or more and 600 nm or less.

  FIG. 6 shows an example of the refractive index and refractive index dispersion (reciprocal of the Abbe number) of the material constituting the optical element 100 of the present embodiment. However, the refractive index is a value with respect to the d-line, and the Abbe number is a value with the d-line as a reference wavelength. FIG. 7 shows the refractive index for each wavelength of each material. In FIG. 6, the refractive index nsub and Abbe number νsub of the substrate material B forming the first substrate 110 and the second substrate 120 are 1.565 and 59.00, respectively. The refractive index (average refractive index) nave and Abbe number νave in the inactivated state of the liquid crystal material B forming the liquid crystal layer 130 are 1.558 and 33.80, respectively. The refractive index (ordinary refractive index) no and the Abbe number νo in the activated state of the liquid crystal material B are 1.497 and 41.40, respectively. The refractive index difference between the substrate material B and the liquid crystal material B is 0.007 in the inactivated state and 0.068 in the activated state. With such a configuration, it is possible to increase the diffraction efficiency of the 0th-order diffracted light in the inactivated state and the diffraction efficiency of the 1st-order diffracted light in the activated state. The power can be changed. In the activated state and the deactivated state, the substrate material B and the liquid crystal material B are a combination of a high refractive index / low dispersion material and a low refractive index / high dispersion material. With such a configuration, high diffraction efficiency can be obtained in a wide wavelength range in the inactivated state and the activated state.

  FIG. 8 is a diagram showing the diffraction efficiency of the optical element 100 of the present embodiment. FIG. 8A and FIG. 8B show the diffraction efficiencies in the inactivated state and the activated state, respectively. In the inactivated state, the diffraction efficiency of the 0th-order diffracted light with a wavelength of 550 nm is 95% or more, and almost no unnecessary diffracted light is generated near the wavelength of 550 nm. In the activated state, the diffraction efficiency of the first-order diffracted light of the light having a wavelength of 550 nm is 95% or more, and almost no unnecessary diffracted light is generated near the wavelength of 550 nm. Further, in the inactivated state and the activated state, sufficiently high diffraction efficiency is obtained in a wide wavelength range from 400 nm to 700 nm. In the inactivated state, the diffraction efficiency of the 0th-order diffracted light of the light having a wavelength of 400 nm is 90% or more, and the diffraction efficiency of the 0th-order diffracted light of the light having a wavelength of 700 nm is 95% or more. In the activated state, the diffraction efficiency of the first-order diffracted light with a wavelength of 400 nm is 80% or more, and the diffraction efficiency of the first-order diffracted light with a wavelength of 700 nm is 80% or more. Therefore, by using the optical element 100 of this embodiment for an optical instrument, it is possible to obtain a good field of view with less flare in the inactivated state and the activated state. In this embodiment, the wavelength at which the diffraction efficiency of the first-order diffracted light is maximized in the activated state may be 500 nm or more and 600 nm or less.

  FIG. 9 shows an example of the refractive index and refractive index dispersion (reciprocal of the Abbe number) of the material constituting the optical element 100 of the present embodiment. However, the refractive index is a value with respect to the d-line, and the Abbe number is a value with the d-line as a reference wavelength. FIG. 10 shows the refractive index for each wavelength of each material. In FIG. 9, the refractive index nsub and Abbe number νsub of the substrate material C forming the first substrate 110 and the second substrate 120 are 1.521 and 60.00, respectively. The refractive index (average refractive index) nave and Abbe number νave in the inactivated state of the liquid crystal material C forming the liquid crystal layer 130 are 1.519 and 41.90, respectively. The refractive index (ordinary refractive index) no and the Abbe number νo in the activated state of the liquid crystal material C are 1.476 and 46.10. The difference in refractive index between the substrate material C and the liquid crystal material C is 0.002 in the inactivated state and 0.045 in the activated state. With such a configuration, it is possible to increase the diffraction efficiency of the 0th-order diffracted light in the inactivated state and the diffraction efficiency of the 1st-order diffracted light in the activated state. The power can be changed. In the activated state and the deactivated state, the substrate material C and the liquid crystal material C are a combination of a high refractive index / low dispersion material and a low refractive index / high dispersion material. With such a configuration, high diffraction efficiency can be obtained in a wide wavelength range in the inactivated state and the activated state.

  FIG. 11 is a diagram showing the diffraction efficiency of the optical element 100 of the present embodiment. FIG. 11A and FIG. 11B show the diffraction efficiencies in the inactivated state and the activated state, respectively. In the inactivated state, the diffraction efficiency of the 0th-order diffracted light with a wavelength of 550 nm is 95% or more, and almost no unnecessary diffracted light is generated near the wavelength of 550 nm. In the activated state, the diffraction efficiency of the first-order diffracted light of the light having a wavelength of 550 nm is 95% or more, and almost no unnecessary diffracted light is generated near the wavelength of 550 nm. Further, in the inactivated state and the activated state, sufficiently high diffraction efficiency is obtained in a wide wavelength range from 400 nm to 700 nm. In the inactivated state, the diffraction efficiency of the 0th-order diffracted light of the light having a wavelength of 400 nm is 90% or more, and the diffraction efficiency of the 0th-order diffracted light of the light having a wavelength of 700 nm is 95% or more. In the activated state, the diffraction efficiency of the first-order diffracted light with a wavelength of 400 nm is 80% or more, and the diffraction efficiency of the first-order diffracted light with a wavelength of 700 nm is 80% or more. Therefore, by using the optical element 100 of this embodiment for an optical instrument, it is possible to obtain a good field of view with less flare in the inactivated state and the activated state. In this embodiment, the wavelength at which the diffraction efficiency of the first-order diffracted light is maximized in the activated state may be 500 nm or more and 600 nm or less.

  FIG. 12 shows spectacles (reading glasses) 10 which is an example of an optical apparatus including the optical element 100 of each embodiment. An optical element 100 is used as the lens of the glasses 10.

  The eyeglass frame holds two optical elements 100 for the left eye and the right eye. The control unit 12 controls the voltage applied to the liquid crystal layer via the electrodes of each optical element to switch the liquid crystal layer between an inactivated state and an activated state. That is, the state is switched between a state where power is not applied to the optical element 100 and a state where power is added.

  The optical element 100 or a liquid crystal optical element having the same configuration as this can be used not only for glasses but also for various optical devices such as binoculars and head mounted displays. According to the present embodiment, it is possible to easily manufacture an optical element having a plurality of states having different powers and an optical apparatus including the same.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

100 electroactive lens (optical element)
110 First substrate (substrate)
130 Liquid crystal layer (electroactive material)

Claims (16)

An optical element switchable between a first state having a first optical power and a second state having a second optical power greater than the first optical power,
A substrate having a diffractive surface;
An electroactive material that is proximate to the substrate and changes a refractive index in response to an applied voltage,
In one of the first and second states, the diffraction order that maximizes the diffraction efficiency for the incident light flux is zero,
In the other state of the first or second state, the diffraction order that maximizes the diffraction efficiency with respect to the incident light beam is 1.
When the birefringence of the electroactive material is Δn,
0.03 <Δn <0.20
An optical element that satisfies the following conditional expression:   The optical element according to claim 1, further comprising an electrode provided so as to sandwich the electroactive material and capable of applying a voltage to the electroactive material.   3. The optical element according to claim 1, wherein in the first state, the diffraction efficiency of the 0th-order diffracted light of the light having a wavelength of 550 nm is 95% or more.   4. The optical element according to claim 1, wherein in the second state, the diffraction efficiency of the first-order diffracted light of the light having a wavelength of 550 nm is 95% or more. 5.   5. The optical element according to claim 1, wherein, in the first state, the diffraction efficiency of the zero-order diffracted light of the light having a wavelength of 400 nm is 90% or more.   6. The optical element according to claim 1, wherein in the second state, diffraction efficiency of first-order diffracted light of light having a wavelength of 400 nm is 80% or more.   7. The optical element according to claim 1, wherein, in the first state, the diffraction efficiency of zero-order diffracted light of light having a wavelength of 700 nm is 90% or more.   8. The optical element according to claim 1, wherein in the second state, diffraction efficiency of first-order diffracted light of light having a wavelength of 700 nm is 80% or more.   9. The optical element according to claim 1, wherein the second wavelength at which the diffraction efficiency of the first-order diffracted light is maximized in the second state is 500 nm or more and 600 nm or less. The refractive index of the substrate is nsub, the refractive index of the electroactive material in the first state is nave, the Abbe number of the substrate is νsub, and the Abbe number of the electroactive material in the first state is νave. and when,
nsub> nave
νsub> νave
The optical element according to claim 1, wherein the following conditional expression is satisfied. The refractive index of the substrate is nsub, the refractive index of the electroactive material in the second state is no, the Abbe number of the substrate is νsub, and the Abbe number of the electroactive material in the second state is νo. and when,
νsub> νo
nsub> no
The optical element according to claim 1, wherein the following conditional expression is satisfied. When the refractive index of the substrate is nsub, and the refractive index of the electroactive material in the first state is nave,
0.001 ≦ nsub-nave ≦ 0.003
The optical element according to claim 1, wherein the following conditional expression is satisfied. When the refractive index of the substrate is nsub and the refractive index of the electroactive material in the second state is no,
0.03 ≦ nsub-no ≦ 0.10
The optical element according to claim 1, wherein the following conditional expression is satisfied. When the Abbe numbers in the first state and the second state of the electroactive material are νave and νo, respectively,
1 / νave-1 / νo ≦ 0.02
The optical element according to claim 1, wherein the following conditional expression is satisfied.   The optical element according to claim 1, wherein the electroactive material is a cholesteric liquid crystal or a nematic liquid crystal to which a chiral twisting agent is added. The optical element according to any one of claims 1 to 15,
An optical apparatus comprising: a control unit configured to change a refractive index of the electroactive material.