JP5195024B2 - Diffraction element, optical attenuator, optical head device, and projection display device - Google Patents

Description

  The present invention provides a diffractive element that stably blocks light that is transmitted in a straight line with respect to incident light, or increases the polarization extinction ratio expressed by the ratio of the linear transmittance of polarization components orthogonal to each other in the incident light. The present invention relates to an optical attenuator, an optical head device, and a projection display device using the diffraction element.

  Optical elements having a diffraction grating structure (hereinafter referred to as diffraction elements) are widely used in projection apparatuses such as optical head apparatuses and projectors that record or reproduce optical recording media. By changing the ratio of the amount of light transmitted through the diffracted light and the amount of light transmitted through the diffracted light, for example, the amount of light transmitted through the light can be controlled. For example, the diffractive element described in Non-Patent Document 1 processes the surface of an isotropic transparent material such as glass or plastic, and the cross section is a rectangle shown in FIG. 22 (a) or a sawtooth or a figure shown in FIG. 22 (b). The sawtooth shown in FIG. 22 (c) has a shape approximating a staircase, and has a structure in which lattices that are linear or curved in a direction perpendicular to the cross section are periodically continued.

  Here, the condition of the perfect diffraction that minimizes the linearly transmitted light with respect to the incident light of the wavelength λ is that the maximum transmission phase difference of the concavo-convex part is 2π × in the case of the N-stage stepped blazed diffraction grating shown in FIG. It is known that (N-1) / N. That is, the diffraction element having the rectangular diffraction grating structure in FIG. 22A is π, and the diffraction element having the sawtooth blazed diffraction grating structure in FIG. 22B is 2π.

  In addition, as a diffraction element having another diffraction grating structure, a diffraction element having a polarizing diffraction grating structure is used to obtain an extinction ratio obtained from a diffraction element having a single polarizing diffraction grating structure. It is described that it can be improved (Patent Document 1). With such a laminated structure, a diffraction element (multilayer diffraction polarizer) having a high extinction ratio with high reproducibility can be realized. Furthermore, it has been reported that the extinction ratio of a variable optical attenuator that can adjust the straight transmitted light according to the applied voltage is improved by integrating the multilayer diffraction polarizer into a liquid crystal element.

International Publication No. 03/019247 Yuzo Ono, Teruhiro Shiono et al., “Introduction to Diffraction Optics”, Optronics Inc., May 20, 1997, p11, p64-65

  However, in the diffraction element of Non-Patent Document 1, it is possible to greatly reduce the linearly transmitted light with respect to light of a specific wavelength. However, for example, variations in individual elements of a semiconductor laser serving as a light source and wavelength fluctuations due to temperature fluctuations. When it occurs, straight transmitted light appears. As a result, there has been a problem that the linearly transmitted light cannot be reduced stably depending on the use environment or the like. In addition, the multilayer diffractive polarizer of Patent Document 1 has a higher polarization extinction ratio than a diffractive element having a single-layer diffraction grating structure, but has a higher level that is stable with respect to incident light in a wide wavelength band. There was a problem that the polarization extinction ratio could not be obtained.

  An object of the present invention is to provide a diffractive element that can stably reduce linearly transmitted light by using a single diffraction grating forming surface in view of the above-described circumstances. It is another object of the present invention to provide a diffractive element capable of stably realizing a high polarization extinction ratio, a diffractive element having the variable light attenuation function using the diffractive element, a variable optical attenuator, an optical head device, and a projection display device.

  The present invention relates to a diffractive element in which light having a wavelength λ is incident and modulates and emits the phase of the light, and the diffractive element has a diffraction grating formed on a translucent substrate, and the diffraction grating has a unit region. Are arranged in a periodic manner, and the unit region is divided into three or more sections that are transmitted in different phases with respect to the light of the wavelength λ, and the light of the wavelength λ that is transmitted through the unit region. The phase difference, which is the difference between the average value of the phase per unit region and the phase of the light of the wavelength λ transmitted through each section, is an integer multiple of π, and the section has zero phase difference And the phase difference is at least three or more small regions (integers of n ≧ 1), the phase difference being a small region where the phase difference is + nπ and the small region where the phase difference is −nπ. Is the area of the small region where + nπ, and the phase difference is −nπ. The area of the region, but provide substantially equal diffraction element.

In addition, the unit region includes one small region where the phase difference is zero, m small regions whose phase difference is different by + π, and m small regions whose phase difference is different by −π (m ≧ 1), when the area of the small region where the phase difference is jπ is represented by S _j (j is an integer of −m to m), i is an integer of (−m + 1) to (m−1), _{S -m: ...: S i:} ...: ratio of _{S m} is, 1: ...: (2m) ! / {(I + m)! X (mi)! }: ...: 1 The diffraction element as described above is provided.

Further, the unit region includes a small region having a phase difference of zero having an area S _0, a small region having a phase difference of π having an area S _+1, and a small region having a phase difference of −π having an area S _−1. And the ratio of the area S ₋₁ : the area S ₀ : the area S ₊₁ is 1: 2: 1.

  With this configuration, a diffraction element having a diffraction grating structure that can greatly reduce the straight-line transmittance of light incident at a wavelength λ and a wavelength shifted from the wavelength λ and is relatively easy to manufacture. realizable.

Further, the unit region includes a small region having a phase difference of zero having an area S _0, a small region having a phase difference of 2π having an area S ₊₂ , a small region having a phase difference of π having an area S ₊₁ , and an area The phase difference consisting of S ₋₁ is a small region of −π, the phase difference consisting of an area S ₋₂ is a small region of −2π,
The area _{S -2:} the area _{S -1:} the area _{S 0:} the area _{S +1:} the ratio of the area _{S +2} is 1: 4: 6: 4: provides a diffractive element according to the 1.

  With this configuration, it is possible to realize a diffractive element that reduces the straight transmittance with respect to light incident at a wavelength that is further shifted from the wavelength λ as compared with the diffraction elements having the diffraction grating shape of the three small regions.

Further, the diffraction grating is a polarization diffraction grating in which a birefringent material having birefringence and an isotropic transparent material constitute a convex part and a concave part of the diffraction grating, and the birefringent material providing a diffraction element according to the ordinary refractive index n _o or the extraordinary refractive index _{n e (n o ≠ n e} ) one of the equal refractive index n _s of the refractive index is isotropic transparent material of. Furthermore, the polarization diffraction grating, together with any value of the level difference in the thickness direction of the grating is a natural number times the minimum value d of the step, the retardation value _| n e _-n o | × d is the wavelength λ The diffraction element described above is provided which is (p + 1/2) times (p is 0 or a positive integer). Furthermore, the polarization diffraction grating laminated two, the refractive index n _s of each ordinary refractive index n _o or the extraordinary refractive index n _e and isotropic transparent material of the polarization grating of the birefringent material matches The diffraction element according to the above, wherein the two polarization diffraction gratings have the same direction to be performed.

In this arrangement, the direction in which the refractive index n _s of the ordinary refractive index n _o or the extraordinary refractive index n _e and the isotropic transparent material of the birefringent material of the polarization grating coincide, the two polarization By making the diffraction grating the same, it is possible to change the linear transmittance of the light according to the polarization direction of the incident light having the wavelength λ, and further, the light having the first polarization direction is orthogonal to the first polarization direction. Accordingly, it is possible to realize a diffractive element that increases the polarization extinction ratio of light transmitted through the light having the polarization direction of 2.

Further, a liquid crystal layer that changes a retardation value between zero and λ / 2 with respect to light having the wavelength λ by applying a voltage to an electrode is disposed between the two polarizing diffraction gratings, The normal light refractive index n _o or the extraordinary light refractive index n _e and the direction in which the refractive index n _s of the isotropic transparent material coincides are orthogonal to or the same in the two polarization diffraction gratings as described above A diffractive element is provided.

  In addition, a liquid crystal layer is disposed between the polarization diffraction grating and the reflective substrate so as to change a retardation value between zero and λ / 4 with respect to light having the wavelength λ by applying a voltage to the electrode. The described diffraction element is provided. In addition, it has a mechanism for propagating light in the emission direction that travels straight through or regularly reflects through the diffraction element described above, and blocks the light emitted in a direction different from the emission direction, and the magnitude of the voltage applied to the liquid crystal layer Provided is an optical attenuator in which the amount of light that propagates in response to the change.

  With this configuration, it is possible to realize a diffractive element capable of controlling the efficiency of light traveling straight by changing the polarization state of light of wavelength λ incident on the liquid crystal cell with good control, and to control the diffractive element. A utilized optical attenuator can be realized.

  In addition, a light source that emits at least light having a wavelength λ, a beam splitter and an objective lens that are sequentially disposed between the light source and the optical disc, and a light that has a wavelength λ that is disposed between the beam splitter and the optical disc. An optical head device including a quarter-wave plate that generates a phase difference of ¼ wavelength with respect to the optical disc, and a photodetector that receives return light from the optical disc via the beam splitter. An optical head device is provided in which the above-described diffraction element is disposed in an optical path between the beam splitter and the beam splitter.

  With this configuration, in the optical path from the light source to the optical disk, only light in a specific linear polarization direction is transmitted, and the light reflected from the optical disk can be efficiently diffracted to reduce the return light to the light source, thereby oscillating the light source. It can be stabilized.

  And a light source, a liquid crystal light valve that modulates visible light emitted from the light source according to an image to be displayed, and a light path disposed between the light source and the liquid crystal light valve to change the polarization state of the light. 1 polarizing means, second polarizing means arranged on the light emitting side of the liquid crystal light valve for changing the polarization state of the light, and projecting means for enlarging and projecting the image generated by the liquid crystal light valve, In the projection display apparatus provided, at least one of the first polarizing means and the second polarizing means is provided with the above-described diffraction element.

  With this configuration, light with a large amount of light does not absorb light, efficiently transmits specific linearly polarized light without diffracting it, efficiently diffracts linearly polarized light orthogonal thereto, and transmits straightly transmitted light according to the polarization. Since the polarizing means can be controlled, heat generated by the polarizing means can be reduced, and stable operation and high quality of the projection display device can be obtained.

  The present invention provides a diffractive element having an effect of reducing linearly transmitted light of incident light by realizing a diffractive element having a single diffraction grating forming surface, an optical attenuator using the diffractive element, an optical head device, and A projection display device can be provided.

(First embodiment)
For example, as shown in FIG. 1, consider a diffraction element 100 in which unit regions 10 for spatially modulating the phase of transmitted light are periodically arranged. This unit region 10 is composed of odd regions (N is a natural number) of (2N + 1) having different phases of transmitted light when light having the same phase and wavelength λ is incident, and is composed of three small regions in the example of FIG. 1 and 2 is divided into four geometric sections on the XY plane. This section has the same phase in the section, and a plurality of sections may have the same phase in one unit region. Accordingly, the unit area 10 is composed of four sections and is composed of three small areas. Next, consider the phase difference expressed by the phase of the light transmitted in each section with respect to the average phase per unit area of the transmitted light of wavelength λ transmitted through the entire unit region 10. At this time, if there are a plurality of sections having the same phase difference, even if they are geometrically separated, they are set as one small region. Then, the transmitted light complex amplitude of a small region where the phase difference of transmitted light is zero among a plurality of small regions is U (0), and the transmitted light complex amplitude of a small region whose phase difference is φ (m) is U (m). . However, m is an integer and is a value from -N to + N. The unit region 10 in FIG. 2 shows an example in which N = 1 and specifically includes three small regions having transmitted light complex amplitudes of U (0), U (−1), and U (+1). It is. In this case, the two sections having U (0) are geometrically separated, but they are combined into one small region.

In order to be different the phase difference of the in each small region, for example, an uneven portion is formed in a grid pattern on a transparent substrate having an isotropic refractive index n _s, the surrounding medium for simplicity as an air, transparent When light of wavelength λ is incident on the substrate surface from the vertical direction, the step d of the concave portion between the small regions having different phase differences is determined so as to be | n _s -1 | · d = (m + λ / 2). To do. Note that the medium in contact with the step of the concavo-convex portion is not limited to air, but may be another transparent material, or an optical material layer having concavo-convex portions in a lattice shape may be formed on a transparent substrate. Further, the material for forming the unevenness in order to develop the phase difference may be an isotropic material or a material having birefringence. The operation of the diffraction element of the present invention will be described below.

As described above, diffracted light is generated when light having a wavelength λ is transmitted through a diffraction element in which unit regions are periodically arranged. The transmitted light complex amplitude spatial distribution of transmitted light is described in, for example, Chapter 3 of “Optical Wave Electronics” (by Jiro Koyama and Hiroshi Nishihara, published by Corona, published in 1978). When this unit region is made of a transparent material with no light loss, the transmitted light complex amplitude U (m) in a small region having a phase difference φ (m) is expressed by the following equation (1).
U (m) = exp {jφ (m)} (1)
J is an imaginary unit. Here, the term “periodic” means that the unit areas are periodically and repeatedly arranged in any direction. For example, the unit regions 10 are arranged in the X direction and the Y direction on the XY plane as in the diffraction element 100 in FIG. 1, or a band-shaped unit region as in the diffraction element 200 in FIG. 20 may be arranged in the X direction at a pitch Px. In the diffraction element 200 of FIG. 3, the Y direction may be repeated at an arbitrary pitch Py. Therefore, the term “periodic” is sufficient as long as unit regions are arranged in at least one direction. In addition, when an area where light is incident on the diffraction element is an effective area, the effective area has a configuration in which at least 3 × 3 or more unit areas 10 are arranged in the diffraction element 100, and the diffraction element 200 has at least the unit area 20. It is preferable that three or more Px are arranged.

Here, in a small region where the sign of m is different, if the area ratio S (m) of each small region to the whole unit region is equal, the complex amplitude A of the 0th-order diffracted light that is transmitted straight is expressed by the following equation (2). It is.
A = S (0)
+ [Exp {jφ (−1)} + exp {jφ (+1)}] × S (1)
+ [Exp {jφ (−2)} + exp {jφ (+2)}] × S (2) +.
+ [Exp {jφ (−N)} + exp {jφ (+ N)}] × S (N) (2)
Note that φ (0) = 0.

Further, in a small region where the sign of m is different, the absolute value of the phase difference φ (m) is equal and the signs are opposite to each other,
A = S (0)
+ 2 × [cos {φ (1)} × S (1)
+ Cos {φ (2)} × S (2) +
+ Cos {φ (N)} × S (N)] (3)
It becomes.

Here, in the equation (3), when φ (m) = mπ (where m is an integer), since cos {φ (m)} = (− 1) ^m , the equation (3) is
A = [S (0) + 2 × {−S (1) + S (2) −...
+ (− 1) ^N × S (N)}] (4)
It becomes.

That is, the condition of the area ratio S (m) of the small region in which the expression (4) becomes zero,
S (0) = 2 × {S (1) −S (2) +... − (− 1) ^N × S (N)} (5)
And φ (m) = mπ, the complex amplitude A of the linearly transmitted light that is the 0th-order diffracted light is zero.

For example, when the phase difference φ (m) has a phase difference shifted from mπ to δ and φ (−m) shifted from −mπ to −δ, the expression (3) is
A = 2 × {1-cos (δ)} × S (1)
-2 × {1-cos (δ)} × S (2) +
-2 (-1) ^N * {1-cos ([delta])} * S (N)
= 4 × {sin (δ / 2)} ²
X {S (1) -S (2) + ...- (-1) ^N xS (N)} (6)
It is represented by

From the condition of equation (5), the complex amplitude A at this time is
A = −2 × S (0) × {sin (δ / 2)} ² (7)
It becomes.

Moreover, since the square of the absolute value of the complex amplitude A of the light intensity, the light intensity I _A of the rectilinear transmitted light,
I _A = {2 × S (0)} ² × {sin (δ / 2)} ⁴ (8)
It is represented by

In addition, as a conventional diffraction grating structure (not shown), when the concave-convex cross-sectional shape of the grating is rectangular and the unit region is composed of two regions of a concave portion and a convex portion, the condition that the linearly transmitted light is zero is the concave portion and the convex portion. It is known that the phase difference of the transmitted light of the wavelength λ in the two areas is 1: 1 and the area ratio of π is π. In this case, when the phase difference of the transmitted light having the wavelength λ in the two regions is shifted from π by δ, the complex amplitude B of the straight transmitted light that is the 0th-order diffracted light is
B = 1/2 + exp {j (π + δ)} / 2
= (− J) × exp (jδ / 2) × sin (δ / 2) (9)
It is represented by

Accordingly, the light intensity I _B of the rectilinear transmitted light,
I _B = {sin (δ / 2)} ² (10)
It is represented by

As another conventional diffraction grating structure (not shown), when the concavo-convex cross-sectional shape of the grating in the X direction is serrated and the Y direction is linear, the condition that the linearly transmitted light is zero is the wavelength It is known that the phase difference in the X direction of the unit region of the transmitted light of λ is described by 2πX (X is normalized by the grating period Px and is a value in the range of 0 ≦ X ≦ 1). Here, when the coefficient for X in the phase difference of the transmitted light having the wavelength λ is shifted from 2π to δ, the complex amplitude C of the straight transmitted light is
C = [exp {j (2π + δ)} − 1] / (2π + δ)
= 2j / (2π + δ) × exp (jδ / 2) × sin (δ / 2) (11)
It is represented by

Therefore, the light intensity I _c of the straight transmitted light is
I _C = {2 / (2π + δ)} ² × {sin (δ / 2)} ² (12)
It is represented by Here, when the formula (8) is compared with the formulas (10) and (12), the power of sin (δ / 2) in the light intensity of the linearly transmitted light with respect to the shift amount δ of the phase difference of the transmitted light is In the diffraction grating structure of the present invention, the power of the conventional diffraction grating structure is squared to the fourth power.

  As a result, even if the phase difference deviation amount δ occurs, the light intensity of the linearly transmitted light can be maintained at a small value close to zero in the diffraction grating structure of the present invention. Here, as a factor of the phase difference deviation amount δ, when the wavelength λ of the incident light in which the phase difference φ (m) = mπ of the transmitted light in the small region is different, it is caused by manufacturing variations in manufacturing such as processing of the diffraction grating shape. Thus, a case where the phase difference deviates from mπ is assumed. In other words, by using the diffraction grating according to the present invention, the light intensity of the linearly transmitted light can be kept small with respect to light incident in a wide wavelength band. Moreover, even if there is a manufacturing variation, the light intensity of the straight transmitted light can be maintained at a small value, so that stable characteristics can be realized.

  The equations (6) to (8) are applied when the phase difference φ (m) is shifted from mπ to + δ and φ (−m) is shifted from −mπ to −δ. Similar effects can be expected compared to conventional diffraction gratings even when the values are different. Next, a specific configuration example and operation of the diffraction grating structure of the present invention will be described.

  Specifically, the structure of the diffraction element 100 according to the first embodiment of the present invention shown in FIG. 1 will be described. The diffraction element 100 is formed on the surface of the translucent substrate 1 from unit regions 10 having a grating pitch Px having a periodic structure in the X direction and a grating pitch Py having a periodic structure in the Y direction. FIG. 2 shows a plan view of the unit region 10. As described above, the unit region 10 is divided into four equal area sections and three small regions having different phases of the transmitted light having the wavelength λ, and the average phase of the transmitted light having the wavelength λ transmitted through the entire unit region. Transmitted light complex amplitude U (0) where the phase difference of transmitted light is zero, transmitted light complex amplitude U (−1) is small where −π, and transmitted light complex amplitude U (+1 where π is π. ). The unit area 10 is composed of four sections with x1 = x2 and y1 = y2 so that the areas of the sections obtained by the Px divided widths x1 and x2 and the Py divided widths y1 and y2 are equal. As a result, the area ratio of U (−1), U (0), and U (+1) is 1: 2: 1.

At this time, (3) When φ (1) = π + δ In Equation, the light intensity _{I A} of the straight transmission light (8) below,
I _A = {sin (δ / 2)} ⁴ (13)
It becomes. The area ratio S (−1): S (0): S (+1) of U (0), U (−1), and U (+1) is an optimum value of 1: 2: 1. On the other hand, even when the area deviates from the optimum value within the range of ± 2% for S (0) and within ± 5% for S (−1) and S (+1), the desired effect can be obtained.

(Second Embodiment)
FIG. 3 is a plan view showing the configuration of the diffraction element 200 according to the second embodiment of the present invention. The diffractive element 200 is formed on the surface of the translucent substrate 1 from unit regions 20 having a lattice pitch Px with a periodic structure in the X direction and a linear structure in the Y direction. FIG. 4 shows a plan view of the unit region 20. As in the first embodiment, the unit region 20 is divided into three small regions having different phases of the transmitted light having the wavelength λ, and the transmitted light level relative to the average phase of the transmitted light having the wavelength λ transmitted through the entire unit region. From a small region of the transmitted light complex amplitude U (0) where the phase difference is zero, a small region of the transmitted light complex amplitude U (−1) where the phase difference is −π, and a small region of the transmitted light complex amplitude U (+1) where the phase difference is π. Become. The unit area 20 is divided into three sections with Px division widths of x1, x2, and x3 so that x1 = x3 = 0.5 * x2. As a result, the area ratio of U (−1), U (0), and U (+1) is 1: 2: 1. At this time, (3) When φ (1) = π + δ in equation becomes (8) than the light intensity of the linear transmitted light I _A is said as in the first embodiment (13).

FIG. 5 is a schematic cross-sectional view of the unit region 20 in the X direction. The concave and convex shapes may be obtained by directly finely processing the surface of the translucent substrate 1 to form the lattice 2, or forming a dielectric film on the surface of the translucent substrate 1, You may process into the shape of 2. As a fine processing method of the grating 2, photolithography using a photomask and dry etching are performed, or the surface of the translucent substrate 1 is directly formed by using a transfer mold of the grating 2, or the translucent substrate is used. The lattice may be transferred and molded on a light-transmitting resin coated on the surface of 1. The depth of the grating 2 in the small area of the transmitted light complex amplitude U (−1) and U (+1) with respect to the small area of the transmitted light complex amplitude U (0) is defined as d (−1) and d (+1). the refractive index of the material of n, when the isotropic refractive index of the transparent material 3, such as air in contact with the grating 2 and n _s the wavelength transmitted light complex amplitude to incident light of λ U (0), U ( - 1) and the phase difference of the small region of U (+1) is φ (0) = 0,
φ (−1) = 2π × (n− _ns ) × {−d (−1)} / λ,
φ (+1) = 2π × (n− _ns ) × d (+1) / λ,
It becomes. here,
φ (+1) = − φ (−1) = π,
In order to achieve this, the lattice depth of the small region of the lattice 2 may be d (−1) = d (+1) = λ / {2 × (n− _ns )}. The same applies to the processing of the grating depth of the small area of the grating of the diffraction element 100 composed of the unit area 10 in the first embodiment.

The unit regions of the first and second embodiments are each composed of three small regions U (−1), U (0), U (+1) having different transmitted light complex amplitudes, and the area ratio is 1: 2. : because the light intensity I _a of the rectilinear transmitted light if 1 is denoted by the same formula may be a division pattern other than the first and second embodiments.

  The first and second embodiments will be described in comparison. If the lengths of Px and Py of the unit region 10 and the unit region 20 are the same, the diffraction element 100 comprising the unit region 10 mainly has (± first-order diffracted light, ± first-order diffracted light) in the (X, Y) direction. Are generated in directions that form an angle of 45 ° with the X direction and the Y direction, but the diffraction element 200 including the unit region 20 mainly generates ± first-order diffracted light in the X direction. When utilizing the diffracted light generated by the diffractive element of the present invention, the optical system may be designed in consideration of such characteristics. Further, since the minimum dimension of the section of the diffractive element 100 is Px / 2 or Py / 2, the minimum dimension of the section of the diffractive element 200 is Px / 4. Therefore, the diffractive element 100 can be easily manufactured.

(Third embodiment)
FIG. 6 is a plan view showing the configuration of the unit region 30 of the diffraction element according to the third embodiment of the present invention. The unit region 30 is divided into six sections and is divided into five small regions having different phases of transmitted light of wavelength λ, and the level of transmitted light with respect to the average phase of transmitted light of wavelength λ transmitted through the entire unit region. A small region of the transmitted light complex amplitude U (0) where the phase difference is zero, a small region of the transmitted light complex amplitude U (−2) where the phase difference is −2π, and a small region of the transmitted light complex amplitude U (−1) where the phase difference is −π. An area consists of a small area of the transmitted light complex amplitude U (+1) that becomes π, and a small area of the transmitted light complex amplitude U (+2) that becomes 2π.

  As shown in FIG. 6, the unit area 30 is divided into six sections with a Px division width of x1, x2, x3, and x4 and a Py division width of y1, y2, y3, and y4, and x1 = x2 = x3 = x4 = It is composed of five small regions with different transmitted light complex amplitudes such that Px / 4 and y1 = y2 = y3 = y4 = Py / 4. Here, the transmitted light complex amplitudes U (−2), U (−1), U (0), U (+1), and U (+2) area ratios S (−2): S (−1): S ( 0): S (+1): S (+2) is 1: 4: 6: 4: 1.

In this case, in (3) φ (1) = π + δ , φ (2) = When 2 [pi + [delta], the light intensity _{I A} of the straight transmission light (8) below,
I _A = (3/4) ² × {sin (δ / 2)} ⁴ (14)
It is represented by Since the area ratio of the transmitted light complex amplitude U with an increase in the number of small areas (0) in comparison with the first and second embodiment is reduced, the light intensity I _A of the rectilinear transmitted light as a ratio (3/4 ) will ^double, to decrease effectively.

Further, in (3) φ (1) = π + δ , when the φ (2) = 2 (π + δ), the light intensity _{I A} of the straight transmission light (8) below,
I _A = {sin (δ / 2)} ⁸ (15)
It is represented by For sin ([delta] / 2) as compared with the first and second embodiments, the number should large, the light intensity I _A of the straight transmission light with respect to the deviation amount [delta] from the design value of the phase difference is reduced effectively.

  Note that the area ratio S (−2): S (−1): S (0): S (U (−2), U (−1), U (0), U (+1), and U (+2). +1): S (+2) is an optimum value of 1: 4: 6: 4: 1, but S (0) is within ± 2% of the optimum value, and S (−1) and S (+1) And S (−2) and S (+2) can obtain a desired effect even when the area deviates from the optimum value within a range of ± 5%.

Here, when the unit region is composed of an odd number of small regions of 3 or more, the average phase difference of the unit regions is zero, the area of the small region where the phase difference is zero is S ₀ , and the phase difference is different by π. subregions area of the S _m, the phase difference is the m different small areas by -π and S _-m,
The ratio of S _−m :...: S ₀ :...: S _m is a binomial distribution represented by a combination of selecting 2 k from 2 m. / {K! × (2m-k)! } Is an integer between k = 0 and 2 m. Here, assuming that the area of a small region having a phase difference of jπ as an integer between j = −m and m is Sj,
(2m)! / {(J + m)! × (m−j)! } (16)
Can be expressed as Therefore, even when the unit region is composed of 7 or 9 small regions, it is preferable to design so as to satisfy the area ratio of equation (16).

(Fourth embodiment)
FIG. 7 is a plan view showing the configuration of the unit region 40 of the diffraction element according to the fourth embodiment of the present invention. The unit region 40 is divided into five sections, and is divided into five small regions having different phases of the transmitted light having the wavelength λ, and the level of the transmitted light with respect to the average phase of the transmitted light having the wavelength λ transmitted through the entire unit region. A small region of the transmitted light complex amplitude U (0) where the phase difference is zero, a small region of the transmitted light complex amplitude U (−2) where the phase difference is −2π, and a small region of the transmitted light complex amplitude U (−1) where the phase difference is −π. An area consists of a small area of the transmitted light complex amplitude U (+1) that becomes π, and a small area of the transmitted light complex amplitude U (+2) that becomes 2π.

As shown in FIG. 7, the unit region 40 has Px division widths x1, x2, x3, x4, and x5, and x1 = x5 = (1/4) × x2 = (1/4) × x4 = (1/6). ) × x3 = is divided into five so as to form five sections. Each of these sections is a small area. As a result, the area ratio of U (−2), U (−1), U (0), U (+1), and U (+2) is 1: 4: 6: 4: 1. At this time, (3) phi in formula (1) = π + δ, φ (2) = When 2π + δ, (8) as in the third embodiment the light intensity _{I A} of the straight transmission light from the equation (14) It becomes. Further, (3) phi in formula (1) = π + δ, φ (2) = 2 if ([pi + [delta]) to the light intensity _{I A} of the straight transmission light from the equation (8) above as in the third embodiment ( 15).

FIG. 8 is a schematic cross-sectional view of the unit region 40 in the X direction. The same parts as those in the second embodiment are denoted by the same numbers to avoid duplication of explanation. When the depth of the grating 2 in the small region of the transmitted light complex amplitudes U (−2) and U (+2) added to the grating 2 shown in FIG. 8 is d (−2) and d (+2), The phase difference between the small areas of the transmitted light complex amplitudes U (−2) and U (+2) with respect to the incident light is expressed by the following equation.
φ (−2) = 2π × (n− _ns ) × {−d (−2)} / λ,
φ (+2) = 2π × (n− _ns ) × d (+2) / λ,
Here, in order to set φ (+2) = − φ (−2) = 2π, the lattice depth of the small region of the lattice 2 is d (−2) = d (+2) = λ / (n−n). _s ).

The same applies to the processing of the lattice depth of the small region of the lattice of the unit region 30 in the third embodiment. The unit areas of the third and fourth embodiments are U (−2), U (−1), U (0), U (+1), and U (+2) 5 having different transmitted light complex amplitudes. one of made small regions, the area ratio is 1: 4: 6: 4: because the light intensity I _a of the rectilinear transmitted light if 1 is denoted by the same formula, division pattern is not limited to this, the third And a division pattern other than the fourth embodiment.

(Fifth embodiment)
FIG. 9 is a plan view of a diffraction element 300 according to the fifth embodiment of the present invention, and FIG. 10 is a schematic cross-sectional view showing the structure of the unit region 50 of the diffraction element 300. The plan view showing the configuration of the diffraction element 300 and the unit region 50 is the same as FIG. 3 and FIG. 4 showing the second embodiment. On one surface of the transparent substrate 1a, a birefringent material layer using a birefringent material of the ordinary refractive index n _o and extraordinary refractive index _{n e (n o ≠ n e} ), the fast axis (the ordinary refractive The direction indicating the rate) is aligned with the X direction in FIG. Next, the birefringent material layer is divided into three small regions for each thickness, and the thickness of the birefringent material layer in each small region is zero, d (−1), d (−1) + d (+1) Then, the Px division widths are x1, x2, and x3, respectively, and processing is performed so that x1 = x3 = (1/2) × x2, thereby forming a grating 4 made of a birefringent material layer.

Then, adhered to at least the recess was filled with isotropic transparent material 5 of the ordinary refractive index n _o or the extraordinary refractive index n _e is equal refractive index n _s of the birefringent material, light-transmissive substrate 1b of the grid 4 Thus, the diffraction element 300 including the unit region 50 is configured. Here, at least the meaning of the concave portion may be filled only with the concave portion or may be filled so as to fill the concave and convex portion. The isotropic transparent material is a transparent material having an isotropic refractive index. Examples of the birefringent material include birefringent crystals such as crystal and LiNbO ₃ , birefringent films obtained by stretching an organic film such as polycarbonate, and liquid crystal monomers having birefringence are oriented in one direction and then solidified by polymerization. Polymer liquid crystal or the like is used. The fifth embodiment shown in FIG. 10 corresponds to an example in which a polymer liquid crystal is used as the birefringent material.

Here, for the wavelength λ of the incident light of the diffraction element 300,
| N _e −n _o | × d (−1) = | n _e −n _o | × d (+1) = λ / 2,
D (−1) and d (+1) are adjusted so that In the diffraction element 300 that is fabricated in this manner, the n o ₌ n linearly polarized light in the X direction in the case of _s, the case of n e ₌ n _s a first polarization direction linearly polarized light in the Y direction, the When light having a polarization direction of 1 is incident on the diffraction element 300, the light passes straight without being diffracted.

On the other hand, when light having a second polarization direction orthogonal to the first polarization direction is incident on the diffraction element 300, the diffraction effect occurs, and transmitted light complex amplitudes U (0), U (− The phase difference between the subregions 1) and U (+1) is described by the following equation.
φ (0) = 0,
φ (−1) = 2π × | n _e −n _o | × {−d (−1)} / λ = −π,
φ (+1) = 2π × | n _e −n _o | × d (+1) / λ = + π,
Further, the area ratio of U (−1), U (0), and U (+1) is 1: 2: 1.

  As a result, for a wide wavelength band of incident light, a high linear transmittance is obtained for incident light in the first polarization direction, and a straight line is stably obtained for incident light in the second polarization direction. A function of blocking transmitted light is obtained. That is, it is possible to realize a diffraction element having a high polarization extinction ratio represented by the ratio of the linear transmittance of polarized light components orthogonal to each other in incident light. In the diffractive element 300 of this embodiment, the unit region composed of the three small regions similar to the second embodiment has been described, but the unit region composed of any of the small regions of the first to fourth embodiments may be used. I do not care.

(Sixth embodiment)
FIG. 11 is a perspective view showing the configuration of a diffraction element 400 according to the sixth embodiment of the present invention, and FIG. 12 is a perspective view showing the configuration of the unit region 60. This example, the polarization diffraction grating and two stacked, the refractive index n _s of the ordinary refractive index n _o or the extraordinary refractive index n _e and isotropic transparent material of each birefringent material polarization grating matches This is an example in which the same direction is set by two polarization diffraction gratings. The unit region 60 is a gap formed by opposing two types of gratings 4a and 4b having the same grating shape as the polarization diffraction grating of the unit region 50 of the fifth embodiment so that the longitudinal directions of the gratings are orthogonal to each other. The structure is filled with the isotropic transparent material 5. Here, the ordinary refractive index of the grating 4a and 4b n _o and extraordinary index n _e is the same direction, i.e., set to the fast axis and slow axis of the grating 4a and 4b are consistent when viewed from X-Y plane To do.

When light is incident from the Z direction in the diffraction element 400, the component of the light in the first polarization direction in which the refractive index n _s and grating 4a, the refractive index of 4b matches the out isotropic transparent material 5 of the incident light is transmitted The light components of the second polarization direction having different refractive indexes are diffracted. Here, since the diffracted light that is diffracted by the incident light of the second polarization direction is generated by both of the two polarization diffraction gratings, the second polarization is compared with the diffraction element 300 including a single polarization diffraction grating. Directly transmitted light in the direction is reduced and the blocking function is improved. As a result, it is possible to realize a diffraction element having a higher polarization extinction ratio with respect to a structure composed of one polarization diffraction grating.

(Seventh embodiment)
FIG. 13 is a schematic cross-sectional view showing the configuration of a diffraction element 500 according to the seventh embodiment of the present invention. In this example, a liquid crystal layer that changes a retardation value between zero and λ / 2 with respect to light having the wavelength λ by applying a voltage to an electrode is disposed between two polarization diffraction gratings. the direction in which the refractive index n _s of the ordinary refractive index n _o or the extraordinary refractive index n _e and isotropic transparent material of the birefringent material matches were to or the same mutually orthogonal two polarization grating Is. In the diffraction element 500 shown in the seventh embodiment, two gratings 504a and 504b having the same grating shape as the diffraction element 300 including the unit region 50 of the fifth embodiment are filled with an isotropic transparent material 505, respectively. The liquid crystal cell 510 is bonded to the light incident side and the light emitting side through the light transmitting substrates 501a and 501b. A portion where the translucent substrate, the birefringent material grating, and the isotropic transparent material are integrated is referred to as a polarization diffraction grating portion, and here, 300a and 300b correspond thereto. Here, the lattice longitudinally ordinary refractive index n _o and consisting direction (fast axis) is the X-direction of the birefringent material of the gratings 504a and the X direction, the ordinary refractive index n _o of the birefringent material of the grating 504b direction (fast axis) of the grating longitudinal direction and Y direction in the Y direction, a structure in which the ordinary refractive index n _o of the refractive index n _s and grating 504a and 504b of the birefringent material of the isotropic transparent material 505 matches .

The liquid crystal cell 510 is arranged on the transparent electrodes 506a and 506b formed on one side of the translucent substrates 501c and 501d so that, for example, the alignment direction of liquid crystal molecules is aligned at an angle of 45 ° from the X direction to the Y direction. alignment film (not shown) is formed, the liquid crystal 507 with the seal 508 is sealed to the layer thickness d _LC. The liquid crystal 507 has a refractive index anisotropy Δn and a dielectric anisotropy Δε, and the orientation direction of the liquid crystal molecules changes according to the voltage applied to the transparent electrodes 506a and 506b. When the dielectric anisotropy Δε is positive, when an alignment film is used in which the liquid crystal 507 is aligned in the 45 ° direction parallel to the translucent substrate when no voltage is applied, the liquid crystal molecules are translucent as the applied voltage increases. Are aligned in the Z-axis direction perpendicular to. When the dielectric anisotropy Δε is negative, the alignment film similar to the above is used, and if necessary, the alignment film surface is vertically aligned. When no voltage is applied, the liquid crystal 507 is aligned vertically to the translucent substrate, As the applied voltage is increased, the liquid crystal molecules are aligned in the direction of 45 ° parallel to the translucent substrate.

The retardation value R generated when the molecules in the liquid crystal layer are tilted in the 45 ° direction in the direction parallel to the translucent substrate at a specific applied voltage is set to λ / 2 with respect to the wavelength λ of incident light. The layer thickness d _{LC of the} liquid crystal 507 is adjusted. Thereby, the liquid crystal cell 510 functions as a half-wave plate, and when the linearly polarized light in the X direction travels in the Z direction and enters, it is emitted as the linearly polarized light in the Y direction. On the other hand, when the molecules in the liquid crystal layer are aligned in the Z direction perpendicular to the translucent substrate, the retardation value R becomes zero, so that when the linearly polarized light in the X direction is incident, the same linearly polarized light is emitted. Thus, since the retardation value R changes from zero to λ / 2 according to the voltage applied to the liquid crystal 507, the outgoing light components of the linearly polarized light in the X direction and the Y direction change.

  Note that the liquid crystal 507 may have a twist alignment other than the homogeneous alignment in which liquid crystal molecules are aligned in one direction in the liquid crystal layer. A nematic liquid crystal is generally used as the liquid crystal, but a smectic liquid crystal or a cholesteric liquid crystal may be used. Further, the substrate constituting the liquid crystal cell and the substrate constituting the diffraction element may be a common substrate. In addition, a configuration in which a phase plate (not shown) is integrated with the liquid crystal cell 510 may be adopted. At this time, the retardation value of the phase plate integrated liquid crystal cell as a whole is multiplied by a natural number of λ and an odd number of λ / 2 by appropriately setting the phase axis direction and retardation value of the phase plate and the retardation value of the liquid crystal cell 510. Therefore, the degree of freedom in designing the voltage setting is increased.

  When linearly polarized light in the X direction is incident on the diffractive element 500 obtained in this way, it passes through the polarization diffraction grating portion 300a and the liquid crystal cell 510 in a straight line. For example, when the liquid crystal cell 510 generates a linearly polarized light component in the X direction and a linearly polarized light component in the Y direction, the linearly polarized light in the X direction is diffracted by the polarization diffraction grating unit 300b, and the linearly polarized light in the Y direction is linearly transmitted. To do. Since the polarization state of the light transmitted through the liquid crystal cell 510 can be controlled by the applied voltage, when the retardation value R of the liquid crystal cell 510 changes from λ / 2 to zero according to the applied voltage, the amount of outgoing light with respect to the amount of incident light A variable optical attenuator in which the straight-line transmittance expressed by the ratio is changed from 100% to zero is obtained. In the case where the polarization diffraction grating portion 300a is not provided, when the incident light includes a component of the polarization component in the Y direction and enters the liquid crystal cell 510, the extinction ratio of the linearly transmitted light cannot be increased. For this reason, the polarization diffraction grating unit 300a is arranged on the incident side of the liquid crystal cell 510, and even if light of the polarization component in the Y direction is incident, it can be diffracted by the polarization diffraction grating unit 300a. be able to.

FIG. 14 shows a schematic cross-sectional view of a transmission means using an optical fiber as an example of an optical system that separates linearly transmitted light and diffracted light in the polarization diffraction grating portion. In FIG. 14, the component of the light that enters parallel light into the diffractive element 500 and goes straight through the diffractive element 500 is collected in the opening of the optical fiber 12 by the condenser lens 11 as a light receiving system having an opening. It is what makes it light. On the other hand, the light diffracted and emitted by the diffractive element 500 is condensed at a position different from the opening of the optical fiber 12 by the condenser lens 11, and therefore cannot propagate through the optical fiber 12. In this way, by controlling the voltage applied to the liquid crystal cell 510 of the diffractive element 500, the light intensity that passes straight through the diffractive element 500 can be controlled. Although the polarization diffraction grating unit 300a is illustrated so as to receive linearly polarized light in the X direction, linear polarization in the Y direction may be input, and the polarization diffraction grating 504a and the isotropic transparent material 505 are accordingly matched. A combination that can be realized by adjusting the refractive index of the lens can be freely set. For example approximate the refractive index n _s of the isotropic transparent material to the extraordinary refractive index n _e of the birefringent material settings, when using a polymer liquid crystal, setting of longitudinal or perpendicular to the direction of the alignment direction grating Is possible.

(Eighth embodiment)
FIG. 15 is a schematic sectional view showing the structure of a diffraction element 600 according to the eighth embodiment of the present invention. In this example, a liquid crystal layer is disposed between a polarizing diffraction grating and a reflective substrate so that a retardation value is changed between zero and λ / 4 with respect to light having the wavelength λ by applying a voltage to the electrode. is there. The polarization diffraction grating portion 300b shown in the seventh embodiment is joined to the light incident / exit side of the reflective liquid crystal cell 610 in which the liquid crystal cell and the light reflecting layer are integrated. Moreover, the same number is attached | subjected to the part which overlaps with the diffraction element 500 of a 7th embodiment, and duplication of description is avoided.

Next, the reflective liquid crystal cell 610 will be described. The difference between the reflective liquid crystal cell 610 and the liquid crystal cell 510 of the seventh embodiment is that a light reflecting layer 609 is first formed on the surface of the translucent substrate 601. The other is that the retardation value R generated when the molecules in the liquid crystal layer are aligned in the 45 ° direction in the direction parallel to the translucent substrate at a specific applied voltage is λ with respect to the wavelength λ of the incident light. / 4 to become so in that it is adjusted to the layer thickness d _LC of the liquid crystal 607, the other structure is the same as the liquid crystal cell 510. In this example, the light reflecting layer 609 is provided on the inner surface of the translucent substrate 601, but a reflecting layer is provided on the outer surface side, the substrate itself is used as a reflecting substrate, or a reflecting plate is provided outside the translucent substrate 601. May be provided.

  Light incident as linearly polarized light in the Y direction of the reflective liquid crystal cell 610 is reflected by the light reflecting layer 609 and passes through the liquid crystal layer twice, so that it functions as a wave plate having a retardation value R that is twice as large as the light reciprocates. As a result, when the retardation value R changes from zero to λ / 4 according to the magnitude of the voltage applied to the liquid crystal 507, the component of light emitted as linearly polarized light in the X direction and the Y direction changes. When linearly polarized light in the Y direction is incident on the diffraction element 600 obtained in this way, it passes straight through the polarizing diffraction grating portion 300b and the liquid crystal 607 layer of the reflective liquid crystal cell 610, and is reflected by the light reflecting layer 609. The light passes through the liquid crystal layer twice and is incident again on the polarization diffraction grating unit 300b.

  Then, the incident light is diffracted by the polarization diffraction grating unit 300b, so that only the linearly polarized light in the Y direction is linearly transmitted. Therefore, when the retardation value R of the reflective liquid crystal cell 610 changes from λ / 4 to zero according to the applied voltage, a variable optical attenuator whose linear transmittance changes from zero to 100% is obtained.

  FIG. 16 is a schematic cross-sectional view of a transmission means using an optical fiber as an example of an optical system that separates linearly transmitted light and diffracted light in the polarization diffraction grating portion. The divergent light emitted from the opening of the optical fiber 12 is collimated using the condenser lens 11 and incident on the diffraction element 600, reflected by the light reflecting layer 609, and again incident on the condenser lens 11. The component that passes straight through is condensed at the opening of the optical fiber 12 and propagates through the optical fiber. On the other hand, the light diffracted and emitted by the diffractive element 600 is condensed by the condenser lens 11 at a position different from the opening of the optical fiber 12, and therefore cannot be fed back through the optical fiber.

(Ninth Embodiment)
FIG. 17 is a schematic diagram showing a configuration of an optical head device 700 according to the ninth embodiment of the present invention. Polarization direction in the direction perpendicular to the paper surface emitted from a two-wavelength laser light source 13 in which a semiconductor laser that emits light in the wavelength band of 660 nm for DVD and a semiconductor laser that emits light in the wavelength band of 785 nm are integrated as an optical disk The linearly polarized divergent light is incident on the diffractive element 300 of the present invention and is transmitted in a straight line. Further, a part of the light reflected from the beam splitter 14 is collimated by the condenser lens 15, is transmitted as circularly polarized light by the quarter wavelength plate 16, and is collected on the information recording surface of the optical disk 18 by the objective lens 17. To be lighted.

  The light reflected by the information recording surface is collimated by the objective lens 17 and enters the quarter-wave plate 16 to be transmitted as linearly polarized light in the direction parallel to the paper surface. Further, the light passing through the beam splitter 14 is collected on the light receiving surface of the photodetector 19 by the condenser lens 15. Further, a part of the light reflected from the beam splitter 14 by the linearly polarized light in the direction parallel to the paper surface enters the diffraction element 300 and is diffracted, and the light returning to the light emitting point of the two-wavelength laser light source 13 is blocked.

  Since the conventional diffraction element cannot realize a sufficiently low linear transmittance for both laser wavelengths of 660 nm and 785 nm, light reflected from the optical disk at the light emitting point of the light source 13 is generated and returned. There was a problem of making laser oscillation unstable. In particular, when laser oscillation is unstable in the light source 13 that emits high-power two-wavelength light used for information recording on the optical disc, it causes a recording error, and thus the return light that reaches the light source that is reflected by the optical disc. It is necessary to shut off. For this reason, by using the diffraction element 300 of the present invention, a high linear transmitted light blocking function is exhibited with respect to the linearly polarized light of the return light in a wide wavelength band, so that the laser oscillation of the light source 13 that emits light of two wavelengths is stabilized. Can be Although the diffraction element 300 is used here, the present invention is not limited to this, and other diffraction elements having the polarization diffraction grating of the present invention may be used.

(Tenth embodiment)
FIG. 18 is a schematic diagram showing a configuration of a projection type liquid crystal display device 800 according to the tenth embodiment of the present invention. The projection light source 31 is a light source that emits visible light, and the emitted visible light is transmitted through the polarization diffraction element 32 as linearly polarized light in the Y direction and diffracted in the X direction. The dichroic prism 38 has a function of reflecting blue light and red light, which will be described later, and transmitting green light. The dichroic mirror 33 transmits blue light having a wavelength of 420 to 480 nm, is reflected by the total reflection mirror 35a, and enters the liquid crystal light valve 36B that forms a blue transmission image. The image of the linearly polarized light component in the Y direction formed by the liquid crystal light valve 36B is transmitted through the linearly polarized light in the Y direction by the polarization type diffraction element 37B, and the linearly polarized light component orthogonal thereto is diffracted, and the blue wavelength reflecting surface of the dichroic prism 38 The transmitted light is collected at the opening of the aperture stop 39 of the projection lens 40.

  Next, green light having a wavelength of 520 to 560 nm is reflected by the dichroic mirror 33 and the dichroic mirror 34, and then enters the liquid crystal light valve 36G that forms a green transmission image. The X-direction linearly polarized light component image formed by the liquid crystal light valve 36G is transmitted by the polarizing diffraction element 37G, and the linearly polarized light component orthogonal thereto is diffracted and transmitted through the dichroic prism 38. The light is collected at the opening of the aperture stop 39 of the projection lens 40.

  Further, the red light having a wavelength of 610 to 670 nm is reflected by the dichroic mirror 33, passes through the dichroic mirror 34, is reflected by the two total reflection mirrors 35 b and 35 c, and then forms a transmission image for red. Incident on 36R. The image of the linearly polarized light component in the Y direction formed by the liquid crystal light valve 36R is transmitted through the linearly polarized light in the Y direction by the polarization type diffraction element 37R, and the linearly polarized light component orthogonal thereto is diffracted, and the red wavelength reflecting surface of the dichroic prism 38 The transmitted light is collected at the opening of the aperture stop 39 of the projection lens 40.

  The blue, green and red transmitted lights generated by the liquid crystal light valves 36B, 36G and 36R are combined by the dichroic prism 38 so that their optical axes are aligned, and a composite image of the liquid crystal light valve is formed on the screen 41 by the projection lens 40. Is done. On the other hand, the light diffracted by the polarization type diffraction elements 32 and 37B, 37G, and 37R cannot be transmitted through the opening of the aperture stop 39 and is blocked, so that it does not form an image on the screen 41. Any of the transmission type diffraction elements having the polarization diffraction grating of the present invention can be disposed at the positions of the polarization type diffraction elements 32 and 37B, 37G, and 37R. It is preferable to dispose the diffraction element 400 which is an aspect.

  Here, a high-pressure mercury lamp that emits visible wavelength light is used as the light source 31 for projection, but LED light sources or LD light sources for blue, green, and red may be used. Further, between the light source 31 and the diffractive element 32 of the present invention, the polarized light that efficiently converts random polarized light emitted from the light source into the optical path to linearly polarized light in the Y direction, and the illumination light of the liquid crystal light valve are uniform. In order to achieve this, an integrator lens array or the like may be arranged. Since the linearly polarized light emitted from the polarization conversion element has a low polarization purity, it is effective to improve the polarization purity by using the diffraction element 32 of the present invention to increase the contrast of the projected image. The projection light source, the liquid crystal light valve, the dichroic mirror, the dichroic prism, the polarization conversion element, and the integrator lens array that are used in the projection type liquid crystal display device are well known and will not be described.

Example 1
One side of a quartz glass substrate as the translucent substrate 1a is processed into a lattice shape by photolithography using a photomask and dry etching, and antireflection films are formed on both sides of the quartz glass substrate. At this time, it is assumed that the grating shape is divided into three small regions of the first and second embodiments, and the diffraction grating shape divided into five small regions of the third and fourth embodiments. . Here, processing is performed to the depth of the grating such that the phase difference φ (m) in the light of wavelength 710 nm of the grating in each small region is mπ (where m = −2, −1, 0, 1, 2). To do. For example, in the unit region 20 of the diffraction element 200 shown in FIG. 3, the refractive index of the quartz glass substrate is 1.455 at 710 nm, and the heights of d (−1) and d (+1) are 0.78 μm. 8 is processed so that the height of d (−2), d (−1), d (+1), and d (+2) is 0.78 μm. When light having a wavelength of 500 to 1000 nm is incident on the diffraction grating shape divided into three and five small regions obtained in this way, the calculation result of the straight transmission light transmittance is shown in FIG. As a comparison, FIG. 19 also shows the calculation result of the linearly transmitted light rate of a diffraction grating having a rectangular cross-sectional shape that is equally divided into two regions as in the prior art. From this result, it is possible to reduce the linear transmittance in a wide wavelength band in the diffraction grating shape divided into three and five small regions of the present invention as compared with the conventional two-region equally divided diffraction grating.

  The fifth embodiment shows the diffraction grating shape divided into three small regions of the first and second embodiments or the diffraction grating shape divided into five small regions of the third and fourth embodiments. Consider a case where a polarization diffraction grating as shown in the diffraction element 300 is provided. The ratio of the linear transmittance of the incident light having the first polarization direction in which the polarization diffraction grating does not exhibit the diffraction action and the second polarization direction orthogonal to the first polarization direction. When the polarization extinction ratio of the specified polarization diffraction grating is expressed in dB unit, the calculation result shown in FIG. 20 is obtained. Compared with the conventional two-region equally-divided polarization diffraction grating, the polarization diffraction grating having a diffraction grating shape divided into three and five small regions according to the present invention provides a high polarization extinction ratio in a wide wavelength band.

  The calculation results shown in FIGS. 19 and 20 are based on the approximate calculation based on the scalar diffraction theory applied when the grating pitch is sufficiently larger than the wavelength and the grating depth is relatively thin. When the grating depth is relatively thick with respect to the grating pitch, the linear transmission increases due to the influence of the grating wall surface, but the relative relationship is maintained.

(Example 2)
The Example of the diffraction element 300 which is a 5th embodiment is shown. As shown in a schematic cross-sectional view of the unit region 50 of the diffraction element 300, an alignment film (not shown) that is aligned in the Y direction is formed on one surface of the quartz glass substrate 1a. A birefringent material layer made of a polymer liquid crystal in which liquid crystal molecules are aligned in the Y direction and aligned in the direction of extraordinary refractive index is prepared by applying a liquid crystal monomer thereon and then irradiating it with ultraviolet rays to solidify it. Here, the polymer liquid crystal layer has an ordinary light refractive index n _o = 1.55 and an extraordinary light refractive index n _e = 1.70 at a wavelength of 720 nm, and the thickness of the layer is 4.8 μm.

  Next, the polymer liquid crystal layer is processed into a polarization diffraction grating 4 having a stepped shape with a thickness of three steps as shown in FIG. 10 and a straight line in the Y direction by photolithography and etching techniques. . In FIG. 10, the grating pitch Px = 6 μm, x1 = x3 = 1.5 μm, x2 = 3 μm, and d (−1) = d (+1) = 2.4 μm.

Further, using an adhesive which is an isotropic transparent material 5 having a refractive index n _s = 1.55 equal to the ordinary refractive index n _o , the concave portion of the polarization diffraction grating 4 is filled and quartz glass is used as the translucent substrate 1b. A diffractive element 300 composed of unit regions 50 is bonded to the substrate. An antireflection film (not shown) is formed on the air interface between the translucent substrates 1a and 1b, which are quartz glass substrates. At this time, the relationship of | n _e −n _s | × d (−1) = | n _e −n _s | × d (+1) = λ / 2 with respect to the wavelength λ = 720 nm of the incident light of the diffraction element 300. Meet.

  The light having the polarization direction in the X direction incident on the diffractive element 300 manufactured in this way is transmitted in a straight line, and the light in the polarization direction in the Y direction is diffracted and is not transmitted in a straight line. At this time, with respect to incident light having a wavelength of 630 nm to 800 nm, the linear transmittance of polarized light in the X direction is 95% or more, and the straight transmittance of polarized light in the Y direction is 0.1% or less. The polarization extinction ratio, which is the linear transmittance ratio of the polarized light in the direction, can be a high value of 1000 or more.

  Also, a polarization extinction ratio equivalent to that of the diffractive element 300 of the first embodiment can be obtained by stacking two layers of conventional polarization diffraction gratings having a rectangular cross section. The diffraction element 300 obtained in this way is used by being mounted on the optical head device 700 shown in FIG. As a result, the light reflected by the information recording surface of the optical disk 18 is diffracted by the diffraction element 300, so that the light returning to the emission point of the two-wavelength laser light source 13 is effectively blocked, and the laser oscillation of the two-wavelength laser light source 13 is suppressed. Can be stabilized.

(Comparative Example 1)
As a comparative example, the configuration of Px in a unit region of a diffraction element having a polarization diffraction grating (not shown) is set to x1 = x2 = 3 μm using FIG. 10, and a conventional rectangle in which x3 and d (+1) correspond to zero In the case of a polarization diffraction grating having a cross-sectional shape, the wavelength at which the linear transmittance of light in the polarization direction in the Y direction is 0.1% or less is limited to a narrow wavelength band of 700 nm to 730 nm, and the average for incident light with a wavelength of 630 nm to 800 nm As a low polarization extinction ratio.

(Example 3)
The Example of the diffraction element 500 which is a 7th embodiment is shown. In the schematic cross-sectional view of the diffraction element 500 shown in FIG. 13, the two types of polarization diffraction grating portions 300a and 300b are polarization diffraction gratings using a polymer liquid crystal layer similar to that of Example 2 as a birefringent material. The gratings 504a and 504b of the polarizing diffraction grating portions 300a and 300b have an ordinary light refractive index n _o = 1.54 and an extraordinary light refractive index n _e = 1.69 at a wavelength of 1550 nm. From the three small regions shown in FIG. In the example of the schematic sectional view of the unit region 50, the lattice pitch Px = 20 μm, x1 = x3 = 5 μm, x2 = 10 μm, and d (−1) = d (+1) = 5.17 μm. Furthermore, using an isotropic transparent material 505 a is adhesive having a refractive index _n s = 1.54 is equal to the ordinary refractive index _{n o,} polarization grating portion 300a quartz glass to fill the recesses of the grating 504a and 504b The transparent substrates 501a and 501c made of a substrate are sandwiched, and the polarization diffraction grating portion 300b is sandwiched between the transparent substrates 501b and 501d made of a quartz glass substrate.

Here, the ordinary refractive index n _o of the grating 504a is a lattice longitudinally and X-direction in the X direction, the ordinary refractive index n _o of the grating 504b to the grating longitudinal direction as the Y direction in the Y direction. At this time, with respect to the wavelength λ = 1550 nm of the incident light of the polarization diffraction grating units 300a and 300b, | n _e −n _s | × d (−1) = | n _e −n _s | × d (+1) = λ Satisfies the relationship of / 2.

  In the case where the polarization diffraction grating of the diffraction element 500 is a unit region consisting of five small regions, the gratings 504a and 504b are processed to a thickness like the grating 2 shown in FIG. 8, and the grating pitch Px = 20 μm, x1 = x5 = 1.25 μm, x2 = x4 = 5 μm, x3 = 7.5 μm, and d (−2) = d (−1) = d (+1) = d (+2) = 5.17 μm.

In the liquid crystal cell 510, the molecular orientation of the liquid crystal 507 is + X when a voltage is applied between the transparent electrodes on the transparent electrodes 506a and 506b made of, for example, ITO formed on one side of the transparent substrates 501c and 501d made of a quartz glass substrate. The polyimide film is aligned by rubbing so that it is aligned at an angle of 45 ° to the + Y direction, and aminosilane as a vertical alignment treatment agent is applied to form a vertical alignment film (not shown). A seal 508 such as an epoxy resin is annularly applied to the peripheral portions of the transparent substrates 501c and 501d provided with the transparent electrode and the alignment film. In the seal, a spacer for obtaining a cell gap of about 8.0 μm and conductive fine particles serving as a conductive path for applying a voltage are mixed in advance. Liquid crystal 507 is injected and filled into the gap from an injection port (not shown) to form a liquid crystal cell 510. The liquid crystal 507 uses a nematic liquid crystal having negative dielectric anisotropy and a refractive index anisotropy Δn = 0.15, and has a layer thickness d _LC = 8.0 μm. At this time, since the molecules in the liquid crystal layer are aligned perpendicularly to the light transmissive substrate when no voltage is applied to the light transmissive substrates 501c and 501d, the retardation value R of the liquid crystal layer becomes zero. On the other hand, when an effective AC voltage V = 4 to 5 Vrms is applied, the retardation value R of the liquid crystal layer becomes R = λ / 2 with respect to the wavelength λ = 1480 to 1620 nm of the incident light, and the retardation value is obtained by changing the applied voltage from zero to 5 Vrms. A liquid crystal cell 510 in which R varies from zero to λ / 2 is obtained.

  When linearly polarized light in the X direction having a wavelength λ = 1480 to 1620 nm is incident on the diffraction element 500 thus obtained, when a voltage is applied to the liquid crystal cell 510 from zero to 5 Vrms, the linear transmittance is from 95 to a maximum of 95%. Change to.

  A diffractive element 500 using a polarization diffraction grating having a unit region composed of three small regions is arranged in the optical system shown in FIG. 14, and light having a wavelength of 1480 to 1620 nm is propagated in the optical fiber 12. With reference to the amount of light propagating through the optical fiber when the diffraction element 500 is not disposed, the optical fiber propagation efficiency when the applied voltage V to the liquid crystal cell 510 is 0 Vrms and the optical fiber propagation when the applied voltage is increased to 5 Vrms. The maximum efficiency in dB is shown in FIG. In addition, FIG. 21 also shows the optical fiber propagation efficiency when the applied voltage V to the liquid crystal cell 510 is 0 Vrms in the case of a diffraction element using a polarization diffraction grating having a unit region consisting of five small regions. In the scalar diffraction theory, the optical fiber propagation efficiency calculation value at 0 Vrms at a wavelength of 1550 nm is −∞ dB, but the grating depth in an actual diffraction grating is divided into two regions (region widths are equal). In the example, it is set to -40 dB, -80 dB when it is composed of three small areas of the present invention, and -100 dB when it is composed of five small areas of the present invention. As described above, it is possible to provide a voltage variable optical attenuator that exhibits a high extinction ratio with a low driving voltage and can be downsized with respect to light in a wide wavelength band from 1480 to 1620 nm.

Example 4
A diffractive element 300 composed of the unit region 50 according to the fifth embodiment of the present invention is arranged at the position of the polarizing diffractive element 32 constituting the projection type liquid crystal display device 800 according to the tenth embodiment, and the polarizing diffractive element 37B, In place of the unit region 50 according to the fifth embodiment of the present invention, a diffractive element composed of the unit region 30 is arranged at the positions 37G and 37R. Details of the diffraction element used in the present embodiment will be described below.

The diffraction element of the present invention is used at the position of the polarizing diffraction element 32, and the shape of the polarization diffraction grating in the unit region is made up of five regions having the shape of the unit region 30 shown in FIG. Here, the polarization type diffraction grating is made of a polymer liquid crystal having an ordinary light refractive index n _o = 1.55 and an extraordinary light refractive index n _e = 1.75 with respect to light having a wavelength of 520 nm, and the transmission complex amplitude of the unit region 30. Processing is performed by photolithography and etching so that the difference in thickness (m is −1, 0, +1, +2) between U (m) and transmission complex amplitude U (m−1) is 1.3 μm. In particular, a small region having a transmission complex amplitude U (−2) is etched so that the thickness of the polymer liquid crystal becomes zero. Further, the lattice pitches Px and Py of the unit region 30 are set to 3.2 μm, and x1 = x2 = x3 = x4 = y1 = y2 = y3 = y4 = 0.8 μm. Further, the direction of the ordinary refractive index n _o of the liquid crystal polymer as a Y direction, the ordinary refractive index n _o is equal refractive index n _{s =} 1.55 diffraction element to fill the voids of the polarization diffraction grating isotropic transparent material And

Thus the direction the ordinary refractive index n _o the position of the polarizing type diffraction element 32 of the projection type liquid crystal display device 800 of the diffractive element prepared FIG 18 is arranged such that the Y-direction. Of the visible light emitted from the projection light source 31, linearly polarized light in the Y direction travels straight through the polarizing diffraction element 32, and linearly polarized light in the X direction is diffracted by the polarizing diffraction element 32 in the X and Y directions. . As a result, the polarization extinction ratio of the linearly transmitted light of the polarizing diffraction element 32 is a calculated value of 50 dB or more for wavelengths 460 to 600 nm and 35 dB or more for wavelengths 430 to 660 nm, and the polarization purity in a wide wavelength range. Highly straight transmitted light can be obtained.

In each of the polarization diffraction elements 37B, 37G, and 37R, the diffraction element of the present invention in which the sectional shape of the polarization diffraction grating of the unit region 50 is composed of three small regions is disposed. The polymer liquid crystal and the isotropic transparent material used for the polarization diffraction grating are the same as the diffraction elements disposed as the polarization diffraction elements 32, but the diffraction elements of the present invention disposed as the polarization diffraction elements 37B, 37G, and 37R are Photolithography and etching are performed so that the layer thicknesses d (−1) = d (+1) of the three small regions of the polarization diffraction grating 4 shown in FIG. 10 are 1.15 μm, 1.4 μm, and 1.58 μm, respectively. Further, the lattice pitches Px and Py of the unit region 50 are set to 3.2 μm, and x1 = x2 / 2 = x3 = 0.8 μm. Further, the direction of the ordinary refractive index n _o of the liquid crystal polymer, a diffraction element to place polarizing diffraction element 37B, the 37R is the Y direction, the diffraction element arranged on the polarizing diffraction element 37G is the X direction, the ordinary refractive index The gaps of the polarization gratings opposed to each other are filled with an isotropic transparent material having a refractive index n _s = 1.55 equal to n _o . Further, in the projection type liquid crystal display device 800, the longitudinal direction of the gratings of the diffraction elements arranged in the polarization diffraction elements 37R, 37G, and 37B is 37 ° with respect to the X direction and the Y direction. , 37B and 37R are arranged to form an angle of 45 ° with respect to the Y direction and the Z direction.

  As a result, in the projection-type liquid crystal display device 800, of the blue light with a wavelength of 420 to 480 nm emitted from the liquid crystal light valve 36B and the red light with a wavelength of 610 to 670 nm emitted from the liquid crystal light valve 36R, linearly polarized light in the Y direction is respectively The linearly polarized light that passes straight through the polarizing diffraction elements 37B and 37R and is orthogonal thereto is diffracted by the polarizing diffraction elements 37B and 37R in a direction perpendicular to the longitudinal direction of the grating. In addition, among the green light having a wavelength of 520 to 560 nm emitted from the liquid crystal light valve 36G, the linearly polarized light in the X direction passes straight through the polarizing diffractive element 37G, and the linearly polarized light orthogonal thereto is transmitted in the longitudinal direction of the grating by the polarizing diffractive element 37G. Is diffracted in a direction perpendicular to. As a result, the polarization extinction ratio of the linearly transmitted light in each wavelength region becomes a calculated value of 40 dB or more, and the linearly transmitted light with high polarization purity is obtained. In this embodiment, visible light is wavelength-separated into blue light, green light, and red light, an image is formed using three types of liquid crystal light valves, and then a wavelength projection is performed to form a color projection image. It was. The same effect can be obtained by using one type of liquid crystal light valve that generates a color image and arranging the polarizing diffraction element of the present invention on the incident and exit sides.

  As described above, the diffraction element according to the present invention is used in the projection display device, which is generated in the case of a polarizing film that absorbs one linearly polarized light used in the conventional projection display device and transmits the linearly polarized light orthogonal thereto. It can be expected that the problem that characteristics deteriorate due to heat generated by light absorption when light of high light intensity is incident can be expected. Especially for heat generation, it is necessary to take heat dissipation measures using an air cooling fan, the brightness of the projected image cannot be improved due to the limitation of the light intensity of the projection light source to be used, and noise and power consumption are increased. However, since the diffractive element of this embodiment does not generate heat due to light absorption, it can be expected to solve such a problem.

  As described above, by using the diffraction grating-shaped diffraction element according to the present invention, the light intensity of the straight transmitted light can be kept small with respect to a wide wavelength band of incident light. In addition, even if there are manufacturing variations of individual elements such as semiconductor lasers, the light intensity of the linearly transmitted light can be maintained at a small value, so that stable characteristics can be realized. In particular, a low linear transmission can be stably achieved with a relatively simple configuration in which the diffraction grating is divided into three small regions or unit regions divided into five small regions are periodically arranged. Furthermore, by using the diffraction element of the present invention, a high linear transmittance can be obtained for incident light in the first polarization direction with respect to a wide wavelength band of incident light, and orthogonal to the first polarization direction. For the incident light in the second polarization direction, a function of stably blocking the straight transmitted light can be obtained, and a diffraction element having a high polarization extinction ratio can be realized. In addition, a diffraction element having a further improved extinction ratio can be realized by adopting a configuration in which the polarization diffraction gratings of the present invention are laminated. Furthermore, a relatively simple configuration using the diffraction element of the present invention can realize a small voltage variable optical attenuator that exhibits a high extinction ratio with a low driving voltage for light in a wide wavelength band.

FIG. 3 is a schematic plan view showing a configuration example of the diffraction element according to the first embodiment of the present invention. FIG. 2 is a schematic plan view showing a unit region of the diffraction element according to the first embodiment of the present invention. The plane schematic diagram which shows the structural example of the diffraction element of the 2nd embodiment of this invention. The plane schematic diagram which shows the unit area | region of the diffraction element of the 2nd embodiment of this invention. The cross-sectional schematic diagram which shows the unit area | region of the diffraction element of the 2nd embodiment of this invention. The plane schematic diagram which shows the unit area | region of the diffraction element of the 3rd embodiment of this invention. The plane schematic diagram which shows the unit area | region of the diffraction element of the 4th embodiment of this invention. The cross-sectional schematic diagram which shows the unit area | region of the diffraction element of the 4th embodiment of this invention. The plane schematic diagram which shows the structural example of the diffraction element of the 5th embodiment of this invention. The cross-sectional schematic diagram which shows the unit area | region of the diffraction element of the 5th embodiment of this invention. The schematic diagram which shows the structural example of the diffraction element of the 6th embodiment of this invention. The perspective view which shows the structural example of the diffraction element of the 6th embodiment of this invention. Sectional schematic diagram which shows the structural example of the diffraction element of the 7th embodiment of this invention. The cross-sectional schematic diagram which shows the structural example of the diffraction element of the 7th embodiment of this invention, and the cross-sectional schematic diagram which shows an example of the optical system which isolate | separates a linearly transmitted light and diffracted light. The schematic diagram which shows the structural example of the diffraction element of the 8th embodiment of this invention. The cross-sectional schematic diagram which shows the diffraction element structural example of the 8th embodiment of this invention, and the schematic diagram which shows an example of the optical system which isolate | separates a linearly transmitted light and a diffracted light. FIG. 10 is a schematic diagram illustrating a configuration example of an optical head device according to a ninth embodiment of the present invention. The schematic diagram which shows the structural example of the projection type liquid crystal display device of the 10th embodiment of this invention. The calculation result of the linearly transmitted light rate of the diffraction grating divided | segmented into the 3 small area | region of Example 1, the diffraction grating divided | segmented into the 5 small area | region, and the conventional 2 area | region equal division | segmentation diffraction grating. The calculation result which shows the wavelength dependence of the polarization-extinction ratio of the polarization diffraction grating divided | segmented into the 3 small area | region of Example 1, the polarization diffraction grating divided | segmented into the 5 small area | region, and the conventional 2 area | region equal division | segmentation polarization diffraction grating. In the liquid crystal element of Example 3, when the polarization diffraction grating divided into three small regions, the polarization diffraction grating divided into five small regions, and the conventional two-region equally-divided polarization diffraction grating were used, at an applied voltage of 0 Vrms. Calculation results of optical fiber propagation efficiency and maximum optical fiber propagation efficiency up to an applied voltage of 5 Vrms. FIG. 19A is a cross-sectional view showing a conventional diffraction grating (FIG. 19A is a rectangular diffraction grating shape, FIG. 19B is a sawtooth blazed diffraction grating shape, and FIG. 19C is a staircase blazed diffraction grating shape).

Explanation of symbols

1, 1a, 1b, 501a, 501b, 501c, 501d, 601 Translucent substrate 2, 4, 4a, 4b, 504a, 504b Lattice 3 Transparent medium (air)
5, 505 Isotropic transparent material 10, 20, 30, 40, 50, 60 Unit region 11, 15 Condensing lens 12 Optical fiber 13 Two-wavelength laser light source 14 Beam splitter 16 1/4 wavelength plate 17 Objective lens 18 Optical disk 19 Photodetector 31 Projection light source 32, 37B, 37G, 37R Polarization type diffraction element 33, 34 Dichroic mirror 35a, 35b, 35c Total reflection mirror 36B, 36G, 36R Liquid crystal light valve 38 Dichroic prism 39 Aperture stop 40 Projection lens 41 Screen 300a, 300b Polarization diffraction grating part 100, 200, 300, 400, 500, 600 Diffraction element 506a, 506b Transparent electrode 507, 607 Liquid crystal 508 Seal 510, 610 Liquid crystal cell 609 Light reflection layer 700 Optical head device 800 Projection type liquid crystal display device

Claims (12)

A diffractive element in which light of wavelength λ is incident and modulates and emits the phase of the light,
The diffraction element has a diffraction grating formed on a translucent substrate, and the diffraction grating is configured by periodically arranging unit regions.
The unit region is divided into three or more sections that transmit with different phases with respect to the light of the wavelength λ,
The phase difference, which is the difference between the average value of the light of the wavelength λ transmitted through the unit region per unit region and the phase of the light of the wavelength λ transmitted through the respective sections, is an integral multiple of π. Yes,
The section is any one of at least three or more small regions including a small region with a phase difference of zero, a small region with a phase difference of + nπ, and a small region with a phase difference of −nπ (n ≧ 1 integer),
A diffraction element in which the area of the small region where the phase difference is + nπ and the area of the small region where the phase difference is −nπ are substantially equal. The unit region includes one small region having a phase difference of zero, m small regions having a phase difference of + π and m small regions having a phase difference of −π (m ≧ 1). integer),
When the area of the small region where the phase difference is jπ is represented by S _j (j is an integer from −m to m),
i is an integer from (−m + 1) to (m−1),
_{S -m: ...: S i:} ...: ratio of _{S m} is,
1: ...: (2m)! / {(I + m)! X (mi)! }: The diffraction element according to claim 1, wherein: The unit region includes a small region having a phase difference of zero having an area S _0, a small region having a phase difference of π having an area S _+1, and a small region having a phase difference of −π having an area S _−1. ,
The diffraction element according to claim 2, wherein a ratio of the area S ₋₁ : the area S ₀ : the area S ₊₁ is 1: 2: 1. The unit region includes a small region having an area S ₀ with a zero phase difference, a small region having an area S _{+2 having a} phase difference of 2π, a small region having an area S _{+1 having a} phase difference of π, and an area S _{−. The} phase difference consisting of ₁ is a small region of -π, and the phase difference consisting of an area S _-2 is a small region of -2π,
The diffraction element according to claim 2, wherein a ratio of the area S ₋₂ : the area S ₋₁ : the area S ₀ : the area S ₊₁ : the area S ₊₂ is 1: 4: 6: 4: 1. The diffraction grating is a polarization diffraction grating in which a birefringent material having birefringence and an isotropic transparent material constitute a convex part and a concave part of the diffraction grating,
The birefringent ordinary refractive index n _o or the extraordinary refractive index _{n e (n o ≠ n e} ) claims equal to the refractive index n _s of one of the refractive index is isotropic transparent material materials 1-4 The diffraction element according to any one of the above. Wherein the polarization diffraction grating, together with the values of the step in the thickness direction of the grating is a natural number times the minimum value d of both the step, the retardation value _| n e _-n o | × d is the wavelength lambda (p + 1 The diffraction element according to claim 5, which is / 2) times (p is 0 or a positive integer). Two polarizing diffraction gratings are laminated,
The direction in which the refractive index n _s of each ordinary refractive index n _o or the extraordinary refractive index n _e and isotropic transparent material of the birefringent material of the polarization grating coincide, the in two polarization grating The diffraction element according to claim 5 or 6, which is the same. Between the two polarizing diffraction gratings, a liquid crystal layer that changes the retardation value between zero and λ / 2 with respect to the light of the wavelength λ by applying a voltage to the electrode is disposed,
The direction in which the refractive index n _s of the ordinary refractive index n _o or the extraordinary refractive index n _e and isotropic transparent material of the polarization grating coincide, the orthogonal or identical to each other in the two polarization grating The diffraction element according to claim 5 or 6.   6. A liquid crystal layer is disposed between the polarization diffraction grating and the reflective substrate, the liquid crystal layer changing a retardation value between zero and λ / 4 with respect to light having the wavelength λ by applying a voltage to the electrode. The diffraction element according to claim 6. Providing a mechanism for propagating light in an outgoing direction that is transmitted through or regularly reflected by the diffraction element according to claim 8 or 9, and blocking light emitted in a direction different from the outgoing direction,
An optical attenuator in which the amount of propagating light changes according to the magnitude of a voltage applied to the liquid crystal layer. A light source emitting at least light of wavelength λ,
A beam splitter and an objective lens sequentially disposed between the light source and the optical disc;
A quarter-wave plate disposed between the beam splitter and the optical disc, which produces a quarter-wave phase difference with respect to light of wavelength λ,
An optical head device comprising a photodetector for receiving return light from the optical disc via the beam splitter,
An optical head device in which the diffraction element according to claim 5 or 6 is arranged in an optical path between the light source and the beam splitter. A light source;
A liquid crystal light valve that modulates visible light emitted from the light source according to an image to be displayed;
First polarizing means disposed in an optical path between the light source and the liquid crystal light valve to change a polarization state of light;
A second polarizing means arranged on the light emitting side of the liquid crystal light valve to change the polarization state of the light;
In a projection display device comprising: a projection unit that enlarges and projects an image generated by the liquid crystal light valve;
8. A projection display device in which at least one of the first polarizing means and the second polarizing means comprises the diffraction element according to claim 5.

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