JP5417815B2 - Diffraction element, optical head device, and projection display device - Google Patents

Description

  The present invention relates to a diffraction element in which the orders of diffracted light diffracted at the highest diffraction efficiency with respect to light incident at a plurality of different wavelengths are different at each wavelength, and an optical system using the diffraction element as a CD, DVD, light The present invention relates to an optical head device that records and reproduces information on an optical recording medium such as a magnetic disk and a high-density optical recording medium such as “Blu-ray” (registered trademark: BD), and a projection display device.

  In a projection apparatus such as an optical head device or a projector that records or reproduces an optical recording medium, a demultiplexing function for allowing light of a plurality of different wavelengths to enter from the same direction and deflecting and separating the light of each wavelength in different directions, or 2. Description of the Related Art Many optical components having a multiplexing function that allows light of different wavelengths to enter from different directions and transmit light of the respective wavelengths in the same direction are often used. As described above, an optical component that is demultiplexed or multiplexed is required to have high light utilization efficiency. For example, in an optical head device, BD light with a wavelength of 405 nm is reflected and a wavelength of 660 nm is reflected. Reported dichroic beam splitter that has the function of transmitting light for DVD and CD light of wavelength 785 nm, and dichroic beam splitter that has the function of transmitting light for BD and reflecting light for DVD and CD (Patent Document 1).

  However, the optical head device described in Patent Document 1 requires two dichroic beam splitters when demultiplexing light of three different wavelengths for BD, DVD, and CD. Further, since the light reflection direction by the dichroic beam splitter is 90 °, it is necessary to arrange another optical component in the reflection direction, and there is a problem that the optical head device is enlarged as a whole structure. .

  Therefore, in order to reduce the size of such a device, diffracted light with different diffraction angles is produced by a diffractive element formed with a diffraction grating as an optical component that demultiplexes or multiplexes light of different wavelengths. Uses demultiplexing or multiplexing. As such a diffractive element, in particular, a diffractive element utilizing the fact that a blazed diffraction grating having a high diffraction efficiency of a specific order of diffracted light is formed and the diffraction angle of diffracted light of the same order differs depending on the wavelength, or There has been reported a diffractive element that utilizes 0th-order diffracted light for light having a wavelength of 1 and 1st-order diffracted light for light of the other wavelength (Patent Document 2).

  Further, as an application example of a diffraction grating structure in which light of a plurality of wavelengths is incident, there is a diffractive lens. In particular, in an optical head device, each of information recording surfaces of a plurality of optical recording media having different cover thicknesses is provided on each information recording surface. A diffractive lens used for condensing light of a wavelength has been reported (Patent Document 3).

JP 2007-179640 A JP 2006-048822 A JP 2008-176932 A

  The diffractive element used in the optical head device described in Patent Document 2 demultiplexes or multiplexes light having a wavelength for DVD and CD using a difference in diffraction angle. In particular, a combination of 0th-order diffracted light and 1st-order diffracted light is used for diffracted light having a wavelength for DVD and diffracted light having a wavelength for CD. However, when such a diffractive element is used, if the difference in diffraction angle between the diffracted lights of these two different wavelengths is small, the positions of the optical parts using these lights may be too close. Due to the arrangement, it is necessary to increase the difference in the diffraction angles of these lights. However, in order to increase the diffraction angle, the grating pitch of the diffraction grating has to be shortened, and there is a problem that high processing accuracy of the diffraction grating is required.

  Further, in the diffractive optical element used in the optical head device described in Patent Document 3, the light having the highest diffraction efficiency with respect to the light of the wavelength for BD, DVD, and CD is zero-order diffracted light (straight forward transmission). The diffraction grating is a combination of orders of diffracted light having the same sign as that of the light. And, in order to collect light well on the information recording surfaces of optical recording media of different standards by these diffracted lights, a refracting surface that further refracts the diffracted light is formed to adjust the divergence / convergence, Thus, a diffraction grating alone with no refracting surface cannot increase the difference in the traveling direction (angle) of light transmitted through the diffractive optical element, and if the diffraction angle difference is increased, the grating pitch of the diffraction grating is shortened. There is a problem that high processing accuracy of the diffraction grating is required.

  In the present invention, in consideration of the above-described circumstances, light of a plurality of wavelengths is incident, the diffraction angles of the light beams having the highest diffraction efficiency in the light of each wavelength are different, and the difference between these diffraction angles can be increased. An object of the present invention is to provide a diffraction element that is easy to manufacture.

The present invention has been made to solve the above problem, and is a diffractive element in which m pieces of light having different wavelengths are incident (an integer of m ≧ 2), and the phase of the light is modulated and transmitted. The diffraction element has a shape in which a diffraction grating is formed on a light-transmitting substrate or one surface of the light-transmitting substrate is a diffraction grating, and the diffraction grating has a width of a grating pitch Px. A unit region extending in a direction orthogonal to the direction of the width of the grating pitch Px is repeatedly arranged in the direction of the width of the grating pitch Px, and the unit region does not form a diffraction grating. When a section composed of a plane parallel to the surface of the substrate and having the same distance is defined as one small region, the small region includes N small regions whose distances from the translucent substrate surface are different from each other. Stretched in a direction perpendicular to the width direction of the lattice pitch Px (Integer N ≧ 3), among the m of the light, the shortest wavelength of the wavelength lambda _1, the longest wavelength and the wavelength _{λ m, λ 1 ≦ λ a} ≦ λ wavelength lambda _a light phase is _m in case the incident, the difference between the highest and the phase of the light which the phase advances passes small areas of zero is a small region, the wavelength lambda _a of the phase of the light transmitted through the small region which is different from the small region of the zero Are each an integer multiple of π, and at least one of the phase differences is an odd multiple of π , and each of the m light beams incident has the highest diffraction efficiency. 1st order diffracted light, and at least one light having the highest + p-order diffraction efficiency and light having the highest −q-order diffraction efficiency (integers of p, q ≧ 1). A diffractive element is provided.

In addition, a diffractive element in which m pieces of light having different wavelengths are incident (an integer greater than or equal to m ≧ 2) and modulates the phase of the light and transmits the diffractive element, and the diffractive element has a diffraction grating on a translucent substrate. Formed or has a shape in which one surface of the translucent substrate becomes a diffraction grating, and a grating pitch on a straight line parallel to the translucent substrate surface with a point A on the translucent substrate as a base point _{P 1, P 2, ...,} P M in the order of _{(P 1> P 2> ...} > P M) having a M unit area including the annular area is a circle with a circular region or an outer edge, said unit The region has N small regions formed by extending along a circumferential direction of a circle centered on the point A, and having a cross section having a plane parallel to the translucent substrate surface and a different height. a (integer N ≧ 3), among the m of the light, the wavelength lambda ₁ of the shortest _wavelength, the longest wavelength is the wavelength lambda _m, lambda ₁ when the wavelength lambda _a light is λ _a ≦ λ _m is incident in phase, and most the phase advances of light transmitted through the small region of zero is a small area phase, the small region different from the zero of the small region phase difference defined by the difference between the wavelength lambda _a of the phase of the light transmitted through is an integer multiple of [pi respectively, at least one of the phase difference is an odd multiple of [pi, incident Each of the m light beams has one diffracted light of the order that can obtain the highest diffraction efficiency, and further has the highest + p-order diffraction efficiency and the light with the highest -q-order diffraction efficiency (p , Q ≧ 1), and a diffraction element including at least one each.
In addition, a diffraction element in which at least one of the phase differences is π is provided.

Also provided is the above-described diffraction element in which the values of p and q of the + p-order diffraction efficiency and the −q-order diffraction efficiency are 1, respectively. In addition, the unit area includes three small areas, and each of the first small area, the second small area, and the third small area from the end of the unit area. When the width is X ₁ , the width of the second small region is X ₂ , and the width of the third small region is X ₃ ,
X ₁ = X ₂ = X ₃ = Px / 3,
The above-described diffraction element is provided.

The first small area is the zero small area, the phase difference of the first small area is φ (0), the phase difference of the second small area is φ (1), and the first small area is When the phase difference of the small region of 3 is φ (2),
φ (0) = 0,
φ (1) = π,
φ (2) = 2π,
The diffraction element having the shape of the unit region is provided.

In addition, the unit area is composed of four small areas, and the first small area, the second small area, the third small area, and the fourth small area from the end of the unit area, respectively, When the width of the first small region is X ₁ , the width of the second small region is X ₂ , the width of the third small region is X ₃ , and the width of the fourth small region is X ₄ ,
X ₁ : X ₂ : X ₃ : X ₄ = 3: 7: 7: 3,
The above-described diffraction element is provided.

The first small area is the zero small area, the phase difference of the first small area is φ (0), the phase difference of the second small area is φ (1), and the first small area is When the phase difference of the third small region is φ (2) and the phase difference of the third small region is φ (3),
φ (0) = 0,
φ (1) = π,
φ (2) = 2π,
φ (3) = 3π,
The diffraction element having the shape of the unit region is provided.

The diffraction grating is a polarization diffraction grating in which a birefringent material having birefringence and an isotropic transparent material constitute a convex portion and a concave portion of the diffraction grating, and the birefringence Provided is the above-described diffraction element in which either one of the ordinary refractive index n _o or the extraordinary refractive index n _e (n _o ≠ n _e ) of the material is equal to the refractive index n _s of the isotropic transparent material.

A light source; a beam splitter that deflects and separates the light from the light source; an objective lens that focuses the light emitted from the beam splitter onto the optical disk ; and a photodetector that detects the light reflected by the optical disk ; And an optical head in which the diffraction element is disposed in an optical path between the light source and the beam splitter and in an optical path between the beam splitter and the photodetector. Providing equipment.

Further, a phase difference of ¼ wavelength is generated with respect to the light, which is disposed between the light source , an objective lens for condensing the light emitted from the light source on the optical disc, and the light source and the optical disc. / 4 wavelength plate and a photodetector for detecting light reflected by the optical disc, comprising: an optical path between the light source and the objective lens; and the objective lens and the photodetector. Provided is an optical head device in which the above-described diffraction element is arranged in an optical path common to the optical path.

  A light source; a beam splitter that deflects and separates light from the light source; an objective lens that condenses the light emitted from the beam splitter onto the optical disc; and a photodetector that detects the light reflected by the optical disc. An optical head device is provided, wherein the diffraction element is disposed in an optical path between the beam splitter and the objective lens.

The light source emits light having three different wavelengths λ ₁ , λ ₂ , and λ _3. The wavelength λ ₁ is a 405 nm wavelength band ranging from 395 to 415 nm, and the wavelength λ ₂ is 640 to 680 nm. range 660nm wavelength band of the wavelength lambda ₃ provides the optical head device is a 785nm wavelength band, in the range of 765～805Nm.

  Further, a projection type display comprising: a light source; a liquid crystal light valve that modulates visible light emitted from the light source according to a displayed image; and a projection lens that magnifies and projects an image generated by the liquid crystal light valve. In the apparatus, there is provided a projection display device in which the diffraction element is disposed in an optical path between the liquid crystal light valve and the projection lens.

  The present invention relates to a diffractive element that divides or multiplexes a plurality of lights having different wavelengths due to a diffraction phenomenon, in particular, a direction (order) in which the diffraction efficiency is highest among lights of one wavelength. The direction (order) in which the diffraction efficiency is the highest among the lights of the other wavelength with respect to the A direction is a diffractive element having an effect of being axially symmetric with respect to the A direction with respect to the optical axis. Miniaturization of optical devices such as an optical head device using an element and a projection display device can be realized.

(First embodiment)
FIG. 1 is a schematic plan view of the diffraction element 100 according to the first embodiment. In the diffractive element 100, unit regions 110 that spatially modulate the phase of transmitted light are periodically arranged on a translucent substrate 120. Here, the term “periodic” means that the unit regions are repeatedly arranged in one direction without any gap. For example, it is assumed that the band-shaped unit regions 110 are arranged with a width of the pitch Px in the X direction orthogonal to the extending direction of the unit regions 110 as in the diffraction element 100 of FIG. Hereinafter, the pitch Px is referred to as a lattice pitch Px. In addition, when an area where light is incident on the diffraction element 100 is an effective area, the effective area is preferably configured to include at least three grating pitches Px of unit areas 110 arranged. In this case, the unit region 110 is periodically repeated in the X direction, and the extending direction of one unit region 110 is parallel to the Y direction (a direction orthogonal to the width of the pitch Px). The outer edge of one unit region 110 is a rectangle extending in the Y direction. However, the shape of the outer edge is not limited to a rectangle, and if two sides are parallel to the Y direction, the line connecting the two sides is the X direction. Not only a straight line but also a curve or the like may be used.

  The unit area 110 includes a plurality of small areas, and in the present embodiment, the unit area 110 includes small areas 110a, 110b, and 110c that are three geometric sections. The small regions 110a, 110b, and 110c are different from each other in the phase of light having a wavelength λ that is transmitted when light having a wavelength λ is incident in the same phase. Further, in one small region, a section where the phase of transmitted light is the same is considered as one unit. The unit region 110 composed of the small regions 110a, 110b, and 110c may be made of a material different from that of the light-transmitting substrate 120, or may be made of the same material as the light-transmitting substrate 120, or may be a light-transmitting substrate. One surface of 120 may be processed into an uneven shape.

  Further, among the small areas 110a, 110b, and 110c, the small area in which the phase of the transmitted light is most advanced is defined as a small small area. Here, the complex amplitude of the transmitted light in the small zero region is defined as U (0). Next, let φ (m) be the phase difference of a small region in which the phase of transmitted light is different from the phase of light transmitted through the small region of zero, and U (m) be the complex amplitude of transmitted light. However, m is an integer of 0 to N-1 where N is the number of steps (= number of small areas) described later. For example, when the small area 110a is a small area of zero, the small area 110a is given as m = 0, small area 110b is given as m = 1, and small area 110c is given as m = 2. Further, from the above definition, the small region of zero has zero phase difference, that is, φ (0) = 0.

  Next, the configuration of the unit area 110 will be described. FIG. 2A is a schematic plan view showing the unit region 110 of the present embodiment, and FIG. 2B is a cross-sectional view taken along the line AA ′ of the unit region 110 shown in FIG. ) And a phase difference generated with respect to incident light, and a diffraction grating having a step is formed. In addition, light shall inject from the normal line direction (Z direction) of the flat translucent board | substrate surface 111 (XY plane). Further, the light transmission side has a step having a constant value at the boundary between the small regions, and the light transmission side of each of the small regions 110a, 110b, and 110c is a flat surface parallel to the translucent substrate surface 111. (Flat part). Further, the number of flat portions in the unit region is defined as a step number N. In this case, the diffraction element 100 has a step number N = 3, and N corresponds to the number of small regions constituting the unit region 110.

Here, for simplicity, the unit area is assumed to one surface of the translucent substrate 120 is isotropic material having a refractive index n _s is formed by machining, in this case, the unit area 110b, 110c Let us consider the phase difference φ (m) of the light passing through. At this time, the refractive index of the (isotropic) medium through which light of the diffraction element 100 is transmitted is n _A , the small region 110a is a small region (phase difference φ (0) = 0), and the small region 110a. When the level difference between the small regions 110b and d _1, a small region 110b passing through the wave phi (1) of light, the optical path length of light passing through the small regions 110a as shown in FIG. 2 (b) and a small area 110b Difference from the optical path length transmitted (= optical path length difference) d ₁ · | n _s −n _A |
_{φ (1) = 2πd 1 ·} | n s -n A | / λ [rad] ··· (1)
It can be expressed as Further, when the medium on the light transmitting side is air (n _A = 1), from the above equation (1),
φ (1) = 2πd ₁ · | n _s −1 | / λ [rad] (2)
It becomes.

Next, the diffractive action of the diffraction element 100 of this embodiment will be described. In the diffraction element 100, the phase difference φ (m) of each small region is determined by determining the material and the shape of the unit region 110 as described above, and the diffraction efficiency of each order is determined by the optical characteristics of the diffraction grating. Is done. The diffraction efficiency is represented by the ratio of the amount of light transmitted and diffracted in a specific direction to the amount of light incident on the diffraction grating. Further, when the diffraction efficiency can be regarded as being thin, the q-order diffraction efficiency η _q of the diffraction grating having the grating pitch Px in the X-axis direction of the diffraction grating is given by the following equation from scalar diffraction theory.

In Expression (3), j is an imaginary unit, and φ (x) is a phase shift function that characterizes the shape of the diffraction grating. When the unit region is made of a transparent material having no optical loss, the complex amplitude U (m) of transmitted light in a small region is given by assuming that the phase shift function φ (x) is φ (m).
U (m) = exp {jφ (m)} (4)
Can be replaced.

Thus, when the diffraction element 100 of the present embodiment is specifically considered, the diffraction efficiency η _q is determined by the divided widths X ₁ and X _{2 of the} small regions 110a, 110b and 110c included in the grating pitch Px of the unit region. And X ₃ and the respective parameters of the phase difference φ (m). In order to obtain an effect that a plurality of lights having different wavelengths are incident and the sign of q, which is the order having the highest diffraction efficiency among the lights of the respective wavelengths, differs between the lights of at least two wavelengths, the division width X ₁ , X ₂ and X ₃ as
X ₁ = X ₂ = X ₃ = Px / 3 (5)
(X ₁ : X ₂ : X ₃ = 1: 1: 1).

Next, when considering the phase difference φ (m),
φ (0) = 0 (6a)
φ (1) = n ₁ π [rad] (6b)
φ (2) = n ₂ π [rad] (6c)
To satisfy the relationship. Note that n ₁ and n ₂ are natural numbers (n ₁ ≠ n ₂ ).

Then, a physical level difference in the unit region for satisfying the expressions (6b) and (6c) will be considered. Further, when the medium on the light transmission side is air using the equations (2) and (6b),
| N _s -1 | · d ₁ = n ₁ · λ / 2 (7a)
So as to satisfy the, so as to determine a step d ₁ of the small region 110b. Furthermore, the phase difference φ (2) of the small region 110c with respect to the small region 110a is also the same as the phase difference φ (1).
| N _s -1 | · d ₂ = n ₂ · λ / 2 (7b)
The step d ₂ may be determined so as to satisfy In addition, the medium which contacts the level | step difference of an uneven | corrugated | grooved part is not restricted to air, and may be another transparent material (n _A > 1, n _A ≠ n _s ). Further, the material of the portion having a step for generating a phase difference is not limited to an isotropic material, and may be a material having birefringence.

Here, in the equations (6b) and (6c), consider a case where n ₁ = 1 and n ₂ = 2, that is, φ (1) = π and φ (2) = 2π (d ₂ = 2 × d _1). If the surrounding medium is air (n _A = 1),
d ₁ = λ / {2 · | n _s -1 |} (8a)
d ₂ = 2λ / {2 · | n _s -1 |} (8b)
It is good to do.

  Such a diffraction grating may be formed by directly microfabricating the surface of the translucent substrate, or a dielectric film is formed on the surface of the translucent substrate 120, and the dielectric film is formed in the shape of the diffraction grating. May be processed. As a microfabrication method of the diffraction grating, a method in which a photolithographic process and a dry etching process are repeated using a photomask is used, or the surface of the translucent substrate 120 is directly applied using a mold for transferring the diffraction grating. You may use the method of carrying out a shaping | molding process or transcription-molding a diffraction grating to the translucent resin coated on the surface of the translucent board | substrate 120. FIG.

Next, the formed diffraction grating gives the diffraction element 100 satisfying the relations of the formulas (5) and (6a) to (6c), and the diffraction efficiency formula (3) is used to calculate the actually incident light. The diffraction efficiency η _q when the wavelength λ is changed is obtained by calculation. At this time, for example, the + 1st order diffraction efficiency η ₊₁ (q = + 1) and the −1st order diffraction efficiency η ₋₁ (q = −) at _a specific wavelength λa not included in the light having the wavelength λ having the band. The value of 1) is equal to about 30%. The value of a particular wavelength lambda 0 order diffraction efficiency corresponding to the rectilinear transmittance in _{a η 0 (q} = ₀₎ is about 11%.

In addition, the material that actually constitutes the diffraction element 100 has wavelength dependency (wavelength dispersion) in which the refractive index varies depending on the wavelength of incident light, and therefore, the diffraction efficiency whose value varies with the change in refractive index. It is necessary to design η _q in consideration of this wavelength dependency. The wavelength dependence n (λ) of the refractive index is
n (λ) = A + B / λ ² + C / λ ⁴ (9)
Given by Cauchy's formula.

  In Equation (9), A, B, and C are intrinsic constants of the respective materials. In the case of quartz glass, A = 1.450, B = 0.002566, and C = 0.001431. It becomes the value of. On the other hand, air, which is a surrounding medium, is 1 regardless of the wavelength, and A = 1, B = 0, and C = 0.

Here, set a specific wavelength lambda _a to 510 nm, in a case where Equation (5), so Equation (6a) ~ formula (6c) is established, further constituting the diffraction element 100 with quartz glass, the wavelength lambda The value is changed in the range of 380 to 820 [nm]. FIG. 3 shows the characteristics of the diffraction efficiency η _q with respect to the wavelength λ under these conditions, and particularly shows the diffraction orders q = −1, 0, +1. In this way, considering the wavelength dispersion characteristics of the material used, for example, the + _1st order diffraction efficiency η ₊₁ is the highest at 68.4% with respect to light of wavelength λ ₁ = 391 [nm], and wavelength λ ₂ = 753. The −1st order diffraction efficiency η ₋₁ is the highest at 68.4% with respect to [nm] light. The order of the diffracted light is diffracted light of the order of plus (+) with respect to the light diffracted to the right (+ X direction) with reference to the traveling direction of the light incident on the translucent substrate surface 111 in FIG. The light diffracted to the left side (−X direction) is the diffracted light of the minus (−) order, and it is interpreted as such unless otherwise described in other embodiments.

As described above, the diffraction element 100 has n ₁ = 1 and n ₂ = 2 in the equations (6a) and (6b), but if n ₁ and n ₂ are natural numbers (n ₁ ≠ n ₂ ) Not limited to combinations. FIG. 4A is a schematic cross-sectional view showing the unit region 130 of the diffractive element, where n ₁ = 1 and n ₂ = 4. Further, the division widths X ₁ , X ₂ and X ₃ of the material and the small regions 130 a, 130 b and 130 c are the same as those of the unit region 110. In FIG. 4A, portions corresponding to the steps are indicated by phase differences φ (1) and φ (2). Similarly, FIG. 4B is a schematic cross-sectional view showing the unit region 140 of the diffractive element, where n ₁ = 1 and n ₂ = 3, and the other conditions are unit. It is the same as the area 130.

Here, similarly to the diffraction element 100 having a unit area 110 to satisfy equation (5), further a specific wavelength lambda _a is set to 510 nm, a unit region 130 is φ (1) = π, φ (2) = Consider a diffractive element having 4π and the unit region 140 having φ (1) = π and φ (2) = 3π. Similarly, when quartz glass is used, the value of the wavelength λ is changed in the range of 380 to 820 [nm], and light is incident from the normal direction of the translucent substrate surface 131 or the translucent substrate surface 141. The characteristic of the diffraction efficiency η _q is calculated. FIG. 5A shows characteristics when the diffractive element having the unit region 130 shown in FIG. 4A is configured, and FIG. 5B shows the diffractive element having the unit region 140 shown in FIG. 4B. It is the calculation result of the characteristic in the case of comprising.

From this result, in FIG. 5A, the + _1st order diffraction efficiency η ₊₁ is the highest at 64.6% with respect to the light of wavelength λ ₁ = 446 [nm], and the light of wavelength λ ₂ = 598 [nm]. In contrast, the −1st order diffraction efficiency η ₋₁ is the highest at 64.6%. In FIG. 5B, the −1st order diffraction efficiency η ₋₁ is the highest at 44.0% with respect to the light with the wavelength λ ₁ = 450 [nm], and the light with the wavelength λ ₂ = 590 [nm]. + 1st order diffraction efficiency η _{+ 1} is the highest at 44.0%. In the above description, the unevenness of the cross section of the unit region has been described as a stepped shape that rises to the right as shown in FIG. 2B. However, the present invention is not limited to this, and has a stepped shape that rises to the left. It may be. In addition, the highest diffraction efficiency for light of a plurality of different wavelengths is preferably 40% or more, more preferably 50% or more, and further preferably 60% or more in order to increase the light utilization efficiency.

Further, when a diffraction angle, which is an angle formed by the traveling direction of the incident light and the direction of the diffracted light, is given by θ, the relationship between the wavelength λ, the diffraction order q, and the grating pitch Px is as follows from Bragg's diffraction formula:
qλ = Px · sinθ (10)
Given in. For example, when the grating pitch Px = 5 μm, the diffraction angle θ ₊₁ (405) ≈4.6 ° of the + 1st order diffracted light having the highest diffraction efficiency among the light with the wavelength of 405 nm is diffracted among the light with the wavelength of 660 nm as shown in FIG. The diffraction angle θ ₋₁ (660) ≈−7.6 ° of the _{−1st order} diffracted light having the highest efficiency is obtained, and the difference between these angles can be made relatively large at 12.2 °.

  On the other hand, unlike the present invention, the diffraction grating having the same angle difference of 12.2 ° is different from the present invention. For example, in the case of a diffraction grating using 0th-order diffracted light with 405 nm light and + 1st-order diffracted light with 660 nm light, The pitch of the grating must be about 3.1 μm. In the case of a diffraction grating using + 1st order diffracted light for both 405 nm light and 660 nm light under the same angle difference condition, the pitch of the diffraction grating must be about 1.3 μm. It becomes smaller than the pitch Px. As a result, even when the diffraction element of the present invention is used in an optical device that splits or multiplexes light of different wavelengths at a constant angle, it is not necessary to make the grating pitch Px finer than the conventional diffraction grating, and processing is easy. Sex is obtained. Thus, until now, in order to increase the angle difference, the grating pitch Px must be reduced, and when the grating pitch Px is increased, the difference in the angle of diffracted light used at different wavelengths is reduced. However, in the diffraction element of the present invention, the difference in angle can be increased, so that it is easy to arrange optical components using these lights, and downsizing of the apparatus can be realized.

(Second Embodiment)
FIG. 6A is a schematic plan view showing the diffractive element 200 according to the second embodiment. The diffractive element 200 is formed by periodically arranging unit regions 210 that spatially modulate the phase of transmitted light. It is. The diffractive element 200 is different from the diffractive element 100 in that the material forming the diffraction grating is made of a material having birefringence, and this generates polarization dependency of incident light. FIG. 6B is a schematic cross-sectional view of the unit region 210, and a birefringent material layer 230 having a diffraction grating shape between the translucent substrates 220 a and 220 b arranged in parallel, and an isotropic property. The material layer 240 is sandwiched.

Further, the shape of the plane (XY plane) of the unit region 210 is the same as that of the unit region 110 of the diffractive element 100 according to the first embodiment, and the unit region 210 includes the small region 210a, the small region 210b, and the small region. It consists of area 210c. The lattice pitch Px, which is the period of the unit region 210, and the division widths X ₁ , X _2, and X ₃ of the small region 210a, the small region 210b, and the small region 210c are the same as in the unit region 110, respectively. Satisfied.

The birefringent material layer 230 has an ordinary light refractive index n _o and an extraordinary light refractive index n _e (n _o ≠ n _e ). For example, the fast axis (direction indicating the ordinary light refractive index) is shown in FIG. ) In the X direction. Moreover, isotropic material layer 240 is a material of the isotropic refractive index n _B optically clear, considered as being constructed of a material that satisfies n o ₌ n _B. In this case, in the above formulas (8a) and (8b), n _s is replaced with _ne , and 1 is replaced with n _{B.
d 1 = λ / {2 ·} | n e -n B |} ··· (11a)
_{d 2 = 2λ / {2 ·} | n e -n B |} ··· (11b)
Steps d ₁ and d ₂ of the birefringent material layer 230 are determined so as to satisfy the above. The isotropic material layer 240 may be formed so as to fill the unevenness (step) of the birefringent material layer 230, and the unevenness (step difference) of the birefringent material layer 230 as shown in FIG. ) May be formed so as to cover the convex portion.

As a material constituting the birefringent material layer 230, birefringent crystals such as quartz and LiNbO ₃ , a birefringent film obtained by stretching an organic film such as polycarbonate, and a liquid crystal monomer having birefringence are unidirectional. For example, a polymer liquid crystal or the like that is polymerized and solidified after being oriented in the above is used. Use of a polymer liquid crystal is preferable because it can provide an optical axis (a fast axis and a slow axis) regardless of the longitudinal direction of the diffraction grating, and has a high degree of design freedom.

With such a configuration of the unit region 210, a difference in refractive index between the birefringent material layer 230 and the isotropic material layer 240 occurs in linearly polarized light in the Y direction of incident light (Δn = | n _e −n _B |), a diffractive action occurs, but the linearly polarized light in the X direction has no difference in refractive index between the birefringent material layer 230 and the isotropic material layer 240 (Δn = | n _o− n _B | = 0), so that the light passes straight without being diffracted. By forming the birefringent material layer 230 in this manner, polarization dependency such as diffracting or linearly transmitting incident light can be exhibited. In particular, it is considered that the wavelength dispersion characteristic of the isotropic material layer 240 coincides with either the wavelength dispersion characteristic in the ordinary light refractive index direction or the wavelength dispersion characteristic in the extraordinary light refractive index direction incident on the birefringent material layer 230. It is preferable because the transmittance in the case where light is transmitted in a straight line (straight) is high.

As a result, when the Y-direction of the linearly polarized light is incident, for example, it has a largest wavelength band + 1-order diffraction efficiency eta _+1, and the greatest wavelength band -1 order diffraction efficiency eta _-1 different wavelength dependency, When linearly polarized light in the X direction is incident, the transmittance is almost 100%, and no diffracted light is generated. Further, although it has been described that n _o = n _B and n _e ≠ n _B , the refractive index n _B of the isotropic material layer 240 is equal to the extraordinary refractive index of the birefringent material layer 230, that is, n _o ≠ n. _B may be n _e = n _B. It is also possible to use a birefringent material in the isotropic material layer 240, whereas this time, the ordinary refractive index n _{o ',} extraordinary refractive index n _e' When either n o _'or n _e' but it may be designed to be equal to either one n _o or n _e of the birefringent material layer 230.

  In the present embodiment, the diffraction element 200 having the unit region 210 as a diffraction grating corresponding to the unit region 110 has been described. However, the present invention is not limited to this, and the unit region of the first embodiment is not limited to light having a specific polarization direction. As in 130, φ (1) = π, φ (2) = 4π, or as in the unit region 140, φ (1) = π, φ (2) = 3π may be used.

  Similarly, in the diffraction element 200 of the second embodiment, even when the diffraction element of the present invention is used in an optical device that demultiplexes or multiplexes light of different wavelengths at a constant angle, the grating pitch is larger than that of the conventional diffraction grating. There is no need to make Px fine, and the ease of processing can be obtained. Further, the demultiplexing and multiplexing can be controlled according to the polarization direction of the incident light. Similarly, it is possible to reduce the size of an optical device that uses these diffracted lights.

(Third embodiment)
FIG. 7 is a schematic plan view of a diffraction element 300 according to the third embodiment. In the diffraction element 300, unit regions 310 that spatially modulate the phase of transmitted light are periodically arranged on a light-transmitting substrate 320. For example, it is assumed that the band-shaped unit regions 310 are arranged at a pitch Px in the X direction as in the diffraction element 300 of FIG. In addition, when an area where light is incident on the diffraction element 300 is an effective area, the effective area may include at least three Px of the unit area 310 arranged.

  The unit area 310 includes a plurality of small areas. In the present embodiment, the unit area 310 includes small areas 310a, 310b, 310c, and 310d that are four geometric sections. The small regions 310a, 310b, 310c, and 110c are different from each other in the phase of light having a wavelength λ that is transmitted when light having a wavelength λ is incident in the same phase. As described above, the unit region 110 of the diffractive element 100 according to the first embodiment is configured by three small regions, whereas the unit region 310 of the diffractive element 300 according to the present embodiment is configured by four small regions. Is different. Here, the unit region 310 may be made of a material different from that of the light-transmitting substrate 320, or may be made of the same material as the light-transmitting substrate 320, or one surface of the light-transmitting substrate 320 is uneven. It may be processed into.

  Next, the configuration of the unit region 310 that gives a phase difference to each small region will be described. FIG. 8A is a schematic plan view showing the unit region 310 of the present embodiment, and FIG. 8B is a cross-sectional view (X direction) of BB ′ of the small region 310 shown in FIG. ) And a diffraction grating having a step is formed. Note that light enters from the normal direction (Z direction) of the flat translucent substrate surface 311 (XY plane). Further, the light transmission side has a step of a certain value at the boundary between the small regions, and the light transmission side of each of the small regions 310a, 310b, 310c, and 310d is flat and parallel to the translucent substrate surface 311. This is a flat surface (flat part). In this case, the number of steps N = 4, and N corresponds to the number of small areas constituting the unit area 310.

In the present embodiment, a plurality of lights having different wavelengths are incident, and the sign of the diffraction order q, which is the order having the highest diffraction efficiency among the lights of the respective wavelengths, is different between the lights of at least two wavelengths. Is the same as the first and second embodiments, but has a different configuration, and the division widths of the small regions 310a, 310b, 310c and 310d are X ₁ , X ₂ , X ₃ and X ₄ respectively. ,
X ₁ : X ₂ : X ₃ : X ₄ = 3: 7: 7: 3 (12)
give.

Next, when the medium on the light transmission side of the diffraction element 300 is air (refractive index = 1), the light is transmitted through the small region 310b, the small region 310c, and the small region 310d with reference to the light transmitted through the small region 310a. The optical phase differences φ (0), φ (1), φ (2), φ (3) are
φ (0) = 0 (13a)
φ (1) = n ₁ π [rad] (13b)
φ (2) = n ₂ π [rad] (13c)
φ (3) = n ₃ π [rad] (13d)
To satisfy the relationship. Note that n ₁ , n _2, and n ₃ are natural numbers (n ₁ ≠ n ₂ ≠ n ₃ ). At this time, assuming that n ₁ = 1, n ₂ = 2 and n ₃ = 3, the steps are adjusted so that φ (1) = π, φ (2) = 2π, and φ (3) = 3π. Since the phase difference is based on the light transmitted through the small region 310a, φ (0) = 0.

The diffraction grating formed as described above gives the diffraction element 300 in which Equation (12) and φ (1) = π, φ (2) = 2π, φ (3) = 3π are given, and the diffraction efficiency equation (3 ) To obtain the diffraction efficiency η _q by changing the wavelength λ of the actually incident light. At this time, for example, the + 1st order diffraction efficiency η ₊₁ (q = + 1) and the −1st order diffraction efficiency η ₋₁ (q = −) at _a specific wavelength λa not included in the light having the wavelength λ having the band. The value of 1) is equal to about 14%. In addition, the value of the 0th-order diffraction efficiency η ₀ (q = 0) corresponding to the straight transmittance is about 0%.

Similarly to the first embodiment, a case where the diffraction element 300 is formed by processing quartz glass in consideration of wavelength dispersion as in the above formula (9) will be considered. Here, a specific wavelength lambda _a is set to 515nm, φ (1) = π , φ (2) = 2π, φ (3) = so that the 3 [pi], giving a level difference between the small regions, the wavelength lambda The value is changed in the range of 370 to 860 [nm]. FIG. 9 shows the calculation results of the diffraction efficiency η _q with respect to the wavelength λ under these conditions, and particularly shows q = −1, 0, +1. Thus, considering the wavelength dispersion characteristics of the material used, for example, the + _1st order diffraction efficiency η _{+ 1} is the highest at 71.6% with respect to light of wavelength λ ₁ = 376 [nm], and wavelength λ ₂ = 856. The −1st order diffraction efficiency η ₋₁ is the highest at 71.6% with respect to [nm] light.

As described above, in the diffraction element 300, n ₁ = 1, n ₂ = 2 and n ₃ = 3 in the expressions (13b) to (13d), but n ₁ , n ₂ and n ₃ are natural numbers (n ₁ if ≠ _{n 2} ≠ _{n 3)} is not limited to this combination. FIG. 10A is a schematic cross-sectional view showing the unit region 330 of the diffractive element, and shows a configuration when n ₁ = 1, n ₂ = 5, and n ₃ = 3. Further, the division widths X ₁ , X ₂ , X ₃ and X ₄ of the material and the small regions 330 a, 330 b, 330 c and 330 d are the same as those of the unit region 310. In FIG. 10A, the portions corresponding to the steps are indicated by phase differences φ (1), φ (2), and φ (3). Similarly, FIG. 10B is a schematic cross-sectional view showing the unit region 340 of the diffractive element, where n ₁ = 1, n ₂ = 4 and n ₃ = 3. The other conditions are the same as those of the unit region 330.

Here, to satisfy the equation (12) as well as the diffraction element 300 having a unit area 310, further a specific wavelength lambda _a is set to 515 nm, a unit region 330 is φ (1) = π, φ (2) = Consider a diffraction element having 5π, φ (3) = 3π, and the unit region 340 having φ (1) = π, φ (2) = 4π, and φ (3) = 3π. Similarly, when quartz glass is used, the value of the wavelength λ is changed in the range of 380 to 820 [nm], and light is incident from the normal direction of the light transmitting substrate surface 331 or the light transmitting substrate surface 341. The characteristic of the diffraction efficiency η _q is calculated. FIG. 11A shows characteristics when the diffractive element having the unit region 330 shown in FIG. 10A is configured, and FIG. 11B shows the diffractive element having the unit region 340 shown in FIG. It is the calculation result of the characteristic in the case of comprising.

From this result, in FIG. 11A, the + _1st -order diffraction efficiency η _{+ 1} is the highest at 68.4% with respect to the light with the wavelength λ ₁ = 391 [nm], and the light with the wavelength λ ₂ = 775 [nm]. On the other hand, the -1st order diffraction efficiency η _-1 is the highest at 68.4%. In FIG. 11B, the + _1st order diffraction efficiency η _{+ 1} is the highest at 38.4% with respect to the light with the wavelength λ ₁ = 441 [nm], and the light with the wavelength λ ₂ = 621 [nm]. -1st order diffraction efficiency η _-1 is the highest at 38.4%.

  As described above, when a plurality of light beams having different wavelengths are incident, the sign of the diffracted light beam having the highest diffraction efficiency of each wavelength is different between the light beams of at least two wavelengths. Thus, even when the diffraction element of the present invention is used in an optical device that demultiplexes or multiplexes light of different wavelengths at a constant angle, it is not necessary to make the grating pitch Px finer than the conventional diffraction grating. Ease is obtained. In addition, when a diffraction element 300 having a phase difference like the unit region 310 shown in FIG. 8B of the second embodiment is used, a diffraction efficiency of 70% or more can be obtained, and a conventional diffraction grating can be obtained. It is not necessary to make the lattice pitch Px finer than that, and the ease of processing can be obtained. Similarly, it is possible to reduce the size of an optical device that uses these diffracted lights.

(Fourth embodiment)
FIG. 12A is a schematic plan view showing the diffractive element 400 according to the fourth embodiment. The diffractive element 400 includes unit regions 410 that spatially modulate the phase of transmitted light and are periodically arranged. It is. The diffractive element 400 is different from the diffractive element 300 in that the material forming the diffraction grating is made of a material having birefringence, thereby generating the polarization dependence of incident light. FIG. 12B is a schematic cross-sectional view of the unit region 410, and a birefringent material layer 430 having a diffraction grating shape between the translucent substrates 420a and 420b arranged in parallel, and an isotropic property. The material layer 440 is sandwiched.

Further, the shape of the plane (XY plane) of the unit region 410 is the same as that of the unit region 310 of the diffraction element 300 according to the third embodiment, and the unit region 410 includes the small region 410a, the small region 410b, and the small region. It consists of a region 410c and a small region 410d. Further, the lattice pitch Px which is the period of the unit region 410 and the division widths X ₁ , X ₂ , X ₃ and X ₄ of each small region satisfy the above formula (12) similarly to the unit region 310.

Birefringent material layer 430 has a ordinary refractive index _{n o} and extraordinary refractive index _n e _{(n o} ≠ _{n e),} for example, the fast axis (direction indicated ordinary refractive index) of FIG. 12 (b ) In the X direction. Furthermore, the isotropic material layer 440 is composed of an isotropic material having a refractive index n _B optically clear, considered as being constructed of a material that satisfies n o ₌ n _B. in this case,
_{d 1 = λ / {2 ·} | n e -n B |} ··· (14a)
_{d 2 = 2λ / {2 ·} | n e -n B |} ··· (14b)
_{d 3 = 3λ / {2 ·} | n e -n B |} ··· (14c)
Steps d ₁ , d ₂ and d ₃ of the birefringent material layer 430 are determined so as to satisfy the above. The isotropic material layer 440 only needs to be formed so as to fill the unevenness (step) of the birefringent material layer 430, and the unevenness (step difference) of the birefringent material layer 430 as shown in FIG. ) May be formed so as to cover the convex portion. The birefringent material layer 430 can be made of the same material as the birefringent material layer 430 of the second embodiment.

By adopting such a unit region 410, linearly polarized light in the Y direction out of incident light is refracted by the birefringent material layer 430 and the isotropic material layer 440, as in the second embodiment. Since a difference in refractive index occurs (Δn = | n _e −n _B |), a diffractive action occurs, but linearly polarized light in the X direction has a refractive index between the birefringent material layer 430 and the isotropic material layer 440. (Δn = | n _o −n _B | = 0), the light passes straight through without being diffracted. By forming the birefringent material layer 430 in this manner, polarization dependency such as diffracting or linearly transmitting incident light can be exhibited. In particular, it is considered that the wavelength dispersion characteristic of the isotropic material layer 440 coincides with either the wavelength dispersion characteristic in the ordinary light refractive index direction or the wavelength dispersion characteristic in the extraordinary light refractive index direction incident on the birefringent material layer 430. It is preferable because the transmittance in the case where light is transmitted in a straight line (straight) is high.

As a result, when the Y-direction of the linearly polarized light is incident, for example, it has a largest wavelength band + 1-order diffraction efficiency eta _+1, and the greatest wavelength band -1 order diffraction efficiency eta _-1 different wavelength dependency, When linearly polarized light in the X direction is incident, the transmittance is almost 100%, and no diffracted light is generated. In addition, although it has been described that n _o = n _B and n _e ≠ n _B , the refractive index n _B of the isotropic material layer 440 is equal to the extraordinary refractive index of the birefringent material layer 430, that is, n _o ≠ n. _B may be n _e = n _B. It is also possible to use a birefringent material in the isotropic material layer 440, whereas this time, the ordinary refractive index n _{o ',} extraordinary refractive index n _e' When either n o _'or n _e' but it may be designed to be equal to either one n _o or n _e of the birefringent material layer 430.

  In the present embodiment, the diffraction element 400 having the unit region 410 as a diffraction grating corresponding to the unit region 310 has been described. However, the present invention is not limited to this, and the unit region of the third embodiment is not limited to this. Φ (1) = π, φ (2) = 5π, φ (3) = 3π as in 330, or φ (1) = π, φ (2) = 4π, φ (2) as in unit region 340 = 3π may be included. Further, the diffraction element 400 of the fourth embodiment is similar to the diffraction element of the third embodiment in that the diffraction device of the present invention is applied to an optical device that demultiplexes or multiplexes light of different wavelengths at a certain angle. Even in the case of using, it is not necessary to make the grating pitch Px finer than that of the conventional diffraction grating, and the ease of processing can be obtained. Further, the demultiplexing and multiplexing can be controlled according to the polarization direction of the incident light. Similarly, it is possible to reduce the size of an optical device that uses these diffracted lights.

(Fifth embodiment)
FIG. 13 is a schematic plan view of a diffractive lens 500 as a diffractive element according to the fifth embodiment, and a schematic cross-sectional view showing a cross section along the X axis. Here, it is assumed that light is incident on the XY plane from the normal direction and the optical axis coincides with the orthogonal coordinates (x, y) = (0, 0). An annular region is formed concentrically on the XY plane around the optical axis. The diffractive lens 500 is in contact with the outer edge of the unit region 510, which is a circular region including the point A that intersects the optical axis, the annular unit region 520 that is in contact with the outer edge of the unit region 510, and the outer periphery of the unit region 520. A ring-shaped unit region 530 is formed with rotational symmetry about the point A. Further, the diffractive lens 500 has a configuration of the unit regions 510, 520, and 530. However, this is a schematic diagram for illustrating the characteristics of the diffractive lens 500, and actually the concentric shape further outward from the unit region 530. The ring-shaped unit area is configured to expand. Further, the “annular zone” is defined as the outer edge of each unit region, and corresponds to the thick line portions, that is, the annular zones 511, 521, and 531 in the schematic plan view of FIG. An area formed by the “ring zone” can also be referred to as a unit area.

The diffractive lens 500 can be considered as a phase type Fresnel zone plate using + 1st order diffracted light or −1st order diffracted light generated with respect to incident light. Here, + 1st order diffracted light is defined as first order diffracted light that diffracts so as to approach the optical axis, and −1st order diffracted light is defined as first order diffracted light that diffracts away from the optical axis. Next, the setting of the radius of the annular zone when the point A is the center will be described. As described above, when considered as a Fresnel zone plate, the maximum optical path difference of light transmitted through each unit region has a shape such that the maximum optical path difference when light having a wavelength of, for example, 405 nm is incident is 405 nm. And the radius rm of the _m- th zone from point A is
r _m = (2mλ ₀ f) ^1/2 (15)
It is represented by

Here, λ ₀ is a reference wavelength for obtaining the maximum diffraction efficiency, and f is a focal length obtained by the lens action. For example, when light having a wavelength λ ₀ is incident from the normal direction of the XY plane based on Expression (15), when the focal length f of the diffracted light is determined, the radius to be set for each annular zone is obtained. be able to. Thus, when each radius of m ring zones is determined, m unit areas are provided.

Next, the configuration of the unit area 510, the unit area 520, and the unit area 530 in FIG. 13 will be described. Here, the unit area 510 is a circular area having a radius r ₁ on the plane according to the equation (15), and can be considered as an area formed by rotating a pitch P ₁ equal to the radius r ₁ around the point A. . Here the unit region 510 having a pitch _{P 1} in the small region 510a serving as a circular radius _{P 11} around the point A, the width width concentrically in small areas 510b and concentric to the annular _{P 12} It consists small region 510c where the annular P _13, dividing the width of each of the small regions _{P 11, P 12} and _{P 13} are
_{P 11 = P 12 = P 13} = P 1/3 ··· (16a)
Have the relationship.

Further, the pitch P ₂ of the unit region 520 corresponds to r ₂ -r _1, and the pitch P ₃ of the unit region 530 corresponds to r ₃ -r ₂ . The unit area 520 includes three concentric small areas 520a, 520b, and 520c. The division widths P ₂₁ , P ₂₂ and P ₂₃ of each small area are:
_{P 21 = P 22 = P 23} = P 2/3 ··· (16b)
The unit region 530 is composed of three concentric small regions 530a, 530b, and 530c, and the divided widths P ₃₁ , P _32, and P ₃₃ of each small region are
_{P 31 = P 32 = P 33} = P 3/3 ··· (16c)
Have the relationship. In the small region, as in the first to fourth embodiments, a section where the phase of transmitted light is the same is considered as one unit.

Next, the phase difference φ (m) will be considered. The phase difference φ (m) is based on the same concept as in the first to fourth embodiments, for example, with reference to the phase of the light transmitted through the small region 510c of the unit region 510, and the light transmitted through the small region 510b. When the phase difference is given as φ (1) and the phase difference of the light transmitted through the small region 510a is given as φ (2),
φ (0) = 0 (17a)
φ (1) = π [rad] (17b)
φ (2) = 2π [rad] (17c)
To satisfy the relationship.

The unit region 520 is set so that the phase difference between the small region 520b and the small region 520a is expressed by the equations (17b) and (17c), respectively, with the small region 520c as a reference. Similarly, the unit region 530 is set so that the phase difference between the small region 530b and the small region 530a is expressed by the equations (17b) and (17c), respectively, with the small region 530c as a reference. Further, steps d ₁ and d ₂ are provided so as to satisfy the expressions (17a) to (17c), respectively, but the diffractive lens 500 is formed of a material having a refractive index n _{s and} the surrounding medium is air. The steps may be set using the equations (8a) and (8b).

Under such conditions, for example, for light with a wavelength of 405 nm for BD, the focal length f is determined so that the + 1st-order diffracted light functions as a convex lens, and the radius of the corresponding annular zone is determined from the equation (15). Further, the wavelength dependency of the diffraction efficiency η _q has a characteristic corresponding to the graph of FIG. 3 which is the characteristic of the diffraction element 100 according to the first embodiment. For example, for the light with a wavelength of 405 nm for BD Wavelength-selective diffractive lens so as to be a concave lens for DVD and CD because it has a large + 1st order diffraction efficiency and a large -1st order diffraction efficiency for DVD wavelength 660 nm and CD wavelength 780 nm. Can be produced.

  FIG. 14 is a schematic diagram showing the condensing characteristics of light when three wavelengths of light for BD, DVD, and CD are incident on the diffraction lens 500. Specifically, FIG. 1 shows an optical system in which light having different wavelengths enters from a lens, and an objective lens 560 is disposed on the light transmission side of the diffraction lens 500 and an optical disk 570 is disposed on the light transmission side of the objective lens. Since the position of the information recording surface of the optical disc 570 differs depending on the respective standards, by using the diffraction lens 500, it is possible to condense well on each information recording surface of BD, DVD and CD. 14 (a) and 14 (b) specifically show condensing characteristics of light 540B and 550B in the 405 nm wavelength band for BD, condensing characteristics of light 540D and 550D in the 660 nm wavelength band for DVD, and for CD. The light condensing characteristics of light 540C and 550C in the 785 nm wavelength band are shown.

  FIG. 14A shows an optical system in which BD light, DVD light, and CD light all enter the diffraction lens 500 as parallel light, and FIG. 15B shows a finite number of light for CD. It may be preferable to use a system arrangement so as to be incident on the diffractive lens 500 as light that travels while diverging because the focal length becomes long and the lens design works advantageously.

  Here, when BD light is incident on the diffractive lens 500, the diffractive lens 500 functions as a convex lens, so that it passes through the objective lens 560 and enters the information recording surface 570B of the optical disc 570 (0.1 mm from the incident surface of the optical disc). Condensate. Further, when DVD light enters the diffractive lens 500, the diffractive lens 500 functions as a concave lens. Therefore, the diffractive lens 500 passes through the objective lens 560 and collects on the information recording surface 570D of the optical disc 570 (0.6 mm from the incident surface of the optical disc). Shine. When the light for CD enters the diffractive lens 500, the diffractive lens functions as a concave lens, and is condensed on the information recording surface 570C of the optical disc 570 (1.2 mm from the incident surface of the optical disc). In this way, by using the diffraction lens 500 and one objective lens 560, it is possible to condense well while suppressing aberration with respect to each information recording surface of an optical disc having different standards at three different wavelengths.

  Moreover, although the diffraction lens 500 was demonstrated as a shape of the schematic diagram of FIG. 13, it is not restricted to this. FIG. 15 is an example showing another configuration of the diffractive lens. FIG. 15A is a schematic cross-sectional view of the same diffractive lens 500 as in FIG. 13, and FIG. 15B is a small region constituting the unit region. FIG. 6 is a schematic cross-sectional view of a diffractive lens 501 in which the inclination of the staircase shape of the cross section of FIG. The diffractive lens 501 shown in FIG. 15B can function as a concave lens for BD light, and can function as a convex lens for DVD light and CD light. Further, a birefringent material layer 504 having the same lattice shape as that of the diffractive lens 500 between the translucent substrates 503a and 503b oriented in parallel like the diffractive lens 502 shown in FIG. The layer 504 and the isotropic material layer 505 may be included. In this case, similarly to the second embodiment, the polarization dependency of the diffraction action can be given to the incident light.

  Further, the phase difference between the three small regions constituting the unit region of the diffractive lens 500 is not limited to satisfying the equations (17a) to (17c), and for example, as shown in FIGS. 4 (a) and 4 (b). It may have such a phase difference. Further, the number of small regions constituting the unit region of the diffractive lens is not limited to 3, and may be 4. In the case of 4, the division width based on the third embodiment satisfies Expression (12), and 4 The phase difference between the two small regions may have a phase difference as shown in FIGS. 8B, 10A, and 10B, for example.

Similarly, the diffractive lens 500 of the fifth embodiment can diffract light of different wavelengths at different angles. For example, similarly to the optical characteristics of the first embodiment, light of a wavelength for BD is used. The difference between the diffraction angle θ ₊₁ (405) of the ₊ 1st order diffracted light having the highest diffraction efficiency and the diffraction angle θ ₋₁ (660) of the _−1st order diffracted light having the highest diffraction efficiency for the DVD wavelength light is Since it is larger than the diffractive lens, the pitches P ₁ , P ₂ , P ₃ ,... Can be set larger than the conventional diffractive lens. Therefore, when the diffractive lens of the present invention is used, it is not necessary to make the pitch fine, and easy processing is obtained.

(Sixth embodiment)
FIG. 16 is a schematic diagram showing a configuration of an optical head device 600 according to the sixth embodiment of the present invention. As a light source, a semiconductor laser 610B that emits light in a wavelength band of 405 nm that is a wavelength for BD, a hybrid type that emits light in a wavelength band of 660 nm that is a wavelength for DVD and light in a wavelength band of 785 nm as a wavelength for CD A semiconductor laser 610D is used. In the following description, it is assumed that the light emitted from each semiconductor laser has linearly polarized light orthogonal to the traveling direction and parallel to the paper surface. The light emitted from each semiconductor laser passes through the diffraction element 620 and becomes linearly polarized light in the Z direction, travels in the X direction, enters the polarization beam splitter 630, and travels in the direction of the optical disk 670 (Z direction). Then, the light transmitted through the collimator lens 640 becomes counterclockwise circularly polarized light by the quarter wavelength plate 650, passes through the objective lens 660, and reaches the optical disk 670. The light reflected by the optical disk 670 becomes clockwise circularly polarized light, passes through the objective lens 660, and becomes linearly polarized light in the Y direction by the quarter wavelength plate. Then, the light travels straight through the collimator lens 640 and the polarization beam splitter 630 and enters the diffraction element 680.

  The light incident on the diffractive element 680 has different diffraction directions (angles) depending on the wavelength of the incident light, and reaches the photodetectors 690B and 690D for BD and for both DVD and CD. For example, if BD light is + 1st order diffracted light, and DVD and CD light is -1st order diffracted light, the diffraction direction (diffraction angle) of DVD and CD light is different from BD light. to differ greatly. In this way, the diffracted BD light, DVD light, and CD light are condensed on the respective light receiving surfaces of the photodetectors 690B and 690D, and the reproduction signal of the information recorded on the optical disk 670, the focus error signal, Optical information such as a tracking error signal is detected. The optical head device 600 includes a focus servo (not shown) that controls the movement of the objective lens 660 in the optical axis direction based on the focus error signal, and the objective lens 660 that is perpendicular to the optical axis direction based on the tracking error signal. And a tracking servo (not shown) for controlling in the direction to be.

  In addition, as the diffraction element 620 and the diffraction element 680 arranged in the optical head device 600, the diffraction elements according to the first to fourth embodiments can be used. Here, it demonstrates as what arrange | positions the diffraction element 100 which concerns on 1st Embodiment as an example. As shown in FIG. 3, the wavelength dependence of the diffraction efficiency of the diffraction element according to the first embodiment has the highest + 1st order diffracted light at the BD wavelength (405 nm), the DVD wavelength (660 nm), and At the wavelength for CD (785 nm), the −1st order diffracted light is the highest.

Here, by using the above equation (10), the BD, DVD, and CD light transmitted through the diffractive element 620 is diffracted and travels in the X direction so that each of the semiconductor lasers The emission direction (angle) can be determined. For example, since light having a wavelength for BD has high + 1st order diffraction efficiency, q = + 1 and λ = 405, and the fixed Px value of the diffractive element 620 is determined, whereby the diffraction angle θ ₁ can be obtained. Similarly, DVD, since the highest is -1 order diffraction efficiency for CD, can each give q = -1 obtaining a diffraction angle theta _2. Here, although the diffraction angles of the −1st order diffracted light of the DVD light and the CD light differ strictly according to the calculation of Expression (10), by adjusting the width of the grating pitch Px, these two wavelengths can be obtained. it can reduce the difference between the diffraction angle of the light, which makes it possible to the diffraction angle substantially the same angle theta _2. In FIG. 16, the sign of the diffraction angle represents the clockwise direction as plus (+) and the counterclockwise direction as minus (−) with respect to the optical axis. In FIG. 16, θ ₁ and θ ₂ are given with reference to the X direction, but the concept of the sign is the same. When the position of each semiconductor laser is adjusted in this way, the light transmitted through the diffraction element 620 travels on the same axis (X direction). Therefore, even when a plurality of light beams having different wavelengths are used, This is preferable in that the optical parts can be shared.

Next, the diffraction element 680 will be described. A diffractive element 680 having the same characteristics as the diffractive element 620 can be arranged, and a plurality of light beams having different wavelengths reflected by the optical disk 670 are incident thereon. Similar to the above description, for example, BD wavelength light entering the diffraction element 680 has the highest + 1st order diffraction efficiency, and DVD wavelength light and CD wavelength light have -1st order diffraction efficiency. Since the diffraction angle of each diffracted light is the highest and the diffraction angles of the BD light among the three lights incident in the same traveling direction are θ ₁ , the diffraction angles of the DVD light and the CD light are It is quite different from θ _2. Accordingly, since a plurality of light beams having different wavelengths incident on the diffraction element 680 can be largely separated, the arrangement of the photodetectors can be facilitated, so that the optical head device can be miniaturized, and other light can be used as noise. Since it becomes difficult to reach the photodetector, a high-quality optical head device can be realized. Further, the same diffraction element 620 and diffraction element 680 may be used, but those that generate diffracted light having different diffraction angle characteristics may be used. + 1st order diffracted light may be used as the light for CD and the light for CD.

(Seventh embodiment)
FIG. 17 is a schematic diagram showing a configuration of an optical head device 700 according to the seventh embodiment of the present invention. The same optical components as those of the optical head device 600 according to the sixth embodiment are denoted by the same reference numerals. Avoid duplication of explanation. The optical head device 700 includes a hybrid semiconductor laser 710 that emits three different wavelengths for BD, DVD, and CD. Further, the diffraction element 720 can be the diffraction element having polarization dependency according to the second embodiment or the fourth embodiment.

Here, a case where the diffraction element 200 according to the second embodiment is used as the diffraction element 720 will be described. The linearly polarized light in the X direction emitted from the semiconductor laser 710 enters the diffraction element 720 and is emitted without changing the polarization state, and reaches the optical disk 670 as counterclockwise circularly polarized light. The light reflected by the optical disc 670 is converted into linearly polarized light in the Y direction by the quarter-wave plate 650 and enters the diffraction element 720 again. At this time, in the diffractive element, a diffractive action occurs due to a difference in refractive index between the birefringent material layer and the isotropic material layer, and the light with the wavelength for BD has a diffraction angle θ ₁ , the light with the wavelength for DVD, and the light for CD Each of the wavelengths of light has a diffraction angle θ ₂ and reaches the photodetectors 690B and 690D, respectively. In this way, by using the polarization-dependent diffraction element 720, the optical components can be further reduced, so that downsizing can be realized, and a plurality of lights having different wavelengths can be largely separated, so that the arrangement of photodetectors and the like can be reduced. In addition, since other light does not easily reach the photodetector as noise, a high-quality optical head device can be realized.

(Eighth embodiment)
FIG. 18 is a schematic diagram showing a configuration of a projection type liquid crystal display device 800 according to the eighth embodiment. As a light source for projection, a semiconductor laser 810B that emits blue light, a semiconductor laser 810G that emits green light, and a semiconductor laser 810R that emits red light are provided. The blue light emitted from each semiconductor laser passes through the liquid crystal light valve 820B, the green light passes through the liquid crystal light valve 820G, and the red light passes through the liquid crystal light valve 820R and enters the diffraction element 830. The light transmitted through the diffraction element 830 in one direction by transmission or diffraction action is condensed on the projection lens 840 and a combined image of each liquid crystal light valve is formed on the screen 850.

As the diffraction element 830, the diffraction element having polarization dependency according to the second embodiment or the fourth embodiment can be used. Here, a case where the diffraction element 200 according to the second embodiment is used will be described. At this time, from the blue semiconductor laser 810B linearly polarized light is emitted in the Y-direction, the image signal of the linearly polarized light component in the Y direction in the liquid crystal light valve 820B is incident at an angle theta _1. Similarly Y direction of linearly polarized light emitted from the red semiconductor laser 810R, the image signal of the linearly polarized light component in the Y direction in the liquid crystal light valve 820R is incident at an angle theta _2. The angle θ ₁ and the angle θ ₂ correspond to the diffraction angle of the diffraction element 830, and the clockwise direction is plus (+) and the counterclockwise direction is minus (−) with respect to the optical axis of the light of each color. ). In FIG. 18, θ ₁ and θ ₂ are given based on the Z direction, but the concept of the sign is the same.

The green semiconductor laser 810G emits linearly polarized light in the X direction, and an image signal of the linearly polarized component in the X direction enters the liquid crystal light valve 820G along the optical axis of the diffraction element 830. In addition, when the diffraction element 830 diffracts light incident in the Y polarization direction and transmits light incident in the X polarization direction, the blue light has a first-order diffraction efficiency. The light is diffracted so as to be the highest, and the red light is diffracted so that the −1st order diffraction efficiency is the highest. Further, since the green light is incident in the polarization direction of the X direction, it is transmitted without being diffracted. At this time, by arranging the semiconductor laser 810B and the liquid crystal light valve 820B so as to be inclined and incident from the optical axis by the diffraction angle θ ₁ of the + _{1st order} diffracted light with respect to the blue light, the blue light transmitted through the diffraction element 830 is optical axis. Proceed along. Similarly, by arranging the semiconductor laser 810R and the liquid crystal light valve 820R so as to be incident on the red light by being inclined from the optical axis by the diffraction angle θ ₂ of the −1st order diffracted light, the red light transmitted through the diffraction element 830 is light. The light beams of the three colors of blue, green, and red are combined and travel along the optical axis to the projection lens 840, and are imaged and displayed on the screen 850.

  In this way, by using a polarization-dependent diffraction element in a transmissive liquid crystal display device, it is possible to combine light of each color with a single element while maintaining high light utilization efficiency, so the number of optical components is reduced. In addition, it is possible to achieve downsizing. Further, the light source is not limited to the semiconductor laser, but may be a light emitting diode (LED) of each color. Here, the order of the highest diffraction efficiency for the blue light and the red light is +1 and −1, respectively. However, the order is not limited to this, and combinations of the −1st order and the + 1st order and other diffractions are also possible. May be used.

Example 1
As Example 1, the diffraction element 100 according to the first embodiment is manufactured based on FIG. A quartz glass substrate is used as the light-transmitting substrate 120, and one surface thereof is processed into a diffraction grating shape extending in one direction by a photolithography process and a dry etching process. Then, antireflection films are formed on both sides of the quartz glass substrate. At this time, the pitch Px of the unit regions 110 based on FIG. 2 is set to 5 μm, and the division widths X ₁ , X _2, and X ₃ of the small regions 110a, 110b, and 110c constituting the unit region 110 are 1.67 μm, respectively. And equally divided into three. When light having a wavelength of 510 nm is incident, the phase difference φ (1) = π of the small region 110b and the phase difference φ (2) = 2π of the small region 110c are set with reference to the phase of the light emitted from the small region 110a. In order to satisfy this, processing is performed so that the level difference d ₁ = 0.552 μm and the level difference d ₂ = 1.104 μm.

When light of 380 to 820 nm is incident on the diffractive element 100, the + 1st order diffraction efficiency η _{+ 1} becomes 68.4% at the wavelength of 391 nm. On the other hand, at the wavelength of 753 nm, the −1st order diffraction efficiency η ₋₁ is the maximum of 68.4%. As described above, when the wavelength of light incident on the diffraction element 100 is different, the order having the highest diffraction efficiency is different, and an effect of being able to be deflected and separated depending on the wavelength of incident light can be obtained.

(Example 2)
As Example 2, the diffraction element 200 according to the second embodiment is manufactured. In FIG. 6, a quartz glass substrate is used as the translucent substrate 220a, and an alignment film (not shown) subjected to alignment treatment in the Y direction is formed. Then, another transparent substrate (not shown) on which the alignment film is formed is arranged in parallel so that the alignment film faces and the alignment direction is aligned, so that the gap thickness is 4.18 μm. To seal. Thereafter, a liquid crystal monomer is injected from an injection port (not shown), and the liquid crystal is polymerized and cured by irradiation with ultraviolet rays. As a result, the thickness is 4.18 μm, the ordinary light refractive index n _o = 1.555, which is the refractive index in the X direction, and the extraordinary light refractive index n _e = 1.669, which is the refractive index in the Y direction, for light with a wavelength of 483 nm. A polymer liquid crystal layer is formed. In the formula (9), A, B and C of the polymer liquid crystal are A = 1.523, B = 0.0007 and C = 0.000168 in the ordinary light refractive index direction, and in the extraordinary light refractive index direction. A = 1.6211, B = 0.090, and C = 0.000488.

Thereafter, the translucent substrate (not shown) is separated, and the polymer liquid crystal layer is processed into a diffraction grating shape extending in one direction by a photolithography process and a dry etching process to form the birefringent material layer 230. At this time, the pitch Px of the unit regions 210 based on FIG. 6B is set to 5 μm, and the division widths X ₁ , X ₂ and X ₃ of the small regions 210a, 210b and 210c constituting the unit region 210 are respectively set. Divide equally into 1.67 μm. Further, in the isotropic material layer 240, A = 1.523, B = 0.0079, and C = −0.000178 in the formula (9), and the characteristics of the polymer liquid crystal layer in the normal light refractive index direction are almost the same. A transparent adhesive showing the same characteristics is used. By doing in this way, the transmittance | permeability of the light which injects in a normal light refractive index direction can be raised. On the other hand, in order to increase the diffraction efficiency when light in the extraordinary refractive index direction is incident, when the light of 483 nm is incident, the phase difference φ of the small region 210b is set with reference to the phase of the light emitted from the small region 210a. In order to satisfy (1) = π and the phase difference φ (2) = 2π of the small region 210c, processing is performed so that the level difference d ₁ = 2.09 μm and the level difference d ₂ = 4.18 μm.

Then, approximately equal the adhesive with a refractive index n _{B =} 1.553 which corresponds to an isotropic material layer 240 of the birefringent material in the ordinary refractive index n _o of the liquid crystal polymer when the light of 483nm is incident The unevenness (step) of the layer 230 is filled and bonded to a quartz glass substrate to be a light-transmitting substrate 220b and flattened. An antireflection film (not shown) is formed on the interface (air contact side) of the quartz glass substrate. In addition, by using the birefringent material layer 230 and the isotropic material layer 240 as described above, the phase difference φ (1) = π with respect to linearly polarized light in the Y direction of light having a wavelength of 483 nm, that is, extraordinary light. Diffraction because the phase difference φ (2) = 2π and the phase difference φ (3) = 3π. On the other hand, linearly polarized light in the X direction, that is, ordinary light, no phase difference occurs, so that the light travels straight. Have

Of the light incident on the produced diffraction element 200, the value of the wavelength λ of linearly polarized light in the Y direction is changed in the range of 380 to 820 [nm]. FIG. 19A shows the characteristics of the diffraction efficiency η _q with respect to the wavelength λ under this condition, and particularly shows the diffraction orders q = −1, 0, +1. At this time, the + 1st order diffraction efficiency η ₊ 1 in the range of 405 ± 10 nm, which is the wavelength band for BD, is 60% or more, and the −1st order diffraction efficiency η in the range of 660 ± 20 nm, which is the wavelength band for DVD. ₋₁ and −1st order diffraction efficiency η ₋₁ in the range of 785 ± 20 nm, which is the wavelength band for CD, show 60% or more.

On the other hand, FIG. 19B shows the characteristics of the diffraction efficiency η _q with respect to the wavelength λ when the value of the wavelength λ of the linearly polarized light in the X direction is changed in the range of 380 to 820 [nm]. As a result, the 0th-order diffracted light η ₀ corresponding to the straight-line transmittance is 94% or more in any wavelength band for BD, DVD, and CD, and the diffraction has transmission or diffraction characteristics depending on the polarization direction of incident light. An element can be obtained.

(Example 3)
As Example 3, the diffraction element 400 according to the fourth embodiment is manufactured. In FIG. 12, a quartz glass substrate is used as the light-transmitting substrate 420a, and an alignment film (not shown) that is aligned in the Y direction is formed. Then, another transparent substrate (not shown) on which the alignment film is formed is arranged in parallel so that the alignment film faces and the alignment direction is aligned, so that the thickness of the gap is 6.4 μm. To seal. Thereafter, a liquid crystal monomer is injected from an injection port (not shown), and the liquid crystal is polymerized and cured by irradiation with ultraviolet rays. As a result, the ordinary light refractive index n _o = 1.554, which is the refractive index in the X direction, and the extraordinary light refractive index n _e = 1.667, which is the refractive index in the Y direction, are 6.4 μm in thickness and have a wavelength of 489 nm. A polymer liquid crystal layer is formed. The wavelength dispersion characteristic of the polymer liquid crystal layer is the same as that of Example 2.

Thereafter, the translucent substrate (not shown) is separated, and the polymer liquid crystal layer is processed into a diffraction grating shape extending in one direction by a photolithography process and a dry etching process to form the birefringent material layer 430. At this time, the pitch Px of the unit regions 410 based on FIG. 12B is set to 10 μm, and the divided widths X ₁ , X ₂ , and the small regions 410a, 410b, 410c, and 410d constituting the unit region 410 are divided. Of X ₃ and X ₄ , X ₁ = X ₄ = 1.5 μm and X ₂ = X ₃ = 3.5 μm. Further, regarding the step of each small region, considering the case where the refractive index n _B of the isotropic material layer 440 is equal to the ordinary light refractive index n _o , the phase of the light emitted from the small region 410a when 489 nm light enters. In order to satisfy the phase difference φ (1) = π of the small region 410b, the phase difference φ (2) = 2π of the small region 410c, and the phase difference φ (2) = 3π of the small region 410c as a reference, the step d ₁ = 2.14 μm, step d ₂ = 4.27 μm, and step d ₃ = 6.40 μm.

Then, the substantially same refractive index _n adhesive B = 1.553 to the ordinary refractive index _{n o} of the liquid crystal polymer when the light of 489nm is incident, filling the irregularities of the birefringent material layer 430 (step), The light-transmitting substrate 420b is bonded and flattened with a quartz glass substrate. The wavelength dispersion characteristic of the adhesive is the same as that of Example 2. An antireflection film (not shown) is formed on the interface (air contact side) of the quartz glass substrate. By using such a birefringent material layer 430 and an isotropic material layer 440, a phase difference φ (1) = π, a phase difference with respect to linearly polarized light in the Y direction of light having a wavelength of 489 nm, that is, extraordinary light. Since it has φ (2) = 2π and phase difference φ (3) = 3π, it is diffracted. On the other hand, linearly polarized light in the X direction, that is, normal light, no phase difference is generated, so that it travels straight and has polarization dependency. .

Of the light incident on the produced diffraction element 400, the value of the wavelength λ of linearly polarized light in the Y direction is changed in the range of 380 to 820 [nm]. FIG. 20A shows the calculation of the characteristics of the diffraction efficiency η _q with respect to the wavelength λ under this condition, and particularly shows the diffraction orders q = −1, 0, +1. At this time, the + 1st order diffraction efficiency η ₊ 1 in the range of 405 ± 10 nm, which is the wavelength band for BD, is 60% or more, and the −1st order diffraction efficiency η in the range of 660 ± 20 nm, which is the wavelength band for DVD. ₋₁ and −1st order diffraction efficiency η ₋₁ in the range of 785 ± 20 nm, which is the wavelength band for CD, show 60% or more.

On the other hand, FIG. 20B shows the calculation of the characteristics of the diffraction efficiency η _q with respect to the wavelength λ when the value of the wavelength λ of the linearly polarized light in the X direction is changed in the range of 380 to 820 [nm]. As a result, the 0th-order diffracted light η ₀ corresponding to the straight-line transmittance is 94% or more in any wavelength band for BD, DVD, and CD, and the diffraction has transmission or diffraction characteristics depending on the polarization direction of incident light. An element can be obtained.

Example 4
In Example 4, the diffraction element 200 shown in FIG. 6 according to the second embodiment is arranged at the position of the diffraction element 830 of the projection type liquid crystal display device 800 according to the eighth embodiment. The manufacturing method of the diffractive element 200 is the same as that of the second embodiment, and the materials and shapes used are also the same.

As such the diffractive element 200 manufactured by the the position of the diffraction element 830 of the projection type liquid crystal display device 800 of FIG. 18, the direction in which the ordinary refractive index n _o of the birefringent material layer 230, the X-direction Deploy. Here, when the linearly polarized light in the Y direction from the semiconductor laser 810B emitting blue light passes through the liquid crystal light valve 820B and enters the diffraction element 830, the diffraction of the + 1st order diffracted light is performed in the same manner as the optical characteristics in the second embodiment. Efficiency η _{+ 1} is generated by 60% or more, and proceeds in the direction along the optical axis of the projection lens 840. Similarly, when linearly polarized light in the Y direction from the semiconductor laser 810R that emits red light passes through the liquid crystal light valve 820R and enters the diffraction element 830, diffraction efficiency η _{−1 of −1st} order diffracted light is generated by 60% or more. Then, it proceeds in the direction along the optical axis of the projection lens 840.

  On the other hand, when linearly polarized light in the X direction from the semiconductor laser 810G that emits green light passes through the liquid crystal light valve 820G and enters the diffraction element 830, the projection lens has a linear transmittance (0th-order diffraction efficiency) of 95% or more. The light passes straight in the direction along the optical axis 840. As a result, the transmitted light of blue, green, and red generated by the liquid crystal light valves 820B, 820G, and 820R is combined so that the optical axes are aligned by the diffraction element 200 of the present invention, and a composite image of the liquid crystal light valve is generated by the projection lens 840. Is imaged on the screen 850.

  Thus, by using the diffraction element of the present invention, it can be realized without using an expensive and three-dimensional dichroic prism used in a conventional projection type liquid crystal display device. . In particular, in the case of a dichroic prism, since there is a restriction that a semiconductor laser having each wavelength must be arranged perpendicularly to each incident surface of the dichroic prism, there is a difficulty in further downsizing. In that respect, the diffractive element of this embodiment is flat and has a great advantage in terms of miniaturization because it is incident perpendicularly or obliquely to the incident surface.

  As described above, by using the diffraction grating-shaped diffraction element of the present invention, when a plurality of light beams having different wavelengths are incident, the sign of the order of the light to be diffracted can be largely deflected depending on the wavelength. it can. In particular, it is a diffraction grating in which unit areas divided into three small areas or unit areas divided into four small areas are periodically arranged, and the above function is achieved with a relatively simple configuration in which the grating pitch is not finer than that of a conventional diffraction grating. realizable. Furthermore, by using the diffractive element of the present invention, the incident light in the first polarization direction has a high linear transmittance for light of any wavelength with respect to light of a plurality of wavelength bands. The incident light in the second polarization direction orthogonal to the direction can be deflected in the direction of transmission by selecting the wavelength. By applying such a diffractive element to an optical head device or a projection type liquid crystal display device, the size of the device can be reduced.

FIG. 2 is a schematic plan view showing a configuration example of the diffraction element according to the first embodiment. Plane schematic diagram and cross-sectional schematic diagram showing a unit region of the diffraction element according to the first embodiment Example graph showing characteristics of diffraction efficiency η _q with respect to wavelength λ of light incident on the diffraction element according to the first embodiment Sectional schematic diagram which shows the other structure of the diffraction element which concerns on 1st Embodiment. Example graph showing characteristics of diffraction efficiency η _q with respect to wavelength λ of light incident on the diffraction element according to the first embodiment Plane schematic diagram and cross-sectional schematic diagram showing a unit region of the diffraction element according to the second embodiment Plane schematic diagram showing a configuration example of a diffraction element according to the third embodiment Plane schematic diagram and cross-sectional schematic diagram showing a unit region of the diffraction element according to the third embodiment Example graph showing characteristics of diffraction efficiency η _q with respect to wavelength λ of light incident on the diffraction element according to the third embodiment Sectional schematic diagram which shows the other structure of the diffraction element which concerns on 3rd Embodiment. Example graph showing characteristics of diffraction efficiency η _q with respect to wavelength λ of light incident on the diffraction element according to the third embodiment Plane schematic diagram and cross-sectional schematic diagram showing a unit region of a diffraction element according to the fourth embodiment Plane schematic diagram and cross-sectional schematic diagram showing a unit region of a diffractive lens according to a fifth embodiment Schematic diagram of an optical system for focusing on an optical disc of different standards using a diffractive lens according to the fifth embodiment Sectional model which shows the other structure of the diffraction lens which concerns on 5th Embodiment. Configuration example of optical head device using diffraction elements according to first to fourth embodiments Configuration example of optical head device using diffractive element according to second and fourth embodiments Configuration example of projection type liquid crystal display device using diffraction element according to second and fourth embodiments In Example 2, the graph of an example which shows the characteristic of diffraction efficiency (eta) _q with respect to wavelength (lambda) of the light which injects into a diffraction element In Example 3, the graph of an example which shows the characteristic of diffraction efficiency (eta) _q with respect to wavelength (lambda) of the light which injects into a diffraction element

Explanation of symbols

100, 200, 300, 400, 620, 680, 720, 830 Diffraction element 110, 130, 140, 210, 310, 330, 340, 410, 510, 520, 530 Unit regions 110a, 110b, 110c, 130a, 130b, 130c, 140a, 140b, 140c, 210a, 210b, 210c, 310a, 310b, 310c, 310d, 330a, 330b, 330c, 330d, 340a, 340b, 340c, 340d, 410a, 410b, 410c, 410d, 510a, 510b, 510c, 520a, 520b, 520c, 530a, 530b, 530c Small region 111, 131, 141, 311, 331, 341 Translucent substrate surface 120, 220, 220a, 220b, 320, 420, 420a, 420 b Translucent substrate 230, 430 Birefringent material layer 240, 440 Isotropic material layer 500, 501, 502 Diffractive lens 511, 521, 531 Ring 540B, 550B Light 540D, 550D for BD 540D, 550D DVD 560 nm wavelength light 540C, 550C 785 nm wavelength light 560, 660 Objective lens 570, 670 Optical disc 570B BD information recording surface 570D DVD information recording surface 570C CD information recording surface 600, 700 Optical head Device 610B Semiconductor laser for BD 610D Semiconductor laser for emitting two wavelengths for DVD / CD 630 Polarizing beam splitter 640 Collimator lens 650 1/4 wavelength plate 690B Photo detector for BD 690D Photo detector for DVD / CD 710 Output 3 wavelengths for BD / DVD / CD Semiconductor laser 800 to be projected Projection type liquid crystal display device 810B Semiconductor laser for blue light 810G Semiconductor laser for green light 810R Semiconductor laser for red light 820B, 820G, 820C Liquid crystal light valve 840 Projection lens 850 Screen

Claims (14)

A diffractive element in which m pieces of light having different wavelengths are incident (an integer of m ≧ 2), and the phase of the light is modulated and transmitted.
The diffraction element has a shape in which a diffraction grating is formed on a translucent substrate or one surface of the translucent substrate becomes a diffraction grating,
The diffraction grating has a width of the grating pitch Px, and unit regions formed by extending in a direction orthogonal to the width direction of the grating pitch Px are repeatedly arranged in the width direction of the grating pitch Px,
The unit regions have different distances from the surface of the light-transmitting substrate when a single region is formed of a section made of a surface that is parallel to the surface of the light-transmitting substrate on which the diffraction grating is not formed and has the same distance. N small regions are included, and the small regions are configured to extend in a direction orthogonal to the width direction of the lattice pitch Px (an integer of N ≧ 3).
of the m of the light, the wavelength lambda ₁ of the shortest _wavelength, the longest wavelength is the wavelength lambda _m, when the wavelength lambda _a light is λ ₁ ≦ λ _a ≦ λ _m is incident in phase, most phase a phase of light transmitted through the small areas of zero is a small region advances, the phase difference is defined by the difference between the phase of the light having the wavelength lambda _a configured to transmit the small region which is different from the small region of the zero respectively an integer multiple of π,
At least one of the phase differences is an odd multiple of π,
The incident m light beams each have one diffracted light beam having the highest diffraction efficiency, and the light having the highest + p-order diffraction efficiency and the light beam having the highest -q-order diffraction efficiency. A diffraction element including at least one each of (p, q ≧ 1). A diffractive element in which m pieces of light having different wavelengths are incident (an integer of m ≧ 2), and the phase of the light is modulated and transmitted.
The diffraction element has a shape in which a diffraction grating is formed on a translucent substrate or one surface of the translucent substrate becomes a diffraction grating,
A grid pitch P ₁ , P ₂ ,..., P _M (P ₁ > P ₂ >...> P _M ) in this order on a straight line parallel to the translucent substrate surface with the point A on the translucent substrate as a base point. M unit areas including a circular area or a ring-shaped area whose outer edge is a circle,
The unit region has N small cross-sections having cross-sections parallel to the translucent substrate surface and different heights, and extending along a circumferential direction of a circle centered on the point A. Has a region (an integer of N ≧ 3),
of the m of the light, the wavelength lambda ₁ of the shortest _wavelength, the longest wavelength is the wavelength lambda _m, when the wavelength lambda _a light is λ ₁ ≦ λ _a ≦ λ _m is incident in phase, most phase a phase of light transmitted through the small areas of zero is a small region advances, the phase difference is defined by the difference between the phase of the light having the wavelength lambda _a configured to transmit the small region which is different from the small region of the zero respectively an integer multiple of π,
At least one of the phase differences is an odd multiple of π,
The incident m light beams each have one diffracted light beam having the highest diffraction efficiency, and the light having the highest + p-order diffraction efficiency and the light beam having the highest -q-order diffraction efficiency. A diffraction element including at least one each of (p, q ≧ 1). The diffraction element according to claim 1 , wherein at least one of the phase differences is π . The diffraction element according to any one of claims 1 to 3 , wherein the values of p and q of the + p-order diffraction efficiency and the -q-order diffraction efficiency are 1, respectively. The unit area is composed of three small areas, and the first small area, the second small area, and the third small area from the end of the unit area,
When the width of the first small region is X ₁ , the width of the second small region is X ₂ , and the width of the third small region is X ₃ ,
X ₁ = X ₂ = X ₃ = Px / 3,
The diffraction element according to any one of claims 1 to 4 . The first subregion is the zero subregion;
When the phase difference of the first small region is φ (0), the phase difference of the second small region is φ (1), and the phase difference of the third small region is φ (2),
φ (0) = 0,
φ (1) = π,
φ (2) = 2π,
The diffraction element according to claim 5 , having a shape of the unit region. The unit area is composed of four small areas, and each of the unit areas includes a first small area, a second small area, a third small area, and a fourth small area from an end of the unit area,
When the width of the first small region is X ₁ , the width of the second small region is X ₂ , the width of the third small region is X ₃ , and the width of the fourth small region is X ₄ ,
X ₁ : X ₂ : X ₃ : X ₄ = 3: 7: 7: 3,
The diffraction element according to any one of claims 1 to 4 . The first subregion is the zero subregion;
The phase difference of the first small area is φ (0), the phase difference of the second small area is φ (1), the phase difference of the third small area is φ (2), and the fourth small area is When the phase difference of the region is φ (3),
φ (0) = 0,
φ (1) = π,
φ (2) = 2π,
φ (3) = 3π,
The diffraction element according to claim 7 , having a shape of the unit region. 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 claim ordinary equal to the refractive index n _o or the extraordinary refractive index _{n e (n o ≠ n e} ) any refractive index n _s of one refractive index is isotropic transparent material materials 1-8 The diffraction element according to any one of the above. A light source;
A beam splitter for deflecting and separating light from the light source;
An objective lens for condensing the light emitted from the beam splitter onto the optical disc;
A light detector for detecting light reflected by the optical disc ,
In the optical path, the diffraction element according to any one of claims 1 or claim 4-9 disposed between the optical path and the light detector, the beam splitter between the light source and the beam splitter Optical head device. A light source;
An objective lens for condensing the light emitted from the light source onto the optical disc;
A quarter-wave plate disposed between the light source and the optical disc, which produces a quarter-wave phase difference with respect to the light;
A light detector for detecting light reflected by the optical disc,
An optical head device in which the diffraction element according to claim 9 is disposed in an optical path common to an optical path between the light source and the objective lens and an optical path between the objective lens and the photodetector. A light source;
A beam splitter for deflecting and separating light from the light source;
An objective lens for condensing the light emitted from the beam splitter onto the optical disc;
A light detector for detecting light reflected by the optical disc,
An optical head device in which the diffraction element according to claim 2 is arranged in an optical path between the beam splitter and the objective lens. The light source emits light of three different wavelengths λ ₁ , wavelength λ ₂ , wavelength λ ₃ ,
The wavelength λ ₁ is a 405 nm wavelength band in the range of 395 to 415 nm,
The wavelength λ ₂ is a 660 nm wavelength band in the range of 640 to 680 nm,
The wavelength λ ₃ is a 785 nm wavelength band in the range of 765 to 805 nm,
The optical head device according to any one of claims 10 to 12 . A light source;
A liquid crystal light valve that modulates visible light emitted from the light source according to an image to be displayed;
In a projection display device comprising a projection lens that magnifies and projects an image generated by the liquid crystal light valve,
A projection display device in which the diffraction element according to claim 9 is arranged in an optical path between the liquid crystal light valve and the projection lens.

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