JP2008268724A - Reflection diffraction polarizer and optical apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reflection diffraction polarizer, having a function to nearly reflect the light to a side where only the light of the circularly polarized light in a specific rotation direction is made incident in a prescribed frequency band, and to transmit the light of the circularly polarized light different from the rotation direction in the prescribed frequency band. <P>SOLUTION: The reflection diffraction polarizer includes a birefringent film comprising a cholesteric phase liquid crystal, and is such that the thickness direction of the birefringent film and the screw axis of the liquid crystal molecules are parallel; the helical pitch of the liquid crystal molecules of the birefringent film is substantially equal to the wavelength of the incident light; a plurality of grooves of a uniform depth are formed on the surface; and the period of the pitch of the grooves adjacent to each other substantially is equal. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical device having a polarizer that converts incident light having a random polarization state such as natural light into a specific polarization state, and an optical component that acts on the specific polarization such as optical imaging, optical storage, and optical communication. About.

  Some light sources used in optical devices have many types of polarization states. In the field of optical imaging, for example, a white light source such as a metal halide lamp used as a light source of a projection display device generally has a random polarization state. On the other hand, semiconductor lasers used in optical storage and optical communication emit linearly polarized light, but may have variations in polarization direction and temporal variations due to manufacturing variations and changes in use environment temperature. Liquid crystal elements that modulate the image information of projection display devices in the field of optical imaging, and polarization beam splitters that are used to switch the light path in the field of optical storage and optical communication depend on the polarization state of the incident light. It is suitable for optical systems that use uniform linearly polarized light. In order to make the polarization direction of light constant, a polarizer that transmits only specific polarized light is used in the optical system. The higher the extinction ratio of this polarizer, the better the characteristics of the optical system. The extinction ratio of the child is regarded as one of the important performances.

  Conventional polarizers have used absorption polarizers that have high absorptivity for light in a specific polarization direction when light is incident, but the temperature of the polarizer itself rises due to light absorption, There was a problem that it was easy to deteriorate. In addition, the dye-based film that is typically used also has a problem that it easily deteriorates under high temperature and high temperature and high humidity conditions. As means for solving such a problem, it has been proposed to use a heat-resistant structural birefringent polarizing plate (for example, see Patent Document 1). Further, a diffractive polarizer has been proposed as a polarizer that does not use absorption (see, for example, Patent Document 2).

  In addition, non-absorbing cholesteric liquid crystals have a constant band of wavelengths when light with the same polarization state as the spiral direction of the liquid crystal molecules and light having a wavelength approximately equal to the spiral pitch is incident parallel to the spiral axis. It has a characteristic that incident light is substantially reflected. On the other hand, light that is incident as circularly polarized light in the direction opposite to the spiral direction of the liquid crystal molecules has a characteristic of almost transmitting (see Non-Patent Document 1).

JP 2001-281615 A JP 2005-18813 A Chandra Carsell's "Physics of Liquid Crystal" Yoshioka Shoten 1995

  However, since the structural birefringent polarizing plate described in Patent Document 1 requires light to be incident obliquely with respect to the optical axis, the polarizing means must be disposed obliquely with respect to the optical axis. Minute space was required, and there was a problem that miniaturization was difficult. In particular, when a black display is displayed on a projection display device, a structural birefringent polarizing plate is also used for a polarizer having the role of an analyzer placed on the side from which light is emitted from the liquid crystal panel used. Therefore, it is necessary to arrange the analyzer obliquely with respect to the optical axis, which makes it difficult to reduce the size.

  In addition, the diffractive polarizer described in Patent Document 2 is advantageous for downsizing, but a polarization component that is not used is diffracted backward, so that it is sufficient from the optical axis to obtain high contrast in a projection display device. It is necessary to set the diffraction angle to be far away from each other. For this reason, there is a problem that there is a restriction that the grating pitch of the diffraction grating structure must be narrowed. In addition, there is a problem that the contrast is likely to be lowered without a diaphragm unit that shields the diffracted light because it is easily affected by reflected stray light from components installed in the optical path of the diffracted light.

  Non-Patent Document 1 describes optical properties of non-absorbing cholesteric liquid crystals, but there is no proposal for a specific mode as a polarizer.

  The present invention has been made to solve such a problem, and an object of the present invention is to provide a polarizer that is stable and has a high extinction ratio and is small in size and durable, and an optical device using the same. And

  In order to achieve the above object, a reflective diffractive polarizer that reflects light in one of the rotation directions of light in a predetermined wavelength range that is incident as clockwise or counterclockwise circularly polarized light, the reflective diffractive polarizer is A birefringent film composed of cholesteric phase liquid crystal having refractive index anisotropy, wherein the thickness direction of the birefringent film is parallel to the helical axis of the liquid crystal molecules of the cholesteric phase liquid crystal and the thickness of the liquid crystal molecules The birefringent film has a diffractive grating structure of a plurality of grooves having substantially the same width and depth on one surface, and the birefringent film has a uniform spiral pitch in the direction. A reflection diffractive polarizer having a constant grating pitch is provided.

  According to this configuration, a reflective diffractive polarizer that reflects and diffracts circularly polarized light having the same rotational direction as that of the cholesteric phase liquid crystal and transmits circularly polarized light having the opposite rotational direction is realized. it can.

  In order to achieve the above object, there is provided the reflective diffractive polarizer according to the above, wherein the birefringent film comprises a cholesteric phase polymer liquid crystal.

  According to this configuration, it is possible to realize a reflective diffractive polarizer using a birefringent film having high durability and reliability.

  Further, in order to achieve the above object, the reflection diffraction according to the above, wherein the unevenness is filled and flattened with an isotropic material having a refractive index between the extraordinary refractive index and the ordinary refractive index of the birefringent film. A polarizer is provided.

  According to this configuration, when circularly polarized light having a predetermined wavelength having a rotation direction opposite to the spiral direction of the liquid crystal molecules of the cholesteric phase liquid crystal is incident, the phase difference of the unevenness formed on the surface of the birefringent film Therefore, a high transmittance can be realized, and a reflection diffractive polarizer having a high extinction ratio can be realized depending on the rotation direction of incident circularly polarized light.

  Moreover, in order to achieve the said objective, the reflection diffraction polarizer as described in the above containing two or more of the birefringent films is provided.

  According to this configuration, a higher extinction ratio can be realized as compared with a reflective diffraction polarizer in which the birefringent film layer is a single layer.

  In order to achieve the above object, there is provided the reflective diffraction polarizer according to the above, wherein the two or more birefringent films have different helical pitches.

  According to this configuration, by stacking cholesteric phase liquid crystals with different reflection wavelength band characteristics, functions such as expanding the wavelength range of light that can provide a high extinction ratio and reflecting and diffracting multiple wavelengths are realized. it can.

  In order to achieve the above object, the reflection diffraction element described above including a quarter-wave plate having a phase difference of (0.25 + m) λ with respect to the wavelength λ of incident light (m is an integer) is provided. Showing).

  According to this configuration, the linearly polarized light that travels straight through the reflective diffractive polarizer is converted into circularly polarized light having one of the rotation directions by the quarter-wave plate, and is the same as the rotation direction of the liquid crystal molecules in the birefringent layer. Circularly polarized light can be selectively reflected.

  In order to achieve the above object, the birefringent film is sandwiched between two quarter-wave plates arranged with the fast axis or slow axis orthogonal to each other, and the reflection diffraction as described above A polarizer is provided.

  According to this configuration, without adding parts, the incident linearly polarized light having the vibration direction in the A direction is the same as the direction of the spiral of the liquid crystal molecules, and the circularly polarized light in the rotational direction can obtain the highest reflection diffraction efficiency. Can be converted to light. On the other hand, linearly polarized light in the B direction having a vibration direction orthogonal to the A direction can be converted into circularly polarized light in the rotational direction that provides the highest transmittance in the direction opposite to the spiral direction of the liquid crystal molecules. . From this, it can be made to act as a reflection diffraction polarizer also to the incident linearly polarized light.

  In order to achieve the above object, a light source, a color separation unit that separates visible light from the light source into light of a plurality of colors, and a plurality of light that modulates the light of the plurality of colors according to an image to be displayed. A liquid crystal panel, a plurality of reflection mirrors for guiding the light of the plurality of colors separated by the color separation means to the corresponding liquid crystal panel, and an optical path disposed on the optical path from the light source to the plurality of liquid crystal panels. A plurality of first polarization means for changing the polarization state, a plurality of second polarization means for changing the polarization state of light disposed on the light transmitting side of the plurality of liquid crystal panels, and the plurality of second polarization means A projection-type display device comprising: a light combining unit that combines light transmitted through the light combining unit; and a projection unit that magnifies and projects the light combined by the light combining unit. The plurality of first polarization units and the plurality of second units Less of polarization means One polarization means also provides a projection display device characterized by being constituted by a reflective diffraction polarizer described above.

  According to this configuration, light of a polarization component that is not used is reflected and diffracted behind the reflection diffraction polarizer, so that there is little stray light component in the forward direction of the reflection diffraction polarizer, and regular reflection in the incident optical axis direction. A compact and high-contrast optical device with little (0-order diffraction) light can be realized with high productivity without any restrictions on the grating pitch of the diffraction grating structure on the surface of the reflective diffraction polarizer. The rear is the direction from the surface toward the light incident side with respect to the film surface on which light is incident, whereas the front is the light incident side from the surface opposite to the film surface on which light is incident. And the direction toward the opposite direction (outgoing side).

  In order to achieve the above object, a light source, an objective lens that condenses the light emitted from the light source on the optical recording medium, and reflected light that is collected and reflected by the optical recording medium A polarization beam splitter that deflects and separates into an optical path different from the optical path, and a monitor photodetector that receives monitor light that is separated from the light emitted from the light source incident on the polarization beam splitter into an optical path different from the optical recording medium; An optical head device comprising: a photodetector for detecting the reflected light that has been deflected and separated; in an optical path between the light source and the photodetector, or between the polarization beam splitter and the monitor photodetector. An optical head device is provided in which the reflection diffraction polarizer described above is installed in the optical path.

  According to this configuration, unnecessary polarization components generated due to product variations of the semiconductor laser as a light source and environmental temperature changes are reflected and diffracted backward. Therefore, there are few components that stray light travels forward, and there is little light that is regularly reflected (0th order diffraction) in the direction of the incident optical axis, so that information can be read and written with high accuracy. In addition, a compact and highly stable optical device can be realized with high productivity without restriction of the grating pitch of the diffraction grating structure on the surface of the reflective diffraction polarizer.

  The present invention has a birefringent film in which the spiral axis direction of the liquid crystal molecules of the cholesteric phase liquid crystal is parallel to and uniform in the thickness direction, and has substantially the same width and depth on one surface of the birefringent film. Provided are a reflection diffraction polarizer having an uneven diffraction grating structure of a plurality of grooves, and a grating pitch of adjacent grooves having a constant period, and an optical device using the reflection diffraction polarizer It is something that can be done.

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

(First Embodiment)
FIG. 1 is a diagram illustrating a conceptual configuration of a reflective diffraction polarizer 10 according to the present embodiment. In FIG. 1A, the reflective diffractive polarizer 10 uses, as a birefringent material, a polymer liquid crystal film obtained by polymerizing and polymerizing a cholesteric phase liquid crystal composed of a liquid crystal having a polymerization site and a chiral material. As shown in FIG. 1A, a polyimide film (not shown) formed on the transparent substrate 11 is applied and baked, and a rubbing process is performed to form an alignment film. A cholesteric phase liquid crystal monomer having a polymerization site is applied onto the alignment film, and then polymerized and fixed by ultraviolet irradiation to form a cholesteric phase polymer liquid crystal film 12. Even if the cholesteric liquid crystal phase is not polymerized and fixed, the same effect can be obtained if the helical axes of the liquid crystal molecules are spiraled at a constant pitch parallel to the thickness direction.

  On the surface of the cholesteric phase polymer liquid crystal film 12, irregularities 13 having a plurality of grooves having the same depth and width are formed. The lattice pitch is the shortest distance between the center points of the recesses of adjacent grooves. The unevenness 13 can be formed by, for example, a photolithography process. The unevenness 13 is filled with an isotropic material 14 having a refractive index substantially equal to the refractive index when circularly polarized light having a rotation direction opposite to the spiral direction of the cholesteric phase polymer liquid crystal 12 is incident in parallel to the spiral axis. The opposing surface is bonded to the transparent substrate 15.

A cholesteric phase liquid crystal is the same as the twist direction of liquid crystal molecules in light incident parallel to the helical axis direction when the helical pitch P is about the same as the product of the wavelength λ of incident light and the refractive index n of the cholesteric liquid crystal phase. The circularly polarized light in the rotational direction is substantially reflected, and the circularly polarized light in the reverse rotational direction has a circular polarization dependency that is substantially transmitted. Central wavelength lambda ₀ of the wavelength band showing the reflection characteristic, the helical pitch P, and ordinary refractive index of the liquid crystal n _o, shown the extraordinary refractive index in relation to when the n _e (1) formula. Further, the reflection bandwidth Δλ is expressed by the relationship of the expression (2). Hereinafter, (λ ₀ ± Δλ) is defined as a reflection wavelength band.

From this, when the light in the reflected wavelength band is circularly polarized light that is parallel to the spiral axis direction of the liquid crystal molecules and has the same rotational direction as the twist direction of the liquid crystal molecules, the cholesteric phase polymer liquid crystal film 12 acts as a reflective film. . The reflectance in the reflection wavelength band depends on the number of helical pitches in the cholesteric phase polymer liquid crystal film 12. The number of helical pitches is represented by the number of rotations of liquid crystal molecules. A spiral pitch number of about 10 revolutions or more shows a high reflectance almost uniformly in the reflection wavelength band without depending on the film thickness. In FIG. 2A, for example, a cholesteric phase polymer liquid crystal film having a thickness of 4.5 μm with a center wavelength λ ₀ of about 455 nm and a reflection wavelength bandwidth Δλ of about 70 nm is provided with the same rotation direction as the twist direction of the liquid crystal molecules The calculated reflection spectrum when circularly polarized light is incident parallel to the helical axis is shown. From this, it can be confirmed that a high reflectance is obtained in the reflection wavelength band.

  It is assumed that light having a wavelength λ is incident, where d is the depth of the periodic unevenness 13 formed on the surface of the cholesteric phase polymer liquid crystal film, and n is the refractive index of the isotropic material 14 filling the unevenness. At this time, when the relationship of the expression (3) is satisfied, the unevenness acts to show the characteristics of total diffraction, and the amount of linearly reflected light becomes substantially zero.

  On the other hand, when circularly polarized light having a rotation direction opposite to the twist direction of the liquid crystal is incident, since there is no reflection wavelength band, the cholesteric phase polymer film 12 is totally transmitted. Furthermore, since the refractive index of the unevenness 13 and the isotropic material 14 filling the unevenness are substantially equal, diffraction does not occur. FIG. 2B shows the reflection zero-order diffraction efficiency of the reflective diffraction polarizer in which the isotropic material 14 has a refractive index n of about 1.7 and a depth d of irregularities on the surface of the cholesteric phase liquid crystal film of about 67 nm. It can be confirmed that the light is diffracted to other than the 0th order around the wavelength of 455 nm, and the 0th order reflected light amount is suppressed.

  As shown in FIGS. 2A and 2B, when circularly polarized light having the same rotational direction as the twist direction of the liquid crystal molecules is incident in parallel to the spiral axis of the liquid crystal molecules, high reflectance and low reflection are obtained. Zero order diffraction efficiency is obtained. On the other hand, when circularly polarized light having a rotation direction opposite to the twist direction of the liquid crystal molecules is incident in parallel to the spiral axis of the liquid crystal molecules, it exhibits high transmittance and non-diffractive characteristics. Functions as a polarizer in light having a wavelength in the reflection wavelength band of the cholesteric phase polymer liquid crystal. For example, as shown in FIG. 1B, the light of the first circularly polarized light 21 having the same rotational direction as the twisted direction of the liquid crystal molecules is reflected and diffracted at almost other than the 0th order, and is opposite to the twisted direction of the liquid crystal molecules. The light of the second circularly polarized light 22 in the rotation direction is substantially transmitted. Therefore, it functions as a reflection diffraction type polarizer having a high extinction ratio depending on the polarization state of incident light.

The center wavelength λ ₀ and the reflection wavelength bandwidth Δλ of the selective reflection wavelength band are not limited to those in this calculation example, and can be arbitrarily set depending on the liquid crystal material or chiral material used and the mixing ratio thereof. In addition, by designing the cholesteric phase polymer liquid crystal film, it is possible to set an arbitrary center wavelength and reflection wavelength bandwidth to act as a polarizer by optimizing the depth of the concave and convex portions.

  The function of the present invention is based on the combined effect of the reflectance characteristic shown in FIG. 2A and the reflection zero-order diffraction characteristic shown in FIG. 2B, and is polarized at wavelengths not included in the reflection wavelength band. It shows high transmittance regardless of the state and does not function as a polarizer. Therefore, it is possible to function as a reflection diffraction type polarizer having wavelength selectivity of transmission or reflection with respect to circularly polarized light having the same rotational direction as the twist direction of the liquid crystal molecules.

The boundary portion between the cholesteric phase polymer liquid crystal film serving as a reflection diffraction polarizer and the isotropic medium only needs to have effective periodic unevenness, and the surface of the substrate having the periodic unevenness prepared in advance is sufficient. The same effect can be obtained by forming a cholesteric phase polymer liquid crystal film. In this case, the transparent substrate itself may be processed into periodic unevenness, or the isotropic material formed on the transparent substrate may be processed into periodic unevenness. Examples of isotropic materials include organic materials such as acrylic resins, epoxy resins, and polyimide resins, inorganic material films such as SiO ₂ , SiON, TiO ₂ , and Ta ₂ O ₅ , and multilayers formed from these materials. You may comprise with a film | membrane etc.

  In addition, it is preferable that the refractive index of the isotropic material in contact with the cholesteric phase polymer liquid crystal film is approximately equal to the refractive index with respect to the circularly polarized light in the rotation direction opposite to the spiral direction of the liquid crystal molecules because a high extinction ratio can be obtained. Specifically, an isotropic material having a refractive index in the range of 1.5 to 1.7 is preferable, and a range of 1.55 to 1.65 is more preferable because higher contrast can be obtained.

(Second Embodiment)
FIG. 3 is a diagram illustrating a conceptual configuration of the reflective diffraction polarizer 30 according to the present embodiment. The difference from the first embodiment is that a multilayer cholesteric phase polymer liquid crystal layer is disposed. As shown in FIG. 3A, the reflective diffractive polarizer 30 has a period on the surface of the first cholesteric phase polymer liquid crystal film 32 formed on the transparent substrate 31 as in the first embodiment. The periodic unevenness 33 is formed, and the periodic unevenness 33 is substantially equal to the refractive index when circularly polarized light having a rotation direction opposite to the spiral direction of the cholesteric phase polymer liquid crystal is incident in parallel to the spiral axis. It is filled with an isotropic material 34, and the opposite surface is bonded to the transparent substrate 35.

  Similarly, periodic irregularities 37 are formed on the surface of the second cholesteric phase polymer liquid crystal film 36 having the same spiral direction as the first cholesteric phase liquid crystal and having a different helical pitch. The molecule is filled with an isotropic material 38 that is substantially equal to the refractive index of circularly polarized light that has a rotational direction opposite to the rotational direction of the helical axis, and the opposite surface is bonded to the transparent substrate 39. These two cholesteric phase polymer liquid crystal films are laminated to form a reflective diffraction polarizer 30.

In FIG. 4A, a cholesteric phase polymer liquid crystal film having a thickness of 4.5 μm with a center wavelength λ ₀ of about 420 nm and a reflection wavelength bandwidth Δλ of about 65 nm has the same rotational direction as the twist direction of the liquid crystal molecules. The reflection spectrum calculation value of the circularly polarized light is shown by a solid line. The reflection wavelength band at this time is defined as a first reflection wavelength band. Similarly, circularly polarized light having the same rotational direction as the twist direction of the liquid crystal molecules is applied to a cholesteric phase polymer liquid crystal film having a thickness of 4.5 μm with a center wavelength λ ₀ of about 490 nm and a reflection wavelength bandwidth Δλ of about 75 nm. The calculated reflection spectrum is indicated by a broken line. The reflection wavelength band at this time is defined as a second reflection wavelength band. It can be confirmed that a continuous reflection wavelength band can be obtained for light having a wavelength of about 390 nm to 525 nm by laminating two cholesteric layer polymer liquid crystals as shown in FIG.

  FIG. 4 (b) shows a reflection diffraction polarizer in which the refractive index n of the isotropic material is about 1.7 and the periodic unevenness depth d corresponding to the first reflection wavelength band is about 61 nm. The calculated spectrum of the folding efficiency is shown by a solid line. Also. A spectral calculation value of the reflection zero-order diffraction efficiency for a reflection diffraction polarizer having a periodic unevenness depth d corresponding to the second reflection wavelength band of about 72 nm is indicated by a broken line. From these calculated values, it can be confirmed that the first reflection wavelength band is diffracted to other than the 0th order around the wavelength of 420 nm and the second reflection wavelength band is 490 nm, and the 0th order reflected light amount is suppressed.

  As shown in FIGS. 4A and 4B, when circularly polarized light having the same rotational direction as the twist direction of the liquid crystal molecules is incident parallel to the spiral axis of the liquid crystal molecules, the first reflection wavelength band High reflectivity and low zero-order diffraction efficiency are obtained at a wide range of wavelengths in the second reflection wavelength band. On the other hand, when the circularly polarized light having the rotation direction opposite to the twist direction of the liquid crystal is incident in parallel with the spiral axis of the liquid crystal molecule, it exhibits high transmittance and non-diffractive characteristics. It functions as a polarizer in a wide range of wavelengths composed of the first reflection wavelength band and the second reflection wavelength band.

  For example, as shown in FIG. 3 (b), the cholesteric phase polymer liquid crystal films 36 and 32 have a reflection wavelength of the first reflection wavelength band and the second reflection wavelength band shown in FIGS. 4 (a) and 4 (b), respectively. A cholesteric phase polymer liquid crystal film to be a band is laminated. In this case, when circularly polarized light having the same rotational direction as the twist direction of the liquid crystal molecules is incident, the light of the circularly polarized light 41 in the first reflection wavelength band is periodically formed on the surface of the cholesteric phase polymer liquid crystal film 36. The light of the circularly polarized light 42 of the unevenness and the second reflection wavelength band is a periodic unevenness formed on the surface of the cholesteric phase polymer liquid crystal film 32, and each light is substantially reflected and diffracted. On the other hand, when circularly polarized light having a rotation direction opposite to the twist direction of the liquid crystal molecules is incident, the light is almost transmitted. Therefore, it functions as a reflection diffraction polarizer having a high extinction ratio depending on the polarization state of incident light.

(Third embodiment)
FIG. 5 is a diagram showing a conceptual configuration of the reflective diffraction polarizer 50 according to the present embodiment. Compared to the first embodiment, the difference is that the cholesteric polymer liquid crystal layer is sandwiched between two retardation plates. As shown in FIG. 5A, the reflective diffractive polarizer 50 forms periodic irregularities 53 on the surface of a cholesteric phase polymer liquid crystal film 52 formed on a transparent substrate 51. The periodic irregularities 53 are filled with an isotropic material 54 that is substantially equal to the refractive index when circularly polarized light having a rotation direction opposite to the spiral direction of the cholesteric phase polymer liquid crystal is incident parallel to the spiral axis. The opposing surface is bonded to the transparent substrate 55. Furthermore, an adhesive layer (not shown) is provided on the upper and lower surfaces of the first retardation plate 56 and the second retardation plate 57 and is laminated on the transparent substrates 58 and 59.

When the cholesteric phase polymer liquid crystal film 54 has the characteristics shown in FIGS. 2A and 2B, the retardation R ₁ of the _first retardation plate 56 is R for the light having the center wavelength λ _{0. A} quarter-wave plate in which ₁ = (0.25 + m) λ ₀ (m represents a positive integer) is used. At this time, when the light incident on the reflection diffraction polarizer 50 is linearly polarized light having a wavelength λ ₀ , the first retardation plate 56 converts the linearly polarized light into circularly polarized light. The light converted into the circularly polarized light is transmitted or reflected and diffracted according to the rotation direction of the spiral liquid crystal molecules of the cholesteric phase polymer liquid crystal film as in the first embodiment. Similarly, the retardation R ₂ of the _second retardation plate 57 is a quarter wavelength that is R ₂ = (0.25 + n) λ ₀ (n represents a positive integer) with respect to the light having the center wavelength λ _0. A plate is used. The circularly polarized light that has passed through the first retardation plate is converted again to linearly polarized light by the second retardation plate and passes through the reflection diffraction polarizer 50.

  Here, the retardation of the first retardation plate and the retardation of the second retardation plate are substantially equal, and the optical axes of the two retardation plates are arranged so as to be orthogonal to each other to transmit light. It is possible to return the polarization state of the light to the polarization state of the light before incidence. Further, when linearly polarized light having a wavelength other than the reflection wavelength band is incident, it is converted into elliptically polarized light according to the wavelength dispersion of the retardation of the first retardation plate. The light is again converted into linearly polarized light before incidence and transmitted. For example, as shown in FIG. 5B, the light of the first linearly polarized light 61 in the vibration direction parallel to the paper surface is converted to circularly polarized light that is the same as the rotation direction of the liquid crystal molecules by the first retardation plate, and is reflected and diffracted. On the other hand, the light of the second linearly polarized light 62 in the vibration direction perpendicular to the paper surface is converted into circularly polarized light that is opposite to the rotation direction of the liquid crystal molecules and is transmitted. Further, since the wavelength not included in the reflection wavelength band is transmitted while maintaining the polarization state of incident light, it also has a wavelength selection function.

  As the material of the retardation plate, a polymer liquid crystal that exhibits refractive index anisotropy by orientation treatment, a polymer film that exhibits refractive index anisotropy by stretching, and the like are preferably used. In addition, in order to improve the conversion characteristics from linearly polarized light to circularly polarized light over the entire reflection wavelength band, a retardation plate formed by laminating a plurality of birefringent material layers is used to reduce the extinction ratio over the entire reflection wavelength band. It may be improved. In this case as well, as in the case of using a single layer retardation plate, by using two retardation plates having opposite polarization conversion characteristics, the light is reconverted to the polarization state of the light before incidence. Can be transmitted.

  Since the reflective diffractive polarizer of the present invention acts on circularly polarized light, a quarter wave plate may be used in combination with linearly polarized incident light. A diffractive polarizer is preferable because the number of parts can be reduced and the size can be reduced. Further, it is easy to combine with other polarizers and devices using polarized light, which is preferable.

(Fourth embodiment)
FIG. 6 is a diagram showing a configuration of a projection display device using the reflection diffraction type polarizer according to the first embodiment of the present invention. In FIG. 6, a projection display device 100 includes a white light source 101 such as a metal halide lamp that emits visible light, and incident light of three color components R (red), G (green), and B (blue). The dichroic mirrors 131 and 132, which are color separation means for separating the light, the plurality of liquid crystal panels 141, 142, and 143 that modulate incident light according to the image to be displayed, and the light of each color separated by the dichroic mirrors 131 and 132, respectively. Reflective mirrors 131a, 133a, and 133b that lead to the corresponding liquid crystal panels 141, 142, and 143, and a reflective diffraction polarizer that serves as a first polarizing means disposed on the optical path from the light source 101 to each of the liquid crystal panels 141, 142, and 143 121, 122, 123 and an analyzer 15 serving as a second polarizing means disposed on the light emission side of each of the liquid crystal panels 141, 142, 143 , 152, 153, a dichroic prism 160 as light combining means for combining light transmitted through the analyzers 151, 152, 153, and a projection lens system 170 as projection means for enlarging and projecting the light combined by the dichroic prism 160 With. Here, the light emitted from the projection lens system 170 is projected onto the screen 180.

  In the projection display device 100, the reflective diffraction polarizer 121 is disposed between the dichroic mirror 131 and the reflective mirror 131 a, the reflective diffraction polarizer 122 is disposed between the dichroic mirror 132 and the liquid crystal panel 142, and the reflective diffraction polarizer 123 is disposed. They are respectively disposed between the reflection mirror 133a and the reflection mirror 133b. That is, the reflection diffraction polarizers 121, 122, and 123 are arranged between the dichroic mirrors 131 and 132 as color separation means and the liquid crystal panels 141, 142, and 143, respectively.

  Randomly polarized white visible light emitted from the light source 101 is transmitted (separated) by R (red) component light by the dichroic mirror 131, and R (red) component light is transmitted through the reflective diffraction polarizer 121. Then, the light is reflected by the reflection mirror 131a and enters the liquid crystal panel 141. In addition, the light having the R (red) component separated and reflected by the dichroic mirror 131 is separated by the G (green) component light reflected by the dichroic mirror 132, and the G (green) component light is reflected and diffracted polarized light. The light passes through the child 122 and enters the liquid crystal panel 142. Further, the light of the B (blue) component that is transmitted after the G (green) component is separated by the dichroic mirror 132 is reflected by the reflection mirror 133a, passes through the reflection diffraction type polarizer 123, and is reflected by the reflection mirror 133b. Incident on the liquid crystal panel 143.

  The light of each color component incident on the liquid crystal panels 141, 142, and 143 is modulated according to the image to be displayed, and light that is transmitted through the analyzers 151, 152, and 153 and linearly polarized in a specific direction is extracted. The lights that have passed through the analyzers 151, 152, and 153 are synthesized again by the dichroic prism 160, and then projected onto the screen 180 via the projection lens system 170 to display a color image.

The reflective diffraction polarizers 121, 122, and 123 have the same configuration as the reflective diffraction polarizer 50 described with reference to FIG. 3 in the third embodiment. Here, the reflection diffractive polarizers 121, 122, and 123 are optimally set so that the reflection wavelength bands substantially coincide with the wavelength bands for R (red), G (green), and B (blue), respectively. Has been. As a specific design example, Table 1 shows the conditions of the central wavelength λ _{0 of} the reflection wavelength band, the reflection wavelength band Δλ, and the periodic unevenness depth d of the cholesteric phase polymer liquid crystal film. FIGS. 7A and 7B show the reflection spectrum and the reflection zero-order diffraction efficiency of the cholesteric phase polymer liquid crystal film used for the reflection diffraction polarizers 121, 122, and 123, respectively.

  By using the respective reflective diffraction polarizers, the degree of polarization of linearly polarized light that is transmitted in any wavelength band of R, G, and B is increased, and in addition, unnecessary polarization components are reflected and diffracted and are not transmitted, resulting in a high extinction ratio. It is done.

  In this embodiment, the reflective diffractive polarizers in which the wavelength bands of R, G, and B substantially coincide with the reflected wavelength band are individually arranged, but the functions of the three reflective diffractive polarizers may be integrated. This is preferable in terms of simplification of adjustment, reduction in the number of parts, miniaturization, and the like. In order to obtain an integrated reflection / diffraction polarizer corresponding to all the wavelength bands of R, G, and B, the three polarizers used in this embodiment may be laminated, or R, G, and B A three-layer cholesteric polymer liquid crystal film corresponding to each wavelength band may be sandwiched between broadband wave plates corresponding to these wavelength bands. In this case, a retardation plate having a wide wavelength band constituted by laminating two or more layers of birefringent materials is preferably used, and the number of laminated layers and the number of transparent substrates are preferably reduced.

  By using a plurality of reflection diffraction polarizers having the same function, it is possible to further improve the contrast. Similarly, a reflection diffraction polarizer integrated in a stacked manner is preferable because the number of components is reduced. In addition, the reflection wavelength band described in the second embodiment and the wavelength band to be diffracted and reflected by using a reflection diffractive polarizer in which the periodic unevenness is wavelength-shifted can be widened, which is preferable.

(Fifth embodiment)
FIG. 8 shows a configuration of an optical head device 200 using the reflection diffraction polarizer according to the first embodiment of the present invention.

  The semiconductor laser 201 emits linearly polarized light (parallel to the paper surface) having a wavelength of about 660 nm for recording / reproducing DVD information. The light is diffracted into three tracking beams by the diffraction element 203, reflected by the polarization beam splitter 204 almost in the direction of the optical disk, and converted into parallel light by the collimator lens 205. The linearly polarized light is converted into circularly polarized light by the quarter-wave plate 206 and condensed by the objective lens 207 on the information recording layer of the DVD optical disk 208. The objective lens 207 is moved by an actuator (not shown) for focus servo and tracking servo. The light reflected by the reflecting surface of the optical disk and converted into circularly polarized light that is reverse to the light traveling toward the optical disk is transmitted through the objective lens 207 and the quarter-wave plate 206 again and is orthogonal to the incident light. It is converted into linearly polarized light having a polarization plane (perpendicular to the paper). The light condensed by the collimator lens 205 is substantially transmitted through the polarization beam splitter 204, is transmitted through the cylindrical lens 209 provided for focus servo by the astigmatism method, and is collected on the photodetector 210.

  In order to stably realize recording / reproducing of an optical disk such as a DVD by the optical head device 200, a monitor light detector uses a condenser lens 211 to detect weak light in which light from a semiconductor laser is slightly transmitted through the polarization beam splitter 204. The light emitted from the semiconductor laser is controlled by being focused on 212. A reflection diffraction polarizer 202, which will be described later, installed in this optical system transmits the reflection diffraction polarizer even if the polarization plane of the emitted light rotates from a predetermined direction due to individual differences of semiconductor lasers, mounting accuracy variations, and environmental temperature. By doing so, the light incident on the polarization beam splitter 204 becomes linearly polarized light in a predetermined direction. As a result, the ratio between the amount of light incident on the optical disc and the amount of light monitored by the monitor light detector matches the polarization separation ratio characteristic of the polarization beam splitter very stably. Therefore, the amount of light incident on the optical disk 208 can be controlled by controlling the amount of light emitted from the semiconductor laser by the weak amount of light from the monitor light detector 212. Light of an unnecessary component or light of an unnecessary frequency is diffracted by the reflection diffractive polarizer, and is reflected off the optical axis, so that the influence on the semiconductor laser 201 is small. Further, since there is no forward stray light component, stable optical head characteristics can be obtained.

As the reflection diffraction polarizer 202, one having the same configuration as that of the reflection diffraction polarizer 50 described with reference to FIG. 5 in the third embodiment is used. The surface of the cholesteric phase polymer liquid crystal film in which the central wavelength λ ₀ of the reflection wavelength band is about 660 nm and the reflection wavelength band width Δλ is about 100 nm has periodic irregularities with a depth d of about 98 nm, and the retardation is about A reflective diffractive polarizer that is sandwiched and laminated between two retardation plates of 165 nm is preferably used. Further, it is preferable to integrate the reflective diffraction polarizer 202 and the diffraction element 203 because the number of parts can be reduced. The diffraction element 203 is preferably formed integrally with the light exit surface of the reflective diffractive polarizer because generation of unnecessary stray light is suppressed. Lamination integration with the reflective diffractive polarizer is not limited to the above-mentioned diffraction element, and lamination integration with elements having various optical functions is possible within the range where the optical system is established, adjustment simplification, This is preferable from the viewpoint of reducing the number of parts and miniaturization.

  Since the reflective diffractive polarizer can be optimized for the wavelength of light used as described above, it is not limited to a DVD having a wavelength of about 660 nm shown in this embodiment. This is preferable because it can be applied to a CD having a wavelength of about 785 nm and a blue optical disc for recording and reproducing at a high density of about 405 nm. In addition, it is possible to selectively act as a polarizer on a semiconductor laser that emits light having a plurality of wavelengths, which is preferable because of a high degree of freedom in designing an optical system.

  Further, since stray light that becomes unnecessary light is reflected backward without being transmitted to the front of the reflective diffractive polarizer, it is possible to suppress the influence on the optical component in front of the reflective diffractive polarizer. Therefore, although the degree of freedom of the grating pitch for determining the diffraction direction is large, the grating pitch is preferably 10 μm or less, and more preferably 5 μm or less in order to reduce the influence of reflected light behind the reflective diffractive polarizer. The lattice pattern may be straight, curved, or concentric. The curved shape or the concentric shape is preferable because it is possible to avoid the incidence of reflected light on an optical component disposed at a specific position behind the reflective diffraction polarizer, and the degree of freedom in optical design is further improved.

  Hereinafter, the present invention will be described more specifically with reference to examples.

Example 1
In this example, a specific method of manufacturing the depolarizer according to the first embodiment will be described with reference to FIGS. 1 and 2. A polyimide film (not shown) formed on the transparent substrate 11 with a low reflection coating (not shown) is applied and baked, and the polyimide film surface is rubbed to form an alignment film. A cholesteric phase liquid crystal film made of a mixture of a liquid crystal having a polymerization site and a chiral material is applied onto the alignment film, and polymerized and polymerized by irradiating with an ultraviolet ray having a wavelength of 365 nm to have a thickness of about 5 μm. And The reflectance spectrum with respect to the wavelength of the circularly polarized light incident on the cholesteric phase polymer liquid crystal film 12 is the same as that shown in FIG. 2A, the central wavelength is about 455 nm, and the reflection wavelength bandwidth is about 65 nm.

A photoresist is applied to the upper surface of the cholesteric phase polymer liquid crystal layer 12, and a resist mask having a lattice pitch of 5 μm is formed using a photomask. By a dry etching process using O ₂ gas as a main component, periodic irregularities 13 having a lattice pitch of 5 μm and a depth of about 68 nm are formed on the surface of the cholesteric phase polymer liquid crystal film 12, and the isotropic state of the monomer state Fill with polymer to parallelize the surface. At this time, the isotropic polymer after polymerization is adjusted to have a refractive index of about 1.7 with respect to light having a wavelength of about 455 nm. Thereafter, it is bonded to a transparent substrate 15 having a low reflection coating (not shown), and is cured by being irradiated with ultraviolet rays having a wavelength of 365 nm. Finally, a dicing saw is used to obtain a reflective diffraction polarizer having an outer shape of about 10 mm × about 10 mm square.

  The light emitted from the light source is arranged so as to have an optical path in the order of the quarter-wave plate and the reflective diffractive polarizer. A linearly polarized light of Ar laser having a wavelength of 457 nm is perpendicularly incident on a quarter-wave plate surface having a retardation of about 114 nm to form circularly polarized light having an ellipticity of about 0.98, and the transparent substrate of the reflective diffraction polarizer 10 When the light is vertically incident on the 15th surface, the light is almost transmitted. On the other hand, when the oscillation direction of linearly polarized light is rotated by 90 ° with respect to the above, the light is substantially reflected when the reversely polarized circularly polarized light having the rotation direction is incident on the reflection diffraction polarizer. The ratio of these transmittances is about 100 or more, and it can be confirmed that a high extinction ratio can be obtained.

(Example 2)
In this example, a specific method for manufacturing the depolarizing element according to the second embodiment will be described with reference to FIGS. Cholesteric phase polymer liquid crystal films 32 and 36 are formed by polymerization / polymerization on the transparent substrate 31 and the transparent substrate 35 on which low reflection coating (not shown) is applied as in the first embodiment. The reflection spectrum of the cholesteric phase polymer liquid crystal film 36 with respect to the wavelength of the incident circularly polarized light is equal to the spectrum exhibiting high reflection characteristics in the first wavelength band indicated by the solid line in FIG. 4A, and the center wavelength is about 420 nm. The reflection wavelength bandwidth is about 60 nm. Further, the reflection spectrum of the cholesteric phase polymer liquid crystal film 32 with respect to the wavelength of the incident circularly polarized light is equal to the spectrum exhibiting high reflection characteristics in the second wavelength band indicated by the broken line in FIG. Is about 490 nm and the reflection wavelength bandwidth is about 70 nm.

  On the cholesteric phase polymer liquid crystal layers 32 and 36, as in the first embodiment, periodic irregularities 33 and 37 having a lattice pitch of 5 μm and a depth of about 61 nm and 72 nm, respectively, are formed. The surface is made parallel by filling with a conductive polymer. In the same manner as in Example 1, the refractive index for light having a wavelength of about 455 nm is adjusted to be about 1.7. Thereafter, these layers are laminated with a transparent substrate 39 having a low reflection coating (not shown), and are cured by irradiation with ultraviolet rays having a wavelength of 365 nm. Thereafter, a dicing saw is used to form a reflection diffraction polarizer having an outer shape of about 20 mm × about 20 mm square.

  The light emitted from the light source is arranged so as to have an optical path in the order of an absorbing polarizer described later, a broadband quarter-wave plate described later, and a reflective diffraction polarizer. An absorptive polarizer is an optical element that converts light from a white light source whose polarization direction is substantially random into linearly polarized light. The broadband quarter-wave plate is formed by laminating a retardation plate having a retardation of about 228 nm and a retardation plate having a retardation of about 114 nm, and the ellipticity is 0 in the wavelength range of linearly polarized light from 400 nm to 510 nm. .9 or more optical element. The linearly polarized light that passes through the absorption polarizer enters the broadband quarter-wave plate, is converted into circularly polarized light, and enters from the transparent substrate 39 side of the reflective diffractive polarizer. At this time, when the optical axis of the broadband quarter-wave plate is rotated by 90 ° so that clockwise or counterclockwise circularly polarized light is incident on the reflection rotating polarizer, the light transmittance ratio is 400 nm. It is about 50 or more in the wavelength range of ˜510 nm, and it can be confirmed that a high extinction ratio is obtained over a wide band.

(Example 3)
In this example, a specific method for manufacturing the depolarizing element according to the third embodiment will be described with reference to FIG. A first retardation plate 56 having a retardation of 1/4 wavelength produced by stretching a polycarbonate having a retardation of 114 nm at a wavelength of 455 nm with an adhesive not shown on the transparent substrates 58 and 59 having low reflection coating (not shown). The second retardation plate 57 is laminated, sandwiched between transparent substrates 51 and 54 having a low reflection coating (not shown), and laminated and adhered with an adhesive layer. The other production methods relating to the filling of the cholesteric phase polymer liquid crystal film and the isotropic material are the same as in Example 1.

  In the same manner as in Example 1, linearly polarized light of an Ar laser having a wavelength of 457 nm is incident from two directions that are orthogonal to each other and become circularly polarized light by the first quarter retardation plate. The ratio of the transmittance of the linearly polarized light, which is the direction of rotation for transmission, and the transmittance of the linearly polarized light, which is the direction of rotation, which is reflected and diffracted, is about 100 or more, and it can be confirmed that a high extinction ratio is obtained.

Example 4
In this example, a projection display device using the depolarizing element according to the fourth embodiment will be specifically described with reference to FIGS. The reflective diffractive polarizers 121, 122, and 123 used in this embodiment have the same configuration as the reflective diffractive polarizer of the third embodiment. The material of the cholesteric phase polymer liquid crystal film of the reflection diffractive polarizer to be arranged and the depth of the periodic unevenness, the reflection wavelength band 121 for red (R), 122 for green (G), 123 for blue ( B). This is equal to each characteristic shown in FIG.

  These reflection diffraction polarizers 121, 122, and 123 are arranged in the projection display device 100 described in the fourth embodiment without a heat dissipation substrate for the absorption polarizer. When an image is displayed using a white light source that emits light of random polarization, it can be confirmed that display characteristics at a practical level with sufficiently high contrast can be obtained. Although the internal temperature of the housing assembled as the projection display device is higher than the room temperature, no change in the characteristics of the reflection diffraction type polarizer due to the temperature rise is confirmed, and good image display can be continued. .

(Example 5)
In this example, an optical head device using the depolarizing element according to the fifth embodiment will be specifically described with reference to FIG. The reflective diffraction polarizer 202 used in this embodiment has the same configuration as that of the third embodiment. The surface of the cholesteric phase polymer liquid crystal film having a central wavelength λ ₀ of the reflection wavelength band of about 660 nm and a reflection wavelength band Δλ of about 100 nm has irregularities with a periodic lattice pitch of 3 μm and a depth d of 98 nm. The reflection diffraction type polarizer 202 is sandwiched and laminated between two retardation plates having a retardation of about 165 nm, and the outer shape is cut to a 2 mm × 2 mm square.

  The reflective diffractive polarizer 202 is arranged so that light is incident perpendicularly at a position 2 mm away from the semiconductor laser 201. The light that passes through the reflective diffractive polarizer 202 and the diffraction element 203 and enters the polarization beam splitter 204 rotates in the range of −15 ° to + 15 ° with respect to the direction of linearly polarized light emitted from the semiconductor laser. Even so, a constant linear polarization state is maintained. Therefore, the ratio of the light directed to the optical disk 208 by the polarization beam splitter 204 and the light incident on the monitor light detector 212 is stable without changing with respect to the rotation of the linearly polarized light from the semiconductor laser within a certain range. By feeding back and adjusting the injection current of the semiconductor laser so that the light amount of the monitor light detector becomes constant, the light amount on the optical disk 208 can be stably controlled.

  According to the present invention, the reflective diffractive polarizer has a function of transmitting incident light having a specific polarization state and wavelength band and reflecting and diffracting other light, and is mounted on a projection display device, an optical head device, or the like. be able to.

The schematic diagram which shows the structural example and effect of the reflection diffraction polarizer in the 1st embodiment of this invention. The figure which shows the optical characteristic of the reflection diffraction polarizer in the 1st embodiment of this invention. The schematic diagram which shows the structural example and effect of the reflection diffraction polarizer in the 2nd embodiment of this invention. The figure which shows the optical characteristic of the reflection diffraction polarizer in the 2nd embodiment of this invention. The schematic diagram which shows the structural example and effect of the reflection diffraction polarizer in the 3rd embodiment of this invention. The schematic diagram of the projection type display apparatus using the reflective diffraction polarizer in the 4th embodiment of this invention. The figure which shows the optical characteristic of the reflection diffraction polarizer in the 4th embodiment of this invention. The schematic diagram of the optical head apparatus which uses the reflective diffraction polarizer in the 5th embodiment of this invention.

Explanation of symbols

10, 30, 50, 121, 122, 123, 202: Reflective diffraction polarizer 11, 15, 31, 35, 39, 51, 55, 58, 59: Transparent substrate 12, 32, 36, 52: Cholesteric phase polymer Liquid crystal films 13, 33, 37, 53: Periodic irregularities 14, 34, 38, 54: Isotropic material 21: First circularly polarized light 22: Second circularly polarized light 41: Circularly polarized light 42 in the first reflection wavelength band : Circularly polarized light 56 in the second reflection wavelength band: first phase difference plate 57: second phase difference plate 61: first linearly polarized light 62: second linearly polarized light 100: projection display device 101: light sources 131 and 132: Dichroic mirrors 131a, 133a, 133b: mirrors 141, 142, 143: liquid crystal panels 151, 152, 153: analyzer 160: dichroic prism 170: projection lens system 180: screen 200: light 201: Semiconductor laser 203: Diffraction element 204: Polarizing beam splitter 205: Collimating lens 206: 1/4 phase plate 207: Objective lens 208: Optical disk 209: Cylindrical lens 210: Photo detector 211: Condensing lens 212 : Monitor light detector

Claims (9)

A reflective diffractive polarizer that reflects light in a rotational direction of either one of light in a predetermined wavelength range that is incident as clockwise or counterclockwise circularly polarized light,
The reflective diffractive polarizer has a birefringent film made of a cholesteric phase liquid crystal having refractive index anisotropy,
The thickness direction of the birefringent film and the helical axis of the liquid crystal molecules of the cholesteric phase liquid crystal are parallel and the helical pitch in the thickness direction of the liquid crystal molecules is uniform,
The birefringent film has a concave and convex diffraction grating structure of a plurality of grooves having substantially the same width and depth on one surface;
A reflective diffractive polarizer in which the grating pitch of adjacent grooves is a constant period.   The reflective diffractive polarizer according to claim 1, wherein the birefringent film is made of a cholesteric phase polymer liquid crystal.   The reflective diffractive polarizer according to claim 1 or 2, wherein the unevenness is filled and flattened with an isotropic material having a refractive index between the extraordinary refractive index and the ordinary refractive index of the birefringent film.   The reflective diffraction polarizer according to any one of claims 1 to 3, comprising two or more birefringent films.   The reflective diffractive polarizer according to claim 4, wherein the two or more birefringent films have different helical pitches.   The reflective diffraction element according to any one of claims 1 to 5, including a quarter-wave plate having a phase difference of (0.25 + m) λ with respect to the wavelength λ of incident light. Show).   The reflective diffractive polarizer according to claim 6, wherein the birefringent film is sandwiched between the two quarter-wave plates arranged such that the fast axis or the slow axis is orthogonal. A light source, a color separation unit that separates visible light from the light source into light of a plurality of colors, a plurality of liquid crystal panels that modulate light of the plurality of colors according to an image to be displayed, and the color separation unit A plurality of reflection mirrors for guiding the plurality of colors of light to the corresponding plurality of liquid crystal panels, and a plurality of first polarizations arranged on an optical path from the light source to the plurality of liquid crystal panels to change the polarization state of the light Means, a plurality of second polarizing means disposed on the light transmitting side of the plurality of liquid crystal panels to change the polarization state of the light, and a light combining means for combining the light transmitted through the plurality of second polarizing means A projection display device comprising projection means for enlarging and projecting the light synthesized by the light synthesis means,
The at least one polarizing means of the plurality of first polarizing means and the plurality of second polarizing means is constituted by the reflective diffractive polarizer according to any one of claims 1 to 7. A projection display device characterized by comprising:   A light source, an objective lens that condenses the light emitted from the light source on the optical recording medium, and the reflected light that is collected and reflected by the optical recording medium is deflected and separated into an optical path different from the optical path of the outgoing light. A polarization beam splitter; a monitor light detector that receives monitor light separated from the light emitted from the light source incident on the polarization beam splitter into a different optical path from the optical recording medium; and detects the reflected light that has been deflected and separated An optical head device comprising: a light detector, wherein the optical head device is in an optical path between the light source and the photodetector or in an optical path between the polarization beam splitter and the monitor photodetector. An optical head device comprising the reflective diffractive polarizer according to claim 7.

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