JP5424329B2 - Optical path switching element, optical path switching apparatus, optical head apparatus, and optical information recording / reproducing apparatus - Google Patents

Description

  The present invention relates to an optical head device or the like for performing recording or reproduction with respect to two types of optical recording media having different optical system conditions. In particular, the present invention is equipped with the optical head device for switching the optical path of incident light. The present invention relates to an optical path switching element, and an optical path switching apparatus, an optical head apparatus, and an optical information recording / reproducing apparatus equipped with the optical path switching element.

An optical path switching element for switching the optical path of incident light is used, for example, in an optical head device for performing recording and reproduction on two types of optical recording media having different optical system conditions for use.
In recent years, a standard of 25 [GB] optical recording medium called BD (Blu-ray Disc) standard and a standard of 15 [GB] optical recording medium called HD-DVD (High Density Digital Versatile Disc) standard have been established. Therefore, there is a demand for an optical head device for performing recording and reproduction on both the BD standard optical recording medium and the HD-DVD standard optical recording medium.

By the way, in the BD standard, the wavelength of the light source is about 400 [nm], the numerical aperture of the objective lens is 0.85, and the thickness of the protective layer of the optical recording medium is 0.1 [mm]. On the other hand, in the HD-DVD standard, the wavelength of the light source is about 400 [nm], the numerical aperture of the objective lens is 0.65, and the thickness of the protective layer of the optical recording medium is 0.6 [mm]. That is, the optical system conditions for use differ between the BD standard optical recording medium and the HD-DVD standard optical recording medium.
Several related examples are known as optical head devices for performing recording and reproduction on two types of optical recording media having different optical system conditions for use (Patent Document 1). , 2).

  The optical head device described in Patent Document 1 includes a semiconductor laser, a BD objective lens that collects light emitted from the semiconductor laser in a BD standard optical recording medium, and reflected light from the BD standard optical recording medium. It has a photodetector for receiving light, a beam splitter for separating the optical path of the reflected light from the optical path of the outgoing light, and an optical path switching element provided between the beam splitter and the BD objective lens.

  An optical head device described in Patent Document 2 includes a semiconductor laser, an HD-DVD objective lens for condensing emitted light from the semiconductor laser in an HD-DVD standard optical recording medium, and an HD-DVD standard. Photodetector for receiving reflected light from optical recording medium, beam splitter for separating optical path of reflected light from optical path of outgoing light, and optical path switching element provided between beam splitter and HD-DVD objective lens And.

  The optical path switching element reflects, for example, the light from the beam splitter and directs it to the BD objective lens and from the BD objective lens when recording or reproducing is performed on the BD standard optical recording medium. Is reflected and guided to the beam splitter. Also, when recording or reproducing on an HD-DVD standard optical recording medium, the light from the beam splitter is transmitted to the HD-DVD objective lens and from the HD-DVD objective lens. The light is transmitted and guided to the beam splitter.

  FIG. 13 shows an example of an optical path switching element 129 provided in the optical head device described in Patent Document 1. The optical path switching element 129 has a configuration in which a Bragg grating 131 is interposed between the substrate 130a and the substrate 130b. Here, electrodes (not shown) for applying an AC voltage to the Bragg grating 131 are provided on the surface of the substrate 130a on the Bragg grating 131 side and the surface of the substrate 130b on the Bragg grating 131 side. The Bragg grating 131 has a structure in which a liquid crystal layer and a polymer layer are periodically arranged.

  When no AC voltage is applied to the Bragg grating 131, the liquid crystal portion in the liquid crystal layer is oriented so that the refractive index of the liquid crystal layer and that of the polymer layer are different. Therefore, the incident light L incident from the left side of the figure is the Bragg grating 131. Reflected and reflected light H is directed upward in the figure. On the other hand, when an AC voltage having a predetermined effective value is applied to the Bragg grating 131, the liquid crystal in the liquid crystal layer is aligned so that the refractive indexes of the liquid crystal layer and the polymer layer are equal. L passes through the Bragg grating 131 and travels as transmitted light T toward the right side of the figure.

  FIG. 14 shows an example of the optical path switching element 132 provided in the optical head device described in Patent Document 2. The optical path switching element 132 has a configuration in which a cholesteric liquid crystal layer 134 is interposed between the substrate 133a and the substrate 133b. Here, an electrode (not shown) for applying an AC voltage to the cholesteric liquid crystal layer 134 is provided on the surface of the substrate 133a on the cholesteric liquid crystal layer 134 side and the surface of the substrate 133b on the cholesteric liquid crystal layer 134 side. .

  When no AC voltage is applied to the cholesteric liquid crystal layer 134, the liquid crystal contained in the cholesteric liquid crystal layer 134 is oriented in a clockwise or counterclockwise spiral, so that incident light L incident from the left side of the figure is incident on the cholesteric liquid crystal layer 134. A clockwise or counterclockwise circularly polarized component is reflected and reflected light H is directed upward in the figure. On the other hand, when an alternating voltage having a predetermined effective value is applied to the cholesteric liquid crystal layer 134, the liquid crystal included in the cholesteric liquid crystal layer 134 is aligned in the thickness direction, and therefore incident light L incident from the left side of the figure is incident on the cholesteric liquid crystal layer 134. Is transmitted to the right side of the figure as transmitted light T.

Separately from this, Patent Document 3 discloses a liquid crystal layer including liquid crystal driven by an electric signal, and a high refractive index layer and a low refractive index which are provided alternately above and below the liquid crystal layer and stacked alternately. There is disclosed a variable wavelength filter having first and second dielectric multilayer films composed of an index layer, and changing the wavelength of light to be transmitted according to an electric signal.
JP 2006-024351 A JP 2006-228369 A JP-T 6-500408

  The optical path switching element included in the optical head device described in Patent Document 1 includes a Bragg grating 131 in which a liquid crystal layer and a polymer layer are periodically arranged as shown in FIG. In this case, the thickness of each liquid crystal layer is as thin as several tens [nm], and since the liquid crystal contained in the liquid crystal layer is less likely to change the orientation direction, the liquid crystal layer and the polymer layer have the same refractive index. In order to achieve such orientation, a relatively high operating voltage of about 50 [V] to 100 [V] is required as the effective value of the AC voltage applied to the Bragg grating 131.

  That is, the optical path switching element 129 described in Patent Document 1 has a disadvantage that the operating voltage is high. The Bragg grating 131 needs to be produced by interference exposure, but the area that can be produced at a time by interference exposure is small. For this reason, the optical path switching element 129 using the Bragg grating 131 is not suitable for mass production, and the cost of the optical path switching element 129 is inevitably high.

  Further, in the optical path switching element 132 included in the optical head device described in Patent Document 2, when no AC voltage is applied to the cholesteric liquid crystal layer 134, the cholesteric liquid crystal layer 134 has a clockwise circularly polarized component of incident light. Only one of the components of the left-handed circularly polarized light is reflected. That is, the optical path switching element 132 described in Patent Document 2 has a property that the optical path switching function depends on the polarization state of incident light.

  On the other hand, if the optical path switching element that operates on the clockwise circular polarization component and the optical path switching element that operates on the counterclockwise circular polarization component are overlapped, the optical path switching function is changed to the polarization state of the incident light. Can be made independent of However, when the two optical path switching elements are overlapped, the absorption loss in the cholesteric liquid crystal layer 134 increases, so that the reflectance and transmittance of the completed optical path switching element 132 are reduced, and at the same time, the size of the optical path switching element 132 is increased. Furthermore, there is a disadvantage that the cost becomes high.

  Further, in the variable wavelength filter described in Patent Document 3 described above, since the thickness direction of the liquid crystal layer is parallel to the direction of incident light, light that does not pass through the variable wavelength filter is incident on the incident light by the variable wavelength filter. Reflected in the same direction as the direction. In order to use this variable wavelength filter as an optical path switching element, the thickness direction of the liquid crystal layer is tilted with respect to the direction of incident light, and light that does not pass through the variable wavelength filter is directed to a direction different from the direction of incident light by the variable wavelength filter Although it is necessary to reflect, Patent Document 3 does not disclose the necessity of such a technique. In addition, this Patent Document 3 describes a configuration for transmitting incident light L without depending on its polarization state, but a configuration for reflecting incident light L without depending on its polarization state. I don't know anything about.

  An object of the present invention is to perform optical path switching without depending on the polarization state of incident light, particularly for two types of optical recording media having different optical system conditions, thereby enabling smooth recording and reproduction. An object is to provide an element, an optical path switching device, an optical head device, and an optical information recording / reproducing device.

  In order to achieve the above object, an optical path switching element according to the present invention includes a liquid crystal layer including a liquid crystal driven by an electric signal and disposed so that a thickness direction is inclined with respect to a direction of incident light, and the liquid crystal layer A first dielectric multilayer film provided on one surface of the liquid crystal layer, and a second dielectric multilayer film provided on the other surface of the liquid crystal layer. The multilayer film has a multilayer structure in which high-refractive index layers and low-refractive index layers are sequentially stacked alternately, and the incident light differs from the direction of the incident light without depending on its polarization state. A first characteristic that reflects in a direction and a second characteristic that transmits the incident light without depending on its polarization state, and the first characteristic and the second characteristic are in accordance with the electrical signal. It is characterized by having a switching property.

  In order to achieve the above object, the optical path switching element according to the present invention corresponds to the first and second intermediate layers on the outside of the first and second dielectric multilayer films of the first invention. And the third and fourth layers forming a multilayer structure in which a high refractive index layer and a low refractive index layer are alternately laminated on the outside of the first and second intermediate layers, respectively. A dielectric multilayer film is provided correspondingly, and each of the first and second intermediate layers has a refractive index and a thickness that are the same as the liquid crystal layer when the alignment state of the liquid crystal is the first or second alignment state. It is characterized in that they are formed of equal members.

  In order to achieve the above object, an optical path switching device according to the present invention has the above-described optical path switching element, and switches the characteristics of the optical path switching element between the first characteristic and the second characteristic. And an optical path switching element driving unit that generates an electric signal and drives the liquid crystal by the generated electric signal.

  In order to achieve the above object, an optical head device according to the present invention is an optical head device including two systems of optical systems for dealing with a first optical recording medium and a second optical recording medium. A first objective lens that condenses the light emitted from the light source in the first optical recording medium, and a first objective lens that condenses the light emitted from the light source in the second optical recording medium. Two objective lenses, a photodetector for receiving the reflected light from the first or second optical recording medium via the first or second objective lens, and the reflected light from the optical path of the emitted light. A light separation means for separating the optical path, and equipped with one optical path switching element between the light separation means and the first and second objective lenses, and this optical path switching element is used as the optical path switching element described above. It is characterized by being configured.

  In order to achieve the above object, an optical information recording / reproducing apparatus according to the present invention comprises the above-described optical head device and the optical recording medium used depending on which of the first and second optical recording media is used. And an optical path switching element driving unit that generates an electric signal for switching the characteristic of the optical path switching element between the first characteristic and the second characteristic and drives the liquid crystal by the electric signal. To do.

  According to the present invention, the reflection characteristics and transmission characteristics of incident light can be switched between predetermined reflection characteristics and transmission characteristics without depending on the polarization state of the incident light corresponding to two types of optical recording media having different optical system conditions. An optical path switching element and an optical path switching device can be provided, and the optical head device and the optical information recording / reproducing device equipped with the optical path switching device have different optical system conditions without depending on the polarization state of incident light. It is possible to provide an excellent optical head device and optical information recording / reproducing apparatus capable of smoothly performing recording and reproduction corresponding to various types of optical recording media.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[First Embodiment]
A first embodiment of an optical path switching element according to the present invention will be described with reference to FIGS. In FIG. 1, an optical path switching element 1A includes a nematic liquid crystal layer 3 using nematic liquid crystal as a liquid crystal, first and second dielectric multilayer films 5a and 5b that hold the nematic liquid crystal layer 3 in layers, Substrate 2a, 2b laminated | stacked on the outer surface side of dielectric multilayer film 5A, 5b, respectively is provided.

  Here, in this embodiment, the optical path switching element body 1Aa is formed by the nematic liquid crystal layer 3 and the first and second dielectric multilayer films 5a and 5b that hold the nematic liquid crystal layer 3 in layers. Substrates 2a and 2b are provided on both outer sides of the optical path switching element body 1Aa, respectively, and an AC voltage for switching the characteristics is applied to the liquid crystal on the inner sides of the substrates 2a and 2b. Transparent thin film electrodes 4a and 4b are respectively provided.

  That is, the optical path switching element 1A includes a nematic liquid crystal layer 3 at the center and dielectric multilayer films 5a and 5b sandwiching the nematic liquid crystal layer 3 at the center, and outer surfaces of the dielectric multilayer films 5a and 5b. The substrates 2a and 2b are stacked on the sides, respectively, and the entire structure is integrally stacked with the substrates 2a and 2b sandwiched therebetween.

  Here, the nematic liquid crystal layer 3 is a liquid crystal layer containing liquid crystal driven by an electric signal, and the dielectric multilayer films (first and second dielectric multilayer films) 5a and 5b are respectively the nematic liquid crystal layers described above. A dielectric multilayer structure in which high refractive index layers 6 and low refractive index layers 7 are alternately laminated from the liquid crystal layer 3 side toward the outer surface is formed. Further, the thickness direction of the substrates 2a and 2b is set at an angle of θ = 45 ° with respect to the direction of the incident light L in use.

  On the other hand, the optical path switching element 1A has a first characteristic (reflection characteristic) that reflects light incident from the left side of FIG. 1 to the upper side of the figure without depending on the polarization state in accordance with an electrical signal, and the left side of the figure. The second characteristic (transmission characteristic) that transmits the light L incident from the right side to the right side of the figure without depending on the polarization state. The first and second characteristics are switched and used by an alternating voltage applied according to the use situation.

  FIG. 2 shows an example of a specific cross-sectional structure of the optical path switching element 1A. As shown in FIG. 2, the optical path switching element 1A includes the dielectric multilayer films 5a and 5b and the nematic liquid crystal layer 3 sandwiched between the dielectric multilayer films 5a and 5b as described above. As described above, each of the dielectric multilayer films 5a and 5b is configured by alternately laminating the high refractive index layers 6 and the low refractive index layers 7.

  In the first embodiment, the number of high refractive index layers 6 in each of the dielectric multilayer films 5a and 5b is six, and the number of low refractive index layers 7 is five. For example, titanium dioxide is used as the material of the high refractive index layer 6, and silicon dioxide is used as the material of the low refractive index layer 7. As described above, the transparent electrode 4a for applying an AC voltage to the nematic liquid crystal layer 3 is applied to the surface of the substrate 2a on the dielectric multilayer film 5a side and the surface of the substrate 2b on the dielectric multilayer film 5b side. Transparent electrodes 4b are respectively provided.

(Orientation direction of nematic liquid crystal)
FIG. 3 shows the alignment direction of the nematic liquid crystal that is the liquid crystal included in the nematic liquid crystal layer 3. The arrow in the figure represents the longitudinal direction of the nematic liquid crystal. The nematic liquid crystal has a uniaxial refractive index anisotropy in which the direction of the optical axis is the longitudinal direction, ne is the refractive index for a polarized component (abnormal light component) in a direction parallel to the longitudinal direction, and is perpendicular to the longitudinal direction. When the refractive index with respect to the direction polarization component (ordinary light component) is no, there is a relationship of ne> no, and ne is larger than no.

  When no AC voltage is applied to the nematic liquid crystal layer 3, the nematic liquid crystal has a first orientation in which the longitudinal direction is oriented in a random direction in a plane perpendicular to the thickness direction, as shown in FIG. It becomes a state. On the other hand, when an AC voltage having a predetermined effective value is applied to the nematic liquid crystal layer 3, the crystal structure of the nematic liquid crystal is aligned with the longitudinal direction of the crystal structure along the thickness direction as shown in FIG. The second orientation state is obtained. The thickness of the nematic liquid crystal layer 3 is about 1 [μm], and the effective value of the AC voltage applied to the nematic liquid crystal layer 3 in order to align the nematic liquid crystal so that the longitudinal direction is the thickness direction is 5 [V]. About 10 [V].

(Specific example of optical path switching element 1A and examination of transmittance and reflectance)
Here, when the wavelength of the incident light L incident on the optical path switching element 1A is λ and the incident angle is θ, the optical path switching element 1A is operated under the conditions of λ = 400 [nm] and θ = 45 °. A design example of the optical path switching element 1A will be described.
When the refractive indexes of the high refractive index layer 6 and the low refractive index layer 7 are nH and nL, respectively, and the refractive angles of light in the high refractive index layer 6 and the low refractive index layer 7 are θH and θL, respectively, θH and θL are respectively It is calculated as follows.
sin θH = sin θ / nH, sin θL = sin θ / nL

Furthermore, when the thicknesses of the high refractive index layer 6 and the low refractive index layer 7 are dH and dL, respectively, dH and dL are obtained as follows.
dH = λ / (4 × nH) × cos (θH)
dL = λ / (4 × nL) × cos (θL)
Here, for example, if nH = 2.35 and nL = 1.46,
dH = 44.6 [nm]
dL = 78.3 [nm].

Further, assuming that the refractive index of the nematic liquid crystal layer 3 when the nematic liquid crystal state is the first alignment state and the second alignment state are n1 and n2, respectively, n1 and n2 are obtained as follows.
n1 = [(2no ² + ne ² ) / 3] 1/2
It is calculated | required by n2 = no.

Here, for example, if ne = 1.73 and no = 1.53,
n1 = 1.60
n2 = 1.53.

  4A and 4B show the relationship between the wavelength of the incident light T to the optical path switching element 1A and the transmittance of the optical path switching element 1A when the thickness of the nematic liquid crystal layer 3 is 975.4 [nm]. An example of calculating the relationship is shown. 5A and 5B show the wavelength of the incident light T to the optical path switching element 1A and the transmittance of the optical path switching element 1A when the thickness of the nematic liquid crystal layer 3 is 1031.8 nm. An example of calculating the relationship is shown.

  FIG. 4A and FIG. 5A are calculation examples when no AC voltage is applied to the nematic liquid crystal layer 3. FIG. 4B and FIG. 5B are calculation examples when an AC voltage having a predetermined effective value is applied to the nematic liquid crystal layer 3. Further, solid lines and dotted lines in the figure represent calculation examples for the P-polarized component and the S-polarized component, respectively. For simplicity, light absorption in the optical path switching element 1A is not considered.

  Assuming that the nematic liquid crystal layer 3 is not present in the transmittance spectrum of the optical path switching element 1A, the wavelength of the P-polarized component is about 340 nm to about 480 due to the action of the dielectric multilayer films 5a and 5b. A wide reflection wavelength band in which the transmittance is approximately 0% is formed in the range of [nm] and the wavelength in the range of about 330 [nm] to about 500 [nm] for the S-polarized component. .

  On the other hand, when the nematic liquid crystal layer 3 is provided, the transmittance of the nematic liquid crystal layer 3 is almost 100 [%] within the reflection wavelength band for both the P-polarized component and the S-polarized component. Three narrow transmission wavelength bands are formed. These transmission wavelength bands will be referred to as a first transmission wavelength band, a second transmission wavelength band, and a third transmission wavelength band, respectively, in order of increasing center wavelength. The first to third transmission wavelength bands can be considered to be formed by a resonator using the nematic liquid crystal layer 3 as a medium and the dielectric multilayer films 5a and 5b as reflecting mirrors.

  Here, when the thickness or refractive index of the nematic liquid crystal layer 3 is changed, the length of the resonator is changed, so that the wavelength (center wavelength) at the center position of the first to third transmission wavelength bands is changed.

(When the thickness of the nematic liquid crystal layer 3 is 975.4 [nm])
Therefore, first, the case where the thickness of the nematic liquid crystal layer 3 is set to 975.4 [nm] will be exemplified. In this case, when no AC voltage is applied to the nematic liquid crystal layer 3, as shown in FIG. 4A, the center wavelength of the second transmission wavelength band for both the P-polarized component and the S-polarized component. Is 400 [nm]. For this reason, the incident light L incident on the optical path switching element 1a transmits almost 100% of both the P-polarized component and the S-polarized component.

  On the other hand, when an AC voltage having a predetermined effective value is applied to the nematic liquid crystal layer 3, as shown in FIG. 4B, the wavelength 400 [nm] is obtained for both the P-polarized component and the S-polarized component. It is located between the second transmission wavelength band and the third transmission wavelength band. For this reason, the light L incident on the optical path switching element 1A reflects almost 100% of both the P-polarized component and the S-polarized component.

  That is, when the nematic liquid crystal state in the nematic liquid crystal layer 3 is the first alignment state and the second alignment state, the characteristics of the optical path switching element 1A correspond to the second characteristics (transmission characteristics), respectively. ), The first characteristic (reflection characteristic).

(When the thickness of the nematic liquid crystal layer 3 is 1031.8 [nm])
Next, the case where the thickness of the nematic liquid crystal layer 3 described above is 1031.8 [nm] will be exemplified.

  When no AC voltage is applied to the nematic liquid crystal layer 3, as shown in FIG. 5A, the wavelength 400 [nm] is the first transmission wavelength band and the second transmission wavelength band for both the P-polarized component and the S-polarized component. Located in the middle of the two transmission wavelength bands. Therefore, almost 100% of the P-polarized component and the S-polarized component are reflected from the light incident on the optical path switching element 1A.

  On the other hand, when an AC voltage having a predetermined effective value is applied to the nematic liquid crystal layer 3, as shown in FIG. 5B, the second transmission wavelength band is applied to both the P-polarized component and the S-polarized component. The center wavelength of is 400 [nm]. For this reason, almost 100% of both the P-polarized component and the S-polarized component are transmitted through the light L incident on the optical path switching element 1A.

  That is, when the state of the nematic liquid crystal in the nematic liquid crystal layer 3 is the first alignment state, the characteristic of the optical path switching element 1A is a reflection characteristic (first characteristic), and the nematic liquid crystal 3 in the nematic liquid crystal layer 3 When the state is the second alignment state, it has been clarified that the characteristics of the optical path switching element 1A are transmission characteristics (second characteristics). Nematic liquid crystal 3

  In the first embodiment, the thickness of the liquid crystal layer 3 is not too thin, and the liquid crystal contained in the liquid crystal layer easily changes the orientation direction, so that the operating voltage of the optical path switching element 1A can be lowered. . Moreover, since the Bragg grating is not used, the cost of the optical path switching element 1A can be reduced. Furthermore, in the optical path switching element 1A of the first embodiment, since the cholesteric liquid crystal layer is not used as the liquid crystal layer 3, the optical path switching function of the optical path switching element 1A may not be dependent on the polarization state of incident light. it can. Further, as illustrated in the related art described above, since it is not necessary to overlap the two optical path switching elements 1A, the reflectance and transmittance of the optical path switching element 1A can be increased, and the size of the optical path switching element 1A can be reduced. Cost can be reduced.

[Second Embodiment]
Next, a second embodiment of the optical path switching element according to the present invention will be described with reference to FIGS. In FIG. 6, the optical path switching element 1B includes a nematic liquid crystal layer 3, dielectric multilayer films (first and second dielectric multilayer films) 5c and 5d that hold the nematic liquid crystal layer 3 in layers, and the dielectric layers. Polymer multilayers (first and second intermediate layers) 8a and 8b are provided on the outer surface sides of the body multilayer films 5c and 5d, respectively.

  Further, the optical path switching element 1B includes a third dielectric multilayer film 5e and a substrate 2a, which are sequentially laminated on the outer side of one of the polymer layers 8a and 8b (first intermediate layer) 8a. And a fourth dielectric multilayer film 5f and a substrate 2b, which are sequentially laminated outside the other polymer layer (second intermediate layer) 8b.

  Here, in the second embodiment, the nematic liquid crystal layer 3, the first and second dielectric multilayer films 5c and 5d that hold the nematic liquid crystal layer 3 in layers, and the dielectric multilayer films 5c and 5d. Polymer layers (first and second intermediate layers) 8a and 8b respectively laminated on the outer surface side of the first and second dielectrics equipped on the outer sides of the polymer layers 8a and 8b, respectively. An optical path switching element body 1Ba is formed by the multilayer films 5e and 5f. Similarly to the case of the first embodiment described above, substrates 2a and 2b are respectively disposed on both outer sides of the optical path switching element body 1Ba, and the liquid crystals are disposed on the inner sides of the substrates 2a and 2b. On the other hand, transparent thin-film electrodes 4a and 4b for applying the AC voltage for switching the characteristics are provided.

  In other words, the optical path switching element 1B includes the nematic liquid crystal layer 3 and the dielectric multilayer films 5c and 5d sandwiching the nematic liquid crystal layer 3 at the center, and one of the dielectric multilayer films 5c and 5d. The third dielectric multilayer film 5e and the substrate 2a are sequentially laminated outside the multilayer dielectric film 5c, and the fourth dielectric multilayer film 5f and the substrate 2b are laminated outside the other dielectric multilayer film 5d. Are sequentially stacked.

  Here, the nematic liquid crystal layer 3 is a liquid crystal layer containing liquid crystal driven by an electric signal, as in the case of the first embodiment described above, and also a dielectric multilayer film (first and second dielectrics). Each of the multilayer films 5a and 5b has a dielectric multilayer structure in which high refractive index layers 6 and low refractive index layers 7 are alternately stacked from the above-described nematic liquid crystal layer 3 side toward the outer surface.

  The thickness direction of the substrates 2a and 2b forms an angle of 45 ° with respect to the direction of the incident light L as in the case of the first embodiment described above. The optical path switching element 1B is incident on the first characteristic (reflection characteristic) for reflecting light incident from the left side of the figure to the upper side of the figure without depending on the polarization state, and from the left side of the figure in accordance with the electrical signal. It has a second characteristic (transmission characteristic) that transmits light to the right side of the figure without depending on its polarization state, and the characteristic is switched between them.

  FIG. 7 is a detailed sectional view of the optical path switching element 1B. Each of the dielectric multilayer films 5c to 5f has a configuration in which the high refractive index layers 6 and the low refractive index layers 7 are alternately stacked as described above. The number of high refractive index layers 6 in each of the dielectric multilayer films 5c and 5d is four, and the number of low refractive index layers 7 is three. The high refractive index layers in each of the dielectric multilayer films 5e and 5f. The number of layers of 6 is 2, and the number of low refractive index layers is 1.

  For example, titanium dioxide is used as the material of the high refractive index layer 6, and silicon dioxide is used as the material of the low refractive index layer 7. A transparent electrode 4a and a transparent electrode 4b for applying an AC voltage to the nematic liquid crystal layer 3 are formed on the surface of the substrate 2a on the dielectric multilayer film 5e side and on the surface of the substrate 2b on the dielectric multilayer film 5f side, respectively. Yes.

  The alignment direction of the nematic liquid crystal that is the liquid crystal included in the nematic liquid crystal layer 3 in the second embodiment is the same as that shown in FIG. 3 in the first embodiment described above.

(Specific example of optical path switching element 1B and examination of transmittance and reflectance)
Here, when the wavelength of light incident on the optical path switching element 1B is λ and the incident angle is θ, the optical path switching element for operating the optical path switching element 1B under the conditions of λ = 400 [nm] and θ = 45 °. A design example of 1B will be described.

When the refractive indexes of the high refractive index layer 6 and the low refractive index layer 7 are n _H and n _L , respectively, and the light refraction angles in the high refractive index layer 6 and the low refractive index layer 7 are θ _H and θ _L , respectively, θ _{H 1} and θ _L are obtained as follows.
sin θ _H = sin θ / n _H , sin θ _L = sin θ / n _L

Further, assuming that the thicknesses of the high refractive index layer 6 and the low refractive index layer 7 are d _H and d _L , respectively, d _H and d _L are as follows as in the case of the first embodiment described above. Desired.
d _H = λ / (4 × n _H ) × cos (θ _H )
d _L = λ / (4 × n _L ) × cos (θ _L )
Here, for example, if n _H = 2.35 and n _L = 1.46,
d _H = 44.6 [nm]
d _L = 78.3 [nm].

Further, assuming that the refractive index of the nematic liquid crystal layer 3 when the nematic liquid crystal state is the first alignment state and the second alignment state are n1 and n2, respectively, n1 and n2 are obtained as follows.
n1 = [(2no ² + ne ² ) / 3] 1/2
It is calculated | required by n2 = no.

Here, for example, if n _e = 1.73 and n _o = 1.53,
n ₁ = 1.60
n ₂ = 1.53.
FIG 8 (a) (b), a nematic liquid crystal layer 3 and the polymeric layer 8a, both the thickness of 8b and 975.4 nm, equal polymer layer 8a, the refractive index of 8b both the _{n 1} 1 The calculation example of the relationship between the wavelength of the light incident on the optical path switching element 1B and the transmittance of the optical path switching element 1B when.

9 (a) and 9 (b), the thickness of the nematic liquid crystal layer 3 and the polymer layers 8a and 8b are both 1031.8 nm, and the refractive indices of the polymer layers 8a and 8b are both n ₂ . A calculation example of the relationship between the wavelength of the light incident on the optical path switching element 1B and the transmittance of the optical path switching element 1B when equal 1.53 is shown.

  Here, FIGS. 8A and 9A are calculation examples when no AC voltage is applied to the nematic liquid crystal layer 3, and FIGS. 8B and 9B show the nematic liquid crystal layer 3. FIG. This is an example of calculation when an AC voltage having a predetermined effective value is applied to. In addition, the solid line and the dotted line in the figure represent calculation examples for the P-polarized component and the S-polarized component, respectively. For simplicity, light absorption in the optical path switching element 1B is not considered.

  If the nematic liquid crystal layer 3 and the polymer layers 8a and 8b are not present in the transmittance spectrum of the optical path switching element 1B, the wavelength of the P-polarized component is about 340 [nm] due to the action of the dielectric multilayer films 5c to 5f. In the range of about 480 [nm], for the S-polarized light component, the wavelength is in the range of about 330 [nm] to about 500 [nm]. It is formed. On the other hand, when the nematic liquid crystal layer 3 is present, three transmission wavelength bands are formed inside the reflection wavelength band for both the P-polarized component and the S-polarized component by the action of the nematic liquid crystal layer 3. Is done.

  These transmission wavelength bands will be referred to as first to third transmission wavelength bands in the order of shorter center wavelength. In addition, when there are polymer layers 8a and 8b, three transmission wavelength bands are formed inside the reflection wavelength band for both the P-polarized component and the S-polarized component by the action of the polymer layers 8a and 8b. Is done. These transmission wavelength bands will be referred to as fourth to sixth transmission wavelength bands in order of increasing center wavelength. It can be considered that the first to third transmission wavelength bands are formed by a resonator using the nematic liquid crystal layer 3 as a medium and the dielectric multilayer films 5c and 5d as reflecting mirrors.

  Here, when the thickness and refractive index of the nematic liquid crystal layer 3 are changed, the length of the resonator is changed, so that the center wavelengths of the first to third transmission wavelength bands are changed. In the fourth to sixth transmission wavelength bands, the resonator using the polymer layer 8a as a medium and the dielectric multilayer films 5e and 5c as reflecting mirrors and the polymer layer 8b as a medium and the dielectric multilayer films 5d and 5f are used. It can also be considered that this is formed by a resonator having a reflecting mirror.

(When the thickness of the nematic liquid crystal layer 3 is 975.4 [nm])
First, the case where the thickness of both the nematic liquid crystal layer 3 and the polymer layers 8a and 8b is 975.4 [nm] and the refractive index of each of the polymer layers 8a and 8b is 1.60 is exemplified.

  When no AC voltage is applied to the nematic liquid crystal layer 3, as shown in FIG. 8A, the first and fourth transmission wavelength bands, the second and fifth transmission wavelength bands, and the third and sixth transmission wavelengths. The bands have the same center wavelength. As a result, three slightly wider transmission wavelength bands are formed with a transmittance of approximately 100%. For both the P-polarized component and the S-polarized component, the center wavelength of the second (same as the fifth) transmission wavelength band is 400 [nm]. For this reason, almost 100% of both the P-polarized component and the S-polarized component are transmitted through the light incident on the optical path switching element 1B.

  On the other hand, when an AC voltage having a predetermined effective value is applied to the nematic liquid crystal layer 3, as shown in FIG. 8B, the first and fourth transmission wavelength bands, the second and fifth transmission wavelength bands, The center wavelengths of the third and sixth transmission wavelength bands are shifted. As a result, three narrow transmission wavelength bands with transmittance of approximately 100% are formed as the first to third transmission wavelength bands, and the transmittance is low as the fourth to sixth transmission wavelength bands. Three transmission wavelength bands having a slightly wider width are formed.

  For both the P-polarized component and the S-polarized component, the center wavelength of the fifth transmission wavelength band is 400 [nm], but the wavelength 400 [nm] is the second transmission wavelength band and the third transmission wavelength. Located in the middle of the belt. For this reason, the light incident on the optical path switching element 1B partially transmits both the P-polarized component and the S-polarized component, but is mostly reflected. The reflectivities for the P-polarized component and the S-polarized component are about 80% and 94%, respectively. That is, when the state of the nematic liquid crystal included in the nematic liquid crystal layer 3 is the first alignment state and the second alignment state, the characteristics of the optical path switching element 1B are the second characteristic (transmission characteristic) and the first characteristic, respectively. (Reflection characteristics).

(When the thickness of the nematic liquid crystal layer 3 is 1031.8 [nm])
Next, the case where the thickness of both the nematic liquid crystal layer 3 and the polymer layers 8a and 8b is 1031.8 [nm] and the refractive index of the polymer layers 8a and 8b is 1.53 is exemplified.

  When no AC voltage is applied to the nematic liquid crystal layer 3, as shown in FIG. 9A, the first and fourth transmission wavelength bands, the second and fifth transmission wavelength bands, and the third and sixth transmission wavelengths. Each band has a different center wavelength. As a result, three narrow transmission wavelength bands with transmittance of approximately 100% are formed as the first to third transmission wavelength bands, and the transmittance is low as the fourth to sixth transmission wavelength bands. Three transmission wavelength bands having a slightly wider width are formed.

  For both the P-polarized component and the S-polarized component, the center wavelength of the fifth transmission wavelength band is 400 [nm], but the wavelength 400 [nm] is the first transmission wavelength band and the second transmission wavelength. Located in the middle of the belt. For this reason, the light incident on the optical path switching element 1B partially transmits both the P-polarized component and the S-polarized component, but is mostly reflected. The reflectivities for the P-polarized component and S-polarized component are about 80% and 94%, respectively.

  On the other hand, when an AC voltage having a predetermined effective value is applied to the nematic liquid crystal layer 3, as shown in FIG. 9B, the first and fourth transmission wavelength bands, the second and fifth transmission wavelength bands, The third and sixth transmission wavelength bands have the same center wavelength. As a result, three slightly wider transmission wavelength bands are formed with a transmittance of approximately 100%. For both the P-polarized component and the S-polarized component, the center wavelength of the second (same as the fifth) transmission wavelength band is 400 [nm]. For this reason, the light incident on the optical path switching element 1B transmits almost 100% of both the P-polarized component and the S-polarized component. That is, when the state of the nematic liquid crystal included in the nematic liquid crystal layer 3 is the first alignment state and the second alignment state, the characteristics of the optical path switching element 1B are the first characteristic (reflection characteristic) and the second characteristic, respectively. (Transmission characteristics).

  The optical path switching element 1B is slightly lower in reflectance in the first characteristic (reflection characteristic) than in the case of the optical path switching element 1A in the first embodiment described above, but is transmitted in the second characteristic (transmission characteristic). Since the width of the transmission wavelength band where the rate is almost 100% is wide, there is an advantage that it is not easily influenced by the wavelength variation of the incident light. Other effects are the same as those in the first embodiment described above.

[Third Embodiment]
Next, a third embodiment will be described based on FIG.
The third embodiment shown in FIG. 10 shows a case where the optical path switching element 1A in the first embodiment described above is implemented as the main part of the optical path switching device.

  In FIG. 10, the optical path switching device 9 shown in the third embodiment includes an optical path switching means 9A having the optical path switching element 1A in the first embodiment as a main component, and the optical path switching means 9A. And an optical path switching element driving circuit 9B for energizing the operation of the switching element 1A.

  That is, the optical path switching device 9 in the third embodiment is obtained by adding the optical path switching element driving circuit 9B to the optical path switching element 1A disclosed in the first embodiment. The optical path switching element driving circuit 9B, which is this optical path switching element driving means, performs switching control in order to switch the characteristic of the optical path switching element 1A between the first characteristic (reflection characteristic) and the second characteristic (transmission characteristic). The nematic liquid crystal in the nematic liquid crystal layer 3 is driven by the electric signal.

  When the optical path switching element 1A has the transmittance spectrum shown in FIG. 4, in order to set the characteristic of the optical path switching element 1A to the first characteristic (reflection characteristic), the optical path switching element drive circuit 9 causes the nematic liquid crystal 3 to On the other hand, an AC voltage having a predetermined effective value is applied. At this time, the incident light L to the optical path switching element 1A is reflected by the optical path switching element 1A in a direction different from the direction of the incident light.

  On the other hand, in order to change the characteristic of the optical path switching element 1 </ b> A to the second characteristic (transmission characteristic), no AC voltage is applied to the nematic liquid crystal layer 3 by the optical path switching element driving circuit 9. At this time, the incident light L to the optical path switching element 1A passes through the optical path switching element 1A.

  On the other hand, when the optical path switching element 1A has the transmittance spectrum shown in FIG. 5, in order to set the characteristic of the optical path switching element 1A to the first characteristic (reflection characteristic), the nematic liquid crystal layer is formed by the optical path switching element driving circuit 9B. No AC voltage is applied to 3. At this time, the incident light L to the optical path switching element 1A is reflected in a direction different from the direction of the incident light L by the optical path switching element 1A.

  On the other hand, in order to change the characteristic of the optical path switching element 1 </ b> A to the second characteristic (transmission characteristic), an AC voltage having a predetermined effective value is applied to the nematic liquid crystal 3 by the optical path switching element driving circuit 9. At this time, the incident light to the optical path switching element 1A passes through the optical path switching element 1A.

  As described above, the optical path switching device 9 in the third embodiment is configured to drive the optical path switching element 1A in the first embodiment by the optical path switching element driving circuit 9B as described above. The thickness of the liquid crystal layer 3 is not too thin, and the liquid crystal included in the liquid crystal layer 3 easily changes its orientation direction, so that the operating voltage of the optical path switching element 1A can be lowered. Further, since the Bragg grating is not used, the cost of the optical path switching element 1A can be reduced. Further, since the cholesteric liquid crystal layer is not used as the liquid crystal layer 3, the optical path switching function of the optical path switching element 1A can be changed to the polarization of the incident light L. It can be made independent of the state.

Here, in the third embodiment, the case where the optical path switching element 1A in the first embodiment described above is equipped as the optical path switching element is illustrated, but the second embodiment described above is used instead of the optical path switching element 1A. You may equip the optical path switching element 1B in a form.
Even in this case, the reflection or transmission operation with respect to the incident light L can be effectively switched as in the case where the optical path switching element 1A is provided.

The optical path switching means 9A described above is between the first characteristic (reflection characteristic) and the second characteristic (transmission characteristic) included in the optical path switching element 1A (or 1B) disclosed in the above-described embodiment. An electrical signal for switching may be input from the outside and applied to the liquid crystal layer of the optical path switching element.
Even in this case, the reflection or transmission operation for the incident light L can be switched effectively.

[Fourth Embodiment]
Next, a fourth embodiment will be described with reference to FIG.
The fourth embodiment shown in FIG. 11 shows an example when the optical path switching element 1A in the first embodiment described above is implemented for the optical head device 10.

  The optical head device 10 shown in FIG. 11 is a BD (Blu-ray Disc) standard optical recording medium which is a first optical recording medium having different optical system conditions and a HD-DVD standard light which is a second optical recording medium. This is an optical head device that can perform recording and reproduction on both recording media, and uses the optical path switching element 1A disclosed in the first embodiment (FIG. 1). Here, the HD-DVD has characteristics as a high-definition version of DVD using a blue laser.

  The optical head device 10 shown in FIG. 11 which can handle both optical recording media collects a semiconductor laser 10A as a light source and light emitted from the semiconductor laser 10A in a disk 17a which is an optical recording medium of the BD standard. A BD objective lens 16a that is a first objective lens that emits light, and a first light that is emitted from the semiconductor laser 10A that is attached to the objective lens 16a and is condensed in a disk 17b that is an optical recording medium of the HD-DVD standard. 2 and an objective lens 16b for HD-DVD.

  In FIG. 11, for the sake of convenience of explanation, the BD standard disc 17a and the HD-DVD standard disc 17b are shown as the same disc. However, in actual use, they are detachably replaced and used. The

  The optical head device 10 further includes a photodetector 20 that receives the reflected light from the disk 17a (or 17b), and a polarization beam splitter 12 that is a light separating unit that separates the optical path of the reflected light from the optical path of the emitted light. And an optical path switching element 1A disposed at a common position between the polarizing beam splitter 12 and the objective lens 16a and between the polarizing beam splitter 12 and the objective lens 16b.

  As described above, the optical path switching element 1A reflects the light from the polarization beam splitter 12 without depending on the polarization state and guides it to the objective lens 16a according to the control electrical signal, and also from the objective lens 16a. A first characteristic (reflection characteristic) that reflects light without depending on its polarization state and guides the light to the polarization beam splitter 12, and transmits the light from the polarization beam splitter 12 without depending on its polarization state, and the objective lens A characteristic (property) that switches the characteristic between the second characteristic (transmission characteristic) that is guided to the polarization beam splitter 12 while being guided to the light beam 16b and transmitted to the polarization beam splitter 12 without depending on the polarization state. I have.

  When recording or reproduction is performed on the disc 17a, which is a BD standard optical recording medium, the characteristic of the optical path switching element 1A is the first characteristic (reflection characteristic). At this time, the emitted light from the semiconductor laser 10 is split by the diffractive optical element 11 into a main beam that is zero-order light and two sub-beams that are ± first-order diffracted light.

  Subsequently, the main beam and the two sub beams are incident on the polarization beam splitter 12 as P-polarized light, and approximately 100 [%] is transmitted. The collimator lens 13 converts the divergent light into parallel light, and the light is switched to the optical path switching element 1A. Nearly 100 [%] is incident as polarized light, then converted from linearly polarized light to circularly polarized light by the quarter wave plate 15a, converted from parallel light to convergent light by the objective lens 16a, and condensed in the disk 17a. Is done.

  The reflected light of the main beam and the reflected light of the two sub beams reflected by the BD standard disc 17a are converted from divergent light to parallel light by the objective lens 16a, and from the circularly polarized light to the forward path and the polarization direction by the quarter wavelength plate 15a. Is converted into orthogonal linearly polarized light, is incident on the optical path switching element 1A as S-polarized light and is reflected by almost 100%, is converted from parallel light into convergent light by the collimator lens 13, and is converted into S-polarized light to the polarizing beam splitter 12. The incident light is reflected by approximately 100%, is given astigmatism by the astigmatism lens 18, the degree of convergence is converted by the concave lens 19, and is received by the photodetector 20.

  On the other hand, when recording or reproducing is performed on the disc 17b which is an optical recording medium of the HD-DVD standard, the characteristic of the optical path switching element 1A is the second characteristic (transmission characteristic). At this time, the emitted light from the semiconductor laser 10A is split by the diffractive optical element 11 into a main beam that is 0th-order light and two sub-beams that are ± 1st-order diffracted light.

  The main beam and the two sub beams are incident on the polarization beam splitter 12 as P-polarized light and almost 100% are transmitted. The collimator lens 13 converts the divergent light into parallel light, and enters the optical path switching element 1A as P-polarized light. Then, almost 100% is transmitted, incident on the mirror 14 as P-polarized light, and almost 100% is reflected, converted from linearly polarized light to circularly polarized light by the quarter-wave plate 15b, and parallel by the objective lens 16b. The light is converted into convergent light and condensed in the disk 17b.

  The reflected light of the main beam and the reflected light of the two sub beams reflected by the disk 17b are converted from divergent light to parallel light by the objective lens 16b, and the forward path and the polarization direction are orthogonalized from the circularly polarized light by the quarter wavelength plate 15b. It is converted into linearly polarized light, is incident on the mirror 14 as S-polarized light, is reflected by approximately 100%, is incident on the optical path switching element 1A as S-polarized light, and is transmitted through substantially 100%, and is collimated by the collimator lens 13. Is converted into convergent light, is incident on the polarization beam splitter 12 as S-polarized light, is reflected by almost 100%, is provided with astigmatism by the astigmatism lens 18, and the degree of convergence is converted by the concave lens 19. Light is received by the photodetector 20.

  The photodetector 20 is provided in the middle of two focal lines (focal points) formed by the collimator lens 13, the astigmatism lens 18, and the concave lens 19, and has a four-divided light receiving unit corresponding to the reflected light of the main beam. And two two-divided light receiving portions corresponding to the reflected lights of the two sub beams. The four-divided light receiving portion of the photodetector 20 is divided into four by a dividing line corresponding to the radial direction of the disks 17a and 17b and a dividing line corresponding to the tangential direction, and the two divided light receiving portions are divided into the disc 17a. , 17b, each of which is divided into two by dividing lines corresponding to the radial direction.

  Based on the voltage signals output from the four-divided light receiving unit and the two two-divided light receiving units, a focus error signal, a track error signal, and a reproduction signal that is a mark / space signal recorded on the disks 17a and 17b are detected. Is done.

  The focus error signal is detected by a known astigmatism method, and the track error signal is recorded by a known phase difference method when the disk 17a or 17b is a reproduction-only disk, and the disk 17a or 17b is write-once or rewritable. Are detected by a known differential push-pull method. The reproduction signal is detected from the high frequency component of the voltage signal output from the quadrant light receiving unit.

  As described above, in the fourth embodiment, the optical path switching element 1A described above polarizes the light from the light separation means (polarization beam splitter 12) according to the energized electric signal. The first objective lens 16a is reflected without depending on the state and guided to the first objective lens 16a, and the light from the first objective lens 16a is reflected without depending on the polarization state and guided to the light separating means. The light from the light separating means is transmitted without depending on the polarization state and guided to the second objective lens 16b, and the light from the second objective lens 16b depends on the polarization state. The second characteristic is that the characteristic is switched between the second characteristic that is transmitted and guided to the light separating means.

For this reason, in the fourth embodiment equipped with such an optical path switching element 1A, recording and reproduction are performed corresponding to two types of optical recording media having different optical system conditions without depending on the polarization state of incident light. An excellent optical head device that can be driven smoothly can be obtained.
Furthermore, according to the fourth embodiment, the thickness of the liquid crystal layer 3 of the optical path switching element 1A used in the optical head device 10 is not too thin, and the alignment direction of the liquid crystal included in the liquid crystal layer 3 is easily changed. The operating voltage of the switching element 1A can be lowered. Moreover, since no Bragg grating is used for the optical path switching element 1A, the cost of the optical path switching element 1A can be reduced.

  In the optical head device 10, since the cholesteric liquid crystal layer is not used as the liquid crystal layer of the optical path switching element 1A, the optical path switching function of the optical path switching element 1A is not dependent on the polarization state of incident light as described above. In addition, since it is not necessary to overlap two optical path switching elements as the optical path switching element 1A, the reflectance and transmittance of the optical path switching element 1A can be increased, and the size of the optical path switching element 1A can be reduced and the cost can be reduced. Can be cheap.

Here, in the fourth embodiment, the case where the optical path switching element 1A in the first embodiment described above is equipped as the optical path switching element is illustrated, but the optical path in the second embodiment described above is used instead of the optical path switching element 1A. You may equip the switching element 1B.
Even in this case, as in the case where the optical path switching element 1A described above is equipped, the reflection or transmission operation with respect to the incident light L can be effectively switched, and the optical operation can be performed without depending on the polarization state of the incident light. It is possible to obtain an excellent optical head device capable of smoothly performing recording and reproducing operations corresponding to two types of optical recording media having different system conditions.

[Fifth Embodiment]
Next, a fifth embodiment will be described with reference to FIG.
The fifth embodiment shown in FIG. 12 shows an example in which the optical path switching element 1A in the first embodiment described above is implemented for the optical information recording / reproducing apparatus 30.

  In FIG. 12, an optical information recording / reproducing apparatus 30 according to the fifth embodiment includes a plurality of optical head apparatuses 10 according to the fourth embodiment described above, and a plurality of components that individually drive and control each component of the optical head apparatus 10. The driving circuit is configured to process information from the photodetector 20 provided in the optical head device 10 and output reproduction data.

  Here, as shown in FIG. 12, the optical information recording / reproducing apparatus 30 described above includes an optical path switching element in the optical head device 10 using the optical path switching element 1a according to the fourth embodiment of the optical path switching element of the present invention. A drive circuit 9A, a modulation circuit 31, a recording signal generation circuit 32, a semiconductor laser drive circuit 33, an amplification circuit 34, a reproduction signal processing circuit 35, a demodulation circuit 36, an error signal generation circuit 37, and an objective lens drive circuit 38 are added. is there. These circuits are controlled by a controller (not shown).

  The semiconductor laser 10A of the optical head device 10 described above is driven based on the recording data input from the outside. Specifically, the recording data input from the outside is modulated for recording by the modulation circuit 31, and based on this, a recording signal is generated by the recording signal generation circuit 32. Based on this recording signal, the semiconductor laser drive circuit 33 is generated. Is activated to output a recording laser beam corresponding to the recording data input from the outside. The information output from the optical detector 20 of the optical head device 10 described above is amplified by the amplification circuit 34, reproduced by the reproduction signal processing circuit 35, then demodulated by the demodulation circuit 36, and then reproduced data. As an external output.

  This will be described in further detail. The optical path switching element driving circuit 9B, which is the optical path switching element driving means, has an optical path switching element 1a depending on which of the BD standard optical recording medium and the HD-DVD standard optical recording medium is used for recording or reproduction. In order to switch the characteristic between the first characteristic (reflection characteristic) and the second characteristic (transmission characteristic), an electric signal for switching control is generated, and the nematic liquid crystal of the nematic liquid crystal layer 3 is generated by the electric signal. To drive.

  When recording data on the disk 17a or 17b, which is a recording medium, the modulation circuit 31 modulates data to be recorded on the disk 17a or 17b according to a modulation rule. The recording signal generation circuit 32 generates a recording signal for driving the semiconductor laser 10 </ b> A according to the recording strategy based on the signal modulated by the modulation circuit 31. The semiconductor laser driving circuit 33 drives the semiconductor laser 10A by supplying a current corresponding to the recording signal to the semiconductor laser 10A based on the recording signal generated by the recording signal generating circuit 32.

  On the other hand, when reproducing data from the disks 17a and 17b, the semiconductor laser drive circuit 33 supplies a constant current to the semiconductor laser 10A so that the power of the emitted light from the semiconductor laser 10A becomes constant, thereby providing a semiconductor. The laser 10A is driven.

  The amplifying circuit 34 amplifies the voltage signal output from the four-divided light receiving unit and the two two-divided light receiving units of the photodetector 20. When data is reproduced from the disks 17a and 17b, the reproduction signal processing circuit 35 generates a reproduction signal that is a mark / space signal recorded on the disks 17a and 17b based on the voltage signal amplified by the amplifier circuit 24, and a waveform thereof. Perform equalization and binarization.

  The demodulation circuit 36 demodulates the signal binarized by the reproduction signal processing circuit 35 according to a demodulation rule. The error signal generation circuit 37 generates a focus error signal and a track error signal for driving the objective lenses 16a and 16b based on the voltage signal amplified by the amplification circuit 34. The objective lens drive circuit 38 supplies a current corresponding to the focus error signal and the track error signal to an actuator (not shown) based on the focus error signal and the track error signal generated by the error signal generation circuit 37, and the objective lens 16a, 16b is driven.

  Further, in the fifth embodiment, a positioner control circuit and a spindle control circuit (not shown) are provided. The positioner control circuit moves the entire optical head device excluding the disks 17a and 17b in the radial direction of the disks 17a and 17b by a motor (not shown). The spindle control circuit has a function of controlling the rotation of the disks 17a and 17b by a motor (not shown).

  The optical path switching element drive circuit 9B generates an electrical signal for switching control based on the focus error signal input from the error signal generation circuit 37, and drives the nematic liquid crystal included in the nematic liquid crystal layer 3 by the electrical signal. To do. Specifically, the thickness of the protective layer of the disks 17a and 17b is determined from the distance between the zero cross point of the focus error signal from the surface of the disks 17a and 17b and the zero cross point of the focus error signal from the recording surface of the disks 17a and 17b. Check out. If the thickness of the protective layer is 0.1 [mm], it is determined that the disc 17a, which is an optical recording medium of the BD standard, is mounted, and the characteristic of the optical path switching element 1A is changed to the first characteristic (reflection). Characteristic).

  On the other hand, if the thickness of the protective layer is 0.6 [mm], it is determined that the disc 17b, which is an optical recording medium of the HD-DVD standard, is loaded, and the characteristic of the optical path switching element 1A is the second characteristic. Characteristics (transmission characteristics).

  When the optical path switching element 1A has the transmittance spectrum shown in FIGS. 4 (a) and 4 (b), the optical path switching element drive circuit 9 uses the nematic to make the characteristic of the optical path switching element 1A the first characteristic (reflection characteristic). An alternating voltage having a predetermined effective value is applied to the liquid crystal 3. At this time, the light from the polarization beam splitter 12 is reflected by the optical path switching element 1A and guided to the objective lens 16a, and the light from the objective lens 16a is reflected by the optical path switching element 1A and guided to the polarization beam splitter 12.

  On the other hand, in order to set the characteristic of the optical path switching element 1A to the second characteristic (transmission characteristic), an AC voltage is not applied to the nematic liquid crystal layer 3 by the optical path switching element driving circuit 9B. At this time, the light from the polarization beam splitter 12 passes through the optical path switching element 1A and is guided to the objective lens 16b, and the light from the objective lens 16b passes through the optical path switching element 1A and is guided to the polarization beam splitter 12.

  On the other hand, when the optical path switching element 1A has the transmittance spectrum shown in FIG. 5, in order to set the characteristic of the optical path switching element 1A to the first characteristic (reflection characteristic), the nematic liquid crystal layer is formed by the optical path switching element driving circuit 9B. No AC voltage is applied to 3. At this time, the light from the polarization beam splitter 12 is reflected by the optical path switching element 1A and guided to the objective lens 16a, and the light from the objective lens 16a is reflected by the optical path switching element 1A and guided to the polarization beam splitter 12.

  On the other hand, in order to set the characteristic of the optical path switching element 1A to the second characteristic, an AC voltage having a predetermined effective value is applied to the nematic liquid crystal 3 by the optical path switching element drive circuit 9B. At this time, the light from the polarization beam splitter 12 passes through the optical path switching element 1A and is guided to the objective lens 16b, and the light from the objective lens 16b passes through the optical path switching element 1A and is guided to the polarization beam splitter 12; The light is reflected by the polarization beam splitter 12 and sent to the photodetector 20.

  As described above, according to the fifth embodiment, recording and reproduction driving can be smoothly performed corresponding to two types of optical recording media having different optical system conditions without depending on the polarization state of incident light. In addition, the optical information recording / reproducing apparatus 30 can be obtained. Furthermore, according to the fifth embodiment, the thickness of the liquid crystal layer of the optical path switching element used in the optical information recording / reproducing device 30 is not too thin, and the alignment direction of the liquid crystal included in the liquid crystal layer is easily changed. The operating voltage of the switching element can be lowered. In addition, since no Bragg grating is used for the optical path switching element, the cost of the optical path switching element can be reduced.

  Further, since the optical information recording / reproducing apparatus 30 does not use a cholesteric liquid crystal layer as the liquid crystal layer of the optical path switching element, the optical path switching function of the optical path switching element is not dependent on the polarization state of incident light as described above. Further, since it is not necessary to overlap two optical path switching elements as the optical path switching element, the reflectance and transmittance of the optical path switching element can be increased, the size of the optical path switching element is reduced, and the cost is reduced. be able to.

  Here, in the fifth embodiment, the case where the optical path switching element 1A in the first embodiment described above is equipped as the optical path switching element is illustrated, but the optical path in the second embodiment described above is used instead of the optical path switching element 1A. You may equip the switching element 1B.

  Even in this case, as in the case where the optical path switching element 1A described above is equipped, the reflection or transmission operation with respect to the incident light L can be effectively switched, and the optical operation can be performed without depending on the polarization state of the incident light. It is possible to obtain an excellent optical information recording / reproducing apparatus 30 that can smoothly perform recording and reproducing operations corresponding to two types of optical recording media having different system conditions.

As described above, the optical path switching element, the optical path switching apparatus, the optical head apparatus, and the optical information recording / reproducing apparatus according to the present invention have been described in detail using the first to fifth embodiments.
The effects of each of these inventions are summarized as follows.
The first effect of the optical path switching element and the optical path switching device according to the present invention is that the optical path switching function of the optical path switching element does not depend on the polarization state of incident light. This is because a cholesteric liquid crystal layer is not used as the liquid crystal layer.

  The second effect of the optical path switching element and the optical path switching apparatus of the present invention is that the operating voltage of the optical path switching element is low. The reason is that the thickness of the liquid crystal layer is not too thin, and the alignment direction of the liquid crystal contained in the liquid crystal layer is likely to change. The third effect of the optical path switching element and the optical path switching apparatus of the present invention is that the reflectance and transmittance of the optical path switching element are high. This is because it is not necessary to overlap two optical path switching elements. The fourth effect of the optical path switching element and the optical path switching apparatus of the present invention is that the size of the optical path switching element is small and the cost is low. The reason is that there is no need to overlap two optical path switching elements and no Bragg grating is used.

  The first effect of the optical head device and the optical information recording / reproducing device of the present invention is that the optical path switching function of the optical path switching element used in the optical head device does not depend on the polarization state of incident light. This is because a cholesteric liquid crystal layer is not used as the liquid crystal layer of the optical path switching element. The second effect of the optical head device and the optical information recording / reproducing device of the present invention is that the operating voltage of the optical path switching element used in the optical head device is low. The reason is that the thickness of the liquid crystal layer of the optical path switching element is not too thin and the alignment direction of the liquid crystal contained in the liquid crystal layer is likely to change.

  The third effect of the optical head device and the optical information recording / reproducing device of the present invention is that the reflectance and transmittance of the optical path switching element used in the optical head device are high. This is because it is not necessary to overlap two optical path switching elements as the optical path switching element. The fourth effect of the optical head device and the optical information recording / reproducing device of the present invention is that the optical path switching element used in the optical head device is small in size and low in cost. The reason is that it is not necessary to overlap two optical path switching elements as the optical path switching element, and a Bragg grating is not used for the optical path switching element.

While the present invention has been described with reference to the embodiments (and examples), the present invention is not limited to the above embodiments (and examples). Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

  This application claims the priority on the basis of Japanese application Japanese Patent Application No. 2007-133520 for which it applied on May 18, 2007, and takes in those the indications of all here.

  It can be used by being incorporated in all optical head devices and optical information recording / reproducing devices that perform recording and reproduction corresponding to two types of optical recording media having different optical system conditions.

It is a block diagram which shows 1st Embodiment of the optical path switching element concerning this invention. It is a fragmentary sectional view which shows the detail of embodiment disclosed in FIG. FIG. 3 is an explanatory diagram showing an alignment direction of a nematic liquid crystal in the optical path switching element disclosed in FIG. 2. FIG. 4A is a diagram showing a calculation example of the relationship between the wavelength of incident light and the transmittance with respect to the optical path switching element disclosed in FIG. 1, and FIG. 4A shows an AC voltage applied to the nematic liquid crystal of the optical path switching element according to the first embodiment. FIG. 4B shows the case where an AC voltage is applied to the nematic liquid crystal of the optical path switching element. FIG. FIG. 5A is a diagram showing a calculation example of the relationship between the wavelength of incident light and the transmittance with respect to the optical path switching element in which the thickness of the optical path switching element disclosed in FIG. 1 is somewhat increased, and FIG. 5A is a nematic liquid crystal of the optical path switching element. Fig. 5B shows the case where an AC voltage is applied to the nematic liquid crystal of the optical path switching element. FIG. It is a block diagram which shows 2nd Embodiment of the optical path switching element concerning this invention. It is a fragmentary sectional view which shows the detail of 2nd Embodiment disclosed in FIG. FIG. 8A is a diagram illustrating a calculation example of the relationship between the wavelength of incident light and the transmittance with respect to the optical path switching element disclosed in FIG. 6, and FIG. 8A illustrates a case where an AC voltage is not applied to the optical path switching element in the second embodiment. FIG. 8B shows the case where an AC voltage is applied to the nematic liquid crystal of the optical path switching element. FIG. 9A is a diagram showing a calculation example of the relationship between the wavelength and the transmittance of incident light with respect to the optical path switching element in which the thickness of the optical path switching element disclosed in FIG. 6 is somewhat increased, and FIG. 9A is a nematic liquid crystal of the optical path switching element. FIG. 9B shows a case where an AC voltage is applied to the nematic liquid crystal of the optical path switching element. It is a block diagram which shows the optical path switching apparatus concerning 3rd Embodiment of this invention. It is a block diagram which shows the optical head apparatus concerning 4th Embodiment of this invention. It is a block diagram which shows the optical information recording / reproducing apparatus concerning 4th Embodiment of this invention. It is explanatory drawing which shows the other optical path switching element in related technology. It is explanatory drawing which shows the further another optical path switching element in related technology.

Explanation of symbols

1A, 1B Optical path switching element 1Ab, 1Ba Optical path switching element main body 2a, 2b Substrate 3 Nematic liquid crystal layer 4a, 4b Transparent electrode 5a-5f Dielectric multilayer 5a, 5c First dielectric multilayer 5b, 5d Second dielectric Body multilayer film 5e third dielectric multilayer film 5f fourth dielectric multilayer film 6 high refractive index layer 7 low refractive index layer 8a, 8b polymer layer 9 optical path switching device 9A optical path switching means 9B optical path switching element driving circuit 10 light Head device 10A Semiconductor laser 20 Photo detector 30 Optical information recording / reproducing device 31 Modulating circuit 32 Recording signal generating circuit 33 Semiconductor laser driving circuit 34 Amplifying circuit 35 Reproducing signal processing circuit 36 Demodulating circuit 37 Error signal generating circuit 38 Objective lens driving circuit

Claims (4)

A liquid crystal layer including a liquid crystal driven by an electric signal and disposed so that a thickness direction is inclined with respect to a direction of incident light; and a first dielectric multilayer film provided on one surface of the liquid crystal layer; And a second dielectric multilayer film provided on the other surface of the liquid crystal layer,
Each of the first and second dielectric multilayer films has a multilayer structure in which high-refractive index layers and low-refractive index layers are sequentially stacked alternately,
The multilayer structure of the multilayer film transmits the incident light without depending on the polarization state and the first characteristic that reflects the incident light in a direction different from the direction of the incident light without depending on the polarization state. A second characteristic, and a characteristic that the first characteristic and the second characteristic are switched according to the electrical signal ,
The liquid crystal is a nematic liquid crystal, and in accordance with the electric signal, a first alignment state aligned in a random direction within a plane perpendicular to the thickness direction and a second alignment aligned along the thickness direction. It has the property that the alignment state switches between the alignment state,
Further, outside the first and second dielectric multilayer films, the first and second intermediate layers are provided correspondingly, respectively.
Third and fourth dielectric multilayer films having a multilayer structure in which high-refractive index layers and low-refractive index layers are sequentially stacked alternately on the outside of the first and second intermediate layers, respectively. Provided for each,
Each of the first and second intermediate layers is formed of a member having the same refractive index and thickness as the liquid crystal layer when the alignment state of the liquid crystal is the first or second alignment state. Optical path switching element. An optical path switching element that generates an electrical signal for switching the characteristics of the optical path switching element between the first characteristic and the second characteristic and drives the liquid crystal by the generated electrical signal Driving means,
The optical path switching element includes a liquid crystal layer including a liquid crystal driven by an electric signal and disposed such that a thickness direction is inclined with respect to a direction of incident light, and a first surface provided on one surface of the liquid crystal layer A dielectric multilayer film, and a second dielectric multilayer film provided on the other surface of the liquid crystal layer,
Each of the first and second dielectric multilayer films has a multilayer structure in which high-refractive index layers and low-refractive index layers are sequentially stacked alternately,
The multilayer structure of the multilayer film transmits the incident light without depending on the polarization state and the first characteristic that reflects the incident light in a direction different from the direction of the incident light without depending on the polarization state. A second characteristic, and a characteristic that the first characteristic and the second characteristic are switched according to the electrical signal ,
The liquid crystal is a nematic liquid crystal, and in accordance with the electric signal, a first alignment state aligned in a random direction within a plane perpendicular to the thickness direction and a second alignment aligned along the thickness direction. It has the property that the alignment state switches between the alignment state,
Further, outside the first and second dielectric multilayer films, the first and second intermediate layers are provided correspondingly, respectively.
Third and fourth dielectric multilayer films having a multilayer structure in which high-refractive index layers and low-refractive index layers are sequentially stacked alternately on the outside of the first and second intermediate layers, respectively. Provided for each,
Each of the first and second intermediate layers is formed of a member having the same refractive index and thickness as the liquid crystal layer when the alignment state of the liquid crystal is the first or second alignment state. Optical path switching device. An optical head device including two optical systems for supporting a first optical recording medium and a second optical recording medium,
One light source, a first objective lens that condenses the light emitted from the light source in the first optical recording medium, and condenses the light emitted from the light source in the second optical recording medium A second objective lens; a photodetector that receives the reflected light from the first or second optical recording medium via the first or second objective lens; and the reflected light from the optical path of the emitted light. Light separating means for separating the optical path of
Equipped with one optical path switching element between the light separating means and the first and second objective lenses,
The optical path switching element includes a liquid crystal layer including a liquid crystal driven by an electric signal and disposed such that a thickness direction is inclined with respect to a direction of incident light, and a first surface provided on one surface of the liquid crystal layer A dielectric multilayer film, and a second dielectric multilayer film provided on the other surface of the liquid crystal layer,
Each of the first and second dielectric multilayer films has a multilayer structure in which high-refractive index layers and low-refractive index layers are sequentially stacked alternately,
The multilayer structure of the multilayer film transmits the incident light without depending on the polarization state and the first characteristic that reflects the incident light in a direction different from the direction of the incident light without depending on the polarization state. A second characteristic, and a characteristic that the first characteristic and the second characteristic are switched according to the electrical signal ,
The liquid crystal is a nematic liquid crystal, and in accordance with the electric signal, a first alignment state aligned in a random direction within a plane perpendicular to the thickness direction and a second alignment aligned along the thickness direction. It has the property that the alignment state switches between the alignment state,
Further, outside the first and second dielectric multilayer films, the first and second intermediate layers are provided correspondingly, respectively.
Third and fourth dielectric multilayer films having a multilayer structure in which high-refractive index layers and low-refractive index layers are sequentially stacked alternately on the outside of the first and second intermediate layers, respectively. Provided for each,
Each of the first and second intermediate layers is formed of a member having the same refractive index and thickness as the liquid crystal layer when the alignment state of the liquid crystal is the first or second alignment state. Optical head device. A two-system optical system for corresponding to the first optical recording medium and the second optical recording medium, one light source, and a first light collecting light emitted from the light source in the first optical recording medium. 1 objective lens, a second objective lens for condensing the light emitted from the light source in the second optical recording medium, and reflected light from the first or second optical recording medium for the first Or a photodetector that receives light through the second objective lens, and a light separation means that separates the optical path of the reflected light from the optical path of the emitted light,
An optical head device equipped with one optical path switching element between the light separating means and the first and second objective lenses;
An electric signal for switching the characteristic of the optical path switching element between the first characteristic and the second characteristic depending on whether the optical recording medium used is the first or second optical recording medium And an optical path switching element driving means for driving the liquid crystal by the electrical signal,
The optical path switching element includes a liquid crystal layer including a liquid crystal driven by an electric signal and disposed such that a thickness direction is inclined with respect to a direction of incident light, and a first surface provided on one surface of the liquid crystal layer A dielectric multilayer film, and a second dielectric multilayer film provided on the other surface of the liquid crystal layer,
Each of the first and second dielectric multilayer films has a multilayer structure in which high-refractive index layers and low-refractive index layers are sequentially stacked alternately,
The multilayer structure of the multilayer film transmits the incident light without depending on the polarization state and the first characteristic that reflects the incident light in a direction different from the direction of the incident light without depending on the polarization state. A second characteristic, and a characteristic that the first characteristic and the second characteristic are switched according to the electrical signal ,
The liquid crystal is a nematic liquid crystal, and in accordance with the electric signal, a first alignment state aligned in a random direction within a plane perpendicular to the thickness direction and a second alignment aligned along the thickness direction. It has the property that the alignment state switches between the alignment state,
Further, outside the first and second dielectric multilayer films, the first and second intermediate layers are provided correspondingly, respectively.
Third and fourth dielectric multilayer films having a multilayer structure in which high-refractive index layers and low-refractive index layers are sequentially stacked alternately on the outside of the first and second intermediate layers, respectively. Provided for each,
Each of the first and second intermediate layers is formed of a member having the same refractive index and thickness as the liquid crystal layer when the alignment state of the liquid crystal is the first or second alignment state. Optical information recording / reproducing apparatus.

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