JP2009186732A - Liquid crystal optical element, method for manufacturing the same and optical head device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal optical element having an inward-protruded shape and nearly free from generation of aberration, its manufacturing method and an optical head device with the liquid crystal optical element mounted thereon. <P>SOLUTION: The liquid crystal optical element is provided in which two transparent substrates opposed to each other are superposed via a square frame-shaped seal material to form a gap and an inward-protruded-shaped liquid crystal layer is disposed in an inside region of the frame-shaped seal material, wherein spacers regulating the gap are mixed in the square frame-shaped seal material and the width of the seal material of four corner parts of the square shape is set to be narrower than the width of the seal material of four sides. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention provides a liquid crystal optical element that is disposed on the optical axis of the laser beam of an optical head device and is used for aberration correction to compensate for coma, astigmatism, spherical aberration, and the like, and a method for manufacturing the same. The present invention relates to an optical head device.

  An optical head device is used to read or write information on an optical disk (recording medium). This optical head device guides laser light emitted from a semiconductor laser light source to a recording medium (DVD or the like) through a liquid crystal optical element, and receives an RF signal (reproduction signal) of the laser light reflected from the recording medium. It can be detected by the instrument. Then, recorded information is read from the RF signal.

  In addition, the liquid crystal optical element mounted on the optical head device has a function of correcting the wavefront aberration of the laser light that follows the above path, and this wavefront aberration (mainly using the Rf signal obtained from the light receiver). Coma and spherical aberration). Then, the transparent electrode formed on the liquid crystal optical element is controlled so as to cancel out the detected wavefront aberration, and the liquid crystal layer sandwiched between the transparent electrodes is locally phase-modulated, so that the wavefront aberration of the laser light is reduced. to correct.

  In order to reduce the size of the optical head device having such a function, the liquid crystal optical element constituting the device is reduced in size to, for example, a rectangular shape having a small size of about 5 mm × 5 mm, and in various environments. It must be possible to correct wavefront aberrations accurately.

  Then, the liquid crystal optical element suitable for such a use was disclosed (for example, refer patent document 1). Among the element forms described in Patent Document 1, a more preferable form is a liquid crystal optical element having a middle convex shape (a cell shape having a convex shape). This medium-convex liquid crystal optical element does not generate bubbles in the liquid crystal layer in the cell even when the external environment temperature changes from room temperature to low temperature, or even when an external impact is applied to the element. The optical head device equipped with can correct the wavefront aberration accurately.

  Here, the medium-convex liquid crystal optical element will be described. FIG. 6 is a plan view and a side view showing a configuration example of the liquid crystal optical element.

  As shown in FIG. 6, the liquid crystal optical element 220 is a square frame-shaped sealing material 205 formed between the outer edge of the transparent substrate 201 and the outer edge of the transparent substrate 202 with a constant width of about 300 μm, for example, and the liquid crystal layer 215. For example, with a gap width of 6 μm and sealed with a sealing material 214.

  Here, the frame-shaped sealing material 205 is formed by mixing spacers with a constant width in order to make the gap width constant. The transparent substrate 201 is about 5 mm × 5 mm.

JP 2002-182225 A (page 4-6, FIG. 1)

As described above, the medium-convex liquid crystal optical element 220 generates bubbles in the liquid crystal layer 215 in the cell even if the external environment temperature changes from room temperature to low temperature or an external impact is applied to the element. However, aberrations occur due to the middle convex shape, and an optical head device equipped with this may cause an error in reading information on the recording medium or a writing error. The reason will be described below.

  First, FIG. 7 shows a cross-sectional shape of the liquid crystal optical element 220 formed in a middle convex shape. 7A shows a plan view of the liquid crystal optical element 220 and a cross-sectional shape in the side direction (X1-X2 direction) of the element, and FIG. 7B shows a plan view of the element and a diagonal direction (Y1-Y2 direction) of the element. 7C is a diagram in which the cross-sectional shapes in the side direction in FIG. 7A and in the diagonal direction in FIG. 7B are compared.

  As shown in FIGS. 7A and 7B, the liquid crystal optical element 220 is defined by the thickness of the gap Db by the spacer mixed in the square frame-shaped sealing material 205, and further has a middle convex shape. In addition, the center convex shape dimension Da is raised at the center of the element.

  Here, in order to reduce the outer size of the liquid crystal optical element 220 (about 5 mm × 5 mm), the square frame-shaped sealing material 205 is close to the diameter R of the effective diameter of the laser beam used in the optical head device. In this case, the interval L1 between the square frame-shaped sealing materials 205 and the interval L2 between the square diagonal frame-shaped sealing materials have different sizes.

  Accordingly, as shown in FIG. 7C, in the vicinity of the outer region P having the effective diameter R, the cross-sectional shapes 201x and 202x of the X1-X2 cross section of the transparent substrate are the cross sections of the transparent substrate of the Y1-Y2 cross section. It can be seen that the shape is different from the shapes 201y and 202y, and in particular, in the outer region P, the curvature shape differs between the X1-X2 cross section and the Y1-Y2 cross section. As described above, when the liquid crystal optical element 220 in which the curvature shapes of the transparent substrates 201 and 202 are different in the X1-X2 cross section and the Y1-Y2 cross section is mounted on the optical head device, the laser light of the liquid crystal optical element 220 passes. It can be easily understood that aberrations are generated within the effective diameter 230, and information reading errors or writing errors may occur.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-described problems and provide a liquid crystal optical element with little aberration even if it has a middle convex shape, a method for manufacturing the same, and an optical head device equipped with the same.

  The liquid crystal optical element and the optical head device of the present invention basically adopt the following configuration.

  In the liquid crystal optical element of the present invention, two transparent substrates facing each other are overlapped via a square frame-shaped sealing material to form a gap, and an intermediate convex liquid crystal layer is formed in the inner region of the frame-shaped sealing material. In the liquid crystal optical element in which the spacers are arranged, the square frame-shaped sealing material is mixed with a spacer that defines the gap of the gap, and the sealing material width of the four corners of the square has four sides of the sealing material side. It is characterized by being set narrower than the width.

  In the liquid crystal optical element of the present invention, two transparent substrates facing each other are overlapped via a square frame-shaped sealing material to form a gap, and an intermediate convex liquid crystal layer is formed in the inner region of the frame-shaped sealing material. In the square frame-shaped sealing material, spacers that define gaps are mixed, and the thickness of the four corners of the square frame-shaped sealing material is the same as that of the four-side sealing material. It is characterized by being formed so as to be thinner than the thickness.

In the method for manufacturing a liquid crystal optical element of the present invention, two transparent substrates facing each other are overlapped via a square frame-shaped sealing material to form a gap, and an intermediate convex shape is formed in the inner region of the frame-shaped sealing material. In the manufacturing method in which the liquid crystal layer is arranged, the sealing material of four corners of the square is formed by the sealing material in which the spacer for defining the gap of the gap is mixed on the surface of one of the two transparent substrates. A seal forming step of forming a frame-shaped seal material having a width narrower than the width of the seal material of the four sides, and the other substrate out of the two transparent substrates are bonded to one substrate, And a substrate bonding step for pressing the inside of the substrate with a uniform pressure from both surfaces of the other substrate, and a sealing material curing step for curing the frame-shaped seal in a state where the substrate thickness in the substrate bonding step is maintained. It is characterized by having .

  In the method for manufacturing a liquid crystal optical element of the present invention, two transparent substrates facing each other are overlapped via a square frame-shaped sealing material to form a gap, and an intermediate convex shape is formed in the inner region of the frame-shaped sealing material. In the manufacturing method in which the liquid crystal layer is arranged, a square frame-shaped sealing material is formed on the surface of one of the two transparent substrates with a sealing material mixed with a spacer for defining a gap in the gap. After the seal forming step and the other of the two transparent substrates are bonded to one substrate, the substrate surface is pressed with a uniform pressure from both sides of the one and the other substrate, In a state where the thickness of the four corners in the frame-shaped sealing material is formed to be thinner than the thickness of the sealing material on the four sides, and the substrate thickness in the substrate bonding step is maintained, Sealing material curing agent that cures the frame seal When, is characterized in that it has a.

  The optical head device of the present invention includes an objective lens that condenses a light beam emitted from a laser light source onto a recording medium, and a light receiver that receives reflected light from the recording medium. The liquid crystal optical element is disposed in the optical path between the two.

  According to the present invention, it is possible to provide a liquid crystal optical element having a moderately convex shape with less aberration, and an optical head device equipped with the liquid crystal optical element.

(First embodiment)
First, a configuration example of the liquid crystal optical element of this example and a method for manufacturing the liquid crystal optical element will be described in detail. FIG. 1 is a plan view and a side view showing a configuration example of a liquid crystal optical element 220 in an optimum embodiment of the present embodiment.

  In the liquid crystal optical element 220 in this embodiment, as shown in FIG. 1, the transparent substrate 201 and the transparent substrate 202 are fixed by a frame-shaped sealing material 205 mixed with a spacer for defining a gap, and defined by a spacer on the inside. In the gap, the liquid crystal layer 215 is sandwiched and sealed with a sealing material 214 and is formed in a middle convex shape.

  The transparent substrate 201 is 5 mm × 5 mm, and the frame-shaped sealing material 205 is formed in a square shape. In FIG. 1, this square frame-shaped sealing material 205 has four sides and four corners 101, and these four corners 101 are formed by oblique straight lines. In addition, the sealing material widths of the four corner portions 101 are formed to be narrower than the four sealing material side widths.

  Here, a spacer mixed with the frame-shaped sealing material 205 to define the gap is 6 μm, the width of the sealing material on the four sides is 300 μm, and the width of the sealing material on the four corners is 100 μm. It was set up as follows.

  The liquid crystal optical element 220 of this embodiment configured in this way has a middle convex shape, and even if the frame-shaped sealing material 205 is provided close to the effective diameter of the laser beam to be used, in the inner area of the effective diameter. And having a desired curvature shape. The liquid crystal optical element 220 is disposed in an optical path between the optical beam emitted from the semiconductor laser light source and an objective lens that condenses the light beam onto the recording medium, and is used to correct wavefront aberration generated by the laser light. If this is the case, the occurrence of extra aberrations can be suppressed. A specific configuration example of this optical head device will be described later.

Next, a method for manufacturing the liquid crystal optical element of this example will be described with reference to FIG.
First, a pattern shape corresponding to target aberration correction such as astigmatism, spherical aberration, and coma is formed on one surface of the two transparent substrates 201 and 202.

  Next, at least one of the transparent substrate 201 and the transparent substrate 202 is formed by using the screen printing method, and has four corner portions 101 each having an injection port in a part of the ring shape and having a narrower sealing material width than the four sides. A square frame-shaped sealing material 205 having the above is printed. The square frame-shaped sealing material 205 is provided with a spacer that defines a gap.

Next, the two transparent substrates 201 and 202 are bonded together via a square frame-shaped sealing material 205, and a pressure of 0.4 to 1.2 kg / cm ² is applied, and a temperature of 120 to 160 ° C. is set to 1. The cells are integrally formed through a pressure firing process of pressure firing in a firing furnace for ˜2 hours. At this time, it is necessary to note that the frame-shaped sealing material 205 is cured while the transparent substrate 201 and the transparent substrate 202 are pressed on the entire surface with a uniform pressure.

  Thereafter, an excessive amount of liquid crystal is injected from the injection port of the frame-shaped sealing material 205, and the liquid crystal layer 215 is formed by sealing the injection port with the sealing material 214 while maintaining an excessively injected state of the liquid crystal. Thus, the target liquid crystal optical element 220 is completed.

  The liquid crystal optical element 220 of the present embodiment formed in this way has a small element outer size by changing the shape of the frame-shaped sealing material 205 in the conventional element manufacturing process, and the effective diameter of the laser beam is frame-shaped. Even when the sealing material 205 is in the vicinity, a liquid crystal optical element in which transmitted wavefront aberration is suppressed as much as possible can be obtained.

  Next, the reason why the above-described liquid crystal optical element 220 is an element having a small convex aberration while having a middle convex shape will be described with reference to FIG. 2A shows a plan view of the liquid crystal optical element 220 of this embodiment and a cross-sectional shape in the side direction (X1-X2 direction) of the element, and FIG. 2B shows a plan view of the element and diagonal lines of the element. The cross-sectional shape in the direction (Y1-Y2 direction) is shown, and FIG. 2C is a diagram comparing the cross-sectional shape in the side direction of FIG.

  Also in the embodiment shown in this figure, the square frame-shaped sealing material 205 is provided close to the effective diameter 230 of the laser beam by minimizing the external size of the element as described above. Shows the case.

  Here, as shown in FIG. 2A, the liquid crystal optical element 220 is defined by the thickness of the gap Db by the spacer mixed in the square frame-shaped sealing material 205, and further has a middle convex shape. The center convex shape has a shape that is raised by Da at the center of the element. At this time, the middle convex shape dimension Dx of the square diagonal cross section (Y1-Y2 cross section) is larger than the middle convex shape dimension Da of the square side cross section (X1-X2 cross section).

  On the other hand, as shown in FIG. 2B, if the sealing material widths of the four corner portions 101 of the square frame-shaped sealing material 205 are formed narrower than the sealing material widths of the four sides, the diagonal lines of the elements are formed. The gap is Dc when viewed in the directional cross section (Y1-Y2). At this time, the relationship of gap Db> gap Dc is established.

  The reason will be described in detail with reference to FIG. FIG. 3 is a conceptual diagram showing a distribution state of the spacers 206 mixed in the square frame-shaped sealing material 205.

As shown in FIG. 3, when comparing the area A1 at the corner 101 of the square frame-shaped sealing material 205 of the liquid crystal optical element 220 of this embodiment with the area A2 of the seal side having the same size as this area A1. It can be seen that the number of the spacers 206 is more dispersed in the area A2 than in the area A1 having the same size.

  This spacer distribution state (dispersed number) is a step of curing the frame-shaped sealing material 205 in a state where the entire surface is pressed with a uniform pressure in the pressure firing step shown in the description of the method of manufacturing the liquid crystal optical element 220. Affects the device gap.

  That is, at the time of pressure baking in the manufacturing process of the liquid crystal optical element 220, the four corners 101 having a narrow seal width of the frame-shaped sealing material 205 are crushed more than the four sides, and the spacer 206 is crushed. As shown in B), an element is formed in which the gap Dc in the diagonal cross section (Y1-Y2 cross section) is narrower than the gap Db in the cross section in the side direction (X1-X2 cross section). As a result, the center convex shape dimension Dx of the square diagonal cross section becomes larger than the center convex shape dimension of the square side cross section.

In summary, in the liquid crystal optical element 220 of the present embodiment, the corner portion 101 with a narrow seal width of the frame-shaped sealing material 205 is further crushed during pressure firing in the manufacturing process, and FIG.
The gap Dc in the Y1-Y2 cross section in FIG. 2 becomes narrower than the gap Db in the X1-X2 cross section in FIG.

  Then, the center convex shape dimension Dx of the square diagonal cross section is larger than the center convex shape dimension Da of the square side cross section, and as shown in FIG. In this area, the X-X2 cross section and the Y1-Y2 cross section can have the same curvature shape.

  In this way, the curvature shapes of the transparent substrates 201 and 202 are made equal in the X1-X2 cross section and the Y1-Y2 cross section within the effective diameter 230 through which the laser light of the liquid crystal optical element 220 of this embodiment passes. Can do.

  Then, the liquid crystal optical element in which the curvature shape of the transparent substrates 201 and 202 is equal in the cross section in the side direction (X1-X2 cross section in FIG. 2A) and the diagonal cross section (Y1-Y2 cross section in FIG. 2B). When 220 is mounted on an optical head device, the occurrence of aberration within the effective diameter 230 of the liquid crystal optical element 220 is suppressed as much as possible, and no information reading error or writing error occurs on the recording medium, so that information can be stably provided. Can read and write.

(Second Embodiment)
Next, another configuration example of the liquid crystal optical element 220 of the present invention will be described. FIG. 4 is a plan view and a side view showing a configuration example of the liquid crystal optical element 220 in the present embodiment.

  As shown in FIG. 4, also in the liquid crystal optical element 220 of the present embodiment, as in the first embodiment, the square frame-shaped sealing material 205 is mixed with a spacer that defines a gap, and has four sides and four sides. The four corner portions 101 are formed so that the width of the sealing material of the four corner portions 101 is narrower than the width of the four sealing material sides. The difference between the configuration of the first embodiment and the configuration of the present embodiment is that the seal material of the four corner portions 101 of the frame-shaped seal 205 is formed in a straight line in the first embodiment, but is formed in a curved line in the present embodiment. It is only a point that has been done. Since it is the same about other structures, the description about a common member is omitted.

  As described above, in the liquid crystal optical element 220 of this embodiment, as in the first embodiment, the spacer that defines the gap is mixed in the square frame-shaped sealing material 205, and the four sides and the four corner portions 101 are mixed. And the sealing material width of the four corners 101 is narrower than the four sealing material side widths. The curvature shape of a cross section and a diagonal direction cross section can be set equally.

  Further, if the liquid crystal optical element 220 having the same curvature shape of the transparent substrates 201 and 202 in the side cross section and the diagonal cross section is mounted on the optical head device, no aberration occurs within the effective diameter 230 of the liquid crystal optical element 220. Thus, no information reading error or writing error occurs on the recording medium, and information can be read and written stably.

(Third embodiment)
Next, the optical head device of the present invention on which the liquid crystal optical element 220 shown in the first and second embodiments is mounted will be described. FIG. 5 is a diagram illustrating a configuration example of the optical head device 100.

  As shown in FIG. 5, the optical head device 100 of the present embodiment includes a semiconductor laser light source 1, an objective lens 6, and a light receiver 14, and is in the optical path of a light beam emitted from the semiconductor laser light source 1. The liquid crystal optical element 220 is provided in front of the objective lens 6. The liquid crystal optical element 220 is formed in a middle convex shape by the manufacturing method shown in Example 1 in advance.

  In FIG. 5, the light beam emitted from the semiconductor laser light source 1 is converted into substantially parallel light having an effective diameter R by the collimator lens 2, and after passing through the polarization beam splitter 3, a liquid crystal optical element having a middle convex shape. Incident at 220. The light beam that has passed through the liquid crystal optical element 220 passes through the quarter-wave plate 5 and is focused on the recording medium 9 (DVD or the like) by the objective lens 6.

  The light beam reflected from the recording medium 9 passes through the objective lens 6, the quarter-wave plate 5 and the liquid crystal optical element 220 again, the optical path is changed by the polarization beam splitter 3, and passes through the condenser lens 13. It is condensed on the light receiver 14. When the light beam is reflected by the recording medium 9, the light beam is amplitude-modulated by the information recorded on the track surface of the recording medium 9 and is output as a light intensity signal by the light receiver 14. Recorded information is read from this light intensity signal (reproduced signal).

  The objective lens 6 is provided with a tracking actuator 7 and wiring 8 for driving the actuator. The objective lens 6 is placed in the direction of arrow A in the figure (radial direction of the circular recording medium 9). By moving, the light beam condensed by the objective lens 6 is configured to accurately follow the track of the recording medium 9.

  The liquid crystal optical element 220 shown here has a function of correcting wavefront aberration generated in the substrate of the recording medium 9. Further, the liquid crystal optical element control circuit 15 detects wavefront aberrations (mainly coma aberration and spherical aberration) generated in the substrate of the recording medium 9 by using the light intensity signal from the light receiver 14, and cancels the detected wavefront aberration. As described above, a voltage is applied to the transparent electrode pattern formed on the liquid crystal optical element 220 through the wiring 16, and the phase of the liquid crystal layer sandwiched between the transparent electrode patterns is locally modulated. Correct. By such control, the wavefront aberration is corrected so that the intensity of the light intensity signal becomes appropriate.

  Even if the liquid crystal optical element 220 of the present invention is formed in an intermediate convex shape, a spacer defining a gap is mixed in a square frame-shaped sealing material 205, and four sides and four corners 101 are formed. Since the sealing material widths of the four corner portions 101 are narrower than the four sealing material side widths, the curvature shape of the side cross section and the diagonal cross section can be set equal. When the liquid crystal optical element 220 having the same curvature shape of the transparent substrates 201 and 202 in the side cross section and the diagonal cross section is mounted on the optical head device 100, the effective diameter of the light beam of the liquid crystal optical element 220 through which the light beam passes can be obtained. No aberration occurs within the range of the diameter R, and no reading error or writing error of information on the recording medium 9 occurs, so that stable reading and writing of information can be performed.

It is the top view and side view which showed the structural example of the liquid crystal optical element of this invention. It is sectional drawing for demonstrating the effect | action of the liquid crystal optical element of this invention. It is a figure for demonstrating the effect | action of the liquid crystal optical element of this invention. It is the top view and side view which showed the structural example of the liquid crystal optical element of this invention. It is drawing for demonstrating the structure of the optical pick-up apparatus of this invention. It is drawing for demonstrating the structure of the conventional liquid crystal optical element. It is drawing for demonstrating the subject of the conventional liquid crystal optical element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor laser light source 2 Collimator lens 3 Deflection beam splitter 5 1/4 wavelength plate 6 Objective lens 7 Actuator 8 Wiring 9 Recording medium 13 Condensing lens 14 Light receiver 15 Liquid crystal optical element control circuit 16 Wiring 100 Optical head apparatus 101 Corner | section 201 Transparent substrate 201x, 201y, 202x, 202y Cross sectional shape of transparent substrate 202 Transparent substrate 205 Frame seal 206 Spacer 214 Sealing material 215 Liquid crystal layer 220 Liquid crystal optical element 230 Effective diameter

Claims (5)

In a liquid crystal optical element in which two transparent substrates facing each other are overlapped via a square frame-shaped sealing material to form a gap, and a medium-convex liquid crystal layer is arranged in an inner region of the frame-shaped sealing material,
The square frame-shaped sealing material is mixed with a spacer that defines the gap of the gap, and the width of the sealing material at the four corners of the square is set to be narrower than the width of the sealing material at the four sides. A liquid crystal optical element characterized by comprising: In a liquid crystal optical element in which two transparent substrates facing each other are overlapped via a square frame-shaped sealing material to form a gap, and a medium-convex liquid crystal layer is arranged in an inner region of the frame-shaped sealing material,
The square frame-shaped sealing material is mixed with a spacer that defines the gap of the gap,
The liquid crystal optical element, wherein the square frame-shaped sealing material is formed so that the thickness of the four corners is thinner than the thickness of the sealing material on the four sides. Production of a liquid crystal optical element in which two transparent substrates facing each other are overlapped with a square frame-shaped sealing material to form a gap, and a medium-convex liquid crystal layer is arranged in the inner region of the frame-shaped sealing material In the method
The sealing material width of the four corners of the square has four sides sealed by a sealing material in which a spacer for defining the gap of the gap is mixed on the surface of one of the two transparent substrates. A seal forming step of forming a frame-shaped seal material narrower than the material side width;
A substrate bonding step of pressing the inside of the substrate surface with a uniform pressure from both sides of the one and the other substrate after bonding the other substrate of the two transparent substrates to the one substrate,
A sealing material curing step of curing the frame-shaped seal in a state where the substrate thickness in the substrate bonding step is maintained. A method for producing a liquid crystal optical element, comprising: Production of a liquid crystal optical element in which two transparent substrates facing each other are overlapped with a square frame-shaped sealing material to form a gap, and a medium-convex liquid crystal layer is arranged in the inner region of the frame-shaped sealing material In the method
A seal forming step of forming a square frame-shaped sealing material with a sealing material mixed with a spacer for defining a gap in the gap on one of the two transparent substrates;
After the other substrate of the two transparent substrates is bonded to the one substrate, the inside of the substrate surface is pressed with a uniform pressure from both surfaces of the one and the other substrate, and the square frame A substrate laminating step for forming the thickness of the four corners of the sealing material to be thinner than the thickness of the sealing material on the four sides;
A sealing material curing step of curing the frame-shaped seal in a state where the substrate thickness in the substrate bonding step is maintained. A method for producing a liquid crystal optical element, comprising: An objective lens for condensing the light beam emitted from the laser light source onto the recording medium, and a light receiver for receiving the reflected light from the recording medium,
An optical head device, wherein the liquid crystal optical element according to claim 1 or 2 is disposed in an optical path between the laser light source and the objective lens.

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