JP2009217157A - Liquid crystal diffractive lens and optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal diffractive lens which has a high efficiency of using light, has a simple driving method and is compact even when providing a focal variable element by using a liquid crystal. <P>SOLUTION: The liquid crystal diffractive lens is configured as follow: closed circular zonal electrodes 404 are cyclically arranged so as to have the same number each set of phase cycles to be generated; connective electrodes 405 corresponding to each cycles are arranged in the order; lead lines 402 are disposed in a shape intersecting the circular zonal electrodes 404; and the circular zonal electrodes 404 are connected with the lead lines 402 via the connective electrodes 405 disposed on through-holes in a transparent insulating film 403. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a liquid crystal diffractive lens capable of electrically modulating a focal length and an optical pickup device including the same.

  For example, there is an optical pickup device that records laser information on an optical recording medium such as an optical disk or reproduces information from the optical recording medium by applying a laser beam emitted from a light source. When this optical pickup device records information on an optical disc with a different cover layer thickness from the optical disc surface to the recording layer or an optical disc having multiple recording layers, or reproduces the recorded information, When the distance to the recording layer is different, spherical aberration may occur, and the recording and reproducing characteristics may be deteriorated. As one method for correcting this spherical aberration, a variable focal length lens is provided between the objective lens and the light source, and the focal length imaged on the recording layer is varied by this variable focal length lens, thereby correcting the spherical aberration. There is a way.

  As a configuration applicable to this variable focus lens, a method of forming a Fresnel zone plate type electrode pattern using liquid crystal is known (for example, see Patent Document 1). Here, the configuration of this conventional variable focus lens will be described. FIG. 9 is a drawing showing the configuration of a conventional variable focus lens, where FIG. 9A is a plan view showing the shape of an electrode pattern formed on one glass substrate, and FIG. It is AA cross section of a top view.

  As shown in FIGS. 9 (a) and 9 (b), the variable focus lens described in Patent Document 1 includes an electrode pattern formed on a glass substrate 901 and another glass substrate on which a common electrode (not shown) is formed. The liquid crystal is sandwiched between and. The electrode pattern formed on the glass substrate 901 has a ring-shaped electrode 904 in a closed ring shape for the purpose of enhancing the imaging characteristics of light, and an electrode lead wire 902 connected to the ring-shaped electrode 906 is connected to the ring-shaped electrode 904. Are arranged in different planes.

  The electrode lead-out line 902 formed on the surface of the glass substrate 901 is covered with an insulating protective film 905, and the insulating protection is provided via the connection portion 903 filled in the through hole formed in the insulating protective film 905. A plurality of annular electrodes 904 disposed on the surface of the film 905 are connected. In this conventional variable focus lens, an electrode lead-out line 902 is connected to each of the annular electrodes 904 so that each of the annular electrodes 904 can be individually driven.

Japanese Patent Laid-Open No. 5-100201 (page 2-3, FIG. 1)

  However, when this variable focus lens is applied to the optical pickup device described above, there are many patterns of the extraction wiring 902 in the effective surface where the light is incident, and the pattern of the extraction wiring 902 diffracts the incident light. End up. When this light diffraction phenomenon occurs, the imaging characteristics on the optical disk deteriorate and there is a problem that the light utilization efficiency is lowered.

  The present invention solves these problems, and an object of the present invention is to provide a liquid crystal that simplifies the lead-out wiring, has high light utilization efficiency, and can be miniaturized while forming a ring-shaped pattern. A diffractive lens is being provided.

  In view of the above points, the liquid crystal diffractive lens of the present invention includes a liquid crystal sandwiched between a first transparent substrate and a second transparent substrate, a common electrode formed on the liquid crystal side of the first transparent substrate, A lead wiring formed on the second transparent substrate; an insulating film provided so as to cover the lead wiring; a plurality of ring-shaped electrodes formed in a ring shape on the liquid crystal side of the insulating film; and a plurality of rings A connection electrode is provided for connecting the strip electrode and the lead-out wiring through the insulating film. Further, when the plurality of ring-shaped electrodes are divided into a plurality of sets having the same number, and when the first and second ring-shaped electrodes are formed from the inside of the ring in each set, the first ring-shaped electrodes, Connect the first ring-shaped electrodes in the other group to a common lead-out wiring, and connect the second ring-shaped electrode and the second ring-shaped electrodes in the other set to another common lead-out wiring. With this relationship, each ring-shaped electrode and each lead-out wiring are connected by connection wiring.

  In this way, by connecting the ring-shaped electrode to a common lead-out line, it is possible to simplify the number of lead-out lines and suppress the influence of light diffraction by the lead-out lines as much as possible.

  The relationship between the connection between the first annular electrode and the common lead wire and the connection between the second annular electrode and the other common lead wire is applied to the aspheric lens area in the lens region. It is good also as composition which has.

  With this configuration, even when the phase distribution is inverted in the radial direction of the liquid crystal diffractive lens, it is possible to simplify the number of lead wires and suppress the influence of light diffraction by the lead wires as much as possible.

  In the optical pickup device of the present invention, the liquid crystal diffraction lens described above is arranged in the optical path between the laser light source and the objective lens, and the liquid crystal diffraction lens is controlled to be emitted from the laser light source and collected on the optical disk. It is configured so that the focus of the laser beam to be emitted can be adjusted.

  With this configuration, it is possible to realize an optical pickup device using a liquid crystal diffractive lens that can simplify the number of lead wires and suppress the influence of light diffraction by the lead wires as much as possible.

  The present invention is a focus variable element that can move the position of a focus by applying a voltage, and has a structure of a diffractive lens having a lens action by a phase periodic structure, and a plurality of closed annular rings that are to be set to the same phase. By connecting the strip electrode to a common lead wire, the number of lead wires can be simplified, the influence of light diffraction by the lead wire is minimized, and as a result, an element with excellent imaging performance and high light utilization efficiency. An optical pickup device using this element can be provided.

(First embodiment)
[Description of optical pickup device: FIG. 1]
First, the configuration of the optical pickup device of the present invention will be described. FIG. 1 is a diagram showing a configuration of an optical pickup device according to the first embodiment of the present invention.

In the optical pickup device 101 shown in FIG. 1, the light beam emitted from the semiconductor laser 102 passes through or reflects the light beam by the polarization beam splitter 103 according to the polarization direction, and passes through the deflection beam splitter 103. The beam is collimated by the collimating lens 104. The light beam that has become the parallel light is changed in focus position by the liquid crystal diffraction lens 105 under the control of the liquid crystal driving device 106, and then linearly polarized light is converted into circularly polarized light by the λ / 4 plate 107, and the objective lens 109. Thus, the light is condensed on the optical disk 108. The light beam reflected by the optical disk 108 is reflected by the polarization beam splitter 103 and condensed on the photodetector 110.

  In this optical pickup device 101, when the light beam is reflected from the optical disk 108, the amplitude is modulated by information (pits) recorded on the track surface on the optical disk 108. The photodetector 110 outputs the received light beam as a light intensity signal, and the recorded information is read from the light intensity signal (RF signal).

  When writing to the optical disk 108, the intensity of the light beam emitted from the semiconductor laser 102 is modulated in accordance with the data signal for writing, and the optical disk 108 is irradiated with the modulated light beam. . On the track surface of the optical disc 108 on which data is written, data is written by changing the refractive index and color of the thin film sandwiched between the optical discs 108 or causing pits in accordance with the intensity of the light beam. .

[Description of operation of optical pickup device: FIGS. 2 to 3]
Next, two types of application examples in the optical pickup device 101 will be described. FIG. 2 and FIG. 3 are conceptual diagrams showing the action of focus movement by the liquid crystal diffraction lens according to the first embodiment of the present invention.

  As shown in FIG. 2, when there are two information recording layers of the optical disc 108, the voltage application to the liquid crystal diffractive lens 105 is controlled to change the focal position of the optical disc 108, so that FIG. The present invention can be applied to an optical pickup apparatus that focuses the light beam on the first information recording layer or switches the focal position to the second information recording layer shown in FIG. .

  In addition, as shown in FIG. 3, when a light beam having the same wavelength is condensed on the optical disk 108 and information recorded on the optical disk 108 having a different cover layer thickness is required to be read or written. Similarly to the above, the present invention can be applied to an optical pickup device that reads information recorded on an optical disc 108 of a different standard by controlling the voltage application to the liquid crystal diffraction lens 105 to change the focal position.

  According to the configuration of the present invention, the liquid crystal diffractive lens 105 itself can move the focal point without a mechanically moving portion, so that a small optical pickup 101 is realized.

[Description of Configuration of Liquid Crystal Diffraction Lens: FIG. 4]
Next, the configuration of the liquid crystal diffraction lens of the present invention will be described. FIG. 4 is a diagram conceptually illustrating a configuration example of the liquid crystal diffraction lens according to the first embodiment of the present invention.

As shown in FIGS. 4A and 4B, the liquid crystal diffractive lens 105 is oriented so as to cover the surface of the electrode pattern formed of the lead-out wiring 402, the connection electrode 405, and the annular electrode 404 formed on the glass substrate 401. The film 406 and the common electrode 409 and the alignment film 408 formed on the glass substrate 410 are opposed to each other with a predetermined gap, and a liquid crystal 407 is arranged inside a seal 412 surrounding the outer periphery of the gap. The The electrode pattern formed on the glass substrate 401, which is a transparent substrate, includes a lead wire 402 made of a transparent conductive film, and a ring-shaped electrode 404 connected to the lead wire 402 via a connection electrode 405. Note that power can be supplied to the lead-out wiring 402 from the outside, and a power supply signal can be supplied between the ring-shaped electrode 404 and the common electrode 409 to supply voltage to the liquid crystal 407. In FIG. 4 (a), the ring-shaped electrodes 404 are composed of three groups, and each group includes a plurality of ring-shaped electrodes (five in this figure, five as shown in FIG. 4 (b)). The ring-shaped electrode) is disposed. Note that the lead-out wiring 402, the connection electrode 405, and the annular electrode 404 formed on the glass substrate 401 side.
Thus, the lens pattern forming layer 411 is formed.

  The lead wiring 402 is formed on the surface of the glass substrate 401, and a transparent insulating film 403 is formed over the whole surface of the substrate so as to cover the lead wiring 402. Further, a ring-shaped electrode 404 made of a transparent conductive film, which is a closed ring for controlling the phase of the liquid crystal 407 to form a diffraction lens, is formed on the upper layer, and the through hole provided in the transparent insulating film 403 is filled. The connection electrode 405 is electrically connected to the lead-out wiring 402 formed in a different layer from the ring-shaped electrode 404. Note that specific pattern forms of the lead wiring 402, the ring-shaped electrode 404, and the connection electrode 305 will be described in detail later.

  Note that the common electrode 409 formed on the other glass substrate 410 is a solid pattern.

[Description of Action of Light Beam in Optical Pickup Device: FIGS. 5-8]
Next, the action of light emitted from the laser light source in the optical pickup device will be described. FIG. 5 is a diagram showing a diffraction phenomenon of a light beam in the optical pickup device.

  In this optical pickup device, it is necessary to consider the problem that diffracted light caused by the lead-out wiring 402 is generated in the liquid crystal diffractive lens 105 shown in FIG. 4 to deteriorate the characteristics of the optical pickup. For example, as shown in FIG. 5, in the optical pickup device 101, when diffracted light is generated at the position of the liquid crystal diffraction lens 105, the signal light of the dotted light beam shown in FIG. is there. However, when the light beam passing through the lead-out wiring 402 in the liquid crystal diffraction lens 105 is diffracted, it becomes a path indicated by a solid line, which becomes stray light on the photodetector 110 and is detected as a noise component. In this figure, the diffraction phenomenon of the return light reflected from the optical disk 108, which is strongly influenced by the photodetector 110, is shown.

  In order to prevent such a loss of extra diffracted light of the incident light beam, the material constituting the transparent insulating film 403, the lead-out wiring 402, the connection electrode 405, and the annular electrode 404 shown in FIG. It is desirable to make the refractive indexes of the transparent conductive films constituting the electrode pattern to be equal to each other, and to form the lens pattern forming layer 411 with a uniform thickness. Therefore, it is important to select the material of each member so that the transparent insulating film 403 and the transparent conductive film of the electrode pattern have a refractive index as close as possible. For example, ITO, tin oxide, or zinc oxide is used as a material for the transparent conductive film, and cerium oxide, silicon oxide, or zirconium oxide is used for the transparent insulating film 403. Here, the reason why the refractive indexes of the transparent insulating film 403 and the electrode pattern are the same is to prevent extra diffraction from occurring in the region where the electrode pattern is formed and the region where the electrode pattern is not formed. .

[Description of Electrode Pattern of Liquid Crystal Diffraction Lens: FIG. 6]
Next, a specific form of the electrode pattern applied to the liquid crystal diffraction lens of the present invention will be described. FIG. 6 is a diagram conceptually showing the shape of the electrode pattern of the liquid crystal diffraction lens 105 of the present invention. (A) shows the structure of the electrode pattern, (b) shows the Fresnel lens shape obtained by the liquid crystal diffraction lens, (c) shows the lens shape, and (d) shows the lead wiring. And a connection form of the ring-shaped electrode.

In the electrode pattern of the liquid crystal diffractive lens 105 shown in FIG. 6A, the obtained lens effect is a spherical lens effect, which has the shape shown in FIG. 6C. The phase pattern to be generated by the liquid crystal diffractive lens 105 takes the shape of FIG. 6B obtained by periodically relieving FIG. 6C, and the pattern of the annular electrode 404 corresponding to this pattern, and the lead-out pattern. Wiring 4
The pattern 02 becomes the shape shown in FIG.

  Here, in FIG. 6A, for each set of phase periods to be generated, the closed ring-shaped electrodes 404 are periodically arranged so as to have the same number, and the connection electrodes 405 corresponding to each period are sequentially arranged. Deploy. In addition, a lead-out wiring 402 is provided at a position intersecting with the ring-shaped electrode 404, and the ring-shaped electrode 404 and the lead-out wiring 402 are connected via a connection electrode 405 disposed in the through hole of the transparent insulating film.

  That is, as shown in FIG. 6D, a plurality of ring-shaped electrodes are divided into a plurality of sets having the same number, and the ring-shaped electrodes 404a located on the innermost side of the ring in each set and the other sets The innermost ring-shaped electrodes 404a are connected to a common lead wire 402a. Similarly, the ring-shaped electrode 404b located outside thereof is also connected to another common lead-out wiring 402b. Further, the relationship between the ring-shaped electrodes 404c to 404e located on the outside and the lead-out wirings 402c to 403e is the same.

  Further, the pattern shape of the lead-out wiring 402 is sufficient with only the number of linear pattern groups that feed power to the ring-shaped electrodes 404a to 404e bundled as a set, and the number of lead-out wirings 402 is reduced as compared with the conventional configuration. Can do. Thereby, the area of the wiring formation area which occupies within the effective diameter of the light beam can be reduced as much as possible. Therefore, it is possible to design the pattern with a stable resistance value while minimizing the influence of light diffraction. Furthermore, if this embodiment is applied, the arrangement area of the lead-out wiring 402 is reduced, so that it is possible to arrange the seal 412 on the outer periphery of the annular electrode 404. As a result, a small liquid crystal diffraction lens and can do.

  Note that, as described above, even if the material of the transparent insulating film and the material of the electrode pattern in the liquid crystal diffractive lens 105 are made of a refractive index material as close as possible, according to the structure of the present invention, There is a transparent insulating film 403 that covers the lead-out wiring 402, and a step corresponding to the thickness of the wiring is generated between the region where the lead-out wiring 402 is formed and the region where the lead-out wiring 402 is not formed. Such a step causes diffraction of the light beam. Here, if the lead wiring 402 is made as thin as possible, the generation of diffraction due to this step can be suppressed.

  Here, when the transparent conductive film constituting the lead-out wiring 402 is thinned, the wiring itself becomes high resistance. However, the lead-out wiring 402 of this embodiment has simplified the number of lead-outs to the limit, and the lead-out wiring 402 can be drawn in a straight line from within the effective diameter of the light beam to outside the effective shape. The resistance between the lead-out wirings 402 can be made substantially the same. Therefore, according to the configuration of the present invention, the transparent insulating film 403 corresponding to the above-described wiring can be provided while the desired lens effect can be exhibited even if the lead-out wiring 402 is a thin film and the wiring resistance is high. Diffraction due to a step can be suppressed. Further, since the areas where the respective lead wires 402 are arranged can be easily made uniform, it is possible to suppress variations in resistance of the lead wires.

  As described above, the liquid crystal diffractive lens of the present embodiment is in a range where the influence of diffraction of the light beam can be ignored, and as a film configuration capable of realizing conductivity and insulation, the lead-out wiring 402, the connection electrode 405, and the annular zone Even if the thickness of the electrode 404 is 100 to 300 mm and the thickness of the transparent insulating film 403 is 300 to 500 mm, the function of the diffraction lens is not impaired.

[Description of Change of Electrode Pattern of Liquid Crystal Diffraction Lens: FIG. 7]
Next, a modified example of the above electrode pattern will be described. FIG. 7 is a diagram conceptually showing the shape of the electrode pattern of the liquid crystal diffractive lens according to the first embodiment of the present invention.

  As a method of further reducing the number of lead wires 402 from the pattern configuration shown in FIG. 6, a set of lead wires 402 may be connected by a resistance electrode 701 as shown in the configuration of FIG. With this configuration, a divided voltage can be supplied to each connection electrode 405, and the number of lead-out wirings 402 can be further reduced as compared with the embodiment shown in FIG.

(Second Embodiment)
[Description of Another Form of Electrode Pattern of Liquid Crystal Diffraction Lens: FIG. 8]
Next, the liquid crystal diffraction lens in the second embodiment will be described. FIG. 8 is a diagram conceptually showing the shape of the electrode pattern of the liquid crystal diffractive lens according to the second embodiment of the present invention.

  In the electrode pattern of the liquid crystal diffractive lens shown in FIG. 8, the lens effect obtained is the aspherical lens shape shown in FIG. The phase pattern to be generated by the liquid crystal diffractive lens takes the shape of FIG. 8B obtained by periodically relieving FIG. 8C, the pattern of the annular electrode 404 corresponding to this pattern, and the lead-out wiring The pattern 402 has the shape shown in FIG.

  In FIG. 8A, for each set of phase periods to be generated, closed ring-shaped electrodes 404 are periodically arranged so as to have the same number, and corresponding connection electrodes 405 are arranged for each period. The lead-out wiring 402 is provided so as to intersect with the belt-like electrode 404, and the ring-like electrode 404 and the lead-out wiring 402 are connected via the connection electrode 405 provided in the through hole of the transparent insulating film.

  At this time, when the polarity of the phase distribution to be generated is reversed, the order of the connection electrodes 405 corresponding to the period of the closed ring-shaped electrode 404 is reversed, compared with the case of the spherical shape, An aspherical lens shape can be realized without changing the pattern shape of the lead wiring 402.

  With this configuration, the aspherical shape can be obtained without increasing the lead-out wiring 402, as in the case of FIG. 6 shown in the first embodiment.

It is a figure which shows the structural example of the optical pick-up apparatus of this invention. It is a figure which shows the effect | action of the optical pick-up apparatus of this invention. It is a figure which shows the effect | action of the optical pick-up apparatus of this invention. It is a figure which shows the structure of the liquid-crystal diffraction lens of this invention. It is a figure which shows the diffraction phenomenon of the light beam in an optical pick-up apparatus. It is a figure which shows the arrangement | positioning form of the electrode pattern of the liquid-crystal diffractive lens of this invention. It is a figure which shows the other arrangement | positioning form of the electrode pattern of the liquid-crystal diffraction lens of this invention. It is a figure which shows the other arrangement | positioning form of the electrode pattern of the liquid-crystal diffraction lens of this invention. It is a figure which shows the structure of the conventional liquid crystal diffraction lens.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Optical pick-up apparatus 102 Semiconductor laser 103 Polarizing beam splitter 104 Collimating lens 105 Liquid crystal diffractive lens 106 Liquid crystal drive device 107 λ / 4 plate 108 Optical disk 109 Objective lens 110 Photo detector 401, 410 Glass substrate 402, 402a-402e Lead-out wiring 403 Transparent Insulating film 404, 404a to 404e Ring-shaped electrode 405 Connection electrode 406, 408 Alignment film 407 Liquid crystal 409 Common electrode 411 Lens pattern forming layer 412 Seal 701 Resistance electrode

Claims (3)

A liquid crystal sandwiched between a first transparent substrate and a second transparent substrate;
A common electrode formed on the liquid crystal side of the first transparent substrate;
A lead-out line formed on the second transparent substrate;
An insulating film provided to cover the lead wiring;
A plurality of ring-shaped electrodes formed in a closed ring shape on the liquid crystal side of the insulating film;
A plurality of ring-shaped electrodes and a connection electrode that connects the lead-out wiring through the insulating film, and the plurality of ring-shaped electrodes are divided into a plurality of sets having the same number,
When the first and second ring-shaped electrodes are formed from the inside of the ring in each set, the first ring-shaped electrode and the first ring-shaped electrodes in the other set are connected to a common lead-out wiring. And
Each ring-shaped electrode and each lead-out wiring are connected by the connection wiring so that the second ring-shaped electrode and the second ring-shaped electrodes in another set are connected to another common lead-out wiring. A liquid crystal diffractive lens, characterized in that The relationship between the connection between the first annular electrode and the common lead wire and the connection between the second annular electrode and the other common lead wire is applied to the aspheric lens area in the lens region. The liquid crystal diffractive lens according to claim 1, wherein: In the optical path between the laser light source and the objective lens, the liquid crystal diffraction lens according to claim 1 or 2 is disposed,
An optical pickup device characterized by controlling the liquid crystal diffractive lens to adjust the focus of a laser beam emitted from the laser light source and condensed on an optical disc.

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