JP2005215027A - Liquid crystal optical element and optical head device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal optical element and an optical head device that can reduce an optical reflection coefficient at an interface between a transparent electrode film and a substrate. <P>SOLUTION: The liquid crystal optical element 100 obtained by arranging two substrates 101 and 102, where transparent electrode films 103 and 104, 1st intermediate films 105 and 106, and alignment films 107 and 108 are laminated in order, opposite each other so that the alignment films 107 and 108 face each other and charging a liquid crystal material between the two substrates 101 and 102 is characterized in that new 2nd intermediate films 109 and 110 are interposed on interfaces where the transparent electrode films 103 and 104 and substrates 101 and 102 come into contact with each other so that the optical reflection coefficient at the interfaces is nearly ≤1% in the wavelength of the light in use. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a liquid crystal optical element and an optical head device.

  FIG. 5 is a diagram showing a schematic cross-sectional configuration of a conventional liquid crystal optical element. In FIG. 5, transparent conductive films 503 and 504 having a thickness of about 200 nm made of a mixed oxide film of In and Sn (hereinafter referred to as ITO film) are formed on glass substrates 501 and 502. The transparent conductive films 503 and 504 are subjected to wiring processing so as to have a predetermined shape. On the transparent conductive films 503 and 504 made of an ITO film, a sol-gel film having a thickness of about 50 nm is applied and formed as an intermediate film 505 and 506, and a polyimide film having a thickness of about 50 nm is formed thereon on a liquid crystal alignment film 507 and 508. It is formed as a coating. The glass substrates 501 and 502 are bonded together using a spacer and a sealing material 511 (not shown) so that the distance between the glass substrate 501 and the glass substrate 502 is within a predetermined range, thereby forming a sealed space. The liquid crystal 512 is injected into the sealed space and sealed to form the liquid crystal optical element 500.

  Here, the refractive indexes of these constituent materials are different from those of other constituent materials, and it is known that the transparent conductive films 503 and 504 are particularly different. For example, when compared at a wavelength near 400 nm where a blue laser is used, the refractive indexes of the glass substrates 501, 502, transparent conductive films 503, 504, intermediate films 505, 506, alignment films 507, 508, and liquid crystal 512 are respectively 1.55, 2.20, 1.55, 1.60, and 1.55.

Therefore, there is a difference in reflectance and transmittance at the used wavelength at the interfaces between the transparent conductive films 503 and 504 and the glass substrates 501 and 502 and at the interfaces between the transparent conductive films 503 and 504 and the intermediate films 505 and 506. It was. As a result, a transmittance ripple, which is a variation in transmittance, occurs in the element. In order to reduce such transmittance ripple, conventionally, attempts have been made to lower the refractive index of the transparent conductive films 503 and 504, and the film thicknesses of the transparent conductive films 503 and 504, the intermediate films 505 and 506, and the alignment films 507 and 508 The refractive index has been adjusted (see, for example, Patent Document 1 or Patent Document 2).
JP 2001-208914 A JP 2002-208158 A

  However, in such a conventional liquid crystal optical element, since the refractive index of the transparent conductive film used in the liquid crystal optical element is a value specific to the material, the film density is changed to adjust the refractive index by changing the film forming conditions. Even if it is attempted to lower, there are problems such as fluctuations in the reliability of the elements and fluctuations in optical characteristics or electrical characteristics.

  Further, in an attempt to control the film thickness and the refractive index while paying attention only to the configuration sandwiched between the transparent conductive film and the alignment film, the reduction of reflection at the interface is insufficient.

  The present invention has been made to solve such problems, and provides a liquid crystal optical element and an optical head device that can reduce the reflectance of light at the interface between a transparent electrode film and a substrate.

  In view of the above points, the invention according to claim 1 is arranged such that two substrates in which a transparent electrode film, a first intermediate film, and an alignment film are sequentially laminated are opposed to each other so that the alignment films face each other. In a liquid crystal optical element obtained by enclosing a liquid crystal material between two substrates, the reflectance of light at the interface between the transparent electrode film and the substrate is approximately 1% or less with respect to the wavelength of the used light. In addition, a new second intermediate film is inserted into each interface between the transparent electrode film and the substrate.

  With this configuration, since the second intermediate film is provided between the transparent electrode film and the substrate so that the optical characteristics can be adjusted, the liquid crystal optical element that can reduce the reflectance of light at the interface constituted by the transparent electrode film and the substrate Can be realized.

  The invention according to claim 2 is the structure according to claim 1, wherein the refractive index of the second intermediate film is set to any value between the refractive index of the transparent electrode film and the refractive index of the substrate. Have.

  With this configuration, in addition to the effect of the first aspect, the refractive index of the second intermediate film is set between the refractive index of the transparent electrode film and the refractive index of the substrate, so that the refractive index on the optical path can be changed smoothly. And a liquid crystal optical element capable of reliably reducing the reflectance can be realized.

  According to a third aspect of the present invention, in the first or second aspect, the thickness of the transparent electrode film is in the range from 1 nm to 50 nm, and the thickness of the second intermediate film is 0.2 of the working wavelength. It has a configuration in the range from double to 0.3 times.

  According to this configuration, in addition to the effect of the first or second aspect, the thickness of the transparent electrode film is set to any one of 1 nm to 50 nm, and the thickness of the second intermediate film is set to (0.25 ± 0.05 ± 0.05). ) × λ (λ is the wavelength of incident light described in nm unit), and the liquid crystal optical element capable of further reducing the reflectance can be realized.

  According to a fourth aspect of the present invention, there is provided a light source, an objective lens for condensing the light emitted from the light source onto an optical recording medium, and light detection for detecting the emitted light that is collected and reflected by the optical recording medium. In the optical head apparatus provided with an optical device, either in the optical path between the objective lens and the light source or in the optical path between the objective lens and the photodetector. The liquid crystal optical element according to the item is arranged.

  With this configuration, an optical head device having the effect of any one of claims 1 to 3 and having high light utilization efficiency can be realized.

  In the present invention, since the second intermediate film is provided between the transparent electrode film and the substrate so that the optical characteristics can be adjusted, the liquid crystal optical element and the light that can reduce the reflectance of light at the interface between the transparent electrode film and the substrate A head device can be provided.

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

(First embodiment)
FIG. 1 is a cross-sectional view showing a conceptual configuration of the liquid crystal optical element according to the first embodiment of the present invention. In FIG. 1, the liquid crystal optical element 100 is configured as follows. First, the outside of the liquid crystal optical element 100 is constituted by substrates 101 and 102 made of a plastic material such as glass or polycarbonate.

  Next, second intermediate films 109 and 110 are formed on the substrates 101 and 102 by vacuum deposition or the like, and transparent conductive films 103 and 104 made of ITO or the like are formed on the second intermediate films 109 and 110. Has been. Here, the transparent conductive films 103 and 104 are processed into a predetermined element shape and electrode shape using techniques such as photolithography and wet etching. Here, it is desirable that the transparent conductive films 103 and 104 are thin in order to increase the transmittance of the liquid crystal optical element, and it is particularly desirable that the thickness be between 1 nm and 50 nm.

The first intermediate films 105 and 106 are formed on the transparent conductive films 103 and 104. The first intermediate films 105 and 106 are sufficiently formed from the viewpoint of preventing a short circuit between the upper and lower electrodes due to contamination of conductive foreign matters. A strong film is desirable. The first intermediate films 105 and 106 may be made of SiO ₂ , ZrO ₂ , TiO ₂ , Al ₂ O ₃ or the like, or a material having a mixed composition of these materials. The first intermediate films 105 and 106 may be formed by applying and baking these substances using a sol-gel method, or by sputtering or vacuum deposition.

  On the first intermediate films 105 and 106, alignment films 107 and 108 for aligning liquid crystal molecules are formed. Here, the alignment films 107 and 108 may be formed by applying polyimide using a technique such as flexographic printing or spin coating, and the alignment films 107 and 108 having a strong bond may be formed by baking after application. Can be formed. A sealing material 111 is provided on the periphery of the substrates 101 and 102 where the second intermediate films 109 and 110, the transparent conductive films 103 and 104, the first intermediate films 105 and 106, and the alignment films 107 and 108 are not formed. The liquid crystal 112 is enclosed between the substrate 101 and the substrate 102, and the liquid crystal optical element 100 is obtained.

  The liquid crystal optical element 100 is provided with second intermediate films 109 and 110, and by adjusting the refractive index and film thickness thereof, the reflectance for light of a specific wavelength at the interface between the substrates 101 and 102 and the transparent conductive films 103 and 104 is adjusted. Can be reduced. Here, it is preferable that the reflectance with respect to light of a specific wavelength at the interface between the substrates 101 and 102 and the transparent conductive films 103 and 104 is approximately 1% or less to suppress interference. Here, approximately 1% or less means a value of 0.2 to 1.5%.

  FIG. 2 is a graph showing the voltage dependence of the transmittance of light incident from one side of the liquid crystal optical element 100. In FIG. 2, the vertical axis of the graph is the transmittance, the horizontal axis is the voltage, and the transmittance is expressed using the wavelength as a parameter. Here, changing the voltage on the horizontal axis can be regarded as changing the refractive index of the liquid crystal with respect to the incident polarized light. The wavelength as a parameter is 400 nm for the line a represented by a white circle (◯), 405 nm for the line b represented by a black circle (●), and a line h represented by a small white square (□). Is 410 nm, and is 420 nm for a large white square (Δ).

  The graph shown in FIG. 2 shows that the liquid crystal optical element is composed of the transparent conductive films 103 and 104, the first intermediate films 105 and 106, and the alignment films 107 and 108. This is a transmittance characteristic of an “element”. As is apparent from FIG. 2, when the wavelength of the semiconductor laser light source is set to, for example, 410 nm, the transmittance of the liquid crystal optical element having the conventional configuration is about 91%. It can also be seen that the transmittance varies by 2% or more when the wavelength or the driving voltage is changed.

FIG. 3 shows a configuration in which an Al ₂ O ₃ film having a refractive index of about 1.7 and a thickness of 100 nm is added as second intermediate films 109 and 110 to a liquid crystal optical element having a conventional configuration (hereinafter referred to as the configuration of the present invention). .) Is a graph showing the voltage dependency of the transmittance. As is apparent from the characteristics shown in FIG. 3, the transmittance is improved to 94% or more by providing the second intermediate films 109 and 110. And it turns out that the fluctuation | variation of the transmittance | permeability when wavelength or a drive voltage changes is settled in 0.3% or less.

FIG. 4 is a graph showing the voltage dependence of the transmittance when the Al ₂ O ₃ films of the second intermediate films 109 and 110 constituting the liquid crystal optical element of the present invention have a thickness of 130 nm. When the film thickness is 130 nm, the transmittance is about 92.5%, and the transmittance ripple is about 2%. In a liquid crystal optical element having an interface with a transparent conductive film that generates reflection, large interference occurs at the interface. However, if the reflection is reduced, the influence of this interference is reduced.

  FIG. 3 shows an interference pattern with respect to wavelength and voltage in the liquid crystal optical element having the second intermediate films 109 and 110 according to the present invention, and FIG. 2 shows the above-described conventional pattern for comparison with the liquid crystal optical element having the structure according to the present invention. The interference pattern with respect to the wavelength and voltage of the liquid crystal optical element of a structure is shown. As can be seen from FIGS. 2 and 3, the liquid crystal optical element 100 having the configuration of the present invention having the second intermediate films 109 and 110 shown in FIG. 3 is the conventional liquid crystal optical element having no second intermediate film of FIG. As compared with the above, a significant reduction in interference amplitude is observed. By reducing the interference amplitude, it is possible to realize a liquid crystal optical element having a high light transmittance and a small variation in transmittance due to a change in driving voltage of the liquid crystal optical element over a wide wavelength range.

Specific examples based on the above-described embodiments of the present invention will be described below. Here, in the liquid crystal optical element according to the present example, a glass substrate having a refractive index of 1.46 with a low reflection coating (not shown) is used as the substrates 101 and 102, and a refractive index of 1.68 is formed thereon. The second intermediate films 109 and 110 made of Al ₂ O ₃ having a thickness of 100 nm and the ITO transparent conductive films 103 and 104 having a refractive index of 2.05 and a thickness of 10 nm were formed on the second intermediate films 109 and 110. (Figure 1). The second intermediate films 109 and 110 are formed using a vacuum deposition method, and the transparent conductive films 103 and 104 have a sheet resistance of about 300Ω / □ and sufficient electrical characteristics to drive a liquid crystal. .

The transparent conductive films 103 and 104 were processed into a predetermined electrode pattern using a photolithography method and a wet etching method. Thereafter, a sol-gel film mainly composed of SiO ₂ is flexographically printed in addition to the peripheral sealing portion, and irradiated with 4000 mJ of UV light using a low-pressure mercury lamp, followed by baking at 300 ° C. for 1 hour. 49. First intermediate films 105 and 106 having a thickness of 50 nm were formed.

  After the formation of the first intermediate films 105 and 106, a polyimide resin having a refractive index of 1.55 was aligned on the first intermediate films 105 and 106 and subjected to flexographic printing. The flexographically printed material was baked at 250 ° C. for 1 hour, and rubbed to give alignment films 107 and 108 for liquid crystal having a thickness of 50 nm. An epoxy sealant 111 containing glass fiber spacers and conductive beads (not shown) is printed on a peripheral portion of the glass substrate 101 where the first intermediate film 105 and the alignment film 107 for liquid crystal are not applied, and two glass substrates 101 and 102 were overlapped. A liquid crystal optical element 100 was configured by vacuum-injecting a liquid crystal 112 having an ordinary light refractive index of 1.51 and an extraordinary light refractive index of 1.61 and sealing it.

  The liquid crystal optical element 100 according to this example exhibited a high transmittance of 94% or more when semiconductor laser light having a wavelength of 410 nm was incident in a polarization direction that felt an extraordinary light refractive index. Further, in the evaluation of the interference amplitude by the spectral evaluation, the reflectance is 1.0% or less in the range from the wavelength of 400 nm to the wavelength of 430 nm, which is a level that can sufficiently cope with the wavelength variation of the semiconductor laser.

  Further, the liquid crystal optical element 100 according to the present embodiment can be applied to an optical element utilizing liquid crystal characteristics, and is particularly suitable for an optical head device component that requires excellent characteristics at a single wavelength. . Examples thereof include phase correction elements using liquid crystals that improve light collection characteristics, such as optical disks such as CDs, CD-ROMs, and DVDs, and magneto-optical disks and phase-change optical disks. When the liquid crystal optical element of the present embodiment is used in an optical head device, a gap between a semiconductor laser serving as a light source and an objective lens of the optical head device that condenses emitted light from the semiconductor laser on an optical recording medium. Install and use in the optical path.

  Further, the liquid crystal optical element 100 according to the present embodiment is particularly effective when optimized for a specific single wavelength as described above. Since layers having different rates can be further added to reduce the average interference and improve the optical characteristics for two specific wavelengths and specific wavelength bands, there is a degree of freedom in design.

  As described above, the liquid crystal optical element and the optical head device according to the first embodiment of the present invention can adjust the optical characteristics by providing the second intermediate film between the transparent electrode film and the substrate. The reflectance of light at the interface between the transparent electrode film and the substrate can be reduced.

  The liquid crystal optical element and the optical head device according to the present invention can also be applied to applications such as a liquid crystal optical element and an optical head device that are useful for reducing the light reflectance at the interface between the transparent electrode film and the substrate.

The figure which shows the notional structure of the liquid crystal optical element which concerns on embodiment of this invention The graph which shows the voltage dependence of the refractive index obtained with the liquid crystal optical element of the conventional structure which does not provide a 2nd intermediate film The graph which shows the voltage dependence of the refractive index obtained with the liquid crystal optical element of this invention which provided the 2nd intermediate film 3 is a graph showing the voltage dependence of the refractive index obtained by the liquid crystal optical element having the configuration shown in FIG. 3 in which the thickness of the second intermediate film is changed. The figure which shows the notional structure of the conventional liquid crystal optical element.

Explanation of symbols

100, 500 Liquid crystal optical element 101, 102 Substrate 501, 502 Glass substrate 103, 104, 503, 504 Transparent conductive film 105, 106, 505, 506 First intermediate film 107, 108, 507, 508 Alignment film 109, 110, 509 , 510 Second intermediate film 111, 511 Sealing material 112, 512 Liquid crystal

Claims (4)

  Liquid crystal optics obtained by placing two substrates, in which a transparent electrode film, a first intermediate film, and an alignment film are sequentially stacked, facing each other so that the alignment films face each other, and enclosing a liquid crystal material between the two substrates In the element, a new reflectance is added to each interface between the transparent electrode film and the substrate so that the reflectance of light at the interface between the transparent electrode film and the substrate is approximately 1% or less with respect to the wavelength of the used light. A liquid crystal optical element, wherein a second intermediate film is inserted.   The liquid crystal optical element according to claim 1, wherein a refractive index of the second intermediate film is set to any value between a refractive index of the transparent electrode film and a refractive index of the substrate.   The thickness of the transparent electrode film is in the range from 1 nm to 50 nm, and the thickness of the second intermediate film is in the range from 0.2 times to 0.3 times the operating wavelength. The liquid crystal optical element described.   In the optical head device comprising: a light source; an objective lens that condenses the light emitted from the light source onto an optical recording medium; and a photodetector that detects the emitted light that is collected and reflected by the optical recording medium. 4. The liquid crystal optical element according to claim 1, wherein the liquid crystal optical element according to claim 1 is disposed in an optical path between the objective lens and the light source or in an optical path between the objective lens and the photodetector. An optical head device, characterized in that

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