JP2004198942A - Phase plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an easily manufacturable phase plate functioning as a uniform quarter wavelength plate for light in a visible light region. <P>SOLUTION: This phase plate is provided with first and second organic thin film layers 1 and 2. The first organic thin film layer 1 has a retardation value of 1/2 wavelength to the light in the visible light region, and the second organic thin film layer 2 has a retardation value of 1/4 wavelength to the light in the visible region. The first and second organic thin film layers 1 and 2 are superposed to form the phase plate 101 so that optical axes of the first and second thin film layers 1, 2 cross each other with a prescribed angle. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a phase plate, and more particularly to a phase plate in which the phase difference or retardation value chromatic dispersion of visible light is controlled.
[0002]
[Prior art]
In a liquid crystal display device using visible light such as a liquid crystal display and a liquid crystal projector, the wavelength dispersion of the phase difference is small in the wavelength band from blue light having a wavelength of around 420 nm to red light having a wavelength of around 650 nm. A phase plate has been sought. Conventionally, in order to solve this problem, a phase plate in which a birefringent material having a large chromatic dispersion and a birefringent material having a small chromatic dispersion are overlapped so that their fast axes are orthogonal to each other to cancel the chromatic dispersion. Was configured.
[0003]
In recent years, DVD optical discs have become widespread as optical recording media (hereinafter referred to as “optical discs”) for recording / reproducing information using a semiconductor laser having a wavelength of about 660 nm (band) as a light source. Yes. Furthermore, in order to increase the amount of recorded information, an optical disc for HD using a semiconductor laser having a wavelength of 405 nm band as a light source has been proposed.
[0004]
For efficient recording and reproduction of DVD and HD optical discs, a linearly polarized light emitted from a semiconductor laser using a phase plate (1/4 wavelength plate) having a retardation value of 1/4 wavelength and a polarizing beam splitter is used. Is condensed on the information recording surface of the optical disc by the objective lens.
[0005]
Linearly polarized light is reflected after being condensed, and is converted into linearly polarized light orthogonal to the forward path by reciprocating a phase plate disposed between the polarizing beam splitter and the objective lens. Thus, an optical head device in which signal light is efficiently detected by the photodetector can be obtained.
[0006]
In order to realize the purpose of improving the efficiency, a phase plate having a retardation value of ¼ wavelength with respect to light having a wavelength of 405 nm band and a wavelength of 660 nm band has been desired.
[0007]
[Patent Document 1]
JP-A-11-149015 [0008]
[Problems to be solved by the invention]
However, it has been difficult to obtain and manufacture a birefringent material having a large wavelength dispersion and a birefringent material having a small wavelength dispersion appropriately and at low cost.
[0009]
The present invention has been made to solve the above-described problems, and provides a phase plate that functions as a uniform quarter-wave plate for visible light having a wavelength of 400 to 680 nm. .
[0010]
[Means for Solving the Problems]
The present invention is a phase plate having a birefringent first organic thin film layer and a second organic thin film layer fixed to at least one transparent substrate, and the first organic thin film layer comprises: The second organic thin film layer has a retardation value of ¼ wavelength with respect to visible light and the light of the first organic thin film layer has a retardation value of ½ wavelength with respect to visible light. The first and second organic thin film layers are overlapped so that the axis and the optical axis of the second organic thin film layer intersect with each other, and are configured to have a retardation value of ¼ wavelength with respect to light in the visible range. A phase plate is provided.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is a phase plate including a first organic thin film layer and a second organic thin film layer having birefringence fixed to at least one transparent substrate. The first organic thin film layer has a retardation value of ½ wavelength with respect to visible light, and the second organic thin film layer has a retardation value of ¼ wavelength with respect to visible light. Further, the first and second organic thin film layers are overlapped so that the optical axis of the first organic thin film layer and the optical axis of the second organic thin film layer intersect with each other, and 1 with respect to light in the visible range. The phase plate is configured to have a retardation value of / 4 wavelength.
[0012]
One or two transparent substrates may be used. Use of a polymer liquid crystal layer as the organic thin film layer having birefringence is preferable from the viewpoint of availability and production. Therefore, the present invention will be described below with reference to the drawings in the case where the polymer liquid crystal layer is taken as an example and the optical axis is a slow axis.
[0013]
The phase plate of the present invention has a configuration in which two polymer liquid crystal layers 1 and 2 are sandwiched between two transparent substrates 3 and 4, for example, as shown in FIG. Further, FIG. 1 also shows a state where linearly polarized light in the visible region is transmitted through the phase plate 101 and emitted as circularly polarized light.
[0014]
A method of laminating a polymer liquid crystal on a transparent substrate will be described with reference to FIG. After applying the alignment film solution onto the transparent substrates 13 and 14 and applying the desired alignment treatment to the alignment films 15 and 16, the alignment film 15 of the transparent substrate 13 is coated with a liquid crystal monomer that becomes a birefringent material. Apply the solution. On the other hand, after a release treatment agent is applied to the alignment film 16 of the transparent substrate 14, spacers for dispersing the thickness of the liquid crystal monomer that becomes the polymer liquid crystal layer 11 are dispersed (not shown).
[0015]
At this time, the thickness d of the liquid crystal monomer used as the polymer liquid crystal layer 11 is determined so that the product Δn · d of the abnormal light refractive index of the polymer liquid crystal and the difference Δn of the ordinary light refractive index is the light having the design center wavelength of the phase plate. On the other hand, it is determined to be approximately equal to a half wavelength or a quarter wavelength. Here, the design center wavelength is a wavelength used when designing and manufacturing the phase plate of the present invention, so that the refractive index dispersion of the polymer liquid crystal used and desired optical characteristics as the phase plate can be obtained. In addition, it is appropriately determined between wavelengths of 480 to 580 nm of visible light.
[0016]
The two types of thickness corresponding to the above-described half wavelength and quarter wavelength correspond to the thicknesses of the polymer liquid crystal layer 1 and the polymer liquid crystal layer 2 of the phase plate 101 in FIG. Next, after the transparent substrates 13 and 14 are stacked so that the alignment treatment direction of the alignment film 15 and the alignment treatment direction of the alignment film 16 coincide with each other, the light source light for photopolymerization is irradiated to polymerize and cure the liquid crystal monomer. Thus, the polymer liquid crystal layer 11 is obtained. As a result, the liquid crystal molecules are aligned in a certain direction within the polymer liquid crystal layer 11.
[0017]
Next, the transparent substrate 14 is released from the interface between the polymer liquid crystal layer 11 and the alignment film 16 to produce a polymer liquid crystal laminated substrate composed of the polymer liquid crystal layer 11 and the transparent substrate 13. Further, by using an optically flat substrate made of an inorganic material such as a glass substrate as the transparent substrate, it is possible to maintain a favorable wavefront aberration of transmitted light with respect to a temperature change.
[0018]
Using the above-mentioned method, two types of polymer liquid crystal laminated substrates having different polymer liquid crystal layer thicknesses are produced, and the liquid crystal molecule alignment directions of each polymer liquid crystal layer, that is, the slow axes are overlapped and bonded. By fixing with an agent, a phase plate 101 as shown in FIG. 1 is formed. FIG. 3 is a view of the phase plate 101 as viewed from the transparent substrate 4 side, and S ₁ and S ₂ indicate the liquid crystal molecular alignment directions of the polymer liquid crystal layers 1 and 2 (FIG. 1), that is, the slow axis. .
[0019]
Θ ₁ and θ ₂ indicate the angles of S ₁ and S _{2 from} the x axis, and the counterclockwise direction is positive. Here, θ ₁ is 75 ± 3 ° and θ ₂ is 15 ± 3 °, or θ ₁ is −75 ± 3 ° and θ ₂ is −15 ± 3 °, or θ ₁ is 15 ± 3 ° and θ ₂ is It is preferable that 75 ± 3 ° or θ ₁ be −15 ± 3 ° and θ ₂ be −75 ± 3 °. Further, setting the value of | θ ₁ −θ ₂ | to 60 ± 3 ° between the slow axes of the two types of polymer liquid crystal layers 1 and ₂ causes the phase plate 101 to emit light in the visible range. When linearly polarized light whose electric field vibrates in the x-axis direction or y-axis direction is incident, it is preferably emitted as substantially circularly polarized light. That is, the phase plate 101 is preferable because it functions as a uniform substantially quarter-wave plate for visible light.
[0020]
FIG. 4 is a graph showing the phase difference characteristics of the phase plate 101 of the present invention having a design center wavelength of 500 nm (curve 31) and the conventional quarter-wave plate (curve 33) for light having a wavelength of 500 nm. It is the graph which showed the ellipticity of the polarization | polarized-light emitted from each phase plate on the vertical axis | shaft, and showed the wavelength on the horizontal axis. Comparing the curve 31 and the curve 33, it can be seen that the phase plate 101 of the present invention has almost no wavelength dispersion in the visible region.
[0021]
Further, a curve 31 in FIG. 4 is a case where the liquid crystal molecule alignment directions of the two polymer liquid crystal layers of the phase plate are (θ ₁ , θ ₂ ) = (− 75 °, −15 °) in FIG. A curve 32 shows a case where the liquid crystal molecular alignment directions of the two polymer liquid crystal layers of the phase plate are (θ ₁ , θ ₂ ) = (− 74 °, −15 °), and the latter is in the visible region. It can be seen that the chromatic dispersion is smaller. That is, it can be seen that the optical characteristics can be easily adjusted by appropriately adjusting the values of (θ ₁ , θ ₂ ).
[0022]
Further, by making the angle of θ ₁ smaller than −74 °, the ellipticity is 1, that is, the wavelength corresponding to circularly polarized light is 405 nm which is the light source wavelength of the optical head device for HD, and the optical head device for DVD is used. The light source wavelength approaches 650 nm. That is, it becomes a quarter wavelength plate in both the wavelength range for HD and DVD.
[0023]
【Example】
This embodiment is a specific example of the phase plate 101 shown in FIG. 1, and a manufacturing process will be described with reference to FIG. On the transparent substrates 13 and 14 made of glass, polyimide for alignment film was applied and cured, and then alignment treatment by rubbing was performed to obtain alignment films 15 and 16. Next, a liquid crystal monomer solution serving as a birefringent material was applied to the alignment film 15 on the transparent substrate 13.
[0024]
On the other hand, after applying a water repellent release agent to the alignment film 16 on the transparent substrate 14, spacers having a particle size of 3.8 μm were sprayed (not shown). Next, after the transparent substrates 13 and 14 are overlapped so that the alignment treatment direction of the alignment film 15 and the alignment treatment direction of the alignment film 16 coincide with each other, the light source light for photopolymerization is irradiated to obtain the liquid crystal monomer. The polymer liquid crystal layer 11 was formed by polymerization and curing. The difference Δn between the extraordinary refractive index and the ordinary refractive index of the polymer liquid crystal cured by photopolymerization was 0.065.
[0025]
Therefore, the retardation value of the polymer liquid crystal layer 11 is 250 nm, which corresponds to a half wavelength with respect to light having a wavelength of 500 nm. Next, the transparent substrate 14 was released at the interface between the polymer liquid crystal layer 11 and the alignment film 16 to produce a polymer liquid crystal laminated substrate composed of the polymer liquid crystal layer 11 and the transparent substrate 13. Also, polymer liquid crystal multilayer substrates having different polymer liquid crystal layer thicknesses were prepared in the same process by changing the particle size of the spacers to 1.9 μm. At this time, the retardation value of the polymer liquid crystal layer is 125 nm, which corresponds to a quarter wavelength with respect to light having a wavelength of 500 nm.
[0026]
The two polymer liquid crystal multilayer substrates prepared as described above face each polymer liquid crystal layer so that the liquid crystal molecule alignment direction of each polymer liquid crystal layer, that is, the angle formed by the slow axis is 59 °. In addition, the phase plate 101 was manufactured by fixing with an epoxy adhesive.
[0027]
In the coordinate system shown in FIG. 3, the angle θ ₁ formed by the optical axis S ₁ of the polymer liquid crystal layer 1 constituting the phase plate 101 and the x axis is 74 °, and the optical axis S ₂ of the polymer liquid crystal layer ₂ and the x axis when the angle theta ₂ of the and 15 °, (vibrates) with the polarization direction in the x-axis direction linearly polarized light incident to the phase plate 101, to measure the polarization state of the emitted light. As a result, almost circularly polarized outgoing light could be obtained in the entire visible range. That is, it was confirmed that the phase plate 101 of the present invention was a uniform quarter-wave plate for visible light.
[0028]
Further, the phase plate 101 of the present invention was used in the polarization conversion optical system shown in FIG. A polarization conversion optical system is used in liquid crystal projectors equipped with a liquid crystal display device premised on linearly polarized incident light. Randomly polarized light emitted from a white light source is converted into linearly polarized light with a uniform polarization plane. This is a conversion system, and includes a light source 41, a polarization beam splitter 42, mirrors 43 and 44, and a quarter-wave plate 45. As a result of using the phase plate 101 of the present invention in place of the quarter-wave plate 45, random polarized light in the visible range emitted from the light source could be converted to linearly polarized light with a uniform polarization plane. As a result, the light emitted from the light source can be efficiently incident on the liquid crystal display element as linearly polarized light, so that the brightness of the display is improved.
[0029]
Next, the phase plate 101 of the present invention was used in a liquid crystal projector using the reflective liquid crystal display element shown in FIG. The reflective liquid crystal display element includes a polarizing beam splitter 51, a polarizer 52, a reflective liquid crystal display element 53, and a quarter-wave plate 54, and changes the voltage applied to the liquid crystal layer of the liquid crystal display element 53. Thus, the amount of light emitted from the polarizer 52 can be adjusted. As a result of using the phase plate 101 of the present invention instead of the quarter-wave plate 54, the change in the amount of light emitted from the polarizer 52 in accordance with the voltage applied to the liquid crystal layer of the liquid crystal display element 53 is the light in the visible range. However, it showed almost uniform behavior. As a result, the uniformity and reproducibility of the display color was improved.
[0030]
【The invention's effect】
According to the present invention, two polymer liquid crystal layers having different thicknesses are formed using polymer liquid crystal, and the slow axes that are the alignment directions of the liquid crystal molecules intersect each other at a predetermined angle. Thus, it is possible to easily manufacture a phase plate that functions as a uniform quarter-wave plate for visible light.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an example of a configuration of a phase plate of the present invention.
FIG. 2 is a cross-sectional view illustrating a method for laminating a polymer liquid crystal on a transparent substrate.
FIG. 3 is a plan view showing liquid crystal molecule alignment directions of two polymer liquid crystal layers constituting the phase plate of the present invention.
FIG. 4 is a graph showing phase difference characteristics between the phase plate of the present invention (quarter wave plate) and a conventional quarter wave plate.
FIG. 5 is a conceptual diagram of a polarization conversion optical system using the phase plate of the present invention.
FIG. 6 is a conceptual diagram of a reflective liquid crystal projector using the phase plate of the present invention.
[Explanation of symbols]
101: Phase plates 1, 2, 11: Polymer liquid crystal layers 3, 4, 13, 14: Transparent substrate 15, 16: Alignment film 41: White light source 42, 51: Polarizing beam splitter 43, 44: Mirror 45, 54: Quarter-wave plate 52: Polarizer 53: Reflective liquid crystal display element

Claims (3)

A phase plate having a birefringent first organic thin film layer and a second organic thin film layer fixed to at least one transparent substrate, wherein the first organic thin film layer is light in the visible range. The second organic thin film layer has a retardation value of 1/4 wavelength with respect to light in the visible range, and the optical axis of the first organic thin film layer and the second The first and second organic thin film layers are stacked so that the optical axis of the organic thin film layer intersects with each other, and has a retardation value of ¼ wavelength with respect to light in the visible range. Feature phase plate. The phase plate according to claim 1, wherein the first and second organic thin film layers are composed of a polymer liquid crystal layer in which a liquid crystal monomer is cured, and an optical axis is a slow axis. The phase plate according to claim 1 or 2, wherein the angle formed by the slow axes of the two polymer liquid crystal layers is approximately 60 °.

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