JP2009282410A - Polarization switching element, projector using polarization switching element, and television - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarization switching element capable of achieving a stable response. <P>SOLUTION: The polarization switching element has at least a pair of transparent substrates having a transparent electrode on each surface thereof, a liquid crystal material arranged between the pair of transparent substrates, a voltage applying means for applying a voltage to the liquid crystal material via the pair of transparent electrodes, and a polarization state detecting means provided in a light-emitting side of the pair of transparent substrates. The voltage applied from the voltage applying means to the liquid crystal material is regulated based on a feedback of a signal from the polarization state detecting means to the voltage applying means. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a polarization switching element and a projector and a television using the polarization switching element, and more particularly to a polarization switching element using a liquid crystal and a projector and a television using the polarization switching element.

  Conventionally, liquid crystal elements have been applied as displays by utilizing the fact that the light transmittance of the liquid crystal can be controlled by voltage. On the other hand, as a use other than the display of a liquid crystal element, a polarization switching element that rotates and emits a polarization plane of incident light is considered (for example, see Patent Document 1).

  In general, a polarization switching element is an element that has two actions of turning or not turning the polarization direction of linearly polarized light by 90 ° and switching the two polarization states by applying a voltage or the like. is there. As this polarization switching element, one using a TN (twisted nematic) liquid crystal material is known.

JP 2007-121893 A

  However, the conventional polarization switching element using liquid crystal has a problem that the response due to the voltage to be applied to the liquid crystal constituting the polarization switching element is relatively unstable.

  An object of the present invention is to provide a polarization switching element that can easily realize a stable switching response.

  Another object of the present invention is to provide a projector and a television using the polarization switching element.

  As a result of diligent research, the present inventor has found that it is extremely effective in achieving the above object to feed back information on the polarization state itself to the voltage to be applied to the liquid crystal in the polarization switching element using the liquid crystal. It was.

  The polarization switching element of the present invention is based on the above knowledge, and more specifically, a pair of transparent substrates each having a transparent electrode on each surface; a liquid crystal material disposed between the pair of transparent substrates; A polarization switching element having at least a voltage applying means for applying a voltage to the liquid crystal material via a pair of transparent electrodes; and a polarization state detecting means provided on the light emitting side of the pair of transparent substrates; The voltage applied from the voltage application unit to the liquid crystal material is adjusted based on feedback of a signal from the detection unit to the voltage application unit.

  The present invention includes, for example, the following aspects.

[1] A pair of transparent substrates having transparent electrodes on each surface;
A liquid crystal material disposed between the pair of transparent substrates;
Voltage applying means for applying a voltage to the liquid crystal material through the pair of transparent electrodes;
A polarization switching element having at least polarization state detection means provided on the light exit side of the pair of transparent substrates;
A polarization switching element, wherein a voltage applied from the voltage application unit to the liquid crystal material is adjusted based on feedback of a signal from the polarization state detection unit to the voltage application unit.

  [2] The polarization switching element according to [1], wherein the liquid crystal material is a polarization-shielded smectic liquid crystal or a ferroelectric liquid crystal.

  [3] By applying a voltage to the liquid crystal material, the first polarization state of light incident from the light incident side of the pair of transparent substrates is changed to a second polarization state different from the first polarization state. The polarization switching element according to any one of [1] or [2].

  [4] The polarization switching element according to [3], which maintains and outputs the light in the first polarization state by adjusting a voltage applied to the liquid crystal material.

  [5] The polarization switching according to [3] or [4], wherein the first polarization state is linearly polarized light, and the second polarization state is linearly polarized light obtained by rotating a vibration plane of the linearly polarized light by 90 °. element.

  [6] The polarization switching element according to any one of [1] to [5], wherein the polarization state detection unit includes at least one polarization unit and a photodetector that detects the intensity of light transmitted through the polarization unit.

  [7] The voltage application means includes a sensor signal detection means for detecting a signal from the polarization state detection means, an input means for inputting a command for designating the polarization state, and a command and sensor signal detection input by the input means. [1] to [6] comprising control means for determining a voltage to be applied to the liquid crystal based on a signal detected by the means, and voltage output means for applying a voltage to the transparent electrode based on a signal from the control means. The polarization switching element according to any one of the above.

  [8] The control means includes storage means; when the light having the first polarization state is output to the storage means, the signal intensity from the polarization state detection means is maximized. The polarization switching element according to [7], wherein a control program for determining a voltage value to be applied to the transparent electrode and sending a signal for outputting the voltage to the voltage output means is stored.

[9] A spatial light modulation element for displaying an input video signal, an illumination optical system, an optical unit, a projection optical system for enlarging and projecting light that has passed through the optical unit, and a spatial light modulation element A projector including at least
The optical unit includes a polarization switching element; and
A pair of transparent substrates having a transparent electrode on each surface; a liquid crystal material disposed between the pair of transparent substrates; a voltage applying means for applying a voltage to the liquid crystal material via the pair of transparent electrodes; A polarization switching element having at least a polarization state detection unit provided on the light exit side of the pair of transparent substrates; the voltage based on feedback of a signal from the polarization state detection unit to the voltage application unit; The projector according to any one of [1] to [8], which adjusts a voltage applied to the liquid crystal material from an application unit.

[10] A television including at least a display device for displaying an input video signal and a polarization switching element;
The polarization switching element is
A pair of transparent substrates having a transparent electrode on each surface; a liquid crystal material disposed between the pair of transparent substrates; a voltage applying means for applying a voltage to the liquid crystal material via the pair of transparent electrodes; A polarization switching element having at least a polarization state detection unit provided on the light exit side of the pair of transparent substrates; the voltage based on feedback of a signal from the polarization state detection unit to the voltage application unit; The polarization switching element according to any one of [1] to [8], which adjusts a voltage applied to the liquid crystal material from an application unit.

  According to the present invention, the polarization switching element that enables a stable switching response by detecting the polarization state of light transmitted through the liquid crystal constituting the polarization switching element and feeding back the detection signal to the voltage application means. Is provided.

(Polarization switching element)
The polarization switching element of the present invention includes a pair of transparent substrates each having a transparent electrode on each surface; a liquid crystal material disposed between the pair of transparent substrates; and the liquid crystal material via the pair of transparent electrodes. It is a polarization switching element having at least voltage application means for applying a voltage; and polarization state detection means provided on the light emission side of the pair of transparent substrates. In the present invention, the voltage applied from the voltage application unit to the liquid crystal material is adjusted based on feedback of the signal from the polarization state detection unit to the voltage application unit.

(Extinction ratio)
In the present invention, the degree of the above-mentioned “stable switching response” is preferably measured using the extinction ratio as an index and adjusted so as to maintain the extinction ratio in an optimum state. Normally, the extinction ratio used in the LCD means a light amount ratio when the transmitted light amount (or reflected light amount) is the smallest and a light amount ratio when the transmitted light amount (or reflected light amount) is the largest. However, the “extinction ratio” used here means that the polarization direction with respect to the intensity of the predetermined linearly polarized light out of the light emitted from the element when the predetermined linearly polarized light is incident on the element is 90. ° The ratio to the intensity of swirled linearly polarized light.

  When this extinction ratio decreases, other polarized light tends to “leak”. From such a point, it is preferable to keep the extinction ratio as high as possible.

(Measurement method of extinction ratio)
The extinction ratio can be measured by the polarization state detector 22 shown in FIG. Referring to FIG. 2, a polarization state detection unit 22 is installed on the light emission side of the element. The polarizing plate 31 uses a material that transmits predetermined linearly polarized light, and the polarizing plate 32 uses a material that transmits linearly polarized light rotated by 90 °. The intensity of the predetermined linearly polarized light out of the light that enters the element and exits from the element can be measured by the photodetector 33, and the intensity of the linearly polarized light rotated 90 ° is detected by the photodetector 34. Can be measured. Then, the light intensity measured by the light detector 34 (**, that is, the intensity of linearly polarized light rotated by 90 °) with respect to the light intensity measured by the light detector 33 (**, that is, the intensity of predetermined linearly polarized light). The extinction ratio can be obtained by calculating the ratio.

(Preferred embodiment of maintaining “extinction ratio”)
The signals obtained by the photodetectors 33 and 34 are constantly monitored by a voltage control unit, which will be described later, so that the extinction ratio calculated from the obtained signals is maintained at or above a predetermined value **. By applying a voltage to the element, the extinction ratio can always be kept at a high value.

(Basic aspect)
FIG. 1 is a schematic cross-sectional view showing a polarization switching element 10 of one aspect (basic aspect) according to an aspect of the present invention. Referring to FIG. 1, a polarization switching element 10 is provided with transparent electrodes 13 and 14 made of, for example, ITO (indium-tin oxide) on two transparent substrates 11 and 12 made of, for example, low expansion glass. A polyimide film or SiO oblique deposition is formed thereon as the liquid crystal alignment films 15 and 16. The transparent substrates 11 and 12 on which the liquid crystal alignment films 15 and 16 are formed have a liquid crystal injection port (not shown) with a spacer member 19 made of glass beads or the like interposed therebetween so as to be uniform in a target gap. ) Is sealed with a sealing material 17 made of, for example, a UV curable adhesive, and then a liquid crystal material 21 such as a PSS (polarization shielding smectic) liquid crystal material or a ferroelectric liquid crystal material is injected from a liquid crystal injection port. The liquid crystal injection port is cured and sealed with an adhesive such as an epoxy adhesive.

  The polarization switching element 10 includes a polarization state detection unit 22 that detects the polarization state of outgoing light, a feedback unit 24 that feeds back a signal from the polarization state detection unit 22, and an electrode based on a signal from the feedback unit 24. A voltage control unit 23 for controlling the voltage applied to 13 and 14 is provided.

  The polarization switching element 10 configured as described above transmits incident linearly polarized light as it is when no voltage is applied between the transparent electrodes 13 and 14, and changes the polarization direction of the incident linearly polarized light when a predetermined voltage is applied. Rotate 90 ° to transmit, thereby acting as a polarization switch. At this time, since PSS liquid crystal or ferroelectric liquid crystal is used as the liquid crystal, switching can be performed at high speed. At this time, the polarization state of the emitted light is detected by the polarization state detection unit 22, and the signal is input to the voltage control unit 23 by the feedback unit 24. Based on the signal, the voltage control unit 23 is connected to the electrode 13. , 14, a stable response can be achieved.

(Polarization state detector)
FIG. 2 is a block diagram illustrating a configuration of the polarization state detection unit (sensor) 22. The polarization state detection unit 22 includes a polarizing plate 31 that transmits light in the first linear polarization state, a polarizing plate 32 that transmits light in the second linear polarization state rotated 90 ° with respect to the first linear polarization state, A light detector 33 for detecting the light intensity transmitted through the plate 31 and a light detector 34 for detecting the light intensity transmitted through the polarizing plate 32 are provided, and signals from the light detectors 33 and 34 are fed back to the voltage control unit 23. Is done.

  As the photodetectors 33 and 34, for example, devices described in Applied Physics Handbook, edited by Japan Society of Applied Physics, Maruzen, 2nd edition, pages 36 to 40 can be used.

  For example, when light in the first linear polarization state is incident on the polarization state detection unit 22, the light passes through the polarizing plate 31, and the transmitted light is detected by the photodetector 33. To the voltage control unit 23. On the other hand, when light in the second linearly polarized state is incident, it passes through the polarizing plate 32, the transmitted light is detected by the photodetector 34, and the signal is sent to the voltage controller 23 via the feedback means 24. It is done.

(Voltage control unit)
FIG. 3 is a block diagram illustrating a configuration of the voltage control unit 23. The voltage control unit 23 includes a sensor signal detection unit 41 input via a feedback unit 24 from the polarization state detection unit (sensor) 22, a voltage output unit 42, an input device 43, and a control unit 44. The input device 43 is a device for inputting a signal for designating the polarization state of the emitted light. The control unit 44 determines the voltage to be applied to the electrodes 13 and 14 based on the designated signal input from the input device 43 and the signal from the sensor signal detection unit 41, and sends a command signal to the voltage output unit 42. . The voltage output unit 42 has a power source, controls the output voltage from the power source based on a command signal from the control unit 44 **, and applies a predetermined voltage to the electrodes 13 and 14.

  The sensor signal detection unit 41 includes an amplification circuit and the like, amplifies the signal from the polarization state detection unit 22, and outputs the amplified signal to the control unit 44. When the signals from the light detection units 33 and 34 are sufficiently large, the signal from the light detection units 33 and 34 is input to the control unit 44 without the signal amplification by the sensor signal detection unit 41. It may be configured.

(Control part)
FIG. 4 is a block configuration diagram of the control unit 44. The control unit 44 includes a microcomputer and includes a CPU 51, an input unit 52, an output unit 53, and a storage unit 54. The storage unit 54 also includes a storage area 55 for storing a control program, a storage area 56 for storing a first voltage value that is a voltage applied to obtain the first polarization state, and a second polarization state. A storage area 57 is provided for storing a second voltage value that is a voltage to be applied.

  The control unit 44 operates as follows. For example, a signal designating the first polarization state is input to the input unit 52 from the input device 43. In accordance with the control program 55, the CPU 51 reads the signal input to the input unit 52 and the first voltage value stored in the storage unit 54, and outputs it from the output unit 53 to the voltage output unit 42. The voltage output unit 42 applies a voltage having a first voltage value to the electrodes. The sensor signal detected by the polarization state detection unit is input from the input unit 52, and the CPU adjusts the voltage output unit 42 by outputting an adjustment signal from the output unit 53 so that the sensor signal is maximized. Thereby, a stable first polarization state can be obtained. For example, a signal specifying the second polarization state is input to the input unit 52 from the input device 43. In accordance with the control program 55, the CPU 51 reads the signal input to the input unit 52 and the second voltage value stored in the storage unit 54, and outputs it from the output unit 53 to the voltage output unit 42. The voltage output unit 42 applies a voltage having a second voltage value to the electrodes. The sensor signal detected by the polarization state detection unit is input from the input unit 52, and the CPU adjusts the voltage output unit 42 by outputting an adjustment signal from the output unit 53 so that the sensor signal is maximized. Thereby, a stable second polarization state can be obtained.

(Operation of polarization switching element)
The operation of the polarization switching element according to the embodiment shown in FIG. 1 will be described with reference to FIGS.

  Referring to FIG. 5, light 60 in the first polarization state (linearly polarized light 61) is incident from the substrate 12 side. For example, a signal designating the first polarization state is input to the input unit 52 from the input device 43 of the voltage control unit 23. In accordance with the control program 55, the CPU 51 reads the signal input to the input unit 52 and the first voltage value stored in the storage unit 54, and outputs it from the output unit 53 to the voltage output unit 42. The voltage output unit 42 applies a voltage having a first voltage value to the electrodes. The sensor signal detected by the polarization state detection unit is input from the input unit 52, and the CPU adjusts the voltage output unit 42 by outputting an adjustment signal from the output unit 53 so that the sensor signal is maximized. Thereby, a stable first polarization state (linearly polarized light 63) can be obtained.

  With reference to FIG. 6, for example, a signal designating the second polarization state is input to the input unit 52 from the input device 43. In accordance with the control program 55, the CPU 51 reads the signal input to the input unit 52 and the second voltage value stored in the storage unit 54, and outputs it from the output unit 53 to the voltage output unit 42. The voltage output unit 42 applies a voltage having a second voltage value to the electrodes. The sensor signal detected by the polarization state detection unit is input from the input unit 52, and the CPU adjusts the voltage output unit 42 by outputting an adjustment signal from the output unit 53 so that the sensor signal is maximized. Thereby, a stable second polarization state (linearly polarized light 65) can be obtained.

(Stable response)
In the embodiment of FIG. 1 described above, there is a polarization state detection means for detecting the polarization state of the light transmitted through the liquid crystal, and the voltage adjusted by the voltage application means is applied to the liquid crystal by the feedback means by the feedback signal. Therefore, there is an effect that a stable response can be made.

(Liquid crystal material)
Unless it is contrary to the meaning of this invention, the liquid-crystal material which can be used for the element of this invention, etc. is not restrict | limited. In general, the response speed of a liquid crystal affects the switching speed of a polarization switching element using the liquid crystal. From the viewpoint of this switching speed, for example, it is preferable to use a PSS liquid crystal or a ferroelectric liquid crystal as will be described later rather than a TN liquid crystal.

(Ferroelectric liquid crystal)
Unless it is contrary to the gist of the present invention, the ferroelectric liquid crystal material usable for the element of the present invention is not particularly limited. From the viewpoint of response speed, the following ferroelectric liquid crystal materials can be preferably used.

(Elements using PSS liquid crystal or ferroelectric liquid crystal)
As described above, in the polarization switching element according to this aspect, it is preferable to use PSS liquid crystal or ferroelectric liquid crystal as the liquid crystal material because the response speed of the liquid crystal is increased. In such an embodiment, there is an effect that the switching speed of the liquid crystal is further increased. By combining such an increase in the switching speed of the liquid crystal with the above-described “stable response” of the present invention, it can be switched at high speed and stably. For example, the present invention was applied to a three-dimensional display for viewing stereoscopic images. In this case, it is possible to obtain a synergistic effect that a stereoscopic image can be viewed with a natural feeling without a sense of incongruity for a viewer to alternately switch between a right-eye image and a left-eye image.

(projector)
Next, a projector using a polarization switching element according to an aspect of the present invention will be described with reference to FIG. FIG. 7 is a schematic cross-sectional view showing a projector according to an aspect of the present invention. This projector 60 is a projector using the above-described polarization switching element 10 according to the present invention, and includes a spatial light modulation element 61 for displaying an input video signal, an illumination optical system 62, and the polarization switching element 10. Optical unit 63, projection optical system 65 for enlarging and projecting light that has passed through optical unit 63 onto screen 64, modulation element driving circuit 66 for driving spatial light modulation element 61, and polarization for driving polarization switching element 10 And a switching element driving circuit 67.

  The projector 60 passes the light from the spatial light modulation element 61 through the polarization switching element 10. At this time, the polarization switching element 10 is operated by the polarization switching element driving circuit 67 in response to a signal from the modulation element driving circuit 66. Thereby, the polarization state is switched, and the light whose polarization state is switched is projected onto the screen. By viewing the projected image with glasses equipped with polarizing plates that transmit light of different polarization directions on the left and right, a stereoscopic image can be viewed. At this time, since the polarization switching element in this aspect switches at high speed and responds stably, a high-quality image can be seen.

(television)
Next, a television using a polarization switching element according to an aspect of the present invention will be described with reference to FIG. FIG. 8 is a block diagram (schematic configuration diagram) illustrating a television according to an aspect of the present invention. The television 70 is a television using the polarization switching element 10 according to the present invention described above, and drives the display device 71 for displaying an input video signal, the polarization switching element 10, and the display device 71. A display device driving circuit 72 and a polarization switching element driving circuit 73 for driving the polarization switching element 10 are provided.

  The television 70 passes light from the display device 71 through the polarization switching element 10. At this time, the polarization switching element 10 is operated by the polarization switching element driving circuit 73 in response to a signal from the display device driving circuit 72. Thereby, the polarization state is switched, and the right-eye image and the left-eye image are emitted in different polarization states alternately in a time division manner. A stereoscopic image can be seen by viewing the image with glasses equipped with polarizing plates that transmit light of different polarization directions on the left and right. At this time, since the polarization switching element in this aspect switches at high speed and responds stably, it is possible to view a video of good quality (for details of the principle of such a stereoscopic video television, for example, see Document: Special (Kaihei 9-219876 can be referred to).

(Liquid crystal element)
A liquid crystal element (liquid crystal switching element) according to an aspect of the present invention includes at least a pair of substrates and a liquid crystal material disposed between the pair of substrates.

(Liquid crystal material)
In the present invention, in order to apply the method of the present invention and as long as it is a liquid crystal material capable of constituting an electro-optic element having rotation of the optic axis direction according to the magnitude and / or direction of the applied electric field, Can be used without restriction. In the present invention, whether or not a certain liquid crystal material can be used can be confirmed by the following “Method for confirming rotation of optical axis direction”. In addition, whether or not a certain liquid crystal material can respond at a sufficient speed so that it can be suitably used from the viewpoint of enabling a predetermined high-speed response in the present invention is determined by the following “response time confirmation method”. Can be confirmed.

(Confirmation method of rotation of optical axis direction)
As a measurement method of the rotation of the optical axis direction as a liquid crystal element, when the liquid crystal element is placed in a crossed Nicol arrangement in which the polarizer is arranged perpendicular to the analyzer, the optical axis coincides with the absorption axis of the analyzer. The intensity of transmitted light is minimized. Accordingly, the angle at which the minimum intensity of transmitted light is obtained in the crossed Nicol arrangement is the angle of the optical axis direction. At this time, an electric field is not applied to the liquid crystal element. Using this as a reference angle, an electric field is applied to the liquid crystal element to find an angle at which the minimum intensity of the transmitted light amount in the crossed Nicols arrangement can be obtained. There is an angle at which the electric field is at its minimum intensity, and the angle at which the minimum intensity is obtained at an angle that deviates from the above-mentioned reference angle. When the magnitude or direction of the electric field is changed, the rotation angle is increased or decreased according to the amount of change. If it is seen, it can be confirmed that the optical axis direction is rotating. As an example of the apparatus for confirmation, it can be confirmed with the configuration of FIG. 13 as in the optical axis direction confirmation method.

(How to check response time)
When the rotation of the optical axis direction is seen in the liquid crystal element, the speed of this rotation corresponds to the response time. A liquid crystal element is arranged at an angle that minimizes the amount of transmitted light during the crossed Nicols arrangement in which the polarizer is arranged perpendicular to the analyzer, and an electric field is applied to the liquid crystal element. Since the optical axis direction is rotated by applying an electric field, the amount of transmitted light changes. Accordingly, the degree of change in the amount of transmitted light is the degree of change in rotation. When the amount of transmitted light in the state where no electric field is applied is 0%, and the amount of transmitted light which has been changed by applying the electric field and finally becomes a steady state is 100%, the amount of transmitted light is reduced by applying the electric field from the state where no electric field is applied. The time from 10% to 90% is the rise response time, and the time from when the electric field is applied to when the electric field is stopped and the amount of transmitted light is 90% to 10% is the fall response time. For example, in the PSS-LCD, both the rising response time and the falling response time are about 400 μs. As an example of the device for confirmation, it can be confirmed with the configuration shown in FIG. 13 as in the case of the “optical axis orientation confirmation method” described later.

(PSS-LCD)
The liquid crystal material that can be suitably used in the present invention is a PSS-LCD, that is, the initial molecular alignment in the liquid crystal material has a direction substantially parallel to the alignment processing direction, and the liquid crystal material is substantially In the absence of an externally applied voltage, it exhibits no spontaneous polarization at least perpendicular to the pair of substrates.

(Initial molecular arrangement)
In the present invention, in the initial molecular alignment (or direction) in the liquid crystal material, the major axis of the liquid crystal molecule has a direction substantially parallel to the alignment treatment direction with respect to the liquid crystal molecule. The fact that the major axis of the liquid crystal molecules has a direction substantially parallel to the alignment treatment direction can be confirmed, for example, in the following manner. In order to enable the liquid crystal device according to the present invention to exhibit desirable display performance, the angle (absolute value) between the rubbing direction and the alignment direction of the liquid crystal molecules measured by the following method is preferably 3 ° or less, More preferably it is 2 ° or less, in particular 1 ° or less. In a strict sense, it is known that when a polymer alignment film such as a polyimide film is rubbed, birefringence is induced in the outermost layer of the polyimide, thereby giving a slow axis. Furthermore, it is generally known that the major axis of liquid crystal molecules is aligned parallel to the slow axis. For almost all polymer alignment films, it is known that some angular deviation occurs between the rubbing direction and the slow axis. In general, the deviation is relatively small and can be about 1-7 degrees. However, this angular misalignment can be 90 degrees as in the case of polystyrene as an extreme example. Therefore, in the present invention, the angle between the rubbing direction and the alignment direction of the major axis (that is, the optical axis) of the liquid crystal molecules can be preferably 3 ° or less. At this time, the major axis of the liquid crystal molecules and the orientation direction of the slow axis provided in the polymer (polyisomide, etc.) and polymer alignment film by rubbing or the like are preferably 3 ° or less, more preferably 2 ° or less, In particular, it can be 1 ° or less.

  As described above, in the present invention, the alignment treatment direction refers to the direction of the slow axis (in the polymer outermost layer) that determines the alignment direction of the major axis of the liquid crystal molecules.

<Method of measuring initial molecular alignment state with respect to liquid crystal molecules>
In general, the long axis of the liquid crystal molecule coincides well with the optical axis. Therefore, when the liquid crystal panel is placed in a crossed Nicol arrangement in which the polarizer is arranged perpendicular to the analyzer, the intensity of the transmitted light is minimized when the optical axis of the liquid crystal is well aligned with the absorption axis of the analyzer. The direction of the initial alignment axis can be measured by a method in which the liquid crystal panel rotates in a crossed Nicols arrangement while measuring the intensity of transmitted light, thereby measuring the angle that gives the minimum intensity of transmitted light. .

<Method for measuring parallelism between liquid crystal molecule major axis direction and alignment treatment direction>
The rubbing direction is determined by a set angle, and the slow axis of the outermost layer of the polymer alignment film provided by rubbing is determined by the type of polymer alignment film, the film production method, the rubbing strength, and the like. Therefore, when the extinction position is provided parallel to the direction of the slow axis, it is confirmed that the molecular long axis, that is, the molecular optical axis is parallel to the direction of the slow axis.

(Spontaneous polarization)
In the present invention, in the initial molecular orientation, spontaneous polarization (similar to spontaneous polarization in the case of a ferroelectric liquid crystal) does not occur at least in the direction perpendicular to the substrate. In the present invention, “the initial molecular orientation that does not substantially provide spontaneous polarization is one in which spontaneous polarization does not occur” can be confirmed, for example, by the following method.

<Method of measuring the presence of spontaneous polarization perpendicular to the substrate>
When the liquid crystal in the liquid crystal cell has spontaneous polarization, particularly when spontaneous polarization occurs in the direction of the substrate in the initial state, that is, in the direction perpendicular to the electric field direction in the initial state (that is, when there is no external electric field), When a low frequency triangular wave voltage (approx. 0.1 Hz) is applied to the liquid crystal cell, the direction of spontaneous polarization is from the upward direction to the downward direction, with the polarity change of the applied voltage from positive to negative, or from negative to positive, or Invert from the downward direction to the upward direction. With such inversion, the actual charge is transported (ie, current is generated). Spontaneous polarization is reversed only when the polarity of the applied electric field is reversed. Therefore, a peak current appears as shown in FIG. The integral value of the peak current corresponds to the total charge to be transported, that is, the intensity of spontaneous polarization. If a non-peak current is observed in this measurement, the absence of spontaneous polarization reversal is directly evidenced by such a phenomenon. Furthermore, when a linear increase in current as shown in FIG. 10 is observed, the major axes of the liquid crystal molecules change continuously or continuously in their molecular orientation direction as the electric field strength increases. Is found. In other words, it has been found that in this case as shown in FIG. 27, the molecular orientation direction changes due to induced polarization or the like depending on the applied electric field strength.

(substrate)
The substrate that can be used in the present invention is not particularly limited as long as it can provide the above-mentioned specific “initial molecular orientation state”. In other words, in the present invention, a suitable substrate can be appropriately selected from the viewpoint of the usage or application of the LCD, its material and size, and the like.

(PSS-LCD material)
The PSS-LCD liquid crystal material that can be suitably used in the present invention is not particularly limited as long as it can give the above-mentioned specific “initial molecular alignment state”. In other words, in the present invention, a suitable liquid crystal material can be appropriately selected from the viewpoints of physical characteristics, electricity or display performance, and the like. For example, various liquid crystal materials (including various ferroelectric or non-ferroelectric liquid crystal materials) as exemplified in the literature can generally be used in the present invention. Specific preferred examples of such liquid crystal materials that can be used in the present invention include:

(Alignment film)
The alignment film that can be used in the present invention is not particularly limited as long as it can give the above-mentioned specific “initial molecular alignment state”. In other words, in the present invention, a suitable alignment film can be appropriately selected from the viewpoint of physical properties, electricity or display performance, and the like. For example, various alignment films as exemplified in the literature can generally be used in the present invention. Specific preferred examples of such alignment films that can be used in the present invention include:

Polymer alignment film: polyimide, polyamide, polyamide-imide Inorganic alignment film: SiO ₂ , SiO, Ta ₂ O ₅ , etc.

  In the present invention, as the above-mentioned substrate, liquid crystal material, and alignment film, as necessary, each item described in “Liquid Crystal Device Handbook” (1989) issued by Nikkan Kogyo Shimbun (Tokyo, Japan) It is possible to use corresponding materials, components or components.

(Other components)
Other materials, components, or components such as transparent electrodes, electrode patterns, spacers, and polarizing plates used to construct the liquid crystal switching element according to the present invention, unless they are contrary to the purpose of the present invention (ie, they are Is not particularly limited as long as the above-mentioned specific “initial molecular orientation state” can be provided). In addition, the method for manufacturing a liquid crystal switching element that can be used in the present invention is particularly limited, except that the liquid crystal switching element should be configured to provide the specific “initial molecular orientation state” described above. Not. For details on the various materials, components, or components used to construct the liquid crystal switching element, refer to the “Liquid Crystal Device Handbook” (1989) published by Nikkan Kogyo Shimbun (Tokyo, Japan) as necessary. Is possible.

(Means for realizing a specific initial orientation)
The means or measures for realizing such an alignment state are not particularly limited as long as it can realize the above-described specific “initial molecular alignment state”. In other words, in the present invention, means or measures for realizing a suitable specific initial orientation can be appropriately selected from the viewpoints of physical characteristics, electrical or display performance, and the like.

(Preferred means for providing initial orientation)
According to the knowledge of the present inventors, the above-mentioned suitable initial alignment uses the following alignment film (in the case of an alignment film formed by baking, the thickness is indicated by the thickness after baking) and a rubbing treatment. This can be easily realized. On the other hand, in a normal ferroelectric liquid crystal element, the thickness of the alignment film is 3,000 A (angstrom) or less, and the rubbing strength (that is, the rubbing push-in amount) is 0.3 mm or less.

  Thickness of alignment film: preferably 4,000 A or more, more preferably 5,000 A or more (particularly 6,000 A or more)

  Rubbing strength (ie, amount of rubbing indentation): preferably 0.3 mm or more, more preferably 0.4 mm or more (particularly 0.45 mm or more)

The above-mentioned orientation film thickness and rubbing strength can be measured, for example, by a method as described in Production Example 1 described later.

  In the present invention, a PSS-LCD having another configuration described in Japanese Patent Application No. 2007-28182 can also be suitably used.

Production Example 1
Using a commercially available FLC mixture material (Merck: ZLI-4851-100), a liquid crystalline photopolymerization material (Dainippon Ink Chemical Co., Ltd .: UCL-001), and a polymerization initiator (Merck: Darocur 1173) A liquid crystal device was assembled based on Japanese Patent Application Laid-Open No. 11-21554 (Japanese Patent Application No. 09-174463). The mixture had 93 wt% ZLT-4851-100 FLC mixture, 6 wt% UCL-001, and 1 wt% Darocur 1173.

  The substrate used here was a glass substrate having an ITO film thereon (borosilicate glass commercially available from Nono Loa Inc., thickness 0.7 mm, size: 50 mm × 50 mm).

  A polyimide alignment film was formed by applying a polyimide alignment material by using a spin coater, then pre-baking the resulting film, and finally baking the resulting product in a clean oven. For details of general industrial procedures to be used here, reference can be made to the document “Liquid Crystal Display Techniques” Sangyo Tosho (1996, Tokyo), Chapter 6, as necessary.

For the liquid crystal molecular alignment film, RN-1199 (Nissan Chemical Industries) was used as a pretilt angle alignment material of 1 to 1.5 °. The thickness of the alignment layer as a hardened layer was set to 4,500 A to 5,000 A. The surface of the cured alignment layer was rubbed with a rayon cloth (trade name 19RY, manufactured by Yoshikwa Kako) so as to form an angle of 30 degrees with respect to the center direction of the substrate as shown in FIG . The pushing amount of rubbing was 0.5 mm for both substrates.

<Rubbing conditions>
Rubbing push-in amount: 0.5mm
Number of rubbing: once Stage movement speed: 2 mm / sec Roller rotation frequency: 1000 rpm (R = 40 mm)

As the spacer, silicon dioxide particles having an average particle diameter of 1.6 microns are used. The finished cell gap was 1.8 microns as measured. The mixed material was injected into the cell at an isotropic temperature of 110 ° C. After injecting the mixed material, the ambient temperature was controlled, and the mixture was gradually cooled at a rate of 2 ° C. per minute until the mixed material showed a ferroelectric liquid crystal phase (40 ° C.). After that, when the panel was sufficiently cooled to room temperature by natural cooling, a triangular wave voltage of +/− 10 V and a frequency of 500 Hz was applied to the panel for 10 minutes (by using a function generator manufactured by NF Circuit Block, product name: WF1946F). ). After voltage application for 10 minutes, irradiation with 365 nm ultraviolet light was performed while maintaining the same voltage application (by using UVP UV light, trade name: UVL-56). The irradiation condition was 5,000 mJ / cm ² . For details of general industrial procedures to be used here, reference can be made to the document “Liquid Crystal Display Techniques” Sangyo Tosho (1996, Tokyo), Chapter 6, as necessary.

  For details on general industrial procedures to be used here, it is possible to refer to the literature “The Optics of Thermotropic Liquid Crystals”, Taylor and Francis: 1998, London, UK; Chapter 8 and Chapter 9. .

Production Example 2
For the liquid crystal molecular alignment film, RN-1199 (Nissan Chemical Industries) was used as a pretilt angle alignment material of 1 to 1.5 °. The thickness of the alignment layer as a hardened layer was set to 6,500 A to 7,000 A. The surface of the cured alignment layer was rubbed with a rayon cloth so as to form an angle of 30 degrees with respect to the center line of the substrate as shown in FIG . The pushing amount of rubbing was 0.5 mm for both substrates. As the spacer, silicon dioxide particles having an average particle diameter of 1.6 microns are used. The finished cell gap was 1.8 microns as measured. In this cell, a commercially available FLC mixture material (Merck: ZLI-4851-100) was injected at 110 ° C. isotropic temperature. After injecting the mixed material, the ambient temperature was controlled, and the mixture was gradually cooled at a rate of 1 ° C. per minute until the FLC material showed a ferroelectric liquid crystal phase (40 ° C.). In this slow cooling process (from 75 ° C. to 40 ° C.) from the smectic A phase to the chiral smectic C phase, a triangular wave voltage of +/− 2 V and a frequency of 500 Hz was applied. After the panel temperature reached 40 ° C., the applied triangular wave voltage was raised to +/− 10V. After that, it was continuously applied by natural cooling until the panel temperature reached room temperature. The initial molecular orientation direction of this panel was the same as the rubbing direction in most fields of view, however, in a very limited plane, it showed +/− 20 degrees and deviated from the rubbing angle.

  In this production example, it was found that applying too much voltage at the slow cooling stage reduces the initial FLC molecular orientation. For example, when a voltage of about +/− 5 V is applied at a temperature showing a smectic A phase, streak-like alignment defects are shown along the rubbing direction. Once this type of defect occurs, the chiral smectic C phase (ferroelectric liquid crystal phase) does not eliminate the defect. Although voltage application at slow cooling is effective, however, the conditions should be strictly controlled. In these production examples, 1 V / μm or less in smectic A, 1.5 V / μm or less from the smectic A phase to 10 ° C. below the transition temperature from the smectic A phase to the chiral SmC phase, and 20 ° C. below the phase transition temperature. It has been shown that 5 V / μm or less up to 7.5 V / μm is preferable in order to obtain good results in a temperature range lower than this.

Production Example 3
For the liquid crystal molecular alignment film, RN-1199 (Nissan Chemical Industries) was used as a pretilt angle alignment material of 1 to 1.5 °. The thickness of the alignment layer as a hardened layer was set to 6,500 A to 7,000 A. The surface of the cured alignment layer was rubbed with a rayon cloth so as to form an angle of 30 degrees with respect to the center line of the substrate as shown in FIG. The pushing amount of rubbing was 0.6 mm for both substrates. As the spacer, silicon dioxide particles having an average particle diameter of 1.8 microns are used. The finished cell gap was measured to be 2.0 microns. In this cell, the literature Molecular Crystals and The liquid crystals; “Naphthalene Base Ferroelectric liquid crystal and Its Electro Optical Properties”; Vol. 243, pp. 77-pp. 90, (1994) was injected at 130 ° C. isotropic temperature. The helical pitch of this liquid crystal material at room temperature was 2.5 mm.

  After injecting the liquid crystal material, the ambient temperature was controlled and gradually cooled from 130 ° C. to 50 ° C. at which the ferroelectric liquid crystal phase was exhibited at a rate of 1 ° C. per minute. In this slow cooling process (from 90 ° C. to 50 ° C.) from the smectic A phase to the chiral smectic C phase, a triangular wave voltage of +/− 1 V and a frequency of 500 Hz was applied. After the panel temperature reached 50 ° C., the applied triangular wave voltage was raised to +/− 7V. After that, it was continuously applied by natural cooling until the panel temperature reached room temperature. The initial molecular orientation direction of this panel was the same as the rubbing direction in most viewing planes. Only a small and small surface showed a deviation of +/− 17 degrees from the rubbing angle. The electrical response measurement of this panel showed analog gradation switching as the average of a field of view range of about 20 times in the polarization microscope measurement. In this production example, the applied voltage during slow cooling is not limited to a triangular wave, and it is also found that a sine wave or a rectangular wave is effective for stabilizing the initial molecular orientation parallel to the rubbing direction. It was.

  The results obtained in the above production examples are summarized in Table 1 below.

Summary of production examples

  The configurations, arrangement relationships, and the like described in the above embodiments are merely examples that can be understood and implemented by the present invention. Therefore, the present invention is not limited to the described embodiment, and can be modified in various forms without departing from the scope of the technical idea shown in the claims.

  As described above, the polarization switching element of the present invention has an excellent feature that a stable response can be easily obtained. For this reason, the polarization switching element of this invention can provide a suitable extinction ratio easily, for example.

  The polarization switching element of the present invention can be suitably used as a polarization switching element for viewing stereoscopic images based on the above characteristics (that is, stable response and / or suitable extinction ratio). Therefore, it can be suitably used as a projector and a television.

It is a schematic cross section which shows the polarization switching element which concerns on the aspect of this invention. It is a block block diagram of the polarization state detection part of the polarization switching element which concerns on the aspect of this invention. 3 is a block configuration of a voltage control unit of a polarization switching element according to an aspect of the present invention. It is a block block diagram of the control part of the voltage control part of the polarization switching element which concerns on the aspect of this invention. It is a figure explaining operation | movement of a polarization switching element. It is a figure explaining operation | movement of a polarization switching element. It is a schematic cross section showing a projector according to an aspect of the present invention. It is a schematic cross section showing a television according to an aspect of the present invention. It is a graph which shows the example of the polarization switching current during the molecular orientation switching under a triangular wave voltage application. 6 is a graph showing an example of polarization switching peak current during switching in the case of a conventional SSFLCD panel. It is a schematic diagram for demonstrating the c-director profile of PS-V-FLCD. It is a schematic diagram for demonstrating the rubbing angle of a laminated panel. It is a model perspective view which shows the structure of an example of an element suitable for the exact measurement of an optical axis direction which can be used in this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Polarization switching element 11,12 Transparent substrate 13,14 Transparent electrode 15,16 Liquid crystal alignment film 17 Seal material 19 Spacer member 21 Liquid crystal material 22 Polarization state detection part (sensor)
Reference Signs List 23 Voltage control unit 24 Feedback means 31, 32 Polarizing plate 33, 34 Photo detector 41 Sensor signal detection unit 42 Voltage output unit 43 Input device 44 Control unit 60 Projector 70 Television

Claims (10)

A pair of transparent substrates having transparent electrodes on each surface;
A liquid crystal material disposed between the pair of transparent substrates;
Voltage applying means for applying a voltage to the liquid crystal material through the pair of transparent electrodes;
A polarization switching element having at least polarization state detection means provided on the light exit side of the pair of transparent substrates;
A polarization switching element, wherein a voltage applied from the voltage application unit to the liquid crystal material is adjusted based on feedback of a signal from the polarization state detection unit to the voltage application unit.   The polarization switching element according to claim 1, wherein the liquid crystal material is a polarization-shielding smectic liquid crystal or a ferroelectric liquid crystal.   A voltage is applied to the liquid crystal material to change the first polarization state of light incident from the light incident side of the pair of transparent substrates to a second polarization state different from the first polarization state. 3. The polarization switching element according to 1 or 2.   4. The polarization switching element according to claim 3, wherein light applied in the first polarization state is maintained and output by adjusting a voltage applied to the liquid crystal material. 5.   5. The polarization switching element according to claim 3, wherein the first polarization state is linear polarization, and the second polarization state is linear polarization obtained by rotating a vibration plane of the linear polarization by 90 °.   The polarization switching element according to claim 1, wherein the polarization state detection unit includes at least one polarization unit and a photodetector that detects the intensity of light transmitted through the polarization unit.   The voltage application means is detected by a sensor signal detection means for detecting a signal from the polarization state detection means, an input means for inputting a command for designating the polarization state, and a command inputted by the input means and the sensor signal detection means. 7. A control means for determining a voltage to be applied to the liquid crystal based on a signal that has been applied, and a voltage output means for applying a voltage to the transparent electrode based on a signal from the control means. Polarization switching element.   The control means includes storage means; when the light having the first polarization state is output while maintaining the storage means, the signal intensity from the polarization state detection means is maximized. 8. The polarization switching element according to claim 7, wherein a control program for determining a voltage value to be applied to the transparent electrode and sending a signal for outputting the voltage to the voltage output means is stored. At least a spatial light modulation element for displaying an input video signal, an illumination optical system, an optical unit, a projection optical system for enlarging and projecting light that has passed through the optical unit, and a spatial light modulation element Including a projector;
The optical unit includes a polarization switching element; and
A pair of transparent substrates having a transparent electrode on each surface; a liquid crystal material disposed between the pair of transparent substrates; a voltage applying means for applying a voltage to the liquid crystal material via the pair of transparent electrodes; A polarization switching element having at least a polarization state detection unit provided on the light exit side of the pair of transparent substrates; the voltage based on feedback of a signal from the polarization state detection unit to the voltage application unit; The projector according to any one of claims 1 to 8, wherein a voltage applied to the liquid crystal material from an application unit is adjusted. A television including at least a display device for displaying an input video signal and a polarization switching element;
The polarization switching element is
A pair of transparent substrates having a transparent electrode on each surface; a liquid crystal material disposed between the pair of transparent substrates; a voltage applying means for applying a voltage to the liquid crystal material via the pair of transparent electrodes; A polarization switching element having at least a polarization state detection unit provided on the light exit side of the pair of transparent substrates; the voltage based on feedback of a signal from the polarization state detection unit to the voltage application unit; The television according to any one of claims 1 to 8, wherein a voltage applied to the liquid crystal material from an application unit is adjusted.

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