JP2005091763A - Optical deflection device, image display device, and optical deflection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform stable optical deflection operation for a long period of time in an optical deflection device. <P>SOLUTION: In the optical deflection device, an electric field direction of a normal electric field applied in a direction nearly orthogonal to the normal direction of a substrate surface and an optical deflection direction is switched to a liquid crystal layer packed between a pair of transparent substrates, homeotropically aligned and capable of forming a chiral smectic C phase. In order to shorten switching time of optical deflection directions, an intense electric field is applied at an optional time overlapping the time when the normal electric field is applied by temporarily applying the intense electric field having electric field intensity higher than that of the normal electric field to the liquid crystal layer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical deflection apparatus, an image display apparatus, and an optical deflection method.

Definition

  In this specification, “light deflecting element” refers to whether the optical path of light is deflected by an external electric signal, that is, the outgoing light is shifted in parallel to the incident light, or is rotated at a certain angle. Alternatively, it means an optical element capable of switching the optical path by combining both of them. In this description, the magnitude of the shift is referred to as “shift amount” with respect to the optical path deflection due to the parallel shift, and the rotation amount is referred to as “rotation angle” with respect to the optical path deflection due to rotation. The “light deflecting device” means a device that includes such a light deflecting element and deflects the optical path of light.

  The “pixel shift element” is an image display element in which a plurality of pixels that can control light according to image information is two-dimensionally arranged, a light source that illuminates the image display element, and an image displayed on the image display element. An optical member for observing the pattern, and a light deflecting means for deflecting the optical path between the image display element and the optical member for each of a plurality of subfields obtained by temporally dividing the image field. Light in an image display device that displays an image pattern in which the display position is shifted in accordance with the deflection of the optical path for each subfield by the light deflecting means to increase the apparent number of pixels of the image display element. Means deflection means. Therefore, basically, it can be said that the optical deflection element and the optical deflection device defined above can be applied as the optical deflection means.

  For example, by using a liquid crystal composed of a chiral smectic C phase, compared to a conventional optical deflection element, the high cost, the size of the apparatus, the light loss, and the optical noise due to the complicated structure are improved. In addition, there is a technique that enables high-speed response by improving dullness of response in a conventional smectic A liquid crystal or nematic liquid crystal (for example, see Patent Document 1).

  In addition, the orientation direction of the liquid crystal molecules is switched by switching the direction of the electric field applied to the liquid crystal layer capable of forming a chiral smectic C phase having homeotropic alignment, thereby switching the tilt direction of the optical axis with respect to the layer normal of the liquid crystal layer. When switching the outgoing optical path for incident light, the electric field strength is such that the layer plane of the smectic layer structure formed in the liquid crystal layer is always parallel to the substrate surface within a certain time region when the applied electric field strength is constant. There is a technique for setting the frequency and voltage value of an alternating voltage whose time change is a rectangular wave (see, for example, Patent Document 2).

JP 2002-328402 A JP 2003-287679 A

  Incidentally, in order to shorten the switching time of the light deflection direction, it is preferable to drive with an electric field as strong as possible (strong electric field).

  However, when driving with a strong electric field is continued, alignment defects may occur in the liquid crystal layer.

  For this reason, it is necessary to continuously drive with a relatively low electric field that is necessary and sufficient for performing an optical deflection operation with a target response time.

  However, depending on the characteristics of the liquid crystal material forming the liquid crystal layer, the domain in the liquid crystal layer may gradually increase due to continuous driving with a relatively low electric field, and the alignment state in the liquid crystal layer may eventually be disturbed. . When disorder occurs in the alignment state in the liquid crystal layer, light scattering and depolarization occur in the liquid crystal layer, and the MTF in the optical deflecting device decreases.

  It has been found that such a MTF lowering phenomenon does not occur when a relatively strong electric field is applied, or recovers even if it occurs. However, when continuously driven by a strong electric field, the alignment in the liquid crystal layer is as described above. A vicious circle in which the disturbance of the state and the load on the power supply increase occurs, which is not preferable.

  An object of the present invention is to perform a stable light deflection operation over a long period of time.

An optical deflecting device according to claim 1 comprises a pair of transparent substrates,
A liquid crystal layer capable of forming a chiral smectic C phase having a homeotropic alignment filled between the substrates, and a normal electric field for deflecting light incident on the liquid crystal layer is applied to the liquid crystal layer on the surface of the substrate. An electric field applying means for applying in a direction substantially perpendicular to the normal direction and the light deflection direction, an electric field direction switching means for switching the electric field direction of the normal electric field, and a strong electric field having a larger electric field strength than the normal electric field to the liquid crystal layer And an electric field control means for applying at an arbitrary timing overlapping the timing at which the normal electric field is applied.

  Accordingly, the MTF is prevented from being lowered due to the disorder of the alignment state in the liquid crystal layer, which is likely to be generated by applying a strong electric field in order to shorten the switching time of the light deflection direction, and the normal electric field is applied at the time of the light deflection operation. By applying a strong electric field at an arbitrary timing that overlaps with each other, it is possible to suppress the occurrence of alignment defects that occur when a strong electric field is continuously applied without hindering switching of the electric field direction.

  According to a second aspect of the present invention, in the optical deflecting device according to the first aspect, the electric field applying means uses a rectangular wave-shaped AC electric field having the same absolute value and time width of the electric field strength in each polarity as a normal electric field. Then, the electric field control means applies a rectangular wave-shaped AC electric field having the same time width as the normal electric field but different in absolute value of electric field strength.

  Therefore, the offset between the normal electric field and the strong electric field is zero, the duty ratio is 50%, and even when the electric field direction is switched, the strong electric field is applied over the entire liquid crystal layer after switching, so that a relatively strong intensity can be obtained. It is possible to converge amplification of alignment disorder generated in the liquid crystal layer in switching of the electric field direction when a small electric field is continuously applied.

  According to a third aspect of the present invention, in the optical deflecting device according to the first aspect, the electric field applying means converts the alternating electric field having a rectangular wave shape in which the absolute value and the time width of the electric field strengths in the positive and negative polarities are equal to each other into the normal electric field. The electric field control means applies the strong electric field by increasing the electric field strength of the normal electric field continuously or stepwise until the electric field direction once switched is switched to the next.

  Therefore, the electric field strength immediately after switching the electric field direction is set to a relatively low electric field strength comparable to the normal electric field strength, so that the change amount of the electric field is set to be relatively small, and thereafter the electric field strength is increased continuously or stepwise. By doing so, it is possible to converge amplification of the disorder of the alignment state generated in the liquid crystal layer in the switching of the electric field direction when the electric field having a relatively low intensity is continuously applied.

  According to a fourth aspect of the present invention, in the optical deflecting device according to the first, second, or third aspect, the electric field control means applies the strong electric field at a randomly generated timing.

  By the way, when a strong electric field is applied at a constant period, there is a concern that a periodic flow occurs in the liquid crystal layer. When such a periodic flow occurs, there is a concern that the flows interfere with each other and deteriorate the alignment state in the liquid crystal layer.

  Therefore, it is possible to prevent the alignment state in the liquid crystal layer from being deteriorated due to the periodic flow that can be generated in the liquid crystal layer by applying a strong electric field at a constant period.

  According to a fifth aspect of the present invention, in the optical deflecting device according to the first, second, third, or fourth aspect, the electric field control means adjusts the application timing, the electric field direction, and the electric field strength, thereby averaging the vectors in unit time. The strong electric field having a value of substantially zero is applied.

  By the way, when a strong electric field is applied at an arbitrary timing, if the direction of the strong electric field is biased to one side, the charge distribution such as charges and ions injected into the liquid crystal layer is biased with time, and the transient at the time of electric field inversion occurs. There are cases where light scattering is deteriorated, alignment defects are generated, and the performance life of the liquid crystal material is shortened.

  Therefore, by setting the arbitrary timing of applying a strong electric field, the electric field direction and the electric field strength so that the average value of the electric field vector applied to the liquid crystal layer within a unit time becomes substantially zero, the liquid crystal The DC balance of charges in the layer is maintained, and deterioration of transient light scattering and occurrence of orientation defects during electric field inversion can be prevented.

  According to a sixth aspect of the present invention, in the optical deflecting device according to any one of the first to fifth aspects, the electric field control means has a direction of the electric field with respect to a switching cycle until the electric field direction once switched is switched to the next. The strong electric field is applied after a normal electric field has been applied for a half period or more after switching.

  By the way, when a strong electric field is applied in the direction of the other electric field from a state in which a strong electric field is applied in the direction of one electric field, the amount of change in the electric field becomes very large. When the amount of change in the electric field is very large, the electrical load on the liquid crystal layer and the power source becomes large.

  Therefore, after applying a strong electric field in one electric field direction, applying a large electric field strength in the other electric field direction after applying a normal electric field for at least a half cycle or more, the amount of change in electric field can be reduced. It can be set small, and the electrical load on the liquid crystal layer and the power source can be reduced.

  A seventh aspect of the present invention is the optical deflection apparatus according to any one of the first to sixth aspects, wherein the electric field control means applies an electric field set to an absolute value of 200 V / mm or more as the strong electric field. .

  Therefore, by temporarily applying a strong electric field sufficiently larger than the normal electric field, disorder of the alignment state in the liquid crystal layer can be reliably suppressed practically.

  According to an eighth aspect of the present invention, in the optical deflecting device according to any one of the first to seventh aspects, the electric field control means is a saturation that is an absolute value of an electric field strength at which the tilt angle of the optical axis is saturated in the liquid crystal layer. An electric field set to an absolute value of 5 times or more with respect to the electric field intensity Ec (V / mm) is applied as the strong electric field.

  Therefore, when the electric field strength at a fixed magnification based on the saturation electric field strength, which is a characteristic value that reflects the physical properties of the liquid crystal material, is applied, the behavior of the electric field strength at a certain electric field strength varies depending on the type of liquid crystal material. Even so, it is possible to reliably suppress the decrease in MTF without being influenced by the difference in the liquid crystal material.

According to a ninth aspect of the present invention, in the optical deflecting device according to any one of the first to eighth aspects, the electric field control means sets the absolute value of the spontaneous polarization of the liquid crystal layer to Ps (nC / cm ² ), the strong intensity. When the absolute value of the electric field is E (V / mm), an electric field set so that the value of Ps × E is 10,000 (μN / cm ² ) or more is applied as the strong electric field.

  Therefore, by defining the product of spontaneous polarization and electric field strength (value proportional to the electrical driving force acting on the liquid crystal molecules), which is a characteristic value reflecting the physical properties of the liquid crystal material, Even if the behavior of the electric field strength with respect to the electric field is different, the MTF reduction can be reliably suppressed without being influenced by the difference in the liquid crystal material.

  A tenth aspect of the present invention is the light deflection apparatus according to any one of the first to ninth aspects, further comprising an increase / decrease detecting means for detecting an increase / decrease in a light scattering amount or a decrease in MTF value in the liquid crystal layer, The electric field control means applies the strong electric field when an increase in the amount of light scattering or a decrease in the MTF value is detected.

  Here, the light scattering amount and the MTF amount may differ depending on the use environment such as the environmental temperature where the light deflector is installed. Therefore, if a strong electric field is applied at an arbitrary timing, it is possible to effectively suppress a decrease in MTF, but there is also a possibility that a side effect due to the application of the strong electric field may occur.

  Therefore, by detecting an increase or decrease in the amount of light scattering or the decrease in MTF value in the liquid crystal layer and temporarily applying a strong electric field at an arbitrary timing when an increase in the amount of light scattering or MTF decrease is detected. In addition, the timing of the application operation of the strong electric field can be suppressed to the minimum necessary.

  An image display device according to an eleventh aspect of the present invention is an image display element in which a plurality of pixels capable of controlling light according to image information are two-dimensionally arranged, illumination means for illuminating the image display element, and the image An optical device for observing an image pattern displayed on the display element; display drive means for driving the image display element in units of a plurality of subfields obtained by temporally dividing the image field; and each pixel of the image display element The optical deflecting device according to any one of claims 1 to 10, wherein an electric field applying unit provided in the optical deflecting device is 30 Hz or more and 100 Hz or less. A rectangular wave AC electric field having a frequency set to be applied to the liquid crystal layer.

  Therefore, it is possible to drive the optical deflecting device at a frequency at which the MTF lowering hardly occurs and at a frequency at which flicker is not generated.

  The light deflection method of the invention described in claim 12 is directed to a liquid crystal layer capable of forming a chiral smectic C phase having a homeotropic alignment filled between a pair of transparent substrates, the substrate surface with respect to the liquid crystal layer. In an optical deflecting device that switches the electric field direction of a normal electric field that deflects incident light that is applied in a direction substantially perpendicular to the normal direction and the optical deflection direction, a strong electric field having a larger electric field strength than the normal electric field Is applied at an arbitrary timing overlapping the timing at which the normal electric field is applied to the liquid crystal layer.

  Accordingly, the MTF is prevented from being lowered due to the disorder of the alignment state in the liquid crystal layer, which is likely to be generated by applying a strong electric field in order to shorten the switching time of the light deflection direction, and the normal electric field is applied at the time of the light deflection operation. By applying a strong electric field at an arbitrary timing that overlaps with each other, it is possible to suppress the occurrence of alignment defects that occur when a strong electric field is continuously applied without hindering switching of the electric field direction.

  According to a thirteenth aspect of the present invention, in the optical deflection method according to the twelfth aspect, when the normal electric field is applied, an alternating electric field having a rectangular wave shape in which the absolute value of the electric field intensity in each polarity is equal to the time width is applied to the normal electric field. When applying the strong electric field, a rectangular wave AC electric field having the same time width as that of the normal electric field but a different absolute value of the electric field intensity was applied.

  Therefore, the offset between the normal electric field and the strong electric field is zero, the duty ratio is 50%, and even when the electric field direction is switched, the strong electric field is applied over the entire liquid crystal layer after switching, so that a relatively strong intensity can be obtained. It is possible to converge amplification of alignment disorder generated in the liquid crystal layer in switching of the electric field direction when a small electric field is continuously applied.

  A fourteenth aspect of the present invention is the optical deflection method according to the twelfth aspect of the present invention, in applying the normal electric field, an alternating electric field having a rectangular wave shape in which the absolute value of the electric field intensity in each positive and negative polarity and the time width are equal is applied. When applying the strong electric field, the strong electric field is applied by increasing the electric field strength of the normal electric field continuously or stepwise until the electric field direction once switched is switched to the next time.

  Therefore, the electric field strength immediately after switching the electric field direction is set to a relatively low electric field strength comparable to the normal electric field strength, so that the change amount of the electric field is set to be relatively small, and thereafter the electric field strength is increased continuously or stepwise. By doing so, it is possible to converge amplification of the disorder of the alignment state generated in the liquid crystal layer in the switching of the electric field direction when the electric field having a relatively low intensity is continuously applied.

  According to a fifteenth aspect of the present invention, in the optical deflection method according to the twelfth, thirteenth, or fourteenth aspect, when the strong electric field is applied, the strong electric field is applied at a randomly generated timing.

  By the way, when a strong electric field is applied at a constant period, there is a concern that a periodic flow occurs in the liquid crystal layer. When such a periodic flow occurs, there is a concern that the flows interfere with each other and deteriorate the alignment state in the liquid crystal layer.

  Therefore, it is possible to prevent the alignment state in the liquid crystal layer from being deteriorated due to the periodic flow that can be generated in the liquid crystal layer by applying a strong electric field at a constant period.

  According to a sixteenth aspect of the present invention, in the optical deflection method according to the twelfth, thirteenth, fourteenth, or fifteenth aspect, when the strong electric field is applied, the application timing, the electric field direction, and the electric field strength are adjusted to adjust the vector in unit time. A strong electric field is applied so that the average value is substantially zero.

  By the way, when a strong electric field is applied at an arbitrary timing, if the direction of the strong electric field is biased to one side, the charge distribution such as charges and ions injected into the liquid crystal layer is biased with time, and the transient at the time of electric field inversion occurs. There are cases where light scattering is deteriorated, alignment defects are generated, and the performance life of the liquid crystal material is shortened.

  Therefore, by setting the arbitrary timing of applying a strong electric field, the electric field direction and the electric field strength so that the average value of the electric field vector applied to the liquid crystal layer within a unit time becomes substantially zero, the liquid crystal The DC balance of charges in the layer is maintained, and deterioration of transient light scattering and occurrence of orientation defects during electric field inversion can be prevented.

  According to a seventeenth aspect of the present invention, in the optical deflection method according to any one of the twelfth to sixteenth aspects, when the strong electric field is applied, the electric field is changed with respect to a switching period until the electric field direction once switched is switched to the next. The strong electric field is applied after a normal electric field has been applied for a half cycle or more after switching the direction.

  By the way, when a strong electric field is applied in the direction of the other electric field from a state in which a strong electric field is applied in the direction of one electric field, the amount of change in the electric field becomes very large. When the amount of change in the electric field is very large, the electrical load on the liquid crystal layer and the power source becomes large.

  Therefore, after applying a large electric field strength in one electric field direction, applying a large electric field strength in the other electric field direction after applying an electric field strength during light deflection operation for at least half a period or more. The amount of change in the electric field can be set small, and the electrical load on the liquid crystal layer and the power source can be reduced.

  The invention according to claim 18 is the optical deflection method according to any one of claims 12 to 17, wherein an electric field set to an absolute value of 200 V / mm or more is applied as the strong electric field when the strong electric field is applied. To do.

  Therefore, by temporarily applying a strong electric field sufficiently larger than the normal electric field, disorder of the alignment state in the liquid crystal layer can be reliably suppressed practically.

  According to a nineteenth aspect of the present invention, in the optical deflection method according to any one of the twelfth to eighteenth aspects, when the strong electric field is applied, the absolute value of the electric field strength at which the tilt angle of the optical axis is saturated in the liquid crystal layer. An electric field set to an absolute value of 5 times or more with respect to the saturation electric field strength Ec (V / mm) is applied as the strong electric field.

  Therefore, when the electric field strength at a fixed magnification based on the saturation electric field strength, which is a characteristic value that reflects the physical properties of the liquid crystal material, is applied, the behavior of the electric field strength at a certain electric field strength varies depending on the type of liquid crystal material. Even so, it is possible to reliably suppress the decrease in MTF without being influenced by the difference in the liquid crystal material.

According to a twentieth aspect of the present invention, in the optical deflection method according to any one of the twelfth to nineteenth aspects, when the strong electric field is applied, the absolute value of the spontaneous polarization of the liquid crystal layer is expressed as Ps (nC / cm ² ), When the absolute value of the strong electric field is E (V / mm), an electric field set so that the value of Ps × E is 10,000 (μN / cm ² ) or more is applied as the strong electric field.

  Therefore, by defining the product of spontaneous polarization and electric field strength (value proportional to the electrical driving force acting on the liquid crystal molecules), which is a characteristic value reflecting the physical properties of the liquid crystal material, Even if the behavior of the electric field strength with respect to the electric field is different, the MTF reduction can be reliably suppressed without being influenced by the difference in the liquid crystal material.

  According to a twenty-first aspect of the present invention, in the light deflection method according to any one of the twelfth to twentieth aspects, when the strong electric field is applied, an increase or decrease in the amount of light scattering or the decrease in MTF value in the liquid crystal layer is detected. A strong electric field is applied when an increase in the amount of light scattering or a decrease in the MTF value is detected using the increase / decrease detection means.

  Here, the light scattering amount and the MTF amount may differ depending on the use environment such as the environmental temperature where the light deflector is installed. Therefore, if a strong electric field is applied at an arbitrary timing, it is possible to effectively suppress a decrease in MTF, but there is also a possibility that a side effect due to the application of the strong electric field may occur.

  Therefore, by detecting the increase or decrease of the light scattering amount or the decrease amount of the MTF value in the liquid crystal layer and applying the strong electric field at an arbitrary timing when detecting the increase of the light scattering amount or the decrease amount of the MTF value, The application operation timing can be minimized.

  According to the optical deflecting device of the first aspect of the invention, it is possible to suppress the decrease in MTF due to the disorder of the alignment state in the liquid crystal layer, which is likely to occur by applying a strong electric field in order to shorten the switching time of the optical deflection direction. It is generated by applying a strong electric field continuously without affecting the switching of the electric field direction by applying a strong electric field at an arbitrary timing that overlaps with the timing at which the normal electric field is applied during the optical deflection operation. Since the occurrence of alignment defects can be suppressed, a stable light deflection operation can be performed over a long period of time.

  According to the second aspect of the present invention, in the optical deflecting device according to the first aspect, the offset between the normal electric field and the strong electric field is zero and the duty ratio is 50%. By applying a strong electric field over the entire liquid crystal layer, it is possible to converge amplification of the alignment state disturbance generated in the liquid crystal layer in the switching of the electric field direction during continuous application of a relatively low electric field. It is possible to suppress disorder of the alignment state and amplification of alignment defects in the layer, and to more reliably suppress a decrease in MTF.

  According to a third aspect of the invention, in the optical deflecting device according to the first aspect, the amount of change in the electric field is obtained by setting the electric field strength immediately after switching the electric field direction to a relatively low electric field comparable to the normal electric field strength. Is set to be relatively small, and then the electric field strength is increased continuously or stepwise, thereby amplifying the disorder of the alignment state generated in the liquid crystal layer in the switching of the electric field direction when the electric field having a relatively low strength is continuously applied. Since it can be made to converge, disorder of the alignment state in the liquid crystal layer and amplification of alignment defects can be suppressed, and a decrease in MTF can be more reliably suppressed.

  According to a fourth aspect of the present invention, in the optical deflecting device according to the first, second, or third aspect, the alignment in the liquid crystal layer is caused by the periodic flow that can be generated in the liquid crystal layer by applying a strong electric field at a constant period. Since the state can be prevented from deteriorating, a stable light deflection operation can be performed over a longer period.

  According to the fifth aspect of the present invention, in the optical deflecting device according to the first, second, third, or fourth aspect, an average value of an electric field vector applied to the liquid crystal layer within a unit time is substantially zero. By setting the arbitrary timing of applying a strong electric field, the electric field direction, and the electric field strength, the DC balance of charges in the liquid crystal layer is maintained, and transient light scattering at the time of electric field inversion and occurrence of alignment defects are prevented. Since it can be suppressed, positive and negative bias of the charge injected into the liquid crystal layer by applying a strong electric field at an arbitrary timing can be prevented, and MTF drop in the optical deflecting device can be stably prevented over a long period of time. can do.

  According to a sixth aspect of the present invention, in the optical deflecting device according to any one of the first to fifth aspects, after applying a strong electric field in one electric field direction, at least a half period or more is during the optical deflection operation. By applying a large electric field strength with respect to the other electric field direction after applying the electric field strength of 1, the electric field change amount can be set small, and the electrical load on the liquid crystal layer and the power source can be reduced. Therefore, the value of the current flowing in the optical deflecting device can be suppressed, and a decrease in the MTF of the optical deflecting device can be suppressed stably over the long term.

  According to the invention described in claim 7, in the optical deflecting device according to any one of claims 1 to 6, the alignment state in the liquid crystal layer is temporarily applied by applying a strong electric field sufficiently larger than the normal electric field. Therefore, the MTF drop in the optical deflecting device can be surely prevented practically.

  According to an eighth aspect of the present invention, in the optical deflecting device according to any one of the first to seventh aspects, the electric field strength at a constant magnification based on a saturation electric field strength that is a characteristic value reflecting the physical properties of the liquid crystal material. Even if the behavior of a certain electric field strength with respect to an electric field varies depending on the type of liquid crystal material, it is possible to reliably suppress a decrease in MTF without being affected by the difference in liquid crystal material. Therefore, it is possible to stably prevent a decrease in MTF in the optical deflection apparatus over a long period of time without being influenced by the difference in the liquid crystal material.

  According to the ninth aspect of the present invention, in the optical deflecting device according to any one of the first to eighth aspects, the product of spontaneous polarization and electric field strength, which is a characteristic value reflecting the physical properties of the liquid crystal material (acts on liquid crystal molecules). Regardless of the difference in the liquid crystal material, even if the behavior of the electric field with a certain electric field strength is different due to the difference in the type of liquid crystal material, etc. Since the MTF reduction can be reliably suppressed, the MTF reduction in the optical deflecting device can be stably prevented over a long period of time without being influenced by the difference in the liquid crystal material.

  According to a tenth aspect of the present invention, in the light deflection apparatus according to any one of the first to ninth aspects, the value of the light scattering amount or the MTF amount depends on a use environment such as an environmental temperature where the light deflection apparatus is installed. Even in different cases, the timing of the application operation of the strong electric field is minimized to effectively eliminate the disorder of the alignment state of the liquid crystal layer, and the MTF degradation in the optical deflecting device can be stably prevented over a long period of time. be able to.

  According to the image display device of the eleventh aspect of the invention, since it can be driven at a frequency at which the MTF of the optical deflecting device is unlikely to decrease and at a frequency that does not generate flicker or the like, An image maintaining a high contrast can be displayed.

  According to the light deflection method of the invention described in claim 12, while suppressing the decrease in MTF due to the disorder of the alignment state in the liquid crystal layer, which is likely to occur by applying a strong electric field in order to shorten the switching time of the light deflection direction. It is generated by applying a strong electric field continuously without affecting the switching of the electric field direction by applying a strong electric field at an arbitrary timing that overlaps with the timing at which the normal electric field is applied during the optical deflection operation. Since the occurrence of alignment defects can be suppressed, a stable light deflection operation can be performed over a long period of time.

  According to the invention of claim 13, in the optical deflection method of claim 12, the offset between the normal electric field and the strong electric field is zero and the duty ratio is 50%. By applying a strong electric field over the entire liquid crystal layer, it is possible to converge amplification of the alignment state disturbance generated in the liquid crystal layer in the switching of the electric field direction during continuous application of a relatively low electric field. It is possible to suppress disorder of the alignment state and amplification of alignment defects in the layer, and to more reliably suppress a decrease in MTF.

  According to the fourteenth aspect of the present invention, in the optical deflection method according to the twelfth aspect, the electric field change amount is obtained by setting the electric field strength immediately after switching the electric field direction to a relatively low electric field comparable to the normal electric field strength. Is set to be relatively small, and then the electric field strength is increased continuously or stepwise, thereby amplifying the disorder of the alignment state generated in the liquid crystal layer in the switching of the electric field direction when the electric field having a relatively low strength is continuously applied. Since it can be made to converge, disorder of the alignment state in the liquid crystal layer and amplification of alignment defects can be suppressed, and a decrease in MTF can be more reliably suppressed.

  According to the fifteenth aspect of the invention, in the optical deflection method according to the twelfth, thirteenth, or fourteenth aspect, the alignment in the liquid crystal layer is caused by the periodic flow that can be generated in the liquid crystal layer by applying a strong electric field at a constant period. Since the state can be prevented from deteriorating, a stable light deflection operation can be performed over a longer period.

  According to the sixteenth aspect of the present invention, in the optical deflection method according to the twelfth, thirteenth, fourteenth or fifteenth aspect, the average value of the vector of the electric field applied to the liquid crystal layer within a unit time is substantially zero. By setting the arbitrary timing of applying a strong electric field, the electric field direction, and the electric field strength, the DC balance of charges in the liquid crystal layer is maintained, and transient light scattering at the time of electric field inversion and occurrence of alignment defects are prevented. Since it can be suppressed, positive and negative bias of the charge injected into the liquid crystal layer by applying a strong electric field at an arbitrary timing can be prevented, and MTF drop in the optical deflecting device can be stably prevented over a long period of time. can do.

  According to the seventeenth aspect of the present invention, in the optical deflection method according to any one of the twelfth to sixteenth aspects, after applying a strong electric field in one electric field direction, at least half a period or more is during the optical deflection operation. By applying a large electric field strength with respect to the other electric field direction after applying the electric field strength of 1, the electric field change amount can be set small, and the electrical load on the liquid crystal layer and the power source can be reduced. Therefore, the value of the current flowing in the optical deflecting device can be suppressed, and a decrease in the MTF of the optical deflecting device can be suppressed stably over the long term.

  According to the invention described in claim 18, in the light deflection method according to any one of claims 12 to 17, the alignment state in the liquid crystal layer is temporarily applied by applying a strong electric field sufficiently larger than the normal electric field. Therefore, the MTF drop in the optical deflecting device can be surely prevented practically.

  According to the nineteenth aspect of the invention, in the light deflection method according to any one of the twelfth to eighteenth aspects, the electric field strength at a constant magnification based on a saturation electric field strength that is a characteristic value reflecting the physical properties of the liquid crystal material. Even if the behavior of a certain electric field strength with respect to an electric field varies depending on the type of liquid crystal material, it is possible to reliably suppress a decrease in MTF without being affected by the difference in liquid crystal material. Therefore, it is possible to stably prevent a decrease in MTF in the optical deflection apparatus over a long period of time without being influenced by the difference in the liquid crystal material.

  According to the twentieth aspect of the present invention, in the light deflection method according to any one of the twelfth to nineteenth aspects, the product of spontaneous polarization and electric field strength, which is a characteristic value reflecting the physical properties of the liquid crystal material (acts on the liquid crystal molecules). Regardless of the difference in the liquid crystal material, even if the behavior of the electric field with a certain electric field strength is different due to the difference in the type of liquid crystal material, etc. Since the MTF reduction can be reliably suppressed, the MTF reduction in the optical deflecting device can be stably prevented over a long period of time without being influenced by the difference in the liquid crystal material.

  According to a twenty-first aspect of the present invention, in the light deflection method according to any one of the twelfth to twentieth aspects, the value of the amount of light scattering or the amount of MTF varies depending on the use environment such as the environmental temperature where the light deflection apparatus is installed. Even in different cases, the timing of the application operation of the strong electric field is minimized to effectively eliminate the disorder of the alignment state of the liquid crystal layer, and the MTF degradation in the optical deflecting device can be stably prevented over a long period of time. be able to.

  A best mode for carrying out the present invention will be described with reference to FIGS. The present invention shows an application example to an optical deflecting device.

  FIG. 1 is a schematic diagram showing an optical deflecting element in an optical deflecting device according to an embodiment of the present invention. As shown in FIG. 1, the light deflection element in the light deflection apparatus of the present embodiment includes a pair of transparent substrates 2 and 3 arranged to face each other. As the transparent substrates 2 and 3, glass, quartz, plastic, or the like can be used. As the transparent substrates 2 and 3, a transparent material having no birefringence is particularly preferable.

  The thickness of each of the substrates 2 and 3 is preferably set to several tens of μm to several mm.

Vertical alignment films 4 and 5 are formed on the inner side surfaces (surfaces facing each other) of the substrates 2 and 3. The vertical alignment films 4 and 5 are not particularly limited as long as the vertical alignment films 4 and 5 are materials that vertically align (homeotropic alignment) liquid crystal molecules in the liquid crystal layer 6 described later with respect to the surfaces of the substrates 2 and 3. As a material for forming the vertical alignment films 4 and 5, it is possible to use a vertical alignment agent for liquid crystal displays, a silane coupling agent, a SiO ₂ vapor deposition film, or the like.

  In the present embodiment, the vertical alignment (homeotropic alignment) includes not only a state in which liquid crystal molecules are aligned vertically with respect to the substrate surface but also an alignment state in which the liquid crystal molecules are tilted to about several tens of degrees.

  In the optical deflection element 1, a spacer 7 is provided between a pair of substrates 2 and 3, and the spacer 7 is sandwiched between the pair of substrates 2 and 3 to define the interval between the substrates 2 and 3. As the spacer 7, it is possible to use a sheet-like member having a thickness of about several μm to several mm or particles having the same particle size. The spacer 7 is preferably provided outside the effective area of the element.

  A liquid crystal layer 6 and an electrode 8 are provided between the substrates 2 and 3 defined by the spacer 7.

  Here, as a material for forming the electrode 8, a metal such as aluminum, copper, or chromium, a transparent electrode such as ITO, or the like can be used. In addition, in order to apply a uniform horizontal electric field in the liquid crystal layer 6, the electrode 8 is preferably made of a sheet-like metal material having a thickness comparable to that of the liquid crystal layer 6. The electrode 8 is provided outside the effective area during light deflection in the light deflection apparatus.

  In FIG. 1, as a more preferable example, the spacer 7 and the electrode 8 are shared by a sheet-like member formed of a metal material, and the thickness of the liquid crystal layer 6 is defined by the thickness of the sheet-like member. .

  A rectangular wave AC voltage source 14 is applied to the electrode 8 by applying a voltage between the electrodes 8 so as to apply an electric field to the liquid crystal layer 6 in a direction substantially perpendicular to the normal direction of the substrates 2 and 3 and the light deflection direction. (See FIG. 4) are connected. Light applied to the liquid crystal layer 6 by applying an electric field to the liquid crystal layer 6 in a direction substantially perpendicular to the normal direction of the substrates 2 and 3 and the light deflection direction by the rectangular wave AC voltage source 14. Are deflected and emitted. In this embodiment, an electric field having this electric field strength is a normal electric field.

  The rectangular wave AC voltage source 14 applies an AC voltage having a rectangular waveform to the electrode 8. For this reason, the direction of the electric field applied to the liquid crystal layer 6 is switched by applying an AC voltage to the electrode 8 by the rectangular wave AC voltage source 14. Here, the electric field direction switching means is realized.

  In the present embodiment, the electric field strength applied to the liquid crystal layer 6 can be variably controlled by varying the voltage applied between the electrodes 8 by the rectangular wave AC voltage source 14. The variable control of the electric field strength will be described later.

  As the liquid crystal layer 6 in the light deflection apparatus of the present embodiment, it is possible to use a liquid crystal capable of forming a smectic C phase.

  In such an optical deflecting device, when deflecting the incident light, a voltage is applied between the electrodes 8 so that the liquid crystal layer 6 is substantially orthogonal to the normal direction of the substrates 2 and 3 and the optical deflection direction. A normal electric field is applied in the direction (horizontal direction of the liquid crystal layer 6). Here, the electric field applying means is realized.

  Note that the optical deflection apparatus of the present embodiment is not limited to the optical deflection element 1 shown in FIG. 1, and may be, for example, an optical deflection element 10 as shown in FIGS. 2 and FIG. 3 includes a plurality of line-shaped transparent electrodes 9 provided on the surfaces of the substrates 2 and 3. A resistance array 11 is connected to each transparent electrode 9. An AC voltage applying device 12 that applies an AC voltage along the arrangement direction of the transparent electrodes 9 is connected to the resistor array 11.

  In the optical deflection element 10 shown in FIG. 2 and FIG. 3, a voltage value that changes stepwise is applied to each transparent electrode 9 by applying a voltage to the resistor array 11. Thereby, a uniform horizontal electric field is applied over a wider area, and a potential gradient along the horizontal direction of the substrates 2 and 3 is forcibly formed in the liquid crystal layer 6, and a uniform horizontal electric field can be formed. .

  In the optical deflection element 10, as shown in FIGS. 2 and 3, a transparent dielectric layer 13 may be provided between the surface on which the line-shaped transparent electrode 9 is provided and the liquid crystal layer 6. Good. In the optical deflection element 10 as shown in FIGS. 2 and 3, since the effective area can be increased to about several centimeters square, for example, a relatively large area is required as in an image display device (see FIG. 21). It is preferable when applied to applications.

  Next, the liquid crystal layer 6 capable of forming a smectic C phase will be described in detail. A “smectic liquid crystal” is a liquid crystal in which the major axis direction of liquid crystal molecules is arranged in a layered manner (smectic layer). Regarding such a liquid crystal, a liquid crystal in which the normal direction of the liquid crystal layer 6 (layer normal direction) and the major axis direction of the liquid crystal molecules coincide with each other is referred to as “smectic A phase”, and a liquid crystal that does not coincide with the normal direction. This is called “smectic C phase”.

  In general, a ferroelectric liquid crystal composed of a smectic C phase has a so-called spiral structure in which the direction of the liquid crystal director is spirally rotated for each smectic layer in a state where an external electric field does not work, and is referred to as a “chiral smectic C phase”. Called.

  Further, the chiral smectic C reciprocal ferroelectric liquid crystal faces the direction in which the liquid crystal directors face each other.

  Since the liquid crystal composed of these chiral smectic C phases has an asymmetric carbon in the molecular structure and is spontaneously polarized by this, the liquid crystal molecules are rearranged in a direction determined by the spontaneous polarization Ps and the external electric field E. Optical properties are controlled.

  In the present embodiment and the like, the light deflection element 1 will be described by taking a ferroelectric liquid crystal as an example of the liquid crystal layer 6, but the present invention is not limited to this, and the liquid crystal layer 6 may be used similarly in the case of an antiferroelectric liquid crystal. it can.

  Next, the principle of operation of the optical deflection apparatus of this embodiment will be described with reference to FIGS. FIG. 4 is a schematic diagram showing the electric field direction and the tilt direction of the liquid crystal molecules in the liquid crystal layer 6. FIG. 4A shows a state where an electric field is applied from right to left in FIG. 4, and FIG. It shows a state where an electric field from left to right is applied. 5 is a perspective view schematically showing the liquid crystal layer 6 in FIG. 4. FIG. 5A is a state where an electric field is applied from right to left in FIG. 4, and FIG. 5B is left in FIG. It shows a state in which an electric field directed from right to right is applied. In FIG. 4, the side where the width of the liquid crystal molecules 6a is drawn wide is shown as being inclined to the upper side of the paper, and the side where the width is drawn is inclined to the lower side of the paper. In FIG. 2, the spontaneous polarization of the liquid crystal (denoted by the symbol Ps) is indicated by an arrow.

  Here, when the electric field direction is reversed, the direction of the tilt angle of the substantially vertically aligned liquid crystal molecules 6a is reversed. FIG. 4 shows the relationship between the electric field application direction and the tilt direction of the liquid crystal molecules 6a when the spontaneous polarization is positive.

  By the way, when the direction of the tilt angle is reversed, the liquid crystal molecules 6a in the liquid crystal layer 6 are considered to rotate in a virtual cone-shaped surface 15 (hereinafter referred to as a virtual cone 15) as shown in FIG. It is done.

  Here, FIG. 6 is a schematic diagram showing the alignment state of the liquid crystal molecules 6a, and FIG. 6 (a) shows a case where an electric field is applied to the liquid crystal layer 6 from the back side to the near side of the drawing, ) Shows a case where an electric field is applied to the liquid crystal layer 6 from the front side to the back side. In FIG. 6, the vertical alignment film 4, the spacer 7, and the electrode 8 are omitted. For convenience, it is assumed that the voltage is applied in the front and back direction in FIG. 6, and the electric field is applied in the front and back direction by applying this electric field. However, the direction of the electric field can be switched corresponding to the target light deflection direction by controlling the rectangular wave AC voltage source 14. The incident light with respect to the light deflecting element 1 is linearly polarized light.

  As shown in FIG. 6A, when an electric field is applied to the liquid crystal layer 6 from the back side to the near side in FIG. 6, the liquid crystal director is shown if the spontaneous polarization of the liquid crystal molecules 6a is positive. The number of liquid crystal molecules 6a tilted to the upper right in 6 (a) increases. At this time, the average optical axis as the liquid crystal layer 6 is also inclined in the upper right direction in FIG. Thereby, the optical deflection element 1 (the liquid crystal layer 6) functions as a birefringent plate.

  Above the threshold electric field at which the helical structure of the chiral smectic C phase can be solved, the liquid crystal directors of all the liquid crystal molecules 6a exhibit a tilt angle θ, and the birefringent plate whose optical axis is inclined at an angle θ on the upper right side in FIG. Become. Note that linearly polarized light incident from the left side as extraordinary light is shifted in parallel upward.

Here, when the refractive index in the major axis direction of the liquid crystal molecules 6a is ne, the refractive index in the minor axis direction is no, and the thickness (gap) of the liquid crystal layer 6 is d, the shift amount S by the liquid crystal layer 6 is shown below. It is expressed by the formula (1) (for example, see “Crystal Optics” Applied Physics Society, Optical Society, p198).
S = [(1 / no) ² − (1 / ne) ² ] sin (2θ) × d
÷ [2 ((1 / ne) ² sin ² θ + (1 / no) ² cos ² θ)] (1)

  Similarly, as shown in FIG. 6B, when the direction of the voltage applied to the electrode 8 is reversed to apply an electric field from the front side to the back side in FIG. 6B, the spontaneous polarization of the liquid crystal molecules 6a. Is positive, the liquid crystal director functions as a birefringent plate tilted to the lower right in FIG. 6B and the optical axis tilted downward at an angle θ. Note that linearly polarized light incident from the left side as extraordinary light is shifted in parallel downward.

  Thus, in the optical deflecting device, the optical path deflection amount for 2S can be obtained by reversing the electric field direction.

  4 to 6 describe an ideal stable state after the liquid crystal molecules 6a are inverted and re-oriented, but in reality, the alignment state is greatly increased in the process of inversion of the liquid crystal molecules 6a. Disturbed and transient light scattering may occur.

  Such inversion of the liquid crystal molecules 6a will be described with reference to FIG. 7A and 7B are schematic views showing the tilted state of the liquid crystal molecules in the light deflection element, as in FIG. 2, where FIG. 7A shows the state before electric field inversion, FIG. 7B shows the light scattering state, and FIG. ) Shows a state where there is a domain flow after reorientation, and (d) shows a state after the domain flow has converged. When the chiral electric field is equal to or higher than the threshold electric field at which the chiral smectic C-phase helical structure can be solved, the liquid crystal molecules 6a are uniformly aligned as shown in FIG.

  In the liquid crystal layer 6, when the applied electric field of the liquid crystal molecules 6a in the state shown in FIG. 7A is reversed in a shorter time than the response time of the liquid crystal molecules 6a, each liquid crystal molecule 6a is as shown in FIG. When the reversal is started along the virtual cone 15, it is estimated that there are an area that rotates clockwise and an area that starts to rotate counterclockwise as shown in FIG. 7B. And it is thought that strong transient light scattering arises in the interface between the domains where this rotation direction differs.

  Thereafter, as shown in FIG. 7C, when the liquid crystal molecules 6a are realigned so as to be inclined substantially uniformly on the opposite side, strong light scattering disappears.

  However, depending on the characteristics of the liquid crystal material, a domain may be formed in the smectic layer even after realignment, and the domain may flow in a wave shape. In addition, the broken line curve in FIG.7 (c) has shown the image of the domain boundary surface.

  Thereafter, as shown in FIG. 7 (d), the flow of the domain converges to show a stable orientation state.

  By the way, it is presumed that the phenomenon in which the MTF decreases as described above greatly affects the convergence time in the state shown in FIG.

  Here, FIG. 8 is a schematic view showing an example of an apparatus (MTF value measuring apparatus) for measuring the MTF value in the optical deflection apparatus. The MTF value measuring apparatus 20 includes an optical system 22 that sets the illumination angle of light from the light source 21 and a polarizing plate 23 that polarizes the light from the optical system 22. In addition, the MTF value measuring apparatus 20 includes a microscope 25 that focuses on the CCD camera 24 that detects the light emitted from the light deflecting element 1 in the light deflecting apparatus that is the target of the MTF value measurement. An MTF chart 26 is provided between the polarizing plate 23 and the microscope 25. The light deflection element 1 in the light deflection apparatus to be measured is arranged between the microscope 25 and the MTF chart 26.

  In the MTF measuring apparatus 20 shown in FIG. 8, the MTF chart 26 having a sinusoidal density distribution with a spatial frequency of 100 periods / mm (10 μm pitch) is illuminated through the polarizing plate 22.

  Then, the microscope 25 and the CCD camera 24 are focused on the surface of the MTF chart 26 via the optical deflection device, and the deterioration of the contrast of the sinusoidal luminance distribution due to the optical deflection device is observed. It was observed that a light shift occurred and the position of the MTF chart 25 was displaced.

A steady-state MTF chart image in which the optical path is shifted in one direction was taken into a computer, and the contrast of the sinusoidal luminance distribution was analyzed by image analysis software. Specifically, the peak value Imax and the bottom value Imin of the luminance distribution are obtained, and the absolute value of the MTF of the optical deflecting element 1 in the optical deflecting device with respect to a spatial frequency of 100 periods / mm (10 μm pitch) is expressed by the following equation (2). Calculated by calculation.
MTF = (Imax−Imin) / (Imax + Imin) (2)

  Further, as a reference, a sample in which matching oil having a refractive index of 1.520 is sandwiched between glass substrates (no alignment film) is used, and the MTF ratio between the optical deflection element 1 and the reference in the optical deflection apparatus to be measured is calculated. did.

This MTF value indicates deterioration of optical characteristics due to only the liquid crystal layer and the alignment film, as shown in the following formula (3).
MTF (liquid crystal layer and alignment film part)
= MTF (optical deflection device) / MTF (matching oil sample) (3)

  Here, FIG. 9 is an explanatory view showing an example of the MTF lowering phenomenon by the conventional electric field application method. A light deflection element 1 as shown in FIG. 1 is prepared using two types of CS1024 and CS2003, which are ferroelectric liquid crystals of Chisso Corporation. As shown in FIG. 10, a rectangular wave alternating current with constant electric field strength is used. An electric field was applied. In the example shown in FIG. 8, the frequency of the rectangular wave AC electric field is set to 98 Hz. In FIG. 9, the horizontal axis represents the absolute value of the electric field strength in the horizontal direction of the liquid crystal layer, and the vertical axis represents the MTF value due to the liquid crystal layer and the alignment film portion in the equation (3).

  As a result, in CS1024, the MTF value began to decrease gradually by continuous driving at an electric field strength of about ± 50 V / mm to 200 V / mm, and settled to a substantially constant value in about several minutes.

  Then, when a relatively strong electric field of ± 300 V / mm or more is applied to the optical deflecting device in a relatively low electric field state where the MTF value is lowered, the MTF value is quickly recovered, and a favorable value of 0.9 or more Showed a good value. When a relatively strong electric field of ± 300 V / mm or more was applied from the beginning, the MTF reduction phenomenon did not occur even when continuously driven. From this experimental result, it is presumed that the MTF lowering phenomenon may be prevented by applying an electric field having an electric field strength of at least ± 200 V / mm.

  On the other hand, in CS2003, by continuously driving with an electric field strength of about ± 50 V / mm to ± 350 V / mm, the MTF value began to gradually decrease and settled to a substantially constant value in about several minutes.

  When a relatively strong electric field of at least ± 550 V / mm is applied to the optical deflecting device in a relatively low electric field state where the MTF value is lowered, the MTF value is quickly recovered and is about 0.9. A good value was exhibited. In addition, when a relatively strong electric field of ± 550 V / mm or more was applied from the beginning, the MTF reduction phenomenon did not occur even when continuously driven. From this experimental result, it is presumed that the MTF lowering phenomenon may be prevented by applying an electric field having an electric field strength of at least ± 350 V / mm.

  By the way, since the ferroelectric liquid crystal materials in the above two examples have different values of the chiral smectic C phase helical pitch and the spontaneous polarization Ps, the influence on the liquid crystal layer may be different even when the same electric field strength is applied. It is assumed that there is.

  Therefore, the comparison was made based on the saturation electric field strength (denoted by the symbol Ec), which is the electric field strength at which the helical structure of the chiral smectic C phase can be almost solved. From the tilt angle measurement result of the optical axis of the chiral smectic C phase with respect to the horizontal electric field strength, the absolute value of the saturation electric field of CS1024 is Ec = 40 V / mm, and the absolute value of the saturation electric field of CS2003 is Ec = 80 V / mm. That is, when CS1024 or CS2003 is used, an electric field strength having an absolute value greater than or equal to the absolute value of the saturation electric field may be applied as the electric field strength of the normal electric field.

  FIG. 11 is a graph showing the result of normalizing and arranging the applied electric field strength with the saturation electric field strength Ec. It is presumed that both CS1024 and CS2003 may be able to suppress MTF reduction when the normalized electric field E / Ec is at least 5 or more. Moreover, according to FIG. 11, it is guessed that MTF fall can be suppressed more reliably by making normalized electric field E / Ec 7 or more.

  By the way, it is considered that the phenomenon that the MTF is lowered is influenced by the flow of the smectic layer after the liquid crystal molecule is inverted. For this reason, it is considered important to quickly converge the flow of the smectic layer.

  Further, it is presumed that the electric driving force acting on the liquid crystal molecules influences the convergence time of the flow of the smectic layer.

Here, FIG. 12 is a graph showing the relationship between the product (Ps · E) of the spontaneous polarization Ps corresponding to the electric driving force acting on the liquid crystal molecules 6a and the electric field strength E and the MTF value. According to FIG. 12, in CS1024 in which the spontaneous polarization Ps is about −47 nC / cm ² , there is a possibility that the decrease in the MTF value can be suppressed when Ps · E is at least 10,000 μN / cm ² or more. I guess that. Further, according to FIG. 12, in CS2003 in which the spontaneous polarization Ps is about −41 nC / cm ² , there is a possibility that a decrease in the MTF value can be suppressed when Ps · E is at least 15000 μN / cm ² or more. Presumed to be.

  From the above results, it is presumed that a decrease in the MTF value can be suppressed by always setting the electric field strength of the rectangular wave AC electric field to ± 200 V / mm or more.

  In this embodiment, a strong electric field that is controlled so that the electric field strength of the rectangular wave AC electric field is always ± 200 V / mm or more is applied. Here, a part of the function as the electric field control means is realized.

  The electric field strength of the rectangular wave AC electric field is more preferably set to ± 350 V / mm or more.

  Further, from the above results, it is presumed that a decrease in the MTF value can be suppressed by always setting the normalized electric field strength E / Ec to 5 or more.

  In the present embodiment, the saturated electric field strength Ec (V / V) is such that the normalized electric field strength E / Ec is always 5 or more, that is, the absolute value of the electric field strength at which the tilt angle of the optical axis is saturated in the liquid crystal layer 6. mm), an electric field set to an absolute value of 5 times or more is controlled to be applied as a strong electric field. Here, a part of the function as the electric field control means is realized.

  The normalized electric field strength E / Ec is more preferably set to 7 or more.

Furthermore, from the above results, it is presumed that the decrease in the MTF value can be suppressed by always setting the electric drive amount Ps · E to 10000 μN / cm ² or more.

In the present embodiment, control is performed so that the electric drive amount Ps · E is always 10000 μN / cm ² or more. Here, a part of the function as the electric field control means is realized.

In addition, it is more preferable to set Ps · E, which is an electric drive amount, to 15000 μN / cm ² or more.

  By the way, when the relatively strong rectangular wave AC electric field, which is the above-described three conditions, is continuously applied, there is a concern that another problem as described below may occur.

  As one of the problems, for example, by constantly applying a relatively strong rectangular wave AC electric field, the entire smectic layer is inclined with respect to the substrates 2 and 3 as shown in FIG. For example, the shift amount changes. In addition, there is a concern that a new domain is generated due to strain in the smectic layer and transient light scattering is deteriorated. Furthermore, there is a concern that the load on the rectangular wave AC voltage source 14 is increased. In addition, there is a concern that the influence of electrical noise and the like on the members disposed around the optical deflection element 1 is increased.

  In this embodiment, a strong electric field is not always applied, but an arbitrary timing that overlaps with a timing at which a normal electric field such as temporary, periodic, or irregular is applied during driving with a relatively low electric field. And control to apply a strong electric field. Here, the electric field control means is realized together with some of the functions described above.

  Thereby, the malfunction at the time of always applying a strong electric field can be prevented, and it can suppress that MTF falls gradually simultaneously. In addition, even when the MTF has greatly decreased, the phenomenon that the MTF recovers quickly by applying a relatively strong electric field is utilized, and the MTF decrease phenomenon becomes apparent by applying a strong electric field in a pulsed manner. Can be prevented proactively.

  Specific examples of the control for applying such a strong electric field include increasing the electric field strength of only the first half of an arbitrary electric field pulse as shown in the electric field waveform shown in FIG.

  As described above, at an arbitrary timing during the optical deflection operation, an electric field having a larger electric field strength (strong electric field) than the electric field strength during the optical deflection operation overlaps with the timing at which the normal electric field is applied temporarily or for a certain period. Apply at any timing. As a result, the domain flow after reorientation as shown in FIG. 7C is converged at an early stage, and the deterioration of the orientation of the liquid crystal layer is amplified by interference with the next domain flow, and the MTF value is greatly reduced. Can be suppressed.

  Next, another best mode for carrying out the present invention will be described with reference to FIG. Note that the same parts as those of the above-described embodiment are denoted by the same reference numerals, and description thereof is also omitted. The same shall apply hereinafter.

  In the optical deflection apparatus described above, as shown in FIG. 14, the case where the electric field strength of the first half of the rectangular wave electric field pulse is set large is illustrated, but the domain flow after reorientation as shown in FIG. It is considered effective to apply a large electric field strength to the latter half of the period when the electric field strength is constant.

  Therefore, in the present embodiment, as shown in FIG. 15, a rectangular wave AC electric field in which the electric field during the light deflection operation has the same absolute value and time width of the electric field strength in each polarity is defined as a normal electric field. On the other hand, an electric field controlled so as to have a rectangular wave shape having the same time width as that during the light deflection operation but different only in the absolute value of the electric field strength is applied as a strong electric field. That is, the offset is set to zero and the duty ratio is set to 50%. Here, the electric field control means is realized.

  As a result, a strong electric field is applied throughout the optical deflection state holding period after the electric field inversion, and the flow of liquid crystal layer 6 and the disturbance of the alignment state that occur after switching of the optical deflection direction can be reliably converged.

  Next, another best mode for carrying out the present invention will be described with reference to FIG.

  In the optical deflecting device described above, the case where the electric field strength in the first half of the rectangular wave electric field pulse is set large as shown in FIG. 14 is exemplified, but the domain flow after reorientation as shown in FIG. In order to converge at an early stage, it is considered effective to apply a strong electric field to the latter half of the period in which the electric field strength is constant.

  Therefore, in the present embodiment, as shown in FIG. 16, at the timing of applying the strong electric field, the strong electric field having the desired electric field strength is continuously or stepwise within the optical deflection state holding period after the electric field inversion. Control to increase. Here, the electric field control means is realized.

  Thereby, since the electric field strength immediately after the electric field switching is a relatively low electric field as in the normal case, the change amount of the electric field can be set to be relatively small. Then, by increasing the electric field intensity continuously or stepwise within the subsequent optical deflection state holding period, the flow and disturbance of the liquid crystal layer after the electric field inversion can be converged relatively quickly.

  Next, another best mode for carrying out the present invention will be described.

  In the optical deflection apparatus described above, as shown in FIGS. 14 to 16, the timing for applying a strong electric field is shown as an arbitrary timing. However, if the illustrated range is repeated as one cycle, there is a concern that some periodic flow occurs in the liquid crystal layer 6 and the flow interferes with each other to deteriorate the alignment state in the liquid crystal layer 6. The

  Although not particularly illustrated, in the present embodiment, control is performed so that the timing of applying a strong electric field is generated randomly. Here, the electric field control means is realized.

  Thereby, a stable light deflection operation can be performed over a long period of time.

  Next, another best mode for carrying out the present invention will be described with reference to FIG.

  In the optical deflection apparatus described above, for example, within the range shown in FIGS. 14 to 16, the strong electric field is applied three times on the plus side and the strong electric field is applied once on the minus side. The direction of application is biased. If the driving is continued for a long time with the direction of the strong electric field biased to one side in this way, the charge distribution such as charges and ions injected into the liquid crystal layer 6 is biased over time, and the switching of the electric field direction is caused. At that time, there is a concern that transient light scattering may deteriorate, alignment defects may occur, and the performance life of the liquid crystal material may be reduced.

  On the other hand, in the present embodiment, as shown in FIG. 18, the timing of applying a strong electric field and the electric field so that the average value of the electric field vector applied to the liquid crystal layer 6 within a unit time is substantially zero. Set direction and field strength. Here, the electric field control means is realized.

  Thereby, the DC balance of the charge in the liquid crystal layer is maintained, and deterioration of transient light scattering at the time of electric field inversion and occurrence of alignment defects can be suppressed.

  Next, another best mode for carrying out the present invention will be described with reference to FIG.

  In the above-described optical deflecting device, as shown in FIGS. 15 and 17, the case where a strong electric field is applied in the other electric field direction immediately after the strong electric field is applied in one electric field direction has been described. However, when the electric field is reversed in such a case, the electric field change amount becomes very large. When the amount of change in the electric field is very large, an electrical load on the liquid crystal layer 6 and the rectangular wave AC voltage source 14 becomes large.

  On the other hand, in this embodiment, as shown in FIG. 18, after applying a strong electric field to one electric field direction, after applying a normal electric field for at least a half cycle or more, in the other electric field direction. In contrast, control is performed so that a strong electric field is applied. Here, the electric field control means is realized.

  Thereby, the amount of change in the electric field can be set small, and the electrical load on the liquid crystal layer 6 and the rectangular wave AC voltage source 14 can be reduced.

  In FIG. 18, after applying a strong electric field in one electric field direction, one cycle is opened. However, the present invention is not limited to this, and may be a half cycle, for example. Even when a half-cycle is opened after applying a strong electric field in one electric field direction, the continuous electric field change amount can be set relatively small.

  The electric field waveforms shown in FIGS. 14 to 18 are examples for explaining the concept of the present invention, and are not limited to the illustrated electric field waveform patterns.

  Next, another best mode for carrying out the present invention will be described with reference to FIG.

  Here, the occurrence state of the MTF lowering phenomenon may vary depending on the usage environment such as the temperature of the optical deflection device itself or the environmental temperature where the optical deflection element 1 is installed. Therefore, as described above, when a strong electric field is applied preventively at an arbitrary timing, a decrease in the MTF value can be effectively prevented, but there is a concern that side effects due to the application of the strong electric field may occur. Specific side effects include various problems as described above.

  In order to prevent such side effects, it is preferable that the timing of applying a strong electric field is as small as possible.

  Here, FIG. 19 is an explanatory view showing a light scattering amount measuring device in a light deflecting device according to another preferred embodiment for carrying out the present invention. Light scattering when the MTF is normal and when the MTF is lowered is shown. The difference in state is shown. As shown in FIG. 19, the light scattering amount measurement device 30 includes a photodetector 31 provided in the vicinity of the light deflection device 1. The photodetector 31 may be provided with a lens (not shown) that efficiently collects light. In FIG. 19, in order to observe forward scattering due to the disorder of the alignment state in the liquid crystal layer 6, a lens is provided on the exit surface side (right side in FIG. 19) of the light deflection element 1 in the light deflection apparatus.

  The position where the lens is provided is not limited to the position shown in FIG. 16. For example, in order to observe the backscattering of the liquid crystal layer 6, the lens is provided on the incident surface side (left side in FIG. 19) of the light deflection element 1 in the light deflection apparatus. May be.

  When the MTF value is a normal value, light scattering in the steady state after switching the electric field direction is small, but when the MTF value starts to decrease, scattered light from the liquid crystal layer 6 is detected even in the steady state. It becomes like this.

  In order to accurately compare the scattered light intensity, it is necessary to make the amount of incident light at the time of measuring the scattered light intensity constant. In particular, when image light is incident, it is preferable to display an image pattern for measurement. The image pattern for measurement is preferably a white background-based image in which scattered light is easily observed, but a bright image pattern may be present only in the vicinity of the photodetector 31. Further, it is more preferable that an instantaneous image pattern for measurement during the detection operation is displayed and the observer cannot recognize. Then, the correlation between the MTF reduction amount under such incident light conditions and the output value of the photodetector due to light scattering is experimentally obtained in advance, so that the MTF value is calculated from the output value of the photodetector 31. The amount of decrease can be detected.

  Note that the photodetector 31 also observes large scattered light due to transient light scattering when the electric field direction is switched. Therefore, the switching timing of the electric field direction in the optical deflecting device and the detection timing of the output value by the photodetector 31 are adjusted to separate the scattered light based on the transient light scattering and the scattered light related to the decrease in the MTF value. It is preferable to detect them.

  Here, FIG. 20 is a schematic diagram showing an image display apparatus that can directly observe the MTF reduction amount in the above-described optical deflection apparatus. As shown in FIG. 20, when the light deflection apparatus is applied to the image display apparatus 40, it is also possible to directly observe the amount of decrease in MTF.

  An image display device 40 shown in FIG. 20 includes a light source 41 as an illumination unit in which LED lamps are arranged in a two-dimensional array. In the traveling direction of light emitted from the light source 41 toward the screen 42, a diffusion plate 43, a condenser lens 44, a transmissive liquid crystal panel 45 as an image display element, and a projection lens 46 as an optical device for observing an image pattern. Are arranged in order. The light source 41 is driven and controlled by a light source drive unit 47, and the transmissive liquid crystal panel 45 is driven and controlled by a liquid crystal drive unit 48 serving as display driving means.

  On the optical path between the transmissive liquid crystal panel 45 and the projection lens 46, an optical deflection device 49 that functions as a pixel shift element is interposed. The light deflection device 49 is connected to the drive unit 50.

  In the present embodiment, as the light deflecting device 49, various light deflecting devices as described above can be used.

  The illumination light that is controlled by the light source drive unit 47 and emitted from the light source 41 becomes uniform illumination light by the diffusion plate 43, and is controlled by the condenser lens 44 in synchronization with the illumination light source by the liquid crystal drive unit 48 to be a transmission type. The LCD panel 45 is critically illuminated. The illumination light spatially modulated by the transmissive liquid crystal panel 45 is incident on the light deflector 49 as image light, and the image light is shifted by an arbitrary distance in the pixel arrangement direction by the light deflector 49. This light is magnified by the projection lens 46 and projected onto the screen 42.

  In addition, in the image display device 40 according to the present embodiment, the transmissive liquid crystal panel 45 is provided with an ineffective image area that is not used for image display. In a portion corresponding to the position of the screen 42 in the ineffective image area, for example, an image sensor 51 such as a CCD or a CMOS is disposed. In the ineffective image area of the transmissive liquid crystal panel 45, for example, a line / space image for each pixel column is displayed as an MTF measurement pattern. Since the line / space image is enlarged on the screen 42, the luminance distribution of the line / space image can be detected relatively finely using the image sensor 51. When the MTF value of the optical deflecting device is lowered, the contrast between the white part and the black part of the line / space image formed on the screen 42 and the image sensor 51 is lowered. The amount of decrease in the MTF value of the deflecting device can be detected. Here, an increase / decrease detection means is realized.

  As described above, the electric field intensity larger than the electric field intensity at the time of the optical deflection operation is detected only when the light scattering amount or the decrease amount of the MTF value in the optical deflecting device is detected and the increase in the light scattering amount or the decrease amount of the MTF value is detected. Is temporarily applied, the timing of the application operation of the strong electric field can be minimized.

  Next, another best mode for carrying out the present invention will be described with reference to FIG. This embodiment shows an application example to an image display device.

  FIG. 21 is a schematic diagram showing an image display apparatus according to another best embodiment for carrying out the present invention. The projection-type image display device 40 has substantially the same configuration as that of the image display device 40 shown in FIG. 20, and includes a light source 41 as illumination means in which LED lamps are arranged in a two-dimensional array. In the traveling direction of light emitted from the light source 41 toward the screen 42, a diffusion plate 43, a condenser lens 44, a transmissive liquid crystal panel 45 as an image display element, and a projection lens 46 as an optical device for observing an image pattern. Are arranged in order. The light source 41 is driven and controlled by a light source drive unit 47, and the transmissive liquid crystal panel 45 is driven and controlled by a liquid crystal drive unit 48 serving as display driving means.

  On the optical path between the transmissive liquid crystal panel 45 and the projection lens 46, an optical deflection device 49 that functions as a pixel shift element is interposed. The light deflection device 49 is connected to the drive unit 50.

  In the present embodiment, it is possible to use various optical deflection devices as described above as the optical deflection device 49. As a specific optical deflection device 49, for example, an optical path in a two-dimensional direction as shown in FIG. A light deflecting device capable of shifting is used. In FIG. 22, the first light deflection apparatus 1A located upstream of the incident optical path, the polarization plane rotating means 60 for rotating the polarization plane of the outgoing light from the first light deflection apparatus 1A by 90 degrees, and the second And an optical deflection apparatus 1B. The optical path shift direction of the first light deflection apparatus 1A is arranged in parallel with the linear polarization plane of the incident light. As the polarization plane rotating means 60, a twisted nematic liquid crystal cell, a twisted nematic liquid crystal film, a half-wave plate or the like is used.

  In such an image display device 40, the illumination light that is controlled by the light source drive unit 47 and emitted from the light source 41 becomes illumination light that is made uniform by the diffuser plate 43, and the condenser lens 44 causes the illumination light source to be emitted by the liquid crystal drive unit 48. The transmissive liquid crystal panel 45 is critically illuminated by being controlled in synchronization. The illumination light spatially modulated by the transmissive liquid crystal panel 45 is incident on the light deflector 49 as image light, and the image light is shifted by an arbitrary distance in the pixel arrangement direction by the light deflector 49. This light is magnified by the projection lens 46 and projected onto the screen 42.

  Here, an image pattern in which the display position is shifted is displayed in accordance with the deflection of the optical path for each of the plurality of subfields obtained by temporally dividing the image field by the light deflecting device 49. Specifically, as shown in the timing chart of FIG. 23, the timing at which the projection optical path is shifted to four positions in the X and Y directions by the two light deflectors 1A and 1B, and four subfields corresponding to the shift positions. Synchronization with the timing of sequentially displaying images on the transmissive liquid crystal panel 84 is performed. Thus, the apparent number of pixels of the transmissive liquid crystal panel 45 can be multiplied and displayed.

  Note that the shift amount by the light deflecting device 49 is set to ½ of the pixel pitch because image multiplication is performed twice as much as the pixel arrangement direction of the transmissive liquid crystal panel 45. At this time, by using the optical deflection device 49 described above, a decrease in the MTF value in the optical deflection device 49 is suppressed, and a high-contrast and high-definition image can be provided.

  By correcting the image signal for driving the transmissive liquid crystal panel 45 by the shift amount according to the shift amount, an apparently high-definition image (four times in this embodiment) can be displayed.

  Here, for example, when each subfield displayed on the transmissive liquid crystal panel 45 is rewritten every 1/240 seconds, the display time of one frame image is 1/60 seconds. That is, the frame frequency of the display image is 60 Hz. In this case, since the period of one cycle of the driving electric field of each of the optical deflectors 1A and 1B in the timing chart shown in FIG. 23 is 1/60 second of the display time of one frame, the rectangular wave AC of the optical deflectors 1A and 1B The drive frequency of the electric field is 60 Hz.

  Here, the influence of the driving frequency on the MTF reduction phenomenon of the optical deflector was examined. FIG. 24 shows the MTF measurement result of CS1024 when a normal rectangular wave AC electric field as shown in FIG. 10 is applied as in FIG. When the drive frequency is 30 Hz, the decrease in MTF is small, and the amount of decrease in MTF increases as the drive frequency increases. From this result, it can be said that the driving frequency of the optical deflection apparatus is preferably about 100 Hz or less. Further, from the viewpoint of preventing flicker as an image display device, the frame frequency of the display image is preferably 30 Hz or more, that is, the driving frequency of one light deflection device is preferably 30 Hz or more. Therefore, it is preferable to set the driving frequency of the optical deflector to 30 Hz or more and 100 Hz or less from the viewpoint of preventing flicker and preventing MTF reduction.

  Examples of the present invention will be described below.

<Example 1>
(Creation of optical deflection device)
First, 100 transparent electrode lines having a width of 10 μm were formed on the surface of a glass substrate having a thickness of 1.1 mm. Each transparent electrode line was provided in parallel, and each interval was formed at a pitch of 100 μm.

  The length of the transparent electrode line was set so that the effective length was 10 mm, and the width and pitch were gradually increased in the longer part, and the contact with each electrode line was increased. The effective area of this transparent electrode line group is 10 mm square.

  A glass having a thickness of 150 μm was pasted onto the transparent electrode line group with an ultraviolet curing adhesive. The thickness of the adhesive at this time was about 10 μm.

As shown in the cross-sectional view of the light deflection element 10 shown in FIG. 2 described above, transparent line electrodes are embedded in the transparent glass as the substrates 2 and 3, and this substrate is used as the substrate in this embodiment. A vertical (homeotropic) alignment film of a polyimide compound having a thickness of 0.06 μm was formed on the surface of the substrate. As the polyimide alignment film, a polyamic acid solution was applied by spin coating, and a polyimide film was obtained by imidization treatment by heat treatment at about 180 ° C. A cell was prepared by sandwiching an 80 μm spacer sheet outside the effective area and facing the two substrates. At this time, the transparent electrode lines within the effective area of the upper and lower substrates were laminated so that they were alternately positioned as seen from above. In a state where the cell is heated to about 90 ° C., a ferroelectric liquid crystal (Chisso CS1024: birefringence Δn = 0.15, tilt angle θ = 25 degrees, helical pitch 20 μm at room temperature, spontaneous polarization Ps = −47 nC / cm ² ) was injected by a capillary method. After cooling, it was sealed with an adhesive to produce a light deflection element having a liquid crystal thickness of 50 μm and an effective area of 1 cm square.

  As shown in FIG. 3 described above, flexible substrates divided so that a voltage can be independently applied to the transparent line electrodes 9 of the substrates 2 and 3 of the optical deflection element 10 are connected to the upper and lower substrates, respectively. The other end was connected between the resistors of the series resistor array 11.

  The transparent line electrodes 9 on both ends of either one of the substrates 2 or 3 are connected to both ends of the resistor array 11 and correspond to the positions of the transparent line electrodes 9 arranged alternately between the upper and lower substrates 2 and 3. The resistance value at the end of the resistor array 11 connected to the other substrate 3 or 2 was adjusted so that the voltage value was also applied alternately. A power source including a pulse generator and a high-speed amplifier is connected to both ends of the resistor array 11. As a result, a current flows through the resistor array 11 to distribute the voltage, and a potential distribution is formed inside the effective area.

(Measurement of MTF of optical deflector)
Subsequently, the MTF in the optical deflection apparatus was measured (see FIG. 8). At this time, the drive frequency of the optical deflecting device was 60 Hz.

  It was observed that the optical path shift phenomenon caused by the switching of the optical axis of the liquid crystal layer 6 was caused by the application of the rectangular wave AC voltage, and the position of the MTF pattern was displaced. At this time, the MTF pattern seemed to move relatively slowly on the image of the CCD camera due to the difference between the frame frequency of the CCD camera and the drive frequency of the optical deflector.

  An image in a state where the MTF pattern is stationary in one side direction was taken into a computer, and the MTF value of the optical deflector was obtained. In addition, the optical path shift amount was obtained by comparing the stationary positions on both sides.

  As a result, at a temperature of about 25 ° C., the optical path shift amount at an electric field strength of 40 V / mm or more was about 9 μm.

  By normalizing the MTF value with the MTF value by the reference element, the MTF caused by the boundary portion between the liquid crystal layer 6 and the vertical alignment film 4 was obtained.

  The MTF value of the above optical deflecting device when no electric field was applied was 0.78, which was a relatively bad value. This is presumably because there are many domains in the liquid crystal layer when there is no electric field, and there is an influence of light scattering on the domain walls.

  Subsequently, an AC voltage application device was configured using two pulse generators, a pulse waveform synthesis circuit, and a high-speed voltage amplifier (see FIG. 3). One pulse generator generates a reference pulse of ± 1.0 V and 60 Hz as shown in FIG. At this time, the pulse width of one rectangle is set to about 8.33 msec.

  The other pulse generator generates an additional pulse as shown in FIG. 25B that repeats the application timing at one cycle of ± 0.8V. At this time, the pulse width of one rectangle is set to about 4 msec.

  By synthesizing these pulses by a synthesis circuit (not shown), a synthesized pulse as shown in FIG. 25C is generated, and this synthesized pulse is input to a high-speed voltage amplifier (not shown). The high-speed voltage amplifier amplifies the input signal 1000 times. For this reason, a voltage in which a pulse voltage of ± 1800 V is repeatedly added to a square wave AC voltage of ± 1000 V and 60 Hz is generated.

  By applying this voltage to the optical deflecting device, an electric field in which a ± 200 V / mm pulse electric field is superimposed on a ± 100 V / mm, 60 Hz rectangular wave AC electric field is formed in an effective region of 10 mm width of the optical deflecting device. Applied.

  The MTF immediately after starting driving with this electric field was 0.90. Thereafter, the MTF after continuous operation for about 1 hour was 0.84. That is, the MTF value decreased compared to the initial stage. However, it is judged that this level of decrease is within a practically acceptable range.

<Comparative Example 1>
Example 2 is the same as Example 1 except that the additional pulse shown in FIG. 25 is not applied. After the start of driving, the MTF gradually began to decrease, and after 10 minutes, the MTF value decreased significantly to about 0.6. For this reason, further continuous operation tests were discontinued.

  Even if the driving electric field was turned off in this state, the state where the MTF was lowered did not recover.

  When the light deflecting device in a state where the MTF value was lowered was placed in the crossed Nicols of two polarizing plates and observed, there was a lot of leakage light, the orientation of the smectic layer was greatly disturbed, and light scattering and depolarization occurred. I understood that.

<Example 2>
As shown in FIG. 26, this example is the same as Example 1 except that the voltage of the additional pulse is set to ± 1.0 V and the pulse width is set to 8.33 msec, which is the same as the reference pulse. With this combined pulse and the high-speed voltage amplifier, an electric field pattern in which a pulse electric field of ± 200 V / mm is superimposed on a rectangular wave AC electric field of ± 100 V / mm and 60 Hz in the effective region of the optical deflector (FIG. 24B ))) Is repeatedly applied. The absolute value of the saturation electric field strength Ec of the liquid crystal material used in this optical deflecting device is 40 V / mm, and the normalized electric field E / Ec in a strong electric field is 4. The absolute value of the spontaneous polarization Ps is 47 nC / cm ² , and Ps · E is 9400 μN / cm ² .

  As a result, the MTF immediately after the start of driving was 0.90, and the MTF after continuous operation for about 1 hour was 0.86. Although the MTF value decreased slightly compared with the initial value, it was determined that it was in a practically acceptable range. Moreover, the effect by lengthening the pulse width of a large electric field pulse has been confirmed.

<Example 3>
As shown in FIG. 26, the voltage waveform of the additional pulse is serrated, the peak voltage value is set to ± 1.0 V, and the pulse width is set to 8.33 msec, which is the same as that of the reference pulse. By this combined pulse and the high-speed voltage amplifier, an electric field in which a ± 300 V / mm sawtooth pulse electric field is superimposed on a rectangular wave AC electric field of ± 100 V / mm and 60 Hz is applied to the effective region of the optical deflector. . The absolute value of the saturation electric field intensity Ec of the liquid crystal material used in this optical deflecting device is 40 V / mm, and the normalized electric field E / Ec when a strong electric field is applied is a sufficiently large value of 7.5. The absolute value of the spontaneous polarization Ps is 47 nC / cm ² , and Ps · E is a sufficiently large value of 14100 μN / cm ² .

  The MTF immediately after driving with this electric field was 0.90. Thereafter, the MTF after continuous operation for about 1 hour was 0.89, and the initial decrease in MTF was hardly observed. Therefore, an effect of a pulse waveform for gradually applying a strong electric field and an effect of driving under conditions with large E / Ec and PsE were obtained.

  Further, the MTF after about 8 hours of continuous operation was lowered to 0.86. Although the MTF value decreased slightly compared with the initial value, it was determined that it was in a practically acceptable range.

  At this time, a white turbid portion due to disorder in the alignment of the liquid crystal layer was generated in the peripheral portion outside the effective region. However, since this is also outside the effective region, it can be determined that there is no practical problem.

  However, the cloudy portion may grow as it is, and the effective region may become cloudy. This is presumably because the DC balance in the liquid crystal layer is broken in the voltage pattern as shown in FIG.

<Example 4>
As in FIG. 28, the third embodiment is the same as the third embodiment except that the waveform is changed so that the applied voltage value of the additional pulse waveform becomes zero when averaged. With this combined pulse and the high-speed voltage amplifier, a ± 300 V / mm sawtooth pulse electric field is superimposed on a rectangular wave AC electric field of ± 100 V / mm and 60 Hz in the effective area of the optical deflector, and within a unit time. The electric field is applied so that the average value of the vector of the electric field applied to the liquid crystal layer becomes substantially zero.

  The MTF immediately after starting driving with this electric field was 0.90. Thereafter, the MTF after continuous operation for about 1 hour was 0.89, and the initial decrease in MTF was hardly observed.

  Furthermore, MTF about 8 hours after continuing the continuous operation also maintained 0.89.

  Further, no white turbid portion due to disordered alignment of the liquid crystal layer was generated in the peripheral portion outside the effective region.

This is presumed that in the voltage pattern as shown in FIG. 28, the DC balance in the liquid crystal layer is maintained, so that stable light deflection operation can be performed for a long time.
<Example 5>
As shown in FIG. 29, the fourth embodiment is the same as the fourth embodiment except that the applied voltage value of the additional pulse waveform is changed to a rectangular wave. By this synthesized pulse and the high-speed voltage amplifier, a rectangular wave pulse electric field of ± 300 V / mm is superimposed on a rectangular wave AC electric field of ± 100 V / mm and 60 Hz in the effective area of the optical deflecting device, and the liquid crystal within a unit time. The electric field is applied so that the average value of the electric field vector applied to the layer is substantially zero.

  The MTF immediately after starting driving with this electric field was 0.90. Thereafter, the MTF after continuous operation for about 1 hour was 0.90, and no initial MTF reduction occurred.

  Further, although the MTF after about 8 hours of continuous operation was maintained at 0.90, the temperature of the resistor array 11 was heated to about 50 ° C. after about 8 hours of continuous operation. This is not a problem in practical use, but a problem may occur when a continuous operation is performed for a longer time. This heat generation is presumed to be because the value of the current flowing through the resistor array 11 is large, that is, the change in electric field is too large.

<Example 6>
As shown in FIG. 30, the timing of the additional pulse waveform is the same as that of the fifth embodiment except that the timing of the additional pulse waveform is set with an interval of a half cycle or more of the reference pulse. By this combined pulse and the high-speed voltage amplifier, a pulsed electric field of ± 300 V / mm and a rectangular wave of ± 300 V / mm are superimposed on a rectangular wave AC electric field of ± 100 V / mm and 60 Hz in the effective area of the optical deflecting device, The average value of the electric field vector applied to the liquid crystal layer becomes substantially zero, and after applying a large electric field strength in one electric field direction, after applying the electric field strength during light deflection operation for at least a half cycle, An electric field is applied so as to control to apply a large electric field strength with respect to one or the other electric field direction. In FIG. 30, a strong electric field is applied in the same direction with a half period. Note that, as shown in FIG. 8, a strong electric field may be applied in the other direction at intervals of one cycle.

  The MTF immediately after starting driving with this electric field was 0.90. Thereafter, the MTF after continuous operation for about 1 hour was 0.90, and no initial MTF reduction occurred.

  Further, the MTF after about 8 hours of continuous operation was maintained at 0.90. However, after about 8 hours of continuous operation, the temperature of the resistor array 11 was about 35 ° C.

  In the fifth embodiment described above, the maximum voltage change is 6000 V, whereas in the present embodiment, the maximum voltage change is suppressed to 4000 V, which is considered to suppress the heat generation of the resistor array 1. In addition, the load on the power source is reduced.

<Example 7>
In the image display device as shown in FIG. 21, three 0.9-inch diagonal XGA (1024 × 768 dots) polysilicon TFT liquid crystal panels were used as image display elements. 21 exemplifies the case where there is one liquid crystal panel, but in this embodiment, the light from the three liquid crystal panels is synthesized by a synthesis prism (not shown) and projected by one projection lens 85. The pixel pitch of the liquid crystal panel is about 18 μm both vertically and horizontally. The aperture ratio of the pixel is about 50%. Further, a microlens array is provided on the light source side of the image display element to increase the collection rate of illumination light. In this embodiment, the frame frequency of image display is 60 Hz, and the subfield frequency for pixel multiplication by 4 times by pixel shift is 240 times, which is 4 times. Each of the three liquid crystal panels is illuminated with light obtained by color separation of RGB three-color light sources or white light sources using a prism or filter, and a full-color image is displayed by combining the images of the respective colors with a combining prism (not shown). Two optical deflecting devices (see FIGS. 2 and 3) having a relatively large area were used as the optical deflecting device, and an optical path shifting operation at four positions in the XY2 direction was enabled (see FIG. 22). The driving timing of the voltages applied to the two light deflectors and the display timing of each subfield of the liquid crystal panel were set in the same manner as in FIG. The optical path shift amount of the optical deflecting device is about 9 μm, which is ½ of the pixel pitch of the liquid crystal panel. Further, the polarization direction of the light emitted from the liquid crystal panel was set to be the same as the shift direction of the optical path of the first light deflector. Further, in order to ensure the degree of polarization of incident light to the optical deflecting device, a linearly polarizing plate is provided on the incident surface side of the optical deflecting device.

  The voltage applied to each optical deflector comprises two pulse generators, a circuit for synthesizing each pulse, and a high-speed high-voltage amplifier. The pulse generation timing of the reference pulse generator of each optical deflector is shown in FIG. Thus, it is set so as to be shifted by a quarter cycle.

  The reference pulse of each optical deflecting device is a square wave AC voltage of ± 1.0 V and 60 Hz as in FIG. 28, and the voltage pattern by the additional pulse generating means has a pulse width of about 8.33 msec and a voltage absolute value of 2 It was set to 0.0V. This was repeated with the voltage application pattern in the time range shown in the lower part of FIG. 30 as one cycle.

  A strong electric field of ± 3000 V in a periodic pattern is applied to a square wave AC voltage of ± 1000 V and 60 Hz as a reference voltage at both ends of the resistor array of the optical deflector, and in synchronization with the switching timing of the optical path shift position. By rewriting the subfield image displayed on the image display element in 1/60 second, a high-definition image in which the apparent number of pixels was multiplied by 4 could be displayed. At this time, the main electric field strength is 100 V / mm. The switching time of the electric field direction in the optical deflecting device is about 1.0 msec. As a result, sufficient light utilization efficiency was obtained.

  Further, even after about 8 hours of continuous operation, no blurring occurred in the image, and high-definition image display could be maintained.

  However, when a still image is displayed, flicker like flicker may be felt depending on the observer. This is considered because the strong electric field application timing for suppressing the decrease in the MTF value has a certain periodicity. If the normal driving electric field is equal to or higher than the saturation electric field Ec, the optical path shift amount does not change even when a higher electric field is applied, but the response speed and the transient light scattering intensity change, so that a periodic change is felt. This is probably because of this.

<Example 8>
An image display device similar to that of Example 7 was prepared except that a random number generation circuit for generating random application timings of the additional pulses of each optical deflecting device was connected to the pal additional pulse generating means.

  A strong electric field of ± 3000 V in a random pattern is applied to both ends of the resistor array 11 of the optical deflector as a reference voltage and a rectangular wave AC voltage of ± 1000 V and 60 Hz, and in synchronization with the switching timing of the optical path shift position. By rewriting the subfield image displayed on the image display element in 1/60 second, a high-definition image in which the apparent number of pixels was multiplied by 4 could be displayed. At this time, the main electric field strength was 100 V / mm, and the switching time of the electric field direction in the optical deflecting device was about 1.0 msec, and sufficient light utilization efficiency was obtained.

  Further, even after about 8 hours of continuous operation, no blurring occurred in the image, and high-definition image display could be maintained.

  Further, even when a still image was displayed, flicker like flicker was not felt. This is considered because the strong electric field application timing for suppressing the decrease in the MTF value is applied randomly.

<Example 9>
As shown in FIG. 31, in the image display device 40 shown in FIG. 21, a photodetector 70 is provided at a position where the projection optical path is not obstructed on the exit surface side of the light deflector 49, and according to the detection result by the photodetector 70. Thus, an image display apparatus similar to that in Example 8 was prepared except that the pulse generation operation of the additional pulse generation means was controlled.

  As shown in FIG. 19, the photodetector 70 is arranged so as to detect the light scattering intensity of the light deflection apparatus.

  First, from the correlation between the MTF value of the light deflector that has been experimentally obtained in advance and the output value of the photodetector 70 for an arbitrary display image pattern, light scattering occurs in the light deflector at the beginning of continuous operation. It was judged that it was not.

  As an arbitrary display image pattern, a white image with a large amount of light was used, and only 1/60 second was displayed so as not to be recognized by an observer.

  The scattered light intensity was measured in accordance with the display timing. Based on the detection result, the image display operation was started without applying a strong electric field by the additional pulse generating means.

  In this embodiment, the scattered light detection operation as described above was performed every 3 minutes. As a result, it was determined that no MTF decrease occurred after 3 minutes from the start of the operation, and the electric field application was continued using only the reference pattern. Then, an increase in scattered light was observed at the second detection timing 6 minutes after the start of operation.

  Subsequently, the superposition operation of the strong electric field by the additional pulse generating means was performed for 1 minute from the time when it was determined from the output value of the photodetector 70 that the MTF had decreased to about 0.86. As a result, at the next detection timing, it was determined that the MTF value had recovered to about 0.90, and the electric field application was continued using only the reference pattern. Thereafter, when the operation was continued for 8 hours in the same manner, no blurring of the display image due to the MTF reduction was observed until the end.

  In this embodiment, since the period during which the strong electric field is applied is short, there is an advantage that the load on the liquid crystal layer and the power source in the optical deflection apparatus is small.

It is the schematic which shows the optical deflection | deviation element in the optical deflection | deviation apparatus of one best embodiment for implementing this invention. It is sectional drawing which shows another optical deflection | deviation element. FIG. The electric field direction and the tilt direction of the liquid crystal molecules are shown in the liquid crystal layer. (A) shows a state in which an electric field from right to left is applied in the figure, and (b) shows an electric field in the figure from left to right in the figure. FIG. FIG. 5 is a perspective view schematically showing the liquid crystal layer in FIG. 4, where (a) shows a state where an electric field is applied from right to left in FIG. 4, and (b) shows an electric field which is applied from left to right in FIG. 4. It shows the state being done. It is a schematic diagram which shows the orientation state of a liquid crystal molecule, (a) shows the case where the electric field which goes to a near side direction from a paper surface is applied with respect to the liquid crystal layer 6, (b) shows with respect to the liquid crystal layer 6. The case where the electric field which goes to a back | inner side direction from the paper front side is shown is shown. It is a schematic diagram which shows the inclination state of the liquid crystal molecule in a light deflection | deviation element, (a) shows the state before an electric field inversion, (b) shows a light-scattering state, (c) has the flow of a domain after re-orientation. The state is shown, and (d) shows the state after the flow of the domain converges. It is the schematic which shows an example of an MTF value measuring apparatus. It is explanatory drawing which shows the example of the MTF fall phenomenon by the conventional electric field application method. It is a timing chart which shows a rectangular wave alternating electric field. It is a graph which shows the result of having normalized and arranged the applied electric field strength by saturation electric field strength Ec. It is a graph which shows the relationship between the product (Ps * E) of the spontaneous polarization Ps equivalent to the electric driving force which acts on a liquid crystal molecule, and the electric field strength E, and MTF value. It is a schematic diagram which shows the inclination state of the smectic layer by a strong electric field application. It is a timing chart which shows the electric field waveform at the time of a strong electric field application. It is a timing chart which shows another electric field waveform at the time of the strong electric field application in the optical deflecting device of another best embodiment for carrying out the present invention. It is a timing chart which shows another electric field waveform at the time of the strong electric field application in the optical deflecting device of another best embodiment for carrying out the present invention. It is a timing chart which shows another electric field waveform at the time of the strong electric field application in the optical deflecting device of another best embodiment for carrying out the present invention. It is a timing chart which shows another electric field waveform at the time of the strong electric field application in the optical deflecting device of another best embodiment for carrying out the present invention. It is explanatory drawing which shows the measuring device of the amount of light scattering in the light deflecting device of another best embodiment for implementing this invention. It is a schematic diagram which shows the image display apparatus which enabled the MTF fall amount in an optical deflection | deviation apparatus to be observed directly. It is a schematic diagram which shows the image display apparatus of another best embodiment for implementing this invention. It is a schematic diagram which shows the optical deflection apparatus which can optical-path shift in a two-dimensional direction, (a) is a perspective view which shows the disassembled state, (b) is a perspective view which shows the assembled state. It is a timing chart which shows the timing which shifts a projection optical path to four positions of X and Y directions by two light deflection apparatuses. It is a graph which shows the MTF measurement result of CS1024 when a normal rectangular wave AC electric field is applied. It is a timing chart which shows an electric field waveform at the time of measurement of MTF of an optical deflecting device. It is a timing chart which shows another electric field waveform at the time of measurement of MTF of an optical deflecting device. It is a timing chart which shows another electric field waveform at the time of measurement of MTF of an optical deflecting device. It is a timing chart which shows another electric field waveform at the time of measurement of MTF of an optical deflecting device. It is a timing chart which shows another electric field waveform at the time of measurement of MTF of an optical deflecting device. It is a timing chart which shows another electric field waveform at the time of measurement of MTF of an optical deflecting device. FIG. 10 is a schematic diagram illustrating an image display device according to a ninth embodiment.

Explanation of symbols

2, 3 Substrate 6 Liquid crystal layer 40 Image display device 41 Illumination means 45 Image display element 46 Optical device 48 Display drive means 49 Optical deflection device

Claims (21)

A pair of transparent substrates;
A liquid crystal layer capable of forming a chiral smectic C phase having a homeotropic alignment filled between the substrates;
An electric field applying means for applying a normal electric field for deflecting light incident on the liquid crystal layer in a direction substantially perpendicular to the normal direction of the substrate surface and the light deflection direction with respect to the liquid crystal layer;
Electric field direction switching means for switching the electric field direction of the normal electric field;
An electric field control means for applying a strong electric field having a larger electric field strength than the normal electric field at any timing overlapping the timing at which the normal electric field is applied to the liquid crystal layer;
An optical deflection apparatus comprising: The electric field applying means applies a rectangular wave-shaped AC electric field as a normal electric field, in which the absolute value and the time width of the electric field strength in positive and negative polarities are equal,
2. The optical deflection apparatus according to claim 1, wherein the electric field control means applies a rectangular wave-shaped AC electric field having a time width equal to that of the normal electric field and different in absolute value of electric field strength. The electric field applying means applies, as the normal electric field, an alternating electric field of a rectangular wave shape in which the absolute value of the electric field strength in each polarity is positive and the time width is equal.
2. The optical deflecting device according to claim 1, wherein the electric field control means applies the strong electric field by increasing the electric field strength of the normal electric field continuously or stepwise until the electric field direction once switched is switched to the next. .   The optical deflection apparatus according to claim 1, 2 or 3, wherein the electric field control means applies the strong electric field at a timing generated randomly.   The electric field control means applies the strong electric field so that an average value of vectors per unit time becomes substantially zero by adjusting an application timing, an electric field direction, and an electric field strength. The light deflection apparatus described.   6. The electric field control means applies the strong electric field after a normal electric field is applied for a half period or more after switching the electric field direction with respect to a switching period until the electric field direction once switched is switched to the next. The light deflection apparatus according to any one of the above.   The optical deflection apparatus according to claim 1, wherein the electric field control unit applies an electric field set to an absolute value of 200 V / mm or more as the strong electric field.   The electric field control means applies an electric field set to an absolute value of 5 times or more of a saturation electric field intensity Ec (V / mm) which is an absolute value of an electric field intensity at which the tilt angle of the optical axis is saturated in the liquid crystal layer. The light deflection apparatus according to claim 1, wherein the light deflection apparatus is applied as an electric field. When the absolute value of the spontaneous polarization of the liquid crystal layer is Ps (nC / cm ² ) and the absolute value of the strong electric field is E (V / mm), the electric field control means has a value of Ps × E of 10,000 (μN The optical deflection apparatus according to any one of claims 1 to 8, wherein an electric field set to be equal to or higher than / cm ² is applied as the strong electric field. An increase / decrease detection means for detecting an increase / decrease in light scattering amount or MTF value decrease amount in the liquid crystal layer;
The light deflection apparatus according to claim 1, wherein the electric field control unit applies the strong electric field when an increase in light scattering amount or a decrease in MTF value is detected. An image display element in which a plurality of pixels capable of controlling light according to image information are two-dimensionally arranged;
Illuminating means for illuminating the image display element;
An optical device for observing an image pattern displayed by the image display element;
Display driving means for driving the image display element in units of a plurality of subfields obtained by temporally dividing an image field;
The light deflecting device according to any one of claims 1 to 10, wherein an optical path of light emitted from each pixel of the image display element is deflected for each subfield;
Comprising
The electric field applying means included in the optical deflection device is an image display device that applies a rectangular wave AC electric field having a frequency set to 30 Hz or more and 100 Hz or less to the liquid crystal layer. A liquid crystal layer capable of forming a chiral smectic C phase having a homeotropic alignment filled between a pair of transparent substrates is substantially orthogonal to the normal direction and the light deflection direction of the substrate surface with respect to the liquid crystal layer. In an optical deflecting device that switches the electric field direction of a normal electric field that deflects incident light applied in the direction,
An optical deflection method, wherein a strong electric field having a larger electric field strength than the normal electric field is applied to the liquid crystal layer at an arbitrary timing overlapping with a timing at which the normal electric field is applied.   When applying the normal electric field, a rectangular wave-shaped AC electric field having the same absolute value and time width of the electric field strength in each polarity is applied as the normal electric field, and when applying the strong electric field, the normal electric field and the time width are 13. The optical deflection method according to claim 12, wherein an AC electric field having a rectangular wave shape with the same absolute value of the electric field strength is applied.   When applying the normal electric field, a rectangular wave-shaped AC electric field having the same absolute value and time width of the electric field strength in each of the positive and negative polarities is applied. When applying the strong electric field, the switched electric field direction is switched to the next time. 13. The optical deflection method according to claim 12, wherein the strong electric field is applied by increasing the electric field strength of the normal electric field continuously or stepwise.   15. The optical deflection method according to claim 12, 13 or 14, wherein the strong electric field is applied at a timing generated randomly.   The strong electric field is applied by applying a strong electric field such that an average value of vectors per unit time becomes substantially zero by adjusting an application timing, an electric field direction, and an electric field strength. The light deflection method according to 13, 14 or 15.   When applying the strong electric field, the strong electric field is applied after a normal electric field is applied for a half period or more after switching the electric field direction with respect to a switching period until the electric field direction once switched is switched to the next. An optical deflection method according to any one of claims 12 to 16.   18. The light deflection method according to claim 12, wherein an electric field set to an absolute value of 200 V / mm or more is applied as the strong electric field when the strong electric field is applied.   When applying the strong electric field, an electric field set to an absolute value of 5 times or more with respect to the saturation electric field strength Ec (V / mm), which is the absolute value of the electric field strength at which the tilt angle of the optical axis is saturated in the liquid crystal layer, is applied. The light deflection method according to claim 12, wherein the light deflection method is applied as a strong electric field. When the strong electric field is applied, the absolute value of spontaneous polarization of the liquid crystal layer is Ps (nC / cm ² ), and the absolute value of the strong electric field is E (V / mm), and the value of Ps × E is 10,000 ( 20. The light deflection method according to claim 12, wherein an electric field set to be equal to or higher than [mu] N / cm < ² >) is applied as the strong electric field. When applying the strong electric field, when an increase / decrease detecting means for detecting an increase / decrease in the amount of light scattering or MTF value decrease in the liquid crystal layer is detected, an increase in the amount of light scattering or MTF value decrease is detected. 21. The light deflection method according to claim 12, wherein a strong electric field is applied.

Images