Optical deflection device and optical deflection method that control occurrence of alignment defect Number:7,038,835 from the United States Patent and Trademark Office (PTO) owispatent

Title: Optical deflection device and optical deflection method that control occurrence of alignment defect

Abstract: An optical deflection device includes an optical deflection element having a pair of transparent boards arranged in a mutually opposing manner. A liquid crystal layer is filled between the boards and forms a chiral smectic C phase. An orientation film orients liquid crystal molecules in the liquid crystal layer in a substantially perpendicular direction with respect to the liquid crystal layer. Electrodes generate an electric field in a substantially parallel direction with respect to the liquid crystal layer. A first voltage application part applies, to the electrodes, an ac voltage of a deflection frequency switching the optical deflection direction of the optical deflection element. A second voltage application part applies, to the electrodes, an ac voltage of a higher frequency than the deflection frequency. A stop process part causes the second voltage application part to apply the ac voltage of the higher frequency than the deflection frequency after causing the first voltage application part to apply the ac voltage of the deflection frequency, when stopping an operation of switching the optical deflection direction of the optical-deflection element.

Patent Number: 7,038,835 Issued on 05/02/2006 to Matsuki,   et al.

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Inventors:	Matsuki; Yumi (Kanagawa, JP); Sugimoto; Hiroyuki (Kanagawa, JP); Tokita; Toshiaki (Kanagawa, JP); Nimura; Shigeaki (Kanagawa, JP); Kobayashi; Masanori (Kanagawa, JP); Takiguchi; Yasuyuki (Kanagawa, JP)
Assignee:	Ricoh Company, Ltd. (Tokyo, JP)
Appl. No.:	441125
Filed:	May 20, 2003

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Foreign Application Priority Data

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May 28, 2002 [JP]			2002-153978
Apr 04, 2003 [JP]			2003-101049

Current U.S. Class:	359/315 ; 359/320; 359/322
Current International Class:	G02F 1/29 (20060101)
Field of Search:	359/315,278,320,322,237,245,252,254

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References Cited [Referenced By]

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U.S. Patent Documents

	5619765		April 1997		Tokita et al.
	5638842		June 1997		Tokita et al.
	5769957		June 1998		Murakami et al.
	5923928		July 1999		Sugimoto
	5926669		July 1999		Sugimoto et al.
	5969780		October 1999		Matsumoto et al.
	6006062		December 1999		Takahashi et al.
	6061042		May 2000		Takahashi et al.
	6144832		November 2000		Nimura et al.
	6151093		November 2000		Takiguchi et al.
	6157795		December 2000		Kadonaga et al.
	6223008		April 2001		Takahashi et al.
	6351299		February 2002		Takiguchi et al.
	6480345		November 2002		Kawashima et al.
	6497488		December 2002		Yamauchi et al.
	6524759		February 2003		Sugimoto et al.
	6537711		March 2003		Nimura et al.
	2002/0135729		September 2002		Tokita et al.
	2003/0098945		May 2003		Sugimoto et al.

Foreign Patent Documents

	5-204001		Aug., 1993		JP
	5-313116		Nov., 1993		JP
	6-18940		Jan., 1994		JP
	6-194695		Jul., 1994		JP
	6-222368		Aug., 1994		JP
	6-258646		Sep., 1994		JP
	6-324320		Nov., 1994		JP
	7-64123		Mar., 1995		JP
	8-262391		Oct., 1996		JP
	9-133904		May., 1997		JP
	9-133931		May., 1997		JP
	10-133135		May., 1998		JP
	11-109304		Apr., 1999		JP
	2000-507005		Jun., 2000		JP
	2000-193925		Jul., 2000		JP
	WO 98/30934		Jul., 1998		WO

Other References

Edited by M. Aoki, 3 pages "Optoelectronic Device", 1986. cited by other.

Primary Examiner: Mack; Ricky L.
Assistant Examiner: Thomas; Brandi
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier & Neustadt, P.C.

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Claims

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What is claimed is:

1. An optical deflection device, comprising: an optical deflection element comprising a pair of transparent substrates arranged in a mutually opposing manner, a liquid crystal layer filling a gap formed between said pair of substrates, a liquid crystal of said liquid crystal layer forming a chiral smectic C phase, each of said substrates carrying thereon an orientation film orienting liquid crystal molecules in said liquid crystal layer in a substantially perpendicular direction with respect to said liquid crystal layer, and electrodes generating an electric field in a substantially parallel direction with respect to said liquid crystal layer; a first voltage application part applying, to said electrodes, an ac voltage of a first frequency so as to cause switching in an optical deflection direction of said optical deflection element; a second voltage application part applying, to said electrodes, an ac voltage of a second frequency different from the first frequency; and a control part causing said second voltage application part to apply an ac voltage of said second frequency after causing said first voltage application part to apply the ac voltage of the first frequency.

2. The optical deflection device as claimed in claim 1, wherein the second voltage application part applies, to the electrodes, said ac voltage with a period of a half cycle shorter than a response time of the liquid crystal molecules.

3. The optical deflection device as claimed in claim 1, wherein the second voltage application part applies said ac voltage of a higher voltage value than a voltage value applied by the first voltage application part.

4. The optical deflection device as claimed in claim 1, further comprising: a third voltage application part applying a pulsed dc voltage to the electrodes, wherein, when stopping the operation of switching the optical deflection direction of the optical deflection element, the control part causes the second voltage application part to apply the ac voltage of said second frequency after causing the first voltage application part to apply the ac voltage of the first frequency and subsequently causing said third voltage application part to intermittently apply the pulsed dc voltage.

5. The optical deflection device as claimed in claim 4, wherein the third voltage application part applies the dc voltage of a higher voltage value than a voltage value applied by the first voltage application part.

6. The optical deflection device as claimed in claim 1, wherein a dielectric anisotropy of the liquid crystal layer forming the chiral smectic C phase is negatiave in a frequency band of an ac voltage having a period of a half cycle shorter than a response time of the liquid crystal molecules.

7. An optical deflection device, comprising: an optical deflection element comprising a pair of transparent substrates arranged in a mutually opposing manner, a liquid crystal layer filling a gap formed between said pair of substrates, a liquid crystal of said liquid crystal layer forming a chiral smectic C phase, each of said pair of substrates carrying thereon an orientation film orienting liquid crystal molecules in said liquid crystal layer in a substantially perpendicular direction with respect to said liquid crystal layer, and electrodes generating an electric field in a substantially parallel direction with respect to said liquid crystal layer; a first voltage application part applying, to said electrodes, an ac voltage of a first frequency so as to cause switching in an optical deflection direction of said optical deflection element; a second voltage application part applying, to said electrodes, an ac voltage of a second frequency different from said first frequency; and a control part causing said first voltage application part to apply the ac voltage of said first frequency after causing said second voltage application part to apply the ac voltage of said second frequency when starting an operation of switching the optical deflection direction of said optical deflection element.

8. The optical deflection device as claimed in claim 7, wherein the second voltage application part applies, to the electrodes, the ac voltage of a higher frequency than the first frequency as said second frequency such that the ac voltage of a lower frequency than the first frequency is applied and thereafter increasing the frequency of the ac voltage continuously or in stages, and the control part causes the first voltage application part to apply the ac voltage of the first frequency following the application of the ac voltage of the second frequency higher than the first frequency by the second voltage application part, when starting the operation of switching the optical deflection direction of the optical deflection element.

9. The optical deflection device as claimed in claim 7, wherein the second voltage application part applies, to the electrodes, the ac voltage of the second frequency set higher than the first frequency, and thereafter decreases the second frequency continuously or in stages so as to apply the ac voltage to the electrodes with a frequency substantially equal to the first frequency, and the control part causes the first voltage application part to apply the ac voltage of the first frequency, following the application of the ac voltage of the second frequency set to substantially equal to the first frequency by the second voltage application part, when starting the operation of switching the optical deflection direction of the optical deflection element.

10. The optical deflection device as claimed in claim 7, wherein the second voltage application part applies, to the electrodes, an ac voltage having a period of a half cycle shorter than a response time of the liquid crystal molecules.

11. The optical deflection device as claimed in claim 7, wherein the second voltage application part applies the ac voltage of a higher voltage value than a voltage value applied by the first voltage application part.

12. The optical deflection device as claimed in claim 7, wherein the second voltage application part applies the ac voltage of a lower voltage value than a voltage value applied by the first voltage application part, and thereafter increases the voltage value of the ac voltage continuously or in stages so as to apply a deflection operation voltage value, when starting the operation of switching the optical deflection direction of said optical deflection element.

13. The optical deflection device as claimed in claim 7, further comprising: a third voltage application part applying a pulsed dc voltage to the electrodes, wherein, when starting the operation of switching the optical deflection direction of the optical deflection element, the start process part causes the second voltage application part to the ac voltage of the second frequency higher than the first frequency, following intermittent application of the pulsed dc voltage by said third voltage application part, and thereafter causes the first voltage application part to apply the ac voltage of the first frequency.

14. The optical deflection device as claimed in claim 13, wherein the third voltage application part applies the dc voltage of a higher voltage value than a voltage value applied by the first voltage application part.

15. The optical deflection device as claimed in claim 7, wherein a dielectric anisotropy of the liquid crystal layer forming the chiral smectic C phase is negative in a frequency band of the ac voltage having a period of a half cycle shorter than a response time of the liquid crystal molecules.

16. An optical deflection method, comprising: an optical deflection step of applying, to electrodes, an ac voltage of a first frequency so as to cause switching in an optical deflection direction of an optical deflection element, said optical deflection element comprising a pair of transparent substrates arranged in a mutually opposing manner, a liquid crystal layer filling a gap between said pair of substrates, a liquid crystal of said liquid crystal layer forming a chiral smectic C phase, each of said pair of substrates carrying thereon an orientation film orienting liquid crystal molecules in said liquid crystal layer in a substantially perpendicular direction with respect to said liquid crystal layer, and said electrodes generating an electric field in a substantially parallel direction with respect to said liquid crystal layer; and a voltage application step of applying, to said electrodes, an ac voltage of a second frequency different from the first frequency, following said optical deflection step.

17. An optical deflection method, comprising: an optical deflection step of applying, to electrodes, an ac voltage of a first frequency so as to cause switching in an optical deflection direction of an optical deflection element, said optical deflection element comprising a pair of transparent substrates arranged in a mutually opposing manner, a liquid crystal layer filling a gap formed between said pair of substrates, a liquid crystal of said liquid crystal layer forming a chiral smectic C phase, each of said pair of substrates carrying thereon an orientation film orienting liquid crystal molecules in said liquid crystal layer in a substantially perpendicular direction with respect to said liquid crystal layer, and said electrodes generating an electric field in a substantially parallel direction with respect to said liquid crystal layer; and a voltage application step of applying an ac voltage of a second, different frequency before said optical deflection step.

18. The optical deflection device as claimed in claim 1, wherein the second voltage application part applies said ac voltage of said second frequency that is higher than said first frequency.

19. The optical deflection device as claimed in claim 7, wherein said second frequency is higher than said first frequency.

20. The optical deflection device as claimed in claim 16, wherein said second frequency is higher than said first frequency.

21. The optical deflection device as claimed in claim 17, wherein said second frequency is higher than said first frequency.

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Description

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BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to optical deflection devices and optical deflection methods.

2. Description of the Related Art

Conventionally, known optical deflection devices deflecting and emitting incident light by using optical deflection elements include electro-optical devices that use materials having great primary electro-optical effect (Pockels effect), such as KH.sub.2PO.sub.4(KDP), NH.sub.4H.sub.2PO.sub.4(ADP), LiNbO.sub.3, LiTaO.sub.3, GaAs and CdTe, and materials having great secondary electro-optical effect, such as KTN, SrTiO.sub.3, CS.sub.2 and nitrobenzene, and include acousto-optical devices that use materials such as glass, silica and TeO2 (for example, refer to "Optoelectronic Device" edited by Masaharu Aoki, Shokodo). Also, there are proposed various optical deflection devices that use optical deflection elements including liquid crystal materials.

For example, as disclosed in Japanese Laid-Open Patent Applications No. 6-18940 and No. 5-313116, there are optical deflection devices (optical beam shifters) that reduce light losses. In addition, as disclosed in Japanese Laid-Open Patent Applications No. 2000-193925, No. 9-133931, and No. 5-204001, there are optical deflection devices that are configured to reduce power of an optical deflecting operation by optical deflection elements and to achieve a smaller size.

Further, as disclosed in Japanese Laid-Open Patent Applications No. 6-194695, No, 6-258646, and No. 6-222368, there are optical deflection devices that extend deflection angles of optical deflection elements. Additionally, as disclosed in Japanese Laid-Open Patent Applications No. 9-133904, No. 2000-507005 (corresponding to International Publication No. WO98/30934), and No. 11-109304, there are optical deflection devices capable of adjusting deflection angles of optical deflection elements. Some of such optical deflection devices can adjust deflection angles of light paths of optical deflection elements without using mechanical moving parts that make the construction complicated, as disclosed in Japanese Laid-Open Patent Applications No. 7-64123 and No. 8-262391.

However, in a case where the electro-optical devices that use the materials having great primary electro-optical effect (Pockels effect) and materials having great secondary electro-optical effect, acousto-optical devices, and the like are used as optical deflection elements, generally, it is necessary to make the light path lengths long so as to obtain sufficiently great optical deflection amounts. For this reason, the present situation is that it is difficult to achieve smaller optical deflection devices, and the use of optical deflection devices is limited since the materials are expensive.

By the way, the above-described optical deflection devices are used for projection optical systems of image display apparatuses that display images displayed on image display elements on such as screens by using the projection optical systems, and for optical switches that use light path shift of an outgoing light with respect to an incident light.

Some image display apparatuses using optical deflection devices display images with improved apparent resolutions by shifting images displayed on image display elements at high-speed in accordance with time by optical deflection elements so as to cause afterimage phenomena in visual perception of human beings. The timings (shift timings) of optical deflection operations by optical deflection devices used for such image display apparatuses must be at speeds high enough to cause afterimage phenomena to visual perception of human beings and must not cause blurring in each image.

However, with the technique disclosed in Japanese Laid-Open Patent Application No. 6-18940, for example, it is difficult to make the speed of response faster to the order of sub-milliseconds, since a nematic liquid crystal is used for the liquid crystal material. Additionally, in the technique disclosed in Japanese Laid-Open Patent Application No. 9-133904, a smectic-A ferroelectric liquid crystal is used for the liquid crystal material. However, since a liquid crystal material in a smectic A phase does not produce spontaneous polarization, it is difficult to make the speed of response high enough. As described above, the optical deflection devices aimed at simplifying the constructions and miniaturization have problems in that it is difficult to speed up the light path shift operations because of the characteristics of the liquid crystal materials used.

Further, as disclosed in Japanese Laid-Open Patent Application No. 5-313116, for example, in a case where the light path shift operation is performed by moving each member arranged on a light path, it is necessary to move in parallel each member arranged on the light path at a high speed and with accuracy, which requires precision and durability of moving parts. With the above-described technique, light losses can be reduced, but problems arise such as occurrence of vibration and noise, and increase in the size of the apparatus.

In addition, as disclosed in Japanese Laid-Open Patent Application No. 6-324320, for example, there is disclosed an image display apparatus that divides an image displayed on an image display element into a plurality of fields, displays an image for each of the fields, and shifts the light path of each of the corresponding fields.

However, with the technique described in Japanese Laid-Open Patent Application No. 6-324320, the construction for driving the optical deflection element becomes complicated, which leads to high cost.

Additionally, Japanese Laid-Open Patent Application No. 10-133135, for example, discloses a technique aimed at entire miniaturization and achieving high precision and high resolution by interposing a translucent piezoelectric element between transparent electrodes and applying voltage so as to vary the thickness and shift the light path.

However, the technique disclosed in Japanese Laid-Open Patent Application No. 10-133135 requires a comparatively large transparent piezoelectric element, and thus the cost of the apparatus is increased.

As described above, in the conventional techniques, it is impossible for the optical deflection devices aimed for simplifying the constructions and miniaturization to sufficiently speed up the light path shift operations. Also, the optical deflection devices intended to speed up the light path shift operations have problems such as complexity of the constructions of the apparatuses, increase in cost caused by the complexity of the constructions of the apparatus, and increase in the sizes of the apparatuses.

The inventors of the present invention have found that high-speed pixel shift can be achieved with a comparatively simple construction: an optical deflection element that performs pixel shift such that liquid crystal molecules are oriented substantially perpendicularly between a pair of boards, and an electric field is generated in a direction substantially parallel to a liquid crystal layer so as to vary the direction of the liquid crystal molecules in a desired direction.

With the optical deflection element, by applying an ac voltage (for example, a square-wave voltage) on the order of several hundred Hz between the pair of electrodes, it is possible to emit lights by switching the light path of incident light in two directions with switching timing of several hundred Hz. As described above, the light path shift uses afterimage phenomena of eyes of human beings. Hence, the switching timing of the light path of incident light may be equal to or more than 30 Hz. However, in order to positively prevent flicker, preferably the switching timing is set to a hundred to several hundred Hz.

By the way, in such an optical deflection element, there is a case where a liquid crystal part becomes clouded when creating the optical deflection element or with successive light path shift driving. In a case where liquid crystal molecules are uniformly oriented perpendicularly in a liquid crystal layer, a black cross-like conoscope image, which is called isogyre, can be clearly observed in the liquid crystal layer. In the clouded part (white turbidity), the conoscope image is very indistinct. Additionally, isogyre is not observed at all in the strongly clouded part. This is the evidence that the perpendicular orientation state of the liquid crystal molecules is disturbed. The director of the liquid crystal molecules in the clouded part is irregular, and it is impossible to obtain a good light path shift function with the clouded optical deflection element. Such white turbidity may occur due to such as influence of an external electric field while the operation of the optical deflection element is suspended for a long time or even for a short period of time. In addition, with the optical deflection element where liquid crystal molecules being greatly disturbed though white turbidity does not occur, there is fear that reliability is degraded.

By the way, it is conceived that disturbance of orientation of liquid crystal molecules and white turbidity may occur due to influence of an external electric field and temperature variation while suspending the operation of optical deflection element. The optical deflection operation with white turbidity remaining causes light scattering and reduction of reliability through growth of alignment defect. Actually, it is confirmed that good light path shift is obtained by bringing liquid crystal molecules to the perpendicular orientation state before starting the optical deflection operation, even if there is no defect such as white-turbidity.

SUMMARY OF THE INVENTION

It is a general object of the present invention to provide an improved and useful optical deflection device and optical deflection method in which the above-mentioned problems are eliminated.

It is another and more specific object of the present invention to speed up the light path shift operation by an optical deflection element having a simplified construction, and to control occurrence of alignment defect caused by repeated use so as to improve reliability of the optical deflection device.

It is still another object of the present invention to speed up the light path shift operation by an optical deflection element having a simplified construction, and to control occurrence of alignment defect caused by repeated use so as to achieve a uniform orientation of liquid crystal molecules in an entire liquid crystal layer.

It is yet another object of the present invention to form a perpendicular orientation state without defect before an optical deflection operation. In addition, that is, it is effective to use an optical deflection operation start process means for maintaining a long-term stable operation of the optical deflection device.

In order to achieve the above-mentioned objects, according to one aspect of the present invention, there is provided an optical deflection device that includes:

an optical deflection element having a pair of transparent boards arranged in a mutually opposing manner, a liquid crystal layer filled between the pair of boards and forming a chiral smectic C phase, an orientation film orienting liquid crystal molecules in the liquid crystal layer in a substantially perpendicular direction with respect to the liquid crystal layer, and electrodes generating an electric field in a substantially parallel direction with respect to the liquid crystal layer;

a first voltage application part applying, to the electrodes, an ac voltage of a deflection frequency switching the optical deflection direction of the optical deflection element;

a second voltage application part applying, to the electrodes, an ac voltage of a higher frequency than the deflection frequency; and

a stop process part causing the second voltage application part to apply the ac voltage of the higher frequency than the deflection frequency after causing the first voltage application part to apply the ac voltage of the deflection frequency, when stopping an operation of switching the optical deflection direction of the optical deflection element.

Accordingly, the direction of an electric field formed in the liquid crystal layer is switched through applying the ac voltage of the deflection frequency to the pair of electrodes by the first voltage application part. The optical deflection direction of the optical deflection element is switched by switching the electric field direction. In addition, when stopping the operation of switching the optical deflection direction of the optical deflection element (when stopping the application of the ac voltage to the electrodes), the stop process part causes the second voltage application part to apply the ac voltage of the higher frequency than the deflection frequency, following the application of the ac voltage of the deflection frequency by the first voltage application part. Hence, in the liquid crystal layer, an electric field switching with a cycle shorter than the switching cycle of the optical deflection direction is formed. This high frequency electric field exerts a force to orient the liquid crystal molecules in the perpendicular direction also on the liquid crystal molecules in the vicinity of the intermediate layer of the liquid crystal layer. Thus, it is possible to bring, to the perpendicular orientation state, the liquid crystal molecules in a part having a tendency to develop white turbidity due to disarrangement in the orientation direction. Hence, it is possible to prevent development of a clouded part caused by fixing of disturbance of the orientation state.

Also, in the optical deflection device according to the present invention, the second voltage application part may apply, to the electrodes, an ac voltage having a period of a half cycle shorter than the response time of the liquid crystal molecules.

Accordingly, the response of the liquid crystal molecules is delayed with respect to the switching time of the electric field direction caused by applying the ac voltage by the second voltage application part. Consequently, the liquid crystal molecules are less slightly oscillated than in the original switching operation. Hence, when there is a part having a tendency to develop white turbidity due to disarrangement of the orientation direction, a force orienting the liquid crystal molecules in the part in the perpendicular direction is exerted, and the liquid crystal molecules are kept mobile by the slight oscillation. Accordingly, it is possible to quickly bring the liquid crystal molecules to the original perpendicular orientation state.

In addition, the second voltage application part may apply an ac voltage of a higher voltage value than the voltage value applied by the first voltage application part.

Accordingly, the force orienting the liquid crystal molecules in the perpendicular direction becomes greater. Hence, even when there is generated a part having a tendency to develop white turbidity, since the orientation state is disturbed through the optical deflection operation by the optical deflection element, it is possible to quickly bring the liquid crystal molecules to the original perpendicular orientation state.

However, in a case where a clouded part in which the orientation direction is disarranged is regionally generated in the liquid crystal layer, even if the liquid crystal molecules in the clouded part are brought to the perpendicular orientation state by applying a high frequency voltage, in some cases, the interface of the clouded part and a normal part bears the mark.

Consequently, the optical deflection device according to the present invention may further include:

a third voltage application part applying a pulsed dc voltage to the electrodes,

wherein, when stopping the operation of switching the optical deflection direction of the optical deflection element, the stop process part may cause the second voltage application part to apply the ac voltage of the higher frequency than the deflection frequency, after causing the first voltage application part to apply the ac voltage of the deflection frequency and subsequently causing the third voltage application part to intermittently apply the pulsed dc voltage.

Accordingly, the direction of an electric field formed in the liquid crystal layer is switched through applying the ac voltage of the deflection frequency to the pair of electrodes by the first voltage application part. The optical deflection direction of the optical deflection element is switched by switching the electric field direction. Additionally, when stopping the operation of switching the optical deflection direction of the optical deflection element (when stopping the application of the ac voltage to the electrodes), the stop process part causes the third voltage application part to intermittently apply the pulsed dc voltage, following the application of the ac voltage of the deflection frequency by the first voltage application part. Thus, after the orientation state of the liquid crystal molecules is temporarily disturbed throughout the liquid crystal layer, the ac voltage of the higher frequency than the deflection frequency is applied by the second voltage application part. Hence, in the liquid crystal layer, before stopping the operation of switching the optical deflection direction of the optical deflection element, an electric field that switches with a shorter cycle than the switching cycle of the optical deflection direction is formed. In other words, when a pulsed dc electric field is intermittently applied, the orientation of the entire liquid crystal layer is greatly disturbed. As a result, the entire liquid crystal layer assumes a state where white turbidity is easily developed. Accordingly, the interface of the clouded part and the normal part no longer exists. Thereafter, by applying a high frequency electric field, the entire liquid crystal layer is brought to the uniform perpendicular orientation state. Hence, it is possible to prevent the interface of a clouded part and a normal part from bearing the mark.

In addition, according to another aspect of the present invention, there is also provided an optical deflection device that includes:

an optical deflection element having a pair of transparent boards arranged in a mutually opposing manner, a liquid crystal layer filled between the pair of boards and forming a chiral smectic C phase, an orientation film orienting liquid crystal molecules in the liquid crystal layer in a substantially perpendicular direction with respect to the liquid crystal layer, and electrodes generating an electric field in a substantially parallel direction with respect to the liquid crystal layer;

a first voltage application part applying, to the electrodes, an ac voltage of a deflection frequency switching the optical deflection direction of the optical deflection element;

a third voltage application part applying a pulsed dc voltage to the electrodes; and

a stop process part causing the third voltage application part to intermittently apply the pulsed dc voltage after causing the first voltage application part to apply the ac voltage of the deflection frequency, when stopping the operation of switching the optical deflection direction of the optical deflection element

Accordingly, the direction of the electric field formed in the liquid crystal layer is switched by applying the ac voltage of the deflection frequency to the pair of electrodes by the first voltage application part. Also, the optical deflection direction of the optical deflection element is switched by switching the electric field. In addition, when stopping the operation of switching the optical deflection direction of the optical deflection element, following the application of the ac voltage of the deflection frequency by the first voltage application part, the stop process part causes the third voltage application part to intermittently apply the pulsed dc voltage. Hence, it is possible to realize the uniform perpendicular orientation state in the entire liquid crystal layer when the liquid crystal molecules are caused to spontaneously orient themselves by the orientation control force of the perpendicular orientation film after the orientation state of the liquid crystal molecules is temporarily disturbed throughout the liquid crystal layer.

Additionally, in each of the above-described optical deflection devices, the third voltage application part may apply the dc voltage of a higher voltage value than the voltage value applied by the first voltage application part.

Accordingly, it is possible to more effectively disturb the orientation state of the liquid crystal molecules throughout the liquid crystal layer. Thus, it is possible to efficiently disturb and eliminate the mark of the interface of the clouded part and the normal part. Hence, it is possible to realize the uniform perpendicular orientation state in the entire liquid crystal layer when the liquid crystal molecules are caused to spontaneously reorient themselves by the orientation control force of the perpendicular orientation film.

Additionally, in each of the optical deflection devices, the dielectric anisotropy of the liquid crystal layer forming the chiral smectic C phase may be negative in a frequency band of an ac voltage having a period of a half cycle shorter than the response time of the liquid crystal molecules.

Accordingly, the dielectric anisotropy of the liquid crystal layer forming the chiral smectic C phase is negative. Consequently, when a high frequency electric field is formed in a substantially parallel direction with respect to the liquid crystal layer by applying the voltage to the electrodes, the liquid crystal molecules attempt to assume the orientation state in a substantially perpendicular direction with respect to the liquid crystal layer so that the electrostatic energy is minimized. Hence, it is possible to exert an electrostatic orientation force on the intermediate part of the liquid crystal layer, in addition to the orientation control force in the vicinity of the board applied by the orientation film. Accordingly, it is possible to positively cause the liquid crystal molecules to assume the perpendicular orientation state.

Additionally, according to another aspect of the present invention, there is also provided an optical deflection device than includes:

an optical deflection element having a pair of transparent boards arranged in a mutually opposing manner, a liquid crystal layer filled between said pair of boards and forming a chiral smectic C phase, an orientation film orienting liquid crystal molecules in said liquid crystal layer in a substantially perpendicular direction with respect to said liquid crystal layer, and electrodes generating an electric field in a substantially parallel direction with respect to said liquid crystal layer;

a fourth voltage application part applying, to said electrodes, an ac voltage of a deflection frequency switching an optical deflection direction of said optical deflection element by varying a voltage value of the ac voltage; and

a stop process part decreasing the voltage value of the ac voltage of the deflection frequency applied by said fourth voltage application part continuously or in stages and stopping the application at a voltage value smaller than the voltage value capable of switching the optical deflection direction, when stopping the operation of switching the optical deflection direction of the optical deflection element.

Accordingly, the direction of an electric field formed in the liquid crystal layer is switched by applying an ac voltage of the deflection frequency to the pair of electrodes by the fourth voltage application part. Also, the optical deflection direction of the optical deflection element is switched by switching the electric field direction. In addition, when stopping the operation of switching the optical deflection direction of the optical deflection element, the stop process part decreases, continuously or in stages, the voltage value of the ac voltage of the deflection frequency applied by the fourth voltage application part and stops the application at a voltage value lower than the voltage value capable of switching the optical deflection direction. Hence, as the applied voltage value becomes lower than the voltage for a saturation electric field (the voltage value for applying a saturation electric field to a liquid crystal) for switching the liquid crystal molecules, it is possible to stop the application near a state where the liquid crystal molecules are brought to the perpendicular state. Thus, it is possible to prevent the liquid crystal molecules from being disturbed in stopping the optical deflection operation. It should be noted that the voltage value smaller than the voltage value of the saturation electric field for switching the liquid crystal molecules includes a state where the voltage value is zero.

Additionally, according to another aspect of the present invention, there is also provided an optical deflection device that includes:

an optical deflection element having a pair of transparent boards arranged in a mutually opposing manner, a liquid crystal layer filled between said pair of boards and forming a chiral smectic C phase, an orientation film orienting liquid crystal molecules in said liquid crystal layer in a substantially perpendicular direction with respect to said liquid crystal layer, and electrodes generating an electric field in a substantially parallel direction with respect to said liquid crystal layer;

a first voltage application part applying, to said electrodes, an ac voltage of a deflection frequency switching an optical deflection direction of said optical deflection element;

a second voltage application part applying, to said electrodes, an ac voltage of a frequency different from the deflection frequency; and

a start process part causing said first voltage application part to apply the ac voltage of the deflection frequency after causing said second voltage application part to apply the ac voltage of a higher frequency than the deflection frequency, when starting an operation of switching the optical deflection direction of the optical deflection element.

It should be noted that "when starting an operation of switching the optical deflection direction of the optical deflection element" refers to a period before the application of the ac voltage of the deflection frequency is started by the first voltage application part so as to perform the original optical deflection operation, and more particularly, preferably, immediately before starting the application of the ac voltage of the deflection frequency by the first voltage application part.

Accordingly, the direction of an electric field formed in the liquid crystal layer is switched by applying the ac voltage of the deflection frequency to the pair of electrodes. Also, the optical deflection direction of the optical deflection element is switched by switching the electric field direction. In addition, when starting the operation of switching the optical deflection direction of the optical deflection element, the start process part causes the second voltage application part to apply the ac voltage of the higher frequency than the deflection frequency, and thereafter causes the first voltage application part to apply the ac voltage of the deflection frequency. Thus, an electric field switched with a shorter cycle than the switching cycle of the optical deflection direction is formed in the liquid crystal layer. This high frequency electric field exerts a force to orient the liquid crystal molecules in the perpendicular direction on the liquid crystal molecules in the vicinity of the intermediate layer of the liquid crystal layer. Thus, it is possible to bring, to the perpendicular orientation state, the liquid crystal molecules in a part having a tendency to form white turbidity since the orientation direction is disturbed during the stoppage of the optical deflection element. Hence, it is possible to prevent generation of a clouded part caused when disturbance of the orientation state is fixed.

In addition, in the above-described optical deflection device, the second voltage application part may apply, to the electrodes, the ac voltage of a higher frequency than the deflection frequency by first applying the ac voltage of a lower frequency than the deflection frequency and thereafter increasing the frequency of the ac voltage continuously or in stages, and the start process part may cause the first voltage application part to apply the ac voltage of the deflection frequency following the application of the ac voltage of a higher frequency than the deflection frequency by the second voltage application part, when starting the operation of switching the optical deflection direction of the optical deflection element.

Accordingly, even in a case where the directions of the liquid crystal molecules are disturbed by influence of such as an external electric field and temperature variation while operation of the optical deflection element is stopped, by giving oscillation to the liquid crystal layer using the ac voltage of a comparatively low frequency so as to make the liquid crystal layer easily flow and change the orientation state, and thereafter increasing the frequency continuously or in stages so as to apply the ac voltage of a high frequency, it is possible to positively obtain the perpendicular orientation state.

Additionally, in the above-described optical deflection device, the second voltage application part may apply, to the electrodes, the ac voltage of a higher frequency than the deflection frequency, and thereafter decrease the frequency of the ac voltage continuously or in stages so as to apply the ac voltage of the deflection frequency to the electrodes, and the start process part may cause the first voltage application part to apply the ac voltage of the deflection frequency, following the application of the ac voltage of the deflection frequency by the second voltage application part, when starting the operation of switching the optical deflection direction of the optical deflection element.

Accordingly, even in a case where the directions of the liquid crystal molecules are disturbed by influence of such as an external electric field while the operation of the optical deflection element is stopped, the directions of the liquid crystal molecules are brought to the perpendicular state by the ac voltage of a high frequency. Thereafter, the frequency is decreased continuously or in stages so as to apply the deflection frequency. Hence, it is possible to prevent disturbance of the liquid crystal molecules that tends to occur when rapidly switching the frequency to the deflection frequency.

Further, the second voltage application part may apply, to the electrodes, an ac voltage having a period of a half cycle shorter than the response time of the liquid crystal molecules.

Accordingly, the response of the liquid crystal molecules is delayed for the switching time of the electric field caused by applying the ac voltage by the second voltage application part. Consequently, the liquid crystal molecules are slightly less oscillated than in the original switching operation. Hence, when there is a part having a tendency to form white turbidity since the orientation direction is disturbed, it is possible to exert a force to orient, in the perpendicular direction, the liquid crystal molecules in the part and to quickly bring the liquid crystal molecules to assume the original perpendicular orientation state, since the liquid crystal molecules are kept mobile with the slight oscillation.

In addition, the second voltage application part may apply the ac voltage of a higher voltage value than the voltage value applied by the first voltage application part.

Accordingly, an electrostatic energy exerted on the liquid crystal molecules is increased, and a force to orient the liquid crystal molecules in the perpendicular direction becomes greater. Hence, even in a case where a part having a tendency to form white turbidity is generated since the orientation state is disturbed by the optical deflection operation of the optical deflection element, it is possible to quickly bring the liquid crystal molecules to the original perpendicular orientation state.

Additionally, when starting the operation of switching the optical deflection direction of the optical deflection element, the second voltage application part may apply the ac voltage of a lower voltage value than the voltage value applied by the first voltage application part, and thereafter increase the voltage value of the ac voltage continuously or in stages so as to apply the deflection operation voltage value.

Accordingly, in a case where disturbance of the liquid crystal molecules occurs while the operation of the optical deflection element is stopped, it is possible to make the liquid crystal molecules switch at an angle nearer to perpendicular than the switching position of the optical deflection direction by applying a voltage lower than the voltage for the saturation electric field of switching the liquid crystal molecules at the beginning. Also, it is possible to bring the liquid crystal molecules closer to the angle of the optical deflection direction continuously or in stages by increasing the applied voltage value continuously or in stages. Hence, it is possible to prevent disturbance of the liquid crystal molecules due to rapid switching to the deflection frequency.

However, when a clouded part where the orientation direction is locally disturbed in the liquid crystal layer is generated, even if the liquid crystal molecules in the clouded part are brought to the perpendicular orientation state by applying a high frequency voltage, there is a case where the interface portion of the clouded part and a normal part bears the mark. Consequently, the optical deflection device may further include:

a third voltage application part applying a pulsed dc voltage to the electrodes,

wherein, when starting the operation of switching the optical deflection direction of the optical deflection element, the start process part may cause the second voltage application part to apply the ac voltage of a higher frequency than the deflection frequency, following intermittent application of the pulsed dc voltage by the third voltage application part, and thereafter cause the first voltage application part to apply the ac voltage of the deflection frequency.

Accordingly, by intermittently applying the pulsed dc voltage by the third voltage application part, the orientation of the entire liquid crystal layer is greatly disturbed, and the entire liquid crystal layer temporarily assumes a state where white turbidity is easily formed. Thus, the interface portion of the clouded part and the normal part is eliminated. Thereafter, the entire liquid crystal layer can be brought to the uniform perpendicular orientation state by applying a high frequency electric field. Hence, it is possible to prevent the interface portion of the clouded part and the normal part from bearing the mark.

In addition, according to another aspect of the present invention, there is also provided an optical deflection device that includes:

an optical deflection element having a pair of transparent boards arranged in a mutually opposing manner, a liquid crystal layer filled between said pair of boards and forming a chiral smectic C phase, an orientation film orienting liquid crystal molecules in said liquid crystal layer in a substantially perpendicular direction with respect to said liquid crystal layer, and electrodes generating an electric field in a substantially parallel direction with respect to said liquid crystal layer;

a first voltage application part applying, to said electrodes, an ac voltage of a deflection frequency switching an optical deflection direction of said optical deflection element;

a third voltage application part applying a pulsed dc voltage to said electrodes; and

a start process part causing said third voltage application part to intermittently apply the pulsed dc voltage and thereafter causing said first voltage application part to apply the ac voltage of the deflection frequency, when starting an operation of switching the optical deflection direction of the optical deflection element.

Accordingly, the orientation state of the liquid crystal molecules is temporarily disturbed throughout the liquid crystal layer by intermittently applying the pulsed dc voltage by the third voltage application part. Thereafter, the liquid crystal molecules can be arranged in the optical deflection direction by applying the ac voltage of the deflection frequency. Hence, it is possible to prevent the interface portion of the clouded part and the normal part from bearing the mark, even if there is white turbidity caused by the application of the pulsed dc voltage before starting the optical deflection operation. Moreover, a short interval of time will be needed for the operation of the start process part.

In addition, the third voltage application part may apply the dc voltage of a higher voltage value than the voltage value applied by the first voltage application part.

Accordingly, the orientation state of the liquid crystal molecules may be more effectively disturbed temporarily. Thus, it is possible to effectively disturb and eliminate the mark of the interface portion of the clouded part and the normal part.

Additionally, the dielectric anisotropy of the liquid crystal layer forming the chiral smectic C phase may be negative in the frequency band of the ac voltage having a period of a half cycle shorter than the response time of the liquid crystal molecules.

When the dielectric anisotropy of the liquid crystal layer forming the chiral smectic C phase is negative, if a high frequency electric field is formed in a substantially parallel direction with respect to the liquid crystal layer by applying voltage to the electrodes, the liquid crystal molecules try to assume the orientation state in a substantially perpendicular direction with respect to the liquid crystal layer so as to minimize the electrostatic energy. Hence, in addition to the orientation control force in the vicinity of the board by the orientation film, it is possible to also exert an electrostatic orientation force on the intermediate portion of the liquid crystal layer so as to positively cause the liquid crystal molecules to assume the perpendicular orientation state.

Further, according to another aspect of the present invention, there is also provided an optical deflection method that includes:

an optical deflection step of applying, to electrodes, an ac voltage of a deflection frequency switching the optical deflection direction of an optical deflection element, the optical deflection element having a pair of transparent boards arranged in a mutually opposing manner, a liquid crystal layer filled between the pair of boards and forming a chiral smectic C phase, an orientation film orienting liquid crystal molecules in the liquid crystal layer in a substantially perpendicular direction with respect to the liquid crystal layer, and the electrodes generating an electric field in a substantially parallel direction with respect to the liquid crystal layer; and

an application stop step of applying, to the electrodes, an ac voltage of a higher frequency than the deflection frequency, following the optical deflection step, when stopping an operation of switching the optical deflection direction of the optical deflection element.

Accordingly, in the optical deflection step, the direction of the electric field formed in the liquid crystal layer is switched through applying the ac voltage of the deflection frequency to the pair of electrodes. Also, the optical deflection direction of the optical deflection element is switched by switching the electric field direction. In addition, when stopping the operation of switching the optical deflection direction of the optical deflection element, following the application of the ac voltage of the deflection frequency, the ac voltage of the higher frequency than the deflection frequency is applied. Hence, in the liquid crystal layer, an electric field switching with a cycle shorter than the switching cycle of the optical deflection direction is formed. This high frequency electric field exerts a force to orient the liquid crystal molecules in the perpendicular direction also on the liquid crystal molecules in the vicinity of the intermediate layer of the liquid crystal layer. Thus, it is possible to bring, to the perpendicular orientation state, the liquid crystal molecules in a part having a tendency to develop white turbidity due to disarrangement of the orientation direction. Hence, it is possible to prevent generation of a clouded part caused when disturbance of the orientation direction is fixed.

Additionally, according to another aspect of the present invention, there is also provided an optical deflection method that includes:

an optical deflection step of applying, to electrodes, an ac voltage of a deflection frequency switching the optical deflection direction of an optical deflection element, the optical deflection element having a pair of transparent boards arranged in a mutually opposing manner, a liquid crystal layer filled between the pair of boards and forming a chiral smectic C phase, an orientation film orienting liquid crystal molecules in the liquid crystal layer in a substantially perpendicular direction with respect to the liquid crystal layer, and the electrodes generating an electric field in a substantially parallel direction with respect to the liquid crystal layer; and

an application stop step of intermittently applying a pulsed dc cur