JP2009258533A - Liquid crystal optical device, optical path switching device, optical scanner, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal optical device having a configuration capable of simplifying an element structure and a process. <P>SOLUTION: The liquid crystal optical device includes: a liquid crystal optical element 20 provided with a pair of substrates, transparent electrodes formed on the pair of substrates and a bistable ferroelectric liquid crystal layer held between the pair of substrates and forming a smectic layer to change the polarizing direction of incident light by voltage application and emit the direction-changed light; a voltage application means 31 for applying a voltage to the ferroelectric liquid crystal layer via the transparent electrodes; a light intensity detection means 32 for detecting intensity of light in a predetermined polarizing direction, which is emitted from the liquid crystal optical element; and a smectic layer rotation direction specification means 33 for determining whether a change in the light intensity is different from a predetermined change state or not during a period until the light intensity detected by the light intensity detection means is fixed and specifying a smectic layer rotation direction from a predetermined direction. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a liquid crystal optical device that can be used in an optical path switching device, an optical scanning device, an image forming device, an image display device, a laser processing device, and the like, an optical path switching device using the liquid crystal optical device, and the optical path switching device. The present invention relates to an optical scanning apparatus, and an image forming apparatus such as a laser printer, a laser plotter, a digital copying machine, a facsimile, or a composite machine including these optical scanning apparatuses.

In recent years, liquid crystal elements have been widely used as optical elements mainly for display applications, taking advantage of features such as thinness, light weight, and low power consumption. Most of these display elements use nematic liquid crystal, and the response speed is known to be not so fast as several msec to several tens msec.
On the other hand, a liquid crystal element using a liquid crystal having a chiral smectic C phase (SmC * phase) exhibiting ferroelectricity has a high-speed response and a memory property of several μsec to several hundred μsec. The application research to the ferroelectric liquid crystal element which makes the best use of the characteristic is energetically performed. However, it is difficult to obtain good alignment in the ferroelectric liquid crystal element, and many problems to be solved remain regarding the alignment stability.

  For example, the optical characteristics of the ferroelectric liquid crystal element are caused by the optical axis composed of liquid crystal molecules, and deviations and fluctuations of the optical axis cause the optical characteristics to deteriorate. That is, the instability of orientation leads to deterioration of optical characteristics. In general, the ferroelectric liquid crystal has a layer structure in which liquid crystal molecules are called smectic layers, and the phenomenon that the optical axis fluctuates due to the rotation of the layer structure is known.

  Regarding such layer rotation, for example, Non-Patent Document 1 (Proceedings of the 22nd (1996) Liquid Crystal Symposium Proceedings p37 to p40) describes that voltage pulses asymmetric to ferroelectric liquid crystals (smectic A phase, smectic C phase) or It has been reported that a smectic layer rotates by applying a DC voltage.

  Further, Patent Document 1 (Japanese Patent No. 3106166) discloses that both electrode substrates facing each other are set so that response speeds of application of electric fields having different polarities are approximately or equal to suppress layer rotation of antiferroelectric liquid crystal. Describes that the alignment conditions are unified and the alignment action is approximated or equalized.

Japanese Patent No. 3106166 Proceedings of the 22nd (1996) Liquid Crystal Symposium p37-p40

In the aforementioned Non-Patent Document 1, the discovery of the layer rotation phenomenon is described, but details of the cause of the layer rotation phenomenon and the stabilization of the alignment in the liquid crystal cell and the measures for preventing the occurrence of the layer rotation phenomenon are mentioned. Absent.
On the other hand, the above-mentioned Patent Document 1 discloses an element structure for the purpose of suppressing layer rotation, and proposes that the alignment conditions of the counter substrate are the same and the alignment action is made equal. However, there is no mention of countermeasures for the case where the smectic layer rotation provided in the present invention described later occurs.
Further, in the prior art described in Patent Document 1, it is provided that the alignment conditions of the counter substrate are the same and the alignment action is made equal. However, since the ferroelectric liquid crystal is very sensitive to the interface state, It is difficult to make the alignment effects of both substrates identical. In addition, when the applied voltage is increased in order to increase the device drive speed, the possibility of layer rotation increases, and there is a limit to this conventional technique alone.

Therefore, in order to solve the above-described problems of the conventional technology, the present inventors firstly made the smectic layer mono-stabilized in the orientation (rubbing) direction by rotating it with a DC voltage, an asymmetrical AC voltage, or the like. It has been proposed (Japanese Patent Application No. 2008-006523).
This prior application proposes a technique for stabilizing the smectic layer, but does not mention a countermeasure against the smectic layer rotation generated during element driving.
Also, in this prior application, one of the bistable alignment states is mono-stabilized in the alignment treatment (rubbing) direction, and the effect of suppressing layer rotation is high, but suddenly applied voltage failure occurs Because of this, layer rotation may be induced, and there are limits to the above measures alone.

The present invention has been made in view of the above circumstances, and it is not necessary to take a layer rotation suppression measure that the above-described conventional technology has taken into the element structure or element formation process, and the liquid crystal having a structure that can simplify the element structure and process. An object is to provide an optical device.
Further, in the above-described prior art, the occurrence of layer rotation is a direct failure factor. In the present invention, however, the layer rotation can be canceled, and the liquid crystal optical device is configured not to be a failure factor but to improve reliability. An object is to provide an apparatus.
It is another object of the present invention to provide an optical path switching device that includes the above-described liquid crystal optical device and has a stable beam quantity when switching the optical path.
A further object of the present invention is to provide an optical scanning device comprising the above-mentioned optical path switching means and having a stable beam quantity during recording.
It is another object of the present invention to provide an image forming apparatus that includes the above-described optical scanning device and that can stably perform image formation at low cost, high speed, and high image quality.

In order to achieve the above object, the present invention employs the following solutions.
The first means of the present invention is a liquid crystal optical device, comprising: “a pair of substrates, a transparent electrode provided on the pair of substrates, and a smectic layer held between the pair of substrates. A bistable ferroelectric liquid crystal layer, and a voltage applied to the ferroelectric liquid crystal layer via the transparent electrode; `` Voltage application means '', `` Light intensity detection means for detecting intensity in a predetermined polarization direction with respect to light emitted from the liquid crystal optical element '', and `` Applied voltage switching timing for switching polarization direction as a starting point, In a period until the light intensity detected by the light intensity detection means becomes constant (hereinafter referred to as a monitoring period), it is determined whether the light intensity change is different from a predetermined change state, and the smectic layer rotates from a predetermined direction. Direction The specific smectic layers rotational direction specifying means for "a, characterized by having a.
According to a second means of the present invention, in the liquid crystal optical device of the first means, “a smectic layer rotation that rotates a smectic layer in a direction to cancel the rotation in accordance with information from the smectic layer rotation direction specifying means”. It is characterized by having "direction adjusting means".

According to a third means of the present invention, in the liquid crystal optical device of the second means, the smectic layer rotating direction adjusting means is also used as the voltage applying means, and the signal is supplied from the smectic layer rotating direction specifying means. The smectic layer rotation direction is adjusted by changing the voltage waveform applied by the voltage applying means.
According to a fourth means of the present invention, in the liquid crystal optical device of the second means, the smectic layer rotation direction adjusting means is a holding member for holding and rotating the liquid crystal optical element.

  According to a fifth means of the present invention, in the liquid crystal optical device of any one of the first to fourth means, one liquid crystal alignment direction in the bistable state of the liquid crystal optical element is parallel to the polarization direction of incident light or Initially set in an orthogonal direction (hereinafter referred to as a direction), the other liquid crystal alignment direction is initially set in a direction rotated by 45 ° from the a direction (hereinafter referred to as b direction), and the smectic layer normal direction s is It is characterized by being initially set in a direction 22.5 ° from the a direction (hereinafter referred to as the c direction), which is a direction that equally divides the a direction and the b direction into two.

According to a sixth means of the present invention, in the liquid crystal optical device of the fifth means, the predetermined polarization direction set in the light intensity detection means is a direction parallel to the polarization direction of the incident light to the liquid crystal optical element, The smectic layer rotation direction specifying means includes a period of monotonically increasing in the initial setting with respect to the light intensity change in the light intensity detecting means in the monitoring period, and the detected intensity does not increase monotonously, but once it increases, it decreases Is determined that the smectic layer normal direction s has rotated from the c direction to the a direction side, and when the smectic layer normal direction s is decreased and then increased, the smectic layer normal direction s is changed to the c direction. It is judged that it rotated to the said b direction side from.
According to a seventh means of the present invention, in the liquid crystal optical device of the fifth means, the predetermined polarization direction set in the light intensity detecting means is a direction parallel to the polarization direction of incident light to the liquid crystal optical element. The monitoring period includes a period in which the smectic layer rotation direction specifying unit monotonously decreases in the initial setting with respect to the light intensity change in the light intensity detecting unit, and the detection intensity does not decrease monotonously but temporarily decreases. In the case that the smectic layer normal direction s is rotated from the c direction to the a direction side, the smectic layer normal direction s is changed to the decrease. It is determined that the rotation is from the c direction to the b direction.

According to an eighth means of the present invention, in the liquid crystal optical device of the fifth means, the predetermined polarization direction set in the light intensity detection means is a direction orthogonal to the polarization direction of incident light to the liquid crystal optical element, The smectic layer rotation direction specifying means includes a period of monotonically increasing in the initial setting with respect to the light intensity change in the light intensity detecting means in the monitoring period, and the detected intensity does not increase monotonously, but once it increases, it decreases Is determined that the smectic layer normal direction s is rotated from the c direction to the b direction side, and when the smectic layer normal direction s is decreased and then increased, the smectic layer normal direction s is the c direction. It is judged that it rotated to the said direction a side.
According to a ninth means of the present invention, in the liquid crystal optical device of the fifth means, the predetermined polarization direction set in the light intensity detection means is a direction orthogonal to the polarization direction of the incident light to the liquid crystal optical element. The monitoring period includes a period in which the smectic layer rotation direction specifying unit monotonously decreases in the initial setting with respect to the light intensity change in the light intensity detecting unit, and the detection intensity does not decrease monotonously but temporarily decreases. In the case where the smectic layer normal direction s is rotated from the c direction to the b direction side, the smectic layer normal direction s is changed to the decrease. It is determined that the rotation has been made from the c direction toward the a direction.

According to a tenth aspect of the present invention, there is provided an optical path switching device including a polarization beam splitting element having a different outgoing optical path depending on an incident polarization direction, and a liquid crystal optical device as any one of the first to ninth means. It is characterized by that.
According to an eleventh means of the present invention, there is provided an optical scanning device comprising: a light source; an optical scanning means having a multi-sided reflecting mirror having a common rotational axis; and an imaging optical system; An optical path switching means of a tenth means is provided between the light source and the optical scanning means.
Further, a twelfth means of the present invention is an image forming apparatus, characterized by comprising the optical scanning device of the eleventh means.

In the liquid crystal optical device of the first means of the present invention, the smectic layer rotation direction specifying means for specifying the rotation direction of the smectic layer is provided, and the smectic layer rotation direction adjusting means after the second means is utilized to make the smectic layer. Measures such as canceling the rotation or rotating the incident polarization direction in accordance with the rotation of the smectic layer can be taken. Here, since the latter countermeasure is not preferable because the polarization direction of the light emitted from the liquid crystal optical element is different from the initial setting, the method using the former smectic layer rotation direction adjusting means is desirable.
In general, the above-mentioned prior art takes a smectic layer rotation suppression measure by incorporating an element structure or a smectic layer rotation suppression means into the elementization process. However, the second means of the present invention specifies the smectic layer rotation direction. Since there is a smectic layer rotation direction adjusting means for rotating the smectic layer in the direction to cancel the rotation according to the information from the means, it is not necessary to introduce the smectic layer rotation inhibiting means, so that the device structure and process can be simplified. . Further, in the above-described prior art, the occurrence of layer rotation becomes a direct failure factor. However, in the present invention, since layer rotation can be canceled, it does not become a failure factor, and reliability can be improved.

In the liquid crystal optical device of the third means of the present invention, in addition to the effects of the first and second means, the smectic layer rotation direction adjusting means can also be used as the voltage applying means, so that the size can be reduced.
In the liquid crystal optical device according to the fourth means of the present invention, in addition to the effects of the first and second means, the smectic layer rotation direction adjusting means is the holding member, so that the smectic layer can be obtained simply by rotating the holding member. Adjustment of rotation is completed and it is simple. In addition, it is easy to visually check the degree of rotation of the smectic layer. Further, when the smectic layer rotation direction adjusting means is also used as the voltage applying means as in the third means, there is a risk of causing orientation failure depending on how the voltage waveform is changed. There is no.
In the liquid crystal optical device of the fifth means of the present invention, in addition to any one of the first to fourth effects, specification by the smectic layer rotation direction specifying means can be easily performed.

  The liquid crystal optical devices of the sixth to ninth means of the present invention are very simple because the rotation direction can be specified only by taking the change of the light intensity detecting means. Normally, the liquid crystal optical element is rotated between the polarizer and analyzer having a crossed Nicol arrangement with the incident optical axis as the rotation axis, and the liquid crystal molecule direction is detected from the maximum and minimum values of transmitted light, and the smectic layer direction is determined. A method of specifying is widely used, but in this method, it is necessary to stop the function of the liquid crystal optical device once. On the other hand, according to the present invention, the smectic layer can be adjusted without stopping the function.

In the optical path switching device of the tenth means of the present invention, by including the polarization separation element whose outgoing optical path differs depending on the incident polarization direction, and the liquid crystal optical device of any one of the first to ninth means, It is possible to provide an optical path switching device that stabilizes the amount of beam at the time of switching the optical path, and it is possible to improve the reliability of the optical path switching device.
Further, in the optical scanning device of the eleventh means of the present invention, the optical path switching means of the tenth means is provided between the light source and the optical scanning means, so that the light beam having a stable beam quantity at the time of recording can be obtained. A scanning device can be provided, and further, the reliability of the optical scanning device can be improved.
Further, the image forming apparatus of the twelfth means of the present invention is provided with the optical scanning device of the eleventh means, so that it is possible to provide a low-cost, high-speed, high-quality compatible and stable image forming apparatus. The reliability of the image forming apparatus can be improved.

Hereinafter, specific configurations, operations, and effects of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic cross-sectional view showing a structural example of a liquid crystal optical element used in the liquid crystal optical device of the present invention. The liquid crystal optical element 20 includes a pair of substrates 21 made of a transparent material, a transparent electrode 22 provided on the pair of substrates, and a bistable strong element formed by forming a smectic layer between the pair of substrates. The dielectric liquid crystal layer 23 is provided, and the polarization direction of incident light is switched by a voltage application and emitted. Although not shown, an alignment film is formed on the transparent electrode 22.
Here, the ferroelectric liquid crystal layer 23 is made of, for example, a chiral smectic C phase having homogeneous orientation. The transparent electrodes 22 on the pair of substrates can apply an electric field in a direction substantially perpendicular to the substrate surfaces. As the alignment film (not shown), a normal alignment film such as polyimide used for TN liquid crystal, STN liquid crystal, or the like can be used. In order to strongly restrict the direction of the liquid crystal director, it is preferable to separately perform a rubbing process or a photo alignment process. Further, an oblique vapor deposition film such as SiO ₂ can be used for the alignment film. Moreover, ITO (Indium Tin Oxide) etc. can be used for the transparent electrode 22.

  FIG. 2 is a schematic diagram for explaining the switching of the ferroelectric liquid crystal. In this figure, the orthogonal coordinate system is described in association with FIG. The ferroelectric liquid crystal layer 23 is parallel to the XY plane in the drawing. In general, a ferroelectric liquid crystal layer composed of a chiral smectic C phase has a helical structure. However, if the liquid crystal layer thickness is sandwiched by an interval (cell gap) smaller than the helical pitch, the helical structure is unwound and the surface-stabilized ferroelectric layer is formed. Liquid crystal layer (SSFLC). As shown in FIG. 2 (1), the SSFLC has two alignment stable states in which the liquid crystal molecules are stabilized with an inclination angle ± θ with respect to the smectic layer normal, and this characteristic is called bistability. Yes. At this time, the angle 2θ formed by each liquid crystal molecule direction is substantially equal to the cone angle of the liquid crystal having a spiral structure. Therefore, by applying an electric field in a direction perpendicular to the plane of the paper, the orientation of the liquid crystal molecules and their spontaneous polarization can be uniformly aligned in either orientation state, and by switching the polarity of the applied electric field, two states Can be switched between.

As will be described in detail later, one of the two alignment states is initially set in a direction parallel or orthogonal to the polarization direction of light perpendicularly incident on the liquid crystal optical element from the Z direction. To do. The other liquid crystal alignment direction is defined as direction b. In this case, the smectic layer normal direction s is formed in a direction that equally divides a and b into two (this direction in the initial setting is defined as the c direction).
When the polarity of the electric field is switched, there is a problem that the smectic layer rotates if there is a symmetric shift in the switching speed and intensity. (2) and (3) in FIG. 2 show this state. (2) shows the case where the smectic layer normal direction s rotates from the c direction to the a direction side, and (3) shows the case where the smectic layer normal direction s rotates from the c direction to the b direction side. In this case, the liquid crystal alignment direction taking the a direction rotates to a ′, a ″, and the liquid crystal alignment direction taking the b direction rotates to b ′, b ″.

FIG. 3 is a schematic diagram showing the operation of the polarization switching element using the surface-stabilized ferroelectric liquid crystal layer (SSFLC) described above. In FIG. 3, the thickness (cell gap) d of the liquid crystal layer is determined by the wavelength λ of incident light (for example, 650 nm or 780 nm) and the refractive index anisotropy Δn at 650 nm or 780 nm of the liquid crystal material,
Δn × d = λ / 2
(Ie, so as to satisfy the half-wave plate condition).

  Here, as the bistable state, when the initial alignment direction is taken in the direction a perpendicular to the polarization direction of the incident polarized light and an electric field of + E is applied, the initial alignment direction is in the angle direction b formed by 45 ° with the polarization direction of the incident polarized light. Suppose that In the initial alignment direction a, the incident polarized light is emitted while maintaining the polarization direction as it is, and in the initial alignment state b, the half-wave plate condition is satisfied, so that the emitted polarized light has a polarization direction rotated by approximately 90 ° from the incident polarized light. . That is, polarization switching can be realized by electric field control. Further, since ferroelectric liquid crystal is used for the liquid crystal optical element 20, the response speed of polarization switching is a high-speed response of several tens μsec to several hundred μsec.

  FIG. 4 is a diagram illustrating a configuration example of a liquid crystal optical device using the liquid crystal optical element 20. The liquid crystal optical device includes the liquid crystal optical element 20, a voltage applying unit 31 that applies a voltage thereto, The light intensity detection means 32 for detecting the intensity in the predetermined polarization direction with respect to the light emitted from the liquid crystal optical element, and the light intensity detected by the light intensity detection means 32 starting from the applied voltage switching timing for switching the polarization direction. A smectic layer rotation direction specifying means 33 for determining whether or not the light intensity change is different from a predetermined change state in a period until the value becomes constant (referred to as a monitoring period), and specifying the smectic layer rotation direction from a predetermined direction; It is the structure which has.

FIG. 4 shows a polarizer 25 for guiding only light in one polarization direction to the light intensity detecting means 32. As will be described later, incident polarized light such as a PBS (polarized beam splitter) is provided here. A polarization separation element having a different emission optical path depending on the direction may be arranged so that the light is distributed according to the polarization direction.
The light intensity detecting means 32 may be a general optical sensor such as a CMOS, CCD, PD (photodiode).

FIG. 5A illustrates an optical signal detected by the light intensity detecting means 32 of the liquid crystal optical device of FIG. Here, PD is used for the light intensity detection means 32. When the liquid crystal molecules of the liquid crystal optical element 20 take a direction orthogonal to the polarization direction of the incident light, that is, the initial alignment direction a in FIG. 3 (direction a in FIG. 2), the polarization state remains as it is without being rotated. Is detected as a “bright state”. In the case of the initial alignment direction b in FIG. 3 (the b direction in FIG. 2), that is, the direction rotated by 45 ° from the a direction becomes a “dark state” because the polarization direction rotation of 90 ° occurs as described above. Therefore, the smectic layer normal direction s may be initially set to a direction (c direction) of 22.5 ° from the a direction, which is a direction that bisects the a direction and the b direction.
Note that the initial setting method of the smectic layer normal direction s is possible by setting the rubbing direction when forming the liquid crystal optical element to be this direction.

  As shown in (1) of FIG. 5, immediately after the voltage output of the voltage applying means is switched, the change of “brightness and darkness” starts, and in this example, the light intensity becomes constant within 30 μs. Therefore, a period of 30 μs from the applied voltage switching timing can be determined as the monitoring period. Here, switching from dark to bright is determined during the monitoring period, but switching from light to dark can also be determined.

  (2) of FIG. 5 is an example of a detection waveform of the light intensity detection means 32 generated when the smectic layer rotates. This is observed when the smectic layer rotation shown in (2) of FIG. 2 occurs. That is, in (2) of FIG. 2, the liquid crystal molecules that were stable in the initial alignment directions a and b are rotated and stabilized in the a ′ and b ′ directions shown in the drawing by the rotation of the smectic layer, and the a ′ position Then, since the incident polarization direction is rotated as compared with the position a, the state becomes slightly brighter. When the liquid crystal molecule direction changes from a ′ to b ′, the detected light amount decreases most when passing through the a direction, and then increases. Since the polarization direction has not been rotated up to 90 ° at the b ′ position, it is constant at a value slightly lower than the detected light amount in the b direction. The change from b 'to a' can be explained in the same way.

  (3) of FIG. 5 is a photodetection waveform observed when the smectic layer rotation shown in (3) of FIG. 2 occurs. That is, in (3) of FIG. 2, the liquid crystal molecules that were stable in the initial alignment directions a and b are rotated and stabilized in the a ″ and b ″ directions shown in the figure by the rotation of the smectic layer, and the a ″ position Then, since the incident polarization direction is rotated as compared with the position a, the state becomes slightly brighter. When the liquid crystal molecule direction changes from a ″ to b ″, the detected light amount increases most when passing through the b direction, Thereafter, the light intensity starts to decrease. At the b ″ position, since the polarization direction has not been rotated up to 90 °, it is constant at a value slightly lower than the detected light amount in the b direction. The change from b ″ to a ″ can be explained in the same way.

Since the waveform pattern in FIG. 5 and the liquid crystal alignment direction in FIG. 2 have a correspondence relationship, the smectic layer rotation direction can be specified by monitoring the waveform pattern in FIG.
That is, as an example, the predetermined polarization direction set in the light intensity detecting means is a direction parallel to the incident light polarization direction, and the smectic layer rotation direction specifying means is initially set for the light intensity change in the light intensity detecting means. When the monitoring period includes a monotonically increasing period and the detected intensity does not monotonously increase, but once increases, it starts to decrease, it is determined that the smectic layer normal direction s has rotated from the c direction to the a direction. However, when it decreases and then increases, it can be determined that the smectic layer normal direction s has rotated from the c direction to the b direction.
As another example, the predetermined polarization direction set in the light intensity detection means is a direction parallel to the incident light polarization direction, and the smectic layer rotation direction specifying means is adapted to the light intensity change in the light intensity detection means. In the initial setting, the period of monotonically decreasing is included in the monitoring period, and when the detection intensity does not decrease monotonously but once decreases and then increases, the smectic layer normal direction s has rotated from the c direction to the a direction. In the case of once increasing and then decreasing, it can be determined that the smectic layer normal direction s has rotated from the c direction to the b direction.

As yet another example, the predetermined polarization direction set in the light intensity detection means is a direction orthogonal to the incident light polarization direction, and the smectic layer rotation direction specifying means is the initial in response to the light intensity change in the light intensity detection means. When the monitoring period includes a monotonically increasing period in the setting, and the detection intensity does not monotonously increase and then once increases, then the smectic layer normal direction s rotates from the c direction to the b direction side. In the case where it is judged and once decreases and then increases, it can be determined that the smectic layer normal direction s has rotated from the c direction to the a direction.
As yet another example, the predetermined polarization direction set in the light intensity detection means is a direction orthogonal to the incident light polarization direction, and the smectic layer rotation direction specifying means is adapted to the light intensity change in the light intensity detection means. In the initial setting, the period of monotonically decreasing is included in the monitoring period, and when the detection intensity does not decrease monotonously but once decreases and then increases, the smectic layer normal direction s rotates from the c direction to the b direction. In the case of once increasing and then starting to decrease, it can be determined that the smectic layer normal direction s has rotated from the c direction to the a direction.

Next, FIG. 6 is a configuration diagram of a liquid crystal optical device in which a smectic layer rotation direction adjusting means 34 is added to the liquid crystal optical device shown in FIG.
The smectic layer rotation direction adjustment 34 can be performed by changing the voltage waveform applied by the voltage applying means 32. FIG. 7 is an example of changes in the applied voltage waveform. (1) in FIG. 7 is a normal state, and (2) and (3) are cases where a bias voltage ΔV is applied for adjusting the smectic layer rotation. In (2), the smectic layer rotates from the stable orientation state when -V is applied to the direction of the stable orientation state when + V is applied. (3) is the opposite. The magnitude of ΔV may be set to 5 to 20% of V, for example. If it is too small, it takes time for the smectic layer to return to the original state, and if it is too large, the orientation state is disturbed.

FIG. 8 shows another configuration example of the smectic layer rotation direction adjusting means, and the holding member 42 for holding and rotating the liquid crystal optical element 20 constitutes the smectic layer rotation direction adjusting means.
The holding member 42 that holds the liquid crystal optical element 20 is rotatably attached to the housing 41. The rotation direction can be determined by the information from the smectic layer rotation direction specifying means 33 and rotated.

FIG. 9 is a diagram illustrating a configuration example of an optical path switching device including a polarization beam splitting element 26 having a different outgoing optical path depending on an incident polarization direction and the above-described liquid crystal optical device. More specifically, instead of the polarizer 25 of the liquid crystal optical device of FIG. 6, an example in which a polarization separation element 26 having a different outgoing optical path depending on the incident polarization direction is arranged to distribute light according to the polarization direction. is there.
As the polarization separation element 26, a polarization beam splitter prism or the like that transmits the p-polarized component and reflects the s-polarized component, or a multi-stage arrangement of diffractive optical elements that exhibit polarization dependency can be used.

[Example 1]
Hereinafter, more specific examples of the present invention will be described.
First, fabrication and operation check of a ferroelectric liquid crystal element will be described as a typical example of an embodiment of the present invention.

(Experiment 1)
An ITO electrode (a thickness of 1500 mm) was formed on a soda glass substrate having a thickness of 1.1 mm. An alignment film (AL3046-R31 manufactured by JSR) was formed on the substrate electrode surface by spin coating to a thickness of about 800 mm, and the substrate surface was subjected to alignment treatment by rubbing. Two glass substrates are used, with the electrode surfaces facing each other so that the rubbing direction is antiparallel, and a few samples of empty cells are bonded together with an adhesive mixed with beads so that the distance between the substrates is about 2 μm. Produced. A ferroelectric liquid crystal (FELIX 018-100 Δn = 0.17, 2θ = 45, manufactured by Clariant) is injected as a liquid crystal layer in the empty cell in a state where the empty cell is heated at 90 degrees on a hot plate, After allowing to cool, the inlet and the like were sealed, and several samples of liquid crystal optical elements as shown in FIG. 1 were produced.
When the alignment state of the prepared sample was observed with an optical microscope under crossed Nicols, a liquid crystal optical element sample in which the rubbing direction and the smectic layer normal direction were in substantially the same alignment state was prepared.

(Experiment 2)
Next, an optical system in which the above-described liquid crystal optical element and polarizing plate were arranged in the optical path of a laser light source composed of a semiconductor laser and a photodiode (PD) was prepared as an optical property evaluation apparatus. In the polarizing plate, the polarization direction of the laser light source was set as the transmission axis, and the amount of transmitted light was maximized without the liquid crystal optical element. The liquid crystal optical element was adjusted and arranged so that the incident polarization direction was the Y direction of (1) in FIG. When a rectangular wave signal with a frequency of 4 kHz and ± 20 V / μm was input to the liquid crystal optical element and the switching between light and dark was observed, it was confirmed that the PD output was in a light and dark state as shown in FIG.

(Experiment 3)
An asymmetric signal having a frequency of 4 kHz, an applied voltage of ± 20 V / μm, and an offset voltage ΔV = + 4 V was input to the sample in this state and left for a while. Thereafter, when the same evaluation as the optical characteristic evaluation was performed, the waveform (2) in FIG. 5 was measured. Observation with an optical microscope confirmed that the smectic layer normal direction s deviated from the rubbing direction. Specifically, as shown in (2) of FIG. 2, the liquid crystal molecules that were stable in the initial alignment directions a and b are rotated and stabilized in the directions a ′ and b ′ shown in the figure by the rotation of the smectic layer. It was converted.

(Experiment 4)
Next, when an asymmetric signal having a frequency of 4 kHz, an applied voltage of ± 20 V / μm, and an offset voltage ΔV = −4 V was input to the sample in this state, the waveform of the above optical characteristic evaluation was observed from (2) of FIG. It was measured that the waveform changed to the waveform of (1) in FIG. When the smectic layer normal direction s was observed with an optical microscope in this state, it was confirmed that the smectic layer was rotated to a position almost overlapping with the rubbing direction.
From the above experiments, it was confirmed that the smectic layer rotation direction can be specified by monitoring the waveform of the optical characteristic evaluation, and that the smectic layer rotation direction can be adjusted by changing the applied voltage waveform.

[Example 2]
In the optical characteristic evaluation apparatus used in Example 1, the member that supports the liquid crystal optical element was a holding member (rotary holder (Σ58 (30) manufactured by Sigma Koki Co., Ltd.)) as shown in FIG.
After Experiments 1 to 3 of Example 1, when the rotating holder was rotated in a direction to cancel the smectic layer rotation direction, the waveform of the optical characteristic evaluation changed from (2) in FIG. 5 to (1) in FIG. It was measured to do.
From the above experiment, it was confirmed that the smectic layer rotation direction can be specified by monitoring the waveform of the optical characteristic evaluation, and that the smectic layer rotation direction can be adjusted by the rotation of the holding member that holds and rotates the liquid crystal optical element.

[Example 3]
Next, an embodiment of the optical scanning device of the present invention will be described.
FIG. 10 shows a part of the optical scanning device. This optical scanning device includes a laser light source 1, a coupling lens (collimating lens) 3, an optical path switching means 4, and a multi-surface reflecting mirror (polygon mirror) 7a, 7b having a common rotational axis and a plurality of stages. And means (optical deflector) 7. In FIG. 10, the cylindrical lens and the imaging optical system for the surface to be scanned are omitted. Further, as the optical path switching means 4, an optical path switching device having the configuration shown in FIG. 9 is used.

  Here, the operation of the optical scanning device will be described. The beam emitted from the laser light source 1 is parallel-shifted in the sub-scanning direction by the electric field application control in the optical path switching means (optical path switching device) 4 described above, and the optical deflector is time-divided. 7 are respectively incident on the polygon mirrors 7a and 7b on the upper and lower stages. Here, the upper and lower polygon mirrors 7a and 7b are configured to use four-surface polygon mirrors having a 45 ° phase shift. In such a configuration, by controlling the application of the electric field in the optical path switching means 4, when the beam from the upper polygon mirror 7a scans the photosensitive surface (scanned surface) as shown in FIG. The beam substantially passes only through the upper optical path and hardly passes through the lower optical path. Also, as shown in FIG. 11B, when the beam from the lower polygon mirror 7b scans the photosensitive member surface (scanned surface), the beam passes only through the substantially lower optical path and hardly passes through the upper optical path. Can be realized. That is, there is no loss of the light amount of the beam from the light source 1, the light source power can be used efficiently, leading to a long life of the light source and a reduction in deterioration establishment. In particular, when a surface emitting laser effective for increasing the density is used as a light source, the effect is increased.

  However, when the polarization direction of switching in the optical path switching means 4 deviates from the set value or changes in the optical axis, the light amount of the beam in the switching optical path changes from the desired value, and the light source power cannot be used efficiently. Therefore, the ferroelectric liquid crystal optical element 20 in which the fluctuation of the optical characteristics is suppressed is used as the polarization switching element of the optical path switching means 4 by rotating the layer so that the orientation during the liquid crystal switching becomes stable as described above. Therefore, it is possible to realize an optical path switching means and an optical scanning device in which the beam light quantity at the time of switching the optical path is stable.

Next, FIG. 12 shows a specific configuration example of the optical scanning device.
In FIG. 12, reference numerals 1 and 1 'are semiconductor lasers (LD) (not shown), 2 is an LD base, 3 and 3' are coupling lenses, and 4 is an optical path switching means (liquid crystal optical device (polarization switching means)). 5 and 5 'are cylindrical lenses, 6 is a soundproof glass, 7 is an optical deflector (light scanning means), 7a is an upper polygon mirror, 7b is a lower polygon mirror, and 8a and 8b are first scanning lenses. (For example, an fθ lens), 9 is a mirror, 10a, 10b are second scanning lenses (for example, an fθ lens, a toroidal lens, etc.), 11a, 1b are photoconductors as scanning surfaces, and 50 is an aperture stop.
Although not shown in the figure, an image forming system including the preceding optical system (optical system 1) from the laser light source (2LD unit) 1, 1 ′ to the cylindrical lenses 5a, 5b after the optical path switching means 4 and the fθ lenses 8a, 8b. An optical scanning device that uses two sets of each of the optical systems (optical system 2) and performs optical scanning on four scanned surfaces with two beams by using an optical deflector 7 having two-stage polygon mirrors 7a and 7b. Can be built. The four scanned surfaces are photoconductors corresponding to four colors (for example, yellow (Y), magenta (M), cyan (C), and black (K)) (in FIG. 12, only two photoconductors 11a and 11b are shown). As shown, an imaging optical system (optical system 2) and a photoconductor having the same configuration are arranged on the opposite side of the optical deflector 7), and light is applied to four photoconductors. A multicolor image forming apparatus can be constructed by performing scanning and writing latent images corresponding to yellow (Y), magenta (M), cyan (C), and black (K).

[Example 4]
Next, FIG. 13 shows a basic configuration example of the multicolor image forming apparatus.
In FIG. 13, reference numerals 11Y, 11M, 11C, and 11K are photosensitive members, 12Y, 12M, 12C, and 12K are charging devices, 13 is a writing unit (optical scanning device), 14Y, 14M, 14C, and 14K are developing devices, and 15Y, 15M and 15C15K are transfer devices, 16Y, 16M, 16C, and 16K are cleaning devices, 17 is a transfer belt, and 18 is a fixing device, where Y is yellow, M is magenta, C is cyan, and K is black. It shows that it corresponds respectively.

  In FIG. 13, photoconductors 11Y, 11M, 11C, and 11K rotate in the direction of the arrow in the figure, and charging devices 12Y, 12M, 12C, and 12K, developing devices 14Y, 14M, 14C, and 14K, and a transfer device are sequentially arranged in the rotation direction. 15Y, 15M, 15C, 15K and cleaning devices 16Y, 16M, 16C, 16K are provided. The charging devices 12Y, 12M, 12C, and 12K are for uniformly charging the surface of the photoreceptor, and are constituted by a charging member such as a charging roller. The surface of the photosensitive member between the charging devices 12Y, 12M, 12C, and 12K and the developing devices 14Y, 14M, 14C, and 14K is irradiated with a laser beam by a writing unit (optical scanning device) 13, and each of the photosensitive members 11Y, 11M, and 11C. , 11K, an electrostatic latent image corresponding to each color is formed. The electrostatic latent images formed on the photoconductors 11Y, 11M, 11C, and 11K are developed with the toners of the colors of the developing devices 14Y, 14M, 14C, and 14K, and the toner images of the colors are formed on the surfaces of the photoconductors. . In synchronization with the formation of the toner image, a recording sheet (not shown) is fed from a sheet feeding unit (not shown) and conveyed to the transfer belt 17. Then, the toner images of the respective colors on the respective photoconductors are transferred onto the recording paper carried and transferred by the transfer belt 17 by being sequentially superimposed and transferred by a transfer device (for example, a transfer charger) 15Y, 15M, 15C, 15K. An image in which four colors are superimposed on each other is formed. The recording paper on which the image is formed is conveyed to the fixing device 18 and the image is fixed on the recording paper by the fixing device 18. The recording sheet on which the image is fixed is discharged to a discharge tray (not shown).

In the image forming apparatus using the optical scanning device provided with the optical path switching means (optical path switching device) 4 capable of switching the optical path by the electric field control as described above, scanning recording from a plurality of stages of polygon mirrors 7a and 7b is supported. Then, by switching the optical path of the laser light source and modulating and driving the light amount, the photosensitive members 11Y, 11M, 11C, and 11K corresponding to the respective colors can be sequentially scanned and recorded, and the beam power loss is reduced while reducing the number of light sources. Therefore, it is possible to realize an image forming apparatus that enables high-speed image output. Further, in the case of using a two-stage polygon mirror in the four-drum tandem system as shown in FIGS. Can do.
The image forming apparatus using the liquid crystal optical device of the present invention for the optical path switching means (optical path switching apparatus) 4 can perform high-speed printing and high-speed scanning because of its fast response speed, and can freely increase its writing speed. Can continue. Therefore, it is possible to provide a stable multi-color image forming apparatus that is low-cost, high-speed, compatible with high image quality.

It is a schematic sectional drawing which shows the structural example of the liquid crystal optical element used with the liquid crystal optical apparatus of this invention. It is a schematic diagram for demonstrating switching of a ferroelectric liquid crystal. It is a schematic diagram which shows operation | movement of the polarization switching element using a surface stabilization ferroelectric liquid crystal layer (SSFLC). It is a figure which shows the structural example of the liquid crystal optical apparatus using the liquid crystal optical element of this invention. FIG. 5 is a diagram illustrating an optical signal detected by a light intensity detection unit of the liquid crystal optical device of FIG. 4. FIG. 5 is a configuration diagram of a liquid crystal optical device having a configuration in which smectic layer rotation direction adjusting means is added to the liquid crystal optical device shown in FIG. 4. It is a figure which shows the example of a change of the applied voltage waveform of the voltage application means of the liquid crystal optical apparatus of FIG. It is a figure which shows another structural example of a smectic layer rotation direction adjustment means. It is a figure which shows the structural example of the optical path switching apparatus of this invention. It is the schematic which shows a part of optical scanning apparatus concerning this invention, (a) is a side view of a part of optical scanning apparatus, (b) is a perspective view of an optical scanning means (optical deflector). It is a figure which shows the deflection scanning state of the light beam in the optical scanning device shown in FIG. It is a principal part perspective view which shows the specific structural example of the optical scanning device based on this invention. 1 is a schematic configuration diagram illustrating a basic configuration example of a multicolor image forming apparatus according to the present invention.

Explanation of symbols

1, 1 ': Light source (semiconductor laser)
2: LD base 3, 3 ': Coupling lens 4: Optical path switching means (optical path switching device)
5a, 5b: Cylindrical lens 6: Soundproof glass 7: Optical deflector (optical scanning means)
7a: Upper polygon mirror (polyhedral reflector)
7b: Lower polygon mirror (polyhedral reflector)
8a, 8b: first scanning lens 9: mirror 10a, 10b: second scanning lens 11Y, 11M, 11C, 11K: photoconductor 12Y, 12M, 12C, 12K: charging device 13: writing unit (optical scanning device)
14Y, 14M, 14C, 14K: Development devices 15Y, 15M, 15C15K: Transfer device 16Y, 16M, 16C, 16K: Cleaning device 17: Transfer belt 18: Fixing device 20: Liquid crystal optical element 21: Substrate 22: Transparent electrode 23: Ferroelectric liquid crystal layer 25: Polarizer 26: Deflection separation element 31: Voltage application means 32: Light intensity detection means 33: Smectic layer rotation direction specifying means 34: Smectic layer rotation direction adjustment means 41: Housing 42: Holding member 42
50: Aperture stop

Claims (12)

A pair of substrates, a transparent electrode provided on the pair of substrates, and a bistable ferroelectric liquid crystal layer formed between the pair of substrates and forming a smectic layer, are incident upon application of voltage. A liquid crystal optical element that emits light by switching the polarization direction of the light;
Voltage applying means for applying a voltage to the ferroelectric liquid crystal layer through the transparent electrode;
A light intensity detecting means for detecting the intensity of a predetermined polarization direction with respect to the light emitted from the liquid crystal optical element;
The light intensity change is a predetermined change during a period (hereinafter referred to as a monitoring period) until the light intensity detected by the light intensity detection means becomes constant, starting from the applied voltage switching timing for switching the polarization direction. A smectic layer rotation direction specifying means for determining whether or not the state is different and specifying the smectic layer rotation direction from a predetermined direction;
A liquid crystal optical device comprising: The liquid crystal optical device according to claim 1.
A liquid crystal optical device comprising: a smectic layer rotation direction adjusting unit that rotates the smectic layer in a direction to cancel the rotation in accordance with information from the smectic layer rotation direction specifying unit. The liquid crystal optical device according to claim 2.
The smectic layer rotating direction adjusting means is also used as the voltage applying means, and the smectic layer rotating direction is adjusted by changing the applied voltage waveform of the voltage applying means according to a signal from the smectic layer rotating direction specifying means. A liquid crystal optical device, wherein: The liquid crystal optical device according to claim 2.
The liquid crystal optical device, wherein the smectic layer rotation direction adjusting means is a holding member that holds and rotates the liquid crystal optical element. The liquid crystal optical device according to any one of claims 1 to 4,
One liquid crystal alignment direction in the bistable state of the liquid crystal optical element is initially set to a direction parallel to or perpendicular to the polarization direction of incident light (hereinafter referred to as a direction), and the other liquid crystal alignment direction is 45 from the a direction. Initially set in a rotated direction (hereinafter referred to as b direction), and the smectic layer normal direction s is a direction (hereinafter referred to as 22.5 °) from the a direction, which is a direction that bisects the a direction and the b direction. a liquid crystal optical device that is initially set in the c direction). The liquid crystal optical device according to claim 5.
The predetermined polarization direction set in the light intensity detection means is a direction parallel to the incident light polarization direction to the liquid crystal optical element,
The smectic layer rotation direction specifying means includes a period of monotonically increasing in the initial setting with respect to the light intensity change in the light intensity detecting means, in the monitoring period,
If the detected intensity does not increase monotonously, but once increases and then decreases, it is determined that the smectic layer normal direction s has rotated from the c direction to the a direction side,
The liquid crystal optical device according to claim 1, wherein if the smectic layer normal direction s is rotated from the c direction to the b direction side when it decreases and then increases. The liquid crystal optical device according to claim 5.
The predetermined polarization direction set in the light intensity detection means is a direction parallel to the incident light polarization direction to the liquid crystal optical element,
The smectic layer rotation direction specifying means includes a period of monotonically decreasing in the initial setting with respect to the light intensity change in the light intensity detecting means, in the monitoring period,
If the detected intensity does not decrease monotonously, but once decreases and then increases, it is determined that the smectic layer normal direction s has rotated from the c direction to the a direction side,
If the liquid crystal optical device is once increased and then turned down, it is determined that the smectic layer normal direction s is rotated from the c direction to the b direction. The liquid crystal optical device according to claim 5.
The predetermined polarization direction set in the light intensity detection means is a direction orthogonal to the incident light polarization direction to the liquid crystal optical element,
The smectic layer rotation direction specifying means includes a period of monotonically increasing in the initial setting with respect to the light intensity change in the light intensity detecting means, in the monitoring period,
If the detected intensity does not increase monotonously, but once increases and then decreases, it is determined that the smectic layer normal direction s has rotated from the c direction to the b direction side,
The liquid crystal optical device according to claim 1, wherein, when the liquid crystal optical device is once decreased and then increased, the smectic layer normal direction s is determined to be rotated from the c direction to the a direction. The liquid crystal optical device according to claim 5.
The predetermined polarization direction set in the light intensity detection means is a direction orthogonal to the incident light polarization direction to the liquid crystal optical element,
The smectic layer rotation direction specifying means includes a period of monotonically decreasing in the initial setting with respect to the light intensity change in the light intensity detecting means, in the monitoring period,
If the detected intensity does not decrease monotonously, but once decreases and then increases, it is determined that the smectic layer normal direction s has rotated from the c direction to the b direction side,
If the liquid crystal optical device is once increased and then turned down, it is determined that the smectic layer normal direction s is rotated from the c direction to the a direction.   An optical path switching device comprising: a polarization beam splitting element having a different output optical path depending on an incident polarization direction; and the liquid crystal optical device according to claim 1. In an optical scanning device comprising a light source, an optical scanning unit having a multi-sided reflecting mirror having a common rotational axis, and an imaging optical system,
An optical scanning apparatus comprising the optical path switching unit according to claim 10 between the light source and the optical scanning unit.   An image forming apparatus comprising the optical scanning device according to claim 11.

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