JP2010020028A - Polarization switching element, polarization switching device, optical path switching device, optical scanner and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarization switching element in which heating efficiency and accuracy can be enhanced by directly heating a liquid crystal material in an optically effective region and reduction of light utilizing efficiency of a heater is eliminated by making the heater serve as an electrode for driving the liquid crystal and productivity can be also enhanced by forming a heater electrode and a driving electrode together. <P>SOLUTION: The polarization switching element 10 includes a pair of transparent substrates 1 and 2, spacers 3, an alignment layers 5 and 6, the liquid crystal 4 having spontaneous polarization by which an alignment state is changed by polarity inversion of an applied electric field, transparent conductive films 8 for heating which can apply a current for heating the liquid crystal 4 formed on the surfaces on the inner sides of the transparent substrates 1 and 2 superposed on the optically effective region 7 of incident light and a transparent conductive film 9 for driving which can apply a driving electric field changing the alignment state of the liquid crystal 4 to between the transparent substrates 1 and 2. The transparent conductive film 8 for heating serves as the transparent conductive film 9 for driving and is formed in the optically effective region 7. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a polarization switching element, a polarization switching device, an optical path switching device, an optical scanning device, and an image forming apparatus, and more specifically, a polarization switching element that includes a liquid crystal having spontaneous polarization and has a function of switching the polarization direction of incident light, Polarization switching device provided with this polarization switching element, optical path switching device comprising polarization switching element or polarization switching device and polarization separation element, optical scanning device provided with this optical path switching device, and copier having this optical scanning device, The present invention relates to an image forming apparatus such as a facsimile, a printer, a plotter or the like, or a multifunction machine having a plurality of functions.

  In general, it is known that the performance of a liquid crystal element (including a liquid crystal display device) depends on an environmental temperature. For example, when the liquid crystal element is used at a low temperature, the viscosity of the liquid crystal material held between the liquid crystal element substrates increases, so that the response speed with respect to the applied electric field decreases and the element performance deteriorates. In order to solve such a problem, several methods for installing a heater for heating the liquid crystal element have been proposed.

  As a conventional liquid crystal element provided with a heater, there is a configuration in which a heating heater separate from the liquid crystal element is placed on the liquid crystal element. For example, a liquid crystal element with a transparent planar heater attached, a change to a mesh heater, an optical compensation element provided separately from the liquid crystal element, and a surface of at least one substrate of the optical compensation element. A film in which a transparent resistance film is formed on almost the entire surface is known (for example, see Patent Document 1).

  The downsizing and productivity of the liquid crystal element can be improved by forming a heater directly on the liquid crystal element substrate and providing a heater integrally with the liquid crystal element. For example, the other side facing the substrate on which the TFT is formed is provided. A black matrix, which is a light-shielding layer provided on the substrate, is used as a heater (for example, see Patent Document 2), or a transparent conductive film for heater is directly formed on the inner surface of the substrate in the non-display region of the liquid crystal element (for example, Patent Document 3).

JP 2000-47247 A JP-A-6-289370 JP 2003-43515 A

  However, in the technique described in Patent Document 1, when a heater separately from the liquid crystal element is provided, the liquid crystal element substrate constituting the liquid crystal element is heated without directly heating the liquid crystal material held between the liquid crystal element substrates. Therefore, there is a problem that a time difference occurs between the start of heating and the temperature rise, and heating requires more energy than necessary. Further, since the thickness of the liquid crystal element becomes thicker than that of the heater substrate and a process for attaching the heater is required, there is a problem that the liquid crystal element is large and productivity is low.

In various conventional liquid crystal elements as described above, when the heater is arranged or formed so as to overlap with an effective (display) region through which light is transmitted, a transparent resistance film or the like (including a transparent conductive film for the heater) is used as the heater. Even if it is used, since the heater does not have complete transparency, there is a problem that the light utilization efficiency (transmittance) decreases as the performance of the element.
The heater of Patent Document 2 is formed in a black matrix for shielding light, and the heater of Patent Document 3 is formed in a non-display area such that light does not pass through, and there is no reduction in light utilization efficiency. In addition, since the liquid crystal material in the light effective (display) region cannot be directly heated, there is a problem that the efficiency and accuracy of heating deteriorate.

  Accordingly, the present invention has been made in view of the above-described circumstances in order to solve the above-described problems. By forming a heater in the light effective region inside the substrate of the liquid crystal element, the liquid crystal material in the light effective region can be obtained. By directly heating, the efficiency and accuracy of heating can be improved, and the heater also serves as an electrode for driving the liquid crystal, so that there is no decrease in light utilization efficiency in the heater, and the heater electrode and the drive electrode are formed in the same way. The main object is to realize and provide a polarization switching element that can improve productivity, and a polarization switching device, an optical path switching device, an optical scanning device, and an image forming apparatus that exhibit the effects described below.

  In order to solve the above-mentioned problems and achieve the above-mentioned object, the present inventors made the following points clarified while conducting experiments including evaluations described in Examples and the like described later and conducting earnest research. . In other words, in a configuration in which a heater is formed directly inside the substrate of the liquid crystal element and a heater is provided integrally with the liquid crystal element, if a heater is formed in the light effective (display) area, a liquid crystal display that requires an intermediate gradation is required. In the case of the apparatus, there is a problem that the optical (display) performance is adversely affected due to the current flowing in the light effective (display) region of the existing configuration when the heater is heated. However, the liquid crystal having spontaneous polarization as in the present invention. When a polarization switching element is used to electrically switch the polarization direction of incident light by using a heater, even if a heater electrode is formed directly in the light effective (display) region inside the substrate of the element, the heater electrode also serves as a drive electrode As a result, it has been found that there is no adverse effect on the optical characteristics during heating, as described above, by applying a driving electric field equal to or higher than the saturation electric field at which the alignment state of the liquid crystal is saturated when the heater is heated.The present invention has been made based on the facts supported by experiments including such evaluation.

In order to solve the above-described problems and achieve the above-described object, the invention according to each claim employs the following characteristic means and configuration.
The invention according to claim 1 is a pair of transparent substrates, an alignment film formed on at least one of the mutually facing inner surfaces of each transparent substrate, a liquid crystal having spontaneous polarization held between the transparent substrates, It consists of a heating transparent conductive film for heating the liquid crystal by applying an electric current and a driving transparent conductive film for driving the liquid crystal by applying an electric field, and the polarization direction of incident light can be electrically switched In the polarization switching element, the heating transparent conductive film is formed on inner surfaces of the transparent substrates facing each other, and also serves as the driving transparent conductive film.

  According to a second aspect of the present invention, in the polarization switching element according to the first aspect, the transparent conductive film for heating is formed in at least a part of an incident light region to each transparent substrate.

  According to a third aspect of the present invention, the liquid crystal is heated and driven by applying a current to the polarization switching element of the first or second aspect and the heating transparent conductive film and applying an electric field to the driving transparent conductive film. In the polarization switching device comprising a voltage applying means, the driving electric field at the time of heating the liquid crystal is not less than a saturation electric field at which the driving state of the liquid crystal in the at least part of the incident light region to each transparent substrate is saturated and stabilized. It is characterized by being.

  According to a fourth aspect of the present invention, the liquid crystal is heated and driven by applying a current to the polarization switching element of the first or second aspect and the heating transparent conductive film and applying an electric field to the driving transparent conductive film. In the polarization switching device comprising a voltage applying means, the driving electric field at the time of heating the liquid crystal is not less than a saturation electric field at which the driving state of the liquid crystal in the at least part of the incident light region to each transparent substrate is saturated and stabilized. And the size thereof is substantially the same in the plane of each transparent substrate corresponding to the at least part of the incident light region.

  According to a fifth aspect of the present invention, the liquid crystal is heated and driven by applying a current to the polarization switching element of the first or second aspect and the heating transparent conductive film and applying an electric field to the driving transparent conductive film. In the polarization switching device comprising a voltage applying means, the driving electric field at the time of heating the liquid crystal is not less than a saturation electric field at which the driving state of the liquid crystal in the at least part of the incident light region to each transparent substrate is saturated and stabilized. In addition, a high-frequency signal that does not change the driving state of the liquid crystal when the driving is saturated is applied.

  A sixth aspect of the invention includes the polarization switching element or the polarization switching device according to any one of the first to fifth aspects, and a polarization separation element that separates two polarization components orthogonal to each other into different optical paths. This is an optical path switching device.

  The invention described in claim 7 comprises a light source, deflecting means for deflecting the light beam from the light source, and an imaging optical system for imaging the light beam deflected by the deflecting means on the surface to be scanned. An optical scanning device includes the optical path switching device according to claim 6 between the light source and the deflecting unit.

  According to an eighth aspect of the present invention, in the optical scanning device according to the seventh aspect of the present invention, the optical scanning device further includes a light amount detecting unit that detects a light amount of a beam in at least one of the plurality of optical paths from the optical path switching device. The liquid crystal in the optical path switching device is heated based on the detection signal.

  According to a ninth aspect of the present invention, in the optical scanning device according to the eighth aspect, the heating of the liquid crystal in the optical path switching device is set to an optical scanning ineffective period.

  A tenth aspect of the present invention is an image forming apparatus including the optical scanning device according to any one of the seventh to ninth aspects.

According to the present invention, the above problems can be solved and a novel polarization switching element, polarization switching device, optical path switching device, optical scanning device, and image forming apparatus can be realized and provided. The effects of the invention for each claim are as follows.
According to the first aspect of the invention, the productivity of the polarization switching element can be improved by the same formation of the heating transparent conductive film (for example, heater electrode) and the driving transparent conductive film (for example, driving electrode). .

  According to the second aspect of the present invention, with the above configuration, it is possible to improve the heating efficiency and accuracy of the liquid crystal without reducing the light utilization efficiency in the heating transparent conductive film (for example, the heater electrode).

  According to the third aspect of the invention, with the above configuration, a uniform polarization switching operation can be realized in at least a part of the incident light region, for example, in the light effective region, and stable high-speed response can be achieved even in a low temperature environment. The polarization switching device shown can be realized and provided.

  According to the fourth aspect of the present invention, with the above-described configuration, a uniform polarization switching operation can be realized by applying a low voltage in, for example, the light effective region plane as at least a part of the incident light region, and stable even in a low temperature environment. It is possible to realize and provide a polarization switching device exhibiting high-speed response.

  According to the fifth aspect of the present invention, the above configuration can improve the heating efficiency and accuracy of the liquid crystal, and can realize and provide a polarization switching device that exhibits stable high-speed response even in a low temperature environment.

  According to the sixth aspect of the present invention, the configuration described above is a combination of the polarization switching element or the polarization switching device and the polarization separation element with improved heating efficiency and accuracy, and is stable even in a low temperature environment. In addition, an optical path switching device capable of switching optical paths at high speed can be realized and provided.

  According to the seventh aspect of the present invention, by applying the optical path switching device according to the sixth aspect having the above-described effect to the optical scanning device by the above configuration, low cost, high speed, high image quality, and low temperature can be achieved. It is possible to realize and provide an optical scanning apparatus capable of stable optical scanning recording even under an environment.

  According to the eighth aspect of the present invention, by the above configuration, the liquid crystal in the optical path switching device is heated based on the detection signal from the light amount detection means, so that the optical path switching time from the detection of the light amount of the scanning beam can be reduced in the optical path switching device. Since the adjustment is performed by heating the liquid crystal, it is possible to realize and provide an optical scanning device in which the response of switching the optical path is further stable even in a low temperature environment.

  According to the ninth aspect of the present invention, the optical path switching time is adjusted by heating the liquid crystal in the optical path switching device from the detection of the light amount of the scanning beam, and the heating timing is set to the optical scanning ineffective period. Therefore, it is possible to realize and provide an optical scanning device that does not deteriorate characteristics even in a low temperature environment.

  According to the invention of claim 10, by applying the optical scanning device having the above-described effect of any one of claims 7 to 9 to an image forming apparatus, low cost, high speed, high image quality can be supported, and Therefore, it is possible to realize and provide an image forming apparatus including a multicolor image forming apparatus capable of stable image formation even in a low temperature environment.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention including examples will be described with reference to the drawings. In each embodiment, components (members and components) having the same function, shape, etc. are described once unless they are confused, and the description is omitted by giving the same reference numerals. . In order to simplify the drawings and the description, even if the components are to be represented in the drawings, the components that do not need to be specifically described in the drawings may be omitted as appropriate. When quoting and explaining constituent elements such as published patent gazettes, parentheses are given to the reference numerals to distinguish them from those of the embodiments and the like.

(First embodiment)
With reference to FIGS. 1 and 2, a first embodiment of the polarization switching element of the present invention will be described. FIG. 1 is a cross-sectional view of the polarization switching element, and FIG. 2 is a view of the polarization switching element as viewed from the light incident optical axis.
As shown in FIGS. 1 and 2, the polarization switching element 10 includes a pair of transparent substrates 1 and 2, a spacer 3 that holds a gap between the transparent substrates 1 and 2, and surfaces of the transparent substrates 1 and 2. Alignment films 5 and 6 formed on opposing inner surfaces and uniformly aligning the liquid crystal 4 with respect to the transparent substrates 1 and 2, and a liquid crystal 4 having spontaneous polarization in which the alignment state changes due to polarity reversal of the applied electric field, The transparent conductive film 8 for heating that can apply a current for heating the liquid crystal 4 formed on the inner surfaces of the transparent substrates 1 and 2 overlapping the light effective region 7 of incident light, and the alignment state of the liquid crystal 4 are changed. It is mainly composed of a driving transparent conductive film 9 that can apply a driving electric field between the transparent substrates 1 and 2.

  Here, in the present embodiment, the heating transparent conductive film 8 also serves as the driving transparent conductive film 9 and is at least a part of the incident light region on the transparent substrates 1 and 2 of the polarization switching element 10. It is characterized by being formed in the light effective region 7. The heating transparent conductive film 8 has the same structure as that of the driving transparent conductive film 9 as described above, and therefore is the same in FIG. For this reason, the transparent transparent conductive film 8 for heating and the transparent conductive conductive film 9 for driving are collectively referred to as “transparent conductive film 8” or “transparent electrode 8” hereinafter unless otherwise specifically described. In both figures, the portions shown in black in the left and right ends of a pair of upper and lower transparent electrodes (transparent conductive film) 8 are applied with voltage for applying current and electric field to the transparent electrode (transparent conductive film) 8. The connection terminal part of a means is represented. That is, the heating and driving transparent conductive film 8 is a common part formed of the same material and shape, so that the productivity is improved and the liquid crystal 4 can be directly heated. Heating efficiency and accuracy can be improved. Furthermore, since it is not the structure which newly provides the transparent conductive film for heating, the fall of light utilization efficiency does not arise, either (refer Claim 1, 2).

With respect to the polarization switching element 10 of FIGS. 1 and 2, the alignment films 5 and 6 can be made of a normal alignment film such as polyimide used for TN liquid crystal, STN liquid crystal, and the like, and have an inorganic alignment film and SiO having good light resistance. _2. Inorganic vapor deposition films such as SiO can also 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. The heating and driving transparent conductive film 8 can be used as long as it is a transparent conductor (resistor). For example, an indium tin oxide (ITO) film can be used. The film thickness is appropriately set depending on the desired transmittance and resistance value.
The liquid crystal 4 only needs to have a spontaneous polarization in which the alignment state changes due to the polarity reversal of the applied electric field, and a ferroelectric liquid crystal or an antiferroelectric liquid crystal can be used.

  As a polarization switching operation of the polarization switching element 10, switching in the case where, for example, a ferroelectric liquid crystal is used as the liquid crystal 4 in FIGS. 3 to 5 will be described. FIG. 3 is a schematic diagram of the configuration of the polarization switching element 10, omitting the alignment films 5 and 6 and the spacer 3 shown in FIG. 1, but has the same cross-sectional configuration as FIG. 1. In general, a ferroelectric liquid crystal layer composed of a chiral smectic C phase has a helical structure. However, as shown in FIG. 3, when sandwiched between cell gaps d thinner than the helical pitch, the helical structure is unwound and the surface It becomes a stabilized ferroelectric liquid crystal layer (hereinafter referred to as “SSFLC”). As shown in FIG. 4A, the SSFLC is an alignment state H1 in which the liquid crystal molecules are inclined and tilted with respect to the smectic layer normal by a tilt angle (tilt angle) −θ (here, θ = 22.5 °). As shown in FIG. 4B, it is possible to realize a state in which a stable alignment state H2 that is inclined in the opposite direction by (+) θ is mixed.

  In FIG. 4, W is the normal direction of the smectic layer, n is the major axis direction of the liquid crystal molecules (director), black circles (●) in circles (◯) in the liquid crystal molecules, + The symbol of represents the direction of spontaneous polarization. By applying an electric field in a direction perpendicular to the paper surface, the direction of liquid crystal molecules and their spontaneous polarization can be made uniform, and that state can be maintained. And switching between two states can be performed by switching the polarity of the electric field to apply.

  That is, when an electric field of −E is applied in FIG. 4, an orientation state inclined by −θ from the smectic layer normal direction W is applied to an orientation state H1 and when an + E electric field is applied, an orientation state inclined by θ from the smectic layer normal direction W is applied. It can be stabilized to H2. Here, when θ = 22.5 °, the alignment state H2 tilted 45 ° from the alignment state H1 can be stabilized.

FIG. 5 is a schematic diagram showing the operation of the polarization switching element 10 using the SSFLC described above. In FIG. 5, 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, and Δn × d = λ / 90, the polarization plane can be rotated by 90 °, so that the half-wave plate condition is satisfied and 2θ is 45 °.
The incident polarization direction needs to be adjusted and arranged so as to be positioned in the short axis direction or the long axis direction of the liquid crystal molecules in one of the two alignment states of the liquid crystal molecules in the liquid crystal layer. Here, as shown to Fig.5 (a), it is set as the short-axis direction of the orientation state H1 when the electric field of -E is applied. As an adjustment method, it is possible to adjust the polarization direction by arranging the phase plate, or to rotate and adjust the liquid crystal element itself.

  By adopting such a configuration, as shown in FIG. 5A, when an electric field of −E is applied between the transparent electrodes (transparent conductive films) 9, as shown in FIG. Takes an orientation state H1 tilted by −θ from the smectic layer normal direction W, and incident polarized light is emitted while maintaining the polarization direction as it is. On the other hand, as shown in FIG. 5 (b), when an electric field of + E is applied between the transparent electrodes 9, the liquid crystal molecules are aligned with an inclination of + θ from the smectic layer normal direction W as shown in FIG. 4 (a). The state H2 is taken. Here, since θ = 22.5 °, the liquid crystal molecule major axis direction (director) is inclined with respect to incident polarized light by 2θ = 45 °. As a result, the half-wave plate condition is satisfied, and the outgoing polarized light has a polarization direction rotated by 90 ° from the incident polarized light. That is, polarization switching can be realized by electric field control. However, as described above, the performance of the liquid crystal element generally depends on the environmental temperature, and as shown in FIG. 6A, there is a problem that the response speed decreases in a low temperature environment.

  Therefore, with reference to FIGS. 7A and 7B, the polarization switching device 11 having a configuration in which the polarization switching element 10 having the configuration shown in FIG. 1 described as the first embodiment of the present invention is provided with voltage applying means. An example of heating and driving will be described. As shown in FIG. 7B, the applied voltage applied from the voltage applying means (not shown) is V11 and V12 toward the transparent substrate 1 (hereinafter also simply referred to as “substrate 1”), and the transparent substrate 2 (hereinafter referred to as “substrate 1”). V21 and V22 are also referred to as “substrate 2”).

First, referring to FIG. 8, in the polarization switching device 11 provided with the polarization switching element 10 shown in FIG. 7B, the signal of the applied voltage and the electric field between the transparent substrates 1 and 2 when driven without heating. An example of the size and direction / polarity of the image will be described. Assume that a rectangular wave signal shown in FIG. 8A is input as an applied voltage signal. At the time of non-heating and driving, applied voltages to the connection terminals (hereinafter also simply referred to as “terminals”) of the respective transparent electrodes 8 are V11 = V12 and V21 = V22, and current flows (applied) on the substrate surface. There is no heating.
At the time of switching the polarization, as shown in FIGS. 8B and 8C, the electric field direction between the substrate 1 and the substrate 2 is switched by the polarity inversion of V12 and V21, and the magnitude is light effective. Since it is the same in the area 7 plane, a uniform polarization switching operation can be realized in the plane of the light effective area 7.

Next, referring to FIG. 9, in the polarization switching device 11 having the polarization switching element 10 shown in FIG. An example of the magnitude and direction / polarity of the electric field will be described. Assume that a rectangular wave signal shown in FIG. 9A is input as an applied voltage signal. The voltages applied to the respective terminals are V11> V12 and V21 = V22. From the relationship of V11> V12, the current I12 or I21 is applied to the surface of the substrate 1 and flows, whereby the liquid crystal 4 can be directly heated.
At the time of switching the polarization, as shown in FIGS. 9B and 9C, the electric field direction between the substrate 1 and the substrate 2 is switched by the polarity inversion of V12 and V21, and the magnitude thereof is the light effective region. Since it is different within the seven planes and | E1 |> | E2 |> | E3 |, in this case, a uniform polarization switching operation cannot be performed within the seven planes of the light effective area.

(Second Embodiment)
Therefore, referring to FIG. 10, as a second embodiment of the present invention, in the polarization switching device 11 having the polarization switching element 10 shown in FIG. An example of the magnitude and direction / polarity of the signal and the electric field between the transparent substrates 1 and 2 will be described. Assume that a rectangular wave signal shown in FIG. 10A is input as an applied voltage signal.
The voltages applied to the respective terminals are V11> V12 and V21 = V22. From the relationship of V11> V12, the current I12 or I21 is applied to the surface of the substrate 1 and flows, whereby the liquid crystal 4 can be directly heated. At the time of switching the polarization, as shown in FIGS. 10B and 10C, the electric field direction between the substrate 1 and the substrate 2 is switched by the polarity inversion of V12 and V21, and the magnitude is light effective. The difference in the plane of the region 7 is | E1 |> | E2 |> | E3 |, but the minimum electric field | E3 | in the light effective region 7 is saturated in the alignment / driving state of the liquid crystal 4 (the optical property of polarization switching is Since the saturation electric field | Eth | is greater than or equal to the saturation), a uniform polarization switching operation can be realized in the plane of the light effective region 7.
Here, the applied voltages are V11> V12 and V21 = V22, but current can be applied to the substrate surface, and the electric field between the substrates 1 and 2 in the plane of the optical effective region 7 is equal to or greater than the saturation electric field | Eth |. If there is, it is not limited to this. By applying a voltage so as to have such an applied current and applied electric field, a uniform polarization switching operation can be realized in the surface of the light effective region 7 even during heating (see claim 3).

(Third embodiment)
Referring to FIG. 11, as another third embodiment of the present invention, in the polarization switching device 11 having the polarization switching element 10 shown in FIG. An example of the magnitude and direction / polarity of the signal and the electric field between the transparent substrates 1 and 2 will be described. Assume that a rectangular wave signal shown in FIG. 11A is input as an applied voltage signal.
The voltages applied to the respective terminals satisfy the relationship of | V11−V21 | ≈ | V12−V22 |, and currents I1-12 and I1-21 on the substrate surface from the relationship of V11 ≠ V12 and V21 ≠ V22, Alternatively, the liquid crystal 4 can be directly heated by applying I2-12 and I2-21. At the time of polarization switching, as shown in FIGS. 11 (b) and 11 (c), the electric field direction between the substrate 1 and the substrate 2 is switched by the polarity inversion of V11, V12, V21, and V22, and the magnitude thereof is increased. Since this is the same in the plane of the light effective area 7, a uniform polarization switching operation can be realized in the plane of the light effective area 7.
Here, the applied voltage is set to | V11−V21 | ≈ | V12−V22 |, but current can be applied to the substrate surface, and the electric field between the substrates 1 and 2 in the plane of the optical effective region 7 is the saturation electric field | Eth. If it is above and the magnitude of the electric field is substantially the same in the plane of the light effective region 7, it is not limited to this. By applying a voltage so as to achieve such an applied current and an applied electric field, a uniform polarization switching operation can be realized in the surface of the light effective region 7 at a low voltage even during heating (see claim 4).

  In addition, as shown in FIG. 12, heating can also be performed by applying a high-frequency signal that does not change the alignment / drive state of the liquid crystal when the drive voltage signal is saturated (the same as the polarization switching optical characteristics do not change). The voltage and frequency of this signal depend on the liquid crystal used, but the frequency is preferably 100 kHz or more (see claim 5).

  Next, as a typical example of the first embodiment, referring to FIG. 1 and FIG. 7 for Example 1 relating to the fabrication of the polarization switching element 10 using ferroelectric liquid crystal and the operation confirmation of the polarization switching device 11. While explaining.

  The substrates 1 and 2 are made of non-alkali glass with a thickness of 1.1 mm and have a size of 30 × 40 mm. The heater electrode as the transparent electrode (transparent conductive film) 8 and ITO ( A film having a thickness of 1000 mm and a sheet resistance of 50Ω / □ was formed. A polyimide 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. Adhesive with bead spacer mixed as spacer 3 using two glass substrates as described above, with ITO electrode faces facing each other so that the rubbing direction is anti-parallel, and the distance between substrates 1 and 2 is about 2 μm. To form an empty cell.

  Next, a ferroelectric liquid crystal (FELIX 018-100 made by Clariant Δn = 0.17, 2θ = 45) is formed as the liquid crystal 4 in the empty cell in a state where the empty cell is heated to 90 degrees (° C.) on a hot plate. After injecting by the capillary method, and allowing to cool after standing, the inlet and the like were sealed to form a liquid crystal layer, and a polarization switching element 10 as shown in FIG. 1 and a polarization switching device 11 as shown in FIG. 7 were produced. The connection terminal for voltage application was formed with solder.

Using the glass substrate alone (substrate 1) on which the heater electrode and the drive electrode used in the polarization switching element 10 are formed, the voltages V11 = 10V and V12 = + 10V are applied to the terminals of the voltage applying means, and the surface of the substrate 1 is applied. Was heated by applying (applying) an electric current. At this time, the temperature of the glass substrate surface on which the electrode was formed and the temperature on the glass substrate surface on which the electrode was not formed were measured using a thermocouple. Showed a faster temperature rise.
Further, using a glass substrate alone having two regions, a region where the heater electrode and the drive electrode are formed on the glass substrate surface (electrode forming region) and a region where no electrode is formed (electrode non-forming region), Similarly, when current was applied to the electrode portion and heated to measure the temperature of the electrode formation region and the electrode non-formation region, the temperature was different in the two regions, and the temperature was higher in the electrode formation region. That is, it was found that the heater electrode formation region has a fast heating time and high heating efficiency and accuracy.

  Next, as an optical characteristic evaluation of the polarization switching element 10, the polarization switching element 10 is sandwiched between polarizing plates under crossed Nicols in the optical path of a laser light source and a photodiode (hereinafter referred to as “PD”), and a voltage is applied to the polarization switching element 10. The polarization switching switching operation was observed after application. Here, the arrangement of the polarization switching element 10 is adjusted so that the incident polarization direction coincides with the major axis direction of the liquid crystal molecules in one of the two alignment states of the liquid crystal alignment, and the PD output is in a bright and dark state. Adjusted and arranged so that

  First, the applied voltage signal has a frequency of 4 kHz, and the applied voltages to the terminals of the substrate (glass substrate) 1 and substrate (glass substrate) 2 are V11 = + 40⇔−40, V12 = + 40⇔−40, V21 = G (ground) , V22 = G (ground), and a rectangular wave signal of ± 20 V / μm is inputted and driven so that the electric field strength between the substrates 1 and 2 (glass substrate) becomes a saturation electric field as shown in FIG. At this time, when the temperature of the surface of the substrate (glass substrate) 1 was measured with a thermocouple, it was 25 ° C., and the response speed (dark 0% → light 100% rise time) was as shown in FIG. 30 μsec.

  Next, the applied voltage signal has a frequency of 4 kHz, the applied voltages to the terminals of the substrate (glass substrate) 1 and substrate (glass substrate) 2 are V11 = + 50⇔−50, V12 = + 40⇔−40, V21 = G (ground) ), V22 = G (ground), and a rectangular wave signal having an electric field strength of ± 20 V / μm (minimum electric field in the light effective region) between the substrates 1 and 2 (glass substrate) was input and driven. At this time, the PD output value was the same as described above, and it was confirmed that there was no deterioration in optical performance. In addition, since current is applied to the substrate (glass substrate) 1, the temperature of the substrate (glass substrate) 1 rises several seconds after driving and heating, and the temperature of the surface of the substrate (glass substrate) 1 is set by a thermocouple. When measured, the temperature was about 40 ° C., and the response speed (dark 0% → light 100% rise time) was about 22 μsec. From this, it was found that high-speed responsiveness can be ensured even at low temperatures by applying an electric field that is equal to or higher than the saturation electric field during heating.

Further, the applied voltage signal has a frequency of 4 kHz, applied voltages to the terminals of the substrate (glass substrate) 1 and substrate (glass substrate) 2 are V11 = + 20⇔−20, V12 = + 20⇔−20, V21 = −20⇔ + 20. V22 = −20⇔ + 20, and driving was performed by inputting a rectangular wave signal having an electric field strength between the substrates (glass substrates) 1 and 2 of ± 20 V / μm (electric field in the light effective region). At this time, the PD output value was the same as described above, and it was confirmed that there was no deterioration in optical performance. In addition, since current is applied to the substrate (glass substrate) 1, the temperature of the substrate (glass substrate) 1 rises several seconds after driving and heating, and the temperature of the surface of the substrate (glass substrate) 1 is set by a thermocouple. When measured, the temperature was about 40 ° C., and the response speed (dark 0% → light 100% rise time) was about 22 μsec.
From this, it was found that high-speed responsiveness can be ensured even at low temperatures by applying an electric field that is equal to or higher than the saturation electric field during heating. From the results of Example 1 described above, it was found that high-speed responsiveness can be ensured by applying a low voltage even at low temperatures by applying an electric field that is equal to or higher than the saturation electric field during heating and maintaining the same electric field strength between the substrates. .

(Fourth embodiment)
With reference to FIG. 13, the configuration and operation of the fourth embodiment according to the optical path switching apparatus of the present invention will be described. As shown in FIG. 13, the optical path switching device 15 of the fourth embodiment includes the polarization switching element 10 described above, and a polarization separation element 13 disposed on the optical path after transmission of incident light in the polarization switching element 10. It comprises the structure which comprised. The polarization separation element 13 can be realized using a birefringence element, a polarization beam splitter (hereinafter also referred to as “PBS”) prism, a diffractive optical element exhibiting polarization dependency, and the like.

  The polarization switching element 10 operates / functions to switch the polarization direction of incident light to two polarization components orthogonal to each other (first polarization direction D1, second polarization direction D2, and so on) by electric field control as described above. have. That is, the polarization plane direction of incident light can be switched by approximately 90 °. In addition, the polarization separation element 13 separates two orthogonal polarization components (polarization direction D1 and polarization direction D2) into different optical paths (first optical path P1, second optical path P2, and so on). have. That is, the two polarization components (polarization direction D1 and polarization direction D2) switched by the polarization switching element 10 can be guided and switched to different optical paths (optical path P1 and optical path P2), respectively. In this way, the optical path switching device 15 can be realized by the configuration of the polarization switching element 10 and the polarization separation element 13. The influence of the optical path switching device 15 on the optical path switching performance differs depending on each element constituting the device. The polarization switching element 10 mainly affects the response and optical characteristics of the optical path switching. Mainly affects the optical path shift amount of optical path switching. Here, since the optical path shift amount greatly depends on the optical path length passing through the element, a desired optical path shift amount can be obtained by appropriately setting the element size of the polarization separation element 13. The polarization separation element 13 is effective when the shift amount is small, and a birefringence element is effective. When a certain amount of shift is required, a PBS prism is effective.

  As described above, since the polarization switching element 10 can heat and drive the liquid crystal and can exhibit high-speed response even in a low temperature environment, the optical path switching operation by the optical path switching device 15 is similarly performed at a low temperature. The optical path can be switched at high speed under the environment (see claim 6).

(Fifth embodiment)
With reference to FIG. 14, a fifth embodiment according to the optical scanning device of the present invention will be described. FIG. 14 shows a part of the optical scanning device. The optical scanning device in FIG. 14 is a light source 16, an optical path switching device 15 according to the fourth embodiment, and a light beam switched by the optical path switching device 15. The configuration includes a polygon mirror 37 as a deflecting means for deflecting, and an optical path switching device 15 is disposed between the light source 16 and the polygon mirror 37.

Further, the first and second optical paths P1 (hereinafter also referred to as “upper optical path”) and the second optical path P2 (hereinafter also referred to as “lower optical path”) from the optical path switching device 15 are detected. The voltage application means 12 is provided with second light quantity detection means 18a and 18b, and has a function of voltage adjustment means for controlling heating and driving to the optical path switching device 15 based on detection signals from the respective light quantity detection means 18a and 18b. It is also characterized by having a configuration comprising
The polygon mirror 37 includes an upper polygon mirror 37a and a lower polygon mirror 37b having a common rotation axis and arranged as a plurality of stages of two-stage rotary reflection polygon mirrors with a phase of 45 °. .

  As an operation of the optical scanning device of FIG. 14, the light beam emitted from the light source 16 passes through the lens 17 and is switched in the sub-scanning direction by the optical path switching by the optical path switching device 15 described above (upper stage as the first optical path P1). The optical path and the lower optical path as the second optical path P2 are shifted, and are incident on the upper polygon mirror 37a and the lower polygon mirror 37b constituting the two-stage polygon mirror 37 corresponding to the first and second optical paths P1 and P2. The

  A common photodiode can be used for the light quantity detection means 18a, 18b. The optical path switching device 15 is heated and driven by the transparent conductive film 8 for heating and driving the liquid crystal of the polarization switching element 10 as described above (see FIGS. 1 and 7). In the case of such a configuration, since the liquid crystal is directly heated, there is an advantage that the time for reaching the set temperature is quick and high-precision heating can be performed (see claim 7).

  Hereinafter, heating and drive control by light amount detection will be specifically described. FIG. 15 shows the scanning recording timing and the detection signals 1s and 2s from the light quantity detection means 18a and 18b. Here, two upper and lower switching optical paths are shown. As shown in FIG. 15, when the amount of light in the upper optical path at the end of recording in the upper optical path is the same as the amount of light in the lower optical path at the start of recording in the lower optical path (the amount of light in the lower optical path at the end of recording in the lower optical path, When the amount of light in the upper optical path at the start of recording in the optical path is the same), the response time for switching the optical path is within the set value and the response performance is ensured, so heating is not necessary.

  However, as shown in FIG. 16, when the amount of light in the upper optical path at the end of recording in the upper optical path is different from the amount of light in the lower optical path at the start of recording in the lower optical path (the amount of light in the lower optical path at the end of recording in the lower optical path, If the light amount of the upper optical path at the start of recording in the optical path is different), it can be seen that the response time of the optical path switching is out of the set value and the response performance is not secured, and it is necessary to heat the light amount to be the same . Here, the heating timing is set to an optical scanning ineffective period in which writing recording at the time of optical scanning from the end of recording to the start of recording is not performed, so that the influence of heating on writing recording is completely eliminated ( (See claims 8 and 9).

  Further, as shown in FIG. 17, a time T in which the light amount in the upper optical path and the light amount in the lower optical path overlap from the end of recording is defined, and a time in which the light amount in the upper optical path and the light amount in the lower optical path overlap from the specified time T from the end of recording. It is also possible to confirm the change in response speed. That is, when T ′> T, it can be seen that the response time of optical path switching is outside the set value and the response performance is not ensured, and it is necessary to adjust the electric field or temperature so that the amount of light is the same. . In the case of this detection method, detection can be performed regardless of the absolute value of the amount of light, so that the specification range of the photodiode as the light amount detection means is expanded.

In the above description, the upper and lower switching optical paths are described. However, the response time depends on whether the difference in the light amount between the start of recording and the end of recording is maximized even in the light amount detection of the upper or lower optical path. Is within the set value (see claim 8).
By detecting the amount of light, the liquid crystal in the optical path switching device 15 is heated and driven and the high-speed response of the optical path switching device 15 is ensured, so that the response time of the optical path switching is set to a desired response time even in a low temperature environment. Since the light quantity performance of the recording scanning light actually used can be ensured, the occurrence of print image deterioration can be reduced.

  Here, as the arrangement of the light quantity detection means, the time for the switching time can be set longer by installing it in front of the polygon mirror 37. Specifically, as shown in FIG. 14, the optical path is further branched and detected by the half mirror prisms 19a and 19b. Reflected light outside the aperture is detected by a mirror having an aperture.

Further, as in the optical scanning device according to the first modification of the fifth embodiment shown in FIG. 18, a configuration for detecting the reflected light of the soundproof glass 36 surrounding the polygon mirror 37 (the reflection intensity is adjusted by a reflection film or the like). However, the present invention is not limited to this as long as the amount of light immediately before the recording scan in the invalid scanning period in which the recording scan is not performed can be detected (recording start and end timing not affecting the recording).
In FIG. 18, reference numerals 45a, 45b, 45c, and 45d denote synchronization detection photodiodes that detect the synchronization of the optical scanning period.

  Further, as another arrangement example of the light amount detection means 18a, 18b, 18c, 18d as in the optical scanning device according to the second modification of the fifth embodiment shown in FIG. 19, it is installed after the polygon mirror 37. Therefore, it is not necessary to install extra parts or reflective films.

  Further, as in the optical scanning device according to the third modification of the fifth embodiment shown in FIG. 20, the light quantity detection / scanning synchronization detection photodiodes 46a, 46b, 46c, By setting it to 46d, the number of parts can be further reduced.

  Referring to FIG. 21, the overall configuration of the optical scanning device according to the fifth embodiment, part of which is shown in FIG. The components (components and components) of the optical scanning device shown in FIG. 18 to FIG. 20 are given the same reference numerals as long as there is no risk of confusion, and detailed descriptions thereof are omitted. It shall conform to the contents.

As shown in FIG. 21, the optical scanning device according to the present embodiment includes a first optical system and a second optical system.
That is, the first optical system includes semiconductor lasers 31 and 31 ′ as light sources, an LD base 32, coupling lenses 33 and 33 ′, an optical path switching device 15 (or polarization switching means and polarization separation means), It is mainly composed of cylindrical lenses 35a and 35b.
The second optical system includes a soundproof glass 36, a polygon mirror 37 having an upper polygon mirror 37a and a lower polygon mirror 37b, first scanning lenses (fθ lenses) 38a and 38b, a mirror 39, and a second mirror. Scanning lenses (fθ lenses) 40a and 40b, photoconductors 41a and 41b, which are drum-shaped image carriers having scanning surfaces, an aperture stop 42, and light quantity detection / scanning synchronization detection photodiodes 46a, 46b, and 46c. , 46d.

Although not shown in FIG. 15, the first optical system from the laser light source (2LD unit) to the cylindrical lenses 35a and 35b after the optical path switching device 15 (or the polarization switching element and the polarization separation element) and the fθ lens are included. By using two sets of the second optical system that is an imaging optical system and a two-stage polygon mirror, it is possible to construct an optical scanning device that writes to four optical scanning locations with two beams.
The four optical scans are photoconductors corresponding to four colors (cyan, yellow, magenta, and black (black)), and a multicolor image forming apparatus can be constructed.

(Sixth embodiment)
Referring to FIG. 22, there is shown a basic configuration of a multicolor image forming apparatus as a sixth embodiment according to the image forming apparatus of the present invention.
The multicolor image forming apparatus shown in FIG. 22 is an example of an image forming apparatus to which the optical scanning device according to any one of the fifth embodiment and the first to fourth modifications according to the present invention is applied.

  The multicolor image forming apparatus shown in FIG. 22 corresponds to four colors of Y (yellow), M (magenta), C (cyan), and K (black), and the photosensitive member 1Y, the photosensitive member 1M, the photosensitive member 1C, and the photosensitive member. Cleaning unit 1K, charger 2Y, charger 2M, charger 2C, charger 2K, writing unit (optical scanning device) 23, developer 4Y, developer 4M, developer 4C, developer 4K Means 5Y, cleaning means 5M, cleaning means 5C, cleaning means 5K, transfer charging means 6Y, transfer charging means 6M, transfer charging means 6C, transfer charging means 6K, transfer belt 24, and fixing means 25 Have

The photoreceptors 1Y, 1M, 1C, and 1K rotate in the direction of the arrow in the figure, and in the order of rotation, the charging devices 2Y, 2M, 2C, and 2K, the developing devices 4Y, 4M, 4C, and 4K, the transfer charging units 6Y, 6M, 6C, 6K and cleaning means 5Y, 5M, 5C, 5K are arranged.
The charging means 2Y, 2M, 2C, and 2K include a charging member that constitutes a charging device for uniformly charging the surface of the photoreceptor.

The writing unit 23 irradiates the photosensitive member surface between the charging units 2Y, 2M, 2C, and 2K and the developing members 4Y, 4M, 4C, and 4K, and an electrostatic latent image is formed on the photosensitive member. It is like that.
Based on the electrostatic latent image, a toner image is formed on the surface of the photoreceptor by the developing members of the developing devices 4Y, 4M, 4C, and 4K.

  Further, a recording sheet (not shown) as a sheet-like recording medium conveyed from a sheet feeding device (not shown) is held on a transfer belt 24 formed of an endless belt, thereby transferring charging means 6Y, 6M, Each of the color transfer toner images is sequentially transferred onto the recording paper by 6C and 6K, and finally the image is fixed on the recording paper by the fixing unit 25.

  In the image forming apparatus using the optical scanning device capable of switching the optical path by the electric field control as described above, the optical path of the laser light source is switched and the light quantity is modulated in response to scanning recording from a plurality of stages of polygon mirrors. Thus, it is possible to realize an image forming apparatus that can sequentially scan and record the photoconductors corresponding to the respective colors, and can reduce the number of light sources without causing loss of beam power and enabling high-speed image output.

  In the 4-drum tandem system as shown in FIG. 22, when a two-stage polygon mirror is used, scanning recording can sequentially scan and record, for example, two photosensitive members of yellow and magenta and cyan and black, respectively. Here, stable scanning recording can be realized by feedback control from the light amount detection means (see claim 10).

  In the above-described sixth embodiment, an example of a direct transfer type tandem type multi-color (color) image forming apparatus that sequentially transfers and superimposes a sheet-like recording medium while being conveyed by a transfer belt as a transfer member has been described. However, the present invention is not limited to this. For example, a tandem type multicolor (color) image forming apparatus that transfers images to an endless belt-like intermediate transfer member and then transfers them to a sheet-like recording medium at the same time is applied to the fifth aspect of the invention. It goes without saying that the optical scanning device according to any one of the embodiments and modified examples 1 to 4 can be applied in the same manner.

  As described above, the present invention has been described with respect to specific embodiments, modifications, and the like. However, the technical scope disclosed by the present invention is limited to those exemplified in the above-described embodiments, modifications, or examples. However, it should be understood that various embodiments, modifications, or examples may be configured within the scope of the present invention in accordance with the necessity and application thereof. It will be clear to the trader.

It is a figure which shows an example of a structure of the polarization switching element which concerns on 1st Embodiment, Comprising: It is sectional drawing of S1-S1 of FIG. It is the figure which looked at the polarization switching element concerning a 1st embodiment from the incident optical axis. It is a schematic sectional drawing which shows the structure of the polarization switching element using ferroelectric liquid crystal as a liquid-crystal layer. 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 means using the surface stabilization ferroelectric liquid crystal layer (SSFLC). (A) is a graph which shows the temperature characteristic of the response speed of a liquid crystal element, (b) is a graph which shows the electric field characteristic of the response speed of a liquid crystal element. FIGS. 7A and 7B are diagrams illustrating an example of a configuration of a polarization switching device including a polarization switching element, in which FIG. 7A is a cross-sectional view taken along the line Sa-Sa in FIG. 7B and FIG. FIG. In a polarization switching device, it is a figure explaining an example of the signal of the applied voltage at the time of driving without heating, and the magnitude | size, direction, and polarity of the electric field between transparent substrates. In a polarization switching device, it is a figure explaining an example of the signal of the applied voltage at the time of driving while heating, and the magnitude | size, direction, and polarity of the electric field between transparent substrates. In the polarization switching device concerning a 2nd embodiment, it is a figure explaining an example of the signal of the applied voltage at the time of driving while heating, and the size, direction, and polarity of the electric field between transparent substrates. In the polarization switching device concerning a 3rd embodiment, it is a figure explaining an example of a signal of an applied voltage at the time of driving while heating, and a size, direction, and polarity of an electric field between transparent substrates. It is a figure which shows the example which heats by applying a high frequency signal in the polarization switching apparatus with which the orientation and drive state of a liquid crystal do not change at the time of saturation of a drive voltage signal. It is a block diagram which shows an example of the optical path switching apparatus which concerns on 4th Embodiment. It is a partial block diagram of the optical scanning device which concerns on 5th Embodiment, Comprising: It is a figure which shows arrangement | positioning etc. of an optical path switching device. In the optical scanning device which concerns on 5th Embodiment, it is a figure which shows the 1st scanning recording timing and the detection signal from a light quantity detection means. In the optical scanning device which concerns on 5th Embodiment, it is a figure which shows the 2nd scanning recording timing and the detection signal from a light quantity detection means. In the optical scanning device which concerns on 5th Embodiment, it is a figure which shows the detection signal from a 3rd scanning recording timing and a light quantity detection means. It is a perspective view which shows the optical scanning device which concerns on the modification 1 of 5th Embodiment. It is a perspective view which shows the optical scanning device which concerns on the modification 2 of 5th Embodiment. It is a perspective view which shows the optical scanning device which concerns on the modification 3 of 5th Embodiment. It is a perspective view which shows the whole structure of the optical scanning device concerning 5th Embodiment. FIG. 10 is a schematic configuration diagram of a multicolor image forming apparatus according to a sixth embodiment.

Explanation of symbols

1, 2 Transparent substrate 3 Spacer 4 Liquid crystal 5, 6 Light distribution film 7 Light effective region (at least part of incident light region)
DESCRIPTION OF SYMBOLS 8 Transparent conductive film for heating, transparent electrode 9 Transparent conductive film for driving, transparent electrode 10 Polarization switching element 11 Polarization switching device 12 Voltage application means 13 Polarization separation element 15 Optical path switching device 18a, 18b Light quantity detection means 23 Writing unit (light Scanning device)
24 Transfer belt 25 Fixing means 31, 31 'Semiconductor laser 32 LD base 33, 33' Coupling lens 35, 35 'Cylindrical lens 36 Soundproof glass 37 Polygon mirror (deflection means)
38a, 38b First scanning lens (imaging optical system)
39 Mirror 40a, 40b Second scanning lens (imaging optical system)
41a, 41b photoconductor (image carrier having a scanned surface)
42 Aperture stop 45a, 45b, 45c, 45d Scanning synchronization detection photodiode 46a, 46b, 46c, 46d Light quantity detection / scanning synchronization detection photodiode

Claims (10)

A pair of transparent substrates, an alignment film formed on at least one of the opposing inner surfaces of each transparent substrate, a liquid crystal having spontaneous polarization held between the transparent substrates, and heating the liquid crystal by applying a current A polarization switching element capable of electrically switching the polarization direction of incident light, comprising a transparent conductive film for heating for driving and a transparent conductive film for driving for driving the liquid crystal by applying an electric field,
The polarization switching element, wherein the heating transparent conductive film is formed on inner surfaces of the transparent substrates facing each other and serves also as the driving transparent conductive film. The polarization switching element according to claim 1,
The polarization switching element, wherein the heating transparent conductive film is formed in at least a part of an incident light region to each transparent substrate. A polarized light comprising: the polarization switching element according to claim 1; and a voltage applying unit that heats and drives the liquid crystal by applying a current to the heating transparent conductive film and an electric field to the driving transparent conductive film. In the switching device,
A polarization switching device, wherein a driving electric field at the time of heating the liquid crystal is equal to or higher than a saturation electric field at which the driving state of the liquid crystal in the at least part of the incident light region to each transparent substrate is saturated and stabilized. A polarized light comprising: the polarization switching element according to claim 1; and a voltage applying unit that heats and drives the liquid crystal by applying a current to the heating transparent conductive film and an electric field to the driving transparent conductive film. In the switching device,
The driving electric field at the time of heating the liquid crystal is equal to or more than a saturation electric field at which the driving state of the liquid crystal in the at least part of the incident light region to each transparent substrate is saturated and stabilized, and the magnitude thereof is at least the part. The polarization switching device characterized by being substantially the same in the plane of each of the transparent substrates corresponding to the incident light region. A polarized light comprising: the polarization switching element according to claim 1; and a voltage applying unit that heats and drives the liquid crystal by applying a current to the heating transparent conductive film and an electric field to the driving transparent conductive film. In the switching device,
The driving electric field at the time of heating the liquid crystal is not less than a saturation electric field at which the driving state of the liquid crystal in the at least part of the incident light region to each transparent substrate is saturated and stabilized, and the driving of the liquid crystal at the time of the driving saturation. A polarization switching device characterized by applying a high-frequency signal whose state does not change.   A polarization switching element or a polarization switching device according to any one of claims 1 to 5, and a polarization separation element that separates two polarization components orthogonal to each other into different optical paths. Optical path switching device. In an optical scanning apparatus comprising: a light source; a deflecting unit that deflects a light beam from the light source; and an imaging optical system that forms an image on the surface to be scanned.
An optical scanning device comprising the optical path switching device according to claim 6 between the light source and the deflecting means. The optical scanning device according to claim 7.
Comprising a light amount detection means for detecting a light amount of a beam in at least one of the plurality of optical paths from the optical path switching device, and heating the liquid crystal in the optical path switching device based on a detection signal from the light amount detection means. An optical scanning device characterized by the above. The optical scanning device according to claim 8.
The optical scanning device according to claim 1, wherein the heating of the liquid crystal in the optical path switching device is set to an optical scanning ineffective period.   An image forming apparatus comprising the optical scanning device according to claim 7.

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