JP2009092943A - Optical scanning device and image forming device - Google Patents

Abstract

An optical scanning device capable of halving the number of light sources, switching optical paths at high speed and with high accuracy, and further suppressing the occurrence of ghosts.
In an optical scanning device that scans a plurality of different scanned surfaces 12K and 12M by deflecting the light beam at different timings while switching the optical path of the light beam from the light source 1, the optical path switching means includes an electrical path switching means. It comprises a polarization switching element 2 (PLZT) having an optical effect and a deflection prism 4 comprising a polarization separation element. While the reflected light from the upper stage 7a of the two-stage polygon mirror 7 with the phase difference is being written to the photosensitive member 12K through the scanning optical system, the reflected light from the polygon mirror surface of the lower stage 7b hits the light shielding plate 14 and is ghosted on the photosensitive body. I don't make a statue.
[Selection] Figure 1

Description

  The present invention relates to an optical scanning apparatus, a printer having the optical scanning apparatus, a facsimile machine, a plotter, an MFP, and an image forming apparatus such as a multi-function machine including at least one of them.

Patent Document 1 discloses a multi-beam scanning device that switches a polarization plane of light emitted from a light source for each scanning by a polarization direction changing unit (PLZT element 4) and distributes an optical path by an optical path switching unit (PBS9).
The polarization state of one laser beam is switched and separated into one of two optical paths according to the polarization state. In this embodiment, the PBS is disposed immediately before the mirror in front of the photoreceptor. According to this method, the number of light sources can be halved.
However, since the incident beam on the polarization separation surface of the PBS is mixed with p-polarized light and s-polarized light depending on the deflection angle by the polygon mirror, light leakage occurs on the other photoconductor during writing on one photoconductor.
Patent Document 2 includes a beam splitter or the like to solve the problem of Patent Document 1 (the polarization coordinate system changes and the separation ratio changes according to the incident angle with respect to PBS within one scan). There is disclosed an optical scanning device that controls optical rotation of a laser beam incident on a spectroscopic means according to the incident angle.

Japanese Patent Laid-Open No. 2-179603 JP-A-7-144434 JP 59-193413 A Japanese Patent Laying-Open No. 2005-092148

In the invention described in Patent Document 2, the polarization plane of the beam is corrected horizontally or vertically with respect to the incident plane on the polarization separation plane of the PBS by the optical rotation control means.
For this purpose, it is necessary to control the polarization plane at high speed and strictly by the optical rotation control means during one scanning period.
However, strict control of the optical rotation control means is extremely difficult for disturbances such as wavelength fluctuations of laser light, and there is a problem from the viewpoint of performing optical path switching at high speed and with high accuracy.
Further, during one scanning period, it is necessary to irradiate PBS only with p-polarized light or s-polarized light. When both components are mixed, a ghost is generated.
In the Japanese Patent Application No. 2007-148365, the present inventors have proposed an optical scanning device that switches an optical path by a polarization switching element made of, for example, a ferroelectric liquid crystal. It was not possible to cope with.

An object of the present invention is to provide an optical scanning device that can halve the number of light sources and perform optical path switching at high speed and high accuracy, and an image forming apparatus having the optical scanning device.
Another object of the present invention is to provide an optical scanning device that can further suppress the occurrence of ghosts and an image forming apparatus having the optical scanning device.

In the present invention, in order to further increase the speed, a polarization switching element having an electro-optic effect is used.
In the system using a multi-stage polygon mirror, when writing on one photoconductor, even if light leakage occurs on the other, it is cut by a light shielding plate and no ghost is generated in principle. In the present invention, this method is used to suppress ghost generation.

  Specifically, in the first aspect of the invention, the light source, the optical path switching means, the deflecting means for deflecting the light beam, and the scanning optics for forming an image of the light beam deflected by the deflecting means on the surface to be scanned. In the optical scanning device that scans a plurality of different scanning surfaces by switching the optical path of the light beam from the light source at different timings while switching the optical path of the light beam from the light source, the optical path switching means It comprises a polarization switching element having an optical effect and a polarization separation element.

According to a second aspect of the present invention, in the optical scanning device according to the first aspect, a λ / 2 plate or a λ / 4 plate is disposed between the optical path switching means and the deflection means.
Here, it aims at aligning the light use efficiency in each optical path.
According to a third aspect of the present invention, in the optical scanning device according to the first or second aspect, the deflecting means is a multi-surface reflecting mirror having a common rotation axis and a two-stage configuration in the sub-scanning direction. Features.
Here, it aims at preventing generation | occurrence | production of a ghost further. Here, the “two-stage configuration” means not only a configuration in which reflecting mirrors of different members are stacked, but also a configuration in which one reflecting mirror has a two-stage reflecting surface (reflection area).

According to a fourth aspect of the present invention, in the optical scanning device according to the third aspect, each stage of the polyhedral reflecting mirror has a phase difference.
Here, it aims at suppressing generation | occurrence | production of a ghost strictly.
According to a fifth aspect of the present invention, in the optical scanning device according to any one of the first to fourth aspects, a collimating lens is disposed between the polarization switching element and the polarization separation element.
Further, the purpose is to drive the polarization switching element at a low voltage.

According to a sixth aspect of the present invention, in the optical scanning device according to any one of the first to fourth aspects, a collimator lens is disposed between the light source and the polarization switching element.
Further, the purpose is to make the polarization control in the beam of the polarization switching element uniform.
According to a seventh aspect of the invention, in the optical scanning device according to the sixth aspect, a rectangular aperture is disposed between the collimating lens and the polarization switching element.
Further, the purpose is to drive the polarization switching element at a low voltage and to facilitate installation.

According to an eighth aspect of the present invention, in the optical scanning device according to any one of the first to seventh aspects, the light source is an array light source, and the polarization switching element is λ / It has two plates, an optical modulator made of an optical material having a Kerr effect, and a λ / 2 plate.
It is another object of the present invention to provide a configuration suitable for low voltage driving.
According to a ninth aspect of the present invention, in the optical scanning device according to any one of the first to seventh aspects, the light source is an array light source, and the polarization switching element is λ / It has two plates, an optical modulator made of an optical material having a Pockels effect, a λ / 4 plate, and a λ / 2 plate.
The present invention further aims to cope with an optical modulator having natural birefringence.

According to a tenth aspect of the present invention, in the optical scanning device according to any one of the first to ninth aspects, the light source is a two-dimensional array, and the polarization switching element is a one-dimensional array.
Here, it aims at the low voltage drive in the case of a two-dimensional array light source.
According to an eleventh aspect of the present invention, in the optical scanning device according to the tenth aspect, an electrode of the polarization switching element is shared with an adjacent array electrode.
The purpose here is further to simplify the wiring.
According to a twelfth aspect of the present invention, an image forming apparatus includes the optical scanning device according to any one of the first to eleventh aspects.

According to the present invention, the number of light sources can be halved, and by using an optical modulator made of an optical material having an electro-optic effect, it is possible to switch the beam at high speed and improve the light utilization efficiency.
By aligning the magnitudes of the p-polarized component and the s-polarized component of the incident light to the polygon mirror, the light use efficiency in the upper and lower polygon mirrors can be made the same, and the display quality can be improved.
An optical scanning device using a two-stage polygon mirror can cope with a high speed, and a ghost can be strictly suppressed by a two-stage polygon mirror having a phase difference.
The polarization switching element can be driven at a low voltage.
The light use efficiency of the upper and lower polygon mirrors can be made uniform, and the display quality can be improved.
The polarization switching element can be driven at a low voltage and can be easily installed.
Further, the operation by natural birefringence can be improved with an optical material capable of increasing the speed.
The optical scanning device using the two-stage polygon mirror can cope with the high speed and can be driven at a low voltage in the case of a two-dimensional array light source.
Wiring can be simplified.

Embodiments of the present invention will be described below with reference to the drawings.
The first embodiment will be described with reference to FIGS. FIG. 1 is a perspective view for explaining an outline of a configuration of an optical scanning device 30 according to the present embodiment.
In the figure, reference numeral 1 is a light source, 2 is an optical modulator as a polarization switching element having an electro-optic effect, 3 is a collimating lens, 4 is a deflection prism as a polarization separation element, 5a and 5b are cylindrical lenses, and 6 is a soundproof glass. , 7 is a two-stage polygon mirror as a deflecting means, 8a and 8b are first scanning lenses (fθ lenses), 9 is a mirror, 10 is a second scanning lens, and 12K and 12M are photoconductors (image carriers). Body) and 14 respectively indicate light shielding plates.
The first scanning lens 8, the mirror 9, and the second scanning lens 10 constitute a scanning optical system.
The optical modulator 2 and the deflecting prism 4 constitute an optical path switching unit in this embodiment.
In FIG. 1, only the configuration corresponding to the two photoconductors 12K and 12M is shown, but in reality, by arranging an optical system similar to the illustrated optical system with the deflecting means 7 interposed therebetween, The photosensitive member is scanned.
FIG. 2 is a side view from the light source 1 to the two-stage polygon mirror 7.

The light source 1 is a semiconductor laser, and an optical modulator 2 is disposed in a diverging optical path to the collimating lens 3. Details of the optical modulator 2 will be described in detail with reference to FIG.
The optical modulator 2 switches the polarization of the emitted light in the vertical direction or the horizontal direction in FIG. The deflecting prism 4 includes a PBS (polarizing beam splitter) and a total reflection prism (or mirror). When vertically polarized light (p-polarized light) is incident, the deflecting prism 4 transmits through the PBS, and passes through the upper cylindrical lens 5a. Is condensed on the upper stage 7a.
The light modulated in the horizontal direction (s-polarized light) by the light modulator 2 is reflected by the PBS, deflected by the total reflection mirror, and condensed on the lower polygon mirror 7b through the lower cylindrical lens 5b.
The two-stage polygon mirror 7 is composed of two polygon mirrors 7a and 7b having a phase difference. While the reflected light from the upper stage 7a is being written to the photosensitive member 12K through the scanning optical system, the lower-stage polygon mirror 7b is used. The reflected light from the surface hits the light shielding plate 14. Because of the switching operation of the optical modulator 2 to be described later, the beam is distributed to the upper stage or the lower stage of the two-stage polygon mirror 7 every time, but leakage light to the other occurs due to disturbance such as wavelength fluctuation of the laser beam. Even if it is cut by the light shielding plate 14, a ghost image is not formed on the photosensitive member.

FIG. 3 is a diagram for explaining the optical modulator 2 used in the present embodiment. The light emitted from the laser light source 1 is linearly polarized light that vibrates in the vertical direction in the figure. A rectangular parallelepiped PLZT (lanthanum-substituted lead zirconate titanate) is rotated by 45 ° with respect to the laser optical axis in the diverging optical path. Hereinafter, the optical modulator 2 is also referred to as PLZT.
Electrodes are installed on two opposing surfaces of the PLZT. Since a voltage signal from the power supply 15 is applied to the electrode and the reflection of the voltage signal occurs depending on the modulation speed, the same resistance R as the transmission impedance is connected in parallel. The voltage application direction is arranged to be inclined by 45 ° with respect to the incident polarized light.
However, when the polarization plane from the light source is inclined 45 ° from the vertical direction, the installation angle of PLZT may be 0 °.
Assuming that the distance between the laser light source 1 and PLZT is 1 mm and the spread angle of the laser light is 10 °, the beam spreads to about 0.4 mm at the emission end face when the length of the PLZT light propagates is 1 mm. However, the refractive index of PLZT is 2.5. When the PLZT thickness is 0.5 mm, the laser beam cannot be emitted from the side surface of the PLZT.

Assuming that the laser wavelength is 780 nm and the PLZT Kerr constant is 10 ^ (-16) [m ² / V ² ], the voltage required to convert the polarization state of incident light in the horizontal direction, so-called half-wave voltage, is
V = 0.5 mm × √ (780 nm / 2.5 ^ 3/8 × 10 ^ (− 16) / 1 [mm]) = 125 [V]
Is required. In order to maintain the longitudinal polarization, the applied voltage may be set to zero. The upper limit of the PLZT size modulation band is estimated. From the capacitance C of the electrode and the parallel resistance R, the modulation band is C = εS / d = 5000 × 8.854 × 10 ^ (− 12) × 1 [mm] × 0.5 [mm] /0.5 [mm] ] = 44 [pF]
(Ε is the product of relative permittivity and permittivity in vacuum, S is the area of the electrode on one side, and d is the thickness of PLZT)
R = 50 [Ω]
f = 1 / π / C / R≈140 MHz
High-speed modulation is possible.

When an electro-optic crystal having a Pockels effect, for example, LiNbO ₃ (lithium niobate) is used for the optical modulator 2, there is birefringence even when the applied voltage is 0V. Since there is so-called natural birefringence, a λ / 4 plate is placed between the LiNbO ₃ crystal and the collimating lens 3 and the rotation is adjusted so that the outgoing polarized light is emitted with the same polarization as the incident polarized light when V = 0.
When a voltage of Vπ is applied after adjusting the λ / 4 plate, polarized light that is orthogonal to 90 ° is output. As a method of not using the λ / 4 plate even if there is natural birefringence, there are a method of applying an applied voltage V1 that does not change the polarization, and a method of applying V1 + Vπ (Vπ is a half-wave voltage) when changing the polarization.
Further, when LiNbO ₃ is used, the capacitance of the electrode is about 27 in terms of relative permittivity, so C = 0.24 [pF], and the modulation band can be switched faster than 26 GHz and PLZT in calculation.

As prior arts in which two photoconductors correspond to one light source and the optical path is divided at a predetermined time (sequentially), there are technologies described in Patent Documents 1, 2, and 3.
However, in these conventional examples, a ghost is generated in an image unless the degree of polarization is high when the polarization is switched by the polarization switching element (or optical rotation control means, optical circulator).
For example, if the operating point of the optical modulator is shifted due to a disturbance or the like, and the intensity ratio of longitudinally polarized light and transversely polarized light becomes 20: 1, in addition to normal writing on the photosensitive member by longitudinally polarized light during the scanning period. Thus, an unnecessary image is written as a ghost on the other photoconductor with an intensity of 1/20.
In the present embodiment, the two-stage polygon mirror 7 with a phase difference is used at any intensity ratio, and unnecessary light is located at a place (shielding plate 14 in FIG. 1) away from the photosensitive member. In principle, no ghost is generated.

A second embodiment will be described with reference to FIG.
In addition, the same part as the said embodiment is shown with the same code | symbol, The description on the structure and function which were already demonstrated is abbreviate | omitted as long as there is no special need, and only the principal part is demonstrated (it is the same also in other embodiment below).
When the divergence angle from the light source 1 is large, if the light modulator 2 is disposed in the diverging light path, the light use efficiency is reduced. For example, it is assumed that the spread from the optical axis is 30 ° (60 ° in all angles).
The optical crystal LiNbO _{3 has} a length of 10 mm and a thickness of 1.5 mm. The x-direction refractive index nx and z-direction refractive index nz in the optical crystal at voltages of 0 and 420 V, the natural birefringence due to 0 ° incidence and 30 ° incidence, and the modulation amount at 420 V were calculated, and both retardations were compared. . The results are shown in Table 1.

At normal incidence, a retardation of π (that is, the vertical polarization is converted to 100% in the horizontal direction) is obtained, but at 30 ° incidence, the retardation is 0.92π, and the conversion is 98%.
Therefore, conversion loss occurs as the incident angle increases. In the case of the configuration of FIG. 3, it means that a difference occurs between the upper beam and the lower beam.
Therefore, in this embodiment, the collimator lens 3, the light modulator 2, the λ / 4 plate, and the polarization separation element 4 are arranged in order from the light source 1.
With this configuration, a parallel beam can be incident on the optical modulator 2, and fluctuations in the light amount of the upper and lower beams can be suppressed. When a Kerr effect optical material is used for the optical modulator 2, the λ / 4 plate is not necessary.
Further, a scanning optical system is used in which a rectangular aperture (not shown) is arranged between the collimating lens 3 and the cylindrical lens 5 in order to obtain a desired beam shape on the polygon mirror.
For example, a scanning optical system in which a rectangular aperture is arranged after a coupling lens disclosed in Patent Document 4 (described as a collimating lens in this specification). In the case of the present embodiment, when the light modulator 2 is arranged after the rectangular aperture, collimated light cut into a predetermined shape can be incident on the light modulator 2, so that the thickness direction can be reduced according to the beam shape, and Assembling becomes easy.

A third embodiment will be described with reference to FIGS.
A two-dimensional array light source 16, an optical modulator 2 ', a collimating lens 3, a polarization separating element 4, a pair of cylindrical lenses 5, a two-stage polygon mirror 7 having a phase difference, and a scanning optical system Consists of.
The optical modulator 2 ′ and the deflecting prism 4 constitute the optical path switching means in this embodiment.
The optical modulator 2 ′ includes a first λ / 2 plate 17, a PLZT, and a second λ / 2 plate 18 from the array light source 16 side. Electrodes are formed on the two surfaces of the PLZT and connected to the power supply 15, and a parallel resistor R for impedance matching is also connected.
FIG. 6 is a diagram for explaining the operation of the optical modulator portion. The array light source 16 has a number of light sources of 4 × 4. The respective light sources are arranged at an array angle of θ with respect to the main scanning direction (broken line in the figure), and are arrayed without an angular difference in the sub-scanning direction (FIG. 6A).
PLZT is grooved as shown in FIG. 7, and an electrode 15 is provided on the side surface of each groove. The direction of the unevenness is adjusted to the array angle θ of the array light source 16. For this reason, the direction of the electric field E generated in the PLZT by the voltage applied in FIG. 7 is inclined by θ from the sub-scanning direction.

As shown in FIG. 6A, since the polarization direction of the light source is the sub-scanning direction or the main scanning direction, the slow axis is set to (θ + 45 °) / 2 or (θ-45 °) / 2. One λ / 2 plate 17 converts the vibration surface to θ + 45 ° (or θ−45 °) from the sub-scanning direction.
When no voltage is applied to PLZT, as shown in FIG. 8, the polarization of the light emitted from PLZT 2b is θ + 45 ° (or θ−45 °) as it is from the sub-scanning direction. By changing the slow axis of the second λ / 2 plate 18 from the sub scanning direction to (θ + 45 °) / 2 (or (θ−45 °) / 2), the polarization plane is converted to the sub scanning direction. .
On the other hand, when a switching voltage (so-called half-wave voltage) is applied to PLZT, the polarized light after PLZT emission is θ + 135 ° (or θ−135 °) as shown in FIG. It is converted to −90 ° (or 90 °) from the sub-scanning direction by the second λ / 2 plate 18.
Therefore, the voltage can be switched to the upper polygon mirror 7a via the polarization separation element 4 at a voltage of 0 and to the lower polygon mirror 7b by applying a half-wave voltage.
In this embodiment, even if the angular polarization direction of the array light source 16 and the array direction are neither parallel nor perpendicular, the polarization separation element (PBS + mirror) 4 can efficiently switch the beam between the upper stage and the lower stage.

Next, a fourth embodiment will be described.
As a modification of the third embodiment, when PLZT (an optical material having a Kerr effect) is replaced with LiNbO ₃ (an optical material having a Pockels effect), birefringence is achieved even when the applied voltage is 0 in an optical material having a Pockels effect ( In order to correct this, a λ / 4 plate is disposed between LiNbO ₃ and the first λ / 2 plate (or the second λ / 2 plate). This λ / 4 plate is rotationally adjusted so that light is output only to the upper or lower polygon mirror at an applied voltage of 0.
When LiNbO ₃ is used, a high-speed response is possible because the relative dielectric constant is lower than that of PLZT as described above. For this reason, it becomes easy to cope with the speed required for the polarization switch as the printer speed increases.
The third and fourth embodiments have a one-dimensional modulator array structure, and are characterized in that the polarization is switched by the modulator array before the array light is overlapped with the array light source 16.
For example, in the case of PLZT, if the distance between the array light source and the PLZT incident surface is 0.2 mm, the PLZT groove is set to 50 μm and the peak width is set to 60 μm, so that no beam is emitted.
However, the spread angle of the angular beam of the laser array light is 7 °. In this case, the half-wave voltage applied between the PLZT electrodes can be driven at a low voltage of about 70V.

The one-dimensional array modulator structure enables low-voltage driving by placing the light source close to the light source. However, it is necessary to process grooves in the optical material, and the light source array pitch becomes narrow or the light source has a large spread angle. Overlap occurs. In that case, it is desirable to install a microlens array corresponding to the array light source up to the one-dimensional modulator array (not shown).
Further, even an array light source can be configured with the light modulator 2 having a rectangular parallelepiped shape described in the first embodiment and the second embodiment (not shown). In this case, the driving voltage becomes high, but the processing of the optical material becomes very easy, and the overlap between the beams is not a problem.

A fifth embodiment will be described with reference to FIGS. 10 and 11.
This embodiment is a modification of the third embodiment, and a PLZT optical modulator portion is shown in FIG. Since the parts other than the optical modulator are the same as those in the third embodiment, the illustration is omitted.
The electrodes of the light modulator 19 are formed so that the side surfaces and the bottom surface of the valley are common in potential. As shown in FIG. 10, wiring is performed so that every other voltage becomes a common potential. When a voltage is applied, an electric field is applied alternately in the positive and negative directions like -E, E, -E, and E from the top. When the polarity of the voltage is reversed, the electric field is applied in the order of E, -E, E, and -E from the top.
This embodiment has an advantage that the line is simplified. Further, when an optical material having a Kerr effect is used like the PLZT of this embodiment, the refractive index is modulated by the square of the applied electric field, so that the optical characteristics of the optical modulator are the same even if the applied electric field is reversed. There is no difference between arrays.
Further, in the case of using the Pockels effect in which the optical material of the optical modulator 19 is refractive-index-modulated by the first order of an electric field such as LiNbO ₃ , λ immediately after or just before the optical modulator as shown in FIG. The λ / 4 plate 20 is arranged, and the λ / 4 plate 20 is rotationally adjusted so that the amount of natural birefringence is mπ (where m is an integer), whereby optical modulation is performed by applying an electric field as shown in FIG. The optical characteristics of each array in the vessel 2 'can be made the same.
Further, since LiNbO ₃ has a lower relative dielectric constant than PLZT, the capacitance can be reduced, so that it can respond faster than PLZT.

Based on FIG. 12, a tandem color image forming apparatus (sixth embodiment) using the above-described optical scanning device 30 will be described.
The color image forming apparatus has four photoconductors 12Y, 12C, 12M, and 12K arranged in parallel along the moving direction of the transfer belt 31. Around the photoreceptor 12Y for yellow image formation, a charger 32Y, a developing device 33Y, a transfer device 34Y, and a cleaning device 35Y are sequentially arranged in the rotation direction indicated by the arrow. Other colors also have the same configuration, and are distinguished by adding European letters (C: cyan, M: magenta, K: black) for each color, and a description thereof is omitted.
The charger 32 is a charging member that constitutes a charging device for uniformly charging the surface of the photoreceptor. Between the charging device 32 and the developing device 33, the surface of the photoconductor is irradiated with a beam by the optical scanning device 30, and an electrostatic latent image is formed on the photoconductor 12.
Based on the electrostatic latent image, a toner image is formed on the surface of the photosensitive member by the developing device 33. The transfer unit 34 sequentially transfers the transfer toner images of the respective colors onto the recording medium (transfer sheet) conveyed by the transfer belt 31, and finally the superimposed image is fixed on the transfer sheet by the fixing unit 36.

It is a principal part perspective view of the optical scanning device which concerns on the 1st Embodiment of this invention. It is a general | schematic side view from a light source to a polygon mirror. It is a perspective view for demonstrating an optical path switching means. It is a figure for demonstrating the fall of the light utilization efficiency of the optical modulator in 2nd Embodiment. It is a perspective view for demonstrating the optical path switching means in 3rd Embodiment. It is a figure which shows the polarization state of array light. It is a perspective view which shows the voltage application structure of an optical modulator (PLZT). It is a figure which shows the polarization state when the voltage is 0. It is a figure which shows the polarization state at the time of a half wavelength voltage. It is a perspective view which shows the voltage application structure of the optical modulator (PLZT) in 5th Embodiment. It is a general | schematic side view of the optical path switching means periphery in the modification of 5th Embodiment. It is a schematic block diagram of the image forming apparatus in 6th Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Optical modulator as polarization switching element having electro-optic effect 3 Collimator lens 4 Deflection prism as polarization separation element 7 Two-stage polygon mirror as deflecting means 12K, 12M Photoconductor as scanning surface 16 Array light source

Claims (12)

A light source, an optical path switching unit, a deflecting unit that deflects the light beam, and a scanning optical system that forms an image of the light beam deflected by the deflecting unit on a surface to be scanned. In an optical scanning device that scans a plurality of different scanned surfaces by deflecting the light beam at different timings while switching the optical path,
An optical scanning device characterized in that the optical path switching means comprises a polarization switching element having an electro-optic effect and a polarization separation element. The optical scanning device according to claim 1,
An optical scanning device, wherein a λ / 2 plate or a λ / 4 plate is disposed between the optical path switching means and the deflection means. The optical scanning device according to claim 1 or 2,
An optical scanning device characterized in that the deflecting means is a multi-surface reflecting mirror having a common rotation axis and having a two-stage configuration in the sub-scanning direction. The optical scanning device according to claim 3.
An optical scanning device characterized in that each stage of the polyhedral reflecting mirror has a phase difference. In the optical scanning device according to any one of claims 1 to 4,
A collimating lens is disposed between the polarization switching element and the polarization separation element. In the optical scanning device according to any one of claims 1 to 4,
A collimating lens is disposed between the light source and the polarization switching element. The optical scanning device according to claim 6.
An optical scanning device comprising a rectangular aperture disposed between the collimating lens and the polarization switching element. In the optical scanning device according to any one of claims 1 to 7,
The light source is an array light source, and the polarization switching element includes a λ / 2 plate, an optical modulator made of an optical material having a Kerr effect, and a λ / 2 plate in order in the light traveling direction. An optical scanning device characterized by comprising: In the optical scanning device according to any one of claims 1 to 7,
The light source is an array light source, and the polarization switching element includes, in order in the light traveling direction, a λ / 2 plate, an optical modulator made of an optical material having a Pockels effect, a λ / 4 plate, and λ / 2. An optical scanning device comprising a plate. In the optical scanning device according to any one of claims 1 to 9,
The optical scanning device characterized in that the light source is a two-dimensional array and the polarization switching element is a one-dimensional array. The optical scanning device according to claim 10.
An optical scanning device characterized in that an electrode of the polarization switching element is shared with an adjacent array electrode.   An image forming apparatus comprising the optical scanning device according to claim 1.

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