JP5321331B2 - Optical scanning apparatus and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner in which birefringent characteristic of a scanning lens in a case where the scanning lens is made of a resin, is accepted, excellent polarized light separation characteristic is secured, and which can be compact (made thin) without causing inefficiency and cost increase. <P>SOLUTION: The optical scanner includes: a semiconductor laser element 1; a coupling lens 2 which optically couples the luminous flux emitted from the semiconductor element 1 to a following optical system; an incident optical system which guides the coupled luminous flux to an optical deflector 5; and a scanning optical system which guides and images the luminous flux deflected with the optical deflector 5 onto a surface to be scanned 8. The scanning optical system includes: a single or a plurality of resin lenses 6; a single anisotropic element 65 which corrects the birefringence of the resin lenses 6; and a single polarized light separation element 60. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

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

Conventionally, optical scanning devices are widely known in connection with image forming apparatuses such as optical printers, digital copying machines, and optical plotters. However, in recent years, image forming apparatuses have become widespread along with high stability, high definition, and high speed. Along with this, there is a strong demand for a reduction in the number of parts and downsizing.
In recent years, multicolor image forming apparatuses that superimpose a plurality of color images have been widely developed. In particular, as a form for realizing a multicolor image forming apparatus, a tandem method in which a plurality of scanning optical systems form light spots on a plurality of photoconductors corresponding to respective colors is often used.

In order to realize the writing of a multicolor image, a method of providing an optical scanning device corresponding to each color is also used, but in this case, the number of parts is increased by arranging optical parts for each color, There is a problem that miniaturization is prevented by mounting a plurality of optical scanning devices in the image forming apparatus.
Therefore, a form of a single optical scanning device incorporating a plurality of scanning optical systems has been proposed for a long time. In general, a plurality of light beams corresponding to the respective colors are incident on a single optical deflector and imaged on each photosensitive member by the respective scanning optical systems.
However, this method limits the downsizing of the optical scanning device because the optical elements corresponding to the respective colors are concentrated around the optical deflector.

As a method of overcoming the limitations of miniaturization as described above, two scanning optical systems that overlap vertically are aggregated with different polarizations and divided by a polarized light beam splitting element (polarization separating element) provided in the scanning optical system. Then, a method of guiding light to each photoconductor is considered. In this method, the size of the optical scanning device is reduced (thinned) in the direction of the rotation axis of the optical deflector, and the number of components is reduced by using the optical elements in the scanning optical system in common at the upper and lower stages. It is effective.
In addition, in the prior art, a method of integrating a scanning optical system using a dynamic active element such as a spatial modulation element, a method of dividing by a dichroic mirror using light sources having different wavelengths, and the like are considered. However, when an active element is used, a drive circuit thereof is required. When a dichroic mirror is used, different light sources are mounted on one optical scanning device, so the number of optical elements in the scanning optical system is reduced. Even if it is done, it is necessary to increase the number of expensive elements as a price.
Therefore, a method using a polarization separation element that is a passive element (polarization separation method) is considered suitable.

Patent Document 1 discloses a polarization beam splitter that is intended to suppress extinction ratio degradation even when the deflection incident angle is high.
Patent Document 2 discloses a scanning optical system configured in the arrangement order of a resin lens, a polarization separation element, and a resin lens.
Patent Document 3 discloses that polarization control is performed by an active element.
Patent Documents 4 to 6 disclose that the deflection direction of scanning light is controlled by a liquid crystal active element without using a polarization separation element.
Patent Document 7 discloses a scanning optical system including two scanning lenses and a polarization separation element.

When thinning the optical scanning device using the polarization separation method, it is necessary to improve the separation characteristics of the polarization separation element. For example, if the light beam incident on the polarization separation element is slightly elliptically polarized or the polarization direction is inclined, the light beams that should be separated from each other are mixed into the other scanning optical system.
The separated light beams are emitted with different time-series signals in order to write image information on each scanned surface. If the polarization separation characteristic is not sufficient, image information that should be written on another surface to be scanned is mixed.
For example, in a multicolor image forming apparatus, information that should be developed in cyan is written on the surface to be scanned for magenta, and is observed as crosstalk between colors on the image.
The main deterioration factor of the polarization separation characteristic is birefringence when the scanning lens is a resin. Resin materials having a low birefringence have been widely studied, but considering the shape of the scanning lens, molding conditions, and production efficiency, their application has a high hurdle.
In order to avoid the birefringence phenomenon, it is easy to consider a method in which the scanning optical system is entirely composed of glass lenses. However, in order to cope with the recent increase in image quality, the inefficiency of glass lens processing for resin injection molding is increased. Sex becomes an issue.

  The present invention has been made in view of such a situation, and it is possible to ensure good polarization separation characteristics while accepting the birefringence characteristics when the scanning lens is a resin, resulting in inefficiency and cost increase. The main object of the present invention is to provide an optical scanning device that can be miniaturized (thinned).

In order to achieve the above object, the invention according to claim 1 is directed to a semiconductor laser element, a coupling lens for coupling a light beam emitted from the semiconductor laser element to a subsequent optical system, and the coupled light beam. In the optical scanning device having an incident optical system that guides the light to the optical deflector and a scanning optical system that guides the light beam deflected by the optical deflector to the surface to be scanned and forms an image, the scanning optical system is a single or a plurality of resin lenses, and the anisotropic element, have a polarization separating element, the anisotropic element, the polarization direction of the light flux incident on the plastic lens to the polarization direction of the light beam emitted from the resin lens It is characterized by correcting the change of .

According to a second aspect of the present invention, in the optical scanning device according to the first aspect, the scanning optical system is arranged in the order of a resin lens, an anisotropic element, and a polarization separation element in accordance with the traveling direction of the light beam. It is characterized by.
According to a third aspect of the present invention, in the optical scanning device according to the second aspect, in the anisotropic element, a principal axis direction projected on a surface on which a light beam is incident changes along the main scanning direction. And Here, the “major axis direction” refers to the major axis direction of the refractive index ellipsoid of the anisotropic medium.
The invention of claim 4, wherein, in the optical scanning device according to claim 3, the main axis direction of the anisotropic element, of the resin lens position on the resin lens scanning light incident on the position to pass through When the direction substantially coincides with the principal axis direction, the sum of the phase difference of the resin lens and the phase difference of the anisotropic element is 2πm, and when the sum is orthogonal, the phase difference of the resin lens and the anisotropic element have The difference from the phase difference is π (2m + 1) (m is an integer) .

According to a fifth aspect of the present invention, in the optical scanning device according to the fourth aspect, a liquid crystal is used for the anisotropic element.
According to a sixth aspect of the present invention, in the optical scanning device according to the fifth aspect, the anisotropic element is made of a polymer curable liquid crystal.
According to a seventh aspect of the invention, in the optical scanning device according to the sixth aspect, electrodes are provided on both surfaces of the anisotropic element.
According to an eighth aspect of the present invention, in the optical scanning device according to the seventh aspect , the electrodes provided on both surfaces of the anisotropic element are composed of domains separated in the main scanning direction. .
According to a ninth aspect of the present invention, in the optical scanning device according to any one of the first to eighth aspects, the resin lens is single.

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 incident optical system is set so as to guide a plurality of light beams to the scanning optical system as orthogonally polarized lights, respectively. It is characterized by.
The invention according to claim 11 is the optical scanning device according to any one of claims 1 to 10, further comprising a light guide element, wherein the light guide element is trapezoidal in a cross section perpendicular to the main scanning direction. It is characterized by that.
According to a twelfth aspect of the present invention, in the optical scanning device according to any one of the first to eleventh aspects, a distance separating the polarization separation element from a rotation center of the optical deflector is a plurality of cylindrical scanning surfaces. It is characterized by being larger than the distance between the axes.
According to a thirteenth aspect of the present invention, in the optical scanning device according to any one of the first to twelfth aspects, the incident optical system includes a diffractive optical element.
According to the fourteenth aspect of the present invention, a plurality of photosensitive image carriers are optically scanned by an optical scanning device to form a latent image corresponding to each color, and the latent image is visualized by a developing unit to be a color image. The image forming apparatus according to claim 1, wherein the optical scanning device according to any one of claims 1 to 13 is used as the optical scanning device.

  According to the present invention, since the birefringence of the resin lens is corrected by inserting an anisotropic element without being based on the low birefringence of the resin lens, the polarization state can be reduced with a simple and low-cost configuration. Disturbance can be suppressed and it can contribute to thickness reduction.

It is a schematic diagram which shows the polarization separation function of a polarization separation element. It is a schematic diagram showing a polarization separation function when a material having birefringence is placed in front of the light beam traveling direction of the polarization separation element. It is a subscanning sectional view in the relation between the conventional optical scanning device and the surface to be scanned. It is a sub-scanning sectional view in the relation between the optical scanning device and the surface to be scanned in the present invention. It is a figure which shows the relationship with the optical path length in case the distance which separates a polarization separation element from the rotation center of an optical deflector is smaller than the inter-axis distance of a to-be-scanned surface. FIG. 6 is a diagram showing the relationship between the optical path length when the distance separating the polarization separation element from the rotation center of the optical deflector is smaller than the inter-axis distance of a plurality of scanned surfaces. It is a figure at the time of maintaining the incident angle to. It is a figure which shows the relationship with the optical path length in case the distance which separates a polarization separation element from the rotation center of an optical deflector is the same as the axial distance of several to-be-scanned surfaces. It is a figure which shows the relationship with the optical path length in case the distance which separates a polarization separation element from the rotation center of an optical deflector is larger than the inter-axis distance of a to-be-scanned surface. FIG. 6 is a diagram showing the relationship between the optical path length when the distance separating the polarization separation element from the rotation center of the optical deflector is larger than the inter-axis distance of a plurality of scanned surfaces. It is a figure at the time of maintaining the incident angle to. It is a perspective view of a line image formation lens. It is a principal part perspective view of the optical scanning device which concerns on the 1st Embodiment of this invention. It is a figure which shows the light emission characteristic of a semiconductor laser. It is a figure which shows the deflection | deviation characteristic of a synthetic | combination element. It is main scanning sectional drawing of an optical scanning device. It is a schematic diagram which shows the function of the anisotropic element using a liquid crystal. It is a schematic diagram which shows the change at the time of giving an electric field to an anisotropic element. It is a figure for demonstrating the birefringence of a resin lens. It is a figure which shows the orientation characteristic of the liquid crystal molecule in an anisotropic element. It is a figure which shows the relationship between the orientation characteristic of the liquid crystal molecule in an anisotropic element, and the principal axis distribution of a scanning lens (resin lens). It is a figure which shows the relationship with scanning-lens main-axis distribution, a rubbing direction, and the orientation direction of a liquid crystal molecule. It is a figure which shows the change of the orientation characteristic of a liquid crystal molecule when an electric field is given. It is a figure which shows the setting method of an applied voltage. It is a figure which shows the polarization separation characteristic by an anisotropic element. It is a figure which shows the polarization separation characteristic by an anisotropic element. It is a figure which shows the function of the anisotropic element in 2nd Embodiment. It is a figure which shows the principal part of the scanning optical system which concerns on 6th Embodiment, and is a figure which shows the structure which joined the anisotropic element and the polarization separation element. It is a perspective view of the polarization splitting element in 1st Embodiment. It is a perspective view of the polarization splitting element in 4th Embodiment. It is a perspective view of the polarization splitting element in 5th Embodiment. 1 is a schematic configuration diagram of an image forming apparatus.

Embodiments of the present invention will be described below with reference to the drawings.
First, before explaining a specific configuration, the concept and principle of the present invention will be explained.
In the scanning optical system, the arrangement of the resin lens, the anisotropic element, and the polarization separation element (polarization light beam splitting element) in the scanning optical system corrects the polarization state disturbance of the light beam incident on the polarization light beam splitting element. This is to improve the polarization separation characteristics of the polarization beam splitting element.

[Polarization separation characteristics]
A general polarization separation element has a function of dividing an incident light beam into orthogonal linearly polarized light. In this specification, the polarization separation characteristic is “when two linearly polarized light La and Lb orthogonal to each other enter the polarization separation element, they are separated as La ′ and Lb ′ according to each polarization direction without being mixed with each other. Represents the good characteristics.
When the light amounts of the light beams La, Lb, La ′, and Lb ′ are defined as A, B, A ′, and B ′, A∝A ′ and B∝B ′ are established in the case of ideal polarization separation characteristics, and A ′, B ′ is not involved in B and A, respectively.
FIG. 1 is a functional schematic diagram of the polarization separation element. The polarization directions corresponding to the linearly polarized light La and Lb are Pa and Pb. In FIG. 1, Pa and Pb are orthogonal to each other, Pa is assumed to be z-axis in the figure, and Pb is parallel to y-axis in the figure. A polarization separation element 60 having ideal polarization separation characteristics separates an optical path in accordance with orthogonal polarization directions as shown in FIG.
Here, consider a case where La and Lb are transmitted through a birefringent material 6c such as a resin lens (FIG. 2). Having birefringence means that “the refractive index at which the light beam is sensed differs depending on the direction”.
In an actual optical scanning device, a high-efficiency production and a complicated surface shape are easily realized, so a resin-made scanning lens is often used, but a resin-made optical element generally has birefringence and optical properties. Behaves like an anisotropic medium.

[Birefringence of resin optical elements]
In the molding process of a general resin material, the polymer in the resin is solidified with the alignment aligned within a certain region, so that the optical element has a partial optical anisotropy. When linearly polarized light is incident on this element, a phase difference occurs in an orthogonal cross section (basic characteristic of an anisotropic medium), so that the polarization direction is rotated.
When two linearly polarized light La and Lb (polarization directions Pa and Pb) perpendicular to the resin lens 6c having birefringence are incident, the polarization direction is rotated. Due to the birefringence, the emitted light becomes rotated linearly polarized light or elliptically polarized light Pe. In either case, the orthogonality of La and Lb is lost.
When the light enters the polarization separation element 60 in such a polarization state, the emitted light amounts A ′ and B ′ of the polarization separation element become A′∝ (A + kB), B′∝ (B + kA) (k is a proportional coefficient), The other light quantity is mixed. In this specification, this phenomenon is referred to as “light quantity crosstalk” and represents deterioration of polarization separation characteristics.

It is considered that the birefringence of the resin lens increases depending on the thickness and thickness deviation (thickness deviation) of the resin lens. This may be due to stagnation of resin flow during injection molding or uneven solidification during cooling. Therefore, a thin resin lens with a small thickness deviation is a lens with relatively little influence of birefringence.
However, it is difficult to correct the aberration on the surface to be scanned with only a single resin lens that is thin and has a small thickness deviation, and there is a possibility that it cannot follow the recent increase in image quality. If the number of resin lenses is increased, the influence of birefringence accumulates, and eventually the polarization separation characteristics are deteriorated.
Therefore, in the present invention, after passing through the resin lens, polarization separation is performed after correcting the influence of birefringence with an anisotropic element. In this embodiment, since the polarization separation characteristic can be secured by the anisotropic element due to the influence of the birefringence of the resin lens, the resin lens can be freely designed according to the required optical performance.

In addition to the above, a system in which a resin lens is disposed after the polarization separation element can be easily considered. Since this method is affected by birefringence after polarization separation, there is almost no deterioration in separation characteristics. However, if a resin lens is disposed in each of the separated optical paths, the layout after the polarization separation element becomes difficult, which is a problem for reducing the thickness of the optical scanning device, which is the object of the present invention.
Conventionally, an optical scanning device applied to a multicolor image forming apparatus has integrated a plurality of spatially separated scanning optical systems into a single optical scanning device (FIG. 3).
In FIG. 3, reference numeral 5 denotes an optical deflector, 6 denotes a resin lens, 7 denotes a mirror as a light guide element, and 8 denotes a scanned surface.
However, in the optical scanning device in which the problem relating to the polarization separation characteristic (light quantity crosstalk) is solved by the present invention, image information corresponding to each scanned surface can be assigned to the light flux separated in the polarization direction. Become.
That is, it means that there is no need for spatial separation, and as shown in FIG. 4, an optical system that scans a plurality of scanned surfaces can be integrated. The integration of the optical system has a great effect on reducing the thickness of the optical scanning device.
In FIG. 4, reference numeral 60 denotes a polarization separating element, and 65 denotes an anisotropic element.
The present invention realizes a reduction in the thickness of an optical scanning device without disturbing the polarization state of a light beam incident on a polarization beam splitter and correcting aberrations well.

[About birefringence compensation by anisotropic elements]
When light, which is a transverse wave of an electromagnetic field, enters a medium and the electromagnetic field in the medium exhibits different behavior with respect to the vibration direction, the medium is said to have “optical anisotropy”. On the other hand, the property of a medium whose behavior does not change in any vibration direction is called isotropic. The refractive index of an isotropic medium is a constant in any direction.
The refractive index of the anisotropic medium can be described as a 3 × 3 matrix tensor, and the electric field vector [Dx, Ey, Ez] with respect to the three axes x, y, z is multiplied by matrix multiplication. Dy, Dz].

By appropriately selecting the three axes x, y, and z, the refractive index tensor can be diagonalized (Formula 1). Such x, y, and z axes are referred to as optical principal axes (hereinafter, principal axes). Here, for simplicity, the anisotropic medium is assumed to be uniaxial as n ₁ = ne, n ₂ = n ₃ = no (ne> no), and the ne direction is representatively referred to as a “main axis”. Such an anisotropic medium behaves as if it has two refractive indexes ne and no depending on the direction. Therefore, the light beam incident on the anisotropic medium is a superposition of the light refracted by ne (abnormal light) and the light refracted by no (ordinary light).
This phenomenon is called birefringence. It can be seen from the birefringence phenomenon that the medium has anisotropy. Due to the phase difference between the extraordinary light and the ordinary light, the polarization state of the emitted light beam becomes a straight line, a circle, or an ellipse.

One method for describing the polarization direction of light is the Jones vector. When the traveling direction of the light beam (TEM wave) is x and the plane perpendicular to the light beam traveling direction is the yz plane, the electric field of the light beam has a complex amplitude of Ay and Az on the yz plane and is a 2 × 1 vector [Ay, Az]. I can write. This vector is called the Jones vector.
The anisotropic medium can be described as a 2 × 2 Jones matrix, and the polarization state after passing through the anisotropic medium can be calculated by multiplying the Jones vector. The Jones matrix J is given by Equation 2 below.

  Here, θ is an angle formed by the coordinate axis of the incident light Jones vector and the principal axis of the anisotropic medium. When the incident light is “linearly polarized light along the coordinate axis” that can be written as [Ay, 0] or [0, Az], θ may be considered as an angle formed by the polarization direction of the incident light and the principal axis of the anisotropic medium. φ and Γ are defined as Equation 3 using the extraordinary refractive index ne, the ordinary refractive index no, the thickness D of the medium, and the wavelength λ of the light beam. In particular, Γ represents the phase difference between the extraordinary refractive index and the ordinary refractive index, and is an important parameter for estimating the polarization state of the emitted light.

A resin lens having birefringence can also be regarded as an anisotropic medium. However, in the case of a long molded product such as a scanning lens, the birefringence is distributed along the lens height. Therefore, a Jones matrix J ₁ (h) can be defined for each lens height h (Equation 4).

When linearly polarized light (Jones vector A ₀ ) is incident on the resin lens as described above, the Jones vector A ₁ of the emitted light is given by A ₁ = J ₁ (h) A ₀ , and generally A ₁ is elliptically polarized light. In order to remove the influence of birefringence, an anisotropic element having A ₁ ∝A ₀ is required. When the Jones vector of the anisotropic element and _{J 2, J 2} is required to be a _J 2 · _J 1 _αE (unit matrix).
Now, taking an optical path as an example and eliminating the notation (h), J ₂ · J ₁ can be written as in Equation 5 below.

From Equation 5, θ ₁ = θ ₂ and W ₂ W ₁ ∝E can be considered as a condition for J ₂ · J ₁ ∝E (unit matrix). First, θ ₁ = θ ₂ means that the main axis of the anisotropic element needs to coincide with the main axis of the resin lens. Second, W ₂ W ₁ ∝E means that the anisotropic element must have a phase difference that corrects the phase difference between ordinary and extraordinary light generated in the resin lens.
When W ₂ W ₁ is written down, Equation 6 is obtained.

W ₂ W ₁ in order to be αE is _{Γ 2 + Γ 1 = 2πm (} m is an integer) It can be seen that must give a gamma ₂ satisfy the anisotropic element.
Another correction condition is to make the principal axis of the anisotropic element orthogonal to the principal axis of the resin lens. At this time, Formula 5 is rewritten as Formula 7.

In this case, when Γ ₁ −Γ ₂ = (2m + 1) π (m is an integer) by setting an appropriate phase difference Γ ₂ , J ₂ · J ₁ ∝E (unit matrix) is established as shown in Equation 8. I understand that

When a resin scanning lens having birefringence is regarded as an anisotropic medium, the principal axis direction and the phase difference have a distribution within the lens. Accordingly, the anisotropic element according to the present invention sets the phase difference distribution Γ ₂ (y) of the anisotropic element appropriately by making the principal axis coincide with or orthogonal to that of the scanning lens birefringence according to the above discussion. This makes it possible to correct birefringence.
A method of measuring the birefringence of the resin scanning lens necessary for setting the main axis and phase difference distribution of the anisotropic element and the actual setting method of the main axis and phase difference distribution will be described later.

[Anisotropic element using liquid crystal]
It is well known that anisotropic elements are composed of crystals, liquid crystals, and subwavelength structures. In particular, anisotropic elements made of liquid crystals can easily control the main axis and phase difference. It is a suitable material.
Liquid crystal refers to a substance that has both the fluidity of a liquid and the anisotropy of a solid / crystal. Molecules of a substance exhibiting liquid crystallinity (hereinafter referred to as liquid crystal molecules) are rod-shaped or disc-shaped, and have a phase that aligns the alignment between molecules under certain conditions. In that phase, the dipole moments of the molecules are aligned, and macroscopic dielectric anisotropy is exhibited in the molecular group. Since the dielectric anisotropy interacts with the oscillating electric field of light (electromagnetic wave), the behavior is observed as optical anisotropy.
For the sake of simplicity, the liquid crystal is considered as a nematic liquid crystal. In nematic liquid crystal, rod-like liquid crystal molecules are aligned, and the positional relationship of each liquid crystal molecule indicates a phase state of liquid crystal molecules such as random. By taking the refractive index ne along the major axis direction of the rod-like molecule and the minor axis direction as no, the nematic liquid crystal element can be handled as a uniaxial anisotropic medium.

For example, as shown in FIG. 15, when sandwiched between two glass substrates separated by a distance D and all the liquid crystal molecules are aligned parallel to the substrate, the element has a phase difference with the liquid crystal alignment direction as the main axis. It can be considered as an anisotropic element of | ne−no | D / λ.
The glass substrate is coated with a polymer such as polyimide and then subjected to a process called rubbing which is rubbed with a soft cloth or the like in the orientation direction.
It is practically possible to select the orientation direction by setting the rubbing direction.
Furthermore, as shown in FIG. 16, consider a system in which a transparent electrode such as ITO is deposited on a glass substrate so that an electric field can be applied. When an electric field is applied in the thickness direction, the liquid crystal molecules begin to realign toward the thickness direction. However, the liquid crystal molecules in the vicinity of the substrate maintain an alignment parallel to the substrate due to a phenomenon called anchoring. The angle j formed between the thickness direction and the liquid crystal molecule major axis can be controlled by the electric field strength E.
The light beam transmitted through the element in this state is subjected to the action of an anisotropic medium in which the principal axis direction is distributed in the thickness direction. If the orientation of the liquid crystal molecules depends on the electric field strength E, the phase difference | ne−no | D / λ received by the light beam passing through a certain portion can be written as Δn (E) D / λ.
From the above, it can be seen that the anisotropic element made of liquid crystal can set the phase difference by controlling the principal axis in the rubbing direction of the substrate and the in-element alignment of the liquid crystal by an electric field or the like.

[Measurement method of birefringence]
The phase difference and principal axis of the anisotropic element comprising the liquid crystal of the present invention are preferably set based on the birefringence measurement result of the resin scanning lens.
Various methods for measuring birefringence are known, such as ellipsometer, senalmon method, optical heterodyne method, and retardation measurement by CCD. In any case, since the phase difference distribution and the main axis distribution of the scanning lens can be finally obtained, the anisotropic element of the present invention can be appropriately set.
In general, the molding conditions of a resin scanning lens are strictly controlled in order to suppress variation in shape accuracy due to injection molding. Therefore, the variation in the birefringence distribution of the resin scanning lens is also suppressed at the same time. Therefore, when mass-producing a resin scanning lens, the effect of the present invention can be obtained even with an anisotropic element reflecting the birefringence of the representative sample.

[Distance separating the polarization separation element from the rotation center of the optical deflector]
Here, this distance is Lpbs as shown in FIG. The distance from the rotation center of the optical deflector to the incident surface of the polarization separation element may be used. However, since there are various types of polarization separation elements such as a prism type and a plate type, the “separation of light flux” from the rotation center of the optical deflector is performed here. The distance is “point”.
When the present invention is applied and an opposing scanning optical system in which scanning optical systems separated into upper and lower stages are aggregated is assumed, the four optical path lengths reaching the scanned surface from the optical deflector are set to be the same. think of.
The “opposing scanning optical system” is an optical system in which light beams are scanned on both sides around the rotation axis of the optical deflector. In this specification, the scanning optical system that scans four scanned surfaces shares a single optical deflector.
The resin lens, the anisotropic element, and the light guide element are omitted. A light guide element is provided in a portion where the optical path is folded. The folding of the optical path by the light guide element is unified at 90 ° for simplicity. The incident angle on the surface to be scanned is 0 degrees because it is not directly related to the discussion on the convenience of layout.
According to the present invention, Lpbs> P is suitable for improving the layout design freedom.

Hereinafter, in order to confirm the effect of claim 12, three cases of Lpbs <P, Lpbs = P, and Lpbs> P are considered.
[Lpbs <P]
As shown in FIG. 5, in order to make the optical path length uniform, it is necessary to extend the optical path of Ll. Assuming that the interval P of the scanned surface 8 and the incident angle to the scanned surface 8 are maintained, the inner optical path is bent as shown in FIG. 6, and the thickness H of the optical scanning device increases. .
[Lpbs = P]
As shown in FIG. 7, since Lh = Ll is established, it is not necessary to align the optical path lengths. However, when this condition is satisfied, since the optical path length of the scanning optical system is determined by P, there is no particular improvement in design flexibility. In addition, since a resin lens and an anisotropic element are disposed in Lpbs, there is a possibility that P may be disadvantageous in terms of aberration correction.
[Lpbs> P]
As shown in FIG. 8, in order to make the optical path length uniform, it is necessary to extend the optical path of Lh. Even if the interval P between the scanning surfaces 8 and the incident angle to the scanning surface 8 are maintained, this can be dealt with by projecting the optical path length outward as shown in FIG. Focusing on the thickness H of the optical scanning device, it can be seen that “the layout is possible without increasing the thickness of the optical scanning device” under the condition of Lpbs> P.

[Regarding Image Forming Apparatus Using Optical Scanning Apparatus of the Present Invention]
Various photosensitive image carriers can be used. For example, a silver salt film can be used as the image carrier. In this case, a latent image is formed by writing by optical scanning, and this latent image can be visualized by processing by a normal silver salt photographic process. Such an image forming apparatus can be implemented as an optical plate making apparatus or an optical drawing apparatus that draws a CT scan image or the like.
As the photosensitive image carrier, it is also possible to use a color developing medium (positive printing paper) that develops color by the thermal energy of the beam spot during optical scanning. In this case, a visible image is directly formed by optical scanning. it can.
As the photosensitive image bearing member, a photoconductive photosensitive member can also be used. As the photoconductive photoconductor, for example, a selenium photoconductor or an organic photo semiconductor, which is used repeatedly in a drum shape, can be used.
When a photoconductive photoconductor is used as an image carrier, an electrostatic latent image is formed by uniform charging of the photoconductor and optical scanning by an optical scanning device. The electrostatic latent image is visualized as a toner image by development. The toner image is directly fixed on the photoconductor when the photoconductor is in the form of a sheet such as zinc oxide paper, and transfer paper or an OHP sheet when the photoconductor can be used repeatedly. It is transferred and fixed on a sheet-like recording medium such as (plastic sheet for overhead projector).

The transfer of the toner image from the photoconductive photosensitive member to the sheet-like recording medium may be directly transferred from the photosensitive member to the sheet-like recording medium (direct transfer method), or may be temporarily transferred from the photosensitive member to an intermediate transfer belt or the like. After transfer to the intermediate transfer medium, transfer from the intermediate transfer medium to a sheet-like recording medium (intermediate transfer method) may be performed.
Such an image forming apparatus can be implemented as an optical printer, an optical plotter, a digital copying apparatus, or the like.
In the image forming apparatus of the present invention, a plurality of the photoconductors are arranged along the conveyance path of the sheet-like recording medium, and an electrostatic latent image is formed for each photoconductor using a plurality of optical scanning devices. The toner image obtained by visualizing these can be transferred and fixed to the same sheet-like recording medium, and can be implemented as a tandem type image forming apparatus that synthetically obtains a color image or a multicolor image.

[About thin optical scanning device]
FIG. 30 shows a schematic diagram of a main part of an image forming apparatus including the optical scanning device 100. In the space separating the photoconductors 1K, 1M, 1C, and 1Y in which image information of each color is written and the optical scanning device 100, toner and waste toner are stored for each color, such as development, charging, and photoconductor cleaning. In general, the image forming units 2K, 2M, 2C, and 2Y are accommodated.
In addition to the configuration of FIG. 30, an actual image forming apparatus includes a mechanism for fixing an image on paper, a mechanism for transporting paper, and the like. The mechanism shown in FIG. This is a factor that determines the size of the device.
If the thinning of the optical scanning apparatus as the final object of the present invention is realized, the image forming units 2K, 2M, 2C, The space allowed for 2Y becomes wider.
Since the image forming units 2K, 2M, 2C, and 2Y are also provided with a toner storage function as described above, if the toner storage portion can be increased, the number of toner replenishments by the user can be reduced. In addition, the photoreceptors 1K, 1M, 1C, and 1Y that repeatedly receive the actions of exposure, development, and cleaning by rotation can be increased in size, and an improvement in durability can be expected.
As described above, by reducing the thickness of the optical scanning device, users of laser printers and the like equipped with the image forming apparatus of the present invention can realize “improved usability” that is not bothered by frequent maintenance and frequent supply of toner. can do.

[Effect of the present invention on the environment]
The present invention realizes a high-quality optical scanning device while reducing the number of parts of the optical scanning device. For this reason, the amount of material used for the production of the optical scanning device can be reduced, and the environmental load is reduced with respect to the amount of mined resources and the amount of plastic waste discharged.

Hereinafter, embodiments of the present invention will be specifically described.
First, the first embodiment will be described.
FIG. 11 is a perspective view showing a main part of the optical scanning device according to the present embodiment. That is, the essential parts of the light source 1 to the scanned surface 8 are extracted and shown. Details of each part will be described below with reference to separate drawings.
[Injection optics]
The light source 1 is a semiconductor laser in which a general end surface light emitting element made of a p-type or n-type semiconductor material is packaged with a metal or the like. FIG. 12 shows a light emitting unit provided inside the semiconductor laser 1. In general, a double heterojunction 101 in which p-type and n-type semiconductor materials are joined is used.
When current is injected into the junction 101, laser light is emitted from the active layer provided in the junction 101. In general, it is known that laser light emitted from such a structure is polarized in a direction parallel to the active layer.
The light source 1 is provided corresponding to each scanned surface 8. Here, as an example, an incident optical system of two light sources corresponding to two scanned surfaces 8 is given.

The emitted laser light is coupled to the subsequent optical system by the coupling lens 2 in any of parallel light, convergent light, and divergent light. The coupled light beam is combined with the other light beam by the combining element 21 and shaped by the aperture 3.
Next, the line image forming lens 4 guides the light deflector 5 as a long line image in the main scanning direction.
An example of the line image forming lens 4 is shown in FIG. This is a diffractive lens having a cylindrical surface on the entrance surface and a linear diffractive surface on the exit surface. The line image forming lens 4 corrects the focus shift on the scanned surface by utilizing the variation of the light source wavelength when the temperature of the optical scanning device varies due to the strong negative dispersion characteristic of the diffractive surface.
The scanning optical system based on the premise of the present invention has a configuration in which the resin lens is close to the optical deflector in the optical path. Accordingly, it is preferable to use a diffractive optical element as the temperature correction means because it tends to be an enlargement system in the sub-scan section and weakens the tolerance.

[Form of optical path synthesis]
FIG. 13 shows one form of optical path synthesis. The combining element 21 includes a triangular prism 210 having a reflecting surface, a λ / 2 wavelength plate 212, and a polarization separation surface 211. The function required of the combining element 21 is “to make a plurality of light beams linearly polarized light orthogonal to each other and to emit them on the same optical path”.
The triangular prism 210 brings one optical path closer to the other, and the λ / 2 wavelength plate 212 rotates the polarization direction of the incident light beam by 90 ° to realize a form orthogonal to the other polarization. The polarization separation surface 211 has a characteristic of transmitting S-polarized light and reflecting P-polarized light orthogonal thereto, and is generally a surface realized by a dielectric multilayer film, a wire grid, or the like.
By defining the mounting posture of the semiconductor laser 1 that emits uniform linearly polarized light as shown in FIG. 12, linearly polarized light parallel to the direction perpendicular to the paper surface can be realized as shown in FIG.

Now, let us say that the polarized light perpendicular to the incident plane (the plane formed by the incident light and the emitted light) of the polarization separation surface 211 is called S-polarized light, and the parallel polarized light is called P-polarized light. A P-polarized light beam (upper stage in the figure) emitted from one semiconductor laser 1 is reflected toward the lower optical path in the figure by the reflection surface of the triangular prism 210 and further reflected by the polarization separation surface 211.
On the other hand, the lower light beam (S-polarized light) in the figure is converted to S-polarized light by the λ / 2 wavelength plate 212 and transmitted through the polarization separation surface 211. Therefore, the converted P-polarized light and S-polarized light are incident on the polarization separation surface 211, and S-polarized light and P-polarized light beams are emitted on the same optical path. In order to separate the light beams emitted from the different light sources by the polarization separation element, it is necessary that the polarization states are orthogonal to each other in front of the optical deflector.
The form of optical path synthesis described in this embodiment is merely an example, and the form where the λ / 2 wavelength plate 212 is attached may be different as long as the function required for the above-described synthesis element 21 can be realized.
In the form of optical path synthesis in the present embodiment, it can be seen that there is a difference between the optical path lengths in the synthesis element 21. Therefore, it is desirable that the coupling lens 2 is adjusted and attached in accordance with the optical path difference in order to form both images, and the positions of the coupling lenses 2 are necessarily different.

[Scanning optical system: optical deflector to polarization separation element]
In FIG. 11, the optical deflector 5 is a six-sided polygon mirror. The number of surfaces is not related to the essence of the present invention, and may correspond to the design requirements of the optical scanning device. One of the two light beams incident on the optical deflector 5 is polarized in a direction parallel to the rotation axis of the optical deflector 5, and the other is polarized perpendicular to it.
The two light beams reflected by the optical deflector 5 pass through the resin lens 6 and are incident on the polarization separation element 60 after correcting the disturbance of the polarization direction by the anisotropic element 65. By arranging the resin lens 6, the anisotropic element 65, and the polarization separation element 60 in this order, the influence of the birefringence of the resin lens is corrected by the anisotropic element, and the light beam is favorably divided by the polarization separation element. Is possible.
The form of the anisotropic element will be described later.
The scanning lens 6 is a single lens designed according to the writing width and optical path length on the image plane, and is obtained by injection molding of a transparent optical resin represented by ZEONEX or the like.
As a result, the number of components can be reduced, and layout can be facilitated when the optical scanning device is thinned.
Although the birefringence of the scanning lens 6 varies depending on molding conditions, thickness deviations, and the like, here, as an example, a main axis distribution θ (y) and a phase difference distribution Γ (y) as shown in FIG. 17 are considered.
The main axis θ is an angle defined on the yz plane in FIG. Any distribution can be corrected by the present invention. FIG. 17 is drawn from the viewpoint of looking at the scanning lens in the incident direction of the light beam. These distributions can be actually obtained by the birefringence measurement method described above.

The distance Lpbs from the rotation center of the optical deflector 5 to the incident surface of the polarization separation element 60 is equal to or larger than the inter-axis distance P (general value 60 mm to 100 mm) of the cylindrical scanning surface. It has become. By setting the distance separating the polarization separation element from the rotation center of the optical deflector wider than the distance between the plurality of scanned surfaces, the degree of freedom in layout design is improved.
As shown in FIG. 27, the polarization separation element 60 is formed by joining long triangular prisms made of glass with a dielectric multilayer film surface 60a as a joining surface. The dielectric multilayer film is designed to perform appropriate polarization separation according to the wavelength of the light source.

[Scanning optical system: polarization separation element to scanned surface]
FIG. 4 shows one form of the optical scanning device in the sub-scan section. In FIG. 4, the light is incident on the surface to be scanned 8 perpendicularly within the sub-scanning section, but may be angled according to the design of the image forming apparatus. The light beam separated by the polarization separation element 60 is guided to the scanned surface 8 by the light guide element 7 which is a mirror.
The light guide element 7 is a long mirror, and is notched so as not to interfere with the upper luminous flux and the wall surface of the optical scanning device. The taper of the light guide element is used not only to prevent vignetting of a light beam passing in close proximity but also to avoid interference with the unit housing. A light guide element having a taper is well known, but by incorporating it into an optical scanning device based on the premise of the present invention, it is effective not only for vignetting of a light beam but also for a thin housing (housing) surrounding the optical scanning device. .
By using the polarization separating element 60, the optical scanning device 100 has a thickness of only two steps in the main scanning plane (FIG. 4), and realizes a thinning that has not been achieved conventionally.

[Anisotropic element]
The anisotropic element 65 is an element in which a liquid crystal material is sandwiched between two glass substrates 65s. An anisotropic element using liquid crystal easily controls the alignment direction with an electric field or the like, and easily realizes a spatial distribution of the alignment state. The alignment direction of the liquid crystal molecules changes depending on the main scanning direction.
A polymer such as polyimide is applied to the surface of each glass substrate sandwiching the liquid crystal, and rubbing is performed in a direction corresponding to the main axis distribution θ (y) of the scanning lens 6.
As shown in FIGS. 18 and 19, the liquid crystal molecules in the liquid crystal material are aligned along the rubbing direction. The birefringence of the resin lens tends to be distributed in the longitudinal direction of the resin lens. Since the main axis in the resin lens is also distributed, it is preferable that the main axis of the anisotropic element is also made to follow the distribution.
Since the light beam is scanned by the optical deflector in the direction radiating from the optical deflector, the scanning lens main axis distribution, the rubbing direction, and the orientation direction of the liquid crystal molecules 65m are made to correspond to each other as shown in FIG. The molecular orientation direction is a distribution in which the main axis distribution of the scanning lens 6 is expanded in the longitudinal direction.
A transparent electrode 65e typified by ITO (indium tin oxide) or the like is deposited on the glass substrate 65s. The electrodes are divided into areas in the longitudinal direction of the anisotropic element 65s so that different electric fields can be applied to the respective areas. An electric field having a distribution with respect to the main scanning direction can be applied, and the main scanning direction distribution of the phase difference can be corrected.

  At the time of manufacturing the anisotropic element, an angle with respect to the optical surface can be given to the liquid crystal molecules in the anisotropic element by applying an electric field using the electrode. By this operation, the birefringence in the anisotropic element can be controlled by the electric field. With the above configuration, a phase difference that corrects the birefringence of the resin lens can be provided. Such an operation can be realized without providing an electrode in the anisotropic element. In this case, however, the orientation of liquid crystal molecules is controlled by applying an electric field from the outside, and a high voltage is required. bad.

When the anisotropic element 65 is manufactured, an electric field is applied to each area electrode corresponding to the phase difference distribution Γ (y) of the scanning lens 6 to give the liquid crystal molecules 65m a rising angle j with respect to the glass substrate 65s.
As shown in FIG. 16, the rising angle j changes the value of | ne-no | when viewed along the light beam traveling direction. Therefore, as shown in FIG. A phase difference that cancels (y) can be applied.
The actual applied voltage may be set so that the polarization separation characteristic is optimal while the anisotropic element 65 is incorporated in the optical scanning device and monitored by the amount of light. In the case of the phase difference distribution in this embodiment, an electric field as shown in FIG. 22 may be applied. When the polarization separation characteristics are the best, the anisotropic element is substantially established as Γ ₂ + Γ ₁ = 2πm (m is an integer) in Equation 6.
Thereby, the birefringence of the resin lens distributed in the main scanning direction (longitudinal direction) can be corrected.

An ultraviolet curable resin material is mixed in the liquid crystal material. When irradiation is performed with an ultraviolet lamp or the like with the applied voltage set as described above, the liquid crystal material is cured while the alignment state of the liquid crystal molecules 65m is preserved.
If the wiring connected to the electrode 65e is removed after this processing, the anisotropic element 65 can be handled as a “passive element” that optimally compensates for the birefringence of the scanning lens 6.
By using the polymer curable liquid crystal, the liquid crystal alignment state of the anisotropic element can be fixed. Accordingly, the orientation of the anisotropic element can be controlled by some method (electric field application, etc.) and then it can be handled as a passive element, thereby simplifying the configuration of the optical scanning device.
The principal axis distribution and the phase difference distribution of the anisotropic element 65 can be confirmed by the same method as the birefringence measurement of the scanning lens 6.
The anisotropic element 65 as described above realizes good polarization separation. As shown in FIG. 23, the polarized light parallel to the sub-scanning direction is reflected to the regular optical path 68l without entering the optical path 68u toward the other surface to be scanned. Further, as shown in FIG. 24, polarized light orthogonal to the light passes through the optical path 68u without being mixed into 68l.

Next, a second embodiment will be described. Note that the same parts as those in the above embodiment are denoted by the same reference numerals, and unless otherwise specified, description of the configuration and functions already described is omitted, and only the main part will be described (the same applies to other embodiments below).
As shown in FIG. 25, this is an example in which the rubbing direction of the glass substrate 65s of the anisotropic element 65 is orthogonal to that of the first embodiment. Also in this example, the birefringence of the scanning lens 6 can be compensated by setting an appropriate applied electric field.
When the polarization separation characteristic is the best, Γ ₁ −Γ ₂ = (2m + 1) π (m is an integer) is established in Equation 7.

Next, a third embodiment will be described.
Depending on the molding conditions and shape of the scanning lens 6, the degree of the main axis distribution and the phase difference distribution may be small and may be considered uniform.
For example, when the main axis distribution is uniform, the rubbing direction of the anisotropic element 65 does not need to have a deviation along the longitudinal direction as shown in FIGS. 19 and 20, and is rubbed only in one direction in the yz plane. You can do it.
Such an anisotropic element 65 has a simple rubbing process and high production efficiency.
If the phase difference distribution is uniform, the electrodes need not be divided into areas as shown in FIG. 21, and may be transparent electrodes deposited uniformly on the glass substrate 65s. Such an anisotropic element 65 eliminates the need for a mask having a complicated shape when vapor-depositing a transparent electrode, so that the production efficiency is increased and the applied voltage only needs to be a single value, so that management of phase difference compensation is simplified.

Next, a fourth embodiment will be described.
As shown in FIG. 28, in any one of the first to third embodiments, the polarization separating element 60 is replaced with a long parallel plate 601 made of resin. The incident surface 601a is a wire grid surface in which nano-sized fine metal wires are regularly stretched. The wire grid pattern is designed according to the required polarization separation characteristics.

Next, a fifth embodiment will be described.
As shown in FIG. 29, in any one of the first to third embodiments, the polarization separating element 60 is replaced with a resin-made long half mirror prism 602. The light beams divided by the half mirror are selected for polarization by a polarizer 602a that is orthogonal to each other.

Next, a sixth embodiment will be described.
As shown in FIG. 26, this is an example in which the anisotropic element 65 and the polarization separation element 60 are joined for any one of the first to fifth embodiments.

[Multicolor image forming apparatus]
FIG. 30 shows an embodiment of an image forming apparatus. This image forming apparatus is a laser printer. The laser printer has a photoconductive photosensitive member formed in a cylindrical shape as photosensitive image carriers 1K, 1M, 1C, and 1Y. Around the image carriers 1K, 1M, 1C, 1Y, charging rollers 3K, 3M, 3C, 3Y as charging means, developing devices 4K, 4M, 4C, 4Y, cleaning devices 5K, 5M, 5C, 5Y, transfer Rollers 6K, 6M, 6C, and 6Y are provided. A “corona charger” can also be used as the charging means.
An optical scanning device 100 that performs optical scanning with laser light is provided, and exposure by optical scanning is performed between the charging rollers 3K, 3M, 3C, and 3Y and the developing devices 4K, 4M, 4C, and 4Y.
In FIG. 30, reference numeral 110 denotes a fixing device, reference numeral 120 denotes a paper conveyance path, and reference numeral 130 denotes an intermediate transfer belt.
When performing image formation, the image carriers 1K, 1M, 1C, and 1Y, which are photoconductive photoreceptors, are rotated counterclockwise at a constant speed, and the surfaces thereof are uniformly charged by the charging rollers 3K, 3M, 3C, and 3Y. Then, an electrostatic latent image is formed by exposure of the optical scanning device 100 by laser beam optical writing. The formed electrostatic latent image is a so-called “negative latent image”, and the image portion is exposed.

The electrostatic latent images are reversely developed by the developing devices 4K, 4M, 4C, and 4Y, and toner images are formed on the image carriers 1K, 1M, 1C, and 1Y. The toner image is transferred to the intermediate transfer belt 130 by the action of the transfer rollers 6K, 6M, 6C, and 6Y. The toner image on the intermediate transfer belt 130 merges with the paper conveyance path 120 and is fixed on the paper by the fixing device 110. The paper on which the toner image is fixed is appropriately discharged through a conveyance path based on the printer design.
The surfaces of the image carriers 1K, 1M, 1C, and 1Y after the toner images are transferred are cleaned by the cleaning devices 5K, 5M, 5C, and 5Y, and residual toner and paper dust are removed.

DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2 Coupling lens 5 Optical deflector 6 Resin lens 8 Scanned surface 60 Polarization separation element 65 Anisotropic element 100 Optical scanning device

Japanese Patent No. 3247497 JP 2008-070599 A JP-A-7-144434 JP 2004-029744 A JP 2004-286846 A JP 2006-133288 A Japanese Patent Laid-Open No. 10-3048

Claims (14)

A semiconductor laser element;
A coupling lens for coupling a light beam emitted from the semiconductor laser element to a subsequent optical system;
An incident optical system for guiding the coupled light beam to an optical deflector;
A scanning optical system having a light beam deflected by the optical deflector guided and imaged on a surface to be scanned,
The scanning optical system, possess a single or plurality of resin lenses, and the anisotropic element, and a polarization separating element,
The anisotropic scanning element corrects a change in a polarization direction of a light beam emitted from the resin lens from a polarization direction of the light beam incident on the resin lens . The optical scanning device according to claim 1,
The optical scanning apparatus according to claim 1, wherein the scanning optical system is arranged in the order of a resin lens, an anisotropic element, and a polarization separation element in accordance with a traveling direction of the light beam. The optical scanning device according to claim 2,
In the anisotropic element, an optical scanning device characterized in that a main axis direction projected onto a surface on which a light beam is incident changes along a main scanning direction. The optical scanning device according to claim 3.
If the spindle direction of the anisotropic element, the scanning light substantially coincides with the main axis direction of the resin lens position on the resin lens passing incident on its position, the phase difference and the anisotropically with the above resin lens When the sum of the phase difference of the directional element is 2πm, which is orthogonal, the difference between the phase difference of the resin lens and the phase difference of the anisotropic element is π (2m + 1) (m is an integer). An optical scanning device. The optical scanning device according to claim 4.
An optical scanning device characterized in that liquid crystal is used for the anisotropic element. The optical scanning device according to claim 5,
The anisotropic scanning element is made of a polymer curable liquid crystal. The optical scanning device according to claim 6.
An optical scanning device characterized in that electrodes are provided on both surfaces of the anisotropic element. The optical scanning device according to claim 7 .
An electrode provided on both surfaces of the anisotropic element is composed of domains separated in the main scanning direction. The optical scanning device according to any one of claims 1 to 8,
An optical scanning device characterized in that the resin lens is single. The optical scanning device according to any one of claims 1 to 9,
The optical scanning apparatus according to claim 1, wherein the incident optical system is set so as to guide a plurality of light beams to the scanning optical system as orthogonal polarized lights. The optical scanning device according to any one of claims 1 to 10,
An optical scanning device further comprising a light guide element, wherein the light guide element is trapezoidal in a cross section perpendicular to the main scanning direction. The optical scanning device according to any one of claims 1 to 11,
An optical scanning device characterized in that a distance separating the polarization separation element from a rotation center of the optical deflector is larger than an inter-axis distance between a plurality of cylindrical scanning surfaces. The optical scanning device according to any one of claims 1 to 12,
The incident optical system includes a diffractive optical element. In an image forming apparatus for forming a latent image corresponding to each color by performing optical scanning with an optical scanning device on a plurality of photosensitive image carriers, and visualizing the latent image with a developing unit to obtain a color image.
An image forming apparatus using the optical scanning device according to any one of claims 1 to 13 as the optical scanning device.

Images