JP2007241182A - Optical scanner and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner which uses a power diffraction surface and reduces variation in beam spot diameter due to temperature variation and variation in beam spot diameter due to variation in oscillation wavelength caused by mode hopping to thereby perform an optical scan with a stable beam spot diameter, and an image forming apparatus. <P>SOLUTION: The optical scanner includes a first optical element 2 which converts the sectional type of a light beam from a semiconductor laser 1 into a desired type, a second optical element 4 which guides a light beam transmitted through the first optical element 2 to an optical deflector 5, and a third optical element 6 which converges a light beam deflected by the optical deflector 5 on a scanned surface 8 to form a light spot and optically scans the scanned surface 8. At least one of the first, second, and third optical elements includes a resin-made lens. At least one of resin-made lenses has a power diffraction surface. At least one of surface shapes of the power diffraction surface is so set that the power of a diffraction part and the power of a refraction part cancel each other. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical scanning device used as an image writing device in an image forming apparatus such as a digital copying machine or an optical printer, and the above-described image forming apparatus using the same.

An optical scanning device has been widely known as an image writing device in an image forming apparatus such as an optical printer, a digital copying machine, or an optical plotter. Therefore, what can form a high image is demanded.
The optical scanning device includes optical components such as various lenses. When various lenses used in the optical scanning device are formed of a resin material, the resin lens is lightweight, can be formed at low cost, and it is easy to form a special surface shape represented by an aspherical surface. By adopting a special surface for the resin lens, the optical characteristics can be improved and the number of lenses constituting the optical system can be reduced. In other words, the use of a resin lens greatly contributes to the reduction in size, weight, and cost of an optical scanning device.

  However, as is well known, the resin lens changes its shape with changes in the environment, especially with changes in temperature, and its refractive index changes. Therefore, the optical characteristics, especially power (refractive index), are designed values. There is a problem that the “beam spot diameter”, which is the diameter of the light spot on the surface to be scanned, varies due to environmental fluctuations. The power fluctuation of the resin lens due to the temperature change occurs in the opposite direction between the positive lens and the negative lens. Therefore, the positive and negative resin lenses are arranged in the optical system of the optical scanning device. There is a well-known method for canceling changes in optical characteristics caused by environmental changes occurring in resin lenses.

In addition, a general semiconductor laser as a light source of an optical scanning device has a property that the emission wavelength shifts to a longer wavelength side when the temperature rises (this property is called “wavelength change due to temperature change”), and “mode hop”. There is also a wavelength change due to. A wavelength change in the light source causes a characteristic change due to chromatic aberration of an optical system used in the optical scanning apparatus, and this characteristic change also causes a beam spot diameter fluctuation.
Therefore, in an optical scanning device that includes a resin lens in the optical system and uses a semiconductor laser as the light source, an optical design that takes into account changes in the optical characteristics accompanying changes in the wavelength of the light source as well as changes in the optical characteristics accompanying changes in temperature. There is a need to do.

  There is known an optical scanning device (laser scanning device) that adopts a power diffractive surface and stabilizes optical properties in consideration of changes in optical characteristics due to temperature changes and wavelength changes in a light source (for example, Patent Documents). 1). In Patent Document 1, a light source optical system for condensing laser light emitted from a laser light source into parallel light in the main scanning direction and in the sub-scanning direction in the vicinity of the deflecting reflection surface of the optical deflector has a rotational symmetry axis. There is disclosed an optical scanning device having one or more reflecting surfaces and two transmitting surfaces, a power diffractive surface provided on the transmitting surface, and a single optical element made of resin. As a comparative example, a power diffractive surface is provided on each of a resin collimator lens that collimates a light beam from a semiconductor laser and a resin cylinder lens that focuses the collimated light beam in the sub-scanning direction. An optical scanning device provided is disclosed. The “power diffractive surface” is a diffractive surface having lens power by diffraction.

JP 2002-287062 A

  Patent Document 1 discloses “one optical element having one or more reflecting surfaces not having a rotational symmetry axis and two transmitting surfaces, provided with a power diffractive surface on the transmitting surface, and made of resin. The light source optical system according to the method requires the formation of a transmission surface and a reflection surface in one optical element, and includes a curved reflection surface, so that it is not always easy to manufacture and the cost of the optical scanning device is low. There is still room for improvement in terms of conversion. In general, in order to form a power diffractive surface, a fine processing technique is required, and an extremely high accuracy is required. For example, when a power diffractive surface having a power equivalent to that of a spherical lens as shown in FIG. 9B is illustrated, the shape is as shown in FIG. 9A. That is, the spherical surface of the spherical lens is divided along contour lines, and the divided spherical surface is arranged on a flat base so as to have a uniform height, thereby forming a corrugated cross section. In other words, it is a shape in which only inclined surfaces on which light is refracted are arranged concentrically. As is apparent from FIG. 9B, the rising angle of the inclined surface that draws an arc increases with the distance from the optical axis, and the gap between the grooves, that is, the interval between adjacent inclined surfaces becomes narrower. It becomes difficult. Furthermore, any power diffractive surface sandwiched between backcuts must be part of a spherical surface. Although this can be approximated as a straight line, in this case, a reduction in diffraction efficiency cannot be avoided. However, when the power diffractive surface is formed so as to form a part of a spherical surface, the roughness of the surface shape becomes conspicuous, the beam spot diameter becomes thick due to the deterioration of wavefront aberration, and the generation of ghost and light Problems such as reduced transmission efficiency occur.

In view of the above-described problems of the prior art, the present invention has not only beam spot diameter fluctuation due to temperature fluctuation but also beam spot diameter fluctuation due to oscillation wavelength change due to mode hop in an optical scanning device using a power diffraction surface. An object of the present invention is to realize an optical scanning device that can perform optical scanning with a reduced and more stable beam spot diameter, and to realize an image forming apparatus using such an optical scanning device.
The present invention also provides an optical scanning device that does not require high accuracy with respect to the shape of the diffractive surface employed in an optical element mounted on these devices, and that can make the optical element inexpensive and easy to mold. It is another object of the present invention to provide an image forming apparatus.

As described in claim 1, the optical scanning device according to the present invention transmits the first optical element that converts the cross-sectional form of the light beam from the semiconductor laser into a desired form, and transmitted through the first optical element. A second optical element for guiding the light beam to the light deflector; a light beam deflected by the light deflector is condensed on the surface to be scanned to form a light spot; An optical scanning device including the optical element is configured as follows.
At least one of the first, second, and third optical elements includes a resin lens.
At least one of the resin lenses has a power diffractive surface.
At least one surface shape of the power diffractive surface is set so that the power of the diffractive portion and the power of the refracting portion cancel each other.

As described in the second aspect of the invention, the surface shape of the power diffractive surface is preferably a staircase structure and has no power or very little power.
As in the third aspect of the invention, the power diffractive surface is set so that the fluctuation of the beam waist position in the main scanning direction and / or the sub-scanning direction due to the mode hop or temperature change in the semiconductor laser becomes substantially zero. Good. As described above, the “power diffractive surface” is a diffractive surface having a diffractive function equivalent to a lens action. The above “because of mode hop and temperature change” means that it is caused by mode hop and / or temperature change.

As in the fourth aspect of the invention, in the optical scanning device according to any one of the first to third aspects, the power diffractive surface is employed in the first optical element, and a rotationally symmetric step structure is provided. it can.
As in the invention described in claim 5, in the optical scanning device described in claim 4, it is preferable that the surface opposite to the power diffraction surface of the first optical element is a rotationally symmetric aspherical surface.
Further, as in the invention described in claim 6, in the optical scanning device according to any one of claims 1 to 3, the power diffractive surface is adopted as the second optical element, and has a line-symmetric step structure. can do.
As in the invention described in claim 7, in the optical scanning device described in claim 6, it is preferable that the second optical element is a lens having no power in the main scanning direction and having positive power in the sub scanning direction. .
As in the eighth aspect of the invention, in the optical scanning device according to any one of the first to seventh aspects, all of the first, second, and third optical elements can be made of resin lenses.

As in the ninth aspect, in the optical scanning device according to any one of the first to eighth aspects, the second optical element is preferably adjustable along the optical axis direction.
The first optical element in the present invention converts the cross-sectional form of the light beam from the semiconductor laser into a desired form. In the invention according to claim 9, the action of the first optical element is a collimating action. Is preferred. Furthermore, it is preferable that the second optical element has no power in the main scanning direction. If the second optical element is configured so as not to have power in the main scanning direction, a processing error at the time of initial assembly of the optical system, or a beam waist position variation in the sub-scanning direction when an assembly error occurs. Can be adjusted without affecting the optical characteristics in the main scanning direction by displacing the second optical element in the optical axis direction. Therefore, even if the accuracy of the shape of the diffractive surface employed in the second optical element is not required at a high level, power fluctuations caused by processing errors can be absorbed by this adjustment. In particular, if the adjustment can be made without affecting the optical characteristics in the main scanning direction, the adjustment can be made independently with the first optical element in the main scanning direction and with the second optical element in the sub scanning direction. The work is greatly simplified.
The power of the second optical element is a power obtained by combining the power of the refractive surface and the power of the power diffraction surface.

Further, as in the invention described in claim 10, in the optical scanning device described in any one of claims 1 to 9, the semiconductor laser can be configured by a semiconductor laser array having a plurality of light emitting portions.
The semiconductor laser used as the light source in the optical scanning device can be a single beam scanning system using one semiconductor laser having a normal configuration. However, as in the invention according to claim 10, a semiconductor laser array or two or more By using this semiconductor laser, the “multi-beam scanning method” can be implemented. In particular, the semiconductor laser array has better assembly stability than the use of a plurality of semiconductor lasers, and the light beam is incident on the anamorphic optical element in substantially the same manner. This is a preferable mode because variation can be reduced.

According to an eleventh aspect of the present invention, there is provided an image forming section for forming a latent image by performing optical scanning by a light scanning unit on a photosensitive image carrier and visualizing the latent image by a developing unit to obtain an image. In the image forming apparatus, the optical scanning unit is the optical scanning apparatus according to any one of claims 1 to 10.
Since the number of image forming units is arbitrary, it is possible to form a monochrome image by using one image forming unit, or to form two or more image forming units to form a two-color image or a multicolor image, The image forming apparatus can also be configured to form a color image.

According to a twelfth aspect of the present invention, there is provided an image forming unit that forms a latent image by performing optical scanning by a light scanning unit on a photosensitive image carrier, and visualizes the latent image by a developing unit to obtain an image. In the image forming apparatus, a plurality of image carriers are arranged, and the optical scanning unit is an optical scanning device according to any one of claims 1 to 10, and can scan with a light beam corresponding to each image carrier. Each light beam is modulated with an image signal corresponding to the color component, whereby a latent image corresponding to the color component is formed on each image carrier, and the developing unit converts each latent image with a toner of a color corresponding to the latent image. It is a color-compatible image forming apparatus that is visualized.
The optical scanning device that performs optical scanning in each image forming unit may be separate for each image forming unit. For example, as known from Japanese Patent Application Laid-Open No. 2004-280056, etc. A part, for example, a part of the optical deflector and the scanning optical system may be shared by a plurality of scanning optical systems.
When there are two or more image forming units, the two or more image forming units can be set at different positions with respect to the same image carrier, or arranged in the front-rear direction as in a so-called tandem color image forming apparatus. An individual image forming unit can be set for each of the plurality of image carriers.

Here, when a resin lens is included in the optical system of the optical scanning device, a change in the beam waist position of the light beam condensed toward the surface to be scanned with respect to an environmental change and a wavelength change will be briefly considered. First of all, the cause of beam waist position fluctuation due to temperature fluctuation is
1. Changes in the refractive index of the resin lens itself due to temperature fluctuations,
2. Plastic lens shape change,
3. Change in refractive index of resin lens due to wavelength change of semiconductor laser (chromatic aberration)
Can be considered.
The change in the refractive index of the resin lens itself appears as a phenomenon in which the refractive index decreases due to a decrease in density due to expansion due to temperature rise.
The change in the shape of the resin lens appears as a phenomenon in which the curvature of the lens surface decreases due to the expansion due to the temperature rise.
A change in the emission wavelength of a semiconductor laser generally appears as a phenomenon that shifts to a longer wavelength side with an increase in temperature. When the wavelength shifts to the longer wavelength side, the refractive index of the resin lens generally shifts to the decreasing side.

As described above, regardless of whether the lens is a positive lens or a negative lens, the absolute value of the power changes as the temperature increases.
On the other hand, since the diffraction angle of the power diffracting surface is proportional to the wavelength, the power of the diffracting portion of the power diffractive surface is positive or negative. The absolute value of tends to increase as the wavelength increases.
Therefore, for example, when the combined power of the resin lens in the optical system of the optical scanning device is positive (or negative), the power of the “diffractive part” of the power diffractive surface is positive (or negative), It is possible to cancel the power change accompanying the temperature fluctuation in the resin lens with the power change accompanying the temperature fluctuation in the “diffractive part” of the power diffractive surface.

The power diffractive surface of the anamorphic optical element in the present invention is not necessarily formed on a flat surface, but includes a surface formed on a spherical surface or a cylindrical surface, and power is also applied to a portion corresponding to the substrate on which the diffractive surface is formed. Will have. Accordingly, in the present specification, this is called a “diffractive portion” of the power diffractive surface in the sense that it is the power of only the diffractive surface excluding the power of the portion that hits the substrate. In order to explain this more specifically, consider the case where the environmental temperature rises when the power of the resin lens contained in the optical system and the power of the “diffractive part” of the power diffractive surface are both positive. .
The beam waist position variation due to the change in the refractive index of the resin lens is A,
The amount of beam waist position fluctuation due to the shape change of the resin lens is B,
A beam waist position fluctuation amount due to a change in refractive index of a resin lens caused by a change in emission wavelength of the semiconductor laser is represented by C,
D, the beam waist position fluctuation amount due to the power change of the “diffractive part” of the power diffraction surface due to the change in the emission wavelength of the semiconductor laser,
And if the change in direction away from the optical deflector is positive,
A> 0, B> 0, C> 0, D <0
It is.
And the total amount of beam waist position fluctuation | variation accompanying this temperature change is A + B + C-D. A to C are determined when an optical system including a resin lens is determined. Therefore, the power of the “diffractive part” of the power diffraction surface is satisfied so that the condition that the beam waist position fluctuation amount is 0: A + B + C−D = 0 is satisfied. By setting this, it is possible to satisfactorily correct the beam waist position fluctuation accompanying the temperature change.

  By the way, as described above, the change in the emission wavelength of the semiconductor laser, which is a light source, is not only due to a temperature change, but also due to a mode hop. The change in the emission wavelength due to the mode hop is caused by a microscopic physical phenomenon, which is very difficult to predict. The change in the emission wavelength due to the mode hop is irrelevant to the change in temperature, and if the change in the emission wavelength due to the mode hop occurs in the state where there is no temperature change from the reference temperature, A and B are 0. Is not corrected because CD <0, and the beam waist position changes greatly.

As described above, when the power diffractive surface is adopted in the optical scanning device, not only the correction of the beam waist position fluctuation due to the temperature fluctuation but also the reduction of the beam waist position fluctuation due to the emission wavelength change due to the mode hop is always performed. A stable beam spot diameter cannot be obtained. In addition to correcting beam waist position fluctuations due to temperature fluctuations, in order to reduce beam waist position fluctuations due to emission wavelength changes due to mode hops, it is necessary to appropriately set the power applied to the “diffractive part” of the power diffractive surface. . If too much power is given to the “diffractive part” of the power diffractive surface, the beam waist position fluctuation due to the emission wavelength change due to the mode hop is increased.
In view of the above technical circumstances, in the optical scanning device according to the present invention, the fluctuation of the beam waist position in the main scanning direction and / or the sub-scanning direction due to the mode hop or temperature change in the semiconductor laser is made substantially zero. Thus, the power of the “diffractive part” of the power diffraction surface is set.

  In general, the power diffractive surface to which the power is set can take various shapes. However, as described above, the formation of the power diffractive surface requires a fine processing technique. Furthermore, the thing with the extremely high precision is requested | required. If high processing accuracy cannot be ensured, a variety of undesirable phenomena such as a decrease in diffraction efficiency, deterioration of wavefront aberration, and generation of scattered light occur. Moreover, in order to ensure such a high processing accuracy, a very good measurement technique is indispensable. However, even a power diffractive surface having a spherical surface as a basic shape is difficult to measure, and it is a fact that a high-quality power diffractive surface cannot be obtained.

  Therefore, the power diffractive surface used in the present invention is characterized by a staircase structure and substantially non-power. In order to obtain a staircase structure, the power of the “diffractive part” and the power of the “refractive part” on the power diffractive surface may be equal in absolute value and different in sign. The power diffractive surface obtained at this time necessarily has a staircase structure. With such a structure, the relationship between the diffractive surface and the backcut is almost right at any angle, and there is an advantage that not only measurement is easy, but also processing is very easy.

Furthermore, since the power diffractive surface having the above configuration is non-powered, even if there is a decentering with respect to the opposite surface, the influence thereof is extremely small, so that it is possible to suppress the demand for processing accuracy. Moreover, if it is a staircase structure, the formation method which does not generate | occur | produce a process trace like shaper process can be employ | adopted, and the process time can also be shortened. The shortening of the processing time is preferable for obtaining a high-precision power diffractive surface because secondary benefits such as reduction of heat generation during processing are derived.
Further, the power of the lens itself is given as a combination of the power of the entrance surface and the exit surface, but a desired lens power can be obtained by appropriately setting the power on the opposite side even if one surface is non-power. Therefore, the power diffractive surface having such a staircase structure can be used for any power lens.
Of course, since the surface accuracy of the diffractive surface is not locally non-planar, it can be finished very smoothly, so that almost no scattering light or beam spot diameter is generated.

The optical scanning device according to the present invention reduces the power of the power diffractive surface so that the fluctuation of the beam waist position in the main scanning direction and / or the sub-scanning direction due to the mode hop or temperature change in the semiconductor laser is substantially zero. Therefore, the beam waist position variation is effectively corrected not only for temperature variation but also for emission wavelength variation due to mode hopping, and optical scanning can always be performed with a stable beam spot diameter.
According to the image forming apparatus of the present invention using such an optical scanning device, stable image formation is possible.

  Embodiments of an optical scanning device and an image forming apparatus according to the present invention will be described below with reference to the drawings.

  FIG. 1 shows an optical arrangement of Embodiment 1 of the optical scanning device. In FIG. 1, reference numeral 1 is a semiconductor laser as a light source, reference numeral 2 is a coupling lens as a first optical element, reference numeral 3 is an aperture, reference numeral 4 is an anamorphic optical element as a second optical element, and reference numeral 5 is light. A polygon mirror (rotating polygonal mirror) which is a deflector, reference numeral 6 denotes a scanning lens as a third optical element, and reference numeral 8 denotes a surface to be scanned. Reference numeral G1 indicates a soundproof glass that closes a window of a soundproof housing (not shown) that houses the polygon mirror 5, and reference numeral G2 indicates the emission of the deflected light beam of the housing that houses the optical system of the optical scanning device shown in FIG. The dustproof glass provided in the part is shown.

  The divergent light beam emitted from the semiconductor laser 1 is converted into a light beam having a desired cross-sectional shape by the coupling lens 2, is shaped by the aperture 3, and enters the anamorphic optical element 4. The light beam that has passed through the anamorphic optical element 4 passes through the soundproof glass G1 while being focused in the sub-scanning direction, and forms a long line image in the vicinity of the deflecting reflection surface of the polygon mirror 5 in the main scanning direction. The light beam is reflected by the deflection reflection surface of the polygon mirror 5, passes through the soundproof glass G 1, and enters the scanning lens 6. The scanning lens 6 is composed of a single lens, and the light beam that has passed through the lens 6 passes through the dust-proof glass G2 and enters the surface to be scanned 8, and the light spot on the surface to be scanned 8 by the action of the scanning lens 6 Form.

  The polygon mirror 5 is driven to rotate at a constant speed by a motor. When the polygon mirror 5 rotates at a constant speed, the light beam reflected by the deflecting reflecting surface is deflected at a constant angular velocity. The scanning lens 6 has an fθ characteristic that allows a light spot by a light beam incident while being deflected at a constant angular velocity to move at a constant speed on the scanned surface 8 in the main scanning direction (vertical direction in FIG. 1). The light spot optically scans the scanned surface 8 at a constant speed. The scanning lens 6 is an anamorphic optical element, and in the sub-scanning direction, the position of the deflecting reflection surface of the polygon mirror 5 and the position of the surface 8 to be scanned are in a geometric optical conjugate relationship. The tilting of the reflective surface is corrected. The scanned surface 8 is essentially a photosensitive surface of a photosensitive medium such as a photosensitive drum.

Next, specific numerical examples of the optical components constituting the above embodiment will be given. Table 1 shows data of the glass material (referred to as “glass 1”) and the resin material (referred to as “resin 1”) used in Example 1.
Table 1

  In Table 1, “median” is the refractive index with respect to the wavelength used at the reference temperature: 25 ° C., and “wavelength jump” is the refractive index when the wavelength jump occurs due to mode hops, and “temperature fluctuation”. This is the refractive index when the temperature rises by 20 degrees from the reference temperature. “Wavelength skip” due to mode hopping assumes a wavelength change of 0.8 nm with a margin.

Table 2 shows optical system data arranged after the optical deflector.
Table 2

In Table 2, R _m is “paraxial curvature in the main scanning direction”, R _s is “paraxial curvature in the sub-scanning direction”, and expressed as D _x , D _y (“X”, “Y” in Table 2). ) Represents “relative distance from the origin of each optical element to the origin of the next optical element”. The unit is mm. For example, regarding D _x and D _y of the optical system subsequent to the optical deflector, the origin of the incident surface of the scanning lens 6 (the optical axis of the incident side surface) when viewed from the rotation axis of the optical deflector (polygon mirror 5). The position is 42.99 mm away in the optical axis direction (X direction, left-right direction in FIG. 1) and 6.91 mm away in the main scanning direction (Y direction, up-down direction in FIG. 1). The thickness of the scanning lens 6 on the optical axis is 13.5 mm, and the distance from the scanning lens 6 to the scanned surface 8 is 176 mm. In addition, between the scanning lens 6 and the to-be-scanned surface 8, as shown in FIG. 1, the dust-proof glass G2 of thickness 1.9mm which uses the glass 1 as a material is arrange | positioned. Each surface of the scanning lens 6 is an aspheric surface, and each surface has a non-arc shape given by “Equation 1” in the main scanning direction, and a sub-scanning section (virtual section parallel to the optical axis and the sub-scanning direction). This is a special surface whose curvature changes in the main scanning direction according to “Expression 2”.

The “non-arc shape” is as follows.
Paraxial radius of curvature in main scanning section: R _m , distance in main scanning direction from optical axis: Y, conic constant: K, higher order coefficients: A ₁ , A ₂ , A ₃ , A ₄ , A ₅ , ... Depth in the optical axis direction: X is expressed by the following formula 1.
Formula 1

The “change in curvature in the sub-scanning section” is as follows.
Curvature in the sub-scanning section: C _s (Y) (Y: coordinates in the main scanning direction with the optical axis position as the origin) is expressed in the sub-scanning section including the optical axis. The radius of curvature of the following equation 2 is represented by the following equation 2 with R _s (0), B ₁ , B ₂ , B ₃ ,.
Formula 2

Table 3 lists the coefficients of the incident side surface (special surface) of the scanning lens 6.
Table 3

Table 4 lists the coefficients of the exit side surface (special surface) of the scanning lens 6.
Table 4

Next, the example which employ | adopted the power diffraction surface which is the characteristic structure of this invention for the coupling lens 2 is shown. The coupling lens 2 is a resin lens having a concentric power diffractive surface having a stepped shape on one surface and a rotationally symmetric aspheric surface on the other surface.
2 is a front view of the coupling lens 2 and a cross-sectional view along the plane including the optical axis. The horizontal direction in the figure is the main scanning direction, and the vertical direction is the sub-scanning direction. FIG. 2A is a view of the power diffraction surface of the coupling lens 2 as viewed from the optical axis direction. FIG. 2B is an end view of the virtually cut end surface of the coupling lens 2 parallel to the sub-scanning direction and the optical axis direction. On one surface of the coupling lens 2, a concentric power diffractive surface is formed by a set of concentric grooves configured in a step shape as shown in FIG. A rotationally symmetric aspherical refracting surface is formed on the other surface of the coupling lens 2 (the right side surface in FIG. 2B).

  A light beam (diverging light beam) incident on the coupling lens 2 as the first optical element from the semiconductor laser 1 side that is a light source is converted into a light beam having a desired cross-sectional shape after passing through the coupling lens 2. The light is guided to the cylindrical lens 4 which is the second optical element. The power is set on the power diffractive surface of the coupling lens 2 so that the fluctuation of the beam waist position in the main scanning direction and / or the sub-scanning direction due to the mode hop or temperature change in the semiconductor laser 1 is substantially zero. .

The specific configuration of each element constituting the optical system of the optical scanning device according to the first embodiment shown in FIG. 1 is as follows.
"light source"
The semiconductor laser 1 which is a light source has a design emission wavelength of 785 nm, and when the temperature rises by 1 ° C. with respect to the standard temperature of 25 ° C., the emission wavelength shifts to the long wavelength side by 0.25 nm. The mode hop assumes a wavelength change of 0.8 nm as described above.
"Coupling lens"
The coupling lens 2 is a resin lens having a power diffraction surface as described above, and is disposed so as to have a focal length: 13.952 mm and a function of converting into a weakly divergent light beam. The surface on one side of the coupling lens 2 is aspherical, and the wavefront aberration of the coupled light beam is sufficiently corrected by the aspherical surface.

The semiconductor laser 1 and the coupling lens 2 are fixedly held by a holding member made of a material having a linear expansion coefficient of 7.0 × 10 ⁻⁵ . Power diffraction surface of the incident surface of the coupling lens 2, the phase _{function: w in} the w _in = _C 0 · ^{r 2}
Where r is r ² = Y ² + Z ²
Y is the coordinate in the main scanning direction with the optical axis as the origin, Z is the coordinate in the sub-scanning direction with the optical axis as the origin, and the coefficient: C ₀ is C ₀ = 5.693 × 10 ⁻² . This diffractive part is formed in a refracting part constituting a spherical surface having a radius of curvature of −8.783 mm. Therefore, the completed power diffraction surface has a staircase shape.

The refracting surface of the exit surface of the coupling lens 2 is a rotationally symmetric aspheric surface, and has a non-arc shape given by “Expression 3”. That is, the paraxial radius of curvature: R, the distance from the optical axis: H, the conic constant: K, the higher order coefficients A ₁ , A ₂ , A ₃ , A ₄ , A ₅ ,..., Depth in the optical axis direction: As X, the rotationally symmetric aspherical surface is expressed by Equation 3.
Formula 3

Table 5 lists the coefficients of the exit side surface of the coupling lens 2.
Table 5

A specific configuration of the “aperture” in the first embodiment shown in FIG. 1 is shown below.
The aperture 3 has a “rectangular opening” having an opening diameter of 2.76 mm in the main scanning direction and an opening diameter of 2.36 mm in the sub-scanning direction, and a sectional shape of the light beam coupled by the coupling lens 2. Is shaped into a predetermined shape.

A specific configuration of the “anamorphic optical element” as the second optical element in the embodiment shown in FIG. 1 is shown below.
The anamorphic optical element 4 is a second optical element that guides the light beam transmitted through the coupling lens 2 as the first optical element to an optical deflector, and has a linear shape with an incident side surface formed in a plane. In this power diffraction surface, a flat surface is formed on the exit side surface.
Power diffractive surface of the incident surface, the phase _function: as _{w in,}
w _in = C _z · Z ²
It is represented by Coefficient: C _z is C _z = −2.5359 × 10 ⁻² .

Specific examples of “optical deflector” and “soundproof glass G1” in Example 1 shown in FIG. 1 are shown below.
The polygon mirror 5 as an optical deflector has a number of reflection surfaces: 6 and an inscribed circle radius: 13 mm.
The soundproof glass G1 is made of the glass 1, has a thickness of 1.9 mm, and an inclination angle α in the Y direction (vertical direction in the figure) is 12 degrees.
Further, the angle formed by the traveling direction of the light beam reflected toward the position of the image height: 0 on the scanned surface 8 by the deflecting / reflecting surface of the polygon mirror 5 with respect to the traveling direction of the light beam incident from the light source side: θ is 68 degrees.

Table 6 shows beam waist position fluctuations in the main scanning direction and the sub-scanning direction in the first embodiment.
Table 6

これらの表からわかるとおり、回折部のパワーと屈折部のパワーが相殺するように設定されているパワー回折面の効果で、それぞれのビームウエスト位置変動が低減されていることがわかる。 On the other hand, if a power diffractive surface is not employed for the coupling lens 2, the beam waist position fluctuation is as shown in Table 7.
Table 7

As can be seen from these tables, it can be seen that each beam waist position variation is reduced by the effect of the power diffractive surface set so that the power of the diffractive part and the power of the refracting part cancel each other.

  FIG. 3 is an optical arrangement diagram showing Example 2 of the optical scanning device according to the present invention. In FIG. 3, reference numeral 1 is a semiconductor laser as a light source, reference numeral 2 is a coupling lens as a first optical element, reference numeral 3 is an aperture, reference numeral 4 is an anamorphic optical element as a second optical element, and reference numeral 5 is light. A polygon mirror of a rotary polygon mirror as a deflector, reference numeral 6 denotes a scanning optical system as a third optical element, and reference numeral 8 denotes a surface to be scanned. Reference numeral G1 denotes a soundproof glass that closes a window of a soundproof housing (not shown) that houses the polygon mirror 5, and reference numeral G2 denotes a deflected light beam of the housing that houses the optical system of the optical scanning device shown in FIG. The dustproof glass provided in the injection | emission part is shown.

  The divergent light beam emitted from the semiconductor laser 1 is converted into a light beam having a desired cross-sectional shape by the coupling lens 2, is shaped by the aperture 3, and enters the anamorphic optical element 4. The light beam that has passed through the anamorphic optical element 4 passes through the soundproof glass G1 while being focused in the sub-scanning direction, and forms a line image in the vicinity of the deflection reflection surface of the polygon mirror 5 as a long line image in the main scanning direction. The other light beam reflected by the deflection reflection surface of the polygon mirror 5 passes through the soundproof glass G1 and enters the scanning optical system 6. The scanning optical system 6 is composed of two lenses 6-1 and 6-2, and the light beam that has passed through these lenses 6-1 and 6-2 passes through the dust-proof glass G2 and enters the scanned surface 8. Then, a light spot is formed on the scanned surface 8 by the action of the scanning optical system 6.

  When the polygon mirror 5 rotates at a constant speed, the light beam reflected by the deflecting reflection surface is deflected at a constant angular velocity. The scanning optical system 6 causes the light spot by the incident light beam while being deflected at a constant angular velocity to move at a constant speed in the main scanning direction (vertical direction in FIG. 3) on the surface 8 to be scanned. The light spot scans the scanned surface 8 at a constant speed. The lenses 6-1 and 6-2 constituting the scanning optical system 6 are also anamorphic optical elements. In the sub-scanning direction, the position of the deflecting reflection surface of the polygon mirror 5 and the position of the surface to be scanned 8 are geometrically optically conjugate. Thus, the tilting of the deflecting / reflecting surface of the polygon mirror 5 is corrected. The scanned surface 8 is actually a photosensitive surface of a photosensitive medium (for example, a photosensitive drum).

  The anamorphic optical element 4 is an anamorphic resin lens having a concentric power diffractive surface having one surface formed into a spherical surface, and the other surface having a linear power diffractive surface formed as a cylindrical surface. FIG. 4 shows the anamorphic optical element 4, in which the horizontal direction in the figure is the main scanning direction and the vertical direction is the sub-scanning direction. FIG. 4A is a front view of the anamorphic optical element 4 viewed from the optical axis direction, and the one side (front side) surface is shown in FIGS. 4A, 4C, and 4D. In addition, a concentric power diffractive surface 4A is formed by a set of concentric grooves. On the other surface (back surface) of the anamorphic optical element 4, as shown in FIGS. 4B, 4C, and 4D, a linear power diffraction surface 4B is formed by a set of linear grooves. ing.

  4C is an end view of a virtual cut surface parallel to the main scanning direction and the optical axis direction of the anamorphic optical element 4, and FIG. 4D is a sub-scanning direction of the anamorphic optical element 4 and the light. It is an end view in the virtual cut surface parallel to an axial direction. As shown in these end views, one surface is an anamorphic lens having a concentric power diffractive surface 4A formed on a spherical surface and the other surface having a linear power diffractive surface 4B formed on a cylindrical surface. ing. When a light beam (parallel light beam) incident on the anamorphic optical system 4 from the light source side is transmitted through the anamorphic optical element 4, the light beam is parallel to the main scanning direction and converged in the sub-scanning direction. The power in the main / sub-scanning direction of the power diffractive surface is set so that the fluctuation of the beam waist position in the main scanning direction and / or the sub-scanning direction due to mode hopping and temperature change in the semiconductor laser 1 is substantially zero. The

Next, a specific example of each component of Example 2 shown in FIG. 3 will be described. Table 8 shows data of glass materials (hereinafter referred to as “glass 1” and “glass 2”) and resin materials (hereinafter referred to as “resin 1”) used in the above-described examples and comparative examples described later.
Table 8

  In Table 8, “median” is the refractive index with respect to the wavelength used at the reference temperature: 25 ° C., and “wavelength jump” is the refractive index when the wavelength jump occurs due to mode hops, and “temperature fluctuation”. This is the refractive index when the temperature rises by 20 degrees from the reference temperature. “Wavelength skip” due to mode hopping assumes a wavelength change of 0.8 nm with a margin.

Each element of the optical system is as follows.
"light source"
The semiconductor laser 1 as the light source has a design emission wavelength of 655 nm, and when the temperature rises by 1 ° C. with respect to the standard temperature of 25 ° C., the emission wavelength is shifted to 0.2 nm and the longer wavelength side. The mode hop assumes a wavelength change of 0.8 nm as described above.

"Coupling lens"
The coupling lens 2 is a glass lens using the glass 1 as a material, and the front principal point is arranged at a position 27 mm away from the light emitting portion of the semiconductor laser 1 so as to have a collimating action at a focal length of 27 mm. An aspherical surface is used for the coupling lens 2, and the wavefront aberration of the collimated light beam is sufficiently corrected by the aspherical surface. The semiconductor laser 1 and the coupling lens 2 are fixedly held by a holding member made of a material having a linear expansion coefficient of 7.0 × 10 ⁻⁵ .

"Aperture"
The aperture 3 has a “rectangular opening” having an aperture diameter of 8.14 mm in the main scanning direction and an aperture diameter of 2.96 mm in the sub-scanning direction, and shapes the light beam collimated by the coupling lens 2. .

"Anamorphic optics"
The anamorphic optical element 4 has a concentric power diffractive surface formed on a spherical surface on the incident side, and a linear power diffractive surface formed on a cylindrical surface on the exit side. Power diffractive surface of the incident surface, the phase function: w _in
w _in = C ₀ · r ²
The power diffractive surface of the incident surface has a phase function: w _out
w _out = C _z · Z ²
It is represented by R is r ² = Y ² + Z ²
Y is a coordinate in the main scanning direction with the optical axis as the origin, Z is a coordinate in the sub-scanning direction with the optical axis as the origin, and coefficients: C ₀ and C _z are C ₀ = −2.0373 × 10 ⁻³ and C _z = −1.504 × 10 ⁻² . The diffractive portion on the incident side surface is formed in a refracting portion constituting a spherical surface having a curvature radius of −246.5 mm. Therefore, the completed power diffraction surface has a staircase shape. The diffractive portion on the exit side surface is formed in a refracting portion constituting a cylinder surface having a curvature radius of 69.16 mm.

"Optical deflector"
The polygon mirror 5 as an optical deflector has five reflecting surfaces and an inscribed circle radius of 18 mm. The distance between the exit side surface of the anamorphic optical element 4 and the rotation axis of the polygon mirror 5 is the arrangement shown in FIG. 3, the distance in the horizontal direction: x, the distance in the vertical direction: y, x = 82.97 mm, y = It is set to 112.77 mm.

  The soundproof glass G1 is made of glass 1, has a thickness of 1.9 mm, and an inclination angle α from the y direction (vertical direction in the drawing): 16 degrees. The angle θ between the traveling direction of the light beam incident from the light source side and the traveling direction of the light beam reflected toward the position of the image height 0 on the scanned surface 8 by the deflection reflecting surface is 58 degrees. is there.

Table 9 shows optical system data after the optical deflector.
Table 9

In the above notation, R _m is “paraxial curvature in the main scanning direction”, R _s is “paraxial curvature in the sub-scanning direction”, and expressed as D _x , D _y (“X” and “Y” in Table 9). ) Represents the relative distance from the origin of each optical element to the origin of the next optical element. The unit is mm. For example, regarding the relative distances D _x and D _{y with} respect to the optical deflector, the origin (incident side surface) of the incident surface of the lens 6-1 of the scanning optical system 6 when viewed from the rotation axis of the optical deflector (polygon mirror 5). Are separated by 79.75 mm in the optical axis direction (x direction, left and right direction in FIG. 1) and 8.8 mm in the main scanning direction (y direction, vertical direction in FIG. 1). The thickness of the lens 6-1 on the optical axis is 22.6 mm, the surface interval between the lenses 6-1 and 6-2 is 75.85 mm, and the thickness of the lens 6-2 on the optical axis is 4. 9 mm, and the distance from the lens 6-2 to the surface to be scanned is 158.71 mm. A dust-proof glass G2 having a thickness of 1.9 mm made of glass 1 is disposed between the lens 6-2 of the scanning optical system 6 and the surface to be scanned, as shown in FIG.

  Each surface of the lenses 6-1 and 6-2 of the scanning optical system 6 is aspheric. The incident side surface of the lens 6-1 and the incident side surface and the exit side surface of the lens 6-2 have a non-arc shape given by “Equation 1” in the main scanning direction, and are in the sub-scanning section (parallel to the optical axis and the sub-scanning direction). This is a special surface in which the curvature in the virtual cross section changes in the main scanning direction according to “Expression 2”. The exit side surface of the lens 6-1 is a rotationally symmetric aspherical surface expressed by “Expression 3”.

Table 10 lists the coefficients of the incident side surface (special surface) of the lens 6-1.
Table 10

Table 11 lists the coefficients of the exit side surface (rotationally symmetric aspheric surface) of the lens 6-1.
Table 11

Table 12 lists the coefficients of the incident side surface (special surface) of the lens 6-2.
Table 12

Table 13 lists the coefficients of the exit side surface (special surface) of the lens 6-2.
Table 13

  FIGS. 5A and 5B show the relationship when the beam spot diameter in the main scanning direction and the sub-scanning direction and the beam waist position are defocused with respect to the surface to be scanned in the second embodiment. These figures show the relationship when the reference temperature is 25 ° C. (hereinafter referred to as “room temperature”), the relationship when there is a temperature increase of 20 ° C. relative to the room temperature (“temperature fluctuation”), and light emission due to mode hops. The relationship when the wavelength is changed by 0.8 nm (“wavelength skip”) is shown.

  5A shows the beam spot diameter in the main scanning direction, and FIG. 5B shows the beam spot diameter in the sub-scanning direction, both of which are when the image height of the light spot is zero. As is apparent from FIG. 5, in the optical scanning apparatus of the second embodiment, the relationship between the beam spot diameter and the defocus amount is substantially the same in the main and sub-scanning directions in the normal temperature state, the temperature fluctuation state, and the wavelength jump state. It does not change. This means that the beam waist position in the main scanning direction and the sub-scanning direction does not substantially change regardless of temperature fluctuations and mode hops.

Next, the case where the power diffraction surface of Example 1 or Example 2 has a processing error will be considered.
For example, the groove interval of the concentric power diffractive surface formed on the spherical surface, which is employed on the incident surface side of the anamorphic optical element of Example 2, gradually decreases as the distance from the optical axis increases. In this embodiment, the minimum value is about 100 μm. On the other hand, it is assumed that there are processing errors of 2 μm, 4 μm, and 6 μm. This processing error greatly fluctuates the power of the anamorphic optical element, and if it is mounted on the optical scanning device as it is, the condensing point of the light beam is greatly deviated from the scanned surface 8 and the beam spot becomes large. When such an optical scanning device is developed especially in a color optical printer or the like, color reproducibility deteriorates and gradation is lost. However, since the deviation of the condensing point of the light beam is almost the same over the entire image height, it can be absorbed by shifting the anamorphic optical element in the optical axis direction.

FIG. 6 is a schematic view showing a mechanism for absorbing the converging point shift of the light beam. In FIG. 6, reference numeral 100 denotes an anamorphic optical element, and 101 denotes a holder for fixing the anamorphic optical element. The holder 101 is positioned by being pressed against an abutting reference pin 102 and a gear 103 provided on the housing by a biasing force of a spring (not shown). A rack-like gear is provided on the side surface of the holder 101 at a portion in contact with the gear 103, and the rack-like gear is engaged with the gear 103. Therefore, when the gear 103 is rotated, the holder 102 is operated along the optical axis direction. With such a configuration, the anamorphic optical element can be shifted in the optical axis direction. Therefore, even when the power diffraction surface employed in the anamorphic optical element has a processing error, a desired beam can be obtained. Spots can be tied on the scanned surface.
Of course, it is not an essential requirement to adopt such a mechanical mechanism, and there is a method of adjusting the position when fixing the anamorphic optical element to the optical scanning device and fixing it with an adhesive. This is advantageous in that there is no adjustment mechanism, and no unnecessary parts are left in the optical scanning device after adjustment.

  As a premise of this method, a desired diffraction effect must be obtained even if the anamorphic optical element has a processing error. However, even if there is a processing error of 2 μm, 4 μm, or 6 μm in the groove interval, a diffraction effect that is completely different from the design median value can be expected. FIG. 7 shows this, and it is understood that when the ambient temperature of the anamorphic optical element changes from 25 ° C. to 10 ° C. and 45 ° C., the focal length variation of the anamorphic optical element is exactly the same. it can.

  FIG. 8 schematically shows an embodiment of an image forming apparatus using the optical scanning device according to the present invention. The image forming apparatus according to this embodiment is a tandem type full-color optical printer. In FIG. 8, a conveyance belt 32 that conveys transfer paper (not shown) fed from a paper feed cassette 30 arranged in a horizontal direction in a substantially horizontal direction is provided at the lower part of the apparatus. On the upper surface side of the conveyance belt 32, a photosensitive member 7Y for yellow Y, a photosensitive member 7M for magenta M, a photosensitive member 7C for cyan C, and a photosensitive member 7K for black K are formed on the transfer paper by the conveying belt 32. They are arranged at equal intervals in the above order from the upstream side in the transport direction. Hereinafter, yellow, magenta, cyan, and black are distinguished by Y, M, C, and K added to the reference numerals. The photoreceptors 7Y, 7M, 7C, and 7K also function as image carriers, and are all formed to have the same diameter, and process members for executing an image forming process according to an electrophotographic process are sequentially disposed around the photoreceptors. . Taking the photoconductor 3Y as an example, a charging charger 40Y, an optical scanning device 50Y, a developing device 60Y, a transfer charger 30Y, a cleaning device 80Y, and the like are sequentially arranged in the clockwise direction that is the rotation direction of the photoconductor. The same applies to the other photoconductors 3M, 3C, and 3K. That is, this image forming apparatus uses the photoconductors 7Y, 7M, 7C, and 7K as the scanning surfaces set for the respective color components, and one optical scanning device 50Y, 50M, 50C, and 50K is provided for each. They are provided in a one-to-one correspondence.

  As the optical scanning devices 50Y, 50M, 50C, and 50K, optical scanning devices each having an optical arrangement as shown in FIGS. 1 and 3 can be used independently. Further, for example, as conventionally known from Japanese Patent Application Laid-Open No. 2004-280056 and the like, the optical deflector (rotating polygonal mirror) is shared, and the lens 6-1 of the scanning optical system in each optical scanning device (FIG. 3) can be shared for optical scanning of the photoconductors 7M and 7Y, and can be shared for optical scanning of the photoconductors 7K and 7C.

  Around the conveyance belt 32, a registration roller 9 and a belt charging charger 10 are provided upstream of the photoreceptor 7Y in the transfer paper conveyance direction, and a belt separation charger is disposed downstream of the photoreceptor 7K. 11, a static elimination charger 12, a cleaning device 13, and the like are provided. A fixing device 14 is provided downstream of the belt separation charger 11 in the transport direction, and is connected to a paper discharge tray 15 by a paper discharge roller 16.

  In such a configuration, for example, in the full color mode, Y, M, and C are applied to the surfaces (that is, the scanned surfaces) of the photoreceptors 7Y, 7M, 7C, and 7K that are uniformly charged by the charger. When the optical scanning is performed by the optical scanning devices 50Y, 50M, 50C, and 50K based on the image signals of the respective colors K, electrostatic latent images are formed on the surfaces of the respective photoreceptors. These electrostatic latent images are developed with a corresponding color toner supplied from a corresponding developing device, and become a toner image. The toner images of these colors are superimposed on the transfer paper that is electrostatically attracted and conveyed on the conveyance belt 32 to form a full color image, which is fixed by the fixing device 14 and then discharged. The paper is discharged onto the tray 15.

  By using the optical scanning device described in the first and second embodiments as an optical scanning device that executes the exposure process of such an image forming apparatus, a stable beam spot diameter can be obtained at all times, and high-definition printing is performed. An image forming apparatus suitable for the above can be realized in a compact and inexpensive manner.

The image forming apparatus according to the present invention can also be configured as a monochrome image forming apparatus including one photoconductor as an image carrier and a corresponding optical scanning device.
At least one of the first, second, and third optical elements may be a resin lens, and a power diffraction surface may be formed on at least one of the resin lenses.

1 is an optical arrangement diagram schematically illustrating Example 1 of an optical scanning device according to the present invention. FIG. (A) which shows the example of the coupling lens which employ | adopted the power diffractive surface in the said Example 1, (b) is a front view, (b) It is sectional drawing in a subscanning direction. FIG. 6 is an optical arrangement diagram schematically illustrating Example 2 of the optical scanning device according to the present invention. (A) which shows the example of the anamorphic optical element which employ | adopted the power diffractive surface in Example 2, (b) is sectional drawing of a subscanning direction, (c) is sectional drawing of a main scanning direction, (d) is It is a rear view. In Example 2, the beam spot diameter in the main scanning direction and the sub-scanning direction and the relationship when the beam waist position is defocused with respect to the surface to be scanned are shown, (a) is in the main scanning direction, and (b) is. It is a graph of a subscanning direction. It is a perspective view which shows typically the example of the mechanism for absorbing the condensing point shift | offset | difference of the light beam applicable to this invention. It is a graph which shows the difference in the diffraction effect when there is a processing error in an anamorphic optical element. 1 is a front view showing an embodiment of an image forming apparatus according to the present invention. It is a figure for demonstrating regarding a power diffraction surface, and is an optical path diagram which shows that the power diffraction surface shown to (a) and (b) is equivalent.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor laser as light source 2 Coupling lens which is 1st optical element 3 Aperture 4 Anamorphic optical element which is 2nd optical element 5 Polygon mirror as optical deflector 6 3rd optical element 7Y As image carrier Photoconductor 7M Photoconductor as image carrier 7CY Photoconductor as image carrier 7K Photoconductor as image carrier 8 Scanned surface

Claims (12)

A first optical element that converts a cross-sectional form of a light beam from a semiconductor laser into a desired form, a second optical element that guides a light beam that has passed through the first optical element to an optical deflector, and an optical deflector An optical scanning device comprising a third optical element that focuses a deflected light beam on a surface to be scanned to form a light spot and optically scans the surface to be scanned,
At least one of the first, second, and third optical elements includes a resin lens,
At least one of the resin lenses has a power diffractive surface,
An optical scanning device in which at least one surface shape of the power diffractive surface is set such that the power of the diffractive portion and the power of the refracting portion cancel each other.   2. The optical scanning device according to claim 1, wherein the surface shape of the power diffraction surface is a staircase structure and has no power or very little power.   3. The optical scanning device according to claim 1, wherein the power diffractive surface has substantially zero fluctuation in beam waist position in the main scanning direction and / or sub-scanning direction due to mode hopping and temperature change in the semiconductor laser. Set optical scanning device.   4. The optical scanning device according to claim 1, wherein the power diffraction surface is employed in the first optical element and has a rotationally symmetric step structure.   5. The optical scanning device according to claim 4, wherein a surface opposite to the power diffraction surface of the first optical element is a rotationally symmetric aspherical surface.   4. The optical scanning device according to claim 1, wherein the power diffractive surface is employed in the second optical element and has a line-symmetric step structure.   7. The optical scanning device according to claim 6, wherein the second optical element is a lens having no power in the main scanning direction and having positive power in the sub-scanning direction.   8. The optical scanning device according to claim 1, wherein all of the first, second, and third optical elements are resin lenses.   9. The optical scanning device according to claim 1, wherein the second optical element is adjustable along the optical axis direction.   10. The optical scanning device according to claim 1, wherein the semiconductor laser is a semiconductor laser array having a plurality of light emitting units. An image forming apparatus having an image forming unit that forms a latent image by performing optical scanning with a light scanning unit on a photosensitive image carrier, and visualizes the latent image with a developing unit to obtain an image.
An image forming apparatus, wherein the optical scanning unit is the optical scanning device according to claim 1. An image forming apparatus having an image forming unit that forms a latent image by performing optical scanning with a light scanning unit on a photosensitive image carrier, and visualizes the latent image with a developing unit to obtain an image.
A plurality of image carriers are arranged,
The optical scanning unit is an optical scanning device according to any one of claims 1 to 10, and can scan with a light beam corresponding to each image carrier,
Each light beam is modulated with an image signal corresponding to a color component, whereby a latent image corresponding to the color component is formed on each image carrier,
A developing unit visualizes each latent image with toner of a color corresponding to the latent image, and a color-compatible image forming apparatus.

Images