JP5059453B2 - Optical scanning apparatus and image forming apparatus - Google Patents

Description

The present invention relates to an optical scanning device, and an image forming apparatus such as a digital copying machine, a printer, a plotter, a facsimile, or a complex machine including the optical scanning device.

  In recent years, colorization of image forming apparatuses using an electrophotographic process has progressed, and a latent image is formed by performing optical scanning corresponding to each color (for example, cyan, magenta, yellow, black) on a photoconductor as an image carrier. The latent image is developed with each color developer to form each color image, and each color image is transferred onto a recording medium such as recording paper or an intermediate transfer member to form a color image. Yes. At this time, if the image writing start position of each color is deviated, image deterioration called so-called color misregistration occurs in the superimposed color image, which is a big problem. However, even in such a case, if the position of the light beam with respect to each color can be detected, a good color image can be obtained by correcting each writing start position by using an appropriate correction unit and aligning with each color. Can do.

  The speed of image forming apparatuses is also increasing, and optical scanning apparatuses that perform optical scanning of a plurality of light beams all at once have been actively used. The light source in this case is a single-beam light source having a single light-emitting point in the past, but has a multi-beam light source composed of a plurality of single-beam light sources or a plurality of light-emitting points with a minute interval of about several tens of μm. A beam array light source is used. In this type of optical scanning device, the so-called density unevenness is particularly caused by the deviation (scanning line pitch deviation) in the sub-scanning direction by shifting the interval (pitch) of the light beams when optically scanning the surface to be scanned. This causes image degradation called "", which is a big problem. However, even in such a case, if the position of each light beam can be detected, the light beam interval can be corrected using an appropriate correction means, and a good image without density unevenness can be obtained.

  In response to the above requirements, it is important to detect the position of the light beam that is being scanned, and in particular, a means for detecting the light beam position in the sub-scanning direction and the light beam interval in the sub-scanning direction is desired. Yes.

Here, regarding an optical system, an optical scanning apparatus, and an image forming apparatus that detect the position of a light beam in the sub-scanning direction, Patent Document 1 discloses two light beam detection means, which are the start ends of the respective light beam detection areas in the main scanning direction. There is disclosed a detecting means for detecting a shift in the interval of a plurality of light beams in the sub-scanning direction by arranging them side by side in the main scanning direction so that the side edges are not parallel to each other.
However, in this prior art, since a plurality of detection means are arranged in the main scanning direction, there is a problem that the size of the photodetector tends to increase in the main scanning direction.

  In general, the photodetector is arranged outside the effective image area in the main scanning direction. Therefore, it is necessary for the scanning optical system to allow the light beam to reach the photodetector in addition to the effective image area width. For this reason, when the photodetector becomes large in the main scanning direction, the scanning optical system becomes large, and the optical scanning device becomes large. In addition, an increase in the size of the scanning optical system causes problems such as an increase in optical path length, a high angle of view, and an increase in effective diameter.

JP-A-7-72399 JP 2002-40350 A

  In order to solve the above-described problems of the prior art, the present inventors separated a light beam outside the effective image area of the optical scanning device into a plurality of beams in the sub-scanning direction, and the separated light beams in the sub-scanning direction. An optical system that detects light beam positions and light beam intervals in the sub-scanning direction by detecting with a plurality of arranged photodetectors is being studied.

As a means for separating a light beam (for example, a laser beam), for example, a parallel plate-shaped half mirror can be considered, and Patent Document 2 describes a configuration using a half mirror as a beam separating means of an optical scanning device. .
However, when a parallel plate-like optical element such as a half mirror or an optical filter (for example, a density filter or a wavelength filter) is used in an optical system using a laser beam, the optical surface (planar) in the optical element is used. Internal interference occurs due to reflection. Therefore, the transmittance and the reflectance are changed only by changing the thickness of the optical element on the wavelength order. Patent Document 2 describes in paragraph [0025] the effect of internal interference of a parallel plate-shaped half mirror, but does not mention the change in transmittance due to the thickness of the parallel plate.

Here, the calculation result of the transmittance | permeability change accompanying the thickness change of a parallel plate is shown in FIG. This is the transmittance of a parallel plate when a laser beam with a wavelength of 633 nm is perpendicularly incident on a parallel plate (refractive index of 1.5) having both surfaces placed in the air (refractive index of 1.0). Show. The horizontal axis represents the thickness (μm) of the parallel plate, and the vertical axis represents the transmittance.
As shown in FIG. 2, a change in transmittance is observed at a period of about 1/3 of the wavelength. For this reason, in order to avoid this change in transmittance, a non-reflective coating is usually applied to the entrance surface and the exit surface of the parallel plate.
The horizontal axis in FIG. 2 shows the calculation result at a very thin value of 0 to 0.5 μm, but it goes without saying that the change in transmittance is the same even when the thickness is increased.

  In recent years, with the progress of processing technology, diffractive optical elements having a structure of micrometer to submicron order have been used. Among them, a parallel plate-like diffractive optical element having a binary or multi-step diffractive surface has come out because of ease of processing. Such a diffractive optical element is often used on the optical axis by vertically incidence of a laser beam, and also has a non-reflective coating on the flat side.

  The present inventors are examining an optical system using a laser beam separation function, which is one of the features of a diffractive optical element, as beam separation means of an optical scanning device. Therefore, a parallel plate-like diffractive optical element having such a diffractive surface will be considered.

FIG. 3 shows a state in which a laser beam perpendicularly incident on a diffractive optical element having a diffractive surface and a plane is separated into zero-order transmitted light and higher-order transmitted diffracted light on the diffractive surface. The plane of the diffractive optical element is usually provided with an antireflection coating.
As shown in FIG. 3, a laser beam perpendicularly incident on a diffractive optical element (refractive index of 1.5) having a diffractive surface and a plane is separated into zero-order transmitted light and higher-order transmitted diffracted light on the diffractive surface. . In general, non-reflective coatings have an incident angle dependency, so that all of zero-order transmitted light incident perpendicular to the plane and higher-order transmitted diffracted light incident obliquely on the plane are made non-reflective. It is difficult to apply.

Next, FIG. 4 shows a state in which a laser beam perpendicularly incident on a diffractive optical element having a flat surface and a diffractive surface is separated into zero-order reflected light and high-order reflected diffracted light that are regularly reflected by the diffractive surface.
Similarly to the above, a laser beam perpendicularly incident on a diffractive optical element (refractive index 1.5) having a plane and a diffractive surface as shown in FIG. Although separated into higher-order reflected diffracted light that is reflected obliquely, it is difficult to apply an appropriate non-reflective coating to both the zero-order reflected light and the higher-order reflected diffracted light.
The zero-order transmitted light and the zero-order reflected light component are as large as 4% even when the refractive index is 1.5 (more when the refractive index is high). Non-reflective coatings for these are necessary, i.e. they cannot be adequately treated for higher-order diffracted light. Therefore, it is difficult to effectively separate the laser beam.

  A specific calculation example is shown below. FIG. 5 is a schematic diagram of a diffractive optical element (refractive index of 1.5) having a diffractive surface and a plane, and FIG. 6 shows the thickness of the diffractive optical element when a laser beam is vertically incident on the diffractive optical element from the diffractive surface side. The transmittance (diffraction efficiency of 0th-order transmitted light) change with respect to the change in thickness D is shown. The structure of the diffractive surface has a grating period P = 0.75 μm, a fill factor F = 0.5 represented by W / P, a grating height H of three levels, and a grating height H = 0.25 μm, 0.5 μm, It was set to 0.75 μm.

  As shown in FIG. 6, at any grating height H, it can be seen that the transmittance is undulating with respect to the thickness D of the diffractive optical element. Keeping this amount of change small is important for suppressing variations in diffraction efficiency of the diffractive optical element. The dotted line in the figure is the transmittance when the plane is 100% transmitting the laser beam, and of course there is no change with respect to the thickness D. In the calculation example described later, the thickness D of the diffractive optical element shows a calculation result with a very thin value of 5 to 5.5 μm. However, even when the thickness increases, the transmittance changes. Needless to say, it will not change.

The present invention has been made in view of the above circumstances, and in order to effectively separate a laser beam using a parallel plate-like diffractive optical element having a diffractive surface, the diffractive optical element can be formed without applying an antireflection coating. An object of the present invention is to provide an optical scanning device including an optical system capable of obtaining a stable diffraction efficiency with respect to a thickness change.
Not using an optical coating not only reduces the environmental burden during production, but is also effective in reducing the cost and recycling of optical elements.

Further, in the present invention, and the light beam position of the sub-scanning direction, the optical scanning device and means capable of detecting a light beam interval in the sub-scanning direction, to provide an image forming apparatus including the optical scanning device Objective.

In order to achieve the above object, the present invention adopts the following means.
A first means of the present invention is an optical scanning device that deflects a light beam from a light source means by a light deflecting means and scans a surface to be scanned through a scanning imaging optical system .
Laser beam detecting means disposed outside the effective image forming area of the scanning imaging optical system, wherein a part of the laser beam is incident on a diffractive optical element, and a plurality of separated laser beams are detected by a plurality of photodetectors. Prepared,
The diffractive optical element is a flat diffractive optical element having a diffractive surface and a plane,
The laser beam is incident on a diffractive surface of the diffractive optical element, is transmitted and diffracted into two or more laser beams on the diffractive surface, and the two or more laser beams are incident on a plane of the diffractive optical element;
All laser beams incident on the plane of the diffractive optical element are P-polarized light, and each incident angle θ is
0 ° <θ < θo
It is set so that it may satisfy | fill.
Here, .theta.o, when the Fresnel reflectance of P Henhikariji at the incident angle alpha was Rp (alpha), the incident angle becomes Rp (0 °) = Rp ( θo).

The second means of the present invention is an image forming apparatus comprising an image carrier, a means for forming a latent image on the image carrier, and a means for developing and developing the latent image on the image carrier. The first optical scanning device is provided as means for forming the latent image.
Further, a third means of the present invention is the image forming apparatus of the second means, comprising a plurality of the image carriers, forming a latent image on the plurality of image carriers, and forming a latent image on each image carrier. After developing with different color developers, the developed image on each image carrier is transferred to a recording medium directly or using an intermediate transfer member to form a multicolor or color image.

In the optical scanning device of the first means, all laser beams incident on the plane of the diffractive optical element are P-polarized light, and each incident angle θ is set to satisfy 0 ° <θ < θo . By reducing the Fresnel reflectivity compared to normal incidence, the effect of the change in transmittance on the change in thickness of the diffractive optical element can be reduced by entering obliquely without applying an anti-reflective coating. be able to.
Furthermore, since the laser beam has a function of separating the laser beam into a plurality, the diffractive optical element that separates the laser beam into a plurality of components can change the transmittance of the diffractive optical element at low cost without applying an anti-reflection coating. Can be reduced, and a stable beam separation system can be obtained.

Further, in the optical scanning device of the first means, by using the diffractive optical element as the light beam detecting means, it is possible to detect the light beam position and the light beam interval particularly in the sub-scanning direction. It is possible to provide an optical scanning device for an image forming apparatus adapted to the conversion.

In the second and third image forming apparatuses, by using the first optical scanning device, it is possible to provide an image forming apparatus adapted to high definition, high speed, and colorization.

  Hereinafter, the configuration, operation, and effects of the present invention will be described in detail based on the illustrated embodiments.

[Example 1]
FIG. 1 is a schematic configuration diagram of an optical system according to a first embodiment of the present invention, which is configured so that a laser beam is incident from the diffraction surface side to a flat diffractive optical element having a diffraction surface and a flat surface. It is an example of a simple optical system.
The laser beam incident on the diffractive surface of the diffractive optical element is transmitted and diffracted into two or more laser beams according to a so-called grating equation and separated. The transmitted diffracted light is incident on the plane at various incident angles θ. Fresnel reflection occurs on the plane, and due to interference with the reflected light, the transmittance of the laser beam that passes through the diffractive optical element changes according to the thickness of the diffractive optical element.

  When the laser beam is incident on the diffractive surface of the diffractive optical element perpendicularly, at least zero-order transmitted diffracted light is generated regardless of the grating period of the diffractive surface and is incident perpendicular to the plane. Due to the Fresnel reflectivity R0 on the plane, the transmittance of the laser beam that passes through the diffractive optical element changes. Therefore, by changing the Fresnel reflectivity in a plane to be smaller than R0 for all the laser beams separated on the diffractive surface, it is possible to reduce the change in transmittance of the laser beam transmitted through the diffractive optical element.

FIG. 7 shows the Fresnel reflectivity for each polarized light when diffracted light is incident on the plane that is the interface from the refractive index 1.5 to the refractive index 1.0 of the diffractive optical element shown in FIG. An enlarged view of Fresnel reflectivity is shown).
7 and 8, R0 = 0.04, and in order to make the Fresnel reflectivity in the plane smaller than R0, P-polarized light is incident on the plane, and its incident angle θ is
0 ° <θ <θo
And it is sufficient.
Where θo is Rp (α) when the Fresnel reflectivity during P-polarization at the incident angle α is
Rp (0 °) = Rp (θo)
Is the incident angle.

  It is possible to obtain Fresnel reflectivity smaller than R0 by entering elliptically polarized light. However, at the same incident angle, linearly polarized light can suppress Fresnel reflectivity smaller than elliptically polarized light. A laser beam typified by a laser is generally linearly polarized light, and has an advantage that it can be used as it is.

In addition, the incident angle θ, when the critical angle is θc,
θc <θ <90 °
It is good.
Higher-order diffracted light enters the plane at a large incident angle. If the incident angle is greater than the critical angle, the laser beam cannot exit the diffractive optical element. In exceptional cases, a so-called resonance effect may be caused by coupling between a grating vector of a diffractive surface and a waveguide vector determined from the structure of the diffractive optical element. In the present invention, such a special situation is of course excluded. Thus, the diffractive optical element should be set.

That is, all the laser beams of the transmitted diffracted light transmitted through the diffractive surface of the diffractive optical element are incident on the plane as P-polarized light, and the incident angle θ is
0 ° <θ <θo or θc <θ <90 °
If the optical system is set as follows, the laser beam can be effectively separated.

[Example 2]
FIG. 9 is a schematic configuration diagram of an optical system showing a second embodiment of the present invention, in which a laser beam is incident on a flat diffractive optical element having a diffractive surface and a plane from the plane side. It is an example of an optical system.
The laser beam perpendicularly incident on the plane side of the diffractive optical element is transmitted through the plane, and on the diffractive surface, regardless of the grating period of the diffractive surface, returns to the plane side as at least zero-order reflected diffracted light. Fresnel reflection occurs at, and due to this interference, the transmittance of the laser beam that passes through the diffractive optical element changes according to the thickness of the diffractive optical element. Therefore, by changing the Fresnel reflectivity at the plane of the laser beam returned from the diffraction surface to be smaller than R0, the change in the transmittance of the laser beam transmitted through the diffractive optical element can be reduced.

The Fresnel reflectivity for each polarized light when incident perpendicularly to the plane from the refractive index 1.5 to the refractive index 1.0 is as shown in FIG. 7 and FIG. 8 described above. In order to make the reflectance smaller than R0, P-polarized light is incident on the plane, and its incident angle θ is
0 ° <θ <θo
And it is sufficient.
Moreover,
θc <θ <90 °
As described above, it is also possible.

That is, all the laser beams of the reflected diffracted light reflected by the diffractive surface of the diffractive optical element are incident on the plane as P-polarized light, and the incident angle θ is
0 ° <θ <θo or θc <θ <90 °
If the optical system is set as follows, the laser beam can be effectively separated.

[Example 3]
FIG. 10 is a schematic block diagram of an optical system showing a third embodiment of the present invention, which is designed to make a laser beam incident from the diffractive surface side to a flat diffractive optical element having a diffractive surface and a flat surface. It is an example of a simple optical system.
The laser beam incident on the diffractive surface of the diffractive optical element is transmitted and diffracted into one or more laser beams according to a so-called grating equation and separated. The transmitted diffracted light is incident on the plane at various incident angles θ. On the plane, the light is refracted according to Snell's law, and the separated laser beam is emitted from the diffractive optical element at an emission angle φ. Here, in order to keep the Fresnel reflectivity on the plane small, P-polarized light is incident on the plane.

  Next, FIG. 11 shows a first example of a diffractive optical element used in the optical system of FIG. 10 (hereinafter referred to as a diffractive optical element (Example 1)). FIGS. 12A and 12B show diffractive optics when a laser beam (wavelength 633 nm) is incident on the diffractive optical element (example 1) (refractive index 1.5) shown in FIG. It shows the transmittance (diffraction efficiency of 0th order transmitted light and −1st order transmitted light) changes with respect to changes in the thickness D of the element. The diffraction surface of the diffractive optical element has a grating period P = 0.38 μm, F = 0.5, and a grating height H = 0.25 μm, 0.5 μm, and 0.75 μm.

  As shown in FIG. 11, when a laser beam is incident on the diffractive surface of the diffractive optical element at 56.4 °, it is separated into zero-order and −1-order transmitted diffracted light according to the grating equation. Both transmitted diffracted lights are incident on a plane at an incident angle of 33.7 °, refracted according to Snell's law, and the separated laser beam is emitted from the diffractive optical element at an emission angle of 56.4 °. Note that the angle is represented by a size without distinguishing between positive and negative. FIGS. 12A and 12B show the transmittances of the 0th-order transmitted light and the −1st-order transmitted light with respect to changes in the thickness D of the diffractive optical element at this time. The vertical axis represents the transmittance, and the horizontal axis represents the thickness D of the diffractive optical element. As shown in FIGS. 12A and 12B, it can be seen that the transmittance is substantially constant with respect to the change in the thickness D.

Here, FIG. 13 shows the Fresnel transmittance for each polarized light when diffracted light is emitted from a plane which is an interface from the refractive index 1.5 to the refractive index 1.0 of the diffractive optical element (Example 1) shown in FIG. Show. An enlarged view of the Fresnel transmittance is shown in FIG. Here, θ ′ and θ ″ are Tp (α) when the Fresnel transmittance during P-polarization at the exit angle α is Tp (α).
Tp (θ ′) = Tp (θ ″) = 0.98 and θ ′ <θ ″
The exit angle is as follows. In this embodiment, θ ′ = 34.7 ° and θ ″ = 66.7 °.

In the diffractive optical element (example 1) shown in FIG. 11, the light is incident on the plane with P-polarized light, and the exit angle emitted from the plane is φ = 56.4 °.
θ '<φ <θ "
The separated laser beam shows a stable transmittance.
Note that the Fresnel transmittance at φ = 56.4 ° is 1.0, which is the total transmittance. Therefore, the 0th-order transmitted light and the −1st-order transmitted light separated by the diffractive surface do not interfere with the reflected light from the plane, and the transmittance is constant without depending on the change in the thickness of the diffractive optical element. Yes.

  Next, FIG. 15 shows a second example of a diffractive optical element (hereinafter referred to as a diffractive optical element (example 2)) used in the optical system of FIG. FIGS. 16A and 16B show diffractive optics when a laser beam (wavelength 633 nm) is incident on the diffractive optical element (example 2) (refractive index 1.5) shown in FIG. It shows the transmittance (diffraction efficiency of 0th order transmitted light and −1st order transmitted light) changes with respect to changes in the thickness D of the element. The diffractive surface of the diffractive optical element has a grating period P = 0.46 μm, F = 0.5, and a grating height H = 0.25 μm, 0.5 μm, 0.75 μm.

  As shown in FIG. 15, when a laser beam is incident on the diffractive surface of the diffractive optical element at 43.5 °, it is separated into 0th-order and −1st-order transmitted diffracted light according to the grating equation. Both transmitted diffracted lights are incident on a plane at an incident angle of 27.3 °, refracted according to Snell's law, and the separated laser beam is emitted from the diffractive optical element at an emission angle of 43.5 °. come. FIGS. 16A and 16B show the transmittance of the 0th-order transmitted light and the −1st-order transmitted light with respect to the change in the thickness D of the diffractive optical element at this time. The vertical axis represents the transmittance, and the horizontal axis represents the thickness D of the diffractive optical element. As shown in FIGS. 16A and 16B, compared to the above-described embodiment (FIG. 12), although the transmittance changes with respect to the change in thickness D, the amount of change can be suppressed to a practical level. ing.

In the diffractive optical element shown in FIG. 15 (Example 2), the light is incident on the plane with P-polarized light, and the exit angle emitted from the plane is φ = 43.5 °.
θ '<φ <θ "
The transmittance change of the separated laser beam is small.
The Fresnel transmittance at φ = 43.5 ° is 0.99, which is almost total transmission. Therefore, the 0th order transmitted light and the −1st order transmitted light separated by the diffractive surface do not interfere with the reflected light from the plane, and the change in transmittance is suppressed without depending on the change in the thickness of the diffractive optical element. ing.

  Next, FIG. 17 shows a third example of the diffractive optical element used in the optical system of FIG. 10 (hereinafter referred to as a diffractive optical element (example 3)). 18A and 18B show diffractive optics when a laser beam (wavelength 633 nm) is incident on the diffractive optical element (example 3) (refractive index 1.5) shown in FIG. It shows the transmittance (diffraction efficiency of 0th order transmitted light and −1st order transmitted light) changes with respect to changes in the thickness D of the element. The diffractive surface of the diffractive optical element has a grating period P = 0.55 μm, F = 0.5, and a grating height H = 0.25 μm, 0.5 μm, 0.75 μm.

  As shown in FIG. 17, when a laser beam is incident on the diffractive surface of the diffractive optical element at 35.1 °, it is separated into 0th order and −1st order transmitted diffracted light according to the grating equation. Both transmitted diffracted lights are incident on a plane at an incident angle of 22.6 °, refracted according to Snell's law, and the separated laser beam is emitted from the diffractive optical element at an emission angle of 35.1 °. come. FIGS. 18A and 18B show the transmittance of the 0th-order transmitted light and the −1st-order transmitted light with respect to changes in the thickness D of the diffractive optical element at this time. The vertical axis represents the transmittance, and the horizontal axis represents the thickness D of the diffractive optical element. As shown in FIGS. 18 (a) and 18 (b), compared with the above-described embodiment (FIGS. 12 and 16), although the change in transmittance is large with respect to the change in thickness D, the amount of change is at a practical level. Is suppressed.

In the diffractive optical element shown in FIG. 17 (Example 3), the light is incident on the plane with P-polarized light, and the exit angles emitted from the plane are both φ = 35.1 °,
θ '<φ <θ "
The transmittance change of the separated laser beam is small.
Note that the Fresnel transmittance at φ = 35.1 ° is 0.98, and the transmittance is high. Therefore, the 0th order transmitted light and the −1st order transmitted light separated by the diffractive surface do not interfere with the reflected light from the plane, and the change in transmittance is suppressed without depending on the change in the thickness of the diffractive optical element. ing.

  In general, even if it is an anti-reflection coating, if it is an optical component for consumer use, its transmittance is about 0.98 or more with respect to the operating wavelength range and angular characteristics. In other words, as long as the conditions shown in the above embodiments are satisfied, it is possible to suppress the transmittance change to the same level as when the antireflection coating is applied, without applying the antireflection coating. That is, the cost and time required for the antireflective coating can be reduced.

In the examples of FIGS. 11, 15, and 17, so-called Bragg conditions are applied to the angles of incidence on the diffractive surface. That is, the incident angle θB is determined by the following equation from the wavelength λ and the grating period P of the diffraction surface.
sinθB = λ / 2P
When this condition is used, two laser beams are separated on the diffraction surface, ie, 0th order transmitted light and −1st order transmitted light, and the exit angles from the diffraction surface are also equal. That is, the incident angle to the plane is also equal, and the exit angle φ from the plane is also equal. Therefore, the transmittances of the two separated laser beams show the same change, and there is no variation between the laser beams.

Further, in the embodiment of FIG. 11, the emission angle from the plane is set to be a Brewster angle φB (an angle at which the Fresnel transmittance at the time of P-polarized light becomes 1.0). Here, when the refractive index of the diffractive optical element placed in the air (refractive index 1.0) is N, the Brewster angle is determined by the following equation.
tanφB = N
At this Brewster angle, since the Fresnel transmittance is 1.0, the transmittance change can be zero.

  In the above embodiment, the Bragg condition and the Brewster angle are applied. However, the Bragg condition and the Brewster angle need not be applied. Examples thereof are shown below.

  FIG. 19 shows a fourth example of a diffractive optical element used in the optical system of FIG. 10 (hereinafter referred to as a diffractive optical element (Example 4)). FIGS. 20A and 20B show diffractive optics when a laser beam (wavelength 633 nm) is incident on the diffractive optical element (example 4) (refractive index 1.5) shown in FIG. It shows the transmittance (diffraction efficiency of 0th order transmitted light and −1st order transmitted light) changes with respect to changes in the thickness D of the element. The diffraction surface of the diffractive optical element has a grating period P = 0.38 μm, F = 0.5, and a grating height H = 0.25 μm, 0.5 μm, and 0.75 μm.

As shown in FIG. 19, when a laser beam is incident on the diffractive surface of the diffractive optical element at 50.0 °, it is separated into 0th order and −1st order transmitted diffracted light according to the grating equation. The 0th order transmitted diffracted light is 30.7 °, the −1st order transmitted diffracted light is incident on the plane at an incident angle of 36.9 °, is refracted according to Snell's law, and is emitted from the diffractive optical element. The exit angles are 50.0 ° and 64.1 °, respectively. FIGS. 20A and 20B show the transmittance of the 0th-order transmitted light and the −1st-order transmitted light with respect to the change in the thickness D of the diffractive optical element at this time. The vertical axis represents the transmittance, and the horizontal axis represents the thickness D of the diffractive optical element. As shown in FIGS. 20A and 20B, the transmittance is suppressed to a practical level with respect to the change in the thickness D. Each exit angle φ emitted from the plane of the diffractive optical element is a condition,
θ '<φ <θ "
Meet.

[Example 4]
FIG. 21 is a schematic configuration diagram of an optical system showing a fourth embodiment of the present invention, in which a laser beam is incident on a flat diffractive optical element having a diffractive surface and a plane from the plane side. It is an example of an optical system.
The laser beam incident on the plane of the diffractive optical element is refracted according to Snell's law and incident on the diffractive surface. The laser beam incident on the diffractive surface is transmitted and diffracted into one or more laser beams according to the grating equation, separated, and emitted from the diffractive optical element at various exit angles. On the other hand, the laser beam reflected and diffracted by the diffraction surface returns to the plane again and is further reflected by the plane. In this embodiment, in order to suppress the Fresnel reflectivity here, P-polarized light is used.

  FIG. 22 shows an example of a diffractive optical element used in the optical system of FIG. 21 (hereinafter referred to as a diffractive optical element (Example 5)). 23A and 23B show the diffractive optical element when a laser beam (wavelength 633 nm) is incident on the diffractive optical element (example 5) (refractive index 1.5) shown in FIG. 22 from the plane side. The transmittance (the diffraction efficiency of the 0th order transmitted light and the −1st order transmitted light) with respect to the change in the thickness D of FIG. The diffraction surface had a grating period P = 0.38 μm, F = 0.5, and a grating height H = 0.25 μm, 0.5 μm, and 0.75 μm.

  As shown in FIG. 22, when a laser beam is incident on the plane of the diffractive optical element at 56.4 °, the laser beam is refracted according to Snell's law and incident on the diffraction surface at an incident angle of 33.7 °. On the diffractive surface, according to the grating equation, it is separated into 0th-order and −1st-order transmitted diffracted light, and both transmitted diffracted light is emitted from the diffractive optical element at an exit angle of 56.4 °. Note that the angle is represented by a size without distinguishing between positive and negative. FIGS. 23A and 23B show the transmittances of the 0th-order transmitted light and the −1st-order transmitted light with respect to changes in the thickness D of the diffractive optical element at this time. The vertical axis represents the transmittance, and the horizontal axis represents the thickness D of the diffractive optical element. As shown in FIGS. 23A and 23B, it can be seen that the transmittance is substantially constant with respect to the change in the thickness D.

A laser beam that causes transmittance fluctuations due to interference is diffracted reflected light that is reflected on the diffraction surface and returns to the plane, and 0th-order and −1st-order reflected diffracted light is generated according to the grating equation. It is incident on the plane at 7 ° (indicated by a broken line in FIG. 22). Here, FIG. 24 shows the Fresnel transmittance for each polarized light when the diffracted reflected light is incident on a plane which is an interface from the refractive index 1.5 to the refractive index 1.0 of the diffractive optical element shown in FIG. An enlarged view of the Fresnel transmittance is shown in FIG. Note that ψ ′ and ψ ″ in FIG. 25 are Tp (α) when the Fresnel transmittance during P-polarization at the incident angle α is Tp (α).
Tp (ψ ′) = Tp (ψ ″) = 0.98 and ψ ′ <ψ ″
The exit angle is as follows. In this embodiment, ψ ′ = 22.3 ° and ψ ″ = 37.7 °.

In the diffractive optical element shown in FIG. 22 (Example 5), the incident angle of the diffracted reflected light incident on the plane with P-polarized light is ψ = 33.7 °.
ψ '<ψ <ψ "
The separated laser beam shows a stable transmittance. Note that the Fresnel transmittance at ψ = 33.7 ° is 1.0, which is total transmission. Therefore, the transmittance of the 0th-order transmitted light and the −1st-order transmitted light separated by the diffractive surface is constant without depending on the change in the thickness D of the diffractive optical element.

  In the above embodiment, the Bragg condition is applied as the condition for entering the diffractive surface, and the Brewster angle is applied to the condition for entering the plane. Of course, the Bragg condition and the Brewster angle are applied. It is not necessary. Examples thereof are shown below.

  FIG. 26 shows another example of a diffractive optical element used in the optical system of FIG. 21 (hereinafter referred to as a diffractive optical element (Example 6)). FIGS. 27A and 27B show diffractive optical elements when a laser beam (wavelength 633 nm) is incident on the diffractive optical element (example 6) (refractive index 1.5) shown in FIG. 26 from the plane side. The transmittance (the diffraction efficiency of the 0th order transmitted light and the −1st order transmitted light) with respect to the change in the thickness D of FIG. The diffraction surface of the diffractive optical element has a grating period P = 0.38 μm, F = 0.5, and a grating height H = 0.25 μm, 0.5 μm, and 0.75 μm.

  As shown in FIG. 26, when the laser beam is incident on the plane of the diffractive optical element at 50.0 °, it is refracted according to Snell's law and incident on the diffractive surface at an incident angle of 30.7 °. On the diffractive surface, according to the grating equation, it is separated into 0th order and −1st order transmitted diffracted light, and the exit angles of the laser beam exiting from the diffractive optical element are 50.0 ° and 64.1 °, respectively. FIGS. 27A and 27B show the transmittances of the 0th-order transmitted light and the −1st-order transmitted light with respect to changes in the thickness D of the diffractive optical element at this time. The vertical axis represents the transmittance, and the horizontal axis represents the thickness D of the diffractive optical element. As shown in FIGS. 27A and 27B, compared with the above-described embodiment (FIG. 23), although the transmittance changes with respect to the change in thickness D, the amount of change can be suppressed to a practical level. ing.

A laser beam that causes transmittance fluctuations due to interference is diffracted reflected light that is reflected by the diffraction surface and returns to the plane. According to the grating equation, 0th order and −1st order reflected diffracted light is generated, and the 0th order reflected light is 30. At -7 °, the −1st order reflected light is incident on the plane at 36.9 ° (indicated by a broken line in FIG. 26).
In the example of the diffractive optical element shown in FIG. 26, the incident angle ψ of the diffracted reflected light that is incident on the plane with P-polarized light, reflected on the diffractive surface, and returned to the plane is
ψ '<ψ <ψ "
The separated laser beam shows a stable transmittance.

[Example 5]
Next, an example of an optical scanning device using the optical system of the present invention and an image forming apparatus including the optical scanning device will be described.
FIG. 28 is a schematic configuration diagram of a laser printer showing an example of an image forming apparatus according to the present invention. The laser printer 100 shown in FIG. 28 includes an optical scanning device 900, a photosensitive drum 901 as a scanning object, a charging charger 902, a developing roller 903 of a developing device, a toner cartridge 904, a cleaning blade 905 of a cleaning device, and a paper feed tray. 906, a paper feed roller 907, a registration roller pair 908, a transfer charger 911, a fixing roller 909, a paper discharge roller 912, a paper discharge tray 910, and the like.

  The charging charger 902, the developing roller 903, the transfer charger 911, and the cleaning blade 905 are disposed in the vicinity of the surface of the photosensitive drum 901, respectively. With respect to the rotation direction of the photosensitive drum 901, the charging charger 902, the developing roller 903, the transfer charger 911, and the cleaning blade 905 are arranged in this order.

A photosensitive layer is formed on the surface of the photosensitive drum 901 which is an image carrier. Here, the photosensitive drum 901 rotates clockwise (in the direction of the arrow) within the plane in FIG.
When image formation is started, the photosensitive drum 901 rotates, and the charging charger 902 charges the surface of the photosensitive drum 901 uniformly.

  The optical scanning device 900 irradiates the surface of the photosensitive drum 901 charged by the charging charger 902 with light modulated based on image information from a host device (for example, a personal computer). As a result, on the surface of the photosensitive drum 901, the charge is lost only in the portion irradiated with light, and a latent image corresponding to the image information is formed on the surface of the photosensitive drum 901. The latent image formed here moves in the direction of the developing roller 903 as the photosensitive drum 901 rotates.

  By the way, the longitudinal direction (direction along the rotation axis) of the photosensitive drum 901 is referred to as “main scanning direction”, and the rotational direction of the photosensitive drum 901 is referred to as “sub-scanning direction”. Of the scanning area in the main scanning direction from the scanning start position to the scanning end position on the photosensitive drum 901, an area where a latent image is formed is also referred to as an “effective image forming area”. The configuration of the optical scanning device 900 will be described later.

  The toner cartridge 904 attached to the developing device stores toner, and the toner is supplied to the developing roller 903. The amount of toner in the toner cartridge 904 is checked when the power is turned on or when printing is completed. When the remaining amount is low, a message prompting replacement is displayed on a display unit (not shown).

  As the developing roller 903 rotates, the toner supplied from the toner cartridge 904 is charged and thinly and uniformly attached to the surface thereof. Further, the developing roller 903 has an electric field in the opposite direction between a charged portion (a portion not irradiated with light) and an uncharged portion (a portion irradiated with light) in the photosensitive drum 901. A voltage is generated to generate. By this voltage, the toner adhering to the surface of the developing roller 903 adheres only to the portion irradiated with light on the surface of the photosensitive drum 901. That is, the developing roller 903 causes the toner to adhere to the latent image formed on the surface of the photosensitive drum 901 and visualizes the image information. Here, the latent image to which the toner is attached moves in the direction of the transfer charger 911 as the photosensitive drum 901 rotates.

  A recording sheet 913 as a transfer object is stored in the sheet feeding tray 906. A paper feed roller 907 is disposed in the vicinity of the paper feed tray 906. The paper feed roller 907 takes out the recording paper 913 one by one from the paper feed tray 906 and feeds it in accordance with the image forming operation described above. Then, it is conveyed to the registration roller pair 908. The registration roller pair 908 is disposed in the vicinity of the transfer roller 911, temporarily holds the recording paper 913 fed by the paper feeding roller 907, and the recording paper 913 is synchronized with the rotation of the photosensitive drum 901. It is sent out toward the gap between the drum 901 and the transfer charger 911.

  A voltage having a polarity opposite to that of the toner is applied to the transfer charger 911 in order to electrically attract the toner on the surface of the photosensitive drum 901 to the recording paper 913. With this voltage, the latent image on the surface of the photosensitive drum 901 is transferred to the recording paper 913. The recording sheet 913 transferred here is sent to the fixing roller 909.

  In the fixing roller 909, heat and pressure are applied to the recording paper 913, whereby the toner is fixed on the recording paper 913. The recording paper 913 fixed here is sent to the paper discharge tray 910 via the paper discharge roller 912 and sequentially stacked on the paper discharge tray 910.

  The cleaning blade 905 removes toner remaining on the surface of the photosensitive drum 901 (residual toner). The removed residual toner is used again. The surface of the photosensitive drum 901 from which the residual toner has been removed returns to the position of the charging charger 902 again, and enters a standby state for the next image formation.

  In the above example, the image forming apparatus is a laser printer. However, if it is configured to include a document image reading apparatus (scanner) or an image processing apparatus, it becomes a digital copier, and a communication function is added to a telephone line, If it is connected to an optical cable, LAN, etc., it can be used as a facsimile or a digital multi-function peripheral.

Next, the configuration and operation of the optical scanning device 900 will be described. FIG. 29 is a schematic configuration diagram showing an example of an optical scanning device 900 used in the image forming apparatus of FIG.
The optical scanning device 900 includes a light source means 20, a shaping optical system 24 including a coupling lens 21, an aperture 22, and a cylindrical lens 23, a light deflection means 25, and a scanning consisting of two scanning imaging lenses 26 and 27. A light beam detecting means 31 including an imaging optical system 28, a separation optical system 29, and a light detector 30, and a processing device (not shown) are provided.

  The light source means 20 generally uses a semiconductor laser as a single beam light source. Alternatively, a multi-beam light source may be used. In this case, as means for forming a plurality of light beams, a semiconductor laser array in which a plurality of semiconductor lasers are mounted close to each other, or a surface emitting laser array that has been developed recently ( VCSEL array) or the like is used.

The coupling lens 21 shapes the light emitted from the light source means 20 into substantially parallel light. Of course, it may be some convergent light or divergent light.
After a part of the light beam is shielded by the aperture 22, it is converged in the sub-scanning direction by the cylindrical lens 23, and is formed as a long line image in the vicinity of the deflection reflection surface of the light deflecting means 25 in the main scanning direction.

  The light deflecting means 25 is composed of, for example, a polygon mirror (rotating polygonal mirror) or a pyramid mirror that is rotationally driven by a motor. The light deflecting means 25 is rotationally driven to deflect and scan the light beam. A light spot is formed on a photosensitive drum 901 that is a surface to be scanned by a scanning imaging optical system 28 including imaging lenses 26 and 27.

A part of the light beam traveling outside the effective image forming area in the main scanning direction via the scanning imaging optical system 28 is incident on the light beam detecting means 31 arranged outside the effective image forming area, and the position of the light beam Is detected.
The light beam detecting means 31 performs so-called synchronous detection in which the position of the light beam in the main scanning direction is detected and the timing to the writing start position in the main scanning direction is adjusted.

Next, FIG. 30 shows a schematic configuration of the light beam detecting means of the optical scanning device shown in FIG. This shows one example in which the optical system of the present invention is used in an optical scanning device as a light beam detecting means. Hereinafter, the configuration and operation of the light beam detection means 31 will be described with reference to FIG.
A part of the light beam that goes out of the effective image forming area via the scanning imaging optical system 28 is a binary type diffractive optical element that is the separation optical system 29 (the diffraction of the optical system described in the first to fourth embodiments). Is incident on an optical element (any one of the diffractive optical elements of Examples 1 to 6), and is separated into two separated light beams C1 and C2 in the sub-scanning direction. The separated light beams C1 and C2 are detected by two photodetectors 30-1 and 30-2 arranged in the sub-scanning direction, respectively.

FIG. 31 shows a schematic configuration of the photodetector of the light beam detecting means shown in FIG. Hereinafter, the arrangement of the photodetectors will be described with reference to FIG.
The photodetectors 30-1 and 30-2 are arranged in the sub-scanning direction, and each of the photodetectors 30-1 and 30-2 performs slit-shaped light receiving unit 32-1 that performs photoelectric conversion on the light beam. , 32-2 are provided. In the embodiment of FIG. 31, the two photodetectors 30-1 and 30-2 are photodetectors having the same shape, but one photodetector 30-2 is disposed at an angle.

  The light beam deflected and scanned by the light deflecting means 25 is separated into two separated light beams C1 and C2 by a diffractive optical element 29 which is a separation optical system, and each photodetector 30-1 in the direction indicated by the arrow in FIG. , 30-2 are scanned and detected. As a result, so-called synchronous detection is performed in which the timing to the writing start position in the main scanning direction is adjusted using one photodetector 30-1, and beam detection means is used using the other photodetector 30-2. The position of the light beam incident on 31 can be detected in the sub-scanning direction.

  As described above, in the optical scanning device according to the present embodiment, the optical system using the diffractive optical element described in the above first to fourth embodiments is used as the separation optical system 29 of the light beam detecting unit 31. The position of the light beam in the sub-scanning direction can be detected. When a multi-beam light source is used as the light source means 20, the light beam interval in the sub-scanning direction can also be detected. It is possible to realize an optical scanning device for an image forming apparatus that is adapted to the realization.

[Example 6]
Next, another example of the image forming apparatus according to the present invention is shown in FIG. This image forming apparatus is an example of a multi-color tandem color printer in which four image forming units having substantially the same configuration as that in FIG. 28 are arranged side by side. The four image forming units basically have the same configuration except that toner colors (for example, yellow, magenta, cyan, and black) used for the developer are different. The configuration of one image forming unit will be described. Around the photosensitive drum 901 that is an image carrier, a charging charger 902 that charges the photosensitive drum 901 to a high voltage, and a light beam exposure unit from the optical scanning device 900. The developing roller 903 of the developing device that attaches the charged toner to the electrostatic latent image recorded by the exposure to make it visible, the toner cartridge 904 that replenishes the developing roller with toner, and the toner remaining on the photosensitive drum 901 A cleaning blade 905 of a cleaning device for scraping is disposed.

  Since the image forming apparatus of FIG. 32 includes four image forming units, the optical scanning device 900 includes the light source means 20 shown in FIG. 29, the coupling lens 21, the aperture 22, and the cylindrical lens 23. Four shaping optical systems 24 are provided, and one light deflection means 25 deflects and scans four light beams. In the optical path from the light deflection means 25 to the four photosensitive drums, four scanning imaging optical systems 28 including a common scanning imaging lens 26 and individual scanning imaging lenses 27 are provided. Each scanning imaging optical system includes a light beam detection means 31 including a separation optical system (diffractive optical element) 29 and a photodetector 30 as shown in FIGS.

  The four image forming units described above are arranged in parallel along the moving direction of the intermediate transfer belt 920, which is an intermediate transfer member (in the direction of the arrow in the figure), and these four image forming units provide yellow, magenta, cyan, and black. After each color toner image is formed on each photoconductive drum 901, primary transfer means (not shown) (transfer charger, transfer roller, transfer brush, etc. disposed on the back side of the belt at a position facing each photoconductive drum) As a result, the images are sequentially transferred onto the intermediate transfer belt 920 at the same timing, and superimposed to form a color image.

  On the other hand, the recording paper 913 is taken out one by one from the paper supply tray 921 by the paper supply roller 922, fed, and sent out by the registration roller pair 923 in accordance with the recording start timing in the sub-scanning direction. A toner image is transferred from the intermediate transfer belt 920 to the recording paper 913 by the secondary transfer roller 920 (secondary transfer roller, transfer brush, transfer charger, etc.). The unfixed toner image transferred to the recording paper 913 is fixed by the roller pair of the fixing device 925 and is discharged to the paper discharge tray 927 via the paper discharge roller 926. As described above, a color image is obtained.

In the example shown in FIG. 32, the intermediate transfer belt 920 is used. However, instead of the intermediate transfer belt, a transfer conveyance belt that conveys recording paper to each image forming unit is used, and the transfer conveyance belt is conveyed. In this case, the configuration of the color image forming apparatus can be simplified and miniaturized.
FIG. 32 shows an example of a tandem type color printer. If a document image reading device (scanner) or an image processing device is provided, a digital color copying machine is added, and a communication function is added to a telephone line, If connected to an optical cable, LAN, etc., it can be used as a color facsimile or digital color multifunction peripheral.

  In the color image forming apparatus of this embodiment, the optical system described in Embodiments 1 to 4 is separated from the optical system described in Embodiments 1 to 4 in the same manner as the optical scanning apparatus described with reference to FIGS. In particular, the light beam position in the sub-scanning direction can be detected by using the optical scanning device 900 used as a light source, and when the multi-beam light source is used as the light source means, the light beam interval in the sub-scanning direction is also detected. Therefore, a color image forming apparatus capable of high definition and high speed can be realized.

It is a schematic block diagram of the optical system which shows the 1st Example of this invention. It is a figure which shows the calculation result of the transmittance | permeability change accompanying the thickness change of a parallel plate. It is a figure which shows a mode that the laser beam perpendicularly incident on the diffractive optical element provided with the diffractive surface and the plane is isolate | separated into 0th order transmitted light and high order transmitted diffracted light by a diffractive surface. It is a figure which shows a mode that the laser beam perpendicularly incident on the diffractive optical element provided with the plane and the diffraction surface is isolate | separated into the 0th-order reflected light and the higher-order reflected diffracted light which were specularly reflected by the diffraction surface. It is a schematic diagram of the diffractive optical element provided with the diffraction surface and the plane. FIG. 6 is a diagram showing a change in transmittance (0th-order transmitted light diffraction efficiency) with respect to a change in thickness D of the diffractive optical element when a laser beam is vertically incident on the diffractive optical element in FIG. 5 from the diffraction surface side. It is a figure which shows the Fresnel reflectance with respect to each polarized light when a diffracted light injects into the plane which is an interface from the refractive index 1.5 of the diffractive optical element shown in FIG. 1 to refractive index 1.0. It is a figure which expands and shows the figure of the Fresnel reflectance of FIG. It is a schematic block diagram of the optical system which shows the 2nd Example of this invention. It is a schematic block diagram of the optical system which shows the 3rd Example of this invention. It is a figure which shows the 1st example of the diffractive optical element used for the optical system of FIG. FIG. 11 shows changes in transmittance (diffraction efficiency) of 0th-order transmitted light and −1st-order transmitted light with respect to changes in the thickness D of the diffractive optical element when a laser beam is incident on the diffractive surface side from the diffractive surface. FIG. It is a figure which shows the Fresnel transmittance | permeability with respect to each polarization | polarized-light when a diffracted light inject | emits from the plane which is an interface from the refractive index 1.5 of the refractive index 1.5 shown in FIG. 11 to the refractive index 1.0. It is a figure which expands and shows the figure of the Fresnel transmittance | permeability of FIG. It is a figure which shows the 2nd example of the diffractive optical element used for the optical system of FIG. FIG. 15 shows changes in transmittance (diffraction efficiency) of 0th-order transmitted light and −1st-order transmitted light with respect to changes in the thickness D of the diffractive optical element when a laser beam is incident on the diffractive surface from the diffractive surface side. FIG. It is a figure which shows the 3rd example of the diffractive optical element used for the optical system of FIG. FIG. 17 shows changes in the transmittance (diffraction efficiency) of the 0th-order transmitted light and the −first-order transmitted light with respect to the change in the thickness D of the diffractive optical element when a laser beam is incident on the diffractive surface side from the diffractive optical element shown in FIG. FIG. It is a figure which shows the 4th example of the diffractive optical element used for the optical system of FIG. FIG. 19 shows changes in transmittance (diffraction efficiency) of 0th-order transmitted light and −1st-order transmitted light with respect to changes in the thickness D of the diffractive optical element when a laser beam is incident on the diffractive surface from the diffractive surface side. FIG. It is a schematic block diagram of the optical system which shows the 4th Example of this invention. It is a figure which shows an example of the diffractive optical element used for the optical system of FIG. The figure which shows the transmittance | permeability (diffraction efficiency) change of 0th order transmitted light with respect to the change of the thickness D of a diffractive optical element when a laser beam injects into the diffractive optical element shown in FIG. 22 from the plane side. It is. It is a figure which shows the Fresnel transmittance | permeability with respect to each polarization | polarized-light when a diffracted reflected light injects into the plane which is the interface from the refractive index 1.5 of the diffractive optical element shown in FIG. 22 to refractive index 1.0. It is a figure which expands and shows the figure of the Fresnel transmittance | permeability of FIG. It is a figure which shows another example of the diffractive optical element used for the optical system of FIG. The figure which shows the transmittance | permeability (diffraction efficiency) change of the 0th-order transmitted light with respect to the change of the thickness D of a diffractive optical element when a laser beam injects into the diffractive optical element shown in FIG. 26 from the plane side. It is. 1 is a schematic configuration diagram of a laser printer showing an example of an image forming apparatus according to the present invention. It is a schematic block diagram which shows an example of the optical scanning device used for the image forming apparatus of FIG. FIG. 30 is a cross-sectional view in the sub-scanning direction showing a schematic configuration of a light beam detecting unit of the optical scanning device shown in FIG. 29. It is a figure which shows schematic structure and the example of arrangement | positioning of the photodetector of the light beam detection means shown in FIG. It is a schematic block diagram of the tandem type image forming apparatus which shows another example of the image forming apparatus which concerns on this invention.

Explanation of symbols

20: Light source means 21: Coupling lens 22: Aperture 23: Cylindrical lens 24: Shaping optical system 25: Light deflection means 26, 27: Scanning imaging lens 28: Scanning imaging optical system 29: Separation optical system (diffractive optical element) )
30 (30-1, 30-2): light detector 31: light beam detection means 32-1, 32-2: light receiving unit 100: laser printer (image forming apparatus 900: optical scanning device 901: photosensitive drum (image) Carrier)
902: Charging charger 903: Developing roller 904: Toner cartridge 905: Cleaning blade 906: Paper feed tray 907: Paper feed roller 908: Registration roller pair 909: Fixing roller 910: Paper discharge tray 911: Transfer charger 912: Paper discharge roller 913 : Recording paper 920: Intermediate transfer belt (intermediate transfer member)
921: Paper feed tray 922: Paper feed roller 923: Registration roller pair 924: Secondary transfer means 925: Fixing device 926: Paper discharge roller 927: Paper discharge tray

Claims (3)

In an optical scanning device that deflects a light beam from a light source means by a light deflecting means and scans a surface to be scanned via a scanning imaging optical system ,
Laser beam detecting means disposed outside the effective image forming area of the scanning imaging optical system, wherein a part of the laser beam is incident on a diffractive optical element, and a plurality of separated laser beams are detected by a plurality of photodetectors. Prepared,
The diffractive optical element is a flat diffractive optical element having a diffractive surface and a plane,
The laser beam is incident on a diffractive surface of the diffractive optical element, is transmitted and diffracted into two or more laser beams on the diffractive surface, and the two or more laser beams are incident on a plane of the diffractive optical element;
All laser beams incident on the plane of the diffractive optical element are P-polarized light, and each incident angle θ is
0 ° <θ < θo
(Here, .theta.o, when the Fresnel reflectance of P Henhikariji at the incident angle alpha was Rp (α), Rp (0 °) = the incident angle becomes Rp (.theta.o))
An optical scanning device that is set to satisfy the above. In an image forming apparatus comprising: an image carrier; means for forming a latent image on the image carrier; and means for developing and developing the latent image on the image carrier .
An image forming apparatus comprising the optical scanning device according to claim 1 as means for forming the latent image . The image forming apparatus according to claim 2.
A plurality of the image carriers are formed, latent images are formed on the plurality of image carriers, and the latent images on the image carriers are visualized with developers of different colors, and then visualized images on the image carriers. An image forming apparatus for transferring a color to a recording medium directly or using an intermediate transfer member to form a multicolor or color image .

Images