JPH11271656A - Optical scanning optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical scanning optical device for reducing a spot diameter without losing light quantity, reducing the increase and decrease of a focus depth, eliminating light quantity fluctuation even in the case of varying the spot diameter of a luminous flux and mitigating the fluctuation of the focus depth as well. SOLUTION: The luminous flux optically modulated and emitted from a light source means 1 corresponding to image signals is led to a deflection means 6, the luminous flux deflected by the deflection means 6 is led through an image formation means 7 onto a recording medium surface 8 and the recording medium surface 8 is scanned. In this case, a light beam control means 4 is provided in an optical path between the light source means 1 and the deflection means 6 and the light beam control means 4 performs shaping to the luminous flux in a ring belt shape for which the light intensity distribution of the luminous flux emitted from there becomes strong at a peripheral part compared to the vicinity of an optical axis and varies the shape of the luminous flux in the ring belt shape based on control information.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning optical device, and more particularly to a light scanning optical device, wherein a beam shape of a light beam emitted from a light source is effectively shaped by using a light beam controller having two optical elements. The present invention relates to an optical scanning optical device suitable for an apparatus such as a laser beam printer (LBP) having an electrophotographic process or a digital copier, which can optically scan the surface to be scanned with a light beam having a spot diameter of.

[0002]

2. Description of the Related Art As means for varying the spot diameter of a light beam (light beam) (spot diameter variable means), means for changing the diameter of a light beam is conventionally known. For example, such means as blades used in cameras and the like are known. There is an aperture.

[0003] The vane diaphragm varies the diaphragm diameter of a light beam by mechanically controlling a plurality of vanes having a predetermined shape. An aperture is formed by the plurality of vanes, and the formed aperture is formed. The aperture diameter of the luminous flux is adjusted by rotating and adjusting the area and the plurality of blade plates.

[0004] With such a blade stop, the spot diameter of a light beam imaged on a photoreceptor surface of a laser printer or the like is adjusted to a predetermined shape and size by adjusting the aperture area by the blade stop. You.

FIG. 6 is a schematic view of a main part of a conventional optical scanning optical apparatus using the blade stop. In the figure, reference numeral 61 denotes a semiconductor laser as light source means, and 62 denotes a collimator lens, which converts a light beam emitted from the light source means 61 into a substantially parallel light beam. 63 is an aperture member (aperture stop),
The size of the cross section of the light beam is adjusted. Reference numeral 73 denotes a blade diaphragm composed of a plurality of blade plates.

A spot diameter varying means using a liquid crystal shutter instead of the above-mentioned blade diaphragm is also known. In this spot diameter varying means, the diameter of the aperture of the light beam is adjusted by electrically controlling the light transmitting portion of the liquid crystal shutter.

[0007]

However, the above-mentioned conventional spot diameter varying means has the following various problems.

First, in the spot diameter changing means using a blade diaphragm, since an opening is formed by a plurality of blade plates, if the shape of the opening is made to be nearly circular, the number of blade plates increases. As a result, there is a problem that the aperture mechanism becomes complicated. Further, there is also a problem that only a circular stop can be supported due to the configuration, and it is difficult to change the stop diameter of the elliptical stop.

On the other hand, the spot diameter varying means using a liquid crystal shutter has a problem that the absolute light quantity is reduced by a polarizing plate or the like which is present when passing through the liquid crystal shutter. There is also a problem that the liquid crystal shutter itself is expensive.

Further, the following problems common to the above-mentioned spot diameter varying means can be cited.

First, in order to change the aperture diameter of the light beam,
The amount of light reaching the recording medium also changes according to the spot diameter of the light beam. For example, when the spot diameter is doubled, the light amount is reduced to 1/4, which greatly changes the characteristics of the recording medium. Conversely, when adjusting the light amount of the light source so as to keep the light amount on the recording medium constant, in a laser beam printer using a semiconductor laser as a light source, for example,
It is very difficult to change the light emission power of the semiconductor laser in a quadruple range.

Second, if the beam shape of the light beam is made variable by changing the aperture, the depth of focus for maintaining a desired spot diameter greatly changes depending on the spot diameter of the light beam. Therefore, in this case, it is necessary to adopt a configuration capable of maintaining the optical performance in the state where the depth of focus is always the narrowest, usually in the state where the spot diameter is the smallest. For example, in a system that employs an adjustment mechanism such as AF (autofocus), it is necessary to focus a minute range with high accuracy when the spot diameter is small. It is necessary to perform focusing with coarse precision. Therefore, the AF mechanism is required to have optical performance for focusing a wide range with high precision, resulting in excessive performance and high cost.

According to the present invention, a light beam control means having first and second optical elements is provided in an optical path between a light source means and a deflecting means, and a light beam emitted from the light source means is effectively shaped. Accordingly, an object of the present invention is to provide an optical scanning optical device capable of obtaining a high-quality image by reducing the spot diameter and reducing the increase / decrease of the depth of focus without losing the light amount.

Further, according to the present invention, by changing the relative distance between the first and second optical elements based on the control information,
An optical scanning optical device that can change the shape of the annular light beam emitted from the light beam control means, and also has a small amount of light fluctuation even when the shape of the light beam is variable, can remarkably reduce the fluctuation of the depth of focus. For the purpose of providing.

[0015]

According to the present invention, there is provided an optical scanning optical device comprising: (1) a light beam which is light-modulated from a light source means in accordance with an image signal and guided to a deflecting means, and is deflected by the deflecting means; In an optical scanning optical device that guides a light beam onto a recording medium surface via an imaging unit and scans the recording medium surface, a light beam control unit is provided in an optical path between the light source unit and the deflection unit. The light beam control means shapes the light intensity distribution of the light beam emitted therefrom into an annular light beam that becomes stronger at the periphery compared to the vicinity of the optical axis, and shapes the annular light beam based on the control information. It is characterized by being variable.

In particular, (1-1) the light beam control means deflects the incident light beam at a predetermined angle around the optical axis, and a second optical element which deflects the deflected light beam around the optical axis again.
By changing the relative distance between the first and second optical elements based on the control information,
(1-2) a first optical system that deflects an incident light beam to a predetermined angle around an optical axis, wherein the shape of the annular light beam emitted from the light beam control means is variable; An element and a second optical element for deflecting the deflected light beam around the optical axis again, and by changing a relative distance between the first and second optical elements based on the control information, The shape of the annular light beam emitted from the light beam control means is changed, and the shape of the light beam in the vicinity of the optical axis where the light intensity distribution is weaker than in the peripheral portion due to the change in the shape of the light beam is changed. (1-3) the first and second optical elements are each composed of a prism rotationally symmetric with respect to the optical axis; and (1-4) the first and second optical elements are optical (1-5) The control information is based on the scanning line density. And it is the image information, (1
-6) the control information is information on a change with time of the recording medium, and (1-7) the first and second optical elements are manufactured from a substrate made of the same type of material. , (1-
8) An aperture stop for restricting a light beam on the outer periphery is provided on a part of the element surface of the first optical element, and (1-9) the light beam control means is provided with an orbicular light beam shape and / or a peripheral light beam. It is characterized in that the shape of the light flux near the optical axis, whose light intensity distribution is weaker than that of the portion, is shaped into an arbitrary shape.

(2) The light flux modulated and emitted from the light source means in accordance with the image signal is guided to the deflecting means, and the light flux deflected by the deflecting means is guided to the recording medium surface via the imaging means. A scanning optical device for scanning the recording medium surface, wherein a light beam control means having first and second optical elements is provided in an optical path between the light source means and the deflection means; The means shapes the light intensity distribution of the light beam emitted therefrom into an annular light beam that becomes stronger at the peripheral portion as compared with the vicinity of the optical axis, and based on the control information, the relative distance between the first and second optical elements. , The shape of the annular light beam emitted from the light beam control means is made variable.

(3) A light beam modulated and emitted from the light source means in accordance with the image signal is guided to the deflecting means, and the light beam deflected by the deflecting means is guided to the recording medium surface via the image forming means. A scanning optical device for scanning the recording medium surface, wherein a light beam control means having first and second optical elements is provided in an optical path between the light source means and the deflection means; The means shapes the light intensity distribution of the light beam emitted therefrom into an annular light beam that becomes stronger at the peripheral portion as compared with the vicinity of the optical axis, and based on the control information, the relative distance between the first and second optical elements. Is changed, the shape of the annular light beam emitted from the light beam control means is changed, and the light intensity distribution of the light beam near the optical axis whose light intensity distribution is weaker than the peripheral portion due to the change in the shape of the light beam is changed. The feature is that the shape is changed.

In particular, in the above (2) and (3), (4-1) the first
The optical element deflects the incident light beam around the optical axis at a predetermined angle, and the second optical element deflects the deflected light beam around the optical axis again; (4-2) The first,
Each of the second optical elements is composed of a prism rotationally symmetric with respect to the optical axis, and (4-3) the first and second optical elements are each composed of a diffractive optical element concentric with the optical axis. And (4
-4) the control information is switching information of the scanning line density, (4-5) the control information is information of the temporal change of the recording medium, (4-6) the first, the The second optical element is manufactured from a substrate made of the same kind of material, and (4-7) an aperture stop is provided on a part of the element surface of the first optical element to regulate a light flux on an outer periphery. (4-8) that the light beam control means shapes the shape of the annular light flux or / and the shape of the light flux near the optical axis where the light intensity distribution is weaker than the peripheral portion into an arbitrary shape. , Etc.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG. 1 is a schematic view of a main part of an optical system of an optical scanning optical device according to a first embodiment of the present invention.
FIGS. 2A and 2B are enlarged explanatory views of a part of FIG. 1, respectively, showing how the light beam control means shapes the beam shape of the light beam emitted from the light source means.

In FIG. 1, reference numeral 1 denotes a light source means, which is composed of, for example, a semiconductor laser. A collimator lens 2 converts a light beam (light beam) emitted from the light source 1 into a substantially parallel light beam. Reference numeral 3 denotes an aperture member (aperture stop) for adjusting the size of the cross section of the light beam.

4 is a light beam control means (aperture variable element)
And a first diffractive optical element 9 as a first optical element for deflecting the incident parallel light beam converted by the collimator lens 2 around the optical axis at a predetermined angle, and re-deflects the deflected light beam to the optical axis. And a second diffractive optical element 10 as a second optical element for deflecting the light into a parallel light beam around the light beam. The light intensity distribution of the light beam emitted from the light beam control means 4 is smaller in the peripheral portion than in the vicinity of the optical axis. It is shaped into an intense orbicular luminous flux.

Further, the light beam control means 4 changes the relative distance between the first and second diffractive optical elements 9 and 10 based on control information to be described later.
The shape (spot diameter) of the annular light beam emitted from the lens is variable. That is, the light beam control means 4 changes the shape of the annular light flux emitted from the light beam control means 4 based on the control information, and the light intensity distribution is weaker than the peripheral portion due to the change in the shape of the light flux. The shape of the light beam near the optical axis is changed.

Reference numerals 11 and 12 denote first and second diffraction gratings of the first and second diffractive optical elements 9 and 10, respectively.

Reference numeral 5 denotes a cylindrical lens having a predetermined refractive power only in the sub-scanning direction. Reference numeral 6 denotes an optical deflector, which is formed of, for example, a polygon mirror, and is rotated at a constant speed in the direction of arrow A by driving means (not shown) such as a motor. Reference numeral 7 denotes an imaging optical system (fθ lens system) having fθ characteristics as an imaging means, which is composed of a single toric lens, and which receives a light beam deflected by the optical deflector 6 as a photosensitive drum 8 as a recording medium. An image is formed on a surface (on a surface to be scanned).

In the present embodiment, the light beam emitted from the light source means 1 after being modulated in accordance with the image signal is converted into a substantially parallel light beam by the collimator lens 2, and the size of the cross section of the light beam is shaped by the aperture member 3. The light enters the light beam control means 4. The light beam control means 4 shapes the beam of light emitted from the light beam control means 4 into a ring-shaped (ring-shaped) light flux that is stronger at the periphery than at the vicinity of the optical axis. Incident on. Of the substantially parallel light beams incident on the cylindrical lens 5, the light beams are emitted as they are in the state of substantially parallel light beams in the main scanning section. In the sub-scan section, the light converges and forms a substantially linear image on the deflection surface (reflection surface) 6a of the optical deflector 6. The light beam deflected and reflected by the light deflector 6 is condensed on the surface of the photosensitive drum 8 via the imaging optical system 7, and the light deflector 6 is rotated in the direction of arrow A in FIG. The surface is scanned at a constant speed in the direction of arrow B (main scanning direction) in the figure. Thus, an image is recorded on the surface of the photosensitive drum 8 as a recording medium.

Next, the means for beam shaping the light beam emitted from the light source means by the light beam control means into an annular light beam will be described with reference to FIGS. 2 (A) and 2 (B).

In FIG. 2A, the light beam emitted from the semiconductor laser 1 is converted into a substantially parallel light beam by the collimator lens 2 as described above, and the size of the cross section of the light beam (outer diameter of the light beam) is changed by the stop member 3. Be regulated. The aperture member 3 suppresses variations in the spot diameter due to variations in the radiation angle of the light beam, so that a stable spot diameter can be obtained under constant control conditions. Thereafter, the light is incident on a first diffractive optical element 9 constituting the light beam control means 4, and the first diffractive optical element 9 spreads a substantially parallel light beam radially around the optical axis while maintaining a predetermined angle. become. Then, the radiated light beam enters the second diffractive optical element 10 and is converted again into a light beam substantially parallel to the optical axis. As a result, the light intensity distribution of the light beam emitted from the light beam control means 4 becomes a ring-shaped (ring-shaped) light beam that is stronger at the peripheral portion than near the optical axis. The light flux near the optical axis where the light intensity distribution is weaker than the peripheral part is hereinafter referred to as “dark part light flux”.

Here, the first and second diffractive optical elements 9 and 10
By arbitrarily selecting the deflection angle and the relative interval of the light beam, the maximum diameter (b in the figure) of the light beam emitted from the light beam control means 4 and the diameter of the dark part (a in the figure) can be arbitrarily shaped. .

Next, the means for changing the shape of the annular light flux emitted from the light beam control means will be described.

In this embodiment, the first diffractive optical element 9 and the second diffractive optical element 10 are moved relative to each other by a driving mechanism such as a motor (not shown) based on control information (variable spot diameter information) described later. Change the typical distance. As the relative distance decreases, the maximum diameter b of the light beam and the dark part diameter a monotonically decrease by the same amount. That is, the beam shape of the light beam emitted from the light beam control means 4 is changed while keeping the value of (ba) constant. As a result, the light flux emitted from the light beam control means 4 is always maintained at a constant light amount. When the relative distance finally becomes zero, that is, when the state shown in FIG. 2B is reached, the incident light flux becomes an emission light flux having the same maximum diameter as the incident light flux having no dark portion.

FIGS. 3A and 3B show light beam control means 4.
1 shows the shapes of the first and second diffractive optical elements 9 and 10 constituting the above.

The first and second diffractive optical elements 9 and 10 in the present embodiment both have a function of bending an incident light beam to a desired angle, and have no optical function such as condensing or diverging. Therefore, as shown in FIGS. 9A and 9B, the grating pitch of each of the diffraction gratings 11 and 12 in both the first and second diffractive optical elements 9 and 10 is a concentric circle centered on the equal pitch optical axis. In FIGS. 7A and 7B, the grating shapes of the first and second diffractive optical elements 9 and 10 are stepped gratings, respectively. However, this is not particularly limited. The present invention can be sufficiently applied to a sawtooth diffraction grating.

Next, a specific example will be described. In the present embodiment, switching information of the scanning line density is used as control information (variable spot diameter information). Here, for example, 300
Consider switching of the scanning line density of / 600 dpi. At this time, it is desirable that the spot diameter is 84.7 μm at 300 dpi and 42.3 μm at 600 dpi.

Generally, the spot diameter has a relationship of φ ₁ = K · F · λ. Here, F is the F number of the imaging optical system, λ is the wavelength used, and K is a factor due to the light amount distribution in the aperture.
In the case of a uniform light beam, K = 1.64, and in the case of a Gaussian beam whose 1 / e ² diameter coincides with the aperture end, K = 1.86. In the present embodiment, it is assumed that K = 1.7 for simplicity,
The following is described.

If the focal length of the imaging optical system is f = 300 mm,

[0037]

(Equation 1) (Used wavelength λ = 0.67 μm), b = 8.0
7 mm. Similarly,

[0038]

(Equation 2) Thus, a = 4.04 mm. Therefore, the aperture of the diaphragm member 3 may be set so that φ = 4.04 mm as the incident light beam.

Next, when the spot diameter is 600 dpi, it becomes the minimum, and the interval t between the first diffractive optical element 9 and the second diffractive optical element 10 becomes the maximum. The maximum interval t is 20 m
m, the diffraction angle θ is

[0040]

(Equation 3) Becomes If the laser wavelength is, for example, λ = 675 nm,
The lattice pitch P is obtained from Psin θ = mλ (m is an integer, in this embodiment, m = 1).

[0041]

(Equation 4) Becomes

Actually, the value of the above-described factor K changes depending on the shape of the annular zone, so the shape may be determined in consideration of these factors. In this case, the spot diameter is substantially proportional to the maximum aperture diameter, and the depth of focus is the F-number f /
Since it depends on (ba), the spot diameter (spot shape) can be made variable while the depth of focus remains substantially constant.

As described above, in this embodiment, the light beam control means 4 having the first and second diffractive optical elements 9 and 10 is provided in the optical path between the semiconductor laser 1 and the optical deflector 6 as described above. By effectively shaping the light beam emitted from the semiconductor laser 1, the spot diameter is reduced, and the increase / decrease in the depth of focus is reduced without loss of light amount, thereby obtaining a high quality image.

Further, in the present embodiment, by changing the relative distance between the first and second diffractive optical elements 9 and 10 based on the control information as described above, the annular shape emitted from the light beam control means 4 is obtained. Can be made variable, and even when the shape of the light beam is made variable, the fluctuation of the light amount is small and the fluctuation of the depth of focus can be remarkably reduced.

In this embodiment, both the first and second optical elements are constituted by diffractive optical elements. However, the present invention is not limited to this. For example, the first and second optical elements are constituted by prisms (axicon prisms) rotationally symmetric with respect to the optical axis. Even so, the present invention can be applied in the same manner as in the first embodiment.

(Second Embodiment) FIG. 4 is a schematic view of a main part of a main part from a light source means to a light beam control means according to a second embodiment of the present invention. 2, the same elements as those shown in FIG. 2 are denoted by the same reference numerals.

The present embodiment differs from the first embodiment in that an aperture stop for restricting a light beam on the outer surface is provided on the incident surface side of the substrate, that is, on a part of the element surface (diffraction grating surface) of the first diffractive optical element 9. (Opening portion) 43 is provided and integrated with the light beam control means 44. Other configurations and optical functions are substantially the same as those of the first embodiment, and thus the same effects are obtained.

That is, in the figure, reference numeral 44 denotes light beam control means, which has first and second diffractive optical elements 9 and 10. Reference numeral 43 denotes an aperture stop provided on a part of the element surface of the first diffractive optical element 9, which is formed on the substrate by means such as vapor deposition or the like, and regulates the light flux on the outer periphery.

As described above, in this embodiment, since the aperture stop 43 is provided on a part of the element surface of the first diffractive optical element 9, the number of components can be further reduced, and the single diffractive optical element 9 can be manufactured with high accuracy. As a result, an inexpensive and high-performance optical scanning optical device is obtained.

(Third Embodiment) Next, a third embodiment of the present invention will be described.

The present embodiment is different from the first embodiment in that the first diffractive optical element and the second diffractive optical element are manufactured using the same material (substrate). Other configurations and optical functions are substantially the same as those of the first embodiment, and thus the same effects are obtained.

As described above, in this embodiment, the first and second diffractive optical elements are manufactured from substrates made of the same kind of material, so that the first and second diffraction gratings have the same grating thickness. For example, when manufacturing the shape of the diffraction grating using a mold or the like, the number of steps for manufacturing the mold can be reduced by half. In addition, the adverse effects caused when the substrate of the first and second diffractive optical elements expands due to a rise in temperature and the pitch of the diffraction grating changes can be minimized.

(Fourth Embodiment) Next, a fourth embodiment of the present invention will be described.

The present embodiment differs from the first embodiment in that the control information (variable spot diameter information) is used as information on the change over time of the photosensitive drum as a recording medium.
Other configurations and optical functions are substantially the same as those of the first embodiment, and thus the same effects are obtained.

That is, the control information in the first embodiment is the switching information of the scanning line density. However, the present invention is not limited to this. For example, the fluctuation of the latent image spot at the same exposure spot diameter due to deterioration of the durability of the photosensitive drum is corrected. The present invention can be applied in the same manner as in the first embodiment even if information from means is used. In this case, if the configuration is such that the deterioration of the photosensitive drum is estimated from a potential sensor or the like provided in the vicinity of the photosensitive drum and the diameter of the exposure spot that is irradiated is changed so as to be the same spot at the latent image level, long-term use It is possible to obtain a highly durable optical scanning device capable of obtaining a stable image later.

(Fifth Embodiment) FIG. 5 is a schematic view of a main part of a main part from a light source means to a light beam control means according to a fifth embodiment of the present invention. 2, the same elements as those shown in FIG. 2 are denoted by the same reference numerals.

This embodiment differs from the first embodiment in that the grating pitch of the first and second diffractive optical elements 59 and 60 is arbitrarily changed, so that the light beam control means 54 is changed.
Shape of the luminous flux emitted from the lens (zonal shape) or /
Near the optical axis where the light intensity distribution is weaker than at the periphery and at the periphery (dark part)
Is that the shape of the light beam is elliptical. Other configurations and optical functions are substantially the same as those in the first embodiment,
Thereby, a similar effect is obtained.

That is, in the figure, reference numeral 54 denotes light beam control means, which has a first diffractive optical element 59 and a second diffractive optical element 60, and the first and second diffractive optical elements 59, 6
By appropriately setting the grating pitch of 0, the shape of the annular light beam emitted from the light beam control means 54 and / or the light beam near the optical axis (dark portion) where the light intensity distribution is weaker than the peripheral portion Is shaped other than circular.

That is, in each of the above-described embodiments, the shape of the light beam is all rotationally symmetric, and is composed of a circular orbicular portion and a dark portion. However, the present invention is not limited to this. As shown, the shape of the light beam on the input side may be a circular shape, and the shape of the light beam on the output side may be an elliptical orbicular opening.

In this embodiment, unlike a normal optical system,
By arbitrarily changing the pitch of the first and second diffractive optical elements 59 and 60 as described above, the shape of the light beam is changed from a circle to an ellipse. By shaping the shape of the light beam into an elliptical orbicular shape in this manner, the present invention can obtain substantially the same effects as those of the above-described embodiments.

Of course, in addition to those shown in FIG. 5, various combinations of luminous flux shapes such as an elliptical entrance side and a circular exit side, a circular orbicular zone and an elliptical dark area are also conceivable. Here, all combinations are not described. For these parameters, an optimum configuration can be selected based on the radiation angle of the light beam and its variation, the imaging magnification of the optical system in the main scanning direction and the sub-scanning direction, the desired spot diameter, and the like.

[0062]

According to the present invention, as described above, a light beam control means having first and second optical elements is provided in the optical path between the light source means and the deflecting means, and a light beam emitted from the light source means is provided. By effectively shaping the beam, it is possible to achieve an optical scanning optical device capable of obtaining a high-quality image by reducing the spot diameter and reducing the increase and decrease in the depth of focus without losing the amount of light.

Further, according to the present invention, by changing the relative distance between the first and second optical elements based on the control information as described above, the shape of the annular light beam emitted from the light beam control means can be changed. It is possible to achieve an optical scanning optical device which can be made variable, and in which even when the shape of the light beam is made variable, the fluctuation of the light amount is small and the fluctuation of the depth of focus can be remarkably reduced.

[Brief description of the drawings]

FIG. 1 is a schematic view of a main part of a first embodiment of the present invention.

FIG. 2 is a schematic diagram of a main part of a main part according to the first embodiment of the present invention.

FIG. 3 is an enlarged explanatory view of first and second diffractive optical elements according to the first embodiment of the present invention.

FIG. 4 is a schematic diagram of a main part of a second embodiment of the present invention.

FIG. 5 is a schematic diagram of a main part of a fifth embodiment of the present invention.

FIG. 6 is a schematic view of a main part of a conventional optical scanning optical device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light source means 2 Collimator lens 3 Aperture member (aperture stop) 4, 44, 54 Light beam control means 5 Cylindrical lens 6 Deflection means (polygon mirror) 7 Imaging means 8 Recording medium (photosensitive drum) 9, 59 First Diffractive optical element 10, 60 Second diffractive optical element 11, 51 First diffraction grating 12, 52 Second diffraction grating

Claims (20)

[Claims] 1. A light flux modulated and emitted from a light source means in accordance with an image signal and guided to a deflecting means, and the light flux deflected by the deflecting means is guided to a recording medium surface via an imaging means. An optical scanning optical device that scans the surface of the recording medium, wherein a light beam control means is provided in an optical path between the light source means and the deflection means, and the light beam control means controls the light intensity of a light beam emitted therefrom. An optical scanning optical device characterized in that the distribution is shaped into a ring-shaped light beam whose distribution is stronger at the peripheral portion than in the vicinity of the optical axis, and the shape of the ring-shaped light beam is variable based on control information. A first optical element for deflecting the incident light beam at a predetermined angle around the optical axis; and a second optical element for deflecting the deflected light beam around the optical axis again. And changing the relative spacing between the first and second optical elements based on the control information to change the shape of the annular light flux emitted from the light beam control means. The optical scanning optical device according to claim 1. A first optical element for deflecting the incident light beam around the optical axis at a predetermined angle, and a second optical element for deflecting the deflected light beam around the optical axis again. And changing the relative spacing between the first and second optical elements based on the control information to change the shape of the annular light beam emitted from the light beam control means, and 2. The optical scanning optical device according to claim 1, wherein the shape of the light flux near the optical axis, the light intensity distribution of which is weaker than the peripheral portion, is changed with the change of the shape. 4. The optical scanning optical device according to claim 2, wherein each of said first and second optical elements comprises a prism rotationally symmetric with respect to an optical axis. 5. The optical scanning optical device according to claim 2, wherein each of the first and second optical elements comprises a diffractive optical element concentric with the optical axis. 6. The optical scanning optical apparatus according to claim 1, wherein the control information is switching information of a scanning line density. 7. The optical scanning optical device according to claim 1, wherein the control information is information on a temporal change of the recording medium. 8. The optical scanning optical device according to claim 4, wherein said first and second optical elements are manufactured from substrates made of the same kind of material. 9. An optical scanning optical apparatus according to claim 4, wherein an aperture stop for restricting a light beam on an outer periphery is provided on a part of an element surface of said first optical element. 10. The light beam control means shapes the shape of an annular light beam and / or the shape of a light beam in the vicinity of an optical axis having a light intensity distribution weaker than that of a peripheral portion into an arbitrary shape. The optical scanning optical device according to claim 1, 2 or 3, wherein 11. A light flux modulated and emitted from a light source means in accordance with an image signal and guided to a deflecting means, and the light flux deflected by the deflecting means is guided to a recording medium surface via an image forming means. A scanning optical device for scanning over the recording medium surface, comprising: a light beam control means having first and second optical elements in an optical path between the light source means and the deflection means; Is shaped into a zonal luminous flux in which the luminous intensity of the luminous flux emitted therefrom becomes stronger in the peripheral part than in the vicinity of the optical axis, and based on the control information, the relative distance between the first and second optical elements is adjusted. An optical scanning optical device characterized in that the shape of an orbicular light beam emitted from the light beam control means is made variable by changing. 12. A light beam modulated and emitted from a light source means in accordance with an image signal and guided to a deflecting means, and the light beam deflected by the deflecting means is guided to a recording medium surface via an image forming means. A scanning optical device for scanning over the recording medium surface, comprising: a light beam control means having first and second optical elements in an optical path between the light source means and the deflection means; Is shaped into a zonal luminous flux in which the luminous intensity of the luminous flux emitted therefrom becomes stronger in the peripheral part than in the vicinity of the optical axis, and based on the control information, the relative distance between the first and second optical elements is adjusted. By changing the shape, the shape of the luminous flux emitted from the light beam control means is changed, and the shape of the luminous flux in the vicinity of the optical axis where the light intensity distribution is weaker than the peripheral portion due to the change in the shape of the luminous flux Optical scanning optics characterized by varying Location. 13. The first optical element deflects an incident light beam at a predetermined angle around an optical axis, and the second optical element deflects the deflected light beam around the optical axis again. 13. The optical scanning optical device according to claim 11, wherein: 14. The optical scanning optical device according to claim 13, wherein each of said first and second optical elements comprises a prism rotationally symmetric with respect to an optical axis. 15. The optical scanning optical device according to claim 13, wherein said first and second optical elements are composed of diffractive optical elements concentric with respect to an optical axis. 16. The optical scanning optical device according to claim 11, wherein the control information is switching information of a scanning line density. 17. The optical scanning optical device according to claim 11, wherein the control information is information on a temporal change of the recording medium. 18. The optical scanning optical device according to claim 14, wherein the first and second optical elements are manufactured from substrates made of the same kind of material. 19. The optical scanning optical device according to claim 14, wherein an aperture stop for restricting a light beam on an outer periphery is provided on a part of an element surface of said first optical element. 20. The light beam control means according to claim 1, wherein the shape of the annular light beam and / or the shape of the light beam near the optical axis having a light intensity distribution weaker than that of the peripheral portion is shaped into an arbitrary shape. 13. The optical scanning optical device according to claim 11, wherein: