JPS63165815A - Optical scanner - Google Patents

Abstract

PURPOSE:To reduce the influence of uneven cutting to be exerted upon a scanning mirror surface by arranging a 1st slit having long sides in an optical beam scanning direction and short sides in its rectangular direction between a scanning mirror and an image forming optical system and arranging a 2nd slit in front of an image forming face. CONSTITUTION:In the optical scanner, a slit A is arranged between a polygon mirror 9 and an image formation lens 10 and a slit B is arranged between the lens 10 and a recording film 11. The slits A, B are the means for restricting diffraction beam component in the direction intersecting with the scanning direction and their aperture are formed so as to have long sides in the scanning direction and short sides in the intersecting direction. When laser beams are radiated from a light source 1 to the polygon mirror 9, diffraction is generated by the uneven cutting work on the reflecting face of the mirror 9, but the influence of the uneven cutting to be exerted upon the scanning mirror surface can be reduced by arranging the slits A, B for transmitting 0th-order diffraction light.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical scanning device, for example, an optical scanning device for optical recording with a laser beam.

[Conventional technology]

Conventionally, this type of optical scanning device has reduced unevenness in the sub-scanning direction intersecting the main scanning direction by incorporating a tilt correction optical system.

[Problem that the invention seeks to solve]

However, it causes a change in the intensity distribution of the scanning mirror beam, which uses a metal surface as a mirror surface. In other words, since the imaging lens (Fθ lens) behind the scanning mirror has only a finite aperture angle, for example, if only the 0th-order light and the 1st-order light pass through, the imaging spot intensity distribution in the sub-scanning direction will be a sinusoidal intensity distribution. Due to the change in the shape of the imaged spot, unevenness occurs in the sub-scanning direction. In order to solve this problem, the applicant has proposed a new device in Japanese Patent Application No. 61-246043.

An object of the present invention is to make further improvements and to reduce as much as possible the effects of cutting marks (scratches) on the scanning mirror surface on the shape of a spot scanned on a screen (for example, a display or recording surface).

[Means to solve the problem]

As a means of solving the above problems, for example, in this embodiment, a first slit opening A1 is provided between the polygon mirror 9 and the Fθ lens 10, and a second slit opening B is provided near the drum 11.

Here, if only the 0th-order light is allowed to pass through the slit opening B, a spot with a 0th-order intensity distribution can be obtained since the 0th-order light has a 0th-order intensity distribution.

[Embodiment] Fig. 1 shows an embodiment of the present invention in which a laser beam 2 from a laser light source 1 passes through a scanning optical system and is exposed to a recording film II on a rotating drum 12'' to record an image. . Note that the drum may be an electrophotographic photosensitive drum.

In FIG. 1, a laser beam 2 is first made into an appropriate beam diameter by a beam compressor 3, and then enters an A10 modulator 4 that modulates the laser beam intensity.

This is to ensure that the beam modulation efficiency and response speed are appropriate depending on the beam diameter incident on the A10 modulator. Note that an aperture (not shown) is arranged between the A10 modulator 4 and the beam expander 5, which cuts off the zero-order light and allows only the first-order light to pass through.

Now, the output diameter of the laser beam is beam expander 5.
You can change it with . The beam spot size on the recording film 11 is determined by d=(4/π)Fno·λ. Here, d is the beam diameter at 1702 intensity with respect to the center intensity, and Fno is the focal length of the imaging lens divided by the incident beam diameter (1/e2 intensity).

λ is the wavelength of the laser light.

It is thereby understood that if the focal length of the Fθ lens is fixed, a beam expander is used to change the size of the imaging spot. Next, the light beam passes through a reflecting mirror 6 and a cylindrical lens 7 which has no refractive power in the plane of the paper but has a refractive power in the direction perpendicular to the plane of the paper, and reaches the polygon mirror 9. The beam C from the rotating polygon mirror 9 forms an image. By entering the Fθ lens 10, which is a lens, the recording film 11 on the rotating drum 12 is scanned. The drum records images in the sub-scanning direction by rotating.

Here, the cylindrical lens 7 directs the light beam emitted from the beam expander 5 onto the polygon mirror 9 in a straight line.
To be more precise, the image is formed by a long elliptical beam. Furthermore, the polygon mirror surface and the recording film surface 11 are in a conjugate relationship with respect to the imaging ability of the F.theta. lens 10 in the direction perpendicular to the plane of the drawing. This is a well-known technique for eliminating unevenness in the sub-scanning direction due to the tilting of each polygon mirror surface. Fθ
Therefore, the lens 10 has different refractive powers in the direction in the plane of the paper and in the direction perpendicular to the plane of the paper. Note that the Fθ lens 10 uses a cylindrical surface or a toric surface.

Next, the diffraction related to the present invention will be explained. The first.

Note that this diffraction pattern is affected by the pitch of the scratches on the polygon mirror surface, the width of the scratches, the radius of the cutting tool, etc. Since the Fθ lens 10 has only a finite aperture angle, only the 0th order diffracted light and other partial diffracted lights enter the Fθ lens IO. As a result, the intensity distribution of the imaged spot generally changes depending on the position of the scanning line scanned by the polygon mirror on the recording film 11 in the main scanning direction. Moreover, it differs depending on each face of the polygon mirror, so
In particular, there is periodic unevenness in the sub-scanning direction depending on the number of surfaces. This situation is shown in Figure 2. Note that the direction of the cutting lines remaining on the reflective surface of the polygon mirror 9 shown in FIG. It is clear that the stitches are not limited to straight stitches, but may also be curved stitches. Returning to FIG. 1, the slit-shaped aperture A placed between the polygon mirror 9 and the recording film 11 has a slit width set so as to pass the zero-order light and limit the higher-order light, and is arranged in a distributed manner at the center of scanning. There is. This slit A
If it is formed into an arc shape approximately centered on the point where the laser beam 2 intersects with the central portion of the polygon mirror, the width of the aperture corresponding to each angle of view can be made more constant. By providing the slit A, the 0th order diffracted light is normally extracted separately from the pond diffracted light, but if the pitch of the slits is large, the bottom part of the 0th order diffracted light and the 1st order diffracted light may be extracted. overlap, and the 0th order diffracted light cannot be completely separated and extracted using slit A alone.

If the 0th order diffracted light is taken out by partially kicking it, the glass intensity distribution of the 0th order light cannot be reproduced on the imaging plane, so the aperture width of the slit A should be small (both necessary to allow the 0th order diffracted light to pass through). Become.

If the primary light enters the slit A, a slit B is provided near the imaging plane to remove the primary light. The slit B can be opened to allow only the 0th order diffracted light to pass through. Although it is desirable that the slit 3 be provided near the image plane, it may be provided in the optical path between the slit 8 and the image plane.

Incidentally, although the above embodiments have been described with respect to a metal scanning mirror, the present invention is not limited thereto, and it is clear that the same surface situation can be applied to mirrors other than metal mirrors.

Further, the scanning mirror is not limited to a rotating mirror such as a polygon mirror, but may also be a vibrating mirror such as a galvano mirror.

In the above embodiments, the sputterer B passes the zero-order light and controls the higher-order light, but specifically, it completely blocks the higher-order light or weakens the intensity thereof.

〔effect〕

As explained above, according to the present invention, by providing the first and second apertures in the shape of long slits in the main scanning direction that limit the zero-order light amount 4, distortion in the spot shape can be prevented in the sub-scanning direction. It is highly effective in reducing unevenness.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention, and FIG. 2 is a diagram showing a diffraction pattern due to a scratch on a polygon mirror surface. In the figure, l is a laser light source, 3 is a beam compressor,
4 is an A10 modulator, 5 is a beam expander, 7 is a cylindrical lens, 9 is a polygon mirror, 10 is Fθ
lens, 11 is a recording film, 12 is a drum, 13 is an incident laser beam, 14 is a spot on a polygon mirror, 15 is a diffraction pattern observation surface, 150 is O-order diffracted light,
151 is the first-order diffracted light, A and B are slit openings, and S is a line on the polygon surface.

Claims (4)

[Claims] (1) In an optical scanning device in which a light beam is incident on a scanning mirror, the light beam is deflected in the scanning direction by the displacement of the scanning mirror, and an image is formed on the imaging plane by an imaging optical system, inside the optical path reflected by the scanning mirror. A light limiting means for limiting the component of the light beam reflected by the scanning mirror surface that is diffracted in the direction intersecting the scanning direction. first and second light restricting means each having a slit-like aperture through which the first light restricting means includes the imaging optical system and between the imaging optical system and the scanning mirror; An optical scanning device characterized in that a second light restricting means is provided between the first light restricting means and the image forming surface. (2) The optical scanning device according to claim 1, wherein the second light restricting means is provided near the image forming plane. (3) The optical scanning device according to claim 1 or 2, wherein the slit-shaped opening of the second light restricting means has a width that allows only the 0th-order diffracted light to pass through. (4) The optical scanning device according to claim 1, wherein the imaging optical system is an Fθ lens system.