JPH0772404A - Optical scanning device - Google Patents

Abstract

(57) [Abstract] [Purpose] To obtain an optical scanning device capable of performing optical scanning with a beam having a deep focal depth by shielding side lobe portions of a Bessel beam. A laser beam emitted from a light source means 1 is made into a Bessel beam in which side lobes are concentrically formed through a Bessel beam generating means 3, the Bessel beam is deflected by a deflecting means 5, and then an imaging optical system is formed. An optical scanning device that guides light onto a surface to be scanned 8 via 6 and optically scans the surface to be scanned, and has a slit member 7 whose longitudinal direction is substantially aligned with the main scanning direction in the vicinity of the surface to be scanned. And a part of a side lobe portion of the Bessel beam is shielded by the slit member.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device, and in particular, a Bessel beam having a minute spot and a deep focal depth is used as a laser beam to optically scan a surface to be scanned to record an image with high accuracy. The present invention relates to an optical scanning device suitable for, for example, a laser beam printer (LBP).

[0002]

2. Description of the Related Art Conventionally, a laser beam has generally been treated as a Gaussian beam and has been restricted by its propagation characteristics. However, in recent years the depth of focus has been very deep,
A Bessel beam (or non-diffractive beam) is attracting attention as a laser beam having a small spot diameter.

The characteristic of this Bessel beam is that the light intensity distribution in a cross section perpendicular to the propagation direction is proportional to the square of the 0th-order Bessel function of the first kind.

FIG. 5 shows a Japanese Patent Application No. 4-1376 filed by the present applicant.
It is a principal part schematic diagram of the optical system of the optical scanning device using the Bessel beam proposed by No. 45.

In the figure, a laser beam L51 which is light-modulated based on image information and emitted from a light source means 51 is a plane A crossing its optical path by a Bessel beam generating means 52.
_It becomes a Bessel beam L52 having a center position of ₀ , is condensed on the plane A ₀ , and then diverges.

The diverging Bessel beam L52 is converged by a condenser lens 53, is incident on a reflecting surface (deflecting surface) of a rotary polygon mirror 54 as an optical deflector, and is then reflected and deflected.
An image is formed on the surface (scanned surface) of the rotating drum (photosensitive drum) D ₀ by the imaging lens 55 having the −θ characteristic, and an electrostatic latent image is formed on the photosensitive member (not shown) on the surface. There is.

In the figure, since the plane A ₀ and the surface of the rotary drum D ₀ are set in an optically substantially conjugate relationship, the Bessel beam is formed near the surface of the rotary drum D ₀ . Since this Bessel beam has a very deep depth of focus as described above, for example, even if the optical system has a field curvature,
Alternatively, the beam spot diameter does not change even if the position of the rotary drum D ₀ is slightly displaced in the optical axis direction, and thus a high-resolution optical scanning device is obtained.

[0008]

As described above, the cross-sectional intensity distribution of the Bessel beam formed in the vicinity of the surface (scanned surface) of the rotary drum D ₀ in the conventional optical scanning device is ₀ for the first kind.
It is proportional to the square of the next Bessel function.

The intensity of the side lobes (diffraction ring) of this Bessel beam is 16 when the intensity of the peak of the central spot is 100%.
%, The intensity of the second side lobe is 9%, and the intensity of the third side lobe is 6%, and the light intensity of the side lobe is relatively high.

Therefore, when this Bessel beam is applied to an optical scanning device (recording device) as a recording beam, for example, the side lobe intensity is too high, which may result in deterioration of the image quality of a recorded image. There was a problem.

According to the present invention, a laser beam is used as a Bessel beam, a slit member having a predetermined shape is arranged near the surface to be scanned, and most of side lobe portions of the Bessel beam formed near the surface to be scanned by the slit member are provided. It is an object of the present invention to provide an optical scanning device that improves the quality of a recorded image by effectively blocking light.

[0012]

The optical scanning device of the present invention comprises:
The laser beam emitted from the light source means is made into a Bessel beam in which side lobes are formed concentrically through the Bessel beam generating means, the Bessel beam is deflected by the deflecting means, and then the scanned surface is passed through the imaging optical system. An optical scanning device that guides light upward and optically scans the surface to be scanned, wherein a slit member having a longitudinal direction substantially aligned with the main scanning direction is arranged in the vicinity of the surface to be scanned, The feature is that a part of the side lobe portion of the Bessel beam is shielded.

[0013]

1 and 2 are a main-scan sectional view and a sub-scan sectional view of a first embodiment of the present invention.

In the figure, reference numeral 1 is a light source means, which is composed of, for example, a semiconductor laser. Reference numeral 2 is a collimator lens, which collimates a laser beam (light beam) emitted from the light source means 1 on the basis of image information after being modulated.

Reference numeral 3 is an axicon as a Bessel beam generating means. The laser beam is vertically incident on the axicon 3. The axicon 3 generates a Bessel beam B1 having an intensity distribution substantially proportional to the square of the 0th-order Bessel function of the first kind having a beam spot with a deep focal depth, and the side lobes of the Bessel beam are formed concentrically. ing.

A condenser lens (condensing means) 4 condenses the Bessel beam and makes it incident on the deflecting surface (reflecting surface) of the optical deflector 5 as the deflecting means. The optical deflector 5 is composed of a rotary polygonal mirror having four deflecting surfaces 5a to 5d, and is rotated at a constant speed in the direction of arrow C about a rotation axis O by a driving means (not shown) such as a motor. .

Reference numeral 6 denotes an f-θ lens (imaging optical system) as an image forming means, which is composed of two spherical lenses 6a and 6b, and is a laser beam (Bessel beam) reflected and deflected by the optical deflector 5. ) Is imaged near the surface 8 to be scanned. The surface 8 to be scanned corresponds to the surface of the photoconductor drum in, for example, a copying machine or LBP.

Numeral 7 is a slit member, which is arranged in the vicinity of the surface 8 to be scanned with a small distance d so that blurring of the spot due to diffraction does not occur. The slit member 7 is provided so that the longitudinal direction of its opening substantially coincides with the main scanning direction.

In this embodiment, as will be described later, the central portion of the Bessel beam is mainly passed through the opening 7a of the slit member 7 and the light blocking portion 7b is used to block most of the side lobe portion.

FIG. 3 shows the slit member 7 shown in FIGS.
FIG. 3 is an enlarged explanatory view of a part of the above when viewed from the f-θ lens side, and in this figure, the positional relationship between the opening 7a of the slit member 7 and the Bessel beam is shown.

As shown in the figure, the opening 7a of the slit member 7 is formed so as to extend long in the main scanning direction and has no influence on the optical scanning. Further, with respect to the sub-scanning direction, the central portion of the beam is mainly passed through, and most of the other portions are shielded by the light shielding portion 7b.

In this embodiment, a part of the side lobe portion reaches the surface to be scanned, but the light intensity of the side lobe portion at this time is much weaker than the peak intensity of the central spot. It is hardly affected when performing scanning.

In the present embodiment, as shown in FIG. 1, the laser beam emitted from the semiconductor laser 1 is converted into a plane wave by the collimator lens 2 and vertically incident on the axicon 3. The laser beams emitted from the axicon 3 interfere with each other to form a Bessel beam B1 having an intensity distribution approximately proportional to the square of the 0th-order Bessel function of the first kind in the vicinity of a plane (position) A crossing the optical path. . The Bessel beam B1 diverges as it moves away from the plane A, but is converged by the condenser lens 4 and condensed in a substantially ring shape in the vicinity of the deflection surface (reflection surface) 5b of the rotary polygon mirror 5.

In the present embodiment, the plane A corresponds to the front focal position of the condenser lens 4, and the deflection surfaces 5a to 5d of the rotary polygon mirror 5 correspond to the rear focal position of the condenser lens 4. Is set.

The laser beam reflected and deflected by the rotary polygon mirror 5 is subjected to a converging action by the f-θ lens 6,
A Bessel beam B2 is formed near the slit member 7. The plane A and the position of the slit member 7 are set in an optically substantially conjugate relationship.

As shown in FIG. 3, most of the side lobes S _{1 to} S _N are formed by the slit member 7 by the slit member 7.
The light is shielded by the light-shielding portion 7b, and only the central spot S ₀ and part of the side lobes S _{1 to SN} pass through the opening 7a of the slit member 7 and reach the surface to be scanned. As a result, an optical scanning device having an extremely high resolution is obtained. At this time, a part of the side lobes reach the surface to be scanned, but since the light intensity of the side lobes is extremely weak as described above, the image quality of the recorded image is hardly affected by the influence.

FIG. 4 shows the slit member 7 shown in FIGS. 1 and 2.
FIG. 6 is a sub-scanning cross-sectional view showing a state of a beam spot formed in the vicinity.

In the figure, the side lobe S _{1 of} the spots S ₀ , S _{1 to} S _N forming the Bessel beam B2 is shown.
Most of _SN are shielded by the light shielding portion 7b of the slit member 7, and the central spot S ₀ mainly passes through the opening 7a of the slit member 7 and reaches the scanned surface 8. .

Further, in the figure, the distance d between the slit member 7 and the surface 8 to be scanned is set to a small value such that blurring of the central spot S ₀ due to diffraction does not occur.

In this embodiment, the rotary polygon mirror 5 is rotated to optically scan the surface to be scanned 8 with a minute spot in the main scanning direction, and the surface to be scanned 8 is moved or rotated in the sub scanning direction. By moving the image, the image is optically scanned (recorded) two-dimensionally.

As described above, in this embodiment, the laser beam formed in the vicinity of the surface to be scanned is a non-diffractive beam (Bessel beam), and this non-diffractive beam has a very deep focal depth as described above. For example, even if the field curvature of the optical system is large or there is an error or variation in the arrangement position of the optical components, the image does not deteriorate, and a high-quality image can always be obtained.

Although the present invention is applied to the rotationally symmetric optical system in the present embodiment, the present invention is also applicable to the rotationally asymmetric optical system having a surface tilt correction function, for example. Can be applied to.

Further, in the present embodiment, the Bessel beam is formed by using the axicon as a means for generating the Bessel beam, but the method is not limited to this forming method, and for example, it has an optical function equivalent to that of the pupil filter or the axicon. The Bessel beam may be formed using a diffraction grating or the like.

Further, in the present embodiment, the distance d between the slit member and the surface to be scanned is set to a small distance such that the spot blur due to diffraction does not occur, but the slit member is a unit including the surface to be scanned. It may be configured integrally with.

For example, when the surface to be scanned is a photosensitive drum, the photosensitive drum unit and the slit member may be integrally formed. This makes it possible to prevent the occurrence of spot blurring due to diffraction.

Further, in the present embodiment, the width of the slit member in the sub-scanning direction is made narrow so that only the central spot S ₀ passes, but this width is adjusted to the sensitivity characteristics of the surface to be scanned, and the central spot S _0. It may be formed to have a wide width such that a plurality of diffraction rings pass through. In this case, the distance d between the slit member and the surface to be scanned can be set larger.

In this embodiment, the slit member is used as a means for shielding the side lobe portion, but any optical member capable of effectively shielding the side lobe portion may be used in the present invention. The same can be applied as.

[0038]

According to the present invention, when the Bessel beam is used to optically scan the surface to be scanned as described above, a large portion of the side lobe portion of the Bessel beam is provided in the vicinity of the surface to be scanned and has a predetermined shape. By effectively blocking light with a slit member having a portion, the surface to be scanned can be optically scanned with only a minute spot having a large depth of focus and a large light intensity, thereby improving the performance of the apparatus. It is possible to achieve an optical scanning device that can perform.

[Brief description of drawings]

FIG. 1 is a main-scan sectional view of a first embodiment of the present invention.

FIG. 2 is a sub-scan sectional view of the first embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a positional relationship between the slit member and the Bessel beam according to the first embodiment of the present invention.

FIG. 4 is an explanatory diagram showing the appearance of spots near the slit member according to the first embodiment of the present invention.

FIG. 5 is a schematic view of a main part of an optical system of a conventional optical scanning device.

[Explanation of symbols]

 1 Light Source Means 2 Collimator Lens 3 Bessel Beam Generating Means (Axicon) 4 Condensing Means 5 Deflection Means 6 Imaging Optical System 7 Slit Member 8 Scanned Surface

Claims (1)

[Claims] 1. A laser beam emitted from a light source means is made into a Bessel beam in which side lobes are concentrically formed through a Bessel beam generating means, the Bessel beam is deflected by a deflecting means, and then an imaging optical system is formed. An optical scanning device that guides light onto a surface to be scanned through and optically scans the surface to be scanned, wherein a slit member having a longitudinal direction substantially aligned with the main scanning direction is arranged in the vicinity of the surface to be scanned, An optical scanning device, wherein a part of a side lobe portion of the Bessel beam is shielded by the slit member.