JPH06148547A - Optical beam scanning device having shading correction function - Google Patents

Abstract

PURPOSE:To realize a beam scanning device having shading correction function requiring no special installation parts such as a wavelength plate used for shading correction so as to facilitate installation work. CONSTITUTION:A semiconductor laser or semiconductor laser array is used as a light source 1, a laser beam flux from this light source 1 is deflected by a beam deflection means having a deflection and reflection surface 5, and it is condensed as a beam spot on a subject surface 9 of scan by a scan lens 6 for performing beam scan, where a wavelength plate 12 to convert a straight deflected beam into a substantially circular deflected beam is disposed integrally with a desired one of other optical elements 2, 3, 4, 11 disposed on a beam passage in the beam passage between the light source and the beam deflection means 5.

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 having a shading correction function.

[0002]

2. Description of the Related Art An optical scanning device that optically scans a surface to be scanned, which is set to match the surface of an optical recording medium such as a photoconductor, with a laser beam is widely known in connection with laser printers and the like. In a general optical arrangement of an optical scanning device, a laser light beam from a laser light source is deflected by an optical deflecting means such as a rotating polygon mirror, and is condensed as a light spot on a surface to be scanned by a scanning lens.

Therefore, the incident angle of the laser beam on the deflective reflection surface of the optical deflecting means and the scanning lens is 1 line scanning,
It changes continuously. Since the reflectance on the deflecting / reflecting surface and the reflectance / transmittance on the lens surface of the scanning lens change depending on the incident angle, the light intensity of the light spot on the surface to be scanned generally changes with the image height. The fluctuation of the light intensity in one line of the optical scanning is called "shading". Shading is remarkable when the light beam incident on the deflecting / reflecting surface is linearly polarized light.

A laser beam emitted from a semiconductor laser or a semiconductor laser array used as a light source of an optical scanning device has an extinction ratio of about 20 dB, and most of the linearly polarized light component is apt to cause shading. Further, recently, in order to miniaturize the optical scanning device, the angle of view of the optical scanning has been widened,
The area of change of the incident angle also becomes large and the shading tends to increase. On the other hand, there is a demand for higher quality of recorded images by optical scanning, and deterioration of image quality of recorded images due to shading is becoming a problem.

In an optical scanning device using a semiconductor laser or a semiconductor laser array as a light source, in order to correct and reduce the shading due to the linear polarization of the laser beam emitted from the light source, on the optical path between the light source and the light deflecting means. 1 /
A four-wave plate or the like may be provided so that the polarization state of the laser light flux that optically scans the surface to be scanned is “circularly polarized”. This is because the reflectance and transmittance of circularly polarized light hardly change within the range of the incident angle at the time of reflection / transmission required for normal optical scanning.

However, when actually trying to do this, 1 /
A mounting part for disposing a four-wave plate or the like between the light source and the light deflecting means is required, and an action for mounting is also required.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances and does not require a dedicated mounting part such as a wave plate used for shading correction and facilitates mounting work. An object is to provide an optical scanning device having a possible shading correction function.

[0008]

An optical scanning device having a shading correction function according to the present invention is "a semiconductor laser or a semiconductor laser array is used as a light source, and a laser beam from this light source is deflected by an optical deflecting means having a deflecting and reflecting surface. , An optical scanning device for performing optical scanning by condensing as a light spot on a surface to be scanned by a scanning lens ".
The optical scanning device described is, "in the optical path between the light source and the light deflecting means, a wave plate for converting linearly polarized light into substantially circularly polarized light is integrated with any other optical element disposed in the optical path. It has been deployed to ".

"Substantially circularly polarized light" includes not only perfect circularly polarized light but also elliptically polarized light close to circularly polarized light to the extent that shading can be effectively corrected. The "optical element that integrates the wave plate" is an optical element provided on the optical path from the light source to the light deflecting means, for example, a collimator lens that collimates the laser light flux from the light source, or a deflection reflection surface for the laser light flux. A cylinder lens or the like for forming a long line image in the vicinity corresponding to the main scanning direction in the vicinity is optional, but may be adhered and integrated with the "aperture for setting the shape of the light spot" (Claim 2). Apertures may be formed on the plate itself by coating or painting (claim 3).
When the wave plate is integrated with the cylinder lens, it may be “adhered to the flat surface of the cylinder lens” and integrated (claim 4).

According to a fifth aspect of the present invention, there is provided an optical scanning device in which "a coating for converting linearly polarized light into substantially circularly polarized light is provided on any other optical element disposed on the optical path between the light source and the light deflecting means. It has been given ”. As the coating material, SnO ₂ , Ta ₂ O ₅ , CeO ₂ , TiO
Various oxides having birefringence such as ₂ are suitable. The "optical element to be coated" is also optional as long as it is on the optical path, and may be applied to the "lens surface of the cylinder lens" (claim 6), or "collimator for collimating a laser light flux from a light source. It may be applied to the "lens surface of the lens" (Claim 7), and when the light deflecting means is a rotary polygon mirror, the coating may be applied to "a necessary portion of the transparent window of the soundproof housing of the rotary polygon mirror". (Claim 8).

[0011]

As described above, in the present invention, since the wave plate or coating for correcting shading is integrated with another optical element, when the optical element is assembled, the optical scanning device is automatically operated. Therefore, it has a shading correction function.

[0012]

EXAMPLES Specific examples will be described below. Figure 1
Referring to (A), this figure generally shows an optical scanning device to which the present invention can be applied. First, this Figure 1
Based on (A), an optical scanning device to which the present invention can be applied will be generally described.

In FIG. 1A, a laser beam emitted from a laser light source 1 passes through a condenser lens 2, passes through an aperture 3, and a cylinder lens 4 causes a sub-scanning corresponding direction (FIG. 1A). A long line image in the direction corresponding to the main scanning direction (the direction parallel to the main scanning direction and in the plane parallel to the drawing) at the position of the deflection reflection surface 5. Image as. Deflection reflection surface 5
The reflected laser light flux due to is deflected as the deflective reflection surface 5 rotates and enters the scanning lens 6. The deflected laser light flux that has passed through the scanning lens 6 is reflected by a mirror 7 for bending the optical path to bend the optical path, and is condensed as a light spot on the surface 9 to be scanned via the cover glass 8 of the optical scanning device. The surface 9 to be scanned is optically scanned. A surface of the photosensitive member or the like is provided on the surface 9 to be scanned.

The condensing lens 2 may be a collimating lens for collimating the laser light flux from the laser light source 1 or a laser light flux from the laser light source 1 having a converging tendency, and vice versa. Alternatively, the laser light flux from the laser light source 1 may be a divergent light flux.
In the example of FIG. 1, the condenser lens 2 is a “collimator lens”.

The aperture 3 is for "setting the shape of the light spot" on the surface 9 to be scanned.

The cylinder lens 4 is for correcting the surface tilt of the deflecting / reflecting surface 5 or for correcting the shape of the light spot on the surface to be scanned. In some cases, it is not necessary when performing the face tilt correction.

The deflecting / reflecting surface 5 is a reflecting surface of the light deflecting means, which reflects the laser light beam and deflects the reflected laser light beam by rotating or oscillating. Examples of the light deflecting means having a rotatable deflecting / reflecting surface include a rotating polygonal mirror, a rotating two-sided mirror, and a so-called hoso-type mirror, and the swinging deflecting / reflecting surface includes a galvano mirror. it can. In the illustrated example, the light deflecting means is a rotating polygon mirror.

The scanning lens 6 is a lens for converging the deflected laser light flux as a light spot on the surface to be scanned, and is generally an "fθ lens" when the light deflecting means has a rotatable deflective reflection surface. In the case of having an oscillating deflecting / reflecting surface, the “fsin θ lens” is used. When the constant velocity of optical scanning is performed by electrical correction, the scanning lens may be a normal imaging lens. In the example shown,
The scanning lens 6 is an “anamorphic fθ lens”, and the position of the deflective reflection surface 5 and the position of the scanned surface 9 are geometrically conjugate with each other in the sub-scanning corresponding direction, and cooperate with the cylinder lens 4. Then, the tilt of the deflective reflection surface 5 is corrected.

In order to correct the surface tilt of the deflecting / reflecting surface, a long cylinder lens or toroidal lens is used "as a part of the scanning lens" without using the cylinder lens 4, and these long lenses are attached to the surface to be scanned. It can also be deployed nearby.

The mirror 7 is for bending the optical path of the deflected laser beam, and is usually provided in many cases depending on the layout requirements of the apparatus. Therefore, the mirror 7 can be omitted. Further, the cover glass 8 is for dustproof of the optical scanning device.

Reference numeral 11 indicates a transparent window. When the rotating polygon mirror is used as the light deflecting means and the rotating polygon mirror is rotated at high speed (for high-speed optical scanning), or when the air bearing is used as the bearing of the drive motor of the rotating polygon mirror, the rotating polygon mirror is rotated. Along with this, a “wind noise” that is unpleasant to the ear is generated, so in such a case, generally, a rotary polygon mirror is installed inside the “soundproof housing” to prevent the wind noise from leaking to the outside, and the soundproof housing is transparent. The window 11 is provided to enable the deflection of the laser beam by the deflecting / reflecting surface.
Therefore, if it is not necessary to provide the light deflecting means in the soundproof housing, the transparent window 11 is of course unnecessary.

Next, the light source 1 will be described with reference to FIG. As described above with reference to FIG. 1A, in the optical scanning device to which the present invention can be applied, a semiconductor laser or a semiconductor laser array is used as a light source.

As shown in FIG. 2A, the semiconductor laser 1A includes a minute light emitting portion L having a rectangular shape elongated in the bonding surface direction.
The emitted laser light having a value of 0 is substantially linearly polarized light whose polarization direction is the longitudinal direction of the light emitting unit L0. The far-field pattern of the emitted laser beam is "elliptical with the uniaxial direction as the polarization direction", as shown by the chain line. In order to improve the light utilization efficiency, the polarization direction is usually set in the sub-scanning corresponding direction. It is deployed in parallel with.
The optical scanning mode in which the optical scanning is performed by making the polarization direction of the light source substantially parallel to the sub-scanning corresponding direction is referred to as “A mode” for convenience.

As shown in FIG. 2B, the semiconductor laser array 1B has a plurality of laser emitting portions L1, L2, L.
3. ． Is a monolithic structure in which one row is arrayed at equal intervals along the joint surface. In this case, the polarization direction of the laser light flux from each light emitting unit is parallel to the array direction. When the semiconductor laser array is used as a light source, the number of lines equal to the number of light emitting parts can be optically scanned at one time.

When the semiconductor laser array 1B is used as the light source 1, it can be considered that the array direction (arrangement direction of the light emitting portions) is used in parallel with the sub-scanning corresponding direction. In this case, the optical scanning mode is the A mode. However, when the semiconductor laser array 1B is used as a light source to perform optical scanning in the A mode, generally, the intervals between lines that are simultaneously scanned become large, and high-density optical scanning is performed in the sub-scanning direction. Is not easy.

For this reason, as shown in FIG. 2B, it is common practice to use the semiconductor laser array 1B with the array direction inclined by a small angle θ (about 5 degrees) with respect to the main scanning corresponding direction. In this case, the arrangement interval of the light emitting units in the light source unit is d · sin θ (d
Is the arrangement pitch of the light emitting portions), so that the interval between adjacent lines in optical scanning can be reduced.

When the semiconductor laser array is used in such an arrangement, the polarization direction of the laser beam emitted from the light source 1 becomes substantially parallel to the main scanning corresponding direction. The optical scanning mode in which the optical scanning is performed by making the polarization direction of the laser light beam emitted from the light source substantially parallel to the main scanning corresponding direction in this way is referred to as “B mode” for convenience.

Although various explanations have been given above regarding the optical scanning device and each part thereof, the present invention can be widely applied regardless of the optical scanning device having various structures and the A and B modes.

1 (B) and 1 (C) show an embodiment of the invention described in claims 1 and 2. In this embodiment, the quarter wave plate 12 is integrated with the aperture 3 by adhesion. FIG. 1B is a front view and FIG. 1C is a side view.
Reference numeral 3'denotes an opening formed in the aperture 3 and has a rectangular shape elongated in the main scanning corresponding direction. The laser light flux emitted from the light source 1 is converted into a parallel light flux by the condenser lens 2 which is a collimator lens, and when passing through the aperture 3, it is transmitted through the quarter wavelength plate 12 and converted into a circularly polarized light flux.

FIG. 3A shows an embodiment of the invention described in claims 1 and 3. In this embodiment, a light-shielding film 12 'that shields the laser beam from the light source is formed on the surface of the quarter-wave plate 12 on the incident side or the emission side by "coating or painting", and an opening is formed in this light-shielding film 12'. The formation of the portion 3 ″ serves as an aperture. That is, the quarter wave plate 12 itself has the aperture formed by the light shielding film 12 '.

3 (B) and 3 (C) show an embodiment of the invention described in claims 1 and 4. This embodiment is an embodiment in which the quarter-wave plate 12 is integrated with the cylinder lens 4 arranged between the aperture 3 and the deflective reflection surface 5 in the optical scanning device of FIG. The cylinder lens 4 is shown in FIG.
As shown in (C), it has a flat lens surface 4 ′ and a convex lens surface 4 ″, and has a positive power in the sub-scanning corresponding direction,
As shown in FIG. 3 (B), the quarter-wave plate 12 is bonded so as to cover the central portion of the flat lens surface 4 ′ (the portion where the laser beam is incident) and is integrated with the cylinder lens 4. ing.

FIG. 4 shows an embodiment of the invention described in claims 5 and 6. In this embodiment, the cylindrical lens 4 provided between the aperture 3 and the deflecting / reflecting surface 5 in the optical scanning device of FIG. 1 (A) converts linearly polarized light into circularly polarized light as in the case of a quarter wavelength plate. This is an example in which the coating 13 is applied. In the figure, (A) is a plan view and (B) is a side view.

The coating 13 is a cylinder lens 4
It is formed so as to cover the central portion (the portion where the laser light flux is incident) of the flat lens surface 4 '. In principle, a coating may be applied to the convex lens surface 4 ″ side of the cylinder lens 4, but a coating having a wave plate effect has a problem of “angle dependency” in processing, and therefore the embodiment shown in the drawings. As described above, coating the flat lens surface 4 ′ is easier to process and yields better than coating the convex lens surface 4 ″.

FIG. 5 shows an embodiment of the invention described in claims 5 and 7. In this embodiment, in the optical scanning device of FIG. 1 (A), the light beam emitting lens surface 2 ″ of the condenser lens 2 which is a collimating lens for converting the laser light beam from the light source 1 into a parallel light beam.
In this embodiment, a coating 13 for converting linearly polarized light into circularly polarized light is applied as in the case of the quarter wavelength plate. Reference numeral 15 indicates a lens barrel that holds the condenser lens 2.

The coating 13 may be applied to the other lens surface 2'of the condenser lens 2, but when the coating is applied to the lens surface 2 ', the divergence of the laser beam emitted from the light source is caused. Although it is possible that the transmittance decreases due to the angle dependence, if the light exit surface 2 '' is coated,
Since the light flux incident on the coating 13 is made into a parallel light flux, the decrease in the transmittance due to the angle dependency is small.

FIG. 6 shows an embodiment of the invention described in claims 5 and 8. As shown in FIG. 6B, in this embodiment, the light deflecting means is the rotary polygon mirror 50, and the rotary polygon mirror 50 is provided in the soundproof housing 16. Soundproof housing 1
6, a transparent window 11 is provided. A light beam from the light source side passes through a fixed position of the transparent window 11 and is incident on the deflecting / reflecting surface as shown in FIG.
And is emitted to the scanning lens side. In this way, the laser light flux entering the deflective reflection surface from the light source side through the transparent window 11 always passes through a predetermined portion of the transparent window 11,
As shown in FIG. 6A, the coating 11 ′ is formed so as to cover a part of the transparent window 11 described above. The coating may be formed on either the inside or outside of the transparent window.

In the example of the optical scanning device shown in FIG.
When the quarter lens or the coating is provided on the condenser lens 2, the aperture 3, the cylinder lens 4, or the transparent window 11 as in the above-mentioned embodiments, the shading is as shown by the graph line 71 in FIG. . The horizontal axis of FIG. 7 represents the main scanning region in correspondence with the incident angle of the fθ lens that is the scanning lens 6.

Shading when the laser light flux incident on the deflecting / reflecting surface 5 from the light source side is S or P deflection (corresponding to A mode and B mode, respectively) is graph lines 72 and 73 in FIG. 7, respectively. As shown in. Comparing these graph lines 72 and 73 with the graph line 71, it can be seen that the present invention corrects shading very well.

[0039]

As described above, according to the present invention, it is possible to provide a novel optical scanning device having a shading correction function. Since this optical scanning device has the above-described configuration, it is possible to correct shading in optical scanning and realize good optical scanning.

Since the wave plate and the coating for correcting the shading are integrated with the optical element originally provided in the optical scanning device, there is no need for a dedicated part for incorporating the wavelength plate or the like into the optical scanning device. There is no need to install a wave plate or the like, and the optical scanning device and its assembly process are not complicated.

[Brief description of drawings]

1A is a diagram for explaining an optical scanning device to which the present invention is applied, and FIGS. 1B and 1C are claims 1 and 2.
It is a figure which shows 1st Example of invention of 2 description only the characteristic part.

FIG. 2 is a diagram for explaining a light source that can be used in the optical scanning device of the present invention, in which (A) is a semiconductor laser. (B) is a diagram for explaining a semiconductor laser array.

FIG. 3 is a diagram for explaining one embodiment of the invention described in claims 1, 3 and 4.

FIG. 4 is a diagram for explaining one embodiment of the invention described in claims 5 and 6;

FIG. 5 is a diagram for explaining one embodiment of the invention described in claims 5 and 7;

FIG. 6 is a diagram for explaining one embodiment of the invention described in claims 5 and 8;

FIG. 7 is a diagram for explaining the effect of the present invention in relation to the embodiment.

[Explanation of symbols]

1 Light Source 2 Condensing Lens 3 Aperture 4 Cylinder Lens 5 Deflection / Reflection Surface 6 Scanning Lens 9 Scanned Surface 12
Quarter wave plate

Claims (8)

[Claims] 1. A semiconductor laser or a semiconductor laser array is used as a light source, a laser beam from this light source is deflected by an optical deflecting means having a deflecting reflection surface, and is condensed as a light spot on a surface to be scanned by a scanning lens. In an optical scanning device that performs optical scanning, a wavelength plate that converts linearly polarized light into substantially circularly polarized light is provided on the optical path between the light source and the optical deflecting means, and any other optical element is provided on the optical path. An optical scanning device having a shading correction function, which is provided integrally. 2. The optical scanning device according to claim 1, wherein the wave plate is integrated with an aperture for setting the shape of the light spot by adhesion.
Optical scanning device with shading correction function. 3. The optical scanning device according to claim 2, wherein the wavelength plate has an aperture formed by coating or painting, and the optical scanning device has a shading correction function. 4. The optical scanning device according to claim 1, wherein the wave plate is bonded to a flat surface portion of the cylinder lens, and the optical scanning device has a shading correction function. 5. A semiconductor laser or a semiconductor laser array is used as a light source, a laser light flux from the light source is deflected by an optical deflecting means having a deflecting and reflecting surface, and is condensed as a light spot on a surface to be scanned by a scanning lens. An optical scanning device that performs optical scanning is characterized in that a coating that converts linearly polarized light into substantially circularly polarized light is applied to any other optical element provided on the optical path between the light source and the light deflection means. An optical scanning device having a shading correction function. 6. The optical scanning device according to claim 5, wherein a coating is applied to the lens surface of the cylinder lens, which has a shading correction function. 7. The optical scanning device according to claim 5, wherein a coating is applied to a lens surface of a collimating lens for collimating a laser beam from a light source. apparatus. 8. The optical scanning device according to claim 5, wherein the light deflecting means is a rotary polygon mirror, and the coating is applied to a necessary portion of a transparent window of a soundproof housing of the rotary polygon mirror. Optical scanning device with shading correction function.