JP2001255480A - Optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a side lobe and the diameter of beam spot of a main beam with small-sized and inexpensive constitution. SOLUTION: An optical converting element 4 consisting of a 1/2 wavelength plate and a polarizing filter 5 are disposed between a light source 1 and a deflector 7. Effective light flux within an area where the light flux of a light beam from the light source 1 is made incident with the diameter of an aperture 3 through a coupling lens 2, is converted into light flux in a polarized light state having a plurality of areas where polarized light directions differ after passage by the optical converting element 4. Only light flux having a specific polarized light direction is passed by the polarizing filter 5, is converged in the subscanning direction by the cylindrical lens 6, and then is made incident on a polarizer 7. Thereby, the diameter of a beam spot on the scan layer of a photoreceptor 10 of a main beam which passed through scanning lenses 8 and 9 is made small.

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 used for an apparatus such as a laser beam printer, a plain paper facsimile, and a digital copying machine.

[0002]

2. Description of the Related Art Hitherto, a method of increasing the resolution by reducing the beam spot diameter of a laser beam has been studied.
For example, IEICE Technical Report 999-09 of the Institute of Electronics, Information and Communication Engineers (application to liquid crystal super-resolution optical elements and optical pickups) describes a proposal to reduce the beam spot diameter using a liquid crystal element and a polarizing filter. Have been. According to this proposal,
The linearly polarized light is converted to a group of orthogonal linearly polarized light by the liquid crystal element to generate a super-resolution effect, and the side lobe is converted to linearly polarized light having a direction different from that of the main lobe, and the side lobe can be removed by the polarizing filter. In addition, Japanese Patent Application Laid-Open
Japanese Patent No. 227992 (Vessel beam generation method and optical scanning device using the same) discloses a technique for obtaining a minute beam spot and a large depth of focus using a Bessel beam. According to this technique, a laser beam is made incident on a diffractive optical element consisting of a binary optical element having optical characteristics substantially equivalent to a conical prism,
A Bessel beam is being generated.

[0003]

However, when the liquid crystal element used in IEICE 999-09 is applied to an optical scanning device, the size of the device becomes large, and the cost and power consumption increase. Become. Also,
In Japanese Patent Application Laid-Open No. Hei 10-227992, although the beam spot diameter of the main beam can be reduced,
There is a problem that the side lobes are rather large.
An object of the present invention is to reduce a side lobe and reduce a beam spot diameter of a main beam by a small and inexpensive configuration.

[0004]

According to a first aspect of the present invention, there is provided an optical scanning device comprising: a light source for emitting a light beam of a light beam (corresponding to the light source in FIG. 1 in the embodiment); and a light beam from the light source. Optical system means (corresponding to the coupling lens 2 in FIG. 1 in the embodiment) and a deflector for deflecting a light beam from the coupling optical system means (in the embodiment, FIG. Between the light source and the deflector,
A light conversion element (corresponding to the light conversion element 4 in FIG. 1 in the embodiment) and a light conversion element that converts the incident light flux in the effective area into a polarized light flux having a plurality of regions having different polarization directions after passing therethrough. The configuration is such that a polarization filter (corresponding to the polarization filter 5 in FIG. 1 in the embodiment) that allows only a specific polarization direction to pass is disposed. According to the configuration of claim 1, after coupling the light beam from the light source, the light beam is converted by the light conversion element into a light beam in a polarization state having a plurality of regions having different polarization directions after passing through the light beam in the effective area. Then, only a light beam in a specific polarization direction is passed by the polarization filter and is incident on the polarizer. In the configuration of the first aspect, as described in the second aspect, the light conversion element has a property of converting the polarization direction of the outgoing light beam to the incident light beam of the linearly polarized light so as to be substantially orthogonal. A second region having a property of emitting an output light beam having the same polarization direction with respect to the incident light beam of the linearly polarized light.
And a region of Further, in the configuration of claim 1, as described in claim 3, the light conversion element is formed with an area smaller than the effective area of the incident light beam, and changes the polarization direction of the output light beam to the polarization direction of the incident light beam. Is characterized in that it has the property of transforming so as to be substantially orthogonal to.

[0005] In the configuration of claim 2 or 3, as described in claim 4, the light conversion element converts the polarization direction of the outgoing light beam so as to be substantially orthogonal to the polarization direction of the incident light beam. The region is arranged at the center of the effective area of the incident light beam. Further, in the configuration of claim 4, as described in claim 5, the light conversion element has an area for converting the polarization direction of the outgoing light beam so as to be substantially orthogonal to the polarization direction of the incident light beam and the area of the incident light beam. The area ratio with the area of the effective area is set to a value that effectively removes the primary side lobe of the emitted light beam. In the configuration of any one of the first to fifth aspects, as described in the sixth aspect, the conversion element has a uniform polarization characteristic in the sub-scanning direction. Further, in the configuration of any one of the first to fifth aspects, as described in the seventh aspect, the conversion element has a uniform polarization characteristic in the main scanning direction. Further, in the configuration according to any one of claims 1 to 7, as described in claim 8, the light conversion element has a center on an axis substantially parallel to a line orthogonal to the main scanning direction and the sub-scanning direction. It is characterized by being rotatable.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an optical scanning device according to the present invention will be described below with reference to the drawings. FIG. 1 is a view in which means of an optical system are developed on a plane including a deflection rotation surface according to the embodiment. In this figure, 1 is a light source composed of a semiconductor laser that emits a light beam, 2 is a coupling lens, 3 is an aperture (aperture opening), 4 is a light conversion element (polarization element), 5 is a polarization filter (polarization element), Reference numeral 6 denotes a cylindrical lens, and reference numeral 7 denotes a polygon mirror (deflector). Reference numerals 8 and 9 denote scanning lenses, and reference numeral 10 denotes a photoconductor. In FIG. 1, laser light emitted from a light source 1 and diverged is coupled by a coupling lens 2 to form a light beam in a certain polarization direction, and enters the light conversion element 4 as a light beam in an effective area corresponding to the aperture 3. The light conversion element 4 is formed of a half-wave plate at the center and a uniform glass plate at the periphery. Therefore, the light conversion element 4 converts the polarization state of the light flux after passing therethrough so as to have a plurality of regions having different polarization directions at the central part and the peripheral part in the effective area of the incident light flux. That is, as shown in FIG. 2, when a light beam whose direction of polarization is perpendicular to the sub-scanning direction (direction of A perpendicular to the paper surface) enters the light conversion element 4, the central part of the light conversion element 4 Of the luminous flux that has passed through the
The light beam is rotated by 0 degrees, converted into a light beam whose polarization direction is horizontal to the sub-scanning direction (direction B in the plane of the paper), and emitted. On the other hand, the light beam that has passed through the periphery of the light conversion element 4 does not change its polarization direction, and exits as a light beam whose polarization direction is perpendicular to the sub-scanning direction (direction C perpendicular to the paper surface). . FIG. 3 shows an amplitude distribution when a light beam is assumed to have passed through the light conversion element 4 under different conditions and is imaged by a scanning lens.
This is an amplitude distribution when it is assumed that the light beam that has entered the light conversion element 4 has passed through the entire range. (B)
Is the amplitude distribution of the light beam when it is assumed that the incident light beam has passed through the central portion of the light conversion element 4, and is a spread beam. (C) shown by a solid line is the amplitude distribution of the light beam when it is assumed that the incident light beam has passed through the periphery of the light conversion element 4, and the main beam is smaller and the side lobe is larger than the distribution of (A). It has a distribution.

Since the light beams (B) and (C) whose polarization directions are orthogonal to each other do not interfere with each other, the light beam in the direction A perpendicular to the plane of FIG. When only the element 4 is inserted, the beam profile has a shape having side lobe portions on both sides of the main beam having a small beam spot as shown in FIG. FIG.
(A) is a vector diagram showing the beam profile of FIG. 4 as a combination of a B portion and a C portion. However, since the phase of the side lobe portion is actually inverted,
As shown in (b), the B portion and the -C portion whose phase is inverted are combined. Therefore, a polarizing filter (linear polarizer) 5 that passes only linearly polarized light in the direction D in FIG. 5A, that is, the direction perpendicular to the direction in which the B portion and the −C (minus C) portion are combined, is connected to the light conversion element. By inserting after 4, it is possible to remove only the side lobe portion and obtain a main beam with a small beam spot diameter.
Moreover, in this case, the half-wave plate light conversion element 4
In addition, since a polarizing filter including a linear polarizer is used, a main beam having a small beam spot diameter can be obtained with a small and inexpensive configuration. In this case, the light conversion element 4 is provided with a central half-wave plate having a property of changing the direction of polarization of the outgoing light beam to the direction of polarization of the incident light beam with respect to the linearly polarized incident light beam. And the area of the peripheral glass plate that has the property of emitting outgoing light in the same polarization direction with respect to the incident light of linearly polarized light, so that the beam spot diameter is small and inexpensive. It is possible to efficiently obtain a main beam having a small size. In this case, as shown in FIG. 6, a half-wave plate 11 smaller than the effective area of the light beam may be attached to the coupling lens 2 by bonding or the like. The light conversion element 11 is formed with an area smaller than the effective area of the incident light beam, and has a property of converting the polarization direction of the output light beam so as to be substantially orthogonal to the polarization direction of the incident light beam. In this case, the size and cost can be further reduced by integrating the light conversion element 11 and the coupling lens 2. Further, in this case, as shown in FIG. 7, the light conversion element 11 has an area SC for converting the polarization direction of the outgoing light beam so as to be substantially orthogonal to the polarization direction of the incident light beam, and an area of the effective area of the incident light beam. S
Is set to a value that effectively removes the primary side lobe of the emitted light beam. Therefore, if the direction of the polarization characteristic of the polarization filter 5 is predetermined,
By appropriately setting this area ratio, the primary side lobe of the emitted light beam can be effectively removed.

In general, the scanning optical system has different power arrangements in the main scanning direction and the sub-scanning direction, and has different light beam diameters. Therefore, depending on the optical system, side lobes can be effectively removed in the main scanning direction as shown in FIG. 5B, but the side lobes may be increased in the sub-scanning direction. In order to solve such a problem, a light conversion element 12 or 13 as shown in FIG. 8 or 9 is used. The light conversion element 12 shown in FIG. 8 has uniform polarization characteristics in the sub-scanning direction, and has a half-wave plate at the center in the main scanning direction. Therefore, the beam spot diameter in the main scanning direction can be reduced, and side lobes can be removed. On the other hand, the light conversion element 13 shown in FIG. 9 has uniform polarization characteristics in the main scanning direction,
It is a two-wave plate. Therefore, the beam spot diameter in the sub-scanning direction can be reduced, and side lobes can be eliminated. Further, it is possible to derive where to set the polarization axis of the polarization filter 5 by calculation. However, in practice, due to the dispersion of the divergence angle of the semiconductor laser constituting the light source 1,
Appropriate set values are shifted. Therefore, in order to obtain an appropriate set value, the light conversion element 4 is configured to be rotatable around an axis substantially parallel to a line orthogonal to the main scanning direction and the sub-scanning direction. In the above embodiment, as shown in FIG. 6, the optical conversion element 11 of the half-wave plate is mounted on the coupling lens 2. However, as shown in a modification shown in FIG. The light conversion element 11 may be mounted on the surface on the incident side of the cylindrical lens 6, and the polarizing filter 5 may be mounted on the surface on the output side of the cylindrical lens 6. Also in this case, the size and cost can be further reduced by integrating the light conversion element 11, the cylindrical lens 6, and the polarizing filter 5. Further, in the above-described embodiment or the modification, the light conversion element 11 or the polarization filter 5 is mounted on the surface of the coupling lens 2 or the surface of the cylindrical lens 6. A configuration may be adopted in which a coating having the polarization characteristics of the filter is applied. In this case, by reducing the number of parts,
Still further downsizing and cost reduction can be achieved. The present invention is most effective when the beam spot diameter defined by 1 / e ＾ 2 diameter of the maximum intensity is 60 μm or less.

[0009]

According to the present invention, after coupling the light beam from the light source, the light beam in the effective area, which is incident by the light conversion element, is converted into a polarized light beam having a plurality of regions having different polarization directions after passing therethrough. The light is converted, and the light passes through only a specific polarization direction of the light beam by the polarizing filter, and is incident on the deflector. Therefore, it is possible to reduce the side lobe and reduce the beam spot diameter of the main beam with a small and inexpensive configuration.

[Brief description of the drawings]

FIG. 1 is a diagram of a configuration of an optical scanning device according to an embodiment of the present invention, as viewed from a deflection rotation surface.

FIG. 2 is an enlarged view of a light conversion element and a polarization filter in FIG.

FIG. 3 is a diagram illustrating an amplitude distribution formed by a scanning optical system under different conditions.

FIG. 4 is a diagram illustrating a beam profile when a polarization filter is removed in FIG. 1;

FIG. 5 is a vector diagram showing a combination of a main beam and side lobes.

FIG. 6 is a diagram illustrating a configuration of a modification of the embodiment in which an optical conversion element is mounted on a coupling lens, as viewed from a deflection rotation surface.

FIG. 7 is a diagram showing an area of an effective area of a light beam and an area of a conversion area in a light conversion element.

FIG. 8 is a plan view showing a half-wave plate portion of a light conversion element according to another embodiment.

FIG. 9 shows 1/1 of a light conversion element in still another embodiment.
FIG. 3 is a plan view showing a part of a two-wave plate.

FIG. 10 is a diagram illustrating a configuration of a modification of the embodiment in which the optical conversion element is mounted on a cylindrical lens, as viewed from a deflection rotation surface.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light source 2 Coupling lens 3 Aperture 4, 11, 12, 13 Light conversion element 5 Polarization filter 6 Cylindrical lens 7 Polygon mirror 8, 9 Scanning lens 10 Photoconductor

Claims (8)

[Claims] A light source for emitting a light beam of a light beam; coupling optical system means for coupling the light beam from the light source; a deflector for deflecting the light beam from the coupling optical system means; Between the deflector, a light conversion element that converts a light beam in the effective area into a polarized light beam having a plurality of regions with different polarization directions after passing the light beam, and passes only a specific polarization direction of the light beam. An optical scanning device comprising a polarizing filter and a polarizing filter. 2. The optical conversion device according to claim 1, wherein
A first region having a property of converting a polarization direction of an output light beam to an incident light beam of linearly polarized light so as to be substantially orthogonal to a polarization direction of the incident light beam; And a second region having a property of emitting the emitted light beam. 3. The light conversion device according to claim 1, wherein
An optical scanning device, which is formed with an area smaller than an effective area of an incident light beam and has a property of converting a polarization direction of an output light beam so as to be substantially orthogonal to a polarization direction of an incident light beam. 4. The light conversion element according to claim 2, wherein a region for converting the polarization direction of the outgoing light beam so as to be substantially orthogonal to the polarization direction of the incident light beam is located at the center of the effective area of the incident light beam. An optical scanning device, being arranged. 5. The light conversion device according to claim 4,
The area ratio between the area that converts the polarization direction of the emitted light beam so as to be substantially orthogonal to the polarization direction of the incident light beam and the area of the effective area of the incident light beam is a value that effectively removes the first-order side lobe of the emitted light beam. An optical scanning device, which is set to: 6. The method according to claim 1, wherein:
The optical scanning device, wherein the light conversion element has uniform polarization characteristics in a sub-scanning direction. 7. The method according to claim 1, wherein:
An optical scanning device, wherein the light conversion element has uniform polarization characteristics in a main scanning direction. 8. The method according to claim 1, wherein
The optical scanning device according to claim 1, wherein the light conversion element is rotatable about an axis substantially parallel to a line orthogonal to the main scanning direction and the sub-scanning direction.