JPH07306376A - Holographic light beam scanning device - Google Patents

Abstract

(57) [Summary] [Object] The most important object of the present invention is to improve the scanning accuracy of a light beam by eliminating the curvature of the scanning line, minimizing aberrations, and eliminating the fluctuation of the focusing position due to the fluctuation of the laser wavelength. To aim. According to the present invention, as a hologram element for scanning a light beam, a rotatable light beam scanning in which interference fringes whose spatial frequency changes in one element in a direction substantially perpendicular to the rotation direction are recorded according to the rotation direction. A hologram lens for focusing is used between the laser light source that generates a light beam and the hologram element for scanning the light beam, and a focusing hologram lens that focuses the light beam from the laser light source and makes it enter the hologram element for scanning the light beam is arranged. It is characterized by setting up.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a holographic light beam scanning device used for scanning a light beam, and in particular, it eliminates the curvature of a scanning line and minimizes aberrations, and the focusing position due to laser wavelength fluctuation. The present invention relates to a holographic light beam scanning device capable of improving the scanning accuracy of a light beam by eliminating the fluctuation of

[0002]

2. Description of the Related Art Conventionally, various types of light beam scanning devices for scanning a light beam have been used. One of them is a light beam scanning device having a light beam scanning hologram element. There is.

In this case, the conventional hologram element for scanning a light beam is manufactured by forming concentric interference fringes in a direction substantially the same as the rotation direction of itself, as shown in FIG. .

However, since this kind of light beam scanning hologram element is the same as the hologram lens, as shown in FIG. 7, the scanning line is curved, a large aberration is generated, or the laser wavelength is increased. There is a problem that the condensing position fluctuates due to the fluctuation of.

Therefore, recently, as a means for solving such a problem, another hologram lens for correcting aberration is separately provided as disclosed in, for example, Japanese Patent Laid-Open No. 172617/1983. The one used has been proposed. However, this type has a problem that the method for manufacturing itself is very complicated.

[0006]

As described above, the conventional light beam scanning device has a problem that the scanning accuracy of the light beam is low. The present invention has been made to solve the above problems, and scans a light beam by eliminating the curvature of the scanning line and minimizing aberrations, and eliminating the fluctuation of the focusing position due to the fluctuation of the laser wavelength. An object of the present invention is to provide a holographic light beam scanning device capable of improving accuracy.

[0007]

In order to achieve the above object, first, in the invention according to claim 1, in a light beam scanning device used for scanning a light beam, a laser light source for generating a light beam. And a rotatable light beam scanning hologram element in which interference fringes are recorded in one element in a direction substantially perpendicular to the rotation direction such that the spatial frequency changes according to the rotation direction, a laser light source and a light beam scanning hologram. And a focusing hologram lens which is disposed between the element and the element and focuses the light beam from the laser light source to make it enter the hologram element for scanning the light beam.

According to a second aspect of the invention, in the holographic light beam scanning device of the first aspect of the invention, a glass for optical path length correction is provided on the emission side of the diffracted light from the light beam scanning hologram element. Is added.

In particular, the hologram element for scanning the light beam is a volume phase hologram element. Also,
The focusing hologram lens is a volume phase hologram element.

[0010]

Therefore, in the holographic light beam scanning device of the present invention, as a light beam scanning hologram element, the spatial frequency is changed in one element in a direction substantially perpendicular to the rotation direction of the light beam scanning device. A rotatable light beam scanning hologram element in which interference fringes are recorded is used, and the light beam from the laser light source is focused between the laser light source that generates the light beam and the light beam scanning hologram element. By arranging the focusing hologram lens to be incident on the beam scanning hologram element, the focusing hologram lens has the focusing function of light and the optical beam scanning hologram element has the scanning function of light. The degree of freedom in design can be increased.

At the same time, the hologram element for scanning the light beam functions not as a lens but as a linear grating, so that the curvature of the scanning line can be eliminated. Further, the aberration can be made sufficiently small irrespective of the hologram element for scanning the light beam because only the focusing hologram lens having the focusing function has the aberration. Further, the focusing hologram lens and the light beam scanning hologram element are arranged and arranged so that the focusing position does not change even when the wavelength of the laser changes.

As a result, the scanning accuracy of the light beam can be improved. Furthermore, by disposing an optical path length correction glass for correcting the optical path length on the emission side of the diffracted light from the light beam scanning hologram element (between the light beam scanning hologram element and the photosensitive drum), It is possible to reduce the spot image in the peripheral portion, that is, to improve the resolution.

On the other hand, by using the volume phase hologram element as the light beam scanning hologram element, unnecessary direct transmitted light and -1st order diffracted light are eliminated as described above, and light can be made incident in the vertical direction. In addition to the above, since the diffraction efficiency is high, the light utilization efficiency is high, and it becomes possible to realize a light beam scanning device even with a low output laser.

This makes it possible to reduce the cost, size, and weight of the device itself. In addition, by using a volume phase hologram element for the focusing hologram lens, unnecessary direct transmitted light and -1st order diffracted light are eliminated as described above, and at the same time, the light utilization efficiency is increased due to the high diffraction efficiency. It is possible to realize a light beam scanning device even with a low-power laser. This makes it possible to further reduce the cost, size, and weight of the device itself.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a plan view showing a configuration example of a light beam scanning hologram element according to the present invention.

That is, as shown in FIG. 1, the hologram element 1 for scanning a light beam according to the present embodiment has a spatial frequency that increases in one element in the direction substantially perpendicular to the direction of rotation of the element. Interference fringes are recorded.

Here, the light beam scanning hologram element 1
Is a volume phase hologram element. Next, FIG. 2 shows a configuration in which the holographic light beam scanning device including the light beam scanning hologram element 1 of this embodiment is applied to a writing unit of a laser printer capable of printing A4 size paper. It is a schematic diagram showing an example.

That is, as shown in FIG. 2, the holographic light beam scanning device of this embodiment includes a semiconductor laser 2 which is a laser light source for generating a light beam, and one element in a direction substantially perpendicular to the rotation direction. The rotatable optical beam scanning hologram element 1 in which interference fringes having a higher spatial frequency are recorded according to the rotation direction is disposed between the semiconductor laser 2 and the optical beam scanning hologram element 1. A focusing hologram lens 3 for focusing the light beam from the laser 2 and making it enter the light beam scanning hologram element 1, and an exit side of the diffracted light from the light beam scanning hologram element 1, that is, the light beam scanning hologram element 1. And an optical path length correcting glass 5 for correcting the optical path length, which is arranged between the photosensitive drum 4 and the photosensitive drum 4.

Here, as the semiconductor laser 2, 78
A 0 nm semiconductor laser is used. The distance from the light beam scanning hologram element 1 to the photosensitive drum 4 is 300.
mm, the scan length is 240 mm.

Further, the focusing hologram lens 3 is a volume phase hologram element. Next, the light beam scanning hologram element 1 is manufactured by any of the following methods.

(A) As shown in FIG. 3, a laser beam from a refractive optical element (or a reflective optical element) 6 having a toric surface is used as an object beam, and this is a reference beam which is a laser beam from a half mirror 7. And the interference fringes are recorded on the photoresist photosensitive material 8 so as to produce the pattern.

That is, according to this method, interference fringes having spatially different spatial frequencies are holographically recorded in the same direction as the radius from the rotation axis of the light beam scanning hologram element 1 toward the circumferential direction. Is the way to do it.

For this reason, the light from the refractive optical element (or reflective optical element) 6 having a toric surface obtained by extending the cylindrical lens in the rotational direction is used as object light. (B) A method in which a pattern of interference fringes is mask-drawn using an electron beam drawing apparatus, a laser drawing apparatus, or another pattern drawing apparatus, and then the pattern is reduced to a required size and photograph reproduction or contact exposure is performed.

That is, according to this method, interference fringes having spatially different spatial frequencies in the same direction as the radius extending from the rotation axis of the light beam scanning hologram element 1 in the circumferential direction are copied from the mask pattern in the same size or reduced size. It is a method of recording by doing.

This mask pattern is produced by drawing and copying at the same size if it is an apparatus capable of fine patterning such as an electron beam drawing apparatus or a laser drawing apparatus. Also,
Laser printers, plotters, film printers, etc., which have low resolving power, are produced by reduction copying.

In this embodiment, as a concrete example, a photoresist photosensitive material 8 is used by using an optical system as shown in FIG.
Interference fringes were recorded on, and developed, washed with water and dried. In this case, a He-Cd laser (442 nm) whose photoresist has high sensitivity was used as a laser as a light source.

The light beam scanning hologram element 1 has a circular shape with a diameter of about 100 mm, and eight hologram elements are arranged therein as shown in FIG.
Next, the operation of the holographic light beam scanning device provided with the light beam scanning hologram element 1 of the present embodiment configured as described above will be described.

In FIG. 2, the diverging spherical wave emitted from the semiconductor laser 2 becomes focused light by the focusing hologram lens 3 having a focal length of 350 mm, diffracted by the light beam scanning hologram element 1 and focused on the photosensitive drum 4. To do. Then, in this case, when the light beam scanning hologram element 1 rotates,
The diffraction angle changes and scanning is performed.

At this time, the angle of the incident light is set to 25 degrees so that the transmitted light does not directly enter the photosensitive drum 4. Therefore, 65.7 lines / mm at the right end and 1018 lines / mm at the left end of one element of the light beam scanning hologram element 1 in FIG.
The diffraction gratings with the spatial frequencies of are recorded respectively. Therefore, the diffraction angle at the right end is 3.2 degrees, and at the left end is 46.8.
It is possible to scan 240 mm on the photosensitive drum 4.

However, when the diffraction angle becomes large, the distance from the light beam scanning hologram element 1 to the photosensitive drum 4 becomes as large as 323 mm, which may cause defocusing. The diffracted light is compensated for the optical path length by the optical path length correction glass 5 and then condensed on the photosensitive drum 4.

Further, in order to avoid the influence of the transmitted light and the minus first-order diffracted light, as shown in FIG. 2, the incident light is made incident from an oblique direction perpendicular to the interference fringes. Further, the focusing hologram lens 3 is used as the light beam scanning hologram element 1.
When the wavelength variation of the semiconductor laser 2 occurs by arranging one element on the low spatial frequency side, the diffraction angle changes in the direction opposite to the light beam scanning hologram element 1 as shown by the broken line in the figure. As a result, the condensing position on the photosensitive drum 4 is prevented from changing.

As described above, in the holographic light beam scanning device including the light beam scanning hologram element 1 of this embodiment, the light beam scanning hologram element is used as a hologram element for light beam scanning in a direction substantially perpendicular to the rotation direction of itself. A rotatable light beam scanning hologram element 1 in which interference fringes having a spatial frequency that increases according to the rotation direction are recorded in one element is used, and a semiconductor laser 2 that generates a light beam and a light beam scanning hologram element are used. Between 1 and
Since the focusing hologram lens 3 that focuses the light beam from the semiconductor laser 2 and makes it enter the light beam scanning hologram element 1 is provided, the focusing hologram lens 3 has the function of focusing the light and the light scanning is performed. Since the light beam scanning hologram element 1 has the function, the degree of freedom in device design can be increased.

At the same time, the light beam scanning hologram element 1 functions not as a lens but as a linear grating, so that it is possible to eliminate the curvature of the scanning line. Further, since the aberration is present only in the focusing hologram lens 3 having the focusing function, it is possible to make the aberration sufficiently small irrespective of the light beam scanning hologram element 1. Furthermore, the focusing hologram lens 3 and the light beam scanning hologram element 1 are arranged and diffracted so that the focusing position does not change even when the wavelength of the semiconductor laser 2 changes. Even when there is a wavelength variation, the focus position does not vary.

As a result, the scanning accuracy of the light beam can be improved. Further, an optical path length correction glass 5 for correcting the optical path length is provided on the emission side of the diffracted light from the light beam scanning hologram element 1, that is, between the light beam scanning hologram element 1 and the photosensitive drum 4. Therefore, it is possible to reduce the spot image in the peripheral portion, that is, to improve the resolution.

On the other hand, since the light beam scanning hologram element 1 is a volume phase type hologram element, the diffraction efficiency can be almost 100%, so that unnecessary direct transmitted light and -1st order diffracted light are eliminated. As shown in FIG. 4, not only is it possible to make light incident in the vertical direction, but also high light utilization efficiency due to high diffraction efficiency, and a light beam scanning device can be realized even with a low-power laser. it can.

As a result, the cost, size and weight of the apparatus itself can be reduced. In addition, since the focusing hologram lens 3 is a volume phase hologram element, unnecessary direct transmitted light and -1st order diffracted light are eliminated as described above, and at the same time, the diffraction efficiency is high and the light utilization efficiency is high. It is possible to realize a light beam scanning device even with a low-power laser.

This makes it possible to further reduce the cost, size and weight of the device itself. On the other hand, when manufacturing the light beam scanning hologram element 1 of the present embodiment, the laser light from the refractive optical element or the reflective optical element 6 having a toric surface is used as the object light and interfered with the reference light. The interference fringes are recorded, or the pattern of the interference fringes is mask-drawn using an electron beam drawing device, a laser drawing device, or another pattern drawing device,
After that, the hologram is manufactured by reducing the size to a required size and performing photocopying or contact exposure, so that it is not necessary to separately use a hologram lens for aberration correction as in the conventional case. Element 1
Can be easily manufactured.

The present invention is not limited to the above embodiment, but can be implemented in the same manner as described below. (A) In the above embodiment, the case where the light beam scanning hologram element 1 is a volume phase type hologram element has been described, but the present invention is not limited to this, and the light beam scanning hologram element 1 is another type hologram element. You may do it.

(B) In the above embodiment, the case where the focusing hologram lens 3 is a volume phase type hologram element has been described, but the present invention is not limited to this, and the focusing hologram lens 3 may be another type hologram element. You may

(C) In the above embodiment, the light beam scanning hologram element is a light beam in which interference fringes are recorded in one element in a direction substantially perpendicular to the rotation direction such that the spatial frequency increases in the rotation direction in one element. Although the case of using the scanning hologram element has been described, the invention is not limited to this.
Also, as a hologram element for scanning a light beam, a hologram element for scanning a beam used in which an interference fringe in which a spatial frequency is lowered in one element in a direction substantially perpendicular to the rotation direction is recorded By applying the invention in the same manner, the same effect as the above case can be obtained.

(D) In the above embodiment, the case where the glass for correcting the optical path length is provided on the exit side of the diffracted light from the hologram element for scanning the light beam has been described. However, the glass for correcting the optical path length is necessary. It should be provided according to the above.

FIG. 5 shows a holographic light beam scanning apparatus equipped with a light beam scanning hologram element 1 of the present embodiment, which does not have a light path length correcting glass 5 for correcting the light path length. It is a schematic diagram showing a configuration example when applied to a writing unit of a laser printer capable of printing.

(E) In the above embodiment, the case where the semiconductor laser is used as the laser light source has been described, but the present invention is similarly applied to the case where other lasers are used as the laser light source. The same effect as in the above case can be obtained.

[0044]

As described above, according to the present invention, as a hologram element for scanning a light beam, interference fringes in which the spatial frequency changes according to the rotation direction in one element in a direction substantially perpendicular to the rotation direction are recorded. Using the rotatable hologram element for scanning a light beam, the hologram element for scanning a light beam is formed by focusing the light beam from the laser light source between the laser light source for generating a light beam and the hologram element for scanning a light beam. A focusing hologram lens to be incident on the optical path length correction glass is disposed, and if necessary, an optical path length correction glass for correcting the optical path length is disposed on the exit side of the diffracted light from the light beam scanning hologram element. Therefore, the curvature of the scanning line is eliminated, the aberration is minimized, and the fluctuation of the focusing position due to the fluctuation of the laser wavelength is eliminated to improve the scanning accuracy of the light beam. Mel is possible holographic optical beam scanning device can be provided.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of a hologram element for scanning a light beam according to the present invention.

FIG. 2 is a schematic diagram showing a configuration example in which the holographic light beam scanning device including the light beam scanning hologram element of the embodiment is applied to a writing unit of a laser printer.

FIG. 3 is a schematic diagram for explaining an example of a method for manufacturing the light beam scanning hologram element according to the embodiment.

FIG. 4 is a schematic diagram showing another configuration example in the case where the holographic light beam scanning device including the light beam scanning hologram element of the same embodiment is applied to a writing unit of a laser printer.

FIG. 5 is a schematic view showing another configuration example when the holographic light beam scanning device including the light beam scanning hologram element according to the present invention is applied to a writing unit of a laser printer.

FIG. 6 is a plan view showing a configuration example of a conventional light beam scanning hologram element.

FIG. 7 is a schematic view for explaining a problem of light beam scanning using a conventional light beam scanning hologram element.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Hologram element for scanning light beam, 2 ... Semiconductor laser, 3 ... Hologram lens for focusing, 4 ... Photosensitive drum, 5
... Glass for optical path length correction, 6 ... Refractive optical element (or reflective optical element), 7 ... Half mirror, 8 ... Photoresist photosensitive material.

Claims (4)

[Claims] 1. A light beam scanning device used for scanning a light beam, wherein a laser light source for generating the light beam and a spatial frequency change in one element in a direction substantially perpendicular to the rotation direction according to the rotation direction. A rotatable light beam scanning hologram element in which such interference fringes are recorded, is arranged between the laser light source and the light beam scanning hologram element, and focuses the light beam from the laser light source to A holographic light beam scanning device comprising: a focusing hologram lens which is made incident on a light beam scanning hologram element. 2. The holographic light beam scanning device according to claim 1, wherein a glass for optical path length correction is added to a side of the diffracted light emitted from the light beam scanning hologram element. And a holographic light beam scanning device. 3. The holographic light beam scanning device according to claim 1, wherein the light beam scanning hologram element is a volume phase hologram element. 4. The holographic light beam scanning device according to claim 1, wherein the focusing hologram lens is a volume phase hologram element.