JPH0445413A - Optical scanning device - Google Patents

Abstract

PURPOSE:To evade a scanning line deviation even if a semiconductor laser varies in wavelength by converging the laser light which is emitted as a nearly parallel beam on a scanned surface by using a parabolic mirror or cylindrical lens. CONSTITUTION:This device is provided with a hologram disk 8 which deflects the laser light emitted by the semiconductor laser 5 and puts it in scanning motion and hologram 7 which are provided between the semiconductor laser and hologram disk and have the same spatial frequency distribution with the hologram disk, and a light converging means 9 is arranged between the hologram disk and scanned surface 10. If the projection point of the laser light 6 on the hologram disk 8 shifts owing to the wavelength variation of the semiconductor laser, it can be considered that R(lambda1) and R(lambda2) are parallel since variation in the angle of projection is a little. Further, a light beam which is made incident in parallel to the axis of symmetry (chain line) of the parabolic mirror 9 is all converged on the focus, so the parabolic mirror 9 is so arranged that R(lambda1) and the axis of symmetry are parallel, and consequently even if the laser light 6 shifts to R(lambda2) owing to the wavelength variation, the light is converged as a spot on a photosensitive drum 10.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical scanning device used in a laser beam printer or the like.

2. Description of the Related Art In recent years, as the use of office automation equipment and the like has become widespread, high-definition, low-noise laser beam printers have been attracting attention as one of their output devices. Current laser beam printers often use polygon mirror scanners as optical scanning devices, but in order to reduce costs, F-θ lensless hologram scanners are also being developed. However, for hologram scanners, when a semiconductor laser is used as a laser light source to take advantage of the diffraction effect of light, if the excavation wavelength changes due to changes in ambient temperature, etc., the diffraction angle changes and linear scanning becomes impossible. There are problems. In order to solve this problem, a method using a two-disc hologram was proposed in Japanese Patent Application Laid-Open No. 59-2010.
This is shown in Publication No. 17.

Hereinafter, an example of an optical scanning device using the above-described conventional hologram scanner will be described with reference to the drawings.

FIG. 3 shows the configuration of a conventional optical scanning device. In the figure, 1 is a laser beam, 2 is a hologram disk,
3 is a surface to be scanned, and 4 is a porogram. FIG. 4 is an explanatory diagram of a two-disc hologram. In the figure, it is assumed that the hologram disk 2 and the hologram 4 are parallel, and the wavelength of the incident light I to the hologram 4 is λ1, and the incident angle is θ11. 4, the emission angle of the diffracted light is θq1
, the incident angle of this diffracted light to the hologram disk 2 is θj1, the exit angle of the diffracted light R is θr1, and the hologram 4
and the spatial frequency distribution of the hologram disk as f
Assuming i and fj, the following relationship exists between them.

sinθq1=fi・λ1−sinθi・・・・・・(
1) sinθr1=fj・λ1−sinθj 1・(
21 Since the hologram 4 and the hologram disk 2 are parallel, s 1 noql=s inθj 1 -----
・−f3) Therefore, sinθrl= (f j−f i) ・λ1+sin
θi・・・・・・
・(4) When the wavelength of the incident light 1 is λ2, and if each subscript is represented by 2, then in the same way as above, si
nθr2= (f j−f i) ・λ2+sinθ
1
・・・・・・(5) From equations (4) and (5), sinθr2−sinθrl= (f j−f i)(
λ2−λ1)=△f・△λ ・・・・・・(
6) Since the hologram 4 and the hologram disk 2 have the same spatial frequency distribution, Δf is extremely small. Therefore, θr2=θr1 (7
). That is, even if a wavelength variation Δλ occurs in the emitted light when a semiconductor laser is used as a light source, the variation in the emission angle of the light beam R from the hologram disk 2 can be made extremely small.

Problems to be Solved by the Invention However, the above configuration has a problem in that the emission point of the laser beam on the hologram disk 2 changes, causing a slight shift on the surface to be scanned.

In view of the above-mentioned problems, the present invention provides an optical scanning device that does not cause scanning line deviation due to changes in the emission point.

Means for Solving the Problems In order to solve the above problems, an optical scanning device of the present invention includes a semiconductor laser, a hologram disk for deflecting and scanning laser light emitted from the semiconductor laser, and a semiconductor laser and a hologram. In an optical scanning device comprising a hologram provided between the hologram disk and a hologram having the same spatial frequency distribution as the hologram disk, there is a space between the hologram disk and the surface to be scanned, in which the holograms are located approximately from each other from different emission points of the hologram disk. The apparatus is equipped with a condensing means for condensing the laser light emitted in parallel onto the scanned surface.

Function The present invention uses the above-described configuration to focus the laser beams emitted substantially parallel from different emission points of the hologram disk onto the scanned surface by the condensing means, so that the emission points of the laser beams generated on the hologram disk can be focused on the surface to be scanned. This is to remove the misalignment.

Embodiment An optical scanning device according to an embodiment of the present invention will be described below with reference to the drawings. 11 shows the configuration of the optical scanning device in the embodiment. In FIG. 1, 5 is a semiconductor laser, 6 is a laser beam, 7 is a hologram, 8 is a hologram disk, and 9 is a parabolic mirror as a condensing means. The curvature is zero in the scanning direction, and a parabolic curved surface is created in the sub-scanning direction. 10
is a photosensitive drum having a surface to be scanned.

Regarding the optical scanning device configured as above, the following is the first part.
The operation will be explained using FIG. First, FIG. 2 is a cross-sectional view of the hologram 7 to photosensitive drum 10 shown in FIG. 1 taken along a plane that includes the laser beam 6 and is perpendicular to the scanning line. In FIG. 2, when the emission point of the laser beam 6 on the hologram disk 8 changes due to wavelength fluctuation of the semiconductor laser, the change in the emission angle is extremely small as shown in the conventional example, so R(λ1) and R (λ2) can be considered parallel.

In addition, all the light rays that are incident parallel to the axis of symmetry of the parabolic mirror 9 (Figure 2 - dotted chain line) are focused on the focal point of the parabolic mirror 9, so that the axis of symmetry is parallel to R (λ1). By arranging the parabolic mirror 9 so that the wavelength changes, the laser beam 6
is shifted to R(λ2), on the photosensitive drum 10, −
The light will be focused on a point.

Note that although a parabolic mirror is used as the condensing means in the above embodiment, a cylindrical lens or the like may also be used.

Effects of the Invention As described above, according to the present invention, even if wavelength fluctuation occurs in a semiconductor laser, scanning line deviation can be avoided.

[Brief explanation of drawings]

FIG. 1 shows an optical scanning device 5 in an embodiment of the present invention.
... Semiconductor laser, 6... Laser light, 7...
... Hologram, 8 ... Hologram disk, 9 ... Parabolic mirror, 10 ... Photosensitive drum. To-koshu・kuchii-ra-1F 6-...L-su "first 1--one claw n7°u4

Claims (1)

[Claims] Light consisting of a semiconductor laser, a hologram disk that deflects and scans laser light emitted from the semiconductor laser, and a hologram that is provided between the semiconductor laser and the hologram disk and has the same spatial frequency distribution as the hologram disk. In the scanning device, a focusing means is provided between the hologram disk and the surface to be scanned, for condensing laser beams emitted substantially parallel to each other from different emission points of the hologram disk onto the surface to be scanned. An optical scanning device characterized by: