JPS61141418A - Optical beam scanner - Google Patents

Abstract

PURPOSE:To decrease the positional fluctuation of a beam on a scanning plane by forming a hologram disk into two-layered constitution in such a manner that the respective layers have diffraction directions of opposite tendencies and that the synthetic sum of the space frequencycies of the two-layered hologram have a max. point at the reconstruction point or near the same. CONSTITUTION:The hologram disk 10 having the two-layered construction is constituted by joining, via a spacer 15, the 1st disk 11 having the hologram 13 of which the interference fringes are made to a monotonic change space frequency by the interference of a spherical wave 17 diverged from one point A on the center line 16 of rotation and a plane wave 18 having the optical axis at the disk plane normal of the incident point of the reconstruction beam and the 2nd disk 12 having the hologram 14 of which the interference fringes are made to the monotonic change space frequency of the interference of the divergent spherical wave 19 diverged from the point (c) on the side outer than the reconstruction point with respect to the axis 16 of rotation and the plane wave 20 having the optical axis at the disk plane normal of the incident point of the reconstruction beam. The incident point of the reconstruction light moves merely near the max. point even if the disk 10 has eccentricity when part of the spherical wave 17 is made incident on the reconstruction point from the point A.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a light beam scanning device using a hologram used in a laser printer or the like.

In a light beam scanning device using a hologram used in a laser printer, improvement in beam position accuracy is required in order to guarantee printing quality.

[Conventional technology]

Causes of darkness deterioration in optical beam scanning devices that use holograms include: ■ Eccentricity of the hologram disk, ■ Tilt of the hologram disk, and ■ Fluctuations in the diffraction angle due to wavelength fluctuations due to temperature changes in the laser diode used as the light source. There is. Of these, ■ and O can be removed by using the reproduced wave 4 on the hologram disk 3 created by the interference of the spherical waves 1 and 2 as shown in FIG. But O cannot be solved. Therefore, as a means to solve O, the fifth
As shown in figure a, two holograms 5 whose diffraction directions are opposite to each other
A method of overlapping 6 and 6 has already been proposed (patent application 1982).
-111636). In this method, when the wavelength of the reproduction light 7 shifts to the longer wavelength side, the diffraction angle by the first hologram 5 increases, but the opposite diffraction angle by the second hologram 6 also increases, so the scanning light 8 On the scanning plane 9, the holograms that are related to the wavelength converge at approximately the same position. In this case, the interference fringes of the upper and lower two holograms are as shown in Figure 5, c. In other words, the hologram 5 is monotonous. The variable spatial frequency hologram 6 is a hologram that has an extreme value at the reproduction point indicated by the cross mark. Therefore, the composite hologram has little beam position variation with respect to wavelength variation (mode hop due to temperature change) of the semiconductor laser.

[Problem that the invention seeks to solve]

With the above configuration, there is a problem in that when the hologram disk has eccentricity, the spatial frequency of the composite hologram changes monotonically, so the beam position is likely to fluctuate due to the influence of eccentricity.

[Means for solving problems]

The present invention provides a light beam scanning device that solves the above-mentioned problems.In the light beam scanning device that scans by diffracting a light beam while rotating a hologram disk, the hologram disk has a two-layer structure. , and the respective layers have diffraction directions with opposite tendencies, and the combined sum of the spatial frequencies of the two hologram layers becomes an extremum value or its vicinity at the reproduction point.

[For production]

The above-mentioned optical beam scanning device has a hologram disk having a two-layer structure, each layer having an opposite diffraction direction, and the combined sum of the spatial frequencies of the two-layer holograms being at or near the extreme value at the reproduction point. By doing so, even if there is some eccentricity, there is little change in the spatial frequency at the reproducing point, so fluctuations in the beam position on the scanning plane are reduced, and highly accurate optical scanning can be performed.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings. 1
FIG. 1 is a diagram for explaining one embodiment of the present invention,
a is a cross-sectional view thereof, b and c are plan views showing interference fringes of each hologram, and d is a plan view showing interference fringes of a composite hologram. In the figure, IO is a hologram disk, 11 is a first disk, 12 is a second disk, 13, 14
15 is a hologram, 15 is a spacer, and 16 is the center of rotation of the disk.

In this embodiment, as shown in figure a, a point A on the rotation center wA16 is used.
The first hologram 13 has a hologram 13 formed so that the interference fringes are monotonically changing spatial frequency as shown in Fig. b due to the interference between the spherical wave 17 diverging from the spherical wave 17 and the plane wave 18 whose optical axis is the normal to the disk surface at the point of incidence of the reproduction beam. disc 11 and rotating shaft 1
6, the interference fringes change monotonically as shown in diagram C due to interference between a diverging spherical wave 19 diverging from point C located outside the reproduction point and a plane wave 20 whose optical axis is the normal to the disk surface at the reproduction beam incident point. A hologram disk 10 having a two-layer structure is constructed by joining a second disk 12 having a hologram 14 formed to have a spatial frequency with a spacer 15 in between.

In this embodiment configured in this way, the hologram 13,
The spatial frequency of the hologram 10 synthesized from hologram 14 is shown in Figure 1d.
It becomes as follows, and it is possible to have an extreme value at the reproduction point indicated by the X mark. Therefore, when part of the spherical wave 17 is incident on the reproduction point from point A as reproduction light, even if the disk 10 is eccentric, the input point of the reproduction light only moves near the extreme value, so it is diffracted by the disk 10. Fluctuations in the position of the emitted scanning beam in the scanning plane are prevented. Note that, as described in the conventional example, this embodiment has the effect of preventing positional fluctuations of the scanning beam due to wavelength fluctuations of the laser diode.

FIG. 2 is a diagram for explaining the second embodiment. The difference between this embodiment and the previous embodiment is that the hologram disk 10 is constructed by bringing the first disk 11 and the second disk 12 into close contact with each other except for the spacer 15, and the effect is the same as that of the previous embodiment. It is.

FIG. 3 is a diagram for explaining the third embodiment, in which a is a sectional view and C is a perspective view. The difference between this embodiment and the first embodiment is that instead of the plane waves 18 and 20 that create the two holograms 13 and 14, a spherical wave 30,
31 was used. Note that this spherical wave may be a conical spherical wave as shown in Figure 3, or a pyramidal spherical wave as shown in Figure 3C, and may be either divergent or convergent.

〔Effect of the invention〕

As explained above, according to the present invention, the hologram disk has a two-layer structure, each layer has a diffraction direction with an opposite tendency, and the combined sum of the spatial frequencies of the two-layer hologram reaches an extreme value at the reproduction point or reaches an extreme value at the reproduction point. By placing them close together, it is possible to prevent the position of the scanning light from shifting on the scanning surface even if there is some eccentricity in the hologram disk or even if there is a wavelength fluctuation of the laser diode used as the light source for generating the scanning light. It is very effective.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the first embodiment of the light beam scanning device of the present invention, FIG. 2 is a diagram for explaining the second embodiment, and FIG. 3 is a diagram for explaining the third embodiment. FIGS. 4 and 5 are diagrams for explaining a conventional light beam scanning device. In the figure, lO is a hologram disk, 11 is a first disk, 12 is a second disk, 13 and 14 are holograms, 15 is a spacer, and 16 is the center of rotation of the hologram disk.

Claims (1)

[Scope of Claims] 1. In a light beam scanning device that diffracts and scans a light beam while rotating a hologram disk, the hologram disk has a two-layer structure, and each layer has an opposite diffraction direction, and A light beam scanning device characterized in that the composite sum of spatial frequencies of two layers of holograms becomes an extremum value or its vicinity at a reproduction point. 2. The above two-layer hologram is created with a wavefront that is symmetrical about the rotation axis for one hologram and a wavefront whose optical axis is the normal to the disk surface at the point of incidence of the reproduction beam, and for the other hologram, the wavefront is symmetrical about the rotation axis, and the wavefront for the other hologram is created using a wavefront that is symmetrical with respect to the rotation axis. The light beam according to claim 1, wherein the light beam has a wavefront whose optical axis is the disk surface normal of the point, and a wavefront which tends to diverge or converge at a position outside the reproduction point with respect to the rotation axis. scanning device.