JPS5821225A - Light scanning device - Google Patents

Abstract

PURPOSE:To shorten the light path length of a light scanning device for scanning the reproduced light of a hologram disk on its scanning surface through a convex mirror to reduce the size of the disk by arranging a ftheta lens between the convex mirror and scanning surface. CONSTITUTION:Laser beam is divided into two coherent beams 10, 11 by a light divider and one beam 10 is vertically penetrated into a hologram recording element 13 as reference light. The other beam 11 is made a parallel beam perpendicular to a rotational axis 12, reflected by a spherical convex mirror 14 having its spherical center on the axis 12 to irradiate a disk 13 and made to interfere with the reference light 10 to form a hologram. A hologram disk 3 is obtained by repeating exposure while rotating the disk 13 intermittently. The reproduced light obtained by irradiating the reference light from the lower part of the disk 3 is reflected by the convex reflecting mirror 7 and an image is formed on a scanning surface P through a ftheta lens L1. Consequently the light path length is shortened by the lens L1 and the size of the device is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical scanning device using a hologram lens as a means for deflecting a scanning beam.

In a laser printer, a light beam emitted by a laser is modulated (flashing) according to an information signal, and the light beam scans the surface of a photoreceptor to form an image corresponding to the information signal. In this case, main scanning is usually performed by deflecting the direction of the light beam, and sub-scanning is usually performed by sending the photoreceptor. Conventional means for deflecting the scanning beam for the main scanning described above is to rotate a pyramid-shaped or prismatic rotating polygon mirror at high speed in synchronization with an information signal, and to sequentially change the direction of reflection of the scanning beam. However, it was extremely difficult to make each mirror surface of this rotating polygon mirror explode in the correct direction, which inevitably led to limitations in accuracy and extremely high costs.

As an optical scanning device that eliminates this drawback, a device that uses a hologram lens as a deflecting means is known. When a hologram lens equipped with a diffraction grating with a stepwise change in grating spacing is moved in a fixed direction and a light beam continues to be irradiated onto the hologram lens from a fixed direction at a fixed position, the light beam will be diffracted according to the grating spacing. , the diffraction direction changes stepwise.

As shown in FIG. 1, the deflection means of a laser printer using this principle consists of arranging a plurality of the above-mentioned hologram lenses 2 on a plane disk l in an annular shape around the rotation axis 6 of the disk. A bologram disk 3 consisting of the second
As shown in the figure, the disc! If a parallel light beam 4 modulated according to an information signal is incident on the hologram lens 2 at a fixed position while the motor M is attached coaxially to the shaft of the motor M and rotated at a constant speed, the hologram lens 20 will rotate and the diffracted reproduced light 5 will be generated. The emitting direction of the light changes gradually, and each porogram lens is deflected within a predetermined angle range, thereby scanning the photoreceptor surface (scanning surface) P.

Scanning of a single hologram lens 2 is performed, and sub-scanning is performed by continuously feeding the photoreceptor in the sub-scanning direction. By continuously rotating the hologram disk 3 in this way and continuing to irradiate a fixed position with the light beam modulated by the information signal, an image corresponding to the information signal is formed on the photoreceptor.

However, if the scanning plane is directly optically scanned by the light 4I5 deflected by the hologram disk 3, the scanning line on the scanning plane will be curved in an arched manner, which is inconvenient.
As shown in the figure, a spherical convex mirror 7t whose spherical center is located at point 0 on the rotational axis 6 of the hologram disk 3 is provided so as to cover the deflection range on the optical path of the above-mentioned diffraction reproduction beam, and a reflected beam 8 by the convex mirror 7 is provided. There is a known method of straightening the scanning line by scanning the scanning plane P using .

As shown in FIGS. 2 and 3, the beam 8 reflected by the convex mirror 7 is deflected at a constant angular velocity within a plane parallel to the surface of the hologram disk 30, thereby drawing a straight scanning line on the scanning plane P. However, this method has two drawbacks: [F] Curvature of field on the scanning surface ■ Non-uniform scanning speed. That is, in this device, the convex mirror 7
The locus of the convergence point of the reflected beam is curved in an arc shape as shown by P' in Fig. 3, and the scanning speed is constant on the 21 plane mentioned above, but on the plane P. 1 is not constant, and the scanning speed becomes faster toward the scanning end. In order to improve these two drawbacks, conventional methods have been to increase the distance between the disk 3 and the scanning surface P so that the amount of curvature of field can be adjusted to the depth of focus. By making the path length longer, the uniform velocity approximately satisfies the allowable value.

However, this method has a long path length, which hinders the miniaturization of a multi-scan device, and also makes it difficult to obtain a long scan length.

An object of the present invention is to improve the above-mentioned drawbacks of an optical scanning device using a conventional hologram lens as a means for deflecting a scanning beam, and to provide an optical scanning device that can be miniaturized by shortening the optical path length. With the goal.

Hereinafter, the present invention will be explained in detail based on drawings showing embodiments thereof.

First, a method for forming a hologram disk used in the optical scanning device of the present invention will be explained with reference to FIG.

A laser beam emitted by a laser (not shown) is split into two mutually coherent beams 10 and 11 by a beam splitter (not shown).
The light beam is perpendicularly incident on a hologram recording material 13, such as a circular flat plate of silver salt, which is the material of a hologram disk, which is coaxially attached to a hologram disk 2, and becomes a reference beam.

The other beam 11 is made into a parallel beam perpendicular to the rotation axis 12, and then reflected by a spherical convex sphere 14 having a spherical center on the axis of the axis 12, and the reflected diverging light 15 is used as the object beam described above. The material disk 13 is irradiated with the reference light lO
The material disk 13 is exposed to light by causing interference with the light.

If the material disk 13 is rotated once while being fed intermittently around the rotating shaft 12, and exposed, developed, and fixed several times during that period, a plurality of hologram lenses 2 as described earlier in FIG. 1 can be formed. Hologram disks 3 arranged in a ring shape are obtained.

Optical scanning using the hologram disk manufactured as described above has already been explained in FIGS. is the conjugate light # (i.e., as shown in FIG.
It is necessary to ensure that the light rays enter perpendicularly from the rear surface). By irradiating the hologram disk in such a direction, reproduction light that travels through the hologram lens 2 in a direction opposite to the object light during hologram production can be obtained. By reflecting this by the convex mirror 7, it becomes a parallel beam that travels in a direction perpendicular to the rotation axis 6. This parallel beam 8 is deflected at a constant angular velocity as the disk 3 rotates, but the conventional apparatus shown in FIGS. 2 and 3 has problems with curvature of field and non-uniform scanning speed. As described above, in the embodiment of the present invention shown in FIGS. An optical system L1 is provided.

Therefore, as the disk 3 rotates, the parallel beam 8 is deflected at a constant angular velocity by the convex mirror 7 and reflected by the optical system LX.
incident on . □ This optical system LX has slightly different characteristics from a normal imaging optical system. In a normal imaging optical system, if the focal length is f1 and the angle of incidence is θ, the image height H is H"f @ tanθ. Become.

On the other hand, the optical system Ll used in the apparatus of the present invention is an optical system having characteristics such that the image height H is H=f·θ, and is often called an fθ lens.

FIG. 7 shows an example of the configuration of this optical system L1. This optical system is composed of a concave lens 20 and a convex lens 22 in order from 9 in the figure. The principal ray of the parallel beam deflected after being reflected by the convex mirror 7 is i'! ! There is a point N (see FIGS. 5 and 6 □) where 'x intersects, and the optical system Ll is arranged so that the vicinity of this N point becomes the entrance pupil.

- As an example, if the focal length is f=100. The details of this optical element in the case of Om are as follows.

Entrance pupil position do=-12-2211From the first surface of IIC] Radius of curvature (w,) Distance between surfaces (■) Refractive index d, =
1. ss The deflected beam refracted by such an optical system Ll focuses scanning light at a position at a focal length f from the second principal point of the lens.

This scanning light forms a scanning spot on one plane, and the scanning speed becomes constant on the scanning plane P.

As described above, the present invention makes it possible to perform plane scanning and uniform speed scanning, which were difficult in conventional optical scanning using a porogram disk, and as a result, the path length of the light beam can be shortened and compactness can be achieved.

In the above embodiment, a parallel beam that is perpendicularly incident on the disk is used as the reference light when producing the hologram.
The reference light is not limited to this, and a diverging light that diverges from a point on the rotation axis may be used as the reference light. In this case, during playback, the hologram can be illuminated with a focused light that focuses on the divergence point of the reference beam of the poem from the opposite side of the disk. Can also be applied to type holograms

[Brief explanation of the drawing]

FIG. 1 is a plan view of a conventional device and a hologram disk used in the present invention, FIG. 2 is a side view showing an example of a conventional optical scanning device using a hologram, FIG. 3 is a plan view thereof, and FIG. The figure is a side view explaining the method for producing a hologram disk, FIG. 5 is a side view showing an embodiment of the present invention, FIG. 6 is a plan view thereof, and FIG. 7 is an example of an optical system used in the present invention. FIG. 2...Hologram lens 3...Hologram disk 4...Information light (reproduction illumination light) 5...Reproduction light 6...Rotation axis 7...Convex mirror P...Scanning surface Ll... Optical system (f/θ lens) Fig. 4 Fig. 6 Fig. 7

Claims (1)

[Claims] A hologram disk consisting of a plurality of hologram lenses arranged annularly on a disk with its rotation axis as the center is rotated around its rotation axis, and reproduced illumination light is incident on the hologram lenses at a fixed position. The reproduction target emitted by the hologram lens is made incident on a convex mirror having a spherical center on the rotational axis of the disk, and is deflected in a plane perpendicular to the rotational axis of the disk, which scans the scanning surface. 1. An optical scanning device characterized in that an optical system is disposed between the above-mentioned convex mirror and the above-mentioned scanning surface to establish a retention proportional to the angle of incidence.