JPH04232913A - optical scanning device - Google Patents

Abstract

PURPOSE:To form beam dots of same size on a photosensitive material in a light scanning device to scan a laser beam with using a hologram, even when the efficiency changes depending on the position of the beam on the hologram. CONSTITUTION:A long-length toric lens 6 is disposed between a hologram disk 4 for scanning and the scanning surface of a photosensitive material 5 in order to shift the focus position of the laser beam in the edge area of the hologram where the efficiency is low. Thus, the cross-sectional diameter of the beam is increased while its peak is decreased, which substantially makes the beam diameter almost equal in any position.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical deflection device used in, for example, a laser printer or a laser copying machine, for linearly scanning a laser beam by deflecting it using a diffraction grating such as a hologram.

0002

2. Description of the Related Art Conventionally, optical scanning devices have been known that deflect a laser beam to scan a surface to be scanned. As a type of such an optical scanning device, one that uses a semiconductor laser as a light source and a hologram disk as a deflection means has been proposed (see, for example, Japanese Patent Laid-Open No. 56-70517 and Japanese Patent Laid-Open No. 57-181523). ).

A conventional optical scanning device for a laser printer will be briefly described below with reference to FIG.

A laser beam emitted from a laser light source 1 passes through a collimator lens 2 and is diffracted by a hologram 3 and a hologram disk 4 as deflection means.
An image is formed on the scanned surface of the photoreceptor 5. Therefore, by rotating the hologram disk 4, the laser spot on the scanned surface of the photoreceptor 5 can be scanned. Further, the hologram disk 4 is composed of a plurality of divided parts, that is, a plurality of facets, and can be scanned by the number of facets in one rotation.

[0005]

However, in the case of a hologram produced by interference between two light sources, variations in the exposure amount occur within the hologram, and as a result, the diffraction efficiency varies depending on the location. For this reason, even if a hologram is optimally designed to form a nearly uniform laser spot on the photoconductor, the dot diameter of the image actually formed on the photoconductor through the optical system is limited to the center and both ends of the scanning line. It will be very different.

[0006] In order to make the diffraction efficiency uniform, it is possible to improve the exposure method and photoresist during hologram production, or to use computer generated holograms, but these methods increase the production cost and are not suitable for mass production. It had some problems.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is an object of the present invention to provide an optical scanning device that can form dots of uniform diameter on a photoreceptor.

[0008]

[Means for Solving the Problems] In order to achieve the above object, the present invention includes a long toric lens between a hologram and a photoreceptor for shifting the focal position of the laser beam back and forth from the surface of the photoreceptor. It is something that is arranged.

[0009]

[Operation] The diameter of the laser spot, which is the optical image formed on the surface of the photoreceptor by the laser beam, is determined to be within a range of 100 μm in order to obtain a predetermined resolution.
When a laser spot with a diameter of
A fluctuation range of about μm is allowed. Normally, the laser spot diameter refers to the diameter at 1/e2 of the peak value (hereinafter 1
/e2 diameter), and when the peak values are different, that is, when the diffraction efficiency of the hologram is different, the areas exposed to light on the photoreceptor are different even if the spots at different positions have the same diameter.

[0010] In order to make the dot diameter of the photosensitive area formed on the photoreceptor during one scan almost the same without changing the output of the laser light source, the laser spot diameter increases as it moves away from the center of the scanning line. In this way, a long toric lens is used to shift the focal point back and forth from the surface of the photoreceptor. As a result, when the laser spot passes through a portion of the hologram with low diffraction efficiency, the light intensity of the entire laser spot decreases, but the area of the spot region with an energy intensity greater than the photosensitive limit of the photoreceptor is approximately the same as the center of the scanning line. can do.

[0011] The energy intensity distribution of the laser spot is usually expressed as a Gaussian distribution. That is, the energy intensity y(x) in the x direction (radial direction of the spot cross section) is expressed by the following equation.

0012

[Math 1]

Here, σ represents the variance of the Gaussian distribution,

[
0014

[Math 2]

##EQU1## represents the peak value of energy intensity. In the above equation, if the energy intensity of the laser spot σ1・P1 and the laser spot σ2・P2 are equal at the same radius x, then

[0016]

[Math 3]

Conversely, when the ratio of P1 and P2 is P1/P2, σ
If the value of satisfies the above equation, the energy intensity of the laser spot is equal at radius x, and if a photoreceptor that is sensitive to incident energy greater than this energy intensity is used, the photosensitive area will be dot-shaped with radius x. . This allows the dots formed on the photoreceptor to have a substantially uniform size.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 to 3.

FIG. 1 shows a schematic configuration of the optical scanning device of this embodiment. In the figure, 1 is a laser light source using a semiconductor, 2
3 is a collimator lens, 3 is a fixed hologram, 4 is a hologram disk, 5 is a photoreceptor, and 6 is a long toric lens.

In the above configuration, the laser light emitted from the laser light source 1 is focused by the collimator lens 2. Further, the wavefront of the laser beam is corrected so that it is diffracted by the hologram 3 and scanned by the hologram disk 4 along a predetermined scanning line on the surface to be scanned on the photoreceptor 5 . In the long toric lens 6, the focal position of the laser beam is adjusted so that uniform dots are formed on the photoreceptor.

The hologram disk 4 is provided with a plurality of holograms, each of which can perform one scan. A hologram is optimally designed to form a predetermined spot diameter on a photoreceptor, but the predetermined spot diameter does not take into account the diffraction efficiency of the hologram.

[0022] Holograms are generally produced by interference exposure using two light sources, but the diffraction efficiency differs between a part close to the light source and a part far from the light source, with the diffraction efficiency being higher in the part closer to the light source. For this reason, the change in spot diameter during one scan was conventionally designed to be as shown in FIG. 2(b), but in this embodiment, as shown in FIG. The focal position is shifted by the long toric lens 6 so that the diameter becomes larger.

FIG. 3 shows the intensity distribution of the laser spot. 7a is the energy intensity distribution of the spot near the center of the scanning line, 7b is the energy intensity distribution of the spot at the end of the scanning line magnified by a long toric lens, and 7c is the energy intensity distribution of the spot at the end of the scanning line, taking into account the diffraction efficiency of the hologram. It is an energy intensity distribution of the spot which passed through the long toric lens of this invention. 7a and 7c are laser spots that actually enter the photoreceptor. The spot diameters at the exposure limit light amount of 7a and 7c are the same, and the sizes of the dots formed at this time are also the same. The difference between 7b and 7c is due to the diffraction efficiency of the hologram.

As described above, according to this embodiment, the laser beam is focused on the smallest laser spot (1
/e2 diameter), and the laser spot is enlarged with a long toric lens 6 (1/e2 diameter By increasing the diameter of the dots formed on the photoreceptor during one scan, the diameter of the dots formed on the photoreceptor during one scan can be made uniform.

In the above embodiment, the fixed hologram 3 is also used for wavelength fluctuation correction, but only the hologram disk 4 may be used.

[0026]

As is clear from the above embodiments, according to the present invention, the laser beam is adjusted to the smallest laser spot (1/e2 diameter ), and the laser spot is enlarged with a long toric lens so that almost the same photosensitive area on the photoreceptor can be obtained except at the scanning center where the diffraction efficiency decreases. It is formed on the photoreceptor during one scan without equalizing the light intensity to equalize efficiency, adjusting the sensitivity of the photoreceptor, or changing the intensity of the laser light source during one scan. Dot diameters can be made uniform.

In addition, in an optical scanning device using a hologram, the position of the laser spot changes greatly due to variations in the wavelength of the laser light source, temperature changes, and wavelength fluctuations due to changes in the applied current. However, by using a long toric lens, these drawbacks can be eliminated at the same time.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an optical scanning device according to an embodiment of the present invention.

FIG. 2 (a) Diagram showing the shape of the laser spot of the optical scanning device of the present invention (b) Diagram showing the shape of the laser spot of the conventional optical scanning device

[Fig. 3] Spot energy intensity distribution diagram of the optical scanning device of the present invention

[Figure 4] Schematic configuration diagram of a conventional optical scanning device

[Explanation of symbols]

1 Laser light source 4 Hologram disc 5 Photoreceptor 6. Long toric lens

Claims (1)

[Claims] 1. An optical scanning device using a hologram and a photoreceptor for scanning a laser beam emitted from a laser light source along a predetermined scanning line, in which a laser beam is emitted between the hologram and the photoreceptor. An optical scanning device characterized by being provided with a long toric lens for shifting the focal point position back and forth from the surface of a photoreceptor.