JPH05203892A - Light beam scanning device - Google Patents

Abstract

PURPOSE:To provide the light beam scanning device which compensates aberrations and speed uniformity of a scanning beam effectively only by holograms without using any expensive image formation system lens. CONSTITUTION:This light beam scanning device which consists of a semiconductor laser and >=2 holograms has a holograms 5 for generating a diffracted wave 7 on the disk surface of a rotary hologram 2 where the calibrated light 4 from the semiconductor laser is made incident. Further, the hologram 5 is installed behind the rotary hologram disk 2 and a diffracted wave 8 generated by the hologram 5 is converged on an image formation point 10 on a photosensitive drum 9. The image formation point 10 moves on the photosensitive drum 9 as the rotary hologram disk 2 rotates. The holograms 5 have concave power and the hologram 3 has convex power. This mixed system effectively compensates the aberrations and speed uniformity of the scanning beam.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light beam for diffracting a light beam from a light source such as a semiconductor laser through two or more holograms and scanning the diffracted light on an image forming body such as a photosensitive drum. The present invention relates to a scanning device.

[0002]

2. Description of the Related Art Conventionally, various types of light beam scanning devices using two or more holograms have been reported. Here, the convergence power of the hologram has either a convex power (converging action) or no power. The conventional technique will be described in more detail below.

As an example of a light beam scanning device having two holograms, one of which is used as a front hologram corresponding to the semiconductor laser side and the other is used as a rotary hologram disk 57-55275
JP-A No. 61-60846 and Japanese Patent Application No. 61-60846.

Further, as an example of a light beam scanning device in which a rotating hologram disk is arranged on the semiconductor laser side and another hologram is placed behind, which also uses two holograms, Japanese Patent Application No. 58-119098. Have been proposed in.

[0005]

In order for this type of light beam scanning device to be preferable, it is necessary to satisfy the following basic items.

These are (a) forming an image of the scanning beam in a sufficiently small size, (b) eliminating the curvature of the scanning beam, and (c) performing uniform scanning of the scanning beam.

However, in the light beam scanning device proposed in Japanese Patent Application No. 57-55275, both the front hologram and the rotating hologram disk are linear diffraction gratings having a constant grating pitch, and any hologram has a converging power. I do not have. Therefore, for example, in order to form an image of the light beam on the scanning surface of the photosensitive drum, an image forming lens system is separately required.

The image forming lens system is required to have not only a narrowing of the light beam but also a correction function for performing constant velocity scanning, and is usually composed of a plurality of lenses including an aspherical surface. There is. As this image forming optical system, an fθ lens is usually used, and it is a very expensive optical component due to difficulty in manufacturability.

Further, in the light beam scanning apparatus proposed in Japanese Patent Application No. 61-60846, both the front hologram and the rotary hologram disk use holograms having spatially different spatial frequency distributions. It is a hologram with. Therefore, in this configuration, f
No imaging lens system such as a θ lens is required.

However, in order to reduce the aberration on the scanning surface, a wavefront having a specific aberration is required at the time of manufacturing the front hologram, and special consideration must be given to the exposure optical arrangement. Further, in an optical system having no fθ lens after the rotating hologram disk, correction for constant velocity scanning cannot be positively performed.

On the other hand, the light beam scanning device proposed in Japanese Patent Application No. 58-119098 has a structure in which another hologram is arranged after the rotating hologram disk for the purpose of constant speed scanning of the light beam. In this case, it is necessary that one or both of the post-production hologram waves have spherical aberration, and special consideration must be given to the setting during production.

As described above, in the conventional light beam scanning device using two or more holograms, various lenses are required, such as an expensive lens is required, constant velocity correction is insufficient, and the manufacturing method is complicated. There was a problem.

The present invention solves the above-mentioned problems of the prior art, and the aberration and the constant velocity of the scanning beam can be effectively corrected only by the hologram without the need for an expensive lens. It is an object of the present invention to provide a light beam scanning device that is inexpensive and can improve reliability.

[0014]

A light beam scanning device of the present invention is a light beam scanning device which diffracts a light beam from a light source through two or more holograms and scans the diffracted light on an image forming body. The two or more holograms are formed with a convex lens power having a converging action and a concave lens power having a diverging action, thereby achieving the above object. It

Preferably, the hologram having the power of the concave lens is formed on a rotating hologram disk, and the hologram having the power of the convex lens is formed at the subsequent stage of the rotating hologram disk.

[0016]

It is assumed that the hologram is produced by the interference of two spherical waves (object wave and reference wave). Here, the focal length f of the hologram depends on the center positions O and R of the object wave and the reference wave, the wavelength of production and reproduction, and the diffraction order, and is approximately given by the following equation.

[0017] 1 / f = n × (λ 2 / λ 1) × (1 / Z O -1 / Z r) ... here, lambda _1: Preparation wavelength lambda _2: reproduction wavelength n: diffraction order Z _O: object Distance between wave center and hologram surface Z _r : Distance between reference wave center and hologram surface.

FIG. 1 shows four types of holograms A, B, C and D for Zo, Zr> 0 and n = ± 1. Of these, the type A hologram is shown in FIG.
As shown in, the hologram acts as a hologram having a convex power of n = 1 and f> 0. The type B hologram acts as a hologram having a concave power of n = −1 and f <0, as shown in FIG. The type C hologram acts as a hologram having a concave power of n = 1 and f <0, as shown in FIG. Type D
As shown in FIG. 1D, the hologram of n = -1,
It acts as a hologram having a convex power of f> 0.

In this way, the hologram acts as a convex lens or a concave lens depending on the position of the manufactured wave and the diffraction order. By utilizing this property and mixing and using these convex and concave holograms, it is possible to satisfy all the basic characteristics described above.

The reason will be described below. For the above-mentioned four types A, B, C, and D holograms, values are entered in the center position O of the object wave and the center position R of the reference wave to calculate the third-order aberration coefficient, and the result of examining the sign is shown. It is shown in Table 1 below. Regarding the aberrations (coma, astigmatism, distortion) due to the angle of view, only the Y direction is shown.

[0021]

[Table 1]

Regarding the calculation formula of the third-order aberration, the following documents are used.

Reinhard W. Meier, Maginification and
Third-Order Aberrations in Holography, Jounal of t
he Optical Society of America, Vol.55, No.8, pp.98
7-992, 1965 JN Latta, Computer-Based Analysis of Hologram Im
agery and Aberrations, Applied Optics, Vol.10, No.
3, pp.599-608, 1971 As can be seen from Table 1, since the polarities of aberrations differ depending on the hologram type, it is possible to reduce aberrations by combining these types.

Since the polarity of the aberration coefficient changes depending on the value of the Y coordinate of the hologram manufacturing arrangement, the results shown in Table 1 are examples, but type A and type B, and type C and type D have opposite polarities. Showing does not change.

Next, the constant velocity property of the light beam and the aberration polarity will be described. The constant velocity is related to the distortion coefficient Dx in the X direction, and can be achieved by intentionally imparting distortion (tal distortion, distortion coefficient is positive). Here, the distortion coefficient Dx changes depending on the angle of view of the reproduction light in the X direction and the rotation angle of the hologram.

For the holograms of types A to D described above, the angle of view, the rotation angle, and the sign of the distortion coefficient Dx were examined, and the results are shown in Table 2 below. The signs of the angle of view and the rotation angle are shown in FIG. When the incident vector of the principal ray of the reproduced wave has a right-handed component in the light traveling direction (Z-axis direction), the angle of view is +, and the hologram is oriented in the light traveling direction (Z-axis direction). The clockwise rotation is defined as + rotation.

[0027]

[Table 2]

From Table 2, it can be understood that the tendency of the distortion characteristics differs depending on the hologram types A to D. With one hologram, a hologram in which the locus of the scanning beam satisfies linearity has a negative distortion, and linear scanning and constant velocity scanning cannot be satisfied simultaneously. On the other hand, when two or more holograms are used, desired distortion characteristics can be created by combining holograms of different types, and it becomes possible to satisfy both linear scanning and constant velocity scanning at the same time.

For the above reasons, according to the light beam scanning device having the above-described structure which constitutes the mixed system of the convex power and the concave power as a whole, the above-mentioned configuration is achieved without using the imaging system lens such as the fθ lens. Of the above, that is, (a) forming the scanning beam into a sufficiently small image, (b) eliminating the curvature of the scanning beam, and (c) performing the uniform velocity scanning of the scanning beam can all be satisfied. ..

[0030]

EXAMPLES Examples of the present invention will be described below.

(Embodiment 1) FIG. 3 shows Embodiment 1 of the light beam scanning device of the present invention. This light beam scanning device has two holograms, and the hologram is used to scan the light beam linearly on the photosensitive drum 9 in the axial direction thereof.

One of the two holograms constitutes a rotating hologram disk 2 which is rotatable in the direction of arrow P. That is, holograms (scanning holograms) 5, 5 that are multi-divided in the circumferential direction are formed on the disk surface of the rotating hologram disk 2. The other hologram 3 is placed after the rotating hologram disc 2. That is, the rotary hologram disk 2 is arranged on the side of a semiconductor laser (not shown) which serves as a light source, and the hologram 3 is fixedly arranged behind it.

In such a structure, the light beam emitted from the semiconductor laser is collimated by a collimating lens (not shown), and subsequently the collimated light 4 is incident on the rotary hologram disk 2. .. As described above, a large number of holograms 5, 5, ... Are formed on the disk surface of the rotating hologram disk 2, and the diffracted wave 7 diffracted by the hologram 5 is generated by the hologram 3.
It is designed to be incident on.

Subsequently, the diffracted wave 8 diffracted by the hologram 3 is focused on the image forming point 10 on the photosensitive drum 9.
The imaging point 10 scans on the photosensitive drum 9 in the axial direction of the rotary hologram disk 2 as the rotary hologram disk 2 rotates in the direction of arrow P. That is, the line-shaped scanning of the light beam is performed.

The above hologram 5 has a concave power,
The hologram 3 has a convex power. These holograms 5 and 3 are specifically manufactured as follows.

The hologram 5 is shown in FIG.
A type B manufacturing arrangement shown in (b), that is, a diffraction order n = −1 and a focal length f <0, is used to provide concave power. On the other hand, the hologram 3 is shown in FIG.
A type A manufacturing arrangement shown in (a), that is, a diffraction order n = 1 and a focal length f> 0 is used to provide convex power. According to the mixed system of the holograms 5 and 3 having such a power, the aberration polarities of the type A hologram 3 and the type B hologram 5 show opposite tendencies, as described in the above section of action. The aberration at the image forming point 10 can be reduced.

FIG. 4 shows a calculation example of the lateral aberration curve at the image forming point 10 (scanning center). Hologram 5 for comparison in the figure
Also, the aberration curves (indicated by type A × 2) when both the hologram 3 and the hologram 3 are manufactured by type A are also shown. When two type A holograms are used so that they both have a convex power, coma and astigmatism appear as shown in FIGS. 4A and 4B. It can be seen that these aberrations are sufficiently corrected in the case of a mixed system of type B holograms (indicated by type A and type B).

FIG. 5 shows a constant velocity error rate. However,
The horizontal axis represents the rotation angle of the rotary hologram disk 2, and the vertical axis represents the constant velocity error ratio. Here, the error rate is given by the following formula.

(X−Xref) / Xref × 100 (%), where X is a scanning position, and Xref is a position that completely satisfies the constant velocity property.

As is apparent from FIG. 5, it is understood that the mixed system of holograms of different types can reduce the constant velocity error more than the case of using holograms of the same type.

As described above, in the case of the light beam scanning device having the above-mentioned configuration, the aberration and the constant velocity property of the scanning beam can be obtained only by combining the holograms 5 and 3 without using an expensive imaging system lens such as an fθ lens. Can be corrected.

(Second Embodiment) FIG. 6 shows a second embodiment of the light beam scanning device of the present invention. This light beam scanning device has a configuration using three holograms. That is, this light beam scanning device includes a front hologram 1 arranged on the semiconductor laser side with reference to the rotating hologram disk 2, and a hologram 5 formed on the rotating hologram disk 2.
It has a total of three types of holograms, which is the rear hologram 3 similar to that of the first embodiment.

In such a structure, the collimated light 4 from the semiconductor laser is first incident on the fixed front hologram 1, and its diffracted wave 6 is followed by a rotary hologram disc having a plurality of holograms 5 formed thereon. Incident on 2.
Then, the diffracted wave 7 from the rotating hologram disk 2
Enters the rear hologram 3. The diffracted wave 8 diffracted by the subsequent hologram 3 is converged on the image forming point 10 on the photosensitive drum 9. The image forming point 10 is the same as the above, as the rotating hologram disk 2 rotates,
Scan the top in the axial direction.

Also in the light beam scanning device having the configuration of the second embodiment, the aberrations at the image forming point 9 can be sufficiently reduced by appropriately distributing the powers of the three holograms 1, 5, and 3. The constant velocity error of the scanning beam can also be made sufficiently small.

Tables 3 and 4 below show specific examples of distribution examples of the convergent power (focal length) of the holograms 1, 5 and 3 in the second embodiment. However, Table 3 shows the specifications of the specific example 1, and Table 4 shows the specifications of the specific example 2.

[0046]

[Table 3]

[0047]

[Table 4]

Although not particularly mentioned in the above Examples 1 and 2, it was confirmed that the curvature of the scanning beam was within 0.4 mm in any case.

[0049]

The light beam scanning device of the present invention described above has a mixed system in which a hologram having a convex power and two or more holograms having a concave power are combined, so that the interaction of these holograms causes Since the aberration of the scanning beam can be effectively corrected and the constant velocity error can be reduced, it is possible to satisfy all the basic characteristics required for this type of light beam scanning device. Further, an expensive imaging system lens such as an fθ lens becomes unnecessary.

For these reasons, the light beam scanning device of the present invention can realize an inexpensive and highly reliable light beam scanning device.

[Brief description of drawings]

FIG. 1 is a principle explanatory view showing the directions of diffracted waves and the state of image formation for each hologram type.

FIG. 2 is a graph showing a coordinate system and a code convention.

FIG. 3 is a perspective view showing a first embodiment of a light beam scanning device of the present invention.

FIG. 4 is a graph showing lateral aberration on an image plane.

FIG. 5 is a graph showing a constant velocity error of a scanning beam.

FIG. 6 is a perspective view showing a second embodiment of the light beam scanning device of the present invention.

[Explanation of symbols]

 1 Front hologram 2 Rotating hologram disc 3 Rear hologram 4 Collimated light 5 Hologram (scanning hologram) 6, 7, 8 Diffracted wave 9 Photoreceptor drum 10 Imaging point

Claims (2)

[Claims] 1. A light beam scanning device for diffracting a light beam from a light source through two or more holograms and scanning the diffracted light on an image forming body, wherein the two or more holograms are converged. A light beam scanning device formed of one having a power of a convex lens having an action and one having a power of a concave lens having a diverging action. 2. The light beam scanning device according to claim 1, wherein a hologram having the power of the concave lens is formed on a rotating hologram disk, and a hologram having the power of the convex lens is formed at a subsequent stage of the rotating hologram disk.