JPS63204222A - Light beam scanner - Google Patents

Abstract

PURPOSE:To obtain a light beam which has small transmission loss and a flat light quantity distribution in a scanning direction by providing aluminum as the lowermost layer of a light beam inflection mirror, a 1st dielectric layer with a small refractive index as its upper layer part, and a 2nd dielectric layer with a high refractive index as its upper layer part. CONSTITUTION:A laser beam 4 which is deflected through a newly provided cylindrical mirror 9 is incident on the inflection mirror 3 and the electric-field directional component E of the laser beam 4 is made nearly perpendicular to a deflection scanning surface. The inflection mirror 3 has an aluminum film 16 on a glass substrate 15, the SiO2 film 17 with the low refractive index on it, and the TiO2 film 18 with the high refractive index further on it. In this case, the respective films are so formed that nd is nearly lambda/4, where (n) and (d) are the refractive indexes of the SiO2 film and TiO2 film and lambda is the wavelength of the laser beam 4. Consequently, the loss of light laser transmission from a light source to a photosensitive body is reduced and the distribution of the quantity of light incident on the photosensitive body can be uniformed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a light beam scanning device used in a device for reading or recording an image by scanning with a laser beam.

[Prior Art] For example, a laser printer is configured to expose a photoreceptor using a light beam scanning device as shown in the cross-sectional view of FIG. That is, in FIG. 7, 1 is a light beam deflector that deflects a laser beam generated from a light source;
2a and 2b are imaging lenses, and 3 is a bending mirror that makes the deflected laser beam 4 enter the scanning surface of the photoreceptor 6 through the exit window 5. FIG. 8 is a conceptual diagram showing the optical development of the configuration shown in FIG. 7, in which a laser beam generated from a light source 8 is deflected by a deflector 1,
The light is incident on the bending mirror 3 via.

At this time, the laser beam 4 is scanned within the mirror surface of the folding mirror 3 with an effective deflection scanning angle α, but the laser beam passing through the center of the scanning angle of α=0'' is incident on the folding mirror 3 at an incident angle β. That is, the bending mirror 3 is held at an inclination angle B in the sub-scanning direction.

In such a light beam scanning device, the bending mirror 3 has conventionally been formed by forming an aluminum film on a glass substrate, and as a protective film for the aluminum film, a dielectric layer having a low refractive index, such as Si02, is formed with a thickness of several ion meters. It consists of a surface reflector. On the other hand, the laser beam 4 is deflected by S-polarized light so that its deflection direction (electric field component direction) E is substantially perpendicular to the deflection scanning plane as shown in FIG. This is because the reflectance of the S-polarization is higher than that of the P-polarization, and the change in the angle of incidence of the laser beam on the deflector 1 is smaller than that of the P-polarization.

[Problems to be Solved by the Invention] However, when the bending mirror 3 is constituted by a surface reflecting mirror having the above-mentioned configuration, the deflection direction of the laser beam 4 at α=0'' can be changed to the non-deflection scanning direction Y or the deflection scanning direction. Even if the bending mirror 3 is aligned with the direction In the scanning direction X, the reflectance R tends to decrease as the scanning angle α increases, and there is a problem in that the transmission loss of the laser beam 4 from the light source 8 to the photoreceptor 6 is large. As a result, a problem arises in that it is necessary to increase the light ω of the light source 8 or to control the rotational speed of the photoreceptor 6 to be low.

Incidentally, FIG. 9 shows the reflectance characteristics when a 30 nm thick 5i02 layer is formed on aluminum.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to provide a light beam scanning device that can obtain a light beam with little transmission loss and a flat light quantity distribution in the scanning direction. .

[Means for Solving the Problems] The present invention provides that, where n = refractive index of the dielectric layer, d = layer thickness, and λ = light beam wavelength, the light beam bending mirror has aluminum in the bottom layer and aluminum in the upper layer. It has a first dielectric layer with a low refractive index formed so that nd=approximately λ/4, and a high refractive index dielectric layer formed on the upper layer so as to have an nd path of λ/4. This structure has a second dielectric layer.

[Function] The mutual refraction of the two dielectric layers increases the reflectance for the incident light beam, and also makes the reflectance distribution substantially uniform.

[Embodiment] FIG. 1 is a perspective view showing an embodiment of a light beam scanning device according to the present invention, and FIG. 2 is a side sectional view thereof.

In these figures, parts that are the same as those in the conventional configuration shown in FIG.
A deflected laser beam 4 is made incident through the laser beam.

Also in this embodiment, the electric field direction component E of the laser beam 4 is substantially perpendicular to the deflection scanning plane as shown.

The structure of the bending mirror 3 is as shown in the cross-sectional view of FIG.
02M18 is formed. In this case 5102 membrane, T
The refractive index of the iO2 film is n, d is the layer thickness, and λ is the laser beam 4.
When the wavelength is , each film is formed so that nd=approximately λ/4.

On the other hand, the effective scanning angle of the bending mirror 3 in this embodiment =
The incident angle β of the center light beam passing through the center of the scanning angle of the laser beam 4 by the deflection device 3 (α=0°) on the bending mirror 3 is approximately 50°.

The relationship between α, β and the incident angle θ1 of a laser beam other than α=0° is shown in Figure 4, as shown in Figure 4, as β increases, θ1 also increases, but the amount of variation in θ1 due to changes in α decreases. do.

On the other hand, the angle ψ between the incident plane (the plane containing the incident light and reflected light) and the plane perpendicular to the deflection scanning plane, which is related to deflection, changes depending on the relationship between β and α, as shown in Figure 6. However, this angle φ
is the reflectance R, Rp (reflectance of p polarization component) and R6 (S
It is used in the formula to calculate the composition of the reflectance of the deflection components.

Specifically, R=COS φ・Rp+sin 2φ−R
The combined reflectance is determined by s-(1).

FIG. 6 is a diagram showing the reflectance characteristics of the conventional folding mirror and the folding mirror of the present invention, and 19 is 5i02 (n=
1.45>, nd = 30 nm film formed on aluminum, which shows a low value of 80%, whereas the reflectance characteristics of the present invention, shown as 20, are lower than the conventional example. It can be seen that the reflectance was increased by 10% and the reflectance distribution became flat.

This reflectance is based on the conventional characteristic 2 characterized by S-polarization.
The reflectance is almost the same as that of No. 1, and the reflectance distribution is also flatter.

Note that the symbols in FIG. 6 mean the following.

5i02 is a conventional folding mirror with a film thickness of 30 nm, 1-(-1
indicates the reflectance of the folding mirror according to the invention, and the subscript p-
s represents the reflectance of P polarization and the reflectance of S polarization, X represents a system set to have S polarization at the scanning center (α-0''), and Y represents a system similarly set to p polarization. There is.

By the way, as a low refractive index dielectric film, H
(lF2, ^1203, etc. can be used, and as a high refractive index dielectric film, in addition to TiO2, SiO, Ce
O2, TiO, etc. can be used.

As described above, according to this embodiment, the light beam transmission loss from the light source to the photoreceptor can be reduced, and the distribution of the amount of light incident on the photoreceptor can be made uniform. This makes it possible to reduce the cost by lowering the amount of light from the light source, to obtain high image quality due to the flat light amount distribution, and to improve the recording/reading speed.

[Effects of the Invention] As is clear from the above description, according to the present invention, it is possible to obtain a light beam with little transmission loss and a flat light amount distribution in the scanning direction. This has the effect of reducing the cost of the light source and improving the recording/reading speed.

[Brief explanation of the drawing]

1 is a perspective view showing an embodiment of a light beam scanning device according to the present invention, FIG. 2 is a side sectional view of FIG. 1, and FIG. 3 is a sectional view showing the configuration of the bending mirror in FIG. Figures 4 and 5 are explanatory diagrams showing the relationship between the angle of incidence of the light beam on the folding mirror and the scanning angle, Figure 6 is a characteristic diagram showing the reflectance characteristics of the folding mirror, and Figure 7 is the conventional light beam scanning. FIG. 8 is an optical development view of FIG. 7, and FIG. 9 is a characteristic diagram showing the reflectance characteristics of a conventional bending mirror. DESCRIPTION OF SYMBOLS 1... Light beam deflector, 2a, 2b... Imaging lens, 3... Bending mirror, 4... Laser beam, 5...
- Output window, 6... Photoreceptor, 8... Light source, 9... Cylindrical mirror, 15... Glass substrate, 16...
・Aluminum film, Fig. 9

Claims (2)

[Claims] (1) In a light beam scanning device having a light beam generator, a light beam deflector, and a light beam bending mirror that guides the deflected light beam to a surface to be scanned, n=refractive index of the dielectric layer;
When d=layer thickness and λ=light beam wavelength, the light beam bending mirror has aluminum in the bottom layer and n in the upper layer.
A first dielectric layer with a low refractive index formed so that d=approximately λ/4, and a second dielectric layer with a high refractive index formed so that nd=approximately λ/4 on the upper layer thereof. A light beam scanning device characterized in that it is formed by laminating a dielectric layer. (2) Deflection direction of the light beam incident on the light beam deflector (
The direction of electric field component) is approximately perpendicular to the deflection scanning plane, and the incident angle to the light beam bending mirror of the light beam passing through the center of the effective deflection scanning angle α (α = 0°) to the light beam bending mirror is β. The light beam scanning device according to claim 1, wherein the light beam scanning device is configured to satisfy the relationship β/α≧1.0.