JPS60423A - Optical scanner - Google Patents

Abstract

PURPOSE:To simplify an optical adjustment by installing a semiconductor laser so that the short axial direction of elliptical laser light which is made incident to an optical scanner becomes a revolving shaft of the optical scanner, passing laser light for optical scanning through a cylindrical lens, and leading it to a surface to be scanned. CONSTITUTION:Laser light from a semiconductor laser 9 is converted to parallel light with high light utilizing efficiency by a coupling lens whose N.A. is large, has a laser light sectional shape of an elliptical shape on a rotary polyhedral mirror 2, and the short axial direction of the light becomes a direction parallel to a revolving shaft of the rotary polyhedral mirror 2. Therefore, a joint surface of the semiconductor laser 9 and the revolving shaft of the rotary polyhedral mirror 2 are placed so as to be parallel to each other. The laser light scanned by the rotary polyhedral mirror 2 is made incident to an image forming lens 7, but as for this lens 7, an Ftheta lens of a focal distance (f) is used, and a cylindrical lens 8 is placed in front of a photosensitive drum 1 functioning as a scanning surface.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention is applicable to optical devices that scan laser light to display and record information on photosensitive materials or screens, such as laser printers, laser COM (Compute
Background of the Invention A conventional scanning optical device will be explained with reference to FIG. 1.

3-1 is a laser beam having a circular cross-sectional shape, 3-2 is a laser beam modulated by a modulator 6, and 4 and 5 are cylindrical lenses. The laser beam 3-3 emitted from the cylindrical lens is a parallel light beam having an elliptical cross-section as shown in FIG. A rotating polygon mirror 2 deflects and scans the laser beam 3-3. 7 is known as an F-θ lens (focal length is f). The F-θ lens 7 has linearity on the photosensitive drum 1 with respect to the deflection angle θ of the rotating polygon mirror 2, that is, if the coordinate X is taken as shown in FIG. It has the ability to focus the laser beam into a minute spot.

Reference numeral 8 is a cylindrical lens, which has a length sufficient to scan the photosensitive drum 1, and has no curvature in the scanning direction of light. 1 is a drum-shaped photosensitive drum coated with a photosensitive material;
The part that the light scans is flat. In electrophotography, Se is often used as a photoreceptor, and around the photoreceptor there is a printing process known as electrophotography, that is, a charger,
Developing device.

Place transfer equipment, cleaning equipment, etc.

The size d2 in the long axis direction of the laser beam having the cross-sectional shape shown in FIG. 2 on the rotating polygon mirror is transferred to the size d in the X direction on the photosensitive drum by the f-θ lens. It is narrowed down to a very small amount. Since the size dl of the laser beam in the short axis direction is small, even if it passes through the F-θ lens, it cannot be narrowed down to a minute size due to diffraction. narrowed down to. As a result, the light is narrowed down to the same size do on the photosensitive drum in both the X and Y directions.

The advantage of this optical system is that it alleviates the accuracy of the rotating polygon mirror. That is, if the angle between the normal line of each surface of the rotating polygon mirror and the rotation axis of the rotating polygon mirror is not constant, that is, there is so-called surface tilt, information with uneven light scanning pitch will be recorded on the photosensitive drum. However, the optical system shown in FIG. 19 has a function of reducing the optical scanning pitch unevenness caused by the surface tilt of the rotating polygon mirror. The function of reducing optical scanning pitch unevenness will be explained with reference to FIG. When the surface tilt angle ψ of the rotating polygon mirror occurs 1 If there is no cylindrical lens 8, the normal scanning line position! The image is formed at a position shifted by ay=fψ. However, in the optical system shown in FIG. 1, since there is a cylindrical lens 8, y
=+ [image is formed at a location shifted from the normal position by cψ.

(However, the focal length of one cylindrical lens 8 is f.

) According to the properties of the fθ lens 7, ψ is smaller than ψ, and since fo<f.

The effect of surface tilt is reduced by (f, ψ)/(fψ).

By the way, in the conventional optical system shown in FIG.
, 5 was used to expand the laser beam in one direction and convert it into a laser beam having an elliptical cross section as shown in FIG. Each of the cylindrical lenses 4.5 cannot be made into a combination lens consisting of a plurality of lenses due to the difficulty of manufacturing and assembly adjustment, so a so-called single lens is used instead of being combined into one lens. However, when a single lens is used as the cylindrical lens 4.5, the laser light emitted from the cylindrical lenses 4 and 5 has a drawback of poor optical quality and a wavefront with aberrations. It is difficult to narrow it down.

Furthermore, in the optical system shown in FIG. 1 using 4.5 cylindrical lenses, it is necessary to match the cylindrical axes of each cylindrical lens to high and vif degrees, making adjustment of the optical system extremely difficult.

[Purpose of the invention]

The present invention has been made to eliminate the above-mentioned drawbacks, and enables high-quality laser recording and display with small optical scanning pitch unevenness even without a unidirectional beam expander that expands the laser beam in one direction using a cylindrical lens. The present invention provides an inexpensive and highly reliable scanning optical device.

[Summary of the Invention] To achieve this object, the scanning optical device of the present invention uses a semiconductor laser that emits laser light in an elliptical shape as a laser light source, and even without a unidirectional beam expander,
It is characterized by easing the surface tilt accuracy of the optical scanner.

FIG. 4 shows the radiation angle distribution of the intensity of laser light emitted by the semiconductor laser. As shown in Figure 4 (aJ), the laser light emitted from the semiconductor laser 9 has a large spread angle of 9 degrees in the direction perpendicular to the semiconductor laser bonding surface (indicated by □ in the figure), and in the direction parallel to the bonding surface (indicated by / in the figure). ), the small beam radiates at 9 angles and has a light intensity distribution with an elliptical cross-sectional shape.Therefore, if the laser light from the semiconductor laser 9 is converted into parallel light by a lens, it is shown in Figure 2. It is possible to obtain a cross-sectional shape of the laser beam, which eliminates the need for a unidirectional beam expander.Therefore, the deterioration of optical properties resulting from the use of a unidirectional beam expander and the optical system adjustment can be avoided. Difficulties can be resolved.

[Embodiments of the invention]

Examples of the present invention will be described in detail below.

FIG. 5 shows an embodiment of the scanning optical device of the present invention. The laser light emitted from the semiconductor laser 9 is converted into parallel light with high light utilization efficiency by a coupling lens with large N and A (focal length f0). Rotating polygon @! 2, the laser beam has an elliptical cross-sectional shape as shown in FIG. 6, and its short axis direction is parallel to the rotation axis of the rotating polygon mirror. To this end, as shown in FIG. 5, the junction surface of the semiconductor laser 9 and the rotation axis of the rotating polygon mirror 2 may be arranged parallel to each other. The laser beam scanned by the rotating polygon mirror 2 enters the imaging lens 7.

As the imaging lens 7, the Fθ lens (focal length is assumed to be f) already explained in FIG. 1 is used. A cylindrical lens 8 is arranged in front of the photosensitive drum 1 as a surface to be scanned. The ratio of the horizontal length d2 and the vertical length dl of the cross-sectional shape of the laser beam shown in FIG. It has value.

Assuming d2/d=5, the method for setting the optical system parameters will be described below. In addition, the laser beam radiation distribution of the semiconductor laser is the fourth
As shown in Figure tb), it is approximately a Gaussian distribution, and in the following calculations, dl and d2 are the sizes of the cross-sectional shape of the laser beam measured at the point where the central light intensity is l/e2.

Also, the diameter do of the light spot narrowed down on the photosensitive drum 1 is
The horizontal length d2 of the cross-sectional shape of the laser beam shown in FIG. 6 is 011 mm in both the direction and the X direction. narrowed down to. do
and d2 is the following formula% formula% where λ is the wavelength of light and f is the Fθ lens focal length.

The aperture indentation in the direction parallel to the rotation axis of the rotating polygon mirror 2, that is, in the It will be done.

f = 300 mm, λ = 0.75 X I 0-
3mm.

If do = 0.1 mm, (υ formula, pd2 = 2.8
6rrHn, d2 /dz =5, then d1:=
Q, 75 mm (.

From equation (2), since do' = 0.5 mm0d and d/ are almost equal, the thickness of the cross-sectional shape of the laser beam in the X direction at the cylindrical lumen position is almost d. 'be equivalent to. d/ is placed on the photosensitive drum 1 by the cylindrical lens 8. Set to narrow down to. That is, one cylindrical lens focal length f. is set by the following formula 0 Substituting the above parameters, f. -52.4mn1.

With the above settings, the laser beam will be focused on the photosensitive drum into a nearly circular laser beam spot with a diameter Q of 1 mm in both the X and X directions. As already explained above, even if the rotating polygon mirror has a surface tilt angle ψ, optical scanning with small optical scanning pitch unevenness can be achieved.

It is known that laser light from a semiconductor laser may be accompanied by astigmatism, but in such cases, adjusting the distance between the cylindrical lens 8 and the photosensitive drum 1 shown in FIG. 5 can eliminate the aberration. It can be corrected.

Although Fig. 5 shows an example using a rotating polygon mirror as an optical scanner, a galvano mirror may also be used.In the radiation angle distribution of the semiconductor laser shown in Fig. 4, the ratio of the spread angle in the / direction is In the optical system of the present invention shown in FIG. 5, a difference from the set value may occur due to variations in the characteristics of the semiconductor laser. In this case, it is effective to arrange the prism between the coupling lens 10 and the rotating polygon mirror 2. That is, if the prism is arranged as shown in Figure 7, the parallel laser beam incident with a width d will have a width d/
is converted into parallel laser light. There is a relationship between d' and d expressed by the following equation.

The apex angle α of the prism is expressed by the following equation.

α=θ.

Here, θ0 is the incident angle, θ is the exit angle, and n is the refractive index of the prism.

Therefore, when using a prism, the angle of incidence θ. By adjusting the width of the laser beam, it is possible to change the width of the laser beam to a desired size.

FIG. 8 shows an embodiment in which the prism described above is applied to the scanning optical system of the present invention. The size of the cross section of the parallel laser beam emitted from the coupling lens 10 is d, d2, and this ratio d2/d1 is changed by the prism 11 to a; / d
1 and enters the rotating polygon mirror 2.

By using the prism described above, the spread of laser light emitted from the semiconductor laser can have a function of compensating for variations in the nine-angle characteristics. Furthermore, the use of a prism has the advantage that the wavefront convergence that occurs in the case of the cylindrical lens shown in FIG. 1 does not pose a problem at all.

〔Effect of the invention〕

As described above, according to the present invention, there is no need for a unidirectional beam expander consisting of a single cylindrical lens, and it is possible to realize a scanning optical device with little deterioration of optical characteristics and with extremely simple adjustment of optics and the like.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a conventional scanning optical device. FIG. 2 and FIG. 3 are diagrams for explaining FIG. 1. FIG. 4 is a diagram showing the radiation angle distribution of the light intensity emitted from the semiconductor laser. FIG. 5 is a diagram showing an embodiment of the present invention. FIG. 6 is a diagram for explaining FIG. 5. FIG. 7 is a diagram explaining the function of the prism. FIG. 8 is a diagram showing another embodiment of the present invention.
Photosensitive drum, 2... Rotating polygon mirror, 7... Fθ lens, 8... Cylindrical lens, 9... Semiconductor laser, 10...
...Coupling lens, 11... Prism 0 side, 1 drawing, 2, Fig. S

Claims (1)

[Claims] (1) A semiconductor laser that emits laser light having an elliptical cross-sectional shape, a lens that converts the laser light emitted from the semiconductor laser into parallel light, an optical scanner, and the scanner; In a scanning optical device comprising an imaging lens that focuses a laser beam for optical scanning onto a surface to be scanned, the short axis direction of the elliptical laser beam incident on the optical scanner is set to be the rotation axis of the optical scanner. A scanning optical device characterized in that the semiconductor laser is installed and the laser beam for optical scanning is guided to the surface to be scanned through a cylindrical lens. 2. A scanning optical device according to claim 1, characterized in that a prism is disposed between the lens and the optical scanner.