JPH1035008A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a stable intermediate gradation image with high quality by a method wherein an optical means that introduces a plurality of light beams selectively outputted from a semiconductor laser element to an image forming face of a photosensitive body so as to form one pixel thereby is provided and an electrostatic latent image is formed on the face of the photosensitive body in accordance with image information. SOLUTION: A lower clad layer 2 consisting of n type Al0.6 Ga0.4 As is formed on an n type Ga As substrate 1. A quantum well active layer 3 consisting of an undoped Al0.11 Ga0.89 quantum well layer and an Al0.3 Ga0.7 As barrier layer, an upper clad layer 4 consisting of a p type Al0.6 Ga0.4 As barrier layer and p type GaAs contact layer 5 are sequentially laminated thereon. A high resistance region 6 is partially formed by injecting proton in order to limit an emission area. A p type electrode 7 having two layer structure of Cr and Au is formed on a portion above each of the emission section an n type electrode 8 having two layer structure of Au-Ge and Au is formed on the rear face thereof. As a result, it is possible to obtain the high resolution image with high quality.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning type image forming apparatus, and more particularly to a scanning type image forming apparatus such as a laser printer or a laser beam copying machine which forms an image by exposing and scanning a photosensitive member surface. The present invention relates to a scanning type image forming apparatus in which the area of an exposure region can be changed in units to enable gradation recording.

[0002]

2. Description of the Related Art An image forming optical system is provided by processing image information on which gradation is expressed by a dither method, and condensing laser beams from a plurality of laser sources as beam spots on a photosensitive member surface. 2. Description of the Related Art A copying apparatus for performing beam recording in which one pixel is formed by a plurality of spots has been proposed (JP-A-63-173074). In this apparatus, as shown in FIG. 11, a laser source 101 in which a plurality of semiconductor laser elements are arranged in a line, and a plurality of laser beams emitted from the An image is formed on the photoconductor 105 by the polygon mirror 103 and the fθ lens 104, and exposure scanning is performed. In addition, a part of the laser light is guided to the photodetector 107 by using the reflecting mirror 106, and an image writing timing for exposure scanning is determined.

In the conventional scanning image forming apparatus configured as described above, since the density of one pixel is changed by using a plurality of beams and gradation expression is performed, a method of changing a lighting time (pulse width modulation method). It is stated that the combination can increase the number of gradations and improve the resolution even when the recording speed is increased.

[0004]

However, in such a scanning type image forming apparatus, a plurality of beam spots are set to one.
Due to the requirement of being confined within a pixel, it is necessary to uniquely determine the light-converging magnification of the imaging optical system according to the emission point interval of the laser array. However, in this case, the light collection magnification must be adjusted in advance according to the size of the pixel. Depending on the combination of these three, there is a possibility that a gap may be formed in the pixel or that the applicable pixel density may be limited. In addition, since the laser element and the optical system change over time due to heat, vibration, and the like, there is no guarantee that the initial settings will be maintained semi-permanently.

[0005] As described above, the conventional scanning image forming apparatus has a small initial setting margin and is troublesome.
There is a concern that the image quality may be deteriorated due to a change over time, which has been a major obstacle to realizing the apparatus.

The present invention has been made in view of the above circumstances, and has as its object to provide an image forming apparatus capable of obtaining a stable and high-quality halftone image.

[0007]

Therefore, according to the present invention, one pixel is constituted by a semiconductor laser configured to extract a plurality of light beams, and an arbitrary number of these light beams are formed. It is characterized in that it is constructed so that it can be taken out and that gradation expression is made possible.

That is, a first feature of the present invention is that a semiconductor laser device configured to be capable of independently outputting a plurality of light beams, and selectively output from the semiconductor laser device according to image information. Optical means for guiding to the image forming surface of the photoconductor so that one pixel is constituted by the plurality of light beams thus formed, and an electrostatic latent image is formed on the photoconductor surface in accordance with the image information. I did it.

A second feature of the present invention is that a light source section includes a large number of semiconductor laser elements arranged in an array so as to be capable of independently outputting a plurality of light beams;
Optical means for guiding to an image forming surface of a photoreceptor so as to constitute one pixel by a plurality of light beams selectively output from the semiconductor laser element according to image information,
According to another aspect of the present invention, an electrostatic latent image is formed on the photoconductor surface in accordance with the image information.

According to the above arrangement, it is possible to easily change the area of the exposure area on the surface of the photoreceptor in units of one pixel by the light spot corresponding to the pixel width, thereby stably expressing a high quality gradation. Can be performed.

According to the above arrangement, the distance between the centers of the plurality of light beams is configured not to be larger than the width of one pixel at a maximum, and an arbitrary number of the plurality of light beams is selected according to image data. By selecting this light beam, the area of the exposure region can be made variable, and good gradation expression can be achieved.

In addition, if a plurality of semiconductor laser elements are arranged in an array to form a light source so that an exposure area corresponding to the width of the photoreceptor can be formed, mechanical scanning in the sub-scanning direction is unnecessary. Thus, a high-precision halftone image can be easily formed. If this light source is formed integrally on one substrate and only one of the electrodes is formed as a divided electrode, it is possible to obtain a light source that is small, easy to manufacture, and highly reliable. Furthermore, when guiding a plurality of beam spots into one pixel, the light spot interval of the original light source can be adjusted to the pixel width and realized by using an imaging optical system of the same magnification. It is possible to greatly simplify the work of initial setting for adjusting the light collection magnification of the system according to the size of the pixel. In addition, since there is no need to use a mechanical scanning drive system, it is possible to perform stable and highly reproducible gradation expression that is not easily affected by changes in the optical system over time due to vibration or the like. Becomes

[0013] It should be noted that such a semiconductor laser element may be used as a light source of a scanning optical system, and an electrostatic latent image may be sequentially formed on the photosensitive member by scanning the light of the semiconductor laser element. .

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

FIG. 1 is an explanatory sectional view showing a divided stripe type semiconductor laser device used in an image forming apparatus according to a first embodiment of the present invention.

This split stripe type semiconductor laser device comprises a lower cladding layer 2 made of n-type Al _0.6 Ga _0.4 As formed on an n-type gallium arsenide (GaAs) substrate 1.
And an undoped Al _0.11 Ga _0.89 quantum well layer formed on the lower cladding layer 2 and an undoped Al _0.3 G
a quantum well active layer 3 comprising an a _0.7 As barrier layer; an upper cladding layer 4 comprising p-type Al _0.6 Ga _0.4 As;
Type GaAs contact layers 5 are sequentially laminated, and the high-resistance regions 6
Are partially formed. The active region below the portion where the proton injection was not performed becomes the light emitting portion. Above each light-emitting portion, a p-layer having a two-layer structure of Cr / Au divided into a plurality of portions for injecting current into the active layer is formed.
A side electrode 7 is formed, and an n-side electrode 8 having a two-layer structure of Au—Ge / Au is formed on the back surface.

Here, one pixel is formed by three light emitting points, and the width of one pixel is determined by the pixel density required for the device. For example, the pixel density is 1200 dp.
In i, the width is 21.17 μm, and therefore, the interval between the three light emitting points needs to be about 7 μm.

Next, the operation of the laser device will be described. In this device, as shown in FIG.
By selecting the light emitting points corresponding to A, 7B, and 7C, the area of the exposure region can be changed.
A gradation can be obtained. Table 1 shows the relationship between the selection of the light emitting point and the light emitting pattern obtained thereby.

By applying a constant voltage to this electrode, a corresponding laser can be driven.

[0020] In this case, four types of light emission patterns can be obtained by adding the case where none of the lasers is driven in addition to the patterns 1 to 3 shown in FIG.

By introducing this light onto the photoreceptor surface using an imaging optical system, the area of the exposure region can be changed, and four gradations can be obtained in image formation.

FIG. 3 shows the actual state of exposure on the surface of the photosensitive drum 24. The pixel section 28 is irradiated with the laser spot 27 in the above-described four patterns, and is exposed.
Note that this pixel section 28 is virtual.

Next, a description will be given of a manufacturing process of the divided stripe type semiconductor laser device.

First, as shown in FIG. 4, n-type gallium arsenide (GaAs) is formed by metal organic chemical vapor deposition (MOCVD).
s) On the (100) substrate 1, an n-type Al _0.6 Ga _0.4 As
Lower cladding layer 2 of undoped Al _0.11 G
a quantum well active layer 3 comprising an a _0.89 quantum well layer and an undoped Al _0.3 Ga _0.7 As barrier layer; and a p-type Al _0.6 G
an upper cladding layer 4 made of a _0.4 As and p-type GaAs
The contact layers 5 are sequentially laminated. Then, the substrate is taken out of the growth chamber, a resist is applied, and a resist mask 9 is formed by photolithography as shown in FIG. Then, proton implantation is performed through the resist mask 9 to form the high-resistance region 6 so as to reach the middle of the p-type upper cladding layer 4. After that, the photoresist 1 again
Then, the substrate is once immersed in monochlorobenzene, which is a kind of organic solvent, to harden a part of the surface of the resist 10 and form a hardened portion 11 as shown in FIG.

Then, as shown in FIG. 7, the resist pattern is formed by photolithography, whereby the hardened portion is hardly etched, and a resist pattern 10 having an umbrella-shaped portion 12 on the surface is obtained.

Thereafter, as shown in FIG. 8, a p-side electrode 7 made of Cr / Au is formed on the upper layer by electron beam evaporation.
To form

Then, the resist pattern 10 is removed by lift-off, and as shown in FIG.
B and 7C are formed. Furthermore, the back side is integrally Au-
An n-side electrode 8 made of Ge / Au is formed.

The laser substrate thus obtained is cleaved to form a cavity and die-bonded to a heat sink module or the like to obtain an edge-emitting type split stripe type semiconductor laser device.

A scanning type image forming apparatus using the divided stripe type semiconductor laser device thus formed will be described. In this apparatus, a slit 22 for controlling the spot diameter of a laser beam 25 is provided at the end of the emitting end of the semiconductor laser element 21 as shown in a side view and a plan view in FIGS. The laser beam 25 is guided to the photosensitive drum 24 via the imaging lens 23.

In this apparatus, since the semiconductor laser element 21 has a light emitting area corresponding to the width of the photosensitive drum 24, the magnification of the imaging lens 23 may be the same. When an edge-emitting laser is used, the light spot shape on the photosensitive drum surface becomes an ellipse whose longitudinal direction is the main scanning direction, which is not necessarily suitable for expressing gradation.
It is preferable to convert to an ellipse having a longitudinal direction in the sub-scanning direction by using 2.

Assuming that the effective width of the photosensitive drum is 297 mm, when writing is performed with three spots corresponding to one pixel at a pixel density of 1200 dpi, the number of spots on the entire element is not necessarily required to light all the spots simultaneously. Therefore, for example, driving of three spots for one pixel may be sequentially moved in the scanning direction. In the above embodiment, each semiconductor layer is formed by metal organic chemical vapor deposition. However, the present invention is not limited to this, and molecular beam epitaxy (MBE) may be used.

In the above-described embodiment, a GaAs / AlGaAs-based semiconductor is used as a material for forming the quantum well active layer. However, the material is not limited to this. For example, a GaInP / AlGaInP-based semiconductor is used for the quantum well active layer. It is also possible. The wavelength of the laser used for image formation is determined by the wavelength characteristics of the photosensitive drum, and usually, light having a wavelength of 880 nm or less is used. Further, as a second embodiment of the present invention, the semiconductor laser device or the semiconductor laser device array as shown in FIG. 1 can be used as a light source of a scanning optical system and can be used in the configuration shown in FIG. Needless to say.

[0033]

As described above, according to the present invention, a high-resolution and high-quality image can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a divided stripe type semiconductor laser device according to an embodiment of the present invention.

FIG. 2 is a diagram showing an operation example of the semiconductor laser device.

FIG. 3 is an explanatory view showing a method for forming one pixel by using the semiconductor laser device.

FIG. 4 is a manufacturing process diagram of the semiconductor laser device.

FIG. 5 is a manufacturing process diagram of the semiconductor laser device.

FIG. 6 is a manufacturing process diagram of the semiconductor laser device.

FIG. 7 is a manufacturing process diagram of the semiconductor laser device.

FIG. 8 is a manufacturing process diagram of the semiconductor laser device.

FIG. 9 is a manufacturing process diagram of the semiconductor laser device.

FIG. 10 is an explanatory view showing an image forming apparatus using the divided stripe type semiconductor laser device according to the embodiment of the present invention;

FIG. 11 illustrates an image forming apparatus.

[Explanation of symbols]

 Reference Signs List 1 n-type gallium arsenide (GaAs) substrate 2 n-type lower cladding layer 3 quantum well active layer 4 p-type upper cladding layer 5 p-type GaAs contact layer 6 high-resistance region 7 p-side electrode 8 n-side electrode 9 resist mask 10 resist mask 11 hardened part 12 resist umbrella

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yasuji Seko 430 Sakai, Nakai-cho, Ashigara-gun, Kanagawa Green Tech Nakai Inside Fuji Xerox Co., Ltd.

Claims (2)

[Claims] A semiconductor laser device configured to independently output a plurality of light beams; and a plurality of light beams selectively output from the semiconductor laser device according to image information. Image forming means for forming pixels, wherein an optical means for guiding to an image forming surface of the photoconductor is provided, and an electrostatic latent image is formed on the photoconductor surface in accordance with the image information. apparatus. 2. A light source unit comprising a large number of semiconductor laser elements arranged so as to be capable of independently outputting a plurality of light beams, and a light source unit comprising: Optical means for guiding to the image forming surface of the photoreceptor so that one pixel is constituted by a plurality of light beams selectively output, and an electrostatic latent image is formed on the photoreceptor surface according to the image information. An image forming apparatus characterized in that it is formed.