JPH0470711A - Laser scanning optical system - Google Patents

Abstract

PURPOSE:To enable fast image formation of high picture quality by using a multiple semiconductor laser constituted by arranging plural lasers having vertical resonator structure as a light source means effectively in one chip. CONSTITUTION:The multiple semiconductor laser 1 is constituted by arranging the three lasers 22 - 23 which has the vertical resonator structure in one chip in array in the subscanning direction on a scanned surface and optically modulated laser beams are emitted at right angles to a substrate 21. This semiconductor laser having the vertical resonator structure is reducible in the size of an oscillation area, so the operating current is suppressed small and the heat generation due to laser light emission is reduced. Consequently, even when the laser beams are emitted, the individual lasers are small in heating value, so there is not the influence of the heat generation upon mutual laser oscillating operation, the light emission quantity and oscillation wavelength of each laser can be controlled independently, and the quantity of light emission is stable, so the fast image formation of high picture quality becomes possible.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a laser scanning optical system, and particularly to a laser scanning optical system that simultaneously scans a surface to be scanned using multiple beam spots to form image information at high speed and high density. The present invention relates to a laser scanning optical system suitable for a device such as a laser beam printer (LBP).

(Prior Art) Conventionally, in laser scanning optical systems such as laser beam printers, light source means consisting of a plurality of semiconductor lasers have been used in order to improve the writing speed of image information such as characters.

That is, a plurality of laser beams emitted from the light source means are guided onto the surface of the photoreceptor, which is the surface to be scanned, through an optical deflector such as a rotating polygon mirror, and a plurality of beam spots are formed on the surface of the photoreceptor. The image writing speed is increased by forming the image and scanning with multiple beam spots at the same time.

As shown in FIG. 7, the multi-semiconductor laser as a light source used in such a laser scanning optical system has a plurality of striped lasers in one chip (in the figure, there are three lasers 71, 72, and 73). They are arranged in one row.

As shown in FIG. 8, the element structure of one laser is formed with two reflective surfaces directly facing each other on a crystal cleavage plane perpendicular to the substrate and each layer. A Fapley-Bello resonator is formed horizontally to the substrate (n) between these two reflective surfaces, and laser oscillation occurs in the oscillation region of the active layer (P) from the horizontal direction with respect to the substrate (n). Laser beams are oscillated from the six directions shown by the arrows in the figure.

The oscillation area of the laser shown in the figure is 5 x 200 ~
It has a long and narrow stripe structure of about 300 μm.

Incidentally, the multi-semiconductor laser having a plurality of lasers having a stripe structure shown in FIG. 7 is constructed so that 0N10FF of laser oscillation can be easily performed independently of each laser.

(Problems to be Solved by the Invention) However, the conventional multi-semiconductor laser consisting of a plurality of lasers with a stripe structure shown in FIG.
Since the current was high at 0 to 80 mA, there was a tendency for the amount of heat generated to increase accordingly. For this reason, the laser with the stripe structure is
If multiple lasers are arranged in a row in a chip, when emitting light, the laser oscillation operation, such as the amount of light emitted or the oscillation wavelength, becomes unstable due to the effect of heat generation from adjacent lasers, which may cause damage to the scanned surface. There was a problem in that intensity unevenness occurred in the image between the upper scanning lines, making it impossible to form (write) good image information.

For this reason, in conventional multi-semiconductor lasers, in order to avoid instability of laser oscillation due to laser heat generation, the distance between each laser is set large, for example, 100 μm or more. For this reason, it is very difficult to improve the quality of images when writing image information, and it is also very difficult to downsize the entire device.

The present invention provides a laser scanning optical system in which a surface to be scanned is simultaneously optically scanned using a plurality of laser beams emitted from a light source means, in which a plurality of laser beams having a vertical cavity structure are used as the light source means in one chip. By using multi-semiconductor lasers that are effectively arranged side by side, the effect of heat generation from adjacent lasers is reduced, and the amount of light emitted from each laser and the laser oscillation wavelength can be controlled independently to achieve stability. An object of the present invention is to provide a laser scanning optical system capable of performing optical scanning with a certain amount of light and forming high-speed and high-quality images.

(Means for Solving the Problems) The laser scanning optical system of the present invention scans a plurality of laser beams emitted from a light source means having a plurality of light emitting parts via a rotatable optical deflector. In a laser scanning optical system that guides light onto a surface, forms a plurality of beam spots on the surface to be scanned, and rotates the optical deflector to scan the surface to be scanned with the plurality of beam spots. The light source means is characterized in that it includes a plurality of multi-semiconductor lasers arranged in a single laser chip having a vertical cavity structure along the sub-scanning direction on the surface to be scanned.

Furthermore, the present invention is characterized in that the laser scanning optical system optically scans the surface to be scanned using an interlace scanning method.

(Embodiment) FIG. 1 is a schematic diagram of a main part of a first embodiment of a laser scanning optical system of the present invention. In the figure, reference numeral 1 denotes a light source means, which is composed of a multi-semiconductor laser having a plurality of light emitting parts.

As shown in FIG. 2, this multi-semiconductor laser 1 includes three lasers 22, 23, and 24 having a vertical cavity structure arranged in a line along the sub-scanning direction on a surface to be scanned in one chip 21. It emits three optically modulated laser beams in a direction perpendicular to the substrate 21.

2 is a collimator lens, and multi-semiconductor laser 1
A plurality of laser beams emitted from the beam are made into a parallel beam of light. Reference numeral 3 denotes an optical deflector consisting of a rotating polygon mirror, which is rotated at a constant speed in the direction of arrow a by a driving means (not shown). Reference numeral 4 denotes an imaging optical system such as an f-theta lens, which condenses a plurality of laser beams from the optical deflector 3 to form a beam spot on a surface to be scanned (not shown).

In this embodiment, a plurality of laser beams emitted from a multi-semiconductor laser 1 are each made into parallel beams by a collimator lens 2 and are incident on a reflecting surface of an optical deflector 3.

Each of the laser beams reflected by the reflective surface of the optical deflector 3 forms a beam spot diameter of a predetermined size on a photoreceptor surface (not shown) which is a surface to be scanned by an imaging optical system 4. Image information is sequentially formed (written) on the body surface.

Next, we will discuss the characteristics of the multi-semiconductor laser, which is a light source means according to the present invention, and is composed of a plurality of lasers having a vertical cavity structure. This will be explained using FIG.

FIG. 2 is an external view of the multi-semiconductor laser 1 which is the light source means shown in FIG.

FIG. 3 is an explanatory cross-sectional view showing the element structure of one of the plurality of lasers shown in FIG. 2, which has a vertical cavity structure.

As shown in FIG. 2, in this example, a multi-semiconductor laser 1
Three lasers with vertical cavity structure 22.23.2
4 are arranged in a line along the sub-scanning direction on the surface to be scanned in one chip, and a plurality of optically modulated laser beams are emitted in a direction perpendicular to the substrate 21.

In this embodiment, a multi-semiconductor laser 1 serving as a light source means
It is also called a surface-emitting semiconductor laser and has an active state as shown in Fig. Since the area is small, it has the advantage that the threshold current can be made very small.

As shown in FIG. 3, the structure of this surface-emitting semiconductor laser includes a cladding layer (n) 32, an active layer (P) 33, and a reflective surface 35 having a high reflectance on the upper and lower surfaces of the cladding layer (P) 34. It is formed directly opposite the reflective surface 36.

The area sandwiched between these two reflective surfaces 35 and 36 is the substrate 31.
It becomes a so-called Fapley-Bello resonator perpendicular to
Laser oscillation occurs in the oscillation region 37 of the active layer (P) 33, and a laser beam is oscillated in a direction perpendicular to the substrate 31, that is, in the direction of the arrow shown in the figure.

In particular, in a semiconductor laser having such a vertical cavity structure, the oscillation region 37 can be made as small as 3 to 5 μm, so that the operating current can be kept low and the heat generated by laser emission can be reduced.

For this reason, even when the laser beam is emitted, the amount of heat generated by each laser is small, so the amount of light emitted from each laser and the oscillation wavelength can be controlled independently without affecting the mutual laser oscillation operation due to heat generation, resulting in stable light emission. quantity is obtained.

Further, each laser constituting the light source means in this embodiment is configured so that it can independently perform optical modulation according to an image signal, that is, it can easily perform 0N10FF laser oscillation. Furthermore, as mentioned above, since the amount of heat generated from one laser is small, a stable amount of light can be obtained without being adversely affected by temperature, so it is recommended to form a large number of lasers on one chip with a spacing of about 20 μm, for example. I can do it.

As described above, in this embodiment, by using a laser having a vertical cavity structure as a light source means, a plurality of lasers can be formed with the distances between the respective lasers close to each other. For this reason, multiple laser spots can be formed adjacently on the photoreceptor surface, which is the surface to be scanned, so it is possible to form a high-density, high-quality image with minimal image intensity unevenness between scanning lines. I can do it.

FIG. 5 is an explanatory diagram showing how a surface to be scanned is optically scanned with a plurality of beam spots according to this embodiment. As shown in the figure, since the beam spots can be formed adjacent to each other, three lines of images can be formed (written) at the same time in a single optical scan without uneven image intensity between the scanning lines. be able to.

FIG. 6 is an explanatory diagram showing the appearance of a laser spot on a surface to be scanned when an interlaced scanning method is used as a scanning method for optically scanning the surface to be scanned with the laser scanning optical system of the present invention.

Generally, if you try to scan light in bright conditions by reducing the F number of the collimator lens and concentrating a large number of laser beams, the distance between adjacent laser beams will become wider, and the distance between the beam spots on the surface to be scanned will increase accordingly. As the area becomes wider, it becomes difficult to obtain a good image.

Therefore, in this embodiment, an interlaced scanning method is used to perform optical scanning by inserting a laser beam from another scanning within the spot interval of that beam, thereby preventing a decrease in image density, increasing the coupling efficiency, and improving the efficiency during image formation. We are trying to improve the image quality.

In this embodiment, as in the previous embodiment, a multi-semiconductor laser in which a plurality of lasers (three in this embodiment) having a vertical cavity structure are arranged side by side in one chip is used as a light source means. For this reason, the distance between each laser is 7th
It can be formed smaller than the conventional stripe structure type semiconductor laser shown in the figure.

This makes it possible to keep the width of the beam spot spacing on the surface to be scanned small, and also to reduce the number of thinnings (the number of laser beams inserted in the middle) in interlaced scanning, which makes it possible to write images. The configuration of the control circuit for this can be simpler than that of a conventional laser scanning optical system using a multi-semiconductor laser with a stripe structure.

In this embodiment, the light source means is constructed using three lasers having a vertical resonator structure, or may be constructed from two or more lasers.

(Effects of the Invention) According to the present invention, as described above, a multi-semiconductor laser is used as a light source means, in which a plurality of lasers having a vertical cavity structure are arranged in one chip along the sub-scanning direction on the surface to be scanned. As a result, when scanning a surface to be scanned simultaneously with multiple beam spots, it is possible to suppress unevenness in image intensity between scanning lines, thereby creating a laser scanning optical system that can form images with improved image quality. It is possible to achieve something.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the main parts of the first embodiment of the laser scanning optical system of the present invention, FIG. 2 is an external view of the semiconductor laser shown in FIG. 1, and FIG. 3 is the vertical resonance shown in FIG. 1. 4 is an explanatory diagram showing the element structure of a semiconductor laser with a vertical cavity structure. FIG. 5 is an explanatory diagram showing the optical output and current characteristics of a semiconductor laser with a vertical cavity structure.
An explanatory diagram showing the state of the beam spot on the scanned surface in the embodiment, FIG. 6 is an explanatory diagram showing the state of the beam spot on the scanned surface when using interlaced scanning of the second embodiment of the present invention , FIG. 7 is an external view of a light source means having a conventional stripe structure type laser, and FIG. 8 is an explanatory diagram showing the element structure of a stripe structure type semiconductor laser. In the figure, 1 is a semiconductor laser, 2 is a collimator lens, and 3 is a semiconductor laser.
4 is a light deflector, and 4 is an imaging optical system. Figure Figure Figure Figure ○ −−□・−・□・□−〉

Claims (2)

[Claims] (1) A plurality of laser beams emitted from a light source means having a plurality of light emitting parts are guided onto a surface to be scanned via a rotatable optical deflector, and a plurality of beam spots are formed on the surface to be scanned. In a laser scanning optical system that optically scans a surface to be scanned with the plurality of beam spots by rotating the optical deflector, the light source means includes a laser having a vertical cavity structure in one chip. A laser scanning optical system characterized by having a plurality of multi-semiconductor lasers arranged in parallel along a sub-scanning direction on a surface to be scanned. (2) The laser scanning optical system according to claim 1, wherein the laser scanning optical system optically scans the surface to be scanned using an interlaced scanning method.