JPS62257184A - Laser projection device - Google Patents

Abstract

PURPOSE:To prevent a laser output from varying by operating at least one of plural light emission parts in a state where image recording is not performed previously and stabilizing a laser chip thermally. CONSTITUTION:This device consists of a semiconductor array laser which has four light emission parts 9-12 on one laser chip 8. Then, electrodes 16 and 19 of dummy light emission parts 9 and 12 among the four light emission parts 9-12 are powered on all the time to saturate the inside of the chip 8 thermally. Consequently, the temperature variation of the light emission parts 10 and 11 until the inside of the chip 8 is saturated thermally prevents the laser output at the time of light emission from decreasing abruptly, and the reliability, specially, the life is not spoiled at all.

Description

[Detailed description of the invention] (Industrial application field) The present invention is a laser beam printer (hereinafter referred to as a laser beam printer).

The present invention relates to a laser emitting device used as a light source such as an LBP (LBP), and particularly relates to stabilizing the output of an array laser having a semiconductor laser structure in which a single chip has a plurality of light emitting parts.

(Prior art) In recent years, light sources 1- used in printers such as LBP
l −r fi,'Q 5 > ns
A JRI le J+(?iT f赳１音：rJI
a! (L'-L" +144) Semiconductor lasers are increasingly being used. The main configuration of laser scanning devices used in LBP is a light source that emits laser light. It consists of a laser emitting device, a polygon mirror that scans the laser beam in the axial direction of the photoreceptor drum, a motor that rotates the polygon mirror at a constant speed, and a lens system that focuses the laser beam on the photoreceptor drum. ing.

Recently, there has been a demand for the above-mentioned LBP to increase the speed of small models. The following two methods can be considered as solutions for a laser scanning device that satisfies this demand for higher speeds. The first method is to increase the laser output and increase the rotation speed of the polygon mirror. In this case, with small models using semiconductor lasers, there is a limit to the ability to increase the laser output and the rotation speed of the polygon mirror, and the printing 'A' is limited.
Currently, the output is A4 size paper #! j! The limit is approximately 50 to 60 sheets/minute. This method uses multiple laser beams and simultaneously prints multiple lines in the rotational direction of the photoreceptor drum during one laser scan, making it possible to print without changing the rotational speed of the polygon mirror much. The speed can be increased by the number of beams. If this method is used, it is possible to increase the printing speed by several hundred sheets.

Conventionally, as a method to increase the number of laser beams, the first method proposed is to use multiple laser emitting devices, but the direction of the laser beam emitted from each laser emitting device and the fluctuation of the output due to environmental changes vary. , it is almost impossible and impractical to keep each of them constant.

Therefore, a method can be considered in which a single laser emitting device generates a plurality of laser beams by using an array laser having a plurality of light emitting parts in one semiconductor laser chip.

(Problems to be Solved by the Invention) However, such prior art has the following problems. This will be explained using FIGS. 4 and 5. :rS4 Figure shows a semiconductor array laser having four light emitting parts 31 to 34 in one laser chip 30, and Figure 5 shows the light emission characteristics of the laser output. Such a semiconductor laser, as shown in FIG.
When a constant drive current is applied during time to to cause light emission, a phenomenon is observed in which the laser output reaches a high PO output and then gradually decreases due to self-heating. This is the self 9! of the light emitting parts 31 to 34! Since it is difficult for the heat generated by the heat to flow to the outside through the mount 35, the temperature difference between the chip before and after light emission is large and the laser threshold '11! , the flow increases significantly,
This is because the laser output decreases at a constant drive current. This decrease in output occurs rapidly, especially in several w seconds immediately after light emission, and once the inside of the chip 30 is thermally saturated to some extent, the rate of decrease in output decreases and reaches a constant value in several tens of seconds.

In the above array laser, when a laser that is not emitting light emits light due to this phenomenon, not only does the laser output of that laser decrease due to heat generation, but also the heat is transferred into the chip, causing nearby light emitting lasers to emit light. There is also a problem in that the output of the laser used is also reduced. When this phenomenon occurs, a problem arises in that the potential of the photosensitive layer on the photosensitive drum fluctuates in response to fluctuations in laser output, resulting in uneven density of the image, which significantly impairs image quality.

In order to solve this problem, we have considered a method of increasing the temperature of the chip by passing a current below the threshold current value at which the laser starts laser oscillation into the laser, thereby reducing the drop in output when emitting light. It will be done.

However, in this case, since the laser is constantly energized, a new problem arises in that reliability, particularly the life of the laser chip, is impaired.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and its purpose is to provide a laser emitting device that prevents fluctuations in laser output and does not impair reliability. It's about doing.

(Means for solving the problem) In order to achieve the above-mentioned purpose, the unfired IJ1 is a laser emitting device using an array laser having a plurality of light emitting parts in one laser chip, in which at least one of the light emitting parts is used. One light emitting section is configured to operate in a state 58 without image recording prior to the other light emitting sections.

(Function) In the present invention, at least one of the plurality of light emitting parts is activated in advance without image recording to thermally stabilize the laser chip.

(Example) The present invention will be explained below based on the illustrated embodiments.

FIG. 3 shows a laser beam printer to which the laser emitting device according to the present invention is applied. In FIG. , 3 is a polygon mirror for scanning the beam, 4 is an fO lens that converts the beam moving at a constant angular velocity into uniform motion and focuses the beam, 5 is a photosensitive drum, 6 is a reflecting mirror,
A beam detector 7 detects the beam in order to control the starting position of the main scanning of the beam. Then, the laser beam B modulated by the image signal is emitted from the laser emitting device l, and the laser beam is transmitted to the collimator lens 2,
Scanning exposure is performed on the photoreceptor drum 5 via the polygon mirror 3 and the fθ lens 4 to form an electrostatic latent image. This electrostatic latent image is developed by a developing device (not shown) and transferred and fixed onto a transfer material to record an image.

FIG. 1 shows an embodiment of a laser emitting device according to the present invention. This laser emitting device ml consists of a semiconductor array laser having one laser chip 8 and four light emitting parts 9, 10° 11.12. Above laser chip 8
are a substrate 13, a first semiconductor layer 14, and a second semiconductor layer 15.

The laser chip 8 is made up of electrodes 16, 17, 18, 19, and is brazed to a mount 20 made of copper, silver, etc. through a layer of silicon or silicon carbide.

In this embodiment, the four light emitting parts 9, 10° 11, 12
Of these, the two inner light emitting parts 10 and 11 are light emitting parts whose output reaches the photoreceptor drum 5, and the two outer light emitting parts 9 and 12 are used as light emitting parts whose output does not reach the photoreceptor drum 5, that is, the image This is a dummy light emitting section that emits light when no recording is being performed. These dummy light emitting parts 9, 12
is always energized. In order to prevent the output of the dummy light emitting section 9.12 from reaching the photosensitive drum 5,
The electrodes 16 and 19 of the laser chip 8 are energized below the threshold current value and used in a state where no laser oscillation is being performed.

In this way, by constantly energizing the electrodes 16 and 19 of the tummy light emitting parts 9 and 12 of the light emitting parts of the laser chip 8, the interior of the chip can be thermally saturated. Therefore, when one light emitting section 10.11 is modulated by an image signal to emit light, the laser chip 8 is thermally saturated and stable, so the laser output decreases due to self-heating of the light emitting section 10.11. Never.

Note that as a method for preventing the output of the dummy light emitting sections 9, 12 from reaching the photosensitive drum 5, the dummy light emitting sections 9, 12
Masking or coating may be applied to the end face 21 on the emission side of the dummy light emitting part to make the emission rate lower than that of the light emitting part 10°11. Since the dummy light emitting section can flow, the amount of heat generated from the dummy light emitting section is large, and thermal stability can be achieved.

In addition, in the above embodiment, the electrode 1 of the dummy light emitting section 9°12
6 and 19 are always energized, but the light emission for recording one image f! In response to s10.11, the dummy light emitting units 9 and 12 may be turned 0N-OFF.For example, as shown in FIG. If this light emission method is used, which may be reversed to the light emission (energization) timing in 10.11, the overall amount of heat generated in the chip will be more constant, and the light emitting part 10.11
The luminescence stability of can be further improved.

Furthermore, in the embodiment described above, the case where the two dummy light emitting sections 9.12 are provided on the outside has been described, but the number of dummy light emitting sections 9.12 may be any one per position, and the total number of light emitting sections may also be arbitrary.

(Effect of the invention) The present invention consists of the above configuration and operation.

By providing a light emitting section that does not record images, it is possible to prevent the laser output during light emission from rapidly decreasing due to temperature changes in the light emitting section that occur until the inside of the chip is thermally saturated. Moreover, it has various effects such as not impairing reliability, especially life span.

[Brief explanation of drawings]

Fig. 1 is a perspective view showing one embodiment of the laser emitting device according to the present invention, Fig. 2 is a graph showing another embodiment of the operation of the same device, and Fig. 3 is a laser to which the same device is applied. FIG. 4 is a schematic perspective view showing a beam printer, FIG. 4 is a front view showing a conventional laser emitting device, and FIG. 5 is a graph showing the operation of the same device. Explanation of symbols l...Laser emission device, i! 1 8... Laser chip 9.12... Dummy light emitting part 10.11... Light emitting part

Claims (1)

[Claims] In a laser emitting device using an array laser having a plurality of light emitting sections in one laser chip, at least one of the light emitting sections is operated without performing image recording prior to other light emitting sections. A laser emitting device featuring: