JPH01251686A - Laser emitting device - Google Patents

Abstract

PURPOSE:To prevent the fluctuation in laser output and to contrive improvement in reliability by a method wherein, using an array laser having a plurality of light-emitting parts on a laser chip, a heatgenerating element is provided in the vicinity of the light-emitting parts. CONSTITUTION:The title beam emitting device consists of the semiconductor array laser having four light-emitting parts 9, 10, 11 and 12 on one laser chip 8. LD1, LD2, LD3 and LD4 are laser diodes corresponding to the light-emitting parts 9, 10, 11 and 12 respectively, and R1, R2, R3 and R4 are heating resistors 35, 36, 37 and 38. Also, C11, C12, C13 and C14 are constant-current circuits, they are ON-OFF controlled by transistors Q1, Q2, Q3 and Q3, and these transistors perform the function of flowing a constant current to the laser diodes LD1, LD2, LD3 and LD4 when the transistors are turned ON. Against the signals (a), (b), (c) and (d) with which the laser diodes LD1-LD4 will be driven, the transistors Q5-Q8, with which the heating resistors R1-R4 will be driven, are driven by -a*(b+c+d), -b*(a+c+d), -c*(a+b+d) and -d*(b+c+d), -b*(a+c+d), -c*(a+b+d) and -d*(a+b+c), and a thermal balance can be maintained for the light-emitting parts.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a laser emitting device used as a light source for a laser beam printer (hereinafter referred to as LBP), and in particular, to a This invention relates to stabilizing the output of an array laser that has multiple light emitting sections on one chip.

(Prior art) In recent years, as a light source used in printers such as LBP,
Semiconductor lasers are increasingly being used because devices can be made smaller and can be easily controlled.

The main components of the laser scanning device used in LBP are: a laser emitting device as a light source that emits laser light; a polygon mirror that scans the laser light in the axial direction of the photoreceptor drum; It consists of a motor that rotates at a constant speed and a lens system that focuses laser light onto a photoreceptor drum.

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 that use semiconductor lasers, there are limits to increasing the laser output and the rotation speed of the polygon mirror, and the printing speed is currently 50% in terms of A4 size paper output.
The limit is about 60 sheets/minute. Another method is to emit multiple beams from the laser and simultaneously print multiple lines in the rotational direction of the photoreceptor drum during one laser scan, without changing the rotational speed of the polygon mirror much. The printing speed can be increased by several times the number of beams. If this method is used, the above printing speed can be several hundred sheets.
It is also possible to increase the speed by a fraction of the time.

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 hold each 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. 9(a) and 9(b) and FIG. 1O.

FIGS. 9(a) and 9(b) are schematic diagrams showing a conventional laser emitting device. This laser emitting device 1 includes one laser chip 8 and four light emitting parts 9. 10. ! 1. 12 semiconductor array lasers. The laser chip 8 includes a substrate 13, a first semiconductor layer 14, and a second semiconductor layer 14.
semiconductor layer 15 and electrode 16. 17. The laser chip 8 is brazed to a mount 20 made of copper, silver, etc. through a layer of silicon or silicon carbide.

FIG. 10 shows the emission characteristics of the laser output.

As shown in FIG. 10, such a semiconductor laser has a time t
. When a constant driving current is applied to cause the laser to emit light, the laser output is
After Po is output, a phenomenon is observed in which the output gradually decreases due to self-heating. This is because the heat generated by the self-heating of the light emitting parts 9 to 12 is difficult to flow to the outside through the mount 20, so the temperature difference between the chips before and after light emission is large (the threshold current of the laser is significantly increased). This is because the laser output decreases at a constant drive current.This decrease in output occurs when the inside of the chip 8 becomes thermally saturated to some extent and the temperature of the light emitting part stabilizes, the rate of decrease in output decreases and the output decreases to a constant value. reach.

When the above array laser is used for LBP, etc., due to this phenomenon, if each light emitting part is driven by an image signal with a greatly different drive rate, then immediately after it is driven by an image signal with a different drive rate, each The temperature due to the heat generated by the light emitting parts varies locally, and as a result, the magnitude of the laser output emitted from each light emitting part differs, which causes the potential of the photosensitive layer on the photosensitive drum to fluctuate. However, there arises a problem in that the image quality is significantly deteriorated due to uneven density of the image. For example, when printing an image pattern in which only light emitting parts 9 and 11 are driven and 10 and 12 are not driven, the temperature of light emitting parts 9 and 11 increases, and the light emitting parts lO
and 12, the temperature does not rise. Immediately after printing the image pattern, when printing an image pattern in which all of the light emitting units 9 to 12 are driven, the light emitting units 9, 11 and 10. 12
The magnitude of the laser output varies due to the temperature difference between the two, resulting in uneven density.

The above-mentioned problems also occur in conventional array lasers having two light emitting sections.

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

However, in this case, a new problem arises in that the laser is constantly energized, which impairs the reliability, especially the life of the laser chip.

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 is about providing.

(Means for Solving the Problems) In order to achieve the above-mentioned object, the present invention provides a laser emitting device using an array laser having a plurality of light emitting parts in one laser chip. It forms a laser array with a structure in which multiple heating elements are placed in front of each light emitting part, and by controlling the heat generated by the erroneous heating elements, the thermal imbalance of the light emitting parts is eliminated.Used for L, LBP, etc. In some cases, the purpose is to prevent uneven density of images.

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

FIGS. 1(a) and 1(b) show an embodiment of a laser emitting device according to the present invention. This laser emitting device 1
, one laser chip 8 has four light emitting parts 9, 10, 1
It consists of a semiconductor array laser with a wavelength of 1.12.

The laser chip 8 includes a substrate 13 and a first semiconductor layer 1.
4, the second semiconductor layer 15, and the electrode 16. 17. 1
8. 19, and the laser chip 8 is mounted on a mount 2 made of copper, silver, etc. through a layer of silicon or silicon carbide.
It is brazed to 0.

Furthermore, electrode 16. 17. 18. Insulating layer 3 on 19
A heat generating resistor 35.
36°37.38 are arranged. The resistance value of the resistor is selected so that the amount of heat generated when each light emitting section is driven is approximately equal to the amount of heat generated when each light emitting section is driven.

As described above, in the present invention, a plurality of heating elements are driven according to the driving states of a plurality of light emitting sections, thereby achieving thermal stability of the light emitting sections.

FIGS. 2(a) and 2(b) show the case where the above is applied to an array laser having two light emitting parts at 9°lO.

FIG. 3 shows an example of an arrangement structure in which the heating element is placed closer to the light emitting part, and 39. 40 is a heat generating resistor wrapped in an insulating layer.

FIG. 4 shows a driving circuit for a laser array having four light emitting sections shown in FIG. 1 according to the present invention. In the figure, LDI,
LD2. LD3. LD4 is a light emitting part 9. 10°11,
12 shows corresponding laser diodes, and RI+
R2+ R3+ R4 is heating resistor 35°36
, 37. 38 is shown. Also, C1l, CI2.
CI3゜CI4 is a constant current circuit, and transistor Qll
G2゜G3. Q4+: Therefore, ON and OFF are controlled,
When the transistor is ON, the laser diode LDI,
LD2゜LD3. Each serves to flow a constant current to LD4.

Note that the current value of the constant current circuit is set by polyurethane (not shown). Also, Gl + G2 + G3
+G4 is an and gate, G5. G6. C7 and C8 are inverters, C9+ GIG r GII * G1
2 is Orgate, Q10. G6. G7. QB is a transistor.

Table 1 is a logic table for the fourth illustrated driving circuit.

Table 1 Signal a for driving each laser diode LD1 to LD4
, b, c, d, each heating resistor R1-R4
Transistors Q5 to Q8 that drive
), d*(a+c), and thermal balance is achieved for each light emitting section as shown in Table 1.

FIG. 5 shows another drive circuit for driving the array laser of FIG. 1 according to the present invention, and the same reference numerals as in FIG. 4 indicate the same components.

In the same figure, G13 + 614 + 015 r
616 is an OR gate, and G1□ is an AND gate.

Table 2 is a logic table for the fifth illustrated driving circuit.

Table 2, Figure 5 shows all laser diode LDs for Figure 4.
When I to LD4 are not driven, heating resistors R1 to R4
A circuit is added to drive all of the printers, and when used for LBP etc., thermal balance can be maintained including the non-printing period.

FIG. 6 shows a circuit for driving the array laser shown in FIG. 2 according to the present invention, in which LDI and LD2 indicate laser diodes corresponding to the light emitting parts 9 and 10, respectively, and R
1 and R2 indicate heating resistors 35 and 36.

Further, C1l and CI2 are constant current circuits, and transistors Q1. ．． The ON/OFF state is controlled by Q2, and the transistor functions to flow a constant current to each of the laser diodes LDI and LD2 at 08:00. Note that the current value of the constant current circuit is set by polyurethane (not shown). In addition,
As another method, when applied to LBP etc., this current value is determined by monitoring the laser output emitted from the laser with a photodiode, and the laser output is set at a predetermined level during non-printing timing between pages in the printing process. You can also set it to the value.

Table 3 Further, Table 3 is a logic table of the sixth illustrated driving circuit.

In the above configuration, the signal a that drives the laser diode LDI drives the resistor R2 as well as the laser diode LDI. Also, the signal for driving the laser diode LD2 is
At the same time, the resistor R1 is also driven.

By doing this, when one laser diode is driven, the heat generating resistor corresponding to the other laser diode is driven, so the amount of heat generated by both light emitting parts is almost the same, and therefore the temperature of the light emitting part is Since the laser diodes are almost the same, the magnitude of the laser output from both laser diodes is almost the same, and as a result, when used for LBP, etc., uneven shading will not occur in the printed image.

FIG. 7 shows another drive circuit for driving the array laser of FIG. 2 according to the present invention, and the same reference numerals as in FIG. 6 indicate the same parts.

Further, in the figure, Gl and G2 are AND gates, G5. G6 is an inverter. Q5. Q6 is a transistor. In the figure, in response to a signal a for driving laser diode LDI and a signal for driving laser diode LD2, transistor Q5. Q
The signals driving 6 are driven by logic signals a*b and a*b, respectively.

Table 4 Further, Table 4 is a logic table of the seventh illustrated driving circuit.

According to the example in FIG. 7, in the example in FIG. 6, the image signals a,
When b drives both laser diodes LDI and LD2, heating resistors R1 and R2 are both driven, but
In the driving circuit of this example, both heating resistors R1 and R2 are not driven.

FIG. 8 shows another drive circuit for driving the array laser of FIG. 2 according to the present invention, and the same reference numerals as in FIG. 7 indicate the same parts. Also, G13 in the same figure. G
14 is an OR gate, and G18 is an AND gate.

Table 5 Further, Table 5 is a logic table of the eighth illustrated driving circuit.

In the example of FIG. 8, as shown in the logic table of Table 5, the signals a,
When both laser diodes LDI and LD2 are not driven, the heating resistors R1 and R2 are driven together, so in any case, that is, when used for LBP etc., the thermal balance is maintained including the non-printing period. It is possible to maintain

(Effects of the Invention) As explained above, according to the present invention, by providing a heating element near each light emitting part of the array laser and controlling the heat generation of the heating element, heat between each chip of the array laser is reduced. This is to prevent imbalance. Therefore, L
When used for BP, etc., it eliminates density unevenness in images and improves image quality.

[Brief explanation of the drawing]

FIGS. 1(a) and (b) are schematic views showing one embodiment of the laser emitting device of the present invention, and FIGS. 2(a), (b), and 3 show other embodiments of the present invention. Schematic diagram, Figure 4. 5, 6, 7, and 8 are diagrams showing drive circuits for driving the laser emitting device of the present invention, and FIG. 9(a),
(b) is a schematic diagram showing a conventional laser emission device;
FIG. 0 is a diagram showing the operation of the apparatus shown in FIG. 1 ・・・・・・・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・
Laser emission device 8・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・
・・・・・・・・・Laser chip 9.10, 11.1
2・・・・・・・・・・・・・・・・・・・・・・・・
...... Light emitting section 35, 36. 37.
38・・・・・・・・・・・・・・・・・・・・・・・・Heating resistor (b) Magbow? , Kasumi (b) 10V 10V Small envy q diagram (b)

Claims (1)

[Claims] (1) A laser emitting device using an array laser having a plurality of light emitting parts in one laser chip, characterized in that a heating element is provided in the vicinity of the light emitting part.