JPH10209574A - Multibeam light source device and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the deterioration in accuracy of light quantity detection by a method wherein the spread angle/emission axis of a plurality of laser beams is changed and the overlapping of the laser beams when simultaneously lighted is decreased. SOLUTION: The width b2 of the active layer on the backside of a multibeam semiconductor laser 12 is widened dissymmetrically wider than the width b1 of the active layer on the front side, the expansion angle of the laser beam directing to a light receiving part 14 is small, and emission axis is inclined to the direction of separation with each other. As a result, the overlap of the laser beams on the light receiving part 14 can be reduced or separated, and consequently, the accuracy of detection of light quantity of the laser beams when simultaneously lighted can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a digital copying machine,
The present invention relates to a multi-beam light source device used as a light source of an image forming apparatus such as a printer or a fax, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus using a multi-beam semiconductor laser as a light source, as a method of individually controlling the amount of light of a plurality of beams, a method of detecting front light emitted from the front of a light emitting area to a photosensitive surface side. (Japanese Patent Laid-Open No. 7-
No. 9698, JP-A-63-146553) and a method of detecting rear light emitted from the rear surface of the light-emitting area (active layer) to the side opposite to the photosensitive surface (see JP-A-2-42639).

In the method of detecting the front light, it is necessary to use a separation lens inside the laser package or to separate the laser beam emitted to the outside by an optical component, so that the number of components increases and the cost increases. Was. Further, since a design for routing a laser beam is required, the image forming apparatus has become complicated and large. Furthermore, mounting optical components inside or on the surface of a laser package requires extremely high-precision lens mounting technology, which complicates the laser manufacturing process and makes multi-beam semiconductor lasers expensive. .

On the other hand, the method of detecting the rear surface light has the advantage that no extra optical components are required in the image forming apparatus by directly detecting the laser beam with a light receiving section having a large number of light receiving elements (particularly). See JP-A-57-78191).

However, when the interval between the laser beams emitted in parallel from the multi-beam semiconductor laser is less than 100 μm, the laser beams overlap at the light receiving section, so that the light amount separation threshold increases to 50% or more, and individual Light quantity detection accuracy is reduced. As a countermeasure, a method is adopted in which the light receiving unit is brought as close as possible to the multi-beam semiconductor laser. This will be described with reference to a conceptual diagram showing the relationship between the multi-beam semiconductor laser 50 and the light receiving unit 52 shown in FIG.

Here, taking the example of a photodiode commonly used as the light receiving section 52 as an example, the distance C between the light receiving section 52 and the multi-beam semiconductor laser 50 needs to be about 1 mm. This is because when bonding the external lead portion and the light receiving portion 52 with a wire, the bonding cannot be performed without a gap corresponding to the height of the wire (500 μm) and a capillary having a size of about several hundred μmΦ. If the distance C is set to about 1 mm, the light receiving section 52 cannot separate the two laser beams unless the light emitting point interval D is about 100 μm or more.

For this purpose, as shown in FIG. 8, a special laser heat sink 54 is used to electrically connect the external lead portion 56 to an area sensor 58 as a light receiving portion. Further, there is a method of bringing the area sensor 58 close to the multi-beam semiconductor laser 50.

However, the laser heat sink 54 is a conventional type laser heat sink 60 as shown in FIG.
The structure becomes complicated and the cost increases as compared with. Further, since the area sensor 58 can approach the multi-beam semiconductor laser 50 only up to a light receiving part beam diameter several times the minimum pixel size (6 × 8 μm) of the area sensor 58, the pixel size of the area sensor 58 is small. There is a limiting condition according to the condition, and the lower limit of the distance C is determined.

Further, when an area sensor / line sensor such as a CCD is used as the light receiving section, the sensitivity of the CCD sensor does not match the laser light amount, so that the laser light amount level is reduced by about 10 to the seventh power until the CCD receives light. There is a need. Therefore, it is necessary to use a special light-attenuated surface on the light-receiving portion, which has the disadvantage of making the linear sensor / area sensor, which is more expensive than the photodiode 52 used conventionally, more expensive. ing.

In order to cope with such a problem, a method has been practiced in which an inexpensive single light-receiving unit such as a photodiode is used to sequentially turn on a laser beam and individually control the amount of light. No. 63-42432.

However, even with this method, when a plurality of laser beams are turned on at the same time, it is not possible to cancel the light amount fluctuation of the light-emitting beam due to the influence of crosstalk or electric leakage due to heat transfer from the adjacent light-emitting beams. In addition, this development tends to become more remarkable as the distance D between the light emitting points of the laser beam is reduced.

Therefore, when the image is formed by turning on a plurality of laser beams at the same time to control the light quantity and simultaneously turn on a plurality of laser beams, the potential level on the photosensitive member surface between the plurality of laser beams fluctuates, and finally the density of the printed image is changed. A problem that caused fluctuations was inevitable. Specifically, when a plurality of laser beams are continuously turned on to form an oblique line with respect to the main scanning direction, a remarkable density reduction line occurs at a step portion of the oblique line.

[0013]

In view of the above facts, the present invention changes the spread angles and emission axes of a plurality of laser beams emitted from a laser beam without using an optical component or a complicated laser package structure. This reduces the overlap of laser beams when they are turned on at the same time, prevents the accuracy of light quantity detection from deteriorating, and cancels density fluctuations caused by crosstalk and electrical leakage due to heat conduction when multiple laser beams are turned on at the same time. And

[0014]

According to the present invention, a laser beam is emitted to the photoreceptor from the front side of the light emitting area of the multi-beam semiconductor laser, and the laser beam is emitted to the light receiving section from the rear side of the light emitting area. Has become.

The width of the light emitting area on the rear side is wider than the width of the light emitting area on the front side, and the spread angle of the laser beam toward the light receiving section is smaller. For this reason, the overlap of the laser beams in the light receiving section can be reduced or separated, so that the accuracy of detecting the light amount of the laser beams during simultaneous lighting can be improved. Further, it is possible to cancel the density fluctuation caused by crosstalk and electric leakage due to heat conduction at the time of simultaneous lighting of a plurality of laser beams.

The width of the light emitting area on the rear surface is asymmetrically widened with respect to the axis of emission of the laser beam emitted from the light emitting area on the front surface, so that the emission angles of the laser beams emitted from the rear surface are mutually different. It can be tilted in the direction away. For this reason, it is possible to further reduce or separate the overlap of the laser beams at the light receiving section.

Further, the multi-beam semiconductor laser of the present invention can be manufactured at a low cost because only the mask pattern for defining the light emitting area needs to be changed.

[0018]

FIG. 1 shows a schematic configuration of an image forming apparatus using a light source device 10 according to the present embodiment.

The light source device 10 includes a multi-beam semiconductor laser 12 and a light receiving section 14 inside a laser package. In response to the image signal, the two laser beams emitted from the multi-beam semiconductor laser 12 as front light are reflected and deflected by the deflecting surface 16A of the polygon mirror 16, and pass on the photoreceptor 20 via the imaging optical system 18. Optical scanning is performed.

Before optical scanning on the photosensitive member 20,
Part of the beam reflected and deflected by the polygon mirror 18 is
The light is reflected by the mirror 22 and guided to the SOS sensor 24, and the scanning start position is detected.

At this time, by performing optical scanning with a plurality of laser beams, a plurality of scanning lines can be simultaneously recorded and displayed, so that the speed of image processing can be increased.

Next, the multi-beam semiconductor laser 12 will be described with reference to FIG.

This multi-beam semiconductor laser 12
It has a lateral refractive index light confinement stripe structure, and from the front surface of two active layers 26 arranged in parallel,
Front light is applied to the photosensitive surface side, and the substrate 2
The rear surface light is emitted to two light receiving units 14 that are separately arranged on the upper surface 8 and detect the light amount.

Here, in order to facilitate understanding, description will be made in comparison with a conventional multi-beam semiconductor laser 50 shown in FIG.

The conventional multi-beam semiconductor laser 50 has a horizontal spread angle θf1 (1/1) of the front light.
e ² ) and the horizontal spread angle θb1 (1 /
e ² ) will be the same. This is because usually, a stripe pattern having an active layer width b1 for defining an optical amplification area inside the multi-beam semiconductor laser 50 is formed in parallel with the front and rear direction of emission and has a uniform width on both front and rear surfaces.

Thus, since the stripes having different refractive indexes are formed uniformly, the structure for stabilizing the light path reflected and amplified by the laser reflecting surface is most stabilized. Has the function of causing. At this time, the relationship between the active layer width b (usually about 2 μm) and the horizontal spread angle θb before and after the emission is generally represented by the following equation (1). (Equation 1) θb = tan ⁻¹ (λ / π / b) θb: Horizontal spread angle of the laser rear surface emitted light (1 / e)
² ), λ: wavelength b: active layer width (Semiconductor laser “Basic and applied” Baifukan p1
18 Excerpt, edited) To be precise, the active layer width b in (Equation 1) is the half beam value of the beam emitted outside near the end face of the multi-beam semiconductor laser. Are substantially the same, so that the relationship of (Equation 1) can be substituted for the active layer width b. Therefore, the beam divergence angle θb has a relationship inversely proportional to the active layer width b.

Also, astigmatism a is a phenomenon in which when a laser beam is observed from the outside, when the beam focal point is observed from the radius of curvature of the wavefront, it appears that the laser beam has a focal point inside the laser. It corresponds to. Generally, any type of semiconductor laser has astigmatism. There are two types, vertical and horizontal. In the vertical direction, a strong refractive index waveguide having a heterostructure thickness of about 0.1 μm is employed. In the horizontal direction, the stripe width (active layer width) is about 2 μm. According to (Equation 1), the vertical direction is wider than the horizontal spread angle, and the astigmatism has the opposite relationship.

In order to separate and receive such laser beams individually, the distance C between the multi-beam semiconductor laser 50 and the light receiving section 52 and the light emitting point interval D must satisfy the following relationship (Equation 2). There is. (Equation 2) D / (C + a) = 2 tan (θb ÷ 2) D: interval between light emitting points, C: distance between laser end face and light receiving section,
a: Astigmatism However, as described in the section of the related art, it is difficult to reduce the distance C from the laser end face to the light receiving portion to 1.0 mm or less in the conventional laser package structure. According to Equation 2), even if the distance C is set to 1.0 mm, the light emitting point interval D needs to be 0.122 mm or more.

That is, in the conventional multi-beam semiconductor laser 50, a plurality of laser beams are individually received by the light receiving section 5.
2 is physically impossible.

Therefore, in the multi-beam semiconductor laser 12 of the present embodiment, by focusing on the relationship of (Equation 1), as shown in FIG. 2, by increasing the active layer width b2 of the rear surface light,
The horizontal spread angle θb2 of the rear light is reduced. Note that the active layer width b2 has a limited range.
When the distance is about m, it is possible to realize a multi-beam semiconductor laser having a transverse mode oscillation wavelength with little light quantity fluctuation.

Here, as an example, the active layer width b2 is set to 5 μm.
m and the light emitting point interval D
And try to calculate. θb2 is about 3 ° from (Equation 1), the light emitting point interval D is about 50 μm from (Equation 2), and the light receiving unit 14 can separate and receive light even when the distance C is 1 mm.

Further, by not only widening the width b2 of the active layer on the rear surface side but also obliquely forming the stripe pattern so as to asymmetrically expand with respect to the emission axis L1 of the front surface light,
The inclination of the emission axis L2 of the rear light is inclined by θs with respect to the emission axis L1 of the front light. This is because the laser beam is output as a composite wave of the wavefront emerging from the emission axis L1 parallel to the stripe pattern and the wavefront guided obliquely at an angle θs to the stripe pattern emission axis. This allows
Even when the light emitting point interval D is further reduced, the laser beam can be separated and received by the light receiving unit 14 without overlapping.

As described above, the multi-beam semiconductor laser 12 used in the light source device 10 of the present embodiment only needs to change the pattern of the stripe active layer width structure. Can be planned. Also, the overlap between the rear exit beams is reduced,
Alternatively, since the light is completely separated, the separated light receiving unit 14 can detect the amount of light with high accuracy for each laser beam.
Furthermore, even if a plurality of laser beams are simultaneously turned on, it is possible to cancel the fluctuation in the amount of light due to heat conduction or electric leakage from the adjacent light-emitting beams, and to suppress the fluctuation in image density. Further, since it is not necessary to make the distance C between the multi-beam semiconductor laser 12 and the light receiving section 14 close to each other, the conventional laser package structure (see FIG. Can respond.

In the above-described example, a partially oblique stripe structure pattern is used. However, similar effects can be obtained by using a partially square stripe structure pattern like the multi-beam semiconductor laser 13 shown in FIG. Is obtained.

Next, a method for manufacturing a multi-beam semiconductor laser according to the present invention will be described. In the method for manufacturing a multi-beam semiconductor laser according to the present invention, no step is added to the normal multi-beam semiconductor laser manufacturing process. The portion to be changed is to change the light-shielding mask pattern defining the light emitting region having an active layer width of about 2 μm arranged in parallel to a mask pattern as shown in FIG. However, at this time, the active layer width b2 needs to be 5 μm or less in order to suppress the fluctuation of the light amount at the same time in the horizontal multi-mode.

There are two types depending on the process method for defining the active layer width by the changed mask pattern.

One is a process method for defining the width of the active layer using the diffusion of impurities such as Si. An n-AlGaAs con? Guration layer / n-AlGaAs clad layer / AlGaAs formed by continuous growth on an n-GaAs substrate. Forming an active layer (including a multiple quantum well structure) / p-AlGaAs cladding layer / pAlGaAs con? Guration layer;
After the formation of the Cap layer / SiN layer, a modified mask pattern for defining the active layer width seen in the present embodiment is adopted to form the SiN layer.
Form a pattern. At this time, since the SiN layer serves as a barrier for diffusion of Si impurities in the amorphous Si layer formed thereon, it is necessary to use a light-shielding mask having a negative pattern. Thereafter, an SiN impurity diffusion barrier pattern is formed by a light-shielding mask and photolithographic etching, amorphous Si is formed, and heat treatment is performed in an As atmosphere at about 800 ° C. to form an active layer pattern as shown in FIG.

The other is an n-AlGaAs compensating layer / n-A continuously formed on an n-GaAs substrate.
lGaAs cladding layer / AlGaAs active layer (including multiple quantum well structure) / p-AlGaAs cladding layer / p
When the AlGaAs compensated layer is completed, the pAlGaAs compensated layer is chemically etched using a positive pattern light-shielding mask to form a mesa-shaped ridge portion of the active layer pattern as shown in FIG.
After that, a ridge buried layer is formed.

Each of the multi-beam semiconductor lasers formed by the above two methods is subjected to the same processing thereafter. That is, p electrode layer formation, p electrode separation pattern formation /
After the active layer cutting step, the chip is divided by polishing / n-electrode formation / substrate division / reflection film formation, and the chip of the multi-beam semiconductor laser of the present invention is formed.

Then, the multi-beam semiconductor laser is mounted on the heat sink and is electrically connected by wires.
Finally, if the laser package is assembled, the light source device 10
Is completed.

Next, a method of manufacturing the light receiving section will be described. The divided light receiving unit 14 can be realized by adding one step to a method of forming a normal photodiode. First, an n-layer, an i-layer, and a p-layer are formed on a normal Si substrate, and then a new photolithography process and chemical etching are performed to cut out the grooves by a number corresponding to the desired number of divisions and to insulate the dug surface. An oxidation treatment is performed to achieve this. The groove depth is Si
It is the depth that reaches the layer. Thereafter, an electrode is deposited on the p / n layer according to a predetermined pattern, and an external electrode pattern is formed by photolithographic etching. Finally, an anti-reflection layer on the surface is formed, and the divided light receiving unit 14 is completed.

Next, a light amount control method using the present light source will be described. This light amount control method is basically the same as the single beam light amount control, except that a plurality of laser beams have control units corresponding to each other on a one-to-one basis. Hereinafter, a brief description will be given with reference to the block diagram of FIG.

The rear surface light individually separated from the multi-beam semiconductor laser 12 is individually converted into a current by the divided light receiving unit 14 and converted into a voltage by a separate sample and hold circuit.

The voltage once stored in the sample hold is compared with a desired voltage. If the voltage is within a predetermined voltage range, a desired drive current is applied to each light emitting area to emit a laser beam and irradiate the photosensitive member. If the respective sample-and-hold voltages are not within the predetermined voltage range, the laser drive current is once increased, and the respective divided light-receiving units 14 detect the respective light amounts again until the respective sample-hold voltages fall within the predetermined voltage range. Form a repeating feedback loop.

This is usually Auto Power Con
This is called a trol (APC) operation, and a dedicated driver made into an IC is used for a laser drive current generation portion other than the sample hold and voltage comparison unit. The timing of the light amount control is performed outside the image area (for example, 1
(Before printing the first sheet of paper, before printing the second sheet of paper, and before and after lighting one line of the image, use the time outside the image line area other than the beam lighting).

As shown in the block diagram of FIG.
The number of the individual signal comparing means 40 may be increased in accordance with the number of laser beams. By adopting this method, even in the case of the inter-line simultaneous lighting light intensity modulation method or the like in which the reference voltage between the lines changes like the desired values 1 and 2, the light amount can be controlled for each of the simultaneous lighting and the single lighting. Become. Further, in the present embodiment, the case where there are two laser beams has been described. However, it is a matter of course that the same light source device can be configured with two or more laser beams and the light amount can be separately controlled.

[0047]

Since the present invention has the above-described structure, the light amount of the laser beam emitted from the multi-beam semiconductor laser can be reduced without using extra optical parts, and even when the light emitting point intervals of the laser beam are close to each other. , It is possible to individually detect the amount of light. For this reason, it is possible to cancel the fluctuation of the light amount due to heat conduction or electric leakage from the adjacent at the time of simultaneous lighting, which was impossible in the related art, and it is possible to provide an inexpensive and simple structure.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of an image forming apparatus using a multi-beam light source device according to an embodiment.

FIG. 2 is a schematic view of emitted light of the multi-beam light source device according to the embodiment.

FIG. 3 is a schematic view of emitted light of a multi-beam light source device according to a modification.

FIG. 4 is a block diagram illustrating a control method of the multi-beam light source device according to the embodiment.

FIG. 5 is a block diagram showing another example of the control method of the multi-beam light source device according to the embodiment.

FIG. 6 is a schematic view of light emitted from a conventional multi-beam light source device.

FIG. 7 is a structural diagram showing a package structure of a general multi-beam semiconductor laser.

FIG. 8 is a structural diagram showing a package structure of a multi-beam semiconductor laser using an area sensor.

[Explanation of symbols]

 12 Multi-beam semiconductor laser 14 Light receiving part 26 Active layer (light emitting area)

Claims (4)

[Claims] 1. A multi-beam light source device comprising a multi-beam semiconductor laser that emits a laser beam in parallel from a front side of a plurality of light emitting areas to a photoreceptor and from a rear side to a light receiving unit. A multi-beam light source device, wherein the width is wider than the width of the light emitting area on the front side. 2. A multi-beam light source device comprising a multi-beam semiconductor laser that emits a laser beam in parallel from a front side of a plurality of light emitting areas to a photoconductor and from a rear side to a light receiving unit. A multi-beam light source device characterized in that the width of the light emitting area on the rear surface side is asymmetrically widened with respect to the emission axis of the emitted laser beam. 3. The method for manufacturing a multi-beam light source device according to claim 1, wherein the mask pattern is changed to a mask pattern for enlarging the width of the light emitting area on the rear surface side by etching by masking or diffusion of Si impurities. A method for manufacturing a multi-beam light source device. 4. The method for manufacturing a multi-beam light source device according to claim 2, wherein the etching is performed by masking or the diffusion of Si impurities is used, and the rear surface of the laser beam is emitted from the light emitting area on the front surface. Characterized in that the width of the light emitting area on the side is changed to a mask pattern that expands asymmetrically.