JPH02150088A - Semiconductor laser scanner - Google Patents

Abstract

PURPOSE:To remove the influence of an output variation due to a crosstalk and to scan from the start point to the end point of each scanning line with predetermined light quantity by supplying a bias current below a threshold value of the laser beam oscillation to oscillation regions of a laser array by oscillation control means. CONSTITUTION:When image signals 101 - 103 are input to input terminals a1 - c1, a driving current flows to oscillation regions 29a - 29c when an image signal is ON, and a bias current flows thereto when the signal is OFF. Thus, the temperature of a cavity is raised by the generation of a natural light of an output Pb with the bias current, the output of a laser beam to be disposed at the original position of the oscillation region adjacently by its thermal interference is reduced, and the output of a laser beam when the signal is ON is held at substantially constant Pd over the all regions.

Description

DETAILED DESCRIPTION OF THE INVENTION A0 Object of the Invention (1) Field of Industrial Application The present invention relates to a semiconductor laser scanning device used in a digital copying machine or an optical disk head.

(2) Prior art Figure 11 shows the schematic structure of a digital copying machine using a semiconductor laser. The reflected light of The value is converted to serial data. Semiconductor laser device 0 that operates according to this serial data
The laser beam emitted from 8 is surrounded by a charging charger 09, a developing unit 010. Transfer charger 01
1. Photosensitive drum 013 with cleaner unit 012
forms an electrostatic latent image on the surface of the And paper tray 01
After the electrostatic latent image on the photosensitive drum 013 is transferred to the paper supplied from the photosensitive drum 013, the paper is discharged to a paper discharge tray 016 through a fixing unit 015.

By the way, in the semiconductor laser used in the above-mentioned digital copying machine, the emission efficiency of the laser decreases due to the increase in cavity temperature accompanying the oscillation of the laser beam, so the output of the laser beam decreases as the cavity temperature increases. . This means that variations in the output, that is, variations in the amount of light, occur due to changes in the cavity temperature due to laser beam oscillation, which has been a cause of deterioration in image quality.

To explain this based on an example of the [current-output-temperature] characteristic of a semiconductor laser shown in FIG. 17, the current ■ supplied to the laser diode is 35~
In the region of 39 mA or less, the output P becomes extremely small, and at this time the laser diode generates spontaneous emission light.

When the supplied current 1 exceeds the above threshold value, the laser diode starts to emit stimulated emission, and its output P increases rapidly.

In the oscillation region of this laser beam, if the current I supplied to the laser diode is 50 mA, the cavity temperature T is 25'C.

As the temperature increases from 50'C to 70°C, the output P becomes 5m.
W, 4mW, and 3mW, decreasing sequentially. This means that
Conversely, in order to obtain a constant output P, the current I applied to the laser diode must be adjusted to compensate for variations in the cavity temperature T.
This shows that it is necessary to control the That is, when the output P of the laser beam decreases due to an increase in the cavity temperature T, the output P can be kept constant by increasing the current I applied to the laser diode.

12 to 14 show a conventional example in which temperature compensation is performed by applying the above-mentioned principle to the semiconductor laser scanning device 08 as a writing device of the digital copying machine.

As shown in FIG. 12, the optical path of a laser array 017 as a semiconductor laser light source that simultaneously irradiates three laser beams includes a collimator lens 018, a cylindrical lens 019, a mirror 0201, a rotating polygon mirror 021, a θ lens 022, and An imaging optical system 024 consisting of a cylindrical lens 023 is disposed, and the photosensitive drum 013 serves as a scanning surface rotatably provided around a central axis.
It is designed to scan the surface of Photosensitive drum 013
An optical sensor 025 is provided at the end of the optical sensor 025, and a beam position detection signal output from the optical sensor 025 sets the output timing of an image signal, which will be described later.

As shown in FIG. 13, the laser array o17 has an insulating layer 028 on the top of a substrate 027 having an electrode 026 on the bottom surface.
Three oscillation regions 029a, 029b, 02 separated by
9c, and by supplying a drive current from output terminals a, b, and c (to be described later) via electrodes 030, each oscillation region 029a, 029b, and 029c emits a laser beam having a fixed polarization direction indicated by an arrow. It is designed to emit light.

Returning to FIG. 12, oscillation control means A of the laser array 017
Three LD drivers o31a, 031b installed in
, 031c are output terminals a, b, c connected to the laser array 017 and two input terminals a+ + at
ib+ + bz ic+ *Ct. And one input terminal a+
The image memory 032 and line memories 033a, 033b, 033c are connected in series to +b++C+, and the other input terminal aZ+b! +C2 is connected to light amount control circuits 034a, 034b, and 034c for controlling the amount of laser light as shown in, for example, Japanese Patent Laid-Open No. 59-198780. The laser array 017 detects the amount of emitted laser beam by measuring the back beam leaking backward at the detector 035.
This light amount signal is compared with the base f$ potential of the light amount reference signal generator 037 in the light amount comparator 036, and the difference is used as a correction signal for each of the light amount control circuits 034a, 03
4b and 034c. Furthermore, the optical sensor 02
5 is connected to a controller 038, and the image memory 032, line memories 033a, 033b are controlled by the timing control signal output from this controller 03.
, 033c, and light amount control circuits 034a, 03
4b and 034c are controlled.

As shown in FIG. 14, the output terminals a, b, c of the laser array 017 to the oscillation control means are connected in series with transistors Tr, . A level converter 0 is connected between the base of the Tr and the input terminal al+blC, respectively.
39a, 039b, 039c are interposed, and the bases of the transistors Tr are connected to the input terminals a, , bt.
+ Connected to C2.

Next, the operation of the conventional example having the above-mentioned configuration will be explained.

Timing 11 output from the controller 038 Each LD driver 031a, 03tb, oa
tc is the three oscillation regions 029a of the laser array 017
, 029b, and 029c sequentially emit a laser beam for setting the light amount. A light amount signal obtained by measuring the back beam of the light amount setting laser beam with the detector 035 is fed back to the light amount comparator 036, where it is compared with the reference potential of the optical M reference signal generator 0370. The correction signal output from this light amount comparator 036 is input to voltage holding circuits 034a, 034b, and 034c and temporarily stored.

Subsequently, a position detection laser beam is emitted from the oscillation region 029a based on the timing control signal output by the controller 038. This position detection laser beam is reflected by the rotating polygon mirror 021 of the imaging optical system 024 and detected by the optical sensor 025. And from now on sensor O2
The beam position detection signal outputted by the controller 038
The feed is packed into the

On the other hand, 3N-2 lines, 3N-1 lines, and 3N lines output from the image memory 032 (N=1.2.
The image signals corresponding to ) are respectively stored in line memory 0.
After being temporarily stored in 33a, 033b, and 033c,
In synchronization with the beam position detection signal, the signals are simultaneously input to the input terminals al, b+, and C+ of the oscillation control means A. At the same time, input terminal at + b of oscillation control means A
2 + C2 includes a light quantity conical/1-0-conile circuit 034
The correction signals temporarily stored in a, 034b, and 034C are input.

The above image signals are sent to level converters 039a, 039b, 03
9C to the base of the transistor Tr+,
Turning on or off the transistor Tr+,
The above correction signal is used to convert the base current of the transistor Tr! whose magnitude changes depending on the amount of light into the transistor Tr! supply to. Therefore, the collector current flowing through the transistors Tr, Trz, that is, the drive current 1d supplied to the three oscillation regions 029a, 029b, 029c, changes according to each correction signal, and the output of the laser array 017 due to temperature change changes. Fluctuations are compensated.

In this way, the laser array 017 is connected to the rotating polygon mirror 02.
Three lines of image data are irradiated at a constant output in synchronization with one rotation, and the three lines on the photosensitive drum 013 are simultaneously scanned. And when the scanning of 3 lines is completed,
The above cycle is repeated to scan the fourth and subsequent lines.

(3) Problems to be Solved by the Invention In the conventional example described above, it is possible to compensate for output fluctuations for each scanning line due to self-heating of the laser array 017.
It was not possible to compensate for output fluctuations for each pixel due to thermal interference between 9a, 029b, and 029c.

That is, as shown in FIG. 15, the three oscillation areas 029a and 029b are activated according to the image signal.

When the drive current 1d is supplied to 029C, the oscillation regions 029a are adjacent to each other in the time domain Δt.

029b and 029c will irradiate laser beams at the same time. Then, as shown in FIG. 16, a so-called crosstalk occurs, which is a phenomenon in which the output Pd decreases from the broken line position to the solid line position in the time domain Δt due to the heat generation of the adjacent oscillation regions 029a, 029b, and 029c. Fluctuations occur in the light intensity of the laser beam, which causes deterioration in image quality.

The present invention was made in view of the above-mentioned circumstances, and eliminates the influence of output fluctuations due to crosstalk between multiple oscillation regions in a laser array, and provides a constant amount of light from the start point to the end point of each scanning line. An object of the present invention is to provide a semiconductor laser scanning device capable of scanning.

B9 Structure of the Invention (1) Means for Solving the Problems In order to solve the above problems, the first invention of the present application provides a laser array having a plurality of oscillation regions each of which can be modulated independently, and a laser array of this laser array. oscillation control means, wherein the oscillation control means supplies each oscillation region of the laser array with a bias current that is equal to or less than a threshold value for laser beam oscillation.

Further, a second invention of the present application is characterized in that the bias current is supplied when at least one of the image signals of each oscillation region is ON.

Furthermore, a third invention of the present application is characterized in that a polarizing filter having the same polarization direction as the laser beam is interposed in the optical path of the laser beam emitted from the laser array.

(2) Effect According to the first invention of the present application having the above-described configuration, each oscillation region of the laser array to which a bias current of less than the threshold value of laser oscillation is supplied, even when the image signal is OFF, the bias current is It is in a state of heat generation due to the electric current. Therefore, the temperature difference between the oscillating region and the non-oscillating region of the laser beam oscillation region is reduced, and fluctuations in the laser beam output due to crosstalk are compensated for.

Further, according to the second invention of the present application, by supplying the bias current when at least one of the image signals of each oscillation region is ON, when all the image signals are OFF, that is, crosstalk Bias current is not supplied when there is no risk of occurrence, thereby preventing wasteful power consumption.

Furthermore, deterioration of the laser is prevented and its lifespan is extended.

Furthermore, according to the third aspect of the present application, the polarizing filter provided in the optical path of the laser beam partially cuts off spontaneous emission light generated by the bias current, thereby preventing the influence of this natural light on scanning. .

(3) Examples Hereinafter, the present invention will be explained in detail based on the drawings.

1 and 2 show an overall view of a first embodiment of the present invention, which is an improvement over the conventional example, and an enlarged view of its laser array. The same symbols are given except for 0.

In this embodiment, a circuit for compensating for the influence of crosstalk is added to the oscillation control means A of the laser array 17 in FIG. 1, and as shown in FIGS. 1 and 2, the optical path of the laser beam is The present invention is characterized in that it includes a polarizing filter 40 having the same polarization direction as that of the laser beam, and the other configurations are the same as those of the conventional example.

FIG. 3 shows the configuration of the oscillation control means of the laser array 17, in which the conventional transistor Tr1 and resistor R1
Another transistor Tr= and a resistor R2 are interposed in series across both ends of the transistor Tr, and resistors R3 and R2 are connected to the base of this transistor Tr.
A predetermined voltage divided by 4 is applied.

With this configuration, the input terminal a.

Regardless of whether the image signal input to bl+cl is ON or OFF, the oscillation regions 29a, 29b, and
A constant bias current 1b is always supplied to the transistor 29c via the transistor Tr3.

This bias current 1b is set slightly lower than the threshold value at which laser oscillation occurs, and due to this bias current 1b, the oscillation regions 29a, 29b, and 29C generate weak natural light, and the temperature of the cavity increases. When the image signal is ON, the transistor 'r
Current Id-1b flows through the oscillation region 29a,
A drive current 1d greater than the threshold value is supplied to 29b and 29c.

To explain this based on the diagram, input terminal abl+cI
image signals 101, 102, 10 as shown in FIG. 4A.
3 is input, as shown in FIG. 4B, a drive current 1d flows through the oscillation regions 29a, 29b, and 29C when the image signal is ON, and a bias current Ib flows when the image signal is OFF. . Then, as shown in Fig. 5, the temperature of the cavity rises due to the generation of natural light of output Pb by the bias current tb, and due to the thermal interference, the output of the laser beam that should originally be at the position of the broken line in the adjacent oscillation region is changed to the solid line. When the image signal is ON, the output of the laser beam is maintained at a substantially constant Pd over the entire area.

Although the output of natural light generated by the bias current 1b is weak and does not interfere with scanning, it is desirable to eliminate its shadow as much as possible. The polarizing filter 40 in FIG. 2 is provided for this purpose. According to this polarizing filter 40, although half of the natural light passing through it is cut, almost all of the laser beam with the same polarization direction is is transmitted, thereby making it possible to reduce the influence of natural light generated by the bias current 1b.

FIG. 6 shows a second embodiment of the oscillation control means A of the laser array.

In this embodiment, three input terminals al+bl+c
The image signals 101, 102, and 103 from T are passed through an OR gate 41, and the output OR signal 201 is sent to a transistor T via level converters 42a, 42b, and 42C.
It is input to the base of rz.

That is, as shown in FIG. 7A, each input terminal al +
bl r Image signal input to CI 101°1
02.103 passes through the OR gate 41 and becomes the OR signal 201, and as shown in FIG. 7B, this OR signal 2
01, each light emitting diode 29a, 29b, 29c
Bias current 1b is supplied to.

In this embodiment, image signals 101, 102.10
The bias current ib is different from the first embodiment in that the bias current ib is not supplied when all 3 are OFF, but as is clear from FIG. It is now possible to obtain a laser beam output Pd of
When this is the case, that is, when the user is not accustomed to the occurrence of crosstalk, the bias current 1b is not supplied, and a pause period for the laser can be provided, thereby preventing deterioration of the laser and extending its life.

FIG. 9 shows a third embodiment of the oscillation control means A for the laser array.

In this example, there are three input terminals a+.

bI+ Image signals 101, 102, 103 from CI
(see Figures 9 and 10A) are passed through the OR gate 41 to obtain the OR signal 201 (see Figures 9 and 10A), and the three image signals 101, 102, and 103 are sent to NOTOR gates 4143b and 43c, respectively. are passed through to obtain NOT signals 111, 112, and 113, and these OR signals 201 and NOT signals 111, 112, and 113 are ANDed.
It is input to gates 44a, 44b, and 44c. AND signals 301, 302, 303 (9th degree, 10th A
(see figure) level converters 42a, 42b.

It is input to the base of the transistor Tr via 42c.

By applying the AND signals 301, 302, 303 as bias signals, each oscillation region 29a,
The currents supplied to 29b and 29c are as shown in FIG. 10B. This FIG. 10B shows the seventh example of the second embodiment.
Since it is the same as FIG. B, the third embodiment can obtain the same effects as the second embodiment.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the embodiments described above, and various small design changes may be made without departing from the scope of the invention as set forth in the claims. It is possible to do so.

For example, the number of oscillation regions of the laser array 17 as a semiconductor laser light source is not limited to three, but may be any number as long as it is plural. Further, as the polarizing filter 40, a reflective type can be used instead of a transmission type. Furthermore, the semiconductor laser scanning device of the present invention can be applied not only to digital copying machines but also to optical disk devices that record and reproduce information. For example, when applied to an optical disk device such as that described in Japanese Patent Application Laid-open No. 63-10340, it is possible to reduce the space talk between multiple laser oscillation regions, thereby reducing information reading errors. Become.

Effects of the C0 Invention According to the semiconductor laser scanning device of the first invention of the present application described above, a semiconductor laser comprising a laser array having a plurality of oscillation regions each of which can be independently modulated, and oscillation control means for this laser array. In the laser scanning device, each oscillation region of the laser array is supplied with a bias current that is less than the threshold for laser oscillation, so the oscillation region to which this bias current is supplied generates heat even when the image signal is OFF.

Therefore, the temperature difference between the oscillation region to which the laser beam is irradiated and the oscillation region to which the laser beam is not irradiated is reduced, and fluctuations in the output of the laser beam due to crosstalk are compensated for. This makes it possible to improve image quality and prevent reading errors in the semiconductor laser scanning device.

Further, according to the second invention of the present application, since the bias current is supplied when at least one of the image signals of each oscillation region is ON, when all the image signals are OFF, that is, crosstalk Bias current is not supplied when there is no risk of occurrence, thereby preventing wasteful power consumption. Furthermore, since no unnecessary current flows, deterioration of the laser is prevented and its lifespan can be extended.

Furthermore, according to the third invention of the present application, since a polarizing filter having the same polarization direction as the laser beam is provided in the optical path of the laser beam, it is possible to cut unnecessary natural light irradiated by the bias current. Become.

[Brief explanation of the drawing]

FIG. 1 is an overall view of a first embodiment of a semiconductor laser scanning device according to the present invention, FIG. 2 is an enlarged view of its laser array, FIG. 3 is a circuit diagram of its oscillation control means, and FIGS. 4A and B are 5 is a diagram showing its output, FIG. 6 is a circuit diagram of the second embodiment of the oscillation control means, and FIGS. 7A and 7B are diagrams showing the image signal and driving current. FIG. 8 is a diagram showing its output, FIG. 9 is a circuit diagram of the third embodiment of the oscillation control means, FIGS. 10A and B are diagrams showing its image signal and drive current, and FIG. 11 is a diagram showing its output. Schematic structural diagram of a digital copying machine,
Figure 12 is an overall diagram of a conventional semiconductor laser scanning device.
FIG. 3 is an enlarged view of the laser array, FIG. 14 is a circuit diagram of its oscillation control means, and FIG. 15 is a diagram showing its driving current.
FIG. 16 is a diagram showing the output, and FIG. 17 is a [current-output temperature] characteristic diagram of the semiconductor laser.

Claims (1)

[Claims] [1] A plurality of oscillation regions (29a,
29b, 29c), and an oscillation control means (A) for the laser array (17), wherein the oscillation control means (A) ) A semiconductor laser scanning device characterized in that a bias current (Ib) below a threshold value for laser beam oscillation is supplied to each oscillation region (29a, 29b, 29c) of the laser beam. [2] The bias current (Ib) is applied to each oscillation region (29
at least one of the image signals a, 29b, 29c)
The semiconductor laser scanning device according to item [1], which is supplied when the laser is ON. [3] Each oscillation region (29a) of the laser array (17)
, 29b, 29c), wherein a polarizing filter (40) having the same polarization direction as that of the laser beam is interposed in the optical path of the laser beam emitted from the laser beam.