JPH02187369A - Semiconductor laser scanner - Google Patents

Abstract

PURPOSE:To scan from the starting point to the ending point of each scanning line with predetermined quality of light by interposing an intermediate oscillation region between adjacent write oscillation regions of a laser array, and supplying a compensating current of the threshold value or less of a laser oscillation to the intermediate oscillation region. CONSTITUTION:A laser array 17 further has two intermediate oscillation regions 29d, 29c at the intermediate positions of three write oscillation regions 29a-29c, and a predetermined compensating current Ic is supplied to the two intermediate oscillation regions 29d, 29e through a transistor Tr 3 always becoming a conducting state. The compensating current Ic is set to a value slightly lower than the threshold value for causing a laser oscillation. The intermediate oscillation regions 29d, 29e generate weak natural lights with the compensating current Ic, and become heat generating state. Cavity concentration becomes substantially equal to that during the laser beam oscillation of other three write oscillation regions 29a-29c, thereby compensating the influence of a crosstalk.

Description

DETAILED DESCRIPTION OF THE INVENTION A9 Object of the Invention (1) Industrial Field of Application The present invention relates to a semiconductor laser scanning device used in a digital copying machine or a write head of an optical disk.

(2) Conventional technology Figure 9 shows the schematic structure of a digital copying machine using a semiconductor laser. lamp 02
The reflected light from the original is transferred to the moving mirror system 03 and the lens 04.
, converges on the image reading section 06 via the fixed mirror system 05, converts it into an electrical signal, and further converts this electrical signal into the image processing section 0.
7, each scanning line is converted into binary serial data. A laser beam emitted from a semiconductor laser device 08 that operates according to this serial data forms an electrostatic latent image on the surface of a photosensitive drum 013, which has a charging charger 09, a developing unit 010, a transfer charger 011, and a cleaner unit O12 around its periphery. Form. Then, the paper fed from the paper tray 014 is transferred to the photosensitive drum 013.
After the above electrostatic latent image is transferred, the fixing unit l-01
5 and is discharged to a paper discharge tray 016.

Incidentally, in the semiconductor laser used in the digital copying machine, the emission efficiency of the laser decreases due to an increase in the cavity temperature accompanying laser beam irradiation, resulting in a decrease in laser beam output. 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. 15, the current I 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 natural light. When the supplied current I exceeds the above threshold value, the laser diode starts stimulating emission, and its output P increases dramatically. In the oscillation region of this laser beam, if the current supplied to the laser diode is 50 mA, the cavity temperature T is 25°C, 150°C, and 170°.
As C increases, the output P becomes 5mW, 4mW, 3m
It is gradually decreasing to W. This means that, conversely, a constant output P
It is shown that in order to obtain this, it is sufficient to control the current I applied to the laser diode so as to compensate for the variation in the cavity temperature T. 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.

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

As shown in FIG. 10, a collimator lens 018, a cylindrical lens 019, a mirror 020, a rotating polygon mirror 021, an fθ 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. 11, the laser array O17 has an insulating section 02.
Three write oscillation regions 029a, 029b separated by 8
, 029c, and output terminals a, b, c, which will be described later.
By supplying a drive current from through the electrode 030, each write oscillation region 029a, 029b, 0
29c emits a laser beam having a fixed polarization direction as indicated by an arrow.

Returning to FIG. 1O, oscillation control means A of the laser array 017
Three LD drivers 031a, 031b installed in
, 031c are output terminals a, b, c connected to the laser array 017 and two input terminals a+ r az
it) + r bt ; C+ + Cz. And one input terminal aI
+ 1) + + Image memory 032 and line memories 033a, 033b, 033c are connected in series to CI, and the other input terminal a2゜b2+cffi
are connected to optical control circuits 034a, 034b, and 034C that control the amount of laser light. The laser array 017 is configured such that the quantity of the emitted laser beam is detected by measuring the back beam leaking backward at the detector 035. This detected light amount signal is compared with a reference potential of a light amount reference signal generator 037 in a light amount comparator 036, and the output of the light amount comparator 036 is sent to each light amount control circuit 034a as a scene control signal.

034b, 034c and -temporarily held.

Furthermore, the optical sensor 025 is connected to a controller 038, and the image memory 032, line memories 033a, 033b, 033C1, and light amount control circuits 034a, 034b, 034c are controlled by the timing control signal output from this controller 03. It has become so.

As shown in FIG. 12, a transistor TrIzF transistor Trz and a resistor R are connected in series to the output terminals a, b, and c of the oscillation control means A of the laser array 017, respectively. Level converters 039a, 039b, 039c are interposed between the bases of the transistors Tr and the input terminals aIt b101, respectively, and the bases of the transistors Tr are connected to the input terminals a, .
b2, connected to C2.

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

Each LD driver 031a, 031b, 031c based on the timing control signal output from the controller 03B.
are the three write 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 this light amount setting laser beam with a detector 035 is fed back to a light amount comparator 036, where it is compared with a reference potential of a light amount reference signal generator 037. The light amount control signal output from this light amount comparator 036 is transmitted to the light amount control circuits 034a, 034b, 0.
34c and is temporarily held.

Subsequently, a laser beam for position detection is emitted from the write oscillation region 029a based on the timing control signal output from the controller 03B. 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. The beam position detection signal output from the optical sensor 025 is transmitted to the controller 0.
It is feedbanked to 38.

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,
The beam position detection signal is simultaneously input to the input terminal al+blrCI of the oscillation control means A in synchronization with the beam position detection signal. At the same time, input terminal a2 of oscillation control means A
The light amount control signal temporarily held in the light amount control circuits 034a, 034b, and 034c is input to +bt+C2.

The above image signals are sent to level converters 039a, 039b, 03
applied to the base of the transistor Tr through 9c,
In addition to turning on or off the transistor Tr+, the light amount control signal supplies a base current whose magnitude varies depending on the amount of light to the transistor Trz. Therefore, the collector current flowing through the transistors Trl and Trz, that is, the three write oscillation regions 029a, 0
The drive current 1d supplied to 29b and 029C changes according to each correction signal, and the laser array 0 due to temperature change changes.
17 output fluctuations are compensated for.

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 above conventional example, 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 029a, 029b, and 029C.

That is, as shown in FIG. 13, when the drive current 1d is supplied to the three write oscillation areas 029a, 029b, and 029c according to the image signal, the adjacent write oscillation areas 029a in the time domain ΔL. ,029b,029
c will simultaneously irradiate the laser beam. Then, as shown in FIG. 14, the adjacent write oscillation area 029
Due to the heat generation of a, 029b, and 029c, the above time domain Δ
At L, a phenomenon in which the output Pd decreases from the position of the broken line to the position of the solid line, so-called crosstalk, occurs, causing fluctuations in the amount of light 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 write oscillation areas in a laser array, and scans with a constant light intensity from the start point to the end point of each scan line. An object of the present invention is to provide a semiconductor laser scanning device that can perform the following steps.

B1 Structure of the Invention (1) Means for Solving the Problems In order to solve the above problems, the present invention provides a semiconductor laser scanning device comprising a laser array having a plurality of writing oscillation regions, each of which can be independently modulated. In: An intermediate oscillation region is interposed between adjacent write oscillation regions of the laser array, and a compensation current below a laser oscillation threshold is supplied to the intermediate oscillation region.

(2) Effects According to the present invention having the above-described configuration, the intermediate oscillation region supplied with the compensation current below the laser oscillation threshold generates natural light and generates heat. Therefore, when one of the adjacent write oscillation regions of the laser array irradiates the laser beam, the intermediate oscillation in the exothermic state occurs regardless of whether the other write oscillation region irradiates the laser beam or not. This area receives constant thermal influence from the write oscillation area, and the thermal influence from the other write oscillation area decreases.

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

Figures 1 and 2 show a first example of the present invention, which is an improvement over the conventional example.
This figure shows an overall view of the embodiment and an enlarged view of its laser array, and the same members as in the conventional example are given the same reference numerals except for the initial O.

In this embodiment, the laser array 17 shown in FIG. 2 further includes two intermediate oscillation regions 29d at intermediate positions between its three write oscillation regions 29a, 29b, and 29c.

29e, and these two intermediate oscillation regions 29d
, 29e are respectively connected to the two LD drivers 31d and 31e provided in the oscillation control means A of the laser array 17 in FIG. 1, and the optical path of the laser beam has the same polarization direction as that of the laser beam. The present invention is characterized in that it includes a polarizing filter 40 having a polarizing filter 40, and the other configurations are the same as those of the conventional example.

FIG. 3 shows the circuit of the oscillation control means A of the laser array, in which the three L
In addition to the D drivers 31a to 31c, the intermediate oscillation region 29d is newly added.

LD driver 31d for driving 29e.

31e is provided. These LD drivers 31
d and 31e are equipped with a transistor Tr3 and a resistor R1 connected in series to the intermediate oscillation regions 29d and 29e, and a resistor R4 and a resistor R1 are connected to the transistor Trx in series.
A predetermined voltage divided by 1 is applied.

With this configuration, two intermediate oscillation regions 2
9d and 29e are transistors T that are always conductive.
A constant compensation current 1c is supplied via rz. This compensation current 1c is set slightly lower than the threshold value at which laser oscillation occurs, and this compensation current 1c causes the intermediate oscillators 29d and 29e to generate weak natural light and become heated. Due to the above heat generation, the cavity temperature of the intermediate oscillation regions 29d and 29e becomes approximately equal to the cavity temperature of the other three write oscillation regions 29a, 29b, and 29c during laser beam oscillation, and thereby the cross The impact of talk will be compensated.

To explain this based on the diagram, three write oscillation areas 2
When driving current 1d as shown in FIG. 4 is supplied to 9a, 29b, 29c according to the image signal, a constant compensation current 1c is always supplied to two intermediate oscillation regions 29d, 29e. Then, as shown in FIG. 5, the compensation current r
Intermediate oscillation region 29d by irradiation of natural light of output PC by c
, 29e rises, and due to the thermal interference, the adjacent write oscillation region is originally (intermediate oscillation region 29e).
d, without 29e) The output of the laser beam, which should be at the position of the broken line, decreases to the position of the solid line, and the image signal turns ON.
The output of the laser beam at this time is maintained at approximately constant Pd over the entire write oscillation region. That is, if the two intermediate oscillation regions 29d and 29e do not exist, the three write oscillation regions 29a, 29b, 2 to which the laser beam is irradiated
Crosstalk occurred intermittently between the adjacent write oscillation areas 29a and 29b and between the write oscillation areas 29b and 29c of 9c, causing fluctuations in image density. 29a and 29b, and write oscillation area 2
Intermediate oscillation region 29 that is always in a state of heat generation between 9b and 29c
d and 29e, each write oscillation region 29
a, 29b, 29c are the intermediate oscillation regions 29d, 29e.
As a result, the output of the laser beam is maintained at a constant value as shown by the solid line.

By the way, the intermediate oscillation region 29 is caused by the compensation current 1c.
The output of the natural light generated by d and 29e is so weak that it hardly interferes with scanning, but it is desirable to eliminate its influence 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, the laser beam with the same polarization direction is completely As a result, the influence of natural light generated by the compensation current IC can be reduced, and a high quality image can be obtained.

According to the first embodiment described above, since a polarizing filter having the same polarization direction as the laser beam is provided in the optical path of the laser beam, unnecessary natural light generated in the intermediate oscillation region can be cut. It is possible to prevent the adverse effects of natural light during writing scanning.

FIG. 6 shows a circuit of oscillation control means A according to a second embodiment of the present invention.

In this embodiment, two intermediate oscillation regions 29d, 2
The compensation current 1c supplied to the input terminal al +
Image signals 101, 102.1 from bI + c+
Controlled by 03. That is, the input terminal al+
Image signals 101 and 102 from bI pass through an EX-OR gate 41, and an EX-OR signal 201 outputted from this EX-OR gate 41 is sent to the intermediate point between the write oscillation regions 29a and 29b via a level converter 39d. Oscillation region 29
It is input to the base of Tr3 connected to d. Similarly, input terminals bI, C+Carano image signals 102, 103
passes through the EX-OR gate 41, and this I! X-O
The EX-OR signal 202 output from the R gate 41 is input to the base of Tr+ connected to the intermediate oscillation region 29e between the write oscillation regions 29b and 29c via the level converter 39e.

As a result, as shown in FIG.
When one of the two is ON, the compensation current 1c is supplied to the intermediate oscillation region 29d, and similarly the adjacent write oscillation region 29b
, 29c is ON, the compensation current IC is supplied to the intermediate oscillation region 29d. Therefore, as shown in FIG. 8, when only one of the write oscillation regions 29a and 29b or only one of the write oscillation regions 29b and 29c irradiates the laser beam, an intermediate Oscillation area 29d
, 29e increases. In this way, the write oscillation regions 29a, 29b, 29C are originally (intermediate oscillation region 29d).

29e)) The output of the laser beam, which should be at the position indicated by the broken line, will be thermally affected by the intermediate oscillation regions 29d and 29e, and as a result, the output of the laser beam will decrease to the position indicated by the solid line. is maintained at approximately constant Pd over the entire region.

According to the second embodiment described above, the adjacent oscillation regions 29a,
Image signals 101.29b and 29c. t.

2.103t! By driving the intermediate oscillation regions 29d and 29e with the X-OR signal, it is possible to cause the intermediate oscillation region to generate heat when only one of the adjacent write oscillation regions 29a, 29b, and 29c irradiates the laser beam. It becomes possible. This minimizes the generation of natural light, improving contrast, and prevents deterioration of the laser array due to heat generation, thereby extending its life.

Although the embodiments of the present invention have been described above in detail, 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 described in the claims. It is possible to do so.

For example, the number of write oscillation regions of the laser array 17 as a semiconductor laser light source is not limited to three, but may be any number. In this case, the number of intermediate oscillation regions is one less than the write oscillation region. In addition, polarizing filter 4
For 0, a reflective type can be used instead of a transmission type.

C0 Effects of the Invention According to the semiconductor laser scanning device of the present invention described above, in a semiconductor laser scanning device comprising a laser array having a plurality of write oscillation regions each of which can be modulated independently, each write oscillation of the laser array is Since an intermediate oscillation region is interposed between the regions and a compensation current below the laser oscillation threshold is supplied to the intermediate oscillation region, the intermediate oscillation region supplied with this compensation current generates natural light and becomes heated. Therefore, regardless of whether or not the write oscillation area adjacent to a certain write oscillation area is in a heat generation state, there is a steady thermal relationship between the write oscillation area that generates weak natural light and the intermediate oscillation area that is in a heat generation state. As a result, the output of the laser beam can be kept constant to improve the image quality of the image reproducing device and to prevent reading errors of optical discs.

[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, and FIG.
4 is a time chart of its drive current, FIG. 5 is a time chart of its output, and FIG. 6 is a circuit diagram of the oscillation control means of the second embodiment of the present invention. Figure 7 is a time chart of its drive current, Figure 8 is a time chart of its output, Figure 9 is a schematic structural diagram of a digital copying machine, Figure 10 is an overall diagram of a conventional semiconductor laser scanning device, and Figure 11. 12 is an enlarged view of the laser array, FIG. 12 is a circuit diagram of its oscillation control means, FIG. 13 is a time chart of its driving current, FIG. 14 is a time chart of its output, and FIG. −Output−Temperature] characteristic diagram. 17... Laser array, 29a, 29b, 29c.
...Write oscillation area, 29d, 29e...Intermediate oscillation area, Ic...Compensation current No. 4 Fig. 3 Fig. 5 Fig. 6 Fig. 8 ■ Fig. 7 Fig. 11 ++---++ ＋＋＋ ＋ ＋ −J
T style

Claims (1)

[Claims] A plurality of write oscillation regions (29a, 2
In a semiconductor laser scanning device comprising a laser array (17) having a laser array (9b, 29c);
9a, 29b, 29c) between the intermediate oscillation regions (29d, 2
9e), and this intermediate oscillation region (29d, 29e)
A semiconductor laser scanning device characterized in that a compensation current (Ic) below a threshold value of laser oscillation is supplied to the semiconductor laser.