JPH05218560A - Optical write-in device - Google Patents

Abstract

PURPOSE:To perform the optical output control of each semiconductor laser with high accuracy and at high speed, in a multibeam system of optical write-in device which performs simultaneous write, using a plurality of semiconductor lasers. CONSTITUTION:In a write-in device, wherein writes for a plurality of lines are performed at the same time by driving a plurality of semiconductor lasers 2 and 3, light receiving elements 4 and 5, which receive and detect the optical output of the semiconductor lasers 2 and 3, are provided separately for each semiconductor laser 2 and 3. And, semiconductor laser driving control circuits 9 and 11, which have optical-electric negative feedback loops 8 and 10 which control the forward currents of the semiconductor lasers 2 and 3 so that the received light signals geared to the optical output of the semiconductor lasers 2 and 3 which are gotten, being detected by each light receiving element 4 and 5 and light emission level command signals may be equal, are provided separately for each semiconductor laser 2 and 3 so as to control them at the same time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical writing device using a semiconductor laser as a writing light source such as a laser printer and a laser facsimile.

[0002]

2. Description of the Related Art Semiconductor lasers have been widely used in recent years as a light source for optical writing devices such as laser printers because they are small in size and can be directly modulated at high speed by a driving current. At this time, in order to enable high-speed and high-density recording, a plurality of semiconductor lasers are provided as a laser device, and a multi-beam writing method for simultaneously driving these semiconductor lasers enables optical writing for a plurality of lines at the same time. There is something.

Here, the light output and forward current characteristics of the semiconductor laser remarkably change depending on the temperature, which is a problem when trying to obtain a high quality image by setting the light output of the semiconductor laser to a desired value. ..

Therefore, the light output of the semiconductor laser is monitored by the light receiving element, and the forward current of the semiconductor laser is constantly controlled so that the signal proportional to the light receiving current generated in the light receiving element becomes equal to the light emission level command signal. An optical / electrical negative feedback loop for performing APC (automatic power control) is disclosed in JP-A-2-205375.

[0005]

However, in the above-described multi-beam type optical writing device, as shown in, for example, Japanese Patent Laid-Open No. 58-30183, a common semiconductor laser is used for a plurality of semiconductor lasers. Only the light receiving element is used for monitoring. That is, this light receiving element is used in a time division manner in the non-writing area to control the light quantity of each semiconductor laser. Such a light amount control method takes a long processing time, and deviates from the purpose of the multi-beam method in which high-speed writing can be performed by a plurality of semiconductor lasers. Further, even if the control signal of the optical output is maintained in the non-writing area, when the adjacent semiconductor laser emits light in the writing area, the optical output of its own semiconductor laser easily changes due to thermal coupling. , In some cases, faithful writing may not be performed.

[0006]

According to a first aspect of the invention, in an optical writing device in which a plurality of semiconductor lasers are simultaneously driven to simultaneously perform optical writing for a plurality of lines, each of the semiconductor lasers is dealt with. A light-receiving element for detecting the light output of the semiconductor laser is provided, and the light-receiving signal corresponding to the light output of the semiconductor laser detected by each light-receiving element and the light-emission level command signal become equal to the forward direction of the semiconductor laser. A semiconductor laser drive control circuit having an optical / electrical negative feedback loop for controlling current is provided independently for each semiconductor laser.

According to a second aspect of the present invention, the semiconductor laser drive control circuit according to the first aspect of the invention is provided with a corresponding semiconductor laser light output / forward current characteristic, and a coupling coefficient between a light receiving element and a semiconductor laser light output. , And a conversion means for converting the light-emission level command signal into a forward current of the semiconductor laser so that the light-reception signal and the light-emission level command signal become equal based on the light input / light-reception signal characteristics of the light receiving element.
The semiconductor laser is driven and controlled by the sum current of the control current of the electric negative feedback loop and the current generated by this conversion means.

Further, in the invention described in claim 3, in the semiconductor laser drive control circuit according to the invention described in claim 2, the semiconductor lasers other than the set semiconductor laser are not made to emit light at the timing before the page writing is started. The conversion current by the conversion means is set for each laser.

According to the invention described in claim 4, in the invention described in claim 1, 2 or 3, the main light receiving signal detected by the light receiving element corresponding to the controlled semiconductor laser and the controlled semiconductor laser are An interference light receiving signal detected by a light receiving element corresponding to an adjacent semiconductor laser is converted into a difference signal between a correction signal obtained by converting the light receiving element and the controlled semiconductor laser based on a coupling efficiency, and a difference signal is supplied to an optical / electrical negative feedback loop. A light receiving signal correction circuit for inputting as a light receiving signal is provided.

According to a fifth aspect of the present invention, in addition to the fourth aspect of the invention, a light reception signal correction circuit in which the difference signal is a current is used.

[0011]

According to the first aspect of the present invention, since each semiconductor laser individually has a semiconductor laser drive control circuit having a light receiving element and an optical / electrical negative feedback loop, an optical output corresponding to a light emission level command signal can be obtained. The exposure energy control can be performed independently and at the same time, and the optical output control is suitable for the multi-beam method capable of high-speed and high-density optical writing. At this time, each semiconductor laser drive control circuit is a high-speed, high-accuracy, high-resolution one having an optical / electrical negative feedback loop, and the exposure energy of each semiconductor laser is highly accurately controlled. There will be no difference in writing.

In particular, according to the second aspect of the present invention, there is provided a semiconductor laser drive control circuit having a conversion means, the optical output / forward current characteristics of the semiconductor laser, the coupling coefficient between the light receiving element and the optical output of the semiconductor laser, Based on the light input and light receiving signal characteristics of the light receiving element, the light emitting level command signal is converted into the forward current of the semiconductor laser and controlled so that the light receiving signal becomes equal to the light emitting level command signal. The control amount of the feedback loop is reduced, and the control speed of the exposure energy is increased and the accuracy of exposure energy control is improved.

According to the third aspect of the invention, the conversion current is set by the conversion means before the page writing is started and the semiconductor lasers other than the semiconductor laser to be set do not emit light. It is possible to prevent the conversion current from becoming excessive due to the setting when the semiconductor laser emits light, and the light output does not exceed the emission level command signal even when the environmental temperature changes.

Further, according to the invention of claim 4, in a combination of a plurality of semiconductor lasers and a light receiving element, adjacent ones may interfere with each other,
A light reception signal correction circuit is provided to generate a light reception signal in which the amount of light from the adjacent semiconductor laser is corrected from the main light reception signal generated in the light receiving element corresponding to the controlled semiconductor laser.
Since the control is performed by the electric negative feedback loop, it is possible to perform the control faithful to the light emission level command signal which is hardly influenced by mutual interference.

According to the fifth aspect of the invention, since the difference signal handled by such a received light signal correction circuit is a current, OP
The light receiving signal correction circuit can be configured without using an amplifier or the like, which is suitable for high speed control.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the invention described in claim 1 will be described with reference to FIG. The present embodiment is applied to an optical writing device of a two-beam writing system, and the laser device 1 has two optical writing devices.
Two semiconductor lasers 2 and 3 are provided. Each of the semiconductor lasers 2 and 3 is separately provided with a light receiving element 4 or 5 for monitoring a part of its optical output. Further, comparison amplifiers 6 and 7 to which the light emission level command signal and the light receiving signals from these light receiving elements 4 and 5 are input are also provided separately.

Here, the comparison amplifier 6, the semiconductor laser 2, and the light receiving element 4 form an optical / electrical negative feedback loop 8, and the comparison amplifier 6 induces a photocurrent (semiconductor laser 2) induced in the light receiving element 4. (Proportional to the optical output of) and a light emission level command signal are compared, and the forward current of the semiconductor laser 2 is controlled by the result so that the light reception signal and the light emission level command signal become equal. A semiconductor laser drive control circuit 9 for the semiconductor laser 2 is mainly composed of such an optical / electrical negative feedback loop 8.

Further, the comparison amplifier 7, the semiconductor laser 3, and the light receiving element 5 form an optical / electrical negative feedback loop 10, and the comparison amplifier 7 induces a photocurrent generated in the light receiving element 5 (of the semiconductor laser 3). The light receiving signal proportional to the light output) is compared with the light emitting level command signal, and the forward current of the semiconductor laser 3 is controlled based on the result so that the light receiving signal and the light emitting level command signal become equal. A semiconductor laser drive control circuit 11 for the semiconductor laser 3 is mainly composed of such an optical / electrical negative feedback loop 10.

As described above, since the semiconductor laser drive control circuits 9 and 11 are separately provided for the respective semiconductor lasers 2 and 3,
The semiconductor lasers 2 and 3 can be independently and simultaneously operated so that the optical output of each of the semiconductor lasers 2 and 3 corresponds to the emission level command signal. Further, both the semiconductor laser drive control circuits 9 and 11 are based on the optical / electrical negative feedback loop system,
Has high resolution control characteristics. Therefore, without deteriorating the characteristics of the multi-beam system having high speed and high density, each semiconductor laser can be controlled at high speed and with high accuracy to provide an appropriate optical output.

Next, an embodiment of the invention described in claims 2 and 3 will be described with reference to FIGS. In the present embodiment, for example, a semiconductor laser drive control circuit 9 is added with a current converter 12 serving as a conversion means. The semiconductor laser drive control circuit 11 side is also not shown,
A current converter is added.

The current converter 12 provided in parallel with the comparison amplifier 6 is preset according to the light emission level command signal so that the light reception signal from the light receiving element 4 and the light emission level command signal become equal. Current (forward output current characteristics of the semiconductor laser 2, the coupling coefficient between the light receiving element 4 and the light output of the semiconductor laser 2, and the light input / forward current characteristics of the light receiving element 4 Current) is output.

Here, the output current converted by the current converter 12 is I, the emission level command signal is i, the differential quantum efficiency is η, and the coupling efficiency between the semiconductor laser 2 and the light receiving element 4 ×
Assuming that the radiation sensitivity is S, a current I that satisfies i≈I × η × S is output from the current converter 12. The sum current of the output current of the current converter 12 and the control current output from the comparison amplifier 6 becomes the forward current of the semiconductor laser 2 and is controlled. When the current converter 12 outputs such a current I, the amount of control current by the optical / electrical negative feedback loop 8 is reduced and the high speed modulation characteristic is improved.

The same applies to the semiconductor laser drive control circuit 11 side with respect to the semiconductor laser 3.

By the way, in the structure shown in FIG. 2, the coupling characteristics between the semiconductor laser 2 and the light receiving element 4 and the light output / light receiving signal characteristics of the light receiving element 4 do not always change during the writing operation. Further, since it can be considered that the environmental temperature does not change during the writing operation, these coupling characteristics and light output / light receiving signal characteristics may be set once before the page writing is started. Further, the semiconductor laser 2 has a light output / forward current characteristic as shown in FIG. 3, but when the temperature of the semiconductor laser 2 rises, its inclination tends to become gentle as shown by the broken line. Therefore, for example, if the above setting is performed while the other semiconductor laser 3 is also emitting light, the converted current may become excessive.

Therefore, in the present embodiment, when setting the conversion current on the semiconductor laser 2 side, the other semiconductor laser 3 is not turned on and there is no thermal coupling between the semiconductor lasers 2 and 3, and , Is performed before the start of page writing. After the start of the writing operation, the semiconductor laser 2 is caused by the other adjacent semiconductor laser 3 emitting light.
Of the optical output and forward current characteristics of the
It may be controlled by the electric negative feedback loop 8.

The same applies to the semiconductor laser 3 and the light receiving element 5 side.

Next, an embodiment of the invention described in claim 4 will be described with reference to FIGS. In this embodiment, the interference between adjacent elements, that is, the light quantity of the semiconductor laser is detected by the corresponding light receiving element provided in the laser device 1 by the optical waveguide, but the light quantity of the adjacent semiconductor laser side is detected. This is because of the fact that it may happen. For example, the case where the light amount of the other semiconductor laser 3 is also incident on and detected by the light receiving element 4 which should receive the light amount of the semiconductor laser 2 is considered.

Therefore, in this embodiment, the light receiving signal of the light receiving element 4 is not directly input to the comparison amplifier 6 in the optical / electrical negative feedback loop 8 but is input through the light receiving signal correction circuit 13 together with the light receiving signal of the adjacent light receiving element 5. It was made to let. The light receiving signal correction circuit 13 interferes with the main light receiving signal detected by the light receiving element 4 corresponding to the controlled semiconductor laser 2 and the light receiving element 5 corresponding to the semiconductor laser 3 adjacent to the controlled semiconductor laser 2. The difference signal between the received light signal and the correction signal obtained by converting the light receiving element 5 based on the coupling efficiency of the controlled semiconductor laser 2 is used as the received light signal by the controlled semiconductor laser 2 as a comparison amplifier 6 of the optical / electrical negative feedback loop 8. To input. In this way, the light received signal corrected for the interference light amount of the adjacent element
By controlling the light output by giving it to the comparison amplifier 6 of the electric negative feedback loop 8, the light output is controlled with high accuracy and faithful to the light emission level command signal.

Here, the received light signal correction circuit 13 is constructed as shown in FIG. 5, for example. First, the semiconductor laser 2
Is Pa, the emission amount of the semiconductor laser 3 is Pb, the emission amount of the semiconductor laser 2 and the coupling efficiency with the light receiving element 5, and the emission amount of the semiconductor laser 3 and the coupling efficiency with the light receiving element 4 are both α. To do. Therefore, the OP amplifiers 14 and 15 for converting the voltage of the current proportional to the amount of light incident on the light receiving elements 4 and 5 are used.
Is provided. The output on the side of the OP amplifier 15 is connected to the OP amplifier 16 having resistors R ₁ and R ₂ and amplifying by −α times by the coupling efficiency α. OP amplifier 14, 1
The output of 6 is inputted to the OP amplifier 17 for addition through the same input resistance r ₁ .

In such a structure, the light receiving elements 4, 5
The current proportional to the amount of light detected at is converted into a voltage by the OP amplifiers 14 and 15 to become Va and Vb. The voltage Vb side is further multiplied by −α by the OP amplifier 16 to become −αVb (correction signal), which is added to Va in the OP amplifier 17. The output signal (difference signal) Vo of this OP amplifier 17 is obtained as a light receiving signal with respect to the light emission amount of the semiconductor laser 2,
The optical output of the semiconductor laser 2 is controlled so that this light reception signal becomes equal to the light emission level command signal.

More specifically, assuming that the feedback resistance of the OP amplifier 17 is r ₂ and the conversion coefficient when converting the amount of light detected by the light receiving elements 4 and 5 into a voltage is m, the output signal Vo of the OP amplifier 17 is Vo = (Va−αVb) (r ₁ / r ₂ ) = {m (Pa + αPb) −αm (Pb + αPa)} (r ₁ / r ₂ ) = m (Pa−α ² Pa)} (r ₁ / r ₂ ) = MPa (1−α ² ) (r ₁ / r ₂ ) ≈mPar ₁ / r ₂ and a light receiving signal proportional to only the light emission amount of the semiconductor laser 2 is obtained. At this time, only the semiconductor laser 2 emits light,
Even if the semiconductor laser 3 does not emit light, generally 1 >> α ² and there is no problem.

In the case of the present embodiment as well, although not particularly shown, a light receiving signal correction circuit is similarly provided on the side of the combination of the semiconductor laser 3 and the light receiving element 5 to receive a light receiving signal proportional to only the semiconductor laser 3. Should be obtained.

In the configuration shown in FIG. 5, the connection between the light receiving element 4 (or 5) and the OP amplifier 14 (or 15)
As shown in FIG. 6, the voltage Va proportional to the amount of light is used.
(Or Vb) may be generated.

Further, an embodiment of the invention described in claim 5 will be described with reference to FIG. This embodiment also relates to the received light signal correction circuit 13 provided on the front side of the comparison amplifier 6 on the set side of the semiconductor laser 2 and the light receiving element 4, for example, but instead of the circuit configuration as shown in FIG. As shown in FIG. 7, the circuit configuration uses a difference signal as a current.

That is, the light receiving signal of the light receiving element 4 is passed through the current mirror circuit 19 having the same emitter resistance r to Ia.
And the received light signal of the light receiving element 5 is R ₂ / R ₁ = α
It is configured so as to be taken out as the correction signal -αIb via the current mirror circuit 21 having the emitter resistors R ₁ and R ₂ set to the relationship described above. A current mirror circuit 22 having the same emitter resistance r for extracting the difference current between them as a received light signal Io is provided. In the optical / electrical negative feedback loop 8, the optical output of the semiconductor laser 2 is controlled so that the received light signal Io which is a difference current becomes equal to the emission level command signal. The semiconductor laser 3 and the light receiving element 5 may be similarly configured on the side of the combination.

According to this embodiment, since the difference signal is processed as a current, the light receiving signal correction circuit 13 can be constructed without using an OP amplifier as shown in FIG. It becomes possible to control the light output.

In the structure provided with the current converter 12, even in the case of multi-gradation recording in which the light emission level command signal has two or more levels, the current converter 12 outputs the light emission level command at that time. Since the forward current is generated according to the signal, it is possible to control the optical output with high accuracy and to perform favorable multi-beam multi-gradation recording. In particular, according to the configuration in which the light reception signal correction circuit 13 is also provided, the light amount of only the controlled semiconductor laser is detected and controlled so as to be equal to the light emission level command signal at that time. It is possible to control the gradation light output.

By setting a plurality of pulse widths for one pixel and selecting any one of these pulse width signals as a light emission level command signal, multi-gradation recording can be performed. The light output can be controlled with high accuracy in the same manner. That is, the current converter 12
On the other hand, the output timing of the light emission level command signal only changes according to the pulse width.

[0039]

Since the present invention is configured as described above, according to the invention of claim 1, a semiconductor laser drive control circuit having a light receiving element and an optical / electrical negative feedback loop is individually provided for each semiconductor laser. Since it is provided in the above, it is possible to control the exposure energy so that the light output corresponding to the light emission level command signal can be performed independently and simultaneously, and the light output suitable for the multi-beam method capable of high-speed and high-density optical writing. In addition, each semiconductor laser drive control circuit is a high-speed, high-accuracy, high-resolution semiconductor laser drive control circuit that has high accuracy in controlling the exposure energy of each semiconductor laser. There is no difference in the optical writing by.

In particular, as in the invention described in claim 2, a semiconductor laser drive control circuit having a conversion means is provided, and the optical output / forward current characteristics of the semiconductor laser, the coupling coefficient between the light receiving element and the optical output of the semiconductor laser, Based on the light input and light receiving signal characteristics of the light receiving element, the light emitting level command signal is converted into the forward current of the semiconductor laser and controlled so that the light receiving signal becomes equal to the light emitting level command signal. The control amount of the feedback loop is reduced, and the control speed of the exposure energy can be increased and the exposure energy can be controlled with high accuracy.

According to the third aspect of the invention, the conversion current is set by the conversion means before the page writing is started and the semiconductor lasers other than the semiconductor laser to be set are not made to emit light. It is possible to prevent the conversion current from becoming excessive due to the setting at the time of emitting another semiconductor laser, and to prevent the light output from exceeding the emission level command signal even when the environmental temperature changes. ..

Further, according to the invention of claim 4, in a combination of a plurality of semiconductor lasers and a light receiving element, adjacent ones may interfere with each other,
A light reception signal correction circuit is provided to generate a light reception signal in which the amount of light from the adjacent semiconductor laser is corrected from the main light reception signal generated in the light receiving element corresponding to the controlled semiconductor laser.
Since it is designed to be controlled by the electric negative feedback loop,
It is possible to perform control faithful to the light emission level command signal that is hardly affected by mutual interference.

According to the fifth aspect of the invention, since the difference signal handled by such a received light signal correction circuit is a current, the received light signal correction circuit can be constructed without using an OP amplifier or the like, which is suitable for high speed control. Can be

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the invention described in claim 1.

FIG. 2 is a block diagram showing an embodiment of the invention described in claims 2 and 3.

FIG. 3 is a characteristic diagram showing temperature characteristics of a semiconductor laser.

FIG. 4 is a block diagram showing an embodiment of the invention described in claim 4;

FIG. 5 is a circuit diagram showing a configuration of a received light signal correction circuit.

FIG. 6 is a circuit diagram showing a modified example.

FIG. 7 is a circuit diagram showing an embodiment of the invention described in claim 5.

[Explanation of symbols]

 2, 3 Semiconductor laser 4, 5 Light receiving element 8, 10 Optical / electrical negative feedback loop 9, 11 Semiconductor laser drive control circuit 12 Conversion means 13 Light receiving signal correction circuit

Claims (5)

[Claims] 1. An optical writing device in which a plurality of semiconductor lasers are simultaneously driven to perform optical writing for a plurality of lines at the same time, and a light receiving element for receiving and detecting an optical output of a semiconductor laser corresponding to each semiconductor laser is provided. An optical / electrical negative feedback loop is provided to control the forward current of the semiconductor laser so that the received light signal corresponding to the optical output of the semiconductor laser detected by each light receiving element and the emission level command signal become equal. An optical writing device characterized in that a semiconductor laser drive control circuit is provided independently for each semiconductor laser. 2. A light receiving signal and a light emitting level command based on the light output / forward current characteristics of the corresponding semiconductor laser, the coupling coefficient between the light receiving element and the light output of the semiconductor laser, and the light input / light receiving signal characteristics of the light receiving element. Equipped with a conversion means for converting this emission level command signal into a forward current of the semiconductor laser so that the signal becomes equal, the sum of the control current of the optical / electrical negative feedback loop and the current generated by this conversion means The optical writing device according to claim 1, wherein the optical writing device is a semiconductor laser drive control circuit for driving and controlling a semiconductor laser. 3. A semiconductor laser drive control circuit for setting a conversion current by the conversion means for each semiconductor laser without emitting semiconductor lasers other than the semiconductor laser to be set at a timing before the start of page writing. The optical writing device according to claim 2. 4. A main light receiving signal detected by a light receiving element corresponding to a controlled semiconductor laser, and an interference light receiving signal detected by a light receiving element corresponding to a semiconductor laser adjacent to the controlled semiconductor laser are provided to the light receiving element and said light receiving element. 2. A light reception signal correction circuit for inputting a difference signal from a correction signal converted based on the coupling efficiency with a controlled semiconductor laser as a light reception signal to an optical / electrical negative feedback loop. 2. The optical writing device according to 2 or 3. 5. The optical writing device according to claim 4, wherein the light receiving signal correction circuit uses a difference signal as a current.