JPS63102544A - Laser recording device - Google Patents

Abstract

PURPOSE:To record a high gradation image at a high speed by having a light output stabilizing circuit to feed back a feedback signal corresponding to the strength of the optical beam to a light emitting level command signal and a correcting table to correct the light emitting level command signal so as to compensate respective types of non-linearity, by a laser action control circuit. CONSTITUTION:A laser action control circuit has a high output stabilizing circuit (APC circuit) 8 and is equipped with a correcting table 40 to correct a light emitting level command signal S1 so as to compensate the non-linearity of the driving current pair light output characteristic of a semiconductor laser 1 and the non-linearity of an incident light strength pair light transmissivity characteristic of an optical element such as a polarizing filter 51 and to make linear the relation of the strength of a scanning beam based on the signal after correction and a signal S1 before correction. The table 40 is constituted of respective tables 12, 13 and 14 of the gradation correction, a reverse log conversion and a V-P characteristic correction. When the signal S1 is corrected by such a table 40 and the gain of the circuit B is lower, the light output characteristic close to the straight line can be obtained concerning the signal S1 before correction and the laser light output. Even when the above-mentioned non-linear characteristic is present at the optical element, it is also compensated by the table 40, and the image concentration can be controlled at an equal concentration interval to the constant quality change of the signal S1.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) According to the present invention, a laser recording device that records a continuous tone image by scanning a photosensitive material with a laser beam modulated based on an image signal, particularly details. The present invention relates to a laser recording device capable of recording high-gradation images by modulating the light intensity of a laser beam in an analog manner.

(Conventional Techniques) Conventionally, optical scanning recording devices have been widely put into practical use that deflect a light beam using an optical deflector to scan a photosensitive material and record an image on the photosensitive material.

A semiconductor laser has conventionally been used as one of the means for generating a light beam in such an optical scanning recording device. This semiconductor laser has many advantages, such as being smaller, cheaper, and consumes less power than gas lasers, and can be directly modulated by changing the drive current.

However, on the other hand, as shown in FIG. 2, this semiconductor laser has light output characteristics with respect to drive current that differ between the LED area (natural luminescence area) and the laser area. There is a problem in that it is difficult to apply to recording continuous tone images because it changes drastically depending on the noise area. In other words, if the intensity modulation is performed using only the one-prong region, the dynamic range of the optical output will be only about two orders of magnitude. As is well known, it is impossible to obtain a high quality continuous tone image with this level of dynamic range.

For example, JP-A-56-115077 and JP-A-56-1
As shown in No. 52372, etc., the optical output of the semiconductor laser is kept constant, and the semiconductor laser is continuously switched to zero.
Attempts have also been made to record a continuous tone image by turning off the scanning beam to make the scanning beam pulsed light, and controlling the number or width of the pulses for each pixel to change the amount of constant distortion light.

However, when performing pulse number modulation or pulse width modulation as described above, for example, when the pixel clock frequency is 1M
At H2, if the resolution of the density scale, that is, the amount of scanning light is to be maintained at 10 bi↑ (approximately 3 digits), the pulse frequency must be set extremely high, at least 10 H2. The semiconductor laser itself is 0 at this frequency.
Although it is possible to turn the pixel clock N-OFF, the pulse count circuit for pulse number control or pulse width control can operate in response to such a high frequency. must be significantly lower than the value of Therefore, the recording speed of the device must be significantly reduced.

Roughly speaking, in the above method, the difference in heat generation of the semiconductor laser chip changes depending on the number or width of pulses output during the recording period of each pixel, and therefore the drive of the semiconductor laser changes. The current versus light output characteristics may change, and the exposure amount per pulse may vary. If this happens, the gradation of the recorded image will shift, making it impossible to obtain a high-quality continuous tone image.

- For example, as shown in Japanese Patent Application Laid-Open No. 56-71374, a method of recording a high-speed image by combining the above pulse number modulation or pulse width modulation with the light intensity modulation described in #J has also been proposed. There is. However, in this case as well, the emission of the semiconductor laser chip depends on the number or width of the pulses as described above. ! A similar problem arises in that the amount of light changes, resulting in a variation in the amount of exposure per pulse.

Considering the above, for example, the concentration scale 1Qbit
In other words, in order to record 9 high-gradation images of approximately 1024 gradations, light intensity modulation is performed across the LED area and the laser emission area shown in Figure 2 above, and the dynamic range of the optical output is increased by 3 lines. It is desirable to be able to secure a certain degree of security. However, in the above two regions, the driving current vs. optical output characteristic of the semiconductor laser naturally becomes non-linear, so in order to easily and precisely record high-gradation images, it is necessary to maintain the same density for a given amount of change in the image signal. In order to be able to control the image density at intervals, it is necessary to compensate for the above-mentioned characteristics in some way to linearly change the relationship between the light emission level command signal of the semiconductor laser and the optical output.

Conventionally, as a circuit that linearizes the relationship between the light emission level command signal of the semiconductor laser and the light output, it detects the light intensity of the laser beam and sends a feedback signal corresponding to the detected light intensity to the light emission level of the single conductor laser. A known optical output stabilizing circuit (hereinafter referred to as an APC circuit) that feeds back a command signal is shown in Fig. 3, which shows an example of this APC circuit. Te APC
The circuit will be explained. The light emission level command signal Vref that commands the light emission intensity of the semiconductor laser 1 is 71I] numb point 2
The voltage-to-current conversion amplifier 3 supplies the semiconductor laser 1 with a drive current proportional to the command signal V ref. A light beam 4 emitted forward from the semiconductor laser 1 is used to scan a photosensitive material through a scanning optical system (not shown).

On the other hand, the intensity of the light beam 5 emitted to the rear side of the semiconductor laser 1 is detected by, for example, a pin photodiode 6 for monitoring the amount of light installed inside the case of the semiconductor laser. The intensity of the light beam 5 thus detected is proportional to the intensity of the light beam 4 actually used for image recording. The intensity of the light beam 5, that is, the output current of the photodiode 6 indicating the intensity of the light beam 4, is converted into a feedback signal (voltage signal) pd by a current-voltage conversion amplifier 7, and the feedback signal Vpd is converted into a feedback signal (voltage signal) pd. It is input to point 2. From this addition point 2, the above light emission level command message @ y
tq difference signal v indicating the deviation between ref and feedback signal Vpd
e is output, and the deviation signal Ve is converted into a current by the voltage-current conversion amplifier 3 to drive the semiconductor laser 1.

In the above APC circuit, if ideal linear compensation is performed, the intensity of the light beam 5 will be determined by the light emission level command signal
is proportional to. In other words, the intensity Pf of the light beam 4 used for image recording (light output of the semiconductor laser 1) is proportional to the light emission level command signal V ref. The solid line in FIG. 4 shows this ideal relationship.

(Problems to be Solved by the Invention) It is relatively easy to control the drive of a semiconductor laser so that the light intensity Pf is always at a constant level using an APC circuit like the one shown above. When driving a semiconductor laser by changing the emission level command signal V ref at high speed in an analog manner in order to record a continuous tone image as shown in FIG. is difficult. In particular, as mentioned earlier, the pixel clock frequency is
It is very difficult to record a high gradation image with a density scale of about 1 Qbit when the frequency is set to about MHz.

The reason for this will be explained below. The drive current vs. optical output characteristic of the semiconductor laser 1 inserted into the system of FIG. 3 is extremely nonlinear, as shown in FIG. In other words, the differential quantum efficiency, which is the gain of a single semiconductor laser, varies greatly between the LED region and the laser emission region, as shown in FIG. 5 when expressed logarithmically. Therefore, the characteristics shown by the solid line in FIG. In order to obtain this, it is necessary to set the loop gain of the system shown in FIG. 3 to a very large value of 8. The curve shown by the broken line in FIG. 4 shows an example of the light output level command signal versus light output characteristic of the semiconductor laser that changes depending on the loop gain, and as shown in the figure, the curve shows the characteristic close to the ideal characteristic shown by the solid line. In order to obtain this, a high gain of about 60 dB is required.

Furthermore, the characteristics shown in FIG. 4 are based on the light emission level command signal ref
However, if the command signal v ref is a high frequency signal, a completely different problem arises.

This point will be explained below. FIG. 6 shows the case temperature dependence of the drive current vs. optical output characteristic of the semiconductor laser shown in FIG. As shown in the figure, the optical output of the semiconductor laser is 1, and if the drive current is constant, it decreases as the case temperature increases. - When a semiconductor laser is applied to a laser recording device, etc., control is carried out to maintain a constant case temperature, but transients in the laser diode chip that occur when a driving current is applied to the semiconductor laser It is completely impossible to suppress even temperature changes. In other words, when a driving current is applied to the semiconductor laser in a stepwise manner as shown in (1) of Fig. 7, the temperature of the laser diode chip changes as shown in Fig. 7 (2). The optical output of the semiconductor laser changes transiently until it reaches a steady state, and as a result, the optical output of the semiconductor laser changes according to the characteristics shown in FIG.
It fluctuates as shown in Figure (3). This is known as the droop characteristic of semiconductor lasers. In the APC circuit shown in Fig. 3, it has been found that the above-mentioned loop gain is required to be about 10 dB in order to correct the nonlinearity of the laser drive current vs. optical output characteristic due to this droop characteristic. When a signal ranging from a low frequency to a high frequency (for example, 1 MHz) is used as V re4, it is necessary to maintain high responsiveness and obtain a light emission level command signal vs. light output characteristic (linearity) close to the solid line in Fig. 4. is a total of 70 dB in the laser firing region, including the aforementioned 60 dB.
A loop gain of about dB is required. At present, it is almost impossible to realize such a high-speed, high-gain APC circuit.

Furthermore, when using a semiconductor laser by modulating its intensity from the LED region to the laser emitting region, there is the problem that the driving current vs. optical output characteristic becomes nonlinear, and the focusing of the scanning beam is impaired. Problems also arise. In other words, the spontaneous luminescence light emitted from a semiconductor laser contains various angular components compared to the laser oscillation light, and for example, in the case of a longitudinal multimode semiconductor laser, the spectral component of the laser oscillation light is about 2 nm. However, since it has a spectral component over about 4 Qnm, when focused by a focusing lens, the laser oscillation light cannot be focused to a small spot diameter. For this reason, when using light in a low power region where naturally emitted light is dominant (of course 100% in the LED region) as well as light in a high power region where laser oscillation light is dominant, the scanning spatial This will result in loss of resolution.

In order to improve the convergence of this scanning beam, for example, a polarizing filter as shown in Japanese Patent Application No. 61-075077 filed by the present applicant, an interference filter as shown in Japanese Patent Application No. 61-150227, and a rough filter are used. 61-19
It is conceivable to use an aperture limiting plate as shown in No. 6352/1111.

In other words, among the light emitted from a semiconductor laser, the laser oscillation light is linearly polarized in a direction parallel to the bonding surface of the laser diode chip, whereas the naturally emitted light is randomly polarized. When the light beam emitted from the laser diode is passed through a polarizing filter that transmits only the light polarized in the direction parallel to the bonding surface of the laser diode chip, the laser beam is emitted (while almost all of the scraps pass through).
Only about 1/2 of naturally emitted light passes through. Therefore, near the threshold value of the semiconductor laser, that is, laser emission 1. If the light beam emitted from the semiconductor laser is passed through the polarizing filter in a region that includes both the properties of a shadow and an LED, the ratio of laser oscillation light in the scanning beam will be further increased, improving the focusing ability of the scanning beam. do.

Furthermore, if the light beam emitted from the semiconductor laser is passed through an interference filter that only transmits light with a wavelength near the wavelength range of the laser oscillation light, the scanning beam can be converted into the laser oscillation light without cutting off the laser oscillation light. It may consist of similar very narrow spectral components. If this happens, the focusing ability of the scanning beam will be improved even if lenses such as a focusing lens arranged in the beam scanning system are not particularly highly accurately corrected for chromatic aberration.

Generally speaking, if an aperture limiting plate with a small aperture that allows only a portion of the light beam to pass is placed between the semiconductor laser and the collimator lens, or between the collimator lens and the focusing lens, the focusing property of the scanning beam will be improved. I know it will improve.

According to the polarizing filter, interference filter, or aperture limiting plate as described above, it is possible to narrow down the scanning beam to a smaller spot and record an image with high sharpness.

However, the polarizing filter, interference filter, and aperture limiting plate described above have a problem in that the light transmittance changes nonlinearly with respect to the intensity of incident light.

This will be explained with reference to FIG. 11, taking the case of a polarizing filter as an example. In FIG. 11, a curve Po indicates the intensity of the light beam emitted from the semiconductor laser. When this light beam is passed through the polarizing filter, the intensity of the output beam changes as shown by curve P in the figure.

That is, in the LED area, only natural light is emitted, and as mentioned above, about 1. /2 (transmits through the polarizing filter (that is, the light transmittance is about 50%). On the other hand -
In the prefecture area as well, naturally emitted light is approximately 1. /2 passes through the polarizing filter, but almost all of the laser oscillation light, which occupies a much larger proportion of the emitted light in this region than naturally emitted light, passes through the polarizing filter. The transmittance of the optical filter (q) of the light beam emitted in the laser beam region is 50% as described above.
significantly higher than that.

Moreover, this light transmittance increases as the intensity of the light beam increases and the ratio of laser oscillation light to it increases.

The above-mentioned problem also occurs when the above-mentioned interference filter is used.

On the other hand, as is well known, the divergence angle of a radiation beam emitted from a semiconductor laser varies as its optical output changes.

Therefore, when the above-mentioned aperture limiting plate is provided, the ratio of the amount of light blocked by the aperture limiting plate, in other words, the light transmittance changes depending on the optical output of the semiconductor laser, that is, the intensity of the light incident on the aperture limiting plate. do.

As mentioned above, if the incident light intensity vs. light transmittance characteristic of an optical element such as a polarizing filter is nonlinear, then even if the above-mentioned A
Even if the ideal characteristics shown by the solid line in Figure 4 are obtained using a PC circuit or the like, the relationship between the intensity of the light beam actually scanning the photosensitive material and the light emission level command signal is not linear, and high gradation It becomes impossible to record images easily and accurately.

Therefore, the present invention does not require the use of a high-gain APC circuit as described above, and also includes the above-mentioned polarizing filter in the beam scanning system.
Even if optical elements such as interference filters or aperture limiting plates are arranged, it is possible to make the emission level command signal vs. scanning beam intensity characteristic of the semiconductor laser linear from the LED region to the laser system region. The object of the present invention is to provide a laser recording device that can record high-gradation images at high speed by modulating light intensity.

(Means for Solving the Problems) A laser recording device of the present invention includes a semiconductor laser and an optical element having a nonlinear relationship between incident light intensity and light transmittance, such as the one-polarization filter, and the semiconductor laser a beam scanning system that scans the light beam emitted from the photosensitive material onto the photosensitive material;
A laser recording apparatus comprising: a laser operation control circuit that generates a light emission level command signal corresponding to an image signal, controls the drive current of the semiconductor laser based on the signal, and modulates the light intensity of the laser beam; The laser operation control circuit includes the APC circuit described above, and controls the light emission level so as to compensate for the nonlinearity of the driving current versus light output characteristic of the semiconductor laser and the nonlinearity of the incident light intensity versus light transmittance characteristic of the optical element. correcting the command signal and determining the intensity of the scanning beam based on the corrected signal;
The present invention is characterized in that it includes a correction table that linearizes the relationship between the light emission level command signals before correction.

(Function) If the emission level command signal of the semiconductor laser is corrected using the above correction table, even if the gain of the APC circuit is low, the emission level command signal before correction and the semiconductor laser light output will be as shown in Figure 4. It is possible to obtain optical output characteristics close to the ideal characteristics shown by the solid line.Also, even if the incident light intensity versus light transmittance characteristics of optical elements such as the polarizing filter, interference filter, and aperture limiting plate described above are nonlinear, is compensated by the above-mentioned correction table, and as a result, it becomes possible to control the image density by one degree at equal density intervals with respect to a constant change in the light emission level command signal.

(Example) Hereinafter, the present invention will be described in detail based on an example shown in the drawings.

FIG. 1 shows a laser recording apparatus according to a first embodiment of the present invention. Image signal generator 10 generates an image signal 81 carrying a continuous tone image. This image signal @S1 is, for example, a digital signal representing a continuous tone image with a 10-bit density scale.

The image signal generator 10 switches signals for one main scanning line based on a line clock S2, which will be described later, and outputs an image signal 81 for each pixel based on a pixel clock S3. In this example, the pixel clock frequency is 1 MHz
In other words, the recording time for one pixel is set to 1 μsec (t2).

The above-mentioned image signal S1 passes through the multiplexer 11 and is sent to the RA
After being subjected to a correction described later in a correction table 40 consisting of M, it is converted into, for example, a 16-bit light emission level command signal S5. This light emission level command signal S5 is inputted to the D/A converter 16 (here, the light emission level command signal Vr consisting of an analog voltage signal) via the multiplexer 15.
converted to ef. This light emission level command signal Vref is input to the addition point 2 of the APC circuit 8. The summing point 2, voltage-current conversion amplifier 3, semiconductor laser 1, photodiode 6, and current-voltage conversion amplifier 7 of the APC circuit 8 are the same as those in the circuit shown in FIG. 3 described above. Therefore, the semiconductor laser 1 emits a light beam 4 having an intensity corresponding to the light emission level command signal ref (that is, corresponding to the image signal S1). This light beam 4 is passed through a collimator lens 17 to form a flat 1':f beam, and is then filtered through the aperture limiting plates 5o and 4q optical filters 5 as described above.
1 to form a light beam of 4. This light beam 4' is passed through a half mirror 52, and then enters a light beam such as a polygon mirror (field direction device 18, where it is reflected by 4%). It passes through a focusing lens 19 consisting of a lens and focuses it on a minute spot on the photosensitive material 20, and the X
scan in the direction (main scan). The photosensitive material 20 is transported by a transport means (not shown) in the Y direction substantially perpendicular to the main scanning direction X, thereby performing sub-scanning of the light beam 4'. In this way, the photosensitive material 20 is two-dimensionally scanned by the light beam 4' and exposed. As mentioned above, the light beam 4
(that is, the light beam 4') is intensity-modulated based on the image signal S1, so this photosensitive material? A continuous tone image carrying the image signal S1 is recorded on O as a photographic latent image. Note that when the light beam 4' scans the photosensitive material 20 as described above, the photodetector 21 detects that the light beam 4' passes through the starting point of main scanning;
The start point detection signal S6 outputted by the clock generator 1 is input to the clock generator 36. The clock generator 36 outputs the aforementioned line clock S2 and pixel clock S in synchronization with the input timing of this start point detection signal S6.

The photosensitive material 20 is then passed through a developer 22 where it undergoes a development process, thereby recording the continuous tone image or visible image on the photosensitive material 20.

Note that the polarizing filter 51 is one that transmits only light polarized in a direction parallel to the bonding surface of the laser diode chip of the semiconductor laser 1. By passing the light beam 4 through the polarizing filter 51 and the aperture limiting plate 50, the light beam (constant distortion beam) 4' that has passed through these can be focused on an extremely small spot as described above. The light-sensitive material 20 is scanned by the scanning beam 4' thus focused.
By scanning it, you will be able to record sharp, high-quality images.

Here, the correction of the image signal S1 in the above-mentioned correction table 40I, : will be explained. The correction table 40 includes a gradation correction table 12, an inverse log conversion table 13, and a correction table (hereinafter referred to as a V-P characteristic correction table) 14 for linearly correcting the light emission level command signal vs. Mitsuda power stability of the semiconductor laser 1. Consisting of

The gradation correction table 12 is a known one for correcting the gradation characteristics of the photosensitive material 20 and its discipline. Although this gradation correction table 12 may have fixed correction characteristics, in this embodiment, the gradation correction table 12 has fixed correction characteristics.
Is the gradation characteristic of the product changing from lot to lot, or is it different from the current model?
? Taking into consideration the fact that the characteristics of the developing solution inside may change over time, the correction characteristics are configured to be able to be modified as appropriate in accordance with the actual gradation characteristics.

That is, from the test pattern generation circuit 26, the photosensitive material 1
A test pattern signal S4 carrying image temperatures in several stages (for example, 16 stages) above '120 is output, and this signal 84 is input to the multiplexer 11. At this time, the multiplexer 11 is switched from the state at the time of image allocation in which the image signal $1 is inputted to the correction table 40 as described above, to the state in which the test pattern signal S4 is inputted to the correction table 40. The semiconductor laser 1 is driven as described above based on this test pattern signal S4, and therefore the light beam 4' is intensity-modulated. Thereby, for example, 16 step wedges (test patterns) or photographic latent images whose density changes stepwise are recorded on the photosensitive material 20. This photosensitive material 20 is processed by a developing machine 22.
and the step wedge is developed. Development 1
The photosensitive material 20 is set on a thermometer 23, and the optical density of each of the step wedges is measured. The optical density thus measured is input to the density value input means 24 in association with each step wedge, and the density value input means 24 outputs a dark signal @S7 indicating the optical density of each step wedge. This live signal @S7 is input to the table creation means 37, and the table creation means 37
Based on the 9 degree signal S7 and the test pattern signal S4, a gradation correction table is created in which the predetermined image density is stopped by one depending on the value of the predetermined image signal 81. As described above, this gradation correction table is made up of the image signals +a of approximately 100 levels corresponding to respective predetermined image density values. The data S8 indicating this gradation correction table is input to the data interpolation means 38, where it is interpolated and 1024
A gradation correction table that can correspond to the image signal S1 of stages (=1 Obit>) is obtained. Based on the data S9 indicating this gradation correction table, the above-mentioned gradation correction table 12 is formed.

When recording an image that blocks the image signal 81, the image signal S1 input to the gradation correction table 12 via the multiplexer 11 is converted into the signal 81 by the gradation correction table 12.
', and then converted into the light emission level command signal @S 1 '' by the inverse 109 conversion table 13.

Next, the -P characteristic correction table 14 will be explained. As mentioned earlier, in the APC circuit 8)! Even if the signal VDd is fed back to the addition point 2, it is difficult to make the relationship between the light emission level command signal and the intensity of the light beam 4 ideal (the relationship indicated by the solid line in FIG. 4). In addition, since the incident light intensity versus light transmittance characteristics of the aperture limiting plate 50 and the polarizing filter 51 are nonlinear as described above, the relationship between the light emission level command signal and the light intensity of the scanning beam 4' is It is difficult to make it linear. The VP characteristic correction table 14 is provided to make the relationship between the scanning beam intensity and the light emission level command signal linear. That is, the light emission level command signal ref and the scanning beam 4'
Assuming that the ideal relationship between the light intensity PS and the light intensity PS is a straight line shown as a in FIG. 8, and the actual relationship is a curve as shown in b in FIG. ” is directly converted into D/A, the voltage value is V
Assuming that the voltage value vin is in, the voltage value vin is formed to be converted into a value V. In other words, if the value of the light emission level command signal Vref is rarely Vin, then P'
1)) cannot be obtained, but if the above conversion is performed, the light intensity of PO can be obtained for the voltage value Vin. In other words, the voltage value Vin corresponding to the light emission level command signal 81'' The relationship between and scanning beam intensity PS is linear.

With this configuration, the density in the photosensitive material 20 can be controlled at equal intervals by varying the image signal S1 by a predetermined amount. Furthermore, the characteristic curve in FIG. 8 shows the relationship between the semiconductor laser 1, its LED area, and the laser beam as described above. , when driving over one area.In this way, a light output dynamic range of about 3 lines is secured, so as mentioned above, a high gradation image of about 1024 levels can be produced.
It becomes possible to record easily and with high precision.

As described above, the driving current vs. optical output characteristic of the semiconductor laser is nonlinear, and the plate 50 with one aperture and the
If the nonlinearity of the light emission level command signal versus scanning beam intensity characteristic caused by the nonlinearity of the incident light intensity versus light transmittance characteristic of the light filter 51 is linearly corrected using the V-P characteristic correction table 14, 1 is obtained. , the addition point 2 of the PC circuit 8 to
Voltage-current conversion amplifier 3, semiconductor laser], photodiode 6, =t=- The loop gain of the system returning from the voltage conversion amplifier 7 to the addition point 2 includes the gain necessary to correct the above 2 nonlinearities. You will no longer need it. In other words, this loop gain corrects deviations from the drive current vs. optical output characteristics of the semiconductor laser 1 due to transient temperature changes that occur during operation of the semiconductor laser 1 or errors in controlling the case temperature of the semiconductor laser 1 to remain constant. However, in general, it is only necessary to secure as much as necessary to correct the drift of the amplifier, etc. Specifically, for example, the pixel clock frequency is 1MH
2, when the semiconductor laser 1 is operating with an optical output of 3 mW, it is sufficient that the loop gain is maintained at about 30 dB once. This level of loop gain can be easily achieved with the current state of the art.

Next, the creation of the VP characteristic correction table 14 will be explained. A table creation device 35 can be connected to the device shown in FIG. 1 as appropriate. This table creation device 35 includes a test signal generation circuit 27, a table creation circuit? 8 and memory 29. ■-)] When creating the characteristic correction table 14, the test signal generation circuit 2
A level-variable digital test signal 310 is output from 7 and input to multiplexer 15 . At this time, the multiplexer 15 outputs the light emission level command signal S5 as described above.
The test signal 310 is switched from the state during image recording in which the signal is sent to the D/A converter 16 to the state in which the test signal 310 is sent to the D/A converter 16.

Also, a half mirror 52 that splits a part of the light beam 4'.
The reflected light beam 4'' is received by a photodetector 53 such as a photodiode.The table creation circuit 28 converts the output of the photodetector 53 into a voltage signal. Connected so that the light amount signal VS output by the amplifier 54 is input.Test signal 3
10 is output so that the level increases or decreases in steps. At this time, the table creation circuit 28
First, a reference signal corresponding to the lowest light intensity is generated from a built-in variable level signal generator, and the reference signal and the light amount signal S are compared. This reference signal has a voltage value Vin shown in FIG. And the table creation circuit? 8 is the test signal S1 when these two signals match.
Latch a value of 0. This latched test signal 81
Since the voltage value indicated by 0 corresponds to the voltage value V in FIG. 8, the relationship between the voltage values Vin and V can be seen. The table creation circuit 28 sets the value of the reference signal to 102.
The voltage values are changed in four ways, and the relationship between the voltage values V and V in each case is determined. As a result, as mentioned earlier, 1024
A correction table for converting the step voltage value ■in to V is created. The correction table created in this way is stored in the memory 29.
After the -T2 is stored, the V-P characteristic correction table 14
is set as . In this way, V-P characteristic correction table 1
4, the table creation device 35 creates the APC circuit 8.
be separated from

As explained above, the relationship between the voltage values V1n and V corresponding to all image densities is determined one by one, and as in the case of creating the tone correction table 12 explained earlier, the voltage values The relationship with V may be determined only in some major cases, and the V-P characteristic correction table 14 may be created by interpolating the data. Further, the VP characteristic correction table 14 can also be created by calculation from the VP characteristic of the semiconductor laser. Roughly, gradation correction table 1? , inverse log conversion table 13, and the above V
The -P characteristic correction table 14 may be formed as a single correction table including all of the respective conversion characteristics, or may be formed into separate forms.

Further, in the embodiment described above, the aperture limiting plate 50 and the light stimulating filter 51 are provided in order to improve the convergence of the scanning beam 4', but only one of these may be used. Alternatively, the above-mentioned interference filter may be used in place of these optical elements, or two or all of these three optical elements may be used in appropriate combination.

Next, a second embodiment of the present invention will be described with reference to FIG. Note that in FIG. 9, elements equivalent to those in FIG. Although FIG. 9 only shows the laser operation control circuit, the parts not shown in the apparatus, such as the light beam scanning system, are formed in the same manner as in the apparatus shown in FIG. In the device of this second embodiment, the light emission level command signal 81'' output from the inverse log conversion table 13 is input as is to the D/A converter 16 through the multiplexer 15. On the other hand, the image signal 81'' is branched. and input into the V-P characteristic correction table 44. This VP characteristic correction table 44 is slightly different from the VP characteristic correction table 14 of the apparatus shown in FIG. 1, and is formed to obtain the difference Δ between the voltage value \l and Vin shown in FIG.

The digital signal 55' indicating this voltage difference ΔV is passed through the D/to converter 45 and converted into an analog signal, and is added to the voltage value group V (corresponding to the light emission level command signal @31'') at the addition point 2. By doing this, the rival station is equivalent to inputting a signal with a voltage value V as the light emission level command signal yref to the zero paralysis point 2 as in the device shown in FIG. A similar effect can be obtained.

Next, a third embodiment of the present invention will be described with reference to FIG. In the device shown in FIG. 10, the light emission level command signal 81 is branched and input into the -P characteristic correction table 44, where the correction as described above is performed, and the obtained signal 35' is sent to the D/A converter. The structure is similar to that of the device shown in FIG. 9 up to the analog conversion step 45. However, the voltage signal ΔV outputted from the D,/A converter 45 is not input to the addition point 2, but is passed through the voltage-to-current conversion amplifier 46 and converted into a current. 1 to this current is 1, and 7JON is applied to the drive current obtained by converting the shoulder difference signal Ve at the '10 calculation point 47 at the subsequent stage of the voltage-current conversion amplifier 3 of the PC circuit 8. The device of the third embodiment differs from the device of the second embodiment only in that the voltage signal ΔV is not directly input to the APC circuit 8, but is converted into a current Δ: and then input to the APC circuit 8. In this case as well, the same effects as in the first embodiment can be obtained.

(Effects of the Invention) As explained above in detail, in the laser recording device of the present invention, the driving current vs. optical output characteristic of the semiconductor laser is nonlinear, and the five-optical filter provided to improve the focusing property of the scanning beam. In addition to the semiconductor laser light output stabilization circuit, a separate circuit was provided to address the nonlinearity of the light emission level command signal versus scanning beam intensity characteristic caused by the nonlinearity of the incident light intensity versus light transmittance characteristic of optical elements such as Since the correction is made using a correction table, even if the loop gain of the closed loop formed by the above-mentioned optical output stabilization circuit is set to a low value that is sufficiently achievable with the current technology level, high responsiveness can be maintained. The relationship between the light emission level command signal and the scanning beam intensity can then be made linear over the ED region laser excavation region. According to a once uninvented device,
By changing the image signal by a predetermined amount, the image density can be controlled at equal temperature intervals, and the optical output dynamic range of the semiconductor laser, that is, the exposure amount of the photosensitive material can be secured over a wide range of about 3 orders of magnitude. 10bl
It becomes possible to record continuous-tone images with extremely high gradations of approximately t at high speed and precision.

Furthermore, in the laser recording apparatus of the present invention, optical elements such as polarizing filters, interference filters, and aperture limiting plates can be placed in the beam scanning system without any problem in image a degree control, so such optical elements can be placed in the beam scanning system. This allows the scanning beam to be focused on a minute spot, making it possible to record highly sharp images.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing a laser recording device according to the first example of effective color of the present invention, Fig. 2 is a graph showing the drive current versus light output characteristics of a semiconductor laser, and Fig. 3 is a semiconductor laser light output stabilization circuit. A block diagram showing an example. Fig. 4 is a graph showing the relationship between the light emission level command signal and the semiconductor laser optical output. Fig. 5 is a graph showing the relationship between the semiconductor laser optical output and differential quantum efficiency. Fig. 6 is a graph showing the temperature dependence of the drive current vs. optical output characteristic of a semiconductor laser, FIG. 7 is a graph explaining the droop characteristic of a semiconductor laser, and FIG. 8 is a graph explaining the effect of the V-P characteristic correction table in the device of the present invention. FIG. 9 is a block diagram showing a semiconductor laser operation control circuit of a laser recording device according to a second embodiment of the present invention, and FIG. 10 is a semiconductor laser operation control circuit of a laser recording device according to a third embodiment of the present invention. FIG. 11 is a graph explaining the action of the polarizing filter according to the invention.L 1... Semiconductor laser 2.47... Addition point 3
．． 46... Voltage-current conversion amplifier 4.4', 5... Light beam 6... Photodiode 7.54... Current-voltage conversion amplifier 8..., APC circuit 10... Image signal R raw type 14.44...-P characteristic correction table 16.4
5...D/Δ converter 17...Collimator lens 18...Light deflector 19...Focusing lens? O...Photosensitive material 35...Table creation device 40...Correction table 50...Aperture limiting plate 51...Polarizing filter 52...Half mirror 53...Light equalizer Sl... Image signal 81pa...Emission level command signal Vre before correction
f... Emission level command signal\/pd... Feedback signal Ve... Deviation signal cylinder 5171 Nine a power (mW) Fig. 6 Noriku power 5. Figure 7 Figure 8 Figure 9 Figure 10

Claims (4)

[Claims] (1) A semiconductor laser that emits a light beam, a beam scanning system that includes an optical element with a nonlinear relationship between incident light intensity and light transmittance and scans the light beam onto a photosensitive material, and a light emission level that corresponds to an image signal. A laser recording device comprising: a laser operation control circuit that generates a command signal, controls a drive current of the semiconductor laser based on the signal, and modulates the intensity of the light beam, the laser operation control circuit comprising: a light output stabilization circuit that detects the intensity of the beam and feeds back a feedback signal corresponding to the detected light intensity to the light emission level command signal; nonlinearity of the drive current versus light output characteristic of the semiconductor laser;
and correcting the light emission level command signal so as to compensate for the nonlinearity of the incident light intensity versus light transmittance characteristic of the optical element, and adjusting the intensity of the scanning beam based on the corrected signal and the light emission level command before correction. A laser recording device comprising: a correction table that linearizes a signal relationship. (2) The laser recording apparatus according to claim 1, wherein the correction table is arranged before the optical output stabilizing circuit. (3) The correction table is arranged on a path branching from the path of the light emission level command signal, and is configured to obtain a correction amount of the light emission level command signal, and the correction signal indicating the correction amount is the light emission level command signal. 2. The laser recording device according to claim 1, wherein the laser recording device is adapted to be added to a signal. (4) The correction table is arranged on a path branching from the path of the light emission level command signal, and is configured to calculate a correction amount of the light emission level command signal and output a current corresponding to this correction amount. 2. A laser recording apparatus according to claim 1, wherein said current is added to said semiconductor laser drive current.