JPH0413242A - Optical information recording and reproducing device - Google Patents

Abstract

PURPOSE:To always accurately and stably perform the stabilizing control of an oscillation output by driving the laser oscillator by using an error signal obtained by monitoring the output of a laser oscillator in reproduction, and the latest error signal within a prescribed range in recording. CONSTITUTION:In the reproduction, monitoring light from a semiconductor laser oscillator 4 is converted to an electric signal by an optical detecting means 11, and difference between the electric signal and a reference level is detected by an error detecting means 13, and the semiconductor laser oscillator 4 is driven by a driving means 30 corresponding to the error signal. Also, it is decided whether or not the error signal is present within the prescribed range ;with a comparison means 14, and the latest error signal within the prescribed range is held with storage holding means 24, 25 controlled by the output of the comparison means 14, and in the recording, the semiconductor laser oscillator 4 is driven by the driving means 30 corresponding to the output of the storage holding means just before the start of the recording and an addition signal to be added so as to obtain second output. In such a manner, it is possible to always accurately and stably perform the stabilizing control of the oscillation output.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention provides a semiconductor laser oscillator output stabilization control means for stabilizing the oscillation output of a semiconductor laser oscillator used as a light source of an optical disk device, for example. The present invention relates to an optical recording/reproducing device having the following features.

[Prior Art] Optical disk devices optically record or reproduce information by irradiating a rotating optical disk with a laser beam, and have recently received a lot of attention as information memory with an unprecedented large capacity. For example, application to large-capacity image file devices is being considered.

Recently, in such optical disk devices, a semiconductor laser oscillator has been used as a light source for the purpose of improving stability by downsizing the optical head and increasing access speed. However, semiconductor laser oscillators have a problem in terms of stability, as their oscillation output fluctuates greatly due to changes in ambient temperature and the like.

That is, in general, the oscillation threshold current (I th) of a semiconductor laser oscillator depends on the junction temperature (Tj), and I t
There is a relationship of hoc exp (Tj /K). Furthermore, in practice, since a heat sink is attached to the semiconductor laser oscillator, the temperature becomes Tj-Ta (ambient temperature). FIG. 4 shows changes in the characteristics of such a semiconductor laser oscillator depending on temperature. As can be seen from this figure, even if the driving current of the semiconductor laser oscillator is constant, the oscillation output fluctuates significantly when the ambient temperature changes.

Therefore, control is usually performed to stabilize the oscillation output by detecting the oscillation monitor light from the semiconductor laser oscillator and feeding it back to the drive circuit of the semiconductor laser oscillator. Some of them are described in Japanese Patent No. 10481. However, since this conventional technology simply detects the oscillation monitor light and applies feedback, it is not suitable for a semiconductor laser oscillator that obtains only laser light for reproduction in a device dedicated to information reproduction as shown in the above-mentioned publication. However, in an optical disk device that uses the recording method described below, it is not suitable for a semiconductor laser oscillator that alternately switches the oscillation output between a first output level and a higher second output level. Well,
Accurate and stable control is not possible at all times.

In other words, recently, in order to realize high-density recording on optical discs, recording tracks are formed in advance on optical discs by grooves (or pre-pit rows) called pre-groups in a spiral shape (or concentric circles). By alternately switching a single laser beam into a reproduction beam and a recording beam with higher energy, data bits are formed in the pregroup by the recording beam while tracking the pregroup with the reproduction beam. Optical disk devices that record information by doing so are being developed. An optical disk device that performs such recording normally outputs a low-level (first output level) reproduction beam light from a semiconductor laser oscillator to perform the above-mentioned tracking, and then generates a beam for recording. When a modulation signal (a recording pulse with a pulse width of several 100 ns or less) is input, the output level (energy) of the semiconductor laser oscillator is switched to produce a high-level (second output level) recording beam light during the period of the modulation signal. By doing so, the above-described recording is performed.

Therefore, in this case, the energy of the recording beam is several ten times that of the reproduction beam in order to melt and deform the metal coating on the optical disk, and a correspondingly high level of monitor light is also input to the detector. The output signal level is more than 10 times that of the monitor light of the reproduced beam light. Because of this, when using the conventional method that detects and feeds back the monitor light of the reproduction beam light, the signal due to the monitor light of the recording beam light is generated as a very large level in the output signal of the monitor photodetector. When the stabilization control loop responds to this monitor light signal, it works to push down the output to a low level during the reproduction beam, making it impossible to perform stable recording.In this way, the signal from the monitor light of the recording beam causes the circuit to operate. This greatly affects the operation, making the operation extremely unstable, and also causing malfunctions, making accurate and stable control impossible at all times.

To deal with this, Japanese Patent Publication No. 63-43819 discloses that when oscillating at the second output level (during recording), the optical output stabilization control loop is disconnected, and the output level is adjusted to the immediately preceding first output level. A technique has been disclosed in which an error signal when a laser beam is output is stored and held, and this signal is used to drive a semiconductor laser oscillator.

[Problems to be Solved by the Invention] However, the apparatus disclosed in Japanese Patent Publication No. 63-43819 uses an error signal when the laser beam at the first output level is output immediately before the start of recording. If a value is stored when there is a momentary fluctuation in the error signal, the amount of light emitted during recording may be too small and recording cannot be performed normally, or the amount of light emitted may be too large and destroy the laser. There is a problem that this may happen.

The present invention has been made in view of the above circumstances, and provides a semiconductor that normally oscillates at a first output level and, if necessary, switches the oscillation output to a second output level different from the first output level for a predetermined period of time. A semiconductor laser that enables accurate and stable stabilization control of oscillation output at all times, regardless of switching of oscillation output level and instantaneous fluctuations, with a relatively simple circuit configuration in an optical recording/reproduction device having a laser oscillator. An object of the present invention is to provide an optical recording/reproducing device having an output stabilization control means.

[Means for Solving the Problems] An optical recording and reproducing apparatus of the present invention records and reproduces information on and from an optical recording medium by irradiating the optical recording medium with a laser beam. When reproducing information from a medium, a laser beam at a first output level is output, and when recording information on the recording medium, a laser beam is output at the first level and a laser beam at a level higher than the first level. a semiconductor laser oscillator that outputs laser light by switching between two output levels; a photodetector that detects monitor light from the semiconductor laser oscillator and converts it into an electrical signal; and an electrical signal from the photodetector; error detection means for detecting a difference from a reference level preset for setting the first output level; and comparison means for determining whether the error signal from the error detection means is within a predetermined range. and a memory holding means which inputs the error signal from the error detection means at least during reproduction and is controlled by the output of the comparison means and stores and holds the latest error signal within the predetermined range; output switching means that inputs the output and the output of the error detection means, outputs the error signal from the error detection means during reproduction, and outputs the output of the memory holding means immediately before the start of recording during recording;
a driving means for driving the semiconductor laser oscillator according to an output signal from the output switching means and an addition signal that is added to obtain the second output level; and the semiconductor laser oscillator driven by the driving means. and an optical system that irradiates the recording medium with laser light output from the recording medium.

[Function] In the present invention, during reproduction, the monitor light from the semiconductor laser oscillator is converted into an electrical signal by the optical detection means, the difference between the electrical signal and the reference level is detected by the error detection means, and the error detection means detects the difference between the electrical signal and the reference level. The semiconductor laser oscillator is driven by the driving means in accordance with the error signal, and the recording medium is irradiated with laser light output from the semiconductor laser oscillator by the optical system. Further, the comparing means determines whether the error signal from the error detecting means is within a predetermined range or not, and at least during reproduction, the error signal from the error detecting means is input and memory storage is controlled by the output of the comparing means. The latest error signal within the predetermined range is held by the means, and during recording, depending on the output of the storage holding means immediately before the start of recording and the addition signal that is added to obtain the second output level, The driving means drives the semiconductor laser oscillator, and the optical system irradiates the recording medium with laser light output from the semiconductor laser oscillator.

[Example] Hereinafter, the present invention will be described in detail with reference to the drawings.

1 and 2 relate to a first embodiment of the present invention, FIG. 1 is a block diagram showing the configuration of an optical disk device, and FIG. 2 is a timing chart for explaining the operation of this embodiment. .

Before explaining the specific configuration of this embodiment, an overview of this embodiment will be explained.

In this embodiment, a temporary storage means is provided in the output stabilization control loop of the semiconductor laser oscillator to store and hold the latest error signal within a predetermined range, and the reproduction device outputs the laser beam at the first output level. Sometimes, the semiconductor laser oscillator is driven according to the error signal, and during recording when the output of the laser light is switched between the first output level and the second output level according to the recording modulation signal, the control loop is disconnected and this recording The semiconductor laser oscillator is driven using the output of the -time memory holding means immediately before the start. If there is an instantaneous fluctuation in the error signal that exceeds a predetermined range immediately before the start of recording, the -time memory storage means stores the latest signal within the predetermined range before the predetermined range is exceeded. An error signal is stored and held, and the output of the semiconductor laser oscillator is controlled using this stored value.

That is, as can be seen from the characteristics of the semiconductor laser oscillator shown in Fig. 4, the oscillation threshold current changes significantly depending on the temperature, but the change in [oscillation output/current] in the oscillation region (
slope) is constant. Therefore, a stabilizing control loop is formed only for the oscillation output necessary for the first output level.

To describe instantaneous fluctuations specifically, in the first embodiment, which uses a so-called rear monitor method in which a monitoring photodetector is provided behind the laser oscillator, this occurs when external noise jumps in. . Another monitoring method is the forward monitor method, which monitors the forward light of the laser oscillator and is free from the effects of backtalk that is a problem with rear monitor methods. Instantaneous fluctuations include changes in reflected light caused by changes in the optical path length due to changes in atmospheric pressure, etc.

The method disclosed in Japanese Patent Publication No. 63-43819 cannot distinguish between normal levels and instantaneous fluctuations, so there is a risk that stable recording may not be possible or that the laser oscillator may be destroyed.

Next, this example will be specifically explained.

As shown in FIG. 1, the optical disc device of this embodiment is an optical disc 1 on which recording tracks are pre-formed in the form of spirals or concentric circles by pre-groups on the front surface (lower surface).
The optical disc 1 includes a motor 2 for rotationally driving the optical disc 1, and an optical head 3 for recording and reproducing arranged to face the optical disc 1. The optical head 3 is moved linearly in the radial direction of the optical disc 1 by a linear motor mechanism (not shown). This optical head 3 includes a semiconductor laser oscillator 4 that outputs laser beam light in two directions, front and rear, a collimator lens 5 that converts the light emitted from the semiconductor laser oscillator 4 into a parallel beam, and a light that has passed through the collimator lens 5 that enters the optical head. and a polarizing beam splitter 6 provided on the optical disk 1 side of the polarizing beam splitter 6.
/4 plate 7 and objective lens 8, a condenser lens 9 and a first photodetector 1o provided on the opposite side of the polarizing beam splitter 6 from the λ/4 plate 7 and objective lens 8, and the semiconductor laser. A second photodetector 1 provided behind the oscillator 4
1.

The laser oscillator 4 is driven and controlled by a drive circuit 3o, and its oscillation output level is switched between two beam powers: a reproduction beam light having a first output level and a recording beam light having a second output level. It has become. The main beam outputted from the front of the laser oscillator 4 is collimated by a collimator lens 5, reflected by a beam splitter 6, passes through a λ/4 plate 7, and is parallelized by an objective lens 8 into approximately 1 mm diameter. The light is focused and irradiated onto the optical disk 1 (bottom surface). Then, the reflected light from the optical disc 1 is transmitted through an objective lens 8. The light passes through the λ/4 plate 7 and enters the polarizing beam splitter 6. At this time, the polarization direction is λ
Due to the action of the /4 plate 7, the polarization direction is perpendicular to the direction of polarization toward the optical disk 1, so that the light passes through the beam splitter 6 and is converged onto the first photodetector 10 by the condensing lens 9. 10, the signal is converted into an electrical signal. The output signal from the first photodetector 1o is sent to a signal processing circuit (not shown) and used as a reproduction signal, a tracking control signal, a focus control signal, and the like. On the other hand, the light output from the rear of the laser oscillator 4 enters the second photodetector 11 as monitor light, where it is converted into an electrical signal.

The output signal of the photodetector 11 is input to an integrating amplifier 12, where it is integrated and amplified.

The output signal a of this amplifier 12 is input to an error amplifier 13, which determines the difference between it and a preset reference signal, and amplifies this difference. Here, the reference signal S is a set voltage for setting the output level (for example, 1 mW) of the reproduction beam light.

The output signal C of the error amplifier 13 is input to a comparator 14 as a comparing means, sample and hold circuits 24 and 25 as temporary memory holding means, and an analog switch 28 as a switching means. The comparator 14 determines whether the output signal C of the error amplifier 13 is within the range set by +vrer and -Vref. This comparator 1
The output d of 4 is a flip flop (hereinafter referred to as FF).

) One clock input terminal CK and each input terminal of FF20,21 are applied. Further, an oscillator <1>i5 that generates a pulse at a constant period, and an oscillator (2) 16 that generates a pulse delayed by a half period from the oscillator (1) 15 are provided. The output pulse e of the oscillator (1) 15 is 1,
: is applied to the delay element 17 that delays the pulse of FF19 very slightly, the D input terminal of the FF19, and the clock input terminal CK of the FF20. Further, the output pulse g of the oscillator (2) 16 is applied to a delay element 18 that delays this pulse very slightly and to the clock input terminal CK of the FF 21.

The output f of the delay element 17 and the mutual output of the FF 20 are -r.
Ite Gate signal S is input to the AND gate 22. Further, the output of the delay element 18, the a output p of the FF 21, and the -rtteGate signal S are input to the unsignal gate 23. The -rite Gate signal S is "1" during playback.
This is a signal that becomes the ``0°'' level during recording. The output m of the AND gate 22 is applied to the control signal input terminal of the sample hold circuit 24, and the output m of the AND gate 23
The output n is applied to the control signal input terminal of the sample hold circuit 25. The sample hold circuit 24
．． 25 samples the error signal C when the signals m and n are at the "1" level, and holds the error signal C when the signals rn and n are at the 0" level, respectively.

The output 0 of the sample hold circuit 24 is input to an analog switch 26, and the output p of the sample hold circuit 25 is input to an analog switch 27. The control input terminal of the analog switch 26 has the F
The Q output i of the FF 19 is applied, and the output j of the FF 19 is applied to the control input terminal of the analog switch 27. The output q of the analog switch 26 and the output of the analog switch 27 are input to an analog switch 29 as a switching means.

Further, a -rite Gate signal r is applied to the control input terminal of the analog switch 28 to which the error signal C is input, and a -rite Gate signal r is applied to the control input terminals of the two analog switches.
The e aate signal S is applied. Furthermore, the above-mentioned Wri
The te cate signal r is a signal that has a "0" level during playback and a "1" level during recording. The outputs of the analog switches 28 and 29 are input to an adder 31 of a drive circuit 30 as a signal t. This adder 31 combines the signal t and the beam modulation signal (Write P
u1se) is added to u. The output of this adder 31 is input to a current supply circuit 32 consisting of a constant current circuit, and this current supply circuit 32 is connected to the adder 3.
A drive current corresponding to the output signal of 1 is supplied to the laser oscillator 4.

Next, the operation of this embodiment will be explained with reference to FIG.

When reproducing information, the optical head 3 is moved to a predetermined position on the optical disk 1, the laser oscillator 4 outputs a reproduction beam light, and the objective lens 8 focuses the beam onto a recording track on the optical disk 1. . At this time, the optical disc 1 is rotating at a predetermined speed, and the reproduction beam starts tracking while detecting the recording track. Note that this tracking control is not the gist of the present invention, and various methods are already well known, so further explanation will be omitted.

Further, the rear monitor light from the laser oscillator 4 is
It is converted into an electrical signal by the photodetector 11, amplified by the amplifier 12, and becomes the R part of the signal a shown in FIG. The difference between the signal a and the reference position, signal, is amplified, and a signal C (FIG. 2(b)) corresponding to the difference is output.

The signal C is sent to the comparator 14. The signal is input to sample and hold circuits 24 and 25 and analog switch 28.

During playback, as shown in FIG. 2(n) and (o), Wri
te Gate signal r is at “0” level, 14rite
Gate signal S is at "1" level. Therefore, the analog switch 28 is turned on, the analog switch 29 is turned off, and the signal C is supplied directly to the adder 31 via the analog switch 28. This adder 31 receives the output signal C of the error amplifier 13 and the beam modulation signal U.
(usually 0 volts) and supplies the addition result to the current supply circuit 32. The current supply circuit 32 supplies the laser oscillator 4 with a drive current according to the input output signal of the adder 31. Through this operation, the output level of the reproduction beam light is controlled to a constant value according to the reference signal. That is, control is performed to stabilize the oscillation output of the laser oscillator 4 during reproduction beam light.

During such reproduction, the output signal C of the error amplifier 13 is also input to the comparator 14. As shown in FIG. 2(C), the output signal d of the comparator 14 is at the "0" level if the signal C is within the comparison voltage range, and is at the "L" level when it exceeds the comparison voltage range. Become. When the output d of the comparator 14 is at “0” level,
As shown in FIGS. 2(j) and 2(k), ρ becomes the "1" level at each output of the FFs 20 and 21 to which this output signal d is input. In addition, the Write Gate signal S is also “1”.
Therefore, the AND gate 22 generates a pulse signal synchronized with the signal f (FIG. 2 (e)) obtained by delaying the output e (FIG. 2 (d)) of the oscillator (1) 15 by the delay element 17. m (Fig. 2 (r)). Then, when this signal m is at the "1" level, the sample and hold circuit 24 samples the output signal C of the error amplifier 13, and the signal m is Similarly, when the AND gate 23 holds the output g (FIG. 2(f)) of the oscillator (2) 16 while the delay element 18 delays the signal h (FIG. 2(g)
)) A pulse signal n ((S) in FIG. 2) synchronized with the pulse signal n is output. Then, when this signal n is at the "1" level, the sample and hold circuit 25 samples the output signal C of the error amplifier 13, and holds this signal while the signal n is at the "0" level. In this way, the sample and hold circuit 24
25 repeats sampling and holding at timings shifted by half a cycle from each other during normal playback, but when the output signal C of the error amplifier 13 exceeds the range of the comparator 14, the output d of the comparator 14 goes to the "1" level. Therefore, the outputs m and n of the AND gates 22 and 23 also become
The sample and hold circuit 24 remains at 0° level.
No. 25 continues the hold state without performing new sampling. In this way, the sample and hold circuit 24.2
5 stores the latest output signal C of the error amplifier 13 within the comparison voltage range of the comparator 14.

Next, in order to record information, when a beam modulation signal -rite pulse (a recording pulse with a pulse width of 100 ns or less) as shown in FIG. 31 adds the beam modulation signal Write Pulse u to the input signal t and supplies the result to the current supply circuit 32 . As a result, the current supply circuit 32
A current corresponding to the amplitude of the beam modulation signal U is
is supplied to the laser oscillator 4 only for a period of . As a result, the laser oscillator 4 generates a beam modulation signal -rite Pu1s
When the signal U is at 0" level, it is a low level (first output level), and when the signal U is at a "1" level, it is a high level (second output level).
By switching the output level so that the output level of the recording beam becomes a recording beam light, data bits are formed in pre-groups forming recording tracks on the optical disk l. At this time, since the monitor light of the recording beam light is input to the second photodetector 11, the output signal a of the amplifier 12 is at a high level (part W) as shown by the broken line in FIG. 2(a). This signal level is several times higher than that of the monitor light of the reproduction beam light.

When such recording is started - Write Gate
The signal r is at “1” level, and the Write Gate signal S
is at the "02 level, so the analog switch 28 is off and the analog switch 29 is on, and the output 0 of the sample and hold circuit 24 (FIG. 2 (j)) or the output p of the sample and hold circuit #I25 (FIG. 2) (m)) passes through the analog switch 26, 27, 29, and the signal t (second
(p)) is supplied to the adder 31.

Here, immediately before the start of recording, if the output signal C of the error amplifier 13 is within the range of the comparison voltage of the comparator 14, both the sample and hold circuits 24 and 25 are in the hold state, and therefore the sample and hold circuits 24 and 25 are in the hold state. In both cases, the output signal C of the error amplifier 13 in the reproduction state immediately before the start of recording is stored and held. Then, one of the outputs o and p of the sample and hold circuit 24.25 passes through an analog switch 26, 27, and 29, and
It is supplied to the adder 31. Which of the outputs o and p is supplied to the adder 31 depends on the state of the outputs i, j of the FF 19 <(h), (i) in FIG. 2). That is, when the output signal C of the error amplifier 13 is finally out of the comparison voltage range of the comparator 14, the output e of the oscillator 15.16
, g are at the "0" level, the output of the sample and hold circuit is supplied to the adder 31.

On the other hand, if the output signal C of the error amplifier 13 is outside the range of the comparison voltage of the comparator 14 immediately before the start of recording, one of the sample and hold circuits 24 and 25
Signal C a predetermined time before the time when the signal C exceeds the range
The value of is memorized and retained. Then, either one of the outputs 0+P of the sample and hold circuits 24 and 25 is supplied to the adder 31 via analog switches 26, 27, and 29. Which of the outputs o and p is supplied to the adder 31 is determined by the output i of the FF 19 as described above.

When the signal C goes out of range due to the state of j, that is, the output signal d of the comparator 14 (FIG.
), the sample and hold circuit corresponding to the side where the output egg of the oscillators 15 and 16 is at the "0" level is already in the hold state, so the value of the sample and hold circuit on this side will be adopted. Become. In this way, the two sample and hold circuits 24 and 25 that sample at timings shifted by half a cycle from each other are provided, and the value of one of them is adopted for the output signal C of the error amplifier 13.
This is to eliminate instability due to asynchronous sampling. In other words, since the timing at which the sample and hold circuit samples is slower than the timing at which the comparator 14 detects whether the signal C is within the range, the sample and hold circuit is in the process of sampling just when the output d of the comparator 14 rises. So,
This sample and hold circuit holds the signal C that exceeds the range of the comparator 14, and the signal C that exceeds the range of the comparator 14 is transferred to the adder 31.
In order to prevent the signals m and n from being supplied to
The one that is at the same level, that is, the one that is already in the hold state, is selected. This allows stable recording at all times. In the example of FIG. 2, the sample and hold circuit 25 samples and holds the signal C that exceeds the range of the comparator 14, so the output of the sample and hold circuit 24 is selected.

In this way, during recording, a large signal due to the monitor light of the recording beam light can be blocked, and the influence of the monitor light signal can be eliminated. That is, during the recording period, the output signal C of the error amplifier 13 monitored at that time is not input to the adder 31, but is input to the sample and hold circuit 24.
The latest output signal C of the error amplifier 13 within the comparison voltage range of the comparator 14 stored in the adder 3
1 is input. Thereby, even during the recording beam, the oscillation output of the laser oscillator 4 is stabilized and controlled only for the monitor light output level of the reproduction beam without being affected by the monitor light signal.

In this way, according to the above-mentioned output stabilization control device, the monitor light of the reproduction beam is outputted both during the reproduction beam and the recording beam.
Stabilization control of the oscillation output will be performed. As a result, the oscillation output during the playback beam period and the oscillation output during the recording beam period can always be accurately and stably controlled regardless of switching between the oscillation output levels of the playback beam and recording beam, resulting in stable recording or playback. becomes possible. Furthermore, as shown in Fig. 4, the oscillation threshold current of a semiconductor laser oscillator changes depending on the temperature, but since the change (slope) of [oscillation output/current] in the oscillation region is constant, the reproduced beam By controlling the stabilization of the oscillation output for the recording beam, the oscillation output for the recording beam can be stabilized at the same time, making even more stable recording possible. can also be set independently.

In addition, in the method shown in Publication No. 63-43819, if an instantaneous fluctuation occurs in the output of the error amplifier 13 just before the start of recording, the difference from the normal level is not recognized, so stable recording is possible. There is a risk of damage to the laser oscillator or damage to the laser oscillator. On the other hand, according to this embodiment, the direct A? at the start of recording? Even if instantaneous fluctuations such as noise occur in the first level output at f or the output of the error amplifier 13,
Since the value of the output of the error amplifier 13 a predetermined time before the specified range was exceeded can be stored and output when recording, the circuit configuration is relatively simple, and the output value can be stored without being affected by the instantaneous fluctuations during recording. Also, accurate and stable stabilization control of the oscillation output is possible.

In this embodiment, a second monitor is installed behind the laser oscillator 4.
This method, in which a photodetector 11 is provided, is called a rear monitor method. The advantage of using this method is that the only cause of instantaneous fluctuations in the output signal of the error amplifier 13 is noise. However, although the instantaneous fluctuations are small, there is a good possibility that ambient noise will jump in.

Therefore, the present invention has a great effect on the stabilization control of the oscillation output of the laser oscillator in the rear monitor system as in this embodiment. In addition, a disadvantage of the rear monitor method is that after the output emitted from the laser oscillator 4 to the front is reflected by the optical disk 1, the polarizing beam splitter 6
The light then returns to the laser oscillator 4 and is superimposed on the second photodetector 11 as so-called backtalk. In order to avoid this backtalk problem, it is preferable to adopt a forward monitoring system as in the following second embodiment.

FIG. 3 is a block diagram showing the configuration of essential parts of an optical disk device according to a second embodiment of the present invention.

In this embodiment, the second photodetector 11 is provided at a position facing the laser oscillator 4 with the polarizing beam splitter 6 in between (on the left side of the polarizing beam splitter 6 in FIG. 3). In this case, the polarizing beam splitter 6 has a characteristic of slightly transmitting the linearly polarized light output from the laser oscillator 4.

The other configurations are the same as in the first embodiment.

The method in which the second photodetector 11 receives the forward emitted light from the laser oscillator 4 is called a forward monitor method. The advantage of this method is that it does not have the backtalk problem mentioned above.

On the other hand, the disadvantage is that it is susceptible to momentary fluctuation factors such as dirt, dust, scratches, etc. on the optical disk 1 in addition to ambient noise. Furthermore, even if the optical path length changes due to changes in atmospheric pressure, etc., this will result in changes in the output of the monitor light.

In this way, the front monitor method has a higher probability of instantaneous fluctuations than the rear monitor method, so
It is difficult to use the method shown in No. 43819 for this forward monitoring method. On the other hand, according to the present invention, since the influence of instantaneous fluctuations can be removed, it is possible to stably control the oscillation output of the laser oscillator even when it is applied to the front monitor system as in this embodiment.

Other functions and effects are similar to those of the first embodiment.

It should be noted that the present invention is not limited to the above embodiments, and for example, the memory holding means ζ is not limited to a sample and hold circuit, but other memory holding means may be used.

However, even when the present invention is applied to an image file device, for example, the recording time for one image is several seconds or less at most, so temporary storage using a simple and inexpensive sample and hold circuit is sufficient.

[Effects of the Invention] As explained above, according to the present invention, output stabilization control is performed using the error signal obtained by monitoring the output of the laser oscillator during reproduction, and when recording, the output is stabilized at a predetermined level immediately before the start of recording. Since the laser oscillator is driven using the latest error signal within the range, the oscillation output is always accurate and stable, regardless of switching of the oscillation output level or instantaneous fluctuations, with a relatively simple circuit configuration. This has the effect of making stabilization control possible.

[Brief explanation of drawings]

1 and 2 relate to a first embodiment of the present invention, FIG. 1 is a block diagram showing the configuration of an optical disk device, and FIG.
Timing chart 1 to explain the operation of the ζ embodiment
, FIG. 3 is a block diagram showing the configuration of essential parts of an optical disk device according to a second embodiment of the present invention, and FIG. 4 is a characteristic diagram showing changes in characteristics of a semiconductor laser oscillator depending on temperature. 3...To optics...I drive 1...Semiconductor laser oscillator 11/2nd photodetector 13...Error amplifier 14...
・Comparator 24.25 - Sample hold circuit

Claims (1)

[Scope of Claims] In an optical recording and reproducing device that records and reproduces information on an optical recording medium by irradiating the optical recording medium with a laser beam, when reproducing information from the recording medium, When outputting a laser beam at a first output level and recording information on the recording medium, the laser beam is switched between the first level and a second output level higher than the first level. a semiconductor laser oscillator that outputs light; a photodetector that detects monitor light from the semiconductor laser oscillator and converts it into an electrical signal; and sets the electrical signal from the photodetector and the first output level. an error detection means for detecting a difference from a reference level set in advance for the purpose of reproduction; a comparison means for determining whether the error signal from the error detection means is within a predetermined range; and at least during reproduction, the error detection means a memory holding means that inputs an error signal from the memory holding means and is controlled by the output of the comparing means and stores and holds the latest error signal within the predetermined range; and an output of the memory holding means and an output of the error detecting means. output switching means for inputting an error signal from the error detecting means during playback and outputting the output of the memory holding means immediately before the start of recording during recording; and an output signal from the output switching means. a driving means for driving the semiconductor laser oscillator according to an addition signal added to obtain the second output level; An optical recording/reproducing device comprising: an optical system for illuminating a medium.