JP2785207B2 - Optical writing control device - Google Patents

Description

The present invention relates to an optical writing control device that controls writing light for recording information on an optical recording medium.

B. Summary of the Invention The present invention relates to an optical writing control device for controlling the optical output of a light source for writing a recording mark of an information recording signal to an optical recording medium, wherein light returned from the optical recording medium of light output from the light source is detected. Means, and when controlling the light output of the light source based on the detected output and the information recording signal,
By controlling the light output pattern for the information recording signal so that the level of the recording mark forming section of the detection output from the light detecting means is constant, the optimum recording mark can be formed irrespective of the variation and aging of the medium. It is like that.

C. Prior Art In recent years, disk-shaped recording media such as optical disks and magneto-optical disks utilizing an optical or magneto-optical signal recording / reproducing method have been developed and are being supplied to the market. These disc-shaped recording media include a read-only memory (ROM) type recording medium such as a so-called compact disc (CD) and a so-called write-once-read-only type in which the user can write data once. 2. Description of the Related Art A type (write-once) recording medium, a recording medium on which data can be rewritten (so-called overwrite) such as a magneto-optical disk, and the like are known.

Here, in an optical disk recording / reproducing apparatus for writing / reading data to / from the write-once type or overwritable optical disk, a spindle servo drives the optical disk to rotate at a constant angular velocity or a constant linear velocity and an optical head. By applying focus servo or tracking servo to the optical disk, the recording track of the optical disk is scanned with a light beam. The optical head includes, for example, a laser diode driven by a laser driving circuit to output a laser beam for recording and reproducing information, and a photodetector that detects reflected light of the laser beam applied to the optical disc. The focus servo and tracking servo are applied based on the output detected by the photodetector.

By the way, in an optical recording / reproducing apparatus for recording / reproducing information on / from an optical recording medium by scanning a recording track with a light beam such as a laser, a laser diode or the like which is pulse-driven in accordance with an information recording signal in a recording mode. A recording mark such as a pit is formed by scanning a recording track on an optical recording medium with writing light emitted from a light source to record information. In this case, a deviation occurs between the irradiation timing of the writing light and the actual recording formation timing of a recording mark such as a pit due to the thermal characteristics of the optical recording medium. For example, as shown in FIG. 8, it is from the start of irradiation of write light pulse P _WR corresponding to the information recording signal to the actual pit PT in the recording track starts being recorded form 300-4
There is a time delay τ of approximately 00Ns, also becomes the level change corresponding to the time lag τ is generated in the detection output waveform D _OP of reflected light was irradiated on the recording track writing light (returning light). That is, during the delay time τ, the pit PT is not formed, so that the reflectance is high, and the detection light level is high. On the other hand, after the delay time τ, the pit PT is formed, and the reflectance decreases. Therefore, the detection light level decreases.

In general, the error occurrence rate at the time of data recording in an optical disk recording / reproducing apparatus has a property of being dependent on the power of output light (laser light or the like) from a data writing light source.
It is known that it is necessary to write data with an optimal light output.

That is, when the writing light output is not appropriate, for example, as shown in FIG. 9, the pits PT _TD tear drop type form, sometimes can not be performed stable recording. This ninth
In the figure, the moving direction of the optical disk due to rotation is indicated by an arrow a
In the case of the direction, the moving direction of the light beam or the moving direction of the photodetector (23) is the direction of the arrow b relatively opposite to the direction of the arrow a.

D. Problems to be Solved by the Invention By the way, the optimum power of the writing light differs depending on, for example, the type of the optical recording medium. Therefore, the laser light for writing the information is provided in a predetermined area of the recording medium such as an optical disk. Record information about power etc. in advance,
The light output from the data writing light source is controlled based on this information. In this case, as a strategy for controlling the writing light output, changing the width of the light pulse, changing the level of the light output, or the like can be considered. For example, a strategy using output light having a pulse width of nT as a light pulse for forming a recording mark such as a pit having n times (n is an integer) the cycle T of a channel clock, and a pulse of (n−α) T Width (0 <α <1)
Considering the case where the strategy using the output light of (1) and the strategy using the output light with the pulse width of (n-1) T are defined in advance, the optimum strategy (specifically, the media supplier side) Specifically, a write light pulse width) is selected, and the information is written in a predetermined position of the recording medium. When the medium is used, the information written in the predetermined position is read out and a recording strategy (write light pulse width) is read. ) Is switched.

However, the state of recording marks (pits and the like) for the same optical output may appear differently due to variations in characteristics of the medium, aging of the characteristics, and the like. For this, a wide margin is required. Therefore, in order to secure such a wide margin, high precision and stability are required for the electric circuit and the optical system, and the recording density of the medium is limited.

Incidentally, the inventor of the present application has previously proposed in the specification and drawings of Japanese Patent Application No. 63-301546 a technique for controlling the optical output of a data writing light source for an optical recording medium based on the detection output of the amount of reflected light. Although it has to change of the reflected light detected waveform by the teardrop pits PT _TD is not considered in this technique.

In view of the above-described conventional circumstances, the present invention has a pit width, such as the teardrop-type pit, which enables an optimum recording mark to be formed irrespective of variations in characteristics of the medium or aging. An object of the present invention is to provide an optical writing control device capable of preventing formation of a changeable recording mark.

E. Means for Solving the Problems According to the optical writing control device according to the present invention, a write pulse generating circuit for generating a write pulse corresponding to an information recording signal, and a laser diode pulse-driven by the write pulse A laser drive circuit that irradiates the optical recording medium with a laser beam and stores the recording mark pattern on the optical recording medium as a recording mark pattern corresponding to the information recording signal;
A photodetector for detecting return light from the optical recording medium of a laser beam corresponding to the write pulse output from the laser diode, and an output level from the detector in a pit formation section from the write pulse generation circuit. A sampling pulse generation circuit for generating a sampling pulse for sampling in accordance with the write pulse of the above, and a level change of a detection output in the pit formation section of the photodetector sampled in accordance with the sampling pulse, and An optical output control circuit for variably controlling at least one of a pulse output waveform of the write pulse generation circuit or a level of a drive output from the laser drive circuit so that the level becomes constant. To solve the problem.

F. Operation The light output control means for controlling the writing light output from the light source based on the information recording signal and the detection output from the light detecting means detects the light output pattern for the information recording signal from the light detecting means. By controlling the level of the output recording mark forming section to be constant, it is possible to form an optimum recording mark, particularly a recording mark having a constant pit width or the like, irrespective of medium variation and aging.

G. Embodiment Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a configuration of a recording / reproducing system when the present invention is applied to an optical disk recording / reproducing apparatus for optically recording / reproducing an optical disk as a write-once optical recording medium. That is, in this recording / reproducing system, the write-once optical disk (1) is driven to rotate at a constant linear velocity by a spindle motor (2), for example, and the light source of the optical head (20) is moved to the recording track of the optical disk (1). The information recording signal of a predetermined data format is optically recorded / reproduced by scanning with light from the laser diode, that is, a laser beam from the laser diode (21).

In the optical disk recording / reproducing apparatus shown in FIG.
The optical head (20) is driven by a laser drive circuit (14) to output a laser beam for recording and reproducing digital data, and a laser diode (21) for outputting a laser beam from the laser diode (21). It has a built-in photodetector (22) for detecting light reflected by the optical disk (1). The optical head (20) scans a recording track of the optical disc (1) with a laser beam output from the laser diode (21) to record and reproduce information on the recording track of the optical disc (1). It is supposed to do.

Next, in the recording system of the optical disk recording / reproducing apparatus,
The digital data D _IN to be recorded from the input terminal (10) via the input / output interface (11) is the encoder (1).
2) is supplied. The encoder (12) converts the input digital data D _IN into a predetermined data format,
For example, the data is converted into a recording data sequence in a so-called CD format, and is modulated into an information recording signal in a signal form to be actually recorded by a modulation method such as a so-called EFM (8-16 modulation). This information recording signal is sent to an optical output control circuit (16) for controlling the optical output of the laser diode (21) of the optical head (20) as the light source. The light output control circuit (16) includes a write pulse generation circuit (1
3) and a laser drive circuit (14) to which a write pulse from the write pulse generation circuit (13) is supplied. That is, an information recording signal is obtained by converting the digital data _DIN into a data string of a predetermined format and modulating the same, and the laser drive circuit (14) uses the optical head (14) with a write pulse corresponding to the information recording signal. By pulse driving the laser diode (21) of (20), a recording mark pattern (pit pattern or the like) corresponding to the information recording signal is recorded on the recording track of the optical disc (1). A so-called APC (automatic power control) circuit (15) is provided to control the power of the laser beam from the laser diode (21) as a light source to a constant value. These write pulse generation circuit (13), laser drive circuit (14) and APC circuit (15)
Is controlled by the system controller (30) according to each operation mode.

Further, in the light output control circuit section (16), the write strategy or the output pattern of the write light pulse is changed to the level of the recording mark (pit or the like) forming portion of the light detection output from the photodetector (22) composed of a photodetector. Can be controlled according to the form of change of Specifically, for example, a write pulse generation circuit (13)
In advance, several types of correspondences of the write pulse width to the pulse width of the information recording signal are prepared in advance, and among the correspondences of the plurality of types of pulse widths, the level of the recording mark forming section of the light detection output is set. Is controlled so that the constant (waveform curve is flat) is selected, the level of the drive output from the laser drive circuit (14) is variably controlled, and the pulse output waveform itself is variably controlled. Etc. are raised.

Next, in the reproducing system of the optical disk recording / reproducing apparatus, a light detection output from a photodetector (22) such as a photodetector of the optical head (20) is supplied as a reproduction RF signal via a reproduction amplifier (31), and a decoder ( 32) etc. In this reproducing system, a decoding process corresponding to the encoding process in the encoder (12) of the recording system described above is performed on the light detection output from the photodetector (22) by the decoder (32).
And the obtained reproduction data _DOUT is output from the output terminal (33). The system controller (30) controls the regenerative amplifier (31) in accordance with each operation mode.

Further, a spindle servo circuit (40), a head servo circuit (41), and the like are provided as a so-called servo system of the optical disk recording / reproducing apparatus. In these spindle servo circuit (40) and head servo circuit (41), a reflected light (return light) detection output by a photodetector (22) of the optical head (20), a so-called reproduction RF signal, is supplied to a reproduction amplifier ( Three
1) is supplied via. Spindle servo circuit (4
In 0), the rotation speed of the spindle motor (2) is detected based on the light detection output, and the spindle motor (2) is detected.
By performing feedback control of the drive circuit (3), spindle servo control is performed so as to keep the rotation of the optical disk (1) at a constant linear velocity, for example. A head servo circuit (41) detects a focus error or a tracking error of the laser beam based on the detection output, and based on the error signal, drives a two-axis actuator (Driving an objective lens of the optical head (20)). (Not shown) to perform head servo control such as focus servo and tracking servo.

Next, control of the above-described optical writing strategy will be described in detail below.

First, recording marks such as pits are recorded and formed by irradiating a writing laser beam from a laser diode (21) as a light source to an optical disc (1) as an optical recording medium. Is influenced by the power and duration (optical pulse width) of the laser beam serving as the writing light, as described above. As a specific pit shape in this case, a shape in which the pit width changes, such as the teardrop type shown in FIG. 9, is not preferable, and a pit width having a constant pit width such as an ellipse is preferable. This corresponds to the level of the output from the photodetector (22) for detecting the reflected light from the optical disk (1), in particular, for example, the pit formation section R in the photodetection output _DOP shown in FIG.
_It can be determined by looking at the change in _PT level.

Therefore, the sampling pulse generating circuit (17) provided by the sampling pulse generator (17), what in the pit formation period R _PT according to the write pulse output P _WR from the write pulse generating circuit (13) A sampling pulse PS for sampling the level of the photodetection output D _{OP at} a point (for example, at time t ₃ , t ₄ ,..., T ₁₁ ) is obtained, and this sampling pulse SP is sampled by the A / D converter (18). Sending to clock input terminal. This A / D converter (1
The 8) is supplied with the light detection output D _OP from the reproducing amplifier (31), the photodetector outputs D _OP said each time point t _3, t _4,
..., by A / D conversion by sampling at t _11, the respective sampling outputs x _3, x _4, ..., so as to obtain the x _11.

The sampling output of the A / D converter (18) is sent to the system controller (30), and the pit formation section
Determining the level change state at R _PT, in particular the level of whether is stable at substantially constant determination is made. For example, A / D
Each sampling output from the transducer (18) value _{x 3, x 4, ...,} x 11
Is determined by the system controller (30) whether or not each absolute value of each sampling value error x ₃ −x ₄ , x ₄ −x ₅ ,..., X ₁₀ −x ₁₁ is within a predetermined threshold ε, It is determined whether or not | x _i −x _{i + 1} | <ε (i = 3 to 10). In addition, when it is determined whether or not | x ₃ −x ₁₁ | <ε, or when the average value of each sampling value is x ₀ , | x _i −x ₀ | <ε (i = 3 To 11) may be determined.

Here, a light detection output suitable for judging a level change due to the recording shape of the pit as described above includes a light-receiving portion (23A) on the trailing side of the photodetector (23) shown in FIG.
It is preferable to use the sum S _AB of the outputs from (23B). That is, in FIG. 3, the photodetector (23) for detecting the return laser beam includes light receiving portions (23A), (2A) divided into four in the track direction and the track width direction.
3B), (23C) and (23D). When the moving direction due to the rotation of the optical disk is the direction of arrow a, the moving direction of the light beam or the moving direction of the photodetector (23) is relatively in the direction of arrow b opposite to arrow a. ) And (23B) are provided on the trailing side in the photodetector moving direction (the direction of the arrow b),
C) and (23D) are provided on the leading side in the direction of arrow b. At this time, the pit PT due to the writing light is recorded and formed so as to extend from the substantially center position of the photodetector (23) in the direction of arrow a.
The detection level of the succeeding light receiving sections (23A) and (23B) changes and appears as the output _DOP in FIG. 2, whereas the output from the preceding light receiving sections (23C) and (23D) is not so large. It does not change. Therefore, it is preferable to use only the outputs from the following light receiving sections (23A) and (23B). Note that this photodetector (2
3) is provided in the photodetector (22), and receives an RF reproduction signal and a tracking signal for the light receiving section (23).
Of course, the sum or difference of the outputs from (A), (23B), (23C) and (23D) is used.

Next, in the light output control circuit section (16), a plurality of write strategies are prepared in advance, and while the system controller (30) judges the level change state in the pit formation section _RPT , By switching and selecting the write strategy, it is possible to find a write strategy that satisfies the above conditions (that is, the level of the recording mark forming section is substantially constant and stable). This means that, for example, at the start of use of a recording medium such as an optical disk, the various write strategies are switched to a predetermined area of the recording medium prior to data recording, for example, to a test writing area such as an inner peripheral side lead-in section of the optical disk. Writing is actually performed while selecting, a write strategy is determined such that the detection output of reflected light or the like satisfies the above conditions, and thereafter, data is written to this medium under the determined write strategy. What should I do? Alternatively, a test write area may be provided in a sector head portion of a disk, and a trial write may be performed on the sector head portion each time data is written to each sector to select an optimal strategy. Further, the determination of the level change state of the light detection output may be continued even during the actual data writing, and the optimal strategy may be selected and controlled in real time.

Here, as a specific example of a plurality of write strategies to be switched and selected, for example, a write pulse generation circuit (1
The case where several types of correspondence relations between the pulse width of the information recording signal and the write pulse width are prepared in 3) will be described. For example, as shown in FIG. 4, a pulse width of nT (T is a channel clock period, n represents an integer) as an information recording signal S _WR relative pulse, for example, (m +
1) Write optical pulses with different pulse widths _PWR- 0, _PWR-
1,..., P _WR -m are set, and a writing light pulse having an optimum pulse width (that is, satisfying the above conditions) is employed in accordance with the writing state of the recording medium. Signals of various pulse widths, the information recording signals S each pulse width the pulse width nT of _WR is nT, nT
−Δ,..., NT−mΔ, and can be easily obtained by using, for example, the configuration shown in FIG. That is, in FIG. 5, the information recording signal is supplied to the input terminal 35, and the information recording signal is supplied to the delay circuit (36).
And an AND gate (38). The delay circuit (36) is configured to output a plurality of delay outputs corresponding to a plurality of delay times different in units of Δ in parallel, and each of these delay outputs is provided by a selection switch (37). Sent to Andate (38). In the AND gate (38), the logical AND of the original information recording signal S _WR and the delayed output signal from the changeover selection switch (37) is obtained, so that the changeover selection switch (3) is output from the output terminal (39).
One of the write light pulses shown in FIG. 4 according to the switching of 7) is obtained. At the time of the selection control of the optimal strategy, the light detection output is determined while switching the changeover selection switch (37) in a predetermined order, and the strategy satisfying the above condition (specifically, the changeover position of the changeover selection switch (37)) )
Is to find out. In this case, the order of the selection control of the write strategy, that is, the switching control of the write light pulse width is, for example, the above ΔΔ from the maximum pulse width nT.
The switching may be stopped when the pulse width satisfies the above condition (the level of the light detection output in the pit formation section becomes substantially constant).
In addition, switching control may be performed so that the minimum pulse width is sequentially increased, or the direction of increase or decrease of the pulse width may be changed according to the level change state of the photodetection output in the pit formation section. In this manner, by writing the recording data with the switch selection switch (37) switched and connected to the switching position found at the time of test writing, for example, data writing in the optimum recording state (pit formation state) Is realized. However, when the pulse width control is performed in real time simultaneously with the data writing, it is necessary to control the increase and decrease of the pulse width according to the level change state in the pit formation section of the photodetection output.

In the case of an organic dye-based recording medium, the write light pulse width is set to (n-1) for an information recording signal having a pulse width of nT.
It has been confirmed by the present inventor that suitable writing can be performed when the value is set near T.

In the above, an example in which the pulse width of the write light pulse is controlled as the write strategy has been described. In addition, by controlling the level and the waveform of the write light pulse, the recording mark forming section of the light detection output is controlled. The level can be constant (the waveform curve is flat).

That is, as shown in FIG. 6, for example, by increasing or _decreasing the output level L _OP of the write light pulse _PSW as shown by the broken line in FIG. 6, the level of the recording mark forming section is kept constant. Control may be performed so that Also, the seventh
As shown in the figure, the write light pulse P _3W- a whose level monotonically increases and the write light pulse P _SW- b whose level monotonically decreases
The control may be performed so that the level of the recording mark forming section is constant by using a writing light pulse having a waveform whose level changes with time as shown in FIG. Further, the pulse width control, the light output level control, the light pulse waveform control, and the like may be arbitrarily combined, for example, the light output level may be variably controlled simultaneously with the pulse width.

Note that the present invention is not limited to only the above-described embodiment. For example, an optical recording medium can be applied not only to an optical disk but also to an optical card and the like. The specific circuit configuration for controlling the pulse width is not limited to the example shown in FIG.

H. Effects of the Invention According to the optical writing control device of the present invention, the output level from the photodetector in the pit formation section is sampled according to the writing pulse, and the level change of the sampled photodetection output is observed. By variably controlling at least one of the write pulse output waveform or the level of the laser drive output so that this level is constant,
Optimum recording marks can be formed so that the width is constant regardless of the variation and aging of the medium.While the signal is being written, the writing light is controlled in real time according to the detection output. The correspondence between the data and the detection output is accurately understood, and as a result, fine control including the time axis can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a recording / reproducing system of an optical disk recording / reproducing apparatus using an optical writing control device as one embodiment of the present invention, and FIG. 2 explains an operation of a main part of the embodiment. FIG. 3 is a plan view schematically showing an example of a photodetector, FIG. 4 is a timing chart for explaining a specific example of write light pulse width control, and FIG. FIG. 6 is a circuit diagram showing a specific configuration for forming a write light pulse, FIG. 6 is a waveform diagram for explaining an example of output level control of the write light pulse, and FIG. 7 is an example of waveform control of the write light pulse. FIG. 8 is a waveform diagram showing the state of recording and forming a pit according to a writing light pulse and the state of detection and output of reflected light, and FIG. 9 is a plan view showing a specific example of a teardrop-shaped pit. is there. (1) Optical disk (13) Write pulse generation circuit (14) Laser drive circuit (16) Optical output control circuit (17) Sampling pulse generation circuit (18) A / D conversion Circuit (20) Optical head (21) Laser diode (22) Photodetector (23) Photodetector

Claims (1)

(57) [Claims] A write pulse generating circuit for generating a write pulse corresponding to an information recording signal, and a laser beam is irradiated on an optical recording medium by pulse driving a laser diode with the write pulse to respond to the information recording signal. A laser drive circuit for recording a recording mark pattern on an optical recording medium as a recording mark pattern to be recorded; a photodetector for detecting return light from the optical recording medium of a laser beam corresponding to the write pulse output from the laser diode; A sampling pulse generation circuit for generating a sampling pulse for sampling an output level from the detector in a section in accordance with a write pulse from the write pulse generation circuit; and the photodetector sampled in accordance with the sampling pulse In the above pit formation section Looking at the level change of the detection output, at least one of the pulse output waveform of the write pulse generation circuit or the level of the drive output from the laser drive circuit so that this level becomes constant.
An optical output control circuit for variably controlling one of the two.