JP2002074695A - Method for detecting signal of optical disk and recording/ reproducing device using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a satisfactory signal and to obtain a stable servo signal by sample-holding the servo signal in recording from a recording laser irradiating position even in a system where gain in recording is lowered in order to avoid saturation in recording. SOLUTION: In such a system that sample-holding is used in recording and the gain of photodetector signal is lowered in recording, a reproducing level during a recording operation is not sample-held, but the signal of the recording level during the recording operation is sample-held to generate the servo signal. In such a case, since the recording signal is steeply changed in accordance with the formation of a mark, only the stable region of a recording power irradiating time is sample-held. Or the signal is detected by using a proper filter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk apparatus for recording and reproducing information on a disk using a semiconductor laser, and more particularly to an optical disk apparatus for stably applying servo during recording.

[0002]

2. Description of the Related Art As a conventional example of a recordable optical disk,
There is a CD-R (CD Recordable) as a one-time writable optical disk using an organic dye material. In order to record on this CD-R disc, a recording mark is formed by recording with a predetermined recording power. In this CD-R, there is a method called running OPC in which the level of the recording power is detected by detecting the waveform of the return light during recording. In order to perform running OPC,
The condition is that the detector is not saturated during recording. For this reason, a method of lowering the gain of the detector during recording is adopted. On the other hand, as a servo method during recording, a method is used in which only the read level during recording is sampled and held to generate an error signal. In the case of such a configuration, since the gain is reduced during recording, there is a problem that a read level during recording is greatly reduced, and a sufficient error signal cannot be obtained.

[0003]

In this CD-R, there is a method called running OPC in which the waveform of the return light is detected during recording to detect the level of the recording power. In order to perform the running OPC, the condition is that the detector is not saturated during recording. For this reason, a method of lowering the gain of the detector during recording is adopted. On the other hand, as a servo method during recording, a method is used in which only the read level during recording is sampled and held to generate an error signal. In the case of such a configuration, since the gain is reduced during recording, there is a problem that a read level during recording is greatly reduced, and a sufficient error signal cannot be obtained.

[0004]

In order to solve the above-mentioned problems, according to the first to third aspects of the present invention, servo is applied by performing sample-hold of a laser irradiation portion for recording using a sample-hold servo during recording. .

According to claims 4 to 8, the return light of the recording signal is:
Since the waveform changes sharply with the formation of the recording mark, a signal is detected via a filter in order to obtain a stable recording waveform.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment according to the present invention will be described with reference to FIG. FIG. 1 is a circuit block diagram of a pickup section and main parts of an optical disk recording / reproducing apparatus according to the present invention. In the recording / reproducing apparatus of the present embodiment, recording / reproducing is performed by condensing the laser beam 10 of the laser diode 11 on the recording film 22 on the disk substrate 21. The system of the present embodiment is a compact disc (CD) used as a recordable disc.
This is a system corresponding to an R recording / reproducing system. The laser diode 11 used had a wavelength of 780 nm and a maximum laser output of 80 mW. The laser diode is controlled by the laser drive controller 1 so that the laser diode 11
Control. The laser drive controller controls the drive current of the laser diode and controls the emission power of the laser diode. Further, the laser driving current is switched in accordance with the recording signal to generate a predetermined recording pulse waveform. A laser beam 10 from a laser diode 11 is split by a beam splitter 12 into two light beams. One is a light beam that passes through the wavelength characteristic correction plate 17 and is input to the front monitor 15, and the other is transmitted through the beam splitter as it is, changes the optical path by the rising prism 13, and is focused on the disk surface by the objective lens 14. is there. In the beam splitter of the present embodiment, 9
0% is transmitted in the direction of the objective lens, and the remaining 10% is reflected in the direction of the front monitor.

The light beam condensed by the objective lens passes through the disk substrate 21 and is focused on the recording film 22, at which point recording and reproduction are performed. In this embodiment, a disk corresponding to a CD-R disk having an NA (numerical aperture) of 0.5 is used. The recording film uses an organic dye material, and the main component is a cyanine dye.

At the time of recording / reproducing, the light reflected on the recording surface returns to the objective lens 14 and the rising prism 13 again, and enters the beam splitter 12 again. The returning light is detected by the beam splitter 12 by the detector 16 and the signal is processed by the signal processing circuit 5 by the preamplifier 4. The signal processing circuit binarizes a reproduction signal on the disc and demodulates the signal into digital data to obtain predetermined data.

FIG. 2 shows the output of the detector during recording. Although the recording waveform is incident in a rectangular shape, it is incident on the detector with a light amount as shown in FIG. 2 with the formation of the recording mark.
Although it depends on the frequency characteristics of the detector, if a detector having a sufficiently high frequency band is used, an output almost equivalent to the amount of light incident on the detector can be obtained.

In the conventional method, the output of the reproducing section (shaded area in the figure) is used for this output by using a sample and hold signal.
Although the sample-and-hold was used, the gain is reduced for those with a large output to avoid saturation. Therefore, as shown in the figure, the overall output level is greatly reduced. Specifically, it is conceivable that the recording speed becomes 1/10 or less at the time of recording. Therefore, the reproduction level is also reduced, and if the reproduction level is sampled and held, a sufficient signal may not be obtained. Therefore, in this embodiment in which the gain at the time of recording is greatly reduced, a signal having a large output can be extracted by sampling and holding the recording level instead of sampling and holding the reproduction level. A problem in the sample-and-hold at the time of recording is a fluctuation of a recording signal. In other words, although the recording signal is originally a rectangular wave, the reflectivity changes with the formation of the mark, so that the recording signal has a waveform as shown in the figure. Therefore, sample-and-hold of the whole leads to instability of the level, and therefore, it is necessary to extract only the latter stable part of the mark forming part.

According to this embodiment, a sufficient signal can be obtained even if the gain is lowered by sampling and holding the servo signal at the time of recording from the recording laser irradiation position, and a stable servo signal can be obtained. . In particular, a stable servo signal can be obtained by extracting a signal only from a position where the signal level of the recording waveform is stable. FIG. 3 shows a circuit configuration for detecting the output of the signal detection unit through a band-pass filter in order to stabilize and obtain this signal. It is desirable that the bandpass filter be switched according to the frequency at the time of recording. That is, as the recording speed increases, the recording frequency must be changed accordingly. In the case of the CD-R shown in this embodiment, the shortest frequency is 720 kHz at 1 × speed recording, and therefore, at 2.times.
It rises to 88 MHz, 5.76 MHz at 8 × speed, and 8.64 MHz at 12 × speed. Therefore, the frequency of the band pass also needs to be changed accordingly.

A groove for tracking is formed on the CD-R disk, and the groove is meandered (wobbled) to control the address and rotation of the disk. Since this signal is much lower than the normal recording signal, it can be detected by sampling and holding a part of the recording signal.

If this signal is not sampled and held at the time of recording, the quality of the wobble signal is remarkably deteriorated because components of the recording signal leak into the wobble signal. In order to avoid this, the sample and hold is performed, but for the same reason as the servo signal, a sufficient wobble signal cannot be obtained in a state where the gain is lowered. Therefore, as seen in the present embodiment, the quality of the wobble signal can be improved by the sample and hold during recording, and a wobble signal with good performance can be detected.

FIG. 4 shows an output signal waveform when the signal passes through a band-pass filter. By using a bandpass filter, a stable servo signal can be detected without taking a steep signal portion.

FIG. 5 shows a case where a multi-pulse signal is used as a recording signal. By using an appropriate band-pass filter, the level of the multi-pulse can be flattened, so that a stable signal level can be detected.

[0016]

According to the present invention, in order to avoid saturation at the time of recording, even in a system in which the gain at the time of recording is reduced, a sufficient signal can be obtained by sampling and holding the servo signal at the time of recording from the recording laser irradiation position. You can get
A stable servo signal can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram of a recording / reproducing apparatus according to a first embodiment.

FIG. 2 is a diagram showing a return waveform of a recording signal and a sample hold signal waveform.

FIG. 3 is a block diagram of a recording / reproducing apparatus according to another embodiment.

FIG. 4 is a waveform diagram after passing through a filter.

FIG. 5 is a recording waveform diagram of a multi-pulse.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 laser drive device 2 controller 3 signal processing circuit 4 preamplifier 5 sample hold signal circuit 11 laser diode 12 beam splitter 13 startup prism 14 objective lens 16
... RF signal detector, 21 ... disk substrate, 22 ... recording film.

Continued on the front page (72) Inventor Kazuhiro Oda 1410 Inada, Hitachinaka-shi, Ibaraki Pref. Digital Media Products Division, Hitachi, Ltd. F-term (reference) 5D090 AA01 BB04 CC01 CC05 DD03 DD05 FF03 GG03 HH01 KK05 LL08 5D118 BA01 BF03 CA26 CC12 CD02 CD03

Claims (7)

[Claims] An optical system for focusing a laser beam on a minute area using a lens, a unit for modulating the laser beam in accordance with a recording signal, and a unit for modulating a signal in accordance with desired recording information. In an optical disc recording / reproducing apparatus having a means for irradiating a laser in a pulse form in accordance with modulated information and recording on a recording medium, and a means for receiving return light from a disc being recorded and detecting it as an electric signal During the recording, during the irradiation of the modulated laser light, the signal level of the detection signal of the return light from the disk during the period in which the recording power of the output higher than the reproduction light is applied to record the mark on the disk. And a servo signal is generated based on this level. 2. The signal detection method according to claim 1, wherein
A signal detection method wherein when detecting the level at the time of recording power irradiation, a servo signal is obtained by sampling and holding the level at the time of recording power irradiation based on a signal synchronized with the recording signal. 3. A signal detecting method according to claim 1, wherein a band-pass filter having an upper limit not more than twice the highest recording frequency and a lower limit frequency not more than の of the lowest recording frequency is used as a cutoff frequency. A signal detection method characterized by detecting a level at the time of recording. 4. A signal detection method according to claim 1, wherein a wobble signal is detected. 5. An optical system for narrowing a laser beam to a minute area using a lens, a unit for modulating the laser beam according to a recording signal, and a unit for modulating a signal according to desired recording information. An optical disc recording / reproducing apparatus having means for irradiating a pulsed laser beam according to modulated information to record on a recording medium, and means for receiving return light from the disc being recorded and detecting it as an electric signal A sample-and-hold signal generating section for generating a sample-and-hold signal corresponding to a period during which recording power having a higher output than the reproduction light is irradiated during recording, and a sample-and-hold section for performing sample and hold based on the sample and hold signal An optical disc recording apparatus comprising: a servo signal generation unit that generates a servo signal based on the sample-held signal. 6. The optical disk recording / reproducing apparatus according to claim 5, wherein the return light is detected using a band-pass filter having a predetermined frequency characteristic in a portion for detecting the return light. 7. An optical disk recording / reproducing apparatus according to claim 5, further comprising a wobble signal detecting section for detecting a wobble signal using the sample-holded signal.