US20090154326A1 - Optical recording and reading equipment - Google Patents
Optical recording and reading equipment Download PDFInfo
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- US20090154326A1 US20090154326A1 US12/379,217 US37921709A US2009154326A1 US 20090154326 A1 US20090154326 A1 US 20090154326A1 US 37921709 A US37921709 A US 37921709A US 2009154326 A1 US2009154326 A1 US 2009154326A1
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
- G11B7/125—Optical beam sources therefor, e.g. laser control circuitry specially adapted for optical storage devices; Modulators, e.g. means for controlling the size or intensity of optical spots or optical traces
- G11B7/127—Lasers; Multiple laser arrays
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
- G11B7/125—Optical beam sources therefor, e.g. laser control circuitry specially adapted for optical storage devices; Modulators, e.g. means for controlling the size or intensity of optical spots or optical traces
- G11B7/126—Circuits, methods or arrangements for laser control or stabilisation
- G11B7/1263—Power control during transducing, e.g. by monitoring
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
- G11B7/125—Optical beam sources therefor, e.g. laser control circuitry specially adapted for optical storage devices; Modulators, e.g. means for controlling the size or intensity of optical spots or optical traces
- G11B7/128—Modulators
Definitions
- the present invention relates to a data recording and reading equipment such as any of optical disk drives of CD-R, CD-RW, DVD-R, DVD-RW, DVD-RAM, Blu-Ray disk, and HD-DVD for driving/controlling laser beam waveforms when recording/reading data on/from data recording media.
- a data recording and reading equipment such as any of optical disk drives of CD-R, CD-RW, DVD-R, DVD-RW, DVD-RAM, Blu-Ray disk, and HD-DVD for driving/controlling laser beam waveforms when recording/reading data on/from data recording media.
- optical recording disk drives have all been expanded in capacity and CD drives using conventional infrared laser beams (wavelength: 780 nm), DVD drives using red laser beams (wavelength: 650 nm), and blu-ray disk drives (BD) and high density (HD) DVD drives using blue laser beams are already under manufacturing.
- each high frequency signal (read RF signals) read from an optical disk includes so-called laser noise generated from the beam irradiated on the optical disk.
- the laser noise characteristic is represented as RIN (Relative Intensity Noise).
- RIN Relative Intensity Noise
- FIG. 2 shows a relationship between system noise and laser noise.
- the system noise is composed of all types of noise such as laser noise, amplification noise, etc. generated from the subject system.
- the BD employs a one-time speed. In case the speed is improved to a 2-time speed or 4-time speed in the future, however, such system noise is required to be reduced and the main system noise, that is, laser noise is required to be further reduced as the operation of the BD is speeded up more and more.
- the required output value is 30 mW or over at present in case a blue laser is used.
- the blue laser power on the surface of the disk when in reading is ruled as 0.35 mW+0.1 by the BD standard.
- the output blue laser power when in reading is required to be 2 mW or under.
- the conventional blue laser cannot satisfy both of the requirements, that is, large output power and less noise generation with any ordinary methods that use the BD respectively.
- JP-A No. 183970/2002 discloses a first multiplier 16 - 1 shown in FIG. 3 , in which a read RF signal rf (t) is multiplied by a DC component of an APC monitor output signal m (t) output from an LPF 15 and the signal that is a result of the multiplication is supplied to a calculator 17 .
- a read RF signal rf(t) is multiplied by a laser noise component of the APC monitor output signal m output from an HPF 18 and the signal that is a result of the multiplication is supplied to the calculator 17 .
- the signal output from the multiplier 16 - 2 is reduced from the signal output from the multiplier 16 - 1 to remove both of the laser noise additive noise component and the modulation noise component.
- Each optical disk drive provided with a reading mechanism is designed to realize desirable reading.
- JP-A No. 229636/2003 discloses a method that forms an attenuator for adjusting an optical output of the laser beam in a semiconductor laser element that includes a laser beam source for irradiating a laser beam onto a semiconductor substrate and a modulator for modulating the laser beam in the same laser structure as that of the laser beam source.
- FIG. 4 shows the characteristic of the RIN (Relative Intensity Noise) of blue lasers.
- RIN Relative Intensity Noise
- FIG. 4 shows the characteristic of the RIN (Relative Intensity Noise) of blue lasers.
- the RIN increases.
- the beam power is high, the RIN decreases.
- the output beam power at the root of the LD goes down to 2 mW or under when in reading from an optical disk due to the beam output from the surface of the disk and the limited efficiency of the optical pick-up for using the beam.
- the conventional laser thus causes the RIN to goes over ⁇ 125 dB/Hz, thereby the read signals are degraded in quality.
- FIG. 4 shows the characteristic of the RIN (Relative Intensity Noise) of blue lasers.
- the RIN depends on the laser power so that the more the laser power increases, the more the RIN decreases. This phenomenon is used to reduce the laser noise when in reading from optical disks. It is assumed that the utility efficiency of the beam from LD output to disk surface is 25%.
- the LD output is 1.4 mW at a reading power of film surface 0.35 mW and the RIN goes over ⁇ 125 dB/Hz at that time.
- a filter is disposed so as to follow the output of the laser so that the filter functions to lower the transmissivity of the laser beam (50%) when in reading. Then, the laser output is increased while the reading power on the surface of the disk is set at 0.35 mW, thereby reducing the noise up to ⁇ 125 dB/Hz that is a target value of the noise reduction.
- the transmissivity of the filter is raised not to lower the power efficiency of the laser beam.
- the laser beam output becomes larger than that when in reading, so that the laser noise problem as described above is ignorable.
- FIG. 5 shows a concept of the response time in a process from reading to recording.
- This liquid crystal attenuator requires about 50 ms for the response time of transmissivity switching. And, this response time, when it is 50 ms, comes to be equivalent to a time within which the subject disk rotates once.
- the laser beam power is not stabilized while the disk rotates once in a switching process from recording to reading or from reading to recording, it causes a problem of the deviation of the focusing servo.
- This focusing servo deviation is a serious problem that disable detection of disk positions, laser spot defocusing, etc. Those problems are thus required to be solved to employ any of such visible light filters.
- the present invention uses a modulator that modulates high speed signals in optical communications.
- chirping of comparatively large waveforms comes to limit both transmission distance and modulation speed in direct intensity modulation by a laser diode.
- the waveform is usually distorted.
- an external light modulator that does not cause chirping so easily is employed for optical communications.
- an external light modulator is an MZ modulator that uses LiNbO3 crystal or compound semiconductor crystal.
- electro absorption type optical modulator (EA modulator) proposed as another external light modulator that can be driven with a power lower than that of the MZ modulator and can be reduced more in size than the MZ modulator.
- the EA modulator absorbs a carrier beam according to an applied voltage (see FIG. 6 ) to generate an intensity-modulated signal beam.
- an EA modulator that uses compound semiconductor crystal is reported as such a modulator.
- This practical EA modulator is provided as a semiconductor chip manufactured with a semiconductor laminating technique.
- the EA modulator is easily united with a laser diode used as a carrier beam source. Consequently, high output and size reduction can be realized by reducing the coupling loss between the carrier beam source and the modulator.
- an EA-DFB laser semiconductor chip obtained by uniting a DFB (Distributed FeedBack)-LD (laser diode) with an EA modulator into one monolithically.
- FIG. 7 shows a configuration of the EA-DFB laser semiconductor chip in which a modulator and a laser are integrated.
- An output beam of this semiconductor laser element 10 is inputted to a modulator 11 disposed adjacently, then passed through a beam modulator 2 in the normal state.
- a high frequency modulation signal is applied to the laser element 10 , the laser beam is transmitted/absorbed repetitively according to a signal voltage change to become high frequency beam signals.
- modulation is made by the laser beam itself on the subject optical disk.
- a DC voltage is applied to the modulator to change the voltage between reading and writing.
- the response time at a power change from reading to writing in the modulator is also improved up to 40 Gb/s (response time: 15 ps, pico: 10 ⁇ 12 ) (see FIG. 8 ).
- the modulator response time is lower enough than the rotation speed of the present optical disks that is limited at 10,000 rpm (revolutions per minutes (cycle: about 6 milliseconds, milli: 10 ⁇ 3 ), the modulator design can be modified without causing any problem to correspond to the laser power of those optical disks.
- the present invention's equipment and method for reading and reading can thus configure an optical disk system with use of a laser having large laser noise.
- the present invention is effective for optical disk storage systems that use a laser of a wavelength 405 nm that has large laser noise respectively.
- FIG. 1 is a block diagram of an optical pick-up of the present invention
- FIG. 2 is a relationship between laser noise and system noise
- FIG. 3 is a block diagram of a circuit used for laser noise cancellation
- FIG. 4 is a graph for describing the dependency of laser noise on power
- FIG. 5 is a graph for denoting a response time in power switching from reading to recording
- FIG. 6 is a graph for denoting a relationship among voltages applied to the modulator and beam-off ratios
- FIG. 7 is a relationship between a circuit configuration in which a laser and a modulator are integrated to be used for optical communications and signals to be provided by the configuration;
- FIG. 8 is an example of frequency characteristic of the modulator
- FIG. 9 is a relationship between a circuit configuration in which a laser of the present invention and a modulator are integrated to be used for optical communications and signals to be provided by the configuration;
- FIG. 10 is a relationship between a configuration in which a conventional laser and a modulator are integrated and signals to be fed back for APC;
- FIG. 11 is a circuit diagram for feeding back information to a laser with use of a signal from the front monitor according to a laser noise reduction method of the present invention
- FIG. 12 is an example of fixing laser power by controlling the attenuation of the modulator with a signal received from a front monitor with use of a laser noise reducing method of the present invention in the third embodiment;
- FIG. 13 is a relationship between photo-current and absorbed beam amount in an electro absorption type modulator
- FIG. 14 is an example of monitoring the photo-current of the electro absorption type modulator in the fourth embodiment to use the monitored photo-current to feed back the laser power;
- FIG. 15 is an example of monitoring the photo-current of the electro absorption type modulator in the fourth embodiment to feed back the photo-current to the voltage applied to the modulator;
- FIG. 16 is an example of an optical disk recording unit in which a modulator in the fifth embodiment is disposed so as to precede the laser.
- an optical disk system that uses a laser disposed so as to precede a modulator in the first embodiment with reference to FIG. 1 .
- the value of the noise level (RIN) is lowered up to a level required by the system when in reading.
- a laser output power with which the required RIN value is reached is set and the attenuation value of the modulator disposed preceding the laser is controlled with a voltage so that the attenuation reaches the specified 0.35 mW on the surface of the subject disk.
- the reading power of the 2-layer disks is set at 0.7 mW. More concretely, in this semiconductor laser element, the beam output from the beam source is inputted to the modulator 11 disposed adjacently. When in recording and erasing, no voltage is applied to the modulator 11 so that the beam passes through the modulator 11 as much as possible.
- a voltage is applied to the modulator 11 so that the laser beam is absorbed in the modulator 11 to be attenuated.
- optical signals are passed through a beam splitter 12 so that the laser beam is irradiated on the subject optical disk as shown in FIG. 1 .
- the laser beam irradiated from the modulator 11 passes through the beam splitter 12 to be supplied to a front monitor 13 (photo-detector) and converted to electric signals.
- the signals output from the photo-detector are APC monitoring signals used to adjust the laser beam power (intensity) automatically. Then, the gain is adjusted in the monitor, then used as APC (Auto Power Control) monitor output signals.
- FIG. 9 shows the second embodiment. Basically, the same items as those in the first embodiment will be omitted here.
- a semiconductor chip in which a modulator and an LD are integrated is used.
- the laser can also be integrated in the semiconductor chip as to be described below.
- This integration is effective to reduce the semiconductor chip in size significantly.
- Slim-sized disk drives have been required to be developed for optical disks of PCs, particularly for lap-top PCs. Those compact-sized disk drives will thus come to be reduced in size more and more indispensably to enable compatibility among CD, DVD, and BD.
- the modulator is to be installed separately in the semiconductor chip, the modulator package should also be integrated in the semiconductor chip so as to enable the chip to be manufactured easily.
- the laser noise can be eliminated just like in the first embodiment.
- FIG. 10 shows a conventional configuration of the APC.
- the APC is roughly divided into two portions; so-called reading power APC performed when reading data from the subject optical disk and writing APC performed when writing data into the optical disk.
- the reading APC is performed to keep the reading laser power at 0.35 mW in a state of high frequency superposition (400 MHz for BD).
- the writing APC is performed to fix the writing laser power while data is recorded with waveforms referred to as strategy, which is specific to optical disks.
- Those APC operations are realized by monitoring the optical output power at a front monitor 13 as shown in FIG. 10 and feeding back the output power to an LD driver.
- the reading APC operation is performed with causing no problem by monitoring a fixed output power, but the reading APC operation is required to be performed by taking consideration to the strategy for monitoring the output power, thereby a wide bandwidth is needed for the reading APC operation.
- a wide bandwidth is also required for a feedback circuit 19 in the configuration shown in FIG. 10 .
- the amplifier is apt to generate large noise and the noise in the laser driving circuit comes to increase, resulting in an increase of laser noise. This is why the conventional writing APC is difficult to cope with such an increase of laser noise as optical disks are improved more and more in operation speed.
- the same problem also occurs even in a laser noise reduction method that uses a modulator as shown in FIG. 11 in case the monitored output power is fed back to the LD driver.
- the modulator is used for APC operations as shown in FIG. 12 , the writing APC can be performed at a high speed without increasing laser noise, although the APC performed by a modulator has been a bottleneck in high speed writing APC.
- the modulator operation speed is realized up to 40 Gb/s (response time 25 picoseconds: pico: 10 ⁇ 12 ).
- window width at a regular speed of BD is about 15 ns (nanosecond: 10 ⁇ 9 )
- this response speed comes to be able to correspond to the 12-time speed of BD (window width: about 1.2 ns) even when the BD rotation speed is to be improved up to a limit (10,000 rpm) in the future.
- FIGS. 13 through 15 show configurations of this fourth embodiment.
- the modulator photo-current signal is fed back to the laser (driving circuit).
- the signal is feed back to the voltage applied to the modulator. Because of those configurations, the modulator can be used effectively for two functions; laser noise reduction and front monitoring.
- data 24 is encoded in an encoding circuit 23 and converted to signals for forming strategy used to write encoded signals on the subject disk in a recording pulse shaping circuit 22 .
- the output of the recording pulse shaping circuit 22 is inputted to an LD driver circuit 21 to drive the LD 10 , thereby a beam is emitted from the LD 10 .
- no voltage is applied to the modulator to pass the laser beam as mush as possible.
- laser beam signals are irradiated on the optical disk through a beam splitter 12 as shown in FIG. 16 .
- This laser beam writes data in a recording medium 20 .
- the laser beam irradiated from the modulator is also supplied to the front monitor 13 (photo-detector) through the beam splitter 12 and converted to electric signals therein.
- the recording operations described above are the same as erasing operations.
- a voltage is applied to the modulator, thereby the laser beam is absorbed and attenuated in the modulator. How much the laser beam is attenuated at that time is determined by a potential applied to the modulator enough to achieve the required attenuation with respect to the laser power set beforehand to lower the required laser noise (RIN) level calculated from the system design. This is why the present invention can build up a system that can lower the RIN level while satisfying the specified laser power (0.35 mW for one laser of BD) on the disk surface.
Abstract
Disclosed herewith is a data recording and reading equipment capable of reducing laser noise easily. At first, a laser beam source that can reduce the laser noise when reading data from a subject optical disk is obtained. A modulator capable of varying laser attenuation with a voltage is disposed so as to precede the laser, thereby the laser noise when reading data from the optical disk can be reduced without lowering the laser power when in writing.
Description
- This application is a Continuation application of U.S. application Ser. No. 11/192,082 filed Jul. 29, 2005. Priority is claimed based on U.S. application Ser. No. 11/192,082 filed Jul. 29, 2005, which claims priority to Japanese Application No. 2004-341380 filed on Nov. 26, 2004, all of which is hereby incorporated by reference into this application.
- The present invention relates to a data recording and reading equipment such as any of optical disk drives of CD-R, CD-RW, DVD-R, DVD-RW, DVD-RAM, Blu-Ray disk, and HD-DVD for driving/controlling laser beam waveforms when recording/reading data on/from data recording media.
- Such optical recording disk drives have all been expanded in capacity and CD drives using conventional infrared laser beams (wavelength: 780 nm), DVD drives using red laser beams (wavelength: 650 nm), and blu-ray disk drives (BD) and high density (HD) DVD drives using blue laser beams are already under manufacturing. In optical disk drives such as optical disk reading/recording drives as described above, each high frequency signal (read RF signals) read from an optical disk includes so-called laser noise generated from the beam irradiated on the optical disk. The characteristic of this laser noise do not differ so much between LSs of CD (wavelength: 780 nm) and DVD (wavelength: 650 nm), since compound semiconductor materials used for those disks, as well as their LD wavelengths are almost the same. In the case of the blue laser used for the next generation DVD drives, however, the characteristic of the LD comes to be different from that of the conventional ones, since a special compound semiconductor material referred to as GaN is used for the blue laser.
- For example, the laser noise characteristic is represented as RIN (Relative Intensity Noise). According to the BD standard, this RIN is ruled as −125 dB/Hz or under.
FIG. 2 shows a relationship between system noise and laser noise. The system noise is composed of all types of noise such as laser noise, amplification noise, etc. generated from the subject system. At present, the BD employs a one-time speed. In case the speed is improved to a 2-time speed or 4-time speed in the future, however, such system noise is required to be reduced and the main system noise, that is, laser noise is required to be further reduced as the operation of the BD is speeded up more and more. - When writing data into an optical disk drive, the required output value is 30 mW or over at present in case a blue laser is used. On the contrary, the blue laser power on the surface of the disk when in reading is ruled as 0.35 mW+0.1 by the BD standard. And, in order to satisfy the requirement, the output blue laser power when in reading is required to be 2 mW or under. The conventional blue laser cannot satisfy both of the requirements, that is, large output power and less noise generation with any ordinary methods that use the BD respectively.
- In order to realize highly accurate data reading, there have been proposed some methods for removing laser noise from read RF signals. For example, the patent document 1 (JP-A No. 183970/2002) discloses a first multiplier 16-1 shown in
FIG. 3 , in which a read RF signal rf (t) is multiplied by a DC component of an APC monitor output signal m (t) output from anLPF 15 and the signal that is a result of the multiplication is supplied to acalculator 17. In a second multiplier 16-2, a read RF signal rf(t) is multiplied by a laser noise component of the APC monitor output signal m output from anHPF 18 and the signal that is a result of the multiplication is supplied to thecalculator 17. And, in thecalculator 17, the signal output from the multiplier 16-2 is reduced from the signal output from the multiplier 16-1 to remove both of the laser noise additive noise component and the modulation noise component. Each optical disk drive provided with a reading mechanism is designed to realize desirable reading. - The patent document 2 (JP-A No. 229636/2003) discloses a method that forms an attenuator for adjusting an optical output of the laser beam in a semiconductor laser element that includes a laser beam source for irradiating a laser beam onto a semiconductor substrate and a modulator for modulating the laser beam in the same laser structure as that of the laser beam source.
- However, in the case of a method for canceling laser noise with use of a conventional circuit, the circuit configuration must be modified significantly. And, this comes to cause the system design to be complicated and the manufacturing cost to increase.
- This is why there has been desired to realize a method that can cancel such laser noise without modifying the circuit configuration.
FIG. 4 shows the characteristic of the RIN (Relative Intensity Noise) of blue lasers. As shown inFIG. 4 , in case the beam power is low, the RIN increases. And, in case the beam power is high, the RIN decreases. The output beam power at the root of the LD goes down to 2 mW or under when in reading from an optical disk due to the beam output from the surface of the disk and the limited efficiency of the optical pick-up for using the beam. The conventional laser thus causes the RIN to goes over −125 dB/Hz, thereby the read signals are degraded in quality. As shown inFIG. 4 , the RIN depends on the laser power so that the more the laser power increases, the more the RIN decreases. This phenomenon is used to reduce the laser noise when in reading from optical disks. It is assumed that the utility efficiency of the beam from LD output to disk surface is 25%. The LD output is 1.4 mW at a reading power of film surface 0.35 mW and the RIN goes over −125 dB/Hz at that time. - In this case, a filter is disposed so as to follow the output of the laser so that the filter functions to lower the transmissivity of the laser beam (50%) when in reading. Then, the laser output is increased while the reading power on the surface of the disk is set at 0.35 mW, thereby reducing the noise up to −125 dB/Hz that is a target value of the noise reduction. On the other hand, when in reading/erasing, the transmissivity of the filter is raised not to lower the power efficiency of the laser beam. When in reading and erasing, the laser beam output becomes larger than that when in reading, so that the laser noise problem as described above is ignorable.
- A visible light filter such as a liquid crystal attenuator that is slow in response should not be used to avoid another problem occurrence.
FIG. 5 shows a concept of the response time in a process from reading to recording. This liquid crystal attenuator requires about 50 ms for the response time of transmissivity switching. And, this response time, when it is 50 ms, comes to be equivalent to a time within which the subject disk rotates once. In case the laser beam power is not stabilized while the disk rotates once in a switching process from recording to reading or from reading to recording, it causes a problem of the deviation of the focusing servo. This focusing servo deviation is a serious problem that disable detection of disk positions, laser spot defocusing, etc. Those problems are thus required to be solved to employ any of such visible light filters. - Under such circumstances, it is an object of the present invention to provide a data recording and reading equipment capable of reducing the laser noise as described above easily and solving the above conventional response time problems.
- In order to solve the above conventional problems, the present invention uses a modulator that modulates high speed signals in optical communications. In each optical fiber communication system, chirping of comparatively large waveforms comes to limit both transmission distance and modulation speed in direct intensity modulation by a laser diode. In case a signal light having chirping passes through an optical fiber having chromatic dispersion (wavelength dispersion), the waveform is usually distorted.
- In order to avoid this problem, an external light modulator that does not cause chirping so easily is employed for optical communications. For example, it is reported that such an external light modulator is an MZ modulator that uses LiNbO3 crystal or compound semiconductor crystal. There is also an electro absorption type optical modulator (EA modulator) proposed as another external light modulator that can be driven with a power lower than that of the MZ modulator and can be reduced more in size than the MZ modulator. The EA modulator absorbs a carrier beam according to an applied voltage (see
FIG. 6 ) to generate an intensity-modulated signal beam. For example, an EA modulator that uses compound semiconductor crystal is reported as such a modulator. - This practical EA modulator is provided as a semiconductor chip manufactured with a semiconductor laminating technique. The EA modulator is easily united with a laser diode used as a carrier beam source. Consequently, high output and size reduction can be realized by reducing the coupling loss between the carrier beam source and the modulator. For example, there is a report about an EA-DFB laser semiconductor chip obtained by uniting a DFB (Distributed FeedBack)-LD (laser diode) with an EA modulator into one monolithically.
- Hereunder, a general EA-DFB laser semiconductor chip will be described with reference to
FIG. 7 .FIG. 7 shows a configuration of the EA-DFB laser semiconductor chip in which a modulator and a laser are integrated. An output beam of thissemiconductor laser element 10 is inputted to amodulator 11 disposed adjacently, then passed through abeam modulator 2 in the normal state. In case a high frequency modulation signal is applied to thelaser element 10, the laser beam is transmitted/absorbed repetitively according to a signal voltage change to become high frequency beam signals. - In this case, modulation is made by the laser beam itself on the subject optical disk. A DC voltage is applied to the modulator to change the voltage between reading and writing. The response time at a power change from reading to writing in the modulator is also improved up to 40 Gb/s (response time: 15 ps, pico: 10−12) (see
FIG. 8 ). And, because the modulator response time is lower enough than the rotation speed of the present optical disks that is limited at 10,000 rpm (revolutions per minutes (cycle: about 6 milliseconds, milli: 10−3), the modulator design can be modified without causing any problem to correspond to the laser power of those optical disks. - The present invention's equipment and method for reading and reading can thus configure an optical disk system with use of a laser having large laser noise. Especially, the present invention is effective for optical disk storage systems that use a laser of a wavelength 405 nm that has large laser noise respectively.
- According to the present invention, therefore, it is possible to provide a data recording and reading equipment capable of reducing laser noise easily.
-
FIG. 1 is a block diagram of an optical pick-up of the present invention; -
FIG. 2 is a relationship between laser noise and system noise; -
FIG. 3 is a block diagram of a circuit used for laser noise cancellation; -
FIG. 4 is a graph for describing the dependency of laser noise on power; -
FIG. 5 is a graph for denoting a response time in power switching from reading to recording; -
FIG. 6 is a graph for denoting a relationship among voltages applied to the modulator and beam-off ratios; -
FIG. 7 is a relationship between a circuit configuration in which a laser and a modulator are integrated to be used for optical communications and signals to be provided by the configuration; -
FIG. 8 is an example of frequency characteristic of the modulator; -
FIG. 9 is a relationship between a circuit configuration in which a laser of the present invention and a modulator are integrated to be used for optical communications and signals to be provided by the configuration; -
FIG. 10 is a relationship between a configuration in which a conventional laser and a modulator are integrated and signals to be fed back for APC; -
FIG. 11 is a circuit diagram for feeding back information to a laser with use of a signal from the front monitor according to a laser noise reduction method of the present invention; -
FIG. 12 is an example of fixing laser power by controlling the attenuation of the modulator with a signal received from a front monitor with use of a laser noise reducing method of the present invention in the third embodiment; -
FIG. 13 is a relationship between photo-current and absorbed beam amount in an electro absorption type modulator; -
FIG. 14 is an example of monitoring the photo-current of the electro absorption type modulator in the fourth embodiment to use the monitored photo-current to feed back the laser power; -
FIG. 15 is an example of monitoring the photo-current of the electro absorption type modulator in the fourth embodiment to feed back the photo-current to the voltage applied to the modulator; and -
FIG. 16 is an example of an optical disk recording unit in which a modulator in the fifth embodiment is disposed so as to precede the laser. - Hereunder, the preferred embodiments of the present invention will be described with reference to the accompanying drawings.
- At first, a description will be made for an optical disk system that uses a laser disposed so as to precede a modulator in the first embodiment with reference to
FIG. 1 . The value of the noise level (RIN) is lowered up to a level required by the system when in reading. At that time, a laser output power with which the required RIN value is reached is set and the attenuation value of the modulator disposed preceding the laser is controlled with a voltage so that the attenuation reaches the specified 0.35 mW on the surface of the subject disk. In the BD standard, correspondence to two-layer disks is also ruled. The reading power of the 2-layer disks is set at 0.7 mW. More concretely, in this semiconductor laser element, the beam output from the beam source is inputted to themodulator 11 disposed adjacently. When in recording and erasing, no voltage is applied to themodulator 11 so that the beam passes through themodulator 11 as much as possible. - When in reading, a voltage is applied to the
modulator 11 so that the laser beam is absorbed in themodulator 11 to be attenuated. After that, optical signals are passed through abeam splitter 12 so that the laser beam is irradiated on the subject optical disk as shown inFIG. 1 . On the other hand, the laser beam irradiated from the modulator 11 passes through thebeam splitter 12 to be supplied to a front monitor 13 (photo-detector) and converted to electric signals. The signals output from the photo-detector are APC monitoring signals used to adjust the laser beam power (intensity) automatically. Then, the gain is adjusted in the monitor, then used as APC (Auto Power Control) monitor output signals. -
FIG. 9 shows the second embodiment. Basically, the same items as those in the first embodiment will be omitted here. In this second embodiment, a semiconductor chip in which a modulator and an LD are integrated is used. This is only a difference from the first embodiment. In case an electro absorption type modulator is used, the laser can also be integrated in the semiconductor chip as to be described below. This integration is effective to reduce the semiconductor chip in size significantly. Slim-sized disk drives have been required to be developed for optical disks of PCs, particularly for lap-top PCs. Those compact-sized disk drives will thus come to be reduced in size more and more indispensably to enable compatibility among CD, DVD, and BD. In case the modulator is to be installed separately in the semiconductor chip, the modulator package should also be integrated in the semiconductor chip so as to enable the chip to be manufactured easily. - In this case, the laser noise can be eliminated just like in the first embodiment.
- Next, the third embodiment of the present invention will be described with reference to
FIGS. 10 through 12 . In this third embodiment, high speed APC is realized and the laser power is actually controlled by a modulator. - At first, the APC will be described briefly.
FIG. 10 shows a conventional configuration of the APC. The APC is roughly divided into two portions; so-called reading power APC performed when reading data from the subject optical disk and writing APC performed when writing data into the optical disk. The reading APC is performed to keep the reading laser power at 0.35 mW in a state of high frequency superposition (400 MHz for BD). The writing APC is performed to fix the writing laser power while data is recorded with waveforms referred to as strategy, which is specific to optical disks. - Those APC operations are realized by monitoring the optical output power at a
front monitor 13 as shown inFIG. 10 and feeding back the output power to an LD driver. The reading APC operation is performed with causing no problem by monitoring a fixed output power, but the reading APC operation is required to be performed by taking consideration to the strategy for monitoring the output power, thereby a wide bandwidth is needed for the reading APC operation. In addition, because the output power is required to be feed back quickly from thefront monitor 13, a wide bandwidth is also required for afeedback circuit 19 in the configuration shown inFIG. 10 . In such a wide bandwidth, the amplifier is apt to generate large noise and the noise in the laser driving circuit comes to increase, resulting in an increase of laser noise. This is why the conventional writing APC is difficult to cope with such an increase of laser noise as optical disks are improved more and more in operation speed. - The same problem also occurs even in a laser noise reduction method that uses a modulator as shown in
FIG. 11 in case the monitored output power is fed back to the LD driver. However, in case the modulator is used for APC operations as shown inFIG. 12 , the writing APC can be performed at a high speed without increasing laser noise, although the APC performed by a modulator has been a bottleneck in high speed writing APC. As described above, the modulator operation speed is realized up to 40 Gb/s (response time 25 picoseconds: pico: 10−12). In case the window width at a regular speed of BD is about 15 ns (nanosecond: 10−9), this response speed comes to be able to correspond to the 12-time speed of BD (window width: about 1.2 ns) even when the BD rotation speed is to be improved up to a limit (10,000 rpm) in the future. - Next, the fourth embodiment of the present invention will be described with reference to
FIGS. 13 through 15 . In case an electro absorption type modulator is used, a photo-current is generated according to the absorption amount in the modulator as shown inFIG. 13 . This photo-current is observed to know a laser power variation as a change of the absorption. This technique is used instead of the front monitor used for the APC mainly in the third embodiment.FIGS. 14 and 15 show configurations of this fourth embodiment. InFIG. 14 , the modulator photo-current signal is fed back to the laser (driving circuit). InFIG. 15 , the signal is feed back to the voltage applied to the modulator. Because of those configurations, the modulator can be used effectively for two functions; laser noise reduction and front monitoring. - Next, the fifth embodiment of the present invention will be described with reference to
FIGS. 1 and 16 . At first, how to record data will be described. As shown inFIG. 16 ,data 24 is encoded in anencoding circuit 23 and converted to signals for forming strategy used to write encoded signals on the subject disk in a recordingpulse shaping circuit 22. The output of the recordingpulse shaping circuit 22 is inputted to anLD driver circuit 21 to drive theLD 10, thereby a beam is emitted from theLD 10. At that time, no voltage is applied to the modulator to pass the laser beam as mush as possible. After that, laser beam signals are irradiated on the optical disk through abeam splitter 12 as shown inFIG. 16 . This laser beam writes data in arecording medium 20. On the other hand, the laser beam irradiated from the modulator is also supplied to the front monitor 13 (photo-detector) through thebeam splitter 12 and converted to electric signals therein. Basically, the recording operations described above are the same as erasing operations. - When reading data from a subject optical disk, a voltage is applied to the modulator, thereby the laser beam is absorbed and attenuated in the modulator. How much the laser beam is attenuated at that time is determined by a potential applied to the modulator enough to achieve the required attenuation with respect to the laser power set beforehand to lower the required laser noise (RIN) level calculated from the system design. This is why the present invention can build up a system that can lower the RIN level while satisfying the specified laser power (0.35 mW for one laser of BD) on the disk surface.
- While the preferred form of the present invention has been described, it is to be understood that modifications will be apparent to those skilled in the art without departing from the spirit of the invention.
Claims (6)
1. A data recording and reading equipment, including:
a laser for emitting a beam, the beam being radiated onto a data recording medium;
a modulator that changes a degree of attenuation of the beam emitted by the laser in accordance with a control voltage applied to the modulator;
a photo-current monitor that detects a photo-current generated at the modulator,
wherein the degree of attenuation is controlled by using an output signal of the photo-current monitor.
2. A data recording and reading equipment, including:
a laser for emitting a beam, the beam being radiated onto a data recording medium;
a modulator that changes a degree of attenuation of the beam emitted from the laser in accordance with a control voltage applied to the modulator;
a photo-current monitor that detects a photo-current generated at the modulator,
wherein power of the laser is controller by using an output signal of the photo-current monitor.
3. The data recording and reading equipment according to claim 1 , further comprising a laser driver that supplies a modulated signal to the laser so as to emit the beam in accordance with data to be recorded in the recording medium.
4. The data recording and reading equipment according to claim 2 ,
a laser driver that supplies a modulated signal to the laser so as to emit the beam in accordance with data to be recorded in the recording medium.
5. The data recording and reading equipment according to claim 3 , wherein said data recording and reading equipment
controls the power of the laser so as to reduce noise of the laser to a value less than a desired value, and
controls the control voltage applied to the modulator so that beam power of the laser on a surface of the recording medium satisfies a value determined by a standard for the recording medium.
6. The data recording and reading equipment according to claim 4 , wherein said data recording and reading equipment
controls the power of the laser so as to reduce noise of the laser to a value less than a desired value, and
controls the control voltage applied to the modulator so that beam power of the laser on a surface of the recording medium satisfies a value determined by a standard for the recording medium.
Priority Applications (1)
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US12/379,217 US20090154326A1 (en) | 2004-11-26 | 2009-02-17 | Optical recording and reading equipment |
Applications Claiming Priority (4)
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JP2004341380A JP2006155698A (en) | 2004-11-26 | 2004-11-26 | Optical recording and reproducing device |
JP2004-341380 | 2004-11-26 | ||
US11/192,082 US7502302B2 (en) | 2004-11-26 | 2005-07-29 | Optical recording and reading equipment |
US12/379,217 US20090154326A1 (en) | 2004-11-26 | 2009-02-17 | Optical recording and reading equipment |
Related Parent Applications (1)
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US11/192,082 Continuation US7502302B2 (en) | 2004-11-26 | 2005-07-29 | Optical recording and reading equipment |
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US20090154326A1 true US20090154326A1 (en) | 2009-06-18 |
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US11/192,082 Expired - Fee Related US7502302B2 (en) | 2004-11-26 | 2005-07-29 | Optical recording and reading equipment |
US12/379,217 Abandoned US20090154326A1 (en) | 2004-11-26 | 2009-02-17 | Optical recording and reading equipment |
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US11/192,082 Expired - Fee Related US7502302B2 (en) | 2004-11-26 | 2005-07-29 | Optical recording and reading equipment |
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JP (1) | JP2006155698A (en) |
Cited By (2)
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US20070121446A1 (en) * | 2005-11-29 | 2007-05-31 | Manabu Shiozawa | Optical disc apparatus and optical disc reproducing method |
CN109119099A (en) * | 2018-07-06 | 2019-01-01 | 中国科学院上海光学精密机械研究所 | The optical information stored digital method of image-type concurrent reading and concurrent writing |
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WO2007148671A1 (en) * | 2006-06-20 | 2007-12-27 | Pioneer Corporation | Optical recording/reproducing method and system, and program |
US8068391B2 (en) * | 2006-06-20 | 2011-11-29 | Pioneer Corporation | Optical recording/reproducing method, system, and program |
JP2011119000A (en) * | 2009-12-07 | 2011-06-16 | Hitachi-Lg Data Storage Inc | Optical disk apparatus and defocus correcting method |
US9197318B1 (en) * | 2013-06-07 | 2015-11-24 | Pmc-Sierra Us, Inc. | Apparatus and method for modulating a laser beam and sensing the optical power thereof |
US10978107B2 (en) * | 2016-05-31 | 2021-04-13 | Sony Corporation | Information processing apparatus, optical storage apparatus, and method for processing information |
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- 2005-07-29 US US11/192,082 patent/US7502302B2/en not_active Expired - Fee Related
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Also Published As
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US7502302B2 (en) | 2009-03-10 |
US20060114777A1 (en) | 2006-06-01 |
JP2006155698A (en) | 2006-06-15 |
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