Abstract:
This patent specification describes a novel optical information recording method for recording mark and space information. The method for recording optical information comprises the steps of generating a peak level current waveform having a high level, generating a bias level current waveform having a low level generating a normal boost level current waveform and a low boost level current waveform, driving a laser light source with the normal boost level current waveform superimposed on the low level current waveform in a normal boost level light emission and switching a drive current waveform for the laser light source to the low boost level current waveform superimposed on the low level current waveform in a peak level sampling operation.

Description:
This patent specification is based on Japanese patent applications, No. 2004-277410 filed on Sep. 24, 2004 in the Japan Patent Office, the entire contents of which are incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method and apparatus for recording optical information, and more particularly to a method and apparatus for recording optical information capable of precisely controlling emission of laser light for recording. 
     2. Discussion of the Background 
     According to a recent spread usage of multimedia, optical readable disks and their associated recording and playback apparatus have been developed rapidly in addition to an increase use of those dedicated to playback mediums such as music CDs, CD-ROMs and DVD-ROMs. More specifically, write-once optical disks using a dye recording medium and phase-change optical disks using phase-change medium have been developed. In these apparatuses, a semiconductor laser light (LD) is commonly used to playback and record. 
       FIG. 1  illustrates a signal set of a channel clock, recording data and a LD waveform generated through a recording operation performed by a background optical information recording apparatus. 
     One example recording waveform for applying power to the LD to record information on the dye recording medium is a single pulse waveform created based on eight-to-fourteen Modulation (EFM), as shown in  FIG. 1 . The single pulse waveform, however, is apt to generate distortions such that recorded marks are rounded due to accumulated heat during a time of recording. Consequently, the recording quality is decreased by these unsharpened recorded marks. 
       FIG. 2  is an illustration of another signal set of a channel clock, a modulation signal and a light waveform to explain advanced waveforms. This signal set represents one example waveform strategy for LD emission to record information on the dye recording medium. Such waveform strategy uses multi pulses based on recording data with eight-to-sixteen (8-16) modulation code to form marks. Recently, faster linear velocity for recording has been required and, as a result, it becomes increasingly difficult to make the LD responds to such a high speed operation as the multi pulse laser light emission. For this reason, a so-called “Castle write Strategy” waveform is proposed. The so-called “Castle write Strategy” waveform includes peak levels at both rising and failing edges of a pulse to emphasize the mark edges. The peak levels are generated by superimposing a power having a predetermined level on a single pulse at its rising and failing edges. A resultant superimposed peak level is called as a boost level. 
       FIG. 3  is an illustration to explain changes of the emission power due to changes of the LD drive current. When the dye recording medium and the phase-change optical medium are recorded, a control of a light emission power is precisely needed because characteristics of drive current versus light emission power (i.e., an I-L curve) may drift with heat generated by the LD itself. To make the light emission power stable, a method called automatic power control (APC) is widely used. In the APC, a part of a laser beam emitted from the LD is detected by a photo detector (PD) and then the LD drive current is controlled by a monitor current generated by the PD, which is proportional to the LD emission power. 
     In a playback operation, a high frequency current is generally superimposed on the LD drive current to reduce electric noises. In this case, a simple configuration of a feedback loop circuit of a low band path can be used to implement the APC because the high frequency current is substantially constant from a viewpoint of a DC current. However, the LD emission power for recording, which changes at an extremely high frequency to form mark/space, needs to be adjusted in a more accurate manner, when the APC is implemented in a recording operation. Therefore, further improvements on the control sequence are strongly requested. The LD drive current can be controlled to some degree with a relatively simple circuit configuration using a fact that a digital sum value (DSV) becomes zero in CDs and DVDs. However, it is almost not possible to precisely control the recording power by such a relatively simple circuit configuration. 
     For example, when a longest data length, i.e., 11-T mark and space is recorded on a CD-R medium with the writing strategy shown in  FIG. 1 , a sample hold circuit may be used to keep emission power. Using the sample hold circuit, a few MHz of frequency band may be enough to control even if a rotating speed of the recording medium increases up to four times faster. Thus, the relatively cheap circuit may be able to control the recording power. 
     During the recording operation, a laser wave length and a sensitivity at the position of the recording disk surface may change due to the increase of temperature in the apparatus and the changes affect suitable recording power of the LD. Therefore, a so-called Running OPC (Running Optimum Power Calibration) is used to adjust recording power in accordance with a level of reflected light (i.e., RF signal) detected during the recording operation. 
       FIG. 4  is an illustration to explain a problem caused when the reflected light is detected. A reflection rate of the reflected light at a recorded spot rapidly decreases soon after the spot is exposed by the laser beam. The RF signal is high at the rising edge of the pulse and is decreasing to low at falling edge of the pulse, as shown in  FIG. 4 . To detect the RF signal properly, sampling may be performed at the last part of the pulse where the pulse becomes relatively stable. 
     However, in a case of a high speed recording on the dye type DVD medium with the so-called “Castle write Strategy” waveform, it is difficult to perform sampling of a peak level at a center of the pulse using a relatively simple sample hold circuit. More specifically, a photo detecting mechanism and assistant circuits following to the photo detecting mechanism need to have very high performance with respect to a control band. Accordingly, the cost of the circuits is high. 
     SUMMARY OF THE INVENTION 
     This patent specification describes a novel optical information recording apparatus for recording mark/space information. The optical information recording apparatus comprises a peak level current drive circuit configured to generate a peak level current waveform having a high level, a bias level current drive circuit configured to generate a bias level current waveform having a low level, a boost level drive current circuit configured to generate a normal boost level current waveform and a low boost level current waveform and a drive current circuit configured to drive a laser light source with the high level current waveform superimposed on the low level current waveform in a peak level light emission, the normal boost level current waveform superimposed on the low level current waveform in a normal boost level light emission, and the low boost level current waveform superimposed on the low level current waveform in a peak level sampling operation. 
     This patent specification further describes a novel optical information recording apparatus in which the boost level drive current circuit includes a switching circuit configured to switch between the normal boost level current waveform and the low boost level current waveform. 
     Further, this patent specification describes a novel method for recording mark and space information comprises the steps of generating a peak level current waveform having a high level, generating a bias level current waveform having a low level generating a normal boost level current waveform and a low boost level current waveform, driving a laser light source with the normal boost level current waveform superimposed on the low level current waveform in a normal boost level light emission and switching a drive current waveform for the laser light source to the low boost level current waveform superimposed on the low level current waveform in a peak level sampling operation 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1  illustrates conventional LD waveforms for recording optical information; 
         FIG. 2  is an illustration to explain advanced LD waveforms for recording optical information; 
         FIG. 3  is an illustration to explain a relationship between an emission power and an LD drive current; 
         FIG. 4  is an illustration to explain a problem when a reflected light is detected; 
         FIG. 5  illustrates a basic configuration of an optical information recording apparatus according to an example embodiment of the present invention; 
         FIG. 6  is a block diagram of an LD power control apparatus and associated circuits included in the optical information recording apparatus of  FIG. 5 ; 
         FIG. 7  is a block diagram of a boost level current drive apparatus included in the LD power control of  FIG. 6 ; 
         FIG. 8  is a time chart to explain a light power waveform having multi power levels; 
         FIG. 9  is a time chart to explain relationships among signals used by the optical information recording apparatus of  FIG. 5 ; 
         FIG. 10  is a time chart to explain different relationships among signals used by the optical information recording apparatus of  FIG. 5 ; and 
         FIGS. 11 ,  12  and  13  are time charts to explain relationships between sampling frequencies used by the optical information recording apparatus of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In describing preferred embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner. Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, particularly to  FIGS. 5 and 6 , a LD power control apparatus according to an embodiment of the present invention is described. 
       FIG. 5  illustrates a basic configuration of an optical information recording apparatus  1 . The optical information recording apparatus includes a recording medium  2 , a semiconductor laser diode (LD)  3 , a collimator lens  4 , a polarizing beam split  5 , a quarter-wavelength (λ/4) plate, an object lens  7 , a detection lens  8 , a divided light-sensitive element  9 , a RF signal demodulation circuit  10 , a Fo/Tr servo-control apparatus  11 , an actuator  12 , a central processing unit (CPU)  13 , a host computer  14 , a semiconductor laser diode (LD) power control apparatus  15 , a converging lens  16 , a front photo detector (PD)  17  and a RF signal demodulation circuit  18 . 
     In this embodiment, code data with DVD format is recorded on a dye type recording medium such as write once DVD+R disk. And a mark edge recording method which is a pulse width modulation (PWM) is used with 8-16 modulation codes as a data modulation method. Mark/space information is recorded onto the recording medium with laser beam with multi pulses emission in accordance with a predetermined emission rule for the LD  3 . 
     In the optical information recording apparatus  1 , the LD  3  is used as an emission source of the laser beam to record on the recording medium  2 . The recording medium  2  is driven to rotate by a spindle (not shown). The laser beam emitted from the LD  3  is passing through collimator lens  4  and is converted to parallel pencil. The converted laser beam, which is passing through the polarizing beam split  5 , the one quarter-wavelength (λ/4) plate and the object lens  7 , is then focused and is exposed to the recording medium  2 . The returning beam reflected from the recording medium  2  is passing again through the object lens  7  and the one quarter-wavelength (λ/4) plate. Then, the returning beam enter the polarizing beam split  5  with the 90 degree rotation of polarizing direction and is reflected and is passing through the detection lens  8 . Finally, the reflected beam enters the divided light-sensitive element  9  which is divided into four segments of a detection area and is detected. 
     Signals generated from the detected light at the four segments of the detection area are bases to generate signals such as a RF signal, a servo signal Fo for focusing and a servo signal Tr for tracking. The RF signal is input to the RF signal demodulation circuit  10  and is used to output a playback data as a playback signal. Meanwhile, the servo signal Fo for focusing and the servo signal Tr for tracking are input to the Fo/Tr servo control apparatus  11  and perform a control of the actuator for focusing and tracking the object lens  7  so that the laser beam to the recording medium  2  is accurately tracking on a track with a focused focal point. 
     The CPU  13  works as an arithmetic device and is arranged to capture the playback data from the RF signal demodulation circuit  10  and performs arithmetic and controlling processing. The host computer  14  is connected to the CPU  13  and controls to receive and transmit the playback data, recording data and other necessary signals. The LD power control apparatus  15  is also connected to the CPU  13  and controls the power and the condition of the LD  3  based on the playback data and the recording data. In this embodiment, the front photo detector (PD)  17  is arranged and is configured to detect a monitoring light. The monitoring light emitted from the LD  3  is reflected and is taking the separate path from outward path at the polarizing beam split  5 . Then the monitoring light is going into PD  17  though the converging lens  16 . 
     Moreover, the RF signal demodulation circuit  18  is arranged and is configured to detect a peak level of a RF signal which is output from the divided light-sensitive element  9  and to output the RF peak level signal to CPU  13 . 
       FIG. 6  is an illustration of the embodiment to explain the operation of the LD power control apparatus  15 . The embodiment includes a bias level current drive apparatus  19 , a boost level current drive apparatus  20 , a peak level current drive apparatus  21 , an I/V converting circuit  22 , a sample hold circuit  23  and an A/D converter  24 . The LD power control apparatus  15  includes a LD drive apparatus  15   a  which feeds drive current to the LD  3 . 
     In this configuration, it is needed to have three powers such as a peak power Pp to form marks with so-called “Castle Write Strategy” waveform shown in  FIG. 4 , a boost power Pbstn to boost the start and the end of the power pulse and a bias power (bottom power) Pb. For this reason, a bias level current drive apparatus (bias level current applying device)  19 , a peak level current drive apparatus  21  and a boost level current drive apparatus  20  are arranged as front circuits to the LD drive apparatus  15   a.    
     The bias level current drive apparatus  19  outputs a bias level drive current signal to the LD drive apparatus  15   a . The peak level current drive apparatus  21  is specifically a Digital-to-Analog converter (D/A converter) and outputs an analog signal of a peak level superimposed current signal based on the LD drive current information set digitally by the CPU  13 . The boost level current drive apparatus  20  outputs to the LD drive apparatus  15   a  with a boost level superimposed current signal which is to be superimposed on the bias level current. This will be described later. 
     The I/V converting circuit  22  is arranged and is configured to convert a power monitor current output from the PD  17  to a voltage signal. Sampling of the peak level power is performed by the sample hold circuit  23 . A sampling signal is digitalized by the Analog-to-Digital converter (A/D converter)  24 . Then, the voltage signal converted is output to the CPU  13 . 
       FIG. 7  is an illustration of the embodiment to explain the operation of the boost level current drive apparatus  20 . The boost level current drive apparatus  20  includes two Digital-to-Analog converters (D/A converter)  36 ,  37  and a switch  38 . The boost level superimposed current is output to the LD drive  15   a  from one of D/A converters  36 ,  37  which is selected by the switch  38  in accordance with a peak level switching signal. 
     One of the D/A converters  36  is set to provide a normal boost level Pbstn in accordance with a normal boost level control signal from the CPU  13 . If the LD  3  emits a laser beam with so-called “Castle Write Strategy” waveform, the switch  38  selects L side in accordance with a boost level switching signal. 
     Another D/A converter  37  is set to provide a predetermined boost level Pbstl in accordance with the single pulse generation boost level control signal from the CPU  13 . A value of the predetermined boost level Pbstl can be taken from a high level down to a null level. If the LD  3  emits a laser beam with the predetermined boost level, the switch  38  selects the H side in accordance with the boost power switching signal. 
     With this configuration, a normal pulse waveform operation is described first. Values of the output current from the boost level current drive apparatus  20  and the peak level current drive apparatus  21  are determined, by the boost level control signal at normal or single pulse generation mode and the peak level control signal output from the CPU  13 . The peak level current drive apparatus  21  outputs to the LD drive apparatus  15   a  with a peak level superimposed current signal which is an analog signal based on the information of the LD drive current set digitally by the CPU  13 . The boost level current drive apparatus  20  outputs to the LD drive apparatus  15   a  with a boost level superimposed current signal. The bias level current drive apparatus  19  outputs to the LD drive apparatus  15   a  with a bias level drive current signal. The LD drive apparatus  15   a  determines the each current value for a bias power (bottom power) Pb and a peak power Pp and a boost power Pbstn in accordance with the bias level drive current signal, the peak level superimposed current signal and the boost level superimposed current signal. 
       FIG. 8  is an illustration to explain the LD drive signals. A channel clock signal, a modulation signal and a light power waveform are shown in  FIG. 8 . The CPU  13  converts the information to be recorded to a 8-16 modulation signal and generates a so-called “Castle Write strategy” light power waveform. In accordance with the light power waveform, the CPU  13  provides a peak power enable signal and a boost power enable signal to the LD drive apparatus  15   a . When the boost power enable signal and the peak power enable signal are both ‘H’ level, the CPU  13  superimposes the superimposed current signals with the corresponding level on the bias level drive current signal and provides it to the LD  3 . 
       FIG. 9  is an illustration to explain the relation ship between the signals. A modulation signal, a peak power enable signal, a boost power enable signal, light power enable signal, a switching signal, sample hold signal and a monitor PD output signal are shown in  FIG. 9 . When the light emission is performed with a boost level, the boost power enable is set ‘H’ and the LD drive apparatus  15   a  superimposes the boost level superimposed current signal on the bias level current signal and provides it to the LD  3 . When the light emission is performed with a peak level, the peak power enable is set ‘H’ and the LD drive apparatus  15   a  superimposes the peak level superimposed current signal on the bias level current signal and provides it to the LD  3 . 
     When the LD drive apparatus  15   a  provides the drive current to the LD  3 , the laser beam is emitted from the LD  3  and is exposed to the recording medium  2  to record the information. While recording, a part of the emission light is input to the PD  17  and a power monitor current proportional to the light emission power is output to the I/V converter circuit  22 . The power level is detected using a power monitor current signal converted from current to voltage by the I/V converter circuit  22 . 
     The so-called “Castle Write Strategy” waveform includes a plurality of peak levels as shown in  FIG. 8 . If a conventional sample hold circuit is used to perform sampling of the peak level, it is requested to take sampling timely at the center of the pulse, not for the boost level on the both edge of the pulse. However, it becomes difficult to take a sampling value just at the center of the pulse when the linear velocity at recording becomes high. Therefore, if sampling of a peak level of emission power waveform is performed, a single pulse is generated for a short period with a single pulse to take sampling value from the single pulse as shown in the right side of the  FIG. 9 . The boost level Pbstl in this operation may be same level as the peak level Pp. 
     This procedure having the single pulse generation period for sampling operation is applicable to two operations such as an APC operation which keeps LD emission level at the predetermined level and a Running OPC operation which keeps the recording quality of the medium constant. The CPU  13  sets parameters for the D/A converter  37  of the boost level current drive apparatus  20  so that the LD  3  emits at the peak level Pp in accordance with the single pulse operation boost level control signal. 
     Meanwhile, the CPU  13  sets the boost power switching signal ‘H’ to change the connection of the switch  38  during a predetermined period of the time (for example, longer than 10 T mark) so that the output of the D/A converter  37  becomes the superimposed current having boost level. At the same time, an emission light sampling hold signal is set ‘H’. Then, during the time period of the appearance of the marks, Pbstl is Pp and the LD  3  emits a laser light with a single pulse of a constant power level Pp. 
     The peak level Pp is detected at the last part of the period even by a relatively rough setting of the emission light sampling hold signal. The CPU  13  is updating the peak level control signal so that the detected peak level is kept the predetermined peak level. Thus, this operation is repeated during a predetermined period of the APC cycle compensating the change of I/V characteristics so that the emission power level for the LD  3  is kept constant while recording. The time interval of the repetition frequency for the APC is defined as a first predetermined interval. 
       FIG. 10  is a similar illustration to  FIG. 9  to explain the relation ship between the signals. A RF sample hold signal and a RF signal output are shown in  FIG. 10 . An appropriate repetition frequency for the APC control to achieve compensation for the change of the I/V characteristics is obtained by experiments in advance. The boost power switching signal is set ‘H’, only at the period of the appearance of the longer than 10 T mark in which sampling is performed. By this setting, the LD  3  is emitted with the so-called “Castle write strategy” method during the data writing except for the sampling period. Namely, the sampling does not affect the recording quality. 
     Meanwhile, at the Running OPC operation, a single pulse emission operation is performed at different repetition frequency from the repetition frequency for the APC to detect a peak level of RF signal. The time interval of the repetition frequency for the Running OPC is defined as a second predetermined interval. 
     The first predetermined interval and the second predetermined interval, more specifically APC control frequency and Running OPC control frequency, are to be set independently. Moreover, the APC operation works to maintain the power, on the other hand, the Running OPC works to renew the power. If the APC operation and the Running OPC operation are performed at similar interval, the apparatus may have a interfere problem among two operations and finally becomes uncontrollable. Therefore, the first and second predetermined intervals are requested to be different from each other in terms of the repetition frequency. And the one interval may need to be severalfold longer than the other interval. 
       FIG. 11 ,  FIG. 12  and  FIG. 13  are illustrations to explain the relationship between sampling frequencies.  FIG. 11 , for example, shows a case where an interval of the clock of APC control is a tenth part of an interval of the clock of Running OPC. The APC is performed more frequently comparing to the Running OPC so that the laser power is stably controlled to the setting power value. On that basis, the setting power value is renewed. 
       FIG. 12  illustrates another example on the contrary to  FIG. 11 . An interval of the clock of Running OPC is a tenth part of an interval of the clock of APC. In this embodiment, The Running OPC is performed more frequently comparing to the APC so that the setting power value is constantly controlled to keep recording quality. On that basis, the laser power is adjusted to I-L characteristics by the APC. 
     There is another example in which sampling frequency is changed in accordance with the change of the linear velocity of the recording. For example, a linear velocity at outer radius of the disk is faster than a linear velocity at inner radius of the disk when CAV method is used. When the linear velocity is fast, variations in the positions of the recording medium become larger. To reduce the variations, it is requested to perform Running OPC more frequently. For that reason, a frequency of the RF sampling signal is to be set higher in accordance with the increase of the linear velocity of the recording as shown in  FIG. 13  to control the recording quality more accurately. 
     Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the disclosure of this patent specification may be practiced otherwise than as specifically described herein.