Patent Publication Number: US-2005117499-A1

Title: Optical information recording and reproducing apparatus, method and computer program for determining a value of current supplied to a laser light source, and computer readable storage medium storing the program

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application claims priority to Japanese Patent Application No. 2003-402940 filed in the Japanese Patent Office on Dec. 2, 2003, the disclosure of which is incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an optical information recording and reproducing apparatus that records information on and reproduces information from an optical disk, such as a CD-R disk, a CD-RW disk, and a DVD disk by use of a laser. The present invention further relates to a method and a computer program for determining a value of current supplied to a laser light source that emits a laser light beam to record information on and reproduce information from a recording medium, such as a CD-R disk, a CD-RW disk, and a DVD disk. The present invention further relates to a computer readable storage medium storing the computer program.  
      2. Discussion of the Related Art  
      In a conventional optical information recording and reproducing apparatus, such as a CD-R drive and a CD-RW drive, which records information data into and reproduces information data from an optical disk, a bias power current is calculated from a reproduction power current control value of a servo amplifier for the reproduction immediately before recording, an erase power is detected by a sample-hold circuit, and the emission of a laser light beam is controlled based on the detected value. Further, a peak power is calculated from an erase power current. This technology is described, for example, in Published Japanese Patent application No. 2001-229561.  
      However, in such a conventional optical information recording and reproducing apparatus, the peak power calculated from the erase power current varies due to the variation of the erase power obtained by a sample-holding operation.  
      Generally, in an optical information recording and reproducing apparatus, before recording information data into an optical disk, a so-called optimum power control (OPC) needs to be performed to determine an optimum intensity value of a recording power of a laser light beam. When performing an OPC operation, test data is recorded on a test area of an optical disk by variously changing an intensity value of a recording power of a laser light beam emitted from a laser light source step by step from a minimum intensity value to a maximum intensity value. The intensity value of the recording power of the laser light beam that provides a highest recording quality is detected by reproducing the recorded test data, and is determined as an optimum intensity value of the recording power of the laser light beam. In such an OPC operation, if a recording power of a laser light beam varies when recording test data on a test area of an optical disk, an optimum intensity value of a recording power of a laser light beam cannot be adequately determined.  
     SUMMARY OF THE INVENTION  
      According to an aspect of the present invention, an optical information recording and reproducing apparatus includes a laser light source configured to emit a digitally modulated laser light beam to an optical recording medium including a light-emitting power calibration area that is used for determining an optimum recording power intensity value of the laser light beam emitted from the laser light source and that includes a test area including a plurality of partitions into which test data is recorded and includes a count area including a plurality of partitions corresponding to the partitions of the test area. The laser light beam emitted from the laser light source includes a laser light beam of first power intensity, a laser light beam of second power intensity greater than the first power intensity, and a laser light beam of third power intensity greater than the second power intensity. The optical information recording and reproducing apparatus further includes a laser light source drive mechanism configured to supply current to the laser light source and drive the laser light source, a light-emitting power detecting mechanism configured to detect a light-emitting power of the laser light beam emitted from the laser light source, a power intensity adjusting mechanism configured to adjust a power intensity of the laser light beam emitted from the laser light source based on the light-emitting power detected by the light-emitting power detecting mechanism by changing a value of the current supplied to the laser light source by the laser light source drive mechanism, and an optimum recording power intensity value determining mechanism configured to determine the optimum recording power intensity value of the laser light beam emitted from the laser light source by recording the test data into one of the partitions of the test area with at least the laser light beam of the third power intensity and the laser light beam of the second power intensity while variously changing the value of the third power intensity and the value of the second power intensity, and by reproducing the test data. The optical information recording and reproducing apparatus further includes a laser efficiency value obtaining mechanism configured to obtain a laser efficiency value of the laser light source by causing the laser light source to emit a laser light beam of predetermined power intensity continuously to the one of the partitions of the test area at a constant power intensity value before recording the test data into the one of the partitions, by obtaining a plurality of values of current supplied to the laser light source during a period in which the laser efficiency value obtaining mechanism causes the laser light source to emit the laser light beam of the predetermined power intensity, and by calculating the laser efficiency value of the laser light source based on the plurality of obtained values of current, and a current value determining mechanism configured to determine a third value of current required to be supplied to the laser light source to emit the laser light beam of the third power intensity when recording the test data into the one of the partitions of the test area based on the laser efficiency value of the laser light source obtained by the laser efficiency value obtaining mechanism, and configured to determine a second value of current required to be supplied to the laser light source to emit the laser light beam of the second power intensity at the start of recording the test data into the one of the partitions of the test area based on the laser efficiency value of the laser light source obtained by the laser efficiency value obtaining mechanism.  
      According to another aspect of the present invention, a method of determining a value of current supplied to a laser light source that emits at least a laser light beam of first power intensity, a laser light beam of second power intensity greater than the first power intensity, and a laser light beam of third power intensity greater than the second power intensity to record information data into a recording medium, includes steps of causing the laser light source to emit a laser light beam of predetermined power intensity continuously at a constant power intensity value during a predetermined period to a test area in the recording medium to be used for determining an optimum recording power intensity value of the laser light beam emitted from the laser light source, obtaining a laser efficiency value of the laser light source based on a relation between the predetermined power intensity of the laser light beam emitted continuously from the laser light source to the test area and a value of current supplied to the laser light source during the predetermined period in which the laser light beam of the predetermined power intensity is continuously emitted to the test area, determining a third value of current required to be supplied to the laser light source to emit the laser light beam of the third power intensity from the laser light source when recording test data into the test area based on the laser efficiency value of the laser light source, and determining a second value of current required to be supplied to the laser light source to emit the laser light beam of the second power intensity from the laser light source at the start of recording the test data into the test area based on the laser efficiency value of the laser light source.  
      According to another aspect of the present invention, a computer program includes program code means that, when executed by a controller of an optical information recording and reproducing apparatus, instructs the apparatus to carry out a method of determining a value of current supplied to a laser light source that emits at least a laser light beam of first power intensity, a laser light beam of second power intensity greater than the first power intensity, and a laser light beam of third power intensity greater than the second power intensity to record information data into a recording medium, the method including steps of causing the laser light source to emit a laser light beam of predetermined power intensity continuously at a constant power intensity value during a predetermined period to a test area in the recording medium to be used for determining an optimum recording power intensity value of the laser light beam emitted from the laser light source, obtaining a laser efficiency value of the laser light source based on a relation between the predetermined power intensity of the laser light beam emitted continuously from the laser light source to the test area and a value of current supplied to the laser light source during the predetermined period in which the laser light beam of the predetermined power intensity is continuously emitted to the test area, determining a third value of current required to be supplied to the laser light source to emit the laser light beam of the third power intensity from the laser light source when recording test data into the test area based on the laser efficiency value of the laser light source, and determining a second value of current required to be supplied to the laser light source to emit the laser light beam of the second power intensity from the laser light source at the start of recording the test data into the test area based on the laser efficiency value of the laser light source.  
      According to yet another aspect of the present invention, a computer readable storage medium stores the above-described computer program. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      A more complete appreciation of the present invention 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  is a diagram for explaining a laser light beam emitted from a laser light source to a CD-RW disk according to an embodiment of the present invention;  
       FIG. 2  is a block diagram of a circuit of a laser controller that performs a constant power control of a light beam emission to a CD-RW disk;  
       FIG. 3  is a time chart showing a relation between a voltage value Vs(P 1 ) output from a first sample-hold (S/H) circuit and an output of a first comparator in a digital control;  
       FIG. 4  is a time chart showing a relation between a voltage value Vs(P 2 ) output from a second sample-hold (S/H) circuit and an output of a second comparator in a digital control;  
       FIG. 5  is a characteristic diagram showing a relation between a current value for driving a laser diode and a light-emitting power of the laser diode;  
       FIG. 6A  is a diagram showing a cross section taken along a radial direction of an optical disk;  
       FIG. 6B  is a diagram showing a test area and a count area in a power calibration area;  
       FIG. 7  is a block diagram of a configuration of an optical information recording and reproducing apparatus according to an embodiment of the present invention;  
       FIG. 8  is a flowchart of current value determining operation steps of a CPU according to an embodiment of the present invention; and  
       FIG. 9  is a block diagram of a configuration of an information processing system including the optical information recording and reproducing apparatus of  FIG. 7 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Preferred embodiments of the present invention are described in detail referring to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views.  
      First, a basic technique of the present invention will be described.  FIG. 1  is a diagram for explaining a laser light beam emitted from a laser light source to a CD-RW disk in an optical information recording and reproducing apparatus.  
      When recording information data into an optical recording medium, for example, into a CD-R disk, in an optical information recording and reproducing apparatus, a laser beam of high power intensity is emitted from a laser diode (hereafter referred to as an “LD”) as a laser light source and is radiated to a recording film of the CD-R disk. Thereby, marks (pits) are formed on the CD-R disk by a thermo-reaction. When recording information data into a CD-RW disk, the phase of a recording film of the CD-RW disk is changed.  
      The information data recorded into the optical recording medium is read out based on an amount of reflected light obtained by irradiating the recording film of the optical recording medium with a laser beam of low power intensity emitted from the LD. Generally, to change the phase of a recording film of a CD-RW disk, a laser light beam is emitted from an LD in a manner shown in  FIG. 1 . In  FIG. 1 , a period from a time “0” to a time “tw” represents a reproduction state, and a time elapsed since the time “tw” represents a state after the start of recording. As shown in  FIG. 1 , a laser light beam of first power intensity P 1  is emitted in the reproduction state. The light-emitting power of the laser light beam of the first power intensity P 1  is low, for example, about 1 mW.  
      In this embodiment, the first power intensity P 1  is kept equal in the reproduction state and the state after the start of recording. However, the first power intensity P 1  may be changed. After the start of recording, the recording film of the CD-RW disk is made amorphous by recording while emitting a laser light beam varied between third power intensity P 3  and the first power intensity P 1  at a high speed. Hereafter, a light-emitting period in which the recording film of the CD-RW disk is made amorphous will be referred to as a “recording period”. Further, the recording film of the CD-RW disk is made crystalline by recording while emitting a laser light beam of second power intensity P 2  continuously. In this case, the second power intensity P 2  of the laser light beam functions as a DC erase power. Generally, the light-emitting power of the laser light beam of the second power intensity P 2  is, for example, about 10 mW, when the light-emitting power of the laser light beam of the first power intensity P 1  is about 1 mW. Hereafter, a light-emitting period in which the recording film of the CD-RW disk is made crystalline will be referred to as an “erase period”.  
      As described above, the weak laser light beam of the first power intensity P 1  is emitted in the reproduction state. The light radiated to amorphous portions of the recording film is not reflected. This condition is similar to a case in which marks (pits) are formed on a CD-R disk. On the other hand, when the weak laser light beam of the first power intensity P 1  is radiated to crystalline portions of the recording film, the light is reflected back. This condition is similar to a case in which marks (pits) are not formed on a CD-R disk. In the erase period, when the laser light beam of the second power intensity P 2  (e.g., the laser light beam of the DC erase power) is radiated to crystalline portions of the recording film, the crystalline portions of the recording film are kept crystalline. On the other hand, when the laser light beam of the second power intensity P 2  (e.g., the laser light beam of the DC erase power) is radiated to amorphous portions of the recording film, the amorphous portions of the recording film are changed to crystalline portions.  
      Each of the recording period and the erase period has a time length in a range of 3T to 11T according to speed. In the recording period, as described above, emissions of laser light beams of the third power intensity P 3  and the first power intensity P 1  are repeated at a high speed. Generally, a period of emitting a laser light beam of the third power intensity P 3  and a period of emitting a laser light beam of the first power intensity P 1  are preset for each optical disk. In addition, a power intensity value between the second power intensity P 2  and the first power intensity P 1  and a power intensity value between the third power intensity P 3  and the first power intensity P 1  are preset for each optical disk.  
      Recently, a recording speed has been increasing. For example, a recording speed of a CD-RW disk is 16 times speed (16×). Generally, the light-emitting power of the laser light beam of the first power intensity P 1  is in a range of about 1 mW to about 2 mW. The light-emitting power of the laser light beam of the second power intensity P 2  is in a range of about 5 mW to about 20 mW. The light-emitting power of the laser light beam of the third power intensity P 3  is in a range of about 10 mW to about 40 mW. Generally, in a CD-RW disk, a laser light beam varied between two different power intensity values is emitted in the recording period, and a laser light beam of one power intensity value is emitted in the erase period as described above. The light-emitting power of an LD typically varies due to a temperature rise caused by its oscillation. In particular, if the light-emitting power of an LD is high, the temperature of the LD rises in a short period of time as compared to a low light-emitting power. Therefore, it is necessary to keep a light-emitting power of an LD at a constant value by controlling a current for driving the LD while monitoring the output of the LD with a light-receiving element in an optical information recording and reproducing apparatus.  
       FIG. 2  is a block diagram of a circuit of a laser controller that performs a constant power control of a light beam emission to a CD-RW disk. In  FIG. 2 , a photodiode (PD) is a light-receiving element. The light incident on the PD is converted to a current in proportion to an intensity of the light by a photoelectric conversion. The PD monitors a part of a laser light beam emitted from the LD, and a large amount of the emitted laser light beam is radiated to a recording film of the CD-RW disk. In this embodiment, the PD functions as a light-emitting power detecting mechanism that detects a light-emitting power of a laser light beam emitted from the LD. Next, an I/V converter  21  converts the current value output from the PD to a voltage value.  
      With respect to voltage values output from the I/V converter  21 , a voltage value obtained by converting a current value corresponding to the laser light beam of the first power intensity P 1  at the time of reproduction is set as a voltage value V(P 1 ), and a voltage value obtained by converting a current value corresponding to the laser light beam of the second power intensity P 2  in the erase period at the time of recording is set as a voltage value V(P 2 ).  
      A laser controller  10  includes a first sample-hold (S/H) circuit  22  that samples and holds the voltage value V(P 1 ) at the time of reproduction, and a second sample-hold (S/H) circuit  23  that samples and holds the voltage value V(P 2 ) in the erase period at the time of recording. The reason why two sample-hold circuits are provided is as follows. Because there is a power difference between the laser light beam of the first power intensity P 1  and the laser light beam of the second power intensity P 2 , if a common sample-hold circuit samples and holds the voltage value V(P 1 ) and the voltage value V(P 2 ), the sampled and held voltage value V(P 1 ) becomes substantially small. Therefore, in the first sample-hold (S/H) circuit  22 , the sampled and held voltage value V(P 1 ) is amplified with a predetermined gain which is different from a gain used for amplifying the sampled and held voltage value V(P 2 ) in the second sample-hold (S/H) circuit  23 .  
      Generally, an optical information recording and reproducing apparatus is configured to record information data into not only a CD-RW disk but also a CD-R disk. In the case of recording information data into the CD-R disk, two sample-hold (S/H) circuits are used for sampling and holding not only the voltage value V(P 2 ) but also the voltage value V(P 1 ) after the start of recording. A detail description of the CD-R disk will be omitted here.  
      As described above, the first sample-hold (S/H) circuit  22  samples the voltage value V(P 1 ) at the time of reproduction. At the time of reproduction, a first sample signal in the first sample-hold (S/H) circuit  22  constantly turns on a switch (SW 1 ) in the first sample-hold (S/H) circuit  22 . Further, the first sample signal constantly turns off the switch (SW 1 ) during the recording period after the start of recording information data into the CD-RW disk. Because a laser light beam of the third power intensity P 3  and a laser light beam of the first power intensity P 1  are emitted alternately at a high speed during the recording period, the period of the emission of the laser light beam of the first power intensity P 1  is too short. Therefore, the first sample-hold (S/H) circuit  22  cannot sample and hold the voltage value V(P 1 ) in the recording period.  
      A second sample signal in the second sample-hold (S/H) circuit  23  constantly turns off a switch (SW 2 ) in the second sample-hold (S/H) circuit  23  at the time of reproduction. After the start of recording, the switch (SW 2 ) in the second sample-hold (S/H) circuit  23  is turned on in the erase period (e.g., the period in which the laser light beam of the second power intensity P 2  is emitted) or in a period shorter than the erase period. In the recording period, the switch (SW 2 ) in the second sample-hold (S/H) circuit  23  is turned off. Thus, the second sample signal is a control signal for taking out only a voltage value Vs(P 2 ) corresponding to the laser light beam of the second power intensity P 2  in a condenser C 2  in the second sample-hold (S/H) circuit  23 .  
      A voltage value Vs(P 1 ) output from the first sample-hold (S/H) circuit  22  at the time of reproduction, and the voltage value Vs(P 2 ) output from the second sample-hold (S/H) circuit  23  after the start of recording, are input to a first comparator  24  and a second comparator  25 , respectively. The first comparator  24  compares the voltage value Vs(P 1 ) with a first reference voltage value (Vref 1 ), and the second comparator  25  compares the voltage value Vs(P 2 ) with a second reference voltage value (Vref 2 ). Each of the first comparator  24  and the second comparator  25  determines if a value of an input signal exceeds a reference voltage value, and outputs signals of a comparison result, that is, binary signals (digital data). Subsequently, a central processing unit (CPU)  26  reads the digital data.  
      Then, the digital data is transmitted from the CPU  26  to a first D/A converter  27  that converts a digital value to an analog value. The first D/A converter  27  outputs a voltage value in proportion to the digital data input thereto to a first V/I converter  31 . Further, the first V/I converter  31  outputs a current value according to the voltage value output from the first D/A converter  27 . Likewise, digital data is transmitted from the CPU  26  to a second D/A converter  28 . The second D/A converter  28  outputs a voltage value in proportion to the digital data input thereto to a second V/I converter  32 . Further, the second V/I converter  32  outputs a current value according to the voltage value output from the second D/A converter  28 .  
      Further, current values output from the first V/I converter  31  and the second V/I converter  32  are amplified by a first current amplifier  33  and a second current amplifier  34 , respectively. At the time of reproduction, the output current of the first current amplifier  33  is supplied to an LD by turning on a switch SW 3  by a light source on signal (LD ON signal), and thereby the LD emits a laser light beam of the first power intensity P 1 . After the start of recording, the output current of the second current amplifier  34  is added to the output current of the first current amplifier  33  by a current adder  35  by turning on a switch SW 4  by a first write pulse superimposed signal, and is supplied to the LD. Then, the LD emits a laser light beam of the second power intensity P 2 . Here, a current value output from the first current amplifier  33  is referred to as “IP 1 ”, and a current value output from the second current amplifier  34  is referred to as “IP 2 ”.  
      The laser controller  10  keeps the light-emitting power of the LD at a constant level in a manner described below.  
      First, at the time of start of reproduction, the CPU  26  outputs “0” to the first D/A converter  27 . Thereby, a current value for a reproduction power of the LD starts from “0”. Then, the CPU  26  gradually increases data to be output to the first D/A converter  27  until the output of the first comparator  24  is inversed, that is, until the voltage value Vs(P 1 ) exceeds the first reference voltage value Vref 1 . Subsequently, the data output from the CPU  26  to the first D/A converter  27  is adjusted such that the voltage value Vs(P 1 ) becomes close to the first reference voltage value Vref 1 .  
       FIG. 3  is a time chart showing a relation between the voltage value Vs(P 1 ) output from the first sample-hold (S/H) circuit  22  and an output of the first comparator  24  in a digital control. As shown in  FIG. 3 , the reproduction power of the LD is kept at a constant level by performing the above-described digital control. As an ideal condition, it is preferable that the voltage value Vs(P 1 ) becomes equal to the first reference voltage value Vref 1 . However, in reality, the voltage value Vs(P 1 ) exceeds and falls below the first reference voltage value Vref 1  as shown in  FIG. 3 .  
       FIG. 4  is a time chart showing a relation between the voltage value Vs(P 2 ) output from the second sample-hold (S/H) circuit  23  and an output of the second comparator  25  in a digital control. Specifically,  FIG. 4  shows a state in which the laser light beam of the first power intensity P 1  emitted from the LD at the time of reproduction changes to the laser light beam of the second power intensity P 2  and is kept at a constant level after the start of recording. In  FIG. 4 , the CPU  26  sets the output of the second D/A converter  28  at “0” at the time of a light emission for reproduction. The voltage value Vs(P 2 ) output from the second sample-hold (S/H) circuit  23  just after the start of recording is substantially equal to the voltage value Vs(P 1 ) output from the first sample-hold (S/H) circuit  22  at the time of reproduction. As shown in  FIG. 4 , the first reference voltage value Vref 1  is multiplied by “α” as a difference of gain in the path. Generally, the value of “α” is set to be less than “1”.  
      Then, the CPU  26  increases data to be output to the second D/A converter  28  by “1” or a predetermined value. The current value according to the voltage value output from the second D/A converter  28  is superimposed on the current value according to the voltage value output from the first D/A converter  27  as a current value for an erase power of the LD. Accordingly, the voltage value Vs(P 2 ) output from the second sample-hold (S/H) circuit  23 , which are obtained by monitoring, sampling, and holding the current value for the erase power of the LD, increases by a predetermined amount such that the voltage value Vs(P 2 ) becomes close to the second reference voltage value Vref 2  as shown in  FIG. 4 . Subsequently, as shown in  FIG. 4 , the erase power of the LD is kept at a constant level as was done similarly at the time of reproduction. As an ideal condition, it is preferable that the voltage value Vs(P 2 ) becomes equal to the second reference voltage value Vref 2 . However, in reality, the voltage value Vs(P 2 ) exceeds and falls below the second reference voltage value Vref 2  as shown in  FIG. 4 .  
      As described above, the voltage of the laser light beam of the first power intensity P 1  is not sampled and held after the start of recording. The output value of the first D/A converter  27  at the start of recording may be set to the output value of the first D/A converter  27  just before the start of recording. Specifically, the laser light beam of the first power intensity P 1  has a low light-emitting power, and the LD emits the laser light beam of the first power intensity P 1  only in the recording period after the start of recording. The laser light beam of the first power intensity P 1  is intermittently emitted from the LD, and is not influenced much by the variation of the light emission of the LD caused by its temperature. Therefore, the output value of the first D/A converter  27  may be set to a constant value. Thus, the laser light beam of the first power intensity P 1  may be emitted from the LD at a constant level in the recording period after the start of recording.  
      In the above-described circuit of the laser controller  10 , a digital control is performed by using the CPU  26  and the D/A converters at the time of reproduction and recording. In place of the digital control, an analog control may be employed to perform a constant power control. For example, in the analog control, a signal output from a first sample-hold (S/H) circuit or a signal output from a second sample-hold (S/H) circuit is input to an error amplifier, such as, an integrator. In the error amplifier, a value of the signal is compared with a reference voltage value. If the value of the signal is different from the reference voltage value, the error amplifier outputs a voltage value for adjusting the difference between the value of the signal and the reference voltage value to a first V/I converter or a second V/I converter.  
      Because the laser light beam of the first power intensity P 1  has a low light-emitting power, even though the analog control is performed, the voltage value output from the error amplifier does not vary significantly just after the start of reproduction. Further, in the analog control, a period of time necessary for making the light-emitting power constant is shorter than that in the digital control. For these reasons, the laser light beam of the first power intensity P 1  is often controlled by the analog control at the time of reproduction.  
      When controlling the laser light beam of the first power intensity P 1  by the analog control, a signal output from the first sample-hold (S/H) circuit is input to the error amplifier. Then, a voltage value output from the error amplifier is directly input to the first V/I converter. In addition, it is configured such that the voltage value output from the first D/A converter is input to the first V/I converter. A switch may be provided to switch the input to the first V/I converter either from the error amplifier or from the first D/A converter. Further, it may be configured such that an A/D converter may check the output level of the error amplifier when the emitting power of the laser light beam of the first power intensity P 1  is made at a constant level at the time of reproduction. After the start of recording, a voltage value output from the first D/A converter in the digital control is made equal to the voltage value output from the error amplifier in the analog control.  
      Thus, a laser power control operation is similarly performed in both the analog control and the digital control. Specifically, the light-emitting power of the LD is monitored. Then, a voltage value corresponding to a laser light beam of a predetermined intensity is compared with a reference voltage value. Then, a drive current value to be input to the LD is controlled such that the voltage value corresponding to the laser light beam of the predetermined intensity becomes close to (ideally, equal to) the reference voltage value.  
       FIG. 5  is a characteristic diagram showing a relation between a current value for driving the LD and the light-emitting power of the LD. As shown in  FIG. 5 , there is a linear functional relation between the current value for driving the LD and the light-emitting power of the LD when the current value exceeds a threshold value “Ith”. The slope of the line segment may vary depending on an LD. Because the light-emitting power of the LD has a specific relation relative to the current value for driving the LD, the light-emitting power of the LD also has a specific relation relative to the voltage value set at the D/A converter for setting the current value for driving the LD. Further, because the voltage value set at the D/A converter for setting the current value for driving the LD is determined based on the reference voltage value of the comparator, there is a linear functional relation between the reference voltage value of the comparator and the light-emitting power of the LD with a predetermined slope.  
      Therefore, if the slope is calculated in advance, the light-emitting power of the LD is obtained from the reference voltage value. If a slope or an intercept of the line is stored in a memory, the light-emitting power of the LD is controlled efficiently. Usually, the relation between the reference voltage value of the comparator and the first power intensity P 1  or the second power intensity P 2  is obtained in advance, for example, as a relational expression in a production process of an optical information recording and reproducing apparatus. When emitting a laser light beam from an LD in an actual operation of the optical information recording and reproducing apparatus, the first power intensity P 1  and the second power intensity P 2  are set by the relational expression.  
      Although the above-described slope of the line segment varies depending on characteristics of an LD, such as a temperature, and the threshold value “Ith” shifts, the CPU  26  controls the light-emitting power of the LD at a constant level by adjusting a current value for driving the LD (e.g., a current value output from the V/I converter) such that the voltage value output from the sample-hold (S/H) circuit becomes close to the reference voltage value of the comparator.  
      Generally, a control for keeping a light-emitting power of an LD at a constant level is referred to as an auto power control (APC). As described above, after the start of recording information data into the CD-RW disk, because the laser light beam of the first power intensity P 1  has a low light-emitting power, and is intermittently emitted from the LD, the laser light beam of the first power intensity P 1  is not sampled and held, so that the laser light beam of the first power intensity P 1  emitted after the start of recording is not subjected to the APC. Only the laser light beam of the second power intensity P 2  (e.g., an erase power) is subjected to the APC after the start of recording.  
      Next, a control for an emission of a laser light beam of the third power intensity P 3  will be described.  
      As described above, when recording information data into and reproducing information data from a CD-RW disk, three different intensity values of light-emitting power (power levels) are used, that is, the first power intensity P 1 , the second power intensity P 2 , and the third power intensity P 3 . When emitting the laser light beam of the third power intensity P 3  from the LD, an output current of a third current amplifier  37  is added to the output current of the first current amplifier  33  and the output current of the second current amplifier  34  by the current adder  35  by turning on a switch SW 5  by a second write pulse superimposed signal, and is supplied to the LD. Then, the LD emits a laser light beam of the third power intensity P 3 . Here, a current value output from the third current amplifier  37  is referred to as “IP 3 ”.  
      In  FIG. 5 , a first current value required to be supplied to the LD for emitting a laser light beam at a power level of the first power intensity P 1  is indicated by “IP 1 ”, a second current value required to be supplied to the LD for emitting a laser light beam at a power level of the second power intensity P 2  is indicated by “IP 2 ”, and a third current value required to be supplied to the LD for emitting a laser light beam at a power level of the third power intensity P 3  is indicated by “IP 3 ”. Specifically, when supplying a current value (IP 1 ) to the LD, the LD emits the laser light beam of the first power intensity P 1 . When supplying a current value (IP 1 +IP 2 ) to the LD, the LD emits the laser light beam of the second power intensity P 2 . When supplying a current value (IP 1 +IP 2 +IP 3 ) to the LD, the LD emits the laser light beam of the third power intensity P 3 .  
      The second power intensity P 2  is controlled such that the voltage value input to the second comparator  25  becomes close to or, ideally, equal to the second reference voltage value Vref 2  by changing the second current value IP 2  (e.g., the voltage value set at the second D/A converter  28 ) by the APC. As provided similarly in connection with the laser light beam of the first power intensity P 1 , the laser light beam of the third power intensity P 3  is intermittently emitted from the LD only in the recording period after the start of recording. Therefore, it is difficult to sample and hold the laser light beam of the third power intensity P 3 . For this reason, a voltage value set at a third D/A converter  29  is input to a third V/I converter  36 . Then, the output current of the third V/I converter  36  becomes the third current value IP 3 .  
      The third power intensity P 3  has a substantially greater power than the first power intensity P 1 . For example, the third power intensity P 3  may have about double the power of the second power intensity P 2 . When emitting the laser light beam of the third power intensity P 3  from the LD, the output of the LD varies due to the increase of the temperature of the LD. In this condition, even if the third current value IP 3  for driving the LD is unchanged, the third power intensity P 3  of the laser light beam emitted from the LD changes. For these reasons, the laser light beam of the third power intensity P 3  needs to be controlled. The power level of the third power intensity P 3  is maintained by changing the third current value IP 3  in the following manner.  
      As shown in  FIG. 5 , there is a linear functional relation between the current value for driving the LD and the light-emitting power of the LD. Assuming that the slope of the line is constant when the current value exceeds the threshold value “Ith”, the slope obtained from the second current value IP 2  and the second power intensity P 2  may be considered as a laser efficiency value, that is, a ratio between the current value and the light-emitting power. The laser efficiency value (i.e., the slope) is unchanged unless the light-emitting power of the LD is close to an upper limit. In the case of recording data into the CD-RW disk, the light-emitting power of an LD does not generally approach the upper limit. Specifically, the third current value IP 3  is determined as follows.  
      First, a laser efficiency value EV 1  is obtained by the following equation, 
 
 EV   1 =( P   2 − P   1 )/ IP   2   (1) 
 
 where P 2  is the second power intensity, P 1  is the first power intensity, and IP 2  is the second current value. 
 
      The laser efficiency value EV 1  is obtained by the above equation because the current value for driving the LD and the light-emitting power of the LD are directly proportional when the current value exceeds the threshold value “Ith” as shown in  FIG. 5 .  
      Next, the third current value IP 3  required to be supplied to the LD to emit a laser light beam at a power level of the third power intensity P 3  is determined by the following equation, 
 
 IP   3 =( P   3 − P   2 )/ EV   1   (2) 
 
 where P 3  is the third power intensity, P 2  is the second power intensity, and EV 1  is the laser efficiency value obtained by equation (1). 
 
      As described above, the first power intensity P 1 , the second power intensity P 2 , and the third power intensity P 3  are preset as target power intensity values. On the other hand, the second current value IP 2  varies by being subjected to the automatic power control (APC). The value of the third power intensity P 3  is maintained by adjusting the third current value IP 3  based on the varied second current value IP 2 .  
      Before recording information data into an optical disk, a so-called optimum power control (OPC) needs to be performed to determine an optimum intensity value of a recording power of a laser light beam. Such an OPC needs to be performed because an optimum intensity value of a recording power of a laser light beam varies depending on factors, such as a recording sensitivity of an optical disk, a laser wavelength, a recording wavelength, and a temperature.  
       FIG. 6A  is a diagram showing a cross section taken along a radial direction of an optical disk.  FIG. 6B  is a diagram showing a test area and a count area in a power calibration area. As shown in  FIG. 6A , the optical disk includes a power calibration area (PCA) where the OPC is performed, and a data area. The PCA is a test recording area used for determining an optimum intensity value of a recording power of a laser light beam. The data area is used for recording various data. The power calibration area is located on the inner radius side, and includes a test area and a count area as shown in  FIG. 6B . The test area includes 100 partitions. Each of these partitions includes 15 frames. A frame is a minimum unit of the recording area on the optical disk.  
      When performing the OPC, a non-recorded partition in the test area is searched. Test data i s recorded on 15 frames of the partition by variously changing an intensity value of a recording power of a laser light beam step by step from a minimum intensity value to a maximum intensity value (e.g., up to 15 intensity values). The intensity value of the recording power of the laser light beam that provides a highest recording quality is detected by reproducing the recorded test data, and is determined to be an optimum intensity value of a recording power of a laser light beam.  
      The count area includes 100 partitions. Each of these partitions includes one frame. Each partition in the count area corresponds to a respective partition in the test area. When a partition in the test area is used, data is recorded in the corresponding partition in the count area and is used for searching a test recording start position of the test area.  
      In a method of calculating a peak power (e.g., the third power intensity P 3 ) from an erase power (e.g., the second power intensity P 2 ), if a signal output from a PD has a high noise and fluctuations, the signal sampled and held by a sample-hold circuit also has a noise and fluctuations. In this condition, the voltage value input to a comparator has various levels. As a result, the second current value IP 2  may be set to, for example, three values or four values even though the temperature of the LD does not vary. Further, the third power intensity P 3  is determined from the three values or four values of the second power intensity P 2 . As the third power intensity P 3  as a peak power is greater than the second power intensity P 2  as an erase power by about two times, fluctuations of the emitted laser light beam of the third power intensity P 3  increase two fold. The fluctuations of the peak power directly exert a negative in fluence on recording quality.  
      In the OPC according to the embodiment of the present invention, test data is recorded on 15 frames of the partition of the test area by variously changing respective intensity values of the laser light beam of the third power intensity P 3  and the laser light beam of the second power intensity P 2 . The emitted laser light beam of the second power intensity P 2  is subjected to the APC in each frame of the partition of the test area and is controlled at a constant level in the APC. In the OPC, a period for recording test data on the test area with respective predetermined intensity values of the laser light beam of the third power intensity P 3  and the laser light beam of the second power intensity P 2  is very short as compared to a case in which actual information data is recorded on the data area. For example, immediately after the laser light beam of the second power intensity P 2  is subjected to the APC and its power intensity value becomes constant in one of 15 frames of a partition of the test area, test data is recorded on another frame of the partition of the test area with respective changed intensity values of the laser light beam of the third power intensity P 3  and the laser light beam of the second power intensity P 2 .  
      As described above, in the laser controller  10  of the present embodiment, if the second current value IP 2  fluctuates, the third current value IP 3  fluctuates accordingly. Further, if the second power intensity P 2  fluctuates between, for example, three values or four values, the third power intensity P 3  also fluctuates between three values or four values. If the above-described OPC is performed in the condition that the laser light beam of the third power intensity P 3  and the laser light beam of the second power intensity P 2  fluctuate, an optimum intensity value of a recording power of a laser light beam cannot be adequately determined. Further, in this condition, if the OPC is performed in the same optical disk under the same condition (e.g., a recording speed), an optimum intensity value of a recording power determined by the OPC varies. Therefore, in the optical information recording and reproducing apparatus according to the embodiment of the present invention, the light-emitting power of the laser light beam emitted from the LD needs to be prevented from fluctuating to determine an optimum intensity value of a recording power in an OPC operation for a CD-RW disk.  
      As shown in  FIG. 2 , the circuit of the laser controller  10  is divided into two sections, that is, an auto power control (APC) section  20  and an LD driver section  30 . The LD driver section  30  functions as a laser diode drive mechanism that drives the LD by supplying current to the LD. The APC section  20  functions as a power intensity adjusting mechanism that adjusts a power intensity of a laser light beam emitted from the LD based on a light-emitting power of a laser light beam detected by the PD by changing a value of the current supplied to the LD by the LD driver section  30 .  
       FIG. 7  is a block diagram of a configuration of an optical information recording and reproducing apparatus according to an embodiment of the present invention. As a non-limiting example of an optical information recording and reproducing apparatus, a description will be made of a CD-RW drive that records and reproduces information data into and from a CD-RW (CD rewritable) disk. The CD-RW disk is a recordable compact disk, into which information data can be recorded a plurality of times.  
      The optical information recording and reproducing apparatus  100  includes a spindle motor  101 , a motor driver  102 , a servo  103 , an optical pick-up  104 , a read amplifier  105 , a CD decoder  106 , a buffer manager  107 , a buffer RAM  108 , an interface (I/F)  109  such as an ATAPI/SCSI, a D/A converter  110 , an ATIP decoder  111 , a CD encoder  112 , a CD-ROM encoder  113 , a laser controller  114 , a CD-ROM decoder  115 , a ROM  116 , a RAM  117 , and a CPU  118  including a register  118   a . A reference symbol “L” in  FIG. 7  indicates a laser light beam. In this embodiment, the laser controller  114  corresponds to the laser controller  10  of  FIG. 2  and performs a method of determining a value of current supplied to a laser light source of the present invention (described below) in accordance with the instruction of the CPU  118 . The control signals at the respective switches in the laser controller  10  of  FIG. 2 , such as the first sample signal, the second sample signal, the LD ON signal, the first write pulse superimposed signal, and the second write pulse superimposed signal, are output from the CD encoder  112 . In  FIG. 7 , arrows indicate the direction of data flow. To simplify the diagram, a detailed connection relation between the CPU  118  and each block controlled by the CPU  118  is not shown in  FIG. 7 .  
      Next, an operation of the optical information recording and reproducing apparatus  100  is now described. An optical disk  200 , such as a CD-RW disk, is rotated by the spindle motor  101 . The spindle motor  101  is controlled, by the motor driver  102  and the servo  103 , such that the optical disk  200  rotates at a constant velocity. The optical pick-up  104  includes an LD, an optical system such as lens, a focus actuator, a track actuator, a photo detector, and a position sensor (all of which are not shown). The focus actuator is configured to move the position of an objective lens in a direction orthogonal to a surface of the optical disk  200  such that a laser light beam comes into a focus on the optical disk  200 . The track actuator is configured to move the objective lens in a sledge direction (i.e., a radial direction of the optical disk  200 ) such that a focal point of a laser light beam traces track grooves. The optical pick-up  104  emits a laser light beam “L” to the recording surface of the optical disk  200 . The optical pick-up  104  is configured to be moved along a sledge direction by a seek motor (not shown). The focus actuator, the track actuator, and the seek motor are controlled to locate a light spot of the laser light beam “L” at a desired position on the optical disk  200  by using the motor driver  102  and the servo  103  based on signals from the photo detector and the position sensor of the optical pick-up  104 .  
      When reproducing data, a reproducing signal obtained from the optical pick-up  104  is amplified by the read amplifier  105  to convert into binary data. The binary data is input to the CD decoder  106 , where de-interleave and error correction are carried out. The CD decoder  106  performs an Eight to Fourteen bit Modulation (EFM) to decode the binary data into decoded data. Recorded data in the optical disk  200  are modulated in EFM that is summed up 8 bits at a time. It is converted 8 bits to 14 bits and then to 17 bits by adding 3 coupling bits in an EFM process.  
      Decoded data is de-interleaved and error-corrected. Subsequently, the data is input to the CD-ROM decoder  115  and subjected to an additional error-correction to improve data reliability. Then, the data is stored in the buffer RAM  108  once by the buffer manager  107 . If the stored data gets into sector datum, the sector datum is transferred to a host computer through the interface  109  as a sector datum unit. In the case of audio data, data output from the CD decoder  106  is input to the D/A converter  110  and is output as analog audio output signals.  
      When recording data, data is transferred from the host computer to the optical information recording and reproducing apparatus through the interface  109  and the data is stored in the buffer RAM  108  once by the buffer manager  107 . A writing process is started by storing a certain level of data in the buffer RAM  108 . Before writing data on the optical disk  200 , the laser spot needs to be set in a write start position. This position is searched with a wobble signal formed on the optical disk  200  as track grooves.  
      The wobble signal contains information on absolute time referred to as Absolute Time In Pre-groove (ATIP) The information on absolute time is obtained from the ATIP decoder  111 . A synchronization signal generated by the ATIP decoder  111  is input to the CD encoder  112 , and this signal makes it possible to write data into an accurate position on the optical disk  200 . Error-correction codes are added to the data in the buffer RAM  108 , and the data is interleaved in the CD-ROM encoder  113  and the CD encoder  112 , before data is written in the optical disk  200  through the laser controller  114  and the optical pick-up  104 .  
      Next, an operation for determining a value of current supplied to a laser light source (hereafter referred to as a “current value determining operation”) performed by the CPU  118  in the optical information recording and reproducing apparatus will be described referring to  FIG. 8 .  FIG. 8  is a flowchart of current value determining operation steps of the CPU  118  according to the embodiment of the present invention. First, the CPU  118  determines a test recording start position of a test area of a power calibration area (PCA) where an OPC operation is to be performed by analyzing a count area of the PCA in step S 101 . As described above, when a partition in a test area is used in an OPC operation, data is recorded in the corresponding partition in a count area and is used for searching a test recording start position of the test area.  
      Then, in step S 102 , the CPU  118  causes the LD to emit a laser light beam of predetermined power intensity (hereafter referred to as a “DC erase power”) continuously to the determined partition of the test area at a constant power intensity value before performing the OPC operation. If the intensity of the DC erase power is too high, a characteristic of an optical disk typically changes. Consequently, a recording operation and an erase operation may not be performed properly relative to the optical disk. If the intensity of the DC erase power is too low, there is a substantial difference between the intensity of a recording power in an OPC operation and the intensity of the DC erase power. Consequently, the temperature of the LD when emitting the laser light beam of the DC erase power is substantially different from the temperature of the LD in an OPC operation, so that the laser efficiency value of the LD obtained when emitting the laser light beam of the DC erase power (described below) may be different from the laser efficiency value of the LD in the OPC operation. For these reasons, the intensity of the DC erase power is preferably set to be greater than the first power intensity (P 1 ) and less than the third power intensity (P 3 ). As a non-limiting example, the LD emits the laser light beam of the DC erase power when supplying a current value (IP 1 +IP 2   a ) to the LD. The current value IP 2   a  (i.e., the voltage value set at the second D/A converter  28 ) is the output current of the second current amplifier  34 , and is added to the first current value IP 1  which is the output current of the first current amplifier  33 .  
      Next, in step S 103 , during a period in which the laser light beam of the DC erase power is continuously emitted to the determined partition of the test area at a constant power intensity value, a plurality of (for example, “Y” number) current values IP 2   a  supplied to the LD are obtained as sample values based on the instruction of the CPU  118  to the D/A converter  28 . Particularly, the “Y” number of current values IP 2   a  are all stabilized current values IP 2   a , and do not include a “X” number of non-stabilized current values IP 2   a  supplied to the LD immediately after the start of emission of the laser light beam of the DC erase power from the LD. Such a “X” number of non-stabilized current values IP 2   a  is preferably preset based on results of experiments. By excluding the “X” number of non-stabilized current values IP 2   a  supplied to the LD immediately after the start of emission of the laser light beam of the DC erase power from the LD, a laser efficiency value of the LD (described below) can be obtained with accuracy. The “Y” number of the current values IP 2   a  obtained by the CPU  118  are stored in the register  118   a.    
      Subsequently, in step S 104 , the CPU  118  obtains an average current value “Z” of the “Y” number of the current values IP 2   a  obtained in step S 103 . If the “Y” number of current values IP 2   a  obtained in step S 103  is relatively great, an overflow error typically occurs. Consequently, the average current value “Z” of the “Y” number of the current values IP 2   a  may not be obtained properly. If the “Y” number of current values IP 2   a  is relatively small, fluctuations of the current values IP 2   a  may not be leveled out properly.  
      Next, in step S 105 , the CPU  118  determines whether the average current value “Z” is less than a threshold value “Zth”. If the answer is YES in step S 105 , the CPU  118  decreases a maximum value of current supplied to the LD according to the average current value “Z” in step S 106 . For example, assuming that the DC erase power of the laser light beam is 10 mW, the value of the second D/A converter  28  set by the CPU  118  for outputting the current value IP 2   a  is set to 100 Least Significant Bits (LSB). Further, in a subsequent OPC operation and a recording period after the OPC operation, the value of the third D/A converter  29  set by the CPU  118  for outputting the current value IP 3  is assumed to be at most 200 LSB based on design calculation and experimental results so long as the LD is not deteriorated.  
      If the maximum value of the third D/A converter  29  set for outputting the current value IP 3  is 400 LSB and if the maximum value of current (IP 3 ) supplied to the LD is 400 mA, the third D/A converter  29  has a ratio of 1 mA/LSB. However, as described above, because the value of the third D/A converter  29  set for outputting the current value IP 3  is assumed to be at most 200 LSB (=200 mA), the maximum value of current (IP 3 ) supplied to the LD can be reduced to 200 mA. Consequently, the third D/A converter  29  has a ratio of 200 mA/400 LSB, that is, 0.5 mA/LSB, and the resolution of the third D/A converter  29  can be enhanced (higher). At the same time, the maximum value of the first D/A converter  27  set for outputting the current value IP 1  and the maximum value of the second D/A converter  28  set for outputting the current value IP 2  are reduced equally. Thus, each resolution of the first D/A converter  27  and the second D/A converter  28  is similarly enhanced. By enhancing the resolution of the second D/A converter  28  and the resolution of the third D/A converter  29 , each fluctuation amount (width of 1 LSB) of the second current value IP 2  and the third current value IP 3  can be reduced. Thus, a recording quality can be enhanced. The above-described threshold value “Zth” in step S 105  is an assumed value of the current value IP 2   a  calculated from the assumed current value IP 3 .  
      If the average current value “Z” is greater than or equal to the threshold value “Zth” (e.g., the answer is NO in step S 105 ), the CPU  118  obtains a laser efficiency value EV 2 , that is, a ratio between a current value and a light-emitting power, by the following equation in step S 107 , 
 
 EV   2 =( Per−P   1 )/ Z   (3) 
          where Per is the DC erase power intensity, P 1  is the first power intensity, and Z is the average current value of the “Y” number of the current values IP 2   a.          

      Further, the CPU  118  determines the third current value IP 3  required to be supplied to the LD to emit a laser light beam at a power level of the third power intensity P 3  in an OPC operation by the following equation in step S 108 , 
 
 IP   3 =( P   3 − P   2 )/ EV   2   (4) 
          where P 3  is the third power intensity, P 2  is the second power intensity, and EV 2  is the laser efficiency value obtained by equation (3).        

      Further, the CPU  118  determines the second current value IP 2  required to be supplied to the LD to emit a laser light beam at a power level of the second power intensity P 2  at the start of recording test data in an OPC operation by the following equation in step S 109 , 
 
 IP   2 =( P   2 − P   1 )/ EV 2  (5) 
          where P 2  is the second power intensity, P 1  is the first power intensity, and EV 2  is the laser efficiency value obtained by equation (3).        

      Subsequently, the CPU  118  performs an OPC operation by supplying the third current value IP 3  determined by equation (4) and the second current value IP 2  determined by equation (5) to the LD in step S 110  and by variously changing respective intensity values of the laser light beam of the third power intensity P 3  and the laser light beam of the second power intensity P 2 .  
      In the above-described current value determining operation, a plurality (i.e., “Y” number) of the current values IP 2   a  are obtained during a period in which the LD emits a laser light beam of DC erase power continuously to the determined partition of the test area at a constant power intensity value before performing the OPC operation. Further, an average current value “Z” of the “Y” number of the current values IP 2   a  is obtained, and thereby fluctuations of the current values IP 2   a  can be leveled out properly. As compared to a case in which the third current value IP 3  is determined based on the laser efficiency value EV 1  obtained from the fluctuated second current value IP 2  (see equations (1) and (2)), the third current value IP 3 , which is determined based on the laser efficiency value EV 2  obtained from the average current value Z, is prevented from fluctuating significantly in the OPC operation. Therefore, in the optical information recording and reproducing apparatus according to the embodiment of the present invention, even if the second current value IP 2  fluctuates in the OPC operation, fluctuations of a peak power (i.e., the third power intensity P 3 ) are avoided in the OPC operation. As a result, a recording quality in the OPC operation is enhanced, and thereby an optimum intensity value of a recording power of a laser light beam is adequately determined.  
      In the above-described step S 109 , the CPU  118  determines the second current value IP 2  required to be supplied to the LD to emit a laser light beam at a power level of the second power intensity P 2  at the start of recording test data in an OPC operation by equation (5). In an OPC operation, respective intensity values of the laser light beam of the third power intensity P 3  and the laser light beam of the second power intensity P 2  are variously changed. As shown in  FIG. 4 , after the start of recording, the second power intensity P 2  increases step by step, and it takes some time to keep the second power intensity P 2  at a constant level after the start of recording. Therefore, by determining the second current value IP 2  that is a stabilized value and used for emitting a laser light beam at a power level of the second power intensity P 2  at the start of recording test data in an OPC operation in step S 109 , the degradation of recording quality immediately after the start of recording test data in an OPC operation can be prevented.  
       FIG. 9  is a block diagram of a configuration of an information processing system including the above-described optical information recording and reproducing apparatus of  FIG. 7 . In the information processing system, the above-described operation for determining a value of current supplied to the LD is performed by using software based on a computer program. The information processing system includes an interface (I/F)  41 , a CPU  42 , a ROM  43 , a RAM  44 , a display device  45 , a storage device  46  such as a Hard Disk, an input device  47 , and the optical information recording and reproducing apparatus  100 . The input device  47  may be at least one of various input media, such as a keyboard, a mouse, and/or a pointing device, etc. The input device  47  notifies the CPU  42  of various types of information input by an operator. The display device  45  may include a Cathode-Ray Tube (CRT), a Liquid Crystal Display (LCD) and a Plasma Display Panel (PDP), etc. The display device  45  displays various types of information from the CPU  42 .  
      A computer program is stored in the storage device  46 . The computer program may be downloaded from a communication network such as the Internet via the interface  41  and installed in the storage device  46 . Then, the computer program stored in the storage device  46  is installed as a firmware in the ROM  116  such as an electrically erasable programmable ROM (EEPROM) and a flash memory. The CPU  118  starts computer program automatically or when a control signal is input to the information processing system from an external device through the interface  41 . Alternatively, the CPU  118  starts computer program in accordance with an instruction input by an operator through the input device  47 . The CPU  118  shown in  FIG. 7  performs processing with respect to the above-described operation for determining a value of current supplied to the LD based on the computer program. The CPU  118  stores a process result in the RAM  44  and the storage device  46 , and causes the process result to display on the display device  45  if necessary.  
      The present invention has been described with respect to the exemplary embodiments illustrated in the figures. However, the present invention is not limited to these embodiments and may be practiced otherwise.  
      As an alternative to the CD-RW drive, the optical information recording and reproducing apparatus  100  may be a DVD-RW drive and a DVD+RW drive. Further, the optical disk  200  may be a DVD-RW disk and a DVD+RW disk in place of the CD-RW disk.  
      Numerous additional modifications and variations of the present invention are possible in light of the above teachings. It is therefore understood that within the scope of the appended claims, the present invention may be practiced other than as specifically described herein.