JPH11354893A - Semiconductor laser driver and driving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To drive a multilevel semiconductor laser current stably with high accuracy at high speed by keeping a voltage being applied to the output section of a semiconductor laser driver at a constant level and setting the power supply voltage to minimize a voltage being applied to the output section within the operable range of the driver. SOLUTION: When a drive current is drawn out from the cathode side of a semiconductor laser 4, a voltage detecting section 21 detects the collector voltage of a transistor 18 at the output section of a laser driver. Output signal from the voltage detecting section 21 is the voltage comparion section 22 and compared with the voltage of a reference voltage supply 23 and comparison result is fed back to a power supply transistor 24 in order to control the collector voltage of the transistor 18 at a constant level during recording, erasing and reproducing operations. When the collector voltage of the transistor 18 is set at a minimum operable level, i.e., a minimum level causing no bottoming saturation, generation of heat in the laser drive current output section can be kept at a minimum level.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the control of a semiconductor laser mounted on an optical pickup of an optical disk device.

[0002]

2. Description of the Related Art An optical disk device emits a semiconductor laser mounted on an optical pickup, condenses weak reproduction light on the disk at the time of reproduction, and reflects the reflectance, phase difference, and deflection of pits recorded on the disk. Detect and read corners, etc.
At the time of recording, the semiconductor laser emits light at a higher power than at the time of reproduction, the laser power is modulated according to the information to be recorded, and the data is recorded on the disk. I do.

For example, in the case of recording on a phase change type optical disk, basically, two values of peak power and bias power are switched, a mark is recorded in a peak power portion, and a recording mark is erased in a bias power portion. .

However, in practice, binary switching is not enough to form a stable recording mark.
As shown in the above, laser power switching of two or more values is required for the purpose of equalizing the amount of heat applied to a mark to be recorded and for adjusting the heat balance at the start and end of the mark.

In recent years, the speed of recording / reproducing of an optical disk has also been increased, and the switching operation of the semiconductor laser requires higher speed.

When the recording pulse shown in FIG. 1 is to be realized at the time of high-speed recording and the pulse waveform of the semiconductor laser is not sufficiently increased, the laser power reaches a desired peak value as shown in FIG. Without this, a heat amount imbalance to the recording mark occurs, and the recording mark is distorted.

In PWM recording having information at the leading and trailing edges of a recording mark, it is necessary to precisely control the edge position of the recording mark. Have been.

[0008]

In a conventional system in which an optical pickup having a semiconductor laser mounted thereon and a semiconductor laser driving device are separated, the driving current of the semiconductor laser is usually transmitted through a flexible cable or the like. In this case, the switching characteristics of the drive current deteriorate due to the distribution constants such as the parasitic capacitance of the flexible cable.

That is, the deterioration of the switching characteristics becomes an adverse effect when the speed of the optical disk device is increased.

The present invention relates to an improvement over the above-mentioned adverse effects, and to power saving for solving the problem of heat concentration caused by the improvement.

FIG. 3 is a graph showing the relationship between a capacitance component parasitic on a conductor between a semiconductor laser and a drive device of an optical disk device and the rise time Tr and fall time Tf of a semiconductor laser drive current when the semiconductor laser is switched in a pulse shape. Show the relationship.

Focusing on the above-mentioned capacitance component, as the capacitance component increases, the high-frequency component of the transmitted pulse current is bypassed through the capacitor before being transmitted to the semiconductor laser, and the rising edge of the drive pulse waveform of the semiconductor laser is increased. Time T
r, the fall time Tf increases. That is, the recording pulse approaches a dull recording pulse as shown in FIG.

If a pulse of the highest frequency f1 is required in the semiconductor laser driving pulse, the minimum pulse width is 0.5 / f1. Therefore, the condition that the amplitude of the driving pulse does not decrease in the pulse of the frequency f1 is Tr <0.5 × 0.5 / f1, and Tf <0.5 × 0.5 / f1 (Equation 1).

For example, in order to realize pulse switching at a maximum frequency of 60 MHz, it is required from Equation 1 that both Tr and Tf are 4.16 ns or less.

From the experimental results shown in FIG. 3, Tr, Tf <
To realize 4.16 ns, the parasitic capacitance component must be 10p
It can be said that F or less is required. In order to satisfy this condition, it is necessary to make the distance between the semiconductor laser and the laser driver close to each other within 5 cm.

Therefore, in order to achieve high-speed laser switching, the distribution constant between the laser driving device and the semiconductor laser,
For the purpose of mainly reducing the capacitance component, it is necessary to bring the laser driver close to the semiconductor laser, that is, mount the laser driver on an optical pickup in which the semiconductor laser is incorporated. Alternatively, it is necessary to attach a laser driving device to the same movable portion as the optical pickup. However, a problem in this case is a problem of heat generated from the semiconductor laser and the laser driving device.

At the time of recording data on the optical disk, the semiconductor laser drive current Iop reaches several hundred mA, and the voltage applied to the output of the drive device is Vd, and the proportionality constant is K1, and the temperature rises by Td = K1 × Vd × Iop Is generated in the driving device.

As described above, since the laser driving device and the semiconductor laser need to be arranged close to each other in order to reduce the influence of the distribution constant such as parasitic capacitance, the heat generated by the driving device is also transmitted to the semiconductor laser.

The driving characteristics of the semiconductor laser greatly differ depending on the temperature. As the temperature increases, the relation (differential efficiency) of the laser emission power P with respect to the driving current Iop deteriorates, and a larger driving current Iop is required. Accelerate the temperature rise of the device.

The semiconductor laser itself is a heat source. The operating voltage of the semiconductor laser is Vop, and the proportional constant is K2.
Then, the temperature rises as follows: Tld = K2 × Vop × Iop (Equation 3) That is, assuming that the conductivity of heat from the drive circuit to the semiconductor laser is K3, the temperature rise of the semiconductor laser is represented by Tld = K2 × Vop × Iop + K3 × K1 × Vd × Iop (Equation 4).

[0021]

As means for solving the above problems, suppression of the drive current Iop, suppression of the proportional constants K1 and K2, suppression of the thermal conductivity K3, voltage Vd applied to the output of the drive unit,
Vld can be suppressed.

Iop is a characteristic inherent to a semiconductor laser.
The proportional constants K1, K2, and K3 depend on the optical pickup configuration and thermal design. Vop also varies with the drive current Iop, but the amount of variation is determined by the diode voltage and the internal series resistance, and is basically a value unique to the semiconductor laser.

Accordingly, by suppressing the voltage Vd applied to the output section of the laser driving device, the heat generation of the optical head section is suppressed.

In order to suppress Vd, a power supply for controlling the voltage supplied to the output of the laser driving device is provided, the voltage of the output of the laser driving device is monitored, compared with a reference voltage, and the difference is fed back to the power supply. By doing so, control is performed so that Vd can always maintain a constant value, and further, the voltage of the power supply unit is set so that Vd becomes the minimum value within the drive operable range of the laser driver output unit.

The power supply section is installed at a place other than the optical pickup on which the semiconductor laser and the semiconductor laser driving device are mounted. That is, the surplus heat generating portion is isolated at a place not thermally related to the semiconductor laser portion.

Further, even if the power supply voltage of the optical disk device fluctuates due to fluctuations in the AC line voltage, fluctuations in the load, and other variations, the voltage Vd of the output section of the semiconductor laser driving device is always maintained.
Is kept constant, and the heat generated in the optical pickup is not related to these fluctuations.

In this way, by keeping the voltage Vd applied to the output portion of the laser driving device at the minimum operable voltage, the heat generation in the optical pickup portion can always be controlled to the minimum state.
As a result, stable high-speed semiconductor laser driving can be realized.

[0028]

Embodiments of the present invention will be described below.

FIG. 4 shows a system configuration diagram of the optical disk recording / reproducing apparatus. The rotation of the optical disc 1 is controlled in a fixed direction by a spindle motor 2. 3 is an optical disk 1
An optical pickup for recording and reproducing data.

FIG. 5 is a structural view of the optical pickup 3 and includes a laser driving device. The semiconductor laser 4 outputs a laser beam a by a driving current Iop supplied from a laser driving device 5. Laser light a output from the semiconductor laser 4 is converted into parallel light by a collimator lens 6, passes through a beam splitter 7, and is incident on an objective lens 8. The laser light is focused by the objective lens 8 and the focused spot is focused on the data recording surface of the optical disc 1.

The laser light reflected on the recording surface is again converted into parallel light by the objective lens 8, the optical path is changed by the beam splitter 7, and the laser light is focused on the photodetector 9.

The optical disk 1 is controlled by the photodetector 9.
Is converted into an electric signal and input to the servo block 10 of FIG. Focus control and tracking control are performed according to an electric signal of the photodetector 9.

4, 5, ie, the focus signal +, the focus signal −, the tracking signal +, and the tracking signal − are input to the servo block 10. In the servo block, a focus error signal is generated from the focus signal + and the focus signal-, and a tracking error signal is generated from the tracking signal + and the tracking signal-.

The focus error signal and the tracking error signal are current-amplified and the actuator 1 of the optical pickup 3
1, and the position of the light emitted from the optical pickup 3 is controlled so as to be focused on the recording surface of the optical disk 1.

The focus signals b and c and the tracking signals d and e output from the photodetector 9 are simultaneously input to the reproduction signal processing block 12, and the high-frequency signal components in the signals are recorded as pits on the optical disk. Detected as information data.

The recording signal processing block 13 modulates the external input data for the optical disk and converts the format, and controls the laser power and timing as described later.

The main control block 14 is composed of the reproduction signal processing block 13 and the recording signal processing block 12 described above.
Is controlling.

FIG. 6 shows, as an example, the power of a semiconductor laser and the recording marks when recording marks on a phase-change optical disk. The peak power 1 (PEAK1) and the peak power 2 (PEAK2) are powers for forming a recording mark on the optical disc 1. Bias power 1
(BIAS1) is the power for erasing the mark recorded on the base. Bias power 2 (BIAS2) is power for reducing the heat accumulation of the mark.

The reproduction power (READ) is always turned on for an area where no recording is performed.

That is, in this example, it means that quinary laser power setting is required for recording and reproducing data on the optical disk.

FIG. 7 shows a configuration diagram of a semiconductor laser driving device. Reproduction power setting current input (IINRD),
Peak power 1 setting current input (IINPK1), peak power 2 setting current input (IINPK2), bias power 1 setting current input (IINBS1), bias power 2
The set current input (IINBS2) is input from the recording signal processing block 13 to the current input buffer unit 15.

The power setting signal takes the form of a current input so that the impedance of the transmission line can be reduced and the influence of noise on a long transmission line such as a flexible cable is minimized. Note that the above IINRD, IINPK1, II
The current input of NPK2, IINBS1, and IINBS2 can take a voltage input form instead of an absolute condition.

The timing signals are a reproduction power timing signal (RDMD) and a peak power 1 timing signal (PK
1MD +, PK1MD-), a peak power 2 timing signal (PK2MD +, PK2MD-), a bias power 1 timing signal (BS1MD +, BS1MD-), and a bias power 2 timing signal (BS2MD).

The power timing signal functions as an enable signal for the power setting current input to the current buffer unit 15 in the current driver.

FIG. 8 shows switching timings of timing signals for realizing the laser emission shown in FIG. The reproduction power timing signal RDMD is always in the active state during the reproduction power emission time, and the bias power 2 timing signal BS2MD is also always in the active state in the recording or erasing area, so that the switching speed does not require much high speed. Therefore, in this example, the two timing signals are input to the single-ended logic input unit 16 using a single-ended timing transmission method.

In FIG. 8, BS2MD is in an active state at L level. Peak power 1 timing signal PK1MD, Peak power 2 timing signal PK2M
D, bias power 1 timing signal BS1MD is shown in FIG.
As shown by, this is a timing signal that requires high-speed switching when forming a recording mark, takes a differential form, and is input to the differential logic input unit shown in FIG. The signals after the operation of the differential input control signal are defined as follows.

PK1MD = (PK1MD +) − (PK1MD−) (Equation 5) PK2MD = (PK2MD +) − (PK2MD−) (Equation 6) BS1MD = (BS1MD +) − (BS1MD−) (Equation 7) PK1MD in FIG. For example, when PK1MD + is at H level and PK1MD- is at L level, the active state is set. For differential data transmission, it is possible to cancel the ingress noise component even on a long transmission line such as a flexible cable. In addition, since the cross point between the positive logic input and the negative logic input is the edge position of the calculation result, even if the duty changes due to voltage fluctuation or noise, it affects the duty after the final difference calculation. Less things.

In an optical disk recording method employing PWM recording having information on the length of a recording mark, the duty preservability of recording pulses is extremely important.

Under the above definition, the relationship between each control line and Iop is as follows. Iop = G × (RDMD × IINRD + PK1MD × IINPK1 + PK2MD × IINPK2 + BS1MD × IINBS1 + BS2MD × IINBS2) (Equation 8) G is the gain of the current driver shown at 18 in FIG.

As described above, for the recording and erasing operations which require high-speed control timing, the timing signal is of a two-signal differential type, and the accuracy is improved by increasing the noise strength. A drive signal is created by using an addition method, and in order to handle and process each element current of a smaller and smaller level dispersed until finally adding and combining, the amount of heat generated in the buffer units 15, 16, and 17 and the switching characteristics are determined. This is advantageous.

FIGS. 9 and 10 are simplified diagrams of the configuration of the output section 18 of the semiconductor laser current driver.

FIG. 9 shows a method of supplying a drive current Iop in a direction of drawing from the cathode side of the semiconductor laser 4, and FIG. 10 shows a method of supplying a drive current Iop in a direction of flowing from the anode side of the semiconductor laser 4.

The laser drive current Iop is on the order of several hundred mA, and most of the power consumed on the optical pickup is due to the laser drive current Iop. The power consumption on the optical pickup 3 can be expressed by P = VCC × Iop (Equation 9). VCC is a power supply voltage, and V
When the CC varies in the largest direction, the power consumption becomes maximum. As shown in FIG. 9, the breakdown of VCC is the operating voltage Vop of the semiconductor laser 4 and the operating voltage Vd of the drive output unit 18.
And VCC = Vop + Vd (Equation 10). The VCC is generally transmitted from the main unit 19 via the flexible cable 20 as shown in FIG. 11, and a voltage drop on the flexible cable can be considered, but is omitted in this example for simplification. Note that the main unit 19 includes a reproduction signal processing block 12, a recording signal processing block 13, a control block, and the like.

The operating voltage Vop of the semiconductor laser 4 is not constant, but changes with the operating current Iop. Generally, the diode voltage Vld and the internal resistance Rs in the semiconductor laser
Then, Vop = Vld + Iop × Rs (Equation 11) is obtained. From the above, rewriting Expression 9 gives P = (Vop + Vd) × Iop (Expression 12) = (Vld + Iop × Rs + Vd) × Iop (Expression 13)

FIG. 12 shows the relationship between the output light power of the semiconductor laser 4 and the drive current Iop.

The semiconductor laser emits power in proportion to the drive current Iop with the gradient of the differential efficiency η with respect to the current equal to or higher than the threshold current Ith. The above characteristics of the semiconductor laser change depending on the use environment temperature and the deterioration of the element due to long-term use.

Ith1 and η1 are graphs showing the relationship between the output laser power and the driving current in the initial state of the use period at room temperature, respectively. When the temperature is high or after long-term use, the graphs show Ith2 and η2. And migrate. That is, the driving current value required to emit a constant laser power P1 is Iop1 in the former, and Iop2 in the latter (Iop1 <Iop1).
2). When the driving current Iop increases, the heat generation of the laser driving device 5 increases as shown in Expressions 2 to 4,
The temperature of the semiconductor laser 4 increases. If the temperature rises, it may lead to a vicious cycle in which a larger drive current Iop is required, and power saving on the optical pickup 3 is important.

From the equations (9) and (13), it is effective to reduce the drive current Iop to save the power of the optical head. However, the semiconductor laser drive current, temperature characteristics, and aging are highly dependent on the semiconductor laser element and can be controlled. difficult.

Therefore, the power can be saved by suppressing VCC according to Equation 9, that is, by suppressing the voltage Vd applied to the output portion of the laser driving device according to Equation 12.

FIGS. 13 and 14 show the circuit of the output section of the laser driving device incorporating the above power saving. FIG. 13 shows the driving current Iop from the cathode side of the semiconductor laser 4 shown in FIG.
The case of a laser driving method of a system for extracting The voltage detection unit 21 is a transistor 1 of the laser driving device output unit.
8 is detected.

The collector current of the transistor 18 is pulse-shaped at the time of recording, DC at the time of reproduction, and pulse-shaped or DC at the time of erasing. Therefore, as an example, the voltage detector 21 has a peak power 2 during recording,
It is appropriate to use a gate-type voltage detection device synchronized with a period in which the drive currents of the bias power 1 at the time of erasing and the read power at the time of reproduction are flowing.

The output signal of the voltage detector 21 is supplied to the voltage comparator 2
In step 2, the voltage is compared with the voltage of the reference voltage source 23, and the comparison result is fed back to the power supply transistor 24. In this example, the collector voltage of the transistor 18 is always controlled to a constant voltage during recording, erasing, and reproducing.

If the collector voltage of the transistor 18 is set to the minimum operable value, that is, the minimum value within a range where the bottoming does not saturate, the amount of heat generated in the laser drive current output unit can be kept to a minimum.

In the above description, the reference voltage source 23 has a constant voltage. However, the reference voltage source 23 can be switched to an optimum value for each of the recording, erasing, and reproducing modes.

FIG. 14 shows an example in which power saving is incorporated in a laser driving method of a method in which a driving current Iop flows from the anode side of the semiconductor laser 4 shown in FIG. As in the case of FIG. 13, the voltage detector 21 detects the collector voltage of the driving transistor 18, and the output of the voltage detector 21 is compared with the voltage of the reference voltage source 23 by the voltage comparator 22. Feedback to 24.

In FIG. 13, since the emitter voltage of the power supply section transistor 24 is the power supply voltage of the optical disk device, there is a variation, but the reference voltage source 23 is constituted by a source having a small voltage fluctuation such as a band gap. The collector voltage of the transistor 18 is stable against the fluctuation.

Collector voltage V of power supply transistor 24
The variation ΔPP in power consumption of the transistor 24 due to the variation ΔVCE in CE is as follows: ΔPP = ΔVCE × Iop (Equation 14). Therefore, the power supply transistor 24 is located at a location separated from the optical pickup, for example, the main unit 19 shown in FIG.
In this case, the heat source is driven from the optical pickup to the main unit even when the power supply voltage of the optical disk device fluctuates.

VCC shown in Equation 9 is the collector voltage of the power supply transistor 24. If the collector voltage is VC, P = Vc × Iop (Equation 15) On the other hand, since VC = Vop + Vd, P = (Vop + Vd) from Equation 14. ) × Iop (Equation 16) = (Vld + Iop × Rs + Vd) × Iop (Equation 17) Vop, Vld, and Rs are values inherent in the semiconductor laser 3 and do not change, so that the power consumption P of the optical pickup 3
It is also found that the power supply is not affected by the power supply fluctuation.

Further, by adjusting the voltage of the reference voltage source 23 so that the output voltage Vd of the laser driving device becomes the operable minimum value, the power consumption on the optical head can be reduced as is apparent from the equations (16) and (17). Is done.

[0070]

As described above, the laser driving device is arranged on the pickup in which the semiconductor laser is incorporated as in this embodiment, and the voltage Vd applied to the output portion of the laser driving device is adjusted to the minimum operable value. Heat generation on the pickup can be minimized, and multi-level semiconductor laser current driving can be stably, accurately, and speeded up. That is, higher-speed recording and reproduction can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a recording pulse waveform and a recording mark of an optical disk.

FIG. 2 is a diagram showing a waveform and an example of a recording mark when “rounding” occurs in a recording pulse and the amplitude decreases.

FIG. 3 is a diagram showing a relationship between a parasitic capacitance of a conductor between a semiconductor laser and a semiconductor laser driver, and a pulse waveform rising time Tr and a falling time Tf.

FIG. 4 is a configuration diagram of an optical disk system.

FIG. 5 is a configuration diagram of an optical pickup.

FIG. 6 is a diagram showing optical disk recording marks and semiconductor laser power correspondence.

FIG. 7 is a configuration diagram of a semiconductor laser driving device.

FIG. 8 is a diagram showing correspondence between a semiconductor laser power and a timing signal.

FIG. 9 is a configuration diagram of an output unit of a laser driving device.

FIG. 10 is a configuration diagram of an output unit of a laser driving device.

FIG. 11 is an optical head layout.

FIG. 12 is a diagram showing output power versus drive current of a semiconductor laser.

FIG. 13 is a configuration diagram of an output unit of a power saving laser driving device.

FIG. 14 is a configuration diagram of an output unit of a power saving laser driving device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical disk 2 Spindle motor 3 Optical pickup 4 Semiconductor laser 5 Laser drive device 6 Collimating lens 7 Beam splitter 8 Objective lens 9 Photodetector 10 Servo block 11 Actuator 12 Reproduction signal processing block 13 Recording signal processing block 14 Main control block 15 Current input buffer section Reference Signs List 16 Single-ended logic input unit 17 Differential logic input unit 18 Laser drive unit output unit 19 Main unit 20 Flexible cable 21 Voltage detection unit 22 Voltage comparison unit 23 Reference voltage source 24 Power supply unit transistor a Laser beam b Focus signal + c Focus signal − D tracking signal + e tracking signal −

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Naoyuki Nakamura 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. 72) Inventor Ikuo Hidaka 1006 Kadoma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (72) Inventor Kiyoshi Nakamori 1006 Odaka Kadoma Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (16)

[Claims] 1. A semiconductor laser driving device for reproducing data and recording data using an optical disk, wherein a maximum frequency f when the semiconductor laser is optically modulated in a pulsed manner.
(F> 0), the relationship between the rise time Ta (Ta> 0) and the fall time Tb (Tb> 0) of the optical modulation waveform is Ta <0.5 × 0.5 ÷ f, Tb <0. 0.5 × 0.5
A semiconductor laser driving device, wherein a distance L between the semiconductor laser driving device and the semiconductor laser is close to a condition of 5 cm>L> 0 so that Δf is satisfied. 2. The semiconductor laser driving device according to claim 1, wherein said semiconductor laser driving device is mounted on the same movable part as an optical pickup. 3. The semiconductor laser driving device according to claim 1, wherein the N laser power setting signal input units (N is a natural number), and the N switching timing signal input units for selecting the N-value laser power setting signals, respectively. A signal adding unit for adding P (P is a natural number equal to or less than N) laser power setting signals selected by the switching timing signal and the P laser power setting signals added by the signal adding unit. 3. The semiconductor laser driving device according to claim 2, further comprising: a current source for supplying a driving current to the semiconductor laser. 4. The semiconductor laser driving device according to claim 3, wherein said N laser power setting signals take a current input form. 5. The apparatus according to claim 3, wherein M (M is a natural number equal to or less than N) timing signal input sections of said N switching timing signal input means have a differential input form. Semiconductor laser drive. 6. A power supply unit and a voltage control unit of the power supply unit for comparing a voltage value applied to a semiconductor laser drive output unit of the semiconductor laser drive device with a reference value and controlling the voltage value to a constant value. 14. The semiconductor laser driving device according to claim 1. 7. The semiconductor device according to claim 6, wherein the power supply unit is controlled such that a voltage value applied to the output unit of the semiconductor laser driving device becomes a minimum value at which the output unit of the semiconductor laser driving device can operate. Laser drive. 8. The semiconductor laser driving device according to claim 6, wherein said power supply section is provided outside the same movable section as said optical pickup. 9. A semiconductor laser driving method for reproducing data and recording data using an optical disk, wherein the maximum frequency f when the semiconductor laser is optically modulated in a pulsed manner.
(F> 0), the relationship between the rise time Ta (Ta> 0) and the fall time Tb (Tb> 0) of the optical modulation waveform is Ta <0.5 × 0.5 ÷ f, Tb <0. 0.5 × 0.5
A method of driving a semiconductor laser, wherein a distance L between the semiconductor laser driving device and the semiconductor laser is close to a condition of 5 cm>L> 0 so that ÷ f. 10. The current driving method according to claim 9, wherein the current driving section of the semiconductor laser is mounted on the same movable section as the optical pickup like the semiconductor laser. 11. An N laser power setting signal (N is a natural number) is input by the current driving method, and the N laser power setting signals are selected by N switching timing signals. 11. The semiconductor laser driving method according to claim 10, wherein (where P is a natural number equal to or less than N) laser power setting signals are added, and a driving current corresponding to the added setting signal is supplied to the semiconductor laser. 12. The laser power driving method according to claim 11, wherein the N-level laser power setting signal is used as a current input. 13. The semiconductor laser driving method according to claim 11, wherein M (M is a natural number equal to or less than N) switching timing signals among the N switching timing signals are transmitted by differential signals. 14. The semiconductor laser drive output section monitors a voltage of the semiconductor laser drive output section, and controls a voltage of a power supply section for supplying a current to the semiconductor laser and the drive output section based on the observed value. 12. The semiconductor laser driving method according to claim 11, wherein the voltage is controlled to be constant. 15. The semiconductor laser driving method according to claim 14, wherein a supply voltage to said semiconductor laser drive output section is controlled to be a minimum value at which said drive output section can operate. 16. The power supply section is provided in a region outside the same movable section as the optical pickup, and supplies a current to a semiconductor laser and a semiconductor laser current drive section mounted on the same movable section as the optical pickup. The method for driving a semiconductor laser according to claim 14, wherein