JP2636488B2 - Laser drive - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser driving device for controlling a semiconductor laser of an optical disk device using a multi-beam semiconductor laser.

2. Description of the Related Art In recent years, a laser drive device has been used in an optical disc device.
It is an important element for performing recording and reproduction with high accuracy and stability, and various developments have been made. In particular, it has become important to respond to a high transfer rate of recording and reproduction in order to improve the performance of the optical disk device. One of the methods to solve this problem is to improve the performance by multi-track simultaneous recording and reproduction using a multi-beam semiconductor laser. Research on transfer rate is being conducted.

[For example, Earl. Katayama Etool “Multi-beam magnet-optical disk drive for parallel read / write operation” SPII (R. Katayama et. Al, “Muliti
−beam mabneto−optical disk drive for parall
el read / write operation "SPIE" Vol.1078, Optical Data Storage Tobi Meeting (Op
tical Data Storage Topical Meeting), pp.98-1
04, 1989] An example of a conventional laser driving device will be described below with reference to the drawings.

FIG. 4 shows an embodiment of a conventional laser driving apparatus, and FIG. 4 shows a driving apparatus for one element of a multi-beam semiconductor laser. In FIG. 4, reference numeral 1 denotes a semiconductor laser device, which is composed of a laser device and a monitor diode for detecting an optical output provided on the back surface thereof. 2
Is a current-voltage converter, which converts a monitor output current of the laser element 1 into a voltage. Reference numerals 3 and 4 denote subtracters. 5, 6 are amplifiers, 7, 8, 17 are switches, 9, 10 are resistors, 11,
Reference numeral 12 denotes a capacitor. 7, 9, 11, and 8, 10, and 12 constitute low-pass filtering / holding circuits 13 and 14. Reference numerals 15 and 16 denote current sources, and reference numeral 18 denotes a controller, which outputs gate signals G1, G2, and D1 for controlling the switches 7, 8, and 17 in accordance with the operation mode of the optical disk device and the recording data signal, and simultaneously refers to the optical output. Output signals REF1 and REF2.

The operation of the laser driving device configured as described above will be described below.

First, during reproduction of the optical disk device, the light output of the semiconductor laser is set to a specific low level, and the switch 17 is turned off,
The switch 7 is on, and the laser element 1 is driven by the current source 15. The current-voltage converter 2 converts a monitor output current obtained in proportion to the optical output into a voltage and outputs the voltage.
The subtractor 3 subtracts the output of the voltage-current converter 2 from the reference signal REF1 corresponding to Pr to a preset reproduction light output, and outputs an error signal. This error signal is amplified by an amplifier 5 and then low-pass filtered by a low-pass filter including a resistor 9 and a capacitor 11. The low-pass filtered error signal becomes a control signal for the current source 15, and as a result, the optical output of the laser element 1 is controlled so that the error signal becomes small. FIG. 6 shows the drive current versus light output characteristics of the laser element 1, and the read light output Pr requires a high power Pw during recording or erasing. When switching from reproduction to recording, first, the switch 17 is turned off, the switch 7 is kept on, and the reference signal REF1 is changed by the controller 18 to the bottom power Pb which is a lower value than during reproduction. The current value Ib of the current source 15 is set so that the light output becomes the low level Pb. After an appropriate time has elapsed, the switch 7 is turned off and the capacitor 11 operates as a hold capacitor, whereby the current value of the current source 15 is held. Subsequently, the switches 8 and 17 are turned on, and the recording power Pw given by REF2 is set by the control loop including the subtractor 4, the amplifier 6, the resistor 10, the capacitor 12, and the current source 16. After an appropriate time, the switch 8 is turned off, and the current value Iw of the current source 16 is held. Thus, the setting of the drive current is completed, and thereafter, the actual recording is performed. During the actual recording, the switch 17 is turned on and off according to the recording data signal, so that an optical output as shown in FIG. 5A is obtained. The operation at the time of erasing is the same as that at the time of recording except that the switches 17 and 8 are always on.
Recording and reproduction of signals are performed by a series of operations described above.

When the above laser driving apparatus is applied to a multi-beam semiconductor laser, the above-described circuits are provided according to the number of laser elements, and the driving current is set according to the characteristics of each laser element. FIG. 7 shows the drive current versus light output characteristics of the multi-beam laser.

However, when a multi-beam semiconductor laser is driven with the above-described configuration, the drive current versus light output characteristics of each laser element may be affected by the heat generated by the adjacent laser elements. In particular, when an adjacent laser element is in a high power state, a driving current required to obtain a predetermined optical output increases. If such thermal interference between neighboring laser elements cannot be ignored, the drive current required for each laser element to obtain a predetermined optical output is determined by the combination of the recording data signals that are the drive signals for the laser elements. However, there is a problem that the optical output cannot be controlled with high accuracy. (For example, Bessho, et al., “High-power four-beam semiconductor laser having current injection region near end face”, Optical Memory Symposium '90, Makuhari Messe, July 1990, pp. 41-42). Another object of the present invention is to provide a laser drive device that obtains a highly accurate and stable output by correcting a drive current of a laser element so as to cancel a change in characteristics due to thermal coupling between adjacent laser elements. It is another object of the present invention to provide a laser driving device for automatically setting the correction amount.

Means for Solving the Problems To solve the above problems, a laser driving device of the present invention is a driving device for driving a multi-beam semiconductor laser,
Comparing means for comparing the output of each laser element with a reference signal;
And an amplifying means for amplifying the error signal, and a control means for controlling the reference signal and the driving means in accordance with an operation mode of the optical disc apparatus and a recording data signal.

According to the present invention, the drive current of the laser element is adjusted according to the recording data signal which is the light emission instruction signal of the adjacent laser element.

Embodiment Hereinafter, a laser driving device according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of the laser driving device according to the embodiment of the present invention. FIG. 2 is a more specific configuration diagram, and FIG. 3 is an operation explanatory diagram. In FIG. 1, 19,
Reference numerals 20 and 21 denote laser elements, and reference numeral 22 denotes a three-beam semiconductor laser. In the figure, a current-voltage converter for converting a monitor current for detecting an optical output of a laser element into a voltage is omitted for simplicity. 23 to 25 are subtracters, and the comparing means 26
Is configured. Reference numerals 27 to 29 denote amplifiers, which constitute amplifying means 30. 31 to 33 are controllers, which together with the coefficient comparator 34 constitute control means 35. Reference numerals 36 to 38 denote current sources, which constitute driving means 39. In FIG. 2, reference numerals 40 to 42 denote current-voltage converters, 43 to 48 denote subtracters, 49 to 54 denote amplifiers, and 55 to 63 denote low-pass filtering / holding circuits. 64 to 73 are current sources, 74 to 80 are switches, and 81 is a controller.

The operation of the laser driving device configured as described above will be described below with reference to FIGS.

FIG. 1 is a diagram showing the configuration of the present invention. During reproduction, each of the laser elements 19, 20, and
21 is controlled by the comparing means 26, the amplifying means 30, and the control means 35 so that the current sources 36, 37, 38 of the driving means 39 become the reproduction light output Pr. At this time, since each laser element emits DC light with a predetermined optical output Pr, interference due to thermal coupling between adjacent laser elements is constant, and has little effect on optical output control accuracy.

At the time of erasing, control is performed so that a predetermined erasing light output is obtained as in the case of reproduction. In this case, since each laser emits DC light, the accuracy of the optical output is not affected.

At the time of recording, first, the bottom power is set in the same manner as at the time of reproduction, and the drive current values Ib1 and Ib1 of the respective laser elements 19, 20, and 21 are set.
Ib2 and Ib3 are stored. Next, while driving each laser element other than the corresponding element to emit light at the recorded bottom power, the drive current value Iw1,
Record Iw2 and Iw3. Next, the elements 20 and 22 are controlled so as to have the recording power Pw, and the drive current values Is1 and Is2 which are different from the case where the above-mentioned operation is performed alone are recorded. Similarly, the differences Is3 and Is4 between the drive current values performed by the elements 19 and 20 are stored, and the setting of the drive current value is completed. When recording actual data, the elements 19, 20, 21
R1 = R2 = R3 for the recording data signals R1, R2, R3 for
When = 0, all lasers emit at bottom power,
When R1 = R2 = R3 = 1, element 19 is Iw1 + Is1, and element 20 is Iw2
+ Is2 + Is3, and the element 21 is driven by Iw3 + Is4. Similarly, R1 =
1, when R2 = R3 = 0, the element 19 is Iw1, R1 = R2 = 1, R
When 3 = 0, element 19 is Iw1 + Is1, and element 20 is Iw2 + Is2
To emit light. Hereinafter, driving will be performed according to this.

FIG. 2 shows a more specific configuration of FIG. 1, and FIG. 3 is an explanatory diagram of its operation.

In FIG. 2, the switches 64 to 73 are off during reproduction, and the drive current values of the current sources 64, 67, 71 are set to a predetermined reproduction power Pr by the reference signal REF1. At the time of erasing, the current values of the current sources 64, 67, 71 are set to the low-pass
5 and 61, the switches 74, 76 and 79 are turned on, and the current sources 65, 68,
72 is adjusted. At the time of recording, as shown in FIG. 3, first, the current sources 64, 67, and 71 adjust the optical output by a predetermined reference signal REF1 so that the optical output of each laser element becomes the bottom power Pb. The current values Ib1, Ib2, Ib3 are held. Next, the switch 74 is turned on, the current source 65 is adjusted so that the optical output of the laser element 19 becomes the recording power Pw, and the current value Iw1 is held. Similarly, the current values Iw of the current sources 68 and 72
2, Iw3 is set and held. Then switches 77 and 79
Is turned on. At this time, the elements 20 and 21 are in a high output state with each other, and their optical output is slightly lower than the predetermined recording power Pw due to thermal coupling. The current sources 69 and 73 are adjusted to compensate for this decrease, and the correction amounts Is3 and Is4 are set and held. Similarly, the current values Is1, Is2 of the current sources 66, 70
Are set, and the setting of the drive current is completed. In the actual data recording to be executed subsequently, the switches 74 to 80 are controlled so that each laser element has a drive current corresponding to the combination of the recording data signal values.

As described above, according to the present embodiment, by providing the control means for correcting the drive current value for each laser element at the time of recording with a combination of the recording data signal which is the light emission instruction signal of each laser element, To compensate for light output fluctuations due to characteristic fluctuations such as those caused by thermal coupling between
High precision of the light output can realize control. Also,
Prior to the start of recording, by sequentially adding a mote for setting a correction value of a drive current corresponding to a recording data signal value of a specific combination, this can be automatically set.

In addition, in order to reduce the noise level of the semiconductor laser, a high-frequency current is generally superimposed on a drive current of each laser element only at the time of reproduction, but such addition of a high-frequency current does not affect the present invention at all.

Further, in the present embodiment, only the characteristic interference due to the thermal coupling between the adjacent laser elements has been considered, but the same can be considered when the interference extends over several elements.

Effect of the Invention As described above, according to the present invention, by correcting the drive current in accordance with the recording data signal for driving each laser element, it is possible to obtain a stable and accurate optical output. Further, the correction amount can be automatically set.

[Brief description of the drawings]

1 is a configuration diagram of a laser driving device according to an embodiment of the present invention, FIG. 2 is a detailed configuration diagram of FIG. 1, FIG. 3 is an explanatory diagram of its operation, and FIG. 4 is a configuration of a conventional laser driving device. Figure, fifth
FIG. 4 is a diagram for explaining the operation of FIG. 4, FIG. 6 is a diagram showing a driving current vs. light output characteristic of the semiconductor laser, and FIG. 7 is a diagram showing a driving current vs. light output characteristic of the multi-beam semiconductor laser. 1 semiconductor laser, 2, 40, 41, 42 current-voltage converter, 3, 4, 23, 24, 25, 43, 44, 45, 46, 47, 48
... subtractors 5, 6, 27, 28, 29, 49, 50, 51, 52, 53,
54 ... Amplifier, 7, 8, 17, 74, 75, 76, 77, 78, 79,
80 ... Switch, 9,10 ... Resistor, 11,12 ... Capacitor, 13,14,55,56,57,58,59,60,61,62,63 ...
... Low-pass filtering / holding circuits, 15, 16, 36, 37, 38, 64, 65,
66, 67, 68, 69, 70, 71, 72, 73 ... current source, 18 ... controller, 19, 20, 21 ... laser, 22 ... 3-beam semiconductor laser, 26 ... comparison means, 30 …… Amplification means, 31, 32, 33…
... Controller, 34 ... Coefficient converter, 35 ... Control means, 39 ...
Driving means, 81 ... Control circuit.

Claims (2)

(57) [Claims] A driving means for driving a semiconductor laser in which a plurality of laser elements are integrated; a comparing means for comparing an optical output of each of the laser elements with a reference signal; and an amplifier for amplifying an error signal obtained by the comparing means. Amplifying means for controlling the driving means, and controlling the reference signal in accordance with the operation mode of each element while simultaneously correcting the drive current of each laser element in accordance with a combination of the level instruction signals of each laser element. Control means for controlling the driving means. 2. The laser driving apparatus according to claim 1, further comprising control means for automatically and automatically setting the correction amount of the driving current of each laser element only at the start of recording.