JPH06274921A - Optical information reproducing device - Google Patents

Abstract

PURPOSE:To obtain an optical information reproducing device by which data is optimally reproduced corresponding to the dispersion of the characteristic and the secular change of an optical pickup. CONSTITUTION:This optical information reproducing device has a laser module 8 applying a driving current constituted by superposing a high frequency current on a DC current to a semiconductor laser; a magneto-optical disk 1 is irradiated with a pulse state laser beam outputted from the semiconductor laser, and reflected light by the disk 1 is detected by an optical signal detection part 9, so that recorded information is reproduced. The device is provided with a D/A converter 11 varying voltage applied to the laser module 8 so that the amplitude of the high frequency current may be changed, and an arithmetic control part 13 judging the superiority degree of reproducing the information and outputting a control voltage signal to the D/A converter 11 so as to improve the superiority degree.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information reproducing apparatus for reproducing recorded information from an optical recording medium such as a magneto-optical disk using a semiconductor laser.

[0002]

2. Description of the Related Art An optical information reproducing apparatus irradiates a laser beam from a semiconductor laser onto an optical recording medium and guides the reflected light to an analyzer to reproduce recorded information. There is a drawback that information reproduction is impaired by noise generated by the return light of the reflected light of the part returning to the semiconductor laser or noise from the semiconductor laser itself.

Therefore, conventionally, there has been proposed a control method for reducing noise by superimposing a high frequency current of several 100 MHz on a DC drive current of a semiconductor laser and modulating the same, and periodically pulsating the semiconductor laser. There is. In this case, a value set in advance in the optical pickup, for example, the frequency value of the above high frequency current is set to a value that minimizes the noise amount.

[0004]

However, due to variations in various characteristics of the optical pickup (characteristics of the high-frequency oscillation circuit, etc.), changes over time, and differences in characteristics of the magneto-optical disk to be used, the above-mentioned preset values are set. The amount of noise cannot be minimized with the various set values. That is,
The conventional optical information reproducing apparatus has a problem in that it cannot cope with the above variations and the like, because the above various set values are fixed at the time of manufacture.

In order to eliminate the drawbacks caused by fixedly setting the frequency of the high-frequency current, a device that makes the frequency variable in accordance with the change in the distance from the light emitting end face of the laser to the recording medium (Japanese Patent Laid-Open No. Hei 4 (1999) -498). No. 186535 (International Patent Classification G11B7 / 125)) or a device for detecting a noise amount and varying the frequency so that the noise amount is equal to or less than a predetermined amount (Japanese Patent Laid-Open No. 4-6635).
Japanese Patent Laid-Open Publication No. G11B 7/125) has been proposed, but this frequency control requires a voltage-frequency conversion circuit, which has the drawback of complicating the circuit configuration.

In view of the above circumstances, the present invention provides an optical information reproducing apparatus capable of optimal data reproduction in response to variations in characteristics of the optical pickup and changes with time without complicating the circuit configuration. The purpose is to provide.

[0007]

In order to solve the above-mentioned problems, an optical information reproducing apparatus of the present invention provides a driving current, which is a superposition of a high-frequency current on a direct current, to a semiconductor laser, and from this semiconductor laser, In the optical information reproducing apparatus, which irradiates the optical recording medium with the emitted pulsed laser light and reproduces the recorded information by detecting the reflected light, the amplitude of the high frequency current is changed to Of these, a ratio changing means for changing the lighting ratio of the laser, a judging means for judging the excellentness of information reproduction, and a control means for controlling the ratio changing means so as to improve the excellentness are provided. It is characterized by that.

[0008]

According to the above construction, when the high frequency current is superimposed on the DC drive current of the semiconductor laser for modulation, the degree of this modulation is made variable, so that variations in the optical pickup, changes with time, or magneto-optical characteristics. It is possible to reduce the occurrence of noise by following changes in various conditions such as differences in the characteristics of the disc.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings showing its embodiments. FIG. 1 is a system configuration diagram showing a main part of an optical information reproducing apparatus.

The movable part 4 of the optical pickup is an optical system including an objective lens 2 and a reflection mirror 3, and a linear motor 5 for moving the optical system in the radial direction of the magneto-optical disk 1.
Composed of and. The reflection mirror 3 guides laser light from a polarization beam splitter 7 described later to the magneto-optical disk 1 and guides laser light reflected by the magneto-optical disk 1 to the polarization beam splitter 7.

The fixed part 10 of the optical pickup comprises a monitor sensor 6, a beam splitter 7, a laser module 8 and an optical signal detection part 9. The laser light output from the laser module 8 passes through the polarization beam splitter 7 and reaches the movable portion 4,
A part of the laser light (which always has a constant ratio to the laser light output) is reflected and enters the monitor sensor 6. The monitor sensor 6 is for detecting the intensity of the laser light, converts the intensity of the incident light into a voltage signal, and outputs the voltage signal to the laser control unit 12.
On the other hand, the reflected laser light returning from the movable section 4 is guided to the optical signal detection section 9 by the beam splitter 7, and this optical signal detection section 9 converts the incident reflected laser light into a voltage signal and outputs it to the signal processing section 14. To do.

The signal processing section 14 converts the analog voltage signal from the optical signal detecting section 9 into a digital signal and outputs it to the arithmetic / control section 13.

The arithmetic / control unit 13 performs error correction and decoding processing on the above digital signal, and the result is represented by a SCSI (Small Computer) not shown.
It is output to, for example, a host computer through a System Interface). The error rate is detected during error correction, and a voltage control signal, which is a digital signal based on the detection result, is output to the D / A converter 11. Further, a reference value signal for constant reproduction power control is output to the laser control unit 12.

The D / A converter 11 D / A converts the voltage control signal from the arithmetic / control section 13 to generate an analog control voltage, which is applied to a high frequency oscillation circuit 16 of the laser module 8 which will be described later. . The above analog control voltage is
The amplitude of the high frequency current flowing through the semiconductor laser by the high frequency oscillation circuit 16 is determined.

The laser control section 12 compares the voltage signal from the monitor sensor 6 with the reference value signal from the calculation / control section 13 and controls the drive voltage applied to the laser module 8 so that the deviation is eliminated. That is,
Feedback control is performed so that the reproduction power of the semiconductor laser is always a constant value.

FIG. 2 is a circuit diagram showing the internal structure of the laser module 8, in which 15 is a condenser and 16 is a condenser.
Is a high frequency oscillation circuit, and 17 is a semiconductor laser. The high frequency oscillation circuit 16 changes the amplitude of the high frequency according to the voltage value applied by the D / A converter 11. Then, a direct current flows through the semiconductor laser 17 due to the drive voltage applied from the laser control unit 12, and the high frequency oscillation circuit 16 supplies the tens of several tens through the capacitor 15.
A high frequency current of 0 MHz is superimposed. Due to this superimposed drive current, the semiconductor laser 17 is turned on in a pulsed manner, so that the semiconductor laser 17 emits light with a plurality of wavelength spectra as if it were a multimode laser, even though it is a single mode laser. Therefore, the influence of the return light and the noise such as the mode hop that are likely to occur in the high power single mode laser are reduced.

FIG. 3 shows the relationship between the laser drive current and the light output intensity. As shown in the graph e of FIG. 3, the light output is substantially 0 up to the threshold current (I _th ), and when the threshold current (I _th ) is exceeded, the light output intensity increases in proportion to the increase in the current. To do. Here, when the drive current (average current I _m1 , amplitude 2I _p1 ) shown in the graph a flows through the semiconductor laser 17, the semiconductor laser 17 is turned on when a current equal to or higher than the threshold current (I _th ) flows, and its light output intensity is It becomes pulsed as shown by b.

On the other hand, when the drive current (average current I _m2 , amplitude 2I _p2 ) shown in the graph c flows through the semiconductor laser 17,
In this case as well, the LED is turned on when a current equal to or higher than the threshold current (I _th ) flows, and its light output intensity becomes pulsed as shown by the graph d. The average current (I _m2 ) at this time is lower than the average current (I _m1 ) in the drive current of graph a. This is because the above-mentioned laser control unit 12 controls the reproduction power to be constant (P _m ).

Here, the average current flowing through the semiconductor laser 17 is I _m , the high frequency current amplitude is I _p, and the depth of modulation is defined as the modulation degree M as shown in the following equation.

[0020]

## EQU1 ## M = ΔI / 2I _p × 100 (%) where ΔI = I _th − (I _m −I _p ).

Therefore, the modulation factor M can be changed by changing the high frequency current amplitude I _p . The high frequency current amplitude I _p can be changed by changing the voltage control signal applied to the D / A converter 11. Note that in FIG. 3, the modulation degree M ₂ is deeper than the modulation degree M ₁ .

FIG. 4 is a graph showing the relationship between the modulation factor M and the error rate. As for the error rate, the modulation degree M is 30% to 60%.
In order to draw a concave curve that becomes the bottom around, the modulation factor is usually set to be between 30% and 60%.

Next, an example of a control method for selecting the optimum modulation factor to minimize the above error rate will be described. First, after turning on the power of the optical information reproducing apparatus, a magneto-optical disk is inserted, and then test data is recorded on this disk, and the modulation degree M is sequentially changed between 30% and 60% by the above-mentioned method. Then, the test data is reproduced, the error rate at each modulation factor is calculated by the arithmetic / control unit 13, and the calculation result is stored in a memory (not shown) as modulation factor determination information. The error rate is calculated by comparing the recorded test data with the reproduced data (raw data without error correction).

Next, the modulation factor (M _{b in} FIG. 4) with the minimum error rate is selected from the error factors at each modulation factor stored in the memory, and the voltage control signal is set to set D / A. Output to the converter 11. After that, the modulation degree is maintained until the disc is replaced. As a result, information is reproduced with the minimum error rate during reproduction of the disc.

As described above, according to the present invention, when the high frequency current is superimposed on the DC drive current of the semiconductor laser 17 for modulation, the degree of this modulation can be changed to an optimum value for reproduction. Even when various conditions such as a change with time of the optical pickup and a difference in characteristics of the magneto-optical disk are changed, the noise and the like can be always minimized.

In this embodiment, the detection target for determining the modulation factor is the error rate, and the process by software is enabled to facilitate the selection of the modulation factor, but the invention is not limited to this.
The arithmetic / control section 13 may be provided with dedicated hardware such as a digital comparator to improve the processing speed. Further, in this embodiment, the function of obtaining the error rate is provided as described above, but instead of this, a function of measuring the jitter characteristic or a function of measuring the C / N characteristic may be provided. .

In this embodiment, the high frequency superposition is given by the high frequency oscillating circuit 16 which is an analog oscillating circuit, but it may be superposed by a digital oscillating circuit. Furthermore, when there is a possibility that various characteristics of the optical pickup, such as the frequency of high-frequency oscillation, may change under operating conditions such as temperature, it may be periodically or equipped with a function such as temperature detection to keep the temperature from the initial setting. It is also possible to reset the modulation degree to the optimum state when a certain difference occurs in the.

[0028]

As described above, according to the present invention, it is possible to prevent noise or error from occurring in response to changes in various conditions such as variations in optical pickup, changes over time, or differences in characteristics of magneto-optical disks. The effect that it can reduce is produced.

[Brief description of drawings]

FIG. 1 is a system configuration diagram showing a main part of an optical information reproducing apparatus of the present invention.

FIG. 2 is a circuit diagram showing an internal configuration of a laser module.

FIG. 3 is a graph showing the relationship between drive current and light output intensity.

FIG. 4 is a graph showing the relationship between modulation factor and error rate.

[Explanation of symbols]

 1 Magneto-Optical Disk 8 Laser Module 9 Optical Signal Detection Section 11 D / A Converter 12 Laser Control Section 13 Computing / Control Section 14 Signal Processing Section 16 High Frequency Oscillator 17 Semiconductor Laser

Claims (1)

[Claims] 1. A drive current formed by superposing a high frequency current on a direct current is applied to a semiconductor laser, and a pulsed laser beam emitted from this semiconductor laser is applied to an optical recording medium, and the reflected light is detected and recorded. In an optical information reproducing device adapted to reproduce information, a ratio changing means for changing the amplitude of the high frequency current to change the ratio of turning on the laser in one cycle thereof, and determining the quality of information reproduction An optical information reproducing device, comprising: a determining unit for controlling the ratio and a control unit for controlling the ratio varying unit so as to improve the quality.