JPH02110835A - Optical information recording and reproducing device - Google Patents

Abstract

PURPOSE:To enable the accurate power control without using a high frequency multiplex method by calibrating the output of a semiconductor laser under the nonfocusing state prior to closing an autofocus control loop. CONSTITUTION:When information is recorded to a recording medium, prior to performing a focusing operation, a voltage corresponding to a high power level for the recording time is given to a voltage/current converting circuit 5 via a differential circuit 4 by a drive controller 2. A current is poured from this voltage/current converting circuit 5 into an activation layer of the semiconductor laser 6 to generate the laser light emission. Its back light is detected by a monitor photodiode 7 and stored in a storage circuit 10. That is, a difference between a voltage from a voltage generator 3 and a voltage from the storage circuit 10 is converted into a current to make the semiconductor laser 6 emit a laser light at a recording level. By this method, the accurate power control can be carried out.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention relates to an optical information system that records information on a recording medium using light emitted from a semiconductor laser and/or reproduces recorded information on the recording medium. The present invention relates to a recording/reproducing device.

[Prior Art and Problems to be Solved by the Invention] The optical information recording and reproducing system has the advantage of being able to record information at a high density. A semiconductor laser is used as a light source in such an optical information recording/reproducing device.

FIG. 2 is a schematic diagram of an optical head of a conventional optical information recording/reproducing device using a semiconductor laser.

In FIG. 2, a light beam emitted from a semiconductor laser 50 is converted into a feather light beam by a collimator lens 51, passes through a beam splitter 52, and is reflected by a mirror 53.
A minute spot (approximately 1 to 2 meters in diameter) is imaged on the recording medium 55 through the objective lens 54 to form a bit (hole) in the recording medium 55 or to change the reflectance of the recording medium 55. , by reversing the direction of magnetization of the recording medium 55,
Information is recorded in a pattern by imparting an optically detectable change to the medium. When reproducing information recorded in this way, the power of the semiconductor laser is lowered than during recording, and the recording medium 55 is irradiated so as not to change the recorded contents of the recording medium. Information is reproduced by detecting optical changes caused by the information pattern on the recording medium.

A part of the reflected light from the recording medium 55 reaches the beam splitter 52 through the same optical path as the incident light, where it is separated from the incident light flux, and passes through the sensor lens 56 to the sensor 5.
The light is focused on 7. An autofocus signal, an autotracking signal, and an information signal can be detected on the sensor 57, and the autofocus signal and autotracking signal are applied to an actuator 58 that drives the objective lens 54 via a servo circuit.

In the configuration of the optical head of such an optical information recording and reproducing device, changes in the optical output of the semiconductor laser make the recording and reproducing states unstable, so it is necessary to perform power control to stabilize the recording and reproducing states. There is. A typical example of power control is the
There are methods described in Japanese Patent Publication No. 8-46879 and Japanese Patent Publication No. 54-10481.

FIG. 3 is a diagram showing the basic structure of such a known method. The semiconductor laser 50 emits a front light 59 that is irradiated onto a recording medium for recording and reproducing information, and a back light 60 that is emitted from the opposite side. This backlight is received by the photodiode 61, and after converting the output into current and voltage,
The power of the optical output of the semiconductor laser 50 is controlled to be constant by feeding back to the laser drive circuit 62.

This method is adopted in most fields of optical information recording and reproducing devices because the structure of the optical head system is simple.

However, in the optical head of FIG. 2, a problem occurs when the reflected light from the recording medium 55 returns to the semiconductor laser 50 via the beam splitter 52.

The beam splitter 52 is a polarizing beam splitter, and a beam splitter 52 is used as a polarizing beam splitter.
It is well known to arrange a 74-wavelength plate to form an isolator system, but if the recording medium 55 has birefringence, the effect will be reduced, and if it is a magneto-optical recording medium, this isolator system will not be effective. Therefore, in the case of such a recording medium, the reflected light from the recording medium 55 returns to the semiconductor laser 50, a so-called self-coupling phenomenon (SCOOP phenomenon) occurs, and a noise component is added to the laser oscillation. Climb big.

To solve this problem, a high frequency superimposition method (see Japanese Patent Publication No. 59-9086) is often adopted. but,
This high-frequency superimposition method reduces the irradiation energy by half compared to the case without superimposition when the peak power is the same, so it cannot be used when generating high power for information recording in the current situation where high-output semiconductor lasers are not available. Therefore,
At present, other solutions are needed.

According to the study results of the present inventor, when the above-mentioned high frequency superimposition method is not used, the monitor photodiode 61 in FIG.
If there is return light, the output from f will be as shown in Figure 4.
4 It was dawn. FIG. 4 is a graph showing output fluctuations of the monitor photodiode 61 when the semiconductor laser 50 is caused to emit light with a constant current without feedback and the objective lens 54 is gradually brought closer to the recording medium 55. In FIG. 4, the output increases significantly when the objective lens 54 and the recording medium 55 are in focus, and at this time there is a lot of returning light. As shown in FIG. 5, the output light on the side decreases significantly when the lens is in focus, making it impossible to record information due to insufficient power. When the high frequency superimposition method is performed, the output from the monitor photodiode 61 is almost constant as shown by the broken line in FIG. 4, so the above phenomenon is considered to be caused by a self-coupling phenomenon.

When recording information such as in I-L, where high frequency transmission is not possible,
In the conventional backlight monitor feedback method, a problem arises due to a self-coupling phenomenon during focusing.

Therefore, the purpose of the final IJJ is to prevent the power reduction of the optical output of the semiconductor laser due to the self-coupling phenomenon during focusing in the light emission monitor feedback method, and to stabilize the optical output of the semiconductor laser.

[L stage for solving the problem] According to the present invention, the following objects are as follows: To provide a semiconductor laser as a recording light source, and to transmit light emitted from the conductor laser to an objective optical system. In an apparatus for recording and reproducing information on an optical information recording medium by focusing the optical information on the recording medium, an optical output suitable for recording or reproducing information on the recording medium is generated from a semiconductor laser. A reference value is determined and stored from the light emitted from the semiconductor laser before the focus state is set, and after the focus state is set, the means for causing the semiconductor laser to emit light is adjusted by referring to the reference value. This is achieved by an optical information recording/reproducing device.

The optical information recording/reproducing device of the present invention includes: a semiconductor laser; an objective lens for driving the semiconductor laser to perform laser dry imaging; a photodiode that receives backlight from the laser, and is connected to the laser driver and selectively connected to the photodiode for generating an optical output suitable for recording or reproducing information on a recording medium; Reference value determination storage means for determining and storing a reference value of from the back light from the semiconductor laser before the in-focus state.

, so that after the in-focus state, the semiconductor laser is caused to emit light by referring to the reference value.

[Example] FIG. 1 is a block diagram showing one embodiment of the end-of-life 1J.

In the figure, l is a sensor, 2 is a drive controller, 3 is a voltage generator, 4 is a differential circuit, 5 is a voltage-current conversion circuit, 6 is a semiconductor laser, 7 is a monitor photodiode, 8 is a current-voltage conversion circuit, 9 is a switch, 10 is a memory circuit, 11 is a servo circuit, 12 is a host controller,
13 is a signal modulation circuit.

The operation will be explained below.

When recording information on a recording medium, before performing a focusing operation, the sensor 1 detects that the recording medium is attached to the device, and then the drive controller 2 applies a voltage via the signal modulation circuit 13. An instruction is sent to the generator 3 to apply a voltage corresponding to the high power level during recording to the voltage-current conversion circuit 5 via the actuating circuit 4. A current is injected from the voltage-current conversion circuit 5 into the active layer of the semiconductor laser 6, thereby causing laser emission. The backlight is detected by a monitor photodiode 7. After converting this output into a voltage in a current-voltage conversion circuit 8, the voltage is stored in a storage circuit 10 via a switch 9. Voltage information is then applied to the differential circuit 4 via the memory circuit IO, thus forming a feedback system via the switch 9. That is, the difference between the voltage from the voltage generator 3 and the voltage from the memory circuit 10 is converted into a current, causing the semiconductor laser 6 to generate laser light at a recording level.

Next, when reproducing the information recorded on the recording medium, the voltage generator 3 is switched to the reproduction level.

Similarly to the above recording, the output voltage from the monitor photodiode 7 is stored in the storage circuit 1O via the switch 9.

This means that a voltage reference value that guarantees the semiconductor laser to emit light at the recording level or reproduction level is set.

When the storage circuit 1O gives the controller 2 information indicating the end of storage, the switch 9 is opened. A required reference voltage is obtained from the memory circuit IO, and information is returned from the controller 2 to the servo circuit 11, and recording or reproduction is placed in a standby state.

Thereafter, recording and reproduction are performed according to instructions from the host controller 12.

In the present invention as described above, it is not possible to correct changes in semiconductor laser output during recording and tlT generation, but
This change is mainly due to thermal effects, and running (warming up) to l-min.
This problem can be solved thermally using a Peltier element, and by using these methods together, the semiconductor laser output can be further stabilized.

[Effects of the Invention] According to the present invention as described above, since the output of the semiconductor laser is calibrated in an out-of-focus state before the autofocus control loop is closed, there is no influence of returned light, and the high-frequency superimposition method is used. Accurate power control is possible without any problems.

7.61: Monitor photodiode.

Claims (2)

[Claims] (1) A semiconductor laser is provided as a light source for recording and reproducing, and the light emitted from the semiconductor laser is collected by an objective optical system and focused on an optical information recording medium to record and reproduce information on the recording medium. In the device, a reference value for generating an optical output from the semiconductor laser suitable for recording or reproducing information on a recording medium is determined from the light emitted from the semiconductor laser before setting the focus state, and is stored, and the reference value is determined from the light emitted from the semiconductor laser before setting the focus state and is An optical information recording and reproducing apparatus characterized in that the latter further comprises means for causing a semiconductor laser to emit light by referring to the reference value. (2) a semiconductor laser; a laser driver that drives this semiconductor laser; an objective lens that focuses the light from the semiconductor laser onto a recording medium; an actuator that adjusts the position of this objective lens to bring it into focus; a photodiode that receives back light from the semiconductor laser, and is connected to the laser driver and selectively connected to the photodiode to generate a light output suitable for recording or reproducing information on a recording medium. reference value determination storage means for determining and storing a reference value for determining and storing a reference value from the back light from the semiconductor laser before the in-focus state, so that after the in-focus state, the semiconductor laser emits light by referring to the reference value. Claim 1, characterized in that:
The optical information recording/reproducing device described in .