JPH03141039A - Optical information recording and reproducing device - Google Patents

Abstract

PURPOSE:To prevent faulty write at the time of recording data by adding offset so that an objective lens is moved to a focusing position at the time of recording before a light source is made to output at the time of recording and setting the focal position of the objective lens corresponding to the change of the output of the light source. CONSTITUTION:At the time of reproducing, a light beam for detecting the focal position is detected by a focus detector 1 and phase-compensated 5 as an FE signal by a differential amplifier 2 and an AGC circuit 4, then it is inputted in an actuator driving amplifier 6. The objective lens 7 is controlled by an actuator 8 so that the FE signal becomes zero and the focal position is held. When write information WT.INF is given in order to store the data, the offset with which the objective lens 7 is moved to the focal position at the time of recording is added to the amplifier 6 by an offset addition circuit 9. An offset signal is added simultaneously with the WT.INF signal and the lens 7 is moved to the focal position at the time of recording. Next, the data is started to be recorded in a data part with a write gate signal and the addition of the offset is stopped with the write gate signal.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical information recording/reproducing device, and more particularly to focus control of an optical pickup.

BACKGROUND ART Conventionally, there has been a device that uses a disk as an information recording medium, records information along spiral or concentric tracks on the surface, and optically reproduces the information signal by irradiating a light beam such as a laser beam. It is used.

Document file systems and the like have also been commercialized as devices that allow a user to record or erase information signals on an optical disk using a laser.

These optical information recording devices narrow down the light beam irradiated onto the medium surface to about the wavelength of the light in order to record a large amount of information at high density or to reproduce the recorded information. There is.

In order to accurately focus such a light beam onto a recording column, focusing control controls the focus point of the light beam in the direction perpendicular to the medium surface and in the radial direction.

and tracking control is performed.

An example of conventional focusing control and tracking control will be described with reference to FIGS. 3 and 4. Third
The figure shows a schematic configuration diagram of an optical head. semiconductor laser lO
The laser beam emitted from the laser beam is converted into parallel light by a collimating lens 11, changed direction at right angles by a beam splitter 12, passes through a quarter-wave plate 13, and is focused onto a recording surface 14 by an objective lens 7.

A part of the focused light beam passes through the recording surface 14, while the other part is reflected and passes through the beam splitter 12, following the optical path of the incident light in the opposite direction. Beam splitter 12 and 1/4
The wave plate 13 constitutes an optical isolator, and uses the polarization of light to bend the incident light at a right angle at the beam splitter 12, but allows the reflected light to pass through immediately, thereby separating the incident light and the reflected light. A portion of the reflected light that has passed through the beam splitter 12 is bent at right angles by the beam splitter 15 and sent to a tracking detector 16 for detecting errors in the radial direction. Recording surface 14
The other light beams go straight through the beam splitter 15, are focused by the condenser lens 18, and are guided to the focus detector 1 which detects the focus error of the objective lens 7.

FIG. 4 shows an example of a focusing control circuit for controlling the focal position of the objective lens 7 of the apparatus shown in FIG.

To briefly explain the operation, the difference and sum of the outputs of the focus detector 1, which is formed by two divided photodiodes, are extracted by the differential amplifier 2 and the summing amplifier 3, and are extracted by the AGC circuit 4, which is an automatic gain adjuster. After the gain is kept constant and the phase is compensated by the phase compensation circuit 5, the signal is amplified by the actuator drive amplifier 6 and supplied to the actuator 8 to control the focus of the objective lens 7.

By the way, when reproducing recorded information on the recording surface 14 and when recording information, although the optical path is the same, the laser output is different. That is, during recording, the output of the semiconductor laser 10 is increased several times that during reproduction, and recording is performed by drilling holes in the recording medium or changing the reflectance.

Problems to be Solved by the Invention However, when recording and reproducing are performed in the same optical path as described above, when the output of the semiconductor laser is increased by changing the output from reproducing to recording, the wavelength of the laser shifts instantaneously. As a result, the focal position of the light spot shifts, resulting in a phenomenon in which writing at the beginning of the data section becomes defective.

This will be explained using FIG. 5. FIG. 5 shows the operation of the objective lens. First, a case will be described in which the address indicated by the ID section is read and then data is recorded in the data section. During playback to read out the ID section, a focused state is maintained by the half-focus servo, but since data is recorded in the data section, when the output of the semiconductor laser is increased to a high output state, the wavelength of the laser light shifts to the longer wavelength side. This is because as the CW (Continuous Wave) optical output of the semiconductor laser increases, that is, as the injection current increases, the main oscillation mode (peak oscillation wavelength) gradually shifts to the longer wavelength side as the temperature of the semiconductor element increases. . As the wavelength shifts to the longer wavelength side, the refractive index of the objective lens decreases, the focal length increases, and the focal position shifts away from the lens as shown in FIG.

As a countermeasure against this focus shift, measures have been taken to reduce the negative effects of the focus shift by selecting materials with low dispersion properties for the lens system, that is, materials that are less affected by wavelength fluctuations, but this is not necessarily sufficient. , there is some focus shift.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an optical information recording device that does not cause write defects by correcting wavelength changes due to output fluctuations of laser light using an electrical circuit. purpose.

Means for Solving the Problems In order to achieve the above object, the position of the objective lens may be moved to the in-focus position during recording before moving from the reproduction state to the recording state, and the optical information recording of the present invention The device includes an objective lens that focuses light emitted by the light emitting device onto an optical recording medium, and a focus error that is a difference between the focal point of the objective lens and a recording surface of the optical recording medium. The optical information recording/reproducing device includes a focus servo circuit that positions the objective lens by using an offset adding circuit that applies an amount of defocus based on a wavelength fluctuation of a light source of the light emitting device to the focus servo circuit as an offset amount. It is characterized by:

The operational focus servo circuit operates to reduce focus errors. Before moving from the reproduction to the recording state where data is recorded, an offset amount corresponding to the amount of defocus based on the wavelength fluctuation of the light source is applied to the focus error signal from the offset addition circuit to the focus servo circuit, and the objective lens is recorded. Recording is performed after moving to the focal position.

Furthermore, when changing from the recording state to the reproducing state, when the output of the light source is reduced to the reproducing state, the wavelength shift of the light source returns to the original state. At this time, since no offset is added, the focus servo circuit is operated by the focus error signal generated by this wavelength shift, so that the in-focus position is maintained during reproduction.

EXAMPLE An example of the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 1 is a block diagram showing the configuration of this embodiment. The focus detector 1 is composed of a two-split photo diode. When the objective lens 7 is in the focused position, the outputs of the two photo diodes are equal. If the outputs are different, the multifocal point is too close or too far depending on the size. The in-focus position is detected by determining whether the focus is too high. Differential amplifier 2 is a 2-split photo
Take the output difference of the diode! ? Outputs FE (focus error) signal. The summing amplifier 4 sums the outputs of the two-split photodiodes and outputs a sum signal. In the case of control using only the FE multiplied signal, the objective lens 7 must be moved away from the disk before the focus pull-in operation is performed. However, by using the sum signal, the sum signal is larger than the threshold value A, and the FE multiplied signal amplitude is If the objective lens 7 is located at a position smaller than the threshold value E (AGE), focus can always be pulled in stably.

AGC (Automatic Ga1n Cont.
rol) circuit 4 makes the focus gain constant, and the phase compensation circuit 5 performs phase compensation. Actuator drive amplifier 6
supplies an excitation current to the actuator 8 that moves the objective lens 7 in the focus direction. Offset addition circuit 9
applies an offset corresponding to the amount of defocus based on the wavelength fluctuation of the FE multiplied signal light source to the actuator drive amplifier 6.

The operation of the apparatus configured as above will be explained using FIG. 2.

FIG. 2 is a diagram showing the signal timing of the focus servo circuit and the operation of the objective lens. During playback, a light beam for focus position detection is detected by a focus detector 1, sent to a differential amplifier 2 and an AGC circuit 4 as a 1) FE multiplied signal, phase compensated by a phase compensation circuit 5, and then sent to an actuator drive amplifier. 6, and the objective lens 7 is controlled by the actuator 8 so that the jDFE signal becomes 0 to maintain the in-focus position. Next, when write information (WT, INF) is issued to store data, an offset is added to the actuator drive amplifier 6 by the offset addition circuit 9 to move the objective lens 7 to the in-focus position during recording. This offset is no longer added as soon as data recording actually starts. This is because the objective lens 7 has already moved to the recording focal position at the start of data recording, so no offset is necessary. and,
The focus servo is always active during playback and recording.

Next, the timing of adding the offset will be explained with reference to FIG.

An offset signal is added at the same time as the WT and INF signals,
The objective lens 7 moves to the in-focus position during recording.

At this time, the address section (ID section) is shifted from the focus position during reproduction, but the amount of focus shift at this time is such that it does not interfere with reading the ID section. Next, data recording is started in the data section by the write gate (WT, GATE) signal, but the addition of the offset is stopped by the WT, GATE signal.

Next, in the ID section, which becomes the reproduction power again, an offset signal is added at the same time as the WT and GATE signals are disconnected so that the focus servo does not work again, and the WT and GATE signals are added again to start recording in the next data section. At the same time, the offset signal is disconnected.

By operating the focus servo in this manner, a good recording condition can be obtained from the beginning of the data section.

Effects of the Invention As is clear from the above explanation, the present invention improves the output of the light source by applying an offset to move the light source to the in-focus position for recording, before outputting the light source during recording. Since the recording focusing position of the objective lens can be set in response to the change, writing errors can be prevented during data recording.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, FIG. 2 is a diagram showing the signal timing of the apparatus shown in FIG. 1 and the operation of the objective lens, and FIG. 3 is a schematic configuration diagram of the optical head. FIG. 4 is a diagram showing an example of the focus servo circuit of the apparatus shown in FIG. 3, and FIG. 5 is a diagram showing changes in the output of the light source and the operation of the objective lens in FIG. 4. 1...Focus detector, 2...Differential amplifier,
3... Adding amplifier, 4... AGC circuit, 5... Phase compensation circuit, 6... Actuator drive amplifier, 7...
...Objective lens, 8...Actuator, 9...Offset addition circuit.

Claims (1)

[Claims] an objective lens that focuses light emitted from a light emitting device onto an optical recording medium; and an objective lens configured to reduce a focus error, which is a difference between the focal point of the objective lens and the recording surface of the optical recording medium. An optical information recording/reproducing device equipped with a focus servo circuit for positioning is provided with an offset addition circuit that applies an amount of defocus based on a wavelength fluctuation of a light source of the light emitting device as an offset amount to the focus servo circuit. An optical information recording and reproducing device.