JPH0554405A - Optical recording device - Google Patents

Abstract

PURPOSE:To provide an optical recording device provided with a focus detecting means whose configuration is simple and its assembling and adjusting are easy. CONSTITUTION:A vibrator 14 is incorporated into a photodetector 1 to form one body and this is vibrated in the direction parallel to the optical axis of the incident light on the photodetector. By detecting the vibration direction and the change of an optical image on the photodetector 1 caused by that vibration by the control part 16, focus position displacement between an objective lens 4 and a disk 3 can be detected and corrected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording / reproducing apparatus using an optical disk, and more particularly to an optical recording apparatus equipped with focus position control means.

[0002]

2. Description of the Related Art A device for optically recording or reproducing a signal on a record carrier such as an optical disk or an optical card has been put into practical use. These are advantageous in that high density recording is possible because recording is performed by irradiating a minute light spot on the record carrier, and high reliability because recording and reproducing are performed without contacting the record carrier. It has a wide range of applications. Among them, the optical disk device will be explained.

An optical disk has a higher recording density than a magnetic disk and is capable of high-capacity recording, but since the track pitch is very small (1 to 2 μm), the light spot emitted from the objective lens is a target track on the disk plate. Must be positioned with high precision. Generally, an objective lens actuator is formed by integrating the objective lens with the actuator, and focus control is performed to move this objective lens in the vertical direction with respect to the disc, and the objective lens is moved in the radial direction of the disc for positioning on the target track. Tracking control is performed.

Taking the example of a magneto-optical disk which is said to be recordable / erasable and will replace the magnetic recording apparatus as an external recording apparatus for computers in the near future,
The configuration and operation of the optical pickup will be described.

FIG. 6 shows the structure of an optical pickup. The light emitted from the semiconductor laser light source 5 is converted into parallel light by the collimator lens 6 and further shaped into a circular light by the beam shaping prism 7 (because the emitted light of the semiconductor laser is an elliptical beam). This light enters the objective lens 4 via the prism 8 and forms a minute light spot having a diameter of 1 to 2 μm on the disk 3. The objective lens 4 is generally formed integrally with a movable actuator, and its position is controlled by a servo error signal described later. The reflected light from the disk 3 returns to 4 and 8 again, and after its optical path is changed, the λ / 2 plate 9 rotates the 45 ° deflection surface, and the polarization beam splitter 12 rotates the light of the P deflection component and the S deflection component. Is separated into The light of the P deflection component passes through the astigmatism lens 11 to the photodetector 1, and the light of the S deflection component enters the detector 2 via the lens 13 to detect the light amount. Here, the astigmatism lens 11 and the detector 1 are elements constituting a focus servo error detection system for controlling the position of the objective lens 4 in the focus direction. Similarly, the detector 2 is for positioning control in the track direction. This is for configuring the tracking error detection system of. The position of the objective lens 4 is controlled by these error signals so that the light spot is irradiated onto the target track.

The detection of the information signal is differentially detected by the difference signal between the detector 1 and the detector 2 (the outputs of both detectors are inverted in phase according to the signals "1" and "0" on the disk). To be done.

There are several methods for focus and tracking error detection. Here, the focus error detection method will be described. Astigmatism is an example of a focus error detection method often used in magneto-optical disk devices.

FIG. 7 shows the principle of the astigmatism method. The astigmatism method includes an astigmatic lens 11 and a photodetector 1, and the photodetector 1 has a light-receiving surface divided into four parts. Due to astigmatism, if the objective lens is too close to the disc, the incident light image as shown in (a), if it is too far, the optical image as shown in (c) of the figure, the same image at the time of focusing The optical image shown in (b) is formed. Therefore, FE =
The positional relationship between the objective lens and the disc can be detected by (S1 + S3)-(S2 + S4).
E can be used as a focus error signal.

Here, in recording and reproducing a signal on the disk surface, if the above-mentioned focus control is not correctly performed,
The recording pit shape becomes irregular, or the spot is not narrowed down, so that sufficient energy required for recording cannot be obtained, so that correct recording and reproducing operations cannot be performed and the reliability of the device is deteriorated. It will be. Therefore, in the optical pickup, the precision of optical parts and mechanical parts is strictly controlled, and in particular, the position of the photodetector of the error detection system and the astigmatism lens are adjusted by placing the light emitted from the objective lens on the disc. Particularly accurate installation position accuracy is required to form spots correctly.

[0010] Therefore, as a method capable of coping with these, Japanese Patent Laid-Open Publication No. 53-17706 and Published Japanese Patent Publication 62-43.
Two methods have been proposed at 254.

The former is a system in which a pinhole 92 capable of oscillating in the optical axis direction is provided in front of the photodetector 1 as shown in FIG. 8, and a focus error is detected by this and a phase comparator 93. In this method, when the objective lens 4 is at the in-focus position, the converging lens 94 is configured to focus in the pinhole, and the oscillator 96, which is the excitation signal generating unit of the vibrator 95, is configured.
And the signal of the photodetector 1 are phase-detected by the phase detector 93,
This is a method of detecting the direction and the amount of focus position shift.

The latter is a method in which the semiconductor laser 101 is integrated with a vibrator 104 to vibrate the semiconductor laser itself, as shown in FIG. At this time, the reflected light from the disk returns to the semiconductor laser 101 via the objective lens 4 and is detected by the photodetector 102 provided at the rear of the semiconductor laser 101. The amount of this feedback light is the oscillation of the semiconductor laser. The effect is the same as that of the former pinhole.

However, the former method requires a pinhole, and there is no significant change in that this positioning requires strict accuracy as in the conventional methods. Further, in the latter method, although the pinhole and its position adjustment are not necessary, the reflected light is returned to the semiconductor laser because the detector in the semiconductor laser performs the signal detection. Semiconductor lasers generally generate noise called return light noise, in which optical output fluctuates when receiving return light. Particularly, in a magneto-optical disk device that requires a high SN ratio, this optical output fluctuation is a serious problem. Becomes

[0014]

As described above, the focus error detection system is required to have a very high position accuracy. If this position accuracy is incorrect, for example, if the position of the astigmatic lens is incorrect and the error signal is not set to zero on the photodetector when focusing, the focus servo will focus. Even though the light spot is correctly focused on the disc in order to perform an operation such that the error signal becomes zero, an error signal is generated and the objective lens is moved to the out-of-focus position. Will end up. Therefore, in the manufacturing process, the position adjustment is performed on the order of micron, and the process is complicated.

On the other hand, as for the structure of the optical pickup, not only is it necessary to reduce the weight in order to perform a high-speed access operation, but also a simpler optical structure is required in order to reduce the cost. There is. However, it can be said that the current system has an astigmatic lens, a pinhole, etc. in the error detection system itself, and has a complicated optical configuration.

The present invention solves the above problems, and an object of the present invention is to provide an optical recording apparatus having a focus detection method with a simple structure and easy adjustment.

[0017]

In order to achieve the above object, the present invention comprises a vibrator capable of vibrating in a direction parallel to the optical axis of reflected or transmitted light from a disk, and is integrally formed with the vibrator. And a photodetector for detecting the diameter or energy density of the incident light beam.

[0018]

It is possible to detect the deviation amount and the deviation direction of the objective lens by vibrating the photodetector in the direction parallel to the incident optical axis and comparing the vibration direction with the incident light image of the photodetector. You can That is, when the distance between the objective lens and the disc is too short as shown in FIG. 1 (a) or too far (c), the photodetector incident light image as shown by a1 and a3 in FIG. Although both cannot be distinguished, when the photodetector is vibrated in the optical axis direction and the photodetector is displaced from 1a1 to 1b1 as shown in (a), the incident light image of the photodetector is detected at this timing. In b1 and (c), it becomes like b3. That is, if the excitation direction is in the z1 direction and the spot diameter of the incident light tends to be large, it means that the objective lens and the disk are too close to each other, and conversely, the spot system tends to be small. Indicates that these are too far.

[0019]

FIG. 2 shows an embodiment of the present invention. In the optical pickup 10, the light emitted from the semiconductor laser 5 is converted into parallel light by the collimator lens 6 and further shaped into circular light by the beam shaping prism 7. This light enters the objective lens 4 through the prism 8 and is focused on the disk 3 to form a minute light spot. The objective lens 4 is integrated with a voice coil type actuator (not shown) including a coil and a yoke, and its position is controlled in the focus and disk radial directions by a focus servo error signal or a tracking error signal. The reflected light from the disk returns to 4 and 8 again, and this time the optical path is changed to the λ / 2 plate 9 side. After the polarization plane is rotated by 45 ° by the λ / 2 plate 9, the light enters the condenser lens 10. The light passing through the condenser lens 10 is separated into P-polarized light and S-polarized light by the polarization beam splitter 12, and is detected by the focus error signal detecting photodetector 1 and the tracking error signal detecting photodetector 2. To be detected. For tracking error detection, the position of the light spot is controlled by the push-pull method using the diffracted light from the track groove on the disk, and a two-divided sensor or the like is used.

Now, the focus error detection system will be described. The focus error photodetector 13 is configured integrally with a vibrator 14 including a piezo element or the like. These are a photodetector configured on a semiconductor substrate and a piezo element made of ceramic or the like, or
It is also possible to form a semiconductor active layer via a dielectric layer or the like on a vibrator made of ceramic or the like.
However, when the displacement of vibration is insufficient, a laminated piezo element in which a plurality of vibrators are laminated may be used to secure this. Further, the microactuator may be composed of a material that can be etched by photolithography, and the photodetector may be vibrated by this. As long as the photodetector can vibrate in the direction parallel to the incident optical axis Good. The movable range may be 5 to 20 μm, depending on the specifications of the optical path length in the condenser lens 10 and the optical pickup.

Next, a method of detecting an actual focus error will be described with reference to FIG. FIG. 3 shows an example in which the objective lens comes too close to the disc. At time t1, the photodetector 1 is at the position where the condenser lens 10 is in focus during focusing, and at this time, an optical image as shown in FIG. Here, at time t2, the photodetector 1
When 3 is moved, the light image on the photodetector becomes large like b2. Further, it is understood that when the photodetector is moved to the position of t3, the optical image on the photodetector becomes small as shown in the figure, so that the objective lens is too close to the disc. On the contrary, when the position of the disc and the objective lens is too far, the opposite optical image is obtained, and similarly, the direction of the shift can be detected. That is, if the light image on the detector 13 and the moving direction of the light detector are known, it is possible to know whether the objective lens is approaching the disk or moving away from the disk.

The configuration of the photodetector utilizes the fact that the diameter of the incident light image changes depending on the focus position shift.
It may be circular as shown in. Since it does not have to have a plurality of divided light receiving surfaces as in the past, the photodetector configuration is simple. At this time, the diameter of the circle should be approximately the same as the spot diameter at the time of focusing when the incident light spot diameter becomes the smallest, and the spot diameter becomes larger as it defocuses, and the energy density of the light entering the photodetector increases. Is smaller, the shift amount can be detected from the change in the output of the photodetector. Further, in order to improve accuracy and facilitate focus servo pull-in, a divided structure as shown in FIG. 5 may be used. Therefore, the signals of the divided portions S1, S2, and S3 of the photodetector 1 have the smallest light spot system at the time of focusing, and light is incident only on S1, but as deviation occurs, light is incident on S2 and S3 as well. The spot diameter becomes larger, and for example, S1-S2-S3 can be used as the focus error signal.

The control unit 16 of FIG. 2 will be described. These are composed of a drive circuit of the vibrator 14 and a signal converter of the photodetector 1. The oscillator 18 and the amplifier 17 serve as a vibration source that vibrates the vibrator 14. The frequency of the oscillator 18 needs to be detected at a time interval corresponding to the surface wobbling amount and speed of the disk, and it is necessary to detect the deviation amount, and it is usually necessary to set the frequency to about 1 to 10 kHz. At such a frequency, a time delay may occur between the vibration waveform of the oscillator 18 and the actual vibration of the vibrator. For this reason, the time delay correction unit 19 is provided as shown in FIG. This is a method in which the vibration signal at the vibration frequency and the time delay of the vibrator 14 are stored in advance and the actual vibration position is known in consideration of this time delay. In addition to this, a method in which a position detector for knowing the position in the optical axis direction is provided near the photodetector 1 and the vibration (displacement) of the photodetector is directly detected by this signal may be used.

The signal from the time delay correction unit 19 is a signal indicating the moving direction of the vibrator 14, and the signal generated in the unit by this correction signal is used as the signal of the photodetector 1 by the timing signal generator 24. Generates timing signals for capture. The input signal from the photodetector 1 is amplified by the amplifier 21, sampled at the timing of t1 to t3 shown in FIG. 3, and the direction discriminating circuit 20 discriminates the direction of the focus position shift. Next, when the vibrator 14 reaches the center position (t2 in FIG. 3), the deviation amount detector 23 samples the deviation amount, and the deviation amount obtained here and the signal of the direction determination circuit 20 are used as error signals. The focus error signal 23 is generated by sending it to the generator 22. This signal 23 becomes a drive signal for the objective lens actuator, and the focus position is corrected.

In order to improve the performance of the servo control in recent years,
Digital control is replacing the way this is done. Digital servo control is a method in which an error is detected at a predetermined sampling cycle and control is performed using this detected value.However, in this embodiment, error detection is periodically performed by the vibration cycle of the vibrator. It is a suitable method.
When viewed comprehensively, it also has the feature that the control configuration of the entire device can be simplified.

As described above, according to the optical recording apparatus of the embodiment of the present invention, since the photodetector that is excited in the direction parallel to the incident optical axis is provided, the detector excitation of the spot diameter on the detector is performed. It is possible to know the distance between the objective lens and the disc by the difference in the tendency of temporal change with respect to.

Although the disk reflected light is used in this embodiment, transmitted light may be used.

[0028]

As is apparent from the above embodiments, according to the present invention, the number of optical components of the error detection system can be reduced, the assembling process is simple, and the adjustment is easy, so that various components are required. The accuracy is also relaxed, so it is smaller, simpler,
An inexpensive optical recording device can be provided.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the principle of an optical recording apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram showing the configuration of the device.

FIG. 3 is a schematic diagram showing an error detection method in the same device.

FIG. 4 is a configuration diagram of a photodetector in the same device.

FIG. 5 is another configuration diagram of a photodetector in the same device.

FIG. 6 is a configuration diagram of a conventional optical pickup.

FIG. 7: Conventional focus error detection method (astigmatism method)

FIG. 8: Conventional focus error detection method

FIG. 9: Conventional focus error detection method

[Explanation of Codes] 1 Photodetector 14 Vibrator

Claims (2)

[Claims] 1. An optical recording apparatus for irradiating a light spot on a record carrier and detecting the reflected or transmitted light thereof with a photodetector to control the position of the light spot on the record carrier, the reflection from the record carrier. Alternatively, a vibrator capable of vibrating in a direction parallel to the optical axis of the transmitted light, and a photodetector configured integrally with the vibrator to detect the diameter or energy density of the incident light beam, the vibration direction of the vibrator, An optical recording device for controlling the position of a light spot on a record carrier by using a signal indicating a position and an output signal from the photodetector. 2. The optical recording device according to claim 1, wherein the vibrator includes a piezo element.