JPS60171639A - Tracking device of optical head - Google Patents

Abstract

PURPOSE:To enable accurate tracking of required light beam when necessary by generating a tracking error signal from each of plural light beams and making tracking selecting one of them according to necessity. CONSTITUTION:Laser light beams of wavelength lambda1, lambda2 respectively emitted from laser diodes 1, 1a are mixed by a dichroic mirror (DM)3 through coupling lenses 2, 2a, and converged separately on the face of the medium of an optical disk 20 through a deflection beam splitter (PBS)4, a lambda/4 plate and an objective lens 6. The reflected light moves backward and reflected by the PBS4. Light of wavelength lambda1 is reflected by DM7, and light of wavelength lambda2 transmitted and reflected by a reflection prism 8 and enters halved light detectors 12, 12a through filters 9, 9a and convex lenses 10, 10a, and tracking error signals are outputted. The signals are selected through a switch, and accurate tracking for desired light beam is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION (al) Technical Field of the Invention The present invention relates to an optical disk storage device, and more particularly to tracking of an optical head in which at least two functions of recording, reproduction, and erasing can be performed simultaneously by the same head. The present invention relates to an optical head in which a desired system for recording, reproducing, or erasing is selected when performing the above operations, and the tracking error signal of the selected system is used to perform tracking of the optical head.

(b) Background of the Technology As electronic computers increase in speed and capacity, storage devices, which are the main part of computers, are also required to have higher density and larger capacity. For this purpose, magnetic recording and reproducing methods such as magnetic disks, which are easy to record and reproduce, are currently the mainstream, but optical disks that record and reproduce information optically are in principle better than current magnetic disks. It has many advantages and is being actively researched.

Optical discs are characterized by their high recording density.

Information is recorded on a recording medium at high density (for example, a disk with a diameter of 30 cm with a storage capacity of 10 bits has been reported) using a laser beam focused to a diameter of around 1 μm. Utilizing reversible changes in the properties of recording media due to light or heat, it is now expanding into the area of rewritable storage devices.

It has a much higher recording density than magnetic disks.

This rewritable optical disk device, which has the potential to achieve the same access time as a magnetic disk and the low cost and performance of a magnetic tape, is ideal for large-capacity storage units in information processing equipment that require frequent rewriting. It is attracting attention as being suitable.

(C1 Prior Art and Problems Currently known recording media for rewritable optical disks include magneto-optical materials, thermoplastics, amorphous thin films,
There are liquid crystals, etc., but as a conventional example, let's talk about an optical disk that uses crystal/amorphous phase transition.

For example, recording media mainly made of tellurium oxide, etc.

Information is transmitted by utilizing the fact that heat treatment easily causes a reversible phase transition between two phases, an amorphous state and a crystalline state, and that the reflectance of the recording medium in both phases differs and the amount of reflection of the incident light beam changes. I can do it□.゛In order to write information, a crystalline (erased state) recording medium is rapidly heated and cooled with a laser beam to form an amorphous state! 3 (recorded state), and information is erased by removing heat with a laser beam and slowly cooling to cause phase transition and return to crystalline state.

In order to meet the purpose of laser beam irradiation as described above, the laser beam spot has two different shapes as shown in FIG. Figure 1fa
t is the shape of the spot of the laser beam for recording (writing) and reproduction (reading), and FIG. 1 (bl shows an example of the shape of the spot for erasing).

The recording spot is circular; [1liI recording spot is heated, the energy density of the laser beam in the spot during recording is high, the irradiation time is short, and the shape of the erasing spot is It has a long elliptical shape and heats and erases several recording points at the same time, but the energy density during erasing is low and the irradiation time is long, making it suitable for heat removal and slow cooling. As mentioned above, in the optical head of this example optical disk device,
It is not possible to use a single laser beam for both recording (reproduction) and erasing by simply controlling the output of the laser light source; at least two laser beams with different cross sections are required.

However, each light beam has a width of approximately 1 μm on the optical disk medium.
Since the width of the track is approximately 0.8 μm, it is necessary to accurately align the relative positions of each light beam with an accuracy of 0.1 μm or less. This accuracy is light-
It is difficult to maintain a constant temperature because it changes very delicately due to thermal expansion differences caused by temperature changes in the head and other related mechanisms, as well as deformation caused by mechanical vibration and stress.

On the other hand, when an optical head has a plurality of laser light beams, conventionally a method has been adopted in which a light beam for a tracking error signal of the optical head is branched from one specific laser light beam and used.

However, although this method guarantees that the laser beam will follow the center of the track on the optical disk, it cannot guarantee tracking of other laser beams, for reasons that will be explained later. Furthermore, as shown in FIG. 1, the problem becomes complicated when the shapes of the light beam spots are different.

In addition to the above example, it also has three light beams that function independently to record and erase information.

Although an optical head has been proposed in which the reproduction task is specialized, in this case it becomes even more difficult to accurately track each light beam. Therefore, depending on the needs of use,
The emergence of an optical head that enables accurate tracking of a required light beam has been long awaited.

(d+ Purpose of the invention The present invention has been made in consideration of the above-mentioned points.

For optical disk devices equipped with an optical head that has multiple light beams for playback and erasing, the tracking function allows the light beam to accurately follow the trunk of the optical disk, and the tracking function is extracted from a predetermined light beam as necessary. - An attempt is made to provide a tracking device that can selectively provide an error signal.

tel Structure of the Invention An object of the above invention is to provide an optical head capable of optically recording, reproducing, and erasing information by simultaneously irradiating a plurality of light beams onto a recording medium of an optical disk storage device. an optical system that simultaneously converges and irradiates at least two of the light beams onto the surface of the recording medium through a common objective lens; and an optical system provided corresponding to each of the at least two sets of optical systems for the plurality of light beams. a tracking error signal detection means for selecting one of the tracking error signals detected from the tracking error signal detection means; and a selection means for selecting one of the tracking error signals detected from the tracking error signal detection means; This can be easily achieved by providing a trunking device composed of a tracking drive means that is driven to perform tracking.

([1 Examples of the invention An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a configuration diagram showing an embodiment of a tracking device for detecting a tracking error signal of an optical head of an optical disk device according to the present invention, which is equipped with two sets of laser beams.

The laser light source has two sets of laser light beam systems each having a different wavelength. For example, the wavelength.

Let wavelength λ+ = 780 nm and wavelength λ2 = 830 nm. Laser light beams with elliptical cross-sections emitted from laser diodes 1 and la with wavelengths λ1 and λ2 are made into parallel light beams by Kampling lenses 2 and 2a with numerical apertures of 0.2 to 0.5, and then are injected into dichroic ink. The mirror 3 mixes the laser beam into a single laser beam, which passes through the polarizing beam splitter 4 and the two-wavelength plate 5, and then is separated onto the medium surface of the optical disk 20 by the objective lens 6 held within the two-dimensional actuator 33. The light beams are projected convergently and connect the respective light beam spots.

Here, the dichroic mirror 3 is a wavelength selection mirror that transmits light of wavelength λ2 and reflects light of wavelength λ1. A
The wavelength plate 5 is provided to convert the P-type light emitted from the laser diodes 1 and 1a into S-type light by passing it back and forth twice.

The laser beam reflected by the optical disk 20 is.

It travels backward along the original optical path, passes through the A wavelength plate 5, becomes S-type polarized light, is reflected by the beam splitter 4, and becomes a dichroic polarized light.
The mirror 7 separates the light into wavelengths λ1 and λ2. Here, the dichroic mirror 7 has a characteristic of reflecting the wavelength λ1 of the laser beam and transmitting the light having the wavelength λ2. The laser beam of wavelength λ2 transmitted through the dichroic mirror 7 is reflected by the reflecting prism 8. The laser light beam of wavelength λ1 reflected by dichroic mirror 7 and the laser light beam of wavelength λ2 reflected by reflection prism 8 are introduced into respective tracking optical systems.

Both tracking optical systems include filters 9 and 9a.

Consisting of convex lenses 10 and 10a, the converged laser beam is transmitted to two-split photodetectors 12 and 1, respectively.
2a, and is detected and output as a tracking error signal. These tracking error signals are always output corresponding to each light beam. Therefore, as shown in FIG.
0 and is switched by the switching signal S to select the tracking error signal obtained from the desired optical beam system, and then it passes through the two-phase compensator P and the power amplifier W to the two-dimensional actuator A of the objective lens 6. Drive the optical disk 2
The position of the spot of the laser beam on the optical disc is modified to follow the trunk of the optical disc.

Of course, in practice, a focusing error signal is extracted in order to automatically maintain the focusing of the laser beam, but in this case, a four-split photodetector is provided instead of a two-split photodetector, and a convex lens 10 is provided. The prism may be placed immediately after the loa. These tracking
Since the detection of the error signal or the focusing error signal and the driving mechanism of the objective lens 6 are not directly related to the present invention, their explanation will be omitted.

Furthermore, if the laser light beam is for reproduction, a part of it is separated and introduced into the reproduction optical system and finally taken out as a reproduction output signal. Since this is also not directly related to the present invention, a description thereof will be omitted, and the configurations of the focusing error signal detection device and the reproducing device are omitted in FIG.

In this embodiment, for example, λ1 is a reproduction-only light beam.

λ2 is used as a recording-only light beam, and for the reflected light of λ2, a 4-split photodetector (not shown) is provided instead of the 2-split photodetector 12a, and a prism (not shown) is installed after the convex lens 10a. Set it up and keep it in focus at all times. Incidentally, since it is easy to focus the two light beams mentioned above on the same plane, either -
By focusing one laser beam, it is possible to accurately focus other light beams.

However, as already mentioned, 1-racking does not work as in the case of focusing.1 For example, when playing back an optical disk device, the tracking signal extracted from the playback-only optical beam λ1 is selected by switching with the analog switch S. The error signal is taken out and the actuator 33 of the convex lens 6 is driven. During recording, recording-only optical beam λ2
The actuator 33 of the objective lens 6 is driven by selecting the tracking error signal extracted from the .

In the above embodiment, the light beam is composed of two beams having wavelengths λ1 and λ2, but a wavelength λ3 is added and each of these beams is used exclusively for recording, reproduction, and erasing. Outputs tracking error signal for recording and playback.

It is obvious that trunking of the optical head can be performed by selecting a tracking error signal corresponding to erasure.

(g) Effect of the invention As is clear from the above explanation, recording and playback.

When an optical head based on the present invention is employed in an optical head of an optical disk device that is equipped with a dedicated light beam for functions such as erasing, and therefore has a plurality of light beams, the conventional trunking problem, that is, the optical head of the optical head Tracking is performed based on the tracking error signal returned from one of the plurality of light beams, but this solves the problem that sufficient tracking cannot be achieved for the optical system of other light beams. be done. It is based on one invention,
Generate respective tracking error signals from each light beam, select one of them by a switching means as necessary, and drive the objective lens drive section of the optical head to perform tracking. This is because it becomes possible.

[Brief explanation of drawings]

FIG. 1 is a plan view showing the shapes of the reproducing/recording light beam and the erasing light beam of a conventional rewritable optical disk, and FIG.
FIG. 2 is a configuration diagram showing an optical configuration regarding tracking when a book light beam is used. FIG. 3 is a block diagram of a circuit that selects one of the tracking error signals obtained from each light beam of the optical head shown in FIG. 2 and sends it to the driving section of the objective lens of the optical head. In the figure, 1. la are wavelengths λ1. λ2 semiconductor laser diode, 2.2a is a coupling lens, 3 and 7 are dichroic mirrors, 4 is a polarizing beam splinter, 5 is an A wavelength plate, 6 is an objective lens, 8 is a reflection prism, and 9.9a is a filter. 10 and 10a are convex lenses, and 12.12a is a two-split photodetector. 20 is an optical disk, 30 is an analog switch, 31 is a phase compensator, 32 is a power amplifier, 33 is an actuator for driving an objective lens, and S is a switching signal.

Claims (1)

[Scope of Claims] An optical head capable of optically recording, reproducing, and erasing information by simultaneously irradiating a recording medium of an optical disk storage device with a plurality of light beams, the optical head comprising: an optical system that simultaneously converges and irradiates at least two light beams onto the surface of the recording medium through a common objective lens, and a tracking error provided corresponding to each of the at least two sets of optical systems for the plurality of light beams. signal detection means; and selection means for selecting one of the tracking error signals detected from the tracking error signal detection means. A tracking device for an optical head, comprising: a tracking drive means for driving the objective lens to perform tracking using a tracking error signal selected by the selection means.