JPS632124A - Optical head device for information recording medium - Google Patents

Abstract

PURPOSE:To start the recording quickly by providing a semiconductor laser as a single light source projecting a linearly polarized light and constituting a projection section of light flux to an optical disk with a polarized beam splitter and a luminous flux reflecting means. CONSTITUTION:The semiconductor laser 22 as a single light source projecting a linearly polarized light is provided to a light source section 24 of an optical head 21. The way of feeding to a coil provided to a Farady cell 28 is varied in response to purposes of information erasure/recording/reproduction to make the linearly polarized light incident in the Farady cell emit as any luminous flux whose polarized planes are perpendicular to each other, and the luminous flux reflected in a polarized light beam splitter 29 and focused onto the optical disk and the luminous flux transmitted through the polarized beam splitter, reflected in a reflection mirror 31 and focused onto the optical disk are switched in response to the direction of the polarized plane of the luminous flux. Thus, high speed over-light starting the recording quickly is executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to the configuration of an optical system of an optical head device that erases, records, and reproduces information by irradiating an information recording medium with light.

[Prior art and its problems]

2. Description of the Related Art Magneto-optical and phase-change optical disks are known as information recording media in which information is erased, recorded, and reproduced by irradiation with light. In both cases, the light is 1μ in diameter.
The information track, which serves as an information recording section, is irradiated by focusing on a minute spot in the vicinity of m.

In the magneto-optical type, the directions of magnetization of the information recording medium in the erased state or recorded state are opposite to each other, so light is irradiated while applying a magnetic field in the direction corresponding to the direction of magnetization in each state to control the temperature of the information recording area. information is erased or recorded by raising the temperature to near the Curie temperature and magnetizing the information recording medium in the direction of the magnetic field. In addition, when reproducing information, when linearly polarized light is reflected by a magnetic material, the polarization plane of the reflected light rotates with respect to the polarization plane of the incident light, making use of the Kerr effect. It detects light intensity signals corresponding to the rotation of the surface, that is, the magnetization of the information recording medium. In the phase change type, information is erased or recorded by utilizing a reversible phase change between a crystalline state as an erased state and an amorphous state as a recorded state through heating by light irradiation. . When reproducing information, the intensity signals of light corresponding to information are detected by utilizing the difference in light reflectance between the crystalline state and the amorphous state. .

FIG. 6 shows a conventional structure of an optical system in an optical head used for irradiating light for erasing, recording, and reproducing information. The optical system of the optical herad 1 is a semiconductor laser 2
．． Collimating lens 3. Beam splitter 41 reflection mirror 5. It consists of an objective lens 6° and a light detection section 9. Of these, the reflecting mirror 5 and the objective lens 6 constitute a beam projection section. Linearly polarized light is projected from the semiconductor laser 2, and collimated into a parallel beam 1o by the collimating lens 3.

The beam passes through a beam splitter 4, is reflected by a reflecting mirror 5, and is formed by a focusing objective lens 6 to form a minute spot 8 on an information track (not shown) of an optical disk 7 as an information recording medium. The light reflected by the information track travels backward along the above path, passes through the objective lens 6 and the reflection mirror 5, and is partially reflected by the beam splitter 4 and enters the photodetector 9 to reproduce the recorded information. . In the case of a magneto-optical optical disc, an analyzer (not shown) is provided on the incident side of the photodetector 9. The light passing through this analyzer changes in intensity according to the rotation of the plane of polarization due to the Kerr effect mentioned earlier.
A photodetector detects the intensity signals of this light. The optical disc 1 that houses the above-mentioned optical system tracks the information track of the optical disc 7, which rotates in the direction of the arrow by the drive of the spindle motor 11, using a servo mechanism (not shown). move in the direction. Further, the objective lens 6 is provided in the objective lens unit 12,
A servo mechanism (not shown), which is separate from the optical helad 1, tracks the information track with even greater precision. 7th
The figures are schematic diagrams showing the state of information recording, in which (a) is a plan view and (b) is a cross-sectional view. r4-shaped information track 15
A minute spot 8 of light is formed inside the disc, and information is recorded as pits 16 and 17 of nine different lengths depending on the information.

In the above configuration, when performing an override in which the pits 16 and 17 as information recorded on the information track 15 are erased and new information is recorded, since the light source is single, the information track 15 is concentrically shaped. After erasing information, the optical disk must rotate once and wait for the erased portion to return to the minute spot position before starting recording. Furthermore, in an optical disc in which the information track 15 is formed in a spiral shape,
As before, recording cannot be started unless the information track is jumped by one more track after waiting for one revolution.

In order to perform an override using an optical head according to the conventional technology that uses a single light source, the above-mentioned rotational waiting time is necessary, so new information is recorded while erasing previously recorded information. It is extremely difficult to perform a fast override. In contrast, it is conceivable to use two optical heads, one for erasing and one for recording and reproducing. However, in order to downsize the information recording and reproducing device, the limited space around the optical disk with a diameter of 13 cTL supported by the drive stand is equipped with the spindle motor for driving the optical disk and the optical head. It must contain mechanical parts such as a tracking mechanism including a motor for causing the head to track an information track, and electronic circuit parts such as a power supply part, an information signal amplification part, and an optical head control part. Furthermore, in the case of a device that uses a magneto-optical optical disk, it is extremely difficult to fit two optical heads into an information recording/reproducing device whose width and depth are miniaturized to nearly the diameter of the optical disk by applying a magnetic field in addition to the above. Have difficulty.

[Purpose of the invention]

This invention solves the above problems and uses a single light source.
To provide an optical head device capable of high-speed overriding that starts recording new information immediately after erasing information without increasing the size of the information recording/reproducing device using multiple optical heads.

[Key points of the invention]

The key point of this invention is that the Faraday cell rotates the plane of polarization of the incident linearly polarized light according to the magnetic field generated by power feeding to the coil provided in the Faraday cell. The plane of polarization can be switched to either one of the beams of light perpendicular to each other, ! Focusing on the fact that the polarized beam splitter reflects the light beam with the plane of polarization perpendicular to the plane of incidence to the side, and transmits the beam with the plane of polarization parallel to the plane of incidence, the light source part receives linearly polarized light. A single semiconductor laser is provided as a single light source for projection, and a Faraday cell as a polarization plane changing means, a polarizing beam splitter as a beam splitting means, and a beam reflecting means are used to project a beam onto an optical disk as an information recording medium. By configuring it with a reflective means as
The method of feeding power to the Faraday cell is changed depending on the purpose of erasing, recording, and reproducing, and the light beam emitted from the Faraday cell is reflected by a polarizing beam splitter depending on the polarization plane and is focused and projected onto the information track of the optical disk. The purpose is to switch between the light beam that passes through the polarizing beam splitter and the light beam that is focused and projected onto the information track of the original disk via a reflection mirror. The projection position of each light beam extends to a distance corresponding to at least y for one sector on the outermost information track of the optical disk, and recording can be started immediately by switching the projection position of the light beam after information is erased.

[Embodiments of the invention]

FIG. 1 shows an embodiment of the present invention.
The first optical system includes a semiconductor laser 22 and a collimating lens 23.
A light source section 24. Beam splitter 25° photodetector 26. Faraday cell 2 with coil 27 & polarizing beam splitter 29. Recording objective lens 30° reflection mirror 31. It is composed of an erasing objective lens 32. Of these, 7 alade cells 28. Polarizing beam splitter 29. Recording objective lens 30. A reflecting mirror 31 and an objective lens 32 for erasing constitute a part for projecting a light beam onto the optical disk 7. The recording objective lens 30 and the erasing objective lens 32 are arranged with their central axes spaced apart from each other by at least one sector of the outermost information track of the optical disc 7.

The rotation direction of the optical disc 7 is the direction of the arrow in the figure.

FIG. 2 shows the functions of the optical head with the above configuration. FIG. 2(a) shows a case where information recorded on the optical disc 7 is being erased. Semiconductor laser 22
is linearly polarized light 33 whose plane of polarization is perpendicular to the plane of the paper, indicated by the symbol ■.
This linearly polarized light 33 is projected by the collimating lens 2
3 to form a parallel beam of light 34.

The light passes through the beam splitter 25 and enters the Faraday cell 28. 7 Coil 27 provided in Allade cell 28
A direct current i is supplied in the direction of the arrow, and due to the action of the magnetic field generated by this, the plane of polarization of the incident light beam rotates 900 times in the Faraday cell 28, and the plane of polarization is parallel to the plane of the paper as shown by symbol 1, a straight line. Faraday cell 2 as a beam of polarized light
8 and enters the polarizing beam splitter 29.

The polarizing beam splitter 29 transmits the light beam whose polarization plane of the incident light is parallel to the plane of incidence (the plane of the paper), and reflects the light beam whose polarization plane is perpendicular to the plane of incidence (the plane of the paper). passes through the polarizing beam splitter and passes through the reflecting mirror 3.
1, it is reflected toward the optical disk 7 and is passed through the erasing objective lens 3.
2, a minute spot 35 with a diameter of about 1 μm is formed at a point A on an information track (not shown) of the optical disc 7.
Erase the information projected and recorded. Figure 2 (
b) shows a case where information is recorded on the optical disc 7 or recorded information is reproduced. In this case, power is not supplied to the coil 27 included in the Faraday cell 28, and therefore the plane of polarization within the Faraday cell 28 does not rotate. Therefore, a light beam whose polarization plane is perpendicular to the plane of the paper enters the polarizing beam splitter. This light beam is reflected by the polarizing beam splitter 29 and focused by the recording objective lens 30, and is made into a minute spot 3 with a diameter of approximately 1 μm, as in the case of erasing.
6, the light is projected onto point B on the information track of the optical disc 7 to record information. In this embodiment, information is reproduced without power being supplied to the Faraday cell 28, similar to when information is recorded. In this case, the light reflected at point B travels backward along the illustrated optical path and is reflected by the beam splitter 25, and the light is reflected by the photodetector 26.
incident on . Note that reproduction may be performed in the power supply state at the time of erasing information.

FIG. 3 schematically shows how information is erased and recorded according to this embodiment. The distance between point A, which is the light spot for erasing information, and point B, which is the light spot for recording and reproducing, is l on the outermost information track of the optical disc.
Since the length of a sector corresponds to y, in the vicinity of the outer periphery of the optical disk, as shown in (a), (b), and (C) in the figure, there is a sector 41 whose information has been erased by the light at point A. The first part will move to point B when all the information in that sector 41 has been erased, so at that point, the light irradiation will be switched to point B.
By switching to point K, recording in sector 41 can be started immediately following erasing of information. (a
) indicates that information in the sector 41 is being erased, and diagonal lines indicate areas where information is recorded. (b) shows a state in which erasure is complete, and (C) shows a state in which new information is being recorded, indicated by intersecting diagonal lines. In the information track on the innermost circumference of the optical disc, the length of the l sector is approximately half the length of the sector on the outermost circumference. (e), (f), and (g) show how information is deleted and recorded in this case.
Shown below. (e) Information in sector 43 is being erased.

(g) indicates that erasing has been completed, and (g) indicates that new information is being recorded. Since the length of the sector is approximately half the interval between points A and B, it takes a waiting time equivalent to the travel time of sector 43 until the beginning of sector 43, where information has been erased, reaches point B. However, this time is much shorter than the waiting time for one revolution of the optical disk in the prior art. That is, 3 times per revolution of the information track.
Since two sectors are allocated, the waiting time for one rotation is only t'/32, and recording can be started immediately after information is erased.

According to the above method, new information is recorded every one sector near the outer periphery of the optical disc, as shown in sectors 41 and 42 shown in FIG. Although this is done every two sectors as in 44, there is no problem since the erasure, recording, and reproduction of normal information is managed for each sector.

FIG. 4 shows an example in which the plane of polarization of the linearly polarized light beam projected from the semiconductor laser 37 is parallel to the plane of the paper, and the configuration of the optical system is exactly the same as that in FIG. 1. , in this embodiment the coil 2 of the Faraday cell 28
Information is erased in the case (a) in which power is not supplied to 7, and recording is performed in the case (b) in which power is supplied. Although it is convenient to reproduce information by projecting light to point A without power being supplied to the coil 27 and detecting the reflected light by the light detection section 26, it is also possible to reproduce the information by projecting light to point B with power supplied. No problem.

FIG. 5 shows the direction of the light beam projected from the semiconductor laser 38 between the collimating lens 23 and the beam splitter 25 and between the beam splitter 25 and the Faraday cell 28 at the bottom of each.

In this embodiment as well, the configuration of the optical system is the same as that in FIG. In this embodiment, the coil 2 of the Faraday cell 28
The direction of the current flowing through the wires is reversed for erasing information and for recording and reading, so that in each case the direction of the current applied is opposite to each other by 45 degrees so that the plane of deflection of the light beam is perpendicular or horizontal to the plane of the paper. It is made to rotate in the direction and emit the light.

(a) is when information is erased, and (b) is when information is recorded. Reproduction of information is possible in any power supply state. In this embodiment, the coil 27 of the Faraday cell 28
There is an advantage that the current value to be passed through the coil 27 or the number of turns of the coil 27 is only half that of the above two examples.

As described above, this invention uses a single light source.

By switching the optical path in two ways, it is possible to erase and reproduce information with one optical head.

〔Effect of the invention〕

This invention includes a single semiconductor laser as a single light source that projects linearly polarized light to a light source section of an optical head device that projects light onto an information recording medium such as an optical disk, and also includes a semiconductor laser as a single light source that projects linearly polarized light. is composed of a Faraday cell, a polarizing beam splitter, a reflecting mirror, and two lens systems for focusing the light beam reflected by the polarizing beam splitter and the light beam reflected by the reflecting mirror onto the information track of the optical disk, respectively. Deletion and recording of information.

Depending on the purpose of reproduction, the method of feeding power to the coil provided in the Faraday cell is changed, and the linearly polarized light incident on the Faraday cell is emitted as either a beam whose polarization plane is perpendicular to each other, and the polarization plane of that beam is Depending on the direction, it is possible to switch between a beam that is reflected by a polarizing beam splitter and focused on the optical disk and a beam that is transmitted through the polarizing beam splitter, reflected by a reflection mirror, and focused on the optical disk.

The projected position of each light beam is set at a distance corresponding to at least 1 sector on the outermost information track of the optical disk, so after information is erased, the light beams can be projected by switching the projection position υ to erase the information. You can have a fast override that starts recording immediately. Therefore, the number of optical heads is 1
Since only one is required, the above-mentioned override can be performed without increasing the size of the information recording/reproducing apparatus.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the invention, FIG. 2 is a schematic diagram showing the functions of an embodiment of the invention, and FIG. 3 is a schematic diagram showing the state of erasing and recording information on the information track of an optical disc. FIGS. 4 and 5 are schematic diagrams showing the functions of different embodiments of the present invention, FIG. 6 is a configuration diagram of an optical head according to the prior art, and FIG. 7 is a schematic diagram showing the state of recording information on an optical disc. be. 1.21: Optical head, 2,22: Semiconductor laser,
5, 31: Reflection mirror, 6: Objective lens, 7: Optical disk. 8.35, 36: minute spot, 24: light source section, 28
: Faraday cell, 29: Polarizing beam splitter, 30
: Recording objective lens, 32: Erasing objective lens. λR Patent Attorney-1-J Colo E=-t (G) (b) Figure 4 Figure 5 Figure 7

Claims (1)

[Claims] 1) In an optical head device that records and erases information on an information recording medium by irradiating light, the light source unit includes a single light source that projects linearly polarized light, and a polarization plane changing means for changing the polarization plane of the linearly polarized light incident on the optical system of the light beam projection unit to a polarization plane having a different inclination from the polarization plane depending on a feeding method, and outputting the linearly polarized light with an inclination different from the polarization plane; a light beam splitting means for splitting the light beam from the optical path of the incident light beam; a first light beam focusing means for focusing the light beam split by the light beam splitting means and projecting it onto a recording portion of the information recording medium in the form of minute dots; a light beam reflecting means for reflecting the light beam transmitted through the light beam splitting means in the same direction as the light beam split by the light beam splitting means; and a light beam reflected by the light beam reflecting means to be focused on the recording section of the information recording medium. The projection point of the light beam focused by the first light beam focusing means is a point at which the light beam is projected in the form of a minute point at least at a distance approximately corresponding to the length of one sector of the information recording area on the outermost periphery of the information recording medium. 1. An optical head device for an information recording medium, characterized in that the optical head device comprises a light beam converging means. 2) An optical head device for an information recording medium according to claim 1, wherein the light source is a semiconductor laser. 3) An optical head device for an information recording medium according to claim 1, wherein the polarization plane changing means is a Faraday cell. 4) An optical head device for an information recording medium according to claim 1, wherein the beam splitting means is a polarizing beam splitter. 5) An optical head device for an information recording medium according to claim 1, wherein the first light beam focusing means is a lens system. 6) An optical head device for an information recording medium according to claim 1, wherein the second light beam focusing means is a lens system.