JPH06215411A - Optical information recording and reproducing device - Google Patents

Abstract

PURPOSE:To obtain an optical information recording/reproducing device capable of reproducing both an optical disk with a narrow track pitch and an optical disk with a wide track pitch. CONSTITUTION:A light from a semiconductor laser 1 is converged by an objective lens 4 and information is recorded/reproduced on an optical disk 5. In this optical information recording/reproducing device, a means 50 for changing the diameter of a beam made incident on the objective lens 4 according to the track pitch of the optical disk 5 is provided. By providing the means 50 for changing the diameter of a beam made incident on the objective lens 4, a spot diameter formed on the optical disk 5 is changed by changing the beam diameter according to the track pitch of the optical disk 5 and an optical disk having a different track pitch is reproduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording / reproducing apparatus for recording / reproducing information on / from an optical disk.

[0002]

2. Description of the Related Art Recording / reproduction is performed on many commercially available optical disks by using laser beams having wavelengths of 780 nm and 830 nm. However, the wavelength of semiconductor lasers has been shortened and the wavelength of 680 nm has been put to practical use. Further development of shorter wavelengths is in progress, and it is SHG
It is realized by using an element (second harmonic generation element). As described above, when the wavelength of the laser beam used is shortened, the spot formed when the laser beam is focused on the optical disc by the objective lens becomes small, the track pitch of the optical disc can be narrowed, and the recording capacity is increased. There is an advantage that can be done.

Here, a diameter ω of a spot formed when a laser beam having a wavelength λ is condensed by an objective lens having a numerical aperture NA is given by ω = K × λ / NA (1) The constant K is 0.
It is 1 for 6,1 / e ² diameter. When a laser beam having a wavelength of 780 nm is condensed by an objective lens having a numerical aperture NA = 0.5, the spot diameter ω is ω (0.5) = 0.94 μm, ω (1 / e ² ) = 1.56
The track pitch of the optical disk corresponding to this is 1.6 μm. When a laser beam having a wavelength of 680 nm is focused by an objective lens having a numerical aperture NA = 0.5, the spot diameter ω is ω (0.5) = 0.82 μm, ω (1 / e ² ) = 1 .36
The track pitch of the corresponding optical disk is 1.4 μm. When a laser beam having a wavelength of 500 nm is focused by an objective lens having a numerical aperture NA = 0.5, the spot diameter ω is ω (0.5) = 0.6 μm, ω (1 / e ² ) = 1 The track pitch of the corresponding optical disc is 1.0 μm. As described above, in the optical information recording / reproducing apparatus using the laser beam having the wavelength of 500 nm, the track pitch of the optical disc is 1.0 μm, and the spot diameter ω is ω.
It becomes as small as (1 / e ² ) = 1.0 μm. Further, the capacity of the optical disk is increased in inverse proportion to the square of the spot diameter.

[0004]

As described above, by shortening the wavelength of the laser light source and reducing the spot diameter, the track pitch of the optical disk can be narrowed and a large capacity can be realized. It is also important from the standpoint of compatibility to be able to reproduce an optical disk having a conventional track pitch of 1.6 μm. Here, FIG. 10 shows a relationship between tracks and spots of a conventional optical disc having a track pitch of 1.6 μm. The width of the guide groove 11 of the conventional optical disk is 0.5 μm, and the track pitch is 1.6 μm. Spot 13 has wavelength λ = 780
It is a spot when the laser beam of nm is focused, and the diameter is ω
(1 / e ² ) = 1.56 μm. At this time, spot 1
Since 3 is also irradiated to the guide grooves 11 on both sides of the land 12, a track signal can be obtained. On the other hand, wavelength 50
In the optical information recording / reproducing apparatus using 0 nm, the diameter is ω (1 /
Since the spot 14 having e ² ) = 1.0 μm is irradiated on the optical disk and the spot 14 is not irradiated on the guide grooves 11 on both sides of the land 12, there is a problem that a desired track signal cannot be obtained. The track signal 61 is shown in FIG. 11, but when the spot 14 is on the land 12, the track signal is almost nonexistent and stable tracking cannot be performed. That is, in the optical information recording / reproducing apparatus using the wavelength of 500 nm, the conventional track pitch is 1.6 μm.
Unable to play the optical disc.

The present invention has been made in view of the above circumstances, and is an optical information recording / reproducing apparatus using a laser beam of a short wavelength, which is capable of reproducing an optical disk having a conventional track pitch of 1.6 μm. The purpose is to provide.

[0006]

In order to achieve the above object, the invention of claim 1 is an optical information recording / reproducing apparatus for recording / reproducing information on / from an optical disk by narrowing down light from a semiconductor laser with an objective lens. It is characterized in that a means for changing the diameter of the beam incident on the objective lens according to the track pitch is provided.

According to a second aspect of the invention, the light from the semiconductor laser is narrowed down by the objective lens to record information on the optical disc.
In an optical information recording / reproducing apparatus for reproducing, when an optical disc having a track pitch larger than a predetermined track pitch is loaded, it is detected and an aperture is inserted in the optical path between the semiconductor laser and the objective lens according to the detection signal. It is characterized by doing.

According to the invention of claim 3, the light from the semiconductor laser is narrowed down by the objective lens to record information on the optical disc.
In an optical information recording / reproducing apparatus for reproducing, when an optical disc having a track pitch larger than a predetermined track pitch is loaded, it is detected and a density filter is provided in the optical path between the semiconductor laser and the objective lens according to the detection signal. It is characterized by inserting.

According to a fourth aspect of the invention, in the optical information recording / reproducing apparatus according to the first, second and third aspects, the shape of the beam incident on the objective lens is changed to an ellipse or the intensity distribution of the beam is changed to an ellipse. Characterize.

[0010]

As described above, the diameter ω of the spot formed when the laser light having the wavelength λ is condensed by the objective lens having the numerical aperture NA is given by ω = K × λ / NA (1) Therefore, the spot diameter increases as the numerical aperture NA of the objective lens decreases. In the optical information recording / reproducing apparatus of the present invention, since the means for changing the diameter of the beam incident on the objective lens according to the track pitch of the optical disc is provided, the beam diameter of the objective lens can be changed according to the track pitch of the optical disc. The effective NA can be changed and the spot diameter can be changed. Therefore, even when a laser beam having a wavelength of 500 nm is used, it is possible to reproduce a conventional optical disc having a track pitch of 1.6 μm.

[0011]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram of an optical pickup section of an optical information recording / reproducing apparatus showing an embodiment of the present invention. In the figure, reference numeral 1 is a laser light source, 2 is a collimator lens, 3 is a beam splitter, and 4 is an objective lens. 5 is an optical disk, 6
Is a condenser lens, 7 is a beam splitter, 8 is a light receiving element for track detection, 9 is a cylindrical lens, and 10 is a light receiving element for focus detection. In FIG. 1, the light emitted from the laser light source 1 is collimated by the collimator lens 2 and transmitted through the beam splitter 3 to be focused by the objective lens 4 to form a minute spot of about 0.6 μm on the optical disc 5. . Then, information is recorded / reproduced on / from the optical disk 5 by this spot. The reflected light from the optical disk 5 passes through the objective lens 4 again, is reflected by the beam splitter 3, is focused by the condenser lens 6, is partially reflected by the beam splitter 7, and is received by the light receiving element 8 for track detection. Incident on. The light flux that has passed through the beam splitter 7 also passes through the cylindrical lens 9 and enters the light receiving element 10 for focus detection.

The laser light source 1 has a wavelength of 500.
nm semiconductor laser is used, but the wavelength is 1000 nm
It may be a unit for converting the semiconductor laser of (1) to a wavelength of 1/2 by an SHG element. In this embodiment, a variable diaphragm 50 is arranged in the optical path between the beam splitter 3 and the objective lens 4 as a means for changing the diameter of the beam incident on the objective lens 4 according to the track pitch of the optical disc 5. An example of this variable diaphragm 50 is shown in FIG. As shown in FIG. 2, in the variable diaphragm 50, the size of the opening 52 can be changed by the diaphragm plate 53, and the light flux has its opening 52.
Pass through. Further, the size of the opening 52 of the variable diaphragm 50 is changed by detecting the track pitch of the optical disc loaded in the drive and by the driving means 200 according to the size of the track pitch.

That is, when an optical disk having a track pitch of 1.0 μm is loaded, the variable diaphragm 50
The diaphragm plate 53 is opened and the opening 52 is wide open. The light emitted from the laser light source 1 and collimated by the collimator lens 2 is collimated by the variable diaphragm 50 by the objective lens 4 without vignetting, and then the optical disc. A minute spot of about 0.6 μm is formed on the film 5. Further, when an optical disc having a track pitch of 1.6 μm is loaded, this is detected, and the driving means 200 stops the diaphragm plate 53 of the variable diaphragm 50 according to the detection signal to reduce the size of the opening 52. Then, the peripheral portion of the collimated light from the collimator lens 2 is broken and the beam diameter is reduced. As a result, the effective NA of the objective lens 4 decreases, and the spot diameter increases. Therefore, even when a laser beam having a wavelength of 500 nm is used, it becomes possible to reproduce an optical disc having a track pitch of 1.6 μm. The spot diameter is 1.
In order to expand from 0 μm to 1.6 μm, the beam diameter incident on the objective lens 4 may be reduced by 1 / 1.6 = 0.6 times.

Next, as another preferred embodiment, the aperture 20 shown in FIG. 3 can be used instead of the variable aperture 50. The radius r2 of the opening 21 of the aperture 20 is
Is set so that the beam diameter incident on the objective lens 4 is reduced by a factor of 0.6. Further, the aperture 20 is inserted (or removed) into the optical path by the driving unit 200 according to the track pitch of the optical disc 5. That is, when an optical disk having a track pitch of 1.6 μm is loaded in the drive, this is detected, and the aperture 20 is moved to the optical path between the beam splitter 3 and the objective lens 4 by the driving means 200 according to the detection signal. insert. As a result, the beam diameter can be reduced and the spot diameter can be increased, as in the case of using the variable diaphragm 50. When an optical disc having a track pitch of 1.0 μm is loaded in the drive, this is detected, and the aperture 20 is removed from the optical path by the driving means 200. In the above embodiment, the variable diaphragm 50 and the aperture 20 are
Although the example has been shown in which is inserted in the optical path between the beam splitter 3 and the objective lens 4, it may be inserted in the optical path between the collimator lens 2 and the beam splitter 3.

Next, as another preferred embodiment, the density filter 30 shown in FIG. 5 can be used instead of the variable aperture 50 (or the aperture 20) in FIG. The density filter 30 has a concentrically reduced transmittance around 31 and reduces the amount of transmitted light in the periphery. The intensity distribution of the spot when the above-mentioned aperture 20 is used is shown in FIG.
Airy disk as shown in, main lobe 2
Side lobes 23 are generated on both sides of 2. The side lobes 23 cause crosstalk and cause a drop in the information signal. However, using the density filter 30 makes it possible to prevent such a problem. Here, in FIG. 6, 33 is the intensity distribution of the parallel light having the diameter r1 collimated by the collimator lens 2 and 3
Reference numeral 4 denotes the intensity distribution of the parallel light after passing through the density filter 30, but the intensity of the parallel light after passing through the density filter 30 smoothly decreases. Therefore, the beam diameter can be reduced and the side lobes can be reduced.

By the way, there is disclosed a technique for reducing the side lobe of the spot by inserting a radiation-attenuating element in the optical path of the radiation beam (see Japanese Patent Laid-Open No. 58-85944), but this is the size of the main lobe. The feature is that the side lobe is reduced while maintaining the same level. However, this technique does not change the spot size, and does not include the idea of changing the spot diameter according to the track pitch of the optical disc. Therefore, with this technique, an optical disc having a track pitch of 1.6 μm cannot be reproduced by an optical information recording / reproducing apparatus having a short wavelength light source. On the other hand, in the present invention, the density filter 30 reduces the beam diameter while reducing the side lobes, so that the spot diameter can be changed and the track pitch is 1.6 μm.
It is possible to reproduce the optical disk of the above with an optical information recording / reproducing apparatus having a short wavelength light source.

In the above embodiments, the wavelength is 500 nm.
Even when the laser light of is used, the track pitch is 1.6
This is an example in which the spot diameter is increased in order to obtain the track signal of the optical disc of μm. In this case,
The spot also grows in the direction along the track. However, it is not always necessary to reproduce with a spot of 1.6 μm for a pit recorded with a spot of 1.6 μm.
That is, reproduction with a spot of 1.0 μm has an advantage of increasing the information signal level of a small pit of about 1.0 μm. Therefore, the opening 52 of the variable diaphragm 50 described above
If the transmittance distribution of the aperture 21 of the aperture 20 and the density filter 30 is made elliptical and the direction along the track of the optical disk is set to the major axis, the spot becomes an ellipse short in the direction along the track and long in the direction orthogonal to the track. Reference numeral 60 in FIG. 7 is an example of an elliptical spot, which has a diameter of 1.0 μm in the direction along the track and a diameter of 1.6 μm in the direction orthogonal to the track. Note that FIG. 8A shows an example of the elliptical aperture 71 of the aperture 70, and FIG. 8B shows an example of the elliptic transmittance distribution 73 of the density filter 72.

FIG. 9 is a diagram showing an example of a cartridge used in the optical information recording / reproducing apparatus of the present invention. The cartridge 40 has a hole 41 for identifying the type of the optical disk housed inside. The hole 41 may be on the back side of the drawing. Here, the type of the optical disk may be one that directly determines whether the track pitch is 1.6 μm or 1.0 μm, or one that can be indirectly determined. For example, for wavelength 780nm or wavelength 5
It may be for determining whether it is for 00 nm. This is because the wavelength and the track pitch correspond to each other.
When the optical disc is identified as an optical disc for nm, the CPU in the drive determines that the track pitch is 1.6 μm, sends a detection signal to the drive means 200, and the variable aperture 50
The aperture may be narrowed or the aperture 20 (70) or the density filter 30 (72) may be inserted in the optical path to enlarge the spot to a predetermined size. Further, the track pitch value may be similarly determined from a plurality of identifiers.

By the way, the shape of the 3.5-inch magneto-optical disk cartridge is determined by the ISO standardization. This is because the identifier which indicates that the conventional disk having a track pitch of 1.6 μm is included in it. Not provided. However, the track pitch for short wavelength is 1.0μ
By providing an identifier that directly or indirectly indicates that the track pitch is narrow in the cartridge for the disk of m, the optical information recording / reproducing apparatus detects this identifier and changes the spot diameter accordingly, It becomes possible to reproduce optical disks having different track pitches. That is, the track pitch is discriminated directly or indirectly from the identifier in the cartridge 40, and the spot diameter is changed accordingly. If there is no discriminator, it is discriminated as a conventional disc having a track pitch of 1.6 μm and the disc size is changed accordingly. Change the spot diameter. The identifier on the cartridge 40 can be detected by providing a known reflection type photo interrupter or contact type switch in the optical information recording / reproducing apparatus.

[0020]

As described above, the explanation will be given based on the embodiments.
The optical information recording / reproducing apparatus according to claim 1 is provided with means for changing the diameter of the beam incident on the objective lens according to the track pitch of the optical disc (for example, a variable diaphragm), so that the beam diameter according to the track pitch of the optical disc. Can be changed to change the effective NA of the objective lens, and the spot diameter can be changed. Therefore, the wavelength 50
Even when a 0 nm laser beam is used, it is possible to reproduce a conventional optical disc having a track pitch of 1.6 μm.

In the optical information recording / reproducing apparatus of the second aspect, since the aperture is used as the means for changing the diameter of the beam incident on the objective lens, it is possible to reduce the cost in addition to the effect of the first aspect. it can.

In the optical information recording / reproducing apparatus of the third aspect, since the density filter is used as a means for changing the diameter of the beam incident on the objective lens, side lobes are eliminated in addition to the effect of the first aspect. It is possible to prevent problems such as an increase in crosstalk and a decrease in information signal.

In the optical information recording / reproducing apparatus of the fourth aspect, the opening 52 of the variable diaphragm 50 and the opening 21 of the aperture 20.
Or the density distribution of the density filter 30 is set to an ellipse and the direction along the track of the optical disc is set to the long axis, and the shape of the beam incident on the objective lens is changed to an ellipse or the intensity distribution of the beam is changed to an ellipse. Since the spot can be an ellipse which is short in the direction along the track (1.0 μm) and long in the direction orthogonal to the track (1.6 μm), there is a merit that the information signal level of a small pit of about 1.0 μm increases. can get.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an optical pickup section of an optical information recording / reproducing apparatus showing an embodiment of the present invention.

FIG. 2 is a view showing an embodiment of claim 1 and is a plan view showing an example of a variable diaphragm.

FIG. 3 is a diagram showing an embodiment of claim 2 and is a plan view showing an example of an aperture.

FIG. 4 is a diagram showing a spot intensity distribution when the aperture shown in FIG. 3 is used.

FIG. 5 is a diagram showing an embodiment of claim 3 and is a plan view showing an example of a density filter.

6 is a diagram showing an intensity distribution of parallel light by a collimating lens and an intensity distribution of parallel light after passing through the density filter shown in FIG.

FIG. 7 is an explanatory diagram of an embodiment of claim 4 and is a diagram showing an example of an elliptical spot formed on a track of an optical disc.

8A and 8B are explanatory views of the embodiment of claim 4, wherein FIG. 8A is a plan view of an aperture having an elliptical opening, and FIG. 8B is a plan view of a density filter having an elliptical transmittance distribution. Is.

FIG. 9 is a plan view showing an example of a cartridge used in the optical information recording / reproducing apparatus of the present invention.

FIG. 10 is a diagram showing a relationship between tracks and spots on a conventional optical disc having a track pitch of 1.6 μm.

FIG. 11 is a diagram for explaining a relationship between a track signal and a spot.

[Explanation of symbols]

 1 ... Laser light source 2 ... Collimating lens 3 ... Beam splitter 4 ... Objective lens 5 ... Optical disk 6 ... Condensing lens 7 ... Beam splitter 8 ... For track detection Light receiving element 9 ... Cylindrical lens 10 ... Light receiving element for focus detection 20, 70 ... Aperture 30, 72 ... Density filter 50 ... Variable diaphragm 200 ... Driving means

Claims (4)

[Claims] 1. An optical information recording / reproducing apparatus for recording / reproducing information on / from an optical disc by narrowing light from a semiconductor laser by an objective lens, and a means for changing a diameter of a beam incident on the objective lens according to a track pitch of the optical disc. An optical information recording / reproducing apparatus characterized by being provided. 2. An optical information recording / reproducing apparatus for recording / reproducing information on / from an optical disk by narrowing light from a semiconductor laser with an objective lens, and detecting this when an optical disk having a track pitch larger than a predetermined track pitch is loaded. An optical information recording / reproducing apparatus characterized in that an aperture is inserted in an optical path between the semiconductor laser and the objective lens according to the detection signal. 3. An optical information recording / reproducing apparatus for recording / reproducing information on / from an optical disc, wherein light from a semiconductor laser is narrowed down by an objective lens to detect when an optical disc having a track pitch larger than a predetermined track pitch is loaded. An optical information recording / reproducing apparatus in which a density filter is inserted in an optical path between the semiconductor laser and the objective lens according to the detection signal. 4. The optical information recording / reproducing apparatus according to claim 1, wherein the shape of the beam incident on the objective lens is changed to an ellipse or the intensity distribution of the beam is changed to an ellipse. Recording / playback device.