JPH11149655A - Optical recorder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical recorder having a condenser lens of material which has an extremely high refractive index, is excellent in transmittance, allows easy production and is extremely excellent in terms of workability. SOLUTION: This optical recorder has an objective lens 4 for converging a laser beam L to be cast to a prescribed beam diameter for the purpose of executing information recording to an optical recording medium D and the condenser lens 5 for further condensing the laser beam L transmitted through the objective lens 4 and casting the optical recording medium D with this beam. The condenser lens 5 consists of a single crystal of any among lithium niobate, lithium tantalate, futile, lead molybdate, tellurium dioxide, strontium titanate and zirconium oxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an optical recording medium such as a magneto-optical disk or a DVD-RAM using laser light.
The present invention relates to an optical recording device such as an optical head capable of at least writing (recording) information.

[0002]

2. Description of the Related Art In order to improve the surface recording density of an optical recording medium such as a magneto-optical disk or a DVD-RAM, it is necessary to make the beam spot diameter of a recording laser beam as small as possible. Generally, the beam spot diameter of the laser light is determined by the wavelength λ of the light source and the NA (numerical aperture) of the objective lens, and is about 0.8 × λ / NA. For this reason, a blue laser using a gallium nitride (GaN) -based material has been developed as a semiconductor laser that can be further shortened from the light wavelength of about 630 nm actually used in the optical disk device.

However, even if such a wavelength of blue laser light is used, it is only about three times the current areal recording density. So, Solid Immersion
An optical system in which a hemispherical lens called a lens (hereinafter, also referred to as SIL) is disposed between the optical recording medium and the objective lens reduces the beam spot diameter transmitted through the objective lens by 1 /. n times (where n is SI
(Refractive index of L) (see, for example, US Pat. No. 5,125,750).

[0004] Here, the laser beam transmitted through the SIL and emitted into the air tries to expand to the original beam diameter again, but the gap between the recording surface of the optical recording medium and the bottom surface of the SIL facing the SIL. However, in a region within about １ ／ of the light wavelength (generally called a near-field region), the laser light
The light is emitted with the same property as the inside of L, and the beam spot diameter is reduced to 1 / n times the diffraction limit.

[0005]

Glass such as borosilicate glass is generally used for the SIL. The refractive index of glass is usually up to about 1.8. To obtain a higher refractive index than this, for example, La ₂ O ₃ , ThO ₂ , Zr
Special glass having a rare element oxide such as O ₂ or Ta ₂ O ₅ as a main component must be used. In addition, even such a special glass has a refractive index of 2.0 or less, and it has been difficult to perform recording at a higher density.

In particular, the near field area is 63
When a laser wavelength near 0 nm is used as a light source, the laser spot diameter is about 300 nm or less, so that the surface of the SIL facing the recording surface of the optical recording medium requires high flatness processing accuracy, and conventional glass hardens. There was a problem of too much. Even if a polycrystalline material having a high refractive index is used for the SIL, the transmittance of light becomes extremely small due to a large number of grain boundaries existing in the polycrystalline material (for example, the transmittance at a used light wavelength of 500 to 600 nm is reduced). 50% or less), it is not possible to provide an optical head having excellent performance.

Therefore, the present invention solves the above-mentioned problems and has a very high refractive index and excellent transmittance.
An object of the present invention is to provide an optical recording apparatus having a condenser lens made of a material which is easy to manufacture and which is very excellent in workability.

[0008]

In order to achieve the above object, an optical recording apparatus according to the present invention comprises a light condensing lens for irradiating at least a laser beam for recording information on an optical recording medium. A recording device, specifically, for example, an objective lens for narrowing a laser beam to be irradiated for performing information recording on an optical recording medium to a predetermined beam diameter, and further condensing the laser beam transmitted through the objective lens, An optical recording device, such as an optical head, including a condenser lens for irradiating a recording medium, wherein the condenser lens is formed of lithium niobate, lithium tantalate, rutile, lead molybdate, tellurium dioxide, titanic acid. It is characterized by being composed of a single crystal made of either strontium or zirconium oxide.

Further, the condenser lens is made of a lithium niobate single crystal containing 3 to 7 mol%, more preferably 4 to 5 mol% of magnesia. Here, if the magnesia is 3 to 7 mol%, not only the light damage resistance is large and the change in the refractive index is very small, but also the grown single crystal is free from cracks and has good crystallinity. ,
It can be suitably used as SIL.

[0010] The optical recording apparatus is only required to be capable of recording at least on an optical recording medium, and may be capable of recording and reproducing.

[0011]

Embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic perspective view illustrating how optical recording is performed on an optical recording medium. FIG. 2 is a schematic partial cross-sectional view taken along the line AA of FIG. A dielectric layer made of, for example, silicon nitride, a magnetic layer made of a Gd-Fe-Co-based alloy, a Tb-Fe-Co-based alloy, or the like, made of silicon nitride, etc. on a substrate 1 made of resin such as polycarbonate or glass. A laser beam L having a wavelength of 500 nm to 600 nm is applied to a magneto-optical disk D having a recording layer 2 including a dielectric layer, a metal layer made of aluminum or the like, and a protective layer made of UV resin or the like by an optical head 3 which is an optical recording device. The light is condensed to irradiate a beam spot having a predetermined diameter. As a result, information is recorded on the magnetic layer in the area of the recording layer 2 of the magneto-optical disk D irradiated with the beam spot. The optical head 3 is supported by a movable arm 7 connected to a control device (not shown).

The recording of information on the magneto-optical disk D by the optical head 3 is performed as follows. First, the laser beam L is converged by the objective lens 4 which is a biconvex lens, and is a hemispherical condenser lens SIL5 which is made of a single crystal such as lithium niobate and has a plane portion for focusing on the lower surface 5a. Thus, the beam spot diameter is reduced to a predetermined value.

The recording layer 2 in the beam spot irradiated on the magneto-optical disk D is heated, and when the area is cooled, the magnetic layer is magnetized by the magnetic field applied by the magnetic field modulation coil 6 to perform recording. Do it. Note that the objective lens 4 may be a one-convex lens.

Here, SIL5 is made of lithium niobate (LiNbO ₃ : melting point 1250 ° C., refractive index no = normal light).
2.29, extraordinary refractive index ne = 2.20), lithium tantalate (LiTaO ₃ : melting point 1450 ° C, no)
= 2.18, ne = 2.17), rutile (TiO ₂ : melting point 1980 ° C, no = 2.61, ne = 2.90), lead molybdate (PbMoO ₄ : melting point 1070 ° C, no =
2.39, ne = 2.26), tellurium dioxide (Te
O ₂ : melting point 733 ° C., no = 2.43, ne = 2.2
7), strontium titanate (SrTiO ₃ : melting point 2)
080 ° C., refractive index 2.41), zirconium oxide (Zr
O ₂ : a single crystal having a melting point of 2690 ° C. and a refractive index of 2.42) is used.

Each of these single crystals has a refractive index of 2.1.
That is, 7 at the used light wavelength of 500 to 600 nm.
It has an excellent transmittance of 0% or more. In particular, lithium niobate, lithium tantalate, and rutile can be very easily grown by the Czochralski method or the like, and are softer than glass (Mohs hardness is 5 to 6). However, it is suitable. further,
There is an advantage that the refractive index fluctuation is smaller than glass (1 × 10 ⁻⁴ or less).

In particular, in the case of lithium niobate, when 3 to 7 mol% of magnesia (MgO ₂ ) is added, there is no change in refractive index (optical damage) due to short-wavelength laser light such as blue-green light, and the condensing lens is used. It can be suitably used. Further, when the magnesia in the lithium niobate single crystal is 4 to 5 mol%, there is almost no change in the refractive index, which is very preferable. If the magnesia in the lithium niobate is less than 3 mol%, the light damage resistance becomes small, and the refractive index fluctuation due to light induction becomes large. On the other hand, when the content of magnesia exceeds 7 mol%, cracks are often generated in the grown single crystal, which is not preferable.

As described above, the above-mentioned single crystal, which has a refractive index much larger than that of a conventional glass, has a smaller refractive index fluctuation than glass, and is very excellent in workability, etc., is very preferably used as an SIL. And the beam spot diameter of the laser beam can be made very small. As a result, the current recording pit size can be significantly reduced, and recording on an optical recording medium can be performed at a density as high as several times that of the current state.

As shown in FIGS. 1 and 2, the optical system for optical recording includes an objective lens 4 and a condenser lens 5 on an optical head 3.
Although an example in which information and the like are provided integrally and the information is recorded has been described, the configuration of the optical system is not limited to this, and an optical head including only a condensing lens without an objective lens may be used. . Also, for example, an optical head capable of recording and reproducing may be used. The optical head is not only a magneto-optical disk but also a DVD-R which is a phase-change type optical disk having an optical recording layer made of, for example, various Te-based alloys.
AM can also be used. In addition, the shape of the condensing lens is not limited to a general hemisphere, and may be a shape such as a so-called super hemisphere having a large curved surface area, as long as a desired spot diameter can be obtained. The shape and the like can be appropriately changed and implemented without departing from the gist of the present invention.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, more specific embodiments according to the present invention will be described.

[Embodiment 1] Next, a more specific embodiment will be described. A rutile single crystal having a diameter of about 3 inches was obtained by the Czochralski method using a resistance heating type growth furnace, and the rutile single crystal was cut into 1.2 mm square wafers. The axis (Z axis (C axis)) is perpendicular to the recording surface of the magneto-optical disk (the refractive index is 2.6 because the ordinary light refractive index and the extraordinary light refractive index match).
1), and a hemisphere having a radius of about 1 mm was polished. This polishing was performed using a general grinding wheel for optical glass. Note that the refractive index variation of the rutile single crystal is 1 × 10
^-5 or less.

Next, a laser beam from a semiconductor laser having a wavelength of 529 nm is condensed by an objective lens of an optical head as shown in FIG.
When the distance between the recording surface of the magneto-optical disk and the plane side of the SIL of the hemisphere was brought close to about 100 nm, which is within 1/4 of the wavelength of the used light, the diameter of the recording spot was measured. A spot of about 180 nm was obtained.

On the other hand, when a hemispherical SIL using a borosilicate glass having a refractive index of 1.8 was used and the recording spot diameter was measured under the same conditions under the same conditions, it was about 260 nm. The spot diameter was large. In addition,
The change in the refractive index of the glass was 5 × 10 ⁻⁴ or more.

Example 2 In the same manner as in Example 1, a single crystal of lithium niobate having a diameter of about 3 inches was obtained by the Czochralski method using a growth furnace of a resistance heating system. At this time, magnesia was added to the single crystal growing raw material so that the amount of magnesia after the growth was 5 mol%.

The change in the photo-induced refractive index of this lithium niobate single crystal was measured by the Senarmont method.
It was 2.0 × 10 ⁻⁵ or less, which was much smaller than the above glass.

The lithium niobate single crystal is 0.7 mm
After cutting into square wafers, the optical axis (Z-axis (C-axis)) of the lithium niobate single crystal is perpendicular to the recording surface of the magneto-optical disk (the ordinary light refractive index and the extraordinary light refractive index match). A hemisphere having a radius of about 0.5 mm was polished. This polishing was performed using a grinding wheel for optical glass as in Example 1.

Next, in the same manner as in the first embodiment,
m laser beam is condensed by an objective lens, and further converged by the SIL composed of the single crystal body,
When the distance between the recording surface of the magneto-optical disk and the plane of the hemisphere SIL was made close to about 100 nm, and the recording spot diameter was measured, a spot diameter of about 205 nm smaller than that of the glass was obtained.

Example 3 In the same manner as in Example 1, a lithium tantalate single crystal having a diameter of about 3 inches was obtained by the Czochralski method using a resistance heating type growth furnace.

The above lithium tantalate single crystal was used for about 1.
After cutting the wafer into 0 mm square wafers, the optical axis (Z axis (C axis)) of the lithium niobate single crystal is perpendicular to the recording surface of the magneto-optical disk (the ordinary light refractive index and the extraordinary light refractive index are different). Since they match, the refractive index is 2.18), and the radius is about 0.8.
The hemisphere of mm was polished. This polishing is performed in Example 1.
In the same manner as described above, the grinding was performed using a grinding wheel for optical glass.

Next, in the same manner as in the first embodiment,
The laser light from the semiconductor laser of m is focused by an objective lens and further narrowed by the SIL composed of the single crystal body, so that the distance between the recording surface of the magneto-optical disk and the plane side of the hemispherical SIL is about 100 nm. The spot diameter of the recording spot was measured in close proximity to the above.

[0030]

As described above, according to the optical recording apparatus of the present invention, lithium niobate, lithium tantalate,
A single crystal of rutile, lead molybdate, tellurium dioxide, strontium titanate, or zirconium oxide was used as a converging lens (solid immersion lens). It is possible to provide a very excellent optical recording apparatus having a condenser lens which is excellent, easy to manufacture, and has good workability.

Since the single crystal has a refractive index of 2.0 or more, the beam spot diameter of the laser beam can be made very small, and the current recording pit size can be greatly reduced. It is possible to provide an excellent optical recording device that can record on an optical recording medium at a density that is several times or more the current density.

Further, magnesia is used as a condenser lens.
By adopting a single crystal of lithium niobate containing up to 7 mol%, more preferably 4 to 5 mol%, an optical recording having an excellent light-collecting lens having high light damage resistance and a very small change in refractive index. Equipment can be provided.

[Brief description of the drawings]

FIG. 1 is a perspective view illustrating an embodiment of an optical system according to the present invention.

FIG. 2 is a schematic partial cross-sectional view taken along line AA in FIG.

[Explanation of symbols]

 1: substrate 2: recording layer 3: optical head (optical recording device) 4: objective lens 5: SIL (condensing lens) 6: magnetic field applying coil D: magneto-optical disk

Claims (2)

[Claims] 1. An optical recording apparatus comprising a condenser lens for irradiating a laser beam for recording information on an optical recording medium, wherein the condenser lens is composed of lithium niobate, lithium tantalate, rutile, An optical recording device comprising a single crystal of any of lead molybdate, tellurium dioxide, strontium titanate, and zirconium oxide. 2. The optical recording apparatus according to claim 1, wherein the condenser lens is made of a single crystal of lithium niobate containing 3 to 7 mol% of magnesia.