JP2000011423A - Information recording and reproducing optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form propagation light to a record medium to a microspot reflecting high NA by a solid immersion lens with a proximity effect by disposing a lightproof means in such a manner that the incident light to the plane part of the solid immersion lens satisfies total reflection conditions and forming the incident light to a non-propagation light when the recording surface does not exist proximatly. SOLUTION: An antireflection coating is applied on the plane part of an SIL(solid immersion lens):2 and the distance between both is held at 1/8 of a light source wavelength λ in order to efficiently condense the reflected light of the record medium 3 to the SIL:2. In addition, a thin transparent protective film which is not significant to λ/8 is applied on the recording medium 3 and is disposed to face the SIL:2. The lightproof means 4 formed by applying elliptic light shileding coatings on glass parallel flat plates is disposed between a semiconductor laser 5 and a beam splitter 7. Only the rays satisfying the total reflection conditions are used within the SIL:2. Then, only the rays satisfying the total reflection conditions are made incident on an objective lens 1 and the microspot below the spot reflecting the high NA of the optical system is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information recording / reproducing optical system, and more particularly to an objective lens optical system having a high numerical aperture (hereinafter, referred to as "NA").

[0002]

2. Description of the Related Art In recent years, an information recording / reproducing optical system using an objective lens optical system having a high NA using a solid immersion lens (hereinafter, referred to as SIL) has been actively researched and developed.

[0003] For example, there is US Pat. No. 5,125,750 (JP-A-5-189796).

A convergent ray from the objective lens system is incident almost perpendicularly on the spherical surface of the SIL facing the objective lens system,
The light is condensed on the plane portion of the SIL facing the recording medium.
In the SIL, the wavelength is 1 / n (n; SI
(The refractive index within L), the NA of the optical system can be made approximately n times the NA of the objective lens system serving as a base.

Therefore, a near-field (near-field or near-field) region for the converging point on the SIL plane portion is
By arranging the recording medium, high-resolution recording / reproduction becomes possible.

In order to further increase the NA, SIL
It is also well known that the thickness of the spherical surface is increased as shown in FIG.

[0007] As shown in FIG.
/ N (r; radius of curvature of SIL), and when the SIL plane is focused by the objective lens serving as a base, the NA of the optical system becomes
Can be set to n ² times the NA of the objective lens system serving as a base.

That is, when the SIL is used, the NA of the optical system can be made n to n ² times the NA of the objective lens system as a base.

[0009]

By the way, assuming that the NA of the objective lens system serving as a base can be increased by n to n ² times,
The NA of the optical system can easily exceed 1.

[0010] However, when the NA of the optical system exceeds 1, the light incident on the SIL plane portion is transmitted and transmitted.
There are those that propagate and those that totally reflect.

In the total reflection area, light in the evanescent mode exists in the space near the SIL plane from the SIL plane to the recording medium. By)
Light propagates.

This evanescent mode light is transmitted and
As compared with the propagating type, the intensity is weaker. Further, when the propagating direction is x, the light in the total reflection area is

[0013]

(Equation 1) However,

[0014]

(Equation 2) Is light that attenuates exponentially in the propagation direction in proportion to.

Therefore, even when the recording medium is close to the recording medium, the light in the total reflection area looks as if the attenuation filter has been applied to the recording medium, and the light in the transmitting and propagating area is predominantly recorded. Seems to reach the medium.

The attenuating filter functions as an optical low-pass filter.

When the angle of incidence on the SIL plane approaches the critical angle (that is, NA is 1), it approaches total reflection, and the transmittance sharply decreases. Therefore, when the NA is almost 0.
It appears that the optical low pass filter is working from diameters above 9.

Therefore, the spot to be imaged is a spot which is effectively formed by a low NA as compared with the NA obtained by using the SIL.

Accordingly, it is an object of the present invention to provide an optical system capable of obtaining a minute spot sufficiently reflecting the high NA of an optical system including an objective lens and an SIL as components of the optical system.

[0020]

In the information recording / reproducing optical system of the present invention, as a means for solving the above-mentioned problems, a light beam from a light source is condensed by an objective lens and focused on a plane portion of the SIL. In an optical system for recording information on a recording surface close to the SIL plane portion or reproducing information recorded on the recording surface, light involved in recording or reproduction is transmitted to the recording surface. When there is no close proximity, the light is assumed to be substantially non-propagating light.

The light involved in recording or reproduction is:
When the recording surface does not exist close to the light source, a light-shielding unit is provided or a light source is provided so that light incident on the plane portion of the SIL satisfies the condition of total reflection, so that the light becomes non-propagating light. A deflecting means for deflecting a part of the light beam from the light source.

With the above arrangement, the light propagating to the recording medium due to the near-field effect reflects the high NA caused by the SIL.

Further, a spot reflecting the high NA by the SIL or a spot smaller than that can be formed by the optical super-resolution effect in which the light in the transmitting / propagating region is not used.

[0024]

[Embodiment 1] Next, Embodiment 1 of the present invention will be described.

FIG. 1 is a schematic diagram of a magneto-optical head optical system for recording and reproduction.

The distance between the SIL 2 and the recording medium 3 is kept at about １ ／ or less of the light source wavelength (λ) by a levitation mechanism (not shown).

The light beam from the semiconductor laser 5 passes through the beam splitter 7 and is imaged by the objective lens 1 and the optical system of the SIL 2 so as to focus on the plane portion of the SIL 2. On the optical path from the semiconductor laser 5 to the beam splitter 7, a light-shielding means 4 having the following specification is provided.

On the recording medium 3, a recording surface covered with a thin transparent protective film that does not have a significant value with respect to the value of λ / 8 is provided facing the SIL 2.

Since the recording surface is located in the near-field light region when viewed from the focal point, which is about λ / 8 from the focal point, recording and reproduction are performed at a spot substantially equivalent to the imaged spot.

The light reflected on the recording surface of the recording medium 3 has information on the recording surface of the recording medium 3 and is guided to the sensor 11. Reference numeral 8 denotes a half-wave plate, and reference numeral 10 denotes a polarization beam splitter.

Then, a focus error, a tracking error, a magneto-optical signal and the like are obtained from the output from the sensor 11 by a known method.

The sensor 12 receives a part of the light beam from the semiconductor laser 5 and monitors the output of the semiconductor laser 5.

FIG. 2 shows the objective lens and SIL of this embodiment.
1 shows a high NA optical system consisting of:

The NA of the objective lens 1 by itself is 0.60.

Considering the NA increasing effect of SIL2, assuming that the thickness increase of SIL2 from the hemisphere is t,

[0036]

(Equation 3) However,

[0037]

(Equation 4) Becomes

In this embodiment, when α ≒ 0.77, n
At $ 1.83, the total NA is set to NA $ 1.68.

Table 1 shows a design example of the lens system. Table 2 shows the aspheric coefficient of the objective lens.

[0040]

[Table 1]

[0041]

[Table 2] The aspherical shape has a ray height h,

[0042]

(Equation 5) It is represented by

The flat portion of the SIL 2 is provided with an antireflection coat having the characteristics shown in FIG. Thereby, the reflected light from the recording medium 3 can be efficiently focused on the SIL 2.

In the figure, the vertical axis represents the transmittance of the SIL2 plane, and the horizontal axis represents the product of the refractive index of the SIL2 and the incident angle θ of the reflected light from the recording medium 3 to the SIL2 plane. Ts is the characteristic of the S-polarized light component, and Tp is the characteristic of the P-polarized light component.

As shown in the figure, the transmittance is very high up to n · Sin θ of about 0.9. That is, the objective lens 1,
When the optical system of SIL2 is viewed as a light receiving system, NA = 0.
About 9 light receiving systems are provided.

Next, the light shielding means 4 will be described.

As the light-shielding means 4, a glass parallel plate coated with an elliptical light-shield is used.

The specification of the light shielding means 4 will be described with reference to FIG.

Let θ _{1 be} the maximum incident angle on the SIL ₂ in this embodiment, and let θ ₂ be within the SIL ₂ . That is, Sin θ ₁ ≒
0.60 and n · Sin θ ₂ ≒ 1.68.

On the other hand, n · Sin θ_FourIf ≒ 1.0,
θ_FourCorresponds to the critical angle. Therefore, θ _FourThe incident light below
Almost transparent.

Therefore, by blocking light rays having an angle of incidence θ ₃ or less on SIL ₂ corresponding to θ ₄ , only light rays satisfying the total reflection condition of θ ₄ to θ ₂ in SIL ₂ can be used.

In FIG. 4, Wt ≒ 1, Wr ≒ 2 (Wt ≒ 2)
Indicates the direction in which the beam shaping works, Wr indicates the direction perpendicular thereto, and the beam shaping ratio of the beam splitter 7 is about 2.0.
It is. ), The above condition can be satisfied. If this value is Wr,

[0053]

(Equation 6) If Wt,

[0054]

(Equation 7) It is calculated from:

When the optical system as described above is used, the distribution of the incident intensity on the objective lens 1 is approximately as shown in FIG. In the figure, the horizontal axis is normalized by the radius of the effective diameter of the objective lens.

The spot intensity distribution on the SIL2 plane is approximately as shown in FIG. In the figure, the horizontal axis is λ / N
Standardized by A. A solid line corresponds to the present embodiment, and a dotted line corresponds to a case where there is no optical super-resolution effect for comparison. It can be seen that the spot diameter is reduced by about 20% due to the optical super-resolution effect.

As can be seen from FIG. 5, a considerable amount of light loss occurs. However, as shown in FIG. 6, since the formed spot is very small reflecting the high NA, the intensity density of the spot is considerably large. There is no problem because it gets bigger and is offset.

By the way, as can be seen from FIG. 6, the side lobe increases as much as the spot diameter is reduced.

However, the above-described total reflection area functions as a light-shielding area when light is received, and only light corresponding to NA <1 returns to the SIL 2 as reflected light from the recording medium, so that intersymbol interference and crosstalk from adjacent tracks occur. Is suppressed.

As described above, the advantage of this embodiment is that only light rays satisfying the condition of total reflection are incident on the objective lens 1 and a minute spot smaller than the spot reflecting the high NA of the optical system is obtained. .

[Embodiment 2] Next, Embodiment 2 of the present invention
Is shown.

FIG. 8 is a schematic view of a magneto-optical head optical system for recording and reproduction.

In this embodiment, the luminous flux from the semiconductor laser 5 is passed through the beam splitter 7 to the objective lens 1, S
An image is formed by the optical system of the IL2 so as to focus on the plane portion of the SIL2. On the optical path from the semiconductor laser 5 to the beam splitter 7, there is provided a deflecting means 13 having a deflecting portion having the same size as the light shielding portion of the light shielding means 4 described above.

The deflecting unit has a blazed diffraction grating as shown in FIG. 9, and the diffraction grating diffracts almost 100% of the light toward the light source output monitor sensor 12.

The optical system including the objective lens 1 and the SIL 2 is the same as that of the first embodiment, and almost the same spot can be obtained.

As described above, the advantage of this embodiment is that, similarly to the first embodiment, only the light beam satisfying the total reflection condition is incident on the objective lens 1 and a minute spot smaller than the spot reflecting the high NA of the optical system. Is to be obtained.

[0067]

As described above, according to the present invention,
Since only a light beam satisfying the condition of total reflection is used in a high NA optical system exceeding 1.0, a spot reflecting the high NA or a small spot smaller in size can be formed. By using the system, it becomes possible to provide an ultra-high-density information recording / reproducing apparatus.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a magneto-optical head optical system according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a high NA optical system according to Embodiments 1 and 2 of the present invention.

FIG. 3 is a diagram for explaining specifications of a light shielding unit.

FIG. 4 is a conceptual diagram illustrating a light shielding unit according to the first embodiment of the present invention.

FIG. 5 is a diagram approximately illustrating an objective lens incident intensity distribution according to Embodiments 1 and 2 of the present invention.

FIG. 6 is a diagram schematically showing a spot intensity distribution according to the first and second embodiments of the present invention.

FIG. 7 is a graph showing characteristics of an anti-reflection coat designed for an SIL flat portion.

FIG. 8 is a schematic diagram showing a magneto-optical optical head optical system according to a second embodiment of the present invention.

FIG. 9 is a conceptual diagram showing a deflection unit according to a second embodiment of the present invention.

FIG. 10 is a diagram illustrating a conventional SIL optical system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Objective lens 2 Solid immersion lens (SIL) 3 Recording medium 4 Shielding means 13 Deflection means

Claims (3)

[Claims] 1. A light beam from a light source is condensed by an objective lens.
Focus on the flat part of the solid immersion lens,
In the optical system for recording information on the recording surface close to the solid immersion lens plane portion or for reproducing the information recorded on the recording surface, the light involved in recording or reproduction is the recording. An information recording / reproducing optical system characterized in that the light is substantially non-propagating light when the surface does not exist in proximity. 2. The information recording / reproducing optical system according to claim 1, wherein a light shielding means is provided so that light incident on a plane portion of the solid immersion lens satisfies a condition of total reflection. 3. A deflecting means for deflecting a part of a light beam from the light source so that light incident on a plane portion of the solid immersion lens satisfies a condition of total reflection. 2. The information recording / reproducing optical system according to 1.