JP2003077166A - Optical recording / reproducing device - Google Patents

Abstract

(57) [Problem] To provide a near-field optical recording / reproducing apparatus capable of stably reproducing a recording signal while keeping a floating amount of a SIL bottom surface from a medium surface constant. SOLUTION: Before incident on a near-field optical recording medium, the recording medium is irradiated with a different polarization distribution in a pupil plane of the incident laser light, and the obtained reproduction light is separated according to the polarization distribution, thereby achieving SIL. The light in the total reflection area at the bottom is separated from the other light, and the light in the total reflection area is used to control the flying height.
The other light is used for reading recorded data.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recordable / reproducible optical recording medium, and more particularly to a floating near-field optical recording for recording, reproducing and erasing information by changing the optical characteristic or magnetic characteristic of a recording layer by a laser beam. The present invention relates to a near-field optical recording / reproducing device equipped with a reproducing optical lens.

[0002]

2. Description of the Related Art Optical recording media are portable recording media capable of high-capacity and high-density recording, and are in high demand as rewritable media for recording large-capacity files and moving images of computers accompanying the recent development of multimedia. It is increasing rapidly.

An optical recording medium is generally formed by forming a multilayer film including a recording layer on a transparent disk-shaped substrate such as plastic, irradiating a laser for recording and erasing, and reproducing by reflected light of the laser.

A laser for recording / reproducing has hitherto been applied to a recording film through a substrate. Recently, so-called near-field optical recording, in which an optical head is brought close to a recording film to perform recording and reproduction, has attracted attention as a means for increasing the recording density (Appl. P.
hys. Lett. 68, p. 141 (1996)).
This recording method uses Solid Immersion Le
By using a ns (hereinafter abbreviated as SIL) head to reduce the laser beam spot size, the conventional recording limit (~ λ / 2) determined by the laser wavelength (λ) of the light source is used.
NA: NA can be reproduced with a mark shorter than the numerical aperture of the objective lens, and recording / reproduction with an ultrahigh recording density can be realized. In this near-field optical recording, since the optical head needs to be close to the recording medium (up to 100 nm), the recording film is not irradiated with the laser beam through the substrate as in the conventional magneto-optical recording medium, but is not passed through the substrate. A method of directly irradiating the recording film with a laser beam is used. At this time, a flying slider head is often used to bring the recording film and the SIL head close to each other.

The flying type slider head is for moving a medium and for generating a buoyancy force on the slider head by the flow of gas generated by the medium and the air bearing slider to cause the head to follow the surface of the optical recording medium.

Although the distance between the recording layer and the SIL can be set to -100 nm by using the floating slider head, the substrate of the optical recording medium is not completely flat and is several tens to several hundreds of μm. There are partial irregularities and the like.
The slider head usually has a shape of about several mm, and the air slider portion has the same shape. For this reason, it is impossible to follow irregularities having a size less than this size.

Under such circumstances, the flying height of the flying slider head can be controlled by controlling the moving speed of the recording medium, but a general optical recording medium has a disk shape. Since the slider head is levitated by rotating, it is difficult to precisely control the number of revolutions for precisely controlling the flying height. In addition, when molding a substrate using resin, it is difficult to make the disk shape a perfect flat surface due to the difference in stamper shape and molding conditions, and microscopically there are irregularities that are smaller than the slider size. However, macroscopically, there is unevenness that causes problems such as surface wobbling when rotated. For the former unevenness, it is physically impossible to control the flying height of the slider, and it is necessary to design a smaller slider. For the latter, it is necessary to develop a slider shape that improves the follow-up speed of the flying height by the air bearing, but it has not been developed yet.

A technique for actively controlling the gap between the optical coupling portion at the bottom of the lens and the recording medium has been proposed (Par).
to of the Internal Symposi
umon Optical Memory and O
optical Data Storage 1999,
p. 9). The method of controlling the air gap between the optical coupling part on the bottom of the lens and the recording medium is based on the near-field theory for recording light in a region that satisfies the condition of total reflection of the angle of incidence on the bottom of the lens, which is determined by the substance (air) in contact with the bottom of the lens. Utilizes the binding condition to the medium. As the light in the region satisfying the condition of total reflection approaches the bottom surface of the lens and the recording medium (up to 100 nm), the reflection at the bottom of the lens decreases and approaches the amount of reflected light when the light propagates to the recording medium. The area satisfying this total reflection condition has a ring shape outside the circle, and the air gap can be controlled by monitoring the amount of reflected light from this ring portion. But,
Since the outer ring region of the reproduction light is detected by masking the central portion of the reproduction light, tracking and data reading are impossible, and it is not suitable for a system for both recording and reproduction.

[0009]

The object of the present invention is to provide an SI
It is an object of the present invention to provide an optical recording / reproducing device that enables the flying height of L to be controlled and can perform recording / reproducing.

[0010]

SUMMARY OF THE INVENTION The present inventor has completed the present invention as a result of intensive studies in view of the above-mentioned current situation.

The light in the total reflection area at the bottom of the lens, which is determined by the refractive index of the lens and the substance (air) in contact with the lens among the incident angles to the medium inside the SIL, is treated as near-field light, and The amount of propagation to the recording medium decreases exponentially as the distance from the recording medium, that is, the flying height increases. When the near-field light and the normally incident light are incident on the recording medium, the effective numerical aperture NA exceeds the convergent spot radius of a general objective lens, and a high NA can be realized.

In particular, the light propagating to the recording medium as near-field light is usually determined by the gap distance between the SIL bottom surface and the recording medium surface, and the light incident from the SIL spherical surface has a distance of 300 n.
If it is sufficiently larger than m, the near-field light does not propagate to the recording medium and is reflected at the bottom of the SIL.

According to the present invention, the distribution of the polarization state is created in the light beam before entering the SIL, so that the refractive index of the lens and the substance (air) in contact with the lens among the incident angles to the SIL bottom surface are determined. The optical recording / reproducing apparatus is capable of separately reproducing the light in the total reflection area at the lens bottom and the light propagating to the recording medium without being restricted by the total reflection condition.

That is, according to the present invention, the light in each minute region of the light spot cross section is SI during the incidence from the laser to the SIL.
Light of the total reflection area at the bottom of L and light other than that are pre-determined, and two kinds of light transmissive substances having different birefringence with respect to the light of each area, or light that continuously changes without a boundary A distribution of polarization states is created in the cross section of the light beam spot by passing the transparent material. The light having the polarization state distribution is reflected from the recording medium and introduced into the reproducing optical system in the recording / reproducing apparatus. The light beam spot has a phase difference distribution due to birefringence in its cross section, and by inserting a polarization separation element before the introduction of the reproduction optical system, it becomes possible to separate the light according to the polarization distribution given in advance, and the SIL The light in the total reflection area at the lens bottom, which is determined by the lens refractive index and the substance (air) in contact with the lens among the incident angles to the medium inside, detects the distance between the SIL bottom and the recording medium. It is possible to use it for the purpose and read the recorded data other than the above.

The present invention will be described in more detail below.

A laser diode LD, which is coherent light, is used as a light source, and the light emitted from the laser diode LD passes through a beam shaping element, a collimating element, and the like, and then passes through a beam expander, a beam splitter, and the like, before being emitted to a recording medium. A medium having birefringence in the inward direction, for example, a liquid crystal or a birefringent crystal having a crystal orientation distributed in the in-plane direction is used to generate a polarization state distribution in the laser beam plane.

When the flying height (hereinafter, the air gap between the optical coupling portion at the bottom of the SIL and the recording medium) is about 100 nm, the light at the high incident angle portion, which is originally totally reflected on the bottom surface of the lens, partially propagates in the thin film. If it becomes about 300 nm, it hardly propagates and is reflected on the bottom surface of the lens and cannot propagate to the recording medium, so that the beam spot size becomes large. FIG. 1 schematically shows the loci of light rays in each minute area of the SIL spherical surface portion. The light incident from the objective lens 1 is SI
The critical incident angle θ1 is determined from the total reflection condition that is determined by the refractive index determined by the material of L2 and the refractive index of the medium existing between the recording medium 3 and the incident angle above this angle increases the flying height. The light reflected directly from the bottom surface of the lens increases according to an exponential function.

In a state where the flying height is sufficiently high, the light reflected from the bottom surface of the SIL shown by the hatched portion in FIG. 1, that is, the light located in the beam spot cross section of the incident light corresponding to the ring-shaped portion of the reproduction light pupil plane is polarized. If the state is changed, it is possible to separate the light with a critical angle θ1 or more and the light in the area with the highest intensity in signal readout by the polarization separation element (polarization beam splitter etc.) installed in front of the reproduction optical system. It is possible to use the signal without waste.

Therefore, before entering the recording medium, the critical angle θ
The phase difference of 90 degrees and -90 degrees is added in advance to the light in the area that can be divided by 1, by the birefringent element, so that the light in the area divided by the critical angle θ1 becomes clockwise and counterclockwise circularly polarized light, respectively. It is incident on the recording medium.

The light reflected from the recording medium returns to the SIL and is guided to the reproducing optical system by the beam splitter. By inserting a quarter-wave plate after the beam splitter for separating from the laser optical axis and before entering the servo control reproduction optical system and the recording signal reproduction optical system, all reproduction light has a 90-degree phase difference. Are added, and the polarization planes are 90 degrees and 0 degrees, respectively, with the incident polarization distribution maintained. The polarization beam splitter splits each polarization distribution component.

The light split into two at the critical angle θ1 is output to a detector for servo control or preformat reading or an optical system for detecting a magneto-optical reproduction signal.

Here, as an element for creating an incident polarized light distribution, a birefringent element having a fast axis shifted by 90 ° is cut in accordance with the distribution and is adhered, or an electrode pattern of a liquid crystal element is required. Those processed according to the polarization distribution may be considered. Further, in the case of producing a continuous phase difference distribution for the light with respect to the incident angle θ in FIG. 1, it is possible to make a convergent light incident on a single flat plate birefringent element through a lens or the like to create a polarization distribution. is there. Further, a Faraday cell or the like may be applied.

The polarization distribution can be freely selected depending on the application, and the incident polarization may be linearly polarized and the angle thereof may be changed for each region, or an arbitrary phase difference may be given for each region. It may be designed by properly using it according to the purpose.

Ring-shaped light having an incident angle equal to or greater than the critical angle θ1 can be converted into a flying height by a voltage value obtained by a detector which is a photoelectric converter. By setting this voltage value at the connection portion between the SIL and the slider and controlling the element having a mechanism for displacing the relative position, for example, a piezoelectric element or a thermal expansion element sandwiched between heater electrodes, the surface of the recording medium is controlled. It is possible to control the flying height that fluctuates depending on the shape and the like to be constant.

[0025]

EXAMPLES Example 1 A stamper having guide grooves with a track pitch of 0.5 μm was prepared using a master exposure device with a laser wavelength of 351 nm, and a PC resin substrate having a diameter of 130 mm was prepared by injection molding using this stamper. did.
Using this substrate, a thin film having the structure shown in FIG. 2 was created. A reflective layer 5 made of a Cu film having a film thickness of 50 nm was formed on the substrate 4 by a DC sputtering method. Coercive force 10 on this
A recording layer 6 made of kOe TbFeCo was formed to a thickness of 20 nm by DC sputtering. Further thereon, a dielectric layer 7 made of SiN is 50 nm by a reactive DC sputtering method using a Si target in a mixed atmosphere of Ar and N ₂ , and a solid lubricating layer 8 made of diamond-like carbon (DLC) is formed by Ar. C in a mixed atmosphere of CH ₄
15 nm by reactive RF sputtering method using a target
Formed. After forming the DLC layer, the perfluoropolyether lubricating layer 9 was applied to 1 nm to manufacture a magneto-optical recording medium.

FIG. 3 shows an optical recording / reproducing apparatus according to the present invention. The recording / reproducing apparatus used a semiconductor laser having a wavelength of 635 nm as the laser used, the diameter of the laser beam immediately after the beam shaping prism 12 was 10 mm, and its polarization was linear polarization. As an element for creating a polarization distribution, a quarter wave plate 13 is used as shown in FIG. 4, and five areas A to E are grouped into groups A, B, C and D, respectively. The fast axis and the slow axis were reversed, that is, the fast axis was rotated by 90 degrees, and it was created using optical contact. At this time, F of FIG. 4 shows the incident linear polarization axis,
The fast axis of the groups A, B, C, and D is G, and the fast axis of the region E is H. Linearly polarized light was made incident on the quarter-wave plate thus created to obtain a polarization distribution region in the pupil plane of the laser beam as shown in FIG. A to E in FIG. 5 are
4 shows polarization distribution regions of light after passing through the quarter-wave plate of FIG. 4, regions A, B, C, and D are right-hand circularly polarized light, and a region E is left-hand circularly polarized light. This light is reflected by the beam splitter 14,
The light enters the recording medium 18 through the objective lens 16 and the SIL 17. At this time, the line segment connecting the areas A and C was made parallel to the guide groove.

The light returning from the optical disk passes through the objective lens again and is guided to the reproducing optical system by the beam splitter 14. Here, the beam splitter 19 splits into a magneto-optical reproducing optical system and a focus / tracking servo signal and uneven information reproducing optical system.

In each optical system, the fast axis of the quarter-wave plate 20 is set in the same direction as the area A. Area A, B, C, D
The light passing through is added with the phase difference of 90 degrees, and the polarization plane is rotated by 90 degrees from the polarization plane after exiting the shaping prism. Further, the light passing through the region E is converted into the linearly polarized light which is the same as the incident polarized light by subtracting the 90 ° phase difference. Here, in the focus / tracking control and the concave / convex information reading optical system, the beam splitter 26 causes the area A,
B, C, and D are arranged so that the light components of the area E can be divided, and the E area is used for the magneto-optical signal detection optical system, and A, B, C, D are used for the tracking detection optical system and the emboss information detection system.
The area is introduced into a 4-division detector, and the sum of the A and C areas of this light quantity is used for flying height control, and the difference signal between A and C of the 4-division detector is used for embossed information reproduction, and D, B
The difference signal of was used for tracking state detection. Further, in the magneto-optical reproducing optical system, the polarization beam splitter 18 is arranged at 45 degrees with respect to the axis of linearly polarized light in each region.

In the floating optical recording / reproducing head, as shown in FIG. 6, a SIL lens 38 as an optical lens is held by an optical lens support member 39 on a slider 37 which generates a buoyancy force by moving the recording medium. The optical lens support member 39 has a function of holding the SIL lens on the slider and changing the relative position between the slider and the SIL.

A piezoelectric element is used as the optical lens supporting member, and the voltage applied to the piezoelectric element so that the flying height detection signal becomes constant is set at the same position (at the same angular position within one round of the disk) with respect to the synchronizing signal of the disk rotating spindle. Micro area)
To 300 mV, and the flying height was set to about 100 nm.

The voltage value of the reproducing light intensity, which is a flying height detection signal when the voltage in the control circuit of the piezoelectric element is changed at a linear velocity of 10 m / s, and the flying height (nm) which is the distance between the SIL and the recording thin film. Is shown in FIG. In FIG. 7, the voltage value in the control circuit of the piezoelectric element was controlled so that the voltage value of the reproducing light intensity was 900 mV.

In the state in which the flying height was controlled as described above, a signal having a mark length of 1 μm was tracked, and one round recording was performed for reproduction.

At this time, the fluctuation of the reproduction signal amplitude value with the mark length of 1 μm was very small, and a value of 2% was obtained.

(Comparative Example 1) A recording / reproducing apparatus similar to the embodiment,
When the flying height control circuit was stopped under the recording medium and the recording conditions to reproduce the signal, the fluctuation of the mark length signal of 1 μm was 15%.

It can be seen that according to the present invention, stable recording / reproducing characteristics can be obtained with little fluctuation of the reproduced signal.

[0036]

EFFECT OF THE INVENTION Optical recording in which incident light has a polarization distribution in the in-plane direction of the incident light before entering the optical recording medium, and the light having the polarization distribution is converged to a minute area of the recording medium by using a lens. In the reproducing device, by pre-assigning a polarization distribution to light in a region propagating to the recording medium by the near field and in a region not propagating in the recording medium, variation of the flying height and the reproducing intensity of the lens and the recording medium, which are the light propagation characteristics in the near field, By detecting the voltage and using it to control the element that relatively displaces the optical coupling portion of the flying slider and the SIL, it is possible to reduce the fluctuation of the flying height due to the shape of the recording medium and the like.

[Brief description of drawings]

FIG. 1 is a schematic diagram of light rays in an objective lens and SIL.

FIG. 2 is a partial cross-sectional view of the magneto-optical recording medium shown in Example 1.

3 is a diagram showing a reproducing optical system used in Example 1. FIG.

FIG. 4 is a diagram showing a relationship between a distribution region of a polarization distribution creating element, an initial linear polarization axis, and a ¼ wavelength plate fast axis.

FIG. 5 is a diagram showing a polarization distribution obtained by a polarization distribution creation element.

FIG. 6 is a schematic view showing a flying type optical head used in Example 1. (A) Plan view, (b) CC side view, (c) D
・ D line cross-sectional view, (d) cross-sectional enlarged view showing the optical lens support member and its periphery

FIG. 7 is a diagram showing an example of a relationship between a flying height and a reproducing light intensity with respect to a piezoelectric element control voltage.

[Explanation of symbols]

1 Objective lens 2 SIL 3 Recording medium surface 4 substrates 5 Reflective film 6 Recording thin film 7 Dielectric protective film 8 Solid lubrication layer 9 Liquid lubrication layer 10 Laser diode 11 Collimator lens 12 Beam shaping prism 13 Polarization distribution creation element 14 Beam splitter 15 beam rising mirror 16 Objective lens 17 SIL 18 recording media 19 Beam splitter 20 1/4 wave plate 21 Polarizing beam splitter 22 Objective lens 23 Photodetector 24 Objective lens 25 photo detector 26 1/4 wave plate 27 Polarizing beam splitter 28 Objective lens 29 Photodetector 30 objective lens 31 Photodetector 32-36 Polarization distribution state at each point 37 Ascending slider 38 SIL 39 Flying height control element 40 electrodes 41 Piezoelectric element

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 5D090 AA01 BB10 DD03 FF05 FF11                 5D118 AA14 BA01 BB06 CC06 CC07                       CC12 CD02 DC02 EA08 EA11                 5D119 AA11 AA22 AA28 BA01 BB05                       CA06 EA03 EC32 JA30 JA43                       MA06                 5D789 AA11 AA22 AA28 BA01 BB05                       CA06 CA21 CA22 CA23 EA03                       EC32 JA30 JA43 MA06

Claims (5)

[Claims] 1. In an optical recording / reproducing apparatus for focusing coherent light by using a lens and irradiating it to a minute area of an optical recording medium, before the coherent light passes through the lens, the traveling direction of the light. An optical recording / reproducing device having a polarization state distribution in a light spot cross section (hereinafter referred to as a pupil plane) observed in a plane perpendicular to the plane. 2. The optical recording / reproducing apparatus according to claim 1, wherein the polarization state distribution is a distribution in which the polarization state is determined according to the distance from the center of the ellipse of the pupil plane of the light spot. 3. The optical recording / reproducing according to claim 1 or 2, wherein the lens has a shape obtained by cutting a spherical lens by a plane perpendicular to a straight line passing through the center of the lens. apparatus. 4. A spherical lens is cut along a plane perpendicular to a straight line passing through the center of the lens so that a plane portion of the lens faces a recording medium, and near-field light is used for the recording medium directly below the lens. 4. The optical recording / reproducing apparatus according to claim 3, wherein the light is coupled by light. 5. A total reflection condition in which an angle of incidence on a flat surface portion of a lens when the light enters the flat surface portion of the lens from a portion having a spherical surface of the lens is determined by a refractive index of a substance in contact with the lens and a refractive index of the lens. 5. The optical recording / reproducing according to claim 4, wherein the light having an incident angle larger than that angle and the light having an incident angle smaller than that angle have different polarization states in the pupil plane, with the angle taking as a boundary being a boundary. apparatus.