JP2000251282A - Near-field optical recording/reproducing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a near-field optical recording/reproducing apparatus in a high-density optical memory utilizing the near-field beam, wherein any change is never generated on the recording layer with the laser beam used for distance control between the near-field optical generating means and an optical recording medium. SOLUTION: This apparatus performs recording and reproducing of information by radiating the near-field beam generated from a small aperture at the end of an optical fiber probe 11 to the optical recording medium 30. The distance control between the end part of the probe 11 and optical recording medium 30 is performed through the share force control by a piezo-element 16 by radiation of laser beam B2 to the probe 11. This laser beam B2 is set to the wavelength not absorbed by the recording layer consisting of the photo-chromic material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a near-field optical recording / reproducing apparatus used for a high-density optical memory or the like.

[0002]

2. Description of the Related Art In recent years, in the field of optical memories for optically recording / reproducing information, a larger amount of information can be recorded, that is, a recording density is remarkably improved with the speeding up of computers and the development of multimedia. Therefore, a near-field optical recording technique has been proposed. In a conventional optical memory using laser light, the upper limit of the recording density is determined by the diffraction limit of light, and recording / reproducing can be performed only for a mark of about the wavelength of light (several 100 nm).

In an optical memory using a near-field light phenomenon proposed in recent years, an optical head is mounted on a recording medium (optical disk) using a probe having a small aperture smaller than the wavelength of light or a solid immersion lens (solid immersion lens). By irradiating the recording / reproducing light with the distance between the recording medium and the recording medium being close to several tens of nm, it is possible to write and reproduce a small mark of several tens of nm as a signal exceeding the diffraction limit of light. .

[0004]

2. Description of the Related Art Conventionally, methods for obtaining near-field light include a method using total reflection, a method using a minute aperture, and a method using metal surface plasmons. As a near-field light generating means using a minute aperture, use of a probe in which the tip of an optical fiber is sharpened has been mainly studied. For fiber probes,
A minute aperture for obtaining near-field light having a small spot size can be produced with relatively high reproducibility. When a fiber probe is used as the near-field light generating means, it is desirable that the diameter of the minute opening at the tip of the fiber be several tens to 100 nm.

[0005] In the case where a near-field light is used, when a substantially circular minute aperture is used, the near-field light only reaches a distance of about the radius from the aperture. Therefore, the distance between the aperture and the optical recording medium is several nm.
To several tens nm. As methods for performing such distance control, conventionally, STM control, share force control, AFM control, evanescent light control, and the like are known.

On the other hand, as an optical recording medium using near-field light, a medium using a heat mode recording method such as a phase change medium and a magneto-optical recording medium, and a medium using a photon mode recording method such as a photochromic medium are known. Considering that the near-field light is very weak, the photon mode recording method is advantageous in that there is no threshold in recording.

[0007] However, in the photon mode recording method, there is no threshold which is an advantageous condition.
On the contrary, when a weak light other than the recording light enters the recording medium, there is a problem that the recording state changes.
The leakage light from the outside can be dealt with by taking measures against light. However, in the case of the distance control method using the shear force control or the AFM control, since the laser light is applied to the fiber probe, such control laser light is used. May be transmitted without being reflected by the fiber probe, or may be scattered by reflection, become stray light in the device, reach the recording layer, and cause recording destruction. It is very difficult to block stray light in such devices.

An object of the present invention is to provide a near-field optical recording / reproducing apparatus which does not cause a change in an object to be recorded / reproduced by a laser beam used for distance control.

[0009]

SUMMARY OF THE INVENTION To achieve the above object, the present invention provides a near-field optical recording / reproducing apparatus for recording or reproducing an object using near-field light photons generated from a near-field light generating means. The reproducing apparatus further includes distance control means for controlling the distance between the near-field light generating means and the object by irradiating the near-field light generating means with laser light, and using the laser light used in the distance control means for the object. It was set to a wavelength that would not be absorbed.

In the present invention, since the laser beam used for distance control is not absorbed by the object, irradiation of the laser beam does not change the object. That is, the laser light for distance control inevitably reaches the target object to irradiate the near-field light generating means, but no matter how much the laser light reaches the target object, no problem occurs.

The laser light for distance control may be emitted from a dedicated light source, or may be shared with a recording / reproducing laser light source. In the case of common use, either the first laser light emitted from the light source or the second laser light obtained from the first laser light via the wavelength conversion means is used for recording / reproduction, and the other is used for distance control. To use.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a near-field optical recording / reproducing apparatus according to the present invention will be described below with reference to the accompanying drawings.

(First Embodiment, see FIGS. 1 to 5) FIG.
1 shows a near-field optical recording / reproducing apparatus 10 according to a first embodiment of the present invention, which uses shear force control. This device 1
0 indicates that the fiber probe 11 is
It is arranged vertically so as to be close to 0, and attached to a driving element 15 in the vertical direction via a piezo element 16.

As shown in FIG. 2, the fiber probe 11 includes a core 12 and a clad 13, and the tip of the core 12 is sharpened and a light-shielding thin film 14 made of a metal material is formed. The light-shielding thin film 14 has a minute opening 14a in a sharpened portion. Laser light B1 emitted from the light source 20 and collected by the lens 21 is incident on the rear end of the fiber probe 11.

Further, a pair of laser light sources 25 and a two-divided photodetector 26 are provided as distance control means. Laser light B2 is emitted from the light source 25 toward the vicinity of the tip of the fiber probe 11, and the photodetector 26 receives the laser light B2.

In the above configuration, the fiber probe 1
The distance between the front end of the optical recording medium 1 and the optical recording medium 30 is controlled as follows.

The driving element 15 is driven while causing the fiber probe 11 to resonate and vibrate in the direction of the arrow X by the piezo element 16, and the tip of the probe 11 gradually approaches the surface of the optical recording medium 30. When the distance between the probe 11 and the optical recording medium 30 becomes very small, the vibration amplitude of the probe 11 starts to decrease. The amplitude is detected by applying the laser beam B2 emitted from the light source 25 to the probe 11, receiving the laser beam B2 with the photodetector 26, and detecting the vibration.
The distance from when the amplitude starts to decrease to when it reaches zero is about 20
The detection result is fed back to the control of the drive element 15 so that the distance between the tip of the probe 11 and the optical recording medium 30 can be controlled to be constant between several nm and 20 nm.

On the other hand, the laser beam B emitted from the light source 20
Numeral 1 is incident on the probe 11, and leaches out as a near-field light from the minute opening 14 a at the tip, and performs recording / reproduction on the optical recording medium 30.

Here, as shown in FIG. 3, the optical recording medium 30 is formed by depositing Al on a glass substrate 31 by a sputtering method to form a reflective layer 32, and further thereon, a diarylethene, which is a photochromic material, is formed. A recording layer 33 is obtained by applying a mixture of a compound and a polystyrene resin by a spin coating method. The melting point of the diarylethene compound is about 115 ° C., and the polystyrene resin has a softening point at about 120 ° C. which is almost the same. FIG. 4 shows the structural formula of the diarylethene compound, and FIG. 5 shows the light absorption spectrum characteristics of the compound.

The photochromic reaction represented by the photochromic material means that the photochromic material in the state shown in FIG. 4A has a wavelength λ1 (for example,
Irradiation at 365 nm (see curve A in FIG. 5) produces the state of FIG. 4B with different absorption characteristics (absorption characteristics are shown in curve B in FIG. 5), and
The wavelength λ2 (for example, 543n) absorbed by the state of FIG.
This is a reversible reaction that returns to the original state (A) by irradiating the light of (m). Rewriting is performed by associating (A) with the recorded state and (B) with the unrecorded state. In addition,
(A) may be an unrecorded state, and (B) may be a recorded state.

In a recording medium of a photon mode recording method using a photochromic material as a recording layer, there is no threshold for recording, and information can be recorded with weak light. In general, the near-field light is very weak, so the photon mode recording method is most suitable for near-field light recording. However, since there is no threshold for recording, there is a possibility that an unrecorded portion may be in a recorded state or the recorded portion may be destroyed by the distance control laser beam B2, which is weak light other than the recording light.

Therefore, in the first embodiment, destruction of the recorded state is prevented by using light having a wavelength not absorbed by the photochromic material as the laser beam B2 used in the shear force control. As shown in FIG. 5, when the diarylethene compound is irradiated with light of 365 nm to be in a colored state, light having a wavelength of up to about 620 nm is absorbed. That is, 620 n is used as the laser beam B2.
Any wavelength equal to or greater than m may be selected.

In the first embodiment, the wavelength of the laser beam B2 is 780 nm, the wavelength of the light (erasing) to be changed to the state shown in FIG. 4B is 365 nm, and the state is changed to the state shown in FIG. (Recording) The wavelength of light was 543 nm. By setting such a wavelength, the recording layer 33 does not change due to the irradiation of the laser beam B2 for distance control,
In particular, it is not necessary to provide a means for shielding the laser beam B2 from the recording layer 33. Incidentally, the same 543 nm light as the recording light was used as the reproducing light. Since there is a possibility that recording destruction may occur during reproduction, the laser beam intensity during reproduction is set to be about three orders of magnitude lower than during recording.

The reason for using a binder resin such as a polystyrene resin for the recording layer 33 is to improve the adhesive strength of the recording layer 33 to the reflection layer 32 and to improve the recording layer 3.
Third, the mechanical strength is improved. If the composition ratio of the diarylethene compound to the polystyrene resin is low, the recording sensitivity is reduced. If the composition ratio is too large, crystals of the diarylethene compound are precipitated, and these crystals scatter during light irradiation, and the scattered light becomes noise during reproduction.

(See Second Embodiment, FIG. 6) A near-field optical recording / reproducing apparatus 40 according to a second embodiment shown in FIG. 6 uses a cantilever type fiber probe 41 as a near-field light generating means, and AFM control is adopted as the distance control means. The same members as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

The fiber probe 41 is bent in an L-shape, and its tip is subjected to the same processing as shown in FIG.
A minute opening is formed. Further, the probe 41 is arranged with the tip thereof close to the optical recording medium 30, and attached to the drive element 35 in the vertical direction via the piezo element 36.

As the distance control means, a pair of laser light sources 45 and a two-divided photodetector 47 are installed, and the laser light B2 emitted from the light source 45 is reflected by a reflecting portion 46 provided on the fiber probe 41. The light is received by the photodetector 47.

The AFM control is classified into a dynamic mode and a contact mode. In the second embodiment, the dynamic mode is adopted because the probe 41 is hard to break and the handling is simple. In the dynamic mode, the fact that the vibration amplitude sharply decreases when the tip of the probe 41 approaches the optical recording medium 30 while vibrating the probe 41 in the arrow Z direction. The detection of the amplitude of the probe 41 is performed by amplifying the displacement of the probe 41 (reflection portion 46) as the displacement of the laser beam B2 by the optical lever method, and receiving the laser beam B2 by the photodetector 47. By feeding back the amplitude detected by the photodetector 47 to the control of the drive element 35, the probe 4
1 to the optical recording medium 30 from a few nm to 20 n
It can be controlled to keep it constant between m.

As the recording layer, the same photochromic material as in the first embodiment is used, and the laser beam B2 for controlling the distance has a wavelength which is not absorbed by the laser beam B2, ie,
780 nm light is used. Therefore, the operation and effect of the second embodiment are the same as those of the first embodiment.

(See Third Embodiment, FIG. 7) A near-field optical recording / reproducing apparatus 50 according to a third embodiment shown in FIG. 7 is a modification of the first embodiment, and is used for distance control. The light source that emits laser light is omitted, and the light source that emits laser light for recording is shared.

The difference from the apparatus 10 shown in FIG. 1 lies in that a half mirror 52 and an SHG (second harmonic generation element) 53 are provided as an optical system. SHG53,
As is well known, it is made of, for example, LiNbO ₃ and has the function of converting the wavelength of incident light into a second harmonic and emitting the same.

That is, the laser beam B emitted from the light source 51
The laser beam B2 is split into two by a half mirror 52, and the reflected laser beam B2 impinges on the lower part of the fiber probe 11 via the mirror 54 and further enters the photodetector 26 to function as light for distance control. The laser beam B2 transmitted through the half mirror 52 is converted into a laser beam B1, which is the second harmonic, by the SHG 53, enters the rear end of the probe 11 via a not-shown condenser lens, and is used for recording or reproduction. Functions as light.

More specifically, when the photochromic material is used as the recording layer, if the wavelength of the laser light emitted from the light source 51 is about 1000 nm, the second harmonic transmitted through the SHG 53 is about 500 nm, and FIG. As shown in (1), light of this wavelength is absorbed by the photochromic material, so that information can be recorded or reproduced. Since the Si photodiode used in the photodetector 26 has sensitivity to light having a wavelength of up to 1100 nm, a laser beam having a wavelength of about 1000 nm can be used for distance control.

Thus, the object of the present invention can be achieved without increasing the number of laser light sources by sharing the light source.

In the third embodiment, the SH
In addition to G, other wavelength converting means, for example, a parametric oscillator, up-conversion glass, or fluorescent light of a light emitter may be used. Alternatively, the laser light emitted from the light source 51 may be directly incident on the probe 11 and used as recording or reproducing light, and the laser light after the wavelength conversion may be used as distance controlling light.

(Other Embodiments) The near-field optical recording / reproducing apparatus according to the present invention is not limited to the above embodiments, but can be variously modified within the scope of the invention. In particular, an element other than the optical fiber probe can be used as the near-field light generating means, and a method other than the shear force control and the AFM control can be used as the distance control means. The configuration of the optical system for guiding the laser beam is arbitrary.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a schematic configuration of a first embodiment.

FIG. 2 is a sectional view showing a distal end portion of the optical fiber probe.

FIG. 3 is a sectional view showing an optical recording medium.

FIG. 4 is a chemical structure diagram showing a photoreaction state of a diarylethene compound used as a recording layer.

FIG. 5 is a graph showing light absorption spectrum characteristics of the diarylethene compound.

FIG. 6 is a perspective view showing a schematic configuration of a second embodiment.

FIG. 7 is a perspective view showing a schematic configuration of a third embodiment.

[Explanation of symbols]

 10, 40, 50: Near-field optical recording / reproducing device 11, 41: Optical fiber probe 14a: Micro aperture 16, 36: Piezo element for distance control 30: Optical recording medium 33: Recording layer (photochromic layer) 20: Recording Light source 25, 45 ... Distance control light source 26, 47 ... Photodetector 51 ... Shared light source 53 ... SHG (wavelength conversion means) B1 ... Recording laser beam B2 ... Distance control laser beam

Claims (5)

[Claims] 1. A near-field light recording / reproducing apparatus that performs recording or reproduction on an object by using photons of near-field light generated from the near-field light generating means, wherein: between the near-field light generating means and the object A distance control means for controlling the distance by irradiating the near-field light generating means with laser light, wherein the laser light used in the distance control means is set to a wavelength not absorbed by the object. Near-field optical recording / reproducing device. 2. The near-field light generating means is a fiber probe in which a metal film is provided on a sharpened optical fiber and a minute opening is formed in a sharp end portion, and the distance control means is a shear force type. The near-field optical recording / reproducing apparatus according to claim 1, wherein: 3. The proximity device according to claim 1, wherein the near-field light generating means is a cantilever-type probe having a small opening formed at a tip thereof, and the distance control means is an AFM method. Field light recording / reproducing device. 4. The laser light used in the distance control means is either a first laser light radiated from a light source or a second laser light obtained by converting the first laser light through a wavelength conversion means. 3. The method according to claim 1, wherein
Or the near-field optical recording / reproducing apparatus according to claim 3. 5. The near-field optical recording / reproducing apparatus according to claim 1, wherein the object is a photochromic layer.