JPH0721564A - Method and device for recording and reproducing optical recording medium - Google Patents

Abstract

PURPOSE:To provide a method and device for controlling the distance between a probe and a recording layer with high accuracy at all times even under any operation state of a P-STM optical memory. CONSTITUTION:A recording layer 502 of an optical recording medium s installed inside a first evanescent field 301 formed by first light 601 guided in a transparent object 1 provided with a fine opening part at the head part at this fine opening part, and information is recorded in this optical recording medium 5 or recorded information is reproduced by using this first light 601. On the other hand, second light 602 with a wavelength different from that of the first light 601 is guided inside this optical recording medium 5, a second evanescent wave 302 formed by the guided light on the surface of this optical recording medium is detected by this transparent object 1, and the intensity of the second light is detected by separating this wave from the guided light of the first light 601 while using a wavelength separating means 12. Thus, the distance between this transparent object 1 and this optical recording medium 5 can be adjusted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording / reproducing method and apparatus utilizing a photon tunnel phenomenon capable of recording information at an ultrahigh density on an optical recording medium.

[0002]

2. Description of the Related Art In recent years, by utilizing the high spatial coherence of a laser beam, the laser beam is recorded on a medium by using a laser spot which is focused to the diffraction limit, or information is recorded from a medium on which information is recorded. An optical disk device for reproducing has been put into practical use as a compact disk for audio and a magneto-optical disk file for computer.

In recording on these optical disks, the recording density is almost determined by the laser wavelength, and the recording density is about 1 bit /
However, research is being conducted to further improve the recording density in order to meet the recent demand for higher capacity recording media.

As one of the promising next-generation ultra-high density optical memories, there is a so-called P-STM (photon scanning tunneling microscope) which records and reproduces by using an evanescent wave generated by a photon tunnel phenomenon. An applied optical memory (or simply P-STM and also referred to as a photon scanning tunneling memory) has been proposed.

Regarding the P-STM, for example, the 11th Japan Society of Applied Physics, "See the Micro World", September 1992.
May 5th text p3-15 “Trends in Super-Optical Microscopy” is explained in detail in Motoichi Otsu.

For example, FIG. 2 shows a diagram for explaining the principle of the P-STM as a microscope. In the figure, the object 5 to be observed is transparent to the wavelength of the light used,
The incident light 6 is incident on the interface 501 of the object 5 at an angle that normally causes total reflection. Reference numeral 7 is a reflected light of the incident light. At this time, the interface 501 near the interface 501 of the object 5
An evanescent field 3 whose intensity decreases exponentially with increasing distance from is formed.

If the interface 501 of the object 5 is perfectly flat, this evanescent field is also uniform in the plane, but if the interface 501 of the object 5 has minute irregularities or minute objects 4, it is formed. The evanescent field will be disturbed accordingly.

When the sharp probe 1 formed of glass fiber or the like is brought close to the evanescent field 3 thus formed, a part of this evanescent light is guided as a normal light 8 through the probe and the detector 2 is detected. The intensity is detected by.

As a result, since the output of the detector 2 corresponding to the disturbance of the evanescent field is obtained, the output 9 representing the object surface shape can be obtained by scanning the probe 1.

The resolution of such a P-STM can be increased as much as the sharpness of the tip of the probe 1 is improved, so that a super resolution exceeding the resolution due to the diffraction limit of light in an ordinary optical microscope can be obtained. It will be possible.

Application as an ultra-high-density optical memory utilizing the above-mentioned super-resolution property, or the proceedings of the 65th Annual Meeting of the Chemical Society of Japan (1993) IIp287, 1
Reported in C630.

FIG. 3 is a diagram showing the principle of this optical memory application technique. In this case, different from the example of FIG. 2 described above, the emitted light 6 from the recording or reproducing light source 10 is first incident on the probe 1 by an appropriate method, and is guided in the probe 1,
An evanescent field 3 having the same extent as the size of the tip is formed at the sharply pointed tip.

On the other hand, a transparent substrate 5 as an object is used as a recording medium.
A recording layer 502 including a photochromic material or the like is formed on the recording layer 502.
Information is recorded by causing a photochromic reaction in the medium by bringing the medium closer to a distance equal to or less than the wavelength of light used for recording, and forming the recording mark 503 by changing the transmittance of a part of the recording layer. .

Similarly, the reproduction of the recorded information is performed by detecting the intensity of the light 8 transmitted from the evanescent field 3 to the substrate 5 side by the photodetector 2. That is, when the probe 1 or the substrate 5 is scanned, a reproduction signal corresponding to the presence or absence of a recording mark can be obtained.

It is considered that such a P-STM type optical memory can realize ultra-high density recording of about 100 times the recording density (about 1 bit / μm) of the conventional optical memory.

[0016]

By the way, in the optical memory device shown in FIG. 3, it is necessary to control the distance between the probe 1 and the recording layer 502 with high accuracy and keep it at a constant value. However, when recording using modulated light, reproducing using light of relatively weak power, or when accessing a specific recording area on the medium, such highly accurate distance control should be performed. Had the problem of being difficult.

The present invention has been made in view of the above problems of the prior art, and a method and a method capable of always controlling the distance between the probe and the recording layer with high accuracy in any operating condition of the P-STM type optical memory. The purpose is to provide a device.

[0018]

According to the method of the present invention, a first light guided in a transparent body having a minute opening at its tip is converted into a light in a first evanescent field formed in the minute opening. A recording layer of a recording medium is provided, information is recorded on or reproduced from the optical recording medium by using the first light, and a wavelength different from that of the first light is recorded in the optical recording medium. The second light is guided, and the second evanescent wave formed by the guided light on the surface of the optical recording medium is detected by the transparent body, and this is guided by the first light by using a wavelength separating means. The distance between the transparent body and the optical recording medium can be adjusted by detecting the intensity of the second light separately.

Further, the apparatus of the present invention comprises a first light source for emitting a first light for recording / reproducing information on / from an optical recording medium, and a minute opening portion for guiding the light from the first light source. A transparent body that forms an evanescent field, and a first detection unit that is provided at a position opposite to the transparent body with respect to the optical recording medium, and that detects first light guided in the optical recording medium,
A second light that emits a second light having a wavelength different from that of the first light.
A light source, means for guiding light emitted from the second light source into the optical recording medium and the transparent body, and the first light source and the transparent body. And a wavelength separating means for separating the second light, a second detecting means for detecting the second light obtained by the wavelength separating means, and the transparent body and the transparent body by the signal obtained by the second detecting means. And a control means for controlling the distance to the optical recording medium.

[0020]

According to the present invention having the above-described structure, the distance between the transparent body and the optical recording medium is controlled with high accuracy in any state such as recording / reproducing, so that recording error and reproducing error can be efficiently performed. Can be suppressed.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A recording / reproducing method and apparatus according to the present invention will be described below in detail with reference to the drawings.

First, FIG. 1 shows a principle diagram of the recording / reproducing method, and the description will be made based on this. The radiated light 601 from the recording / reproducing light source 101 as the first light source is
1 and a dichroic mirror 12 as a wavelength separating means for reflecting a distance control light 602 from a second light source having a wavelength different from that of the first light source, and is recorded by the same operation as that described in FIG. Information is recorded on the layer 502 and the recorded information is reproduced.

On the other hand, regardless of the intensity of the beam of the emitted light 601, the presence or absence of modulation, etc., the distance control light 602 guided through the medium substrate 5 as a transparent body is uniform on the surface of the medium 5 within its plane. And an evanescent field 302 whose intensity changes exponentially in the normal direction.

As the distance controlling light 602, light in a wavelength range in which the photochromic material contained in the medium 5 does not absorb is selected so as not to cause an undesired photochromic reaction in the recording layer 502.

Now, the probe 1 uses this evanescent field 3
02 is detected and converted into a normal guided light 802, reflected by the dichroic mirror 12 and photoelectrically converted by the second detector 202, and the converted signal is transmitted to the control circuit 11 for distance control.

Next, an apparatus for realizing the recording / reproducing method of the optical recording medium based on the above principle will be described with reference to FIG. Since many of the photochromic materials that are the materials of the medium 5 have absorption in the ultraviolet to visible wavelength range, the recording / reproducing light source 100 that is the first light source uses a visible semiconductor laser or an SHG element, A light emitting diode which is a coherent light source can be used.

The light source 100 emits light whose intensity is modulated according to a recording signal by the driving circuit 13 with a relatively strong power when the information is recorded, and has a constant and relatively weak power when reproducing the recorded information. It is controlled to be emitted.

The light emitted from the light source 100 is reflected by the lens 19
1 and dichroic mirror 1 as wavelength separating means
2 and then enters the glass capillary probe 1 through the lens 192.

The tip of the probe 1 has a diameter of 0.
It is sharpened to the order of 1 μm, and an evanescent field 3 is formed at the tip. And probe 1 and medium 5
The distance between and is kept below the order of the wavelength of the evanescent wave forming the evanescent field 3, and recording by the evanescent wave and reproduction by the first detector 201 are performed.

On the other hand, the distance control light source 60 as the second light source.
For 0, a near-infrared semiconductor laser that can emit light having a wavelength that many photochromic materials do not absorb can be used. The laser beam emitted from the light source 600 with a constant power by the drive circuit 16 is shaped into parallel light by the collimator lens 193, reflected by the mirror 17 and incident on the medium 5.

At this time, the beam incident angle from the light source 600 and the polarization state are adjusted so that the light is totally reflected on the surface of the medium 5. It should be noted that reflection of light on the surface 500 of the medium 5 on the side opposite to the probe 1 causes a loss of light in the detector 201 and a stray light component. Further, it is desirable to provide a filter that transmits only the wavelength of the recording / reproducing light so that the light from the distance control light source 600 does not enter the entire surface of the detector 201.

The evanescent field formed on the surface of the medium 5 by the light emitted from the distance control light source 600 is
The light is picked up by the probe 1, guided to the lens 192, reflected by the dichroic mirror 12, and then photoelectrically converted by the second photodetector 202.

The converted voltage is compared by a comparator 18 with a reference voltage which is predetermined so that the distance between the probe 1 and the medium 5 is optimum. Then, the difference signal output from the comparator 18 is input to the control circuit 11, and the control signal of the control circuit 11 drives the piezo element 14 mounted in the vicinity of the probe 1, and the piezoelectric displacement operation of the piezo element 14 causes the piezo element 14 to move. The probe 1 is vertically displaced so that the absolute value of the difference signal output becomes small.

The recording or reproducing light is scanned on the medium 5 by driving the medium 5 by the horizontal drive system 15 so that the light can be scanned over the entire surface of the medium 5. ing. Therefore, the distance between the probe 1 and the medium 5 can be maintained at a constant value with high accuracy at any time, and super-high density recording / reproducing can be stably performed.

[0035]

As described above, according to the present invention, PS
It is expected that an ultra-high density recording / reproduction by the TM type optical memory can be realized while maintaining high accuracy.

[Brief description of drawings]

FIG. 1 is a block diagram showing the principle of the method of the present invention.

FIG. 2 is a block diagram showing the principle of a general P-STM (microscope).

FIG. 3 is a block diagram showing the principle of a conventional P-STM (memory).

FIG. 4 is a block diagram showing an outline of the device of the present invention.

[Explanation of symbols]

 10 recording / reproducing light source 600 distance control light source 201 first detector 202 second detector 1 probe 12 dichroic mirror 5 medium 193 collimating lens 17 mirror 3, 301, 302 evanescent field 9 reproduction signal

Claims (2)

[Claims] 1. A recording layer of an optical recording medium is installed in a first evanescent field formed in a minute opening by a first light guided in a transparent body having a minute opening at its tip. Information is recorded on or reproduced from the optical recording medium by using the first light, and second light having a wavelength different from the first light is guided in the optical recording medium, The second evanescent wave formed by the guided light on the surface of the optical recording medium is detected by the transparent body, and the second evanescent wave is separated from the guided light by the first light by using the wavelength separating means to obtain the intensity of the second light. A recording / reproducing method for an optical recording medium, wherein the distance between the transparent body and the optical recording medium can be adjusted by detecting the. 2. A first light source that emits a first light for recording and reproducing information on an optical recording medium, and a light from the first light source is guided to form an evanescent field in the minute opening. And a transparent body which is provided at a position opposite to the transparent body with respect to the optical recording medium and which is guided in the optical recording medium.
Detecting means for detecting the light, a second light source for emitting a second light having a wavelength different from that of the first light, and a light emitted from the second light source in the optical recording medium and Means for guiding light in the transparent body, wavelength separating means for separating the first and second light provided between the first light source and the transparent body, and obtained by the wavelength separating means. Optical recording having second detecting means for detecting the second light, and control means for controlling the distance between the transparent body and the optical recording medium by the signal obtained by the second detecting means. Medium recording / reproducing apparatus.