JPH11166934A - Proximity field optical probe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable recording and playing back from a high-density storage medium at a good S/N ratio at high speed with high efficiency in using light by providing a condensing means between an optical waveguide part and a micro opening and placing the micro opening at the location of condensation of light. SOLUTION: A condensing lens 2 is provided concentrically with an optical fiber 1, and a material with a refractive index lower than that of the condensing lens 2 such as a resin is used for a dielectric coating 3. In the condensing lens 2, a focal distance is selected so that propagating light 7 may be condensed at a point at a distance of a few microns to tens of microns from the condensing lens 2 according to optical wavelengths and the refractive index of the dielectric coating 3, and the coating surface of the dielectric coating 3 is matched to this. A micro opening 5 is provided in a metal coating 4 formed on the dielectric coating 3 at the location of condensation of the propagating light 7. Therefore, proximity field light 6 present approximately only in the area of the diameter of the opening smaller than the wavelength of the propagating light 7 is formed from the micro opening 5. At this time, as the amount of light reaching the micro opening 5 can be increased in size approximately by two orders of magnitude than before through the use of the condensing lens 2, efficiency in using light is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information system for detecting information at high speed using near-field light and a near-field optical probe used for light detection in a near-field optical microscope.

[0002]

2. Description of the Related Art High-density recording is required with the increase in capacity of information recording. However, in optical recording such as a conventional magneto-optical recording device, the recording density is limited in principle due to the diffraction limit of light. Is reaching.

[0003] In order to achieve a recording density exceeding the diffraction limit of light, an optical recording / reproducing method using near-field light from a minute aperture has been studied in recent years. FIG. 7 is a configuration diagram showing a conventional near-field optical probe that generates near-field light from a minute aperture. In the figure, reference numeral 1 denotes an optical fiber for transmitting light for forming near-field light, 4 denotes a metal coating, and 5 denotes a metal coating.
A small aperture formed on the optical fiber 1 and having a size smaller than the wavelength of the propagation light of the optical fiber 1, 6 is near-field light, 7 is propagation light of the optical fiber 1, and 13 is an object. This near-field optical probe is composed of an optical fiber 1 covered with a metal coating 4 such as aluminum, for example, and the tip of the portion facing the subject 13 is sharpened to form a minute aperture. This opening diameter is smaller than the wavelength of light, and is configured, for example, at about 100 nm. When propagating light 7 from the end of the optical fiber 1 opposite to the probe tip is present, near-field light is emitted as evanescent light from a sharp opening at the end of the fiber to a region of about the diameter of the small opening. . Further, when the tip of the optical fiber probe is brought close to the subject 13 at a distance about the size of the minute aperture in a state where the evanescent light is present on the surface of the subject 13, the evanescent light passes through the minute aperture at the tip of the optical fiber probe. Propagation inside the optical fiber probe. If the intensity of this signal light is measured by a photodetector, information on the unevenness on the surface of the subject 13 can be obtained. Near-field light using such an optical fiber probe has a spatial resolution that is at least one order of magnitude smaller than the wavelength of ordinary light.

[0004] The near-field light from the minute aperture has been applied to a near-field optical microscope having higher resolution than a normal optical microscope. A near-field optical microscope is configured by using a probe holding technique of a normal scanning tunnel microscope by feedback control of a piezo element for holding an optical fiber probe. Regarding such a near-field optical probe and its application, for example, see Journal of Lightwave Technology, Vol. 13, pages 1200-1221.
(1995).

Attempts have also been made to perform recording / reproduction on a magneto-optical recording medium using near-field light from the minute aperture. A bit is written by scanning with the above-described near-field optical microscope, fixing an optical fiber probe at a specific position on the magneto-optical recording medium, and irradiating near-field light. For this application,
For example, it is described in Applied Physics Letters, Vol. 61, pp. 142-144 (1992).

[0006]

In the near-field optical microscope and the optical recording apparatus as described above, there is a great advantage in using a semiconductor laser which is a small solid-state laser as a light source. In this case, the intensity of incident light is at most. It is about 10 mW. Also, the light incident on the optical fiber probe has a low coupling efficiency with the outgoing near-field light (conversion efficiency to evanescent light), and in many cases, the light intensity ratio is about 1/5. Therefore, at present, when a semiconductor laser is used as the light source, the intensity of the near-field light is weak from nW to μW or less.

In general, high-capacity recording requires high-speed writing / reading at the same time as high-density recording. In the above-described conventional technique, even if high-density recording can be achieved, the intensity of light to be detected or irradiated is high. And high-speed writing / reading is impossible.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical information system using near-field light, which utilizes the characteristics of high-density recording and realizes a high-speed optical information system capable of realizing sufficiently high-speed recording / reproduction corresponding to a large recording capacity. A field light probe is provided.

Another object of the present invention is to provide a near-field optical microscope using near-field light, in which the amount of detected light is increased, and
An object of the present invention is to provide a near-field optical probe with high light use efficiency that can realize signal detection with an improved ratio.

[0010]

A near-field optical probe according to the first aspect of the present invention has a near-field optical probe provided with a small opening at the tip of an optical fiber or an optical waveguide which is smaller than the wavelength of light and generates near-field light. In the field light probe, a light condensing means is provided between a portion where light is guided and the small opening, and the small opening is set in accordance with a position where light is collected.

A near-field optical probe according to a second configuration of the present invention is the near-field optical probe according to the first configuration,
A condenser lens is used as the condenser means.

A near-field optical probe according to a third configuration of the present invention is the near-field optical probe according to the first configuration,
A Fresnel lens is used as the light collecting means.

Further, a near-field optical probe according to a fourth configuration of the present invention is characterized in that a tip of an optical fiber or an optical waveguide has a reflection smaller than a wavelength of light between a portion where light is guided and the minute aperture. It is provided with a prevention layer.

A near-field optical probe according to a fifth configuration of the present invention is the near-field optical probe according to the fourth configuration,
As the antireflection layer, an optical fiber having a different effective refractive index from the portion where light is guided is used.

The near-field optical probe according to a sixth configuration of the present invention is the near-field optical probe according to the fourth configuration,
As the antireflection layer, a dielectric thin film made of a material having a different refractive index from a portion where light is guided is used.

A near-field optical probe according to a seventh aspect of the present invention is a near-field optical probe having a small aperture at the tip of an optical fiber or an optical waveguide, which is smaller than the wavelength of light and generates near-field light. Providing a light condensing means between a portion where light is guided and the small aperture, installing the small opening in accordance with a position where light is collected, and simultaneously providing a portion where light is guided and the small opening. And an antireflection layer is provided between them.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a configuration diagram showing a near-field optical probe using a condenser lens according to Embodiment 1 of the present invention. In the figure, 1 is an optical fiber that propagates light for forming near-field light, 2 is a condensing lens installed at the tip of the optical fiber 1, 3 is made of a material having a refractive index lower than that of the condensing lens 3. Dielectric coating,
4 is a metal coating formed on the dielectric coating 3, 5 is formed on the metal coating 4, and has a small aperture smaller than the wavelength of the propagation light of the optical fiber 1, 6 is near-field light, and 7 is propagation of the optical fiber. Light. As the optical fiber 1, for example, a single mode fiber is used, and the condensing lens 2 is installed with the center axis of the fiber aligned. The dotted line in FIG.
Indicates that light is collected. The lens diameter is set to be larger than the mode spread of the propagating light 7. As a light source of the propagation light 7,
For example, a semiconductor laser in the visible to near infrared region is used. As the condenser lens 2, a biconvex lens, a spherical lens, or the like may be used in addition to the plano-convex lens. The material of the condenser lens is preferably a high refractive index resin or a high refractive index glass. The end face of the optical fiber may be processed into a convex surface to form a condenser lens. Dielectric coating 3
Uses a material having a lower refractive index than the condenser lens. It is preferable that the difference in the refractive index from the material of the condenser lens is large. As a material, for example, a resin having a low refractive index is used. The condensing lens 2 condenses the optical fiber propagating light 7 at a distance of about several μm to several tens μm from the condensing lens 2 in accordance with the used light wavelength and the used refractive index of the dielectric coating 3. Other characteristics can be selected as well as the focal length. The thickness of the dielectric coating 3 is set to several μm to several tens μm so that the point where the propagating light is condensed is the coating surface. A metal coating 4 is formed on the dielectric coating 3. Aluminum or gold as metal is about 100nm thick
To form a film. When gold is used, chromium is formed to a thickness of several nm before gold is formed, and gold is formed thereon.
The film is formed by vacuum evaporation, sputtering, electroless plating, or the like. A minute opening 5 is provided in the metal coating 4. This opening diameter is smaller than the wavelength of the light propagating through the optical fiber 1, for example, 100
nm. The dielectric coating 3 is shaped so as not to be reflected and scattered by the metal coating 4 while the light is being collected. The opening is formed by ion beam processing, etching, mechanical processing, or the like. The position of the minute aperture is adjusted to the position where the propagating light is collected by the lens. Protrusions are formed on the surface of the dielectric coating 3 in accordance with this position, thereby facilitating the production of a minute opening. When the near-field optical probe is used as a probe of a near-field optical microscope, such a projection is effective as a means for measuring a shear force or an atomic force for controlling a probe position.

With the above-described configuration, most of the light propagated through the optical fiber 1 is condensed and radiated to the position of the minute aperture 5 in a region of about a wavelength. From the small opening,
Near-field light that exists only in a region having an aperture diameter smaller than the wavelength of the propagating light is formed.

In the conventional near-field optical probe, an optical fiber probe is used in which the tip of the optical fiber is sharpened and a minute aperture is provided as it is. I have. Therefore, the light intensity is lower than when light is converged on a region of the same order as the wavelength. By using the condenser lens 2, the light can be condensed to the same size as the light wavelength. Therefore, compared with a structure in which the tip of the optical fiber is sharpened and a minute opening is simply provided, the amount of light reaching the minute opening is 2. It can be increased by an order of magnitude, and the light use efficiency can be improved. Also, in the case where near-field light existing outside the probe is detected through a minute aperture, the numerical aperture of light that can be condensed is increased due to the presence of the condenser lens, so that light utilization efficiency is improved. In the conventional near-field optical probe, the proportion of the light propagated through the optical fiber that hits the metal coating in the process of reaching the micro opening at the tip is high. At this time, a part of the light is absorbed by the metal coating as heat, and the probe temperature rises, so that there is a problem that the probe is damaged. In the present invention, by adopting the above-described configuration, the propagation light of the fiber does not hit the metal coating other than the vicinity of the minute opening, and thus the resistance of the probe to thermal damage due to light absorption is improved.

Embodiment 2 FIG. 2 is a configuration diagram 2 showing a near-field optical probe using a condenser lens according to Embodiment 2 of the present invention. In this embodiment, a Fresnel lens 8 is used as a condenser lens in the near-field optical probe described in the first embodiment. As the Fresnel lens, a flat lens such as a holographic lens can be applied. The Fresnel lens 8 condenses the fiber propagating light 7 at a point separated from the Fresnel lens 8 by a distance of about several μm to several tens μm according to the used light wavelength and the used refractive index of the dielectric coating 3. Other characteristics such as focal length can be selected. The thickness of the dielectric coating 3 is set so that the point where the propagating light is condensed is the coating surface, and the thickness is several μm.
m to several tens μm. A metal coating 4 is formed on the dielectric coating 3. As the metal, aluminum or gold is formed with a thickness of about 100 nm. When gold is used, chromium is formed to a thickness of several nm before gold is formed, and gold is formed thereon. The film is formed by vacuum evaporation, sputtering, electroless plating, or the like. A minute opening 5 is provided in the metal coating 4.
This aperture diameter is smaller than the wavelength of the light propagating through the optical fiber,
For example, the thickness is about 100 nm. The opening is formed by ion beam processing, etching, mechanical processing, or the like. As in the first embodiment, the position of the minute aperture is adjusted to the position where the propagating light is collected by the lens. It is also effective to form a projection on the surface of the dielectric coating 3 in accordance with this position.

When a Fresnel lens is used, in addition to high light use efficiency as described in the first embodiment,
Since there is no significant non-planarity such as the convex surface of the lens in the structure of the probe, there is an advantage that the formation of the dielectric coating 3 becomes easy.

Embodiment 3 FIG. FIG. 3 is a configuration diagram showing a near-field optical probe using an antireflection layer according to Embodiment 3 of the present invention. In the figure, 1 is an optical fiber, 9 is an anti-reflection layer provided at the tip of the optical fiber 1, 10 is a metal coating formed on the anti-reflection layer 9, and 5 is the wavelength of light propagating through the optical fiber formed on the metal coating 10. A small aperture having a smaller size, 6 is a near-field light, and 7 is a propagation light of an optical fiber. As the optical fiber 1, for example, a single mode fiber is used. As a light source of the propagation light 7, a semiconductor laser in the visible to near infrared region is used. As the antireflection layer 9, a structure in which the effective refractive index of the optical fiber 1 is different from the refractive index is used. For example, an optical fiber having a core diameter or a refractive index of the core and the clad different from that of the optical fiber 1 is used. A metal coating 10 is formed on the antireflection layer 9. As the metal, aluminum or gold is formed with a thickness of about 100 nm. When gold is used, chromium is formed to a thickness of several nm before gold is formed, and gold is formed thereon. The film is formed by vacuum evaporation, sputtering, electroless plating, or the like.
The minute opening 5 is provided in the metal coating 10. This aperture diameter is smaller than the wavelength of the light propagating through the optical fiber 1, for example, 100 n
m. As in the first embodiment, it is also effective to form a projection on the surface of the antireflection layer 9 in accordance with this position. The opening is formed by ion beam processing or the like. The thickness of the antireflection layer 9 is set so as to form a cavity between the interface between the antireflection layer 9 and the optical fiber 1 and the metal coating 10. That is, the light of the wavelength to be used is reflected at the interface between the antireflection layer 9 and the optical fiber 1, transmitted through the interface between the antireflection layer 9 and the optical fiber 1, reflected by the metal coating 10, and then returned to the antireflection layer again The phase of the light transmitted through the interface between the optical fiber 1 and the optical fiber 1 is set to be opposite.

With such a configuration, multiple reflection of light occurs between the interface between the optical fiber 1 and the antireflection layer 9 and the metal coating 10, so that the light use efficiency is improved and the proximity formed by the minute aperture 5 is improved. The intensity of the field light 6 increases. In this manner, a near-field optical probe with high light use efficiency can be configured.

Embodiment 4 FIG. 4 is a configuration diagram showing a near-field optical probe using an anti-reflection layer according to Embodiment 4 of the present invention. In this embodiment, the dielectric thin film 11 is used as an anti-reflection layer in the near-field optical probe described in the third embodiment. As the dielectric thin film 11, a thin film of a material having a different refractive index from the optical fiber 1 is used. It is preferable to use a thin film of a high refractive index material to make the difference in the refractive index from the optical fiber 1 as large as possible. Instead of a single-layer dielectric thin film, it is also possible to use a dielectric multilayer film whose reflectance is designed for light of a wavelength to be used.

In the case where a dielectric thin film is used, Embodiment 3
In addition to the high light utilization efficiency shown in the above, there is an advantage that the anti-reflection layer can be easily formed using a film forming process.

Embodiment 5 FIG. 5 is a configuration diagram showing a near-field optical probe using a condenser lens and an antireflection layer according to a fifth embodiment of the present invention. In this embodiment, the near-field optical probe described in the first, second, third, and fourth embodiments has both an antireflection layer and a condenser lens. In this case, since the antireflection layer in the third and fourth embodiments also functions as the dielectric coating in the first and second embodiments, the antireflection condition of the antireflection layer with respect to the light of the wavelength to be used is satisfied. The focal length of the condenser lens is chosen so that the thickness is equal to the distance until the light is collected by the condenser lens. Further, it is preferable to provide an anti-reflection coating on the surface of the lens. As in the first embodiment, the position of the minute aperture is adjusted to the position where the propagating light is collected by the lens. It is also effective to form a projection on the surface of the antireflection layer in accordance with this position. With such a configuration, the propagation light 7 propagating through the optical fiber 1 is condensed and radiated to a region having a wavelength around the position of the minute aperture 5, and the light once reflected by the metal coating is also reflected. The near-field optical probe which is reflected at the interface between the prevention layer and the optical fiber and is irradiated again to the area centered on the position of the minute opening 5 can be used with high light use efficiency.

In the first to fifth embodiments, the near-field optical probe is formed at the tip of the optical fiber. However, a similar near-field optical probe can be formed for a general optical waveguide.

Embodiment 6 FIG. FIG. 6 is a configuration diagram showing a near-field optical microscope using a near-field optical probe according to Embodiment 6 of the present invention. In the figure, reference numeral 13 denotes an object of the microscope, and the near-field optical probe 12 has a structure similar to that of the first embodiment.

Irradiation light 14 is emitted from the back side of the subject 13. The irradiation light 14 is condensed by an optical system so as to focus on the surface of the subject. The intensity of the irradiation light 14 is several mW. In this state, when the tip of the near-field optical probe 12 is brought close to the subject 13 at a distance about the size of the minute aperture, the near-field light of the subject is transmitted through the minute aperture at the tip of the near-field optical probe 12 to the near-field. The light propagates inside the optical probe 12 with higher efficiency than the conventional probe. As the near-field light probe 12, the probe having the structure described in the second, third, fourth or fifth embodiment can be used, and near-field light can be detected with the same high efficiency. In this case, if a projection is formed at the position of the minute aperture, the distance between the near-field optical probe and the subject can be controlled by using a means for detecting a shear force, an atomic force, and the like generated between the projection and the subject. Can be easily performed.

The near-field light of the subject, which has propagated into the near-field optical probe 12, is more prominent when the tip of the near-field optical probe 12 faces the convex portion of the surface of the subject 13 than when it faces the concave portion. growing. This is because the near-field light on the surface of the subject 13 is evanescent light, and the intensity of the signal light rapidly decreases exponentially when the near-field light is away from the surface of the subject 13 by about 100 nm or more. Thus, the subject 13
The near-field light on the surface of the subject is propagated inside the near-field optical probe 12, the signal light is detected by the photodetector 17, and the control circuit 15 controls the piezo element 16 for controlling the probe position while controlling the probe position control piezo element 16. By scanning the surface, the subject 13
Information on the surface irregularities can be obtained.

When the near-field optical probe 12 scans a row of irregularities on the surface of the subject 13 using the mechanism of the near-field optical microscope, the detection signal is a time-series signal corresponding to the irregularities on the surface of the subject 13. However, since it has a sufficient signal strength as described above, high-speed reading of 100 MHz or more with respect to 100 kHz of the conventional device becomes possible. In this way, a near-field optical microscope that can scan at high speed can be configured. In the case where the same scanning mechanism as that of the conventional apparatus is used, the signal SN
By improving the ratio, a near-field optical microscope with improved observation resolution can be configured. In this embodiment, the configuration in which the near-field light on the surface of the subject 13 is detected by the near-field optical probe 12 has been described. However, for example, the near-field light probe 12 irradiates the surface of the subject 13 with the near-field light. In addition, it can be used as a highly efficient near-field optical probe in a near-field optical microscope, such as a configuration in which transmitted light or fluorescence is detected by an objective lens or the like, or a configuration in which reflected light or fluorescence is detected by the same near-field optical probe 12.

Further, a disk type optical recording apparatus can be constructed by using a disk having minute irregularities on the surface as an information recording medium instead of the subject 13 and using the near-field optical probe 12 as a proximity type signal detection head. . In this case, the near-field optical probe 12 is installed on a floating slider, for example, or the distance from the disk is maintained by a piezo element or the like. The distance from the disk is set to a distance at which the near-field light probe 12 can efficiently detect near-field light on the surface of the recording medium, for example, 50 to 100 nm.
By irradiating light from the back surface of the disk to a position where the tip of the near-field optical probe 12 is close to the surface of the disk to generate near-field light on the surface of the disk, the above-described mechanism enables high-density and high-speed reading. An optical recording device can be configured.

Although the above description has been made on the assumption that the concavo-convex information is detected, other optical characteristics for modulating the amount of evanescent light, for example, optical information such as transmittance, reflectance, refractive index, electric dipole, etc. Can also be used for detection.

[0034]

Since the present invention is constructed as described above, it has the following effects.

In the near-field optical probe according to the first to third configurations of the present invention, the light use efficiency is high, and high-speed recording and reproduction with a high SN ratio can be performed from a high-density recording medium.

In the near-field optical probe according to the fourth to sixth configurations of the present invention, recording and reproduction with a high SN ratio can be performed at high speed from a recording medium having a high light use efficiency and a high recording density. Is easy.

In the near-field optical probe according to the seventh configuration of the present invention, light utilization efficiency is further improved, and recording and reproduction with a high SN ratio can be performed at high speed from a high-density recording medium.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a near-field optical probe using a condenser lens according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram showing a near-field optical probe using a condenser lens according to a second embodiment of the present invention.

FIG. 3 is a configuration diagram showing a near-field optical probe using an anti-reflection layer according to a third embodiment of the present invention.

FIG. 4 is a configuration diagram showing a near-field optical probe using an antireflection layer according to a fourth embodiment of the present invention.

FIG. 5 is a configuration diagram showing a near-field optical probe using a condenser lens and an antireflection layer according to a fifth embodiment of the present invention.

FIG. 6 is a configuration diagram showing a near-field optical microscope using a near-field optical probe according to a sixth embodiment of the present invention.

FIG. 7 is a configuration diagram showing a conventional near-field optical probe.

[Explanation of symbols]

1 optical fiber, 2 lens, 3 dielectric coating, 4
Metal coating, 5 small aperture, 6 near-field light, 7 propagating light,
8 Fresnel lens, 9 Anti-reflection layer, 10 metal coating,
Reference Signs List 11 dielectric thin film, 12 near-field optical probe, 13 subject, 14 irradiation light, 15 control circuit, 16 piezo element for probe position control, 17 photodetector.

Claims (7)

[Claims] 1. An optical fiber or an optical waveguide, comprising:
In a near-field optical probe having a small aperture that is smaller than the wavelength of light and generates near-field light, light is collected by providing a light-condensing means between a portion where light is guided and the small opening. A near-field optical probe, wherein the minute aperture is provided in accordance with a position. 2. The near-field optical probe according to claim 1, wherein a condenser lens is used as the condenser. 3. The near-field optical probe according to claim 1, wherein a Fresnel lens is used as the light collecting means. 4. An optical fiber or an optical waveguide, comprising:
A near-field optical probe having a small aperture smaller than the wavelength of light and providing near-field light, wherein an anti-reflection layer is provided between a portion where light is guided and the small aperture. Field light probe. 5. The near-field optical probe according to claim 4, wherein an optical fiber having an effective refractive index different from that of a portion through which light is guided is used as an anti-reflection layer. 6. The near-field optical probe according to claim 4, wherein a dielectric thin film made of a material having a different refractive index from that of a portion where light is guided is used as an antireflection layer. . 7. An optical fiber or an optical waveguide, comprising:
In a near-field optical probe having a small aperture that is smaller than the wavelength of light and generates near-field light, light is collected by providing a light-condensing means between a portion where light is guided and the small opening. A near-field optical probe, wherein the minute aperture is provided in accordance with a position, and an antireflection layer is provided between a portion where light is guided at the same time and the minute aperture.