A near-field light-generating element has a support member and a minute aperture having a size smaller than the wavelength of incident light provided on the support member so as to produce near-field light in response to incident light directed thereto. The minute aperture has a contour in a given plane with one side lying along a line perpendicular to a direction of polarization of the incident light and an opposite side in the given plane defining an apex.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an element for generating near-field light, a head for a high-density information recording device making use of it, and a probe for a high-resolution microscope.

2. Description of the Related Art

Near-field light-generating elements are used in optical heads within optical recording devices for making high-density information recordings and in optical probes within near-field optical microscopes for making observations at high resolutions.

As amounts of information of still images and moving images have increased explosively in recent years, high-density optical recording devices have been developed actively. It is known that optical disks typified by compact discs (CDs) have limited recording densities due to diffraction limit of light. To exceed this limitation, a method utilizing a shorter wavelength of light and a method making use of near-field light have been proposed. An optical recording device using near-field light is a method consisting of causing light to enter an optically small aperture having a subwavelength size, causing the near-field light spreading a little past the aperture to interact with the surface of the recording medium, and detecting scattered light transmitted or reflected to thereby read out microscopic data marks. Since the minimum mark size capable of being recorded and read is limited not by the wavelength of the incident light but by the size of the aperture, the recording density can be enhanced by fabricating a microscopic aperture.

In an optical recording device employing nearfield light, the aperture is required to be placed close to the surface of the recording medium. Furthermore, to achieve a high data transfer rate, the aperture needs to scan over the surface of the recording medium at a high speed. To satisfy these requirements, a flying head method similar to that used in conventional magnetic recording has been proposed (Issiki, F. et al. Applied Physics Letters, 76(7), 804 (2000)). The head is fabricated by forming a floating slider and a minute aperture on a planar substrate by semiconductor processes. For example, a SiO2layer is laminated on a Si substrate. A resist pattern for a tip is formed by lithography. The SiO2layer is etched to fabricate the conical tip made of SiO2. Al is deposited to 200 nm by vacuum evaporation and then the front end of the tip is cut by the FIB (focused ion beam) method. As a result, a tip having an optical aperture at its front end is fabricated. The contour shape of the aperture is determined by the shape of the resist pattern for the tip. To fabricate a microscopic aperture finally, the contour is preferably circular or rectangular. However, a rectangle is not desirable because there is the possibility that the front end becomes like a blade. Where the aperture shape is a circle, it is not necessary to control the direction in handling the head subsequently. Therefore, a circular aperture is normally formed.

An optical probe used in a near-field optical microscope is fabricated by heating, drawing, and cutting an optical fiber, depositing a light-shielding film of Al, and then cutting the front end to form an optical aperture.

Incident light from a laser light source is directed to the aforementioned optical head or probe to thereby produce near-field light. The incident light is guided from the laser by an optical fiber and propagated through air to the microscopic aperture. The light from the laser is linearly polarized light. When the light is being guided by the fiber, the polarization is disturbed. When the light is propagated through air, it is unlikely that the device is so operated that the shape of the aperture, the scanning direction, and the direction of polarization are controlled.

The problem with the aforementioned near-field optical probe or head is that the intensity of near-field light (herein referred to as the light efficiency of the probe) generated from the aperture is small compared with the intensity of the incident light. The incident light is reflected off the inner wall of the probe or absorbed before the light reaches the aperture. Thus, the light is lost as thermal energy. Even with respect to the light reaching the aperture, only small energy can pass through, because the aperture size is smaller than the wavelength. If the intensity of the generated near-field light is weak, sufficient contrast cannot be obtained. In the case of a microscope, the accuracy of the output image will be insufficient. In the case of a data storage device, the data transfer rate will be insufficient.

Contrivances have been made to improve the light efficiency, for example, in Veerman, J. A. et al., Applied Physics Letters, 72(24), 3115 (1998), where the front end of a probe is cut by FIB, the beam is directed to the probe from just beside it to flatten the front end. Conversely, in Ohtsu, M., J. Lightwave Tech., 13(7), 1200 (1995), an attempt is made to improve the resolution by forming a microscopic protrusion within a plane of an aperture.

However, it is known that where the size of the aperture is reduced to improve the resolution of the microscope or the recording density of the storage device, the light efficiency deteriorates. A method of improving the light efficiency is being explored.

SUMMARY OF THE INVENTION

It is therefore an aspect of the present invention to provide a near-field light-generating element having an optically small aperture having a size smaller than the wavelength of incident light, the near-field light-generating element being designed to produce near-field light by directing the incident light to the small aperture. The near-field light-generating element is characterized in that a first side of the outer periphery, or contour, of the small aperture is substantially perpendicular to the direction of polarization of the incident light and a second side opposite the first side is not perpendicular to the direction of polarization of the incident light.

Thus, the first portion of the contour of the small aperture which is substantially perpendicular to the direction of polarization of the incident light produces near-field light of high intensity. Consequently, a high resolution and a high light efficiency are compatible.

It is another aspect of the present invention to provide a near-field light-generating element, wherein the contour is a polygon having one side that is substantially perpendicular to the direction of polarization.

As a result, a high-performance near-field optical head can be fabricated economically simply by fabricating a mask of simple shape. Furthermore, the portion of the contour of the aperture which produces strong near-field light is only one. This permits improvement of the resolution.

It is another aspect of the present invention to provide a near-field light-generating element, wherein the contour is a triangle having one side that is substantially perpendicular to the direction of polarization.

This permits fabrication of a minute aperture based on the triangular shape whose vertex can be readily formed. Stable near-field light-generating elements can be fabricated at high yield.

It is another aspect of the present invention to provide a near-field light-generating element, wherein the minute aperture is formed at the front end of a conical tip that transmits light. Surroundings of the minute aperture are covered with a light-shielding film.

This makes it possible to form a minute aperture having a size smaller than a structure capable of being fabricated by lithography.

It is another aspect of the present invention to provide a near-field light-generating element, wherein one side of the contour is made of a material that excites plasmons by incident light.

As such, the generated near-field light strongly localizes near the one side of the minute aperture. The near-field light-generating element has a high S/N and corresponds to high-density recording.

It is another aspect of the present invention to provide a near-field light-generating element, wherein the material includes any of gold, silver, and copper.

This makes it possible to fabricate a high-performance near-field light-generating element by easy fabrication processes.

It is another aspect of the present invention to provide a near-field optical recording device which comprises an optical head, a light source, a recording medium, means for scanning the optical head across a surface of the recording medium, optical incident means for guiding incident light from the light source to the optical head, and optical detection means for detecting scattered light produced by interaction of the optical head with the surface of the recording medium via near-field light. The device is characterized in that the optical incident means includes means for keeping or controlling polarization of the incident light and in that the optical head is a near-field light-generating element set forth in any one of the above descriptions.

In consequence, the portion of the contour of the aperture that produces strong near-field light is only one. The resolution can be enhanced. Furthermore, a high-performance near-field optical head can be fabricated economically by a simple method. In addition, in a digital storage device, high-density recording and high transfer rate are compatible.

It is another aspect of the present invention to provide a nearfield optical microscope which comprises an optical probe, a light source, optical guiding means for guiding incident light from the light source to the optical probe, and optical detection means for detecting scattered light produced by interaction of the optical probe with the surface of the specimen via near-field light. The microscope is characterized in that the optical quiding means incudes means for keeping or controlling polarization of the incident light and in that the optical probe is a near-field light-generating element as described above.

Thus, only the portion of the contour of the minute aperture which is substantially perpendicular to the direction of polarization of the incident light produces near-field light of high intensity. High resolution and high light efficiency are compatible. High resolution and high S/N of the microscope can be accomplished. A high-performance near-field optical probe can be manufactured economically by a simple method.

It is another aspect of the present invention to provide a near-field optical recording device or a near-field optical microscope, wherein the optical detection means includes a polarizing optical element.

Thus, differences in optically microscopic states on a recording medium or specimen are detected by selectively detecting only certain polarized component of detected light produced by interaction of the recording medium or specimen with the near-field light. Consequently, high-density recording or high-resolution observation can be made.

It is another aspect of the present invention to provide a near-field optical microscope, wherein one location of the contour of the minute aperture which is substantially perpendicular to the direction of polarization of the incident light is located closer to the front end than other portions of the contour in the optical probe.

This makes it possible to place the portion of the contour of the minute aperture, where near-field light strongly localizes, closer to the surface of the specimen. Consequently, a high-resolution microscope can be accomplished.

It is another aspect of the present invention to provide a near-field optical microscope, wherein a line connecting one location of the contour of the minute aperture substantially perpendicular to the direction of polarization of the incident light and a portion opposite thereto is substantially perpendicular to the direction of the front end of the optical probe.

Consequently, only a region of the portion of the contour of the minute aperture that is still closer to the edge can be placed close to the specimen, it being noted that near-field light strongly localizes in the portion. A high-resolution microscope can be accomplished.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1is a view illustrating the structure of an information recording-and-reading device of the present embodiment 1. A near-field optical head104having a minute aperture (not shown) for producing near-field light is placed at a short distance of tens of nanometers from the surface of a recording medium105. Under this condition, the recording medium105is rotated at a high speed in a direction indicated by the arrow112. To float the near-field optical head104with a constant relative arrangement with the recording medium105at all times, a flexure108is formed at the front end of a suspension arm107. The suspension arm107can be moved radially of the recording medium105by a voice coil motor (not shown).

The near-field optical head104is so arranged that the minute aperture is opposite to the recording medium105. To guide light fluxes from a laser101to the near-field optical head104, an optical waveguide103consisting of a core and a clad fixed to a lens102and the suspension arm107is used. A polarization-maintaining waveguide having a rectangular core cross section is used as the optical waveguide103to preserve the direction of polarization possessed by the light fluxes from the laser. If necessary, the laser101can be intensity-modulated by a circuit system110. A light-receiving head106for reading information recorded on the recording medium105is mounted to a suspension arm109. The suspension arm109is mounted to the voice coil motor (not shown) in the same way as the suspension arm107.

FIG. 2is a view illustrating the waveguide and near-field optical head of an information recording-and-reading device according to embodiment 1 of the invention. To realize a lens function for a head, an aperture substrate111comprises a transparent glass plate, for example, on which a microlens205is formed. An air bearing surface204is formed on the side of the recording medium of the substrate to permit floating with a constant relative arrangement. The aperture substrate111is coated with a light-shielding film (not shown) except for the microlens205, the air bearing surface204, and the minute aperture206. The light-shielding film at the bottom surface of the aperture substrate111is provided with the minute aperture206. The microlens205collects light fluxes from the optical waveguide103into the minute aperture206. A mirror substrate210having a mirror surface203and the optical waveguide103are fixed on top of the aperture substrate111. Al (not shown) having a thickness of 200 nm is deposited on the mirror surface203. The optical waveguide103consists of a core201and a clad202. In this embodiment, a glass substrate that transmits light of the wavelength of the used laser is used as the aperture substrate111. Also, the aperture substrate111may be made of a material that transmits light of wavelength used only for the microlens205and a portion where a light flux transmits, by using a silicon substrate or the like. In addition, an ordinary spherical or aspherical lens, refractive index distribution lens, Fresnel lens, or the like can be used as the microlens205. Especially, where a Fresnel lens is used, a planar lens can be fabricated. If a lens having a large diameter is fabricated, the thickness of the near-field optical head can be reduced. Fresnel lenses can be mass-produced by using photolithography technology.

The present invention is characterized by the portion of the head structure shown inFIG. 2which is close to the minute aperture206and by polarization of the incident light.FIG. 3is a view showing the vicinities of the minute aperture at the bottom surface of the optical head of the information recording-and-reading device according to the present embodiment 1. A triangular pyramid211consisting of SiO2and having a height of about 10 microns is formed on (bottom surface) of an aperture substrate111. A light-shielding film (not shown) of Al is formed up to about 200 nm on the surface of the triangular pyramid211. The vertex of the triangular pyramid211is cut by a plane parallel to the bottom surface to remove the light-shielding film. The optically small aperture206is formed. Since the triangular pyramid211is a regular tetrahedron, the minute aperture206has a contour of an equilateral triangle. This head is scanned in a direction indicated by x relative to the surface of the recording medium. Near-field light produced from the minute aperture206is made to interact with the surface of the medium.

FIG. 4is a view showing a cross section through the optical head according to the present embodiment 1 and its bottom surface. The aperture substrate111has the microlens205on its top surface and the triangular pyramid211provided with the minute aperture206on its bottom surface.

FIG. 5is a view showing the state in which the optical head according to the present embodiment 1 scans over a data mark on the surface of a recording medium. The data mark,221, has a length of 72 nm and a width of 56 nm, and is an amorphous area formed on the surface of a phase-change recording material made of Ge2Sb2Te5. This is the shortest mark length owing to (1, 7) modulation signal. It corresponds to a recording density of 100 Gb/in2. The minute aperture206floats at a height of 20 nm above the surface of the recording medium. A constant posture is maintained because the floating force of air generated by rotation of the recording medium at 2.25 m/sec is balanced by the load on the suspension arm107shown inFIG. 1. The light incident on the minute aperture206has linearly polarized light222. At this time, the polarized light222is vertical to the right side of the minute aperture206.

Use of the information recording-and-reading device constructed in this way improves the signal intensity by a factor of about 10 and the corresponding recording density by a factor of about 1.5 compared with one having a conventional circular or square, minute aperture and one in which light is made to enter without controlling polarization. This mechanism is described using computer simulation by referring toFIG. 6.

FIG. 6(a) shows a conventional, circular minute aperture231.FIG. 6(b) shows a triangular minute aperture232according to the present invention.FIG. 6(c) is a view comparing the shapes and sizes of both apertures. The circular minute aperture231inscribes the triangular minute aperture232.

FIG. 7shows the results of the computer simulation performed to find the electric field energy distribution at a location that is 20 nm just under the minute aperture. To indicate the relative position to the aperture, the aperture contours or shapes shown inFIG. 6(a), (b) are shown overlapped.FIG. 7(a) shows the case of the circular minute aperture.FIG. 7(b) shows the case of the triangular minute aperture. The incident light has linear polarization in the X-direction shown in the figure. In the case (a), the energy is distributed over the whole aperture. In the case (b), the energy localizes to the right side of the triangle because light localizes at the edge perpendicular to the direction of polarization.

InFIG. 8, the profiles on lines A–A′ ofFIGS. 7(a), (b) are shown overlapped. The profile242ofFIG. 7(b) has an intensity and a full width at half maximum which are 10 times and 0.8 time, respectively as large as those of the profile241of (a). It is considered that the cause of the increase of the intensity is that the aperture area of the triangular opening is larger than the circular opening as shown inFIG. 6. It is also considered that localization of the light in the triangular aperture as shown inFIG. 7has reduced the width of the profile.

The output signal intensity and the recording density can be improved simultaneously be well controlling the polarization of the incident light in practice, shaping the aperture into a triangular form, and placing the polarization of the incident light perpendicular to one side of the triangular aperture.

A method of fabricating the triangular pyramid shown inFIG. 3is described, the method being embraced in methods of fabricating the optical head of the information recording-and-reading device according to the present embodiment 1 ofFIG. 9. In step S301, a SiO2layer311having a thickness of 15 microns is formed on the top surface of a Si substrate312having a thickness of 400 microns by plasma CVD. In step S302, a shape314of a triangular pyramid is formed by isotropic etching, using a triangular-shaped mask patterned by photolithography. Then, in step S303, an Al film317is deposited to a thickness of 200 nm by vacuum evaporation. Finally, in step S304, the front end is cut by the FIB (focused ion beam) method and an optically small aperture206is fabricated. The minute aperture206can be formed without using FIB in step S304by applying mechanical pressure to remove only a front-end portion of the Al film317.

This method makes it possible to mass-produce minute apertures206as described in the present embodiment 1. Of the head structure shown inFIG. 2, those portions excluding the minute aperture206can be fabricated by existing semiconductor processes and assembly techniques. Where they are combined, near-field optical heads or probes according to the present invention can be mass-produced economically by batch processing.

As described thus far, in the information recording and reading device according to embodiment 1, the contour of the minute aperture producing near-field light is substantially a regular triangle. One side thereof is substantially perpendicular to the polarization of the incident light. Therefore, the generated near-field light localizes around it. The opposite side is the tip and does not cause much localization of generated near-field light. Consequently, a near-field optical head having a larger output signal intensity and a larger corresponding recording density can be accomplished than those of a device having a conventional circular aperture or rectangular aperture or a device which has a triangular aperture but in which the polarization of incident light is not well controlled. Furthermore, with respect to the manufacturing method, in the case of the conventional circular aperture, it has been necessary to form a circular cone at a high shaping accuracy. In the case of a rectangular aperture, it has been necessary to form a quadrangular pyramid at a high shaping accuracy. In the case of the triangular aperture in the present embodiment, it suffices to form a triangular pyramid or projection that always stands only on its one vertex. Apertures can be manufactured at improved yield.

In the present embodiment, the aperture is shaped into a triangular form. Since this shape is formed by mask patterning, any desired aperture shape can be formed. It is to be noted, however, that the shape must have a contour having only one side that is perpendicular to the direction of polarization of the incident light. For instance, inFIG. 10(a), (b), minute apertures have shapes other than triangular form. In the shape of (a), the triangle has one side that is a curved line. The section or portion251that is perpendicular to the direction222of polarization of the incident light is the only location of the contour of the aperture where nearfield light is localized. Therefore, advantages similar to those produced in the case of a triangular aperture can be obtained. In the shape of (b), every side is a curved line. The section or portion252perpendicular to the direction222of polarization of the incident light is also the only location of the contour of the aperture where near-field light is localized. As shown, the contours of these apertures have no section extending inwardly toward the center of the apertures. Where the incident light having polarization as shown is directed to the apertures having these shapes, nearfield light localizes only in the section or portion substantially perpendicular to the the polarization of the incident light. Where this phenomenon is utilized, a high-resolution head producing a high signal intensity is obtained.

FIG. 11is a view showing the configuration of an information recording-and-reading device according to embodiment 2 of the present invention. Its main configurations are similar to those ofFIG. 1described in embodiment 1. Same components are indicated by same symbols. The difference is that in the present embodiment, a method of introducing light into a near-field optical head104consists of shaping light from a laser101into collimated light301using a lens102, propagating the light through air, and bending the light vertically with a mirror302. In other respects, the present embodiment is similar to embodiment 1 and thus description of these similar points will be omitted. In the present embodiment, light from the laser101is propagated through air and so the light can be admitted into the near-field optical head104while preserving the direction of polarization of the light. The important point of the present invention is that near-field light is localized by placing only the portion of the contour of the minute aperture forming the near-field light vertically to the polarization of the incident light. Among others, the present embodiment has the advantage that it can well control the polarization of the incident light. In consequence, information can be recorded and read at a high density with high S/N.

FIG. 12is a view showing the vicinities of a minute aperture at the bottom surface of a near-field optical head used in an information recording-and-reading device according to embodiment 3 of the present embodiment.FIG. 12is similar toFIG. 3except that an Al light-shielding film411deposited on the surface of a triangular pyramid is shown inFIG. 12. One face of the three faces of the triangular pyramid is a Ag film412instead of Al. A SiO2or Al layer is deposited to about 100 nm on the surface of the Al light-shielding film411and the Ag film412, although not shown. The front end of the triangular pyramid is cut horizontally to form an optically minute aperture206.

FIG. 13is a plan view of the minute aperture shown inFIG. 12. The minute aperture206has a substantially triangular contour. Its right side is substantially perpendicular to the direction of scan x of the head. The portion in contact with this side is the Ag film412. The other two sides are made of Al film411. Where light having the direction of polarization in the x-direction as shown is made to enter the near-field optical head having this structure, the surface of the Ag excites plasmons, so that near-field light localizes strongly on the surface of the Ag film. As a result, further localization and increase of the energy can be accomplished, in addition to the light-localizing effect possessed by the structure implemented in embodiment 1 or 2.

FIG. 14illustrates a method of fabricating the near-field optical head of the present embodiment. In step S401, a SiO2layer311having a thickness of 15 microns is formed on the top surface of a Si substrate312having a thickness of 400 microns by plasma CVD. In step S402, a form314of a triangular pyramid is formed by isotropic etching, using a triangular mask patterned by photolithography. Then, in step S403, an Ag film412is formed on one face of the triangular pyramid form314. An Al film411is formed on the other two faces. This can be easily accomplished by placing the substrate at an angle to the evaporation source. In step S404, an Al film413is formed over the whole surface. Then, in step S405, the front end is cut to fabricate an optical aperture206. As also described in embodiment 1, the optical aperture206can also be formed by a cutting operation making use of FIB. It can also be attained by applying mechanical force to the front end.

FIG. 15is a schematic view of a near-field optical probe1000according to embodiment 4. The near-field optical probe1000comprises a tip701, a lever702, a base portion703, a light-shielding portion704, and a minute aperture705. The conical tip701and the lever702that is a cantilevered thin sheet are formed integrally. The tip701is formed on the lever702protruding straight from the base portion703and on a surface opposite to the base portion703. The light-shielding film704is formed on the surface of the lever702opposite to the base portion703and on the surface of the tip701. Although it is not necessary to form the light-shielding film704over the whole surface opposite to the base portion703of the lever702, the film704is preferably formed over the whole surface.

The minute aperture705is free of the light-shielding film704over the tip701. The vertex of the tip701protrudes from the end surface of the light-shielding film704. The front end of the tip701may be flush with the end surface of the light-shielding film704. The near-field optical probe1000can emit near-field light from the minute aperture705by introducing incident light999from the outside. Furthermore, optical information from a specimen can be detected owing to the minute aperture705. In addition, illumination of the near-field light from the minute aperture705and detection of optical information about the specimen at the minute aperture can be performed simultaneously.

The tip701and lever702are made of a material transparent to the wavelength of incident light999used in a scanning near-field microscope. Where the wavelength of the incident light999is in the visible range, the material can be dielectric materials (such as silicon dioxide and diamond) and polymers typified by polyimide. Where the wavelength of the incident light999is in the UV range, the material of the tip701and lever702is a dielectric material such as magnesium difluoride or silicon dioxide. Where the wavelength of the incident light999is in the infrared region, the material of the tip701and lever702is zinc selenium or silicon. The material of the base portion703is a dielectric material such as silicon or silicon dioxide or a metal such as aluminum or titanium. The material of the light-shielding film704shows a high light-shielding factor for the incident light999and/or for the wavelength of light detected by the minute aperture705such as aluminum and gold. The height of the tip701is microns to tens of microns. The length of the lever702is tens of microns to thousands of microns. The thickness of the lever702is on the order of microns. The thickness of the light-shielding film704is tens of nanometers to hundreds of nanometers, though it varies according to the light-shield factor. With respect to the size and shape of the minute aperture705as viewed from the bottom surface ofFIG. 15, it is a triangle inscribing a circle whose diameter is less than the wavelength of the incident light999and/or the light detected by the minute aperture705.

At this time, the incident light999is linearly polarized light from a laser light source. Its direction of polarization is substantially perpendicular to one side of the triangular contour of the minute aperture705.

FIG. 16is a view showing the structure of a scanning probe microscope20000fitted with the near-field optical probe1000according to the embodiment 4 of the present invention. This scanning probe microscope20000comprises the near-field optical probe1000shown inFIG. 15, a light source601for measurement of optical information, a lens602placed in front of the light source601, an optical fiber603for propagating light collected by the lens602to the near-field optical probe1000, a prism611placed below a specimen610and reflecting propagating light produced at the front end of the tip, a lens614for collecting the propagating light reflected by the prism611, and a light detection portion609for receiving the collected, propagating light. The optical fiber603is a polarization-maintaining fiber for preserving the direction of polarization of the incident light.

A laser generator604for producing laser light, a mirror605for reflecting the laser light reflected off the interface between the lever702of the near-field optical probe1000shown inFIG. 15and the light-shielding film704, and a photoelectric converter portion606for receiving the reflected laser light and performing a photoelectric conversion are mounted above the near-field optical probe1000. The photoelectric converter portion606is vertically divided into two. Furthermore, there are provided a rough motion mechanism613and a fine motion mechanism612for moving and controlling a specimen610and a prism611in the X-, Y-, and Z-directions, a servo mechanism607for driving these rough motion mechanism613and fine motion mechanism612, and a computer608for controlling the whole apparatus.

The operation of this scanning probe microscope20000is next described. Laser light emitted from the laser generator604is reflected off the interface between the lever702of the near-field optical probe1000shown inFIG. 15and the light-shielding film704. When the minute aperture705and the surface of the specimen610come closer to each other, the lever702of the near-field optical probe1000is distorted by the attraction or repulsion between the lever and the specimen610. Therefore, the optical path of the reflected laser light varies. This is detected by the photoelectric converter portion606.

The signal detected by the photoelectric converter portion606is sent to the servo mechanism607. The servo mechanism607controls the rough motion mechanism613and the fine motion mechanism612such that the deflection of the near-field optical probe1000is kept constant, based on the signal detected by the photoelectric converter portion606when the near-field optical probe1000approaches the specimen610or the surface is observed. The computer608receives information about the surface topography from the control signal from the servo mechanism607. Furthermore, the light emitted from the light source601is condensed by the lens602and reaches the optical fiber603. The light propagating through the optical fiber603is admitted into the tip701of the near-field optical probe1000via the lever702while the polarization is maintained. The light is directed to the specimen610from the minute aperture705. On the other hand, optical information about the specimen610reflected from the prism611is collected by the lens614and introduced into the light detection portion609. The signal from the light detection portion609is gained via the analog input interface of the computer608and detected as optical information by the computer608. The method of introducing light into the tip701may consist of collecting the light emitted from the light source601directly onto the tip701by a lens and admitting the light without using the optical fiber603. In the description with reference toFIG. 16, an illumination mode has been described in which light is admitted into the near-field optical probe1000and near-field light is directed to the specimen from the minute aperture705. The near-field optical probe1000can also be used in a collection mode in which near-field light produced at the surface of the specimen610is detected by the minute aperture705. In addition, the near-field optical probe1000can be used in an observational method in which the illumination mode and the collection mode are simultaneously effected.

InFIG. 16, a transmission mode in which light transmitted through the specimen610is detected has been described. The near-field optical probe1000can also be used in a reflection mode in which light reflected from the specimen610is detected. Additionally, the near-field optical probe1000can be used in a dynamic focus mode in which the lever702is vibrated by applying vibration to the near-field optical probe1000using a bimorph or the like and the distance between the tip701and the specimen610is controlled so as to maintain constant the variation in the amplitude of the lever702or frequency variation of the vibration of the lever702that is caused by the repulsion or attraction exerted between the tip701and the specimen610.

Where the specimen surface is observed using the scanning probe microscope of the construction described above, a phenomenon similar to that described in embodiment 1 occurs. That is, near-field light is strongly localized near one side of the minute aperture because the direction of polarization of the incident light is substantially perpendicular to the one side of the minute aperture. Consequently, it strongly interacts with a microscopic area on the specimen surface. An observation at high resolution and high S/N is made possible. Similar advantages can be obtained if the minute aperture is substantially triangular as described in embodiment 1 or shapes shown inFIGS. 10(a),(b). The main point is that the portion of the contour of the minute aperture which is substantially perpendicular to the direction of polarization of the incident light is localized in one portion.

FIGS. 17 and 18illustrate a method of fabricating the near-field optical probe1000of embodiment 4 of the present invention.FIG. 17(a) shows a state in which a transparent body801becoming a tip701and a lever702is deposited on a substrate802. In the description given below, the top of each figure is referred to as the front surface, while the bottom portion is referred to as the rear surface. The transparent body801is deposited by plasma CVD or sputtering on the substrate802having a masking material803on the rear surface. The amount of the deposited transparent body801is about equal to or slightly greater than the sum of the height of the tip701and the thickness of the lever702.

After depositing the transparent body801, a mask804for the tip is formed on the transparent body801by a method typified by photolithography as shown inFIG. 17(b). The mask804for the tip is a dielectric material such as photoresist or polyimide. After forming the mask804for the tip, the tip701is formed as shown inFIG. 17(c) by isotropic etching such as wet etching or dry etching.

After forming the tip701, a mask805for the lever is formed on the transparent body801as shown inFIG. 18(a). After forming the mask805for the lever, a lever702is formed as shown inFIG. 18(b) by anisotropic dry etching typified by reactive ion etching (RIE).

After forming the lever702, the masking material803is patterned by photolithography. Then, the lever702is released and the base portion703is formed as shown inFIG. 18(c) by crystal anisotropic etching using tetramethyl ammonium hydroxide (TMAH) or potassium hydroxide (KOH) or anisotropic dry etching. Finally, a light-shielding film704is deposited on the front surface. Undesired portions of the light-shielding film704are removed by a focused ion beam or pressing the tip701against the specimen during observation. As shown inFIG. 18(d), a minute aperture705is formed, and the near-field optical probe1000can be obtained.

FIG. 19shows the shape of the minute aperture of a near-field light-generating element according to embodiment 5 of the present invention. Incident light polarization222is parallel to x-direction. The length901of the portion of the contour of the minute aperture which is substantially perpendicular to the incident light polarization222is shorter than the vertical width902of the aperture. As mentioned previously, near-field light distribution903localizes in the portion substantially perpendicular to the incident light polarization222. In this embodiment, the near-field light distribution903localizes vertically more narrowly than the vertical width902of the minute aperture. The near-field light can be localized vertically as well as in the left and right directions in the figure by the combination of the minute aperture of this shape and the incident light polarization.

Where this near-field light-generating element is used as a head of an optical recording device, the recording density in the track direction can be improved, as well as the density of the linear direction. Furthermore, where this near-field light-generating element is used as a probe in a near-field optical microscope, a near-field optical microscope having high resolution in every direction within the specimen surface can be accomplished.

FIG. 20is a view illustrating the configuration of a near-field optical recording device that makes use of the near-field light-generating element according to embodiment 6 of the present invention as a head. The configuration is similar toFIG. 1described in embodiment 1. Same components are indicated by same reference numerals, and their description is omitted. The difference withFIG. 1is that a polarizing plate911is inserted in a portion that detects scattered light. The scattered light is produced by interaction between a near-field optical head104and a recording medium105via near-field light. Only a certain polarized component is taken from the scattered light by the polarizing plate911and received by a light-receiving head106. In the present invention, the direction of polarization relative to the near-field optical head104is controlled to enter the light. Interaction with the recording medium105disturbs the polarized light. This disturbance depends on data mark that is a minute optical characteristic difference on the surface of the recording medium105. A high-contrast signal reproduction can be performed by selectively detecting it. In consequence, recording and reading can be performed at a still higher density.

Since the polarizing plate is mounted on the detection side in this way, similar advantages can be obtained where a near-field light-generating element is used as a probe in a near-field optical microscope in a manner not illustrated. In the case of a microscope, the resolution can be enhanced.

FIG. 21is a view illustrating the manner in which a near-field light-generating element according to embodiment 7 of the present invention is used in a probe of a near-field optical microscope.FIG. 21(a) is a side elevation, and (b) is a plan view of an aperture. InFIG. 21(a), a cantilever921has a triangular pyramid922near its front end, the pyramid being made of SiO2. Its front end is cut parallel to the cantilever921, whereby an optically small aperture is formed. In (b), incident light is a linearly polarized light in the left and right directions in the figure. A side924substantially vertical to the direction of polarization928has a height925above a specimen surface923. This height925is lower than a height926of a vertex927taken from the specimen surface923. As mentioned previously, in the present invention, near-field light localizes on the side924substantially vertical to the incident light polarization928. In the present embodiment, this portion is brought closer to the specimen. This improves the resolution. Also, the signal intensity and S/N are enhanced.

FIG. 22is a view illustrating the manner in which a near-field light-generating element according to embodiment 8 of the present invention is used in a probe of a near-field optical microscope. The configuration of the present embodiment is similar to that of embodiment 7. One difference is that the optically small aperture has rotated through 90° relative to a cantilever921. Another difference is that the direction of polarization928of the incident light is vertical direction in the figure. A side931substantially perpendicular to the direction of polarization928is tilted relative to a specimen surface923. The height925of the left end932of this side931above the specimen surface923is lower than the height926of the right end933. As mentioned previously, near-field light localizes near the side931vertical to the incident light polarization928. The left end932of this near-field light distribution is closer to the specimen surface923than the right end933. Since the near-field light spatially attenuates exponentially toward the specimen surface923, the near-field light near the right end933does not strongly interact with the specimen surface923. Only the near-field light near the left end932interacts with the specimen surface923. In the past, the resolution has been determined by the size of the optical aperture. In the present invention, the resolution is determined by the length of one side of the aperture. Furthermore, in the present embodiment, the resolution is determined by one end of that side. Hence, the resolution can be enhanced further.

A structure similar to embodiment 7 or 8 can also be used in a head of a near-field recording device.FIG. 23illustrates a method of fabricating a near-field optical head of the present embodiment. Embodiment 3 is similar to the fabrication method illustrated inFIG. 14. Identical parts are indicated by identical symbols. In step S401, a SiO2layer311having a thickness of 15 microns is formed on the top surface of a Si substrate312having a thickness of 400 microns by plasma CVD. In step S402, a shape314of triangular pyramid is formed by isotropic etching, using a triangular-shaped mask patterned by photolithography. Then, in step S1003, an Al film1001is formed on the form314of a triangular pyramid. In step S1004, the front end of the triangular pyramid is cut by FIB to form an aperture206. At this time, the end is cut obliquely to the substrate instead of parallel to it. In this way, the aperture of the shape described in embodiment 7 and 8 is formed.

As described thus far, a near-field light-generating element according to the present invention has an optically small aperture of a size smaller than the wavelength of incident light, the near-field light-generating element being designed to produce near-field light by directing the incident light to the optically small aperture. The near-field light-generating element is characterized in that one location of the contour of the small aperture is substantially perpendicular to the direction of polarization of the incident light.

Thus, only the portion of the contour of the small aperture which is substantially perpendicular to the direction of polarization of the incident light produces near-field light of high intensity. Consequently, a high resolution and a high light efficiency are compatible.

In one feature of the near-field light-generating element, the contour is a polygon having one side that is substantially perpendicular to the direction of polarization.

As a result, a high-performance near-field optical head can be fabricated economically simply by fabricating a mask of a simple shape. Furthermore, the portion of the contour of the aperture which produces strong near-field light is only one. This permits improvement of the resolution.

In another feature of the near-field light-generating element, the contour has a triangle having one side that is substantially perpendicular to the direction of polarization.

This permits fabrication of a minute aperture based on a triangular shape whose vertex can be readily formed. Stable near-field light-generating elements can be fabricated at high yield.

As one feature of the near-field light-generating element, the minute aperture is formed at the front end of a conical tip that transmits light. Surroundings of the minute aperture are covered with a light-shielding film.

This yields the advantage that it is possible to form a minute aperture having a size smaller than a structure capable of being fabricated by lithography.

As another feature of the near-field light-generating device, one side of the contour is made of a material that excites plasmons by incident light.

This presents the advantage that the generated near-field light strongly localizes near the one side of the minute aperture and so the near-field light-generating element has a high S/N and corresponds to high-density recording.

In a further feature, the material includes any of gold, silver, and copper.

This makes it possible to fabricate a high-performance near-field light-generating element by easy fabrication processes.

In a still further feature, the length of one location of the contour which is substantially perpendicular to the direction of polarization is shorter than the width of the aperture in a direction vertical to the polarization.

This results in the advantage that a near-field light-emitting element having high resolution in a direction vertical to the direction of polarization as well as in the direction of polarization can be accomplished.

In addition, a near-field optical recording device is provided which comprises an optical head, a light source, a recording medium, means for scanning the optical head across a surface of the recording medium, optical incident means for guiding incident light from the light source to the optical head, and optical detection means for detecting scattered light produced by interaction of the optical head with the surface of the recording medium via near-field light. The device is characterized in that the optical incident means includes means for keeping or controlling polarization of the incident light and in that the optical head is a near-field light-generating element set forth in any one of the above descriptions.

In consequence, the portion of the contour of the aperture that produces strong near-field light is only one and, therefore, the resolution can be enhanced. Furthermore, a high-performance near-field optical head can be fabricated by a simple method economically. In addition, in a data storage device, high-density recording and high transfer rate are compatible.

Further, a near-field optical microscope is provided which comprises an optical probe, a light source, optical incident means for guiding incident light from the light source to the optical probe, and optical detection means for detecting scattered light produced by interaction of the optical probe with the surface of the specimen via near-field light. The microscope is characterized in that the optical incident means includes means for keeping or controlling polarization of the incident light and in that the optical probe is a near-field light-generating element set forth in any one of the above descriptions.

Thus, only the portion of the contour of the minute aperture which is substantially perpendicular to the direction of polarization of the incident light produces near-field light of high intensity. High resolution and high light efficiency are compatible. Hence, high resolution and high S/N of the microscope can be accomplished. A high-performance near-field optical probe can be economically manufactured by a simple method.

In a yet other feature, the optical detection means includes a polarizing optical element.

As a consequence, microscopic distribution of an optical property on the surface of a recording medium or specimen surface can be detected as a disturbance to the polarization and thus a recording device of higher density or a microscope of higher resolution can be accomplished.

In a still other feature, one location of the contour of the minute aperture which is substantially perpendicular to the direction of polarization of the incident light is located closer to the front end than other portions of the contour in the optical probe.

This yields the advantage that the produced near-field light can be brought closer to the specimen surface and thus a high-resolution microscope can be accomplished.

In an additional feature, a line connecting one location of the contour of the minute aperture substantially perpendicular to the direction of polarization of the incident light and a portion opposite thereto is substantially perpendicular to the direction of the front end of the optical probe in the optical probe.

This creates the advantage that only a part of the near-field light that is localized can be utilized. Hence, a microscope of still higher resolution can be accomplished.