JP3597181B2 - Optical fiber probe, measurement method - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical fiber probe that can be attached to, for example, a near-field optical microscope or a superconducting quantum interference device (SQUID) microscope, which is one of probe scanning microscopes, and a measurement method using the same.
[0002]
[Prior art]
In recent years, based on the development of microfabrication technology, devices having a nanometer-sized microstructure, such as a single-molecule optical memory and a single-electron device, have been put to practical use. A near-field optical microscope having a resolution on the order of nanometers has attracted attention as a technology indispensable for the development or evaluation of the above-described device. The near-field optical microscope can detect the physical properties of the sample from the light emission and transmitted light obtained from the sample, for example, by detecting the light intensity, wavelength, polarization, and the like of the light emitted or transmitted from the sample.
[0003]
The near-field optical microscope has a sharpened portion formed by sharpening the core at one end of an optical fiber provided with a clad around the core, and the sharpened portion is coated with a metal such as Au or Ag. And an optical image having a resolution exceeding the wavelength of light can be obtained. That is, by using such a near-field optical microscope, in addition to measuring the physical properties of the sample with a resolution of the order of nanometers, it becomes possible to perform memory operations such as writing and reading, and further, optical processing and the like.
[0004]
Incidentally, when measuring the physical properties of the sample by the near-field optical microscope, the shape of the sample is measured by detecting evanescent light localized in a region smaller than the wavelength of light on the surface of the sample. Then, evanescent light generated by irradiating the sample with light under the condition of total reflection is scattered by the above-described probe and converted into propagation light. The converted propagation light is guided to the core of the optical fiber through the sharp portion where the probe is formed, and is detected by a detector connected to the other emission end of the optical fiber. That is, this near-field optical microscope can perform both scattering and detection by the probe provided at the sharp portion.
[0005]
[Problems to be solved by the invention]
Meanwhile, in order to accelerate the progress of optical communication and optical information processing systems at higher speeds and larger capacities, it is necessary to perform material manipulation and physical property measurement on devices with a resolution of several tens of nanometers. However, with the above-mentioned conventional near-field optical microscope, it has been difficult to realize highly accurate measurement on a scale of several tens of nanometers.
[0006]
Therefore, the present invention has been devised in view of the above-described conventional circumstances, and has as its object the proximity of a device capable of realizing highly accurate physical property measurement with a resolution of several tens of nanometers. An object of the present invention is to provide an optical fiber probe attachable to a field optical microscope or a SQUID microscope, and a measurement method using the same.
[0007]
[Means for Solving the Problems]
The optical fiber probe to which the present invention is applied has a sharpened portion formed by sharpening the core at one end of an optical fiber provided with a clad around the core, in order to solve the above-described problem, and In an optical fiber probe that can be attached to a near-field optical microscope that measures the shape of a sample by detecting propagating light through an optical fiber, a core detects a magnetic field excited based on light applied to the sample The superconducting thin film is formed excluding the sharp portion, and the sharp portion scatters the evanescent light generated by irradiating the sample with light, and detects this to make propagation light.
[0008]
The optical fiber probe to which the present invention is applied has a sharpened portion formed by sharpening the core at one end of an optical fiber provided with a clad around the core, in order to solve the above-described problem, In a fiber optic probe that can be attached to a superconducting quantum interference device (SQUID) microscope that captures changes in the magnetic field, a superconductor that detects a magnetic field excited based on light applied to the sample is centered around the core. As a superconducting coil part formed in a ring shape at the sharp part, and a U-shaped superconductor is juxtaposed to the sharp part so as to be juxtaposed to the superconducting coil part A SQUID junction for capturing a change in the magnetic field detected by the superconducting coil section, and an insulator sandwiched between the SQUID junction, and the sharpened portion To Detect and propagation light which causes scatter evanescent light generated by morphism.
[0009]
The measuring method to which the present invention is applied, in order to solve the above-described problems, an optical fiber probe having a sharpened portion formed by sharpening the core at one end of an optical fiber provided with a clad around the core. In a measurement method for measuring the shape of the sample by detecting the propagating light, a magnetic field excited based on the light applied to the sample, a magnetic field detection step of detecting the superconducting thin film formed except for a sharp portion, Evanescent light generated by irradiating the sample with light is scattered by the sharp portion of the optical fiber probe, and the light is detected and converted to propagation light.
[0010]
A measuring method to which the present invention is applied is an optical fiber probe having a sharpened portion formed by sharpening the core at one end of an optical fiber provided with a clad around the core in order to solve the above-described problem. In a measurement method that measures the shape of a sample by detecting propagating light, a magnetic field excited based on light applied to the sample is formed into a ring at a sharp point around the core as a superconductor. A magnetic field detecting step for detecting by a superconducting coil portion composed of a body, and a U-shaped superconductor is formed so as to be juxtaposed to the superconducting coil portion and protruded so as to taper to a sharp portion. SQUID detection that captures a change in the magnetic field detected by the superconducting coil unit by an interference element composed of a SQUID junction formed on a broken core and an insulator sandwiched by the SQUID junction Has a step, the evanescent light generated by irradiating light to the sample, and a light detection step of the propagation light detects this causes scattered by the sharpened tip of the optical fiber probe.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0012]
FIG. 1 shows an optical fiber probe 1 according to a first embodiment of the present invention. The optical fiber probe 1 is used, for example, in a near-field optical microscope or the like that identifies physical properties based on light emission or transmitted light obtained from a sample, and includes an optical waveguide section 11 and a sharpened section 12 as shown in FIG. .
[0013]
The optical waveguide 11 is composed of an optical fiber in which a clad 21 is provided around a core 20. The core 20 and the clad 21 are each made of SiO ₂ -based glass, and the structure is controlled by adding F, GeO ₂ , B ₂ O _3, etc. so that the refractive index of the clad 21 is lower than that of the core 20. .
[0014]
The sharpened portion 12 is formed by sharpening a core 20 a protruding from the clad at one end of the optical waveguide portion 11. The protruding core 20a may be provided with a gradient such that it gradually tapers to the sharpened portion 12 as shown in FIG. A superconducting thin film 13 is formed on the protruding core 20a except for the sharpened portion 12.
[0015]
The superconducting thin film 13 is a thin film made of a superconducting material such as Pb. The electric resistance of the superconducting thin film 13 suddenly disappears at cryogenic temperature and becomes zero, and the superconducting thin film 13 is completely diamagnetic due to the Meissner effect. Hereinafter, the temperature at which the electric resistance becomes 0 is referred to as a superconducting critical temperature Tc. The superconducting thin film 13 may be made of a superconducting material other than Pb, such as an In alloy.
[0016]
By cooling the optical fiber probe 1 below the superconducting critical temperature Tc, the superconducting thin film 13 formed on the protruding core 20a exhibits perfect diamagnetism based on the Meissner effect. If a magnetic field exists near the superconducting thin film 13 that has caused the Meissner effect, a large reaction force is applied to the entire optical fiber probe 1 on which the superconducting thin film 13 is formed. By detecting this reaction force by, for example, a shear force method or an AFM (Atomic Force Microscope) method, the magnetic force distribution of the sample can be measured with a resolution of the order of nanometers.
[0017]
The optical fiber probe 1 according to the first embodiment measures an evanescent light localized in a region smaller than the wavelength of light on the surface of the sample through the sharpened portion 12 to measure the shape of the sample. It is also possible to attach it to a field microscope. For example, evanescent light generated by irradiating the sample with light under the condition of total reflection is scattered and converted into propagation light. The converted propagating light is guided to the optical waveguide section 11 through the sharp section 12, and detected by a detector (not shown) connected to the other output end of the optical fiber. That is, according to the present invention, both scattering and detection can be performed with extremely high resolution by the optical fiber probe 1 provided with the sharpened portion 12.
[0018]
Further, the optical fiber probe 1 according to the first embodiment, when a magnetic field in a specific direction is applied to the superconducting thin film 13 described above, It is possible to make it easy for specific polarized light to enter from the sharp portion 12. For example, when a magnetic field in a specific direction is applied to the superconducting thin film 13, dextrorotatory circularly polarized light is more likely to enter from the sharpened portion 12 of the optical fiber probe 1 than leftwardly circularly polarized light. . Therefore, by forming the superconducting thin film 13 on the optical fiber probe 1 and applying a magnetic field to the superconducting thin film 13, it becomes possible to select the polarized light incident from the sharp portion 12.
[0019]
Next, a second embodiment of the present invention will be described. FIG. 2 shows an optical fiber probe 3 according to a second embodiment of the present invention. This optical fiber probe 3 is used in a superconducting quantum interference device (SQUID) microscope capable of capturing a change in a magnetic field with a resolution of several tens of nanometers, and as shown in FIG. 32, a superconducting coil section 33, a SQUID joint section 34, and an insulator 35.
[0020]
The optical waveguide section 31 is composed of an optical fiber in which a clad 41 is provided around a core 40. The core 40 and the clad 41 are each made of SiO ₂ -based glass, and their structures are controlled by adding F, GeO ₂ , B ₂ O ₃ or the like so that the refractive index of the clad 41 is lower than that of the core 40. .
[0021]
The sharp portion 32 is formed by sharpening the core 40 at one end of the optical waveguide 31. The protruding core 40a may be provided with a gradient such that it gradually tapers to the sharp portion 32 as shown in FIG.
[0022]
The superconducting coil portion 33 is made of a ring-shaped superconducting thin film with the protruding core 40a wound around the center, and for example, the protruding core 40a is formed so as to form a double coil as shown in FIG. Coated on top. The superconducting coil section 33 may be formed into a double coil shape by cutting the optical fiber probe 1 on which the above-described superconducting thin film 13 is formed by ion irradiation based on a focused ion beam. The superconducting coil section 33 is coated on the core 40a excluding the sharp section 32 in order to input and output light to and from the sample.
[0023]
The SQUID joint 34 is made of a superconducting thin film, and is coated on the protruding core 40 a so as to form a U-shape in a direction parallel to the winding direction of the superconducting coil 33. . The SQUID junction 34 may be formed into a U-shape by, for example, cutting the optical fiber probe 1 on which the above-described superconducting thin film 13 is formed by ion irradiation based on a focused ion beam. Incidentally, the U-shaped shape of the SQUID joint 34 is such that a part of a ring made of a superconducting thin film is cut off as shown in FIG. 2 (in other words, if it is not annular). Any shape may be used. The SQUID junction 34 is connected to an electric signal detector (not shown) for detecting an electric signal.
[0024]
The insulator 35 is sandwiched between U-shaped SQUID joints 34 and is made of an insulating material such as SiO ₂ . That is, a so-called superconducting quantum interference device (SQUID) is constituted by the U-shaped SQUID junction 34 and the insulator 35 sandwiched between the SQUID junctions 34.
[0025]
Incidentally, the superconducting thin film used for the superconducting coil unit 33 and the SQUID junction unit 34 is a thin film coated with a superconducting material such as Pb, but is not limited to Pb. It may be coated. Further, these superconducting thin films to be coated exhibit complete diamagnetism based on the Meissner effect when cooled to a superconducting critical temperature Tc or lower. Therefore, when the optical fiber probe 3 is actually used, it is necessary to cool the optical fiber probe 3 to the superconducting critical temperature Tc or lower.
[0026]
As shown in FIG. 3, when a voltage Vc is externally applied to the SQUID composed of the SQUID junction 34 and the insulator 35, the current flowing through the SQUID junction 34 oscillates at a constant cycle. Incidentally, the period of this vibration is proportional to the magnetic flux density penetrating through the SQUID junction 34 made of a superconducting thin film. Therefore, by detecting the current flowing through the SQUID junction 34, the magnetic flux density penetrating the SQUID junction 34 can be identified. Therefore, since the magnetic flux penetrating the SQUID junction 34 is induced by the magnetic field based on the superconducting coil 33, the change in the magnetic field of the sample detected via the superconducting coil 33 can be detected with high accuracy.
[0027]
That is, the optical fiber probe 3 according to the second embodiment detects a change in the magnetic field of the sample through the sharp portion. The detected change in the magnetic field is transmitted to the SQUID junction 34 via the superconducting coil 33. The SQUID junction 34 to which the voltage Vc is applied can detect a change in the transmitted magnetic field in the cycle of the current oscillation and transmit this to a detection unit (not shown).
[0028]
Thus, the optical fiber probe 3 according to the second embodiment can more accurately detect the magnetic force distribution of the sample. Further, since the optical fiber probe 3 is disposed at the tip of the optical fiber having the clad 41 formed around the core 40, light is emitted from the sharp portion 32 of the core 40 to the sample, and the light is emitted based on the magneto-optical effect. Thus, the magnetic field excited on the sample surface can be detected.
[0029]
Furthermore, the spatial resolution of the entire optical fiber probe 3 can be further improved by reducing the size of the superconducting coil portion 33 provided on the core 30a protruding from the optical fiber probe 3. For example, in the superconducting coil unit 33, by reducing the size of the coil ring located below (close to the sample) to a diameter of several tens of nanometers, it is possible to perform magnetic field observation with a resolution of several tens of nanometers. Can be. Therefore, by reducing the size of the lower coil ring to a diameter of about 10 nm, it is possible to observe the magnetic field of the sample on the order of about 10 nm.
[0030]
Note that the first and second embodiments of the present invention are not limited to the above-described embodiments. For example, the present invention is applicable to a probe that does not emit or emit light. As a result, the present invention can be applied to a case where only a magnetic field observation is performed without the need for a light excitation type observation in which the sample is irradiated with light. In such a case, a material made of, for example, an insulating material is used as an alternative to the optical fiber in which the claddings 21 and 41 are provided around the cores 20 and 40, and all other components are the same as those in the first embodiment or the second embodiment. The members and elements described in the above embodiments may be applied.
[0031]
【The invention's effect】
As described in detail above, the optical fiber probe according to the present invention coats the superconducting thin film in the vicinity of the sharp part, so that the magnetic force distribution in the vicinity of the superconducting thin film causing the Meissner effect can be resolved at a nanometer-level resolution. It becomes possible to detect with high sensitivity.
[0032]
Further, the optical fiber probe according to the present invention can also measure the shape of the sample by detecting evanescent light localized in a region smaller than the wavelength of light on the surface of the sample through the sharp portion.
[0033]
Further, since the optical fiber probe according to the present invention has a superconducting thin film formed at the tip, by applying a magnetic field to the superconducting thin film, it is possible to select polarized light incident from a sharp part. Become.
[0034]
Further, by reducing the size of the superconducting coil section 33 provided on the protruded core 30a of the optical fiber probe 3, it is possible to observe the magnetic field of the sample on the order of about 10 nm.
[Brief description of the drawings]
FIG. 1 is a diagram showing an optical fiber probe according to a first embodiment of the present invention.
FIG. 2 is a diagram showing an optical fiber probe according to a second embodiment of the present invention.
FIG. 3 is a diagram schematically showing a magnetic circuit of a SQUID junction and an insulator.
[Explanation of symbols]
1,3 Optical fiber probe, 11,31 Optical waveguide, 12,32 Sharp, 20,40 core, 21,41 clad, 33 Superconducting coil, 34 SQUID joint, 35 Insulator

Claims (17)

One end of an optical fiber having a cladding provided around the core has a sharpened portion formed by sharpening the core, and measures the shape of the sample by detecting propagation light through the optical fiber. An optical fiber probe that can be attached to a near-field optical microscope
The core, a superconducting thin film for detecting a magnetic field excited based on the light applied to the sample is formed except for the sharp portion,
An optical fiber probe, wherein the sharp portion scatters evanescent light generated by irradiating the sample with light, and detects the scattered evanescent light to generate the propagation light. The optical fiber probe according to claim 1, wherein the sharp portion irradiates the sample with light propagated from the core. The optical fiber probe according to claim 1, wherein a magnetic field in a specific direction is applied to the superconducting thin film. 2. An optical fiber probe according to claim 1, wherein said superconducting thin film is cooled to a superconducting critical temperature Tc or lower. The optical fiber probe according to claim 1, wherein the superconducting thin film is a Pb alloy. At one end of an optical fiber having a cladding provided around a core, the optical fiber has a sharpened portion formed by sharpening the core and can be attached to a superconducting quantum interference device (SQUID) microscope that captures a change in a magnetic field. In an optical fiber probe,
A superconductor that detects a magnetic field excited based on light applied to the sample, a superconducting coil portion formed in a ring shape at the sharp portion with the core as a winding center,
The U-shaped superconductor is formed on a core protruding so as to be tapered until reaching the sharpened portion so as to be juxtaposed with the superconducting coil portion. A SQUID junction for capturing a change in the detected magnetic field;
An insulator sandwiched from the SQUID junction,
An optical fiber probe, wherein the sharp portion scatters evanescent light generated by irradiating the sample with light, and detects the scattered evanescent light to generate the propagation light. The optical fiber probe according to claim 6, wherein the sharp portion irradiates the sample with light propagated from the core. 7. The optical fiber probe according to claim 6, wherein said superconducting thin film is cooled to a superconducting critical temperature Tc or lower. The optical fiber probe according to claim 6, wherein the superconductor is Pb. The optical fiber probe according to claim 6, wherein the superconductor in the superconducting coil portion has a diameter of several tens of nanometers. In a measurement method for measuring the shape of a sample by detecting propagating light with an optical fiber probe having a sharpened portion formed by sharpening the core at one end of an optical fiber provided with a clad around the core,
A magnetic field excited based on the light applied to the sample, a magnetic field detection step of detecting the superconducting thin film formed except for the sharp part,
A light detecting step of scattering the evanescent light generated by irradiating the sample with the sharpened portion of the optical fiber probe and detecting the scattered light to generate the propagation light. The measuring method according to claim 11, further comprising an irradiation step of irradiating the light from the sharpened portion. The method according to claim 11, wherein in the magnetic field detecting step, the magnetic field is detected by a superconducting thin film to which a magnetic field in a specific direction is applied. 12. The measuring method according to claim 11, wherein at least in the magnetic field detecting step, the optical fiber probe is cooled to a superconducting critical temperature Tc or lower. In a measurement method for measuring the shape of a sample by detecting propagating light with an optical fiber probe having a sharpened portion formed by sharpening the core at one end of an optical fiber provided with a clad around the core,
Magnetic field detection in which a magnetic field excited based on light irradiated on the sample is detected by a superconducting coil portion formed of a superconductor formed in a ring shape at the sharp portion with the core as a winding center. Steps and
A SQUID joining portion formed on a core formed by projecting so that a U-shaped superconductor is tapered to reach the sharpened portion so as to be juxtaposed with the superconducting coil portion; An SQUID detection step of capturing a change in a magnetic field detected by the superconducting coil unit by an interference element formed of an insulator sandwiched from a joint,
A light detecting step of scattering the evanescent light generated by irradiating the sample with the sharpened portion of the optical fiber probe and detecting the scattered light to generate the propagation light. The measuring method according to claim 15, further comprising an irradiation step of irradiating the light from the sharpened portion. 16. The method according to claim 15, wherein at least in the magnetic field detecting step, the optical fiber probe is cooled to a superconducting critical temperature Tc or lower.

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