JP3887274B2 - Guided near-field probe and method for manufacturing the same, aperture creating method, near-field spectroscopic device using the same, and optical head - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a near-field probe, and more particularly to an improvement in its tip structure.
[0002]
[Prior art]
In general, the limit of resolution of an apparatus or apparatus using optical technology is determined by the wavelength of light used. There is a technique using a near field as means for exceeding the limit due to the wavelength of light. Since the optical fiber probe used in the technique using the near field is used for a small region below the wavelength of light, the length of the protruding core tip is usually several microns.
In order to measure near-field and irradiate near-field light, a mask is formed on the surface of the probe with a light-shielding and ductile material, and has a diameter of several tens to several hundreds of nanometers that allows light to pass through only the tip part. A minute opening is formed. As a technique for creating such a minute opening, there are a pressing method, an oblique deposition method, FIB, and the like.
[0003]
Moreover, since the near-field light is localized on the order of nm, it is necessary to bring the probe and the sample very close to each other. However, since the probe is fine as described above, there is a high possibility of damage due to contact with the sample. Therefore, it is necessary to carefully control the distance between the probe and the sample. Such control methods include optical system control such as shear force control and tuning hawk control.
[0004]
[Problems to be solved by the invention]
However, the above-described opening creation and distance control are related to a very fine region and are difficult techniques.
For example, in the pressing method, the tip portion of the probe is pressed against a flat substrate, the mask portion in contact with the substrate is stretched, and light is transmitted through the portion. Although the opening is formed in this way, it is necessary to accurately monitor the amount of light emitted from the tip of the probe in order to control the size of the opening.
In the oblique deposition method, it is difficult to control the deposition amount and angle of the mask, and it cannot be produced with good reproducibility. Also, FIB requires very expensive equipment.
[0005]
In the distance control of the optical system such as the shear force control and the tuning hawk control described above, the degree of freedom of movement of the probe is small and a sample moving at high speed cannot be measured.
An object of the present invention is to provide a near-field probe that facilitates the control of the opening diameter and the control of the distance to the sample in creating the opening as described above.
[0006]
[Means for Solving the Problems]
To achieve the above object, the guided near-field probe of the present invention comprises a clad and an optical fiber having a core functioning as a light guide, and the clad is substantially hemispherical surrounding the core on the end face of the optical fiber. A core having a recess and a core surrounded by the recess has a sharpened tip. In addition, a portion of the end surface where the cladding is not recessed is used as a guide surface, and the tip of the core is substantially at the same height as the guide surface, and the guide surface is used for controlling the distance between the sample and the probe. And In the guided near-field probe, at least the surface of the core tip has a mask made of a material opaque to light, and an opening for transmitting light is provided in the tip of the core. It is also preferable that the guide surfaces are parallel.
[0007]
It is also preferable that the opening is in the shape of an ellipse or a slit.
It is also preferable that the guided near-field probe has a plurality of the cores in the cladding.
The method for manufacturing a guided near-field probe of the present invention uses an optical fiber comprising a clad and one or more cores, and immerses the end face of the optical fiber in an etching solution having a faster core dissolution rate than the cladding dissolution rate. A recess forming step for recessing the core and the cladding around the core, and sharpening for sharpening the core of the recess by immersing the end face of the fiber having the recess in an etching solution whose core dissolution rate is slower than the cladding dissolution rate Process. Then, the cladding around the core is recessed into a substantially hemispherical shape at the end face of the optical fiber, and the optical fiber is processed so that the tip of the core is sharpened.
[0008]
The method for creating an aperture of a guided near-field probe of the present invention comprises an optical fiber comprising a clad and one or more cores, and the clad has a substantially hemispherical recess surrounding the core on the end face of the optical fiber. The core surrounded by the concave portion has a sharpened tip portion, and at least the surface of the core tip portion is covered with a light-shielding mask portion, and guides a portion of the end face where the cladding is not recessed. Using a guided near-field probe as a surface, press the guide surface against a flat plate to create an opening that transmits light to the tip of the core, and adjust the distance that the core protrudes from the guide surface. It is characterized by controlling the aperture.
[0009]
In addition, the guided near-field probe of the present invention can be suitably used for a near-field spectrometer.
Furthermore, the guided near-field probe of the present invention can be suitably used as an optical head for recording / reading information for an optical memory.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the guided near-field probe of the present invention will be described in detail.
FIG. 1 is a perspective view of an end portion of a guided near-field probe 2 according to the present invention. The guided near-field probe 2 shown in the figure is formed using an optical fiber including a clad 4 and a core 6 that functions as a light guide. A clad 4 and a core 6 are exposed concentrically on the end face of the fiber, and the clad 4 around the core 6 has a concave portion 4a recessed in a substantially hemispherical shape. On the other hand, the core 6 has a tip portion 6a protruding from the recess 4a and sharpened in a substantially conical shape. Further, the end surface portion of the cladding 4 which is not recessed is defined as a guide surface 8. The tip 4a of the core is almost the same height as the guide surface 8, and the guide surface 8 can be used to control the distance between the sample and the probe.
The near-field probe according to this embodiment is configured as described above, and the operation thereof will be described below.
[0011]
FIG. 2 shows a method of using the probe according to this embodiment. As shown in the figure, the guide surface 8 at the end face of the probe 2 is pressed against the sample 14. At this time, since the guide surface 8 and the core tip portion 6a are in a fixed positional relationship, the core tip portion 6a can be in proper contact with the sample 14 or can maintain a constant separation state. Therefore, special distance control devices such as shear force control and tuning hawk control are not required. As a result, the probe 2 and the sample 14 can be freely and rapidly moved, and the apparatus can be downsized and the operation can be simplified.
The advantage of the guide surface 8 being formed by the clad 4 that is originally provided in the optical fiber is that it is easier to produce compared to the case where a holding material for other distance control is attached to the fiber. It is done. In addition, since the guide surface 8 is flat and has a large area, the contact surface between the guide surface 8 and the sample 14 is large, and the positional control between the probe 2 and the sample 14 is stable. Furthermore, since the guide surface 8 protects the tip 6a of the core 6, there is little possibility of damage to the probe tip even if the probe or sample is moved at high speed. In this way, it is possible to deal with a sample moving at a high speed, and therefore it is possible to measure a sample moving on a line.
[0012]
In order to irradiate / collect near-field light from the tip of the optical fiber, the periphery of the core must be covered with a metal or the like, and a small opening that allows light to pass through only the tip of the core must be provided. Next, a near-field probe provided with this opening will be described. 3 is a perspective view thereof, and FIG. 4 is a sectional view thereof. The parts corresponding to those in FIG.
The surface of the optical fiber in FIG. 3 is covered with a mask portion 10 made of a material opaque to light. In addition, the mask portion 10 is thinly extended at the front end portion of the core, and an opening surface 12 that facilitates light transmission is provided. The opening surface 12 has the same height as the guide surface 8, and the opening surface 12 and the guide surface 8 are parallel to each other.
[0013]
The distance to the sample is controlled by pressing the guide surface against the sample 14 as shown in FIG. Since the opening 12 at the tip of the core and the guide surface 8 are on the same plane, the sample 14 and the opening 12 at the tip of the core 6 are in complete contact with each other.
In FIG. 4A, light is incident from the end face of the optical fiber, near-field light 22 is generated from the tip of the core 6 on the other end face, irradiated to the sample 14, and the scattered light is condensed at the opening 12. 4B shows a case where the tip of the core is inserted into the near-field light 22 on the surface of the sample 14 to collect the light. Yes.
[0014]
In either case, the intensity of near-field light greatly decreases according to the distance. Thus, when the aperture 12 for irradiating / condensing the near-field is brought into close contact with the sample 14, light can be used without waste. Efficiently desirable.
In addition, for measurement and use in consideration of light polarization, a near-field probe having an elliptical core cross section and an elliptical or slit aperture is also used. FIG. 5 shows such a near-field probe using the technique of the present invention. The part corresponding to FIG. 3 is denoted by reference numeral 100, and detailed description thereof is omitted. The opening 112 in FIG. 5 has a slit shape, and the transmittance of light that is linearly polarized in the major axis direction is higher than that in the direction orthogonal thereto. Here too, the guide surface 108 is made of the clad 104 and can be formed almost simultaneously with the work of leading the core 106.
[0015]
Due to the shape of the probe of the present invention, the scattered light 22 scattered at the tip of the probe 2 is reflected by the substantially hemispherical or semi-ellipsoidal concave portion 4a of the cladding 4 around the core 6 as shown in FIG. It is also possible to increase the light collection efficiency by focusing on the focus.
It is also possible to apply the above-described guided near-field probe technique to a multi-probe having a plurality of cores in the clad. The multi-probe is composed of a plurality of cores that are light guide paths included in one optical fiber, and is applied to an optical head of a high-density recording apparatus.
[0016]
FIG. 6 shows the application of the technique of the present invention to a multi-array type multi-probe. A portion corresponding to FIG. 1 is denoted by reference numeral 200, and detailed description thereof is omitted. As in the case of FIG. 1, the end face of the fiber has a recess 204a in which the cladding 204 around the core 206 is recessed in a substantially hemispherical shape. By pressing the end surface of the clad 204 that is not recessed as a guide surface 208 against the sample, the tip end portion 206a of the core 206 can appropriately contact the sample or maintain an appropriate distance. Further, since the area of the guide surface 208 is large, the adhesion surface with the sample is also increased, and the positional relationship between the probe and the sample is stabilized. By using the clad 204 that is originally provided in the optical fiber as the guide surface 208 for controlling the distance from the sample, the guide surface 208 can be created simultaneously with the leading edge of the core 206, and therefore, the creation becomes easy.
[0017]
FIG. 7 illustrates an example of a manufacturing procedure of the guided fiber probe of the present invention. FIG. 7A shows an optical fiber before processing. The clad 4 is made of SiO ₂ , and the core 6 is made of SiO ₂ doped with GeO ₂ . The manufacturing procedure is roughly divided into a step of forming a recess and a step of sharpening the core.
First, in order to form a recess, the fiber shown in FIG. 7A is used as a first etching solution made of an HF-NH ₄ buffer solution whose composition ratio is adjusted so that the dissolution rate of the core 6 is faster than the dissolution rate of the cladding 4. Immerse the end face. Then, as shown in FIG. 7 (B), the core 6 is removed preferentially, the core 6 portion is recessed, and the clad 4 is more dissolved in the portion close to the core 6. As a result, the core 6 and the cladding 4 around the core are recessed in a substantially hemispherical shape.
[0018]
Next, the process proceeds to a core sharpening process. As the second etching solution, an HF-NH ₄ buffer solution having a composition such that the dissolution rate of the core 6 is slower than the dissolution rate of the clad 4 is prepared. When the fiber end face of FIG. 7B is immersed in the second etching solution for a predetermined time, the core 6 is sharpened while the cladding 4 is removed. As a result, as shown in FIG. 7C, the sharpened core 6 protrudes from the recess 4a of the clad 4.
Further, an HF-NH ₄ buffer solution having a composition ratio is prepared as the third etching solution so that the relative dissolution rate of the clad 4 with respect to the core 6 is faster than that of the second etching solution. When the fiber end face of FIG. 7C is immersed in this third etching solution, as shown in FIG. 7D, the cladding 4 around the core 6 has a substantially hemispherical recess 4a, and the core tip 6a. Is formed in a two-step taper shape in which the taper angle of the first-stage taper shape 6b is larger than the taper angle of the second-stage taper shape 6c.
[0019]
Moreover, the distance h from the guide surface 8 of the clad to the tip 6a of the core 6 can be adjusted by appropriately performing these series of operations. As will be described later, the size of the opening can be adjusted by the distance h in creating the opening. In the present invention, since chemical etching is used as described above, the length can be adjusted precisely, and therefore the opening diameter can also be adjusted precisely.
Since the guide portion is formed of the clad, the guide portion is flat and has a large area and a stable shape as compared with the case where the guide portion is formed of another holding material. Moreover, since the guide portion is created simultaneously with the processing for making the tip of the core, it does not take time.
[0020]
Here, the outline of a method for manufacturing a probe with a guide having a two-step taper core at the core tip has been described. Of course, other components can be obtained by adjusting the composition of the etching solution and the immersion time in the core sharpening process. -It can also be shaped like a pad. In the case of the above-described multi-probe, it can be produced by the same procedure as described above using an optical fiber having a plurality of cores.
[0021]
Next, the creation of the probe aperture will be described. In order to irradiate / collect near-field light and measure a very fine area beyond the diffraction limit of light, the aperture must be made very fine and precise. However, the conventional aperture creation technique requires a special device for creating the aperture and controlling the size of the aperture. The opening creation according to the present invention is basically a pressing method in which the tip of the core is pressed against a flat plate, and a portion pre-coated with a light-shielding substance is stretched to create an opening through which light can easily pass. . However, in the conventional pressing method, in order to control the aperture diameter, it is necessary to control the aperture diameter by measuring the amount of light emitted from the aperture through the optical fiber during the creation of the aperture. On the other hand, in the present invention, no special device is required, and the aperture diameter can be controlled by adjusting the amount by which the tip of the core protrudes from the guide surface in the production of the near-field probe.
[0022]
This opening creation method will be described with reference to FIG. The same components as those in FIG. In FIG. 8A, the surface of the probe 2 is covered with a mask portion 10 having light shielding properties and ductility. The distance h is the distance from the guide surface 8 to the tip 6a of the core 6. As shown in FIG. 8B, by pressing the guide surface 8 of the probe 2 against the flat substrate 16, the mask 10 at the tip portion 6 a of the core 6 in contact with the flat plate 16 is stretched to form an opening 12. Here, the distance h of the tip 6a of the core 6 protruding from the guide surface 8 determines the amount of the core tip 6a that contacts the sample, and as a result, the opening diameter r can be controlled. Since the shape of the probe 2 is formed by a highly accurate selective chemical etching method, the distance h of the tip 6a of the core 6 protruding from the guide surface can be accurately controlled. That is, it is possible to accurately control the opening diameter r. Further, when the probe is pressed against the flat plate, only the guide surface 8 is pressed so as to be in close contact with the flat plate 16, so that no special device is required, and the guide surface 8 and the opening surface 12 become completely parallel.
[0023]
The above aperture creation method can be performed in the same procedure for the multi-probe shown in FIG. 6 and the polarization type probe shown in FIG.
By using the guided probe of the present invention, a special device for controlling the distance to the sample is not required, and the degree of freedom of movement of the probe is increased as compared with a device using a distance control device such as shear force control. .
[0024]
【Example】
Thus, application examples using the guided near-field probe of the present invention will be described below.
<Near-field spectrometer>
FIG. 9 is a conceptual diagram of a near-field spectrometer. In the figure, the light irradiated to the end face of the optical fiber by the light irradiation means 36 passes through the optical fiber and is irradiated to the sample as near-field light from the opening of the guided near-field probe 20. Then, the near-field light scattered by the sample is collected again from the aperture, and the collected light passes through the fiber, is reflected by the beam splitter 42, and is sent to the spectroscopic means 30.
Regarding the movement of the probe in the Z-axis direction, when a normal probe is used, nm order control is required and a special device is required. However, in the present invention, no special device is required for distance control. It is only necessary to press 20 against the sample 14.
[0025]
However, in FIG. 9, a two-stage control unit including a coarse motion drive unit 32 and a fine motion drive unit 34 is provided in the probe 20 in order to move the probe more precisely in the XY axis directions. First, an XYZ three-axis stage for driving is attached to the coarse motion drive unit 32, and the probe moves greatly. The coarse drive unit 32 can be moved manually. Further, the coarse movement drive unit 32 is pressed against the sample, and the fine movement drive unit 34 attached to the side surface of the probe 20 moves the tip of the probe 20 as shown by the dotted line in FIG. Can be done.
FIG. 10 shows an example of an apparatus for manually controlling the movement of the probe. The probe 20 is covered with a protective covering portion 28, and a manual control portion 26 is attached to the end face side that comes into contact with the probe sample. The other end face of the probe is connected to the spectroscopic means 30. The position of the tip of the probe 20 can be controlled by manually moving the manual control unit 26 and pressing it against the sample.
[0026]
In these near-field spectroscopic apparatuses, it may be detected that the probe and the sample are in contact with each other using a deflection sensor, a contact sensor, a pressure sensor, an ultrasonic sensor, or the like.
As described above, since it is not necessary to control the optical system for controlling the distance between the sample and the probe, the operation can be facilitated and the apparatus can be downsized. Furthermore, it is possible to measure a sample moving at a high speed such as a sample flowing on the line.
[0027]
After measuring a point on the sample, move the probe to a place where the intensity of the near-field light is sufficiently low to measure the background, and repeat the procedure of measuring the other point on the sample to repeat the mapping operation. It is also suitable to do.
Here, only the illumination collection type near-field spectroscopic device has been described, but it goes without saying that the guided fiber probe of the present invention can also be used for the collection type and illumination type near-field spectroscopic devices.
[0028]
<Optical head>
The guided fiber probe 20 of the present invention, the guided multi-probe 202 shown in FIG. 6 and the like can be suitably used as an optical head for recording / reading information for a near-field optical memory. FIG. 11 is a conceptual diagram thereof. In the figure, the recording surface 18 is rotated at high speed by a rotating means 38. The writing / reading means 40 writes and reads information by making light incident on each of a plurality of cores from the end face of the guided near-field probe 202 or detecting light from an optical fiber. Information is written / read on the recording surface 28 by irradiating / condensing light from the sharpened core to the recording surface 18 on the other end face of the fiber.
[0029]
In order to control the distance between the recording surface 10 and the optical head 202, it is only necessary to press the guide surface against the recording surface 18, so that it is not necessary to use special optical system control, and the apparatus is miniaturized. Moreover, since the tip of the core is in proper contact with the recording surface 18, light can be used without waste.
In addition, since the area of the guide surface made of the clad is large, the area of the contact surface with the recording surface is large and stable, and the case where the recording surface moves at high speed can also be handled.
[0030]
【The invention's effect】
As described above, by using the guided near-field probe of the present invention, it is easy to create an opening at the tip of the probe and it is not necessary to control the distance to the sample. Moreover, according to the method for manufacturing a guided near-field probe of the present invention, the aperture diameter can be accurately controlled, and the probe can be easily created.
In addition, by using the guided near-field probe of the present invention for the probe of the near-field spectroscopic device and the optical head of the optical storage device, the control of the probe and the optical head can be facilitated, and it can be applied to a sample moving at high speed. it can.
[Brief description of the drawings]
FIG. 1 is a perspective view of a guided near-field probe of the present invention.
FIG. 2 is an explanatory diagram of distance control between a probe and a sample.
FIG. 3 is a perspective view of a guided near-field probe having an opening.
FIG. 4 is an explanatory diagram of distance control between a probe and a sample.
FIG. 5 is a perspective view of a guided near-field probe having a slit-type opening.
FIG. 6 is a perspective view of a guided near-field multi-probe having a plurality of cores.
FIG. 7 is an explanatory diagram of a method for manufacturing a guided near-field probe.
FIG. 8 is an explanatory diagram of an opening creation method.
FIG. 9 is a conceptual diagram of a near-field spectrometer using a guided near-field probe.
FIG. 10 is a conceptual diagram of a manual probe moving device.
FIG. 11 is a conceptual diagram of an optical storage device using a guided near-field probe as an optical head.
[Explanation of symbols]
2 Near-field probe with guide 4, 104, 204 Cladding 4a, 104a, 204a Recessed cladding 6, 106, 206 Core 6a, 106a, 206a Core tip 6b First tapered shape 6c Second tapered shape 8, 108, 208 Guide Surface 10, 110 Mask part 12, 112 Aperture 14 Sample 16 Flat substrate 18 for opening Recording surface 20, 120 Guided near-field probe 22 Near field 24 Scattered light 26 Manual control part 28 Protective film part 30 Spectroscopic means 32 Coarse movement drive section 34 Fine movement drive section 36 Light irradiation means 38 Rotating means 40 Writing / reading device 202 Guided near-field multi-probe h Distance from guide surface to core tip r Aperture diameter

Claims (8)

In an optical fiber consisting of a core that functions as a cladding and a light guide,
The clad has a substantially hemispherical recess surrounding the core on the end face of the optical fiber,
The core surrounded by the recess has a sharpened tip;
The not-depressed portion of the cladding at the end surface is a guide surface,
The core tip is substantially at the same height as the guide surface,
A near-field probe with guide, wherein the guide surface is used for controlling a distance between the sample and the probe. The guided near-field probe according to claim 1,
At least the surface of the core tip has a mask portion made of a material opaque to light,
An opening for transmitting light is provided at the tip of the core,
A near-field probe with guide, wherein the opening and the guide surface are parallel to each other. The near-field probe according to claim 2,
A guided near-field probe, wherein the opening is elliptical or slit-shaped. The guided near-field probe according to claims 1 to 3,
A guided near-field probe comprising a plurality of cores in the cladding. Using an optical fiber consisting of a clad and one or more cores,
A recess creating step in which the end face of the optical fiber is immersed in an etching solution having a faster core dissolution rate than the cladding dissolution rate to dent the core and the cladding around the core;
A sharpening step of sharpening the core of the recess by immersing the end face of the fiber having the recess in an etching solution having a core dissolution rate slower than the dissolution rate of the cladding;
Consists of
A method of manufacturing a guided near-field probe, wherein an optical fiber is processed such that a cladding around the core is recessed into a substantially hemispherical shape on an end face of the optical fiber, and a tip of the core is sharpened. Consisting of an optical fiber with a cladding and one or more cores,
The clad has a substantially hemispherical recess surrounding the core on the end face of the optical fiber,
The core surrounded by the recess has a sharpened tip;
At least the surface of the core tip is coated with a light-shielding mask,
Using a near-field probe with a guide, which is a non-dented portion of the cladding on the end face,
Create an opening that transmits light at the core tip by pressing the guide surface against a flat plate,
An opening creation method for a near-field probe, wherein an opening diameter is controlled by adjusting a distance by which the core protrudes from the guide surface. In a near-field spectrometer using a near-field probe,
A near-field spectrometer using the guided near-field probe according to claim 1. As an optical head for recording / reading information for optical memory,
A guided optical head using the guided near-field probe according to claim 1.

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