JP3391521B2 - Optical frequency wave transmission line - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a novel lightwave transmission line and
The optical frequency wave transmission line can be used for, for example, information writing, reading, processing, manipulation and the like of high spatial resolution, and is a very small and high-performance optical modulator, detector, optical circuit, optical reading head, optical writing head, sensor For head,
There are a wide range of application fields such as optical probes for STM, micro-processing machines, heads for optical tweezers / manipulators, and optical disks.

[0002]

2. Description of the Related Art As a conventional optical waveguide, for example, an optical confinement type dielectric waveguide mainly comprising a high refractive index medium as a core and a low refractive index medium as a clad, as represented by an optical fiber, is studied. Have been.

[0003] In this optical confinement type dielectric waveguide, the light wave is formed by repeating total reflection of the light at a discontinuous portion of the refractive index in the waveguide, or by bending the traveling direction of the light with a lenticular medium. Suppresses lateral progression and diffraction spread,
It is the principle of an optical waveguide that an optical wave is equivalently propagated only in the axial direction.

[0004] Therefore, the light wave is a three-dimensional electromagnetic field which has not only the main transmission component (axial transmission component) but also some lateral transmission components as standing waves. That is, the real part of the wave number vector (phase constant) has a three-dimensional component.

[0005]

The transverse component of the conventional wave vector is defined to a specific value (eigenvalue) from the cross-sectional structure (lateral boundary condition) of the waveguide, thereby defining a so-called propagation mode. You.

For a light beam having a lateral propagation component, the thickness of the light beam is at least about half a wavelength in principle. In an actual example, the cladding is further thickened because the change in the refractive index is small, for example, like an optical fiber. For this reason, optical circuits and optical elements are thicker and larger than optical wavelengths, and cannot be highly integrated as compared with semiconductor electronic elements or circuits that are now becoming smaller than sub-μm, which is said to be disadvantageous.

On the other hand, even if a three-dimensional light wave propagating in free space is collected, the spot size cannot be reduced below the wavelength due to the diffraction limit.
There is a problem that the spatial density and resolution of the processing or manipulation are limited.

Further, even if the guided light of the conventional optical waveguide or its leakage is used instead of the free-space condensed beam, the thickness of the beam in the waveguide does not become less than about half a wavelength. For example, in the application fields exemplified above, there is a problem that the spatial resolution is limited.

The only exception is the optical scanning tunneling microscope (Photon ST, which utilizes the leakage of the photoelectric field from a hole smaller than the wavelength (which does not propagate and is called an evanescent wave).
M), but in this case, there is a problem that the smaller the hole, the lower the efficiency.

It is known that metal behaves as a plasma medium rather than a conductor in the lightwave region, and is a negative dielectric medium having approximately a negative dielectric constant and an imaginary refractive index. Furthermore, it is also known that a two-dimensional light wave (called a surface wave) plasmon (herein referred to as a surface plasmon ) that does not have a real part of the wave number in a direction perpendicular to the metal interface and does not propagate in this direction propagates. I have. A research paper on the transmission of two-dimensional light waves through a metal thin film using this technique is also available in, for example, Physical Review B, Vol. 33, pp. 5186-5201 (1986) (PHYSICAL R
EVIEW B vol 33, 5186 (1986)).

[0011] Since the actual metal can not be ignored is the real part of the imaginary part and the refractive index of the dielectric constant, the transmission loss of the surface plasmon transmission transmission 10 ² to 10 ⁴ cm ^-1 and incomparably compared with the conventional optical transmission path There is a drawback that the loss is large, 10 ^{over 1 ~10k}
From the standpoint of a general researcher familiar with waveguides with a low loss of about m ^{- 1} , this optical waveguide using surface plasmons is considered to be totally unusable, and is discarded and research is not proceeded. and Gyakuyo the size of, since the surface plasmon is a particular polarization, coupled with ordinary thick dielectric waveguide, waveguide type for cutting the polarization mode of binding to the surface plasmon of the high loss Is used as a polarization filter.

On the other hand, in consideration of the fact that a semiconductor electronic circuit of μm size, which is orders of magnitude smaller than the wavelength, can be constructed for a low-frequency electromagnetic wave whose wavelength is longer than km, the wavelength can be as long as there is no problem with the waveguide. An optical circuit of sub-μm should be able to be made smaller originally.

The reason why an optical circuit or an optical transmission line cannot be reduced is that a waveguide equivalent to a waveguide referred to by microwave is used for an optical waveguide. In fact, when a TV set in the VHF band having a wavelength of several meters is constituted by a metal waveguide circuit, it becomes a huge electronic device having a size of about one room.

Therefore, there is a demand for the development of a waveguide that can be made narrow without being restricted by the wavelength of an electromagnetic wave or a light wave.

However, even though the thickness is large, the thickness of the conventional optical waveguide is about μm, which is sufficiently smaller than that of a microwave or millimeter wave waveguide. Optical fibers are dramatically lower loss, useful, too brilliant, and have not yet fully utilized their capabilities, leading to ultra-fine optical frequency waves.
There seem to be few researchers, except the present inventors, who would proceed with transmission line development research.

According to the present invention, when transmitting an optical signal, the lower limit of the thickness of an optical waveguide or a light beam, which is considered to be limited by the wavelength of the light and cannot be narrowed, is made much smaller than the wavelength,
Miniaturization of the optical circuit Hakare, light can be applied to various devices which light the electromagnetic field is utilized to be able to localize a sufficiently small range than the light wavelength in the optical frequency wave transmission line <br/> periphery or tip vicinity of the very fine It is an object to provide a frequency wave transmission line .

[0017]

According to the present invention, there is provided the following optical frequency wave transmission line .

[0018] (1) has a single column-shaped, and encloses the real part of the dielectric constant negative negative dielectric medium the dielectric constant at positive positive dielectric medium, the longitudinal direction of the negative dielectric medium The length of the cross section that intersects with
It is a characteristic optical frequency wave transmission line. Also a single
Diagonal line of at least one cross section that has a columnar shape, and the real part of the dielectric constant surrounds the negative dielectric medium having a negative dielectric constant with a positive dielectric medium having a positive dielectric constant, and intersects the longitudinal direction of the negative dielectric medium. An optical frequency wave transmission line characterized in that either the major axis or the diameter has a shape with a distance smaller than the optical wavelength.
Road. Further, the negative dielectric medium has a single cylindrical shape and the real part of the dielectric constant is a negative dielectric medium surrounding the positive dielectric medium with a negative dielectric medium, and the negative dielectric medium is in the longitudinal direction of the cylindrical shape. diagonal of at least one cross section intersecting, one of the major axis or diameter is a optical frequency wave transmission line, characterized by <br/> have a cylindrical shape having an inner diameter smaller than the light wavelength.

(2) Surrounding a single negative dielectric medium whose real part is negative with a positive dielectric medium having a positive dielectric constant,
Alternatively, a positive dielectric medium having a positive dielectric constant is surrounded by a single negative dielectric medium in which the real part of the dielectric constant is negative , and a surface plasmon is formed on an interface between the negative dielectric medium and the positive dielectric medium. A transmission line for transmission, in which a part of a cross section intersecting the main propagation direction of the positive dielectric medium is given a refractive index distribution having a refractive index equivalent to that of a peripheral portion, and intersects the main propagation direction. the thickness of the negative dielectric medium, especially smaller than the light wavelength
This is an optical frequency wave transmission line. Further , a single negative dielectric medium having a negative real part of the dielectric constant, a positive dielectric medium A having a positive dielectric constant, and a positive dielectric medium B having a lower refractive index than the positive dielectric medium A Wherein the negative dielectric medium is surrounded by the positive dielectric medium A or the positive dielectric medium A is surrounded by the negative dielectric medium, and a boundary between the negative dielectric medium and the positive dielectric medium A is included. A transmission line for transmitting surface plasmons to a surface, wherein the negative dielectric medium is present in a part of a cross section of the positive dielectric medium A crossing the main propagation direction, and the negative dielectric medium crosses the main propagation direction. The thickness of the negative dielectric medium is smaller than the light wavelength, and the surface of the negative dielectric medium that is not in contact with the positive dielectric medium A is contacted with the positive dielectric medium B.
An optical frequency wave transmission line characterized by being surrounded by
You.

[0020]

The basic structure of the present invention is based on the interaction at the boundary between a negative dielectric medium having a negative real part and a positive dielectric medium having a positive dielectric constant.

That is, either a negative dielectric medium (when the negative dielectric medium has a columnar shape) or a negative dielectric medium (when the negative dielectric medium has a cylindrical shape) having a diameter sufficiently smaller than the wavelength. A shape that transmits only in the axial direction along the boundary surface, cannot transmit in any direction in the radial direction, and has a phase constant only in the axial direction, or a positive dielectric medium and a negative dielectric medium
It has a shape joined with the material .

For example, in a cylindrical transmission line, the field distribution becomes a modified Bessel function radial distribution unlike a conventional Bessel type corresponding to an exponential function or a hyperbolic function of a rectangular coordinate system. Or, a conventional dielectric material containing a thicker than normal dielectric and repeating total internal reflection inside
The waveguide principle is completely different from that of the three-dimensional lightwave cylindrical waveguide.

[0023] That is, the transmission line of the present invention, polarization oscillates at optical frequencies generated inside the negative dielectric medium by irradiating light to the negative dielectric medium surface, excites the nearby polarization, which relays Polarized wave transmission. Therefore,
The principle is completely different from the conventional optical waveguide that propagates in the same way as electromagnetic wave propagation in free space except for reflection at the boundary, and the thickness of the transmission path of the optical frequency wave transmission line of the present invention is not limited by wavelength. .

As a result, in a wavelength range where the medium has a negative dielectric constant, no cutoff occurs even if the waveguide is made thinner than the wavelength, so that the optical frequency is narrow without being limited by the wavelength.
A wave transmission line can be configured, and a high-density optical circuit can be configured without being limited by wavelength.

Therefore, since it is a very small optical circuit capable of producing an optical circuit within the order of mm or within the order of the wavelength, it is sufficient to propagate the optical circuit by a distance of the order of mm or, in some cases, the wavelength. Even a large transmission loss that was out of consideration can be used, and utilizing this surface wave more is the motivation of the present invention and is unique.

Such an idea was recommended by the present inventors in 1984, and an optical transmission line for transmitting a voltage / current in an optical frequency band in the same manner as low frequency or direct current is disclosed in Japanese Patent No.
No. 23538, which has already been obtained by the present inventor. Although the present invention is slightly related to the above patent in that there is no wavelength limitation, the idea is to use a surface plasmon having a different structure and waveguide principle. They have evolved into waveguides or polarized waveguides, both of which are different.

[0027]

1 shows a first embodiment of an optical frequency wave transmission line according to the present invention.
An example of the embodiment will be described. In FIG. 1, a positive dielectric medium 2 surrounds a columnar negative dielectric medium 1, and is coupled to an optical waveguide 3 such as an optical fiber from one end via a coupling matching section 4.

It should be noted that, for example, as shown in FIG. 2, a structure in which a wire-like negative dielectric medium 1 is embedded in a positive dielectric medium 2 may be used, or for example, as shown in FIG. Needless to say, the cladding 5 may be provided outside the cladding of the positive dielectric medium 2.

FIG. 4 shows another embodiment of the optical frequency wave transmission line of the present invention. In FIG. 4, a negative dielectric medium 1 surrounds a columnar positive dielectric medium 2, and is coupled to an optical waveguide 3 such as an optical fiber from one end via a coupling matching section 4. That is, this is the case where the negative dielectric medium 1 is cylindrical.

The thickness of the negative dielectric medium 1 surrounding the positive dielectric medium 2 may be, for example, as thin as shown in FIG. 5 or, for example, as shown in FIG. Is the negative dielectric medium 1 surrounding the positive dielectric medium 2
And the protective cladding in FIG. 6 may be a positive dielectric medium.

The feature of the present invention is that, for example, FIG.
When the negative dielectric medium 1 as shown in FIG. 4 has a columnar shape, the size of the cross section intersecting the transmission direction of the columnar shape or, for example, when the negative dielectric medium 1 as shown in FIG. Is the size of the hole in the cross section intersecting the transmission direction, which is smaller than the wavelength of light. Accordingly, for example, when the protective cladding 5 shown in FIG. 6 is a positive dielectric medium, the positive dielectric medium may be in a form smaller than the wavelength of light. Needless to say, the cladding 5 may be a negative dielectric medium.

Accordingly, for example, the cross-sectional shape crossing or orthogonal to the transmission direction of the negative dielectric medium 1 shown in FIG. 1 or the cross section of the hole crossing or orthogonal to the transmission direction of the negative dielectric medium 1 shown in FIG. The shape may be any shape such as a circle, an ellipse, or a polygon.
Or the distance in the cross-sectional direction, such as the diameter of the inner diameter of the negative dielectric medium 1 in FIG. 4, the long axis or the diagonal line, may be smaller than the wavelength.

As the material of the negative dielectric medium 1 of the present invention,
Ordinary metals, alloys, semiconductors, etc. can be applied and are not special materials. However, for example, as shown in FIG. 1, it is necessary to process the outer diameter smaller than the wavelength, or as shown in FIG. 4, it is necessary to process the inner diameter smaller than the wavelength. Is preferred.

Further, the material of the positive dielectric medium 2 of the present invention may be a material which can be generally applied as an optical fiber or a waveguide, for example, a material which is optically transparent to the wavelength used such as LiNbO ₃ , LiTaO _3, etc. Quartz, alumina,
Inorganic compounds such as magnesia, zirconia, magnesium fluoride, chalcogen compounds, various glasses, and high molecular compounds such as polymethyl methacrylic resin and polystyrene are used.

The positive dielectric medium 2 in FIG. 1 or FIG. 4 may be vacuum or air. In this case, for example, in FIG. 1, a thin wire of the negative dielectric medium 1 is used, and in FIG. It becomes the negative dielectric medium 1.

However, the coupling matching section 4 in FIGS. 1 and 4 couples the optical frequency wave transmission line of the present invention composed of the negative dielectric medium 1 and the positive dielectric medium 2 with the ordinary waveguide 3. Any structure may be used as long as the transmission impedance between the optical frequency wave transmission line of the present invention and the waveguide 3 can be matched and the optical power can be coupled and transmitted therebetween as much as necessary. Not essence.

The optical waveguide 3 shown in FIGS.
, A conventional optical waveguide can be applied and is not the essence of the present invention.

Further, when the optical frequency wave transmission line of the present invention is used as, for example, an optical head, any object such as a metal material, a semiconductor material and an insulator material can be applied.

However, when the optical frequency wave transmission line of the present invention is applied to, for example, an optical head, either a columnar negative dielectric medium facing a target or a cylindrical negative dielectric medium is used. Must be exposed from the end of the positive dielectric medium. Further, when the negative dielectric medium has a columnar shape, the thickness of the negative dielectric medium near the exposed portion, or,
When the negative dielectric medium has a cylindrical shape, it is needless to say that one of the inner diameters of the cylindrical shape near the exposed portion is preferably smaller than the light wavelength.

In the first embodiment of the present invention, for example, a combination as shown in FIGS. 7 to 13 may be used.

That is, as shown in FIG. 7, for example, a negative dielectric medium 1 is surrounded by a positive dielectric medium 2, and another negative dielectric medium 1 ′ is surrounded outside the positive dielectric medium 2. It is a form. The form shown in FIG. 8 is a form in which the thickness of the outer negative dielectric medium 1 ′ is small.

For example, as shown in FIG. 9, the outside of the negative dielectric medium 1 is surrounded by a positive dielectric medium 2, and the outside of the positive dielectric medium 2 is surrounded by another negative dielectric medium 1 '. In this embodiment, the outside of the negative dielectric medium 1 'is surrounded by another positive dielectric medium 2', and the outside of the positive dielectric medium 2 'is surrounded by another negative dielectric medium 1 ". In the form, the inside and outside of the negative dielectric medium 1 whose inner diameter is smaller than the wavelength are respectively provided with positive dielectric media 2 and 2 ′, and another negative dielectric medium 1 ′ is provided outside the positive dielectric medium 2 ′. It is an enclosed form.

FIG. 11 shows a form in which the negative dielectric media 1 and 1 'are arranged in parallel, that is, the positive dielectric medium is air or vacuum. FIG. 12 shows a case where the negative dielectric media 1 and 1 ′ in FIG. 11 are cylindrical, the positive dielectric media 2 and 2 ′ may be positively inserted, or air or vacuum may be used. . Further, in FIG. 13, a plurality of negative dielectric media 1 and 1 ′ are surrounded by a positive dielectric medium 2, and the surrounding of the positive dielectric medium 2 is another negative dielectric medium 1 ″.
It is the form surrounded by.

It is preferable to have a multilayer structure as shown in FIGS. 7 to 13 because surface plasmons generated can be strengthened as compared with a single-layer structure as shown in FIG. 1 or FIG.

By the way, with respect to a conventional three-dimensional light wave which is a light wave, for example, in a rectangular waveguide made of a positive dielectric medium as shown in FIG. 14A, as shown in FIG. The lateral distribution of the electromagnetic wave progresses in a zigzag manner inside the core and becomes a sine wave function with a standing waveform, and attenuates exponentially in the outer clad portion as shown in FIG. 14C.

Further, as shown in FIG. 15A , in a waveguide of a cylindrical dielectric material such as a cylindrical one, for example, as shown in FIG. 15B, the waveguide progresses in a zigzag manner inside the core. The field distribution has a Bessel function (corresponding to the Bessel function in the core portion and the Neumann function in the outside) as shown in FIG.

In the microwave region or the far-infrared region, a waveguide using a metal is often used, and a metal square waveguide corresponding to the former and a metal cylinder having a diameter of about the wavelength shown in FIG. As a Couveau line as shown in FIG. 17B and a cylindrical waveguide having an inner diameter of about a wavelength, a hollow waveguide as shown in FIGS. 16A and 16B is known. , The field distribution is as shown in FIG. 17 (c) or FIG. 16 (c), respectively.

If the negative dielectric medium is considered to be a metal, these can be seen as if they are similar to FIG. 1 or FIG. 4, but in the microwave or far-infrared wavelength range, the properties of the negative dielectric are considered. It acts as a conductor with very high electrical conductivity and forms the boundary of the waveguide as a perfect reflector for three-dimensional electromagnetic waves traveling in zigzag equivalently, so for example, the difference between a microwave waveguide and a gas pipe Furthermore, these two are completely different. Further, the waveguide has a cutoff wavelength depending on the aperture, and transmission cannot be performed unless the aperture is about half a wavelength or more.

On the other hand, in the light wave region as in the present invention, metal basically acts as a negative dielectric medium having a negative dielectric constant, and high density plasma also acts as a negative dielectric medium. I do.

For example, as shown in FIG. 18A, when a light wave enters a negative dielectric medium 1 from a normal optical transparent medium having a positive dielectric constant (positive dielectric medium 2), the photoelectromagnetic wave is converted into a light electromagnetic wave as shown in FIG.
As shown in FIG. 8 (b), although it penetrates exponentially into the negative dielectric medium 1, as a result, it is totally reflected like the ionosphere and cannot propagate inside.

However, in the TM mode, for example, FIG.
As shown in (a), a surface wave called a surface plasmon that can propagate in the form of a surface wave can exist only along the interface between the vicinity of the inner boundary of the negative dielectric medium 1 and the vicinity of the inner boundary of the positive dielectric medium 2. In the horizontal direction perpendicular to the boundary surface, as shown in FIG. 19B, both the inside of the negative dielectric medium 1 and the inside of the positive dielectric medium 2 are exponentially generated without sinusoidal vibration. It attenuates and becomes a two-dimensional light wave (accurately, a two-dimensional light wave is an electromagnetic wave, but is not a light but a plasma wave propagating at an optical frequency).

Further, FIGS. 20 (a) and 21 (a)
As shown in the figure, the negative dielectric medium 1 and the positive dielectric medium 2
In the gap with the thin plate, the adjacent negative dielectric medium / positive dielectric medium
Since two quality boundaries can be formed, the surface waves at the two boundary surfaces are combined, and two alternative two-dimensional light wave modes having different evenness are configured as shown in FIGS. 20 (b) and 21 (b). .

As a result, although it depends on the magnitude relationship of the absolute values of the dielectric constants of the positive dielectric medium 2 and the negative dielectric medium 1, either of the cases of FIG. 20A and FIG. Also, there is a mode in which transmission is not interrupted even if the plate thickness and the gap are made sufficiently smaller than the optical wavelength.

The basic structure of the present invention is that the outer diameter or inner diameter of the negative dielectric medium 1 obtained by winding the negative dielectric medium 1 shown in FIG. 19 (a) or the thin cylindrical shape shown in FIGS. 20 (a) and 21 (a). Is sufficiently smaller than the wavelength and cannot be transmitted in any direction in the radial direction, so that a one-dimensional wave transmission line having a phase constant only in the axial direction is obtained.

FIGS. 22A and 22B and FIG.
(A) and (b) of FIG. 19 (a) are the main parts of a form in which either the negative dielectric medium or the positive dielectric medium is wound around an axis parallel to the surface plasmon propagation direction. FIGS. 24 (a) and 24 (b) and FIGS. 25 (a) and 25 (a)
(B) corresponds to a mode in which the two-dimensional light wave is slightly wound around an axis parallel to the propagation direction of the two-dimensional light wave in each of FIGS. 20 (a) and 21 (a). According to the exponential function or the hyperbolic function of the rectangular coordinate system, the field distributions are shown in FIGS.
4 (c) and a modified Bessel function (Kn (αr), In (αr), where α is a constant) as shown in FIG. 25 (c). Therefore, the guiding principle is completely different from that of a conventional three-dimensional lightwave cylindrical waveguide including a positive dielectric band having a thickness of about half a wavelength inside.

One-dimensional optical frequency of the first configuration of the present invention
The wave transmission line is the most suitable for a micro-sized optical head of an optical device that utilizes the fact that a laser beam can be focused on a small-sized spot, for example, focusing a light beam on a target using a short focal length convex lens. Can be widely applied to the tip.

As shown in FIGS. 26 and 27 applied to an optical head and FIG. 28 applied to an optical STM optical head, for example, the optical frequency wave waveguide according to the present invention is applied as a conventional optical head tip. it can. That is, FIG. 26 can be used for a general free propagation type optical head, FIG. 27 can be used for a waveguide type optical head, and FIG. 28 can be used for an evanescent type optical STM head.

The optical frequency wave of the present invention is applied to such an optical head.
When a dynamic transmission line is applied, for example, the form shown in FIGS. 29 and 30 can be taken. That is, in FIG. 29, basically, the configuration of FIGS. 1 to 10 can be applied as it is, and the configuration can be extremely simple in any case.

In the configuration shown in FIG. 29, as a method for solving the problems that the transmission line portion of the head is extremely thin, has poor mechanical strength, or damages an object such as a disk and is cheap, FIG. A structure in which a protective layer made of a material to which light does not easily enter is loaded on the outside of the transmission line as shown in FIG.

Further, in FIGS. 29 and 30, the tip of the head remains cut off the one-dimensional transmission line in both cases.
For example, a structure in which the cross section of the transmission line is chamfered into a spherical or ellipsoidal shape as shown in FIG. 31, FIG. 32, or FIG. 33 is also effective.

When the optical frequency wave transmission line of the present invention is applied to, for example, an optical disk, the electromagnetic field spot size is about 30 nm, so that the spatial density is about 1000 times larger than the current method having a beam diameter of about 1 μm or more. For example, one music CD can have a capacity of several hundred Gbits.
Continuous performance for more than one month is possible.

FIGS. 34 and 35, FIGS. 36 and 37
In the second embodiment of the present invention, a plate of a negative dielectric medium ( hereinafter referred to as a plate)
The lower negative dielectric plate 1 is a plate of a positive dielectric medium (hereinafter referred to as a positive dielectric plate ).
Collector plate hereinafter) 2 Oyo b2 '(ie positive dielectric medium A
FIGS. 38, 39, 40, 41, 42, 43 and 44 show a negative dielectric plate according to a second embodiment of the present invention. 1 shows an embodiment in which a boundary surface is formed between a reference numeral 1 and a positive dielectric plate.

[0063] That is, the form of FIG. 34 and FIG. 35 FIG. 19, FIGS. 36 and 37 is either a part of the positive dielectric medium and a negative dielectric medium in the form of FIGS. 20 and 21, the traveling direction leaving a long rod-shaped, and removing the peripheral portion, is obtained by loading a positive dielectric medium having a refractive index less than the refractive index of the medium from the original to the removed portion. The positive dielectric medium having a refractive index smaller than the refractive index of the original positive dielectric medium may be vacuum or air.

FIG. 36, FIG. 37, FIG. 38, FIG. 39 and FIG. 40 show that both the positive dielectric plate 2 and the negative dielectric plate 1 in the forms of FIG. 19, FIG. It is a form cut into a long plate in the traveling direction. In this case, not only air or vacuum but also a positive dielectric medium having a lower refractive index than a rod-shaped positive dielectric medium may be arranged around the periphery.

With these structures, an equivalent refractive index distribution is generated in a direction parallel to the horizontal boundary between the negative dielectric medium and the positive dielectric medium and perpendicular to the main transmission direction.
Is equivalently made to have a high refractive index to give a light confinement effect used in a conventional optical waveguide in this direction.

FIG. 41, FIG. 42, FIG. 43 and FIG.
As shown in FIG. 4, FIG. 36, FIG.
38, 39, and 40, the positive dielectric plate 2 'having a smaller refractive index than the original refractive index of the positive dielectric plate 2 is either vacuum or air. Alternatively, it may be air.

In such a two-dimensional optical frequency wave transmission line , when the negative dielectric plate 1 and the positive dielectric plate 2 are in contact with each other,
The fact that a two-dimensional light wave of surface plasmon can be transmitted to this boundary surface is the same operation and effect as in the first embodiment of the present invention.

That is, as shown in FIG. 45, for example, in a typical surface plasmon transmission model, in the x direction perpendicular to the boundary surface, the electromagnetic field only attenuates exponentially and does not transmit. Transmission is completely free in a plane. Therefore, the main transmission component is wound around this boundary surface as an axis (in the drawing, the z-axis as an example), and the transmission component is not provided in any direction in the yz plane. Light circumference
It is a wave number wave transmission line .

On the other hand, in the configuration as shown in FIG. 46 or FIGS. 34 to 44, since an equivalent refractive index distribution is provided in the y direction as in the conventional dielectric waveguide, y
In the direction, there is a y component in the real part of the phase constant in the core portion in the field distribution of the standing waveform, and conventional light confinement is performed in the y direction. As a result, a flat two-dimensional optical frequency wave is confined as a surface wave in the x-direction as a surface wave far thinner than the wavelength, and confined in the y-direction to the same thickness (ie, about the wavelength) as a conventional optical waveguide. It becomes a transmission line .

As described above, the surface plasmon (plasmon surface wave) that can be transmitted to the interface between the negative dielectric plate having a negative real part and the positive dielectric plate having a positive dielectric constant is: A form in which a refractive index distribution is given to the positive dielectric plate in a direction parallel to the boundary surface and perpendicular to the main transmission direction so that a part thereof has an equivalently higher refractive index than the periphery, or the positive dielectric plate 1 (That is, the positive dielectric medium A) and another positive dielectric plate 2 having a lower refractive index than the positive dielectric plate 1 (that is, the positive dielectric medium B) are joined to each other. Two-dimensional light in one of the forms where a negative dielectric plate is present in the part
A frequency wave transmission line can be manufactured.

In other words, this line has a negative dielectric medium in two directions orthogonal to the main transmission direction of the light wave and in one direction.
The light wave is confined as a surface wave by the boundary between the material and the positive dielectric medium, and for the other direction orthogonal to this,
This is an optical frequency wave transmission line that performs light wave confinement by the same refractive index distribution as a conventional optical waveguide.

Since the thickness can be made extremely thin in the direction of confining the surface wave, a multilayer structure can be formed in this direction. Such a multilayer structure is of course included in the present invention. The equivalent refractive index distribution may be a gradient type or a stepwise distribution, or may be a method used in an ordinary optical waveguide.

The two-dimensional optical frequency wave transmission line of the present invention
Compared with a conventional three-dimensional light waveguide, the cross-sectional area of a guided light beam can be reduced, and a high-density optical circuit can be formed.

Incidentally, in the second embodiment of the optical frequency wave transmission line of the present invention, it goes without saying that a part of the negative dielectric plate may be inserted into the positive dielectric plate.

In the second embodiment of the present invention, it is required that surface plasmon be transmitted at the boundary between the negative dielectric plate and the positive dielectric plate. The thickness of the waveguide in the crossing direction can be sufficiently smaller than the wavelength used.

The term “smaller than the optical wavelength” in the first and second embodiments of the optical frequency wave transmission line of the present invention means a size in consideration of a loss when applied to an actual circuit or the like. Assuming that the wavelength is about ３ or less of the used wavelength.

Such an optical frequency wave transmission line of the present invention uses light as input energy and obtains a local electromagnetic field as an output, and can exert an effect on an extremely fine portion. The present invention can be applied to an optical head for writing or reading information having a super-spatial resolution, for a sensor, for generating a very small light modulation, and the like.

Example 1 An optical frequency wave transmission line according to the first embodiment of the present invention can be manufactured by the following steps.

A silver thin wire having an outer diameter of 3.5 mm is inserted into a quartz tube having an outer diameter of 20 mm and an inner diameter of 4 mm, and the quartz tube into which the silver thin wire has been inserted is evacuated and sealed with a vacuum pump.

Using a oxyhydrogen burner, the sealed quartz tube was
A preform can be obtained by applying so-called collapsing in which the hollow portion is crushed by heating to about 2000 ° C.

The preform was passed through a resistance heating furnace for about 2 hours.
Pull while passing through a die while heating to 000 ° C., outer diameter of quartz 30 nm, outer diameter of silver (ie inner diameter of quartz) 2
The optical frequency wave transmission line of the present invention as shown in FIG. 1 of 0 nm can be obtained.

(Example 2) If the optical frequency wave transmission line obtained in Example 1 is cut to a length of 100 µm, the loss due to the transmission is estimated to be about 1/10, and the oscillation wavelength is 0.8 µm from one end. Assuming that a 1 mW GaAs semiconductor laser element is used as a light source, a normal optical fiber is used through a rod lens, and 100 μW is input to the optical frequency wave transmission line of the present invention, about tens of μW is considered in consideration of coupling loss. An optical output is obtained from the other end, and it can be confirmed that an optical circuit within about 100 μm can operate satisfactorily.

Further, the optical frequency wave transmission line of the present invention is, for example, an optical head for writing or reading various recording media, an optical head for processing, an optical head for sensor, an optical probe for STM, an optical head for manipulator, etc. The possibility of application to various optical heads was confirmed.

Further, in the embodiment shown in FIG. 4, for example, the positive dielectric medium 2 is made of, for example, low melting point glass and filled in a silver tube to produce the optical frequency wave transmission line of the present invention in the same manner as in the first embodiment. Further, for example, the form in FIG. 34 can be created by, for example, forming a material that is transparent to light to be used and has a different refractive index on a negative dielectric plate by, for example, a sputtering method,
Further, for example, the configuration shown in FIG. 41 can be created by a technique such as forming a positive dielectric plate on a negative dielectric plate such as a metal by sputtering or the like.

[0085]

According to the present invention, (1) surrounds has a single column-shaped, and the dielectric constant negative dielectric medium permittivity real part is negative is at positive positive dielectric medium, the negative the length of the section crossing the longitudinal direction of the dielectric medium, characterized in that it has a shape smaller than the optical wavelength
An optical frequency wave transmission line. It also has a single pillar shape.
And the real part of the dielectric constant surrounds the negative dielectric medium having a negative dielectric constant with a positive dielectric medium having a positive dielectric constant, and has a diagonal line, a long axis or a diameter of at least one cross section intersecting the longitudinal direction of the negative dielectric medium. Has a shape with a distance smaller than the light wavelength.
It is an optical frequency wave transmission line characterized by the following. Ma
Further, the real part of the permittivity has a single cylindrical shape, and the dielectric constant surrounds the positive dielectric medium with a negative dielectric medium with a negative dielectric medium, and the negative dielectric medium has a longitudinal direction of the cylindrical shape. At least one cross section of the diagonal, the major axis or the diameter of
An optical frequency wave transmission line, characterized in that have a cylindrical shape having an inner diameter smaller than the light wavelength.

(2) Surrounding a single negative dielectric medium whose real part is negative with a positive dielectric medium having a positive dielectric constant,
Alternatively, a positive dielectric medium having a positive dielectric constant is surrounded by a single negative dielectric medium in which the real part of the dielectric constant is negative , and a surface plasmon is formed on an interface between the negative dielectric medium and the positive dielectric medium. A transmission line for transmission, in which a part of a cross section intersecting the main propagation direction of the positive dielectric medium is given a refractive index distribution having a refractive index equivalent to that of a peripheral portion, and intersects the main propagation direction. the thickness of the negative dielectric medium, especially smaller than the light wavelength
This is an optical frequency wave transmission line. Further , a single negative dielectric medium having a negative real part of the dielectric constant, a positive dielectric medium A having a positive dielectric constant, and a positive dielectric medium B having a lower refractive index than the positive dielectric medium A Wherein the negative dielectric medium is surrounded by the positive dielectric medium A or the positive dielectric medium A is surrounded by the negative dielectric medium, and a boundary between the negative dielectric medium and the positive dielectric medium A is included. A transmission line for transmitting surface plasmons to a surface, wherein the negative dielectric medium is present in a part of a cross section of the positive dielectric medium A crossing the main propagation direction, and the negative dielectric medium crosses the main propagation direction. The thickness of the negative dielectric medium is smaller than the light wavelength, and the surface of the negative dielectric medium that is not in contact with the positive dielectric medium A is contacted with the positive dielectric medium B.
An optical frequency wave transmission line characterized by being surrounded by
You.

When the light of the present invention uses a transmission line, the light energy can be packed in a thin transmission line without being limited by the wavelength and transmitted, and the leakage of the photoelectromagnetic field at the tip is extremely small compared to the wavelength. It can be localized and concentrated, and sufficient energy can be applied.

By utilizing this localized electromagnetic field, it is possible to sense the electromagnetic wave response in a minute area, and it is possible to apply the present invention to an optical device such as an ultra-high-precision sensor head and a high-density optical integrated circuit.

Further, also in the form of the plate-shaped transmission line of the present invention, the sectional area of the guided light beam can be reduced,
There is an effect that a high-density optical circuit can be configured.

[Brief description of the drawings]

FIG. 1 is a conceptual perspective view of a connection example in an embodiment of a first embodiment of an optical frequency wave transmission line of the present invention.

FIG. 2 is an enlarged conceptual perspective view of an essential part of an embodiment of the first embodiment of the optical frequency wave transmission line of the present invention.

FIG. 3 is an enlarged conceptual perspective view of an essential part of one embodiment of the first embodiment of the optical frequency wave transmission line of the present invention.

FIG. 4 is a conceptual perspective view of a connection example in another embodiment of the first embodiment of the optical frequency wave transmission line of the present invention.

FIG. 5 is an enlarged conceptual perspective view of an essential part of one embodiment of the first embodiment of the optical frequency wave transmission line of the present invention.

FIG. 6 is an enlarged conceptual perspective view of a main part of an embodiment of the first embodiment of the optical frequency wave transmission line of the present invention.

FIG. 7 is an enlarged conceptual perspective view of an essential part of an embodiment of the first embodiment of the optical frequency wave transmission line of the present invention.

FIG. 8 is an enlarged conceptual perspective view of an essential part of one embodiment of the first embodiment of the optical frequency wave transmission line of the present invention.

FIG. 9 is an enlarged conceptual perspective view of an essential part of one embodiment of the first embodiment of the optical frequency wave transmission line of the present invention.

FIG. 10 is an enlarged conceptual perspective view of a main part of an embodiment of the first embodiment of the optical frequency wave transmission line of the present invention.

FIG. 11 is an enlarged conceptual perspective view of a main part of one embodiment of the first embodiment of the optical frequency wave transmission line of the present invention.

FIG. 12 is an enlarged conceptual perspective view of a main part of an embodiment of the first embodiment of the optical frequency wave transmission line of the present invention.

FIG. 13 is an enlarged conceptual perspective view of an essential part of one embodiment of the first embodiment of the optical frequency wave transmission line of the present invention.

14A is a longitudinal cross-sectional view illustrating a configuration of a conventional optical waveguide, FIG. 14B is a side cross-sectional view illustrating a configuration of a conventional optical waveguide, and FIG. Conceptual graph showing examples

15A is a longitudinal sectional view illustrating a configuration of a conventional optical waveguide, FIG. 15B is a side sectional view illustrating a configuration of the conventional optical waveguide, and FIG. 15C is a side sectional view illustrating a field distribution of the conventional optical waveguide. Conceptual graph showing examples

16A is a longitudinal cross-sectional view illustrating a configuration of a conventional microwave millimeter-wave waveguide, FIG. 16B is a side cross-sectional view illustrating a configuration of a conventional microwave millimeter-wave waveguide, and FIG. Conceptual graph showing an example of the field distribution of a microwave and millimeter wave waveguide

17A is a cross-sectional view illustrating a configuration of a conventional microwave / millimeter-wave transmission coubo line, FIG. 17B is a side cross-sectional view illustrating a configuration of a conventional microwave / millimeter-wave transmission coubo line, and FIG. Graph showing an example of the field distribution of a microwave and millimeter-wave transmission coubo transmission line

FIG. 18A is a side sectional view for explaining the behavior of light at the interface between a positive dielectric medium and a negative dielectric medium, and FIG. 18B is a conceptual graph showing the behavior of an electric field on the reflection surface;

FIG. 19A is a cross-sectional side view for explaining the penetration of surface plasmons in the thickness direction, and FIG. 19B is a conceptual graph of the electric field normal component of the surface wave.

[Figure 20 (a) is negative dielectric medium and a positive dielectric medium of the present invention
Side cross-sectional view second boundary plane illustrating the structure when it is in parallel with the quality (b) a two-dimensional light waves (two surfaces plasma in the same configuration
Concept graph showing how bound ones) Mont

FIG. 21 (a) is a graph showing two types of a negative dielectric medium and a positive dielectric medium.
A cross-sectional side view (b) for explaining another configuration when the boundary planes are parallel is a two-dimensional light wave (two surface plasmas ) in the same configuration.
Concept graph showing how bound ones) Mont

FIG. 22 (a) is a one-dimensional optical frequency wave transmission line of the present invention.
A sectional view (b) for explaining the behavior of one embodiment of the road is a side sectional view for explaining the behavior of one embodiment of the one-dimensional optical frequency wave transmission line , and (c) is an electric field component of the one-dimensional light wave of the same embodiment. Concept chart of

FIG. 23 (a) is a one-dimensional optical frequency wave transmission line of the present invention.
A sectional view (b) for explaining the behavior of one embodiment of the road is a side sectional view for explaining the behavior of one embodiment of the one-dimensional optical frequency wave transmission line , and (c) is an electric field component of the one-dimensional light wave of the same embodiment. Concept chart of

FIG. 24 (a) is a one-dimensional optical frequency wave transmission line of the present invention.
A sectional view (b) for explaining the behavior of one embodiment of the road is a side sectional view for explaining the behavior of one embodiment of the one-dimensional optical frequency wave transmission line , and (c) is an electric field component of the one-dimensional light wave of the same embodiment. Concept chart of

FIG. 25 (a) is a one-dimensional optical frequency wave transmission line of the present invention.
A sectional view (b) for explaining the behavior of one embodiment of the road is a side sectional view for explaining the behavior of one embodiment of the one-dimensional optical frequency wave transmission line , and (c) is an electric field component of the one-dimensional light wave of the same embodiment. Concept chart of

FIG. 26 is a configuration diagram of a conventional optical head.

FIG. 27 is another configuration diagram of a conventional optical head.

FIG. 28 is a configuration diagram of one embodiment of a conventional optical STM head.

FIG. 29 is a configuration diagram illustrating an application example in which the optical frequency wave transmission line of the present invention is applied to an optical head.

FIG. 30 is a configuration diagram illustrating another application example in which the optical frequency wave transmission line of the present invention is applied to an optical head.

FIG. 31 is an enlarged conceptual sectional view showing a configuration of an application example of the optical frequency wave transmission line of the present invention.

FIG. 32 is an essential part enlarged conceptual sectional view showing the configuration of another application example of the optical frequency wave transmission line of the present invention.

FIG. 33 is an enlarged conceptual sectional view showing the configuration of another application example of the optical frequency wave transmission line of the present invention.

FIG. 34 is a conceptual perspective view of an example of the second embodiment of the optical frequency wave transmission line of the present invention.

FIG. 35 is a conceptual perspective view of one embodiment of the second embodiment of the optical frequency wave transmission line of the present invention.

FIG. 36 is a conceptual perspective view of an example of the second embodiment of the optical frequency wave transmission line of the present invention.

FIG. 37 is a conceptual perspective view of an example of the second embodiment of the optical frequency wave transmission line of the present invention.

FIG. 38 is a conceptual perspective view of one embodiment of the second embodiment of the optical frequency wave transmission line of the present invention.

FIG. 39 is a conceptual perspective view of an example of an optical frequency wave transmission line according to a second embodiment of the present invention.

FIG. 40 is a conceptual perspective view of an example of a second embodiment of the optical frequency wave transmission line of the present invention.

FIG. 41 is a conceptual perspective view of an embodiment of the second embodiment of the optical frequency wave transmission line of the present invention.

FIG. 42 is a conceptual perspective view of an example of a second embodiment of the optical frequency wave transmission line of the present invention.

FIG. 43 is a conceptual perspective view of one embodiment of the second embodiment of the optical frequency wave transmission line of the present invention.

FIG. 44 is a conceptual perspective view of an example of the second embodiment of the optical frequency wave transmission line of the present invention.

FIG. 45 is a diagram illustrating transmission of surface plasmons .

FIG. 46 is a view for explaining light wave transmission in the two-dimensional light wave transmission line of the present invention.

[Explanation of symbols]

1 Negative dielectric medium 2 Positive dielectric medium 3 Optical waveguide 4 Coupling matching part 5 Cladding for protection

Claims (9)

(57) [Claims] 1. A has a single column-shaped, and the real part of the dielectric constant negative negative dielectric medium surrounding the dielectric constant is at positive positive dielectric medium, in the longitudinal direction of the negative dielectric medium the length of the cross section intersecting the optical frequency wave transmission line and having a shape smaller than the optical wavelength. 2. A negative dielectric medium having a single column shape and a real part of a dielectric constant having a negative dielectric constant is surrounded by a positive dielectric medium having a positive dielectric constant , and extending in a longitudinal direction of the negative dielectric medium. An optical frequency wave transmission line, characterized in that at least one of the cross sections, at least one of a diagonal line, a long axis and a diameter, has a shape having a distance smaller than an optical wavelength. 3. A negative dielectric medium having a single cylindrical shape and a real part of a dielectric constant having a negative dielectric constant surrounding a positive dielectric medium having a positive dielectric constant, wherein the negative dielectric medium has a cylindrical shape. longitudinally diagonal of at least one cross section intersecting, one of the major axis or diameter is, to have a cylindrical shape having an inner diameter smaller than the wavelength of light
Optical frequency wave transmission line, characterized in that that. 4. The method according to claim 1, wherein one of the negative dielectric medium and the cylindrical negative dielectric medium is projected from an end of the positive dielectric medium. An optical frequency wave transmission line as described. 5. An optical circuit according to claim 1, wherein :
An optical frequency wave transmission line comprising a plurality of wave number wave transmission lines arranged in parallel. 6. A single negative dielectric medium having a real part of negative permittivity surrounded by a positive dielectric medium having a positive permittivity, or a positive dielectric medium having a positive permittivity is a real number of permittivity. part is negative der
Ri surrounds at single negative dielectric medium, wherein a negative dielectric medium and the transmission line for transmitting a surface plasmon at the interface between the positive dielectric medium, intersecting the main direction of propagation of said positive dielectric medium A part of the cross-section to be formed is provided with a refractive index distribution having a refractive index equivalent to that of the peripheral part, and the thickness of the negative dielectric medium crossing the main propagation direction is smaller than the light wavelength. Optical frequency wave transmission line. 7. A single negative dielectric medium having a negative real part of a dielectric constant, a positive dielectric medium A having a positive dielectric constant, and a positive dielectric medium having a lower refractive index than the positive dielectric medium A. And the negative dielectric medium is surrounded by the positive dielectric medium A or the positive dielectric medium A is surrounded by the negative dielectric medium, and the negative dielectric medium and the positive dielectric medium A are surrounded by the negative dielectric medium A. A transmission line that transmits surface plasmons to the boundary surface with
The negative dielectric medium is present in a part of the cross section of the positive dielectric medium A crossing the main propagation direction, and the thickness of the negative dielectric medium crossing the main propagation direction has a shape smaller than the light wavelength. ,
An optical frequency wave transmission line, wherein a surface of the negative dielectric medium that does not contact the positive dielectric medium A is surrounded by the positive dielectric medium B. 8. The waveguide according to claim 6 , wherein the thickness of the waveguide in the main propagation direction and in the direction intersecting the boundary surface between the positive dielectric medium and the negative dielectric medium is smaller than the optical wavelength. The optical frequency wave transmission line according to any one of the above. 9. The method according to claim 8, wherein the optical waveguide is connected to an optical frequency wave transmission line.
Through a coupling matching section that measures transmission impedance
Optical frequency wave transmission line optically coupled to the optical waveguide
An optical frequency wave according to any one of claims 1 to 8,
An optical frequency wave transmission line characterized by using a transmission line.