KR100850779B1 - Optical waveguide for transmitting surface plasmon polariton - Google Patents

Abstract

The present invention relates to an optical waveguide for surface electromagnetic wave transmission for minimizing propagation loss of light.

The optical waveguide for surface electromagnetic wave transmission of the present invention includes a metal thin film having a triangular cross-sectional shape; A pair of dielectric layers having different refractive indices and positive (+) or negative (-) dielectric constants on and below the metal thin film, the opposing surfaces being bonded to each other; It includes, to minimize the propagation loss of the light propagating through the optical waveguide can improve the transmission distance of the light in the entire wavelength band, the light distribution is formed to be close to the circular coupling with the optical fiber coupled to one end This has the advantage of reducing losses at the same time.

Optical waveguide, first dielectric layer, second dielectric layer, metal thin film

Description

Optical waveguide for transmitting surface plasmon polariton

1 is a perspective view of an optical waveguide for transmitting a conventional surface electromagnetic wave.

2 is a perspective view of an optical waveguide according to the present invention.

Figure 3 is a graph showing the refractive index of the dielectric applied to the optical waveguide according to the present invention.

4 is a cross-sectional view of an optical waveguide according to the present invention.

5 to 7 are graphs showing the propagation loss according to the change in the cabinet angle of the metal thin film for each wavelength band,

5 is a case of a wavelength of 633 nm,

6 is a case of a wavelength of 980 nm,

7 is the case of 1550 nm wavelength.

8 is a photograph of the size distribution of the light traveling through the optical waveguide according to the present invention.

<Explanation of symbols for the main parts of the drawings>

100. Optical waveguide 110. First dielectric layer

120. Second dielectric layer 130. Metal thin film

The present invention relates to an optical waveguide for transmitting surface electromagnetic waves, and more particularly, a thin metal structure in which surface electromagnetic waves are transmitted to form a triangular cross section, so that dielectric layers having different refractive indices on the upper and lower sides thereof face each other. By combining, it relates to an optical waveguide for surface electromagnetic wave transmission to improve the propagation distance of light through the metal structure.

Surface plasmon (SP) is an oscillation wave of charge density, whose dielectric constant propagates along an interface having opposite signs, and is generally present at the boundary between a metal having a negative (−) and a dielectric having a positive (+). Vibration can be excited by electrons and light waves accelerated at high speed. Such electromagnetic waves traveling in conjunction with the surface plasmon SP are called surface plasmon polaritons (hereinafter, referred to as "SPP").

Since the wave vector of the surface plasmon (SP) is larger than the wave vector of the surrounding material, SPP is a wave bound to the metal surface. Therefore, the interface between the metal and the dielectric can be thought of as a two-dimensional flat waveguide having a binding condition perpendicular to the interface.

From the viewpoint of the optical waveguide, SPP generated at the interface between the metal and the dielectric has a very high efficiency of being bound to the surface, but has a short propagation distance of several tens of micrometers in the visible region. However, by limiting the thickness of the metal in the range of several nm to several tens of nm, and combining the SPPs traveling at the upper and lower boundaries of the metal, the long distance transmission of light is possible. This is called the Long Range Surface Plasmon Polariton (LR-SPP) mode. The field profile of the LR-SPP is widely distributed in the dielectric around the metal thin film so that the light propagates. The loss is small and the coupling property with the optical fiber has a good advantage, it is applied to various optical device fields.

In general, a surface-plasma polariton (SPP) optical waveguide interposed with a metal thin film has a thickness of several tens of nm or less and propagates light over a long distance. LR-SPP (Long Range Surface Plasmon Polariton) and a mode for propagating light through a relatively small waveguide (SR-SPP: Short Range Surface Plasmon Polariton).

In particular, by using a metal thin film having a finite cross-sectional area, the binding conditions of the SPP can be reduced in three dimensions, and an LR-SPP optical waveguide having a function similar to that of a dielectric optical waveguide can be formed.

Therefore, since the electric field distribution of the LR-SPP is widely distributed in the dielectric around the metal thin film and is very sensitive to the optical change of the peripheral dielectric, long distance transmission is possible, and the long-distance surface-plasma polaritone (LR-SPP) is currently It is applied to various optical waveguide devices such as optical modulators, switches, couplers, filters, and optical sensors.

As described above, a technical configuration of an optical waveguide for surface electromagnetic wave transmission applied to various fields is described in Japanese Patent Laid-Open No. 2005-114768. The description is as follows.

1 is a perspective view of a conventional optical waveguide for surface electromagnetic wave transmission, and as shown, the conventional optical waveguide 10 is a negative dielectric on the surface of the substrate 11, which is a dielectric having a positive dielectric constant. By forming an optical waveguide pattern in which the strip structure portion 12 of the metal having a constant is formed, as the diameter of the light through the strip structure portion 12 becomes smaller, the transmission distance of several μm to several tens of μm is obtained.

The optical waveguide 10 first forms a V-shaped groove 11a on the surface of the substrate 11 by ion milling or dry etching, and then fills the V-shaped groove 11a with a metal material by sputtering. By forming a wide strip 12 by film formation on the top surface of the substrate 11 including the top surface of the metal material filled in the V-shaped groove 11a, the metal layer 12a and the strip 12b having a triangular cross section are formed. An integral strip structure 12 is formed.

In this case, the triangular cross-sectional metal layer 12a may be formed to be exposed to the upper portion of the strip 12b.

In the conventional optical waveguide structure, since the electric field is concentrated in the triangular cross-sectional metal layer 12a, the diameter of the light beam propagating along the strip 12b can be narrowed, so that the diameter of the beam is within 200 nm. It can be constrained, and can exhibit a transmission distance of about 10 μm similar to the surface electromagnetic wave transmission distance in a metal thin film having infinite width.

However, the conventional optical waveguide structure for surface electromagnetic wave transmission has various shapes because its transmission distance is only a few tens of micrometers even though the diameter of the beam is limited to 200 nm or less due to the electric field concentrated on the metal layer 12a of the triangular cross section. Since it is substantially applied to optical modulators, switches, couplers, filters, and optical sensors, it has been difficult to be used as a sensing element using an optical waveguide.

Therefore, the present invention was devised to solve the above-mentioned disadvantages and problems in the conventional optical waveguide for surface electromagnetic wave transmission, and a pair of metal thin films having triangular cross-sectional shapes having different refractive indices and dielectric constants facing each other are opposed to each other. By interposing between the dielectric layers, it is an object of the present invention to minimize the propagation loss of the light propagating through the optical waveguide to improve the transmission distance of the light beam for each wavelength band.

The object of the present invention is a metal thin film having a triangular cross-sectional shape, and having different refractive indices and positive (+) or negative (-) dielectric constants on and under the metal thin film, and opposite surfaces thereof. It is achieved by providing an optical waveguide for surface electromagnetic wave transmission comprising a pair of dielectric layers joined to be welcoming.

The metal thin film is characterized in that the light incident from one end is transmitted along the surface of the metal thin film in the SPP (Surface Plasmon Polariton) method.

The metal thin film has a triangular cross section, preferably an isosceles triangular cross section, and is made of a material having a relatively high charge density and is coupled to an optical fiber at one end thereof so that light is incident on the metal thin film in the longitudinal direction of the metal thin film. Light transmission takes place.

The metal thin film is mainly composed of gold (Au) or silver (Ag), and an alloy of gold and silver or gold and silver are sequentially surface-plated.

The dielectric layers have different refractive indices, and the positive and negative dielectric constants ε and refractive indices may be changed by changing thicknesses.

In addition, the dielectric layer may have the same refractive index.

Meanwhile, the metal thin film defines width and height for each wavelength band (633 nm, 980 nm, and 1550 nm), and transmits along the longitudinal direction of the metal thin film while varying the size of the opposite inner angle of the triangular cross section, that is, the angle between the isosceles. The propagation loss and the transmission distance are measured.

At this time, the larger the included angle of the metal thin film having a predetermined width and height for each wavelength band is formed as a metal thin film having a trapezoidal cross-sectional shape, and in the case of 90 ° has a rectangular cross-sectional shape having a predetermined width. When measuring the transmission distance in consideration of propagation loss during the longitudinal light transmission of the metal thin film, an optimum transmission distance is obtained when an isosceles triangular cross-sectional metal thin film is formed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION The detailed description of the above object of the optical waveguide for surface electromagnetic wave transmission and the effect thereof will be clearly understood by the following detailed description with reference to the drawings in which preferred embodiments of the present invention are shown.

First, Figure 2 is a perspective view of the optical waveguide according to the present invention, Figure 3 is a graph showing the refractive index of the dielectric applied to the optical waveguide according to the present invention, Figure 4 is a cross-sectional view of the optical waveguide according to the present invention.

As shown, the optical waveguide 100 for transmitting surface electromagnetic waves of the present invention includes a first dielectric layer 110 having a positive dielectric constant and a second dielectric layer 120 having a negative dielectric constant. And a metal thin film 130 interposed therebetween.

The first dielectric layer 110 and the second dielectric layer 120 face each other so that their opposite surfaces are in contact with each other, and the first dielectric layer 110 and the second dielectric layer 120 have a negative dielectric constant. The upper and lower surfaces of the metal thin film 130 are formed.

The first dielectric layer 110 and the second dielectric layer 120 is made of a material having a different dielectric constant and refractive index, it is preferably formed of a material having a relatively low charge density. That is, the inorganic material may be composed of silicone, glass, and polymer-based resins.

In addition, the first dielectric layer 110 and the second dielectric layer 120 may be formed of a material having the same refractive index, for example, a ceramic sheet, and the like, and the metal thin film 130 may be formed on the first dielectric layer 110. After lamination, the second dielectric layer 120 having the same or different refractive index as the first dielectric layer 110 is integrated by baking.

In this case, it can be seen that the difference in refractive index between the first dielectric layer 110 and the second dielectric layer 120 should be maintained at 0.00043 or less. That is, the first dielectric layer is changed when the refractive index is changed while changing the thickness of the second dielectric layer 120 coupled to the top surface of the first dielectric layer 120 while the thickness of the first dielectric layer 110 serving as the substrate is fixed. The difference in critical refractive index between 110 and the second dielectric layer 120 is generated, which is 0.00043.

When the difference in the critical refractive index is 0.00043 or more, the light beam transmitted from the metal thin film () through the two dielectric layers 110 and 120 leaks out, so that guiding of the light transmitted along the metal thin film 130 is impossible. Therefore, it is impossible to manufacture the optical waveguide 100 having a predetermined transmission distance.

In more detail, a typical optical waveguide includes a metal thin film 130 as a core and a cladding surrounding the metal thin film 130, that is, the first dielectric layer 110 and the second dielectric layer ( The effective index extracted by coupling 120 is required to be greater than the effective refractive index formed on the dielectric layers 110 and 120 outside the metal thin film 130.

The optical waveguide 100 has a property that light transmitted along the metal thin film 130 is distributed in a dielectric layer having a high refractive index in LR-SPP mode, thereby reducing the amount of light present in the metal thin film 130. The propagation loss of light through the metal thin film 130 in the LR-SPP mode is reduced.

That is, the metal encapsulated by the first and second dielectric layers 110 and 120 due to the property that radiation light propagating along the metal thin film 130 is distributed in the dielectric layers 110 and 120 having a higher effective refractive index. Since the amount of light present in the thin film 130 is reduced, the propagation loss due to the dispersion of the light transmitted through the metal thin film 130 is reduced.

On the contrary, when the metal thin film 130 disposed inside the first and second dielectric layers 110 and 120 has a high refractive index, the radiated light on the metal thin film 130 is not radiated to the outside and the metal thin film ( As it is concentrated in 130, the propagation loss is increased by concentrating light around the metal thin film 130.

In this case, since the light propagated through the metal thin film 130 is integrated in a very small size, it is applicable to other fields using the same.

Meanwhile, according to the present invention, as shown in FIG. 3, the effective refractive indices of the first and second dielectric layers 110 and 120 surrounding the metal thin film 130 are set to 1.500 and based on the effective refractive index, The change in the effective refractive indices of the dielectric layers 110 and 120 obtained in the optical waveguide 100 is shown by the difference in the refractive indices caused by the change in the refractive indices of the first and second dielectric layers 110 and 120.

3, as the difference in refractive index between the first and second dielectric layers 110 and 120 deepens, that is, the refractive index of any one of the first and second dielectric layers 110 and 120 is different from one another. It can be seen that the effective refractive index of the metal thin film 130 is lowered at the same time significantly lower than.

At this time, the effective refractive index of the metal thin film 130 obtained through the optical waveguide () is lower than the predetermined refractive index 1.500 of the first and second dielectric layers 110 and 120, which are claddings surrounding the metal thin film 130. The difference in refractive index between the first dielectric layer 110 and the second dielectric layer 120 at the point is 0.00043.

Therefore, in order to reduce the propagation loss by the light emitted through the metal thin film 130 is directed toward a material having a higher refractive index as described above, the refractive index difference of each dielectric layer 110, 120 should be maintained at 0.00043 or less. The condition must be satisfied.

Meanwhile, the metal thin film 130 has a triangular cross-sectional shape having a finite length, a limited line width (W) and a height (t), and is formed of a metal material having a relatively high charge density.

The metal thin film 130 is formed of gold (Au) and silver (Ag) or an alloy of gold and silver so that light transmission means (not shown) for light incidence is connected to one end side. The light transmission means may be, for example, an optical fiber.

The metal thin film 130 has an internal angle (θ) facing each other under a condition having a refractive index difference of 0.00043 or less between the first dielectric layer 110 and the second dielectric layer 120. The optical waveguide 100 may be changed within a certain wavelength range and a predetermined line width () and height () are set for each typical wavelength band (633 nm, 980 nm, and 1550 nm) of the light transmitted through the metal thin film 130. Propagation loss and transmission distance of light through

5 to 7 are graphs showing the propagation loss according to the change in the internal angle of the metal thin film for each wavelength band, FIG. 5 is a wavelength of 633 nm, FIG. 6 is a wavelength of 980 nm, and FIG. Is the case of 1550 nm wavelength.

First, the optical waveguide 100 to which light having a wavelength of 633 nm is transmitted has a predetermined line width W and a height t between the first dielectric layer 110 and the second dielectric layer 120, and faces each other. A metal thin film 130 whose height is changed according to the angle size of θ is interposed, and the surface electromagnetic wave having a wavelength of 633 nm is transmitted through an optical fiber connected to one end of the metal thin film 130. .

In this case, the inner angle θ of the triangular cross-section of the metal thin film 130 is converted into an angle within 0 ° to 90 ° in a state where the line width W is limited to about 1 μm, thereby near 0 °. It is formed into an isosceles triangular cross-section of extremely thin shape, and has a cross-sectional shape close to a rectangle in the vicinity of 90 and changes.

In the case of the wavelength of 633 nm, as shown in FIG. 5, the maximum propagation loss of the transmitted light is generated at the point where the inner angle θ of the metal thin film 130 is approximately 20 °, and the It can be seen that the smaller the size, the smaller the propagation loss of light. Therefore, it can be seen that the structure of the metal thin film 130 having the smallest propagation loss in the transmission of light has a cross-sectional shape of an isosceles triangle having the smallest angle while the inner angle θ is greater than 0 °.

In addition, the optical waveguide 100 through which light having a wavelength of 980 nm is transmitted may be formed according to the angle of the inner angle θ facing the predetermined line width W between the first dielectric layer 110 and the second dielectric layer 120. A metal thin film 130 having a height t is interposed therebetween, and the surface electromagnetic wave having a wavelength of 980 nm is transmitted through an optical fiber connected to one end of the metal thin film 130.

At this time, when the opposite angle θ of the triangular cross-section metal thin film 130 is converted from an angle of 0 ° or more to an angle of 90 ° or more, maximum propagation loss occurs from a point of about 5 ° or more as shown in FIG. 6. To start.

Therefore, in the case of 980 nm, similar to the wavelength of 633 nm, the shape of the metal thin film 130 which can extend the transmission distance with the minimum propagation loss is the smallest angle with the opposite angle θ of 0 ° or more. It is preferable that it is formed of an isosceles triangle structure having.

Next, as described above, the metal thin film 130 having the height t is changed according to the angle of the inner angle θ facing the predetermined line width W between the first dielectric layer 110 and the second dielectric layer 120. The surface electromagnetic wave having a wavelength of 1550 nm was transmitted through an optical fiber connected to one end of the metal thin film 130.

In this case, the propagation loss measured as the opposite angle θ of the triangular cross-section metal thin film 130 is converted to an angle within 0 ° to 90 ° is generated at an arbitrary point of about 10 ° or more.

Therefore, in the case of 1550 nm, similar to the wavelength of 633 nm and the wavelength of 980 nm, the propagation loss when the opposite angle θ of the metal thin film 130 is formed into an isosceles triangle structure having the smallest angle of 0 ° or more. The maximum optical transmission distance is measured by reducing the maximum.

As described above, the shape of the metal thin film 130 of the optical waveguide 100 in which light of three wavelength bands is transmitted is inferred in actual unit of length, and all three wavelength bands have an extremely small height (t, Nm), it is substantially formed as an isosceles triangular structure close to a plane having an extremely small internal angle θ with respect to the line width W.

As described above, the propagation loss and the transmission distance of light measured using the metal thin film 130 having a limited size in an embodiment in the wavelength band applied to the optical waveguide according to the present invention are shown in Table 1 below.

Wavelength (nm) Size (W × t) Propagation Loss (dB / mm) Transmission distance (mm) 633 1 μm × 15 nm 4.24 1.89 980 4 μm × 16 nm 0.45 17.78 1550 4 μm × 24.4 nm 0.06 133.3

As can be seen from Table 1, the maximum transmission distance is 1.89 mm for the wavelength of 633 nm, the maximum transmission distance of light for the wavelength of 980 nm is 17.78 mm, and the transmission distance of light for the 1550 nm wavelength is measured as 133.3 mm.

Such a transmission distance of the light is a sufficient distance to produce an optical waveguide having a size applicable to an optical modulator, a switch, etc., such as a sensor, and it can be seen that the transmission distance of the optical waveguide is improved by several hundred times or more.

Finally, FIG. 8 shows the shape of an isosceles triangle close to the plane defined above when the light having a specific wavelength band (633 nm, 980 nm, 1550 nm) is transmitted through the metal thin film 130. It is a photograph of the size distribution of light propagating along the metal thin film 130 so that the light is transmitted.

Since the distribution of light as shown in FIG. 8 obtained through the optical waveguide according to the present invention can be made close to a circular shape, it is formed very similar to the shape of the light distribution of the optical fiber connected to one end of the optical waveguide, thereby easily coupling the optical fibers. And thus the coupling loss can be minimized.

Preferred embodiments of the present invention described above are disclosed for the purpose of illustration, and various substitutions, modifications, and changes within the scope without departing from the spirit of the present invention for those skilled in the art to which the present invention pertains. It will be possible, but such substitutions, changes and the like should be regarded as belonging to the following claims.

As described above, the optical waveguide for surface electromagnetic wave transmission of the present invention is interposed between a pair of dielectric layers in which triangular cross-sectional metal thin films are in opposing contact with different refractive indices and dielectric constants, thereby proceeding through the optical waveguide. By minimizing the propagation loss of the light can improve the transmission distance of the light in the entire wavelength band, there is an advantage that can be reduced at the same time the coupling loss with the optical fiber coupled to the end is formed so that the light distribution is close to the circular.

Claims (13)

A metal thin film having a triangular cross-sectional shape; A pair of dielectric layers having different refractive indices and positive (+) or negative (-) dielectric constants on and below the metal thin film, the opposing surfaces being bonded to each other; Optical waveguide for surface electromagnetic wave transmission comprising a The method of claim 1, The metal thin film is an optical waveguide for surface electromagnetic wave transmission, characterized in that the light incident from one end portion is transmitted along the surface of the metal thin film in the SPP (Surface Plasmon Polariton) method. The method of claim 1, The metal thin film is an optical waveguide for surface electromagnetic wave transmission, characterized in that coupled to the light transmission means for injecting light to one end. The method of claim 1, The metal thin film is composed of gold (Au) or silver (Ag), and an optical waveguide for surface electromagnetic wave transmission, characterized in that an alloy of gold or silver and a sequential surface plating layer of gold and silver are formed. The method of claim 1, The metal thin film is an optical waveguide for surface electromagnetic wave transmission, characterized in that formed in an isosceles triangular cross section. delete The method of claim 1, In the dielectric layer, the first and second dielectric layers bonded to the upper and lower portions of the metal thin film have different refractive indices, and the refractive indices and the positive and negative dielectric constants ε are varied according to the change in thickness. ) Is an optical waveguide for transmitting surface electromagnetic waves. The method of claim 1, And said dielectric layer has the same refractive index. The method of claim 1, The dielectric layer is an optical waveguide for surface electromagnetic wave transmission, characterized in that any one of an inorganic material, silicon, glass, polymer-based resin. The method of claim 7, wherein The refractive index difference between the first dielectric layer and the second dielectric layer is maintained at 0.00043 or less optical waveguide for surface electromagnetic wave transmission. The method of claim 1, The optical waveguide for surface electromagnetic wave transmission is integrated by laminating a metal thin film on the first dielectric layer and then firing a second dielectric layer having the same refractive index as the first dielectric layer. The method of claim 1, The metal thin film is an optical waveguide for surface electromagnetic wave transmission, characterized in that the distribution of light emitted to the outside is formed in a form close to a circular shape. delete

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