JP2007074043A - Electromagnetic wave waveguide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electromagnetic wave waveguide of simple arrangement comparatively insusceptible to external impact. <P>SOLUTION: The electromagnetic wave waveguide transmits an electromagnetic wave having an arbitrary frequency region between 30GHz and 30THz. The electromagnetic wave waveguide comprises a single line 101 formed of a conductor, and a dielectric member 102 covering the single line 101. An electromagnetic wave coupling portion 103 performing at least one of input and output of an electromagnetic wave may be provided at a part of an electromagnetic wave waveguide of such an arrangement. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a high-frequency electromagnetic wave transmission technique having a frequency region in a millimeter wave to terahertz wave region (30 GHz to 30 THz).

In recent years, non-destructive inspection techniques have been developed using high-frequency electromagnetic waves (hereinafter also referred to as terahertz waves) having an arbitrary band in the millimeter wave to terahertz wave region (30 GHz to 30 THz). It is known that terahertz waves have absorption lines of various substances including biomolecules. Therefore, as an application field in this frequency domain, there is a technique for performing imaging by applying to a safe fluoroscopic inspection apparatus that replaces X-rays. In addition, there is a spectroscopic technique for examining the binding state of molecules by obtaining an absorption spectrum and a complex dielectric constant inside a substance. In addition, biomolecule analysis technology, technology for evaluating carrier concentration and mobility, and the like are expected.

As an object inspection apparatus using terahertz waves, a configuration as shown in FIG. 9 is disclosed (see Patent Document 1). As shown in FIG. 9, this inspection apparatus is an apparatus that irradiates the object 4 with a terahertz wave propagating in space and measures the constituent material of the object 4 from a change in the propagation state of the transmitted wave from the object 4. In this technique, terahertz waves propagate through space.

It is known that terahertz waves propagate on transmission lines as well as many high-frequency electromagnetic wave signals. As shown in FIG. 10, it is known to propagate on a single line (see Non-Patent Document 1). The single line 1001 is often composed of a conductor. The terahertz wave propagating through the single line 1001 exhibits low loss and low dispersion propagation characteristics.
JP-A-8-320254 Nature, vol. 432, p376-379, 2004

In general, terahertz waves are strongly absorbed by moisture. Therefore, when the terahertz wave is propagated to the atmosphere as in the technique of Patent Document 1, the terahertz wave may be greatly attenuated due to absorption by moisture in the atmosphere. In such a case, it is desired that the electromagnetic wave be confined in a certain region and transmitted using a waveguide technique such as that used in many electromagnetic wave and optical technologies, for example, a fiber waveguide. However, fiber waveguides are difficult to handle due to dispersion problems. For example, if only a single frequency is used, the influence of this dispersion problem is small, but if a terahertz wave having a certain band is transmitted, there is a concern that the shape of the terahertz wave changes in the propagation process. This is because the influence of the dispersion of the fiber waveguide received by each frequency component constituting the terahertz wave is different. For this reason, a configuration in which terahertz waves are corrected using means for correcting the influence of dispersion is also conceivable. However, the addition of correction means tends to increase the device configuration. Such a dispersion problem also applies to a general transmission line technology used for propagation of a high-frequency signal.

On the other hand, as a waveguide shape for propagating terahertz waves, there is a single-line structure as in the technique of Non-Patent Document 1. As described above, this structure exhibits low loss and low dispersion characteristics with respect to terahertz waves. The terahertz wave is coupled to the single line 1001 and propagates as shown in FIG. However, since the single line 1001 is exposed to the outside, the terahertz wave 1003 propagating through the single line 1001 is easily affected by the outside. For example, the terahertz wave 1003 is not a little influenced by the atmosphere surrounding the single line 1001. Also, it is easily affected by crosstalk caused by an external electromagnetic wave source.

In view of the above problems, the electromagnetic wave waveguide of the present invention is an electromagnetic wave waveguide for transmitting an electromagnetic wave having an arbitrary frequency region of 30 GHz to 30 THz, and a single line formed of a conductor and And a dielectric member covering the single line.

According to the present invention, since the single line is covered with the dielectric member, an electromagnetic wave waveguide that is relatively hardly affected by the outside can be configured.

EMBODIMENT OF THE INVENTION Below, the form for implementing this invention is demonstrated with reference to drawings. In addition, the same code | symbol is used about the same element in a figure.

FIG. 1 is a schematic configuration diagram of an electromagnetic wave waveguide in the present embodiment. As shown in FIG. 1, the electromagnetic wave waveguide of the present embodiment includes a single line 101, a dielectric member 102, and electromagnetic wave coupling portions 103 (a) and 103 (b) for performing input and / or output. . The single line 101 is made of a conductor.

FIG. 2 is a cross-sectional view of a portion where an electromagnetic wave propagates in the electromagnetic wave waveguide of the present embodiment. As shown in FIG. 2, the electromagnetic wave waveguide of the present embodiment has a configuration in which the dielectric member 102 is coated on the single line 101. In FIG. 2, d is the film thickness of the dielectric member 102, and is the distance from the interface between the single line 101 and the dielectric member 102 to the outer peripheral surface of the dielectric member 102. In FIG. 2, the coating thickness d is expressed as a uniform thickness, but it is not necessarily required to be uniform. Partially varying thicknesses are possible. That is, in FIG. 2, the cross section of the single line 101 and the dielectric member 102 is circular, but it can take various shapes in addition to this shape.

As shown in FIG. 1, the electromagnetic wave waveguide of this embodiment has electromagnetic wave coupling portions 103 (a) and 103 (b). The electromagnetic wave coupling portions 103 (a) and 103 (b) have a function of coupling terahertz waves generated outside or inside to a waveguide portion where the electromagnetic waves propagate. In FIG. 1, the electromagnetic wave coupling portions 103 (a) and 103 (b) are drawn independently with respect to the single line 101 and the dielectric member 102 constituting the waveguide portion. However, in actuality, it is configured in close contact with the waveguide portion, and is internally supported (enclosed) or externally supported by the dielectric member 102. In FIG. 1, two electromagnetic wave coupling portions are depicted, but the present invention is not limited to this. Depending on the configuration of the waveguide, there may be one, or two or more. Further, in the form of FIG. 1, the position of the electromagnetic wave coupling portion is at the end of the single line 101 and the dielectric member 102, but this position is also arbitrary.

FIG. 3 shows the calculation result of the propagation characteristics of the electromagnetic wave transmission portion constituted by the single line 101 and the dielectric member 102 in the electromagnetic wave waveguide. Here, as the single line 101, gold having a diameter of 10 μm and a length of 1 mm is used. Further, BCB (benzocyclobutene) is used as the dielectric member 102. In the calculation, the dielectric member 102 is concentrically arranged with respect to the single line 101, and the film thickness d is changed. However, the material of the single line 101 and the dielectric member 102 is not limited to this. The single line 101 may be a conductor. The dielectric member 102 is preferably a material that has a small loss and dispersion with respect to the electromagnetic wave to be used. Moreover, there is no restriction | limiting regarding length, It is good also as a fiber-shaped waveguide.

The above calculation was performed using a finite integration method. Here, in addition to the propagation characteristics when the coating thickness d is changed to 50 μm (■ in the figure), 150 μm (● in the figure), and 250 μm (▲ in the figure), the calculation result when there is no dielectric member 102 ( □) in the figure is also included for comparison. According to FIG. 3, it can be seen that the configuration in which the single line 101 is coated with the dielectric member 102 has improved propagation characteristics than the configuration without the dielectric member 102. Moreover, it can be seen that the propagation characteristics improve as the coating thickness d increases. Observing the electromagnetic field distribution in the case of only the single line 101, it was found that the electromagnetic field propagated in the TEM mode as in the coaxial cable. Even when the dielectric member 102 exists, this propagation mode does not change.

When the coating thickness d of the dielectric member 102 was small, a tendency for the electromagnetic field to be reflected on the outer peripheral surface of the dielectric member 102 was observed. This is reflection caused by the difference in refractive index at the boundary between the outer peripheral surfaces, and this tendency becomes stronger as the difference in refractive index between the dielectric member 102 and the outside increases. Depending on the degree of reflection of the electromagnetic field, the electromagnetic field propagation mode may be disturbed. Further, when the film thickness d is small, the electromagnetic field component leaking outside from the dielectric member 102 increases. As a result of the verification, it was confirmed that most of the electromagnetic field components were confined in the dielectric member 102 by securing the film thickness to 1 / 2λ or more with respect to the effective wavelength λ of the electromagnetic wave propagating through the electromagnetic wave waveguide. When the electromagnetic wave to be used has a certain frequency band, this effective wavelength is the effective wavelength of the lowest frequency in the frequency band of the electromagnetic wave. By using such a condition of the film thickness d, the electromagnetic wave waveguide of the present embodiment can obtain low loss and low dispersion characteristics while being hardly affected by external influences.

In the calculation of FIG. 3, the electromagnetic wave waveguide is concentric, but it has been confirmed that the same result can be obtained even if the shape of the dielectric member 102 changes. What is important in the design of the electromagnetic wave waveguide is that the minimum distance from the interface where the single line 101 and the dielectric member 102 are in contact to the outer peripheral surface of the dielectric member 102 is 1 / 2λ or more. Therefore, as long as this condition is satisfied, the shape of the dielectric member 102 is arbitrary.

Further, in FIG. 3, the propagation characteristics on the high frequency side are not so much improved as compared with the propagation characteristics on the low frequency side, but this is due to the physical properties (dielectric constant, etc.) of the dielectric material used for the dielectric member 102. This is due to the frequency dependence characteristics. For example, when a material such as high resistance silicon (which has high transparency with respect to terahertz waves) is used as the dielectric member 102, it is known that the propagation characteristics on the high frequency side are also improved. As described above, it is preferable to secure a film thickness of 1 / 2λ or more. Of course, even when the film thickness of the dielectric member is 1 / 2λ or less, it can be hardly affected by external influences. Thus, an electromagnetic wave waveguide having relatively low loss and low dispersion characteristics can be obtained.

As described above, with the configuration of the present embodiment, the electromagnetic field is concentrated inside the dielectric member, and the terahertz wave leaking to the atmosphere is suppressed, so that attenuation by the atmosphere can be suppressed and highly efficient transmission of electromagnetic waves can be realized. . Further, the electromagnetic field of the terahertz wave is concentrated inside the dielectric member. Therefore, when the atmosphere outside the electromagnetic wave waveguide changes (for example, the humidity changes), or when an element (for example, an element containing metal) that disturbs the electromagnetic field exists in the vicinity of the electromagnetic wave waveguide. However, there is almost no influence on the electromagnetic field distribution of the terahertz wave. In this way, stable transmission characteristics can be obtained.

That is, the electromagnetic wave waveguide of this embodiment has an effect that it is not easily affected by the outside. Therefore, handling of the electromagnetic wave waveguide is also simplified. Further, the concentration of the terahertz wave electromagnetic field in the dielectric member means that even if the electromagnetic wave waveguides of this embodiment are brought close to each other, the respective waveguides are not affected. This makes it easier to integrate and downsize the existing equipment.

In addition, the electromagnetic wave waveguide of the present embodiment is configured to include or externally support the electromagnetic wave coupling portion with a dielectric member. This eliminates the need for a member for spatially arranging the electromagnetic wave coupling portion, which has been conventionally required, and simplifies the waveguide configuration. In addition, when this is applied to an apparatus, it is easy to reduce the size of the apparatus configuration. Further, since the electromagnetic wave coupling portion is supported by the dielectric member, the positional relationship between the single line and the electromagnetic wave coupling portion is always constant. For this reason, the coupling condition with the terahertz wave flying from the outside is always constant, and the adjustment of the coupling state, which has been conventionally required, becomes unnecessary, and the handling becomes simple. Furthermore, since such adjustment work becomes unnecessary, a stable coupling state can be realized at all times, and a highly reliable electromagnetic wave waveguide can be provided.

Regarding these points, in the technique of Non-Patent Document 1, a single line 1002 is further used to couple the terahertz wave 1003 to the single line 1001 as shown in FIG. The single line 1002 is arranged in a space so that the longitudinal direction of the single line 1002 intersects the longitudinal direction of the single line 1001 perpendicularly, and the terahertz wave 1003 propagating in the space is coupled between the single lines.

Therefore, for example, when the single line 1001 is isolated in the space in order to eliminate external influences, the single line 1002 used for coupling the terahertz waves needs to be also arranged in the space. Thus, since a member for spatially arranging each single line is required, the structure of the waveguide increases as a result. Furthermore, adjustment work for spatial arrangement of the waveguide itself and spatial arrangement of each single line is also necessary. In particular, the terahertz wave coupling state to the single line 1001 is expected to be affected by the spatial arrangement of each single line. Therefore, in such a method of spatially arranging each single line, in order to reproduce the same coupled state of terahertz waves, precise spatial positioning is necessary, and adjustment work is difficult.

Hereinafter, more specific embodiments will be described with reference to the drawings.

(Example 1)
The first embodiment is a configuration example in which a terahertz wave propagating in space is coupled to a waveguide composed of a single line 101 and a dielectric member 102 using a grating structure 401 as the electromagnetic wave coupling unit 103.

In the first embodiment, as shown in FIG. 4, the grating structure 401 that is the electromagnetic wave coupling portion 103 is engraved at an arbitrary position of the single line 101 having a rectangular cross section. By inserting such a single line 101 into a mold filled with a liquid dielectric member 102 and curing the dielectric member 102 with heat, the electromagnetic wave waveguide of this embodiment can be manufactured. Of course, the manufacturing method is not limited to this, and a known process technique can be used. When the grating structure 401 is used as the electromagnetic wave coupling unit 103, the electromagnetic wave waveguide of the present embodiment selectively propagates the terahertz wave having a wavelength corresponding to the period of the grating among the terahertz waves propagating in the space. Can do.

(Example 2)
FIG. 5 shows Example 2. In FIG. 5, a cross-wire structure 501 is used as an electromagnetic wave coupling unit 103 that couples a terahertz wave propagating in space to a waveguide. The cross wire structure 501 is a structure in which conductors are arranged substantially perpendicular to the single line 101. As a manufacturing method, for example, there is a technique of patterning the cross-wire structure 501 on the outer peripheral surface of the dielectric member 102 including the single line 101. However, the manufacturing method is not limited to this. 5 is fabricated on the outer peripheral surface of the dielectric member 102, the cross wire structure 501 may be embedded in the dielectric member 102. When the cross wire structure 501 is used as the electromagnetic wave coupling unit 103, as seen in Non-Patent Document 1, a terahertz wave having a wide frequency range can be propagated with respect to a terahertz wave propagating in space.

The configuration of the electromagnetic wave coupling unit 103 is not limited to that of the first and second embodiments. For example, an antenna structure can also be used. In short, any structure that can couple a terahertz wave propagating in space to a waveguide is acceptable. In addition, although the structure of the input part which propagates the terahertz wave which propagates in the space to the waveguide was demonstrated as the electromagnetic wave coupling part 103, these structures are applicable also to an output part as it is.

By having the structure as in the first and second embodiments, the coupling condition for coupling the terahertz wave to the waveguide composed of the single line 101 and the dielectric member 102 can be made constant, thus simplifying the adjustment work for coupling. Can be

(Example 3)
The third embodiment is a configuration example in which the electromagnetic wave coupling unit 103 has a function of generating a terahertz wave and couples the terahertz wave to a waveguide formed by the single line 101 and the dielectric member 102.

In the third embodiment, as shown in FIG. 6, a photoconductive switch structure 601 is used as the electromagnetic wave coupling portion 103. As shown in FIG. 6, the photoconductive switch structure 601 includes an electrode 602 drawn from the single line 101 and an electrode 603 formed on a part of the dielectric member 102, which are spaced apart from each other by a minute interval. In addition, a semiconductor (for example, low-temperature grown gallium arsenide: LT-GaAs) having high carrier mobility and short carrier lifetime is closely attached to the gap. The operation of the photoconductive switch structure 601 generates a terahertz wave by optically gating from the outside using an ultrashort pulse laser beam with an electric field applied to the gap portion. Then, the terahertz wave generated in the photoconductive switch structure 601 is coupled to the waveguide constituted by the single line 101 and the dielectric member 102 and propagates. These electrodes 602, 603 are patterned by a known process. In addition, the semiconductor constituting the photoconductive switch structure 601 is made into a thin film and attached to the dielectric member 102, for example.

In the present embodiment, the photoconductive switch structure 601 is formed on the end face of the waveguide constituted by the single line 101 and the dielectric member 102, but is not limited to this configuration. The dielectric member 102 may be formed inside or on the outer peripheral surface. The electrode 603 is patterned concentrically with respect to the single line 101. This is because the propagation mode of the waveguide composed of the single line 101 and the dielectric member 102 is the same TEM mode as that of the coaxial cable, and in order to maintain a better coupling state, the terahertz wave generation side This is because the structure is also a coaxial structure. However, what is important is that the electric field only needs to be applied to the gap between the conductors constituting the photoconductive switch structure 601, so that the present invention is not limited to this coaxial structure.

(Example 4)
The fourth embodiment is another configuration example in which the electromagnetic wave coupling unit 103 has a function of generating a terahertz wave and couples the terahertz wave to a waveguide formed by the single line 101 and the dielectric member 102. In this embodiment, as shown in FIG. 7, an electromagnetic wave gain structure 701 is used as the electromagnetic wave coupling part 103. As shown in FIG. 7, the electromagnetic wave gain structure 701 is in the terahertz wave region with respect to the electrode 702 drawn from the single line 101 and the electrode 703 formed on a part of the dielectric member 102, which are separated by a minute interval. It is a structure in which an electromagnetic wave gain substance having a gain is adhered.

The electromagnetic wave gain material is a semiconductor element that can obtain an electromagnetic wave gain represented by, for example, a resonant tunnel diode (RTD), a Gunn diode, or the like. As described above, this electromagnetic wave gain material is designed to obtain gain in a desired frequency band of terahertz waves. Therefore, terahertz waves can be generated by applying an electric field to the electrodes 702 and 703 at both ends of the electromagnetic wave gain structure 701. Then, the terahertz wave generated in the electromagnetic wave gain structure 701 is coupled to the waveguide constituted by the single line 101 and the dielectric member 102 and propagates. These electrodes 702 and 703 are also patterned by a known process.

In this embodiment as well, the electromagnetic wave gain structure 701 is formed on the end face of the waveguide constituted by the single line 101 and the dielectric member 102, but the present invention is not limited to this configuration. The dielectric member 601 may be formed inside or on the outer peripheral surface. The electrode 703 is also patterned concentrically with respect to the single line 101. The reason for this is as described in the third embodiment. Here, the electric field only needs to be applied to the gap between the conductors constituting the electromagnetic wave gain structure 701, so that the present invention is not limited to this coaxial structure.

In the third and fourth embodiments, the configuration of the portion that generates the terahertz wave is shown as the electromagnetic wave coupling unit 103, but it goes without saying that these configurations can be applied to the detection portion as they are.

By having the configuration as in the third and fourth embodiments, the terahertz wave generated in the electromagnetic wave coupling portion 103 propagates through the waveguide constituted by the single line 101 and the dielectric member 102. Here, since the electromagnetic wave coupling unit 103 has a configuration for generating and detecting terahertz waves, there is an effect that the device configuration is reduced in size.

(Example 5)
Example 5 is a configuration example in which the electromagnetic wave coupling unit 103 has a waveguide conversion function and couples a terahertz wave propagating through another high-frequency module to a waveguide composed of a single line 101 and a dielectric member 102. .

In this embodiment, as shown in FIG. 8, a waveguide conversion structure 801 is used as the electromagnetic wave coupling portion 103. FIG. 8 shows a top view (a), a sectional view (b), and a side view (c). As shown in FIG. 8, the waveguide conversion structure 801 includes a first conductor 802 and a second conductor 803 with respect to a transmission line (microstrip line) composed of the dielectric member 102, the first conductor 802, and the second conductor 803. The end of the single line 101 is inserted between the two. By having such a structure, the terahertz wave propagating in the high-frequency module is coupled to the waveguide constituted by the single line 101 and the dielectric member 102 in the waveguide conversion structure 801 and propagates.

The transmission line structure constituting the waveguide conversion structure 801 is not limited to the microstrip line as shown in FIG. For example, a transmission line structure used for propagating a high-frequency electromagnetic wave signal such as a coplanar waveguide can also be used. A three-dimensional waveguide structure such as a waveguide or a coaxial structure can also be applied. Further, in the waveguide conversion structure 801, in order to reduce impedance mismatching and further improve the terahertz wave coupling state, a mode in which the shapes of the single line 101 and the dielectric member 102 are partially changed may be considered. For example, at the end of the waveguide conversion structure 801, the size of the single line 101 or the dielectric member 102 may be partially thickened, thinned, or a tapered shape may be used.

Here, as the electromagnetic wave coupling unit 103, a configuration is shown in which terahertz waves propagating through other high-frequency modules are converted and coupled so as to be adapted to the electromagnetic wave waveguide of the present embodiment. However, it goes without saying that these configurations can be applied to a configuration in which the terahertz wave propagating through the electromagnetic wave waveguide of the present embodiment is coupled to another high-frequency module.

With the above configuration, terahertz waves propagating through other high-frequency modules can be coupled and propagated to the electromagnetic wave waveguide structure of the present embodiment. For example, a functional part that performs terahertz wave signal control or the like is performed by a conventional high-frequency circuit using a transmission line, and only the transmission part is performed by the electromagnetic wave waveguide of this embodiment. Can do. As a result, it is possible to suppress the attenuation and dispersion of the signal that has been a problem in the transmission line. Therefore, it is possible to easily provide a high-frequency module that is more complicated and rich in functionality.

The schematic block diagram of one Embodiment of the electromagnetic wave waveguide in this invention. FIG. 2 is a cross-sectional view of a terahertz wave propagation portion of the electromagnetic wave waveguide of FIG. The figure which shows the calculation result of the propagation characteristic of the terahertz wave propagation part of some electromagnetic wave waveguides. FIG. 3 is a diagram illustrating Example 1 using a grating structure as an electromagnetic wave coupling portion. FIG. 6 is a diagram illustrating Example 2 using a cross wire structure as an electromagnetic wave coupling portion. FIG. 6 is a diagram illustrating Example 3 using a photoconductive switch structure as an electromagnetic wave coupling unit. FIG. 6 is a diagram illustrating Example 4 using an electromagnetic wave gain structure as an electromagnetic wave coupling unit. FIG. 6 is a diagram illustrating Example 5 using a waveguide conversion structure as an electromagnetic wave coupling unit. The figure explaining the conventional test | inspection apparatus. The figure explaining propagation of the terahertz wave to the conventional single line.

Explanation of symbols

4 objects
101 single line
102 Dielectric material
103 Electromagnetic coupling
401 grating structure
501 Cross wire structure
601 photoconductive switch structure
602 electrode
603 electrodes
701 Electromagnetic gain structure
702 electrode
703 electrode
801 Waveguide conversion structure
802 1st conductor
803 Second conductor
1001 single line
1002 single line
1003 terahertz wave

Claims (6)

An electromagnetic wave waveguide for transmitting an electromagnetic wave having an arbitrary frequency region of 30 GHz to 30 THz,
An electromagnetic wave waveguide comprising: a single line formed of a conductor; and a dielectric member that covers the single line. 2. The electromagnetic wave waveguide according to claim 1, further comprising an electromagnetic wave coupling portion for performing at least one of input and output of electromagnetic waves. The shortest distance from the interface where the single line and the dielectric member are in contact to the outer peripheral surface of the dielectric member is 1 / 2λ or more when the effective wavelength of the electromagnetic wave is λ. The electromagnetic wave waveguide according to 1 or 2. 4. The electromagnetic wave waveguide according to claim 1, wherein the electromagnetic wave coupling portion is a grating, a cross wire, or an antenna structure. 4. The electromagnetic wave waveguide according to claim 1, wherein the electromagnetic wave coupling portion has a photoconductive switch structure or an electromagnetic wave gain structure. 4. The electromagnetic wave waveguide according to claim 1, wherein the electromagnetic wave coupling portion has a waveguide conversion structure.

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