JP2011253142A - Bandpass filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bandpass filter having a sufficient transmission characteristics and no polarization property.SOLUTION: This bandpass filter emitting electromagnetic wave of specific frequency out of electromagnetic waves entering one face side or reflecting it to the one face side, includes a substrate 3, and a mask section 4 covering one face 3a of the substrate 3. A plurality of openings 2 are provided in a grid shape on the mask section so as to expose the one face of the substrate 3. Four or more projecting sections are provided on the opening 2, which are tapered from the edge of the opening 2 toward the central direction. The aperture angle of the tip of the projecting sections is 30° or less, and the minimum interval d between the tips is 0.1-10 μm. The problem can be solved by using the above bandpass filter 10.

Description

The present invention relates to a bandpass filter. In particular, the present invention relates to a terahertz wave band-pass filter.

In recent years, terahertz technology has been attracting attention because it is used for security systems, drug identification in envelopes, adhesion evaluation of heat-resistant foam, and the like. Conventionally, there has been no good signal source and it has been difficult to use, but in recent years it has become possible to use a good signal source.
A terahertz wave refers to an electromagnetic wave in a band of 0.1 to 100 THz. This band is a band corresponding to molecular vibrations and intermolecular interactions, and it is expected that information that could not be obtained conventionally can be obtained.
However, the terahertz wave has a problem that it is easily absorbed by water vapor in the air. Therefore, practical use in the atmosphere has been difficult.

One method for using terahertz waves in the atmosphere is to use a bandpass filter. A band-pass filter is a filter that passes only electromagnetic waves of a necessary range of frequencies and does not pass electromagnetic waves of other frequencies, and is used in signal processing techniques and the like.
If a frequency component that is not affected by moisture is selected from the terahertz wave using the bandpass filter, the terahertz wave can be used for various inspections and communications in the atmosphere.
However, few practical terahertz wave bandpass filters have been reported.

  Patent Document 1 relates to a resonance type terahertz wave or infrared filter, and discloses a highly transmissive multiple resonance filter in which transmission resonance characteristics are controlled by an asymmetric shape of a through hole. However, this band pass filter has problems such as insufficient transmission characteristics and polarization characteristics.

Non-Patent Document 1 describes a bandpass filter composed of a metal thin film provided with a plurality of circular holes and a dielectric substrate. However, this band-pass filter also has an electromagnetic wave transmittance of 90% or less in the frequency range of 0.1 to 3.0 THz, and the transmission characteristics are not sufficient.

  Non-Patent Documents 2 and 3 provide a plurality of holes in a metal film by using a thick transparent substrate such as single crystal Si or Tsurupica (product name) with high resistivity from a practical viewpoint. A band-pass filter with improved durability and handleability compared to other meshes is described. However, these bandpass filters also have insufficient transmission characteristics.

Non-Patent Document 4 describes a band-pass filter having an opening in which two fan-shaped portions are connected. However, this bandpass filter also has problems such as insufficient transmission characteristics and polarization characteristics.

JP 2007-193298 A

A. K. Azad and W.M. Zhang, Resonant terhertz transmission in subwavelength metallic arrays of sub-skin-depth thickness, Opt. Lett. , 30, 2945-2947 (2005) D. Dragoman and M.D. Dragoman, Trahertz fields and applications, Prog. Quantum Electron. , 28, 1-66 (2004) E. Kato, K .; Suizu, and K.K. Kawase, Strong Resonance and Terahertz Wave Transmission Enhancement of Low-Porosity Metal Array with Bow-Tie-Shaped Apples, App. Phys. Express, 2,122302-1-122302-3 (2009) K. Ishihara, K .; Ohashi, T .; Ikari, H .; Minamide, H.M. Yokoyama, J. et al. Shikata, and H.K. Ito, Appl. Phys. Lett. , 89, 201120-1-201120-3 (2006)

It is an object of the present invention to provide a band-pass filter having sufficient transmission characteristics and no polarization characteristics.

The band-pass filter of the present invention is a band-pass filter that emits only an electromagnetic wave having a specific frequency out of an electromagnetic wave incident on one surface side from the other surface side or reflects to the one surface side. Or it has a mask part which covers both sides, and the mask part is provided with a plurality of openings which expose one side of the substrate in the shape of a lattice, and the opening part is centered from the edge of the opening part. Four or more projecting portions tapered toward the direction are provided, the opening angle of the tip portion of the projecting portion is 30 ° or less, and the shortest interval between the tip portions is 0.1 to 10 μm. It is characterized by being. When the opening angle is larger than 30 °, the sharpness as a filter is lowered, and the full width at half maximum (FWMH) cannot be about 0.05 THz or less. For this reason, it is preferable to set it as 30 degrees or less. When the shortest distance between the tips is 10 μm or more, the signal intensity of the transmitted or reflected wave decreases. For this reason, it is preferable to set it as 10 micrometers or less.

The band-pass filter of the present invention is characterized in that the opening angle of the tip is 5 to 25 °.
The bandpass filter of the present invention is characterized in that the centers of the openings are equally spaced from each other, and the distance is 30 to 500 μm. This distance has a large correlation with the peak frequency of the band-pass filter. In order to obtain the peak frequency in the band of 0.1 to 3.0 THz, it is desirable that the center distance between the openings is 30 to 500 μm.
The bandpass filter of the present invention is characterized in that the thickness of the substrate is 0.1 to 3.0 mm. When the thickness is 0.1 mm or less, not only the diffraction peak due to the opening but also the peak due to multiple reflection in the substrate becomes large. Conversely, when the thickness is 3.0 mm or more, the transmission strength decreases. For this reason, it is preferable that the thickness of a board | substrate is 0.1-3.0 mm.

The bandpass filter of the present invention is characterized in that the substrate is made of Si, a light transmissive resin, or a light transmissive glass.
The bandpass filter of the present invention is characterized in that the mask portion has a thickness of 0.1 to 1.0 μm. When the thickness is 0.1 μm or less, the skin depth of the electromagnetic wave becomes smaller, so that even a non-opening portion of the mask portion can be transmitted, so that it does not function as a bandpass filter having a sharp band. . On the other hand, the transmittance is saturated when the thickness is 1.0 μm or more, and decreases when the thickness is further increased. For this reason, it is preferable that the thickness of a mask part is 0.1-1.0 micrometer.
The bandpass filter of the present invention is characterized in that the mask portion is made of a metal or an alloy.

The bandpass filter of the present invention is characterized in that the metal is made of any one of Al, Au, Cu, Ag, Pt, Cr, Pb, and Ni.
The band-pass filter of the present invention is characterized in that the alloy contains any metal of Al, Au, Cu, Ag, Pt, Cr, Pb, or Ni.
By irradiation with the terahertz wave, an electromagnetic surface wave propagates on the surface of the mask portion. When a periodic aperture exists, this surface wave causes diffraction interference at the aperture, and is transmitted as a transmitted wave or a reflected wave having a resonance peak corresponding to the periodicity of the aperture. For this reason, the surface of the mask portion is a conductor, and it is necessary that the electromagnetic wave can propagate at least several hundred μm. The higher the electrical conductivity of the material, the longer the propagation distance of the surface electromagnetic wave, the resonance can be achieved even if the aperture period is large, and the control range of the peak frequency of the filter can be increased.
The bandpass filter of the present invention is characterized in that only the terahertz wave having a peak frequency within the range of 0.10 to 3.00 THz out of the terahertz wave incident on one surface side is emitted from the other surface side.
In the band-pass filter of the present invention, an even number of protrusions are provided at each opening, and the tip of each protrusion is provided so as to face the tip of any other protrusion. It is characterized by.

The band-pass filter of the present invention is a band-pass filter that emits only an electromagnetic wave having a specific frequency out of an electromagnetic wave incident on one surface side from the other surface side or reflects to the one surface side. Or it has a mask part which covers both sides, and the mask part is provided with a plurality of openings which expose one side of the substrate in the shape of a lattice, and the opening part is directed from the edge of the opening part toward the center. Four or more projecting portions having a tapered shape are provided, the opening angle of the tip portion of the projecting portion is 30 ° or less, and the shortest interval between the tip portions is 0.1 to 10 μm. Therefore, a band-pass filter having sufficient transmission characteristics and no polarization characteristics can be provided by interference of multiple reflections in the substrate and near-field interference by regularly arranged openings.

It is a top view which shows an example of the band pass filter which is embodiment of this invention. It is the A section enlarged view of FIG. FIG. 3 is a cross-sectional view taken along line B-B ′ of FIG. 2. It is an enlarged view of the C section of FIG. It is an apparatus configuration schematic diagram for measuring the transmittance of a bandpass filter. It is the schematic of the sample and sample holding part seen from the arrow D direction of FIG. It is an optical microscope photograph of the bandpass filter of Example 1, and is a photograph in which the openings are arranged in a lattice pattern. It is an enlarged photograph of one opening part. 3 is a graph showing the measurement results of the transmittance of the bandpass filter of Example 1. It is a graph which shows the measurement result of the area | region of 0.6-1.0 THz of FIG. It is the schematic which shows the incident position of the incident wave seen from the arrow D direction of FIG. It is a graph which shows the measurement result of the transmittance | permeability of the band pass filter of Example 1 obtained by moving the incident position of an incident wave. It is the schematic explaining the measuring method of the transmittance | permeability of the incident electromagnetic wave in the polarization direction. It is a graph which shows the transmittance | permeability of electromagnetic waves when a band pass filter is rotated in XY plane.

(Embodiment of the present invention)
Hereinafter, a band-pass filter according to an embodiment of the present invention will be described with reference to the accompanying drawings.
1 is a plan view showing an example of a band-pass filter 10 according to an embodiment of the present invention, FIG. 2 is an enlarged view of a portion A in FIG. 1, and FIG. 3 is a cross-sectional view taken along line BB ′ in FIG. FIG. 4 is an enlarged view of a portion C in FIG.
As shown in FIG. 1, the band-pass filter 10 is configured by providing openings 2 in a lattice pattern in a mask portion 4 that covers a part of a substrate 3 in a substantially square shape.
As shown in FIG. 2, in the opening 2, the intervals 1 between the centers O are equally spaced from each other.
The interval l is preferably 0.03 to 0.5 mm, more preferably 0.05 to 0.3 mm, and still more preferably 0.08 to 0.15 mm. Further, the angle β between the lines connecting the opening 2a to the two adjacent openings 2b and 2c is set to 60 °.

The symmetrical openings 2 are thus preferably arranged regularly. By arranging the openings 2 regularly at the interval l, near-field interference can be enhanced.
In the present embodiment, the angle β between the lines connecting one opening 2a to the two adjacent openings 2b and 2c is 60 °, but the angle β is not limited to this, and may be 90 °, for example. .

As shown in FIG. 3, a mask portion 4 is laminated on one surface 3 a of the substrate 3. The opening 2 provided in the mask portion 4 penetrates the mask portion 4 and exposes one surface 3a of the substrate 3.
The thickness of the substrate 3 is preferably 0.1 to 3.0 mm, more preferably 0.2 to 2.5 mm, and still more preferably 0.3 to 1.4 mm. By setting the thickness of the substrate 3 within the above range, multiple reflection interference can be efficiently generated in the substrate 3.
Moreover, it is preferable that the board | substrate 3 consists of either Si, light transmissive resin, or light transmissive glass. For example, when a Si substrate is used, sufficient transmission characteristics can be exhibited by combining interference of multiple reflections in the Si base material and interference of near-field by the regularly aligned openings 2. . As described above, the bandpass transmittance is affected not only by the mask portion 4 made of Al but also by interference in the substrate 3. That is, the interference is affected by the thickness of the substrate 3.
The electromagnetic wave incident on the band pass filter 10 may be incident from either the one surface 4a side of the mask part 4 or from the other surface 3b side of the substrate 3. The electromagnetic wave is incident on each surface from a direction substantially perpendicular to the surface.

The thickness of the mask portion 4 is preferably 100 nm to 1.0 μm, more preferably 200 nm to 905 nm, and still more preferably 300 nm to 800 nm. By setting the thickness of the mask part 4 within the above range, it is possible to increase near-field interference due to the regularly arranged openings 2.
The mask portion 4 is preferably made of a metal or an alloy, and the metal is preferably made of any one of Al, Au, Cu, Ag, Pt, Cr, Pb, or Ni, and the alloy is made of Al, It is preferable to contain any metal of Au, Cu, Ag, Pt, Cr, Pb, or Ni. By making the mask portion 4 made of the metal or the alloy, it is possible to enhance near-field interference due to the regularly arranged openings 2.

As shown in FIG. 4, the opening 2 includes four protrusions 6 that are tapered from the edge 5 toward the center. The tip portion 7 is formed to face the other tip portion 7.
By providing four sharply facing tip portions 7, the generation of surface plasmons at the Si / Al interface is promoted, and the THz electromagnetic field incident on the mask portion 4 is strengthened. As a result, the terahertz light is narrowed to a special resonance frequency in a narrow gap between the tip portions, i.e., increases the transmission to the opposite side of the mask portion.

In addition, although the opening part 2 of the band pass filter 10 which is embodiment of this invention was set as the structure which has the four protrusion parts 6, it is not restricted to this, What is necessary is just four or more. By providing four or more protrusions 6, the effect of the near field generated at the tip 7 can be increased.
It is preferable to provide an even number of protrusions 6 in each opening 2, and it is preferable to provide the tip 7 of each protrusion 6 so as to face the tip 7 of any other protrusion 6. Accordingly, the protrusions 6 can be arranged symmetrically around the center of each opening 2, and even if the substrate is rotated in the light irradiation surface while maintaining the direction of the light irradiation surface, the light is polarized. It does not cause any characteristics.

The opening angle α of the tip 7 is 30 ° or less. The opening angle α of the tip 7 is more preferably 5 to 25 °, and further preferably 7 to 20 °. Thereby, the effect of the near field which generate | occur | produces in the front-end | tip part 7 can be strengthened.

A gap (gap) is provided between the tip portions 7 so that the tip portions 7 of the protrusions 6 do not contact each other. When an electromagnetic wave is irradiated onto the mask part 4 having the opening 2, a near field is formed between the gaps (gap), and the electromagnetic wave can be emitted to the substrate 3 side.
The shortest distance d between the tip portions 7 of the protrusion 6, that is, the gap d is preferably 0.1 to 10 μm, more preferably 0.5 to 5 μm, and more preferably 1 to 3 μm. More preferably. Thereby, the effect of the near field which generate | occur | produces in the front-end | tip part 7 can be strengthened.
The diameter m of the opening 2 is preferably 10 to 200 μm, more preferably 20 to 100 μm, and still more preferably 30 to 50 μm. Thereby, the effect of the near field which generate | occur | produces in the front-end | tip part 7 can be strengthened.

By providing the opening 2 having the above structure, the transmittance of terahertz light (terahertz wave) is increased.
In addition, by controlling the structure of the opening 2 in this manner, the position of the band pass can be adjusted within the THz region, and the sharpness of the resonance transmittance, that is, the half-value width can be controlled.

<Characteristic evaluation of bandpass filter>
FIG. 5 is a schematic diagram of an apparatus configuration for measuring the transmittance of the bandpass filter.
As shown in FIG. 5, a femtosecond pulse laser 11 is disposed on one end side of the band pass filter characteristic evaluation apparatus 100. The light emitted from the femtosecond pulse laser 11 is separated into the pump light 13 and the probe light 21 by the beam splitter 12. The pump light 13 passes through the lens 14a and enters the photoconductive antenna 15a made of a GaAs substrate and a low-temperature grown GaAs film. A voltmeter 16 is attached to the photoconductive antenna 15a so that the photoconductivity can be controlled. The pump light emitted from the Si lens 18a of the photoconductive antenna 15a enters the bandpass filter 10 as a sample from the one surface 10a side via the two off-axis parabolic mirrors 17a and 17b. Thereafter, light is emitted from the other surface 10b side of the bandpass filter 10 and is incident on the Si lens 18b of the photoconductive antenna 15b via the two off-axis parabolic mirrors 17c and 17d. The photoconductive antenna 15b is provided with an ammeter 19 and connected to a current amplifier 25 so that a change in current is recorded in the recording system 24.

The probe light 21 separated by the beam splitter 12 passes through two mirrors 20a and 20b, one corner mirror 23, three mirrors 20c, 20d and 20e, and a lens 14b, and a photoconductive antenna 15b. It is set as the structure which injects into. The corner mirror 24 is movable, and can be configured to control the delay time (Time delay) of the probe light with respect to the pump light. Thereby, the electric field change by pump light in a different timing can be measured, and the electric field change of pump light can be measured as a time waveform by combining the measurement results in each delay time.

FIG. 6 is a schematic view of the sample and the sample holder as seen from the direction of arrow D in FIG.
As shown in FIG. 6, the band-pass filter 10 composed of the substrate 3 covered with the partial mask portion 4 on the one surface side is attached to the sample folder 31. The sample folder 31 is movable on the holding member 30 in the X direction. Thereby, the irradiation position of the electromagnetic wave on the band pass filter 10 can be moved in the X direction.
The sample folder is rotatable in the Y direction perpendicular to the X direction by the rotating unit 32. Thereby, the polarization characteristic of the band pass filter 10 can be measured.

Next, an example of the manufacturing process of the band pass filter 10 which is embodiment of this invention is demonstrated. The mask portion 4 is formed by a lithography method.
First, both surfaces of the substrate 3 having a predetermined size are polished by a known method.
Next, a resist is applied to one surface of the mask portion 4 and then dried. Next, the resist is exposed after disposing an exposure mask provided with a predetermined pattern on the resist.
Next, after removing only the resist in the exposed portion, the mask portion 4 is formed by vapor deposition.
Next, the resist is completely removed using a resist remover, and the opening 2 is formed in the mask portion 4 to manufacture the band-pass filter 10 according to the embodiment of the present invention.

The band-pass filter 10 according to the embodiment of the present invention is a band-pass filter that emits only an electromagnetic wave having a specific frequency from the other surface side among electromagnetic waves incident on one surface side, and includes a substrate 3 and one surface of the substrate 3. A plurality of openings 2 that expose one surface 3a of the substrate 3 in a lattice shape, and the openings 2 have openings 2 There are provided four or more projecting portions 6 tapered from the edge 5 toward the center O direction, and the opening angle α of the tip 7 of the projecting portion 6 is 30 ° or less. Since the shortest distance between the tip portions 7 of each is 0.1 to 10 μm, the generation of surface plasmons at the Si / Al interface can be promoted, and the electromagnetic waves incident on the mask portion 4 can be strengthened. Special feature of electromagnetic waves due to narrow gap between parts 7 To provide a bandpass filter with sufficient transmission characteristics and no polarization characteristics due to interference of multiple reflections in the substrate and near-field interference due to regularly arranged openings. Can do.

Since the bandpass filter 10 according to the embodiment of the present invention has a configuration in which the opening angle α of the tip 7 is 5 to 25 °, the narrow gap between the tips 7 can narrow the electromagnetic wave to a special resonance frequency, The electromagnetic wave can be emitted from the substrate 3 side.

The band pass filter 10 according to the embodiment of the present invention has a configuration in which the intervals 1 between the centers O of the openings 2 are equal to each other and the intervals l are 10 to 300 mm. A band-pass filter having sufficient transmission characteristics and no polarization characteristics due to near-field interference can be provided.

The band-pass filter 10 according to the embodiment of the present invention has a configuration in which the thickness of the substrate 3 is 0.1 to 3.0 mm. Therefore, interference of multiple reflections is efficiently generated in the substrate 3, and sufficient transmission characteristics are obtained. It is possible to provide a bandpass filter that is provided and has no polarization characteristics.

The band pass filter 10 according to the embodiment of the present invention has a configuration in which the substrate 3 is made of any one of Si, a light transmissive resin, and a light transmissive glass. It is possible to provide a bandpass filter having characteristics and having no polarization characteristics.

The band-pass filter 10 according to the embodiment of the present invention has a configuration in which the thickness of the mask portion 4 is 100 nm to 1.0 μm. Therefore, the interference of the near field by the regularly arranged openings 2 is strengthened and sufficient transmission is achieved. It is possible to provide a bandpass filter having characteristics and having no polarization characteristics.

The bandpass filter 10 according to the embodiment of the present invention has a configuration in which the mask portion 4 is made of a metal or an alloy, so that interference in the near field by the regularly arranged openings 2 is strengthened, and sufficient transmission characteristics are provided. A band-pass filter having no characteristics can be provided.

The band-pass filter 10 according to the embodiment of the present invention has a configuration in which the metal is made of any one of Al, Au, Cu, Ag, Pt, Cr, Pb, or Ni, and therefore the openings 2 arranged regularly. By strengthening near-field interference due to the above, it is possible to provide a bandpass filter having sufficient transmission characteristics and no polarization characteristics.

The band-pass filter 10 according to the embodiment of the present invention has a structure in which the alloy contains any metal of Al, Au, Cu, Ag, Pt, Cr, Pb, or Ni. The interference of the near field by 2 can be strengthened, and a band pass filter having sufficient transmission characteristics and no polarization characteristics can be provided.

The band-pass filter 10 according to the embodiment of the present invention has a configuration in which a terahertz wave is incident on one surface side. Therefore, the multi-reflection interference is efficiently generated in the substrate 3, and the proximity by the openings 2 regularly arranged therewith. A band-pass filter that emits a terahertz wave having sufficient transmission characteristics and no polarization characteristics due to field interference can be provided.

In the band-pass filter 10 according to the embodiment of the present invention, an even number of protrusions 6 are provided in each opening 2, and the tip 7 of each protrusion 6 is the tip 7 of any other protrusion 6. Since the interference is caused by multiple reflections efficiently in the substrate 3 and the interference of the near field by the openings 2 regularly arranged therewith, it has sufficient transmission characteristics, A band-pass filter that emits terahertz waves having no polarization characteristics can be provided.
The bandpass filter according to the embodiment of the present invention is not limited to the above-described embodiment, and can be implemented with various modifications within the scope of the technical idea of the present invention. Specific examples of this embodiment are shown in the following examples. However, the present invention is not limited to these examples.

Example 1
<Band pass filter manufacturing process>
A mask portion was formed on the substrate by lithography as follows.
First, both surfaces of a Si substrate having a plate thickness of 400 μm, a length of 30 mm, and a width of 30 mm were polished by a known method.
Next, a resist was applied to a predetermined position on one surface of the Si substrate, and then dried.
Next, an exposure mask provided with a predetermined pattern in a grid pattern was placed on the resist, and then the resist was exposed.
Next, after removing the exposed portion by a known method, a mask portion made of Al having a thickness of 0.4 μm, a length of 1 cm, and a width of 1 cm was formed by vapor deposition.
Next, the resist was completely removed using a resist remover, and an opening was formed in the mask portion to manufacture a bandpass filter.

7 and 8 are SEM photographs of the mask part and the opening part of the bandpass filter prepared by the above process. As shown in FIG. 8, an opening having an opening diameter of 50 μm is provided, and four protrusions having a tapered shape protruding to the center of the opening are provided, the interval between the tips of the protrusions is 10 μm, and the opening angle of the protrusion is 20 °. A bandpass filter with a mask was created.

<Characteristic evaluation of bandpass filter>
Next, the band pass filter characteristic evaluation result of Example 1 was performed using the band pass filter characteristic evaluation apparatus shown in FIG.
FIG. 9 and FIG. 10 show the characteristics evaluation results (Array on Si in air) of the band-pass filter of the first embodiment. The measurement results when the sample is not placed, that is, the measurement results for air (Air) and the measurement results for only the Si substrate (Si substrate in Air) are also shown for comparison.
As shown in FIG. 9, the bandpass filter of Example 1 had a plurality of peaks in the range of 0.5 to 1.5 THz, and showed the largest peak at 0.81 THz.
The emitted light having a first peak at 0.81 THz has a second peak near 0.83 THz, and emitted light at 0.78 to 0.85 THz. That is, the band filter of Example 1 emitted only electromagnetic waves having a specific frequency of 0.78 to 0.85 THz from the other surface side.

As shown in FIG. 10, the light intensity of the bandpass filter is 2 × 10 ⁵ compared to the light intensity of 1.6 × 10 ⁵ of the Si substrate at 0.81 THz, and the transmittance is 145% with respect to the Si substrate. showed that.

Next, as shown in FIG. 11, the transmittance of the bandpass filter of Example 1 was measured by moving the incident position of the incident wave in the X direction.
First, an electromagnetic wave is irradiated from a direction substantially perpendicular to the one surface 10a of the band-pass filter 10 at the position of X ₀ shown in FIG. 11, it takes in the electromagnetic waves in oncoming by passage of air by parabolic mirror photoconductive antenna, strength Was measured.
Thereafter, the electromagnetic wave intensity from X ₀ to X ₅₄₀₀₀ was measured while moving the sample folder 31 on the holding member 30.
As a result, electromagnetic waves at positions corresponding to Air, Si, Al, Array, Al, Si, Air shown in FIG. 11 were obtained.

FIG. 12 is a graph showing the measurement result of the electromagnetic wave at this time, and is a graph showing the measurement result of the transmittance of the bandpass filter of Example 1 obtained by moving the incident position of the incident wave.
In addition to the case of using an electromagnetic wave of 0.81 THz as the electromagnetic wave, the case of using an electromagnetic wave of 1.85 THz is shown for comparison. In the area of the mask portion 4 (shown as “Array” in FIG. 12), the intensity of the outgoing electromagnetic wave is almost 0 in the case of the electromagnetic wave of 1.85 THz, whereas it is about 45 in the case of the electromagnetic wave of 0.81 THz. % Transmittance. Since the transmittance of the Si substrate was about 35%, it was found that the transmittance was improved by about 10% by the mask portion 4 (Array).

  Next, as shown in FIG. 13, the bandpass filter was rotated counterclockwise by 45 ° and 90 ° in the XY plane, and the influence on the transmittance in the polarization direction of the incident electromagnetic wave was measured. Incident electromagnetic waves were polarized so that the direction of the electric field was in the horizontal direction in the figure.

  FIG. 14 is a graph showing the transmittance of electromagnetic waves at this time. No change in transmittance was observed at any angle of 0 °, 45 °, and 90 °. This confirmed that it functions as a bandpass filter of the same frequency band regardless of the polarization state of the incident wave.

The band-pass filter of the present invention can be used as a terahertz wave band-pass filter and can be used in industries such as security systems using terahertz technology, drug identification in envelopes, and evaluation of heat-resistant foam adhesion.

2 ... opening, 2a, 2b, 2c ... opening, 3 ... substrate, 3a ... one side, 3b ... other side, 4 ... mask part, 4a ... one side, 5 ... edge, 6 ... protrusion, 7 ... tip DESCRIPTION OF SYMBOLS 10 ... Band pass filter, 10a ... One side, 10b ... Other side, 11 ... Femtosecond pulse laser, 12 ... Beam splitter, 13 ... Pump light, 14a, b ... Lens, 15a, b ... Photoconductive antenna, 16 ... Voltmeter, 17 ... off-axis parabolic mirror, 18a, b ... lens, 19 ... ammeter, 20a, b, c, d, e ... mirror, 21 ... probe light, 23 ... corner reflector, 24 ... recording system, 25 ... Current amplifier, 30 ... Sample folder base, 31 ... Sample folder support, 100 ... Characteristic evaluation device, l, m, d ... Length, α, β ... Angle.

Claims (11)

A band-pass filter that emits only an electromagnetic wave having a specific frequency out of an electromagnetic wave incident on one surface side, or reflects to the one surface side,
A substrate and a mask portion covering one or both surfaces of the substrate;
In the mask portion, a plurality of openings for exposing one surface of the substrate are provided in a lattice shape,
The opening is provided with four or more protrusions tapered from the edge of the opening toward the center,
The band-pass filter characterized in that the opening angle of the tip of the protrusion is 30 ° or less, and the shortest distance between the tips is 0.1 to 10 μm. The band-pass filter according to claim 1, wherein an opening angle of the tip is 5 to 25 °. The bandpass filter according to claim 1 or 2, wherein the distance between the centers of the openings is equal to each other, and the distance is 30 to 500 µm. The bandpass filter according to any one of claims 1 to 3, wherein the substrate has a thickness of 0.1 to 3.0 mm. The bandpass filter according to any one of claims 1 to 4, wherein the substrate is made of any one of Si, a light transmissive resin, and a light transmissive glass. The bandpass filter according to claim 1, wherein the mask portion has a thickness of 0.1 to 1.0 μm. The bandpass filter according to claim 1, wherein the mask portion is made of a metal or an alloy. The bandpass filter according to claim 6, wherein the metal is made of any one of Al, Au, Cu, Ag, Pt, Cr, Pb, and Ni. The bandpass filter according to claim 6, wherein the alloy contains any one of Al, Au, Cu, Ag, Pt, Cr, Pb, and Ni. The terahertz wave incident on the one surface side only emits a terahertz wave having a peak frequency in the range of 0.10 to 3.00 THz from the other surface side. The described bandpass filter. An even number of protrusions are provided in each opening, and the tip of each protrusion is provided so as to face the tip of any other protrusion. The bandpass filter according to any one of 10 above.