JP2007078666A - Method and device for detecting electromagnetic wave shape - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a device for detecting an electromagnetic wave shape without depending on the polarization direction with a simple constitution using a photo-conduction aerial. <P>SOLUTION: In this detecting method, the electromagnetic wave shape is detected using the photo-conduction aerial. The detecting device comprises a substrate, three or more electrodes constituted by metal films formed on the surface, a wire connected to each electrode, and a current measuring means for measuring current between the electrodes. Sampling light is radiated between the electrodes by a sampling light radiating means; the electromagnetic wave to be detected is radiated between the electrodes by a detected wave radiating means; a group of the electrodes measured with the current measuring means is selected and controlled by an electrode control means; and the electromagnetic wave shape in the polarization direction corresponding to the arrangement of the electrode group on the substrate is calculated by an electromagnetic wave shape arithmetic means based on the electrode group selected by the electrode control means and the current value measured by the current measuring means. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for detecting an electromagnetic wave shape using a photoconductive antenna and an apparatus for carrying out the method.

 In recent years, research on new generation and detection methods is rapidly progressing in the far infrared and submillimeter wave regions, and terahertz waves have attracted attention. This region is located between infrared and millimeter waves, in other words, at the boundary between light waves and radio waves. In contrast to the development of light and radio waves along with important applied technologies, they are still in the process of being developed both in terms of technology and application.

The terahertz wave band has not been studied much because there has been no appropriate light source and detector for a long time. In the second half of the 20th century, when semiconductor engineering and laser engineering developed, a phenomenon was found in which terahertz waves were emitted by exciting antenna elements made of semiconductors with femtosecond pulse lasers.
According to Non-Patent Document 1, it is possible not only to radiate terahertz waves easily with a small apparatus compared to the conventional method, but also to measure the radiated terahertz waves in the time domain, so that amplitude information and phase information can be obtained simultaneously. There is a big advantage.
DH Auston, KP Cheung, and PR Smith, Appl.Phys. Lett. 45, 284 (1984)

As a result of this research result, research on terahertz waves has been rapidly developing. Effective use of frequency bands in wireless communication, support for ultra-high speed communication, imaging utilizing the characteristics of electromagnetic waves in this frequency band, and environmental measurement Terahertz research is expected to become increasingly important in the future, including various tests, biotechnology and medical applications.
In addition, a wide range of basic applications such as the elucidation of physical phenomena, life phenomena, and material structures that have not been elucidated because light sources and detectors have not been developed so far, and the measurement and diagnosis of space, atmosphere, living organisms, plasmas, etc. It leads to field development.

 The terahertz wave band is difficult to generate and detect, and is a technically undeveloped area. In particular, a simple broadband wavelength tunable light source is an indispensable light source for making significant progress in applied research in this area. It is awaited by many researchers. In particular, the development of a simple broadband wavelength tunable light source that covers the vicinity of 0.2 to 3 terahertz (wavelength 100 to 1500 μm) is particularly required.

 Conventional methods for generating terahertz waves using optical technology include the following. In other words, differential frequency light generation (DFG) using nonlinear optical crystal, parametric oscillation using nonlinear optical crystal, light mixing using photoconductive (PC) element, ultrashort electromagnetic by femtosecond optical pulse using PC element One example is pulse generation.

 The DFG using the nonlinear optical crystal and the parametric oscillation using the nonlinear optical crystal are configured such that a light wave is incident on a crystal having a second-order nonlinear optical effect and a terahertz wave is generated under phase matching conditions. In DFG, the wavelength of the terahertz wave to be generated is controlled by changing the wavelength interval (˜nm) of two incident lights. On the other hand, the method using parametric oscillation has the advantage that the wavelength of the terahertz wave to be generated can be controlled only by changing the incident angle of incident light.

Ultrashort electromagnetic pulse generation by light mixing using a PC element and femtosecond light pulse using a PC element is not a nonlinear optical effect, but light using a photoconductive effect in a low-temperature-grown GaAs thin film with a carrier lifetime of picoseconds or less. It differs from the above method in that mixing is performed and a bias electric field is required.
CW-terahertz waves in the frequency range of 0.2 to 3 THz are generated by optical mixing of two LD outputs in the 850 nm band using a PC element that integrates a micro dipole antenna and a spiral antenna. Moreover, by irradiating a similar PC element with femtosecond light pulses, it is possible to generate ultrashort electromagnetic pulses having a wide range of frequency components including terahertz waves.

On the other hand, when detecting a terahertz wave, when a photoconductive antenna is used, only a terahertz wave having a specific polarization direction can be detected due to its structure.
In order to detect the electromagnetic wave shape using the photoconductive antenna, sampling light is irradiated between two electrodes on the substrate while gradually changing the irradiation timing, and the current generated between the electrodes is measured.
However, the terahertz wave detected with high sensitivity is limited to an electromagnetic wave having a polarization direction parallel to the direction of the set of two electrodes facing each other.

  Therefore, an object of the present invention is to provide a method and an apparatus capable of detecting an electromagnetic wave shape without depending on a polarization direction with a simple configuration using a photoconductive antenna.

In order to solve the above problems, the electromagnetic wave shape detection method of the present invention comprises the following configuration.
That is, in a method for detecting the shape of an electromagnetic wave using a photoconductive antenna, a substrate, three or more electrodes made of a metal film formed on the surface, wiring connected to each electrode, and a gap between the electrodes A device equipped with a current measuring means for measuring current is irradiated with sampling light between the electrodes by the sampling light irradiation means, and an electromagnetic wave to be detected is irradiated between the electrodes by the detected wave irradiation means, thereby controlling the electrodes. The electrode set to be measured by the current measuring means is selected and controlled by the means, and the electrode set on the substrate is selected from the electrode set selected by the electrode control means and the current value measured by the current measuring means by the electromagnetic wave shape calculating means. The electromagnetic wave shape in the polarization direction corresponding to the arrangement of is calculated.

  Here, the electrodes are composed of three thin films symmetrically arranged radially at an angle of 120 ° to each other, and two sets of two electrodes are selected from the three electrodes in two different combinations. The electromagnetic wave shapes in two orthogonal polarization directions may be obtained simultaneously by adding or subtracting each current measurement value obtained by each of the two combinations.

  An electromagnetic wave shape detection apparatus for performing such a method is an apparatus for detecting an electromagnetic wave shape using a photoconductive antenna, and includes a substrate, three or more electrodes made of a metal film formed on the surface thereof, and each of the electrodes. Wiring connected to the electrodes, current measuring means for measuring the current applied between the electrodes, sampling light irradiating means for irradiating sampling light between the electrodes, and detected wave irradiating means for irradiating a detection target electromagnetic wave between the electrodes Corresponding to the arrangement of the electrode set on the substrate from the electrode control means for selectively controlling the electrode set to be measured by the current measurement means, the electrode set selected by the electrode control means and the current value measured by the current measurement means And electromagnetic wave shape calculation means for calculating the electromagnetic wave shape in the polarization direction.

  Here, you may comprise an electrode with the 3 or more thin film arrange | positioned radially.

  According to the present invention, since three or more electrodes are provided and the electrode set for current measurement is selected and controlled, the direction of the electrode set can be changed two-dimensionally, and the electromagnetic wave shape in an arbitrary polarization direction can be detected. .

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a perspective explanatory view showing a main part of the electromagnetic wave shape detection device.
The photoconductive antenna has a substrate (11) and an antenna pattern (12) made of a metal film patterned on the surface thereof. The antenna pattern (12) is connected to a current measuring means (14) for measuring a current applied between the lines via the wiring (13).
As the substrate (11), low-temperature grown GaAs or the like can be used.

The terahertz wave detection apparatus irradiates a sample with pulsed light in a frequency region of about 0.01 × 10 ^{12 to} 100 × 10 ¹² Hz, and detects transmitted light or reflected light from the sample, thereby electrically measuring the sample. It can be used as a device for measuring characteristics and component concentrations.
The terahertz wave (21) from the sample is incident on the photoconductive antenna via a lens (15) such as a hemisphere, and is irradiated between the lines of the antenna pattern (12). On the other hand, pulsed light (22) as sampling light is also irradiated there.
As the light source of the pulsed light (22), for example, a femtosecond pulse laser can be used. The light flux of the pulsed light (22) may be reduced by inserting a condenser lens.

  Between the lines of the antenna pattern (12), an electric field is generated by the terahertz wave (21), and a photocurrent corresponding to the electric field strength is generated depending on the pulsed light (22) as sampling light. By measuring it with the current measuring means (14), the electric field strength depending on the terahertz wave (21) can be obtained.

FIG. 2 is an explanatory front view showing a main part of the electromagnetic wave shape detection device according to the present invention.
In the present invention, three or more electrodes of the antenna pattern (12) are provided. In the illustrated example, three electrodes (12a) (12b) (12c) are symmetrically arranged radially at an angle of 120 ° with respect to each other.
When there are three or more electrodes, it is possible to select a plurality of electrode sets for measuring current. For example, when there are three electrodes, the current A is measured by the current measuring means (14a) from the set of the electrode (12a) and the electrode (12c), and from the set of the electrode (12b) and the electrode (12c) The current B is measured by the current measuring means (14b).

When the current A obtained from the pair of the electrode (12a) and the electrode (12c) and the current B obtained from the pair of the electrode (12b) and the electrode (12c) are added, the longitudinal direction (T) shown in the figure The current A obtained from the pair of the electrode (12a) and the electrode (12c), and the current B obtained from the pair of the electrode (12b) and the electrode (12c) are obtained. Is obtained, the electromagnetic wave shape in the polarization direction in the horizontal direction (Y) shown in the figure is obtained.
In this way, by adding or subtracting the respective current measurement values obtained by the two combinations, the electromagnetic wave shapes in the two orthogonal polarization directions (T) (Y) can be simultaneously obtained by one measurement. it can.

  The number and arrangement of the electrodes are arbitrary as long as the number of electrodes is 3 or more and linearly independent. Depending on the arrangement of the electrodes and the arrangement of the electrode sets to be selected, the electromagnetic wave shape in the desired polarization direction can be obtained by a calculation that linearly combines the current values obtained from them.

According to the present invention, an electromagnetic wave shape in an arbitrary polarization direction can be detected. For example, the electromagnetic wave receiving antenna for communication, a detection device in the field of sensing systems, and a spectroscopic device can be used in a terahertz wave band. It can be used for detection devices.
Terahertz wave technology is also promising as an atomic chip, atomic optics, BEC technology as a means for controlling the quantum state of atomic systems, and a new observation means for material systems, and the present invention contributes to various uses of terahertz waves. .
The application fields of terahertz waves range from basic research such as physical properties, molecular spectroscopy, and biological research to application fields such as quality evaluation of various materials such as semiconductors, high-sensitivity gas detection, and ultrahigh-speed communication.
In addition, terahertz waves have the shortest wavelength, that is, high resolution among electromagnetic waves that pass through semiconductors, plastics, vinyl, paper, rubber, wood, teeth, bones, and dry foods. Expectation for practical use as an alternative safe non-destructive inspection light source.
Furthermore, it is becoming clear that the skeletal vibration frequencies of biopolymers such as DNA, proteins, and enzymes are present in the terahertz wave region, which is also promising in fields such as medical applications and bioimaging.
In addition, early diagnosis of skin cancer and breast cancer, diagnosis of burn depth, tomography of caries, inspection of semiconductor silicon substrate, prevention of foreign matter contamination in powdered milk, moisture content inspection of dried food, moisture content such as timber and paper Since it covers many fields such as quantity inspection, it has high industrial utility value.

Perspective explanatory view showing the main part of the electromagnetic wave shape detection device Front explanatory drawing which shows the principal part of the electromagnetic wave shape detection apparatus by this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Board | substrate 12 Antenna pattern 12a-12c Electrode 13 Wiring 14, 14a-14b Current measuring means 15 Lens 21 Electromagnetic wave 22 of detection object 22 Pulsed light as sampling light

Claims (4)

An apparatus for detecting an electromagnetic wave shape using a photoconductive antenna,
A substrate, three or more electrodes made of a metal film formed on the surface thereof, wiring connected to each electrode, current measuring means for measuring a current applied between the electrodes, and sampling light irradiation between the electrodes Sampling light irradiating means for detecting, and detected wave irradiating means for irradiating an electromagnetic wave to be detected between the electrodes,
An electrode control means for selectively controlling a set of electrodes measured by the current measurement means;
An electromagnetic wave shape calculating means for calculating the electromagnetic wave shape in the polarization direction corresponding to the arrangement of the electrode set on the substrate from the electrode set selected by the electrode control means and the current value measured by the current measuring means. An electromagnetic wave shape detection device. The electromagnetic wave shape detection apparatus according to claim 1, wherein the electrode is composed of three or more thin films arranged radially. A method of detecting an electromagnetic wave shape using a photoconductive antenna,
For an apparatus comprising a substrate, three or more electrodes made of a metal film formed on the surface thereof, wiring connected to each electrode, and current measuring means for measuring a current applied between the electrodes,
The sampling light irradiation means irradiates the sampling light between the electrodes, and the detected wave irradiation means irradiates the detection target electromagnetic wave between the electrodes,
The electrode control means selectively controls the electrode set to be measured by the current measurement means,
The electromagnetic wave shape calculating means calculates the electromagnetic wave shape in the polarization direction corresponding to the arrangement of the electrode set on the substrate from the electrode set selected by the electrode control means and the current value measured by the current measuring means. An electromagnetic wave shape detection method. The electrode is composed of three thin films arranged symmetrically radially at an angle of 120 ° to each other,
By selecting a pair of two electrodes from the three electrodes in two different combinations, and adding or subtracting each current measurement value obtained by each of the two combinations, two orthogonal polarization directions can be obtained. The electromagnetic wave shape detection method according to claim 3, wherein the electromagnetic wave shape is obtained simultaneously.

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