A testing system and method for the dielectric properties of materials in the terahertz band.

Abstract

This invention provides a testing system for the dielectric properties of materials in the terahertz band, comprising a laser, an optical beam splitter, an emitter, a detection stage, a first reflector, a second reflector, a detector, and a signal processor. The laser emitted by the laser is split into two paths by the optical beam splitter. The first path's output laser enters the emitter and is converted into a terahertz wave. The terahertz wave passes through the sample under test and is transmitted to the first reflector, where it is reflected and then enters the detector. The second path's output laser is reflected by the second reflector and then enters the detector. The second path's output laser generates photogenerated carriers upon entering the detector, while the first path's output laser, in terahertz wave form, generates a bias voltage in the detector, causing the photogenerated carriers in the detector to form a current or voltage. After processing by the signal processor, the electrical signal of the material under test is obtained. The testing system of this invention has advantages such as high integration, high testing accuracy, low cost, and reliable test results.

Description

Technical Field

[0001] This invention relates to the field of terahertz band material testing technology, and in particular to a testing system and method for the dielectric properties of terahertz band materials. Background Technology

[0002] Terahertz waves (THz) are electromagnetic waves that lie between microwaves and light waves. They possess both the electronic properties of microwaves and the photonic properties of light waves. Due to their advantages such as strong penetration, high safety (low energy), good directionality, and high bandwidth, they are widely used in various fields such as industry, agriculture, communications, medicine, security inspection, and military.

[0003] Due to the limited means of generating terahertz waves, research on the properties of materials in the terahertz band is currently very limited. The main method currently used is the THz time-domain spectroscopy system to test the dielectric properties of materials in the terahertz band; however, this system is difficult to build and suffers from problems such as large equipment size and low testing accuracy.

[0004] Therefore, based on the above problems, it is necessary to provide a testing system and method for the dielectric properties of materials in the terahertz band. Summary of the Invention

[0005] This invention provides a testing system and method for the dielectric properties of terahertz band materials, which can solve the problems of difficult construction of testing systems, large equipment size and low testing accuracy of terahertz band materials in related technologies.

[0006] In a first aspect, the present invention provides a testing system for the dielectric properties of materials in the terahertz band, comprising a laser, an optical beam splitter, a transmitter, a testing stage, a first reflector, a second reflector, a detector, and a signal processor; wherein:

[0007] The testing station is located between the transmitter and the first reflector and is used to place the material to be tested.

[0008] The laser emitted by the laser is split into two paths by the optical beam splitter. The first laser output enters the transmitter and is converted into a terahertz wave. The terahertz wave passes through the sample under test and is transmitted to the first reflector. After being reflected by the first reflector, it enters the detector. The second laser output enters the detector after being reflected by the second reflector.

[0009] The laser output from the second path enters the detector and generates photogenerated carriers. The laser output from the first path enters the detector in the form of a terahertz wave and generates a bias voltage, so that the photogenerated carriers in the detector form a current or voltage. After processing by the signal processor, the electrical signal of the material under test is obtained.

[0010] Preferably, the laser is an infrared laser, including a first infrared laser and a second infrared laser; wherein the frequency difference between the laser emitted by the first infrared laser and the second infrared laser is 0.1 to 10 THz.

[0011] Preferably, the system further includes an optical mixer and an optical amplifier; wherein:

[0012] The lasers emitted by the first infrared laser and the second infrared laser are mixed into one path by the optical mixer, amplified by the optical amplifier, and then transmitted to the optical beam splitter.

[0013] Preferably, the transmitter is an optical mixing terahertz transmitter.

[0014] Preferably, the laser is a femtosecond laser.

[0015] Preferably, the transmitter is a photoconductive antenna type terahertz transmitter.

[0016] Preferably, the detector is a photoconductive antenna without voltage bias.

[0017] In a second aspect, the present invention also provides a method for testing the dielectric properties of materials using a testing system for the dielectric properties of materials in the terahertz band as described in any one of the first aspects, the method comprising:

[0018] (1) Obtain the electrical signals of the standard material and the material under test at the same thickness respectively; wherein, the electrical signals of the standard material and the material under test are measured by a terahertz band material dielectric property testing system;

[0019] (2) Perform Fourier transform on the electrical signal of the standard material and the electrical signal of the material under test respectively to obtain the amplitude and phase of the terahertz wave after passing through the standard material and the material under test respectively;

[0020] (3) The dielectric properties of the test material are calculated based on the amplitude and phase of the standard material and the test material; wherein the dielectric properties include the absorption coefficient and refractive index of the standard material.

[0021] Preferably, the amplitude and phase of the terahertz wave after passing through the standard material and the material under test are calculated using the following formula:

[0022]

[0023]

[0024] In the formula, The electrical signal of the standard material. A is the electrical signal of the material under test.ref (f) represents the amplitude of the terahertz wave after passing through the standard material, φ ref A represents the phase of the terahertz wave after passing through the standard material. test (f) represents the amplitude of the terahertz wave after passing through the material under test, φ test This represents the phase of the terahertz wave after it passes through the material under test.

[0025] Preferably, the dielectric properties of the material to be tested are calculated using the following formula:

[0026]

[0027]

[0028] In the formula, α(f) is the absorption coefficient of the material to be tested, and n test (f) is the refractive index of the material to be tested, A ref (f) represents the amplitude of the terahertz wave after passing through the standard material, A test (f) represents the amplitude of the terahertz wave after passing through the material under test, φ ref (f) represents the phase of the terahertz wave after passing through the standard material, φ test (f) represents the phase of the terahertz wave after passing through the material under test, n ref (f) is the refractive index of the standard material, k is the wave number in vacuum, and d is the thickness of the material to be tested.

[0029] Compared with the prior art, the present invention has at least the following beneficial effects:

[0030] This invention provides a testing system and method for the dielectric properties of materials in the terahertz band. In this testing system, a laser emitted from a laser is split into two paths by an optical beam splitter. The laser output from the second path enters a detector and generates photogenerated carriers. The laser output from the first path enters the detector in the form of a terahertz wave, generating a bias voltage. This causes the photogenerated carriers in the detector to form a current or voltage. After processing by a signal processor, the electrical signal of the material under test is obtained. The material dielectric property testing system provided by this invention has advantages such as high system integration, high testing accuracy, low cost, and reliable test results. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1This is a schematic diagram of a testing system for the dielectric properties of terahertz band materials according to an embodiment of the present invention;

[0033] Figure 2 This is a schematic diagram of a testing system for the dielectric properties of terahertz band materials according to another embodiment of the present invention;

[0034] Figure 3 This is a schematic diagram of the structure of an optical mixing terahertz transmitter in a testing system for the dielectric properties of terahertz band materials according to an embodiment of the present invention.

[0035] Figure 4 This is a schematic diagram of the structure of a photoconductive antenna-type terahertz transmitter in a testing system for the dielectric properties of terahertz band materials according to an embodiment of the present invention.

[0036] Figure 5 This is a flowchart of a method for testing the dielectric properties of terahertz band materials according to an embodiment of the present invention. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0038] like Figure 1 As shown, this embodiment of the invention provides a testing system for the dielectric properties of materials in the terahertz band, including a laser, an optical beam splitter, a transmitter, a testing stage, a first reflector, a second reflector, a detector, and a signal processor; wherein:

[0039] The testing station is located between the transmitter and the first reflector and is used to place the material to be tested.

[0040] The laser emitted by the laser is split into two paths by the optical beam splitter. The first laser output enters the transmitter and is converted into a terahertz wave. The terahertz wave passes through the sample under test and is transmitted to the first reflector. After being reflected by the first reflector, it enters the detector. The second laser output enters the detector after being reflected by the second reflector.

[0041] The laser output from the second path enters the detector and generates photogenerated carriers. The laser output from the first path enters the detector in the form of a terahertz wave and generates a bias voltage, so that the photogenerated carriers in the detector form a current or voltage. After processing by the signal processor, the electrical signal of the material under test is obtained.

[0042] This invention provides a system and method for testing the dielectric properties of materials in the terahertz band. In this system, a laser emitted from a laser is split into two paths by an optical beam splitter. The laser output from the second path enters a detector and generates photogenerated carriers. The laser output from the first path enters the detector in terahertz wave form, generating a bias voltage. This causes the photogenerated carriers in the detector to form a current or voltage. After processing by a signal processor, the electrical signal of the material under test is obtained. The material dielectric property testing system provided by this invention has advantages such as high system integration, high testing accuracy, low cost, and reliable test results.

[0043] According to some preferred embodiments, the laser is an infrared laser, including a first infrared laser and a second infrared laser; wherein the frequency difference between the laser emitted by the first infrared laser and the second infrared laser is 0.1 to 10 THz.

[0044] According to some preferred embodiments, the system further includes an optical mixer and an optical amplifier; wherein: the lasers emitted by the first infrared laser and the second infrared laser are respectively mixed into one path by the optical mixer, amplified by the optical amplifier, and then transmitted to the optical beam splitter.

[0045] According to some preferred embodiments, the transmitter is an optical mixing terahertz transmitter.

[0046] In this embodiment of the invention, the test system is constructed in two forms: one based on an optical mixing terahertz transmitter, and the other based on a photoconductive antenna terahertz transmitter. Compared to traditional test systems, the choice can be made according to actual application requirements. The system construction is simple, and the transmitter has high source power, resulting in high test accuracy. Specifically, when based on an optical mixing terahertz transmitter, such as... Figure 2As shown, the test system also includes an optical mixer and an optical amplifier, and the lasers are infrared lasers, including a first infrared laser and a second infrared laser. During testing, the system first emits two beams with frequencies f1 and f2, respectively, with a frequency difference of 0.1–10 THz. These beams are mixed by the optical mixer, amplified by the optical amplifier, and then split into two paths by the optical beam splitter. The first path is coupled into an optical mixer-type terahertz transmitter, which generates terahertz waves through its integrated broadband antenna. These terahertz waves pass through the test sample material on the testing stage, are reflected by a first reflector, and then coupled into a detector. Simultaneously, the second path transmits laser light from the second transmitter to excite the detector. The light in the second path generates photogenerated carriers in the detector. The terahertz waves in the first path act on the detector's antenna, generating a bias voltage that causes the photogenerated carriers to move directionally, forming a current or voltage in the external circuit. Finally, the electrical signal output from the detector is processed by a signal processor to obtain the electrical signal information of the test material.

[0047] In this embodiment, the structural schematic diagram of the optical mixing type terahertz transmitter is shown in Figure 3. The transmitter consists of a traveling-wave single-carrier optical waveguide detector integrated with a broadband antenna. One beam of light is coupled to the traveling-wave single-carrier optical waveguide detector and absorbed in the P-type doped absorption layer, generating photogenerated carriers. Under the action of an applied reverse bias voltage, these carriers undergo directional drift, forming a photocurrent. This photocurrent serves as a signal source to drive the broadband antenna, radiating terahertz waves. Specifically, as shown... Figure 3 As shown, the optical mixing terahertz transmitter includes a substrate layer, a waveguide structure placed on the substrate, an antenna, and two ground electrodes. The waveguide structure is located between the substrate and the signal electrodes. The cross-section of the structure formed by the waveguide structure and the substrate layer is convex. The two N-electrodes are symmetrically arranged about the waveguide structure. The waveguide structure consists of an N-waveguide layer, an I-coupling layer, an N-waveguide layer, a P-absorption layer, and a P-contact layer from bottom to top.

[0048] According to some preferred embodiments, the laser is a femtosecond laser.

[0049] According to some preferred embodiments, the transmitter is a photoconductive antenna type terahertz transmitter.

[0050] In this embodiment of the invention, when the incident light source is based on a photoconductive antenna type terahertz transmitter, such as Figure 1As shown, the laser in the test system is a femtosecond laser. During testing, the femtosecond laser emits an extremely narrow light pulse, which is split into two paths by an optical beam splitter. The first path is coupled into a photoconductive antenna-type terahertz transmitter, generating a terahertz wave based on the photoconductive effect (internal photoelectric effect). The terahertz wave passes through the sample material on the test stage and reaches the detector via the first reflector. The second path transmits the laser emitted from the second transmitter to excite the detector. The light in the second path is used to generate photogenerated carriers in the detector. The terahertz wave in the first path acts on the detector's antenna to generate a bias voltage, causing the photogenerated carriers to move in a directional manner, forming a current or voltage in the external circuit. Finally, the electrical signal output by the detector is processed by a signal processor to obtain the electrical signal information of the material under test.

[0051] In this embodiment, the photoconductive antenna type terahertz transmitter is shown in Figure 4. This transmitter consists of a photoconductive antenna. One beam of light is coupled into the semiconductor layer of the photoconductive antenna and absorbed, generating photogenerated carriers. Under the action of an applied bias voltage, these carriers move directionally, forming a photocurrent. This photocurrent serves as a signal source to drive the broadband antenna, radiating terahertz waves. Specifically, to improve mode coupling efficiency, the transmitter includes a substrate and two horizontally tapered upper and lower waveguide structures located on the substrate surface. The light beam output from the optical fiber is incident on the input end of the transmitter, where mode coupling occurs, gradually moving from the upper cone to the lower cone. The length of the upper waveguide structure is preferably 1000–1100 μm, and the length of the lower waveguide structure is preferably 1250–1265 μm. When the upper waveguide length is 1100 μm and the lower waveguide length is 1265 μm, the coupling efficiency is high, but the transmitter size is large, which is not conducive to integration. When the length of the upper waveguide structure is 1000μm and the length of the lower waveguide is 1250μm, the coupling efficiency does not decrease significantly, and the transmitter size is relatively small, resulting in higher integration.

[0052] According to some preferred embodiments, the detector is an unbiased photoconductive antenna.

[0053] In this embodiment of the invention, the laser emitted by the laser is split into two paths by an optical beam splitter. The laser in the first path is converted into a terahertz wave after passing through the transmitter and passes through the sample material to be tested, and then is transmitted to the detector to generate an external bias electric field. At the same time, the laser in the second path is also transmitted to the detector and acts on the semiconductor layer thereon to generate charge carriers. The charge carriers undergo fixed movement under the action of the terahertz wave, realizing photoelectric conversion, and finally obtaining the information of the test sample in the signal processor.

[0054] like Figure 5 As shown, the present invention also provides a method for testing the dielectric properties of materials using a testing system for the dielectric properties of materials in the terahertz band as described in any of the above claims, the method comprising:

[0055] (1) Obtain the electrical signals of the standard material and the material under test at the same thickness respectively; wherein, the electrical signals of the standard material and the material under test are measured by a terahertz band material dielectric property testing system;

[0056] (2) Perform Fourier transform on the electrical signal of the standard material and the electrical signal of the material under test respectively to obtain the amplitude and phase of the terahertz wave after passing through the standard material and the material under test respectively;

[0057] (3) The dielectric properties of the test material are calculated based on the amplitude and phase of the standard material and the test material; wherein the dielectric properties include the absorption coefficient and refractive index of the standard material.

[0058] In this embodiment of the invention, a standard sample material of a predetermined thickness (wherein the dielectric properties of the standard sample material are known) is first placed on the testing stage, and its electrical signal is measured using a terahertz band material dielectric property testing system. After testing, a sample of the same thickness as the standard sample is placed on the testing stage, and its electrical signal is monitored using the testing system. The test is conducted by performing Fourier transforms on the standard sample and the test sample material respectively through a signal processor to obtain the amplitude and phase of the standard material and the test material. Finally, the absorption coefficient and refractive index of the test sample material can be calculated based on the obtained amplitude and phase.

[0059] According to some preferred embodiments, the amplitude and phase of the terahertz wave after passing through the standard material and the material under test are calculated using the following formula:

[0060]

[0061]

[0062] In the formula, The electrical signal of the standard material. A is the electrical signal of the material under test. ref (f) represents the amplitude of the terahertz wave after passing through the standard material, φ ref A represents the phase of the terahertz wave after passing through the standard material. test (f) represents the amplitude of the terahertz wave after passing through the material under test, φ test This represents the phase of the terahertz wave after it passes through the material under test.

[0063] According to some preferred embodiments, the dielectric properties of the material under test are calculated using the following formula:

[0064]

[0065]

[0066] In the formula, α(f) is the absorption coefficient of the material to be tested, and n test (f) is the refractive index of the material to be tested, A ref (f) represents the amplitude of the terahertz wave after passing through the standard material, A test (f) represents the amplitude of the terahertz wave after passing through the material under test, φ ref (f) represents the phase of the terahertz wave after passing through the standard material, φ test (f) represents the phase of the terahertz wave after passing through the material under test, n ref (f) is the refractive index of the standard material, k is the wave number in vacuum, and d is the thickness of the material to be tested.

[0067] In summary, the embodiments of the present invention provide a testing system and method for the dielectric properties of materials in the terahertz band. The fabrication technology from the terahertz source to the terahertz detector is independently controllable, and it has the advantages of high system integration, high testing accuracy, low cost, and reliable and applicable testing system. It is of great significance for accurately determining the parameters of THz band materials and promoting the development of THz technology.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for testing the dielectric properties of materials using a terahertz band dielectric property testing system, characterized in that, The method includes: (1) Obtain the electrical signals of the standard material and the material to be tested at the same thickness respectively; wherein the electrical signals of the standard material and the material to be tested are measured by a terahertz band material dielectric property testing system; (2) Perform Fourier transform on the electrical signal of the standard material and the electrical signal of the material under test respectively to obtain the amplitude and phase of the terahertz wave after passing through the standard material and the material under test respectively; (3) The dielectric properties of the test material are calculated based on the amplitude and phase of the standard material and the test material; wherein the dielectric properties include the absorption coefficient and refractive index of the standard material; A testing system for the dielectric properties of materials in the terahertz band includes a laser, an optical beam splitter, a transmitter, a testing stage, a first reflector, a second reflector, a detector, and a signal processor; wherein: The testing station is located between the transmitter and the first reflector and is used to place the material to be tested. The laser emitted by the laser is split into two paths by the optical beam splitter. The first laser output enters the transmitter and is converted into a terahertz wave. The terahertz wave passes through the sample under test and is transmitted to the first reflector. After being reflected by the first reflector, it enters the detector. The second laser output enters the detector after being reflected by the second reflector. The laser output from the second path enters the detector and generates photogenerated carriers. The laser output from the first path enters the detector in the form of a terahertz wave and generates a bias voltage, so that the photogenerated carriers in the detector form a current or voltage. After being processed by the signal processor, the electrical signal of the material under test is obtained. The dielectric properties of the material under test are calculated using the following formula: In the formula, The absorption coefficient of the material to be tested is denoted as . The refractive index of the material to be tested is . The amplitude of the terahertz wave after passing through the standard material. The amplitude of the terahertz wave after passing through the material under test. This represents the phase of the terahertz wave after passing through the standard material. The phase of the terahertz wave after passing through the material under test. The refractive index of the standard material is... d is the wave number in vacuum, and d is the thickness of the material to be measured.

2. The method according to claim 1, characterized in that, The laser is an infrared laser, including a first infrared laser and a second infrared laser; wherein the frequency difference between the laser emitted by the first infrared laser and the second infrared laser is 0.1~10THz.

3. The method according to claim 2, characterized in that, The system also includes an optical mixer and an optical amplifier; wherein: The lasers emitted by the first infrared laser and the second infrared laser are mixed into one path by the optical mixer, amplified by the optical amplifier, and then transmitted to the optical beam splitter.

4. The method according to claim 2, characterized in that, The transmitter is an optical mixing terahertz transmitter.

5. The method according to claim 1, characterized in that, The laser is a femtosecond laser.

6. The method according to claim 5, characterized in that, The transmitter is a photoconductive antenna type terahertz transmitter.

7. The method according to claim 1, characterized in that, The detector is a photoconductive antenna without voltage bias.

8. The method according to claim 1, characterized in that, The amplitude and phase of the terahertz wave after passing through the standard material and the material under test are calculated using the following formula: In the formula, The electrical signal of the standard material. The electrical signal of the material under test. The amplitude of the terahertz wave after passing through the standard material. This represents the phase of the terahertz wave after passing through the standard material. The amplitude of the terahertz wave after passing through the material under test. This represents the phase of the terahertz wave after it passes through the material under test.

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