Method for simultaneously measuring the amplitude, polarization, and phase of terahertz waves

Abstract

The present invention discloses a method for simultaneously measuring the amplitude, polarization, and phase of a terahertz wave. The method comprises providing a terahertz field-effect heterodyne detector comprising n field-effect transistors and n antennas arranged in a regular polygonal configuration; placing the terahertz field-effect heterodyne detector in a heterodyne testing system; and simultaneously measuring and outputting multiple intermediate frequency voltages and phases of the terahertz wave, wherein the intermediate frequency voltage represents the amplitude of the measured intermediate frequency signal; and performing trigonometric function processing on the intermediate frequency voltage to obtain the polarization angle. The present invention can simultaneously measure the amplitude, polarization, and phase of a terahertz wave, and also simplifies the measurement system and reduces measurement costs.

Description

Technical Field

[0001] The present invention particularly relates to a method for simultaneously measuring the amplitude, polarization and phase of a terahertz wave, and belongs to the technical field of terahertz detection. Background Art

[0002] Terahertz wave is a section of electromagnetic spectrum resources that has not yet been widely used by humans. Its wavelength is roughly from 30μm to 3mm and its frequency range is between 0.1 and 10THz. It is also called submillimeter wave and far infrared wave.

[0003] Terahertz waves have high transmittance, low energy, fingerprint characteristics, high bandwidth, transient properties, coherence, and high resolution. For non-destructive testing, security imaging, and other travel and food safety fields, a high-speed, high-sensitivity, and portable terahertz 3D holographic imaging system is needed, which also puts forward stringent requirements on terahertz detectors. For unknown terahertz beams, it is hoped that more information covered by the electromagnetic wave can be measured at the same time, so that the beam can be better characterized and analyzed to obtain more information. At present, there is no detector that can measure the three types of information, namely amplitude, polarization, and phase, at the same time. The existing terahertz detectors need to be combined with polarizers or photoelectric crystals in a heterodyne detection system to obtain amplitude, polarization, and phase information at the same time. The system is complex and cumbersome, and it also increases the cost of detection. Summary of the Invention

[0004] The main purpose of the present invention is to provide a method for simultaneously measuring the amplitude, polarization and phase of a terahertz wave, thereby overcoming the deficiencies in the prior art.

[0005] To achieve the aforementioned object of the invention, the technical solutions adopted by the present invention include:

[0006] An embodiment of the present invention provides a method for simultaneously measuring the amplitude, polarization, and phase of a terahertz wave, including:

[0007] A terahertz field-effect heterodyne detector is provided. The terahertz field-effect heterodyne detector includes n field-effect transistors and n groups of antennas. Each group of antennas cooperates with a field-effect transistor. The n groups of antennas are arranged in a regular polygon, and a selected edge of the regular polygon is arranged along the x-axis direction of a three-dimensional coordinate system. The y-axis direction of the three-dimensional coordinate system is designated as a zero polarization angle.

[0008] The terahertz field effect heterodyne detector is placed in a heterodyne test system, so that the local oscillator terahertz wave and the measured terahertz wave are incident on n groups of antennas of the terahertz field effect heterodyne detector along the z-axis direction of the three-dimensional coordinate system, and the heterodyne test system directly obtains n groups of intermediate frequency signals of the local oscillator terahertz wave and the measured terahertz wave with amplitudes of V1, V2, ..., V n, the phase of n groups of intermediate frequency signals is

[0009] The polarization angle θ of the measured terahertz wave is calculated by simultaneously solving at least three equations in the following equation group:

[0010]

[0011] in, is the medium frequency AC current, It is the maximum intermediate frequency current when the polarization direction of the detector antenna is parallel to the polarization direction of the terahertz wave, n≥3, 3≤m≤n, and m and n are both positive integers.

[0012] Compared with the prior art, the advantages of the present invention include:

[0013] 1) An embodiment of the present invention provides a method for simultaneously measuring the amplitude, polarization, and phase of a terahertz wave. This method has a wide range of applicability to field-effect detectors and is applicable to a variety of antenna types and transistor structures.

[0014] 2) The embodiment of the present invention provides a method for simultaneously measuring the amplitude, polarization and phase of a terahertz wave, which also simplifies the measurement system and reduces the measurement cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a schematic structural diagram of a terahertz field effect heterodyne detector provided in a typical embodiment of the present invention;

[0016] Figure 2 yes Figure 1 A partial enlarged view of the structure A;

[0017] Figure 3 1 is a schematic cross-sectional view of a field effect transistor detector provided in a typical embodiment of the present invention;

[0018] Figure 4 It is a structural diagram of a heterodyne test system;

[0019] Figure 5 It is a circuit structure diagram of a terahertz field-effect heterodyne detector and a low-noise amplifier (LNA) in a typical implementation case of the present invention. DETAILED DESCRIPTION

[0020] In view of the shortcomings of the prior art, the inventors of this case, after long-term research and extensive practice, have proposed the technical solution of the present invention. The following will further explain this technical solution, its implementation process and principles.

[0021] An embodiment of the present invention provides a method for simultaneously measuring the amplitude, polarization, and phase of a terahertz wave, including:

[0022] A terahertz field-effect heterodyne detector is provided. The terahertz field-effect heterodyne detector includes n field-effect transistors and n groups of antennas. Each group of antennas cooperates with a field-effect transistor. The n groups of antennas are arranged in a regular polygon, and a selected edge of the regular polygon is arranged along the x-axis direction of a three-dimensional coordinate system. The y-axis direction of the three-dimensional coordinate system is designated as a zero polarization angle.

[0023] The terahertz field effect heterodyne detector is placed in a heterodyne test system, so that the local oscillator terahertz wave and the measured terahertz wave are incident on n groups of antennas of the terahertz field effect heterodyne detector along the z-axis direction of the three-dimensional coordinate system, and the heterodyne test system directly obtains n groups of intermediate frequency signals of the local oscillator terahertz wave and the measured terahertz wave with amplitudes of V1, V2, ..., V n , the phase of n groups of intermediate frequency signals is

[0024] The polarization angle θ of the measured terahertz wave is calculated by simultaneously solving at least three equations in the following equation group:

[0025]

[0026] in, is a medium frequency alternating current, n≥3, 3≤m≤n, and both m and n are positive integers.

[0027] In a specific embodiment, the n groups of intermediate frequency signal amplitudes V1, V2, ..., V of the local oscillator terahertz wave and the measured terahertz wave are: n There is a maximum value if and only if (k is a natural number), |V n |The maximum value can be obtained; it should be noted that the heterodyne test system outputs multiple sets of intermediate frequency signal amplitudes. When the maximum value of the multiple sets of intermediate frequency signal amplitudes is taken for imaging, the signal-to-noise ratio is higher, which is more conducive to achieving three-dimensional imaging.

[0028] In a specific embodiment, the phases of the n groups of intermediate frequency signals of the local oscillator terahertz wave and the measured terahertz wave are are all equal.

[0029] In a specific embodiment, the intermediate frequency signal amplitudes and phases of the local oscillator terahertz wave and the measured terahertz wave are directly output by a lock-in amplifier or an IQ mixer in a heterodyne test system.

[0030] In a specific embodiment, the polarization angle of the local oscillator terahertz wave is known and can be any known value, and the polarization angle of the local oscillator terahertz wave is independent of the polarization angle of the measured terahertz wave.

[0031] In a specific implementation, the n groups of antennas are arranged in a regular n-gon, and each group of antennas is correspondingly arranged on a side of the regular n-gon.

[0032] In a specific embodiment, the n field effect transistors and the n groups of antennas coordinated therewith are arranged in a regular n-gon, and each field effect transistor and the group of antennas coordinated therewith are arranged on one side of the regular n-gon.

[0033] In a specific embodiment, the antenna includes a source antenna, a drain antenna and a gate antenna that cooperate with the field effect transistor, the source antenna and the drain antenna are located on the same straight line, the gate antenna is parallel to the source antenna, and the source antenna, the drain antenna and the gate antenna are electrically connected to the source, drain and gate of the field effect transistor respectively.

[0034] In a specific embodiment, the field effect transistor includes but is not limited to any one of MOSFET, FINFET, MESFET, and HEMT.

[0035] In a specific embodiment, the antenna includes but is not limited to any one of a butterfly antenna, a dipole antenna, and a patch antenna.

[0036] In a specific embodiment, the method for simultaneously measuring the amplitude, polarization and phase of a terahertz wave includes: placing a terahertz field-effect heterodyne detector between a low-noise amplifier and an off-axis parabolic mirror of a heterodyne test system, and connecting the terahertz field-effect heterodyne detector to the low-noise amplifier.

[0037] The technical solution, its implementation process and principles will be further explained below in conjunction with the accompanying drawings and specific implementation cases. It should be noted that the terahertz field effect heterodyne detector and heterodyne test system used in the embodiments of the present invention are well known to those skilled in the art.

[0038] An embodiment of the present invention provides a method for simultaneously measuring the amplitude, polarization, and phase of a terahertz wave. The method is implemented using a specific terahertz field-effect heterodyne detector in a heterodyne test system. The terahertz field-effect heterodyne detector (referred to as a detector) is composed of an antenna and a field-effect transistor (referred to as a transistor) matched thereto. Specifically, the terahertz field-effect heterodyne detector includes n (n≥3) field-effect transistors and n groups of antennas corresponding one to one with the n field-effect transistors. The n groups of antennas are distributed in a regular polygonal pattern, and each group of antennas includes a drain antenna, a source antenna, and a gate antenna. The terahertz field-effect heterodyne detector is placed in the heterodyne test system. The terahertz field-effect heterodyne detector can simultaneously measure and output multiple groups of intermediate frequency voltages and phases of terahertz waves (including local oscillator terahertz waves and measured terahertz waves), where the intermediate frequency voltage represents the amplitude of the measured intermediate frequency signal. The polarization angle can be obtained by performing trigonometric function processing on the intermediate frequency voltage (the zero polarization angle must be defined first).

[0039] Example 1

[0040] The following describes a method for simultaneously measuring the amplitude, polarization, and phase of a terahertz wave, taking a terahertz field-effect heterodyne detector comprising three field-effect transistors and three antennas (i.e., n=3, m=3) as an example.

[0041] 1) Provide terahertz field effect heterodyne detectors, such as Figure 1 and Figure 2 As shown, the terahertz field effect heterodyne detector includes three field effect transistors and three groups of antennas. Each group of antennas cooperates with a field effect transistor. The three groups of antennas are arranged in a triangle, wherein each group of antennas is composed of a three-petal quarter-wavelength dipole antenna, namely a source antenna, a drain antenna and a gate antenna. Figure 2 and Figure 3 , the source antenna and the drain antenna are electrically connected through the two-dimensional electron gas, and the dotted area in the figure is the active area of ​​the two-dimensional electron gas; it can be understood that the terahertz field-effect heterodyne detector includes three field-effect transistor detectors, and illustratively, the field-effect transistors can be AlGaN / GaN transistors, etc.;

[0042] The working mechanism of the field-effect transistor detector is as follows: when the incident terahertz wave is incident perpendicularly on the antenna, the antenna generates an induced electric field after receiving the terahertz wave. The induced electric field is localized in the gate-controlled region and simultaneously applies an operating gate voltage to the gate, which optimizes the signal-to-noise ratio. At this point, the induced electric field can effectively regulate the two-dimensional electron gas at the interface between the barrier layer and the channel layer, changing the concentration and migration speed of the electron gas, thereby generating a photoresponse current along the source-drain direction. The self-mixing submillimeter wave photoelectric response obtained earlier is:

[0043]

[0044] Among them, P THz is the incident power of the terahertz wave, μ is the electron mobility, n is the two-dimensional electron gas concentration, W and L are the gate width and length respectively, is the effective distance between the gate and the two-dimensional electron gas, S A Represents the effective area of ​​the antenna, dn / dV g It is the field effect factor, which is used to characterize the gate voltage control capability of the transistor. and They represent the electric field enhancement factors of the terahertz antenna (i.e., antenna) in the horizontal direction (i.e., the x-axis direction of the three-dimensional coordinate system) and the vertical direction (i.e., the z-axis direction of the three-dimensional coordinate system), respectively. V and φ represent the free space impedance (377Ω) and the phase difference of the horizontal and vertical electric fields, respectively.

[0045] The detector internal resistance r can be expressed as:

[0046]

[0047] Define the mixing factor Λ (dimension is cm) and the two-dimensional electron gas field effect factor Ξ (dimension V -1 cm -2 )

[0048]

[0049] Of course, the field effect self-mixing detection theory is also applicable to heterodyne mixing detection;

[0050] When a frequency is f LO , power is P LO The local oscillator terahertz wave with a frequency of f THz , power is P THz When the measured terahertz waves are incident on the detector at the same time, a transverse electric field is formed in the two-dimensional electron gas channel in the near field area of ​​the antenna. and longitudinal electric field It will also form a horizontal and vertical of the terahertz electric field.

[0051] The total response photocurrent i T Including DC photocurrent generated by self-mixing and frequency ω IF =|ω-ω LO |Heterodyne Mixed AC Current

[0052]

[0053] Since the butterfly antenna is evolved from the dipole antenna, its antenna lobe length AL can be obtained according to equations 1), 2), and 3:

[0054] AL=λ eff / 2 8)

[0055]

[0056] λ0=c / f010)

[0057] Where f0 is the antenna resonant center frequency, ε eff is the effective dielectric constant of the detector device. Equation 1) is only applicable to conventional butterfly antenna structures with very small coplanar stripline lengths. From the above formula, it can be seen that as the antenna lobe length increases, its central resonant frequency f0 must decrease. The specific antenna dimensions are obtained from electromagnetic simulation software. In this embodiment, the center frequency f0 of the antenna is 220 GHz, the gate length of the transistor is L = 0.6 μm, the gate width is W = 6.5 μm, and the gate-drain spacing is equal to the source-drain spacing D gs =D gd =0.6μm.

[0058] 2) Please refer to Figure 4 , the terahertz field effect heterodyne detector is placed as follows Figure 4 In the heterodyne test system shown, the heterodyne system includes a heterodyne optical path, a local oscillator source, a source to be measured, a frequency doubling link (including frequency doubling link #1 and frequency doubling link #2), a power divider (including power divider #1 and power divider #2), a power amplifier (PA), a phase-locked loop (PLL*N), a filter, a phase-locked amplifier and a low-noise amplifier, etc.; a selected edge of the regular triangle is set along the x-axis direction of a three-dimensional coordinate system, and the y-axis direction of the three-dimensional coordinate system is designated as a zero polarization angle.

[0059] 3) The terahertz wave is incident on n groups of antennas of the terahertz field-effect heterodyne detector along the z-axis direction of the three-dimensional coordinate system, and the n groups of intermediate frequency signal amplitudes and phases of the terahertz wave are directly obtained by the heterodyne test system, and the intermediate frequency voltage is processed by trigonometric functions to obtain the polarization angle.

[0060] In this embodiment, the local oscillator (LO) is provided by a microwave source (SMR-20) with an output frequency of 9 to 14 GHz and a power of 5 dBm. The source under test is provided by a microwave source (SMR-100) with an output frequency of 9 to 14 GHz and a power of 5 dBm. The LO and the source under test are correlated via a 10 MHz reference signal. The LO and the source under test are split into two paths by power splitters #1 and #2, respectively:

[0061] One way, through the mixer, the local oscillator signal and the measured signal are mixed and then enter the power amplifier. The mixed output signal is amplified and then enters the phase-locked loop to perform N=18 frequency multiplication. The multiplied signal is input to the phase-locked amplifier (Lock-in 7265) as a reference signal (frequency is f Ref , power is P Ref );

[0062] On the other hand, the local oscillator drives the frequency multiplication link #1 (VDI) with a multiplication factor of N=18, and transmits the frequency f through the front-end horn antenna. LO =162~252GHz terahertz beam, after collimation by off-axis parabolic mirror (OAP#1), the measured source drives the frequency multiplication link #2 (VDI) with a multiplication factor of N=18, and transmits the frequency f through the front horn antenna THz = The terahertz beam of 162 to 252 GHz is collimated by an off-axis parabolic mirror (OAP#2), and the two beams pass through a beam splitter and are finally converged by an off-axis parabolic mirror (OAP#3) onto a terahertz field-effect heterodyne detector.

[0063] In heterodyne mixing, a low-noise amplifier is generally used to amplify the detector output signal, which is then read out by a lock-in amplifier. The circuit of the terahertz field-effect heterodyne detector and the low-noise amplifier (LNA) is as follows: Figure 5 As shown, where R g represents the gate series resistance, V g represents the applied gate voltage. The output voltage of the terahertz field-effect heterodyne detector is related to the input impedance of the voltage preamplifier. The input impedance of the LNA is Z0 = 50Ω, and the gain is G. The amplitude of the intermediate frequency signal input from the terahertz field-effect heterodyne detector to the LNA is:

[0064]

[0065] The amplitude of the intermediate frequency signal output by the lock-in amplifier is:

[0066]

[0067] When the terahertz light spot converges at the center of the chip, the terahertz wave power received by the three field-effect transistor detectors distributed in a regular triangle is equal. Ignoring the error caused by the preparation process, the intermediate frequency AC current generated by the three field-effect transistor detectors is After passing through the LNA, the intermediate frequency signals output by the phase-locked amplifier are V1, V2, and V3, and the phase-locked amplifier outputs equal phases.

[0068] Specifically, the vertical direction (z-axis direction of the three-dimensional coordinate system) is defined as the polarization zero point (θ=0°). Due to the triangular distribution of the three field effect transistor detectors, the intermediate frequency AC generated by them is There are the following relationships:

[0069]

[0070] The simultaneous use of formulas 13), 14), and 15) can determine a unique θ value, and thus measure the polarization information of the terahertz wave being measured.

[0071] Example 2

[0072] A method for simultaneously measuring the amplitude, polarization, and phase of a terahertz wave in this embodiment is substantially the same as that in Example 1, except that: the terahertz field-effect heterodyne detector in this embodiment includes a terahertz field-effect heterodyne detector comprising five field-effect transistors and five antennas (i.e., n=5, m=3, 4, 5), and the five antennas are arranged in a regular pentagon;

[0073] When the terahertz light spot converges at the center of the chip, the terahertz wave power received by the five field-effect transistor detectors distributed in a regular pentagon is equal. Ignoring the error caused by the preparation process, the medium-frequency AC current generated by the five field-effect transistor detectors is After passing through the LNA, the intermediate frequency signals output by the lock-in amplifier are V1, V2, V3, V4, and V5. The lock-in amplifier can output equal phases.

[0074] Specifically, the vertical direction (the y-axis direction of the three-dimensional coordinate system) is defined as the polarization zero point (θ = 0°). Due to the triangular distribution of the three field effect transistor detectors, the intermediate frequency AC generated by them is There are the following relationships:

[0075]

[0076]

[0077] By combining any three of formulas 16), 17), 18), 19), and 20), a unique θ value can be determined, and the polarization information of the measured terahertz wave can be measured.

[0078] An embodiment of the present invention provides a method for simultaneously measuring the amplitude, polarization, and phase of a terahertz wave. The method has a wide range of applicability to field-effect detectors and is applicable to various antenna types and various transistor structures. Furthermore, the embodiment of the present invention provides a method for simultaneously measuring the amplitude, polarization, and phase of a terahertz wave, simplifies the measurement system, and reduces measurement costs.

[0079] It should be understood that the above embodiments are merely illustrative of the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit and substance of the present invention are intended to be encompassed within the scope of protection of the present invention.

Claims

1. A method for simultaneously measuring the amplitude, polarization, and phase of a terahertz wave, characterized in that: include: A terahertz field-effect heterodyne detector is provided. The terahertz field-effect heterodyne detector includes n field-effect transistors and n groups of antennas. Each group of antennas cooperates with a field-effect transistor. The n groups of antennas are arranged in a regular polygon, and a selected edge of the regular polygon is arranged along the x-axis direction of a three-dimensional coordinate system. The y-axis direction of the three-dimensional coordinate system is designated as a zero polarization angle. The terahertz field effect heterodyne detector is placed in a heterodyne test system, so that the local oscillator terahertz wave and the measured terahertz wave are incident on n groups of antennas of the terahertz field effect heterodyne detector along the z-axis direction of the three-dimensional coordinate system, and the heterodyne test system directly obtains n groups of intermediate frequency signals of the local oscillator terahertz wave and the measured terahertz wave with amplitudes of V1, V2, ..., V n , the phase of n groups of intermediate frequency signals is The polarization angle θ of the measured terahertz wave is calculated by simultaneously solving at least three equations in the following equation group: in, is the medium frequency AC current, It is the maximum intermediate frequency current when the polarization direction of the detector antenna is parallel to the polarization direction of the terahertz wave, n≥3, 3≤m≤n, and m and n are both positive integers.

2. The method for simultaneously measuring the amplitude, polarization, and phase of a terahertz wave according to claim 1, wherein: n groups of intermediate frequency signal amplitudes V1, V2, ..., V n There is a maximum value if and only if When |V n |The maximum value can be obtained, k is a natural number.

3. The method for simultaneously measuring the amplitude, polarization, and phase of a terahertz wave according to claim 1, wherein: n groups of intermediate frequency signal phases are all equal.

4. The method for simultaneously measuring the amplitude, polarization, and phase of a terahertz wave according to claim 1, wherein: The intermediate frequency signal amplitudes and phases of the local oscillator terahertz wave and the measured terahertz wave are directly output by a lock-in amplifier or an IQ mixer in a heterodyne test system. In addition, the polarization angle of the local oscillator terahertz wave is known and is independent of the polarization angle of the measured terahertz wave.

5. The method for simultaneously measuring the amplitude, polarization, and phase of a terahertz wave according to claim 1, wherein: The n groups of antennas are arranged in a regular n-gon, and each group of antennas is correspondingly arranged on one side of the regular n-gon.

6. The method for simultaneously measuring the amplitude, polarization, and phase of a terahertz wave according to claim 1 or 5, characterized in that: The n field effect transistors and the n groups of antennas matched therewith are arranged in a regular n-gon, and each field effect transistor and the group of antennas matched therewith are arranged on one side of the regular n-gon.

7. The method for simultaneously measuring the amplitude, polarization, and phase of a terahertz wave according to claim 6, wherein: The antenna includes a source antenna, a drain antenna and a gate antenna that cooperate with the field effect transistor. The source antenna and the drain antenna are located on the same straight line, and the gate antenna is parallel to the source antenna. The source antenna, the drain antenna and the gate antenna are electrically connected to the source, the drain and the gate of the field effect transistor respectively.

8. The method for simultaneously measuring the amplitude, polarization, and phase of a terahertz wave according to claim 1, wherein: The field effect transistor includes any one of MOSFET, FINFET, MESFET, and HEMT.

9. The method for simultaneously measuring the amplitude, polarization, and phase of a terahertz wave according to claim 1, wherein: The antenna includes any one of a butterfly antenna, a dipole antenna, and a patch antenna.

10. The method for simultaneously measuring the amplitude, polarization and phase of a terahertz wave according to claim 1, wherein: include: The terahertz field effect heterodyne detector is placed between a low noise amplifier and an off-axis parabolic mirror of a heterodyne test system, and the terahertz field effect heterodyne detector is connected to the low noise amplifier.

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