Optical fiber type terahertz photoconductive antenna

Abstract

The invention provides an optical fiber type terahertz photoconductive antenna, and the antenna comprises an optical fiber splitter which is used for connecting an optical fiber, converting a single-path optical signal in the optical fiber into N-path optical signals, and outputting the N-path optical signals; the micro-lens array is fixed at the output end of the optical fiber splitter and is used for converging the N paths of optical signals output by the optical fiber splitter to a light guide excitation region of the terahertz antenna chip; and the terahertz antenna chip radiates terahertz signals based on the N paths of optical signals. Wherein the micro lens array comprises N micro lens units, the terahertz antenna chip comprises a terahertz antenna array unit, and the terahertz antenna array unit comprises N terahertz antenna arrays which are connected in parallel. According to the optical fiber type terahertz photoconductive antenna, combined photocurrent signals are generated through N terahertz antenna arrays which are connected in parallel, so that the terahertz output power under the same optical power input is improved by N times, and the photoelectric conversion efficiency is further improved.

Description

Technical Field

[0001] This invention relates to the field of radio antennas, and in particular to a fiber optic terahertz photoconductive antenna. Background Technology

[0002] Terahertz waves typically refer to electromagnetic waves with frequencies in the range of (0.1 to 10) THz. Terahertz waves occupy a very special position in the electromagnetic spectrum and have unique properties such as broadband, directionality, selective transmission and penetration, and fingerprint characteristics. Therefore, radio measurement systems based on the terahertz principle have high application value in broadband communication, medical imaging, non-destructive testing, security inspection and other fields.

[0003] Terahertz generating devices are the core functional components of terahertz systems. In the low-frequency band, they are mainly achieved through electronic frequency doubling, while in the high-frequency band, they are mainly achieved through photonic methods, such as free-electron lasers, photoconductive effects, optical rectification effects, and electro-optic effects. In systems with high integration requirements, fiber optic terahertz photoconductive antennas are currently the most commonly used type of terahertz generating device, and they have been widely used in terahertz spectrometers and terahertz imagers.

[0004] Traditional terahertz photoconductive antennas use a single antenna element, and their photoelectric conversion efficiency is limited by the semiconductor substrate material that makes up the terahertz photoconductive antenna chip. This results in low power of the radiated terahertz waves and low electromagnetic conversion efficiency, which greatly restricts the development and technological progress of terahertz photoconductive antennas. Summary of the Invention

[0005] This invention provides a fiber-optic terahertz photoconductive antenna, comprising:

[0006] A fiber optic splitter is used to connect optical fibers and convert a single optical signal in the fiber into N optical signals for output.

[0007] A microlens array, fixed at the output end of a fiber optic splitter, is used to converge the N optical signals output by the fiber optic splitter to the photoconductive excitation region of the terahertz antenna chip.

[0008] Terahertz antenna chip, based on N optical signals, radiates terahertz signals.

[0009] Furthermore, the microlens array includes N microlens units, and the centers of the N microlens units correspond one-to-one with the output positions of the N optical signals.

[0010] Furthermore, the terahertz antenna chip includes: a terahertz chip substrate, a terahertz antenna array unit, and a microstrip patch antenna, wherein the terahertz antenna array unit and the microstrip patch antenna are fabricated on the surface of the terahertz chip substrate.

[0011] Furthermore, the terahertz antenna array unit is used to generate the combined photocurrent signal, including: N terahertz antenna arrays connected in parallel, and the N terahertz antenna arrays connected in parallel are arranged in a one-to-one correspondence with the N microlens units.

[0012] Furthermore, the terahertz antenna array includes, in sequence, terahertz generating electrodes, an impedance converter, and terahertz power supply electrodes.

[0013] in,

[0014] The terahertz generating electrode is used to apply a DC bias voltage to the photoconductive excitation region;

[0015] Impedance transformers are used to achieve impedance matching and reduce signal reflection;

[0016] The terahertz power supply electrode is used to supply power to the terahertz generating electrode.

[0017] Furthermore, the impedance transformer is a quarter-impedance transformer.

[0018] Furthermore, the quarter-impedance converter is connected to a sector line, and the radius of the sector line is one-quarter of the wavelength of the N optical signals.

[0019] Furthermore, the fiber optic terahertz photoconductive antenna also includes a terahertz focusing lens, used to focus the terahertz signal radiated by the terahertz antenna chip.

[0020] Furthermore, the terahertz focusing lens has a bullet-shaped structure, which includes a sub-hemispherical and a cylindrical shape. The terahertz antenna chip is located at the center of the bullet-shaped structure and is fixed with UV adhesive.

[0021] Furthermore, the terahertz focusing lens is made of high-resistivity single-crystal silicon.

[0022] This invention provides a fiber-optic terahertz photoconductive antenna. The fiber optic splitter converts a single optical signal in the optical fiber into N optical signals and outputs them. The microlens array converges the N optical signals to the photoconductive excitation region of the terahertz antenna chip through N microlens units. The N parallel terahertz antenna arrays generate a combined photocurrent signal. By utilizing the characteristic that the terahertz photoconductive antenna is similar to a current source, the terahertz output power is increased by N times under the same optical power input, thereby improving the photoelectric conversion efficiency.

[0023] In addition, the impedance transformer in the terahertz antenna array is a quarter impedance transformer, which is used to achieve impedance matching and reduce signal reflection.

[0024] In addition, the quarter-impedance transformer is connected to a sector line to prevent the DC bias circuit from affecting the impedance characteristics of various parts of the AC circuit.

[0025] In addition, the terahertz focusing lens has a bullet-shaped structure, which includes a sub-hemispherical and a cylindrical part. The terahertz antenna chip is set at the center of the bullet-shaped structure and fixed with ultraviolet glue to achieve a better terahertz focusing effect.

[0026] In addition, the terahertz focusing lens is made of high-resistivity single-crystal silicon to minimize the loss of terahertz radiation when it passes through the lens.

[0027] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description, claims, and accompanying drawings. Attached Figure Description

[0028] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings:

[0029] Figure 1 This is a schematic diagram of the structure of a fiber-optic terahertz photoconductive antenna according to an embodiment of the present invention;

[0030] Figure 2 This is a schematic diagram of the structure of a terahertz antenna chip in a fiber-optic terahertz photoconductive antenna according to an embodiment of the present invention.

[0031] Figure 3 This is a schematic diagram showing a simulation comparison of the radiation power of a fiber optic terahertz photoconductive antenna according to an embodiment of the present invention and an existing single-antenna fiber optic terahertz photoconductive antenna at different radiation angles.

[0032] Figure label:

[0033] 1: Fiber optic splitter; 2: Microlens array; 3: Terahertz antenna chip; 4: Terahertz focusing lens; 31: Optical guide excitation region; 32: Terahertz chip substrate; 33: Terahertz antenna array unit; 33': Terahertz antenna array; 34: Microstrip patch antenna; 331: Terahertz generating electrode; 332: Impedance converter; 333: Terahertz power supply electrode; 334: Sector line. Detailed Implementation

[0034] To address the technical issues of low output power and low electromagnetic conversion efficiency of terahertz photoconductive antennas, an optical fiber terahertz photoconductive antenna is provided.

[0035] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention. Furthermore, the embodiments and features in the embodiments of the present invention can be combined with each other without conflict.

[0036] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of the embodiments of the present invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments described herein can be implemented in a sequence other than that illustrated or described herein.

[0037] like Figure 1 As shown, the fiber optic terahertz photoconductive antenna provided in this embodiment of the invention is described in [reference needed]. Figure 1 The fiber-optic terahertz photoconductive antenna includes:

[0038] Fiber optic splitter 1 is used to connect optical fibers and convert a single optical signal in the optical fiber into N optical signals and output them, where N ≥ 2 and is a natural number.

[0039] The terahertz photoconductive antenna is fiber optic and the terahertz substrate material is InGaAs.

[0040] Specifically, the center wavelength of fiber optic splitter 1 is 1550nm.

[0041] Specifically, the fiber optic splitter 1 is a 1×N splitting structure, used to split a single optical signal into N channels with the same power ratio, and the optical path lengths of the N optical signals are the same, thereby ensuring that the phases of the corresponding N optical currents are the same when they are combined.

[0042] This embodiment takes N=2 and both the single-channel optical signal and the N-channel optical signal as laser signals as an example. Those skilled in the art should understand that N can also be other natural numbers greater than 2, and the single-channel optical signal and the N-channel optical signal can also be other optical signals. This application does not limit them in this regard.

[0043] The microlens array 2 is fixed at the output end of the fiber optic splitter 1 and is used to converge the N optical signals output by the fiber optic splitter 1 and converge the N optical signals to the photoconductive excitation region 31 of the terahertz antenna chip 3.

[0044] Specifically, the microlens array 2 includes N microlens units, the centers of which correspond one-to-one with the output positions of the N optical signals output by the fiber optic splitter 1, thereby focusing the N optical signals onto the photoconductive excitation region 31 of the terahertz antenna chip with a suitable focal length.

[0045] Furthermore, the N microlens units have the same structure, all being hemispherical.

[0046] Terahertz antenna chip 3, based on N-channel optical signal radiating terahertz signal.

[0047] Specifically, Figure 2 This is a schematic diagram of the structure of a terahertz antenna chip in a fiber-optic terahertz photoconductive antenna according to an embodiment of the present invention. See also... Figure 2 The terahertz antenna chip 3 includes: a terahertz chip substrate 32, a terahertz antenna array unit 33, and a microstrip patch antenna 34.

[0048] Furthermore, the terahertz chip substrate 31 is an InGaAs substrate. The InGaAs substrate generates photogenerated carriers under the excitation of a 1550nm wavelength laser and changes from a high-resistance state to a conducting state based on the photoconductive effect.

[0049] The surface of the terahertz chip substrate 32 is used to fabricate the terahertz antenna array unit 33 and the microstrip patch antenna 34.

[0050] Furthermore, the terahertz antenna array unit 33, used to generate the combined photocurrent signal, includes: N terahertz antenna arrays 33' connected in parallel, and the N terahertz antenna arrays 33' connected in parallel are arranged in a one-to-one correspondence with the N microlens units.

[0051] The essence of a terahertz photoconductive antenna is similar to that of a current source. Taking 500 GHz as an example, the simulated input impedance of a terahertz antenna array element 32 with N=2 is 23+j12Ω, and the simulated input impedance of a terahertz antenna array element 32 with N=1 is 26+j14Ω. For two devices with similar resistance values, the power is proportional to the square of the current. N terahertz antenna arrays can increase the radiated power by N. 2 Because the fiber optic splitter 1 causes the laser power received by each terahertz antenna array to be 1 / N of the original laser power, the overall radiated power of the terahertz antenna array element 32 increases by 1 / N×N. 2＝ N times.

[0052] Figure 3 This diagram illustrates a simulation comparison of the radiated power of a fiber-optic terahertz photoconductive antenna according to an embodiment of the present invention and a conventional single-antenna fiber-optic terahertz photoconductive antenna at different radiation angles. (See attached diagram.) Figure 3Simulation results show that in the radiation direction with a Theta angle of 0°, the radiated power of the terahertz antenna array unit 33 with two terahertz antenna arrays 33' provided in this embodiment is approximately 5.4 dB higher than that of a single-antenna fiber-optic terahertz photoconductive antenna. Furthermore, within the Theta angle range of -30° to 30°, the radiated power of the terahertz antenna array unit 33 with two terahertz antenna arrays 33' provided in this embodiment is significantly higher than that of a single-antenna fiber-optic terahertz photoconductive antenna. Considering the chip dielectric loss and other system losses, the power amplification effect is basically consistent with the theoretically calculated effect.

[0053] Furthermore, the microstrip patch antenna 34 is connected to the terahertz antenna array element 33 via a 50Ω microstrip line.

[0054] In this embodiment, for signals near 500 GHz and an InGaAs substrate material with a thickness of 100 μm, the microstrip patch antenna 34 has a size of 110 μm * 40 μm.

[0055] The terahertz antenna array 33' includes a terahertz generating electrode 331, an impedance converter 332, and a terahertz power supply electrode 333 arranged sequentially.

[0056] The terahertz generating electrode 331 is used to apply a DC bias voltage to the photoconductive excitation region 31. It includes a dipole antenna structure. The dipole gap 25um in the dipole antenna structure constitutes the photoconductive excitation region 31. When the photoconductive excitation region 31 is subjected to bias voltage and laser excitation, it generates photogenerated carriers and forms a photocurrent.

[0057] The spacing between the terahertz generating electrodes 331 of adjacent terahertz antenna arrays 33' is the same as the spacing between the output beams of the fiber optic splitter 1.

[0058] Impedance transformer 332 is a quarter impedance transformer 332, used to achieve impedance matching and reduce signal reflection.

[0059] The quarter-impedance converter 332 is connected to the sector line 334 to prevent the DC bias circuit from affecting the impedance characteristics of various parts of the AC circuit. The radius of the sector line 334 is one-quarter of the wavelength of the optical signal, and the connection point is equivalent to a short circuit to the AC. When connected to the quarter-wavelength converter, it is equivalent to an open circuit to the AC at the connection point of the quarter-impedance line.

[0060] The terahertz power supply electrode 333 is used to supply power to the terahertz generating electrode 331. In this embodiment, the voltage of the coaxial cable is output to the terahertz power supply electrode 333 by means of gold wire bonding.

[0061] The fiber-optic terahertz photoconductive antenna further includes:

[0062] Terahertz focusing lens 4 is used to focus the terahertz signal radiated by terahertz antenna chip 3.

[0063] If the sample volume is small and the emitted terahertz signal is not focused, the energy of the terahertz signal radiated to the sample surface will be very small due to the large divergence angle during the outward radiation process. Therefore, it is necessary to use a terahertz focusing lens 4 to focus the terahertz signal generated by the terahertz antenna chip 3 before radiating it outward.

[0064] Specifically, the terahertz focusing lens 4 has a bullet-shaped structure, which is composed of a sub-hemispherical and a cylinder. The terahertz antenna chip 3 is set at the center of the bullet-shaped structure and fixed with ultraviolet glue to achieve a better terahertz focusing effect.

[0065] Specifically, the terahertz focusing lens 4 is made of high-resistivity single-crystal silicon, which has minimal absorption of terahertz radiation, thus minimizing the loss of terahertz radiation when it passes through the terahertz focusing lens 4.

[0066] In summary, the fiber optic terahertz photoconductive antenna provided in this embodiment of the invention uses a fiber optic splitter 1 to convert a single optical signal in the optical fiber into N optical signals and output them. A microlens array 2 uses N microlens units to converge the N optical signals to the photoconductive excitation region 31 of the terahertz antenna chip 3. The N parallel terahertz antenna arrays 33' generate a combined photocurrent signal. By utilizing the characteristic that the terahertz photoconductive antenna is similar to a current source, the terahertz output power is increased by N times under the same optical power input, thereby improving the photoelectric conversion efficiency.

[0067] In addition, the impedance transformer 332 in the terahertz antenna array 33' is a quarter impedance transformer 332, which is used to achieve impedance matching and reduce signal reflection.

[0068] In addition, the quarter-impedance transformer 332 is connected to the sector line 334 to prevent the DC bias circuit from affecting the impedance characteristics of various parts of the AC circuit.

[0069] In addition, the terahertz focusing lens 4 has a bullet-shaped structure, which includes a sub-hemispherical and a cylinder. The terahertz antenna chip 3 is set at the center of the bullet-shaped structure and fixed with ultraviolet glue to achieve a better terahertz focusing effect.

[0070] In addition, the terahertz focusing lens 4 is made of high-resistivity single-crystal silicon to minimize the loss of terahertz radiation when it passes through the terahertz focusing lens 4.

[0071] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the invention.

[0072] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A fiber-optic terahertz photoconductive antenna, characterized in that, include: Fiber optic splitter (1) is used to connect optical fibers and convert a single optical signal in the optical fiber into N optical signals and output them. A microlens array (2) is fixed at the output end of the fiber optic splitter (1) and is used to converge the N optical signals output by the fiber optic splitter (1) to the optical guide excitation area (31) of the terahertz antenna chip (3). Terahertz antenna chip (3) radiates terahertz signals based on N optical signals.

2. The fiber-optic terahertz photoconductive antenna according to claim 1, characterized in that, The microlens array (2) includes N microlens units, and the centers of the N microlens units correspond one-to-one with the output positions of the N optical signals.

3. The fiber-optic terahertz photoconductive antenna according to claim 2, characterized in that, The terahertz antenna chip (3) includes: a terahertz chip substrate (32), a terahertz antenna array unit (33), and a microstrip patch antenna (34), wherein the terahertz antenna array unit (33) and the microstrip patch antenna (34) are fabricated on the surface of the terahertz chip substrate (32).

4. The fiber-optic terahertz photoconductive antenna according to claim 3, characterized in that, The terahertz antenna array unit (33) is used to generate combined photocurrent signals, including: N terahertz antenna arrays (33') connected in parallel, and the N terahertz antenna arrays (33') are arranged in a one-to-one correspondence with the N microlens units.

5. The fiber-optic terahertz photoconductive antenna according to claim 4, characterized in that, The terahertz antenna array (33') includes a terahertz generating electrode (331), an impedance transformer (332), and a terahertz power supply electrode (333) arranged sequentially. in, The terahertz generating electrode (331) is used to apply a DC bias voltage to the photoconductive excitation region (31); The impedance transformer (332) is used to achieve impedance matching and reduce signal reflection; The terahertz power supply electrode (333) is used to supply power to the terahertz generating electrode (331).

6. The fiber-optic terahertz photoconductive antenna according to claim 5, characterized in that, The impedance transformer (332) is a quarter impedance transformer (332).

7. The fiber-optic terahertz photoconductive antenna according to claim 6, characterized in that, The quarter impedance converter (332) is connected to a sector line (334), and the radius of the sector line (334) is one-quarter of the wavelength of the N optical signals.

8. The fiber-optic terahertz photoconductive antenna according to claim 1, characterized in that, Also includes: Terahertz focusing lens (4) is used to focus the terahertz signal radiated by the terahertz antenna chip (3).

9. The fiber-optic terahertz photoconductive antenna according to claim 8, characterized in that, The terahertz focusing lens (4) has a bullet-shaped structure, which includes a sub-hemispherical and a cylindrical structure. The terahertz antenna chip (3) is located at the center of the bullet-shaped structure and is fixed with UV adhesive.

10. A fiber-optic terahertz photoconductive antenna according to claim 8, characterized in that, The terahertz focusing lens (4) is made of high-resistivity single-crystal silicon.

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