Terahertz photoconductive antenna and method of adjusting

Abstract

The application discloses a terahertz photoconductive antenna and a regulating method, and solves the problem of determining whether the focal length of laser focused on the light guide excitation area of a terahertz antenna module is appropriate. The terahertz photoconductive antenna comprises a laser beam splitting unit, which is used for transmitting laser output by a laser source module to a laser converging unit and reflecting laser returned by the laser converging unit. The laser converging unit is used for focusing the laser transmitted by the laser beam splitting unit to the light guide excitation area of the terahertz antenna module and receiving the laser reflected by the terahertz antenna module. The terahertz antenna module comprises a terahertz antenna chip, which is used for receiving and reflecting the laser focused by the laser converging unit, receiving the laser for generating or detecting a terahertz signal and reflecting the laser to the laser converging unit. An imaging unit receives the reflected laser and generates a projection image. The application enables an operator to observe and regulate the relative position of the terahertz antenna chip and the laser spot and the size of the laser spot in real time.

Description

Technical Field

[0001] This application relates to the field of radio metrology and testing technology, and in particular to a terahertz photoconductive antenna and its adjustment method. Background Technology

[0002] Terahertz waves typically refer to electromagnetic waves with frequencies ranging from 0.1 to 10 THz. Terahertz waves occupy a unique position in the electromagnetic spectrum, possessing distinctive properties such as broadbandness, directionality, selective transmission and penetration, and fingerprint characteristics. Therefore, measurement systems based on terahertz principles have high application value in fields such as broadband communication, medical imaging, non-destructive testing, and security inspection.

[0003] Terahertz sources are the core components of terahertz measurement systems, primarily implemented through physical principles such as photoconductivity, optical rectification, and electro-optic effects. Antennas based on different principles vary significantly in terms of achievable specifications, development costs, and ease of use. From a current application perspective, photoconductive terahertz antennas are the most commonly used. Traditional terahertz photoconductive antennas mostly employ spatial light excitation, which requires a high-quality optical environment and is complex to operate. Newer fiber-optic terahertz photoconductive antennas are mostly directly packaged using precision mechanical structures, making it difficult to determine the appropriate laser focal length focused on the photoconductive excitation area of ​​the terahertz antenna module. Furthermore, chip replacement or secondary adjustments are challenging, significantly limiting the development and technological advancement of terahertz photoconductive antennas. Summary of the Invention

[0004] This application provides a terahertz photoconductive antenna and its adjustment method, which solves the problem in the prior art of determining whether the laser focal length focused on the photoconductive excitation area of ​​the terahertz antenna module is appropriate.

[0005] This application also provides a terahertz photoconductive antenna, comprising a laser source module, a laser beam splitter, a laser focusing unit, a terahertz antenna module, and an imaging unit. The laser beam splitter transmits laser light output from the laser source module to the laser focusing unit and reflects laser light returned from the laser focusing unit. The laser focusing unit focuses the laser light transmitted from the laser beam splitter to the photoconductive excitation region of the terahertz antenna module and receives laser light reflected from the terahertz antenna module. The terahertz antenna module includes a terahertz antenna chip for receiving and reflecting laser light focused by the laser focusing unit; the received laser light is used to generate or detect terahertz signals, and the reflected laser light is used to return to the laser focusing unit. The imaging unit receives laser light reflected from the laser beam splitter and generates a projected image.

[0006] Furthermore, the laser source module includes an optical fiber and an optical fiber collimator. The optical fiber is used to output laser light. The optical fiber collimator is used to convert the laser light output from the optical fiber into a spatial laser with a small divergence angle.

[0007] Furthermore, the terahertz antenna module also includes a terahertz focusing lens. The terahertz focusing lens is installed on the side of the terahertz antenna chip away from the laser source module, and is used to radiate the terahertz signal generated by the terahertz antenna chip or to focus the externally radiated terahertz signal to the terahertz antenna module.

[0008] Furthermore, it also includes an adjustment component. The adjustment component is used to adjust the distance and relative position of the laser focusing unit and the terahertz antenna module.

[0009] Preferably, the reflection direction and the transmission direction are at a 90-degree angle.

[0010] Preferably, the imaging unit is a CCD camera. The CCD camera receives the laser light reflected back from the terahertz antenna module to the laser beam splitter, and the laser light reflected by the laser beam splitter forms an image of the metal structure portion of the terahertz antenna chip illuminated by the laser.

[0011] Preferably, the terahertz focusing lens is a bullet-shaped lens composed of a sub-hemispherical structure and a cylinder. The terahertz antenna module is fixed at the center of the bottom surface of the cylinder on the side furthest from the sub-hemispherical structure.

[0012] Furthermore, it also includes several parallel limiting beams. The fiber collimator, laser beam splitter, laser focusing unit, and terahertz antenna module all have through holes corresponding to the limiting beams. The limiting beams connect the above components and limit their displacement in directions other than the incident direction of the laser source module, keeping the optical path in a straight line.

[0013] More preferably, one end of the limiting beam is fixedly connected to the laser source module, and the other end is fixedly connected to the terahertz antenna module. The laser source module and the terahertz antenna module form a cage-like structure to limit other components in the middle.

[0014] This application also provides a method for adjusting a terahertz photoconductive antenna, using the terahertz photoconductive antenna described in any of the above embodiments, comprising the following steps:

[0015] Turn on the laser source module and observe the size and relative position of the laser spot imaged on the metal structure part of the terahertz antenna chip illuminated by the laser on the imaging unit.

[0016] The control and adjustment components adjust the distance and relative position of the laser focusing unit and the terahertz antenna module, thereby adjusting the size and relative position of the laser spot on the imaging unit.

[0017] The above-described technical solutions adopted in the embodiments of this application can achieve the following beneficial effects.

[0018] The advantage of the technical solution described in this invention lies in that the relative positions between the substructures are first determined through the cage structure, and then the laser beam splitting unit reflects the laser incident on the surface of the terahertz antenna chip into the CCD camera. This allows the operator to observe the relative position of the terahertz antenna chip and the laser spot, as well as the size of the laser spot, in real time. Furthermore, the laser spot size can be adjusted by single-axis adjustment of the laser's incident focal length through the laser focusing unit. Simultaneously, the relative position of the terahertz antenna chip and the laser spot can be finely adjusted at the micrometer scale through the two-dimensional adjustment unit. Since the overall structure is connected by a cage structure, the terahertz antenna components fixed on the two-dimensional adjustment unit can also be removed and replaced, greatly reducing the packaging and adjustment costs of the terahertz antenna. Attached Figure Description

[0019] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0020] Figure 1 This is a structural diagram of an embodiment of a terahertz photoconductive antenna according to this application;

[0021] Figure 2 This is a flowchart illustrating an embodiment of a terahertz photoconductive antenna adjustment method according to this application. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0023] The technical solutions provided by the various embodiments of this application are described in detail below with reference to the accompanying drawings.

[0024] Figure 1 This is a structural diagram of an embodiment of a terahertz photoconductive antenna according to this application.

[0025] A terahertz photoconductive antenna includes a laser source module 1, a laser beam splitting unit 2, a laser focusing unit 3, a terahertz antenna module 4, and an imaging unit (not shown in the figure).

[0026] The laser source module includes an optical fiber 11 and an optical fiber collimator 12. The optical fiber is used to output laser light.

[0027] A fiber optic collimator is used to connect optical fibers and convert the laser light within the fibers into spatial light output. In other words, it converts the laser light output from the optical fiber into spatial laser light with a smaller divergence angle.

[0028] For example, since the terahertz antenna chip is fiber-optic, the wavelength of the external laser excitation is 1550nm. The selected fiber collimator is an air-gap triple-lens fiber collimator, which can provide better beam quality than an aspherical lens collimator and can convert the laser in the fiber into a spatial laser with a smaller divergence angle.

[0029] The laser beam splitter unit transmits the laser output from the laser source module to the laser focusing unit and reflects the laser returned from the laser focusing unit. The transmission direction and the reflection direction are not parallel. It should be noted that "reflection" here can also be expressed as refraction.

[0030] It should be noted that the reflection direction and the transmission direction are not parallel, and the angle between them can be any angle. However, if the angle is too small, it may be necessary to extend to a distance to install the imaging unit. Therefore, the angle between them should be closer to 90 degrees. For the convenience of installation inside the laser beam splitter, it is preferable that the reflection direction and the transmission direction are at a 90-degree angle.

[0031] For example, a laser beam splitter unit is used to transmit the laser output from the fiber optic collimator and transmit the laser reflected from the surface of the photoconductive antenna chip to the CCD camera. The laser beam splitter unit is a cuboid beam splitter with a fit-cage structure, a splitting ratio of 50:50, and a matching laser wavelength of 1550 nm. The angle between the transmission and reflection directions of this beam splitter is 90 degrees, and the transmission direction is the same as the laser output from the laser collimator. After the laser exits the fiber optic collimator, it passes through the laser beam splitter unit and enters the laser focusing unit. The laser focusing unit then focuses the laser onto the terahertz antenna chip and reflects it back along the original path. The reflected laser passes through the laser focusing unit and then enters the laser beam splitter unit, reflecting at a 90-degree angle along the laser transmission direction to the CCD camera. The CCD camera can then observe the illuminated metal structure of the terahertz chip.

[0032] The laser focusing unit is used to focus the laser transmitted by the laser beam splitter to the optical guide excitation region of the terahertz antenna module and to receive the laser reflected by the terahertz antenna module.

[0033] The laser focusing unit is used to focus the laser transmitted from the cage-type laser beam splitter unit, so that the laser is focused on the photoconductive excitation region of the terahertz antenna chip.

[0034] For example, the laser focusing unit includes an aspherical lens coated with a double-sided anti-reflective film, an aspherical lens adapter, and a cage-type single-axis adjustment structure. The size of the laser spot on the terahertz antenna chip can be observed in a CCD camera using the laser beam splitting unit.

[0035] The terahertz antenna module includes a terahertz antenna chip 41, which is used to receive and reflect the laser focused by the laser focusing unit. The received laser is used to generate or detect terahertz signals, and the reflected laser is used to reflect the laser to the laser focusing unit.

[0036] The terahertz antenna chip is used to generate or detect terahertz signals. When used to generate terahertz signals, a voltage signal is applied through the coaxial cable connected to the terahertz antenna chip. When used to detect terahertz signals, a current signal is output through the coaxial cable connected to the terahertz antenna chip.

[0037] For example, the terahertz antenna chip uses an InGaAs / InAlAs superlattice structure as the antenna semiconductor substrate and a butterfly-shaped metal structure as the antenna radiating electrode. When the antenna chip is used to generate terahertz signals, photogenerated carriers are generated when the surface of the antenna chip is excited by a laser. These photogenerated carriers move under the drive of the voltage applied to the coaxial cable, generating terahertz radiation. When the antenna chip is used to detect terahertz signals, photogenerated carriers are generated when the surface of the antenna chip is excited by a laser. These photogenerated carriers move under the action of the detected terahertz electric field, forming a photocurrent, which is output through the coaxial cable.

[0038] The terahertz antenna module also includes a terahertz focusing lens. The terahertz focusing lens is installed on the side of the terahertz antenna chip away from the laser source module, and is used to radiate the terahertz signal generated by the terahertz antenna chip or to focus the externally radiated terahertz signal to the terahertz antenna module.

[0039] A terahertz focusing lens is used to radiate or focus terahertz signals. When the terahertz antenna chip is used to generate a terahertz signal, it can radiate the generated signal outwards. When the terahertz antenna chip is used to detect a terahertz signal, it can focus the externally radiated terahertz signal onto the surface of the terahertz antenna chip. Because the divergence angle is large during terahertz radiation, 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. Similarly, if the terahertz signal to be detected is not focused, the terahertz signal energy received by the terahertz antenna chip will be very low, the signal-to-noise ratio of the acquired data will be extremely low, and useful information will be submerged in noise.

[0040] For example, a bullet-shaped lens is chosen as the terahertz focusing lens. The bullet-shaped structure consists of a sub-hemispherical structure and a cylinder. The terahertz antenna chip is attached to the center of the bottom surface of the bullet-shaped lens on the side away from the sub-hemispherical side and fixed with UV adhesive. High-resistivity single-crystal silicon is chosen as the lens material, as this material has minimal absorption of terahertz radiation, ensuring minimal loss of terahertz radiation after passing through the terahertz focusing lens. Therefore, preferably, the terahertz focusing lens is a bullet-shaped lens composed of a sub-hemispherical structure and a cylinder. The terahertz antenna module is fixed to the center of the bottom surface of the cylinder on the side away from the sub-hemispherical side.

[0041] The imaging unit receives the laser reflected from the laser divider and generates a projected image.

[0042] Preferably, the imaging unit is a CCD camera. The CCD camera receives the laser light reflected back from the terahertz antenna module to the laser beam splitter, and the laser light reflected by the laser beam splitter forms an image of the metal structure portion of the terahertz antenna chip illuminated by the laser.

[0043] Furthermore, it also includes an adjustment component 5. The adjustment component is used to adjust the distance and relative position of the laser focusing unit and the terahertz antenna module.

[0044] The adjustment assembly includes a cage-type single-axis adjustment structure 51 located on the laser focusing unit. The cage-type single-axis adjustment structure can adjust the relative distance between the aspherical lens on the laser focusing unit and the terahertz antenna chip, thereby focusing the laser onto the photoconductive excitation area of ​​the terahertz antenna chip with a suitable focal length.

[0045] The adjustment component includes a two-dimensional adjustment unit 52 located in the terahertz antenna unit, used to adjust the relative position between the laser focused by the laser focusing unit and the photoconductive excitation region of the terahertz antenna chip.

[0046] For example, an XY translation adjustment frame that fits a cage-like structure can be selected. The XY translation adjustment frame has a circular hole in the center. Since the terahertz converging lens is a bullet-shaped structure, the cylindrical part of the bullet-shaped structure can match the central circular hole of the translation adjustment frame very well.

[0047] It also includes several parallel limiting beams 6 and a cage-like structural plate 7. The fiber optic collimator, laser beam splitter, and terahertz antenna module all have through holes corresponding to the limiting beams. Because the laser focusing unit is relatively narrow, it needs to be mounted on a cage-like structural plate with a width comparable to that of the laser beam splitter and terahertz antenna module. The cage-like structural plate has corresponding through holes. The limiting beams connect these components and limit their displacement in directions other than the incident direction of the laser source module, ensuring the optical path remains straight.

[0048] One end of the limiting beam is fixedly connected to the laser source module, and the other end is fixedly connected to the terahertz antenna module. The laser source module and the terahertz antenna module form a cage structure to limit other components in the middle.

[0049] The cage structure is used to connect the fiber collimator, laser beam splitter, laser focusing unit and terahertz antenna two-dimensional adjustment unit, so that the centers of the components are on the same horizontal line.

[0050] Figure 2 This is a flowchart illustrating an embodiment of a terahertz photoconductive antenna adjustment method according to this application.

[0051] A method for adjusting a terahertz photoconductive antenna, using the terahertz photoconductive antenna described in any of the above embodiments, includes the following steps:

[0052] Step 101: Turn on the laser source module and observe the size and relative position of the laser spot imaged on the metal structure part of the terahertz antenna chip illuminated by the laser on the imaging unit.

[0053] This allows the operator to observe the relative position of the terahertz antenna chip and the laser spot, as well as the size of the laser spot, in real time.

[0054] Step 102: Control the adjustment components to adjust the distance and relative position of the laser focusing unit and the terahertz antenna module, thereby adjusting the size and relative position of the laser spot on the imaging unit.

[0055] The laser spot size can be adjusted by single-axis adjustment of the laser incident focal length through the laser focusing unit, and at the same time, the relative position of the terahertz antenna chip and the laser spot can be finely adjusted at the micrometer scale through the two-dimensional adjustment unit.

[0056] The device provided in this embodiment of the invention has the same implementation principle and technical effect as the aforementioned method embodiment. For the sake of brevity, any parts not mentioned in the device embodiment can be referred to the corresponding content in the aforementioned method embodiment.

[0057] The above description is merely an embodiment of this application and is not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A terahertz photoconductive antenna, characterized in that, It includes a laser source module, a laser beam splitter unit, a laser focusing unit, a terahertz antenna module, and an imaging unit; The laser beam splitting unit is used to transmit the laser output from the laser source module to the laser focusing unit and reflect the laser returned by the laser focusing unit. The laser focusing unit is used to focus the laser transmitted by the laser beam splitter to the optical guide excitation area of ​​the terahertz antenna module and to receive the laser reflected by the terahertz antenna module. The terahertz antenna module includes a terahertz antenna chip and a terahertz focusing lens. The terahertz antenna chip is used to receive and reflect the laser focused by the laser focusing unit. The received laser is used to generate or detect terahertz signals, and the reflected laser is used to return to the laser focusing unit. The terahertz focusing lens is installed on the side of the terahertz antenna chip away from the laser source module. It is used to radiate the terahertz signals generated by the terahertz antenna chip or to focus externally radiated terahertz signals to the terahertz antenna module. The terahertz converging lens is a bullet-shaped lens composed of a sub-hemispherical and a cylindrical component. The terahertz antenna chip is fixed on the center of the bottom surface of the cylinder on the side away from the sub-hemispherical side; The imaging unit receives the laser reflected from the laser divider and generates a projected image.

2. The terahertz photoconductive antenna according to claim 1, characterized in that, The laser source module includes an optical fiber and an optical fiber collimator; The optical fiber is used to output laser light; The fiber collimator is used to convert the laser output from the fiber into a spatial laser with a smaller divergence angle.

3. The terahertz photoconductive antenna according to claim 1, characterized in that, It also includes adjustment components; The adjustment component is used to adjust the distance and relative position of the laser focusing unit and the terahertz antenna module.

4. The terahertz photoconductive antenna according to claim 1, characterized in that, The reflection direction and the transmission direction are at a 90-degree angle.

5. The terahertz photoconductive antenna according to claim 1, characterized in that, The imaging unit is a CCD camera; The CCD camera receives the laser reflected back from the terahertz antenna module to the laser beam splitter unit, and the laser beam splitter unit reflects the laser to form an image of the metal structure of the terahertz antenna chip illuminated by the laser.

6. The terahertz photoconductive antenna according to claim 3, characterized in that, The adjustment component includes a cage-type single-axis adjustment structure for adjusting the relative distance between the laser focusing unit and the terahertz antenna chip.

7. The terahertz photoconductive antenna according to claim 3, characterized in that, The adjustment assembly includes an XY translation adjustment frame with a circular hole at its center, and the cylindrical portion of the bullet-shaped lens matches the circular hole.

8. The terahertz photoconductive antenna according to any one of claims 1-7, characterized in that, It also includes several parallel limiting beams; The fiber collimator, laser beam splitter, laser focusing unit and terahertz antenna module are all provided with through holes corresponding to the limiting beam. The limiting beam connects the aforementioned components and limits their displacement in directions other than the incident direction of the laser source module, so that the optical path remains in a straight line.

9. The terahertz photoconductive antenna according to claim 8, characterized in that, The limiting beam is fixedly connected to a laser source module at one end and a terahertz antenna module at the other end. The laser source module and the terahertz antenna module form a cage structure to confine other components in the middle.

10. A method for adjusting a terahertz photoconductive antenna, characterized in that, Using the terahertz photoconductive antenna according to any one of claims 1-9, the steps include: Turn on the laser source module and observe the size and relative position of the laser spot imaged on the metal structure part of the terahertz antenna chip illuminated by the laser on the imaging unit. The control and adjustment components adjust the distance and relative position of the laser focusing unit and the terahertz antenna module, thereby adjusting the size and relative position of the laser spot on the imaging unit.

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