Optical fiber coupling terahertz photoconductive antenna

Abstract

The utility model discloses an optical fiber coupling terahertz photoconductive antenna, which comprises an optical fiber collimation module, a first focusing lens, a frequency doubling module, a second focusing lens, a photoconductive antenna and a shell, the input end of the terahertz photoconductive antenna is connected with a femtosecond laser through an optical fiber with the wavelength of 1560nm + / -40nm, the femtosecond laser emits femtosecond laser with the central wavelength of 1560nm + / -40nm, and the optical fiber coupling terahertz photoconductive antenna is connected with the shell. The photoconductive antenna is a terahertz photoconductive antenna excited by femtosecond laser with the wavelength of 780nm + / -20nm, the optical fiber collimation module is used for parallelly exporting pulsed light with the central wavelength of 1560nm + / -40nm transmitted in an optical fiber with the wavelength of 1560nm + / -40nm, the first focusing lens is used for focusing the parallel light to the frequency doubling module, the frequency doubling module is used for converting light with the wavelength of 1560nm + / -40nm into femtosecond laser with the wavelength of 780nm + / -20nm, and the femtosecond laser is used for outputting the femtosecond laser with the wavelength of 780nm + / -20nm. The second focusing lens focuses the frequency doubling light to an electrode gap of the photoconductive antenna; and the photoconductive antenna receives frequency-doubled pulse light with the wavelength of 780nm + / -20nm. The antenna packaging structure is feasible, simple and small in size.

Description

Technical Field

[0001] The utility model belongs to the technical field of terahertz spectroscopy and imaging, and in particular relates to an optical fiber-coupled terahertz photoconductive antenna for 1.5um laser input. Technical Background

[0002] The terahertz time-domain spectroscopy system includes a femtosecond laser, a photoconductive transmitting antenna and a photoconductive detecting antenna, wherein the photoconductive transmitting antenna and the photoconductive detecting antenna are collectively referred to as photoconductive antennas. The femtosecond pulse sequence emitted by the femtosecond laser is divided into pump light and detection light. The pump light is focused on the photoconductive transmitting antenna after being transmitted through the optical path, and a terahertz pulse is generated under the action of the bias voltage. The detection light is incident on the photoconductive detecting antenna to generate photogenerated carriers. The photogenerated carriers generate a transient induced current under the drive of the terahertz electric field. The intensity of the induced current is proportional to the intensity of the terahertz electric field. At the same time, the current output circuit external to the photoconductive detecting antenna outputs the generated transient induced current to the signal acquisition device, and then the complete terahertz pulse time domain waveform can be obtained by sampling and measuring. In the above process, the femtosecond laser can be transmitted to the photoconductive transmitting antenna and the photoconductive detecting antenna in two ways, one is the free optical path transmission composed of optical components, and the other is the optical fiber transmission. The stability and anti-interference ability of optical fiber transmission are far better than that of free optical path transmission.

[0003] There are two mature terahertz photoconductive antennas at present. One is a fiber-coupled terahertz photoconductive antenna excited by a femtosecond laser with a wavelength of about 1560nm (±40nm). The GaInAs material used is difficult to grow and expensive. The other is a terahertz photoconductive antenna excited by a femtosecond laser with a wavelength of about 780nm (±20nm). It usually uses GaAs or low-temperature grown LT-GaAs materials and has a lower cost. The transmission loss of 780nm (±20nm) polarization-maintaining optical fiber is much greater than that of the general 1560nm (±40nm) band polarization-maintaining optical fiber. Therefore, the development process of the terahertz time-domain spectroscopy system faces the problem that the terahertz band corresponding to the optical fiber with low transmission loss and the low-cost photoconductive antenna is not unified. For this reason, the present invention provides a fiber-coupled terahertz photoconductive antenna for 1.5um laser input to build a more cost-effective terahertz time-domain spectroscopy system or imaging system. Utility Model Content

[0004] The purpose of the utility model is to provide a fiber-coupled terahertz photoconductive antenna for 1.5um laser input, which solves the problem of inconsistency between the terahertz band corresponding to the low-transmission-loss optical fiber and the low-cost photoconductive antenna faced in the development process of the existing terahertz time-domain spectroscopy system.

[0005] In order to achieve the above purpose, the utility model adopts the following technical solutions:

[0006] A fiber-coupled terahertz photoconductive antenna comprises a fiber collimation module, a first focusing lens, a frequency doubling module, a second focusing lens, a photoconductive antenna and a housing. The fiber collimation module, the first focusing lens, the frequency doubling module, the second focusing lens and the photoconductive antenna built into the housing are sequentially arranged along the incident direction of a femtosecond laser. The input end of the terahertz photoconductive antenna is connected to a femtosecond laser through a 1560nm±40nm wavelength optical fiber. The femtosecond laser emits a femtosecond laser with a central wavelength of 1560nm±40nm. The photoconductive antenna is 780nm± A terahertz photoconductive antenna excited by a 20nm femtosecond laser, wherein the optical fiber collimation module is used to parallelize the pulse light with a central wavelength of 1560nm±40nm transmitted in the 1560nm±40nm wavelength optical fiber, the first focusing lens focuses the parallel light to the frequency doubling module, the frequency doubling module is used to convert the 1560nm±40nm wavelength light into a 780nm±20nm wavelength femtosecond laser, the second focusing lens focuses the frequency doubling light to the electrode gap of the photoconductive antenna 5; the photoconductive antenna receives the 780nm±20nm wavelength frequency doubling pulse light.

[0007] Terahertz photoconductive antennas use LT-GaAs or Si-GaAs antennas.

[0008] It should be noted that the fiber collimation module, the first focusing lens, the frequency doubling module, and the second focusing lens constitute a frequency doubling focusing module, and the frequency doubling focusing module also includes a first lens barrel, a second lens barrel, a sleeve, a first pressure ring, a second pressure ring, and a third pressure ring. The first focusing lens is fixed in the first lens barrel by the first pressure ring, and the first lens barrel is fixed in the cavity on the rear side of the sleeve. The front end of the fiber collimation module is also placed in the cavity on the rear side of the sleeve, and the front end of the fiber collimation module is close to the rear end of the first lens barrel. The second focusing lens is fixed in the second lens barrel by the second pressure ring, and the rear end of the second lens barrel is fixed in the cavity on the front side of the sleeve. The frequency doubling module is fixed in the cavity on the front side of the sleeve by the third pressure ring, and the front end of the third pressure ring is close to the rear end of the second lens barrel.

[0009] Further explanation: the frequency doubling module adopts periodically poled lithium niobate crystal PPLN, MgO:PPLN, the frequency doubling module is a double frequency doubling module, the input end face of the frequency doubling module is plated with an anti-reflection film of 1560nm±40nm, and the output end face is plated with an anti-reflection film of 780nm±20nm.

[0010] The fiber-coupled terahertz photoconductive antenna also includes an internal supporting structure, which includes a circular base and an arc-shaped shell arranged coaxially. The circular base is fixed on the photoconductive antenna. A circular hole is provided in the center of the circular base, and the circular hole is aligned with the electrode gap of the photoconductive antenna. The frequency doubling focusing module is fixed in the cavity of the arc-shaped shell, and there is a certain adjustment gap between the outer surface of the frequency doubling focusing module and the cavity of the arc-shaped shell. The frequency doubling focusing module and the cavity of the arc-shaped shell are arranged coaxially.

[0011] The optical fiber-coupled terahertz photoconductive antenna also includes a circuit board, which is plugged into the internal supporting structure.

[0012] The fiber-coupled terahertz photoconductive antenna also includes a flexible sealing ring. The outer shell consists of a cylinder and a back cover. The frequency doubling focusing module, the internal supporting structure and the photoconductive antenna are placed together in the cylinder. A mounting hole is provided in the middle of the back cover. The fiber collimation module in the frequency doubling focusing module passes through the mounting hole, and a flexible sealing ring is provided between the outer wall at the rear end of the fiber collimation module and the mounting hole.

[0013] Furthermore, a groove is provided at the bottom of the cylinder, and a boss is provided at the bottom of the arc-shaped shell. The boss corresponds to the groove, and the cylinder is sleeved on the entire structure, and the boss is engaged in the groove.

[0014] To further explain, the outer surface of the frequency doubling focusing module and the inner surface of the shell are both treated to be conductive, and the outer surface of the shell is treated to be insulating.

[0015] Compared with the prior art, the utility model has the following advantages: (1) It is the first time to propose frequency doubling at the front end of a GaAs photoconductive antenna, which increases the applicable scope of the GaAs antenna and makes it easy to form a remote terahertz emission system with flexibly configurable optical fiber length, which is a feasible low-cost optical fiber terahertz photoconductive antenna integration solution; (2) Low-loss pulse light with a wavelength of 1560nm is transmitted by optical fiber to achieve remote optical frequency doubling outside the cavity, which has better output power stability and lower transmission loss than intra-cavity frequency doubling, and is conducive to the formation of high-power, reliable photoconductive antenna products; (3) Based on temperature control and optimized selection (selection of light-through length), the transmitter can obtain terahertz pulse radiation with stable power and pulse width output under the premise of ensuring stable frequency doubling conversion efficiency and minimum pulse broadening effect, and the detector can accurately detect the terahertz pulse radiation output by the transmitter; (4) A feasible, simple and small antenna packaging structure is provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of the principle of the fiber-coupled terahertz photoconductive antenna involved in Example 1.

[0017] Figure 2 This is a schematic diagram of the internal structure of the fiber-coupled terahertz photoconductive antenna involved in Example 1.

[0018] Figure 3 This is a schematic diagram of the explosion structure of the frequency doubling focusing module involved in Example 1.

[0019] Figure 4 for Figure 3 Cross-sectional view of .

[0020] Figure 5This is a schematic diagram of the structure of the internal support structure 8 involved in Example 1.

[0021] Figure 6 A schematic diagram of the structure of the shell. DETAILED DESCRIPTION

[0022] In order to more clearly explain the content of the utility model, the utility model is further described below in conjunction with the drawings and specific embodiments. The first, second, etc. involved in this embodiment are only for distinguishing and explaining the components and do not constitute a limitation on the scope of protection. The directional words such as front and back are based on the direction of light transmission.

[0023] Example 1

[0024] like Figure 1 As shown, a fiber-coupled terahertz photoconductive antenna involved in this embodiment includes a fiber collimation module 1, a first focusing lens 2, a frequency doubling module 3, a second focusing lens 4, a photoconductive antenna 5 and a housing 7. The fiber collimation module 1, the first focusing lens 2, the frequency doubling module 3, the second focusing lens 4 and the photoconductive antenna 5 built into the housing 7 are sequentially arranged along the incident direction of the femtosecond laser. The input end of the terahertz photoconductive antenna is connected to the femtosecond laser through a 1560nm (±40nm) wavelength optical fiber. The femtosecond laser emits a femtosecond laser with a central wavelength of 1560nm (±40nm). The photoconductive antenna 5 is a terahertz photoconductive antenna excited by a 780nm (±20nm) femtosecond laser, and preferably uses an LT-GaAs or Si-GaAs antenna.

[0025] Among them, the optical fiber collimation module 1 is used to parallelize the pulse light with a central wavelength of 1560nm (±40nm) transmitted in the 1560nm (±40nm) wavelength optical fiber, the first focusing lens 2 focuses the parallel light to the frequency doubling module 3, the frequency doubling module 3 is used to convert the 1560nm (±40nm) wavelength light into a 780nm (±20nm) wavelength femtosecond laser, the second focusing lens 4 focuses the frequency doubling light to the electrode gap of the photoconductive antenna 5; the photoconductive antenna 5 receives the 780nm (±20nm) wavelength frequency doubling pulse light.

[0026] It should be noted that the fiber collimation module 1, the first focusing lens 2, the frequency doubling module 3, and the second focusing lens 4 constitute a frequency doubling focusing module 6, and the frequency doubling focusing module 6 also includes a first lens barrel 601, a second lens barrel 602, a sleeve 603, a first pressing ring 604, a second pressing ring 605, and a third pressing ring 606.

[0027] The first focusing lens 2 is fixed in the first lens barrel 601 through the first pressing ring 604. The first lens barrel 601 is fixed in the cavity at the rear side of the sleeve 603. The front end of the optical fiber collimation module 1 is also placed in the cavity at the rear side of the sleeve 603, and the front end of the optical fiber collimation module 1 is close to the rear end of the first lens barrel 601.

[0028] The second focusing lens 4 is fixed in the second lens barrel 602 through the second pressing ring 605. The rear end of the second lens barrel 602 is fixed in the front cavity of the sleeve 603.

[0029] The frequency doubling module 3 is fixed in the front cavity of the sleeve 603 through the third pressing ring 606 , and the front end of the third pressing ring 606 is close to the rear end of the second lens barrel 602 .

[0030] It should be noted that the outer surface of the first pressing ring 604 is threadedly connected to the inner surface of the first lens barrel 601, and the first focusing lens 2 is fixed in the first lens barrel 601 by rotating the thread to prevent the first focusing lens 2 from moving; the outer surface of the front end of the optical fiber collimation module 1 is threadedly connected to the inner surface of the cavity at the rear side of the sleeve 603, and the two are fixed by rotating the thread. After the distance and polarization direction of this overall structure are adjusted in the cavity at the rear side of the sleeve 3, an appropriate amount of glue is infiltrated into the long strip hole of the sleeve 603 for curing; the outer surface of the third pressing ring 606 is threadedly connected to the inner surface of the cavity at the front side of the sleeve 603; the outer surface of the rear end of the second lens barrel 602 is threadedly connected to the inner surface of the cavity at the front side of the sleeve 603. The above-mentioned connections are all threaded, which is convenient for assembly, and at the same time ensures the stability of the optical element, thereby ensuring the stability of the optical path.

[0031] Through the above structure, the relative positions of the optical fiber collimation module 1, the first focusing lens 2 and the frequency doubling module 3 and the polarization direction of the light incident on the frequency doubling module can be reasonably controlled to control the spot size irradiated on the frequency doubling module 3. It is generally recommended to select a spot size when the Rayleigh length is half the crystal length, and the crystal should be within the Rayleigh distance of laser focusing to ensure the highest conversion efficiency; through the above structure, the relative positions of the frequency doubling module 3, the second focusing lens 4 and the photoconductive antenna 5 can be reasonably controlled to control the spot size irradiated on the photoconductive antenna electrode. It is generally recommended to select a spot size not less than 1.2 times the electrode gap, so as to obtain the highest excitation efficiency while ensuring that the antenna will not be damaged due to excessive pulse energy.

[0032] The specific use process of the fiber-coupled terahertz photoconductive antenna involved in this embodiment is as follows: the femtosecond pulse laser with a central wavelength of 1560nm (±40nm) transmitted in the optical fiber is collimated by the optical fiber collimation module 1 and focused by the first focusing lens 2, and then irradiated onto the frequency doubling module 3. The femtosecond pulse interacts with the frequency doubling module 3. Based on the second harmonic generation (SHG) effect, the laser with a wavelength of 1560nm (±40nm) will be frequency-doubled, and finally outputs a femtosecond pulse light with a wavelength of 780nm (±20nm). The femtosecond laser of 780nm (±20nm) generated after frequency doubling is focused by the second focusing lens 4 and then incident on the electrode of the photoconductive antenna 5. When the photoconductive antenna is used as a photoconductive transmitting antenna, it generates a strong terahertz pulse radiation with adjustable power under the action of the bias voltage. When the photoconductive antenna is used as a photoconductive detection antenna, it receives the frequency-doubled pulse light and the terahertz wave at the same time, and obtains the complete terahertz pulse time domain waveform by the sampling measurement method.

[0033] It is further explained that the femtosecond laser pulse will introduce a certain negative chirp before being injected into the terahertz photoconductive antenna to neutralize the pulse broadening effect of the optical pulse in free space and the frequency doubling crystal. At the same time, the injected femtosecond pulse light should be e-polarized.

[0034] Further explanation, the frequency doubling module 3 may be selected from (but not limited to) periodically poled lithium niobate crystal PPLN, MgO:PPLN, etc. Based on the femtosecond pulse system, a frequency doubling crystal length of less than or equal to 1 mm is selected, which will facilitate the formation of a more compact antenna device.

[0035] To further illustrate, a temperature control unit is integrated in the frequency doubling module 3, which controls the polarization period and operating temperature of the frequency doubling crystal in the frequency doubling module to ensure its stable conversion efficiency at the central wavelength.

[0036] Furthermore, considering the broadening effect of the frequency doubling module 3 on high peak power femtosecond pulses, a double frequency doubling module with small pulse broadening and high damage threshold is selected, ultimately ensuring a narrow pulse width and a wide spectrum range of the terahertz radiation.

[0037] Further explanation: the selected optical devices need to be coated with anti-reflection films of corresponding wavelength bands to reduce the loss during the pulse laser transmission process. In particular, the frequency doubling module 3 can introduce part of the sum frequency light and difference frequency light based on the second harmonic generation (SHG) effect. The input end face of the frequency doubling module 3 is coated with an anti-reflection film of 1560nm (±40nm) and the output end face is coated with an anti-reflection film of 780nm (±20nm), thereby filtering out clutter and increasing the transmittance of the corresponding wavelength band of each face to more than 99%.

[0038] The fiber-coupled terahertz photoconductive antenna involved in this embodiment also includes an internal support structure 8, which includes a circular base 801 and an arc-shaped shell 802 arranged coaxially, the circular base 801 is fixed on the photoconductive antenna 5 by pins and screws, a circular hole 803 is arranged at the center of the circular base 801, and the circular hole 803 is aligned with the electrode gap of the photoconductive antenna 5, the frequency doubling focusing module 6 is fixed in the cavity of the arc-shaped shell, and there is a certain adjustment gap between the outer surface of the frequency doubling focusing module 6 and the cavity of the arc-shaped shell, and the frequency doubling focusing module 6 is arranged coaxially with the cavity of the arc-shaped shell. The adjustment gap facilitates the adjustment of the frequency doubling focusing module 6 and the cavity of the arc-shaped shell coaxially, and after adjustment, the frequency doubling focusing module 6 is well aligned with the electrode gap of the photoconductive antenna 5, and at the same time facilitates the movement of the frequency doubling focusing module 6 in the axial direction, ensuring that the light spot irradiated on the electrode gap is minimized, and then an appropriate amount of glue is infiltrated into the adjustment gap to fix the frequency doubling focusing module 6 in the arc-shaped shell 802.

[0039] The fiber-coupled terahertz photoconductive antenna involved in this embodiment also includes a circuit board 9, which is plugged into the internal support structure 8. When the photoconductive antenna is used as a photoconductive transmitting antenna, the circuit board is used as a diode for anti-reverse protection to prevent the antenna from being damaged by reverse bias connection. When the photoconductive antenna is used as a photoconductive detection antenna, the circuit board is used as a TIA signal amplification to process the detected signal.

[0040] It should be noted that the circular base 801 is provided with a slot 804 , which is connected to the circular hole 803 , and the slot 804 facilitates the connection of the wires.

[0041] The fiber-coupled terahertz photoconductive antenna involved in this embodiment also includes a flexible sealing ring 10. The outer shell 7 is composed of two parts: a cylinder 701 and a back cover 702. The frequency doubling focusing module 6, the internal support structure 8 and the photoconductive antenna 5 are placed together in the cylinder 701. A mounting hole is provided in the middle of the back cover 702. The fiber collimation module 1 in the frequency doubling focusing module 6 passes through the mounting hole, and a flexible sealing ring 10 is provided between the outer wall of the rear end of the fiber collimation module 1 and the mounting hole to improve the sealing of the connection.

[0042] To further illustrate, the flexible sealing ring 10 may be selected as (but not limited to) a rubber tower-shaped sheath, which can ensure the sealing of the overall structure while leaving a certain amount of moving space for the frequency doubling focusing module 6, so that the frequency doubling focusing module 6 can be better aligned with the electrode gap of the photoconductive antenna 5.

[0043] Furthermore, a groove 703 is provided at the bottom of the cylinder 701, and a boss is provided at the bottom of the arc-shaped shell 802. The boss corresponds to the groove 703, and the cylinder 701 is put on the entire structure, and the boss is engaged in the groove. The polarization direction of the antenna is perpendicular to the direction of the antenna electrode. Only when the polarization directions of the transmitter and the detector are consistent can the strongest terahertz signal be detected, so it is necessary to mark the polarization direction of the antenna in the structure. In addition, mounting holes are provided in the horizontal polarization direction and the vertical polarization direction of the antenna, so that the antenna can freely switch the polarization direction.

[0044] Further explanation, the outer surface of the frequency doubling focusing module 6 and the inner surface of the housing 7 are both treated with conductive treatment, and the outer surface of the housing 7 is treated with insulation treatment. If necessary, a conductive pad can be covered inside to achieve a good effect of shielding electromagnetic interference. The outer surface of the frequency doubling focusing module 6 includes the outer surfaces of the second lens barrel 602 and the sleeve 603.

Claims

1. A fiber-coupled terahertz photoconductive antenna, characterized in that: The invention comprises an optical fiber collimation module, a first focusing lens, a frequency doubling module, a second focusing lens, a photoconductive antenna and a shell. The optical fiber collimation module, the first focusing lens, the frequency doubling module, the second focusing lens and the photoconductive antenna built in the shell are sequentially arranged along the incident direction of the femtosecond laser. The input end of the terahertz photoconductive antenna is connected to the femtosecond laser through a 1560nm±40nm wavelength optical fiber. The femtosecond laser emits a femtosecond laser with a central wavelength of 1560nm±40nm. The photoconductive antenna is a 780nm±20nm femtosecond laser. A light-excited terahertz photoconductive antenna, wherein the optical fiber collimation module is used to parallelize the pulse light with a central wavelength of 1560nm±40nm transmitted in the 1560nm±40nm wavelength optical fiber, the first focusing lens focuses the parallel light to the frequency doubling module, the frequency doubling module is used to convert the 1560nm±40nm wavelength light into a 780nm±20nm wavelength femtosecond laser, the second focusing lens focuses the frequency doubling light to the electrode gap of the photoconductive antenna; the photoconductive antenna receives the 780nm±20nm wavelength frequency doubling pulse light.

2. The optical fiber coupled terahertz photoconductive antenna according to claim 1, characterized in that: Terahertz photoconductive antennas use LT-GaAs or Si-GaAs antennas.

3. The optical fiber coupled terahertz photoconductive antenna according to claim 1, characterized in that: The frequency doubling module adopts periodically poled lithium niobate crystal PPLN, MgO:PPLN, the frequency doubling module is a double frequency doubling module, the input end face of the frequency doubling module is plated with a 1560nm±40nm anti-reflection film, and the output end face is plated with a 780nm±20nm anti-reflection film.

4. The optical fiber-coupled terahertz photoconductive antenna according to claim 1, characterized in that: The fiber collimation module, the first focusing lens, the frequency doubling module, and the second focusing lens constitute a frequency doubling focusing module, which also includes a first lens barrel, a second lens barrel, a sleeve, a first pressure ring, a second pressure ring, and a third pressure ring. The first focusing lens is fixed in the first lens barrel through the first pressure ring, and the first lens barrel is fixed in the cavity on the rear side of the sleeve. The front end of the fiber collimation module is also placed in the cavity on the rear side of the sleeve, and the front end of the fiber collimation module is close to the rear end of the first lens barrel. The second focusing lens is fixed in the second lens barrel through the second pressure ring, and the rear end of the second lens barrel is fixed in the cavity on the front side of the sleeve. The frequency doubling module is fixed in the cavity on the front side of the sleeve through the third pressure ring, and the front end of the third pressure ring is close to the rear end of the second lens barrel.

5. The optical fiber-coupled terahertz photoconductive antenna according to claim 4, characterized in that: The optical fiber-coupled terahertz photoconductive antenna also includes an internal supporting structure, which includes a circular base and an arc-shaped shell arranged coaxially. The circular base is fixed on the photoconductive antenna. A circular hole is provided at the center of the circular base, and the circular hole is aligned with the electrode gap of the photoconductive antenna. A frequency doubling focusing module is fixed in the cavity of the arc-shaped shell, and there is a certain adjustment gap between the outer surface of the frequency doubling focusing module and the cavity of the arc-shaped shell. The frequency doubling focusing module and the cavity of the arc-shaped shell are arranged coaxially.

6. The optical fiber-coupled terahertz photoconductive antenna according to claim 5, characterized in that: The optical fiber coupled terahertz photoconductive antenna also includes a circuit board, which is plugged into the internal supporting structure.

7. The optical fiber-coupled terahertz photoconductive antenna according to claim 6, characterized in that: The fiber-coupled terahertz photoconductive antenna also includes a flexible sealing ring. The outer shell consists of a cylinder and a back cover. The frequency doubling focusing module, the internal supporting structure and the photoconductive antenna are placed together in the cylinder. A mounting hole is provided in the middle of the back cover. The fiber collimation module in the frequency doubling focusing module passes through the mounting hole, and a flexible sealing ring is provided between the outer wall at the rear end of the fiber collimation module and the mounting hole.

8. The optical fiber-coupled terahertz photoconductive antenna according to claim 7, characterized in that: A groove is arranged at the bottom of the cylinder, and a boss is arranged at the bottom of the arc-shaped shell. The boss corresponds to the groove, and the cylinder is sleeved on the entire structure, and the boss is engaged in the groove.

9. The optical fiber-coupled terahertz photoconductive antenna according to claim 8, characterized in that: The outer surface of the frequency doubling focusing module and the inner surface of the shell are both treated with conductivity, and the outer surface of the shell is treated with insulation.

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