A fiber-coupled terahertz time-domain spectroscopy compact field measurement system

Abstract

The present application relates to a kind of optical fiber coupling terahertz time-domain spectroscopy tight field measurement system, it is related to terahertz wave measurement field, including generation path and detection path, generation path and detection path are all through the output laser of optical fiber coupling laser generation, the laser output of generation path is converted into terahertz wave and is transmitted to target area, target area is reflected to detection path, and detection path receives terahertz wave by laser excitation receiver, and terahertz wave is converted into electric current and is measured, the present application has the advantages that the technical problems such as device selection, system integration encountered when the middle optical fiber coupling technology is applied to terahertz time-domain spectroscopy tight field measurement system.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of terahertz wave measurement, and particularly to an optical fiber coupled terahertz time domain spectroscopy compact field measurement system. BACKGROUND

[0002] Terahertz waves are between microwaves and infrared, and have natural band advantages. Due to the lack of efficient hardware devices, the terahertz band has great development potential and great application prospects in the field of radar target characteristics. In the compact field measurement, the microwave and millimeter wave bands have mature system construction schemes, while the terahertz band is limited by the development of device level, and has not formed a standard measurement system. The terahertz time domain spectroscopy technology has the characteristics of large bandwidth, high signal-to-noise ratio and high time domain resolution, and has unique technical application scene advantages in compact field measurement.

[0003] The optical fiber coupled terahertz time domain spectroscopy technology has the advantages of simple optical path, easy operation, easy polarization adjustment and excellent performance, and has been applied in the field of spectral measurement, but has not been applied in the compact field measurement with a large static zone size. There are still many technical problems in device selection and system integration.

[0004] Therefore, in view of the above problems, an optical fiber coupled terahertz time domain spectroscopy compact field measurement system is needed. SUMMARY

[0005] (I) Technical problems to be solved

[0006] The technical problem to be solved by the present application is to solve the problem that the existing terahertz time domain spectroscopy compact field measurement has not formed a standard system.

[0007] (II) Technical scheme

[0008] In order to solve the above technical problems, the present application provides an optical fiber coupled terahertz time domain spectroscopy compact field measurement system, which comprises a generating path and a detection path. The generating path and the detection path both generate output laser through an optical fiber coupled laser. The generating path converts the output laser into terahertz waves and transmits the terahertz waves to a target area. The target area reflects to the detection path. The detection path receives the terahertz waves through a laser excitation receiver, and converts the terahertz waves into an electric current for measurement.

[0009] As a further description of the present application, preferably, the generating path is an optical path for generating terahertz waves and a transmission optical path of the terahertz waves, and the detection path is a transmission optical path of a laser excitation receiver. The optical path difference between the generating path and the detection path is an integer multiple of the spatial period of the laser pulse.

[0010] As a further illustration of the present application, preferably, the generating path comprises a generating path power attenuator, a transmitting antenna, a first parabolic mirror and a second parabolic mirror, the generating path power attenuator receives and attenuates laser power generated from the fiber-coupled laser, the transmitting antenna generates terahertz waves after receiving the attenuated laser from the generating path power attenuator, and the terahertz waves are transmitted to the target area via the first parabolic mirror and the second parabolic mirror.

[0011] As a further illustration of the present application, preferably, the detecting path comprises a detecting path power attenuator, a fiber delay line and a receiving antenna, the detecting path power attenuator receives and attenuates laser power generated from the fiber-coupled laser, the fiber delay line receives the attenuated laser from the detecting path power attenuator and performs scanning, and the receiving antenna generates carriers after receiving the laser from the fiber delay line, the carriers in the receiving antenna receive terahertz waves reflected from the target area, generate current after being modulated, and the terahertz waves are measured by detecting the current.

[0012] As a further illustration of the present application, preferably, the second parabolic mirror is further provided with a mirror and a main parabolic mirror, the second parabolic mirror transmits the terahertz waves to the mirror, the mirror reflects the terahertz waves to the main parabolic mirror, and finally the terahertz waves are reflected to the target area by the main parabolic mirror.

[0013] As a further illustration of the present application, preferably, the main parabolic mirror receives the terahertz waves reflected from the target area, reflects the terahertz waves to the mirror, and the terahertz waves are reflected to the receiving antenna via the mirror.

[0014] As a further illustration of the present application, preferably, the transmitting antenna is located at the focal point of the first parabolic mirror, the second parabolic mirror and the main parabolic mirror form an expanded beam optical path, and the expansion ratio is the focal length ratio.

[0015] As a further illustration of the present application, preferably, the fiber-coupled laser outputs a pulse width less than 100 fs, the interface is FC / APC, and a polarization maintaining optical fiber transmission line is used.

[0016] As a further illustration of the present application, preferably, the generating path power attenuator and the detecting path power attenuator are the same, and the polarization extinction ratio is greater than 16 dB.

[0017] As a further illustration of the present application, preferably, the fiber delay line outputs a power fluctuation less than 2.5 dB, and the insertion loss is better than 1.5 dB.

[0018] (Three) beneficial effects

[0019] The above technical scheme of the present application has the following advantages:

[0020] The application designs a fiber-coupled terahertz time-domain spectroscopy compact field measurement system, which can not only accurately detect terahertz waves, but also establishes a normative reference for the setting of such measurement systems, and fills the technical gap in compact field measurement with a larger static zone size. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a measurement system composition diagram of the application.

[0022] Figure 2 is a flat plate time-domain signal diagram measured by the measurement system of the application.

[0023] In the figure: 1, fiber-coupled laser; 2, generating path power attenuator; 21, transmitting antenna; 22, first parabolic mirror; 23, second parabolic mirror; 3, detecting path power attenuator; 31, fiber delay line; 32, receiving antenna; 33, third parabolic mirror; 4, bias voltage source; 5, reflecting mirror; 6, main parabolic mirror; 7, target area. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical scheme and advantages of the embodiments of the application more clear, the technical scheme in the embodiments of the application will be clearly and completely described below in combination with the drawings of the embodiments of the application. Obviously, the described embodiments are part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the application.

[0025] A fiber-coupled terahertz time-domain spectroscopy compact field measurement system, as shown in Figure 1 includes a generating path and a detecting path, both of which generate output laser through a fiber-coupled laser 1. The fiber lengths of all devices in the generating path and the detecting path are combined with the optical path of terahertz waves, the fiber lengths of the generating path and the detecting path are preset, and the pre-dispersion compensation length of the fiber-coupled laser 1 is set accordingly. The pulse width of the fiber-coupled laser 1 is preferably within 100 fs, the recommended interface is FC / APC, and the connection is through polarization maintaining optical fiber. The selection fully considers the insertion loss of each device, so that the laser power reaching the antenna can meet the requirements of the antenna. The fiber-coupled laser 1 outputs laser with a specific pulse width and wavelength into two paths. The optical path difference between the generating path and the detecting path is an integer multiple of the spatial period of the laser pulse, so as to ensure that the signal can be detected.

[0026] As shown in Figure 1As shown, the generation path includes a generation path power attenuator 2, a transmitting antenna 21, a first parabolic mirror 22, and a second parabolic mirror 23. The detection path includes a detection path power attenuator 3, an optical fiber delay line 31, and a receiving antenna 32. The generation path power attenuator 2 and the detection path power attenuator 3 are of the same model, and both function to receive and attenuate the laser power generated by the fiber-coupled laser 1. The maximum input power of the generation path power attenuator 2 and the detection path power attenuator 3 should be greater than the maximum power of the fiber-coupled laser 1, the polarization extinction ratio should be greater than 16dB, the attenuation should be continuously adjustable from zero to the maximum output power of the fiber-coupled laser 1, and the fiber wavelength should be consistent with that of the fiber-coupled laser 1. Preferably, both interfaces are FC / APC, connected via polarization-maintaining fiber.

[0027] like Figure 1 As shown, the generation path is the optical path for generating terahertz waves and the transmission path for those waves. Specifically, the generation path power attenuator 2 receives and attenuates the laser power generated from the fiber-coupled laser 1. Then, the transmitting antenna 21 receives the attenuated laser power from the generation path power attenuator 2 and generates terahertz waves, which are then transmitted to the target area 7 via the first parabolic mirror 22, the second parabolic mirror 23, the reflector 5, and the main parabolic mirror 6. The transmitting antenna 21 is located at the focal point of the first parabolic mirror 22. The second parabolic mirror 22 and the main parabolic mirror 6 form a beam-expanding optical path with a beam-expanding ratio equal to the focal length ratio. A bias voltage source 4 is connected to the transmitting antenna 21 for signal amplification. The output of the bias voltage source 4 is controlled by a TTL signal generated by a lock-in amplifier.

[0028] like Figure 1 As shown, the detection path is the optical path transmitted by the laser excitation receiving detector. Specifically, the detection path power attenuator 3 receives and attenuates the laser power generated from the fiber-coupled laser 1 to match the photoconductive receiving antenna. The fiber delay line 31 receives the laser power attenuated by the detection path power attenuator 3. Then, by controlling the change in the length of the optical path, the optical path difference between the generation path and the detection path is always kept as an integer multiple of the laser pulse period, thereby scanning the signal within a distance range at one end. The distance domain is the same as the time domain (QUOTE). QUOTE (Speed ​​of light). After receiving the laser light from the fiber delay line 31, the receiving antenna 32 generates charge carriers. These charge carriers in the receiving antenna 32 receive the terahertz waves reflected from the target region 7 by the main parabolic mirror 6 and the reflecting mirror 5, and combine them with... Figure 2 The current is generated through modulation, and the terahertz wave is measured by detecting the current through the built-in current amplifier and lock-in amplifier. The output power fluctuation of the fiber delay line 31 is less than 2.5dB, the insertion loss is better than 1.5dB, and it is connected through polarization-maintaining fiber, preferably with an FC / APC interface. The scanning range is selected according to the size requirements of the test target.

[0029] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced by equivalent features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A fiber-coupled terahertz time-domain spectroscopy compact field measurement system, characterized by: The generating path and the detecting path are provided, the generating path is an optical path for generating terahertz waves and transmitting the terahertz waves, and the detecting path is an optical path for transmitting the light received by a laser excitation receiver, and an optical path difference between the generating path and the detecting path is an integer multiple of a spatial period of laser pulses; The generating path and the detecting path both generate output laser through a fiber-coupled laser (1), the fiber-coupled laser (1) has an output pulse width less than 100 fs, an interface of FC / APC, and uses a polarization maintaining optical fiber transmission line; the generating path includes a generating path power attenuator (2), a transmitting antenna (21), a first parabolic mirror (22), and a second parabolic mirror (23), the generating path power attenuator (2) receives and attenuates laser power generated from the fiber-coupled laser (1), the transmitting antenna (21) is located at a focal point of the first parabolic mirror (22), the second parabolic mirror (23) and a main parabolic mirror (6) form an expansion light path with a focal length ratio as an expansion ratio; the transmitting antenna (21) generates terahertz waves after receiving the laser attenuated from the generating path power attenuator (2), and transmits the terahertz waves to a target area (7) via the first parabolic mirror (22) and the second parabolic mirror (23), the target area (7) reflects to the detecting path, the detecting path includes a detecting path power attenuator (3), a fiber delay line (31), and a receiving antenna (32), the detecting path power attenuator (3) receives and attenuates laser power generated from the fiber-coupled laser (1), the fiber delay line (31) receives the laser attenuated from the detecting path power attenuator (3) and performs scanning, and the receiving antenna (32) generates carriers after receiving the laser of the fiber delay line (31), the carriers in the receiving antenna (32) receive the terahertz waves reflected by the target area (7), generate electric current after modulation, and measure the terahertz waves by detecting the electric current.

2. The fiber-coupled terahertz time-domain spectroscopy compact field measurement system according to claim 1, characterized in that: The second parabolic mirror (23) and the target area (7) are further provided with a reflecting mirror (5) and the main parabolic mirror (6), the second parabolic mirror (23) transmits the terahertz waves to the reflecting mirror (5), the reflecting mirror (5) reflects the terahertz waves to the main parabolic mirror (6), and finally the terahertz waves are reflected to the target area (7) through the main parabolic mirror (6).

3. The fiber-coupled terahertz time-domain spectroscopy compact field measurement system according to claim 2, characterized in that: The main parabolic mirror (6) receives the terahertz waves reflected by the target area (7), and reflects the terahertz waves to the reflecting mirror (5) again, and the terahertz waves are reflected to the receiving antenna (32) via the reflecting mirror (5).

4. The fiber-coupled terahertz time-domain spectroscopy compact field measurement system according to claim 3, characterized in that: The generating path power attenuator (2) and the detecting path power attenuator (3) are the same, and both have a polarization extinction ratio greater than 16 dB.

5. The fiber-coupled terahertz time-domain spectroscopy compact field measurement system according to claim 4, characterized in that: The fiber delay line (31) has an output power fluctuation less than 2.5 dB and an insertion loss better than 1.5 dB.

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