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He J.,Harbin Institute of Technology | He J.,Capital Normal University | He J.,Beijing Key Laboratory for Metamaterials and Devices | Wang S.,Harbin Institute of Technology | And 5 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2016

Based on metasurface, two beam shapers are designed to modulate the wavefront of the terahertz beam. One of the beam shapers is THz ring-Airy beam generator and the other is THz four-focus lens. Each beam shaper is composed of a serious of C-shaped slot antennas, which can be used to modulate the phase and amplitude of the cross-polarized scattered wave. A THz holographic imaging system is utilized to measure the field of the generated beams. The ring- Airy beam shaper is designed by replacing both the phase and amplitude of its initial electric field with the corresponding antennas. In the experiment, an abrupt focus following a parabolic trajectory is subsequently observed. This method can be expanded to other wavebands, such as the visible band, in which the ring-Airy beam shaper can replace traditional computer-generated holography to avoid undesirable multiple diffraction orders. The phase distribution of the four-focus lens is obtained by using the Yang-Gu amplitude-phase retrieval algorithm and then encoded to the antennas. Both the focusing and imaging properties are demonstrated. A clear image can be obtained with a bandwidth of 110 GHz. This type of transmissive metasurface beam shaper serves as an attractive alternative to conventional diffractive optical elements based on its small size, ease of fabrication, and low cost. © 2016 SPIE.


Wang H.,Beijing Key Laboratory for Metamaterials and Devices | Wang H.,Capital Normal University | Xie Z.,Beijing Key Laboratory for Metamaterials and Devices | Xie Z.,Capital Normal University | And 19 more authors.
Optics and Laser Technology | Year: 2016

A miniaturized optical fiber microphone (OFM) is created by fabricating a concentric nanorings grating and microsprings structured half spherical diaphragm on the end facet of a single-mode fiber (SMF). The diaphragm is fabricated via the method of two-photon 3D lithography. The thin nanorings grating patterned diaphragm is actually a resonant grating-waveguide. It exhibits high reflectivity when resonance is excited. A microlens is fabricated at the core of the fiber, which is used to diverge the output light to make it be normally incident onto the diaphragm, then reflected back to the fiber. The intensities of the reflected back light will be changed if the resonant conditions of the resonant grating-waveguide are broken due to the sound pressure induced geometrical changes of the configuration. This makes such device be an acoustic sensor. The microsprings are designed to improve the sensitivity to the sound pressure. Acoustic inspections show that this OFM can detect the weak sound in air with frequency band from 400 to 2000 Hz. © 2015 Elsevier B.V. All rights reserved.


Yuan M.,Capital Normal University | Yuan M.,Beijing Key Laboratory for Metamaterials and Devices | Sun W.,Capital Normal University | Sun W.,Beijing Key Laboratory for Metamaterials and Devices | And 8 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2015

Pulsed terahertz reflected imaging technology has been expected to have great potential for the non-invasive analysis of artworks. In this paper, three types of defects hidden in the plaster used to simulate the cases of defects in the murals, have been investigated by a pulsed terahertz reflected imaging system. These preset defects include a circular groove, a cross-shaped slit and a piece of "Y-type" metal plate built in the plaster. With the terahertz reflective tomography, information about defects has been determined involving the thickness from the surface of sample to the built-in defect, the profile and distribution of the defect. Additionally, three-dimensional analyses have been performed in order to reveal the internal structure of defects. Terahertz reflective imaging can be applied to the defect investigation of the murals. © 2015 SPIE.


He J.,Harbin Institute of Technology | He J.,Capital Normal University | He J.,Beijing Key Laboratory for Metamaterials and Devices | Wang S.,Harbin Institute of Technology | And 5 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2015

Based on the localized surface plasmons (LSPs), a series of C-shaped slits antennas are designed to modulate the phase and amplitude of the cross-polarized transmitted wave in THz waveband. By adjusting the structure parameters of the antenna unit, arbitrary phase and amplitude modulation of the cross-polarized THz wave can be obtained. The C-shaped slit antenna units are designed at two operating frequencies f=0.8 THz and f=1.0 THz using a commercial software package (Lumerical Solutions), which is based on the finite-difference time-domain method. According to the simulated results, principles for modulating the phase and amplitude of THz wave are summarized as follows. Firstly, the operating wavelength depends on the effective length of the antenna and the operating wavelength increases as the effective length increases; Secondly, the phase of the cross-polarized wave can be modulated from 0 to 2π by changing the opening angle of the split; Thirdly, the amplitude transmittance of the cross-polarized wave can be changed from the extinction state to the maximum value by rotating the symmetry axis of the C-shaped slit. These principles can be used to direct the design of the field modulator in any other working frequency. © 2015 SPIE.


Wang S.,Harbin Institute of Technology | Wang S.,Capital Normal University | Wang S.,Beijing Key Laboratory for Metamaterials and Devices | Wang X.,Capital Normal University | And 4 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2015

Focusing of terahertz (THz) surface plasmon polaritons (SPPs) excited by linearly and circularly polarized THz radiation is investigated experimentally and theoretically. A high-speed THz-SPPs imaging system is built up to measure both the amplitude and phase of the excited THz-SPPs. For the horizontally polarized THz radiation, the THz-SPPs will be focused in the centre of the semicircular slit and the phase images reveals a p/2 Gouy phase shift though the focal spot of THz-SPPs. With the illumination of vertically polarized THz radiation, the focal spot in the centre will split into two focal spots in the y-direction. For the circularly polarized incident THz radiation, the focal spot of THz-SPPs will shift upward or downward in the y-direction. FDTD simulations are performed and compared with the experimental results. A good agreement between experimental results and simulation results can be found. © 2015 SPIE.


Wang H.,Beijing Key Laboratory for Metamaterials and Devices | Wang H.,Capital Normal University | Xie Z.,Beijing Key Laboratory for Metamaterials and Devices | Xie Z.,Capital Normal University | And 19 more authors.
Optics and Laser Technology | Year: 2015

A miniaturized optical fiber microphone (OFM) is created by fabricating a concentric nanorings grating and microsprings structured half spherical diaphragm on the end facet of a single-mode fiber (SMF). The diaphragm is fabricated via the method of two-photon 3D lithography. The thin nanorings grating patterned diaphragm is actually a resonant grating-waveguide. It exhibits high reflectivity when resonance is excited. A microlens is fabricated at the core of the fiber, which is used to diverge the output light to make it be normally incident onto the diaphragm, then reflected back to the fiber. The intensities of the reflected back light will be changed if the resonant conditions of the resonant grating-waveguide are broken due to the sound pressure induced geometrical changes of the configuration. This makes such device be an acoustic sensor. The microsprings are designed to improve the sensitivity to the sound pressure. Acoustic inspections show that this OFM can detect the weak sound in air with frequency band from 400 to 2000. Hz. © 2015 Elsevier Ltd.


Yuan M.,Capital Normal University | Yuan M.,Beijing Key Laboratory for Metamaterials and Devices | Sun W.,Capital Normal University | Sun W.,Beijing Key Laboratory for Metamaterials and Devices | And 9 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2015

Terahertz time-domain spectroscopy (THz-TDS) imaging technology has been proposed to be used in the non-invasive detection of murals. THz-TDS images provide structural data of the sample that cannot be obtained with other complementary techniques. In this paper, two types of defects hidden in the plaster used to simulate the cases of defects in the murals, have been investigated by the terahertz reflected time domain spectroscopy imaging system. These preset defects include a leaf slice and a slit built in the plaster. With the terahertz reflective tomography, information about defects has been determined involving the thickness from the surface of sample to the built-in defect, the profile and distribution of the defect. With this THz tomography, different defects with the changes of optical thickness and their relative refractive index have been identified. The application of reflective pulsed terahertz imaging has been extended to the defect detection of the murals. © COPYRIGHT 2015 SPIE.

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