Liting Niu

A flexible approach for terahertz (THz) generalized perfect vortex beams (GPVBs) is proposed and experimentally showcased in various spatial modes. By the predefined curved trajectories and topological charges, we construct the amplitude and phase profiles of THz GPVBs to induce corresponding pure phase holograms computed by a modified dual-constraint Gerchberg-Saxton algorithm. In experiments, we fabricate the phase hologram plates to realize the THz GPVBs in single, multiplexed, coaxial, and arrayed curve modes, and the result indicates that the geometrical characteristics and carried topological charges of the THz GPVBs can be flexibly manipulated and customized. These THz GPVBs exhibit significant potential for encoding information in high-capacity THz mode-division multiplexing communications.

An efficient method is proposed to measure the topological charge (TC) of terahertz (THz) vortex beams with a focal hyperbolic (FH) lens at 0.1 THz. The FH lens is designed and fabricated by 3D printing. The diffraction fringes acquired in the focal plane of the FH lens can judge the number and sign of the TC. Furthermore, after the horizontal or vertical measurement curve is recorded by rotating the FH lens to a suitable angle, the TC value can then be simply and effectively identified. The TC value of the experiment measurement reaches 5. The experiment results are in excellent accord with the simulation.

A conventional millimeter-wave stepped frequency continuous wave (SFCW) synthetic aperture radar (SAR) imaging system generally utilizes IQ modulation technique to acquire the amplitude and phase of the waves scattered from a target object. Due to measure both in-phase signal and quadrature signal, the transceiver of the conventional system is complicate and costly, and the IQ imbalance problem makes the system difficult to calibrate. To reduce hardware complexity and enhance efficiency-cost ratio, a novel SFCW SAR imaging system only measuring in-phase signal is proposed and demonstrated. For lack of quadrature signal measurement, an algorithm based on Fourier transform is proposed to estimate the amplitude and phase. The ultimate images are obtained through an image-reconstruction algorithm, which uses the estimated amplitude and phase as input parameters. The proposed system is verified by both simulation and experiment, where the frequencies are set from 24GHz to 30GHz. The imaging results with high resolution and low noise are demonstrated. Compared to the conventional system, the image quality of the proposed system is almost identical, but the transceiver of the proposed system is greatly simplified.

An effective experiment scheme is proposed to generate the terahertz (THz) perfect optical vortex (POV) beams by diffractive elements at the frequency of 0.1THz. Two diffractive elements are designed and fabricated by 3D-printing to form the generation system. The ring radius of the generated beams is independent of the topological charge and positive linear relationship with the radial wave vector. By controlling the radial wave vector, the ring radius can be freely adjusted. The experiment results are shown to corroborate the numerical simulation ones. Such generated beams hold promise for developing the novel THz fiber communication systems.

Novel diffractive elements are presented to produce zero-order Bessel beams in the terahertz (THz) band. First, diffractive elements are designed as phase plates to change the direction of the incident Gaussian beam. Then, they are fabricated by the emerging 3D printing technology. Last, zero-order Bessel beams are generated by the diffractive elements at 0.3 THz. To verify the feasibility of this approach, the generated zero-order Bessel beams are monitored and compared with the ones generated by the axicons. The comparison confirms that the diffractive elements can produce Bessel beam effectively and efficiently. In addition, the diffractive elements are applied to introduce zero-order Bessel beam to a THz reflection imaging system. A resolution test phantom is imaged by the THz reflection imaging system with zero-order Bessel beam and a conventional THz reflection imaging system. The results indicate that the THz reflection imaging system with Bessel beam offers a significantly extended depth of field and high anti-interference capability.

We first present the one-dimensional (1-D) terahertz (THz) Airy beam with a 0.3-THz continuous wave. The required phase modulation and the optical Fourier transform are implemented with a 3-D printed cubic-phase plate (CPP) and a cylindrical lens, respectively. According to the parameter of the designed CPP, we numerically calculate the intensity distributions of the 1-D THz Airy beam in the free space. The experimental results show a good accordance with the theoretical ones. Additionally, by blocking part of the generated 1-D Airy beam with a metal screen, the beam exhibits a self-healing property, i.e., tends to reform during propagation.