We experimentally demonstrate the orbital angular momentum (OAM) conversion by the coupled nonlinear optical processes in a quasi-periodically poled LiTaO3 crystal. In such a crystal, third-harmonic generation (THG) is realized by the coupled second-harmonic generation (SHG) and sum-frequency generation (SFG) processes, i.e., SHG is dependent on SFG and vice versa. The OAMs of the interacting waves are proved to be conserved in such coupled nonlinear optical processes. As we increase the input OAM in the experiment, the conversion efficiency decreases because of the reduced fundamental power density. Our results provide better understanding for the OAM conversions, which can be used to efficiently produce an optical OAM state at a short wavelength.
A folded slot antenna is presented for use in a quasi-optical mixer. The simple uniplanar quasi-optical mixer uses the effect of orthogonal modes in the folded slot antenna fed by slotline and coplanar waveguide on opposite sides Input impedance of the antenna is analyzed with the space domain integral equation technique. Experiments at 11 GHz have demonstrated antenna and mixer operation.
Mode swapping in characteristic mode analysis (CMA) affects consistent interpretation of the modal data. Mode tracking based on the eigenvector correlation can effectively determine the correct ordering of modes at each sampling frequency. However, there has been a lack of corresponding preprocessing for this mode-tracking algorithm. For example, the applicable frequency band cannot be determined in advance. In this paper, cosine similarity is used to calculate the correlation between modes of adjacent frequencies. It is then proposed that the 3/2 proportional relationship between the maximum size of the structure and the minimum operating wavelength can be used to choose the reliable operating band range of the algorithm. Meanwhile, it is recommended that the meshing side length should be less than one-tenth of a wavelength, and the adjacent sampling frequency interval should be less than the relative bandwidth of 10%. Through this preprocessing, correlation-based algorithms can efficiently implement mode tracking for open conductors.
Combined with characteristic mode analysis, the idea of degenerate mode synthesis can be used to guide the construction of a single antenna, which radiates vortex electromagnetic waves carrying orbital angular momentum (OAM). In this paper, an arc segment outside a circular patch is applied to disturb the structure symmetry to achieve a single‐fed antenna with orthogonal degenerate mode synthesis. Experimental results show that degenerated characteristic modes of circular patches radiate vortex waves one order lower than source modes. If two degenerate TM21 source modes are superimposed, the first‐order OAM mode is generated. Since the arc segment as a disturbance element is independent of the radiation element, OAM modes of different orders can be realized by adjusting its length.
A compact wideband filtering power divider is presented in this paper, by using coupled transmission lines at two output ports to realize filtering function. The return loss and insertion loss of the design in the passband are improved by inserting fan-shaped open stubs and etching a T-shaped slot at the input port. The central frequency of the power divider is 2.4 GHz. The measured results show a 10-dB fractional bandwidth of 60%, and a wideband filtering response can be obtained. The material object is designed by using FR4, and the size is 0.4λ g * 0.2λ g. The design is well used in the WiFi band.
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