Tailoring the electromagnetic responses by metasurface greatly expands one's capabilities to manipulate light in a controlled manner. Either amplitude or phase of the incident wave can be altered during the light–matter interaction, and thus opens the possibility of information modulation without conventional analog or digital circuits. A prototype of quadrature phase‐shift keying (QPSK) wireless communication based on time‐domain digital coding metasurface, whose reflection properties can be varied within different time slots by changing the biasing voltages of varactor diodes in specially designed meta‐atoms, is developed here. As the information is transformed into binary bit streams and mapped to pulse sequences of the biasing voltage, the baseband digital signal is directly modulated to the carrier wave through the digital coding metasurface. Compared to the earlier version of binary frequency‐shift keying architecture based on digital coding metasurface, the proposed QPSK system has a much higher data‐transmission rate for wireless communications. A proof‐of‐concept experiment is conducted to prove the real‐time transmission ability of this system, where a video is delivered between the transmitter and receiver with high accuracy and date rate. The presented work is promising in the development of next‐generation wireless communication technologies.
In this letter, we apply a non-equalization orthogonal frequency-division multiplexing (NE-OFDM) technique in optical turbulence channel for coherent free-space optical (FSO) systems, utilizing multilevel differential phase-shift-keying (MDPSK). We adopt the modified Rician distribution as the optical turbulence channel for coherent FSO systems, where both amplitude fading and phase distortion are taken into consideration. The differential encoding process of MDPSK based NE-OFDM can be performed either in the frequency domain (FD) or in the time domain (TD). Our simulation results show that NE-OFDM using FD-MDPSK achieves nearly the same bit-error-rate (BER) performance as that using TD-MDPSK, but with a relatively lower hardware complexity and a higher spectral efficiency. It is also revealed that FD-MDPSK based NE-OFDM attains a comparable BER performance to the conventional OFDM with pilot tones or training sequences assisted channel estimation and equalization. Hence, FD-MDPSK based NE-OFDM is promising for coherent FSO communication.
We study the thermodynamics of QCD system under external magnetic field via the 2+1 flavor Polyakov-loop quark-meson model. To incorporate quantum and thermal fluctuations, the functional renormalization group approach is implemented in our work. Pressure, entropy density, magnetic susceptibility and other thermodynamic quantities are calculated and analyzed to investigate the effect of magnetic field on the QCD system. The calculated results are in reasonable agreement with lattice QCD simulations and perturbation theory. We then give an intuitive picture for the response of QCD system to the magnetic field.
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