This manuscript presented the programmable metasurface based on LC (liquid crystal) material to manipulate the THz (terahertz) wave. To manipulate the EM (electromagnetic wave), the programmable and digital coding metasurfaces have been widely used in the microwave range using the semiconductor controlling elements (PIN diode and varactor diode). However, in the THz range, these semiconductor components have limited applications. Herein, a 1-bit digital programmable metasurface based on LC is proposed to achieve the THz wave manipulation with electrical control. The 1- bit digital coding metasurface is composed of two kinds of meta-atoms including “0” and “1” digital codes corresponding to the opposite reflection phase response “0” and “π” respectively. The reflection phase of the metasurface element is nearly 180° manipulating between biased (1) and unbiased (0) states of the coding sequence. When the different coding sequence is applied to the metasurface array, the phase profile between metasurface elements is changed dynamically and manipulate the incident THz beam. The proposed LC-based THz metasurface unit cell is applied with the different biasing voltages and in result the relative permittivity of the LC material is changed from 2.63 to 3.67 based on the orientation of the LC molecules. However, the resonant frequency is switching from 0.121 THz to 0.108 THz and achieved the 180 degree phase differences. Furthermore, 36x36 metasurface array is enabled to perform multi-functionalities including dual beam and multi-beam steering, beam splitting that could be implemented in the application of sensing, imaging, defence RCS (radar cross section) reduction and wireless communication such as RIS (Reconfigurable Intelligent Surfaces).
The construction of optical receivers using heterodyne detection techniques is a significant challenge due to the need for complex and power-intensive DSP approaches. Additionally, it is practically difficult to construct a local oscillator laser at the receiver that has the same frequency as the carrier laser for homodyne detection. Therefore, we propose a polarization multiplexed self-coherent detection method that sends both the message signal and the carrier through the same fiber while utilizing polarization diversity. Quadrature Amplitude Modulation is used for modulating the message signal. The system is capable of transmitting a data rate of 150 Gbps. We demonstrate an integrated polarization stabilizer that consists of cascaded Mach-Zehnder interferometers with a fast-tracking algorithm that can track the polarization of an incoming signal at the receiver and an integrated polarization converter based on Stokes vector that minimizes the effect of mixing of signals of orthogonal polarizations in the optical fiber. The algorithm used to feed the polarization controller can change the polarization of an incoming signal at the receiver to the polarization it had when it left the transmitter. Consequently, reducing the impact of PMD (Polarization mode dispersion) on transmission in fiber.
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