Simple approach for Doppler frequency shift estimation based on a dual-polarization quadrature phase shift keying (DP-QPSK) modulator.

A simple approach to estimating microwave Doppler frequency shift (DFS) based on a single dual-polarization quadrature phase shift keying (DP-QPSK) modulator is proposed and experimentally demonstrated. The scheme is capable of estimating both the value and direction of the DFS simultaneously and precisely owing to the introduction of the reference signal. In the proposed approach, the transmitted signal (microwave carrier) and the reference signal are loaded on the upper branch of the DP-QPSK modulator to generate carrier suppression double-sideband signals, respectively, while the echo signal is loaded on the lower branch of the DP-QPSK modulator to perform carrier suppression single-sideband modulation. Then optical sidebands of two branches are combined and sent to a low-speed photodetector to heterodyne. The value of the DFS is equivalent to the frequency of the beat signal between the transmitted and reference signals; meanwhile, the direction can be distinguished by comparing the frequency of the beat signal between the transmitted and reference signals with the frequency of the beat signal between the echo and reference signals. In the experiment, the accurate measurement of DFSs from $ - {100}\;{\rm kHz}$-100kHz to $ + {100}\;{\rm kHz}$+100kHz at the carrier frequencies of 15, 20, 35, and 39 GHz is implemented with errors less than $ \pm {10}\;{\rm Hz}$±10Hz.

Wideband and compact TM-pass polarizer based on hybrid plasmonic grating in LNOI.

Based on the transverse electric (TE)/transverse magnetic (TM) polarization diversity in plasmonic Bragg gratings, a compact TM-pass/TE-stop polarizer is theoretically proposed on thin-film lithium niobate on insulator (LNOI) platforms. By introducing a large misalignment between metal gratings on both sides of the LNOI waveguide, we demonstrate a polarizer with a high extinction ratio of 20 dB, a low insertion loss of 2.5 dB, a wide waveband from 1.48 to 1.62 µm, and a compact size of only 23 µm on simulation.

Piezoelectric constants for ZnO calculated using classical polarizable core-shell potentials.

We demonstrate the feasibility of using classical atomistic simulations, i.e. molecular dynamics and molecular statics, to study the piezoelectric properties of ZnO using core-shell interatomic potentials. We accomplish this by reporting the piezoelectric constants for ZnO as calculated using two different classical interatomic core-shell potentials: that originally proposed by Binks and Grimes (1994 Solid State Commun. 89 921-4), and that proposed by Nyberg et al (1996 J. Phys. Chem. 100 9054-63). We demonstrate that the classical core-shell potentials are able to qualitatively reproduce the piezoelectric constants as compared to benchmark ab initio calculations. We further demonstrate that while the presence of the shell is required to capture the electron polarization effects that control the clamped ion part of the piezoelectric constant, the major shortcoming of the classical potentials is a significant underprediction of the clamped ion term as compared to previous ab initio results. However, the present results suggest that overall, these classical core-shell potentials are sufficiently accurate to be utilized for large scale atomistic simulations of the piezoelectric response of ZnO nanostructures.