A method based on equal frequency resampling is proposed to suppress laser nonlinear frequency sweeping for the ultimate spatial resolution in optical frequency domain reflectometry. Estimation inaccuracy of the sweeping frequency distribution caused by the finite sampling rate in the auxiliary interferometer can be efficiently compensated by the equal frequency resampling method. With the sweeping range of 130 nm, a 12.1 µm spatial resolution is experimentally obtained. In addition, the sampling limitation of the auxiliary interferometer-based correction is discussed. With a 200 m optical path delay in the auxiliary interferometer, a 21.3 µm spatial resolution is realised at the 191 m fibre end. By employing the proposed resampling and a drawing tower FBG array to enhance the Rayleigh backscattering, a distributed temperature sensing over a 105 m fibre with a sensing resolution of 1 cm is achieved. The measured temperature uncertainty is limited to ±0.15 °C.

Phase-sensitive optical frequency domain reflectometer (Φ-OFDR) is investigated to deliver an accurate distributed measurement with high spatial resolution. It is found that random phase noise and quadrant discrimination during phase calculation are the main reasons for the random hopping in Φ-OFDR. By efficiently eliminating random hopping in the phase unwrap and suppressing the laser-induced nonlinear sweep for the theoretical spatial resolution, the proposed Φ-OFDR is proved to be able to decouple the limitation between resolution and accuracy in coherent OFDR (C-OFDR). Distributed strain measurement with 20 mm spatial resolution in Φ-OFDR is obtained and analysed. Measurement with little deviation and uniform sensitivity between applied strain and phase change both validate the efficient noise suppression for extreme resolution measurement. Then the influence of the initial sweep frequency between two times measurements is studied. With a further reduced 800 µm spatial resolution, the proposed Φ-OFDR is able to retain accurate distributed measurement compared to conventional C-OFDR methods. Besides, the computation time of the Φ-OFDR is only 3.2% of the C-OFDR.

Light Detection and Ranging (LiDAR) sensors can precisely determine object distances using the pulsed time of flight (TOF) or amplitude-modulated continuous wave (AMCW) TOF methods and velocity using the frequency-modulated continuous wave (FMCW) approach. In this paper, we focus on modelling and analysing the reflection of vector beams (VBs) and vector vortex beams (VVBs) for optical sensing in LiDAR applications. Unlike traditional TOF and FMCW methods, this novel approach uses VBs and VVBs as detection signals to measure the orientation of reflecting surfaces. A key component of this sensing scheme is understanding the relationship between the characteristics of the reflected optical fields and the orientation of the reflecting surface. To this end, we develop a computational model for the reflection of VBs and VVBs. This model allows us to investigate critical aspects of the reflected field, such as intensity distribution, intensity centroid offset, reflectance, and the variation of the intensity range measured along the azimuthal direction. By thoroughly analysing these characteristics, we aim to enhance the functionality of LiDAR sensors in detecting the orientation of reflecting surfaces.

This paper presents the total angular momentum-conserving Poincaré sphere (TAM-C PS), which offers a novel framework for efficiently characterizing a wide range of vector vortex beams. Unlike other types of Poincaré spheres, the TAM-C PS achieves a better balance between generality and validity, while also providing clearer physical interpretation. By linking the poles of different spheres, the study also introduces two distinct categories of TAM-C PS braid clusters, enabling the representation of various Poincaré spheres within a unified framework. The Poincaré spheres include classical, higher-order, hybrid-order, Poincaré sphere with orbital angular momentum, and TAM-C PS. This is the first clear and unified approach to express multiple Poincaré spheres within a single framework. The TAM-C PS and its braid cluster can be employed to guide the creation of targeted vector vortex light beams, offer a geometric description of optical field evolution, and calculate the geometric phase of optical cyclic evolution.

On-chip millimeter-wave interconnects are becoming crucial for advancing on-chip and inter-chip transmission technologies, improving transmission efficiency and system scalability, especially in Wireless Network-on-Chip (WiNoC) and chip-scale 2.5D and 3D integration. However, due to the inherent limitations of on-chip integration related to antenna size and microfabrication compatibility. On-chip wireless channels often necessitate the use of compact, planar antennas. These antennas typically suffer from limited transmission gain, lack of beam control, and poor interference immunity, posing challenges to the reliability and versatility of millimeter-wave interconnects. This paper presents a 1-bit digital-coding metamaterial to address these challenges. The metamaterial features a 3x5 tunable unit-cell array, with each cell switchable between the ’0’ or ’1’ state with a distinct refractive index. The refractive index distribution within the unit cell array can be controlled through different binary coding sequences to manipulate the electromagnetic waves and achieve different transmission functions. When integrated with an on-chip dipole antenna, the metamaterial can achieve adjustable beamsteering in the range of ± 40°, 3.3 dB transmission gain enhancement, 90° beam splitting, and efficient energy attenuation. The proposed digital-coding metamaterial allows precise control and reconfiguration of the wireless signal distribution on silicon, significantly enhancing the flexibility, efficiency, and scalability of on-chip millimeter-wave communications.

In modern wireless communication systems, data transmission is achieved through the collaboration of digital modulation circuits and antennas. Digital baseband signals are first modulated in terms of amplitude, frequency, and phase of the carrier wave and then transmitted directionally via antennas. However, in intra-chip environments, the performance of on-chip antennas is fundamentally constrained by micro-fabrication and integration requirements. As a result, these antennas often exhibit low gain and efficiency and are susceptible to interference among closely spaced transmission channels. To address these limitations, we propose a digital coding metamaterial for direct signal modulation within intra-chip wireless channels, providing an alternative solution to achieve directional signal delivery without depending on the antenna’s intrinsic radiation pattern. The proposed metamateiral can directly convert digital control inputs into discrete phase shifts of a 70 GHz TE-mode surface wave, enabling post-radiation modulation as the electromagnetic wave propagates through the metamaterial. When combined with a single broadcast antenna, multiple metamaterial units can perform simultaneous, multi-directional modulation and transmissions. The proposed metamaterial supports various phase shift modulation schemes, including BPSK, QPSK, and 8-PSK. Furthermore, it enables hybrid modulation and beam steering modes, offering a beam steering range of up to $$\pm 28^{\circ }$$ . The proposed metamateiral presents an innovative method for information routing in intra-chip transmission, helps reduce signal crosstalk under parallel transmission, and expands wireless channel capacity and spectral efficiency.