Showing papers by "Daqing Zhang published in 2023"

WiTraj: Robust Indoor Motion Tracking With WiFi Signals

Abstract: WiFi-based device-free motion tracking systems track persons without requiring them to carry any device. Existing work has explored signal parameters such as time-of-flight (ToF), angle-of-arrival (AoA), and Doppler-frequency-shift (DFS) extracted from WiFi channel state information (CSI) to locate and track people in a room. However, they are not robust due to unreliable estimation of signal parameters. ToF and AoA estimations are not accurate for current standards-compliant WiFi devices that typically have only two antennas and limited channel bandwidth. On the other hand, DFS can be extracted relatively easily on current devices but is susceptible to the high noise level and random phase offset in CSI measurement, which results in a speed-sign-ambiguity problem and renders ambiguous walking speeds. This paper proposes WiTraj, a device-free indoor motion tracking system using commodity WiFi devices. WiTraj improves tracking robustness from three aspects: 1) It significantly improves DFS estimation quality by using the ratio of the CSI from two antennas of each receiver, 2) To better track human walking, it leverages multiple receivers placed at different viewing angles to capture human walking and then intelligently combines the best views to achieve a robust trajectory reconstruction, and, 3) It differentiates walking from in-place activities, which are typically interleaved in daily life, so that non-walking activities do not cause tracking errors. Experiments show that WiTraj can significantly improve tracking accuracy in typical environments compared to existing DFS-based systems. Evaluations across 9 participants and 3 different environments show that the median tracking error $<2.5\%$<2.5% for typical room-sized trajectories.

Mode-insensitive 3-dB power splitter based on multimode-interference coupler

Abstract: We proposed a broadband 3-dB power splitter based on multimode-interference coupler formed by polymer waveguide, which is insensitive to the arbitrary input modes, and demonstrated the operation functions of the design in the experiment. The design shows a mode-insensitive 3-dB power splitting for the E11, E21 and E12 modes with an imbalance power less than 0.11, 0.13 and 0.03 dB, respectively, over a 100 nm bandwidth that ranges from 1520 to 1620 nm. Our presented mode-insensitive 3-dB power splitter could find applications in mode (de)multiplexing systems where ultra-broadband power splitting is required.

Dual-Mode Variable Optical Attenuator Based on Polymer Waveguide Mach–Zehnder Interferometer

Abstract: The variable optical attenuator is one of the key components in optical communication system, but it is scarce for mode division multiplexing system. Here, we designed and experimentally demonstrated an ultra-broadband dual-mode variable optical attenuator based on Mach–Zehnder interferometer with thermo-optic phase shifters. We fabricated the device with polymer waveguide and characterized the function of the variable optical attenuator. The presented device can attenuate E11 and E12 modes simultaneously at a low power-consumption ( $\sim $ 4.8 mW) over 1500 - 1620 nm, which proves that our device is mode-insensitive and wavelength-insensitive. The presented variable optical attenuator can be widely used in mode division multiplexing system where mode-insensitive attenuating or switching is needed.

Design of an on-chip ultra-small thermo-optic tunable SOI waveguide microdisk resonator for optical information storage

Abstract: With the development of integrated photonic circuits, optical waveguide microdisk resonators (MRR) devices which can be easily integrated with photonic chips are becoming more and more important in optical communication systems. As the core execution unit to improve response sensitivity, field-programmable gate array, optical waveguide MRR has high applicability in esonators due to its smaller mode volume, and larger free spectral range (FSR). Specially, SOI waveguide fabrication technology is easy to be compatible with CMOS foundry processing and integrated circuit technology with smaller size and lower cost, so it can overcome the shortcomings of micro resonators fabricated by other materials. And SOI waveguide MRR has important research significance and distinguished application prospects, which has considered to be the future large-scale integrated photonic circuit basic devices. Because of its powerful optical signal processing ability, MRR has been widely used in various optical systems. With the advantages of simple manufacturing process, ease integration, and multitudinous functions, the waveguide MRR has become the basic structural unit of integrated photonic system and considered as the basic device of large-scale integrated optical path. Based on the high thermo-optic (TO) coefficient of Si material, the tunable function of the SOI MRR can be realized by TO modulation. A waveguide MRR with large tuning range, low optical transmission loss, simple electrode fabrication method, and high TO efficiency is proposed. In order to enhance the applicability of the designed SOI waveguide MRR at different wavelength bands, a tunable SOI MRR was designed.