Mingming Luo

Indoor three-dimensional (3D) visible light positioning (VLP) suffers from non-line-of-sight multipath reflections and receiver-height uncertainty, which degrade positioning accuracy. To address these challenges, we propose a weighted least-squares-improved crested porcupine optimizer (WLS-ICPO) positioning method. The method first employs WLS for coarse localization to construct 3D region-of-interest (ROI) constraints and then applies ICPO within the ROI for refined optimization. ICPO incorporates a three-tier elite stratification strategy, independent Gaussian perturbation along the z-axis, and simplex-based local search, enabling a balance between global exploration and local exploitation. In a 5 m3×5 m3×3 m3 environment, simulation results show that WLS-ICPO achieves an average positioning error of 3.38 cm, representing reductions of 90.54% and 78.50% compared with WLS and conventional crested porcupine optimizer, respectively. The method also maintains low positioning errors across the tested signal-to-noise ratio levels, indicating its potential for indoor VLP applications.

This paper innovatively proposes a physical-layer security-enhanced scheme for orthogonal frequency division multiplexing visible light communication (OFDM-VLC) based on high-dimensional multi-mode index modulation (HD-MMIM). The scheme deeply integrates a 1D Logistic chaos model and the 4D hyperchaotic model, establishing a multi-level and all-around dynamic protection framework including bit stream XOR encryption, index table encryption, and HD constellation rotation. Experimental results show that HD-MMIM effectively improves the transmission performance of the VLC system. Compared with 4D-MMIM and 5D-MMIM, the 6D-MMIM has a Q-factor increase of 0.63 dB and 1.12 dB, respectively, and the optimal operating range of bias current for 6D-MMIM is extended by 29.38 mA and 19.15 mA, respectively. Meanwhile, the designed physical layer encryption scheme has a key space of up to 10¹⁹⁸; unauthorized users cannot demodulate the signal without the correct key, greatly resisting brute-force attacks and enhancing system security.

A Fresnel mirror is introduced at a hollow-core photonic bandgap fiber end by fusion splicing a short single-mode fiber segment, to reflect the light backward to an optical frequency domain reflectometry. The backward Fresnel reflection is used as a probe light to achieve light speed measurement with a high resolution and a high signal-to-noise ratio. Thus, its group velocity is obtained with the round-trip time delay as well as the beat frequency at the reflection peak. Multiple Fresnel peaks are observed from 2180.00 Hz to 13,988.75 Hz, corresponding to fusion-spliced hollow-core fiber segments with different lengths from 0.2595 m to 1.6678 m, respectively. The speed of light in the air guidance is calculated at 2.9753 × 10⁸ m/s, approaching that in vacuum, which is also in good agreement with 2.9672 × 10⁸ m/s given by the numerical analysis with an uncertainty of 10⁻³. Our demonstration promises a key to hollow-core waveguide characterization for future wide-bandwidth and low-latency optical communication.

The birefringence in a dual-hole microstructured optical fiber is numerically calculated and characterized with an optical frequency domain reflectometry (OFDR) method. Due to the asymmetric dual air holes in the cross-section, the polarized LP₀₁ ^x and LP₀₁ ^y modes propagate with different group velocities and time delays. Through a polarized coherent OFDR system in experiment, the Fresnel reflection peaks for each mode are separated in the frequency domain with their corresponding beat frequency. Thus, the group birefringence −9.68×10⁻⁴ is calculated with a beat frequency difference of 50.03 Hz between the LP₀₁ ^x and LP₀₁ ^y modes at a 6.2 m fiber end, which is in good agreement with that of −9.54×10⁻⁴ from the theoretical simulation. Our demonstration provides an accurate and flexible method for group birefringence characterization in microstructured optical fibers with complex cross-sectional structures.

Stimuli-responsive luminescent materials have received great attention for their potential application in anti-counterfeiting and information encryption. Manganese halide hybrids have been considered an efficient stimuli-responsive luminescent material due to their low price and adjustable photoluminescence (PL). However, the photoluminescence quantum yield (PLQY) of PEA₂MnBr₄ is relatively low. Herein, Zn²⁺- and Pb²⁺-doped PEA₂MnBr₄ samples are synthesized, and show an intense green emission and orange emission, respectively. After doping with Zn²⁺, the PLQY of PEA₂MnBr₄ is elevated from 9% to 40%. We have found that green emitting Zn²⁺-doped PEA₂MnBr₄ could transform to a pink color after being exposed to air for several seconds and the reversible transformation from pink to green was achieved by using heating treatment. Benefiting from this property, an anti-counterfeiting label is fabricated, which exhibits excellent “pink-green-pink” cycle capability. Pb²⁺-doped PEA₂Mn_0.88Zn_0.12Br₄ is acquired by cation exchange reaction, which shows intense orange emission with a high QY of 85%. The PL of Pb²⁺-doped PEA₂Mn_0.88Zn_0.12Br₄ decreases with increasing temperature. Hence, the encrypted multilayer composite film is fabricated relying on the different thermal responses of Zn²⁺- and Pb²⁺-doped PEA₂MnBr₄, whereby the encrypted information can be read out by thermal treatment.