Time-domain data-processing-based Brillouin optical correlation-domain analysis (TD-BOCDA) offers highspatial- resolution distributed sensing over extended distances, but its sensing range is constrained by the residual pump power. To overcome this limitation, we propose a pump-recoveryassisted TD-BOCDA scheme that employs an asymmetric doublesideband (DSB) probe with higher power in the upper sideband to replenish the pump power along the fiber via stimulated Brillouin scattering. We extend an analytical pump-depletion framework to TD-BOCDA to describe the dependence of pump recovery on the sideband power difference. The operating condition is then assessed experimentally using the measured Brillouin gain spectrum and Brillouin frequency shift (BFS) profiles. Experimental results at an effective spatial resolution of approximately 5 cm show that the sensing range is limited to approximately 35 km with a symmetric DSB probe, whereas the asymmetric DSB probe with a 2.0-mW sideband power difference extends the range to 50 km while effectively suppressing BFS errors across the entire fiber under test. The effects of excessive sideband power imbalance are also examined, showing improved BFS stability from enhanced residual pump recovery but systematic BFS upshifts at larger power differences. These results establish the asymmetric DSB probe as a practical approach to longrange, high-resolution TD-BOCDA sensing without additional amplification along the sensing fiber.
Simultaneous transmission of RF and baseband signals over an optical fiber can improve resource utilization in a radio-over-fiber (RoF) links. In this paper, we develop a hybrid optical modulation framework for frequency-division-multiplexed (FDM)-RoF systems that enables the simultaneous transmission of one baseband and multiple RF signals over optical fiber using a single optical source and a single photodetector. The proposed optical hybrid modulation scheme overlays multiple RF signals over a conventional fiber communication link with only one additional modulator and no other hardware modifications. We develop the mathematical framework and the closed-form analytical bit-error-rate (BER) model of the proposed FDM-RoF link. The conditions for non-overlapping spectra for inter-channel interference isolation are outlined, and the minimum bandwidth requirement for the proposed scheme is derived. The scheme is validated through analytical, simulation, and experimental results, demonstrating the simultaneous transmission of a baseband signal and a three-channel FDM signal, achieving a fourfold spectrum utilization. The impact of baseband-RF signal beating interference and its mitigation using deterministic signal subtraction is also demonstrated. Further, the scalability of the scheme across sub-6 GHz and mmWave bands highlights its potential for 5G and beyond RoF deployments.
High sensitivity and low phase noise are essential for fiber-optic current sensors in power-grid monitoring. This paper proposes a reflective dual-circulation phase-shift fiber-loop ring-down (PS-FLRD) current sensor with feedback-assisted noise suppression to overcome the sensitivity and stability limitations of conventional fiber-optic current sensors. The dual-circulation topology increases the effective number of optical traversals through the sensing fiber, enhancing the Faraday-induced polarization-to-intensity conversion and yielding a quadratic current-to-phase response. A Faraday rotator mirror (FRM) suppresses reciprocal polarization perturbations caused by environmental disturbances. In addition, a PID-based feedback loop adjusts the modulation voltage according to the measured demodulation noise, thereby reducing the phase noise from $\text{0.0333}~\text{deg}$ to $\text{0.006}~\text{deg}$ while preserving the intrinsic current-to-phase sensitivity. Experimental results demonstrate a quadratic sensitivity of $0.3075~\mathrm{deg/A^{2}}$ over $0$–$10~\mathrm{A}$, corresponding to a $13.4$-fold enhancement over the conventional FLRD configuration. The system also exhibits a long-term phase fluctuation of approximately $\text{0.01}~\text{deg}$ over $2~\mathrm{h}$, along with a vibration-induced phase fluctuation below $\text{0.03}~\text{deg}$. These results confirm that the dual-circulation optical path and the feedback control independently enhance the sensitivity and noise performance of the sensor.
This paper presents a two-layer physical-layer encryption scheme for CO-OFDM systems, integrating a four-dimensional (4D) hyperchaos-driven dynamic three-dimensional (3D) Baker mapping with chaotic phase rotation. The first three state variables of the 4D hyperchaotic system dynamically regenerate the spatial partition parameters of the 3D Baker mapping, replacing the fixed scrambling rule of conventional Baker maps. The fourth state variable is used to perform phase rotation on the scrambled constellation points, introducing random angular perturbations in three-dimensional space and further obscuring the constellation structure. To improve power efficiency, a geometrically optimized 3D 16-QAM constellation is employed, achieving a constellation figure of merit (CFM) of 0.9078. The proposed scheme is experimentally validated over an 80-km standard single-mode fiber (SSMF) link. At the hard-decision forward error correction (HD-FEC) threshold, the complete proposed system requires approximately 3.6 dB lower OSNR than the conventional 2D-16QAM baseline. Meanwhile, the encryption process introduces only a negligible PAPR increase of approximately 0.108 dB. Over the investigated OSNR range, the unauthorized eavesdropper maintains a BER close to 0.5, indicating that the transmitted information cannot be effectively recovered without the correct key. The scheme provides a theoretical key space of approximately ${{10}^{60}}$, offering strong resistance to brute-force attacks. These results demonstrate that the proposed scheme combines enhanced physical-layer security with improved transmission robustness, providing a practical solution for high-speed and long-distance secure optical communications.
Multicore fiber (MCF) amplifiers provide a power scalable platform for the parallel amplification of multiple coherent laser channels. Existing demonstrations of structured light generation from MCF amplifiers, however, generally rely on free-space tiled-aperture superposition of the individual core outputs. The finite fill factor of the beam array limits target mode combining efficiency, while the required bulk optical components impose demanding alignment and phase-stability requirements and increase system footprint and complexity. Here, we propose and experimentally demonstrate an alternative coherent-combining approach based on a custom-designed and in-house fabricated non-mode-selective multicore fiber photonic lantern. Within the monolithic tapered device, the independently controlled fields carried by the individual cores are coherently mapped into the guided-mode space of a common few-mode output, enabling coherent power combining and structured-mode synthesis within the same waveguide. Adaptive control of the amplitude, phase, and polarization of each input channel compensates for channel-dependent transformations and enables the reconfigurable synthesis of diverse spatial beams, including linearly and circularly polarized Gaussian beams, cylindrical vector beams, and optical vortex beams with topological charges of l = ±1. Mode purities exceeding 99% are achieved for the generated vortex beams, together with an overall combining efficiency of ∼80%, with the remaining loss primarily associated with the measured single-channel insertion losses of 0.6–0.9 dB. To the best of our knowledge, this is the first experimental demonstration of reconfigurable scalar and vector structured light generation through coherent combining in a non-mode selective multicore-fiber photonic lantern. The demonstrated device could subsequently be integrated with a multicore fiber amplifier to coherently combine its parallel amplified outputs, providing a promising route toward efficient, compact, and high power reconfigurable structured-light sources.
