We propose and demonstrate a photonic system that simultaneously measures the angle of arrival (AOA) and Doppler frequency shift (DFS) of microwave waveforms. The proposed system uses a dual-drive Mach-Zehnder modulator (DDMZM) to optically process a pair of echo signals with an inherent phase difference together with one reference signal. A stimulated Brillouin scattering (SBS) enabled microwave photonic filter (MPF) is adopted to output a carrier-suppressed single-sideband (CS-SSB) optical waveform. Through optical heterodyning, the DFS and AOA information can be encoded in the frequency and power of a single IF signal of a single intermediate-frequency (IF) signal, enabling a high-resolution measurement. Experimental verification at the proof-of-concept level reveals that the DFS measurement error is restricted to ± 0.2 Hz for 10 GHz microwave signals under a measurement bandwidth covering ± 100 kHz. Moreover, the adoption of a constant-frequency reference signal achieves unambiguous identification of DFS deflection direction. Meanwhile, with the introduction of a fixed reference signal, the information related to the down-converted intermediate frequency signal is frequency-shifted, effectively separating the target mDFS signal from the second-order intermodulation distortion (IMD2) component and achieving mDFS measurement with an error of less than ± 0.14 Hz within the range of ± 10 kHz without IMD2 interference. It is also verified that the error of the microwave AOA is within ± 1.5° without direction ambiguity.
Optical beams with spatially inhomogeneous polarization host polarization singularities-points at which the polarization azimuth is undefined, typically accompanied by a circulating azimuthal phase gradient. This study investigates the focal-plane intensity distributions and phase singularity dynamics produced by the tight focusing of degenerate, positive-indexed hybrid-order Poincaré-sphere (HyOPS) beams. Specifically, for degenerate left-handed dark C-points with index I_C = 1/2 , numerical analysis reveals the emergence of multiple phase singularities within the transverse focal plane. We demonstrate that the focal-plane intensity texture is governed by the polarization morphology of these positive-indexed C-points. By tailoring the orbital angular momentum content of the circular components of the C-points, we realize focal fields with reconfigurable dark-core geometries. These fields exhibit symmetric and asymmetric intensity distributions in the axial and transverse planes, respectively, with the axial profiles featuring symmetric, outward-shifting lobes. Such control over the zero-intensity regions is pivotal for applications requiring reconfigurable dark spots.
Soil health is the foundation for global food security, however, traditional monitoring of soil nutrients is still limited by lab-based workflows, expensive reagents and the lack of field multi-analyte, real-time data. Exploiting photonic bandgap engineering, guided mode resonances, and bound states in the continuum, photonic crystal (PC) sensing provides label-free, high sensitivity optical transduction of chemical and biological analytes with a compact device footprint suitable for field deployment. By coupling with machine learning (ML) algorithms, i.e., support vector machines (SVM), partial least-squares regression (PLSR), deep neural networks (DNN), and physics-informed models, PC sensor platforms can resolve overlapped spectral patterns, simultaneously identify multiple soil nutrients, as well as correct for environmental cross-sensitivities which affect traditional readout. Covering 95 references, this perspective review spans photonic crystal detection fundamentals, soil health monitoring demands, machine learning for analysis of optical signals as well as nascent applications such as inverse design, federated learning and digital twins. Comparative tables, figures of data and an integrated workflow are provided. Critical challenges—such as selectivity for complex soil matrices, calibration drift, scalable fabrication, data security issues, and robustness in field conditions—are thoroughly discussed and a research prospect toward enabling multi-nutrient PC sensor systems is presented. While photonic crystal sensing combined with machine learning offers a promising path toward real-time multi-nutrient soil monitoring, most reported sensor platforms remain at the simulation or laboratory validation stage, and in-situ soil deployment has not yet been demonstrated.
We present a scheme for continuous variable (CV) quantum state transfer based on a driven dissipative two mode parametric resonator incorporating a third-order (χ ^3) Kerr medium. By linearizing the quantum fluctuations around nonequilibrium steady states and solving the stationary Lyapunov equation, we characterize the open system dynamics and determine the operating regimes associated with bipartite entanglement and teleportation fidelity. Our results show that Kerr induced self phase modulation interacts with parametric gain to modify the quadrature fluctuations and bipartite entanglement of the generated resource state. Within dynamically stable operating regimes, the system can achieve coherent state teleportation fidelities exceeding the classical benchmark, with ( F_tel>0.5 ). These results demonstrate that Kerr nonlinearities provide a controllable mechanism for engineering nonclassical correlations and continuous variable quantum teleportation in driven dissipative integrated photonic systems.
This work develops effective channel representations and a composable-security framework for distributed passive-user Loop-Back quantum key distribution (QKD). Alice provides trusted preparation-and-measurement infrastructure at local service points, while two source-free and detector-free users, B_1 and B_2 , apply independently selected polarization rotations R(±π /8) to the same optical carrier. Two complementary derivations describe the honest operation. Direct averaging over the composed rotations gives the observable Loop-Back map, while an operationally equivalent representation on the Bennett–Brassard 1984 (BB84) preparation-and-measurement data is a balanced mixture of conjugate-basis dephasings, or an anisotropic Pauli channel with identity, X , and Z components and no Y component. Both recover the ideal conclusive-event probability P_conc=1/4 . Security is established without restricting the adversarial action to this effective channel. Eve may implement an arbitrary coherent attack with quantum memory on the single untrusted interface between the two local rotations. In the single-photon sector, a Choi-operator identity yields the exact ideal relation e_1,p=3e_1,b/2 , together with a low-error robust angular bound e_1,p≤κ _rote_1,b . Phase-randomized weak coherent pulses, decoy-state estimation and generalized entropy accumulation then give a finite-key composable bound. A common optical model compares asymptotic and finite-block rates and quantifies their convergence with block size. The analysis also identifies the trusted-interface condition required to exclude loss-assisted operation-discrimination attacks and specifies the hardware assumptions needed for optical implementation.
