Abstract Conventional single-transceiver radio-frequency (RF) phase-stabilized fiber transmission systems suffer from degraded error-signal detection accuracy over long transmission distances because of return-link signal attenuation. To overcome this limitation, a 55 km RF phase-stabilized fiber transmission system based on a dual-transceiver architecture is proposed and experimentally demonstrated. Independent directly modulated lasers (DML) are employed at the central and remote sites to realize bidirectional transmission using independent optical carriers, thereby enhancing the return-link optical power, recovered RF signal power, and the signal-to-noise ratio of the error-signal detection. In addition, both fiber-link propagation disturbances and intrinsic phase drifts of the transmitting and receiving modules are incorporated into the compensation loop, improving the long-term phase-error suppression capability at the system-architecture level. The influences of power-supply stability, mixer input-power matching, and environmental temperature fluctuations on the long-term stability are systematically investigated, while the characteristics of the DMLs and the residual stability are also experimentally evaluated. Experimental results show that, over a 55 km fiber link under a 70 000 s environmental temperature perturbation, the peak-to-peak residual delay fluctuation remains within 0.135 ps. The corresponding modified Allan deviation reaches 5.4705 × 10 −15 at 1 s and 1.6194 × 10 −19 at 10 000 s. These results verify the effectiveness of the proposed dual-transceiver architecture in improving the long-term stability of RF phase-stabilized fiber transmission systems and demonstrate that it provides an effective solution for long-distance dissemination of ultra-stable RF reference signals.
Abstract The advancement of multiband detection technologies and high-power devices has driven a growing demand for solutions that integrate multispectral stealth with thermal management, particularly in the context of space satellite countermeasures. Such applications require low observability against dark, cold backgrounds and spectrally selective thermal emission in the infrared regime. This study presents a Fabry–Perot-based multilayer film structure (Cu/ZnS/Ti/ZnS/Ge/ZnS/MgF 2 ) that achieves high visible-light absorption and spectrally selective infrared emission. The optimized structure exhibits high absorptivity ( ϵ = 0.91) in the visible range (0.38–0.80 μ m), high emissivity ( ϵ = 0.83) in the mid-wave infrared (3–5 μ m), and low emissivity ( ϵ = 0.23) in the long-wave infrared band (8–14 μ m), thereby enabling concurrent high visible absorption and selective infrared emission. The spectral selectivity of the structure is further validated and analyzed through radiative intensity, electromagnetic field distribution, and power loss density simulations. This multilayer film opens new avenues for multispectral camouflage of space satellites, as well as for applications in solar–thermal conversion, thermal management, energy efficiency, and detection technologies.
Abstract This paper presents a trust-region expanding method for the blind calibration of linear Stokes imaging polarimeter to address the inherent 90° branch ambiguity that limits conventional alternating iterative optimization (AIO). The method reduces the optimization to a compact parameter space of analyzer azimuths through variable projection, suppresses per-channel branch flips by enforcing polarization constraints through physical normalization, and locks the search onto the physically correct solution through a deterministic trust-region expansion strategy. The method is validated through numerical simulations and demonstrated experimentally on a custom-built Division-of-Aperture imaging polarimeter. Results consistently demonstrate that the proposed method maintains reliable convergence and delivers accurate polarization measurements across all tested conditions even when the reference polarizer angles are confined to a narrow range, whereas AIO suffers from frequent convergence failures under limited angular coverage. The proposed method also exhibits superior noise robustness and negligible sensitivity to hyperparameters over practical operating ranges.
Abstract Non-ionising optical tomography offers a safer alternative to traditional imaging techniques for radiation-sensitive biological and, particularly, human tissues. In this study, we developed a laser scanning system incorporating axial, transverse, and rotational motion to acquire projection data from diffuse media. A 632.8 nm laser was used to illuminate translucent targets embedded within water, clear gelatin, red gelatin and green gelatin -selected to simulate biologically relevant scattering environments. By capturing transmitted and scattering light with a CCD array and constructing sinograms, we applied the inverse Radon transform to reconstruct cross-sectional images of the embedded targets. The results demonstrate successful localisation and identification of inclusions within the scattering media, representing a promising step toward practical optical tomography in biomedical imaging applications.
Abstract We study Smith–Purcell radiation generated by an electron beam propagating between two one-dimensional photonic crystals with slightly mismatched periods, forming a superperiodic or moiré lattice. The emission spectrum is dominated by two diffraction orders corresponding to the −1 orders of the individual sub-crystals and arises from the hybridization of their Bloch modes. This behavior is accurately captured by a simple two-mode coupled-mode theory. Unlike symmetric double-grating configurations, the superperiodic crystal exhibits an emission spectrum that is remarkably insensitive to lateral displacement, providing enhanced robustness against relative misalignment between the gratings. We further show that the relative weight of the dominant orders enables frequency-dependent control of the emission angle.
