We propose and experimentally demonstrate an inter-core skew measurement method for multi-core fibers (MCFs) based on broadband incoherent interferometry of spectrum-sliced amplified spontaneous emission (ASE) noise. The technique avoids the need for narrow-linewidth lasers and tolerates the random power fading due to coherent coupling among neighboring cores. By utilizing a calibrated interference spectrum to extract the delay value through cascaded filtering and fitting, the proposed technique achieves sub-picosecond measurement accuracy. Both the back-to-back and 41-km MCF experiments demonstrate stable performance with root mean square errors of <60 fs, comparable to the typical measurement scheme based on a vector network analyzer. The simplicity, robustness, and sub-picosecond precision make the proposed scheme an ideal solution for non-intrusive, online inter-core skew monitoring in multi-core fibers.

The anisotropic electronic properties of SnSe provide distinctive opportunities for studying polarization-dependent carrier dynamics. However, resolving such directional effects remains challenging for conventional spectroscopy techniques. Here, time-resolved high-harmonic spectroscopy (TR-HHS) is utilized to capture the anisotropic ultrafast processes in SnSe thin film. The TR-HHS signal evolves over the hundred-femtosecond to few-picosecond regime and demonstrates strong crystal orientation dependence. These results are attributed to anisotropic electronic relaxation encompassing electron thermalization and phonon-mediated hot-electron cooling. Our findings demonstrate that TR-HHS can serve as a powerful all-optical tool for probing symmetry-governed electron dynamics in anisotropic materials and provide new strategies for developing polarization-tunable optoelectronic devices.

We study the use of separate cores of a multicore erbium-doped fiber amplifier (MC-EDFA) in a noise-canceled link for ultrastable optical frequency transfer. We demonstrate fractional frequency instability of 5×10 −19 at 1000 s averaging time for the stabilized MC-EDFA alone and 1.4×10 −18 at 1000 s averaging time when integrated with a 40-km-long 7-core spooled fiber. This study further establishes multicore fiber (MCF) networks as a promising platform for ultrastable frequency transfer, serving as an important step toward incorporating precision time and frequency distribution into future MCF communication infrastructures.

We propose what we believe is a novel sensitivity-enhancement method for extrinsic Fabry–Perot accelerometers (EFPAs) based on a wavelength-division multiplexing (WDM) cascading scheme. The core mechanism relies on an opto-mechanical coupling (OMC) technology, in which an integrated filter–collimator forms a cascaded dual-interferometer cavity structure. Under vibration, the two reflective surfaces move in opposite directions, inducing a push–pull spectral shift in the two cavities simultaneously. This configuration amplifies the optical response through two synergistic effects: effective cavity length extension and increased spectral spacing, thereby significantly enhancing sensitivity. Meanwhile, the dual Fabry–Perot cavity configuration enables common-mode noise suppression. Experimental results demonstrate that, without sacrificing the operational bandwidth, the proposed OMC-based accelerometer achieves fourfold improvement in sensitivity compared to conventional EFPAs, reaching a maximum sensitivity of 29.38 nm/g at 460 Hz, with a low noise level of 8.3 pm.

Optical multipath interference (MPI) is a major performance-limiting impairment in IM-DD links, inducing strong signal-dependent intensity fluctuations, particularly when large-linewidth DFB lasers and high-order PAM formats are used. In the frequency domain, MPI manifests as low-frequency and narrowband noise. In this Letter, we propose a low-complexity joint mitigation scheme that combines minimum block digital sum (MBDS) notch coding at the transmitter with a 2nd-order polynomial nonlinear filter (PNLF) equalizer at the receiver. The MBDS scheme enables a significantly deeper and wider low-frequency notch with lower overhead, while the PNLF further suppresses MPI-induced level fluctuations with minimal computational cost. Experimental results of 40 Gbaud and 56 Gbaud MPI-impaired PAM-4 O-band IM-DD systems demonstrate the SIR tolerance improvements of 3.25 dB and 5.23 dB by the proposed joint scheme, respectively, outperforming existing schemes.

Harmonic interference in frequency division multiplexed quasi-distributed acoustic sensing (FDM-QDAS) fundamentally limits its accuracy in ultrasonic detection. This study introduces a bidirectional linear frequency sweep (LFS) multiplexing scheme that effectively suppresses these harmonics by leveraging the distinct cross-correlation properties of forward and backward LFS signals. The method was experimentally validated by successfully recovering submerged single-frequency signals and demodulating 1 MHz ultrasonic pulses with a 10μs width propagating on a metal plate. By enabling high-fidelity measurement of narrow acoustic pulses without sacrificing bandwidth efficiency, this work significantly advances the performance of QDAS for applications in ultrasonic non-destructive testing and imaging.

We report an asymptotic analytical model for astigmatic rainbow refractometry, synthesized from complex angular momentum theory and the generalized 4D Collins formula. This closed-form solution describes astigmatic wavefront evolution while moving beyond the phenomenological limits of conventional geometric models. The proposed framework elucidates the phase-coupling mechanism behind fringe rotation and characterizes the fine-scale interference ripple structure. These results establish a theoretical foundation for quantitative volumetric diagnostics of complex spray systems.