Orbital angular momentum can be used to implement high capacity data transmission systems that can be applied for classical and quantum communications. Here we experimentally study the generation and transmission properties of the so-called perfect vortex beams and the Laguerre-Gaussian beams in ring-core optical fibers. Our results show that when using a single preparation stage, the perfect vortex beams present less ring-radius variation that allows coupling of higher optical power into a ring core fiber. These results lead to lower power requirements to establish fiber-based communications links using orbital angular momentum and set the stage for future implementations of high-dimensional quantum communication over space division multiplexing fibers.

We analyze the evolution of superfluidity for nonzero orbital angular momentum channels from the Bardeen-Cooper-Schrieffer (BCS) to the Bose-Einstein condensation (BEC) limit in three dimensions. First, we analyze the low-energy scattering properties of finite range interactions for all possible angular momentum channels. Second, we discuss ground-state $(T=0)$ superfluid properties including the order parameter, chemical potential, quasiparticle excitation spectrum, momentum distribution, atomic compressibility, ground-state energy, and low-energy collective excitations. We show that a quantum phase transition occurs for nonzero angular momentum pairing, unlike the $s$-wave case where the BCS to BEC evolution is just a crossover. Third, we present a Gaussian fluctuation theory near the critical temperature $(T=T_{\mathrm{c}})$, and we analyze the number of bound, scattering, and unbound fermions as well as the chemical potential. Finally, we derive the time-dependent Ginzburg-Landau functional near $T_{\mathrm{c}}$, and compare the Ginzburg-Landau coherence length with the zero-temperature average Cooper pair size.

The possibility of magnetic exchange coupling between two ferromagnets (F) separated by a superconductor (S) spacer is analyzed using the functional integral method. For this coupling to occur three prima facie conditions need to be satisfied. First, an indirect exchange coupling between the ferromagnets must exist when the superconductor is in its normal state. Second, superconductivity must not be destroyed due to the proximity to ferromagnetic boundaries. Third, roughness of the $F/S$ interfaces must be small. Under these conditions, when the superconductor is cooled to below its critical temperature, the magnetic coupling changes. The appearance of the superconducting gap introduces a new length scale (the coherence length of the superconductor) and modifies the temperature dependence of the indirect exchange coupling existent in the normal state. The magnetic coupling is oscillatory both above and below the the critical temperature of the superconductor, as well as strongly temperature-dependent. However, at low temperatures the indirect exchange coupling decay length is controlled by the coherence length of the superconductor, while at temperatures close to and above the critical temperature of the superconductor the magnetic coupling decay length is controlled by the thermal length.

The use of multicore optical fibers is emerging as a key solution to implement space-division multiplexing, essential for overcoming the capacity limits of conventional single-mode fibers. However, next-generation high-capacity optical networks will require new devices compatible with these fibers. In this work, we present an all-fiber architecture for a high-speed core-selective switch, crucial for efficient signal distribution in multicore networks. The device leverages multicore interference to achieve rapid core-switching within 0.7 μs-three orders of magnitude faster than state-of-the-art micro-electromechanical system switches. It also maintains an average inter-core crosstalk below −18 dB, ensuring compatibility with diverse network tasks. We validated the device’s functionality by routing optical signals ranging from 1 to 600 Gbps and successfully switching signals over a field-installed multicore fiber network. These results demonstrate, for the first time, a multicore optical fiber switch operating under real-world conditions with speeds far surpassing existing commercial devices. Potentially compatible with standard multiplexing techniques, this switch represents a significant advancement in enabling high-capacity multicore telecommunication networks. Its performance and adaptability position it as a key technology for the development of next-generation optical communication systems.

Fiber-optic Mach–Zehnder interferometers are widely used in research areas such as telecommunications, spectroscopy, and quantum information. These optical structures are known to be affected by phase fluctuations that are usually modeled as multiparametric noise. This multidimensional noise must be stabilized or compensated for to enable fiber-optic Mach–Zehnder architectures for practical applications. In this work, we study the effectiveness of a modified Perturb-and-Observe (P&O) algorithm to control multidimensional phase noise in fiber-based multi-arm Mach–Zehnder interferometers. We demonstrate the feasibility of stabilizing multidimensional phase noise by numerical simulations using a simple feedback control scheme and analyze the algorithm’s performance for systems up to dimension $8\times 8$. We achieved minimal steady-state errors that guarantee high optical visibility in complex optical systems with $N\times N$ matrices (with $N=[2,3,4,5,6,7,8]$).

Soft failures cause gradual quality-of-transmission degradation in optical links and difficult fault management. We experimentally demonstrate a two-stage machine-learning pipeline on a 200 km coherent link used to detect and localize soft-failures. Stage 1 detects anomalies from 60 s window statistics of the received pre-FEC BER and OSNR. An autoencoder trained only on normal DP-QPSK data with per-format min–max scaling and P99 normal-error thresholds achieves F1=1.00 on DP-QPSK and ≥0.99 when transferred to DP-8QAM and DP-16QAM. Stage 2 classifies and localizes failures using EDFA power-telemetry delta features, reaching 100% accuracy. Results support practical, modulation-robust soft-failure management.