Orbital angular momentum beam excitation through direct phase-matched coupling is experimentally demonstrated using an all-fiber weakly fused mode selective coupler consisting of a single-mode fiber and a ring-core fiber. Experimental results showing the excited OAM mode purity of up to 75% measured through the standard ring technique not only demonstrate the proof of concept but also provide a baseline for further improvement.

Self-healing of light refers to the ability of a light field to recover its structure after being damaged by a partial obstruction placed in its propagation path. Here, we will give a comprehensive review of the history and development of self-healing effects, especially highlighting its importance in vector vortex beams carrying spin and orbital angular momenta. Moreover, an unified zoology of self-healing, structured light is proposed to unveil a deeper understanding of its physical mechanism and provide a bird’s eye view on diverse forms of self-healing effects of different kinds of complex structured light. Finally, we outline the open challenges we are facing, potential opportunities and future trends for both fundamental physics and applications.

The stable generation of TE ₀₁ and TM ₀₁ beams is demonstrated through a novel all-fiber fused coupler fabricated from a standard single mode fiber (SMF) and a custom air-core fiber. The fundamental mode in the SMF is directly coupled to the TM ₀₁ or TE ₀₁ mode by appropriately phase matching the modes in the fibers resulting in efficiency of ~67% and ~85%, and polarization purity of 70% and 82%, respectively. The phase matching is achieved through pre-tapering the SMF with precise control of the tapering ratio. The air-core fiber ensures selective excitation of the desired modes, thereby improving propagation stability and polarization quality of the TE ₀₁ and TM ₀₁ beams.

We experimentally demonstrate 15 dB of Raman amplification of 1115 nm pulses in an orbital angular momentum mode (OAMM) with charge $l=+2$, $S=+1$ in 5 m of step-index 25 μm-diameter-core fiber. The total output reaches 4.5 kW of peak power and 68.5 μJ of energy in $\sim 15\mathrm{ns}$ pulses at 4 kHz repetition rate. An Yb-doped fiber source pumps the Raman amplifier at 1060 nm with 60 ns pulses. Using a spatial light modulator for modal decomposition, we measure 83% purity for the amplified target OAMM of selected polarization. To the best of our knowledge, this is the first time high energy, peak power, gain, and purity are achieved in a fiber Raman amplifier for a single OAMM.

We demonstrate efficient pulse-energy extraction from a partly quenched erbium-doped aluminosilicate fiber amplifier. This has a high erbium concentration that allows for short devices with reduced nonlinear distortions but also results in partial quenching and thus significant unsaturable absorption, even though the fiber is still able to amplify. Although the quenching degrades the average-power efficiency, the pulse energy remains high, and our results point to an increasingly promising outcome for short pulses. Furthermore, unlike unquenched fibers, the conversion efficiency improves at low repetition rates, which we attribute to smaller relative energy loss to quenched ions at higher pulse energy. A short (2.6 m) cladding-pumped partly quenched Er-doped fiber with 95-dB/m 1530-nm peak absorption and saturation energy estimated to 85 µJ reached 0.8 mJ of output energy when seeded by 0.2-µs, 23-µJ pulses. Thus, according to our results, pulses can be amplified to high energy in short highly Er-doped fibers designed to reduce nonlinear distortions at the expense of average-power efficiency.

This study examines the influence of quenching dynamics on the efficiency of erbium-doped fiber amplifiers (EDFAs) with high erbium-ion (E3+-ions) doping concentrations, comparing pulsed and continuous wave core-pumping methods. Our findings indicate that quenching, driven by energy transfer upconversion, substantially impacts signal gain in these fibers. The core-pumping configuration demonstrated significantly higher gain per unit length than both low-doping EDFAs and cladding-pumping systems, with effective energy storage achievable through short pump pulses to reduce concentration quenching effects. The highly doped homemade fiber (fiber under test - FUT No. 3) achieved a gain per unit length exceeding 8.4 dB/m, outperforming the lower doped commercial fiber (FUT No. 4) by a factor of 6.4, although FUT No. 4 displayed better compatibility with the core-pumping system. Additionally, the highest gain per unit length for a counter-directional, cladding-pumped amplifier configuration with a high-concentration fiber was recorded at 5.9 dB/m at a 1560 nm signal wavelength with a 2 μs pulse duration, positioning FUT No. 3 as a highly efficient option for high-gain applications despite its high doping concentration. Our experimental analysis of quenching dynamics not only highlights an approach for scaling pulse energy using shorter fiber lengths to mitigate nonlinear effects but also provides valuable insights into quenching-influenced gain behavior in pulsed fiber amplifier systems.