OAM beam generation using all-fiber fused couplers

We demonstrate the orbital angular momentum (OAM) beam generation using an all-fiber fused coupler based on single mode fiber (SMF) and air-core fiber. The fabricated device is directly SMF compatible with ~80% power coupling efficiency

OAM Generation in optical fibre and free space devices

Orbital angular momentum (OAM) beam generation has been investigated using all-fibre and free space configurations. In the first approach, the composite fused coupler is based on a single mode fibre (SMF) and an air-core fibre. The second approach exploits geometrical phase introduced by nanostructuring of silica glass. Both approaches are demonstrated to achieve power coupling efficiencies in excess of 80% at telecom wavelengths

Efficient extraction of high pulse energy from partly quenched highly Er3+-doped fiber amplifiers

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

9 W average power, 150 kHz repetition rate diamond Raman laser at 1519 nm, pumped by a Yb fibre amplifier

Commercially available pulsed fibre lasers at ~1.5 μm have many uses in imaging, defense, communications and light radar (LIDAR) [1]. For 3D scanning LIDAR, higher signal-to-noise ratio requires lasers with high average power and high pulse repetition rate (ideally several MHz) for faster scanning rate, whereas to improve distance resolution requires pulse durations <10 ns [2,3]. One limitation of the pulsed fibre lasers at ~1.5 μm is scaling to high average powers [4]. Raman frequency conversion of high average power fibre master oscillator power amplifier (MOPA) systems at ~1 μm is a potential alternative. The large Raman shift and Raman gain of diamond allows two-stage Raman conversion to ~1.5 μm for ~1 μm pumping [5]. Excellent thermal properties make diamond suitable for high average powers [6]. Much work has been done on conversion of 1.064 μm lasers to 1.485 μm using diamond [7]; however, the “eye-safety” requirements for LIDAR typically call for wavelengths above 1.5 μm, due to the order of magnitude higher Maximum Permissible Exposure limit [8]. Developing such a diamond Raman laser (DRL) was the major motivation for this research

Dataset for 15-dB Raman Amplification of an Optical Orbital Angular Momentum Mode in a Step-Index Fiber

Dataset for abstract en titled &quot;15-dB Raman Amplification of an Optical Orbital Angular Momentum Mode in a Step-Index Fiber&quot;, presented on OSA Laser Congress: Advanced Solid State Lasers (ASSL), Boston, USA, 04-08 Nov 2018 with DOI 10.1364/ASSL.2018.AW2A.4</span

All-fiber fused coupler for stable generation of radially and azimuthally polarized beams

The stable generation of TE01 and TM01 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 TM01 or TE01 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 TE01 and TM01 beams

Classically “entangled” toroidal pulses

Toroidal light pulses are few-cycle pulses with doughnut-like electromagnetic field configuration and non-separable, “entangled”-like spatiotemporal structure. Toroidal light pulses exhibit self-similar and skyrmionic topological features and exotic propagation dynamics including isodiffracting and non-diffracting effects. Following the recent observation of such pulses, this talk will report on metamaterial-based schemes for their generation and detection and introduce tomography approaches for characterizing their “entangled” spatiotemporal profile. Implications for light-matter interactions, in particular in the context of toroidal electrodynamics, non-radiating configurations, and Lorentz non-reciprocity, will also be discussed

Raman amplification of optical beam carrying orbital angular momentum in a multimode step-index fiber

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 ∼15 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.</p

Amplification of orbital angular momentum beam in a fiber Raman amplifier

We experimentally demonstrate 6.5 dB amplification of an orbital angular momentum (OAM) beam through a co-pumped fiber Raman amplifier based on a commercial step-index few mode fiber. Preliminary estimate of mode purity upon amplification is 85%