We provide a perspective overview of the emerging field of nonlinear optics in multimode optical fibers. These fibers enable new methods for the ultrafast light-activated control of temporal, spatial, and spectral degrees of freedom of intense, pulsed beams of light, for a range of different technological applications.

Multimode nonlinear fiber optics, a spatiotemporal avenue

In the present work, a series of Dy3+ ion doped tellurite glasses in the (50-x)TeO2-25WO3-25Li2O-xDy2O3 system were synthesized using conventional melt quenching technique to investigate colorimetric and radiative properties of Dy3+ ions in a new and stable host for their evaluation as solid-state lighting materials. Physical and structural properties were studied through density calculations, refractive index measurements, and Fourier-transform IR spectroscopy analysis. Thermal properties of glasses – glass transition (Tg) and crystallization (Tc/Tp) temperatures and temperature difference (ΔT) – were determined using differential scanning calorimetry. Optical absorption spectra of glasses were recorded with Vis-NIR spectrophotometer. CIE color coordinates, correlated color temperature, color rendering index and yellow to blue emission intensity ratio values were obtained through photoluminescence analysis. Radiative properties such as, radiative transition probability, stimulated emission cross-section, branching ratio and optical bandwidth gain were calculated according to Judd-Ofelt theory. The obtained optical spectroscopy results were found to be comparable or better than other reported glass systems. From the derived results, glasses with Dy3+ ion concentration lower than 0.5 mol% were found to show the closest CIE color coordinate values to pure white light and highest CCT and CRI values revealing good potentiality to be used for applications in white LEDs and solid-state lasers.

Dy3+ doped tellurite glasses for solid-state lighting: An investigation through physical, thermal, structural and optical spectroscopy studies

YNbO4 phosphors with various Er3+ and Yb3+ concentrations were synthesized via a traditional high-temperature solid-state reaction method. Their crystal structure was investigated by means of X-ray diffraction (XRD) and Rietveld refinements, and it was confirmed that the obtained samples exist in monoclinic phase. The Er3+ and Yb3+ concentration-dependent up-conversion (UC) luminescence was studied under 1550 nm excitation. By inspecting the dependence of UC intensity on the laser working current, it was found that four-photon and three-photon population processes were co-existent for generating the green UC emissions in the samples with higher Yb3+ concentrations. In addition, it was observed that the temperature sensing properties of YNbO4: Er3+/Yb3+ phosphors were sensitive to both Er3+ and Yb3+ doping concentrations. Furthermore, based on the obtained temperature response of the UC luminescence phosphors, 1550 nm laser-irradiation-induced thermal effect was studied, and it was discovered that the sample temperature was very sensitive to the doping concentrations of Er3+ and Yb3+ and the excitation power.

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Up-conversion luminescence, temperature sensing properties and laser-induced heating effect of Er 3+ /Yb 3+ co-doped YNbO 4 phosphors under 1550 nm excitation.

Rare earth doped materials can usually achieve high efficiency upconversion luminescence (UCL) under high power density infrared laser excitation, in which process the heat generation cannot be avoided, and then induce temperature dependent UCL quenching. This paper dealt with the temperature sensing property and 1550 nm laser irradiation induced thermal effect of Er 3+ /Yb 3+ co-doped NaYF 4 microcrystals. The sample was synthesized via a microwave-assisted hydrothermal route, and its crystal structure and microscopic morphology were characterized by means of XRD and FE-SEM. To describe the temperature quenching behaviors for the two typical green emissions of Er 3+ , a model was proposed and well explained the temperature dependence of two green UCL intensities. Temperature sensing property for NaYF 4 : Er 3+ /Yb 3+ microcrystals were studied by fluorescence intensity ratio technique, and the temperature sensitivity were also obtained. Furthermore, the 1550 nm laser induced thermal effect was studied, and the result showed that the sample temperature increased with increasing excitation power density.

Microwave-assisted hydrothermal synthesis, temperature quenching and laser-induced heating effect of hexagonal microplate β-NaYF4: Er3+/Yb3+ microcrystals under 1550 nm laser irradiation

With growing interest in the mid-infrared spectral region, dysprosium has recently been revisited for efficient high-performance infrared source development. Despite historically receiving less attention than other rare earth ions, in recent years lasers utilizing the dysprosium ion as the laser material have set record mid-infrared performance, including tunability from 2.8 to 3.4 um (in addition to 4.3 um lasing), continuous wave powers exceeding 10 W, greater than 73% slope efficiencies, and even ultrafast pulsed operation. Herein, the unique energy level structure and spectroscopy of the dysprosium ion are examined and the major developments that have led to this resurgence of interest and subsequent record mid-infrared laser performance are surveyed. Also mid-infrared applications of emerging dysprosium lasers are highlighted, in addition to surveying the many opportunities that lie ahead.

Dysprosium mid-infrared lasers: current status and future prospects

Mid-infrared photo-luminescence and energy transfer around 2.8 μm from Dy 3+ /Tm 3+ co-doped tellurite glass

In the present Letter, a high-emission intensity of 2.0 μm is reported for Ho3+/Er3+ co-doped fluoride glass sensitized by Tm3+ ions under 1550 nm excitation. The measured absorption spectra do not show clustering in the local ligand field, which also demonstrates that Er3+ ions are efficiently excited by pumping and energy transfer (ET) to Ho3+ and Tm3+ ions. The enhanced Ho3+:2.0  μm emission has a maximum emission cross section (4.8×10−21  cm2). An ET mechanism based on the enhanced 2.0 μm emission and other reduced near-infrared emissions is discussed. Results show that the addition of Tm3+ ions populates the Ho3+:I75 level through the channel at the Tm3+:F43 level between Er3+ and Ho3+ ions. The spectroscopic characteristics and thermal property of Er3+/Ho3+/Tm3+ tri-doped ZBYA glass reveal that the material is an attractive host for 2.0 μm lasers.

Ho³⁺/Er³⁺ co-doped fluoride glass sensitized by Tm³⁺ pumped by a 1550 nm laser diode for efficient 2.0 μm laser applications.

We experimentally demonstrated a passively mode-locked all-fiber Tm laser using a no-core-graded-index multimode fiber structure as a saturable absorber based on the nonlinear multimode interference. Stable fundamentally mode-locking operation was obtained at a pump threshold of 180 mW. The output soliton pulses had a centre wavelength, spectral width, pulse duration, and repetition rate of 1895.7 nm, 3.3 nm, 1.25 ps, and 18.91 MHz, respectively. This is a simple, low-cost, stable, and convenient laser oscillator, with many potential applications in eye-safe ultrafast photonics.

Self-starting mode-locked Tm-doped fiber laser using a hybrid structure of no core - graded index multimode fiber as the saturable absorber

The invention discloses a 2 [mu] m mode-locked fiber laser based on an SMF-SIMF-GIMF-SMF fiber structure The laser is of an annular cavity structure and comprises a pumping source, a wavelength division multiplexer, a gain fiber, a non-polarization-maintaining isolator and a polarization controller, an all-fiber saturable absorption device serving as a mode locking device and a coupler serving as an output; the all-fiber saturable absorption device is composed of an input single-mode fiber, a step multimode fiber, a gradient multimode fiber and an output single-mode fiber The laser mode locking mechanism disclosed by the invention adopts the nonlinear multimode interference effect in the multimode fiber, has the advantages of all-fiber structure, high damage threshold, self starting of model locking, high stability and compact structure, and has a wide application prospect

2 [mu] m mode-locked fiber laser based on SMF-SIMF-GIMF-SMF fiber structure

The invention discloses a 2-micron dissipative soliton mode-locking fiber laser based on an SMF-SIMF-GIMF-SMF filter structure The laser is of an annular cavity structure, and comprises a pumping source, a wavelength division multiplexer, a gain fiber, a non-PM isolator, a polarization controller, a high numerical aperture fiber used for dispersion compensation, an all-fiber saturable absorption device as a mode-locking device, and a coupler as output; and the all-fiber saturable absorption device consists of an input single-mode fiber, a phase step multi-mode fiber, a gradually-changed multi-mode fiber and an output single-mode fiber which are welded in sequence The laser disclosed by the invention realizes mode locking by using a non-linear multi-mode interference effect in the multi-mode fiber, and then dissipative soliton output is realized by introducing dispersion compensation fiber, so that the laser has the characteristics of all-fiber structure, high damage threshold, high stability, compact structure and the like and has a wide application prospect

Li Huanhuan

Papers

Mid-infrared photo-luminescence and energy transfer around 2.8 μm from Dy 3+ /Tm 3+ co-doped tellurite glass

Ho³⁺/Er³⁺ co-doped fluoride glass sensitized by Tm³⁺ pumped by a 1550 nm laser diode for efficient 2.0 μm laser applications.

Self-starting mode-locked Tm-doped fiber laser using a hybrid structure of no core - graded index multimode fiber as the saturable absorber

2 [mu] m mode-locked fiber laser based on SMF-SIMF-GIMF-SMF fiber structure

2-micron dissipative soliton mode-locking fiber laser based on SMF-SIMF-GIMF-SMF filter structure