Analytical models of rare-earth-doped fiber lasers were proposed in the past as very efficient yet reliable alternative to comprehensive numerical models. Cross-relaxation in thulium-doped fiber ...lasers has a great impact on their efficiency through a two-for-one process but it has not been addressed in analytical models so far. Here, the analytical model of thulium-doped fiber laser is proposed that respects the cross-relaxation mechanism of a type: <inline-formula><tex-math notation="LaTeX">^{3}</tex-math></inline-formula>H<inline-formula><tex-math notation="LaTeX">_{4}\rightarrow ^{3}</tex-math></inline-formula>F<inline-formula><tex-math notation="LaTeX">_{4}</tex-math></inline-formula>, <inline-formula><tex-math notation="LaTeX">^{3}</tex-math></inline-formula>H<inline-formula><tex-math notation="LaTeX">_{6}\rightarrow ^{3}</tex-math></inline-formula>F<inline-formula><tex-math notation="LaTeX">_{4}</tex-math></inline-formula>. The model is based on a two-level model and enables to express the threshold power and slope efficiency in a closed form. The effect of intrinsic losses is modeled by a physically motivated semi-empirical formula. The model is compared with the numerical one and with experimental data. Its application limits are discussed. An approximate method for checking validity conditions of the model is proposed.
We propose and demonstrate 1, 1.5, and 2 μm passively Q-switched fiber lasers by exploiting a few-layer Molybdenum sulfide (MoS 2 ) polymer composite as broadband saturable absorber (SA), ...respectively. The few-layer MoS 2 nanosheets are prepared by the liquid-phase exfoliation method, and are composited with polyvinyl alcohol (PVA). The PVA-MoS 2 film is sandwiched between two fiber ferrules to form the fiber-compatible SA. The few-layer MoS 2 not only shows good transparency from ultraviolet to mid-infrared spectral region, but also possesses the nonlinear saturable absorption. The modulation depth and saturation optical intensity of the PVA-MoS 2 film are measured to be 1.6% and 13 MW/cm 2 at 1566 nm by the balanced twin-detector technique, respectively. By further inserting the filmy PVA-MoS 2 SA into the cavities of Yb-, Er- and Tm-doped fiber lasers, we achieve stable Q-switching operations at 1.06, 1.56, and 2.03 μm, respectively. The output characteristics of the Q-switched pulses at the three wavelengths have been investigated, respectively. The MoS 2 -based Q-switching enables the large pulse energy of ~1 μJ with a pulse width of 1.76 μs. This is, to the best of our knowledge, the first demonstration of MoS 2 -based Q-switched fiber lasers in a wide wavelength range (from 1 to 2 μm). Our results experimentally confirm that the new-type 2-D material, few-layer MoS 2 , is a promising broadband SA to Q-switch fiber lasers covering all major wavelengths from near- to mid-infrared region.
Tellurene is a new 2D nonlayered material, which have obvious structural differences in both horizontal and vertical directions compared to layered materials. However, photonic devices related to its ...nonlinear optical characteristics are currently less studied. Herein, ultrathin 2D tellurene nanosheets were harvested from bulk tellurium crystals by liquid-phase exfoliation method. The low saturable intensity (1.06 MW/cm 2 ) and the high modulation depth (35.64%) of tellurene nanosheets were characterized by two-arm detection technology. To the best of our knowledge, this is the first attempt to utilize tellurene-microfiber as a saturable absorber, and achieved a picosecond passive mode-locked erbium-doped fiber laser. Stable picosecond pulses were generated at 1558.8 nm with a pulse duration of 1.03 ps. This work highlights the promise of 2D tellurene in short pulse lasers and will promote the applications of 2D nonlayered materials in ultrafast photonics.
We present a passively mode-locked Erbium-doped fiber laser with tunable parameters including central wavelength, 3-dB bandwidth, and pulse duration. The mode-locking mechanism of the laser is ...realized by using single-walled carbon nanotubes (SWCNTs) polyvinyl alcohol composite film as a saturable absorber. The tunable operation is implemented via a fiber birefringence filter consisting of a polarization maintaining (PM) fiber and a Brewster fiber grating. The laser achieves a maximum spectral tuning range of 36 nm with 8-cm PM fiber. The maximum spectral width variation of 5.19 nm is acquired when the PM fiber is 12 cm. Simultaneously, the spectral widths of pulses at different central wavelengths are also adjustable. Furthermore, the total cavity length is 8.28 m, which is the shortest cavity length to obtain such wide tuning range in an Erbium-doped fiber laser based on SWCNTs.
A gain-switched pulsed laser based on a commercial, heavily holmium-doped fluoroindate glass fiber, is designed to emit in the middle-infrared range, at the wavelength <inline-formula><tex-math ...notation="LaTeX">\boldsymbol{\lambda } = 3.92\ {\boldsymbol{\mu } \bf{ m}}</tex-math></inline-formula>. The laser, pumped at <inline-formula><tex-math notation="LaTeX">{\boldsymbol{\lambda }} = 888{\bf{\ nm}}</tex-math></inline-formula>, is modeled by a six-level system, by taking into account experimental spectroscopic parameters, to identify a feasible laser configuration. An output signal peak power of about <inline-formula><tex-math notation="LaTeX">{\boldsymbol{P}}_{\boldsymbol{s}}^{{\boldsymbol{peak}}} = 14.62{\bf{\ W}}</tex-math></inline-formula> with a full width at half maximum (FWHM) pulse duration less than <inline-formula><tex-math notation="LaTeX">{{\boldsymbol{\tau }}_{\boldsymbol{s}}} = 73\ {\boldsymbol{ns}}</tex-math></inline-formula> and pulse energy <inline-formula><tex-math notation="LaTeX">{{\boldsymbol{E}}_{\boldsymbol{s}}} = 1.214\ {\boldsymbol{\mu } \bf {J}}</tex-math></inline-formula> is predicted, by considering an input peak power of <inline-formula><tex-math notation="LaTeX">{\boldsymbol{P}}_{\boldsymbol{p}}^{{\boldsymbol{peak}}} = 10{\bf{\ W}}</tex-math></inline-formula>, and pump repetition rate of <inline-formula><tex-math notation="LaTeX">{\boldsymbol{f}} = 100{\bf{\ kHz}}</tex-math></inline-formula>, by employing a 8 cm-long fluoroindate fiber with holmium concentration <inline-formula><tex-math notation="LaTeX">{{\boldsymbol{N}}_{{\boldsymbol{Ho}}} = 100\ 000{\bf{\ ppm}}</tex-math></inline-formula>. The obtained result encourages the construction of a pulsed laser based on commercially available optical fiber, for applications in different fields as sensing and biomedicine.
This study proposed a high-quality fiber ring laser combining four-subring resonators and a saturable absorber within a ring cavity. An un-pumped erbium-doped fiber is introduced as the saturable ...absorber (SA) within the ring structure. By employing the vernier effect, we arrange four subrings with different lengths to form the four-subring resonators, achieving a single-longitudinal-mode (SLM) operation. At a pump power of 100 mW, the laser output power and wavelength deviations during a one-hour test were measured to be 0.01 dB and 0.059 nm, respectively. Additionally, using the delayed self-heterodyne measurement system and Lorentzian fit analysis, we measured an ultra-narrow linewidth of 623.1 Hz.
Compared with Yb, Nd has potential in 1120 nm fiber lasers, with the characteristics of larger emission cross section and four-level structure. In this work, Nd-doped fiber (NDF) oscillator and ...Nd-Raman fiber (NRF) oscillator were built using single-mode 5/125 NDF to study the lasing characteristics at 1120 nm, especially the suppression of amplified spontaneous emission at 1060 nm. Limited by the parasitic oscillation at 1060 nm, the NDF oscillator achieved 5 W output at 1120 nm. The NRF oscillator removed the limitation due to the Raman shift from 1064 nm to 1120 nm and obtained an output of 7.7 W at 1120 nm with a spectral peak-to-peak contrast of 36 dB. This work provides experimental basis for the application of NDF in 1.1 μm.
A dual-wavelength bright-dark pulse pair has been experimentally demonstrated in a mode-locked fiber laser based on thulium-doped fiber (TDF). By appropriately adjusting the polarization state, the ...dual-wavelength bright-dark pulse pairs with fundamental frequency of 20.56 MHz can be successfully obtained under the pump power ranging from 150 to 500 mW. The largest pulse energy is 2.84 nJ, and the conversion efficiency exceeds 10%. The generation mechanism of the bright-dark pulse pair in the cavity is primarily attributed to the cross-phase modulation (XPM) induced by the interaction of the bright soliton and dark soliton locating at different wavebands. Additionally, the dynamics of the bright-dark pulse pair is influenced by the polarization effect. To the best of our knowledge, this is the first demonstration of a bright-dark pulse pair laser employing TDF as the saturable absorber (SA). Its superiority for mode-locking has been fully proved, making it enormous potential in the fields of ultrafast lasers and nonlinear optics. Furthermore, this pulsed laser may offer a novel path for the development of high-power fiber lasers.
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