Germanene saturable absorber for mode-locked operation in an all-fiber laser with multiple dispersion environments.

In this paper, a high-quality germanene-polyvinyl alcohol (PVA) saturable absorber (SA) with a modulation depth of 3.05% and a saturation intensity of 17.95M W/c m 2 was prepared. Stable conventional mode-locking and harmonic mode-locking (HML) were achieved in germanene-based Er-doped fiber lasers (EDFL) using dispersion management techniques. In a cavity with a net dispersion value of -0.22p s 2, the conventional soliton had a center wavelength of 1558.2 nm, a repetition frequency of 19.09 MHz, and a maximum 3 dB spectrum bandwidth of 3.5 nm. The highest repetition frequencies achieved in cavities with net dispersion values of -2.81p s 2, -1.73p s 2, and -1.09p s 2 were 9.48 MHz, 12.75 MHz, and 12.10 MHz for HML, respectively. Furthermore, the effects of dispersion, power, and the polarization state on HML were systematically investigated. Our research results fully demonstrate the capability of germanene as an optical modulator in generating conventional mode-locked and harmonic mode-locked solitons. This provides meaningful references for promoting its application in ultrafast fiber lasers.

Evolution between bright and dark pulses in a MoxW1-xTe2 based fiber laser.

We proposed an erbium-doped fiber laser mode-locked with a MoxW1-xTe2-based nonlinear optical modulator for the first time to our best knowledge. This fiber laser can deliver bright pulses, bright-dark pulse pairs, dark pulses, bright-dark-bright pulses, and dark-dark-bright pulses. The modulation depth and saturation intensity of the MoxW1-xTe2-based saturable absorber were about 7.8% and 8.6 MW/cm2, respectively. When 10% of the laser in the cavity was output, conventional soliton pulses with central wavelength of 1560.1 nm can be obtained in the cavity. When 70% of the laser was output, dual-wavelength domain-wall dark pulses appeared in the laser cavity. This experiment revealed that an appropriate increase in the ratio of output energy can improve the chance of dark pulses in fiber lasers. The mode-locking states in this fiber laser can evolve with each other between bright pulses, bright-dark pulse pairs and dark pulses by adjusting the polarization controller. The results indicated that the MoxW1-xTe2 can be used to make modulators for generating dark pulses. Furthermore, our work will be of great help to improve the chance of the generation of dark pulse in fiber lasers.

Nanosized indium selenide saturable absorber for multiple solitons operation in Er3+-doped fiber laser.

With the advances in the field of ultrafast photonics occurring so fast, the demand for optical modulation devices with high performance and soliton lasers which can realize the evolution of multiple soliton pulses is gradually increasing. Nevertheless, saturable absorbers (SAs) with appropriate parameters and pulsed fiber lasers which can output abundant mode-locking states still need to be further explored. Due to the special band gap energy values of few-layer indium selenide (InSe) nanosheets, we have prepared a SA based on InSe on a microfiber by optical deposition. In addition, we demonstrate that our prepared SA possesses a modulation depth and saturable absorption intensity about 6.87% and 15.83 MW/cm2, respectively. Then, multiple soliton states are obtained by dispersion management techniques, including regular solitons, and second-order harmonic mode-locking solitons. Meanwhile, we have obtained multi-pulse bound state solitons. We also provide theoretical basis for the existence of these solitons. The results of the experiment show that the InSe has the potential to be an excellent optical modulator because of its excellent saturable absorption properties. This work also is important for improving the understanding and knowledge of InSe and the output performance of fiber lasers.

Dual-shearing interferometer for multi-modal hyperspectral imaging.

A dual-shearing interferometer (DSI) for multimodal hyperspectral imaging is presented. Two orthogonally stacked pairs of coherent beams are generated by a pair of novel, to the best of our knowledge, birefringent lateral shearing splitters. Consequently, two sets of interferograms with full pixel resolution are captured alternately in a time sequence in the double Nyquist frequency mode. Modals of dual-field-of-view hyperspectral imaging and differential-polarization hyperspectral imaging are introduced, and verification experiments are performed. The feasibility of other modals is discussed. The proposed method can effectively improve the instrument's performance in terms of the field of view, polarization, spectral resolution, and spectral range.

Generation of bright-dark solitons in an Er-doped fiber laser employing InSb as a saturable absorber.

In this paper, an indium antimonide (InSb) saturable absorber (SA) was successfully fabricated. The saturable absorption properties of the InSb SA were studied, and they show a modulation depth and a saturable intensity of 5.17% and 9.23M W/c m 2, respectively. By employing the InSb SA and building the ring cavity laser structure, the bright-dark soliton operations were successfully obtained by increasing the pump power to 100.4 mW and adjusting the polarization controller. As the pump power increased from 100.4 to 180.3 mW, the average output power increased from 4.69 to 9.42 mW, the corresponding fundamental repetition rate was 2.85 MHz, and the signal-to-noise ratio was 68 dB. The experimental results show that InSb with excellent saturable absorption characteristics can be used as a SA to obtain pulse lasers. Therefore, InSb has important potential in fiber laser generation, further applications in optoelectronics, laser distance ranging, and optical fiber communication, and it can be widely developed.

Optimization of the cavity length and pulse characterization based on germanene as a saturable absorber in an Er-doped fiber laser.

In this study, germanene-nanosheets (NSs) were synthesized by liquid-phase exfoliation, followed by an experimental investigation into the nonlinear saturable absorption characteristics and morphological structure of germanene. The germanene-NSs were employed as saturable absorbers, exhibiting saturation intensity and modulation depth values of 22.64M W/c m 2 and 4.48%, respectively. This demonstrated the feasibility of utilizing germanene-NSs passively mode-locked in an erbium-doped fiber laser (EDFL). By optimizing the cavity length, improvements in the output of EDFL characteristics were achieved, resulting in 883 fs pulses with a maximum average output power of 19.74 mW. The aforementioned experimental outcomes underscore the significant potential of germanene in the realms of ultrafast photonics and nonlinear optics.

Soliton phenomena in normal and anomalous dispersion regions in Er-doped mode-locked fiber lasers based on Cr2Si2Te6 saturable absorbers.

Investigations of optical solitons have always been a hot topic due to their important scientific research value. In recent years, ultrafast lasers based on two-dimensional materials such as saturable absorbers (SAs) have become the focus of optical soliton research. In this work, various soliton operations are demonstrated in Er-doped fiber lasers (EDFLs) based on ${{\rm Cr}_2}{{\rm Si}_2}{{\rm Te}_6}$ SAs. First, a low-threshold passively mode-locked EDFL with traditional soliton output is constructed, and the pump threshold is as low as 10.1 mW. Second, by adjusting the net dispersion of the cavity, stable dissipative soliton operation can also be obtained. Traditional soliton mode-locked operation with controllable Kelly sidebands from first order to fourth order is realized by adjusting the pump power in a double-ended pumped structure, and the SNR is as high as 55 dB. All results prove that ${{\rm Cr}_2}{{\rm Si}_2}{{\rm Te}_6}$ used as SA material has great potential and wide application prospects in investigating optical soliton operations in mode-locked fiber lasers with both normal and anomalous dispersion.

Third-order harmonic mode-locked and Q-switched Er-doped fiber laser based on a Cr2Ge2Te6 saturable absorber.

This paper reports the generation of fundamental solitons and third-order solitons in an erbium-doped fiber laser (EDFL) by a Cr2Ge2Te6-polyvinyl alcohol (CGT-PVA) saturable absorber (SA). Stable fundamental solitons at 1559.09 nm at a repetition frequency of 5.1 MHz were detected, and third-order solitons with a maximum output power of 6.807 mW and narrowest monopulse duration of 615.2 fs were obtained under a repetition frequency of 15.3 MHz by changing pump power. To the best of our knowledge, it is the first time to achieve a Q-switched pulse with a minimum pulse duration of 2.2 µs and maximum single pulse energy of 12.11 nJ in EDFL based on CGT-PVA SA after reducing the cavity length. Its repetition rate monotonically increased from 18.8 kHz to 61.8 kHz with a tuning range of about 43 kHz. The experimental results sufficiently demonstrate that CGT has enormous potential as an ultrafast photonics device.

Passively mode-locked fiber laser based on GeTe as a saturable absorber.

In this work, we fabricate a saturable absorber based on GeTe with saturation intensity and modulation depth of 12.6M W/c m 2 and 7%, respectively. We obtain stable conventional soliton and stretched soliton mode-locking operation. For the conventional soliton state, the average output power increased from 0.93 to 8.70 mW with the increase of pump power, and the fundamental repetition rate was 7.8351 MHz. Its central wavelength and 3 dB bandwidth were 1564.72 and 4.78 nm, respectively. For the stretched soliton state, when the pump power was increased from 87.4 to 420.3 mW, the average output power increased from 2.05 to 10.46 mW. When the maximum average output power reached 10.46 mW, the maximum average single-pulse energy was 0.86 nJ. The experimental results show that GeTe nanosheets will have broad application potential in the field of ultrafast photonics.

Generation of bright-dark soliton pairs based on a ferromagnetic insulator Cr2Si2Te6 as a modulator in an Er-doped fiber laser.

In this work, a saturable absorber (SA) based on Cr2Si2Te6 (CST), with a modulation depth of 14.90% and saturation intensity of 4.81MW/cm2, was prepared by a liquid phase stripping method. Its nonlinear optical properties and application in obtaining mode-locked pulse output of bright-dark solitons are studied. When the pump power was 1250 mW, the maximum output power was 26.60 mW; the energy of the single pulse was 15.02 nJ, and the repetition rate was 1.77 MHz. Our results provided evidence that CST can be used as an excellent SA for a mode-locked laser and demonstrated that ferromagnetic insulators can be used for the study of bright-dark soliton pairs.

Passively mode-locked Er-doped fiber laser based on a ferromagnetic insulator Cr2Si2Te6 as a saturable absorber.

In our work, a new-type, to the best of our knowledge, ferromagnetic insulator and its nonlinear optical absorption characteristics and related ultrafast modulation applications were investigated. Cr2Si2Te6 saturable absorbers (SAs) with a modulation depth and a saturable intensity of 9.7% and 3.5MW/cm2 were fabricated. By adjusting the pump power to 120 mW and optimizing the polarization state, traditional soliton operations were obtained successfully; the corresponding duration of pulse and the fundamental repetition rate were ∼1.33ps and 6.70 MHz, and the signal-to-noise ratio was 50 dB. The experimental results reveal that Cr2Si2Te6 with excellent saturable absorption characteristics can be used as a SA to obtain ultrafast pulse lasers.

Ultrahigh hydrogen storage capacity of holey graphyne.

Holey graphyne (HGY), a novel two-dimensional (2D) single-crystalline carbon allotrope, was recently synthesized by Castro-Stephens coupling reaction. The naturally existing uniform periodic holes in the 2D carbon-carbon network demonstrate its promising potential in energy storage. Herein, we conduct density functional theory (DFT) calculation and ab initio molecular dynamics simulations (AIMD) to predict the H storage properties of a single-layer HGY sheet modified by Li metal atoms. The DFT calculations demonstrate that Li atoms can bind strongly to the HGY sheet without forming clusters, and each Li atom can anchor four H2 molecules with an average adsorption energy of about -0.22 eV/H2. The largest H storage capacity of the doped HGY sheet can reach as high as 12.8 wt%, showing that the Li/HGY complex is an ideal H storage material at ambient conditions. In addition, we investigate the polarization mechanism of the storage media and find that the polarization originates from the electric field induced by both the ionic Li atoms and the weak polarized H2 molecules. Finally, the desorption mechanism of the adsorbed H2 molecules is thoroughly investigated using a kinetic AIMD method.

Ultra-high hydrogen storage capacity of holey graphyne.

Holey graphyne (HGY), a novel two-dementional 2D single-crystalline carbon allotrope, was recently synthesized by Castro-Stephens coupling reaction. The naturally existing uniform periodic holes in the 2D carbon-carbon network demonstrate its promising potential in the energy storage. Herein, we conducted density functional theory (DFT) calculation to predict the hydrogen storage capacity of HGY sheet. It is found the Li-decorated single-layer HGY can serve as a promising candidate for hydrogen storage. Our DFT calculations demonstrate that Li atoms can bind strongly to the HGY sheet without the formation of Li clusters, and each Li atom can anchor four H2 molecules with the average adsorption energy about 0.22 eV/H2. The largest hydrogen storage capacity of the doped HGY sheet can reach as high as 12.8 wt%, largely surpassing the target of the U. S. DOE (9 wt%), showing the Li/HGY complex is an ideal hydrogen storage material at ambient conditions. In addition, we investigate the polarization mechanism of the storage media and find that the polarization is originated from both the electric field induced by the ionic Li decorated on the HGY and the weak polarized hydrogen molecules dominated the H2 adsorption process.

Baseline kidney function is associated with vancomycin-induced acute kidney injury in children: a prospective nested case-control study.

BACKGROUND: Children with kidney insufficiency are susceptible to vancomycin-induced acute kidney injury (VIAKI), but there is a lack of compelling clinical data. We conducted a nested case-control study to evaluate the relationship between kidney insufficiency and incidence of VIAKI in children. METHODS: Patients were considered to have VIAKI if they met the criteria for eGFR change according to pRIFLE-I or p-RIFLE-F. Case group comprised patients who developed VIAKI. Case-control ratio was 1:3; patients were matched for age, severity, and nature of illness and initial vancomycin dose. Primary endpoint was incidence of VIAKI at three levels of kidney function, calculated using Kaplan-Meier curve and log-rank test. Secondary endpoint was treatment-related in-hospital mortality amongst case and control groups. RESULTS: Amongst 386 children who fit study criteria, 31 developed VIAKI (8.03%). Thirty-one cases and 93 controls were selected from the observed cohort. Three risk factors were identified for VIAKI: moderate kidney insufficiency (OR 8.8, 2.4-32.8), vancomycin trough concentration ≥ 15 µg/mL (OR 7.7, 1.7-34.4), and furosemide use (OR 24.8, 6.4-98.2). A significant difference in time to VIAKI was noted between patients with moderate kidney insufficiency and patients with mild kidney insufficiency or normal kidney function (p < 0.001). In-hospital mortality rate in case group was 45.2%, compared to 18.3% in control group (p < 0.01). CONCLUSIONS: Children with moderate kidney insufficiency are more likely to develop VIAKI than those with normal and mild kidney insufficiency. Patients who develop VIAKI have higher in-hospital mortality than those who do not develop VIAKI.

Passively Q-switched and mode-locked erbium-doped fiber lasers based on tellurene nanosheets as saturable absorber.

Various two-dimensional (2D) materials show unique optical properties and excellent performance in acting as saturable absorber (SA) for demonstrating all-fiber ultra-fast lasers. Tellurene, as a new-fashioned few-layer 2D monoelemental material, was designed as an excellent saturable absorber to achieve Q-switched and mode-locked operations within erbium-doped fiber (EDF) lasers in our experiment. High-quality tellurene-based SA with a modulation depth of 0.97% was obtained by blending few-layer tellurene nanosheet solution prepared by liquid phase exfoliation method and the polyvinyl alcohol (PVA) solution. Inserting the SA into the EDF laser cavity by sandwiching the tellurene-PVA film between two fiber ferrules, either the passively Q-switched or the passively mode-locked operations can be obtained. The repetition rate varies from 15.92 to 47.61 kHz, and the pulse duration decreases from 8.915 to 5.196 µs in the passively Q-switched operation. To the best of our knowledge, this is the first demonstration focusing on the modulation application of tellurene in designing Q-switched pulsed laser operations. Additionally, mode-locked operations were also achieved by adjusting the polarization state. The obtained results fully indicate that tellurene can be developed as an efficient SA for pulsed fiber lasers.

Conventional solitons and bound-state solitons in an erbium-doped fiber laser mode-locked by TiSe2-based saturable absorber.

Conventional solitons (CSs) as well as bound-state solitons in a passively mode-locked erbium-doped fiber (EDF) laser based on 1 T-phase titanium diselenide (1 T-TiSe2) saturable absorber (SA) have been systematically demonstrated for the first time. The mode locker is assembled by sandwiching the 1 T-TiSe2 film between two fiber ferrules to improve compatibility with the all-fiber-integrated ring cavity configuration. The modulation depth, saturation intensity and nonsaturable loss of the prepared 1 T-TiSe2 SA are 14.36%, 1.33 MW cm-2 and 9.44%, respectively. The system is switchable between two states: CS and bound-state CS, by carefully adjusting the orientations of the polarization controller (PC). In the CS mode-locked regime, the oscillating wavelength is centered at 1558.294 nm with a pulse duration of 1.74 ps, a pulse repetition rate of 3.23 MHz and a maximum average output power of 2.904 mW. In the bound-state CS regime, two identical solitons form the bound-state pulses with a temporal separation of 6.1 ps, and the bound-state pulses are equally distributed at a repetition rate of 3.23 MHz, corresponding to the fundamental cavity repetition rate. The experimental results further indicate that 1 T-TiSe2 SA is competitive with the existing SAs explored so far and will promote the applications of 1 T-TiSe2-based SAs in the field of ultrafast lasers.

ZrSe2 nanosheet as saturable absorber for soliton operations within an Er-doped passive mode-locked fiber laser.

Two-dimensional materials have extensively promoted the development of ultrafast photonics in the past decade. In our work, the saturable absorption properties of ZrSe2 were presented. The saturation intensity, modulation depth, and nonlinear absorption coefficient of the ZrSe2 saturable absorber (SA) are about 13.14MW/cm2, 6.09%, and 1.85∗10-1cm/GW. In the experiment, based on the ZrSe2 SA, two types of solitons were recorded. A conventional soliton with a pulse width of 985 fs and a three-pulse bound state soliton have been obtained. Our experiment reveals that ZrSe2 can be employed for generating multiple ultrafast soliton generations and possess promising application in ultrafast photonics.

Nonlinear optical absorption properties of zirconium selenide in generating dark soliton and dark-bright soliton pairs.

Our work reports the preparation of zirconium selenide (ZrSe2)-polyvinyl alcohol (PVA) film-type saturable absorber (SA) and its nonlinear absorption performance in obtaining dark soliton and dark-bright soliton pairs in an Er-doped fiber (EDF) laser for the first time, to the best of our knowledge. The saturation intensity and modulation depth of the ZrSe2-PVA SA were ∼12.72MW/cm2 and 2.3%, respectively. Due to the modulation of the SA, under a pump power of 525.2 mW, stable dark soliton operation with an average output power of 9.75 mW, and a pulse repetition frequency of 20.84 MHz, a pulse width of 3.85 ns was attained successfully. By adjusting the state of the polarization controllers, dark-bright soliton pairs were also observed. To the best of our knowledge, this was the first demonstration focusing on the nonlinear optical absorption applications of ZrSe2 in obtaining dark soliton and dark-bright soliton pairs. Our results show that ZrSe2 is a good two-dimensional SA material for acting as an ultrafast optical device due to its suitable nonlinear optical absorption properties.

CVD-Bi2Te3 as a saturable absorber for various solitons in a mode-locked Er-doped fiber laser.

In this work, we report about high energy and various solitons' operation by using high-efficiency topological insulator bismuth telluride (Bi2Te3) nanofilms as broadband saturable absorbers in the passively mode-locked Er-doped fiber laser. The Bi2Te3 film was successfully synthesized by chemical vapor deposition (CVD). Excellent characteristics of the dark-bright pulse pairs, bright pulses, and multiharmonics have been investigated experimentally by adjusting the polarization state. At the same time, the maximum average output power was 40.18 mW, and the single-pulse energy was 20.91 nJ. As we all know, it is the various solitons of the first generation with large pulse energy in an Er-doped fiber laser with Bi2Te3 as saturable absorber. The experimental results show that CVD Bi2Te3 can be used as an excellent candidate in mode-locked fiber lasers.

Fully controlled photonic spin in highly confined optical field.

As an intrinsic attribute of light, the spin angular momentum (SAM) of photons has aroused considerable attention because of the fascinating properties emerging from light-matter interactions. We show that a diffraction-limited focal field with a steerable photonic spin structure in three dimensions can be produced under a 4π microscopic system. This is achieved by focusing two counter-propagating configurable vector beams produced in the coherent superposition of three different beams with x-polarization, y-polarization, and radial-polarization. By altering the amplitude factors of these resultant beams, the ratios between the three mutually orthogonal polarized components can be freely tuned within the focal plane, thereby allowing dynamic control over the spin orientation and ellipticity of the tightly focused optical field. The results demonstrated in this paper may find applications in spin-controlled nanophotonics.