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Passively harmonic mode-locking has been experimentally demonstrated in an erbium-doped fiber laser with large normal dispersion using single-multi-single mode structure as artificial saturable absorber. By increasing the pump power under the same polarization setting, the mode-locking operation can switch from fundamental mode-locked to 5th order harmonic mode-locked. Highest repetition rate of 4.26 MHz (5th order harmonic) is observed, with pulse width and pulse energy ascertained at 290 fs and 3.0 nJ, respectively. Excellent signal-to-noise ratio (SNR) of above 50 dB is observed for all harmonic orders. The findings validated that SMS structure can be used to generate stable and switchable high order of harmonic mode-locked. The low-cost SMS fiber for harmonic mode-locked generation technique could lay the groundwork for future sustainable industrial growth. [ABSTRACT FROM AUTHOR]

In this work, all‐optical polarisation state modulation using a tungsten disulfide (WS2) coated side‐polished fibre (SPF) as modulator is experimentally demonstrated. A bulk layer WS2 is exfoliated into a few‐layer WS2 thin film using liquid phase exfoliation technique. The few‐layer WS2 film is then coated onto a SPF to serve as an optical polarisation state modulator based on the thermo‐optic effect. The rotation of the polarised signal light is controlled using a pump laser. Throughout the pump power range of 514.5 mW, the polarisation state of the polarised signal light has rotated ∼70°, with a minor ellipticity fluctuation of <6°. The proposed experiment is carried out on the basis of the photon‐modulate‐photon principle and achieved all‐optical modulation in a fibre laser system. [ABSTRACT FROM AUTHOR]

• Domain wall dark pulse generation in EDFL using thin-core thulium fiber as interferometer. • Up to 7th harmonic order dark pulse are generated. • The shorted pulse width was observed as 60 ns at 7th harmonic order. In this work, the harmonic domain-wall dark pulse is experimentally demonstrated in C-band fiber laser. The domain-wall dark pulse was self-started at pump power of 112 mW. The fundamental dark pulse repetition rate was measured as 0.96 MHz, pulse duration of 250 ns and highest average pulse energy of 3.24 nJ. As the power increased, dark pulses up to the 7th harmonic order were visualized and quantified. Pulse temporal width reduced as harmonic order increased, with the minimum pulse width of 60 ns recorded in the 7th order. The harmonic dark pulse fiber laser demonstrated adequate stability, with signal-to-noise ratios above 50 dB throughout all harmonic operations. The endeavor of harmonic dark pulse dark soliton could lay the groundwork for future sustainable industrial growth. [ABSTRACT FROM AUTHOR]

In this work, we demonstrated Poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS) as a saturable absorber (SA) to produce mode-locking operation in different length of Erbium-doped fiber laser (EDFL). The PEDOT: PSS was embedded into polyvinyl alcohol to form a thin film that acts as an absorber into the laser setup. The three different mode-locked EDFL were successfully demonstrated with different cavity length and output coupler ratio. The pulse repetition rate/width of 3.417 MHz/710 fs, 4.831 MHz/510 fs, and 6.049 MHz/460 fs were obtained by utilizing optical coupler/ cavity length of 20:80/60.7 m, 10:90/42.7 m, and 5:95/33.7 m, respectively. All experiments generated a stable and mode-locked operation at a central wavelength of 1570.76 nm, 1570.3 nm, and 1569.95 nm with 3 dB bandwidth of 4.8 nm, 5.6 nm, and 6.5 nm, respectively. The long-time stability of the ultrafast fiber lasers was investigated for each setup via 120 min. The proposed PEDOT: PSS has proven as a promising material to induce mode-locking operation in different fiber laser setup. [ABSTRACT FROM AUTHOR]

In this work, polarization modulator utilizing MXene material, namely Nb2C is demonstrated. S band signal is injected into Nb2C thin film and is modulated by 1400 nm laser diode. A total of 39.81° of polarization rotation is attained when the pump power is increased to 223 mW. The rotation of light is due to thermo-optic effect. The efficiency of polarization modulator is calculated at 0.1974°/mW. [ABSTRACT FROM AUTHOR]

In this work, all fiber temperature measurement based on change of light polarization is demonstrated using tapered fiber coated with graphene. The large evanescent field of tapered fiber allows graphene to absorb the surrounding heat and subsequently this changes the refractive index of graphene coated tapered fiber. The change of refractive index is due to thermo‐optic effect. When there is a change in surrounding temperature, refractive index of the coated tapered fiber changes and this subsequently modifies the injected light polarization. The proposed temperature sensor can measure temperature up to 250°C and its sensitivity is ascertained at 0.48°/°C. The proposed temperature sensor is beneficial for future Internet of Things (IoT) applications. [ABSTRACT FROM AUTHOR]

MAX phase materials have garnered significant attention due to their corrosion resistance, impressive antioxidation and high electrical and optical conductivity. One such material, Titanium Tin Carbide (Ti 2 SnC), has demonstrated notable nonlinear optical properties. The saturable absorption of Ti 2 SnC, embedded into a polyvinyl (PVA) film, was measured to assess its potential. The Ti 2 SnC -PVA film exhibited a calculated modulation depth of 7.8%. In the context of practical applications, the Ti 2 SnC-PVA film was employed as a saturable absorber (SA) in an Erbium-doped fiber laser (EDFL) cavity. This configuration enabled the generation of stable Q-switched and mode-locked pulse trains. Q-switched operation occurred in a pump power range of 51.67 mW–83.83 mW, reaching a peak pulse energy of 110.94 nJ. Transitioning to mode-locking operation, the laser cavity demonstrated efficiency in the pump power range of 105.27 mW–196.39 mW. At a pump power of 196.39 mW, the fiber laser cavity achieved its highest pulse energy of 5.42 nJ, characterized by a pulse width of 2.32 ps and a pulse repetition rate of 1.825 MHz. These results highlight the promising potential of Ti2SnC-PVA thin film as a cutting-edge material for applications in pulsed laser systems. The material's excellent nonlinear optical properties make it a compelling candidate for advancing the field of pulsed laser technology. • The Ti 2 SnC embedded into a polyvinyl (PVA) film, exhibited a modulation depth of 7.8%. • Q-switched operation occurred in a pump power range of 51.67 mW–83.83 mW, reaching a peak pulse energy of 110.94 nJ. • Transitioning to mode-locking operation in the pump power range of 105.27 mW–196.39 mW. • Mode-locked pulses exhibit a pulse width of 2.32 ps and a repetition rate of 1.825 MHz. • At 196.39 mW, the mode locked EDFL achieved its highest pulse energy of 5.42 nJ. [ABSTRACT FROM AUTHOR]

• Generation of soliton dark pulses using a Molybdenum Aluminium Boride (MoAlB) as saturable absorber (SA). • MoAlB was coated onto side-polished fiber to improve the birefringence and nonlinearity. • The dark pulses are generated based on cubic-quintic nonlinear Schrödinger equation mechanism. • The SA has a modulation depth of 6.5 %, a saturation intensity of 100 MW/cm2 and non-saturable loss of 50%. • The laser operated at 1560.6 nm with a pulse duration of 152 ns and repetition rate of 1.87 MHz. We demonstrate the generation of dark pulses from an Erbium-doped fiber laser (EDFL) using a Molybdenum Aluminium Boride (MoAlB) as a saturable absorber for the first time. Molybdenum Aluminium Boride (MoAlB) was coated onto side-polished fiber (SPF) to improve the birefringence and nonlinearity inside the EDFL cavity with net anomalous dispersion. The soliton dark pulses are obtained from the laser cavity based on cubic-quintic nonlinear Schrödinger equation (CQNLSE) mechanism. The laser operated at 1560.6 nm with a pulse duration of 152 ns and repetition rate of 1.87 MHz as the pump power is set within 200 mW to 370 mW. At the maximum pump power, the average output power and pulse energy are recorded at 6.93 mW and 3.77 nJ, respectively. We think that this research is the first to show MoAlB 's potential for dark pulse generation. [ABSTRACT FROM AUTHOR]

Single and double Brillouin frequency spacing multi-wavelength Brillouin Erbium-doped fiber laser based on micro-air gap cavity is proposed and demonstrated. A 6.90-km dispersion shifted fiber is used as Brillouin gain medium to induce stimulated Brillouin scattering in the ring cavity. The micro-air gap cavity is constructed by aligning two polished fiber facets coaxially, and induces strong Fresnel reflection to switch the Brillouin frequency spacing from a double spacing to single spacing regime. Under the Brillouin pump power of 13 dBm and the laser diode pump power of 300 mW, five Stokes with a wavelength spacing of 0.160 nm and six Stokes with a wavelength spacing of 0.084 nm are generated. The fluctuation of the Stokes for both single and double Brillouin spacing regimes in the proposed setup are less than 3 dB throughout a 1-h time span. The variation of the cavity efficiency between the single and double spacing regimes is less than 1.2 dB. [ABSTRACT FROM PUBLISHER]

A simple multi-wavelength passively Q-switched Erbium-doped fiber laser (EDFL) is demonstrated using low-cost multi-walled carbon nanotubes (MWCNTs)-based saturable absorber, which is prepared using polyvinyl alcohol as a host polymer. The multi-wavelength operation is achieved based on non-linear polarization rotation effect by incorporating 50?m long photonic crystal fiber in the ring cavity. The EDFL produces a stable multi-wavelength comb spectrum for more than 14 lines with a fixed spacing of 0.48?nm. The laser also demonstrates a stable pulse train with the repetition rate increasing from 14.9 to 25.4?kHz as the pump power increases from the threshold power of 69.0?mW to the maximum pump power of 133.8?mW. The minimum pulse width of 4.4??s was obtained at the maximum pump power of 133.8?mW while the highest energy of 0.74 nJ was obtained at the pump power of 69.0?mW. [ABSTRACT FROM AUTHOR]

In this work, an all‐fibre phase shifter using tapered fibre coated with molybdenum tungsten disulfide ‐ reduced graphene oxide (MoWS2‐rGO) is demonstrated. The large evanescent field of tapered fibre allows MoWS2‐rGO to absorb injected light from a 1400‐nm pump. It subsequently modifies the refractive index of both an MoWS2‐rGO solution and tapered fibre because of the thermo‐optic effect. A maximum wavelength shift of 2.489 nm is observed and the equivalent phase shift is 0.91π. The efficiency of the phase shifter is calculated at 0.0175 nm/mW. The proposed phase shifter is beneficial for a variety of applications, specifically for future optical beam‐forming networks and all optical signal processing devices. [ABSTRACT FROM AUTHOR]

In this work, NaGdF4: 20%Yb, 2%Er microcrystals with varying contents of Cr3+ doping were obtained by conventional hydrothermal process. The microcrystal phase structure, morphology, upconversion luminescence mechanism, as well as temperature sensing behaviour under different treatment methods were researched. Based on the thermally coupled 2H11/2 and 4S3/2 levels of Er3+ and the dependence of fluorescence intensity ratio (FIR) on temperature, the optical temperature sensing behaviour of micrometer crystals were experimentally demonstrated. The NaGdF4: 20%Yb, 2%Er, 7%Cr microcrystals treated with high-temperature annealing show the best temperature sensing behaviour within the temperature span of 298–498 K. NaGdF4: 20%Yb, 2%Er, 7%Cr microcrystals with high temperature annealing presented the feasibility and promising properties for optical temperature sensing. The endeavour of emerging materials could lay the groundwork for future sustainable photonics engineering industrial growth. [ABSTRACT FROM AUTHOR]

We propose and demonstrate a passively mode-locked all-fiber laser utilizing a multimode interference effect in graded-index multimode fiber (GIMF). The mode-locking is obtained due to the Kerr effect in GIMF, which induces the intensity modulation inside the ring cavity laser. We obtain stable soliton mode-locked pulses at a center wavelength of 1574.1 nm, with a fixed repetition rate of 22 MHz and a pulse duration of 650 fs, when the pump power is changed in the range from 66.2 to 140.0 mW. The maximum average output power and pulse energy are recorded at 9.82 mW and 448 pJ, respectively, at a pump power of 140 mW. This proves that a nonlinear optical response in GIMF can be used as a new modulation mechanism for obtaining ultra-short pulses based on all-fiber ring cavity. [ABSTRACT FROM AUTHOR]

In this letter, we propose a passively Q-switched all-fiber laser and demonstrate how to utilize a multimode double-clad Erbium–Ytterbium co-doped fiber as an active medium. The Q-switching is obtained based on the Kerr effect of multimode interference, which induced intensity modulation inside the linear cavity laser. Stable Q-switched pulses are obtained at 1552.3 nm with the repetition rate varying from 50.3 to 222.2 kHz, when the pump power is changed in the range from 1.00 to 3.09 W. We record the minimum pulse width and the maximum pulse energy at 2.1 μs and 2.7 μJ, respectively, at a pump power of 2.42 W. This proves a new modulation mechanism for obtaining high energy pulses based on all-fiber linear cavity. [ABSTRACT FROM AUTHOR]

A tunable mode-locked fiber laser based on the non-linear polarization rotation (NPR) technique is proposed and demonstrated. A passively generated mode-locked output is obtained with a repetition rate of about 70 ns and an average output power of 0.7 mW, as well as a laser efficiency of 0.53%. The mode-locked pulses can be tuned over a span of 4.4 nm, from 1560.6 nm to 1556.2, corresponding to a stretching of the tapered fiber from 0 to 100 µm in 10 µm increments. The pulses have an average signal-to-noise ratio of about 41 dB in the frequency domain, indicating a highly stable mode-locked output. The system can repeat and reverse the generation of these pulses, a crucial criterion of many communications and sensing applications. [ABSTRACT FROM AUTHOR]

Multi-wavelength and Q-switched EDFLs are demonstrated using a MoS2thin film as stabilizer and saturable absorber, respectively. For a multi-wavelength output, a 50-m-long PCF is incorporated into the cavity to induce unstable multi-wavelength oscillation and a MoS2thin film is further incorporated into the cavity to achieve stable multi-wavelength. The laser generates 11 lasing wavelengths with constant spacing of 0.47 nm at pump power of 250 mW. In the case of the Q-switched EDFL, MoS2thin film is utilized as a saturable absorber. Q-switched operation occurrs at a threshold pump power of 28.86–51.48 mW and the spectrum is centered at 1561.15 nm. The pulse repetition rate showed increasing trend from 18.57–30.72 kHz whereas the pulse width decreased from 53.85–32.54 μs in the Q-switched pump power range. The highest pulse energy of 30.73 nJ is obtained at pump power of 51.48 mW. [ABSTRACT FROM AUTHOR]

We propose and demonstrate a new Q-switched thulium-doped fiber laser (TDFL) by utilizing a passive saturable absorber (SA) based on Molybdenum–Aluminium boride (MoAlB). The MoAlB is a metal–ceramic-based material; it is embedded in polyvinyl-alcohol (PVA) material to operate as the SA. The laser successfully generates stable Q-switched pulses operating at 1974.7 nm with a maximum repetition rate of 57.7 kHz and a minimum pulse width of 1.79 μs. A maximum pulse energy of 90.2 nJ is recorded at 436 mW pump power. Our experiment is the first demonstration on the use of MoAlB for the pulse laser generation in the 2 μm wavelength region. [ABSTRACT FROM AUTHOR]

• A Sm3+ single-doped LaGaO 3 is reported to have excellent multimodal and multicolor luminescence. • The system responds to UV, X-ray and temperature-dependent emission. • Distinct excitation property and precise trap local units achieve multicolor emission. Multimodal Excitation Response (MMER) phosphors hold pivotal importance for anti-counterfeiting and encryption abilities correlated to the information and data safety. Existing options commonly display static monochromatic luminescence under fixed stimulation, making it susceptible to replication, and developing multicolor and multimodal luminescence in a single material. Herein, we report a Sm3+ single-doped LaGaO 3 perovskite phosphor as an efficient multimodal luminescence material with color-tunable luminescence that responds to convenient light sources including ultraviolet (UV) and X-ray tube. Additionally, it demonstrates temperature-induced multicolor luminescence and anti-thermal-quenched emission. The comprehensive tests prove that the multicolor response to UV/X-ray and temperature stimulation derives from different excitation properties between host and Sm3+ ions, and precise emitter/trap local units. Optical information encryptions and anti-counterfeiting devices are designed by integrated luminescence properties, achieving relaxed detection of multimodal emission features under different stimulations. The combination of photo-stimulated, persistent and temperature-stimulated luminescence in LaGaO 3 : Sm3+ phosphor provides significant prospect for the industrial growth of multifunctional optical materials and devices. [ABSTRACT FROM AUTHOR]

Organic materials have been widely explored in various of electronic and photonic applications. poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS) is one of the organic materials that exhibits excellent optical properties including wide operating bandwidth and fast relaxation time. These properties are important for fiber laser applications to induce ultrafast phenomenon. In this experiment, PEDOT: PSS thin film was successfully fabricated based on spin coating technology for use as a saturable absorber (SA) and it featured saturation intensity of 0.21 M W / c m 2 and modulation depth of 22%. The incorporation of PEDOT: PSS SA into erbium-doped fiber laser cavity successfully induced a 1.74 ps mode-locked laser at wavelength of 1567.6 nm. The pulse energy and output power were achieved at about 2.79 nJ and 6.89 mW respectively. This is the first time that PEDOT: PSS is applied as a SA to generate a soliton mode-locked laser at wavelength of 1.55 μm. • Poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS) based absorber. • PEDOT: PSS spin-coated onto polyvinyl alcohol thin film as mode-locker. • Modulation depth of 22%. • A 1.74 ps mode-locked soliton laser at wavelength of 1567.6 nm. • The pulse energy and output power were achieved at about 2.79 nJ and 6.89 mW respectively. [ABSTRACT FROM AUTHOR]

The band structure of semiconducting photocatalysts plays a crucial role in determining their charge carrier transport characteristics and photocatalytic activity. In this work, a simple method to modulate the band structures of carbon nitride by infusing dopants and porous materials is experimentally demonstrated. A combination of trithiocyanuric acid and ammonium chloride to calcinate in an air environment, sulfur dopants and a significant amount of porosity are infused into carbon nitride concurrently. The sulfur-doped and porous carbon nitride material shows remarkable performance in photocatalytic hydrogen production, achieving a maximum hydrogen evolution rate of 4516.84 μmol g−1 h−1. Furthermore, infusion of sulfur dopants and abundant porous into carbon nitride allows for substantial and continuous tuning of the conduction and valence band positions. The band structures modulation enhanced the optical absorption in visible light region, making it suitable for efficient solar energy conversion. The findings of this work are feasible to pave a foundation for future clean energy technology. • Fabrication of 3D foam sulfur-doped CN nanosheets using a one-step medium-assist method. • Enhancement of surface area and light absorption using 3D foam sulfur-doped CN nanosheets. • Enhancement of hydrogen generation efficiency using 3D foam sulfur-doped CN nanosheets. [ABSTRACT FROM AUTHOR]

In this work, rare‐earth composite as an optical upconversion temperature dual mode sensing is practically demonstrated. NaGdF4:Yb3+/Er3+/Zn2+ phosphor was synthesized by the solvothermal method. The phase purity, crystal structure and morphologies were characterized by X‐ray diffraction (XRD) and scanning electron microscopy (SEM). The enhancement of upconversion luminescence is achieved by aliovalent doping in Zn2+ co‐doped NaGdF4: Yb3+/Er3+ phosphors. The temperature sensing behaviours based on the luminescence intensity and luminescence lifetime in phosphors are recorded in the temperature range from 75 to 297 K, and the maximum sensitivity is obtained as 13.4 × 10−3 K−1 at 75 K and 2.52 × 10−3 K−1 at 225 K, respectively. [ABSTRACT FROM AUTHOR]

A temporal and amplitude modulator based on few-layers bismuth telluride (Bi2Te3) flakes is demonstrated for C-band operation. The few-layers thick Bi2Te3 flakes are prepared by mechanically exfoliating a Bi2Te3 crystal. As an optical pulse modulator, the Bi2Te3-based saturable absorber (SA) provides stable Q-switching operation at 1561.1 nm with a maximum repetition rate of 70.92 kHz and minimum pulse width of 2.38 µs. As an optical amplitude modulator, two linear regions at different pump power ranges are obtained in the regression line of the peak intensity. The first linear region covers a pump power range from 0.0 to 80.32 mW and corresponds to a modulation efficiency of 0.05 dB/mW, while the second linear region covers a pump power range of 80.32–98.64 mW with a modulation efficiency of 0.81 dB/mW. [ABSTRACT FROM AUTHOR]

The Er3+, Tm3+, Ho3+ activated, and Tm3+, Ho3+ co-doped NaBiF 4 : Yb3+ microcrystals are achieved by a hydrothermal method, and the optimum synthesis condition is explored. The phase purity, crystal structure, morphology, upconversion luminescence (UCL) performance and thermal stability of the target products are investigated. By doping different rare earth ions and changing the doping concentration, the UCL color can be adjusted, and the color purity is high under the 980 nm irradiation. Meanwhile, The NaBiF 4 :20%Yb3+, 0.5%Tm3+, 1.5%Ho3+ microcrystals synthesized under the optimal conditions realize the upconversion white emission. Furthermore, the light-emitting diode (LED) devices are fabricated by integrating a near-infrared LED chip with different microcrystals, displaying bright white and other colors emitted light. These achieved features implied that the NaBiF 4 microcrystals doped with rare earth ions are promising functional materials for lighting and display devices. • Series of pure hexagonal NaBiF 4 : Yb microparticles have been synthesized by hydrothermal synthesis. • NaBiF 4 :Yb microparticles doped with Er3+, Tm3+, Ho3+ ions to induce multi-colors emission under 980 nm laser excitation. • White light emission is achieved of NaBiF 4 :20%Yb3+, 0.5%Tm3+, 1.5%Ho3+ upconversion microcrystals. [ABSTRACT FROM AUTHOR]

We successfully demonstrated a stable Q-switched erbium-doped fiber laser (EDFL) using Molybdenum Aluminum Boride (MoAIB), a metal ceramic-based material as saturable absorber (SA). The thin layer of MoAIB was obtained by mechanical exfoliation method and acquired onto the end surface of a standard FC/PC fiber connector to function as SA. The features of MoAIB-SA are experimentally evaluated in two output coupling ratios, which are 50:50 and 95:5. From the experimental results, MoAIB-SA is well-functioning as SA to modulate the CW lasing into Q-switching operation. The 95:5 coupler setup presented better pulse quality, in term of pulse repetition rate and pulse width. Additionally, 50:50 coupler setup allows higher pump power and pulse energy to extract from the fiber laser system. [ABSTRACT FROM AUTHOR]

The applications of graphene thin film as a nonlinear medium and stabilizer to generate a stable multi-wavelength is proposed and demonstrated. A 50 m long highly nonlinear photonic crystal fiber (PCF) is incorporated into the cavity to achieve unstable multi-wavelength based on nonlinear polarization rotation (NPR) effect. By introducing the graphene thin film into the cavity, a stable multi-wavelength oscillation is obtained. The laser generates more than 7 lasings with constant spacing of 0.47 nm. The output is highly stable with power fluctuation of less than 3 dB within a period of 30 min. The multi-wavelength EDFL exhibits a tunability from the center wavelength of 1550 nm to 1560 nm. [ABSTRACT FROM AUTHOR]