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Abstract We experimentally demonstrated the generation of domain-wall dark pulse in an Erbium-doped fiber laser using the combination of a 10 cm graded index multimode fiber sandwiched by single mode fibers as artificial saturable absorber. The interaction of phase difference in grade index multimode fiber allowed the stable dual-wavelength oscillation in the cavity. The dual-wavelength centered at 1567.2 nm and 1569.4 nm produces the topological defect in temporal domain and achieved a dark pulse formation with repetition rate of 21.5 MHz. The highest average pulse energy is calculated as 769.6 pJ with pulse width of 5 ns. Throughout the operating pump power range, the average pulse energy and output power increase linearly, with R2 of 0.9999 and achieved the laser efficiency of 9.33%. From the measurement in frequency domain, the signal-to-noise ratio is measured as 49 dB. As compared to reported DW dark pulse works, the proposed structure only required a short length of multimode fiber, which allowed the domain-wall dark pulse to achieve higher pulse repetition rate. The venture of domain wall dark pulse is potentially to pave the foundation toward sustainable industrial growth.

In this work, we theoretically simulate the modulation of a soliton molecule that has an initial chirped Gaussian pulse shape in a 1 μm extra-cavity optical fiber modulation system. Different soliton parameters in orthogonal polarizations are applied to achieve controllable optical solitons' output with specific properties in the time/frequency domain. For instance, when the phase difference is changed, both pulse shapes' and corresponding optical spectra's peak intensities will have a sudden change when the orthogonal phase difference is π/2. These simulation results provide a beneficial reference value for extra-cavity shaping of different solitons that come from nonlinear optical systems. Optimally, the reported results could pave the groundwork for industrial growth in ultrafast laser design. [ABSTRACT FROM AUTHOR]

A relative humidity sensor was fabricated by exploiting an evanescent wave (EW) on a U-bent tapered plastic optical fiber (POF) coated with zinc oxide (ZnO) nanorods. The POF was tapered manually using a polishing method to a diameter of 0.5 mm, a length of 5 cm, and a radius of 5 cm. ZnO nanorods were synthesized using a hydrothermal method and grown on the POF by a seeding process for 12 h. A significant response of the sensor was observed when the sensor was exposed to 35 to 90%RH due to the intense chemisorption process and changeable relative index in the POF. The sensitivity and resolution of the sensor have been improved by factors of 1.23 and 2.18, respectively, compared to the conventional tapered POF sensor without ZnO coating. Besides, the ZnO-coated sensor also exhibited better repeatability properties in terms of output voltage when exposed to 35 to 90%RH for three repeated measurements. The obtained results revealed that the proposed new POF sensor has an excellent sensing performance as an RH sensor in terms of sensitivity, repeatability, and stability properties.

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]

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, 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]

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]