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We report on the demonstration of a switchable and adjustable spacing multiwavelength nanosecond pulsed ytterbium-doped fiber laser (YDFL) operating in a mode-locking regime by macrobending loss tuning induced in a figure-eight knot shape. The figure-eight knot-based Mach–Zehnder interferometer (MZI) was established by wrapping a section of single-mode fiber into two elliptical loops by twisting one end of the fiber onto the other without splicing. Combining the proposed MZI with a polarization controller (PC) acts as a selective comb filter and a nanosecond pulse generator. By appropriately adjusting the bending diameter of the MZI structure inside the YDFL cavity, the laser can be operated in a single- and dual-wavelength with a maximum spacing range of 18.5 nm. Furthermore, the number of lasing wavelengths was directly controlled by only altering the pump power; dual and triple wavelengths were achieved as the pump power was increased from 127 to 210 mW, respectively. The appropriate adjustment of the PC cascaded with the proposed comb filter in the laser cavity allows for the generation of up to quadruple switchable wavelengths of nanosecond mode-locking pulses with a pulse duration of 6.2 ns and repetition rate of 71.4 MHz located between 1061.17 and 1038.92 nm. The experimental results indicate that the proposed configuration of the MZI-based comb filter can provide great potential in various photonics applications. [ABSTRACT FROM AUTHOR]

A simple and compact temperature sensor based on a Mach–Zehnder modal interferometer has been fabricated by bending a single-mode fiber into a balloon-like configuration. Three different fiber sections, fiber without stripping, fiber with a stripped-off protective coating and fiber with a polyvinyl alcohol (PVA) coating have been utilized, each with a small bending diameter of 1 cm that mimics a balloon-like shape. The PVA-coated segment sensor structure showed the highest sensitivity of ∼−1.492 nm °C−1, a fast response time of ∼2.78 ms and a good resolution of ∼3 × 10−4 °C, for the temperature range 30 °C–55°C, benefiting from the good thermo-optical properties of PVA. This sensor can potentially be used in various temperature monitoring processes such as food industries, chemical analysis, detection of molecular analysis and label-free biomedicine. [ABSTRACT FROM AUTHOR]

We propose and demonstrate the implementation and application of a new configuration of an all-fiber comb filter based on the Vernier effect produced by parallel-connected two in-line Mach–Zehnder interferometers (MZIs). Each in-line MZI was fabricated by fusion splicing a section of panda-type polarization maintaining fiber (PMF) with peanut-shaped tapers between two single-mode fibers. These two in-line MZIs, respectively, form reference and sensing interferometers, which are parallel-connected by two 3-dB optical fiber couplers to realize the Vernier effect. By incorporating the proposed comb-filter into the erbium-doped fiber laser cavity, two output channels at 1533.2 and 1558.2 nm have been achieved. Further, the combination of the parallel-connected two in-line MZIs and polarization controllers (PC1 and PC2) promotes the lasing in a switchable and selective way. To the best of the authors' knowledge, this is the first demonstration of a comb filter that employs paralleled two peanut-shaped MZIs in PMF. The experimental results indicate that the proposed filter has the potential to be used in communication systems. [ABSTRACT FROM AUTHOR]

In this work, a simple design and cost-effective displacement-curvature sensor based on macro-bend single-mode fiber (SMF) is planned and demonstrated. The optical fiber sensor encompasses a bending configuration and the macro-bending losses were exploited as the sensing process for the capturing of angular displacement motion in an angle span between 0° and 90° (that corresponds to curvature displacement between 0 and 49.5 cm). A straight SMF shape and other four bent sensor structures (U-like, drop-like, Knot-like, and eight-like) have been fabricated from sections of 90 cm length SMF. These five sensor configurations will provide high maneuvering for versatile applications. In these adjustable sensing schemes, the fiber sensors were described by monitoring the power loss corresponding to the diverse angular displacement at various bending structures in terms of the shape of the bend, the bending diameter, and the number of wrapping turns. Then, these measurement schemes based on the macro-bending losses were employed to detect the human motion elbow joint, and a proper sensing scheme was adopted to examine the flexion/extension joint motion in detail. The proposed sensors showed enhanced sensitivity to flexion/extension joint motion range between −0.25 and −0.477 dB/° and good sensitivity to curvature ranging between −0.552 and −1.052 dB/cm. The demonstrated and planned sensing techniques are adjustable and accessible for different types of human and mechanical movements. [Display omitted] • Wearable Optical Fiber Sensor based macro-bending loss for Biomechanical Motion Evaluation. • A simple design and cost-effective displacement-curvature sensor based on macro-bend single-mode fiber (SMF) has been integrated into elbow joint phantoms and measuring its response to various elbow joint movements in the range of 0°-90°. • A straight SMF shape and other four bent sensor structures (U-like, drop-like, Knot-like, and eight-like) have been exploited as the sensing process for the capturing of angular displacement motion in a span between 0 and 49.5 cm. • Adjustable sensing measurement schemes based on the macro-bending losses have been employed to detect the human motion elbow joint, and a proper sensing scheme has been adopted to examine the flexion/extension joint motion in detail. [ABSTRACT FROM AUTHOR]

We report on the demonstration of a multi-wavelength ytterbium-doped fiber laser (YDFL) by exploiting a nanocomposite film to act as both a Fabry-Perot (FP) filter and a nonlinear material inside the ring cavity. The proposed filter is formed by combining an FP structure based on a large core diameter single-mode fiber (SMF) with a nanocomposite film. The nanocomposite film was prepared by coating gold nanostars with zinc-oxide nanorods/multi-walled carbon nanotubes (ZnO-NRs@Au-NSs/MWCNTs) embedded into polyvinyl alcohol (PVA) polymer. Moreover, the fabricated hybrid nanocomposite film exhibits a high nonlinear optical response that fulfilling the requirement to induce the FWM effect employed to suppress the mode-competition. Four lasing lines of uniform power-symmetry distribution with a spacing of ~160 GHz have been generated by appropriately adjusting the pump power strength to 230 mW. The results suggest that ZnO-NRs@Au-NSs/MWCNTs nanocomposite film could be a promising filter for stable multi-wavelength generations at room temperature. [ABSTRACT FROM AUTHOR]