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In this article, we present a vibration measurement system based on low-frequency cantilever-based fiber Bragg grating accelerometers (CFAs) for a suspension bridge. Each accelerometer has an end-loaded cantilever beam, specifically tailored to achieve a uniform sensitivity for a frequency range of 0–4 Hz, a suitable detection range for the vibration analysis. In the field test, seven CFAs were installed at specific positions along the deck of a 110-m-long suspension bridge for synchronous multipoint vibration measurements. The reflection spectra of the CFA array were recorded and processed using the pseudo-high-resolution scheme to improve the signal quality and measurement accuracy. Three natural vibration frequencies: 1.15, 1.54, and 3.17 Hz have been identified from the measurement. Following that, the acquired time-domain signals were processed by a digital bandpass filter to retrieve the waveform at each natural frequency to determine the corresponding mode shapes. The results are in agreement with the phase difference between the frequency domain signal for each natural frequency. This investigation has shown the feasibility of the proposed measurement system for determining the mode shapes and dynamic frequency analysis of a suspension bridge. It is a potential method for structural health monitoring for other similar civil structures.

Bismuth telluride (Bi2Te3), a type of topological insulators, is currently in hot pursuit due to its unique physical properties. Therefore, this paper describes a simple Q-switched Ytterbium-doped fiber laser (YDFL) by using Bi2Te3 thin-film as saturable absorber. The few layers Bi2Te3 film was fabricated using optical deposition technique and subsequently, was used in an all-fiber, YDFL setup. As a result, a self-starting Q-switching pulses were first occurred when the laser pumping power reached 88.6 mW. As the pump power level increased, the observed pulses repetition rates had increased steadily from 17 to 29.63 kHz. Hence, this work demonstrated that Bi2Te3 thin-film can be used to successfully generate Q-switching pulses at 1-micron region and is well suited for many photonic applications operated at this wavelength region.

The pre-treatment of few-mode fibers (FMFs) has been successfully done with CO2 laser. The wavelength difference, Δλ between the two resonant wavelengths in the few-mode fiber Bragg grating (FMFBG) varies with temperature increment during the annealing process. The results show that the treated fibers with lower stresses have lower thermal sensitivity in Δλ than that of non-treated fiber. However, the treated fibers produce FMFBGs with better thermal durability and regeneration ratio. It is conceived that the presence of those stresses in the pristine fiber is responsible for the high thermal sensitivity in Δλ. The thermal relaxation of stresses and structural rearrangement during the thermal annealing process are responsible for the degradation of the strength and resilience of the regenerated grating.

The selection of a suitable cladding material for a fibre optic is crucial, and the application of polymeric material in high temperature conditions is garnering much attention from many researchers. However, polymer suffers from a weak thermal resistance, limiting its use in high temperature conditions. Therefore, this study aims to develop a new potential cladding material that has a good balance between optical and thermal properties. Two sets of cladding materials are proposed, namely the blend of polycarbonate/polymethyl methacrylate (PC/PMMA) and polymethylpentene (PMP). The cladding materials were dissolved in different solvents, followed by the casting on a glass plate to form a flat sheet cladding layer. PC/PMMA blend showed a miscible blending with a single Tg value and physical blending. Both PC/PMMA blend and PMP claddings demonstrated more than 90% of luminous transparency. The materials also showed high thermal stability with the onset degradation temperature of ∼ 300 °C. The optimum ratio for PC/PMMA was 80/20. Next, the cladding layer was fabricated by coating the core in 80/20 PC/PMMA and PMP. The scanning electron microscopy (SEM) image reveals that core–clad ratio for the PC fibre is 1.02 for both materials. The maximum tensile strength for the PC with PMP cladding was higher than that of the PC with PC/PMMA cladding. PMP-clad fibre has higher power output, which was a 60% increment from bare PC fibre output compared to PC/PMMA-clad fibre, with only 28.8% power output increment. Though both materials have huge potential to be used as the cladding for PC core, PMP cladding showed superior performance compared to PC/PMMA cladding.

A tunable single-wavelength of an erbium-doped fiber ring laser is proposed and demonstrated. The laser integrates a tapered in-line Mach-Zehnder interferometer (IMZI) in its ring loop as an intracavity filter. The light spectrum is adjusted by changing an axial strain of the interferometer in a 60 μm range. As a result, a total tuning range of 6.19 nm that covers the wavelength from 1552.94 nm to 1559.13 nm is observed, and the sensitivity of 103.5 pm/μm is recorded. This high sensitivity lasing behavior is useful for high selectivity and fine tuning for narrow wavelength applications.

Achieving high quality porous silicon (PSi) materials with desired porosity remains challenging. Three good qualities of PSi samples are prepared by Photo electro-chemically etching a piece of n-type Si inside the solution of 20 M HF, 10 M C2H5OH and 10 M H2O2 at fixed etching time duration (30 min) and varying current density (15 mA/cm2, 30 mA/cm2 and 45 mA/cm2). As-prepared sample morphologies are characterized via scanning electron microscopy (SEM) and atomic force microscopy (AFM). The gravimetric method is used to estimate the thickness and porosity of the prepared samples. Current density (etching time) dependent morphologies, electronic bandgap and room temperature photoluminescence (PL) properties of such PSi nanostructures are evaluated. These PSi structures revealed enhanced rectifying characteristics with increasing current density.

This work describes the fabrication and evaluation of fluoropolymer surface coating on polymer fibre core prepared from polymethyl methacrylate (PMMA) using ultraviolet (UV) photopolymerisation curing method. The curing condition has a significant influence on the coating adhesion on the core. The focus of this study was to evaluate an effective and simple process for polymer optical fabrication using UV curing with dip-coating method. The coating performance was evaluated through surface morphology analysis and physical properties. FESEM–EDX images indicate that the fluoropolymer coating formed a compact structure with a cladding thickness of 67.63 μm for the highest UV irradiation strength. FTIR analysis revealed the presence of fluorine elements on coated fibre with EDX surface mapping of fluorine dispersion. The performance of the fibre was studied and compared with commercially available polymer optical fibre in terms of fibre spectral fluorescence properties and light attenuation. The dip-coating photopolymerisation method was effective in forming the cladding for step-index polymer fibre with similar spectral excitation wavelength recorded at 620 to 630 nm with the lowest power loss at −13.40 dBm.

We have successfully generated a Q-switched ytterbium-doped fiber laser pulses using few layers of Molybdenum Selenide (MoSe2) as saturable absorber (SA). The setup was a ring fiber laser cavity with few-layer MoSe2, deposited onto a fiber ferrule using an optical deposition technique. A stable pulses started at input power of 68.8 mW with repetition rate ranging from 14.2 kHz to 34.0 kHz was achieved with highest pulse energy, shortest pulse width and highest output power of 3.6 nJ, 4.4 µs and 0.12 mW were observed, respectively.

In this work, we have successfully fabricated the fiber Bragg grating (FBG) with 1 cm and 3 cm grating length, respectively. The different grating length fabricated by adjusting the slit aperture in order to control UV light transmission while inscribing on the single mode fiber. Then the FBG was demonstrated through different grating length over temperature sensor to determine the differences for temperature sensing. The range for temperature The measured sensitivity of 1 cm and 3 cm grating length is 0.0103 nm/°C and 0.0132 nm/°C respectively at the same value of applied temperature. As a results, the shorter grating length, 1 cm has higher sensitivity response compared to 3 cm grating length over temperature sensing.

We have demonstrated an ultrafast mode-locked pulses generation by sandwiching graphene thin film between fiber ferrules in a simple erbium-doped fiber laser (EDFL) ring cavity setup. The incorporation of graphene thin film acted as a saturable absorber (SA) and had generated a stable mode locked pulse with repetition rate of 8.3 MHz, narrowest pulse duration of 1.38 picoseconds and 1558.8 nm wavelength.

We have successfully fabricated and demonstrated a simple, cost-effective and easy to use of fiber Bragg grating (FBG) based on single mode, and multimode fiber which have been employed for temperature monitoring. The study purposely compared the performance of two types of FBGs; single mode FBG (SM-FBG) and multimode FBG (MM-FBG). The FBGs sensor is fabricated by phase mask technique which being exposed to ArF excimer laser with 20 mm uniform grating length and 99% reflectivity. The proposed FBG is studied for temperature monitoring starting at room temperature until 120 °C, and the configurations with SM-FBG and MM-FBG achieved a sensitivity of 10.9 pm/°C and 13.23 pm/°C, respectively whereas linear response correlation coefficient of 0.98229 and 0.99929. These show the MM-FBG has better sensitivity to be used in sensor applications.

Fabrication of polycarbonate polymer optical fibre core using various extrusion temperatures and drawing speeds was experimentally demonstrated. Extrusion temperature had a significant effect on fibre performance. The optimum temperature in which fibre exhibited the best thermal and optical properties was 290 °C, however, at higher temperature due to degradation of the polymer the fibre lost its quality for light propagating. The mechanical properties of the fibre were influenced by its diameter. Increasing the drawing speed to 20 rpm reduced the diameter of the fibre to ~341 μm and Young’s modulus and tensile strength increased to 2.12 and 119.06 MPa, respectively. Our comprehensive investigation of polycarbonate polymer core features may propose a novel method for precise fabrication of polymer optical fibre suitable in optical industries.

In this work a passively Q-switched dual-wavelength ytterbium-doped fiber laser using a titanium dioxide-based saturable absorber is proposed and proven. The system also utilizes a side-polished fiber in a ring cavity configuration to obtain the desired pulse train. A stable dual-wavelength pulse output is obtained at 1034.7 and 1039.0 nm, with a maximum pulse energy of 2.0 nJ, and a shortest pulse width of 3.2 μs. The generated pulse train is stable, and has a pulse repetition rate from 31.2 to 64.5 kHz.

We demonstrate the design and operation of novel narrow spacing and stable dual-wavelength fiber laser (DWFL). A 70-cm ytterbium-doped fiber has been chosen as the gain medium in a ring cavity arrangement. Our design includes a short length photonic crystal fiber, acting as a dual-wavelength stabilizer based on its birefringence coefficient and nonlinear behavior and tunable band pass filter (TBPF) to achieve narrow spacing spectrum lasing. Our laser output is considered to be highly stable, with power fluctuation less than 0.8 dB over a period of 15 min. The flexibility and tunability of TBPF, together with polarization controller enable the spacing tuning of the DWFL from 0.03 nm up to 0.07 nm for 1040 nm region, and 0.10 nm up to 0.40 nm for 1060 nm region. The tunable wavelength spacing shows the flexibility of the DWFL in addition to stable and reliable properties of fiber laser in 1-m region.

This paper describes a demonstration of a passively dual-wavelength Q-switched ytterbium-doped fiber laser using a selenium bismuth-based saturable absorber. By utilizing a short-length photonic crystal fiber in a ring cavity and performing adjustments to the polarization state of an incorporated polarization controller (PC), we obtained a stable dual-wavelength Q-switched output at 1037.14 and 1037.69 nm, with maximum pulse energy of 0.65 nJ, shortest pulse width of 8.46 μs, and pulse repetition rate from 15.37 to 59.24 kHz. The Q-switched laser output consistently achieved high-power stability with a 0.8 dB maximum fluctuation over a period of 20 min.

We have investigated the operation principle of the switchable EDFL which stands for the erbium-doped fiber laser, where a non-adiabatic microfiber has been fabricated and used. Utilizing the flame-brushing technique, the optical microfiber has been fabricated and afterward, it has been inserted into the EDFL cavity, therefore by proposing the setup configuration, the single and multi-wavelength laser could be generated. By applying the different filtering effects of the microfiber, the results of a single wavelength laser (one set), dual-wavelength laser (three sets) and triple wavelength laser (two sets) could be generated over a wavelength range of 1560–1565 nm. The signal to noise ratio (SNR) of 42–50 dB is obtained from the experiment with acceptable wavelength and power fluctuation over the test period of 30 min. Proposed switchable EDFL shows tunable and stable single and multi-wavelength laser generation in C band region.

We have demonstrated dual-wavelength domain-wall (DW) dark pulse operation based on Molybdenum disulfide (MoS2). MoS2 is fabricated as a film and sandwiched between two pigtails to function as a saturable absorber in the laser cavity. The DW dark pulse exhibited two peaks, which are located at 1037 and 1039 nm. The pulse repetition rate was maintained at 17.4 MHz throughout the DW dark pulse operation. The highest pulse energy of 46 pJ was obtained at pump power of 242.5 mW. Besides, DW dark pulse operation was demonstrated at high stability with SNR of 50 dB.

This paper describes the dual-wavelength operation in the 1060 nm region by applying an ytterbium-doped gain medium fiber and a highly nonlinear fiber (HNLF) as the wavelength selective filter. Due to its nonlinear properties and birefringence co-efficient, the HNLF also functions as a stabilizer for dual-wavelength fiber laser operation. Results from the experiment show that the fluctuated power of the system is less than 0.6 dB when continuously run for 20 min, indicating the system's stability. The spacing of the dual-wavelength output is obtained by fine-tuning the polarization controller within the fiber ring laser setup. The spacing ranges between 2.7 nm-21.05 nm.

In this paper, we propose and demonstrate the generation of dual wavelength based photonic crystal fiber passively Q-switched using few-layer TI:Bi2Te3 (bismuth telluride) saturable absorbers in a 1 micron waveband. The system employs a few-layer bismuth, induced onto a fiber ferrule using a dry oven method. A centered dual-wavelength output at 1042.76 and 1047.0 nm was produced from the Ytterbium doped fiber laser setup by incorporating 10 cm of photonic crystal fiber and finely adjusting the polarization controller. The self-started Q-switch had a pump power of 132.15 mW and a frequency ranging from 3.79 to 15.63 kHz. Therefore, TI:Bi2Te3 was suitable as a potential broadband SA in a 1 micron region.

A tunable single- and dual-wavelength ytterbium-doped fiber laser, incorporating a 16-channel arrayed waveguide grating is proposed and demonstrated. The side mode suppression ratio from the proposed setup has an average value of 52.97 dB (single-wavelength generation) and 58.19 dB (dual-wavelength generation). The tunable dual wavelength ranged from 1039.98 nm to 1047.48 nm with wavelength spacing ranging from 0.50 nm to 7.5 nm. A stability test from the experiment shows a power variation of 0.8 dB, and a wavelength fluctuation of 0.02 nm indicates the stability and reliability of the proposed work.

A Q-switched ytterbium doped fiber laser (YDFL) with a ZnO saturable absorber (SA) is used to demonstrate the generation of pulses in the 1 micron region. The system has a Q-switching threshold of approximately 115.2 mW, and can generate pulses with a 3.0 µs full-width at half maximum as well as a peak-to-pedestal ratio of 53.0 dB. No spectral modulations are observed, indicating a highly stable system. The pulse output of the proposed system has repetition rates and pulse widths of approximately 50 kHz and 1.6 µs, as well as an average output power of 0.14 mW and a pulse energy of 2.8 nJ at its highest pump power of 196 mW. This is the first time, to the authors' knowledge, that a ZnO based SA has been used to generate pulses in the 1 micron region with a YDFL.

A simple ytterbium doped fiber laser (YDFL) setup was used to generate Q-switching pulses by using a D-shaped polished fiber as a wavelength selective filter. The gain medium used in the cavity was ytterbium doped fiber with length 70 cm. By utilizing a MoSe2 film as saturable absorber into the cavity, a stable dual wavelength was produced at 1036.69 and 1039.22 nm. The wavelength separation of the output spectrum was 2.53 nm. We found a maximum pulse energy of 0.99 nJ and shortest pulse width of 1.2 µs. We have determined consistent dual-wavelength Q-switching pulses for the 1-micron region.

A compact, passively Q-switched fiber laser with a tunable output is demonstrated. The proposed system uses a short length ytterbium doped fiber to create a very stable and compact optical circuit that uses black phosphorus (BP) as a saturable absorber to generate the desired short pulses. A stable Q-switch pulse train is obtained, with an operational wavelength range from 1056.6-1083.3 nm. Concurrently, a maximum pulse energy and minimum pulse width as well as a repetition rate range of 7.1 nJ, 4 μs and 6.0-44.8 kHz respectively was obtained. The proposed system will be able to cater to a multitude of applications that require a compact yet robust and cost-effective pulse laser.

Using a few-layer black phosphorus (BP) thin film that acts as a saturable absorber (SA) in an ytterbium-doped fiber laser setup, we experimentally demonstrated a passively dual-wavelength Q-switching laser operation. The setup also incorporated a D-shaped polished fiber as a wavelength selective filter. As the SA was used in the ring cavity, a dual-wavelength Q-switch produced consistent outputs at 1038.68 and 1042.05 nm. A maximum pulse energy of 2.09 nJ with a shortest pulse width of 1.16 µs was measured for the achieved pulses. In addition, the repetition rate increased from 52.52 to 58.73 kHz with the increment of the pump level. Throughout the measurement process, the results were obtained consistently and this demonstrates that the BP film is a very good candidate to produce Q-switching pulses for the 1 micron region.

We describe a successful demonstration of highly stable and narrowly spaced dual-wavelength output via an ytterbium-doped fiber laser. A microfiber-based Mach-Zehnder interferometer and a tunable bandpass filter were both placed into the laser ring cavity for the purpose of ensuring a stable and narrowly spaced dual-wavelength output. Experimental results comprised three sets of dual-wavelength lasing output with wavelength spacing of 0.06, 0.09, and 0.22 nm, respectively, and side-mode suppression ratio of ∼50 dBm. A subsequent stability test provided evidence that maximum power and wavelength fluctuation were less than 0.8 dB and 0.01 nm, respectively, and thus, the obtained output was considered to be highly stable in dual-wavelength operation. The proposed system offers advantages of flexibility in dual-wavelength laser generation in addition to excellent reliability.

In this paper, stable dual-wavelength generation using a strain technique for a ytterbium-doped fiber laser is successfully demonstrated. A microfiber-based Mach-Zehnder interferometer is inserted into the laser ring cavity and stretched using the xyz translation stage. Four sets of dual-wavelength output lasing are obtained when the strain is applied onto a microfiber. The dual-wavelength output possesses spacing between 7.12 and 11.59 nm, with displacement from 2 to 190 μm from the central wavelength. The obtained side-mode suppression ratio is ∼48 dBm, while the maximum power fluctuation and wavelength shift are less than 0.6 dB and 0.01 nm, respectively. The results demonstrate that this setup generates a stable dual-wavelength laser in the 1 μm region.

This paper describes the demonstration of a simple ytterbium-doped fiber (YDF) laser that utilized a short length of photonic crystal fiber (PCF) in a ring cavity and adjustments to the polarization state of an incorporated polarization controller (PC) to achieve a stable dual-wavelength output. The dual-wavelength lasing operation exploited the Mach-Zehnder interferometer effect, and the laser output consistently achieved high power stability with a 0.8 dB fluctuation over a period of 30 min. This proposed setup has the capability for adjustable spacing of two lasing wavelengths from a minimum of 0.40 nm to a maximum of 3.40 nm, allowing for flexibility in dual-wavelength laser generation in addition to stable and reliable system features. © 2016 Astro Ltd.

In this work, we demonstrate a simple Q-switched pulsed ring ytterbium-doped fiber laser based on a few-layer TI:Bi2Se3 saturable absorber (SA). Few-layer bismuth selenide within a suspension was induced onto a fiber ferrule at room temperature via an optical deposition method, resulting in a simple SA for the laser. Stable Q-switched pulsed lasing was achieved at a low pump threshold of 122.2 mW at 974 nm. The pulse repetition rate ranged from 18.97 to 45.41 kHz, and the narrowest pulse width and the maximum pulse energy were 13.1 μs and 5.88 nJ respectively. Results indicated that TI:Bi2Se3 was also compatible with the 1 μm waveband, and hence could be considered a potential broadband SA for passively mode-locked and Q-switched optical fiber lasers.