A.Z. Zulkifli

2.0-

A compact Q-switched thulium-doped fiber laser (TDFL) operating near the 2.0- μm region is proposed and demonstrated. The proposed laser uses a 2-m-long thulium-doped fiber with a core absorption of 27 dB/m at 793 nm as the active medium and a graphene oxide (GO)-based saturable absorber (SA) as the Q-switching element. The SA is fabricated by optically depositing GO particles dissolved in distilled water onto the face of a fiber ferrule, which is then used to assemble the SA. The proposed TDFL is capable of generating pulses with a maximum repetition rate of 16.0 kHz and pulsewidths as narrow as 9.8 μs, as well as having maximum average output power and pulse energy of 0.3 mW and 18.8 nJ, respectively. The combination of the easily fabricated GO-based SA, together with the TDFLs ability to operate in the eye-safe region of 2.0 μm, gives the proposed Q-switched TDFL a high potential for a multitude of real-world applications, including range-finding, medicine, and spectroscopy.

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A graphene-based Q-switched erbium-doped fiber laser (EDFL) with a tunable fiber Bragg grating (TFBG) acting as a wavelength tuning mechanism is proposed and demonstrated. The proposed setup utilizes a newly-developed ‘ferrule-to-ferrule transfer’ technique to obtain a single graphene layer that allows for Q-switch operation in the EDFL using a highly doped-gain medium. A TFBG is used as a wavelength tuning mechanism with a tuning range of 10 nm, covering the wavelength range from 1547.66 nm to 1557.66 nm. The system has a wide repetition rate range of over 206.613 kHz from 1.387 kHz to 208.000 kHz with pulse durations of between 94.80 μs to 0.412 μs. The laser output is dependent on the pump power, with energy per pulse of 4.56 nJ to 16.26 nJ. The system is stable, with power and wavelength variations of less than 0.47 dBm and 0.067 nm. The output pulse train is free from self-mode locking and pulse jitters.

Q-Switched Thulium-Doped Fiber Laser With Graphene Oxide Saturable Absorber

In this work, the fabrication of a Zirconia-Erbium co-Doped Fiber (Zr-EDF) and its application in the generation of non-linear effects as well as use in a compact pulsed fiber laser system is described. The Zr-EDF is fabricated by the Modified Chemical Vapor Deposition (MCVD) technique in combination with solution doping to incorporate the glass modifiers and nucleating agent. The resulting preforms are annealed and drawn into fiber strands with a 125.0 ± 0.5 µm diameter. Two Zr-EDFs, ZEr-A and ZEr-B, are fabricated with erbium ion concentrations of 2800 and 3888 ppm/wt and absorption rates of 14.5 and 18.3 dB/m at 980 nm respectively. Due to its higher erbium dopant concentration, a 4 m long ZEr-B is used to demonstrate the generation of the Four-Wave-Mixing (FWM) effect in the Zr-EDF. The measured FWM power levels agree well with theoretical predictions, giving a maximum FWM power - 45 dBm between 1558 nm to 1565 nm, and the generated sidebands are as predicted. The non-linear coefficient of ZEr-B is measured to be 14 W−1km−1, with chromatic and slope dispersion values of 28.45 ps/nm.km and 3.63 ps/nm2.km respectively. The ZEr-B is also used together with a graphene based saturable absorber to create a compact, passively Q-switched fiber laser. Short pulses with a pulse width of 8.8 µs and repetition rate of 9.15 kHz are generated at a pump power of 121.8 mW, with a maximum average output power of 161.35 µW and maximum pulse energy value of 17.64 nJ. The fabricated Zr-EDF has many potential applications in multi-wavelength generation as well as in the development of compact, pulsed laser sources.

Tunable graphene-based Q-switched erbium-doped fiber laser using fiber Bragg grating

A highly stable tunable dual-wavelength fiber laser (TDWFL) using graphene as a means to generate a highly stable output is proposed and generated. The TDWFL comprises a 1 m long, highly doped erbium-doped fiber (EDF) acting as the linear gain medium, with a 24-channel arrayed waveguide grating acting as a wavelength slicer as well as a tuning mechanism to generate different wavelength pairs. The tuned wavelength pairs can range from 0.8 to 18.2 nm. A few layers of graphene are incorporated into the laser cavity to induce the four-wave-mixing effect, which stabilizes the dual-wavelength output by suppressing the mode competition that arises as a result of homogenous broadening in the EDF.

Fabrication and application of zirconia-erbium doped fibers

A steel beam compressive strain sensor using single-mode-multimode-single-mode (SMS) fiber structure is demonstrated. Parallel measurements are made using an electrical resistance (ER) strain gauge along with the SMS to sense the compressive strain on the steel beam. The ER strain gauge result shows that the steel beam has an elastic limit at a compressive load of 42 kN, as predicted via calculation. On the other hand, the SMS sensor is capable to detect the elastic limit by its significant increase in the slope of the peak center wavelength from compressive strain of 0.000261-0.001986 mm/mm. Moreover, the SMS sensor exhibits compressive strain sensitivity of -1411.2 nm/(mm/mm) from the initial load until it reaches the beam elastic limit.

Highly stable graphene-assisted tunable dual-wavelength erbium-doped fiber laser

A Q-switched dual-wavelength fiber laser using a graphene oxide-based saturable absorber to generate the desired output pulses is proposed and demonstrated. The system utilizes a singlemode–multimode–singlemode fiber structure to control the net losses in the cavity so that only two dominant wavelengths are allowed to oscillate. The proposed system is capable of generating an output with a high repetition rate of 27.1 kHz and a narrow pulse width of 4.03 µs. The output pulses also have average output power and pulse energy of up to 0.5 mW and 18.5 nJ, respectively. The 1st harmonic obtained has a high signal-to-noise ratio of 33.2 dB, indicating a highly stable pulse output with minimum mode hopping.

Steel Beam Compressive Strain Sensor Using Single-Mode-Multimode-Single-Mode Fiber Structure

We present a UV detector based on an integrated microfiber resonator. In fabrication, a thin layer of polyaniline (PAni) is deposited on a ~1-mm-diameter microfiber ring resonator-the sensing region of the detector. Red shift is observed in the output spectrum when PAni is irradiated with a UV light with a peak wavelength at 365 nm. This phenomenon can be due to the high absorbance in the UV region and photothermal effect of PAni. The wavelength shift is linearly proportional to the UV light intensity and the measured sensitivity is 6.61 nm/(W·cm-2).

Q-switched dual-wavelength fiber laser using a graphene oxide saturable absorber and singlemode–multimode–singlemode fiber structure

A 2 × 2 microfiber knot resonator (MKR) coupler is demonstrated. The hybrid device is obtained by forming a knot within the coupling region of a microfiber coupler with a 50:50 splitting ratio. The microfiber coupler is successfully fabricated by laterally fusing and tapering two optical fibers using a flame-brushing technique. The coupler has an overlapping length of 40 mm with a uniform waist of around 5 μm. With an MKR structure, the coupler produces a resonant response at both output ports. The free spectral range of the output spectrum from both ports is obtained at 0.2 nm at a knot diameter of 260 μm. The resonance extinction ratio of the device varies from 2 to 6 dB while the calculated Q factor and finesse are ~25646 and 3.3, respectively, at both output ports.

A Polyaniline-Coated Integrated Microfiber Resonator for UV Detection

An efficient and low cost optical method for directly measuring the concentration of homogenous biological solutes is proposed and demonstrated. The proposed system operates by Fresnel reflection, with a flat-cleaved single-mode fiber serving as the sensor probe. A laser provides a 12.9 dBm sensor signal at 1,550 nm, while a computer-controlled optical power meter measures the power of the signal returned by the probe. Three different mesenchymal stem cell (MSC) lines were obtained, sub-cultured and trypsinized daily over 9 days. Counts were measured using a haemocytometer and the conditioned media (CM) was collected daily and stored at −80 °C. MSCs release excretory biomolecules proportional to their growth rate into the CM, which changes the refractive index of the latter. The sensor is capable of detecting changes in the number of stem cells via correlation to the change in the refractive index of the CM, with the measured power loss decreasing approximately 0.4 dB in the CM sample per average 1,000 cells in the MSC subculture. The proposed system is highly cost-effective, simple to deploy, operate, and maintain, is non-destructive, and allows reliable real-time measurement of various stem cell proliferation parameters.

Fabrication and Characterization of a 2×2 Microfiber Knot Resonator Coupler

In this paper, a novel optical approach is proposed and demonstrated for the non-contact measurement for the thickness of silica thick films. This approach is based on the principal of an optical based displacement sensor. The calibration curve for the measurement of the thickness of an unknown sample is obtained using four sample with known thicknesses of 6.90, 10.23, 19.69 and 25.47 μm respectively. As compared to a prism coupler, which is assumed to provide the most precise measurement of thick film thicknesses, the proposed system has an error of approximately 8%. The proposed method is able to provide a simple, low cost and time saving approach in measuring thick films thicknesses during fabrication.