A lutetium oxide (Lu2O3) film was proposed and demonstrated for Q-switching operation at 1.55 μm region. It was obtained by solving Lu2O3 powder into isopropyl alcohol and mixing the solution into polyvinyl alcohol (PVA) solution to form a composite precursor solution via stirring, sonicating, and centrifuging processes. The thin film was formed through a drop and dry process and a small piece of this film was integrated into erbium-doped fiber laser (EDFL) cavity to modulate the cavity loss via Q-switching mechanism for pulse generation. The Q-switched laser operated at 1 565 nm with the repetition rate of 75.26 kHz as the pump power was raised to the maximum value of 145.83 mW. The maximum pulse energy of 41.85 nJ was recorded at 145.83 mW pump power. The mode-locked pulse operated at 968.5 kHz with a pulse width of 510 ns was also realized in an extended EDFL cavity. The simple and cost-effective laser should have various applications including material processing, sensing and biomedical areas.

In this letter, a titanium aluminum carbide (Ti3AlC2) coated D-shaped fiber is proposed and demonstrated as a new saturable absorber (SA) for Q-switched laser pulse generation. In preparing the SA, the Ti3AlC2 powder is dispersed in liquid polyvinyl alcohol (PVA) before the solution is dropped and left to dry onto a polished surface of D-shape fiber. The SA is added to an erbium-doped fiber laser (EDFL) cavity to modulate the cavity loss for Q-switching. The Q-switched laser is obtained at 1 561 nm. The pulse width of the pulses can be varied between 7.4 μs and 5.1 μs with a corresponding repetition rate range from 41.26 kHz to 54.35 kHz, when the pump power is increased from 42.2 mW to 71.5 mW. At 71.5 mW pump, the pulse energy is obtained at 70.3 nJ. The signal-to-noise ratio (SNR) of the fundamental frequency is recorded at 67 dB, which indicates the stability of the laser.

In this letter, single-walled carbon nanotubes (SWCNT) coating was used on the D-shaped silica fiber for ethanol sensing in aqueous solution. The performance of this structure as an ethanol sensor was studied here by monitoring output power variation and wavelength shift with changing ethanol concentration. In the concentration range of 5%—50% of ethanol, the SWCNT coated structure showed an improved sensitivity compared to the uncoated sample. The sensitivity is improved from 0.013 5 dB/% to 0.040 9 dB/% with the coating. The SWCNT coated sample also showed a peak wavelength shift of 0.1 nm with the change of ethanol concentration in the same range.

Q-switched erbium doped fiber laser (EDFL) was passively realized using vanadium pentoxide (V2O5) embedded into polyethylene glycol (PEG) film as saturable absorber (SA). The laser could successfully generate stable self-starting pulses when the V2O5 film was placed in an EDFL cavity. It operated at 1 562.4 nm wavelength. The repetition rate can be varied from 91.7 kHz to 128.2 kHz while the pulse width shrank from 10.90 μs to 7.81 μs with rising pump power from 110.9 mW to 166.5 mW. The pulse energy recorded was 3.2 nJ at pump power of 166.5 mW. The results indicate that the saturable absorption of V2O5 has promising nonlinear photonic applications especially in fiber laser development for 1.5-μm region.

A sensitive tapered optical fiber sensor incorporating graphene oxide (GO) and polyvinyl alcohol (PVA) composite film for the rapid measurement of changes in relative humidity was proposed and experimentally demonstrated. The sensing principle was based on the intensity modulation of the transmitted light induced by the refractive index changes of the sensitive coatings. The sensing region was obtained by tapering a section of single-mode optical fiber (SMF) from its original 125 μm diameter down to 9.03 μm. The tapered structure was then modified through deposition of GO/PVA nanocomposites by using the dip-coating technique. The field emission scanning electron microscope (FESEM) and Raman spectroscopy were used to characterize the structure of the composite film. As evidenced by a Fourier transform infrared spectroscopy (FTIR) analysis, the presence of oxygen functional groups (such as –OH and COOH) on the GO structure enabled the attachment of PVA molecules through hydrogen bonding and strong adhesion between GO/PVA layers. The performance of the sensor was tested over a wide range (20% RH to 99.9% RH) of relative humidity. The sensor showed a good response with its signal increasing linearly with the surrounding humidity. The tapered optical fiber sensor with the coating of GO/0.3 g PVA achieved the highest sensitivity [0.5290 RH (%)]. The stability, repeatability, reversibility, as well as response time of the designated sensor were also measured and analyzed.

Passively Q-switched thulium doped fiber laser (TDFL) has been successfully demonstrated using gold nanoparticles (GNPs), which were embedded into polyvinyl alcohol as saturable absorber (SA). The stable self-starting Q-switched laser was generated to operate at 1 891 nm when a tiny piece of the prepared film was slot in between two fiber ferrules and incorporated into the laser cavity. The repetition rate can be adjusted from 48.54 kHz to 49.64 kHz while the pulse width decreased from 3.52 μs to 2.38 μs with the increase of 1 550 nm pump power from 840 mW to 930 mW. The corresponding pump power output power linearly increased from 3.62 mW to 6.3 mW with a slope efficiency of 2.53%. The maximum peak power and pulse energy were recorded at about 39 mW and 0.12 μJ, respectively at pump power of 930 mW. The Q-switching operation was caused by the surface plasmon resonance absorption of GNPs.

The whispering gallery mode (WGM) based micro-bottle resonator (MBR) sensor has been proposed and demonstrated for relative humidity measurement by using an agarose gel as a transducer. MBR was fabricated by using a soften- and-compress method to form a 190 μm bulge bottle. The micro-bottle was optically excited by a 3 μm tapered fiber and it exhibits a resonance with a Q factor in an order of 105. The agarose coated MBR produces a good sensing response towards humidity with the sensitivity of 0.107 dB/%RH and linearity of 99.614%. The agarose hydrophilic nature and its changing porosity and refractive index with increasing relative humidity made the coated MBR structure to be more sensitive than the uncoated structure. This humidity sensor has a simple fabrication and is showing good sensitivity, linearity, resolution, response time and operational in a wide humidity range.

In this letter, a humidity sensor is demonstrated by applying a whispering gallery mode (WGM) from a microsphere resonator onto the ZnO nanorods coated glass surface. The diameter of the microsphere was 234 μm and the glass surface was coated with ZnO nanorods using the hydrothermal method at growth duration of 12 h. A significant response to humidity level ranging from 35%RH to 85%RH has been observed with the sensitivity of 0.014 2 nm/%RH. The proposed humidity sensor has successfully employed to enhance interaction between the whispering gallery mode evanescent and surrounds analyte with the assistance of ZnO nanorods coated glass.