Sensitive and specific protein sensing using single-mode tapered fiber immobilized with biorecognition molecules

We examine and demonstrate a biosensor using single-mode tapered fiber that has been immobilized with biorecognition molecules to sense targeted proteins. Interaction of evanescent waves with the external medium surrounding the tapered region produces an interferometric-patterned spectrum, which shifts correspondingly to any changes of refractive index (RI) in the external medium. The proposed setup managed to obtain an RI sensitivity and concentration sensitivity of 2526.8 nm/RIU and 20.368 nm/μM, respectively, which, to our knowledge, is highly sensitive when compared with previous studies. The dynamic performance, good specificity, and high sensitivity of the proposed method highlight an immensely beneficial choice for immunological diagnostics

Fabrication and characterization of micro fluidic based fiber optic refractive index sensor

A refractive index sensor was proposed by using 3 dimension (3D) grayscale lithography technique. Optical fiber with taper diameter of 12 μm was embedded in a closed microfluidic channel. Taper area of optical fiber is in floating condition at the center of micro channel. Grayscale variation range used for this sensor was 70%–74% and thickness variation 430 μm–694 μm was achieved. The dimension of the sensor was 7.5 cm in length and 2 cm in width. Fabricated sensor was characterized with air condition and solution concentration from 0.1 M to 1 M. A sensitivity of 1457 nm/RIU is achieved. The measured results show a good repeatability and low temperature cross-sensitivity. Keywords: Grayscale lithography, Microfluidic chip, Refractive index sensor, Tapered optical fibe

Saturable absorber incorporating graphene oxide polymer composite through dip coating for mode-locked fiber laser

Fabrication of microfiber saturable absorbers (SA) is a tedious process. This work demonstrates a simplified method of microfiber SA fabrication by integrating graphene oxide/polymethylsiloxane (GO/PDMS) using dip-coating technique. The idea is to enhance light-matter interaction between graphene and propagating light modes within the microfiber by enhancing the binding strength and proximity of the graphene-polymer composite to the microfiber. The implementation of GO/PDMS SA in an erbium-doped fiber laser cavity has successfully generated ultrashort pulses with pulse duration of 629 fs in the C-band emission region. The success of this work contributes to better insight towards simplifying the fabrication technique of microfiber SAs

L-band Q-switched fiber laser with gallium/thulium-doped silica fiber saturable absorber

An L-band Q-switched fiber laser was demonstrated using gallium/thulium-doped silica fiber saturable absorber. At 10 cm in length, the saturable absorber generated Q-switched fiber laser at a pump power threshold of 39.6 mW and a central wavelength of 1601.93 nm. Beyond 53.3 mW, a spectrum with a central wavelength at 1602.00 nm was generated. On the other hand, the pulse repetition rate was obtained from 3.44 to 7.47 kHz whereas the pulse width reduces from 100.2 to 58.6 µs for pump power ranges from 39.6 to 53.3 mW. Within this range, the pulse energy is attained between 0.2600 and 0.2843 µJ, at a laser power slope efficiency of 6.94%. The constantly operated Q-switched fiber laser over 50 min observation time at 53.3 mW pump power ensures the feasibility of this pulse laser source as a practical device

Taper biosensor in fiber ring laser cavity for protein detection

This paper demonstrates the integration of a bio-functionalized tapered fiber sensor in a fiber laser cavity for sensing of biological molecules. Interferometric effect from the taper generated single wavelength lasing output that was spatially measured to detect any changes. The sensing performance of the integrated system was assessed by immersing the biosensor in various concentrations of avidin ranging from 1 to 10 pM at laser threshold (40 mW) and at the maximum pump power of 200 mW. Selectivity of the sensor was ensured by immobilizing biotin on the surface of the tapered region that would act as complementary molecules to avidin. The proposed setup obtained sensitivity values of 0.40 nm/pM and 1.02 nm/pM at pump power of 40 mW and 200 mW, respectively. The integrated system simplifies the sensing output and analysis without compromising the performance of tapered optical fiber-based biosensor