Single mode tapered fiber-optic interferometer based refractive index sensor and its application to protein sensing

We demonstrate refractive index sensors based on single mode tapered fiber and its application as a biosensor. We utilize this tapered fiber optic biosensor, operating at 1550 nm, for the detection of protein (gelatin) concentration in water. The sensor is based on the spectroscopy of mode coupling based on core modes-fiber cladding modes excited by the fundamental core mode of an optical fiber when it transitions into tapered regions from untapered regions. The changes are determined from the wavelength shift of the transmission spectrum. The proposed fiber sensor has sensitivity of refractive index around 1500 nm/RIU and for protein concentration detection, its highest sensitivity is 2.42141 nm/%W/V

Investigating the effect of taper length on sensitivity of the tapered-fiber based temperature sensor

A temperature sensor using single-mode tapered fiber is presented. To better understand the behaviour of a tapered optical fiber, transmission experiments with different taper profiles, specifically waist length were performed. The effects of taper profiles on the sensitivity of the sensor were also investigated. It is demonstrated that careful selection of the taper profile can increase the sensitivity of the sensor. In our experiment, a good temperature sensing result was achieved using the optimum parameter. The best sensitivity achieved was 45.5 pm/°C that measured the range of temperature from 30°C to 120°C. The fabricated sensors are easy to fabricate and relatively low cost. Our results indicate that the tapered fiber based temperature sensor has high sensitivity and good repeatability

Asymmetric fiber taper for temperature sensing applications

Optical fibers can be tapered in order to change their light coupling or light propagation properties. The evanescent wave can interact with environmental perturbations surrounding the waist region thus affecting the light propagation. This allows the waist region to be employed as an effective sensing region. This work is focused on a new fiber taper structure referred to as asymmetric fiber taper for temperature sensing application. Asymmetric tapered fiber is fabricated with different down-taper and up-taper lengths. By subjecting the sensor to temperature variation, wavelength shifts corresponding to different temperature can be observed. Comparison with symmetric taper sensor, asymmetric exhibits better sensitivity making it a feasible choice for this application. The best sensitivity is obtained from taper profile 2-15-8 which is 0.2395nm/°C

Determining salinity using a singlemode tapered optical fiber

We report and experimentally demonstrate a salinity determination method by using a tapered single-mode fiber. The change of refractive index due to the exposure of the tapered area to concentrations of Sodium chloride (NaCl) was detected by the wavelength shifts produced in the interference spectral response. Results of the experiment depict that better sensitivity can be achieved at particular waist lengths as the proposed setup managed a maximum sensitivity of 2834.3nm RIU-1 [refractive index range of 1.3324 1.3411] with waist length, L = 15mm, and waist diameter, α= 10μ The high sensitivity achieved without any coating or modification to the tapered fiber offers simplicity, lesser financial burden, and reliability

Refractive index sensor with asymmetrical tapered fiber based on evanescent field sensing

We report and demonstrate a single-mode asymmetric tapered fiber as a refractive index (RI) sensor based on evanescent field sensing. The proposed setup managed to sense the changes of RI when the tapered region was exposed to different concentrations of Sodium chloride (NaCl). This was possible due to the output interference spectrum shifting in response to the changes of RI. Different environmental sensitivities were achieved by manipulating the transition lengths of the tapered fiber. Experimental results depict RI sensitivities of 3914.7 nm/RIU (refractive index unit) and 3395.7 nm/RIU for taper profiles with down-taper transition lengths of 2 mm and 8 mm, respectively, which is higher than previously reported asymmetric taper RI sensors. Such findings may find itself beneficial in low cost, reliable and simplified sensors

Detection of dengue using PAMAM dendrimer integrated tapered optical fiber sensor

The exponential escalation of dengue cases has indeed become a global health crisis. This work elaborates on the development of a biofunctionalized tapered optical fber (TOF) based sensor with the integration of polyamidoamine (PAMAM) dendrimer for the detection of dengue E protein. The dimension of the TOF generated an evanescent feld that was sensitive to any changes in the external medium while the integration of PAMAM promoted more adhesion of bio-recognition molecules; antiDENV II E protein antibodies; that were complementary to the targeted protein. This in return created more active sites for the absorption of DENV II E proteins onto the tapered region. The resolution and detection limit of the sensor are 19.53nm/nM and 1 pM, respectively with Kd=1.02×10−10M

Hydrous ferric oxide-magnetite-reduced graphene oxide nanocomposite for detection of arsenic using surface plasmon resonance

Surface plasmon resonance sensor coated with hydrous ferric oxide-magnetite-reduced (Fe2H2O4-Fe3O4-rGO) graphene oxide nanocomposite film was demonstrated to detect two toxic heavy metals; Arsenic (III) [As(III)] and Arsenic (V) [As(V)] in aqueous solution. The proposed nanocomposite film exhibited successful absorption of As with enhanced sensitivity and selectivity. Resultantly, when tested with different concentrations of As(III) and As(V), (0.1-1.0 ppb) the sensor ranged linearly with sensitivity of 2.196 °ppb-1 and 0.960 °ppb-1, respectively, and achieved a detection limit as low as 0.1 ppb. These results validate the potential of Fe2H2O4-Fe3O4-rGO nanocomposite material for optical sensing applications in As detection

Reduced graphene oxide/maghemite nanocomposite for detection of lead ions in water using surface plasmon resonance

A prism-based surface plasmon resonance (SPR) sensor deposited with reduced graphene oxide/maghemite is presented for the detection of lead ions (Pb 2+ ) in water. The SPR setup proposed followed the Kretschmann configuration with the installment of the nanocomposite integrated bilayer sensor chip onto the prism. For protection, the nanocomposite active layer was coated with 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimidehydrochloride/N-hydroxysuccinimide. When the sensor was tested with different concentrations of Pb 2+ in static water, the limit of detection was achieved at 0.001 ppm with a resonance angle shift of 0.184°. As an improvisation, a sample circulation design was adapted into the setup in order to increase the interaction rate between the sample and the sensing layer. This managed to improve the detection limit to 0.3 ppb

Open cavity hybrid Raman-erbium random fiber laser with common pump

A symmetrical 80-km open cavity erbium-integrated hybrid random distributed feedback fiber laser (HRFL) was proposed and experimentally demonstrated. A variation of pumping schemes and cavity lengths was first investigated prior to the integration of the EDF. The impact of Raman and EDF hybrid amplification was then investigated through EDF length variation. The proposed scheme used a single common pump to incite both Raman and erbium gain to produce a single peak at a 1567-nm wavelength with maximum OSNR of 62.37 dB. A maximum total output power generation of 1420 mW was achieved with high-slope efficiency of 38%. The proposed hybrid setup has shown improved performance despite using open-ended cavity sustained by only a single pump in contrast to previous more complex hybrid schemes. Prolonged chaotic regime manifesting spontaneous pulse burst was also observed before the stable regime. The simple operation with the high performance of the proposed configuration offers a great potential for long distance or remote access applications such as heavy metals sensing or even for biological hazard sensing

Dengue E protein detection using a graphene oxide integrated tapered optical fiber sensor

We report the use of a biofunctionalized tapered optical fiber based sensor with the integration of graphene oxide (GO) for the detection of Dengue virus (DENV) II E proteins. The tapered region was deposited with GO and functionalized with anti-DENV II E protein IgG antibodies to be tested with different concentrations of DENV II E proteins. The sensor obtained a detection limit of 1 pM with a sensitivity value of 12.77 nm/nM, which was better compared to previously reported studies. The sensor also showed high precision, great selectivity, and high affinity toward E protein with a dissociation constant of Kd = 1.11 × 10–9 M–1. The proposed sensor has undoubtedly exhibited the immense potential of nanomaterial integration for future advancements of dengue diagnostics