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In this article, a cost-effective hollow core fiber (HCF)-based refractive index (RI) sensor using surface plasmon resonance (SPR) is designed and demonstrated. The sensor consists of a metal nanowire inside an HCF along with the sensing medium of various refractive indices. SPR effect between polaritons and the guided core mode of designed HCF is exploited to enhance the sensing performance. A full vectorial finite element method (FEM) is used for the design and analyses of the sensing probes which exhibit very high sensitivities of 12,400 nm/RIU, 10560 nm/RIU, and 6400 nm/RIU for copper (Cu), gold (Au), and silver (Ag), respectively with a resolution of 1.61 × 10−6 RIU. Additionally, the influence of metal wire dimension is also investigated in this paper. The reported simple and low-cost sensor exhibits high sensitivity for liquid with refractive indices slightly higher than that of the dielectric tube, such as olive oil, turpentine, kerosene, chloroform, carbon tetrachloride, glycerol, and toluene.

A dual core photonic crystal fiber (DCPCF) consisting single analyte channel is proposed in this article for the detection of petrol adulteration. The sensing probe is numerically studied using finite element method. The adulterated petrol sample is infiltrated in circular analyte channel which is situated at the center of the fiber between two solid light guiding cores. The mode coupling between these two cores as well as sensitivity of the designed probe are investigated by varying adulteration level of petrol. Also the structure is optimized step by step. The numerical simulation result shows very high sensitivity of 20,161.2 nm/RIU for practically usable small probe. A portable adulteration detection sensor can be manufactured using this simple structured DCPCF probe which will be useful to study environmental pollution, maintaining long engine lifetime, save revenue.

A highly sensitive refractive index (RI) sensor based on a microfluidic channel (MFC) incorporated in a single-mode fiber (SMF), filled with Ag-graphene composite nanowire is presented and analyzed here. The sensing performance and the coupling properties of designed sensor are numerically analyzed by using a full vectorial finite element method (FEM) incorporating amplitude and wavelength interrogation techniques in the detection range varied from ${n_a}$ = 1.330-1.350. The maximum wavelength and amplitude sensitivity are obtained of 13700 nm/RIU and 1026 RIU−1, respectively. Here, the Ag-graphene composite nanowire can not only solve the problem of oxidation but also enhances the sensitivity of the sensor. In addition of high sensitivity, it also provides better performance than other sensing devices based on similar technologies such as Ag nanowire-filled sensors. Moreover, the influences of polishing depth (D), nanowire radius (rn), graphene layer (Lg) and channel size (s) on the designed sensor, are also thoroughly investigated here. The present work can provide a base for designing a real-time, highly sensitivity, remote sensing, and distributed SPR based RI sensor.

In present work we report the fabrication and characterization of optical fiber pH sensor using smart hydrogel coating over Zinc Oxide (ZnO) microflowers. ZnO microflowers were hydrothermally grown over chemically etched tapered multi-mode fiber (MMF). Mainly, the sensing head contains two layers in which one is ZnO microflower and another is pH sensitive hydrogel layer. The variation in pH of liquid around the sensing probe causes the swelling and shrinkage of hydrogel which leads the change in its refractive index (RI). The work of ZnO microflower is to enhance the evanescent waves that interact with the change in RI of hydrogel which causes the variations of wavelength dips with respect to each pH solutions. The sensitivity was estimated by using wavelength interrogation technique. The ZnO microflower based sensor is highly sensitive for wide range pH values (both high and low range of pH varied from pH = 3 to pH = 7 and pH = 7 to pH = 11, respectively). The sensitivity of ZnO microflower based MMF sensor was found to be 2.59 nm/pH and 0.70 nm/pH for both acidic and basic media, respectively. In addition to high sensitivity, the proposed sensor shows fast response time and good stability and reproducibility.

An optical fiber sensor is fabricated and characterized in this communication for salinity detection. The proposed sensor consists of a multimode fiber (MMF) and a section of no core fiber (NCF) with a round tip. The sensor detects the intensity variation of the back reflected light caused by changing concentration of the salt solution surrounding the probe. The parameters of the sensor were studied for better performance. A down tapering is also introduced to enhance the sensitivity of the sensor and a high sensitivity of 0.773 dB/% is obtained for a salinity range of 0–20%. Due to its high sensitivity, low cost and compact size, the proposed sensor can be very much useful in water quality monitoring for environmental, healthcare and industrial applications.

In the present study we report the fabrication and characterization of no-core fiber sensor (NCFS) using smart hydrogel coating for pH measurement. The no-core fiber (NCF) is stubbed between two single-mode fibers with SMA connector before immobilizing of smart hydrogel. The wavelength interrogation technique is used to calculate the sensitivity of the proposed sensor. The result shows a high sensitivity of 1.94 nm/pH for a wide range of pH values varied from 3 to 10 with a good linear response. In addition to high sensitivity, the fabricated sensor provides a fast response time with a good stability, repeatability and reproducibility.

In the present paper the fabrication and characterization of down-tapered optical fiber based pH sensor have been reported. The sensing probe is formed by fusing single mode fibers (SMF) to make it down-tapered which is spliced with multi-mode fiber (MMF). The sensing region is immobilized with sol-gel prepared by mixture of tetraethyl orthosilicate with three different pH indicators on to cladding of middle SMF. The proposed sensor utilizes intensity interrogation method and operates in low and high pH values. The maximum sensitivity of 0.49 dBm/pH is obtained with a good linear response for wide range of pH value varied from 4 to 13. In addition to high sensitivity, this sensor has additional advantages of good stability, fast response time and capable of using in remote sensing.

An intrinsic intensity modulated no core fiber sensor (NCFS) is presented in this paper for rapid detection of adulteration in petrol with kerosene. The sensing principle is based on the phenomenon of absorption of evanescent waves. The sensing head of NCFS is fabricated by stubbing a small section of no core fiber (NCF) between two multi-mode fibers (MMF). A high sensitivity 390 nW/% and 110 nW/% are obtained by the proposed sensor for low and high level of adulteration. The intensity variation and confinement loss with different concentrations of the kerosene in petrol are then verified theoretically by using finite element method. It is found that the theoretical results agree very well with experimental results. The proposed sensor exhibits fast response time and good repeatability in addition to its high sensitivity. The sensor can be useful in industries and automotive companies due to its small size, easy to fabricate, safe with inflammable fuels and required small amount for detection.

In this paper, a hexagonal structure of ethanol filled solid core photonic crystal fiber having dispersion shifted properties is presented. The guiding properties, like effective mode area and dispersion, of the ethanol filled photonic crystal fiber are studied by using the full vectorial finite element method. The numerical simulation results show that the selectively filling of the ethanol in the cladding holes of photonic crystal fiber shifts the zero dispersion wavelength from near infrared region (0.98 μm) to mid infrared region (1.55 μm). This kind of photonic crystal fiber structure is very useful for dispersion compensating tool, sensing applications, fiber laser devices and non-linear applications like supercontinuum generation.

In the present paper a novel cone shaped nano-fiber (CSNF) pH sensor using multi-mode fiber (MMF) has been fabricated and demonstrated. Three different pH indicators, chlorophenol red, bromothymol blue and cresol red with precursor tetraethyl orthosilicate (TEOS) have been used for fabrication of pH sensing layer. A significant enhancement in sensing properties of pH sensor with TiO 2 thin film has been observed. The pH sensor with TiO 2 thin film shows the quite high sensitivity (1.16 dBm/pH) as compared to sensor with simple pH coating (0.81 dBm/pH) at 1550 nm with a good linear response. Moreover, the sensor with TiO 2 film exhibits fast response time of ∼ 25 s for pH values ranging from 4 to 11 with excellent stability and durability.

In the present paper, a new kind of concave shaped refractive index sensor (CSRIS) exploiting localized surface plasmon resonance (LSPR) is proposed and numerically optimized. The LSPR effect between polaritons and the core guided mode of designed CSRIS is used to enhance the sensing performance. The sensor is characterized for two types of sensing structures coated with gold (Au) film and Au nanowires (AuNWs), respectively. The influence of structural parameters such as the distance (D) of the concave shaped channel (CSC) from the core, the diameter of the nanowire (dn) and the size (s) of the CSC are investigated here. In comparison to Au film, the AuNWs are shown to significantly enhance the sensitivity and the performance of the designed sensor. An enhanced sensitivity of 4471 nm/RIU (refractive index unit) is obtained with AuNWs, for a wide range of analytes refractive index (na) varying between 1.33 to 1.38. However, for conventional Au film, the sensitivity of 808.57 nm/RIU is obtained for the same range of analytes.

A wide range and highly sensitive U shaped optical fiber pH sensor utilizing titanium dioxide (TiO 2 ) layer with multiple sol-gel coating has been fabricated and demonstrated in this paper. TiO 2 layer is deposited over uncladded U-shaped fiber to enhance the evanescent field in the pH sensing film. The wide range sensing film is prepared by using three different indicators of various pH ranges. The higher sensitivity of 0.68 dBm/pH was obtained for double layer of sol-gel at 1550 nm with a good linear response. The sensor is also demonstrated for stability, durability and fast response time.

The present work describes the fabrication and characterization of an optical fiber pH sensor using a sol–gel technique. The sensing head configuration is incorporated using a short section of no-core fiber, coated with tetraethyl orthosilicate and spliced at the end of a single mode fiber with a bulge. Different types of indicators (bromophenol blue, cresol red, and chlorophenol red) were used to achieve a wide pH range from 2 to 13. High sensitivities of the fabricated device were found to be 1.02 and ? 0.93 ?? nm / pH for acidic and alkaline solutions, respectively. From the characterization results, it was noted that there is an impact of ionic strength and an effect of the temperature of liquid on the response characteristic, which is an advantage of the existing device over the other pH sensors. The fabricated sensor exhibited good reflection spectrum, indicating a blueshift in resonance wavelength for alkaline solutions and a redshift for acidic solutions.