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A biosensor for detecting DNA hybridization via refractive index sensing has been demonstrated using a subwavelength grating (SWG) waveguide. Waveguide dimensions are selected by parametric optimizations to increase the mode-analyte overlap with considerations of typical silicon-on-insulator fabrications technology. DNA layer is added with a linker layer on silicon pillars of the SWG waveguide to optimize and detect the DNA hybridization. Some essential characteristics such as mode overlap factor, change in effective refractive index, waveguide sensitivity, and shift in resonance wavelength are computed for the different dimensional parameters of the SWG waveguide in DNA hybridization along with mode field intensity and normalized power using the finite element method. The DNA hybridization is shown by variation in normalized power of interacting light in cladding region of the waveguide for 0% to 100% fractional change of dsDNA and ssDNA. Waveguide sensitivity, shift in resonance wavelength, device sensitivity, and intrinsic limit of detection are obtained to ∼ 0.157, 7.01, 605 nm/RIU, and 1.30 × 10−4 RIU, respectively, for the optimized structure of SWG waveguide in sensing of DNA hybridization, which could be suitable aspects for detecting DNA hybridization. [ABSTRACT FROM AUTHOR]

An optical fiber sensing structure based on double-cladding fiber (DCF) is described. The core and outer cladding of the DCF both supports more than one guided mode and the cladding mode resonance as well as modal interference in the fiber. Due to the W-type refractive index (RI) distribution, the outer cladding generates a stronger evanescent field to obtain higher sensitivity. In the transmitted spectrum, all three dips shift to the longer wavelength with the external RI changing from 1.33 to 1.43, and the high sensitivities are 595, 741, and 686 nm/RIU, respectively. [ABSTRACT FROM AUTHOR]

To improve the sensitivity of seawater refractive index (RI) measurement, fluorine-doped fiber (FDF)-sandwiched Mach–Zehnder interferometer (MZI) is proposed, which is fabricated by splicing a short section of FDF between two sections of single-mode fibers (SMFs) with a large lateral offset. In FDF-sandwiched MZI, the two light paths are the FDF cladding and the measured seawater. The FDF cladding has lower RI than that of normal single-mode fiber (SMF), so the FDF-sandwiched MZI has higher sensitivity than that of SMF-sandwiched MZI. The results show that the RI sensitivity of the proposed sensor can be up to −14,638 nm/RIU, which is about 10.9% higher than that of SMF-sandwiched MZI. Temperature cross-sensitivity of our sensor is only 1.7 × 10−6 RIU/°C. The proposed sensor has the potential application in real physical, chemical, and biological sensing. [ABSTRACT FROM AUTHOR]

A gold-coated D-shape photonic crystal fibre sensor based on surface plasmon resonance (PCF-SPR) is designed with microfluidic channels and numerically investigated for detection of a wide range of refractive indexes. The D-type structure and microfluidic channels improve the performance of the sensor by reducing the distance between the core and channel and increasing the coupling strength of the fundamental and plasmonic modes. By optimizing the structural parameters, the PCF-SPR sensor can realize a broad range of detection for low RIs changing from 1.23 to 1.36. The maximum spectral sensitivity of 18,000 nm/RIU and optimal resolution of 5.56 × 10−6 RIU are observed for RIs between 1.35 and 1.36. The sensor is capable of detecting analytes with RIs below 1.36 and has great potential in medical diagnosis, drug development, food safety, and water testing. [ABSTRACT FROM AUTHOR]

In this paper, we propose a photonic crystal fiber (PCF) refractive index (RI) sensor based on the surface plasmon resonance (SPR) effect. The coupling and sensing characteristics of the proposed PCF-SPR RI sensor are investigated by the finite element method. The proposed PCF-SPR RI sensor can achieve the dual-wavebands measurement. By controlling the analytes height and incident light wavelength, the PCF-SPR RI sensor shows different sensing performances. The maximum wavelength sensitivities of the proposed PCF-SPR RI sensors can be up to 2000 and 4000 nm/RIU in the wavelength ranges of 0.75 to 1.0 and 1.2 to 2 μm, respectively. [ABSTRACT FROM AUTHOR]

A highly sensitive refractive index (RI) sensor based on the surface plasmon resonance (SPR) phenomenon is proposed and demonstrated. The sensor is composed of a quasi D-shape ten-fold photonic quasi-crystal fiber (PQF) and indium tin oxide (ITO) film. The quasi D-shape and eccentric core structure strengthen coupling between the core mode and surface plasmon polariton (SPP) mode to enhance the sensing sensitivity, while the mechanical strength of the PQF is preserved. The properties of the sensor are determined numerically and optimized by the finite element method. In the RI range of 1.40–1.44, the maximum wavelength sensitivity and average wavelength sensitivity are 62,000 nm/RIU and 26,500 nm/RIU, respectively. Meanwhile, the loss spectra show smaller full-width at half-maximum and maximum FOM of 542.5 RIU−1. This novel sensor which boasts ultra-high-sensitivity and excellent FOM has large potential in the determination of liquid RIs. [ABSTRACT FROM AUTHOR]

In this paper, three designs of Square Ring resonator (SRR) based on metal-insulator-metal (MIM) WG are reported. The transmission spectra and electric field distribution of the sensor structure are simulated using finite element method (FEM). The effect of structural parameters on the spectral characteristics and sensing performance are investigated comprehensively. The maximum achieved sensitivity and figure of merit of the sensor reached 1320 nm/RIU and 16.7, respectively. Due to the high performance and easy fabrication, this kind of plasmonic structures can find noteworthy applications in integrated optical circuits and on-chip nano-sensors. [ABSTRACT FROM AUTHOR]

The effect of the temperature on refractive index (RI) sensors based on U and Coil-shaped plastic optical fiber (POF) was investigated. For this purpose, four POF-RI sensor probes were produced, and RI changes caused by ethanol changes in solutions were detected. Two of the produced probes were U-shaped, while the other two were Coil-shaped. For the first time in the literature, the effect of both the geometry of the U and Coil-shaped POF-RI sensors on the sensor parameters and the effect of the medium temperature have been analyzed together. As a result of the experiments conducted at 25°C, the best RI change detection sensitivity, linearity, and resolution values were determined as 821%/RIU, 0.9974 (R2), 5.18 × 10−4. In addition, temperature dependence loss (TDL) and temperature dependence RI deviation (TDR) were measured at different temperatures (25–40°C) in the 1.3346–1.45 RI range, and the effect of temperature change on POF-RI sensor probes was characterized. [ABSTRACT FROM AUTHOR]

In this paper, a comprehensive study is conducted to determine the optimum geometry for tapered fibre-optic gas sensors. A staircase concatenation method is introduced to investigate the effects of taper angle and fibre taper diameter on the sensitivity of the tapered-fibre sensors. The simulations show that the sensitivity of the tapered fibre-optic sensor increases by increasing the taper angle and reducing the taper diameter. To evaluate the predictions of the presented model, different tapered-fibre sensors have been fabricated and tested. The surface of the tapered fibres has been coated with palladium in order to determine the sensitivity of the sensors to hydrogen exposure. By increasing the percentage of the hydrogen in the surrounding environment, a shift of the output interference spectrum is observed. The experimental results confirm the simulation results obtained for the effect of geometry on the sensitivity of the sensors. [ABSTRACT FROM AUTHOR]

In this work, we incorporated Bragg gratings in the standard ring resonator design in order to enhance the sensitivity of the refractive index sensor. The transmission spectrum and electric field distribution of the device are simulated using the finite element method (FEM). The numerical simulation results obtained from the transmission spectrum are used to examine the sensing characteristics of the structure. The size of the grating teeth has a significant effect on the intensification of surface plasmons which in turns enhances the interaction between the ambient medium and the light. Bragg grating embedded resonator cavity design has the best sensitivity, FOM and Q-factor of 1680 nm/RIU, 48 and 48.4, respectively which is much higher than several previously reported values. [ABSTRACT FROM AUTHOR]

A plasmonic square ring resonator sensor design based on metal–insulator-metal waveguide is proposed. The transmission spectra and electric field distribution of the resonator are simulated using the finite element method (FEM). The numerical simulation results achieved from the transmission spectra are used to investigate the sensing characteristics of the structure. The effect of structural parameters on the spectral characteristics and sensing performance are investigated in detail. The sensitivity is obtained to a value as high as 1367 nm/RIU with a figure of merit of ∼25. The suggested design can possibly be applied in optical network-on-chip and on-chip nanosensors. [ABSTRACT FROM AUTHOR]

A kind of compact fibre-optic sensor based on no-core fibre (NCF) cascaded with a strong coupling long-period fibre grating (LPFG) is proposed and experimentally demonstrated. The sensing mechanism is based on the Mach-Zehnder-like interference between the core fundamental mode and cladding mode of the fibre structure. The NCF and LPFG are used as the mode exciter and combiner, respectively. Due to the particular properties of the strong coupling LPFG, the measurements of refractive index (RI) and temperature with high sensitivity are realized by monitoring the transmission spectrum with intensity and wavelength interrogation techniques, respectively. The achieved RI sensitivity reaches -580.269 dB/RIU in the range of 1.436-1.454 and the temperature sensitivity reaches 27.2 pm/°C. [ABSTRACT FROM AUTHOR]

A compact and high sensitivity refractive index sensor based on a photonic crystal fibre Mach–Zehnder mode–mode interferometer is proposed. The sensing part is formed by in fibre SMF-PCF-SMF structure (SMF: single-mode fibre; PCF: photonic crystal fibre) using fusion splicing method. The fully collapse air holes of photonic crystal fibre make coupling of fibre core and cladding mode in the splicing collapse region which establish a Mach–Zehnder interferometer. The Mach–Zehnder interferometers with different photonic crystal fibre length are fabricated to investigate refractive index sensing characteristics. The refractive index measuring sensitivity can reach 224.2 nm/RIU (RIU: Refractive Index Unit) with a length of PCFL = 4 cm, experimentally. The proposed refractive index sensor is attractive due to its simple production process, compact size and high sensitivity. [ABSTRACT FROM PUBLISHER]

We propose a plasmonic nanosensor based on an open box-like metal nanocavity. Surface plasmon polaritons (SPPs) excited at the metal/dielectric interface oscillate in the cavity, and then, plasmonic resonance modes are formed. Since the cavity is open, a part of the resonance light of the SPPs is scattered to light. By monitoring the shift in the scattering spectrum, the refractive index change of the sensed material can be derived. Because of the high reflectivity of the metallic walls, the sensitivity and figure of merit (FOM) are higher than those using single nanoparticle or nanoantenna. A sensitivity of 1046 nm/RIU (RIU denotes refractive index unit) and a FOM of 23.4 are derived for a 700 nm long and 350 nm high square cavity. Furthermore, the sensing area of the proposed sensor is smaller than 1 μm2and the performance of the nanosensor can be further tuned by varying the cavity dimensions. The proposed sensor is well suited for observing small changes in biological and chemical reactions. [ABSTRACT FROM PUBLISHER]

This study proposed and demonstrated a fiber Bragg grating sensor for simultaneous detection of the temperature and refractive index of a liquid. The fiber Bragg grating is composed of three index layers: an inner core, an outer core, and a cladding. The cladding was etched for evanescent wave coupling between the outer core mode and an external liquid. The Bragg wavelength of the inner core mode is used for obtaining temperature data, while the refractive index for the liquid was determined by using the difference between the Bragg wavelength of the inner core mode and that of outer core mode. [ABSTRACT FROM AUTHOR]

A superimposed long period fiber grating design proposed for refractive index sensing is shown to be superior to conventional dual resonance and turnaround point gratings and can operate at any chosen wavelength region by appropriate design. Numerical simulations carried out on standard single mode fibers show that such sensors can operate over a wide refractive index range (1.33-1.42) exhibiting a high sensitivity of ~500--1545 nm/RIU, yielding ~ 10--6-- 10--7 refractive index change corresponding to the resonance relative shift of 1 pm with potential applications to chemical and biological industries. The proposed scheme can also discriminate between refractive index and temperature changes. [ABSTRACT FROM AUTHOR]