A compact fiber-optic magnetic field sensor is proposed by packaging an orthogonal dual-frequency fiber grating laser and a copper wire with alternating electrical current together inside epoxy resin. The alternating current generates Ampere force in a magnetic field, which changes the birefringence of the fiber laser and hence tunes the frequency of the beat signal after photodetection. The magnetic flux density can then be detected by measuring the frequency change of the beat signal. The sensitivity of the sensor can be tuned with a maximum response of 35.21 kHz/kGs demonstrated. Moreover, the sensor shows good immunity to environment interference.

We present a new procedure for protecting micro-optical fibers (tapered fibers) by using the 3-dimensional (3D) printing technology. A standard single-mode optical fiber was tapered down to the diameter of 1 μm and embedded in a polymeric matrix obtained by an additive manufacturing routine. We show that the proposed structure protects the fiber taper against environmental humidity while keeping permeability to gas flow and the possibility of the realization of gas detection experiments. To our knowledge, this is the first time 3D printed casings were applied to protect fiber tapers from humidity deterioration. We envisage this new approach will allow the development of new fiber taper devices to better resist in humid environments.

A fiber-optic shape sensing based on 7-core fiber Bragg gratings (FBGs) is proposed and experimentally demonstrated. The investigations are presented for two-dimensional (2D) and three-dimensional (3D) shape reconstruction by distinguishing bending and twisting of 7-core optical fiber with FBGs. The curvature and bending orientation can be calculated by acquiring FBG wavelengths from any two side cores among the six outer cores. And the shape sensing in 3D space is computed by analytic geometry theory. The experiments corresponding of 2D and 3D shape sensing are demonstrated and conducted to verify the theoretical principles. The resolution of curvature is about 0.1 m–1 for 2D measuring. The error of angle in shape reconstruction is about 1.89° for 3D measuring. The proposed sensing technique based on 7-core FBGs is promising of high feasibility, stability, and repeatability, especially for the distinguishing ability on the bending orientation due to the six symmetrical cores on the cross-section.

The aim of the present study is to develop a surface plasmon resonance sensor for the detection of vitamin B2, vitamin B9, and vitamin B12 in food samples by using the molecular imprinting technique. The vitamin B2, vitamin B9, and vitamin B12 imprinted and the non-imprinted surface plasmon resonance sensor chip surfaces were characterized by using contact angle measurements, atomic force microscopy, ellipsometry, and Fourier transform infrared-attenuated total reflectance. The real-time detection of vitamin B2, vitamin B9, and vitamin B12 was analyzed by using aqueous solutions in the concentration range of 0.01 ng/mL - 10 ng/mL for vitamin B2, 0.1 ng/mL - 8.0 ng/mL for vitamin B9, and 0.01 ng/mL - 1.5 ng/mL for vitamin B12. The limit of detection values was calculated as 1.6×10-4 ng/mL for vitamin B2, 13.5×10-4 ng/mL for vitamin B9, and 2.5×10-4 ng/mL for vitamin B12, respectively. Selectivity experiments were performed by using vitamin B1 and vitamin B6. The reproducibility of surface plasmon resonance sensors was investigated both on the same day and on different days for four times. Validation studies of the prepared surface plasmon resonance (SPR) sensors were performed by liquid chromatography-tandem mass spectrometry (LC-MS/MS).

Contrary to the conventional detection method like radiography, the near infrared light source has been demonstrated to be suitable for dental imaging due to different reflectivity among enamel, dentin, and caries lesion. In this paper, three light sources with different bandwidths based on a transillumination method are compared. The contrast among enamel, dentin, and caries lesion is calculated in different situations. The experimental results show that the random fiber laser has the best comprehensive quality in dental imaging due to its high spectral density, low coherence, and deep penetration. This work provides a guidance for light source selection in dental imaging.

This work presents a surface plasmon resonance biosensor for the figure of merit enhancement by using Ga-doped zinc oxide (GZO), i.e., nanostructured transparent conducting oxide as plasmonic material in place of metal at the telecommunication wavelength. Two-dimentional graphene is used here as a biorecognition element (BRE) layer for stable and robust adsorption of biomolecules. This is possible due to stronger van der Waals forces between graphene’s hexagonal cells and carbon-like ring arrangement present in biomolecules. The proposed sensor shows improved biosensing due to fascinating electronic, optical, physical, and chemical properties of graphene. This work analyses the sensitivity, detection accuracy, and figure of merit for the GZO/graphene SPR sensor on using the dielectric layer in between the prism and GZO. The highest figure of merit of 366.7 RIU-1 is achieved for the proposed SPR biosensor on using the nanostructured GZO at the 3000 nm dielectric thickness. The proposed SPR biosensor can be used practically for sensing of larger size biomolecules with due availability of advanced techniques for the fabrication of the nanostructured GZO and graphene.

A waveguide coupled surface plasmon sensor for detection of liquid with high refractive index (RI) is designed based on polymer materials. The effects of variation of the thickness of the Au film, polymethyl methacrylate (PMMA) buffer, and waveguide layer on the sensing performance of the waveguide are comprehensively investigated by using the finite difference method. Numerical simulations show that a thinner gold film gives rise to a more sensitive structure, while the variation of the thickness of the PMMA buffer and waveguide layer has a little effect on the sensitivity. For liquid with high RI, the sensitivity of the sensor increases significantly. When RI of liquid to be measured increases from 1.45 to 1.52, the sensitivity is as high as 4 518.14 nm/RIU, and a high figure of merit of 114.07 is obtained. The waveguide coupled surface plasmon RI sensor shows potential applications in the fields of environment, industry, and agriculture sensing with the merits of compact size, low cost, and high integration density.

Zero-mode waveguides have become important tools for the detection of single molecules. There are still, however, serious challenges because large molecules need to be packed into nano-holes. To circumvent this problem, we investigate and numerically simulate a novel planar sub-wavelength 3-dimension (3D) structure, which is named as near-field spot. It enables the detection of a single molecule in highly concentrated solutions. The near-field spot can produce evanescent waves at the dielectric/water interface, which exponentially decay as they travel away from the dielectric/water interface. These evanescent waves are keys for the detection of fluorescently tagged single molecules. A numerical simulation of the proposed device shows that the performance is comparable with a zero-mode waveguide. Additional degrees-of-freedom, however, can potentially supersede its performance.

In this paper, we propose two kinds of composite structures based on the one- and two-dimensional (1D&2D) gold grating on a gold film for plasmonic refractive index sensing. The resonance modes and sensing characteristics of the composite structures are numerically simulated by the finite-difference time-domain method. The composite structure of the 1D gold semi-cylinder grating and gold film is analyzed first, and the optimized parameters of the grating period are obtained. The sensitivity and figure of merit (FOM) can reach 660 RIU/nm and 169 RIU–1, respectively. Then, we replace the 1D grating with the 2D gold semi-sphere particles array and find that the 2D grating composite structure can excite strong surface plasmon resonance intensity in a wider period range. The sensitivity and FOM of the improved composite structure can reach 985 RIU/nm and 298 RIU–1, respectively. At last, the comparison results of the sensing performance of the two structures are discussed. The proposed structures can be used for bio-chemical refractive index sensing.