High-visibility photonic crystal fiber interferometer as multifunctional sensor

High-sensitivity plasmonic sensor by narrowing Fano resonances in a tilted metallic nano-groove array

Plasmonic sensors exhibit enormous potential in the areas of environmental monitoring, biomedical diagnostics, healthcare, food safety, security, and chemical reactions. However, the large bandwidths of surface-plasmon response spectra greatly reduce the sensitivities and detection limits of plasmonic sensors. Herein, we propose to tilt a metallic nano-groove array to reduce linewidths of Fano resonances, and the figure of merit (FOM) of a refractive index sensor is greatly increased. The Fano resonances stem from interference between narrow SPP resonant modes and a broad LSP mode in the metallic nano-groove array. When tilting the metallic nano-groove array, new Fano resonances emerge, greatly compressing the linewidth of Fano resonance of interest to ∼1.1 nm in the simulation. Experimentally, a narrow Fano resonance with a linewidth of Δλ≈2.5 nm is achieved, and a high-FOM (FOM ≈ 263) plasmonic sensor is demonstrated. This value of FOM is more than 4.7 times that (FOM ≤ 55) of Fano sensors based on SPP modes, and it is even approximately twice that (FOM ≈ 140) of the previous Fano sensor based on Wood's Anomaly.

Highly sensitive refractive index sensor based on a TiO2 nanowire array

We propose a novel, highly sensitive refractive index (RI) sensor by means of combining the Kretschmann prism with a TiO₂ nanowire array and do not use a metallic layer in the Kretschmann configuration. Its RI sensing performance was investigated through measuring different concentrations of sodium chloride solution. Experimental results showed that, with increasing RI of liquid, the resonant wavelength in the reflectance spectrum redshifted gradually in the visible light range. There was a very good linear relationship between resonant wavelength and RI in the range of 1.3330 to 1.3546. More importantly, in contrast to the surface plasmon resonance (SPR) sensor, the interferometric sensors showed higher sensitivity to the external RI. In the case of the transverse magnetic mode, the RI sensitivity is up to 320,700.93 a.u./RIU (refractive index unit) by expression of light intensity, which is 9.55 times that of the SPR sensor. As for the transverse electric mode, it achieves 4371.76 nm/RIU by expression of the resonant wavelength, which is increased by a factor of 1.4 in comparison with the SPR sensor. Moreover, the experimental results have favorable repeatability. A TiO₂ nanowire array sensor has also other advantages, such as easy manufacturing, low cost, and in situ determination, etc. To our knowledge, this fact is reported for the first time. It has great potential applications in the field of biological and chemical sensing.

In-fiber Mach-Zehnder interferometer for gas refractive index measurements based on a hollow-core photonic crystal fiber

We describe an in-fiber interferometer based on a gas-filled hollow-core photonic crystal fiber. Expressions for the sensitivity, figure of merit and refractive index resolution are derived, and values are experimentally measured and theoretically validated using mode field calculations. The refractive indices of nine monoatomic and molecular gases are measured with a resolution of δn_s < 10^-6.

A Core-Offset Mach Zehnder Interferometer Based on A Non-Zero Dispersion-Shifted Fiber and Its Torsion Sensing Application

In this paper, an all-fiber Mach-Zehnder interferometer (MZI) based on a non-zero dispersion-shifted fiber (NZ-DSF) is presented. The MZI was implemented by core-offset fusion splicing one section of a NZ-DSF fiber between two pieces of single mode fibers (SMFs). Here, the NZ-DSF core and cladding were used as the arms of the MZI, while the core-offset sections acted as optical fiber couplers. Thus, a MZI interference spectrum with a fringe contrast (FC) of about 20 dB was observed. Moreover, its response spectrum was experimentally characterized to the torsion parameter and a sensitivity of 0.070 nm/° was achieved. Finally, these MZIs can be implemented in a compact size and low cost.

Locally pressed photonic crystal fiber interferometer for multiparameter sensing

A mode interferometer consisting of a short section of photonic crystal fiber (PCF) fusion spliced to a standard single-mode optical fiber with localized perturbations is proposed for multiparameter sensing. In this sensing configuration, the parameter being sensed changes the visibility (an absolute parameter) of the interference pattern and also causes a shift (a relative parameter) to the interference pattern. To achieve this dual effect, a portion of the PCF is squeezed on localized regions with a serrated mechanical piece. In this manner, we introduce attenuation losses and effective refractive index changes to the interfering modes, hence, visibility changes and a shift to the interference pattern. Our device is suitable for monitoring diverse physical parameters, such as weight, lateral force, pressure, load, etc., with the advantage that compensation to temperature or power fluctuations is not required. Moreover, the sensor sensitivity can be adjusted in a simple manner.

Toward a new generation of photonic humidity sensors

This review offers new perspectives on the subject and highlights an area in need of further research. It includes an analysis of current scientific literature mainly covering the last decade and examines the trends in the development of electronic, acoustic and optical-fiber humidity sensors over this period. The major findings indicate that a new generation of sensor technology based on optical fibers is emerging. The current trends suggest that electronic humidity sensors could soon be replaced by sensors that are based on photonic structures. Recent scientific advances are expected to allow dedicated systems to avoid the relatively high price of interrogation modules that is currently a major disadvantage of fiber-based sensors.