Highly sensitive photonic crystal fiber salinity sensor based on Sagnac interferometer

For a sensor, high sensitivity, structural simplicity, and longevity are highly desired for measurement of salinity in seawater. This work proposed an ultrahigh sensitive photonic crystal fiber (PCF) salinity sensor based on the sagnac interferometer (SI). The propagation characteristics of the proposed PCF are analyzed by the finite element method (FEM). The achieved sensitivity reaches up to 37,500 nm/RIU and 7.5 nm/% in the salinity range from 0% to 100%. The maximum resolutions of 2.66 × 10−06 RIU and 1.33 × 10−02% are achieved with high linearity of 0.9924 for 2.20 cm length of the proposed PCF. Owing to such excellent results, this proposed sensor offers the potential to measure the salinity of seawater

High-Sensitivity Salinity Sensor Based on Optical Microfiber Coil Resonator

In recent years, salinity sensing has attracted much attention in potential areas ranging from marine monitoring, marine circulation, marine climate and environment protection in oceanography [1–4]. Generally, traditional methods of salinity measurement have been based on electronic methods (electrochemical) to detect the existence of chlorine ions of the seawater [5,6]. However, this method is affected greatly from the harsh environment, such as high corrosivity, extreme temperature and strong electromagnetic interference and is not used widely in micro scale due to its large size and complex structure. Electrochemical sensors are also prone to cross-sensitivity from and can even be damaged by other species e.g. nitrates (from Agriculture) and Sulphuric compounds (e.g. from dissolved SO2) Therefore, there is a clear need for new sensors with compact size, high stability, good selectivity and electromagnetic immunity

Numerical calculation of temperature sensing in seawater based on microfibre resonator by intensity-variation scheme

A seawater temperature sensing and detection method based on microfibre resonator (MR) by intensity-variation scheme is proposed, which has the advantages of high sensitivity and low detection limit. The dependences of sensitivity on probing wavelength, fibre diametre and ring diametre are studied. Results show that probing wavelength influences the sensitivity by the absorption loss predominantly. Larger absorption loss results in lower sensitivity, which is much different with resonant-wavelength-shift scheme. And sensitivity increases with the increasing ring diametre due to the decreasing bending loss and increasing Q-factor. In addition, there may exist an optimal fibre diametre, with which the sensitivity is maximized. By tuning the parameters of system, sensitivity can be tuned from 0.0784NI/ºC to 13.79 NI/ºC (NI is the abbreviation of normalized intensity). Correspondingly, dynamic range changes from 11.77ºC to 0.08ºC. Additionally, the dependences of detection limit on wavelength, fibre diametre, and ring diametre are also investigated, which are opposite to that of sensitivity. For different temperatures, the dependences of sensitivity and detection limit at some typical temperatures are studied, which shows that high sensitivity and low detection limit are related to high temperature, and the optimal fibre diametres for high sensitivity and low detection limit are the same at different temperatures. The lowest detection limit is estimated to be 10^-7ºC level, which is four orders of magnitude smaller than that of the traditional method. Results shown here are beneficial to find the optimal parameters for the temperature sensors, and offer helpful references for assembling micro-photonics device used in seawater sensing and detection

Combined microfiber knot resonator and focused ion beam-milled Mach-Zehnder interferometer for refractive index measurement

A Mach-Zehnder interferometer was created from a cavity milled in the taper region next to a microfiber knot resonator. A focused ion beam was used to mill the cavity with 47.8 micrometers in length. The microfiber knot resonator was created from an 11 micrometers diameter taper, produced using a filament fusion splicer. After milling the cavity, the microfiber knot resonator spectrum is still visible. The final response of the presented sensor is a microfiber knot resonator spectrum modulated by the Mach-Zehnder interference spectrum. A preliminary result of -8935 +/- 108 nm/RIU was obtained for the refractive index sensitivity of the cavity component in a refractive index range of n = 1.333 to 1.341. Simultaneous measurement of refractive index and temperature using this combined structure is a future goal.André D. Gomes, Ricardo M. Andréa, Stephen C. Warren-Smith, Jan Dellith, Martin Becker, Manfred Rothhardt, and Orlando Frazão

In-line microfiber-assisted Mach-Zehnder interferometer for microfluidic highly sensitive measurement of salinity

We present a microfluidic U-shaped micro-cavity sensor by splicing a segment of microfiber of a few hundred micrometers in length tapered from a single-mode fiber (SMF) between two SMFs with predesigned lateral offset for highly sensitive salinity measurement. The proposed sensing probe serves as an in-line microfiber-assisted Mach-Zehnder interferometer (MAMZI) with an ultra-high refractive index sensitivity of 104 nm/RIU. Three Mach-Zehnder interferometer structures with different cavity lengths of 351.82 ?m, 242.56 ?m and 181.31 ?m are fabricated, by which microfluidic sensing systems are established for in-line measurement of sodium chloride (NaCl) solution. Experimental results indicate that the detection limit of NaCl solution is as low as 4×10-3 wt% and the response time is less than 15 s, which would make the MAMZI-based microfluidic measuring system play an important role in label-free biological and chemical detection applications

Micro-/Nano-Fiber Sensors and Optical Integration Devices

The development of micro/nanofiber sensors and associated integrated systems is a major project spanning photonics, engineering, and materials science, and has become a key academic research trend. During the development of miniature optical sensors, different materials and micro/nanostructures have been reasonably designed and functionalized on the ordinary single-mode optical fibers. The combination of various special optical fibers and new micro/nanomaterials has greatly improved the performance of the sensors. In terms of optical integration, micro/nanofibers play roles in independent and movable optical waveguide devices, and can be conveniently integrated into two-dimensional chips to realize the efficient transmission and information exchange of optical signals based on optical evanescent field coupling technology. In terms of systematic integration, the unique optical transmission mode of optical fiber has shown great potential in the array and networking of multiple sensor units.In this book, more than ten research papers were collected and studied, presenting research on optical micro/nanofiber devices and related integrated systems, covering high-performance optical micro/nanofiber sensors, fine characterization technologies for optical micro/nanostructures, weak signal detection technologies in photonic structures, as well as fiber-assisted highly integrated optical detection systems

Novel Specialty Optical Fibers and Applications

Novel Specialty Optical Fibers and Applications focuses on the latest developments in specialty fiber technology and its applications. The aim of this reprint is to provide an overview of specialty optical fibers in terms of their technological developments and applications. Contributions include:1. Specialty fibers composed of special materials for new functionalities and applications in new spectral windows.2. Hollow-core fiber-based applications.3. Functionalized fibers.4. Structurally engineered fibers.5. Specialty fibers for distributed fiber sensors.6. Specialty fibers for communications