High-quality optical fibers can be produced now at a low cost and large quantity, and this has further promoted the development of fiber optic (chemical) sensors. After over 30 years of innovation, fiber optic sensing technology has become mature because of acceptable costs, compact instrumentation, high accuracy and the capability of performing measurements at inaccessible sites, over large distances, in strong (electro)magnetic fields and in harsh environment. The technology is still proceeding quickly in terms of innovation, and respective applications have been found in highly diversified fields. This review covers work published in the time period between October 2015 and October 2019. It is written in continuation of previous reviews.

Fiber-Optic Chemical Sensors and Biosensors (2015-2019).

Recent development of fiber-optic chemical sensors and biosensors: Mechanisms, materials, micro/nano-fabrications and applications

Optical Fiber Optofluidic Bio-Chemical Sensors: A Review

We propose a D-shaped photonic crystal fiber (PCF) refractive index sensor with ultrahigh sensitivity and a wide detection range. The gold layer is deposited on the polished surface, avoiding filling or coating inside the air holes of the PCF. The influences of the gold layer thickness and the diameter of the larger air holes are investigated. The sensing characteristics of the proposed sensor are analyzed by the finite element method. The maximum sensitivity can reach 31,000  nm/RIU, and the refractive index detection range is from 1.32 to 1.40. Our proposed PCF has excellent sensing characteristics and is competitive in sensing devices.

Ultrahigh sensitivity refractive index sensor of a D-shaped PCF based on surface plasmon resonance.

The mesmerizing properties of nanomaterials and the features offered by optical fibers can be combined to result in an attractive new platform for chemical sensing. This review (with 230 refs.) summarizes the progress made in the past five years in the field of fiber-optic sensors: The first group comprises metals and metal oxides and their composites, and the second group comprises graphene, graphene oxides and CNTs, and its composites. By combining these nanocomposites with various optical fiber geometries, numerous sensors have been realized. Following an introduction, first section summarizes fiber-optic configuration for chemical sensing (including Fabry-Perot and Mach-Zehnder interferometry, surface plasmon resonance, and optical fiber gratings of the FBG and LPG type). The second section covers typical nanomaterials used in such sensors, with a first subsection on metals, metal oxides, their composites and nanostructured modifications, and a second subsection on graphenes, graphene oxides, carbon nanotubes, and their derivatives. Section 3 summarizes sensors (i) for various gaseous species (NH3, H2, CH4, H2S, CO2, NO2, O2), (ii) for volatile organic compounds (such as ethanol, methanol, acetone, toluene, and formaldehyde), and (iii) for heavy metal ions (such as Hg2+, Pb2+, Mg2+, Cd2+, Ni2+, and Mn2+). The merits and limitations of these nanomaterials and numerous examples for nanomaterial-based sensors are discussed and presented in the form of tables. A concluding section addresses technological challenges and future trends.

A review on nanomaterial-modified optical fiber sensors for gases, vapors and ions

Novel Reflection-type Optical Fiber Methane Sensor Based on a No-core Fiber Structure

The invention discloses a tapered multimode interference-based high-sensitivity optical fiber methane sensing device. The device comprises a broadband light source, a STMS-structure tapered multimode porous sensitive film-coated optical fiber sensing device, a testing air chamber, a switch valve, a mass flow controller, a spectrum analyzer and a computer. The STMS-structure optical fiber sensing device is prepared by single-mode optical fiber-multimode optical fiber-single-mode optical fiber melting connection and then multimode optical fiber tapering. The outer surface of the tapered multimode optical fiber is pre-treated by a silane coupling agent. The sensitive film is a cage molecule A-containing alpha-hydro-omega-hydroxy-polydimethylsiloxane porous methane-sensitive film. When methane gas to be detected reacts with the porous methane-sensitive film, a sensitive film refractive index is fast changed so that sensor interference spectrum characteristic wavelength lambda c is moved. Through analysis of interference spectrum characteristic wavelength movement amount delta lambda c before and after contact between the sensor and methane gas, a concentration of methane to be detected is obtained. The device has the characteristics of high sensitivity, fast response speed, good selectivity and good stability.

Tapered multimode interference-based high-sensitivity optical fiber methane sensing device

The invention discloses a photonic crystal optical fiber methane sensing device based on modular interference. The device is composed of a broadband light source, an optical circulator, a photonic crystal optical fiber methane sensor cladding an air hole coated polymer sensitive film, a testing air chamber, a switching valve, a quality flow controller, a spectrum analyzer and a computer, wherein the optical fiber methane sensor consists of a single mode fiber, a photonic crystal optical fiber and a welding area of the two fibers; the adopted photonic crystal optical fiber refers to an endless single mode solid core photonic crystal optical fiber; the polymer sensitive film refers to a polycarbonate resin methane sensitive film containing a cage molecule E-(OC2H5)6, and the inner wall of the cladding air hole of the photonic crystal optical fiber is coated with the film by virtue of an air pressure driving device; when the to-be-tested methane gas acts with the sensitive film on the inner wall of the cladding air hole of the photonic crystal optical fiber, the refractive index of the sensitive film changes, the reflection interference spectrum characteristic wavelength of the sensor is moved, the average movement amount shown in the description of the reflection interference spectrum characteristic wavelength before and after contacting the sensor with the methane gas is analyzed, so that the concentration of the to-be-tested methane gas can be obtained. The device disclosed by the invention has the characteristics of high sensitivity, high stability, high selectivity and the like.

Photonic crystal optical fiber methane sensing device based on modular interference

The invention discloses a detection device for multiple parameters of oil and gas concentration. The detection device comprises a broadband light source, a methane sensor, an ethane sensor, a propane sensor, a humidity sensor, a temperature sensor, optical switches, a testing gas chamber, a computer, a mass flow controller and the like, wherein the front ends of all the sensors are connected with the broadband light source through the optical switch I; the rear ends of all the sensors are connected with a spectrum analyzer through the optical switch II; all the sensors are positioned in the testing gas chamber; sensitive membranes of the tilted long-period fiber grating methane, ethane and propane sensors are low refractive index ultraviolet-curing fluorosilicone sensitive membranes containing cage molecules (a cage molecule A, a cage molecule E-(OC3H7)6 or a cage molecule M-(OC3H7)6) and graphene; when methane, ethane and propane to be detected interact with the corresponding sensitive membranes, refractive indexes of the sensitive membranes are changed, and transmission spectra of the methane sensor, the ethane sensor and the propane sensor are enabled to drift; by means of the drift amount of the transmission spectra in the spectrum analyzer, the concentrations of the methane, the ethane and the propane can be measured.

Detection device for multiple parameters of oil and gas concentration

A ammonia sensor depositing with a polyelectrolyte thin film composed of poly(acrylic acid) (PAA) and poly(allyamine hydrochloride) (PAH) via the layer-by-layer (LbL) self-assembly technique, is demonstrated with a thin-core fiber modal interferometer (TCFMI).

Thin-core fiber modal interferometer for ammonia sensing

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