Intensity-Modulated Polymer Optical Fiber-Based Refractive Index Sensor: A Review

Simultaneous measurement of liquid level and R.I. sensor using POF based on twisted structure

In this paper, a dual-parameter liquid level and refractive index (R.I.) sensor is fabricated using three pieces of bare polymer optical fibers (POFs), which can independently and simultaneously sense the liquid level and R.I. The proposed sensor design utilizes the twisted coupling technique, in which two optical fibers are twisted and coupled with macro-bending. The liquid level measurement depends on the coupling loss, where the light is transmitted to emission fiber (EF) and twisted with coupled acceptor fiber (AF). The proposed liquid level sensor can measure depths up to 125 mm with a sensitivity of 8.03 nW/mm. Moreover, R.I. sensing depends on the twisted coupled macro-bending (TCMB) technique, where the EF generates bend loss and the AF couples the loss, where the coupled power varies due to the transformation in R.I. of coupling medium. The R.I. sensor revealing a notable sensitivity of -2663%/RIU and an impressive resolution of 3.754 × 10-4 in the different NaCl-saturated liquids featuring R.I. range extending from 1.333 to 1.361. The experimental findings indicate the sensor exhibits excellent stability and reliability. The sensor's straightforward, comprehensive, and cost-effective design enables its application in chemical, petroleum, and other industries.

Citrate polymer optical fiber for measuring refractive index based on LSPR sensor

Fiber optic localized surface plasmon resonance (LSPR) sensors have become an effective tool in refractive index (RI) detection for biomedical applications because of their high sensitivity. However, using conventional optical fiber has caused limitations in implanting the sensor in the body. This research presents the design and construction of a new type of polymer-based LSPR sensors to address this issue. Also, finite element method (FEM) is used to design the sensor and test it theoretically. The proposed polymer optical fiber (POF) based on citrate is biocompatible, flexible, and degradable, with a rate of 22% and 27 over 12 days. The step RI structure utilizes two polymers for light transmission: poly (octamethylene maleate citrate) (POMC) as the core and poly (octamethylene citrate) (POC) as the cladding. The POF core and cladding diameters and lengths are 700 µm, 1400 µm, and 7 cm, respectively. The coupling efficiency of light to the POF was enhanced using a microsphere fiber optic tip. The obtained results show that the light coupling efficiency increased to 77.8%. Plasma surface treatment was used to immobilize gold nanoparticles (AuNPs) on the tip of the POF, as a LSPR-POF sensor. Adsorption kinetics was measured based on the pseudo-first-order model to determine the efficiency of immobilizing AuNPs, in which the adsorption rate constant (k) was obtained be 8.6 × 10-3 min-1. The RI sensitivity of the sensor in the range from 1.3332 to 1.3604 RIU was obtained as 7778%/RIU, and the sensitivity was enhanced ~ 5 times to the previous RI POF sensors. These results are in good agreement with theory and computer simulation. It promises a highly sensitive and label-free detection biosensor for point-of-care applications such as neurosciences.

Silver-coated hollow fiber surface plasmon resonance sensor for glucose detection with enhanced limit of detection

A fiber-optic surface plasmon resonance (SPR) biosensor based on a silver-coated hollow fiber (HF) structure for glucose detection is presented. The sensor surface was immobilized with 4-mercaptophenylboronic acid (PMBA) acting as a glucose recognition monolayer. Then, gold nanoparticles (AuNPs) modified with 2-aminoethanethiol (2-AET) and PMBA were introduced onto the sensor surface after glucose was captured to enhance the wavelength shift of the SPR phenomenon excited by the light transmitted in the wall of the HF sensor. Instead of the conventional one-step sensitization pretreatment commonly used in the deposition process of silver films for fiber-optic SPR sensors, a sensitization-activation two-step activation method was adopted in the fabrication of the proposed sensor. Experiments for glucose detection were performed on the fabricated sensors in the concentration range of 1 nM-1 mM. Results showed that the sensor fabricated by the two-step activation method has a much larger shift of resonance wavelength than the sensor fabricated using the one-step sensitization method. The resonance wavelength shift was found to be linear to the logarithm of the concentration in the range of 1 nM-1 mM. The sensor achieved a limit of detection (LOD) of as low as 1 nM, which is at least an order of magnitude lower than that of other fiber-optic sensors for glucose detection reported previously. The presented HF glucose sensor has the potential for biosensing applications and provides a large reference value in the study of optical fiber SPR sensors for biosensing.

Sensitivity Analysis of Intensity-Modulated Plastic Optical Fiber Sensors for Effective Aging Detection in Rapeseed Transformer Oil

As the focus tilts toward online detection methodologies for transformer oil aging, bypassing challenges associated with traditional offline methods, such as sample contamination and misinterpretation, fiber optic sensors are gaining traction due to their compact nature, cost-effectiveness, and resilience to electromagnetic disturbances that are typical in high-voltage environments. This study delves into the sensitivity analysis of intensity-modulated plastic optical fiber sensors. The investigation encompasses key determinants such as the influence of optical source wavelengths, noise response dynamics, ramifications of varying sensing lengths, and repeatability assessments. Our findings highlight that elongating sensing length detrimentally affects both linearity response and repeatability, largely attributed to a diminished resistance to noise. Additionally, the choice of the optical source wavelength proved to be a critical variable in assessing sensor sensitivity.

Gold film effect on temperature compensation of a POF sensor with different structures

In this paper, temperature compensation of plastic optical fiber (POF) is studied and gold absorbability is utilized. Gold film is modified on the surface of POF by magnetron sputtering. The temperature output characteristics of different structures such as ordinary (POF-N), side-polished (POF-SP), U-shaped (POF-U), and narrow groove structure (POF-NGS) are tested, and the effects of gold film thickness, polishing area, and sputtering sequence on the temperature output characteristics are also investigated. The power change of the sensor at different temperatures is recorded. The experimental results show that when the temperature is between 25°C and 50°C and the sputtering gold film thickness is 50 nm, the temperature stabilities of POF-N, POF-U, POF-SP, and POF-NGS are 1.02 µW/°C, 0.77 µW/°C, 0.18 µW/°C, and 0.35 µW/°C, respectively. The compensation effect is enhanced as the gold film thickness increases. When the thickness is 100 nm, the temperature stability of POF-NGS is 0.06 µW/°C. The proposed temperature compensation method is competitive and straightforward.

Multifunctional Integration of Optical Fibers and Nanomaterials for Aircraft Systems

Smart sensing for aeronautical applications is a multidisciplinary process that involves the development of various sensor elements and advancements in the nanomaterials field. The expansion of research has fueled the development of commercial and military aircrafts in the aeronautical field. Optical technology is one of the supporting pillars for this, as well as the fact that the unique high-tech qualities of aircrafts align with sustainability criteria. In this study, a multidisciplinary investigation of airplane monitoring systems employing optical technologies based on optical fiber and nanomaterials that are incorporated into essential systems is presented. This manuscript reports the multifunctional integration of optical fibers and nanomaterials for aircraft sector discussing topics, such as airframe monitoring, flight environment sensing (from temperature and humidity to pressure sensing), sensors for navigation (such as gyroscopes and displacement or position sensors), pilot vital health monitoring, and novel nanomaterials for aerospace applications. The primary objective of this review is to provide researchers with direction and motivation to design and fabricate the future of the aeronautical industry, based on the actual state of the art of such vital technology, thereby aiding their future research.

Side-Polish Plastic Optical Fiber Based SPR Sensor for Refractive Index and Liquid-Level Sensing

In this work, a simple side-polish plastic optical fiber (POF)-based surface plasmon resonance (SPR) sensor is proposed and demonstrated for simultaneous measurement of refractive index (RI) and liquid level. The effects of side-polish depths on the sensing performance were studied. The experimental results show that the SPR peak wavelength will be changed as the RI changes, and the SPR peak intensity will be changed with the liquid level variation. By monitoring the changes in peak wavelength and intensity, the RI and liquid level can be detected simultaneously. Experimental results show that an RI sensitivity of 2008.58 nm/RIU can be reached at an RI of 1.39. This sensor has the advantages of simple structure and low cost, which has a good prospect in the field of biochemical sensing.

Highly sensitive refractive index sensor based on plastic optical fiber balloon structure

A novel, to the best of our knowledge, design of plastic optical fiber (POF) balloon-based refractive index sensor for the detection of different concentrations of sodium chloride is proposed and experimentally investigated. The experimental characterization supports the finding that the transmission loss is sensitive to the external environment's targeted refractive index changes of the analyte. The proposed sensor achieves a maximum intensity-based sensitivity of 3105 RIU^-1, resolution of 3.22 ×10^-7, and the figure of merit (FOM) is 326 RIU^-1 from 2 to 2.5 Mol/L of the analyte with the chosen refractive index changes at 680 nm for a diameter D = 0.1 cm of the POF balloon structure. Furthermore, a high linear performance of 0.9896 is achieved with good robustness against the fabrication imperfection. The ultra-sensitiveness to the refractive index with a simple demonstration of the POF balloon-based structure has potential applications in the chemical, biological, and food safety sensing fields.

In Situ Synthesis of Gold Nanoparticles in Layer-by-Layer Polymeric Coatings for the Fabrication of Optical Fiber Sensors

A new method is proposed to tune the interferometric response of wavelength-based optical fiber sensors. Using the nanoparticle in situ synthesis (ISS) technique, it is possible to synthesize gold nanoparticles (AuNPs) within a pre-existing polymeric thin film deposited at the end-face of an optical fiber. This post-process technique allows us to adjust the optical response of the device. The effect of the progressive synthesis of AuNPs upon polymeric film contributed to a remarkable optical contrast enhancement and a very high tuning capability of the reflection spectra in the visible and near-infrared region. The spectral response of the sensor to relative humidity (RH) variations was studied as a proof of concept. These results suggest that the ISS technique can be a useful tool for fiber optic sensor manufacturing.