Optical Fiber Refractive Index Sensor Research Articles

Ultra-Long Range Refractive Index Fiber Sensor

The dynamic range of optical fiber refractive index sensors is mainly determined by the refractive index (RI) of the sensor surface in contact with the sample under test. In case of the refractive index sensor based on the hybrid fiber Fabry–Perot interferometer (HFFPI), the largest measurable refractive index value is equal to that of the fiber core. In this work, we demonstrate that it is possible to extend the refractive index dynamic range of a HFFPI by simply adjusting the optical path length (OPL) of the air and solid cavity to be equal or differ by just a small amount. Two isometric versions of the HFFPI (i-HFFPI) with a total length of 100 and 172 μm, where the OPL of the air and solid cavity are very similar, were fabricated and tested. The interferometers were immersed in different samples with a refractive index ranging from 1.000 to 1.733. The response of the interferometers was analyzed in the Fourier domain, and it was possible to establish a one-to-one relationship between the refractive index of the liquid sample and the amplitude of one of the peaks in the Fourier spectra. The amplitude of this peak experienced a linear increment when the RI of the surrounding medium was increased. Tracking the amplitude changes of a Fourier spectrum peak is straightforward which simplifies the online monitoring of the sensor. These features make this compact refractive index fiber sensor very appealing for biosensing applications.

A study of highly sensitive D-shaped optical fiber surface plasmon resonance based refractive index sensor using grating structures of Ag-TiO2 and Ag-SnO2

In this study, we propose a design and simulation of a highly sensitive surface plasmon resonance (SPR) based single-mode D-shaped optical fiber refractive index sensor in the near-infrared (NIR) region. It consists grating structure of silver coated with titanium dioxide (TiO2) and Tin dioxide (SnO2) layer on the core-cladding interface. With the help of the finite element method (FEM), the proposed optical fiber sensors are optimized with various geometrical parameters. Proposed optimized structures are investigated and various performance parameters are calculated. It is found that performance parameters enhance with TiO2/SnO2 coated on Ag grating structure at a particular thickness of TiO2/SnO2. Due to this more generations of surface plasmons take place on metal-metal oxide structures. We find the maximum sensitivity of 15.31 μm / RIU and 9.81 μm / RIU for Ag-TiO2 and Ag-SnO2 grating structure respectively which shows a better result in comparison to the other reported work. So proposed structure may have great potential to enhance the sensing ability of optical fiber-based sensors as compared to the other conventional SPR based optical fiber sensors.

Optical fiber refractive index sensor based on the double cladding fiber

An optical fiber sensing structure based on double-cladding fiber (DCF) is described. The core and outer cladding of the DCF both supports more than one guided mode and the cladding mode resonance as well as modal interference in the fiber. Due to the W-type refractive index (RI) distribution, the outer cladding generates a stronger evanescent field to obtain higher sensitivity. In the transmitted spectrum, all three dips shift to the longer wavelength with the external RI changing from 1.33 to 1.43, and the high sensitivities are 595, 741, and 686 nm/RIU, respectively.

Differential Refractive Index Sensor Based on Coupled Plasmon Waveguide Resonance in the C-Band.

We proposed a differential fiber-optic refractive index sensor based on coupled plasmon waveguide resonance (CPWR) in the C-band. The sensor head is a BK7 prism coated with ITO/Au/ITO/TiO2 film. CPWR is excited on the film by the S-polarized components of an incident light. The narrow absorption peak of CPWR makes it possible to realize dual-wavelength differential intensity (DI) interrogation by using only one incident point. To implement DI interrogation, we used a DWDM component to sample the lights with central wavelengths of 1529.55 and 1561.42 nm from the lights reflected back by the sensor head. The intensities of the dual-wavelength lights varied oppositely within the measurement range of refractive index, thus, a steep slope was produced as the refractive index of the sample increased. The experimental results show that the sensitivity is 32.15/RIUs within the measurement range from 1.3584 to 1.3689 and the resolution reaches 9.3 × 10−6 RIUs. Benefiting from the single incident point scheme, the proposed sensor would be easier to calibrate in bio-chemical sensing applications. Moreover, this sensing method is expected to be applied to retro-reflecting SPR sensors with tapered fiber tip to achieve better resolution than wavelength interrogation.

Highly sensitive refractive index sensing based on PCF modal interferometer

A high sensitive optical fiber refractive index (RI) sensor based on Mach-Zehnder interferometer (MZI) is proposed. The sensor consists of single mode fiber-multimode fiber-photonic crystal fiber-single mode fiber (SMPS) structure using fusion technology. The experimental results have shown that the RI sensitivity of the SMPS structure is as high as 342.78 nm/RIU in the range of 1.3330–1.3775. Meanwhile, the effects of different length of PCF on the RI are also investigated. It was found that the shorter the length of PCF, the higher the sensitivity. In addition, a temperature sensitivity of 16.37 pm/℃ for the sensor is achieved. The sensor has advantages of high fringe visibility over 20 dB and simple fabrication, which has displayed great potential in the field of RI measurement.

GeO2 Doped Optical Fiber Plasmonic Sensor for Refractive Index Detection

In this article, a D-shaped optical fiber refractive index (RI) sensor based on surface plasmon resonance effect is demonstrated. The gold film is placed at the flat portion of the optical fiber along with the sensing analytes of the different RIs to excite the plasmonic interactions. Sensing properties are investigated by using the finite element method. The maximum sensitivity of the proposed sensor is achieved as high as 20863.20 nm/RIU with the maximum resolution of 4.79 × 10−6 RIU and figure of merit of 308.38 RIU−1 for an analyte with RI 1.43 by optimizing the different parameters of the sensor with maximum phase matching between the core mode and surface plasmon mode. The high sensitivity of the sensor offers a promising approach for the detection of unknown RI analyte in chemical and biological fields in the near-infrared region.

Highly sensitive surface plasmon resonance sensor using perforated optical fiber for biomedical applications

In this paper, a novel mechanism for design of optical fiber refractive index sensors based on surface plasmon resonance (SPR) is suggested. In the proposed method, the internal part of the fiber core is removed to guide the incident light closer to the clad-core interface. Thereafter, the clad is removed and a thin film of gold is coated on the outer part of the core. In the proposed structure, the light beam is guided between the inner and outer parts of the core, where surface plasmons (SPs) are excited. As a result, the absorption reaches to a maximum at SPR wavelengths. The proposed structure is numerically analyzed using finite difference time domain (FDTD) method. The absorption values at the transmitted power spectra correspond to the dielectric constants of the analyte which surrounds the metal. The refractive indices of bio-materials in the range of 1.3 and 1.41 can be measured by the proposed sensor. According to the simulation results, the proposed biosensor has a maximum sensitivity of about 10570 nm/RIU and its average figure of merit is equal to 97.88. The simulation results confirm that the presented structure can be used for bio-sensing applications.

Characterization study of Optical Fiber Refractive Index Sensor Based on Fabry-Perot Interferometer

In this work, an optical fiber refractive index sensor based on the Fabry-Perot interferometer technique is submitted. Single-mode fibers with different diameters (125, 60, and 50) μm were used. The chemical etching technique is used to reduce the fiber diameters. The sensor heads were immersed into liquids of different refractive indices. Two types of liquids were tested, salty and sugary liquids with different refractive indices. From the obtained results all the sensors have a high linearity and good wavelength and intensity sensitivity. For all tested sensors, the wavelength sensitivity was higher for sensors immersed in salty liquids. The sensitivity is 34338 pm/RIU for sensors with a diameter of 50 μm. The response of changing the intensity is also observed the higher intensity sensitivity is 1116.859 μW/RIU for sensors with a diameter of 125 μm immersed into sugary liquids.

Novel Intensity-demodulated Fiber-optic Refractive Index Sensor Based on Splicing Point Tapered Fiber

Novel Intensity-demodulated Fiber-optic Refractive Index Sensor Based on Splicing Point Tapered Fiber

Hollow-core fiber refractive index sensor with high sensitivity and large dynamic range based on a multiple mode transmission mechanism.

To balance the tradeoff between the high sensitivity and large dynamic range, a fiber optic refractive index sensor based on the anti-resonant reflecting optical waveguide (ARROW) and mode interference has been proposed and experimentally demonstrated. A double-layered ARROW was formed in a hollow core fiber, and a mode interference was also generated in the fiber skeleton using offset splicing. The proposed fiber optic refractive index sensor possesses both high sensitivity and large dynamic range due to the different refractive index sensitivities of the ARROW and mode interference. The experimental results show that a high refractive index sensitivity of 19014.4 nm/RIU for mode interference and a large dynamic range from 0.04 RIU for ARROW can be achieved simultaneously. The proposed fiber optic refractive index sensor can be used in chemical and biological applications.

Investigations on the Highly Sensitive Metal-Coated Broad Range D-Shaped Optical Fiber Refractive Index Sensor

Investigations on the Highly Sensitive Metal-Coated Broad Range D-Shaped Optical Fiber Refractive Index Sensor

Tip optical fiber refractive index sensor based on a thin copper film

We report a refractive index tip fiber optic sensor based on a modal interferometer coated with a thin copper film. This device can be used for solute concentration in aqueous mixture measurement. The copper film increases the device reflectivity and, as a result, increases the multimodal interference pattern visibility. To validate the sensor device, different water-glycerol weight concentrations were used in the range from 0 to 45 Glycerol %. The recorded spectral responses show a redshifting, and a sensitivity of 19 pm / (Glycerol % by weight) from 0 to 18 % and 4.7 pm / (Glycerol % by weight) from 18 to 45 % was achieved. Besides, using a phase analysis we calculated a sensitivity of -15 rad/RIU.

Manifestation of a highly sensitive evanescent wave absorption-based refractive index sensor realized by radiating with an optical Airy beam

In this research, a theoretical perception on the notion of an ultra-high sensitive evanescent wave-based fiber-optic refractive index sensor has been proposed by shining an optical Airy beam. The sensing configuration consists of a multimode fiber which is decladded from the middle to aptly sculpt the evanescent wave. In presence of the Airy beam, effectual coupling of high-order modes within the sensing structure has been affirmed by using the classical wave-optic model. To corroborate our theoretical study, an Eigenmode expansion solver (EME) propagation analysis was conducted in commercially offered Mode solution software (Lumerical Inc.) to investigate the transmission characteristics of Airy beam within the waveguide structure. Compared with conventional Gaussian beam-based sensor, the proposed refractive index sensor renders a maximum 19.15 fold superior sensitivity of 992.39 dB/RIU with an admirable sensing resolution of ∼1.00 × 10−5 RIU. Thus, this nascent-class of beam called Airy beam manifests a new degree of freedom which demonstrates the viability of the proposed scheme for the usage of chemical and biological sensing.

Simultaneous Measurement of Temperature and Refractive Index Using High Temperature Resistant Pure Quartz Grating Based on Femtosecond Laser and HF Etching.

The optical fiber temperature and refractive index sensor combined with the hollow needle structure for medical treatment can promote the standardization of traditional acupuncture techniques and improve the accuracy of body fluid analysis. A double-parameter sensor based on fiber Bragg grating (FBG) is developed in this paper. The sensor materials are selected through X-ray diffraction (XRD) analysis, and the sensor sensing principle is theoretically analyzed and simulated. Through femtosecond laser writing pure silica fiber, a high temperature resistant wavelength type FBG temperature sensor is obtained, and the FBG is corroded by hydrofluoric acid (HF) to realize a high-sensitivity intensity-type refractive index sensor. Because the light has dual characteristics of energy and wavelength, the sensor can realize simultaneous dual-parameter sensing. The light from the lead-in optical fiber is transmitted to the sensor and affected by temperature and refractive-index; then, the reflection peak is reflected back to the lead-out fiber by the FBG. The high temperature response and the refractive index response of the sensor were measured in the laboratory, and the high temperature characteristics of the sensor were verified in the accredited institute. It is demonstrated that the proposed sensor can achieve temperature sensing up to 1150 °C with the sensitivity of 0.0134 nm/°C, and refractive sensing over a refractive range of 1.333 to 1.4027 with the sensitivity of −49.044 dBm/RIU. The sensor features the advantages of two-parameter measurement, compact structure, and wide temperature range, and it exhibits great potential in acupuncture treatment.

Surface plasmon based fiber optic refractive index sensor

This paper has proposed a surface plasmon resonance-based photonic crystal fiber (PCF) sensor to detect even a small change in refractive index (RI) values of analytes. The impact on sensor performance by Bezier polygon core structure of the PCF and gold coating in an air hole have been carried out. The sensor resonance wavelength and the respective confinement loss are analyzed for various Bezier polygon parameters and for various gold coating thicknesses. Also, a comparison between gold filling and gold coating in an air hole of PCF have been undertaken to show the superiority of the gold coating in sensor performance. The promising sensor performance has been noted down above the analyte RI of about 1.3 with an upright sensitivity of about 7000 nm/RIU. This type of sensor is of great interest in medical and industrial applications.

Создание и определение чувствительности волоконно-оптического рефрактометра на основе поверхностного плазмонного резонанса

A fiber-optic refractive index sensor using the phenomenon of surface plasmon resonance has been developed. A 1 nm layer of chromium and a 50 nm gold film were applied to a section of a standard multimode optical fiber with a partially protected shell. The transmission spectra were measured as a function of the refractive index of the external medium into which the sensor was immersed. When the refractive index of the external medium changed, the minimum in the transmission spectrum caused by the excitation of the surface plasmon-polariton at the boundary between the gold film and the analyte shifted. The sensor sensitivity was 1400 nm/RU.

Fabrication and performance evaluation of reflectorless refractive index fiber optic sensors using etched enhanced backscattering fibers

We propose and evaluate a technique for the fabrication and interrogation of fiber-optic refractive index (RI) sensors based on etched MgO-based nanoparticle doped fibers. The discussed method does not require to inscribe a reflective element into the fiber. Instead, light backscattered by the fiber can give sufficient information that is necessary for detection, by performing the cross-correlation of Rayleigh scatter signatures in the etched zones. The performance of the sensor is monitored using distributed sensing, which allows to interrogate several points along the length of the fiber. The sensitivities of several etched fibers are compared. The largest sensitivity that has been achieved is 45.95 nm/RIU (RI units), with the possibility of implementing temperature compensation.

In-Situ Monitoring of Solidification Process of PVA Solution by Fiber Optic Sensor Technique

In this research, we monitored the solidification process of PVA solution using a fiber optic refractive index sensor. During the monitoring process in this paper, two Fabry-Perot cavities were used to monitor the temperature and the refractive index of the PVA sample. The advantage of this method is that the related refractive index change is obvious, and the status of materials can be directly observed during the testing process. Furthermore, this method can be more cost-effective compared with its heat flow-based counterpart. Differential scanning calorimetry (DSC) tests were performed with the same material and the heating rate. Compared with the result given by DSC, the detected temperature range when the phase of PVA solution changes is much narrower. The method suggested in this paper is potentially useful to monitor the solidification process of transparent materials in an easier and cost-effective way.

Lossy mode resonance-based highly sensitive fiber optic refractive index sensor using the bilayer of FTO/HfO2 for operation in the visible region

A lossy mode resonance (LMR) based fiber optic refractive index (RI) sensor utilizing a layer of fluorine-doped tin oxide (FTO) over the unclad core of the fiber is theoretically analyzed. To enhance its sensitivity, the thickness of the FTO layer is optimized. For further sensitivity enhancement, an over-layer of two different materials, T i O 2 and H f O 2 , is used. The sensitivity of F T O / T i O 2 and F T O / H f O 2 bilayer based LMR sensors increases with the increase in the thickness of the over-layer for a fixed thickness of the bilayer. Further, the sensitivity of the sensor utilizing the F T O / H f O 2 bilayer is found to be more than the sensitivity of the F T O / T i O 2 bilayer sensor. To keep the operating spectral range of the sensor in the visible region, the total thickness of the bilayer is adjusted. It is found that a total bilayer thickness of 30 nm with 90% thickness of H f O 2 gives the maximum sensitivity of 4400 nm/RIU for 1.33 RI of the sensing medium, which is more than three times the sensitivity of the FTO coated LMR sensor. The sensitivity of the proposed LMR sensor utilizing the F T O / H f O 2 bilayer is compared with the other LMR sensors reported in the literature, and it is found that the proposed sensor possesses the highest sensitivity. The other advantage of the proposed sensor is that it works in the visible region, which reduces the cost of the sensor.

Optical fiber refractive index sensor based on SMF-TCF-NCF-SMF interference structure

A novel optical fiber refractive index (RI) and strain sensor based on the combination of single-mode fiber (SMF), thin-core fiber (TCF), and no-core fiber (NCF) was proposed. Due to the inter-mode interference caused by the mode mismatch, the sensor is sensitive to the RI of the environment but insensitive to temperature. The experimental results show that in the RI range of 1.3333–1.3794, the sensitivity of dip A (1543 nm) and dip B (1565 nm) are 101.9446 nm/RIU and 109.9009 nm/RIU, respectively. In the temperature range of 15–85 ℃, the maximum wavelength shifts are only -3.5 pm/℃ and -4.9 pm/℃ respecitvely for dip A and dip B, indicating that the sensor can eliminate the cross-sensitivity of temperature to the RI. The sensor was used to detect alcohol, sucrose, NaCl and glycerin solution with the same RI and there is no obvious dip shift of the interference spectra. This sensor has the advantages of high RI sensitivities, strong anti-temperature interference ability, compact structure and has the potential application in the health and security monitoring.