Banshi D. Gupta

Fiber-Optic Sensors Based on Surface Plasmon Resonance: A Comprehensive Review

Since the introduction of optical fiber technology in the field of sensor based on the technique of surface plasmon resonance (SPR), fiber-optic SPR sensors have witnessed a lot of advancements. This paper reports on the past, present, and future scope of fiber-optic SPR sensors in the field of sensing of different chemical, physical, and biochemical parameters. A detailed mechanism of the SPR technique for sensing purposes has been discussed. Different new techniques and models in this area that have been introduced are discussed in quite a detail. We have tried to put the different advancements in the order of their chronological evolution. The content of the review article may be of great importance for the research community who are to take the field of fiber-optic SPR sensors as its research endeavors.

Surface Plasmon Resonance-Based Fiber Optic Sensors: Principle, Probe Designs, and Some Applications

Surface plasmon resonance technique in collaboration with optical fiber technology has brought tremendous advancements in sensing of various physical, chemical, and biochemical parameters. In this review article, we present the principle of SPR technique for sensing and various designs of the fiber optic SPR probe reported for the enhancement of the sensitivity of the sensor. In addition, we present few examples of the surface plasmon resonance- (SPR-) based fiber optic sensors. The present review may provide researchers valuable information regarding fiber optic SPR sensors and encourage them to take this area for further research and development.

On the performance of different bimetallic combinations in surface plasmon resonance based fiber optic sensors

In the present work, we have investigated the capability of different bimetallic combinations to be used in a fiber optic sensor based on the technique of surface plasmon resonance. The metals considered for the present analysis are silver, gold, copper, and aluminum. The performance of the sensor with different bimetallic combinations is evaluated and compared numerically. The performance is analyzed in terms of three parameters: sensitivity, signal-to-noise ratio (SNR), and operating range. On the basis of the comparison and some logical criteria, the best possible bimetallic combination along with requisite thickness distribution is predicted. The bimetallic combination is capable of simultaneously providing the larger values of sensitivity, SNR, and operating range, which is not possible with any single metallic layer.

Fibre-optic evanescent field absorption sensor based on a U-shaped probe

A fibre-optic evanescent field absorption sensor based on a U-shaped sensing probe is described. The influences of fibre core diameter, bending radius of the probe and the refractive index of the fluid on the sensitivity of the sensor are evaluated experimentally. The results are compared with the theoretical results obtained using geometrical optics and based on two-dimensional treatment. A good qualitative agreement is found between them.

Fibre-optic sensor based on surface plasmon resonance with Ag–Au alloy nanoparticle films

The design of a fibre optic surface plasmon resonance (SPR) sensor based on silver–gold alloy nanoparticle film is studied. The performance of the proposed sensor is theoretically analysed in terms of its signal-to-noise ratio (SNR) and sensitivity under different conditions related to the metal layer with silver and gold nanoparticles embedded together in layers to form a single alloy film. The effects of related parameters such as alloy composition ratio, metal nanoparticle size, and alloy film thickness are studied and the physical reasoning behind the results is given. A logical comparison is carried out between a previously proposed metal-host based fibre optic SPR sensor and the present one. The alloy based fibre optic SPR sensor is shown to have better performance than the metal-host based fibre optic SPR sensor.

Surface-plasmon-resonance-based fiber-optic refractive index sensor: sensitivity enhancement

We have experimentally studied the surface plasmon resonance (SPR)-based fiber-optic refractive index sensor incorporating a high-index dielectric layer using the wavelength interrogation method. Silver and gold have been used as SPR active metals followed by a high-index dielectric layer of silicon. Experimental results predict a redshift in the resonance wavelength with the increase in the refractive index of the sensing layer for a given thickness of the silicon layer. Further, as the thickness of the silicon layer increases, the sensitivity of the sensor increases. The upper limit of the silicon film thickness for the enhancement of the sensitivity has been found to be around 10 nm. The experimental results obtained on sensitivity match qualitatively with the theoretical results obtained using the N-layer model and the ray approach. The increase in sensitivity is due to the increase in the electric field intensity at the silicon-sensing-region interface. In addition to an increase in sensitivity, the silicon layer can be used to tune the resonance wavelength and can protect the metal layer from oxidation and hence can improve the durability of the probe.

Fiber optic evanescent field absorption sensor: Effect of fiber parameters and geometry of the probe

A comparative experimental study of the fiber-optic evanescent field absorption sensor based on straight and U-shaped probes is presented. The effects of numerical aperture and the core radius of the fiber on the sensitivity of the sensor are experimentally investigated. Increase in the numerical aperture of the fiber increases the sensitivity of the sensor in the case of both the probes. The effect of core radius on the sensitivity depends on the bending radius of the probe. In the case of straight probe (i.e. infinite bending radius) the fiber with smaller core radius has high sensitivity while in the case of U-shaped probe with 0.17 cm bending radius, the fiber with larger core radius has high sensitivity. Thus, which fiber (with small or large core radius) has maximum sensitivity depends on the bending radius of the probe. For a given fiber, decrease in the bending radius increases the sensitivity of the U-shaped probe. An inverse power law relationship between the bending radius and the evanescent absorbance and hence the sensitivity is established.

Detection of heavy metal ions in contaminated water by surface plasmon resonance based optical fibre sensor using conducting polymer and chitosan

Optical fibre surface plasmon resonance (SPR) based sensor for the detection of heavy metal ions in the drinking water is designed. Silver (Ag) metal and indium tin oxide (ITO) are used for the fabrication of the SPR probe which is further modified with the coating of pyrrole and chitosan composite. The sensor works on the wavelength interrogation technique and is capable of detecting trace amounts of Cd(2+), Pb(2+), and Hg(2+) heavy metal ions in contaminated water. Four types of sensing probes are fabricated and characterised for heavy metal ions out of these pyrrole/chitosan/ITO/Ag coated probe is found to be highly sensitive among all other probes. Further, the cadmium ions bind strongly to the sensing surface than other ions and due to this the sensor is highly sensitive for Cd(2+) ions. The sensors performance is best for the low concentrations of heavy metal ions and its sensitivity decreases with the increasing concentration of heavy metal ions.

Fiber optic evanescent field absorption sensor: effect of launching condition and the geometry of the sensing region

Fiber optic evanescent wave absorption sensors based on four different designs are described. The launching condition and the geometry of the sensing region are found to be the main parameters that can influence the sensitivity of the sensor. High sensitivity is achieved by launching the selected rays into the fiber having tapered sensing regions. The experimental results obtained are qualitatively explained using a simple model based on meridional rays.

A long-range fiber optic pH sensor prepared by dye doped sol-gel immobilization technique

A long-range fiber optic pH sensor based on evanescent wave absorption is presented. The probe is prepared by immobilizing a mixture of three pH-sensitive dyes (cresol red, bromophenol blue and chlorophenol red) on the surface of the fiber core using sol-gel technology. The sensor has a linear and reproducible pH response in the pH range from 4.5 to 13.0. Due to its long dynamic pH range the sensor is expected to find wide applications.