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.
We
theoretically propose a surface-plasmon-based fiber optic biosensor
in metal/graphene/MoS2 configuration with molybdenum disulfide
(MoS2) as a bio recognition layer. The proposed configuration
works in the visible region of the electromagnetic spectrum with a
very high sensitivity. A comparative theoretical study of the sensors
with different metallic layers of gold (Au), copper (Cu), and aluminum
(Al) has been performed. The sensor has been found to be the most
sensitive in both Cu/graphene/MoS2 and Al/graphene/MoS2 configurations with sensitivity of 6.2 μm/RIU. In both
of the configurations the thicknesses of Cu and Al layers is 50 nm
and the number of layers of graphene is 16 and 27, respectively, while
only a single layer of MoS2 has been used. The sensitivity
of the sensor in the Au/graphene/MoS2 configuration is
5.0 μm/RIU with comparatively high depth of resonance.
Surface Plasmon resonance based tapered fiber optic sensor with different taper profiles is presented. Present probe design is found to be much better than the uniform core fiber optic sensor in terms of its sensitivity.
IntroductionThe phenomenon of surface plasmon resonance is being utilized for sensing purposes since last one decade. The most famous configuration for the excitation of the surface plasmons is Kretschmann's configuration in which the lower part of the prism with high refractive index is coated by a thin metallic layer [1]. The medium which is to be sensed is kept in contact with the metal layer. A p-polarized light is then incident from one face of the prism and the intensity of the reflected light is then recorded at the other face. If the angle of incidence is greater than the critical angle for the prism metal interface the incident light is totally internally reflected and an evanescent wave is produced which decays exponentially in the metal. If the wave vector of the evanescent wave and that of the surface plasmon wave are equal to each other, resonance takes place which causes a dip in the intensity of the reflected light. The position of this dip is very much sensitive to the refractive indices of the surrounding medium. By measuring the shift in the resonance parameter we can calculate the sensitivity of the sensor. Since light guidance in the fiber takes place because of the total internal reflection phenomenon so a there is a possibility for the evanescent wave to excite the surface plasmon wave at the core metal interface if we coat the fiber with a metal layer such as gold. Here we are presenting a tapered fiber optic probe for environmental sensing. The core of the fiber is first tapered and then coated with a metal layer of gold. The performance of the tapered probe is then compared with that of the uniform core fiber optic sensor.
Theoretical modeling of a surface plasmon resonance (SPR) based fiber optic sensor with a conducting metal oxide [indium tin oxide (ITO)] as the SPR active material is proposed. The theoretical analysis reveals that the proposed sensing probe can be utilized for sensing in the IR region, where most of the gases show their absorption regime. Comparison of sensitivity predicts that an ITO-layer-coated SPR-based fiber optic sensor is about 60% more sensitive than a gold-coated fiber optic sensor. The physical reasons behind sensitivity enhancement are provided. Apart from this, various advantageous features of the ITO over the noble metals, silver and gold, are addressed.
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