We investigate an intensity and wavelength modulation combined plasmon resonance-based fiber-optic sensor technology. Composed of gold nanoparticles (GNPs) and sandwich configuration of Au/indium tin oxide (ITO)/Au film, two sensing regions are fabricated separately along with unclad portions of the fiber-optic probe. It can simultaneously monitor both the light intensity from the Au NP channel and the wavelength from the Au/ITO/Au film channel with a single detector. As the refractive index (RI) of the external environment changes, the transmission intensity and resonance wavelength in the two channels are modified, which provides an interrogation of intensity and wavelength modulation. The sandwich film structure is formed using magnetron sputtering technology, and the GNPs functioning as localized surface plasmon resonators are coated on a multimode optical fiber via the layer-by-layer method. The experimental results reveal that the RI sensitivities of the two sensing channels are 334.1% RIU−1 and 1963.2 nm/RIU, respectively. Based on the above sensing design, we conduct real-time and label-free monitoring of IgG/anti-IgG and Con A/RNase B biomolecular interaction. The resonant dips excited by different sensing modes make it more attractive as a multichannel surface plasmon resonance analysis technology, which is valuable in biological and life sciences research and rapid diagnostics.
Interactions between different resonance modes in optoelectronic structures may introduce coupled modes that can be utilized to explore special optical functions that cannot be realized by conventional methods. A novel dual band filter based on sub-wavelength metal grating with groove caved in and waveguide layer below is proposed in this paper. The metal grating is caved with a groove in the middle of every metal trip, and a waveguide layer with higher refractive index is placed between the metal grating and glass substrate. Using the finite-difference time-domain (FDTD) method, we research the implied physical mechanism by investigating the transmission spectrum with the changing of the structural parameters and the electromagnetic field distributions at some specific wavelengths, such as peaks and valleys in the transmittance. In our simulation, we chose Ag as the grating material and Drude-Lorentz model is employ to describe the dielectric constant. It is found that the two resonance bands are determined by different structural parameters, which due to different mechanism, FP resonance and waveguide resonance, and we also take the groove cavity mode into account when the standing wave oscillates in the groove and result in the dips between two peaks. Besides, the most notable of these features is that the increase of the grating height doesn’t shift these two resonance wavelength at all, and groove parameters only move the first peak wavelength regularly, which could be an excellent candidate for dual band filter in the telecom wavelengths. Our proposed structure with subwavelength may provide potential applications in optoelectronic devices.
A novel gold nanorods (GNRs) modified optical fiber localized surface plasmon resonance (LSPR) sensor for biochemical detection is demonstrated. The gold nanorods (GNRs) assembled film as the sensing layer was built on the polyelectrolyte (PE) multilayer modified sidewall of an unclad optical fiber. Poly (allylamine hydrochloride) (PAH)/poly (sodium 4-styrenesulfonate) (PSS) films were formed through layer-by-layer (LbL) assembly. The influence of the thickness of polyelectrolyte films was investigated. Simultaneously, the feasibility of the proposed film coupled nanorods optical fiber LSPR sensor in monitoring a series of concentration sucrose solutions with different refractive index is examined. Results suggest that the compact sensor can perform qualitative and quantitative detection in real-time biomolecular sensing.
Optical sensors based on nanoparticles induced Localized Surface Plasmon Resonance are more sensitive to real-time
chemical and biological sensing, which have attracted intensive attentions in many fields. In this paper, we establish a
simulation model based on nanoparticles imprinted polymer to increase sensitivity of the LSPR sensor by detecting the
changes of Surface Plasmon Resonance signals. Theoretical analysis and numerical simulation of parameters effects to
absorption peak and light field distribution are highlighted. Two-dimensional simulated color maps show that LSPR lead
to centralization of the light energy around the gold nanoparticles, Transverse Magnetic wave and total reflection become
the important factors to enhance the light field in our simulated structure. Fast Fourier Transfer analysis shows that the
absorption peak of the surface plasmon resonance signal resulted from gold nanoparticles is sharper while its wavelength
is bigger by comparing with silver nanoparticles; a double chain structure make the amplitude of the signals smaller, and
make absorption wavelength longer; the absorption peak of enhancement resulted from nanopore arrays has smaller
wavelength and weaker amplitude in contrast with nanoparticles. These simulation results of the Localized Surface
Plasmon Resonance can be used as an enhanced transduction mechanism for enhancement of sensitivity in recognition
and sensing of target analytes in accordance with different requirements.
Comparing to core-modes of optical fibers, some cladding-modes are more sensitive to the surroundings which are very
valuable to sensing application; recently, a novel type of FBG sensor with core-offset structure attracts more and more
interests. Normally, the forward core-mode is not only reflected and coupled to the backward core mode by the Fiber
Bragg Grating in the step-type photosensitive single mode fiber, but also coupled to the backward cladding-modes and
the radiation modes, eventually they will leak or be absorbed by the high refraction index coating layer. These backward
cladding-modes can also be used for sensing analysis. In this paper, we propose and develop a core-offset structure to
obtain the backward core-mode and backward cladding-modes by using the wavelength shift of the backward core-mode
and the power of the backward cladding-modes in Fiber Bragg Grating sensor, and the power of the backward
cladding-modes are independent from temperature variation. We develop a mode coupling sensor model between the
forward core-mode and the backward cladding-modes, and demonstrate two coupling methods in the core-offset
structure experimentally. The sensor is fabricated and demonstrated for refractive index monitoring. Some specific works
are under investigation now, more analysis and fabrication will be done to improve this cladding-mode based sensor
design for applicable sensing technology.
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