Abstract
In the phase-sensitivity-based surface plasmon resonance (SPR) sensing scheme, the highest phase jump usually happens at the darkness or quasi-darkness reflection point, which results in low power for detection. To overcome such a limitation, in this paper, a waveguide-coupled SPR configuration is proposed to work at near-infrared. The coupling between surface plasmon polariton (SPP) mode and photonic waveguide (PWG) mode results in electromagnetically induced transparency (EIT) and asymmetric Fano resonance (FR). Near the resonance, the differential phase between p-polarized and s-polarized incident waves experience drastic variation upon change of the surrounding refractive index. More importantly, since the FR occurs at the resonance slope of SPP mode, the corresponding phase change is accompanied with relatively high reflectivity, which is essential for signal-to-noise ratio (SNR) enhancement and power consumption reduction. Phase sensitivity up to 106 deg/RIU order with a minimum SPR reflectivity higher than 20% is achieved. The proposed scheme provides an alternative approach for high-performance sensing applications using FR.
Highlights
Surface plasmon resonance (SPR)-based sensors—characterized by their advantages of label-free, high sensitivity, and low limit of detection for the inspection of liquids and gases—are regarded as a powerful sensing tool in chemistry and biology [1]
Intensity interrogation is relatively simple, but intensity fluctuation of light source can significantly bottleneck the achievable low detection limit [4]. Such a drawback in the detection limit can be overcome by passing from intensity interrogation to phase interrogation [5,6,7,8]. This is because, firstly, the phase jump takes place in the very dip of the SPR curve, whereas maximal amplitude variation is observed on the resonance slope, which means the light-matter interaction is stronger for phase interrogation, secondly, under suitable detection scheme, phase noises of laser sources are generally orders of magnitude lower compared to the intensity ones, phase interrogation provides better
The Kretschmann configuration consists of a rutile prism, an indium tin oxide (ITO) layer with thickness t1, an MgF2 layer with thickness t2, a silicon consists of a rutile prism, an ITO layer with thickness t1, an MgF2 layer with thickness t2, a silicon layer with thickness t3 semi-infinitely surrounded by water
Summary
Surface plasmon resonance (SPR)-based sensors—characterized by their advantages of label-free, high sensitivity, and low limit of detection for the inspection of liquids and gases—are regarded as a powerful sensing tool in chemistry and biology [1]. There exists a reflectivity–sensitivity trade-off in conventional phase-sensitive SPR sensors To overcome this drawback, on one hand, polarimetry schemes with low noise and high sensitivity photodetectors can be employed to extract the phase information, but they may increase the cost and complexity of the sensors. Transparent conductive oxide, indium tin oxide (ITO), has gathered significant attentions as an alternative material for plasmonic and metamaterials applications [25,26] This is because the carrier concentration of ITO can be modified by heavily doping, electrical gating, post-deposition, or rapid thermal annealing processes [27,28]. The high concentration of carriers in ITO can modify its permittivity significantly and make it metallic Owing to this advantage, ITO material enables a cost-effective solution to Photonics 2018, 5, x FOR PEER REVIEW construct SPR sensor at NIR regime instead of the noble metals.
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