An Ag-graphene layers-coated H-shaped photonic crystal fiber (PCF) surface plasmon resonance (SPR) sensor with a U-shaped grooves open structure for refractive index (RI) sensing is proposed and numerically simulated by the finite element method (FEM). The designed sensor could solve the problems of air-holes material coating and analyte filling in PCF. Two big air-holes in the x-axis produce a birefringence phenomenon leading to the confinement loss and sensitivity of x-polarized light being much stronger than y-polarized. Graphene is deposited on the layer of silver in the grooves; its high surface to volume ratio and rich π conjugation make it a suitable dielectric layer for sensing. The effect of structure parameters such as air-holes size, U-shaped grooves depth, thickness of the silver layer and number of graphene layers on the sensing performance of the proposed sensor are numerical simulated. A large analyte RI range from 1.33 to 1.41 is calculated and the highest wavelength sensitivity is 12,600 nm/RIU. In the linear RI sensing region of 1.33 to 1.36; the average wavelength sensitivity we obtained can reach 2770 nm/RIU with a resolution of 3.61 × 10−5 RIU. This work provides a reference for developing a high-sensitivity; multi-parameter measurement sensor potentially useful for water pollution monitoring and biosensing in the future.

We present and numerically characterize a photonic crystal fiber (PCF)-based surface plasmon resonance (SPR) sensor. By adjusting the air hole sizes of the PCF, the effective refractive index (RI) of core-guided mode can be tuned effectively and the sensor exhibits strong birefringence. Alternate holes coated with graphene-Ag bimetallic layers in the second layer are used as analyte channels, which can avoid adjacent interference and improve the signal to noise ratio (SNR). The graphene's good features can not only solve the problem of silver oxidation but also increase the absorption of molecules. We theoretically analyze the influence of the air hole sizes of the PCF and the thicknesses of graphene layer and Ag layer on the performance of the designed sensor using wavelength and amplitude interrogations. The wavelength sensitivity we obtained is as high as 2520 nm/RIU with the resolution of 3.97 × 10 −5 RIU, which can provide a reference for developing a high-sensitivity, real-time, fast-response, and distributed SPR sensor.

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A surface plasmon resonance (SPR) sensor based on hollow-core photonic crystal fibre (HC-PCF) filled with silver nanowires is designed. The analyte and silver nanowires are full filled in the air holes of the HC-PCF to realise the SPR sensing, which is more convenient than silver coated in operation. The designed sensor is analysed through numerical simulations and demonstrated by experiments. All the results show that a blue-shift is obtained with increase of the analyte refractive index (RI), and the silver nanowires concentration has no effect on spectral sensitivity. The highest average spectral sensitivity of 14 240 nm/RIU is obtained by experiments, which is higher than that previously reported for the same type of sensors. The sensor is useful for detecting small analyte RI changes, and can also provide a reference for the implementation and application of PCF-SPR sensors with high sensitivity.

To solve the problem of air hole coating and analyte filling in microstructured optical fiber-based surface plasmon resonance (SPR) sensors, we designed an exposed-core grapefruit fiber (EC-GFs)-based SPR sensor. The exposed section of the EC-GF is coated with a SPR, supporting thin silver film, which can sense the analyte in the external environment. The asymmetrically coated fiber can support two separate resonance peaks (x- and y-polarized peaks) with orthogonal polarizations and x-polarized peak, providing a much higher peak loss than y-polarized, also the x-polarized peak has higher wavelength and amplitude sensitivities. A large analyte refractive index (RI) range from 1.33 to 1.42 is calculated to investigate the sensing performance of the sensor, and an extremely high wavelength sensitivity of 13,500 nm/refractive index unit (RIU) is obtained. The silver layer thickness, which may affect the sensing performance, is also discussed. This work can provide a reference for developing a high sensitivity, real-time, fast-response, and distributed SPR RI sensor.

A surface plasmon resonance (SPR) sensor based on D-shaped microstructured optical fiber (MOF) is proposed to realize the simultaneous measurement of refractive index (RI) and temperature. The D-shaped flat surface coated with a gold layer is in direct contact with analyte as a sensing channel of RI, and one of the air holes near the fiber core is filled with chloroform to detect temperature. Two separate channels and birefringence caused by the asymmetric structure can distinguish the variations of RI and temperature independently, thus completely solving the cross-sensitivity problem. This is the first time to realize the simultaneous measurement of multiple parameters without matrix equations, to the best of our knowledge. Results show that the y-polarized peak supported by channel I only shifts with RI variation and is unaffected by the temperature floating. Similarly, the x-polarized peak supported by channel II is only influenced by the change of temperature in the external environment. The effect of gold layer thickness is investigated numerically, and the sensor sensitivity is identified both in wavelength and amplitude interrogations. This work is very helpful for the design and implementation of a highly sensitive, real-time, and distributed SPR sensor for multi-parameter measurement applications.