A broadband SPR sensor based on a no-core fiber coated with gold-silver for refractive index and temperature measurement

Dual-parameter sensor has relatively small detection range because of restriction on resonance wavelength range. To overcome this problem, we propose a cascaded gold and silver SPR dual-parameter sensor. As the resonance wavelength ranges of gold and silver are different, cascading the two metals to make one sensor broadens the resonance wavelength range, thus increasing the sensor's detection range. The sensor uses no-core fiber as the probe and multimode fiber (MMF) as the input (output) coupler, which constitutes an MMF-NCF-MMF sensing structure. By using Magnetron sputtering, gold and silver are deposited on the outer surface of NCF. The effects of coating time and NCF length on the sensing performance were experimentally investigated to determine the optimal coating time and NCF length. The experimental results shows that the two channels of the sensor are independent of each other without crosstalk and have an extensive range of parameters to be measured. The maximum sensitivity is 3231 nm/RIU in the RI range of 1.333–1.385. It has a maximum temperature sensitivity of 6.68 nm/°C from 0 to 80 °C. In addition, the sensor has good stability and repeatability. The proposed sensor has a simple and integrated structure and is suitable for applications requiring large detection range sensing.