Abstract
The generation of surface plasmon resonances (SPRs) in gold-coated weakly tilted fiber Bragg gratings (TFBGs) strongly depends on the state of polarization of the core guided light. Recently, it was demonstrated that rotating the linear state of polarization of the guided light by 90° with respect to the grating tilt allows to turn the SPR on and off. In this work, we measure the Jones matrix associated to the TFBG transmission properties in order to be able to analyze different polarization-related parameters (i.e. dependency on wavelength of polarization dependent loss and first Stokes parameter). As they contain the information about the SPR, they can be used as a robust and accurate demodulation technique for refractometry purposes. Unlike other methods reported so far, a tight control of the input state of polarization is not required. The maximum error on refractive index measurement has been determined to be ~1 10(-5) refractive index unit (RIU), 5 times better than intensity-based measurements on the same sensors.
Highlights
Refractometry is used in various areas such as quality control in the food industry, process monitoring or biomedicine
We have demonstrated the operating principle of a new demodulation technique applied to plasmonic fiber grating sensors using gold-coated tilted fiber Bragg gratings (TFBGs)
The proposed technique exploits the information contained in the Jones matrix associated to the TFBG transmitted signal
Summary
Refractometry is used in various areas such as quality control in the food industry, process monitoring or biomedicine. To measure surrounding refractive index (SRI) changes by monitoring the resonant wavelength of fiber gratings, the guided light has to be brought in contact with the outer boundary of the fiber cladding In this way, the evanescent field of the optical modes penetrates into the external medium to sense the SRI. Contrary to long period fiber gratings refractometers [1], they provide temperatureinsensitive SRI measurements [2,3,4] and are much less sensitive to bending effects [5] To further improve their sensing performances, nano-scale coatings have been used to tailor the TFBGs amplitude spectral characteristics or to develop (bio-)chemical sensors based on surface plasmon resonances (SPRs) when functionalized gold overlays are used [6,7]
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