Improving the sensitivity of SPR sensors based on gratings by double-dips method (DDM)

The sensitivity of surface plasmon resonance (SPR) sensors based on gratings using angular interrogation is improved by optimizing the 1st-order diffraction dip recently but still can not exceed the prism-based systems. To improve the sensitivity of grating-based systems in another way, we realize sharp dips of the higher diffraction orders and propose double-dips method (DDM), a new way using the separation of two sharp dips of different orders to improve the sensitivity of SPR sensors based on gratings with good linearity. By DDM, the grating-based systems' sensitivity is improved into more than 237 deg/RIU, more sensitive than the prism-based systems in the same condition, and the quality parameter (Chi) factor reaches more than 95. In different performance comparisons, DDM has roundly better performances than other methods. Moreover, when the grating profile errs from rectangle, DDM still works well.