Enhancing the quality factor of grating coupled plasmon resonance in optical recording media

Optical recording media such as Digital Video Discs (DVDs) or Blu-ray discs provide a readily available source for high quality 1D diffractive structures at the sub-wavelength scale in the visible spectrum. These are useful for several optical sensing methodologies such as Surface Plasmon Resonance (SPR) where the grating couples incident light into plasmon modes supported by the structure. The gratings available in these off-the-shelf devices are not optimized for SPR based sensing. Here we describe a simple method to improve the quality factor, an important performance metric of SPR based sensors, of optical recording media based plasmonic sensors. We reduced the linewidth of SPR response from a DVD based SPR sensor by an order of magnitude using a 100 nm thick polyelectrolyte multilayer film deposited using sequential layer by layer assembly from solutions. Numerical modeling and Atomic Force Microscopy studies established the origin of quality factor improvement from the change in the topography of the grating due to a polymer assembly. We demonstrate a limit of detection (LoD) of 7 × 10⁻⁶ RIU using the modified DVD based grating coupled SPR sensor.