Combined Plasma-Based Fiber Etching and Diamond-Like Carbon Nanooverlay Deposition for Enhancing Sensitivity of Long-Period Gratings

This paper presents an application of reactive ion etching followed by diamond-like carbon nanooverlay deposition using radio frequency plasma-enhanced chemical vapor deposition method for effective tuning of the refractive index (RI) sensitivity of long-period gratings (LPGs). Both etching and deposition take place within one process. Combination of both plasma-based processes allows for well-controlled tuning of the LPG sensorial response up to its operation at both dispersion turning point of higher order cladding modes and mode transition regime. As a result of the processing, the RI sensitivity has been enhanced up to over 12 000 nm/RIU per single resonance in narrow RI range (1.3344-1.3355 RIU) and over 2000 nm/RIU in broader RI range (1.34-1.356 RIU). Experimental results have been supported by numerical analyses that show capabilities for further significant improvement of both RI sensitivity and range of RI measured with the enhanced sensitivity.