Multi-layer hollow-core PMMA grating tube waveguides for THz sensing applications

•The multi-layer cases can produce a delayed response with an improved extinction ratio.•The multi-layer cases could confine more electric field in the core area with an increase of about 21%.•A double tube combination consisted with varying grating could improve extinction ratio.•The PMMA grating tube for THz sensing could realize an improved detection sensitivity of about 18 dB/mL.