Design of highly sensitive interferometric sensors based on subwavelength grating waveguides operating at the dispersion turning point

In this paper, a dual-mode interferometric sensor based on a subwavelength grating (SWG) waveguide is proposed. The design operates at the dispersion turning point (DTP) of the two dispersive TE modes in the periodic structure, exhibiting a group velocity difference of almost zero, to improve the performance of refractive index (RI) sensors. The necessary conditions for realizing DTP in SWG are analyzed. Moreover, the interference spectrum characteristics and the influence of structural parameters on gas RI sensing performance are further studied. The results show that the sensitivity value of the proposed sensor can reach ∼38,000nm/RIU. The proposed structure can also achieve a gas pressure sensitivity of ∼105nm/MPa. The proposed sensors provide a potential platform for highly sensitive RI sensors.