Optimization of temperature insensitive refractometer

Abstract

Experimentally, in the open-top ridge waveguides, the sensitivities of core and cladding resonances to the surrounding medium's refractive index are different while the temperature sensitivities are similar. Based on these characteristics, a temperature insensitive refractometer has been proposed. To increase the sensitivity of these devices, a theoretical model is developed to investigate the performance of some potential waveguide and Bragg grating structures. Relationships between the waveguide core size, refractive index distribution, tilt angle of the Bragg gratings as well as the relative evanescent sensitivity of the core and cladding modes are examined. As a result, we find that sensitivity can be enhanced by decreasing the waveguide core size, making the effective index of the waveguide close to the expected refractive index of the analyte, and incorporating tilt in the Bragg grating structures. Furthermore, the inclusion of tilt also appears to reduce the grating's birefringence for the waveguide structure examined.