A temperature-insensitive refractometer based on transverse electric (TE) and transverse magnetic (TM) modes in open-top ridge waveguides

A technique for creating a temperature-insensitive refractometer that utilizes transverse electric (TE) and transverse magnetic (TM) modes in an open-top ridge waveguide design is presented. By using the TE mode resonance as a temperature reference, the relative shift of the TM mode can be monitored in order to measure the refractive index of liquids under test. Specifically, the device fabricated here produces a resonance shift of 1 pm for every 1 x 10(-4) of measured index change, with a temperature sensitivity less than 0.5 pm degrees C-1. To increase the sensitivity of these devices, a theoretical model is developed to investigate the performance of some potential waveguide structures. Relationships between the waveguide core size, refractive index distribution, as well as the relative evanescent sensitivity of TE and TM modes are examined.