Design of flexible mechanical sensor based on PDMS grating

Grating devices are widely used in optical force or vibration sensing. However, conventional gratings made of rigid materials have small strain which only arises little change of the resonance wavelengths by force, furthermore the resonant wavelengths are susceptible to temperature and humidity, thus accurate perception of pressure is hard and complicated. In this work, we designed and fabricated a flexible and stretchable PDMS-TiO2-PDMS grating waveguide type pressure sensor where the sensing mechanism is based on waveguide resonance, meaning the resonant wavelengths are shifted linearly with the change of grating pitch and are rarely affected by temperature and humidity. Finite element analysis (COMSOL Multiphysics) is used to simulate the dynamic deformation of the grating structure under stress or tension, and the spectral changes of the gratings under above mechanical conditions are simulated by using Finite Difference Time Domain (FDTD) simulation. We found that the wavelengths of waveguide resonance are in good linearity to the changing of grating period and is insensitive to the grating height and line width. The proposed flexible grating device provides a new sensing method for optical sensors, which can be practically applied in various circumstances including strong electromagnetic interference and high variation of temperature or humidity.