Miniaturized silicon photonics multi-sensor operating at high temperatures for use in composite materials industrial applications

Composite materials offer significant performance advantages due to their lightweight, high-strength, and high stiffness. This led to their adoption in several industrial sectors with particular emphasis on the aerospace industry which has undergone a transformation towards a composite-dominated new standard. In order to respond to the increased demand, it is mandatory to focus on an efficient and well-controlled curing cycle of the resin, which will lead to a significant reduction of cost and an increase in production speed. Currently, manufacturers use filling and curing cycles with high safety margins which can be optimized by applying process monitoring techniques, which up to now use thermocouples and dielectric sensors. However, these electric solutions suffer in terms of operating capabilities and the facilitation of integrating them in composite materials (due to their size and electrically conductive aspect when using carbon fibers). We present the design and evaluation of a miniaturized novel photonic integrated sensor, fabricated in 220 nm top SOI platform, capable of measuring key monitoring values that facilitate optimization of the curing process. The operation principle is the spectral shift of a silicon Bragg grating component's resonant wavelength. Bragg grating design and postprocessing of the integrated chip allows for measuring different key values such as temperature, refractive index and pressure all in ~1.5 mm diameter. The fabricated temperature sensors achieve a significant 0.084 nm/°C thermo-optic efficiency with high accuracy (0.5 °C) and repeatability across a very wide dynamic range (temperature 27 to 180 °C).