The use of composite materials has seen widespread adoption in modern aerospace industry. This has been facilitated due to their combined favorable mechanical characteristics, namely leveraging their low weight, high stiffness and increased strength. Wide adoption of composites requires an effort to avoid costly and cumbersome autoclave-based manufacturing processes. The up and coming “out-of-autoclave” composite manufacture processes also have to be optimized, to allow for consistent high quality of the parts produced as well as keeping the cost and production speed as low as possible. This optimisation can be achieved offline as well as by trying to have constant monitoring and controlling the resin injection and curing cycles.
Capitalizing on the benefits of Silicon Photonic Integrated Circuits (PICs), namely the fast response, miniature size, ability to operate at high temperatures, immunity to electromagnetic interference (allowing carbon fibers in composites), and their compatibility with CMOS fabrication techniques, a passive PIC based temperature sensor embedded in a composite tool is demonstrated, used to produce RTM-6 composite parts.
The design and development methodology of the PIC based sensor (fabricated in an Multi Project Wafer run of 220 nm Silicon-on-Insulator (SOI) platform and based on periodic Bragg grating elements) as well as the experimental results and comparison with the industry standard thermocouples, during a thermal cycling of the tool are presented. We measured the embedded PIC temperature sensor to have sensitivity of around ~85 pm/°C, while the RTM-6 fabrication cycle requires the tool to operate up to 185°C.
With the increased interest in silicon photonics, integration and packaging technologies are essential to transforming photonic integrated circuits (PICs) into functional photonic systems. We describe in detail the process to obtain a fully packaged miniature photonic temperature sensor starting from bare PIC dies having Bragg grating sensors in a silicon waveguide. It is also shown that PICs fabricated via multiproject wafer services can show some variability, e.g., in the effective index, which has significant impact on the device functionality (Bragg wavelength) and optical interface (red-shifted grating coupler spectra at default coupling angles). To obtain a final sensor device that is as small as possible the PIC is interfaced from the back side using a 300 μm ball lens. Furthermore, this ensures that the top surface remains clear of any interfacing fibers. Based on this optical interfacing concept, we developed a solution for integrating a 1 mm × 1 mm sensor PIC with a single-mode fiber and packaging it in a 1.5 mm inner-diameter metal protective tube. The accurate position of the ball lens is ensured using a laser-fabricated fused silica precision holder. It is shown that the additional insertion loss caused by the ball lens interface is very limited. A packaged sensor was achieved by sequentially mounting the holder on a ceramic ferrule and then the PIC on the holder and finally gluing a protective metal tube surrounding the assembly, taking care that the PIC surface is flush with the end face of the tube. We demonstrated this concept by realizing a packaged phase-shifted silicon Bragg grating temperature sensor operating around 1550 nm, which could be read out in reflection using a commercial interrogator. A temperature sensitivity of 73 pm / ° C was found, and we demonstrated sensor functionality up to 180°C.
We demonstrate a sensing platform for composite manufacturing (RTM-6) process based on silicon photonics, being controlled by novel Process Monitoring Optimization Control (PMOC) system. The photonic multi-sensor is based on bragg grating components, allowing measurements of temperature, pressure and refractive index, and is packaged employing a ball lens fiber-to-chip interface. We present results of the packaged temperature photonic sensor regarding bandwidth, linearity and thermo-optic efficiency, being controlled by our PMOC system. We experimentally achieve 0.074 nm/C with R^2 = 0.995 linearity for temperature up to 180°C (RTM-6 compatible) with 1 kHz data acquisition and 0.2°C accuracy.
With the increased interest in silicon photonics, smart integration and packaging technologies are essential to transform photonic integrated circuits (PICs) into functional photonic systems. Especially for sensing, the currently existing standard packaging technologies are too expensive and bulky. We developed a solution for integrating a 1 mm x 1 mm sensor PIC with a single mode fiber and packaging it in a 1.5 mm inner-diameter metal protective tube. The concept relies on interfacing a grating coupler with a fiber from the back side of the PIC employing a 300 μm ball lens mounted in a laser-fabricated fused silica precision holder. It is shown that the additional insertion loss caused by the ball lens interface is very limited. A packaged sensor was achieved by sequentially mounting the holder on a ceramic ferrule, then the PIC on the holder and finally gluing a metal tube surrounding the assembly, taking care that the PIC surface is flush with the end face of the tube. The back side fiber interface ensures that the PIC’s surface remains accessible for sensing, while the tube protects the fiber-to-PIC interface. We demonstrated this concept by realizing a packaged phase shifted silicon Bragg grating temperature sensor operating around 1550 nm, which could be read out in reflection using a commercial interrogator. A temperature sensitivity of 73 pm/°C was found, and we demonstrated sensor functionality up to 180°C.
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. We investigate, a photonic solution, able of measure key monitoring values that facilitate optimization of the curing process. Simulation and evaluation results on a bragg grating based photonic integrated sensor, developed in 220 nm Silicon-onInsulator platform, are presented. A multi-sensor deployment is considered, enabling monitoring of the temperature and the refractive index of the resin. Serially coupled bragg grating photonic elements will enable concurrent monitoring of both temperature and refractive index. Several bragg configurations have been investigated and experimentally evaluated, specifically regular and phase-shifted ones. Both TE and TM polarization operation sensors that have been designed and fabricated, will be presented. Their sensitivity on resin temperature and refractive index variation will be discussed, resulting in a comparative study outlining the benefits and disadvantages of each solution. Refractive index sensors are realized by employing post-processing etching techniques on Multi-Project-Wafer run fabricated silicon chips, on top of the periodic bragg grating element. The comparative study takes into consideration TE and TM polarization operation, regular and phase-shifted bragg grating configuration elements, while evaluating their sensitivity in temperature and refractive index variations. Temperatures considered are in the range of 27°C to 200°C, while refractive index values lay between 1.5 and 1.6. A Figure-of-Merit is proposed to facilitate the selection of multi-sensor deployment for specific temperature and refractive index ranges.
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).
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