Performance and reliability requirements for modern optical systems dictate that they can no longer be simulated in isolation without reference to external and environmental factors which can adversely impact image quality. Simultaneously, advances in multi-physics simulation techniques have made it possible to couple the impacts of, for example, thermal changes and structural stresses to optical analysis to better predict performance in operational conditions. Applications where light propagates through a fluid surrounding or within an optical system present a particular simulation challenge in this regard, and one that requires new simulation techniques. In the near-field, variations in pressure, temperature, and density of the fluid give rise to corresponding variations in refractive index that will, in turn, induce optical aberrations in a transmitted wavefront. These aberrations can lead to degraded image quality and line-of-sight errors. Accurate and robust analysis of such effects necessitates the coupling of computational fluid dynamics (CFD), for simulation of turbulent flow, shock waves, etc. with ray tracing to compute key optical metrics. Furthermore, this analysis can be combined with far-field atmospheric effects, including emissivity, absorption, scattering, refraction, to build a comprehensive picture of system performance. The ability to perform multi-physics simulations early in the design process provides the opportunity to develop strategies to identify and mitigate negative performance drivers. We present a solution to model the effects of light propagation through optical fluids accurately and combine this with analysis of structural and thermal effects. This solution will be demonstrated in use cases including electro-optic infrared airborne systems.
There are some systems that have been traditionally regarded as too complex for simulation, this mindset results in expensive protypes to conduct build and break scenarios. As the need to understand increasingly complex systems evolves, so must the tools. This work seeks to demonstrate that not only is simulation possible with a complex multi-physics problem, but it is accurate, while providing incredible time and cost savings when compared to alternative methods. Simulation of complex systems early in the design and development phases can reduce the number of prototypes created, the number of test flights required and provide design insights earlier in the product life cycle. Design modification while still in the development phase facilitates potential for greater flexibility. Failure to include simulation early, can result in more costly prototyping, greater number of test flights required and the further into a product life cycle issues are discovered, the more limited the options are for modification. Simulation can provide early insights and cost savings.
We report recent work on acoustic measurements using a Bragg grating based Fabry-Perot sensor system. A single Fabry-Perot sensor using a path matched Michelson interferometer was developed, and a digital demodulation scheme based on the phase stepping technique was used to measure acoustic sound pressure from 100 Hz to 600 Hz. This sensor is designed to work in a multiplexed architecture to provide inputs to a feed-forward adaptive control system. This control system will be used to actively control the sound pressure level within an enclosure. A series of experiments were performed to investigate the possibility and potential use of this sensor system for acoustic noise detection. In this paper, we present initial test data from the prototype optical sensor microphone. We also illustrate the envisioned multiplexed sensor scheme and control system.
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