Simulation method for large subwavelength devices in infrared imaging systems and comparison with experiment
Résumé
In the field of uncooled Long Wave Infra Red (LWIR) imaging, CMOS compatible bolometers technology is being more and more popular, exhibiting precise temperature measurement at moderate cost. The price of this technology is proportional to the number of components produced per wafer, leading to a shrinkage of the pixel. Enhancing the resolution level of the focal plane array (FPA) requires an improvement of the point spread function (PSF) of the optical system, leading to more and more complex aspheric lenses and an increased cost of imaging systems. We propose to add a sub-wavelength blade to the existing parts of the imaging system to improve the image quality in applications with a constraint budget. The main function of such a subwavelength blade should be to control the phase of the light into an optical system to compensate optical aberrations. A cost effective solution consists to make such devices using microelectronics based collective fabrication process. The main difficulty is to predict the subwavelength blade behavior within an optical system that is to say combining millimeter sized optical components that are modeled using ray-tracing or electromagnetic simulations. In this paper we present the results obtained from an effort to simulate, fabricate and characterize an all-dielectric subwavelength blade. Our method is based on Fourier Modal Method and Angular Spectrum Method coupled with ray tracing to simulate subwavelength optics into an optical system and the comparison between our simulations results and experiments shows a good agreement.