Optical sensitivity analysis of a bent micro reflector array in uncooled infrared imaging

In an optomechanical infrared (IR) detection system, the optical detection sensitivity, a key factor that affects the noise equivalent temperature difference (NETD), is influenced by the length and bend of micro-cantilever reflector of a focus plane array (FPA). The influence on optical detection sensitivity by such a bend due to the bulk micromachining techniques is discussed based on Fourier optics. In this study, the reflectors of the fabricated FPAs with pixel sizes 200 μm, 120 μm and 60 μm have the curvature radii of 23 mm, 11 mm and 8 mm, respectively. Theoretical analysis and experiments show that the sensitivities are degraded by the undesired bend of the micro-cantilever reflector. Moreover, the study demonstrates that the sensitivity reaches the maximum value when the reflector length L and the curvature radius R of the micro-cantilever reflector satisfy the relation: L²/R = λ (λ is the wavelength of illumination light) and this result provides an approach for optimizing the optical sensitivity as the diminishing of the pixel size of FPA. Finally, the methods of optimizing the sensitivity are discussed.