The study of fixing field curvature by flexible image sensor array

Field curvature is one of the most common aberrations in an optical system. The phenomenon of field curvature occurs when the resulting image is curved at the projective plane after light propagates through spherical lenses. Therefore, if the projective plane can be a curved surface that fits the curvature of the image, we can obtain a non-distorted projective image. In this study, a curved image sensor is employed to verify the effect of image modification on field curvature as well as to capture a better result. The curved image sensor is fabricated using surface-mount technology (SMT) to package image sensors on flexible printed circuit. The image sensor arrays are fixed on three kinds of curved substrates, 120 mm, 60 mm and 40 mm respectively. The image signals are captured by image sensor arrays with different curvatures through a plano-convex lens (R1: 133 mm, R2: - ∞) with diameter of 101 mm. The signals are then sent to the computer for analysis using the IEEE standard facsimile test chart - IEEE Std 167A-1987 as the testing object. The sharpness of the captured images from the sensors at the same position of different substrates is compared. According to the analysis of captured images, the use of the curved substrate with curvature of 60 mm yields the best result which can obtain a clear and uniform image. In addition, the illuminance on different projective planes are analyzed by an optical simulation software. The variation coefficients of the illuminance on a plane surface and three kinds of curved surfaces are calculated to map the light intensity on the sensors. Based on the simulated results, the smallest variation of illuminance coefficient on projective plane shows a uniform illumination at the curvature of 60 mm, which matches the experimental results.