Aspherical glass or plastic lenses are usually adapted in the camera module of handheld phone. Recently, slimmer
cameras are required according to reducing thickness of handheld phone. In this paper, we present an ultra slim camera
module using multiple freeform off-axis imaging lenses. New optical concept of multiple lens system introduces the
planar optics with freeform shaped aspherical lens surface on the wafer, which can achieve the thickness of 50%
compared to the conventional symmetric lens system. In order to achieve the resolution specification, we separate the
field of view in camera module. As the result, two inverted images are produced on a same imaging sensor and the
acquired inverted images are processed by photo stitching algorithm so as to combine them. Finally, in order to verify
the new imaging system, we manufacture the new slim lens through the UV embossing replication process. We found the
new imaging system is feasible for VGA resolution and it can be expandable to the high resolution system.
A novel image quality evaluation method, which is based on combination of the rigorous grating diffraction theory and the ray-optic method, is proposed. It is applied for design optimization and tolerance analysis of optical imaging systems implementing diffractive optical elements (DOE). The evaluation method can predict the quality and resolution of the image on the image sensor plane through the optical imaging system. Especially, we can simulate the effect of diffraction efficiencies of DOE in the camera lenses module, which is very effective for predicting different color sense and MTF performance. Using this method, we can effectively determine the fabrication tolerances of diffractive and refractive optical elements such as the variations in profile thickness, and the shoulder of the DOE, as well as conventional parameters such as decenter and tilt in optical-surface alignments. A DOE-based 2M-resolution camera lens module designed by the optimization process based on the proposed image quality evaluation method shows ~15% MTF improvement compared with a design without such an optimization.