Hybrid refractive/diffractive micro-optical component for high-efficiency image sensor

Micro-optical components have been extensively applied to many fields since 1980s, including the displays, optical pick-up heads, optical interconnection, bio-medicine and image sensors, etc. This thesis reports on a hybrid refractive/diffractive micro-optical color-separation component for the application of color separation, which was based a successful UV LIGA process to fulfill the mass-production of the component, for the purpose of replacing the action of color filter on filtering the 2/3 incident light we need.
Color-separation optics is a critical component for converting the color information of surroundings into electronic data. Our hybrid refractive/diffractive micro-optical Color-separation component comprises of a microlens arrays together with a layer of diffractive blazed grating, which were made on the different side of a plastic thin film. The microlens arrays play roles of focusing and positioning the incident light onto the active region of image sensor; however, the blazed grating are three-dimensional elements consisting of period-repeating right angle structures, which retard the incident wave by a modulation of the surface profile to diffract the incident light on different angles proportional to wavelengths. Thus, the Hybrid refractive/diffractive micro-optical color-separation component has the dual functions rather than focus on unique purpose.
In order to combine the advantages of refractive optics and diffractive optics, considerable work has been invested in the development of hybrid elements, including the setup of specifications, simulation of the light path, and the fabrication of the complicated three-dimensional micro-structures. Moreover, we use the inclined exposure method which comes from the idea of energy absorption in the photo-resist to improve the profile of the blazed grating.
The profile of our microlens is 25μm in diameter, 1.8 μm in lag, and the radius of curvature is about 80 μm. Fill factor of our microlens can approach 100%. The +1 order diffraction efficiency of blazed grating is above 41 %, superior to the best efficiency 33% of conventional color filter; besides, the diffraction efficiency of the high order terms can reduce to below 8%. Thus, our hybrid refractive / diffractive micro-optical color-separation component can increase the efficiency of the image sensor when it goes to high quality, and small pixel size.