In this work we have developed new types of color splitters, which separate spectrally and spatially the light that falls on image sensors by exploiting the nanojet (NJ) beam phenomenon. The proposed method relies on light diffraction on the edges of constitutive parts of the studied multi-material elements embedded in a host medium with lower refractive index. Diffraction of light on the edge of a dielectric microstructure forms a tilted focused beam whose deviation angle depends on the refractive index ratio between the materials of the elements creating this edge. The characteristics of the generated NJ beams are also controlled by the geometry of multi-material elements (size and base angle of the edge) and the angle of wave incidence. Combination of two or more dielectric materials with different refractive indexes leads to the creation of multiple NJs with different angles of deviation, length and intensity. In the case of normally incident plane wave, the generated NJ beams originating from different edges of the constitutive parts of a multi-material microstructure, recombine and contribute to the formation of NJ beam deflection away from the normal direction in the near zone. The possibility to split color-bands of the incident light by combining two or more dielectric materials in such a way that the generated NJ beams create a spectrally dependent NJ beam deflection is discussed. We demonstrate that the proposed topologies of multi-material microlenses help to reduce the size of the color splitting element and optical crosstalk through the active Si layer. We show that the color splitting functionality of the proposed exists for inclined incident light as well. Applying these color splitters to actual image sensors allows to improve the optical efficiency by splitting the incoming light between the image sensor pixels, instead of filtering out part of the received light.
“Nanojet-based dielectric multi-material color splitters for image sensor applications.“, Oksana Shramkova*, Valter Drazic, Laurent Blondé, Bobin Varghese, Valérie Allié, SPIE Photonics Europe, April 2020, Strasbourg, France (Online).