Total internal reflection holography for optical interconnections

Planar diffractive optical elements are well suited to fulfill the needs of optical interconnections. They are efficient and can serve as focusing elements, imaging elements, beam deflectors, and fan-out elements. Almost any shape of structure can be realized. This flexibility allows complex and compact interconnections. Two different types of diffractive optical elements exist: the holographic optical elements (HOEs) and the computergenerated elements .Modernmicrofabrication technology enables the realization of efficient computer-generated diffractive elements. Difficulties arise with the actual technology for the fabrication of complex structures with more than 1000 lines/mm employing blazed profiles, which is necessary for off-axis elements. Therefore, the holographic recording remains an interesting technique for elements with small features. However, the positioning precision is a problem for multifacet elements, such as lenslet arrays. In this paper, we demonstrate how the precision of e-beam lithography and the advantage of holography can be brought together to record large lenslet arrays. Special emphasis is given to record compact lenslet arrays with short focal lengths. These elements are of interest in planar architectures.' Near-field total internal reflection (TIR) holography2 is an appropriate technique to record such elements.