High efficiency blazed gratings in resonance domain

Oliva, Maria GND

This thesis was focused on the design and fabrication of high efficiency blazed gratings in resonance domain. To achieve high efficiency gratings working at normal incidence and for visible wavelength, a close feedback between design and technology is required. Within this work, two different gratings, a three-level and a new kind of composed multilevel structure, have been optimized taking into account fabrication constraints. The two blazed gratings achieve high efficiency (>90%) for the two different directions of the incident light, through the grating substrate or from air, respectively. A physical interpretation of the high efficiencies has been provided. It is based on a three-wave interference mechanism for the three-level grating, and on a modal analysis for the composed multilevel structure. Due to the demanding profile of the gratings (critical dimension CD ≈100nm and aspect ratio AR>10), three new technologies have been proposed for a successfully fabrication. The new approaches introduce additional fabrication steps to the standard multistep binary optics technology in order to overcome its limitations. In particular, the Three-Resist-Layer Technology- based on the introduction of a planarization layer- is devoted to avoid the typical sizing error occurring within the second lithographic step. The Relaxed-Alignment Technology- based on the use of a unique coded chromium mask for the whole fabrication process- has been developed to avoid misalignment errors between two consecutive lithographic steps. The third technology, i.e. ALD- enhanced technology- introduces the Atomic Layer Deposition technique within the grating fabrication in order to improve the sidewall profile for high AR structures. The two different blazed gratings have been fabricated by means of the standard and new technologies. Thanks to the new approaches, both gratings achieve high blazed efficiency (>90%) and the experimental results are in a good agreement with the simulations.



Oliva, Maria: High efficiency blazed gratings in resonance domain. 2015.


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