Proceedings PaperIncoherent Multifocus Hololens Design and Fabrication
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Several 5 x 5 multifocus Hololenses have been produced with diffraction efficiencies between 20% and 75%. Low intermodulation noise was achieved by going off axis 16 degrees and using SHG and DCG materials to record the master and copies respectively. Astigmatism and Bragg tilt errors were minimized but images showed more coma than prior art. Both coherent and incoherent copies were made, the oherent copies were always low in efficiency because of very high intermodulation noise or because beam ratios were made high to avoid intermodulation noise. Incoherent copies proved to be only a little more difficult to fabricate and the master copy process in an index matching fluid proved to be more versatile as well as optically cleaner. Problems with uniformity from exposure to exposure were found and cured or probable causes were found. A limit to uniformity probably exists that relates to random coherent phasing of overlapping Bragg structures added to very small thermal and mechanical instabilities during exposure. All copies are made in a contact copy jig with each exposure running about 2 seconds. The process for obtaining an unaberrated master at 633 nm while making copies at 488 nm is described for both the coherent and incoherent methods. Test results for an incoherent 5x5 array working at 633 nm are given including an intensity profile of a spot, power distribution and output with crosstalk. Suggestions for further improvements are given.