Diffractive optical elements with continuous relief fabricated by focused ion beam for monomode fiber coupling.

The design, microfabrication and testing of diffractive optical elements (DOE's) with continuous relief used for fiber coupling are discussed in detail. DOE's with diameters as small as 50 mm are fabricated by means of focused ion beam (FIB) technology. A focused Ga+ ion beam is used to mill a continuous relief microstructure at a 50 kV acceleration voltage. The optical performance of DOE's made in this way was compared with that of DOE's fabricated by other methods. The focusing performance of DOE's fabricated with three and six annulus by FIB milling was investigated. Testing of the system which has a coupling efficiency of -1.25 dB (75%) shows that the design meets the application's requirement for fiber coupling, and that DOE's manufactured by our FIB technology are practicable. Compared with a conventional fiber coupling system that uses a plano - convex lens, our system has the advantages of simplicity, short focal length, low cost for the lens and high coupling efficiency.