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

The design, microfabrication and testing of diffractive optical elements (D OE's) with continuous relief used for fiber coupling are discussed in detai l. DOE's with diameters as small as 50 mm are fabricated by means of focuse d ion beam (FIB) technology. A focused Ga+ ion beam is used to mill a conti nuous relief microstructure at a 50 kV acceleration voltage. The optical pe rformance of DOE's made in this way was compared with that of DOE's fabrica ted by other methods. The focusing performance of DOE's fabricated with thr ee and six annulus by FIB milling was investigated. Testing of the system w hich has a coupling efficiency of -1.25 dB (75%) shows that the design meet s the application's requirement for fiber coupling, and that DOE's manufact ured by our FIB technology are practicable. Compared with a conventional fi ber coupling system that uses a plano - convex lens, our system has the adv antages of simplicity, short focal length, low cost for the lens and high c oupling efficiency. (C) 2000 Optical Society of America.