Hybrid microdiffractive-microrefractive lens with a continuous relief fabricated by use of focused-ion-beam milling for single-mode fiber coupling

The design, microfabrication, and testing of a hybrid microdiffractive-micr orefractive lens with a continuous relief that is used with a laser diode f or monomode fiber coupling is discussed. The hybrid microlens with a diamet er as small as 65 mum and a numerical aperture of 0.25 is fabricated direct ly onto a spherical surface by use of focused-ion-beam milling technology. A focused Ga+ ion beam is used to mill the continuous relief microstructure at an acceleration voltage of 50 kV. From the test results a coupling effi ciency of 71% (-1.49 dB) was achieved at room temperature. A diffraction ef ficiency of the main diffractive order, -1, was measured to as high as 90.5 % at a wavelength of 635 nm. This indicates that the hybrid microlens was s uitably designed within the application requirements and satisfactorily man ufactured with focused-ion-beam milling. (C) 2001 Optical Society of Americ a.