Optical performance investigation of focused ion beam nanostructured integrated Fabry-Perot microcavities in Al2O3

Focused ion beam (FIB) milling is an emerging technology that enables fast, reliable and well-controlled nanometer-size feature definition. Since the method involves physical removal of material by a beam of ions, the technique can be adapted and optimized almost for any material system. Recently we have reported on an optimized approach of FIB nano-structuring, which enabled patterning of DBR gratings on Al2O3 channel waveguides with smooth and uniform sidewalls [1]. Here we address the optical performance and limits of FIB-patterned integrated waveguide Fabry-Perot (F-P) microcavities. The 520-nmperiod surface-relief DBR gratings on dielectric channel waveguides, see Fig. 1(a), were realized using a FEI Nova 600 dual-beam FIB machine. The acceleration voltage was set to 30 kV and the milling current was chosen to be 48 pA. The grating structures were milled by about 200 nm and the length of each grating was ~47.5 μm. The cavity length was varied between 100-450 μm.