Fabrication of 500 nm distributed Bragg reflector using Nb2O5-MgF2 multi-layer films

At first, we use an n & K analyzer to measure the optical properties (including refractive index n and extinction coefficient k ) of MgF2 and Nb2O5 single-layer films, in a wavelength range of 200–1700 nm for MgF2 film and in a wavelength range of 350–1500 nm for Nb2O5 film. After the refractive indexes of MgF2 and Nb2O5 single-layer films are measured, we use the measured results to calculate the needed thicknesses of the quarter-wave (1/4 wavelength) MgF2 and Nb2O5 films for the designed green-light (500 nm) distributed Bragg reflectors (DBRs). After that, an E-beam is used to deposit the MgF2-Nb2O5 bilayer films (called as one period) with different periods (two, four, and six periods are deposited in this study) on glass substrates to fabricate the DBRs with a central wavelength of 500 nm. Then we use the field emission scanning electron microscopy (FESEM) to observe the surface images of Nb2O5 films on the different periods of MgF2-Nb2O5 bilayer films. The important novelty is that we use a Focused Ion Beam (FIB) to prepare the samples for the observations of the cross-sections of MgF2-Nb2O5 bilayer films, and those results can be sued to confirm the thicknesses of the bilayer films with different periods. We also compare the reflective ratio of the fabricated DBRs at the designed central wavelength with those calculated values by using the equation investigated by Sheppard. We find that the measured reflective ratios of the fabricated DBRs meet the calculated results obtained from Sheppard’s equation.