Integrable wide-free-spectral-range Fabry–Perot optical filters using free-standing LiNbO_3 thin films

We demonstrate the use of free-standing thin films of a complex oxide for chip-scale optical filtering. The films are used as low-order etalons with very large free spectral ranges that exceed $6.78\mathrm{THz}$ ($>50\mathrm{nm}$ at $1550\mathrm{nm}$) and use a small chip area $(<500\mu {\mathrm{m}}^2)$ when they are integrated. The films are produced by crystal ion slicing; this process exfoliates a micrometers-thin layer of single-crystal optical material from a bulk parent by means of high-energy-ion implantation. The etalons, which are $10\mu \mathrm{m}$ thick with Ag deposited on both surfaces, are integrated into a silica-on-silicon waveguide block.