Compact Integrated Folded Šolc Filter using Periodic 90°-Domain Structures in KNbO3 Single Crystals

A compact integrated folded Solc filter using periodic 90°-domain structures in KNbO3 single crystals is proposed. The periodic 90°-domain structures with a period of 200 µm are fabricated on 0.7-mm-thick (101)-cut KNbO3 single-crystal plates by applying an electric field of 200 V/mm. Using the refractive index change between 90°-domains, we can construct the same arrangement for a folded Solc filter. The measured filtering properties agree well with the calculated ones. This is the first demonstration of an optical filter using periodic domain structures other than 180°-domain structures. It is now possible to fabricate a compact folded Solc filter without inconvenient alignment.