Hybrid integrated polarization mode converters and low-voltage electrooptic modulators using crystal-ion-sliced LiNbO_3 films

摘要

Lithium Niobate (LiNbO_3) films produced by the crystal ion slicing (CIS) method are introduced in various components in use in the optical telecommunications market. The CIS technique employs high-energy ion implantation to create a narrow (～0.2 μm) planar layer of localized damage, buried ～10 μm beneath the surface of the implanted LiNbO_3 wafers. This sacrificial layer allows for slicing of microns-thick LiNbO_3 films, either by selective wet chemical etching or by thermal shock. The obtained films have bulk material properties and morphology suitable for integrated optics applications. Slices of X-cut LiNbO_3 were used to produce zero-order wave retarders that can be inserted in slots cut into planar lightware circuits, resulting in TE-TM polarization mode conversion with high extinction ratio (30 dB) and low excess loss (< 0.1 dB). Conventional LiNbO_3 waveguide fabrication techniques were combined with the CIS process to produce CIS films of Z-cut LiNbO_3 with optical circuits patterned prior to lift-off, having propagation losses typical of bulk LiNbO_3 waveguides. Using thin sheets of LiNbO_3, velocity- and impedance-matched modulators can be fabricated with low V_πL(～7.6 V·cm) and low microwave losses (0.3 dB/cm·GHz~(1/2)). The CIS film optical circuits can be integrated into hybrid systems with otherwise incompatible, yet technologically important materials platforms.