Periodic domain inversion in x-cut single-crystal lithium niobate thin film

Abstract

We report the fabrication of periodically poled domain patterns in x-cut lithium niobate thin-film. Here, thin films on insulator have drawn particular attention due to their intrinsic waveguiding properties offering high mode confinement and smaller devices compared to in-diffused waveguides in bulk material. In contrast to z-cut thin film lithium niobate, the x-cut geometry does not require back electrodes for poling. Further, the x-cut geometry grants direct access to the largest nonlinear and electro-optical tensor element, which overall promises smaller devices. The domain inversion was realized via electric field poling utilizing deposited aluminum top electrodes on a stack of LN thin film/SiO2 layer/Bulk LN, which were patterned by optical lithography. The periodic domain inversion was verified by non-invasive confocal second harmonic microscopy. Our results show domain patterns in accordance to the electrode mask layout. The second harmonic signatures can be interpreted in terms of spatially, overlapping domain filaments which start their growth on the +z side.

Status and Potential of Lithium Niobate on Insulator (LNOI) for Photonic Integrated Circuits

“…In LNOI waveguides, QPM can be achieved by inverting the spontaneous polarization of the lithium niobate crystal periodically along the waveguide. The inversion of the crystal direction, also called domain inversion, can either be done before the lithium niobate thin‐film is bonded on the silica buffer layer in the LNOI wafer fabricated process or afterwards on the LNOI wafer itself . A method to generate domain patterns on LNOI is the electric field poling technique.…”

“…The electrode fingers are oriented along the crystallographic Z‐direction as it is illustrated in Figure b. The domain inversion process occurs when a high voltage is applied to one electrode and the other electrode of the pair is connected to ground, which generates a high electric field at the tips of the electrode fingers exceeding the coercive field . The fingers separation is in the order of tens of microns and the applied voltages are in the order of several hundreds to a few thousand volts.…”

“…The inversion of the crystal direction, also called domain inversion, can either be done before the lithium niobate thin-film is bonded on the silica buffer layer [79] in the LNOI wafer fabricated process or afterwards on the LNOI wafer itself. [28,54,80,81] A method to generate domain patterns on LNOI is the electric field poling technique. This technique reverses the direction of the spontaneous polarization by locally applying an electric field along the polar z-axis of the crystal, exceeding the so-called coercive field.…”

“…The domain inversion process occurs when a high voltage is applied to one electrode and the other electrode of the pair is connected to ground, which generates a high electric field at the tips of the electrode fingers exceeding the coercive field. [80] The fingers separation is in the order of tens of microns and the applied voltages are in the order of several hundreds to a few thousand volts. This domain engineering method has successfully been used to achieve domain inversion with periods down to 2.4 μm.…”

A Theoretical Study on Rib‐Type Photonic Wires Based on LiNbO3 Thin Film on Insulator

“…Nowadays, a full wafer-scale (3 in. [7,[37][38][39][40][41][42][43][44][45][46] These devices are highly efficient, possess great application prospect, and are expected to replace most conventional devices. [6][7][8][9] Based on the LNOI thin-film, researchers have made much effort to develop various ultra-compact micro-photonic devices over the past years.…”