All-optical logic gates including AND, XOR, and NOT gates, as well as a half-adder, are realized based on two-dimensional lithium niobate photonic crystal (PhC) circuits with PhC micro-cavities. The proposed all-optical devices have an extinction ratio as high as 23 dB due to the effective all-optical switch function induced by two-missing-hole micro-cavities. These proposed devices can have potential implementation of complex integrated optical functionalities including all-optical computing in a lithium niobate slab or thin film.

Developing natural “free space” frequency upconversion is essential for photonic integrated circuits. In a single-crystal lithium niobate thin film planar waveguide of less than 1 μm thickness, we achieve type I and type II mode phase-matching conditions simultaneously for this thin film planar waveguide. Finally, by employing the mode phase matching of e+e→e with d33 at 1018 nm, we successfully achieve a green second-harmonic wave output with the conversion efficiency of 0.12%/(W·cm2), which verifies one of our simulation results. The rich mode phase matching for three-wave mixing in a thin film planar waveguide may provide a potential application in on-chip frequency upconversions for integrated photonic and quantum devices.

Using a lithium niobate (LN) material, we propose a broadband polarization beam splitter (PBS) with high efficiency by employing a negative refractive photonic crystal (PhC) wedge slab with an angle of 60°. It can split the incident light into two parts at about 90° with TE and TM polarizations. The transmissions of polarized light for an LN-based PBS are more than 80% with a broad angle and wavelength bandwidth of 8° and 70 nm at 1.55 μm, while with a Si-based PhC, no PBS with high efficiency can be realized for the relatively lower transmission of TM output light.