Broadband enhancement of Čerenkov second harmonic generation in a sunflower spiral nonlinear photonic crystal

Polarization sensitive microstructures fabricated on lithium niobate surfaces by using femtosecond laser pulses

Polarization sensitive microstructures with different morphologies were induced by irradiating dual lithium niobate crystals with femtosecond laser pulses. An upper lithium niobate crystal served as a mask plate to tailor light field, which led to the formation of crater and arc-shaped structures on the surface of a lower lithium niobate crystal. In single-shot irradiation, the orientation and morphology of resultant microstructures can be tailored by controlling the focusing position, because focus splitting took place when a focused laser light propagated through dual lithium niobate crystals. In scanning, the width and morphology of laser scan lines can be governed using various combinations of focusing position and scanning direction. Furthermore, large-area micro/nanostructures with different topography features were successfully fabricated on the crystal surface and their absorption spectra indicated that the absorptance in the visible wavelength range was strongly dependent on fabricated micro/nanostructures. This new type of structured lithium niobate surfaces can be potentially applied in optical and photonic devices.

Research development on fabrication and optical properties of nonlinear photonic crystals

Since the lasers at fixed wavelengths are unable to meet the requirements of the development of modern science and technology, nonlinear optics is significant for overcoming the obstacle. Investigation on frequency conversion in ferroelectric nonlinear photonic crystals with different superlattices has been being one of the popular research directions in this field. In this paper, some mature fabrication methods of nonlinear photonic crystals are concluded, for example, the electric poling method at room temperature and the femtosecond direct laser writing technique. Then the development of nonlinear photonic crystals with one-dimensional, two-dimensional and three-dimensional superlattices which are used in quasi-phase matching and nonlinear diffraction harmonic generation is introduced. In the meantime, several creative applications of nonlinear photonic crystals are summarized, showing the great value of them in an extensive practical area, such as communication, detection, imaging, and so on.

Efficient nonlinear beam shaping in three-dimensional lithium niobate nonlinear photonic crystals

Nonlinear beam shaping refers to spatial reconfiguration of a light beam at a new frequency, which can be achieved by using nonlinear photonic crystals (NPCs). Direct nonlinear beam shaping has been achieved to convert second-harmonic waves into focusing spots, vortex beams, and diffraction-free beams. However, previous nonlinear beam shaping configurations in one-dimensional and two-dimensional (2D) NPCs generally suffer from low efficiency because of unfulfilled phase-matching condition. Here, we present efficient generations of second-harmonic vortex and Hermite-Gaussian beams in the recently-developed three-dimensional (3D) lithium niobate NPCs fabricated by using a femtosecond-laser-engineering technique. Since 3D χ⁽²⁾ modulations can be designed to simultaneously fulfill the requirements of nonlinear wave-front shaping and quasi-phase-matching, the conversion efficiency is enhanced up to two orders of magnitude in a tens-of-microns-long 3D NPC in comparison to the 2D case. Efficient nonlinear beam shaping paves a way for its applications in optical communication, super-resolution imaging, high-dimensional entangled source, etc.

Generation of light with desirable amplitude and phase profiles with nonlinear wavefront shaping is of great interest for optical technologies. Here, the authors demonstrate efficient nonlinear beam shaping using three-dimensional lithium niobate photonic crystals fabricated using a femtosecond-laser-engineering technique.