Experimental Research on Single-Pass SHG from Periodically Poled LiNbO_3 Crystal

Quasi phase matching (QPM) periodical poled LiNbO 3(PPLN) is designed and successfully fabricated to enable second harmonic generation(SHG).The samples were Z cut 0.5 mm thick and grating period is Λ=6.8 μm for the first order QPM of continual wave λ=1.064 μm which is emitted by Nd∶YAG laser at room temperature 27 ℃. The output single pass SHG power was tested by an authorized optical system. The normalized max conversion efficiency is calculated to be 0.25 0 0(W·cm) -1 .The fabrication and parameters calculated method are introduced, and testing scheme is described in this paper. Even some ideas to improve conversion efficiency are offered.

Investigation of Domain Wall Velocity to External Fields for High-Quality Waveguide-Type Periodically Poled LiNbO_(3) Fabrication

The Ti-doped waveguide-type periodically poled LiNbO_(3)(PPLN)were fabricated and the dependence of domain wall velocity on an external field applied for domain inversion was investigated.The whole polarization reversal process was computer-controlled to regulate domain wall expansion at a feedback time shorter than 5μs.The coercive voltage and several values of excess voltage were applied on 500μm-thick wafers serially connected to a 1-MOhm external resistor which had an effect of the poling current reduction,i.e.the deceleration of domain wall expansion.The domain wall velocity is sensitive to the poling voltage,precisely speaking,to the excess voltage.The domain wall velocities were 28.70,16.02 and 5.75μm·s^(-1)under poling field of 23.5,22.0 and 21.0 kV·mm^(-1),respectively.Moreover,average duty cycle of PPLN is about 49.93%.

The geometric phase in nonlinear frequency conversion

The geometric phase of light has been demonstrated in various platforms of the linear optical regime, raising interest both for fundamental science as well as applications, such as flat optical elements. Recently, the concept of geometric phases has been extended to nonlinear optics, following advances in engineering both bulk nonlinear photonic crystals and nonlinear metasurfaces. These new technologies offer a great promise of applications for nonlinear manipulation of light. In this review, we cover the recent theoretical and experimental advances in the field of geometric phases accompanying nonlinear frequency conversion. We first consider the case of bulk nonlinear photonic crystals, in which the interaction between propagating waves is quasi-phase-matched, with an engineerable geometric phase accumulated by the light. Nonlinear photonic crystals can offer efficient and robust frequency conversion in both the linearized and fully-nonlinear regimes of interaction, and allow for several applications including adiabatic mode conversion, electromagnetic nonreciprocity and novel topological effects for light. We then cover the rapidly-growing field of nonlinear Pancharatnam-Berry metasurfaces, which allow the simultaneous nonlinear generation and shaping of light by using ultrathin optical elements with subwavelength phase and amplitude resolution. We discuss the macroscopic selection rules that depend on the rotational symmetry of the constituent meta-atoms, the order of the harmonic generations, and the change in circular polarization. Continuous geometric phase gradients allow the steering of light beams and shaping of their spatial modes. More complex designs perform nonlinear imaging and multiplex nonlinear holograms, where the functionality is varied according to the generated harmonic order and polarization. Recent advancements in the fabrication of three dimensional nonlinear photonic crystals, as well as the pursuit of quantum light sources based on nonlinear metasurfaces, offer exciting new possibilities for novel nonlinear optical applications based on geometric phases.

LiNbO_3 based optical devices for fiber communication

Lithium niobate （LiNbO3） is a useful photonic material for its electro-optic and nonlinear optical properties. In this paper, I will report developments of LiNbO3 based optical devices for fiber communication, including high-performance modulators and high efficiency wavelength converters.