Guangzhen Li

Broadband sum-frequency generation using d 33 in periodically poled LiNbO 3 thin film in the telecommunications band

We demonstrate the first, to the best of our knowledge, type-0 broadband sum-frequency generation (SFG) based on single-crystal periodically poled LiNbO3 (PPLN) thin film. The broad bandwidth property was largely tuned from mid-infrared region to the telecommunications band by engineering the thickness of PPLN from bulk crystal to nanoscale. It provides SFG a solution with both broadband and high efficiency by using the highest nonlinear coefficient d33 instead of d31 in type-I broadband SFG or second-harmonic generation. The measured 3 dB upconversion bandwidth is about 15.5 nm for a 4 cm long single crystal at 1530 nm wavelength. It can find applications in chip-scale spectroscopy, quantum information processing, LiNbO3-thin-film-based microresonator and optical nonreciprocity devices, etc.

Enhanced Kerr electro-optic nonlinearity and its application in controlling second-harmonic generation

We demonstrated a large enhancement of Kerr electro-optic nonlinearity through cascaded Pockels effects in a domain inversion ferroelectric crystal. We designed a structure that can implement the cascaded Pockels effects and second-harmonic generation simultaneously. The energy coupling between the fundamental lights of different polarizations led to a large nonlinear phase shift, and thus an effective electro-optic nonlinear refractive index. The effective nonlinearity can be either positive or negative, causing the second-harmonic spectra to move towards the coupling center, which in turn, offered us a way to measure the effective electro-optic nonlinear refractive index. The corresponding enhanced Kerr electro-optic nonlinearity is more than three orders of magnitude higher than the intrinsic value. These results open a door to manipulate the nonlinear phase by applying external electric field instead of light intensity in noncentrosymmetric crystals.We proposed a new scheme of controlling second-harmonic generation by enhanced Kerr electro-optic nonlinearity. We designed a structure that can implement the cascaded Pockels effect and second-harmonic generation simultaneously. The energy coupling between the fundamental lights of different polarizations led to a large nonlinear phase shift and, thus, an effective electro-optic nonlinear refractive index. The effective nonlinearity can be either positive or negative, causing the second-harmonic spectra to move toward the coupling center, which, in turn, offered us a way to measure the effective electro-optic nonlinear refractive index. The corresponding enhanced Kerr electro-optic nonlinearity is more than three orders of magnitude higher than the intrinsic value. These results open a door to manipulate the nonlinear phase by applying an external electric field instead of light intensity in noncentrosymmetric crystals.

Optical half-adder and half-subtracter employing the Pockels effect.

The Pockels effect in periodically poled lithium niobate made it possible to switch optical signals between two orthogonal optical linear polarizations of the vertical and horizontal polarization states. Based on this effect, we demonstrated polarization-based binary optical logic gates: AND, and OR gates. By combining these basic gates with other polarization-based optical logic gates such as XOR gate accomplished in our previous researches, half-adder and half-subtracter of digital signals with a high extinction ratio of about 10dB have been demonstrated in our experiment, which made it possible to run more complex logical calculus.

Tunable temporal gap based on simultaneous fast and slow light in electro-optic photonic crystals

We demonstrated a tunable temporal gap based on simultaneous fast and slow light in electro-optic photonic crystals. The light experiences an anomalous dispersion near the transmission center and a normal dispersion away from the center, where it can be accelerated and slowed down, respectively. We also obtained the switch between fast and slow light by adjusting the external electric filed. The observed largest temporal gap is 541 ps, which is crucial in practical event operation inside the gap. The results offer a new solution for temporal cloak.