Noise Analysis of Second-Harmonic Generation in Undoped and MgO-Doped Periodically Poled Lithium Niobate

Yong Wang,Chang-Qing Xu,Wan-Guo Liang,Ignacio Vargas-Baca,Jorge Fonseca-Campos

doi:10.1155/2008/428971

Abstract

Noise characteristics of second-harmonic generation (SHG) in periodically poled lithium niobate (PPLN) using the quasiphase matching (QPM) technique are analyzed experimentally. In the experiment, a0.78 μm second-harmonic (SH) wave was generated when a 1.56 μm fundamental wave passed through a PPLN crystal (bulk or waveguide). The time-domain and frequency-domain noise characteristics of the fundamental and SH waves were analyzed. By using the pump-probe method, the noise characteristics of SHG were further analyzed when a visible light (532 nm) and an infrared light (1090 nm) copropagated with the fundamental light, respectively. The noise characterizations were also investigated at different temperatures. It is found that for the bulk and waveguide PPLN crystals, the SH wave has a higher relative noise level than the corresponding fundamental wave. For the same fundamental wave, the SH wave has lower noise in a bulk crystal than in a waveguide, and in MgO-doped PPLN than in undoped PPLN. The 532 nm irradiation can lead to higher noise in PPLN than the 1090 nm irradiation. In addition, increasing temperature of device can alleviate the problem of noise in conjunction with the photorefractive effect incurred by the irradiation light. This is more significant in undoped PPLN than in MgO-doped one.

Highlights

Among a variety of nonlinear optical processes, secondharmonic generation (SHG) is one of the most well-known wavelength-conversion schemes [1,2,3]
We can see that in both bulk and waveguide periodically poled lithium niobate (PPLN), the fluctuation amplitude of the fundamental wave is lower than that of the SH wave, and for each wave, its noise is higher in the waveguide PPLN than in the bulk
We have shown the noise characteristics of the SH waves in bulk and waveguide PPLN crystals

Summary

Introduction

Among a variety of nonlinear optical processes, secondharmonic generation (SHG) is one of the most well-known wavelength-conversion schemes [1,2,3]. Any wavelength can be phasematched in the transparent range of a LiNbO3 crystal by choosing a suitable poling period in the QPM structure; the largest nonlinear component (i.e., d33) can be obtained; the propagating waves can undergo the largest nonlinear interaction in the crystal, enhancing the conversion efficiency and offering the possibility of engineering the nonlinearity [2,3,4,5] In such nonlinear SHG processes, it is well known that the conversion efficiency of SHG is proportional to the power of the fundamental wave [1,2,3]. In both bulk and waveguide PPLN crystals, the phase-matching conditions are influenced by the temperature distribution along the optical path of the interacting wave; and high-power irradiation is apt to generate uneven temperature distribution [2, 7, 13]

Methods

Results

Conclusion