Method for increasing bandwidth of quasi-phase matching frequency multiplication conversion

Abstract

The invention provides a method for increasing the bandwidth of quasi-phase matching frequency multiplication conversion. A crystal used in the method is provided with a non-period structure, multi-wavelength frequency multiplication conversion can be achieved at the same time, and the crystal meets quasi-phase matching and group velocity matching conditions at the same time within a specific wavelength range. The optimal structure of the crystal is obtained through a genetic algorithm. The preference structure of the crystal is a non-period polarized lithium niobate crystal, the crystal is in a cuboid shape, the upper surface and the lower surface are parallel and are polished, the crystal is uniformly divided into unit domains with the equal length in the light wave propagation direction, the spontaneous polarization direction of each unit domain is selected to be upward or downward, and the unit domains with a few continuous signals being the same form one positive domain or one negative domain. According to the method, the quasi-phase matching and group velocity matching conditions are met at the same time, higher and smooth conversion efficiency is kept within a certain specific wavelength range, the bandwidth of the frequency multiplication conversion can be increased, and the method has great theoretical and practical significance.

Description

technical field [0001] The invention relates to a method for improving the bandwidth of quasi-phase matching frequency multiplication conversion. Background technique [0002] The second-order nonlinear optical effects, such as frequency doubling, sum frequency, difference frequency and optical parametric oscillation, have always been the research hotspots of nonlinear optics. Using the second-order nonlinear coefficient of the material, second-order nonlinear processes such as frequency conversion can be realized. However, since the propagation speeds of the fundamental wave and the harmonic wave in the material are inconsistent, it will cause phase mismatch and reduce the conversion efficiency [Ye Peixian, nonlinear optics, China Science and Technology Press, Beijing, 1999.]. Taking optical doubling as an example, the frequency of the fundamental wave is ω, the frequency of the second harmonic is 2ω, and the refractive indices of the fundamental wave and the second harmon...

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Problems solved by technology

However, each technology has certain limitations, so the problem of high-efficiency harmonic conversion of broadband lasers has not been well resolved

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