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Quasi-phase-matching is a technique in non … Quasi-phase-matching is a technique in nonlinear optics which allows a positive net flow of energy from the pump frequency to the signal and idler frequencies by creating a periodic structure in the nonlinear medium. Momentum is conserved, as is necessary for phase-matching, through an additional momentum contribution corresponding to the wavevector of the periodic structure. Consequently, in principle any three-wave mixing process that satisfies energy conservation can be phase-matched. For example, all the optical frequencies involved can be collinear, can have the same polarization, and travel through the medium in arbitrary directions. This allows one to use the largest nonlinear coefficient of the material in the nonlinear interaction. Quasi-phase-matching ensures that there is positive energy flow from the pump frequency to signal and idler frequencies even though all the frequencies involved are not phase locked with each other. Energy will always flow from pump to signal as long as the phase between the two optical waves is less than 180 degrees. Beyond 180 degrees, energy flows back from the signal to the pump frequencies. The coherence length is the length of the medium in which the phase of pump and the sum of idler and signal frequencies are 180 degrees from each other. At each coherence length the crystal axes are flipped which allows the energy to continue to positively flow from the pump to the signal and idler frequencies. The most commonly used technique for creating quasi-phase-matched crystals has been periodic poling. More recently, continuous phase control over the local nonlinearity was achieved using nonlinear metasurfaces with homogeneous linear optical properties but spatially varying effective nonlinear polarizability. Optical fields are strongly confined within or surround the nanostructures, nonlinear interactions can therefore be realized with an ultra-small area down to 10 nm to 100 nm and can be scattered in all directions to produce more frequencies. Thus, relaxed phase matching can be achieved at the nanoscale dimension.an be achieved at the nanoscale dimension.
, 准相位匹配（Quasi-phase-matching）是非线性光学频率转换的一种重要 … 准相位匹配（Quasi-phase-matching）是非线性光学频率转换的一种重要技术，其思想最早由J. Armstrong等人于1962年提出，V. Berger于1998年将它推广到，并提出非线性光子晶体的概念。非线性频率转化中要求动量守恒，在普通非线性晶体中由于色散的存在较难实现，特别是同时多个非线性相互作用的，而非线性周期性结构提供的倒格矢则能较容易地实现相位匹配。通过在非线性介质中构造周期性的结构（非线性光子晶体），它能有效的实现非线性频率转化。相对通常的完美相位匹配（温度匹配，角度匹配），这种方法称为准相位匹配，它能更容易利用较大的非线性系数。因此，现在这种技术已广泛应用于非线性光学领域，并且实现了一些普通晶体中难以做到的现象。 准相位匹配需要在非线性光子晶体中实现，在非线性光学发展初期，这种技术主要停留在理论阶段。20世纪90年代，随着非线性晶体生长和极化技术的提高，非线性光子晶体的制作得到极大发展。1993年，Yamada等人首次利用电极化反转的方法制作出光学超晶格；1995年，M. Fejer等人制作出大块周期性极化铌酸锂（periodically poled lithium niobate, PPLN）; 1997年，闵乃本等人（N.B. Ming et al.）制作出准周期极化光学超晶格，并用首次利用单束光单块晶体实现了三倍频绿光的产生；1999年，N. Broderick等人制作出第一个二维，并验证了非线性布拉格衍射。现在，非线性光子晶体中的准相位匹配技术已广泛应用于二次，三次和高次谐波的产生，波长转换，参量转换等过程。中的准相位匹配技术已广泛应用于二次，三次和高次谐波的产生，波长转换，参量转换等过程。
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准相位匹配（Quasi-phase-matching）是非线性光学频率转换的一种重要 … 准相位匹配（Quasi-phase-matching）是非线性光学频率转换的一种重要技术，其思想最早由J. Armstrong等人于1962年提出，V. Berger于1998年将它推广到，并提出非线性光子晶体的概念。非线性频率转化中要求动量守恒，在普通非线性晶体中由于色散的存在较难实现，特别是同时多个非线性相互作用的，而非线性周期性结构提供的倒格矢则能较容易地实现相位匹配。通过在非线性介质中构造周期性的结构（非线性光子晶体），它能有效的实现非线性频率转化。相对通常的完美相位匹配（温度匹配，角度匹配），这种方法称为准相位匹配，它能更容易利用较大的非线性系数。因此，现在这种技术已广泛应用于非线性光学领域，并且实现了一些普通晶体中难以做到的现象。此，现在这种技术已广泛应用于非线性光学领域，并且实现了一些普通晶体中难以做到的现象。
, Quasi-phase-matching is a technique in non … Quasi-phase-matching is a technique in nonlinear optics which allows a positive net flow of energy from the pump frequency to the signal and idler frequencies by creating a periodic structure in the nonlinear medium. Momentum is conserved, as is necessary for phase-matching, through an additional momentum contribution corresponding to the wavevector of the periodic structure. Consequently, in principle any three-wave mixing process that satisfies energy conservation can be phase-matched. For example, all the optical frequencies involved can be collinear, can have the same polarization, and travel through the medium in arbitrary directions. This allows one to use the largest nonlinear coefficient of the material in the nonlinear interaction.the material in the nonlinear interaction.
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准相位匹配
, Quasi-phase-matching
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