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Abstract
Third-harmonic generation can be realized via both χ(3) and cascaded χ(2) nonlinear processes in a triply-resonant microcavity. It is still unknown how these processes interfere with each other and the optimization of the conversion efficiency still remains as a question. In this work, the interplay between the direct third-harmonic generation and the cascaded process combining of the second-harmonic generation and the sum-frequency generation are investigated. It is found that the interference effect between these two processes can be used to improve the conversion efficiency. By optimizing the cavity resonance and the external coupling conditions, the saturation of the nonlinear conversion is mitigated and the third-harmonic conversion efficiency is increased. A design rule is provided for achieving efficient third-harmonic generation in an optical microcavity, which can be generalized further to the high-order harmonic generations.
Highlights
Nonlinear photonics based on the third-order nonlinear process (χ(3)) can be used for various applications in classical and quantum fields [1,2,3,4]
To enhance the efficiency of the third-harmonic generation (THG), one should increase the nonlinear susceptibility of the nonlinear processes, reduce the mode volume, optimize the modal overlap as well as increase the quality factor of the microcavity [6]
One should notice that the quality factor of an microcavity is usually limited due to the fabrication imperfection and the material absorption, which builds a barrier to increase the efficiency of THG
Summary
Nonlinear photonics based on the third-order nonlinear process (χ(3)) can be used for various applications in classical and quantum fields [1,2,3,4]. The efficiency of the third-order nonlinear process is very low, due to the very weak χ(3) susceptibilities in most materials. To enhance the efficiency of the third-harmonic generation (THG), one should increase the nonlinear susceptibility of the nonlinear processes, reduce the mode volume, optimize the modal overlap as well as increase the quality factor of the microcavity [6]. People have demonstrated the secondharmonic generation (SHG), sum-frequency generation (SFG), as well as THG could be observed simultaneously under the multiple-resonant condition in a cavity by introducing materials with both χ(2) and χ(3) nonlinearity, e.g., Lithium Niobate and Aluminum Nitride (AlN). When operating with a high pump power, one should optimize the resonant frequencies and the external coupling ratio of the MRR to compensate the saturation effect for achieving a maximal conversion efficiency
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