Nonlinear increase, invisibility, and sign inversion of a localized fs-laser-induced refractive index change in crystals and glasses.,Light: Science & Applications

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Nonlinear increase, invisibility, and sign inversion of a localized fs-laser-induced refractive index change in crystals and glasses.
Light: Science & Applications ( IF 20.6 ) Pub Date : 2020-04-20 , DOI: 10.1038/s41377-020-0298-8
Jerome Lapointe ₁ , Jean-Philippe Bérubé ₁ , Yannick Ledemi ₁ , Albert Dupont ₁ , Vincent Fortin ₁ , Younes Messaddeq ₁ , Réal Vallée ₁

Affiliation

Multiphoton absorption via ultrafast laser focusing is the only technology that allows a three-dimensional structural modification of transparent materials. However, the magnitude of the refractive index change is rather limited, preventing the technology from being a tool of choice for the manufacture of compact photonic integrated circuits. We propose to address this issue by employing a femtosecond-laser-induced electronic band-gap shift (FLIBGS), which has an exponential impact on the refractive index change for propagating wavelengths approaching the material electronic resonance, as predicted by the Kramers-Kronig relations. Supported by theoretical calculations, based on a modified Sellmeier equation, the Tauc law, and waveguide bend loss calculations, we experimentally show that several applications could take advantage of this phenomenon. First, we demonstrate waveguide bends down to a submillimeter radius, which is of great interest for higher-density integration of fs-laser-written quantum and photonic circuits. We also demonstrate that the refractive index contrast can be switched from negative to positive, allowing direct waveguide inscription in crystals. Finally, the effect of the FLIBGS can compensate for the fs-laser-induced negative refractive index change, resulting in a zero refractive index change at specific wavelengths, paving the way for new invisibility applications.

中文翻译：

晶体和玻璃中局部fs激光诱导的折射率变化的非线性增加，不可见性和符号反转。

通过超快激光聚焦的多光子吸收是唯一允许对透明材料进行三维结构修改的技术。然而，折射率变化的幅度相当有限，从而阻止了该技术成为制造紧凑型光子集成电路的首选工具。我们建议通过使用飞秒激光诱导的电子带隙位移（FLIBGS）来解决此问题，如Kramers-Kronig关系所预测的那样，该位移对传播波长接近材料电子共振的折射率变化具有指数影响。。在理论计算的支持下，基于修正的Sellmeier方程，Tauc律和波导弯曲损耗的计算，我们实验证明了几种应用可以利用此现象。首先，我们演示了波导弯曲向下至亚毫米半径的情况，这对于fs激光写入的量子和光子电路的更高密度集成非常感兴趣。我们还证明，折射率对比可以从负切换为正，从而可以在晶体中直接进行波导刻写。最后，FLIBGS的效果可以补偿fs激光引起的负折射率变化，从而在特定波长处导致零折射率变化，为新的隐形应用铺平了道路。允许直接在晶体中刻写波导。最后，FLIBGS的效果可以补偿fs激光引起的负折射率变化，从而在特定波长下导致零折射率变化，从而为新的隐形应用铺平了道路。允许直接在晶体中刻写波导。最后，FLIBGS的效果可以补偿fs激光引起的负折射率变化，从而在特定波长下导致零折射率变化，从而为新的隐形应用铺平了道路。

更新日期：2020-04-24

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