Nguyen Huu-Dat, Ródenas Airán, Vázquez de Aldana Javier R, Martín Guillermo, Martínez Javier, Aguiló Magdalena, Pujol Maria Cinta, Díaz Francesc
Opt Express. 2017 Feb 20;25(4):3722-3736. doi: 10.1364/OE.25.003722.
We report mid-infrared LiNbO depressed-index microstructured cladding waveguides fabricated by three-dimensional laser writing showing low propagation losses (~1.5 dB/cm) at 3.68 µm wavelength for both the transverse electric and magnetic polarized modes, a feature previously unachieved due to the strong anisotropic properties of this type of laser microstructured waveguides and which is of fundamental importance for many photonic applications. Using a heuristic modeling-testing iteration design approach which takes into account cladding induced stress-optic index changes, the fabricated cladding microstructure provides low-loss single mode operation for the mid-IR for both orthogonal polarizations. The dependence of the localized refractive index changes within the cladding microstructure with post-fabrication thermal annealing processes was also investigated, revealing its complex dependence of the laser induced refractive index changes on laser fabrication conditions and thermal post-processing steps. The waveguide modes properties and their dependence on thermal post-processing were numerically modeled and fitted to the experimental values by systematically varying three fundamental parameters of this type of waveguides: depressed refractive index values at sub-micron laser-written tracks, track size changes, and piezo-optic induced refractive index changes.
我们报道了通过三维激光写入制造的中红外铌酸锂低折射率微结构包层波导，其在3.68 µm波长下，横向电偏振和磁偏振模式的传播损耗均较低（约1.5 dB/cm），由于这类激光微结构波导具有很强的各向异性特性，这一特性此前尚未实现，而对于许多光子应用而言，这一特性至关重要。采用考虑包层引起的应力 - 光学折射率变化的启发式建模 - 测试迭代设计方法，所制造的包层微结构为中红外波段的两种正交偏振提供了低损耗单模运行。还研究了包层微结构内局部折射率变化与制造后热退火工艺的关系，揭示了激光诱导折射率变化对激光制造条件和热后处理步骤的复杂依赖性。通过系统地改变这类波导的三个基本参数：亚微米激光写入轨道处的低折射率值、轨道尺寸变化和压光诱导折射率变化，对波导模式特性及其对热后处理的依赖性进行了数值建模，并与实验值进行了拟合。
