Near-surface optical waveguides were fabricated in alkaline earth boro-aluminosilicate glass (Eagle2000), by femtosecond laser direct writing, using two distinct approaches. First, the capability of directly inscribing optical waveguides close to the surface was tested, and then, compared to the adoption of post writing wet etching to bring to the surface waveguides inscribed at greater depths. Laser ablation was found to limit the minimum surface to core center distance to 6.5 µm in the first method, with anisotropic wet etching limiting the latter to 3 µm without any surface deformation; smaller separations can be achieved at the cost of the planar surface topography. Furthermore, the waveguide's cross-section was seen to vary for laser inscription nearing the surface, observations that were also corroborated by its distinct guiding characteristics when compared to the adoption of post writing wet etching. The spectral analysis (in the 500–1700 nm range) also evidenced an increase in insertion loss for longer wavelengths and smaller surface to core center separations, caused, most likely, by coupling loss due to the interaction between the propagating mode and the surface. Different lengths of waveguide exposed to the surface were also tested, revealing that scattering loss due to surface roughness is not an issue at the centimeter scale.

中文翻译：

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通过飞秒激光写入在玻璃中刻写表面波导以增强倏逝波重叠

近表面光波导是在碱土硼铝硅酸盐玻璃 (Eagle2000) 中通过飞秒激光直写制造的，使用两种不同的方法。首先，测试了接近表面直接刻录光波导的能力，然后与采用写入后湿蚀刻的方式进行比较，使表面波导刻录到更深的深度。在第一种方法中，发现激光烧蚀将最小表面到核心中心距离限制为 6.5 µm，各向异性湿蚀刻将后者限制为 3 µm，没有任何表面变形；可以以平面形貌为代价实现更小的分离。此外，可以看到波导的横截面因靠近表面的激光刻字而变化，与采用写后湿蚀刻相比，其独特的引导特征也证实了这些观察结果。光谱分析（在 500-1700 nm 范围内）还证明了更长波长和更小的表面到核心中心间距的插入损耗增加，这很可能是由传播模式和表面之间的相互作用引起的耦合损耗引起的。还测试了暴露于表面的不同长度的波导，表明由于表面粗糙度导致的散射损失在厘米尺度上不是问题。由于传播模式和表面之间的相互作用引起的耦合损耗。还测试了暴露于表面的不同长度的波导，表明由于表面粗糙度导致的散射损失在厘米尺度上不是问题。由于传播模式和表面之间的相互作用引起的耦合损耗。还测试了暴露于表面的不同长度的波导，表明由于表面粗糙度导致的散射损失在厘米尺度上不是问题。