Photonics integrated circuitry would benefit considerably from the ability to arbitrarily control waveguide cross-sections with high precision and low loss, in order to provide more degrees of freedom in manipulating propagating light. Here, we report a new method for femtosecond laser writing of optical-fiber-compatible glass waveguides, namely spherical phase-induced multicore waveguide (SPIM-WG), which addresses this challenging task with three-dimensional on-chip light control. Fabricating in the heating regime with high scanning speed, precise deformation of cross-sections is still achievable along the waveguide, with shapes and sizes finely controllable of high resolution in both horizontal and vertical transversal directions. We observed that these waveguides have high refractive index contrast of 0.017, low propagation loss of 0.14 dB/cm, and very low coupling loss of 0.19 dB coupled from a single-mode fiber. SPIM-WG devices were easily fabricated that were able to perform on-chip beam rotation through varying angles, or manipulate the polarization state of propagating light for target wavelengths. We also demonstrated SPIM-WG mode converters that provide arbitrary adiabatic mode conversion with high efficiency between symmetric and asymmetric nonuniform modes; examples include circular, elliptical modes, and asymmetric modes from ppKTP (periodically poled potassium titanyl phosphate) waveguides which are generally applied in frequency conversion and quantum light sources. Created inside optical glass, these waveguides and devices have the capability to operate across ultra-broad bands from visible to infrared wavelengths. The compatibility with optical fiber also paves the way toward packaged photonic integrated circuitry, which usually needs input and output fiber connections.

光子集成电路将从以高精度和低损耗任意控制波导横截面的能力中受益匪浅，以便在操纵传播光时提供更多的自由度。在这里，我们报告了一种用于光纤兼容玻璃波导的飞秒激光写入的新方法，即球形相位诱导多芯波导 (SPIM-WG)，它通过三维片上光控制解决了这一具有挑战性的任务。在高扫描速度的加热状态下制造，仍然可以沿波导实现横截面的精确变形，形状和尺寸在水平和垂直横向方向上具有高分辨率的精细可控性。我们观察到这些波导具有 0.017 的高折射率对比度，0.14 dB/cm 的低传播损耗，以及从单模光纤耦合的 0.19 dB 的极低耦合损耗。SPIM-WG 设备易于制造，能够通过不同的角度执行片上光束旋转，或针对目标波长操纵传播光的偏振态。我们还展示了 SPIM-WG 模式转换器，可在对称和非对称非均匀模式之间提供高效的任意绝热模式转换；示例包括来自 ppKTP（周期性极化磷酸氧钛钾）波导的圆形、椭圆形模式和非对称模式，这些波导通常应用于频率转换和量子光源。这些波导和设备在光学玻璃内部创建，能够在从可见光到红外波长的超宽带范围内工作。