Sun Bangshan, Morozko Fyodor, Salter Patrick S, Moser Simon, Pong Zhikai, Patel Raj B, Walmsley Ian A, Wang Mohan, Hazan Adir, Barré Nicolas, Jesacher Alexander, Fells Julian, He Chao, Katiyi Aviad, Tian Zhen-Nan, Karabchevsky Alina, Booth Martin J
Department of Engineering Science, University of Oxford, Oxford, OX1 3PJ, UK.
School of Electrical and Computer Engineering, Ben-Gurion University of the Negev, P.O.B. 653, Beer-Sheva, 8410501, Israel.
Light Sci Appl. 2022 Jul 7;11(1):214. doi: 10.1038/s41377-022-00907-4.
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.
光子集成电路将从高精度、低损耗地任意控制波导横截面的能力中受益匪浅，以便在操纵传播光方面提供更多自由度。在此，我们报告一种用于飞秒激光写入光纤兼容玻璃波导的新方法，即球面相位诱导多芯波导（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。在加热状态下以高扫描速度制造时，沿波导仍可实现横截面的精确变形，其形状和尺寸在水平和垂直横向方向上均可实现高分辨率的精细控制。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时仅0.19 dB的极低耦合损耗。易于制造的SPIM-WG器件能够通过改变角度在片上执行光束旋转，或操纵目标波长下传播光的偏振态。我们还展示了SPIM-WG模式转换器，其能在对称和非对称非均匀模式之间高效地提供任意绝热模式转换；例如圆形、椭圆形模式以及通常应用于频率转换和量子光源的来自周期性极化磷酸钛氧钾（ppKTP）波导的非对称模式。这些波导和器件在光学玻璃内部制成，能够在从可见光到红外波长的超宽带范围内工作。与光纤的兼容性也为通常需要输入和输出光纤连接的封装光子集成电路铺平了道路。
