We report a novel mode modulator based on a KTN crystal waveguide produced by femtosecond laser (fs-laser) writing. The KTN waveguide is a typical dual-line structure that depends on the decrease of refractive index at the focus area. The propagation loss of the waveguide along the TE polarization is as low as ~0.9 dB/cm at 632.8 nm. The investigation of confocal micro-Raman spectra reveals that the microstructure of the waveguide region has no obvious change during the femtosecond laser direct writing (FsLDW) procedure. Under the applied direct current (DC) electric field, the waveguide modes in the guiding structure can be modulated, resulting in mode conversion from TE00 to TE02. Both the experimental results and the theoretical simulation indicate that the mode modulation phenomenon originates from the space-charge-field induced refractive-index increment between the waveguide core and the bulk substrate. The simplicity and remarkable performance of the demonstrated device paves the way for integrating low-cost and high-efficient electric-optical modulator on photonics circuits.

我们报告基于飞秒激光（fs激光）写入产生的KTN晶体波导的新型模式调制器。KTN波导是一种典型的双线结构，取决于焦点区域折射率的降低。波导沿TE极化的传播损耗在632.8 nm处低至〜0.9 dB / cm。共聚焦显微拉曼光谱的研究表明，在飞秒激光直接写入（FsLDW）过程中，波导区域的微观结构没有明显变化。在施加的直流（DC）电场下，可以调制导引结构中的波导模式，从而实现从TE00到TE02的模式转换。实验结果和理论模拟均表明，模式调制现象源于波导核与块状衬底之间的空间电荷场诱导的折射率增量。演示设备的简单性和出色的性能为将低成本和高效的电光调制器集成到光子电路上铺平了道路。