Photonic bound states in the continuum (BIC) have excellent effects in localizing light fields. Low propagation loss of TM mode has been achieved in different orders of BICs on an etchless lithium niobate (LiNbO) platform. Herein, we simulatively demonstrate a 1 × 2 MMI (Multimode interference) power splitter based on waveguides constructed by low-refractive-index structure (ZEP-520A) on a high-refractive-index thin membrane (LiNbO), which can optimize the bandwidth, insertion loss and other performance indicators of optical devices. Simulation results show that the working wavelength cover the entire communication band ranging from 1260 nm to 1675 nm, and the transmission efficiency is more than 48.7%, while the insertion loss is less than 0.01 dB covering a 415 nm bandwidth. The field distribution results verify that the designed MMI demonstrated high mode purity at the output, and the mode field is well localized in the LiNbO film, leading to a reduce of the dependence of the transmission efficiency originated from the quality of the sidewall of the device, and the device can evenly distribute the TM mode of the ultra-broadband incident light to the two output ports. Furthermore, the fabrication process of the MMI device can be immensely simplified by a one-step exposure method, which reduces the scattering loss and asymmetry caused by the fabrication.

中文翻译：

---

1.26 至 1.67 μm 的超宽带 MMI 功率分配器，具有连续谱中的光子束缚态

连续体中的光子束缚态（BIC）在光场局域化方面具有优异的效果。在无蚀刻铌酸锂 (LiNbO) 平台上，不同阶数的 BIC 实现了 TM 模式的低传播损耗。在这里，我们模拟演示了一种基于高折射率薄膜（LiNbO）上的低折射率结构（ZEP-520A）构建的波导的1×2 MMI（多模干涉）功率分配器，它可以优化带宽、插入损耗等光器件性能指标。仿真结果表明，工作波长覆盖1260 nm~1675 nm整个通信频段，传输效率超过48.7%，415 nm带宽插入损耗小于0.01 dB。场分布结果验证了设计的MMI在输出端表现出高模式纯度，并且模式场很好地定位在LiNbO薄膜中，从而减少了源于器件侧壁质量的传输效率的依赖性，该器件可以将超宽带入射光的TM模式均匀地分配到两个输出端口。此外，通过一步曝光方法可以极大地简化MMI器件的制造工艺，减少制造过程中造成的散射损耗和不对称性。