The lithium-niobate-on-insulator (LNOI) platform has recently emerged as a promising candidate for advanced photonic functions due to its excellent electro-optic coefficient. However, there remain some challenges associated with the etching of LNOI, which typically results in a decreased performance of the fabricated devices. For instance, fabrication errors may reduce the bandwidth of the mode multiplexer and demultiplexer (MMUX/DEMMUX), thereby limiting the capacity of the communication transmission. In this study, a four-channel broadband MMUX/DEMMUX based on an LNOI strip waveguide is experimentally demonstrated by employing an asymmetrical directional coupler structure. To avoid phase mismatch caused by etching depth error, an LNOI strip waveguide was introduced instead of a ridge waveguide. Additionally, an auxiliary spiral loss line was introduced to consume the residual energy of incomplete coupling due to fabrication error and ensure the low crosstalk of the device. Experimental results show that the device achieves a bandwidth exceeding 130 nm with a crosstalk of less than −10.6 dB, making it achieve the largest multiplexing bandwidth reported for LNOI-based platforms. Furthermore, a clear eye diagram at 64 Gbps demonstrates the capability for the high-speed communication offered by the fabricated device.

中文翻译：

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基于薄膜铌酸锂平台的四通道宽带模式（解）复用器


绝缘体上铌酸锂（LNOI）平台最近因其优异的电光系数而成为先进光子功能的有前途的候选者。然而，LNOI 蚀刻仍然存在一些挑战，这通常会导致所制造器件的性能下降。例如，制造错误可能会减少模式复用器和解复用器（MMUX/DEMMUX）的带宽，从而限制通信传输的容量。在这项研究中，通过采用非对称定向耦合器结构，实验演示了基于 LNOI 条形波导的四通道宽带 MMUX/DEMMUX。为了避免蚀刻深度误差引起的相位失配，引入了LNOI条形波导而不是脊形波导。此外，还引入了辅助螺旋损耗线，以消耗由于制造误差导致的不完全耦合的残余能量，保证器件的低串扰。实验结果表明，该器件实现了超过 130 nm 的带宽，串扰小于 -10.6 dB，使其实现了基于 LNOI 的平台所报道的最大复用带宽。此外，64 Gbps 下的清晰眼图展示了所制造设备提供的高速通信能力。