High Performance Thin-Film Lithium Niobate Modulator With Suppressed Slot-Line Mode on Quartz Substrate Fabricated by Photolithography
Yongqian Tang, Heng Li, Quanan Chen, Xiangyang Dai, Juan Xia, Qiaoyin Lu, Lirong Huang, Weihua Guo
Abstract
In this work, we report high performance thin-film lithium niobate (TFLN) modulators with capacitively loaded traveling-wave electrodes (CL-TWEs) on quartz substrate. Photolithography is employed for fabrication due to its high efficiency compared to electron beam lithography. By utilizing a folded design, the length of the modulator is reduced to a third. A theoretical model is proposed to analyze the electro-optic response of the designed modulators, which considers the impact of the folding design. Additionally, various bend structures of CL-TWEs are fabricated to analyze the dips in the EE response caused by the slot-line mode, and a narrow signal is employed in the bend part to suppress the EE response dips. By introducing the suitable-length delay line, the light wave and microwave in the bend part can match with each other, which further improves the bandwidth. Experiments show that the unfolded modulator with 10-mm modulation length exhibits a low fiber-to-fiber insertion loss of 3.9 dB, a low half-wave voltage of 2.2 V, and an electro-optic response with a 2-dB roll-off at 67 GHz. The modulator demonstrates a π-phase shift thermal power of 15 mW, with an extinction ratio close to 26 dB. The folded modulator with 12-mm modulation length exhibits a low half-wave voltage of 1.85 V and an electro-optic bandwidth exceeding 67 GHz. This work provides a solution for fabricating TFLN modulators with CL-TWEs on quartz substrate.