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• Chinese Optics Letters
• Vol. 20, Issue 2, 022502 (2022)
Fan Yang1、2, Xiansong Fang1、2, Xinyu Chen1、2, Lixin Zhu1, Fan Zhang1、2, Zhangyuan Chen1、2, and Yanping Li1、2、*
Author Affiliations
• 1State Key Laboratory of Advanced Optical Communication Systems and Networks, Department of Electronics, Peking University, Beijing 100871, China
• 2Frontiers Science Center for Nano-optoelectronics, Peking University, Beijing 100871, China
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Abstract

High-performance thin film lithium niobate (LN) electro-optic modulators with low cost are in demand. Based on photolithography and wet etching, we experimentally demonstrate a thin film LN Mach–Zehnder modulator with a 3 dB bandwidth exceeding 110 GHz, which shows the potential of boosting the throughput and reducing cost. The fabricated modulator also exhibits a comparable low half-wave voltage-length product of $∼2.37 V·cm$, a high extinction ratio of $>23 dB$, and the propagation loss of optical waveguides of $∼0.2 dB/cm$. Besides, six-level pulse amplitude modulation up to $250 Gb/s$ is successfully achieved.

1. Introduction

Exponentially increasing global network traffic poses severe challenges to the bandwidth of optical transceivers. Electro-optic modulators (EOMs) with a large bandwidth, low-power consumption, a small footprint, and the possibility of large-scale manufacturing are in demand. In the past few years, tremendous efforts have been made towards a variety of platforms such as silicon (Si)[1,2], germanium-Si (GeSi)[3], indium phosphide (InP)[4], polymers[5], plasmonics[6], and thin film lithium niobate (TFLN)[712]. Among them, monolithic TFLN EOMs, with etched lithium niobate (LN) waveguides, have attracted more and more attention since they retain excellent material and electro-optic (EO) properties while improving the ability of integration. Several monolithically integrated TFLN Mach–Zehnder modulators (MZMs)[1316] demonstrated high bandwidth and low half-wave voltage-length product (VπL), which met the requirements for future photonic systems. In those high-performance devices, electron-beam lithography (EBL) with high-exposure resolution served a crucial function of defining high-quality waveguides or electrodes. However, the devices are still on the chip scale, need more exposure time, and are expensive for large-scale manufacturing. For application scenarios like data-center interconnects, EOMs with low cost are necessary. Therefore, photolithography is expected to be applied in the fabrication of monolithic TFLN EOMs due to its high-efficiency exposure on the wafer scale. Previously, photolithography was utilized cooperating with dry etching, but the difficulty of obtaining smooth etching[17,18] via dry etching limited the performance of the manufactured devices. A two-step masking technique[17] and wet etching[18] were proposed to address this problem. Recently, photolithography-exposed EOMs[1921] were demonstrated on the wafer scale. Although a low VπL[21] was reported, further improvement of bandwidth is also a primary requirement for many applications. Figure 1 shows the comparison of the TFLN EOMs fabricated by EBL and photolithography.

Copy Citation Text
Fan Yang, Xiansong Fang, Xinyu Chen, Lixin Zhu, Fan Zhang, Zhangyuan Chen, Yanping Li. Monolithic thin film lithium niobate electro-optic modulator with over 110 GHz bandwidth[J]. Chinese Optics Letters, 2022, 20(2): 022502
Category: Optoelectronics
Received: Sep. 11, 2021
Accepted: Nov. 2, 2021
Published Online: Nov. 25, 2021
The Author Email: Yanping Li (liyp@pku.edu.cn)