• 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.

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    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
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    Category: Optoelectronics
    Received: Sep. 11, 2021
    Accepted: Nov. 2, 2021
    Published Online: Nov. 25, 2021
    The Author Email: Yanping Li (liyp@pku.edu.cn)