近日，瑞士洛桑联邦理工学院的Tobias J. Kippenberg及其研究小组与美国科罗拉多矿业大学的Gabriel Santamaria-Botello等人合作并取得一项新进展。经过不懈努力，他们在钽酸锂中实现超宽带集成电光频率梳。相关研究成果已于2025年1月22日在国际权威学术期刊《自然》上发表。

该研究团队通过一种集成的三重共振架构，同时克服了上述两项挑战，该架构将单片微波集成电路与基于新兴薄膜钽酸锂（LiTaO₃）的光子集成电路（PIC）相结合。利用钽酸锂中共振增强的电光相互作用和减小的双折射，研究人员实现了梳状谱跨度扩展四倍，功率降低至传统非共振微波设计的十六分之一。该梳状谱发生器由混合集成激光二极管驱动，谱宽超过450纳米（超过60太赫兹），包含2000多条谱线，且发生器体积紧凑，仅占1平方厘米。研究人员还观察到，强烈的电光耦合使得梳状谱的存在范围扩大，接近光学微谐振器的全自由光谱范围。这种超宽带梳状谱发生器，结合与失谐无关的操作特性，有望推动芯片级光谱学和超低噪声毫米波合成的进步，并开启跨倍频程电光梳状谱的应用。微波与光子学的协同设计方法可广泛应用于各种集成电光应用。

据悉，基于克尔参数振荡的集成频率梳发生器已催生出芯片级、吉赫兹间隔的频率梳，其新应用涵盖了超大规模电信、低噪声微波合成、激光雷达以及天体物理光谱仪校准等领域。近期，在铌酸锂（LiNbO₃）光子集成电路（PIC）方面取得的进展，促成了芯片级、电光（EO）频率梳的诞生，它提供了精确的频率梳谱线定位，且操作简单，无需依赖耗散克尔孤子的形成。然而，当前的集成电光频率梳由于驱动非共振电容电极所需的大功率微波以及铌酸锂本身强烈的固有双折射，面临着光谱覆盖范围有限的挑战。

附：英文原文

Title: Ultrabroadband integrated electro-optic frequency comb in lithium tantalate

Author: Zhang, Junyin, Wang, Chengli, Denney, Connor, Riemensberger, Johann, Lihachev, Grigory, Hu, Jianqi, Kao, Wil, Blsin, Terence, Kuznetsov, Nikolai, Li, Zihan, Churaev, Mikhail, Ou, Xin, Santamaria-Botello, Gabriel, Kippenberg, Tobias J.

Issue&Volume: 2025-01-22

Abstract: The integrated frequency comb generator based on Kerr parametric oscillation has led to chip-scale, gigahertz-spaced combs with new applications spanning hyperscale telecommunications, low-noise microwave synthesis, light detection and ranging, and astrophysical spectrometer calibration. Recent progress in lithium niobate (LiNbO₃) photonic integrated circuits (PICs) has resulted in chip-scale, electro-optic (EO) frequency combs, offering precise comb-line positioning and simple operation without relying on the formation of dissipative Kerr solitons. However, current integrated EO combs face limited spectral coverage due to the large microwave power required to drive the non-resonant capacitive electrodes and the strong intrinsic birefringence of LiNbO₃. Here we overcome both challenges with an integrated triply resonant architecture, combining monolithic microwave integrated circuits with PICs based on the recently emerged thin-film lithium tantalate (LiTaO₃). With resonantly enhanced EO interaction and reduced birefringence in LiTaO₃, we achieve a fourfold comb span extension and a 16-fold power reduction compared to the conventional, non-resonant microwave design. Driven by a hybrid integrated laser diode, the comb spans over 450nm (more than 60THz) with  more than 2,000 lines, and the generator fits within a compact 1-cm² footprint. We additionally observe that the strong EO coupling leads to an increased comb existence range approaching the full free spectral range of the optical microresonator. The ultra-broadband comb generator, combined with detuning-agnostic operation, could advance chip-scale spectrometry and ultra-low-noise millimetre wave synthesis and unlock octave-spanning EO combs. The methodology of co-designing microwave and photonics can be extended to a wide range of integrated EOs applications.

DOI: 10.1038/s41586-024-08354-4

Source: https://www.nature.com/articles/s41586-024-08354-4