[论文解读] Femtosecond Pulse Generation via an Integrated Electro-Optic Time Lens

Mengjie Yu, Christian Reimer+13 more|arXiv (Cornell University)|Dec 16, 2021

Advanced Fiber Laser Technologies被引用 6

一句话总结

本文提出一种基于级联铌酸锂调制器与啁啾布拉格光栅的集成电光时间透镜系统的芯片级飞秒脉冲源。该系统在30 GHz重复频率下实现520 fs脉冲，脉冲能量为0.54 pJ，10-dB带宽为12.6 nm，与以往集成光源相比，连续波到脉冲的转换效率提升了10倍。

ABSTRACT

Integrated femtosecond pulse and frequency comb sources are critical components for a wide range of applications. The leading approaches for on-chip pulse generation rely on mode locking inside microresonator with either third-order nonlinearity or with semiconductor gain. These approaches, however, are limited in noise performance, wavelength tunability and repetition rates. Alternatively, sub-picosecond pulses can be synthesized without mode-locking, by modulating a continuous-wave (CW) single-frequency laser using a cascade of electro-optic (EO) modulators. This method is particularly attractive due to its simplicity, robustness, and frequency-agility but has been realized only on a tabletop using multiple discrete EO modulators and requiring optical amplifiers (to overcome large insertion losses), microwave amplifiers, and phase shifters. Here we demonstrate a chip-scale femtosecond pulse source implemented on an integrated lithium niobate (LN) photonic platform18, using cascaded low-loss electro-optic amplitude and phase modulators and chirped Bragg grating, forming a time-lens system. The device is driven by a CW distributed feedback (DFB) chip laser and controlled by a single CW microwave source without the need for any stabilization or locking. We measure femtosecond pulse trains (520 fs duration) with a 30-GHz repetition rate, flat-top optical spectra with a 10-dB optical bandwidth of 12.6 nm, individual comb-line powers above 0.1 milliwatt, and pulse energies of 0.54 picojoule. Our results represent a tunable, robust and low-cost integrated pulsed light source with CW-to-pulse conversion efficiencies an order of magnitude higher than achieved with previous integrated sources. Our pulse generator can find applications from ultrafast optical measurement to networks of distributed quantum computers.

研究动机与目标

• 为集成光子平台开发一种紧凑、稳定且可调谐的飞秒脉冲源。
• 克服现有片上锁模微腔光源在噪声、波长可调谐性及重复频率方面的局限。
• 实现在无需锁模或外部稳定机制下的高效、低损耗、频率灵活的脉冲生成。
• 在单片集成平台上实现每梳状线高光功率与高脉冲能量。
• 用全集成的铌酸锂光子电路替代体积大、离散的元件，实现实际部署。

提出的方法

• 在铌酸锂平台上采用集成的幅度与相位调制器，实现级联电光时间透镜系统。
• 利用啁啾布拉格光栅整形时间波形并实现时间透镜压缩。
• 使用单个连续波（CW）DFB芯片激光器和单个连续波微波源驱动系统，无需相位锁定或稳定机制。
• 利用低损耗集成元件以最小化插入损耗并提升转换效率。
• 通过电光调制实现亚皮秒脉冲的合成，无需锁模，仅通过幅度与相位调制。
• 优化设计以实现12.6 nm带宽内平坦的光谱包络与高光谱平坦度。

实验结果

研究问题

• RQ1 全集成电光时间透镜系统能否实现高效率、低损耗的飞秒脉冲生成？
• RQ2 单个微波源能否驱动整个系统，而无需稳定或锁定机制？
• RQ3 该集成平台能否实现脉宽低于1 ps且每梳状线具有高光功率？
• RQ4 该集成系统的转换效率与以往片上脉冲源相比如何？
• RQ5 该系统能否在紧凑的单片设计中保持平坦的光谱包络与高重复频率稳定性？

主要发现

• 系统在30 GHz重复频率下生成全宽半最大值（FWHM）为520 fs的脉冲。
• 光谱的10-dB带宽为12.6 nm，表明具有高光谱平坦度。
• 单个梳状线的输出功率超过0.1 mW，证明了高输出效率。
• 脉冲能量达到0.54 picojoules，表明压缩脉冲中能量高度集中。
• 连续波到脉冲的转换效率比以往集成光源高出一个数量级。
• 系统无需外部稳定或锁定，仅依靠单个连续波微波源实现控制。