[论文解读] Parity-Time Synthetic Laser

Liang Feng, Zi Jing Wong+3 more|arXiv (Cornell University)|May 12, 2014

Quantum Mechanics and Non-Hermitian Physics参考文献 36被引用 7

一句话总结

本文提出并实验演示了一种利用光子微环结构中平衡的增益与损耗实现本征单模激光的宇称-时间（PT）综合激光器。通过设计复共轭的增益与损耗系数，系统在PT对称性破缺下实现无阈值激光，尽管增益带宽较宽，仍能将宽带光学增益压缩至单一模式。

ABSTRACT

Parity-time (PT) symmetry is a fundamental notion in quantum field theories. It has opened a new paradigm for non-Hermitian Hamiltonians ranging from quantum mechanics, electronics, to optics. In the realm of optics, optical loss is responsible for power dissipation, therefore typically degrading device performance such as attenuation of a laser beam. By carefully exploiting optical loss in the complex dielectric permittivity, however, recent exploration of PT symmetry revolutionizes our understandings in fundamental physics and intriguing optical phenomena such as exceptional points and phase transition that are critical for high-speed optical modulators. The interplay between optical gain and loss in photonic PT synthetic matters offers a new criterion of positively utilizing loss to efficiently manipulate gain and its associated optical properties. Instead of simply compensating optical loss in conventional lasers, for example, it is theoretically proposed that judiciously designed delicate modulation of optical loss and gain can lead to PT synthetic lasing that fundamentally broadens laser physics. Here, we report the first experimental demonstration of PT synthetic lasers. By carefully exploiting the interplay between gain and loss, we achieve degenerate eigen modes at the same frequency but with complex conjugate gain and loss coefficients. In contrast to conventional ring cavity lasers with multiple modes, the PT synthetic micro-ring laser exhibits an intrinsic single mode lasing: the non-threshold PT broken phase inherently associated in such a photonic system squeezes broadband optical gain into a single lasing mode regardless of the gain spectral bandwidth. This chip-scale semiconductor platform provides a unique route towards fundamental explorations of PT physics and next generation of optoelectronic devices for optical communications and computing.

研究动机与目标

• 探索宇称-时间（PT）对称性在光子系统中的应用，以实现新型激光运转。
• 通过非厄米光子学克服传统多模激光的局限性。
• 实验实现一种PT综合激光器，通过工程化增益与损耗实现无阈值单模激光。
• 展示一种芯片级平台，用于基础PT物理研究及下一代光电子器件。

提出的方法

• 设计具有空间调制增益与损耗区域的半导体微环腔，以满足PT对称性条件。
• 通过在介电常数中工程化复共轭的增益与损耗系数，实现相同频率下的简并本征模。
• 利用芯片级III-V族半导体平台，高精度集成增益与损耗元件。
• 测量激光阈值与模式特性，以确认单模运转及PT相变。
• 分析系统在PT对称性破缺相变区域的行为，以验证无阈值激光。
• 采用数值模拟预测并验证PT对称性条件与模式简并。

实验结果

研究问题

• RQ1 能否利用PT对称性在光子微腔中实现单模激光？
• RQ2 在PT对称系统中，增益与损耗的相互作用如何影响激光阈值与模式选择？
• RQ3 具有复共轭增益与损耗的简并本征模在实现无阈值激光中起什么作用？
• RQ4 能否通过PT综合工程将宽带光学增益有效压缩至单一激光模式？
• RQ5 芯片级激光系统中PT对称性破缺的实验特征是什么？

主要发现

• 尽管增益带宽较宽，PT综合微环激光器由于无阈值的PT对称性破缺相，表现出本征单模激光。
• 实验观测到具有复共轭增益与损耗系数的相同频率简并本征模，证实了PT对称性。
• 系统实现无阈值激光，即在无限小泵浦功率下仍可产生激光，这是PT相变的典型特征。
• 芯片级平台成功展示了PT综合激光器在集成光子器件中的可行性。
• 实验结果验证了非厄米光子系统中PT对称性的理论预测，与模拟结果高度一致。
• 激光模式具有鲁棒性与稳定性，未观察到模式竞争，证实了多模振荡被有效抑制。