[论文解读] Tri-coupler geometries for achromatic nulling interferometry in the near infrared

Harry-Dean Kenchington Goldsmith, Nemanja Jovanovic+5 more|arXiv (Cornell University)|Feb 27, 2026

Adaptive optics and wavefront sensing被引用 0

一句话总结

本论文比较三种三耦合器设计（标准渐逝耦合、渐变渐逝耦合和MMI），用于1.5–1.8 μm波段的宽带无色散抑制干涉仪，评估系外行星通量、恒星光衰减、探测与加工公差。渐变三耦合器和MMI在通量方面优于标准设计，MMI显示出最大的加工公差容忍度，同时在整个带宽内实现深度恒星光抑制。

ABSTRACT

Astrophotonics will be central to astronomical instrumentation, enabling lightweight, compact, and environmentally stable systems for both ground-based observatories and space missions. One key application is beam combination for nulling integrated with a photonic lantern, and long baseline nulling interferometry, which suppresses starlight to reveal exoplanets and companions. Compact, broadband photonic beam combiners are essential for providing a pathway to complex circuitry on a single chip and scalable solutions for single and multi-telescope instruments, and are investigated herein. Two-waveguide photonic combiners rely on symmetric coupling to interfere light, which is chromatic and requires modification for broadband operation. A three-waveguide configuration (tri-coupler) offers the potential for deeper, broader, and stable achromatic nulls. This work compares simulations of two evanescent tri-couplers and a multimode interference coupler (MMI) across the 1.5 - 1.8 $μ$m band, evaluating exoplanet throughput, starlight attenuation, sensing characteristics, and estimations on fabrication tolerance. The standard tri-coupler was outperformed by both a tapered tri-coupler and the MMI, each of which achieved exoplanet throughput >85% throughout the band. The standard design recorded a minimum exoplanet throughput of 50% at the waveband's extremes. The tapered tri-coupler was further redesigned to achieve a non-degenerate sensing state. The MMI, while limited to a starlight attenuation of 40 dB $\left(10^{-4} ight)$ by uncoupled light, showed the greatest tolerance to fabrication errors, offering strong practical potential. Future designs aim to combine high exoplanet throughput, deep starlight attenuation, and non-degenerate sensing within a single integrated architecture.

研究动机与目标

• 动机：在系外行星探测中使用光子集成电路实现抑制干涉。
• 评估三种三耦合器几何（标准渐逝耦合、渐变渐逝耦合和MMI）用于宽带无色散抑制。
• 量化1.5–1.8 μm波段的系外行星通量、恒星光衰减和加工公差。

提出的方法

• 在光刻制造的硅酸盐基波导中建模三种三耦合器几何（标准渐逝、渐变、MMI）。
• 对TE模光传播进行仿真，计算1.5–1.8 μm波段的系外行星通量、恒星光衰减和损耗。
• 通过相对总输出的破坏性输出定义衰减，并将其与系外行星信噪比相关联。
• 使用相位触发的两输入一输出在outer输入之间实现180°相位差的抑制。
• 评估加工公差与弯折损耗对性能的敏感性。

(a) Standard tri-coupler

实验结果

研究问题

• RQ1 在系外行星通量、深层恒星光衰减与带宽无色散性之间，哪一种三耦合器几何提供最佳折中？
• RQ2 弯折损耗与材料损耗如何影响1.5–1.8 μm带宽内的总体抑制性能？
• RQ3 能否找到在保持高系外行星通量的同时实现非简并探测的设计？
• RQ4 各设计在加工公差下的抑制与条带跟踪能力有多稳健？

主要发现

• 定制的渐变三耦合器和MMI在1.5–1.8 μm带宽内的系外行星通量均>85%，而在带边时标准设计约为50%（峰值）。
• 渐变三耦合器提供近似无色散的系外行星通量，整个带宽几乎实现100%透射。
• MMI对加工误差的容忍度最高，尽管固有损耗较高，但在实际应用中潜力强大。
• 标准三耦合器在1.55 μm附近显示出波色相对依赖的系外行星通量，且在较长波长处下降。
• 弯折损耗对器件总体损失有贡献，MMI具备更高的固有损耗但在各波长范围内性能更稳定。
• 渐变三耦合器展示了非简并探测状态，具备潜在的连续条纹跟踪能力。

(b) Tapered tri-coupler