用于天体光子学的连续波紫外激光与飞秒红外激光刻写的光纤布拉格光栅滤波器损耗对比分析
Comparative analysis of fiber Bragg grating filter losses inscribed by continuous wave UV and femtosecond-IR lasers for astrophotonics
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中文总结 AI 辅助
本研究对比了连续波紫外激光与飞秒红外激光刻写的光纤布拉格光栅滤波器损耗，探索降低高NA光纤插入损耗的方法，提出可减少熔接点数量50%的紧凑型桥接光纤方案，两种滤波器平台均适用于天体光子系统。
中文摘要 AI 辅助
光纤布拉格光栅（FBG）滤波器已被证实是天体光子学仪器中用于近地基观测的有前途组件。鉴于天文应用的光子匮乏特性，最大限度降低天体光子学组件的插入损耗至关重要。除特种光纤和刻写技术引入的插入损耗（IL）外，FBG还存在包层模式（CM）损耗。本研究在三种光敏光纤（低数值孔径（NA）光纤、高NA抗弯曲光纤、包层模式抑制（CMS）光纤）及非光敏光纤SMF-28中，研究了五条滤波器线的损耗特性。滤波器采用两种基于相位掩模的照明方法刻写：一种是具备复杂相位掩模以实现多通道滤波器的连续波紫外（UV）激光，另一种是集成整形光阑以控制光谱轮廓的飞秒红外（fs-IR）激光。结果表明，高NA抗弯曲光纤中UV刻写的光栅在光敏光纤中呈现最低的CM损耗（约0.5 dB），但IL最高（4.6 dB）；非光敏SMF-28光纤中fs-IR刻写的FBG实现最低的IL（<0.05 dB），同时CM损耗相对较高（0.93 dB）。为降低高NA光纤的高IL，探索了拉锥和桥接方法，发现桥接可使IL降低约3 dB。研究表明，两种滤波器平台均适用于集成到天体光子系统，IL低于1 dB。最后，提出了一种紧凑型桥接光纤方案，有望将IL进一步降低至0.5 dB以下，同时使桥接光纤数量减少50%，从而减少熔接点数量50%。
英文摘要
Fiber Bragg grating (FBG) filters have been demonstrated as promising components in astrophotonic instrumentation for near-infrared ground-based observations. Given the photon-starved nature of astronomical applications, it is critical to minimize insertion losses across astrophotonic components. In addition to the insertion loss (IL) introduced by specialty fibers and inscription techniques, FBGs exhibit cladding mode (CM) losses. In this work, we studied the loss characteristics of five filter lines in three photosensitive fibers, i.e., a low-numerical-aperture (NA) fiber, a high-NA bend-insensitive fiber, and a cladding-mode-suppressed (CMS) fiber, and in a non-photosensitive fiber, SMF-28. The filters were inscribed using two phase mask-based illumination methods: a continuous wave ultraviolet (UV) laser with a complex phase mask allowing for multi-channel filters, and a femtosecond infrared (fs-IR) laser with phase mask integrated shaping apertures for spectral profile control. Our results show that UV-inscribed gratings in high-NA bend-insensitive fiber yield the lowest CM losses ($\approx$ 0.5 dB) among photosensitive fibers, but exhibit the highest IL (4.6 dB), and FBGs in non-photosensitive SMF-28 fiber, inscribed with fs-IR, achieve the lowest IL (< 0.05 dB) with a comparatively higher CM loss (0.93 dB). To reduce the high IL in high-NA fiber, we explored tapering and bridging methods and report that bridging reduces IL by $\sim$ 3 dB. We show that both filter platforms remain viable for integration into an astrophotonic system, with IL below 1 dB. Finally, we propose a compact bridge-fiber scheme with the potential to further reduce IL to below 0.5 dB while reducing the number of bridging fibers and, consequently, the number of splice junctions by 50%.
