Recirculating frequency shifter (RFS) loops can be used for electronically programmable, variable-spacing multiline spectrum generation, which can benefit the development of fully flexible optical communications and other frequency comb applications. Here, we report on and explain the observation of significant performance variations between chip-based gain in semiconductor optical amplifiers (SOA) and fiber-based gain in erbium-doped fiber amplifiers (EDFA) when used as the gain element in the RFS. Previously, SOAs and EDFAs have been demonstrated in different RFS experiments and studied separately from each other; thus, discussion mainly focused on the noise from amplified spontaneous emission. We show that SOA effects, including four wave mixing, can be measured, which impose limits to the wavelength spacing of the combs, and that this effect is mitigated by increasing the RF drive frequency of the RFS and operating SOA in deeper saturation.

中文翻译：

---

半导体和光纤放大器在循环移频器中的性能比较

循环移频器（RFS）环路可用于电子可编程，可变间隔的多线频谱生成，这可以有益于开发完全灵活的光通信和其他频率梳应用。在这里，我们报告并解释当用作RFS中的增益元件时，半导体光放大器（SOA）中基于芯片的增益与掺do光纤放大器（EDFA）中基于光纤的增益之间显着性能变化的观察。以前，SOA和EDFA已在不同的RFS实验中得到证明，并且彼此分开研究。因此，讨论主要集中在放大的自发辐射产生的噪声上。我们表明，可以测量SOA效应，包括四波混频，这会限制梳子的波长间隔，