Kim Dongwan, Harfouche Mark, Wang Huolei, Santis Christos T, Vilenchik Yaakov, Satyan Naresh, Rakuljic George, Yariv Amnon
Department of Applied Physics and Materials Science, California Institute of Technology, Pasadena, CA, 91125, USA.
Department of Electrical Engineering, California Institute of Technology, Pasadena, CA, 91125, USA.
Sci Rep. 2022 Jan 10;12(1):312. doi: 10.1038/s41598-021-03314-8.
We have recently introduced a new semiconductor laser design which is based on an extreme, 99%, reduction of the laser mode absorption losses. In previous reports, we showed that this was achieved by a laser mode design which confines the great majority of the modal energy (> 99%) in a low-loss Silicon guiding layer rather than in highly-doped, thus lossy, III-V p[Formula: see text] and n[Formula: see text] layers, which is the case with traditional III-V lasers. The resulting reduced electron-field interaction was shown to lead to a commensurate reduction of the spontaneous emission rate by the excited conduction band electrons into the laser mode and thus to a reduction of the frequency noise spectral density of the laser field often characterized by the Schawlow-Townes linewidth. In this paper, we demonstrate theoretically and present experimental evidence of yet another major beneficial consequence of the new laser design: a near total elimination of the contribution of amplitude-phase coupling (the Henry [Formula: see text] parameter) to the frequency noise at "high" frequencies. This is due to an order of magnitude lowering of the relaxation resonance frequency of the laser. Here, we show that the practical elimination of this coupling enables yet another order of magnitude reduction of the frequency noise at high frequencies, resulting in a quantum-limited frequency noise spectral density of 130 Hz[Formula: see text]/Hz (linewidth of 0.4 kHz) for frequencies beyond the relaxation resonance frequency 680 MHz. This development is of key importance in the development of semiconductor lasers with higher coherence, particularly in the context of integrated photonics with a small laser footprint without requiring any sort of external cavity.
我们最近推出了一种新的半导体激光器设计，该设计基于将激光模式吸收损耗大幅降低99%。在之前的报告中，我们表明这是通过一种激光模式设计实现的，该设计将绝大多数模态能量（>99%）限制在低损耗的硅波导层中，而不是像传统III-V族激光器那样限制在高掺杂因而有损耗的III-V族p[公式：见正文]和n[公式：见正文]层中。结果表明，由此减少的电子-场相互作用导致受激导带电子向激光模式的自发发射率相应降低，从而降低了通常以肖洛-汤斯线宽表征的激光场频率噪声谱密度。在本文中，我们从理论上进行了论证，并给出了新激光器设计的另一个主要有益结果的实验证据：在“高频”下几乎完全消除了幅度-相位耦合（亨利[公式：见正文]参数）对频率噪声的贡献。这是由于激光器弛豫共振频率降低了一个数量级。在这里，我们表明这种耦合的实际消除使得高频下的频率噪声又降低了一个数量级，对于超过弛豫共振频率680 MHz的频率，产生了130 Hz[公式：见正文]/Hz的量子极限频率噪声谱密度（线宽为0.4 kHz）。这一进展对于开发具有更高相干性的半导体激光器至关重要，特别是在激光占用面积小且无需任何外部腔的集成光子学背景下。
