3-kHz Spectral Linewidth Laser Assembly With Coherent Optical Negative Feedback

Advances in narrow linewidth diode lasers

“…Its noise level is 5 and 3 orders of magnitude lower than that of conventional DFB lasers and external cavity lasers, respectively. From 2015 to 2018, Aoyama team [65,66] of Tohuku University proposed a coherent optical negative feedback method to reduce the linewidth of single-mode semiconductor lasers. The linewidth of the laser was optimized from 13.5 MHz to 3 kHz by using external cavity negative feedback lenses.…”

Advances in narrow linewidth diode lasers

“…随后, 德国 FBH 研究 所 [3] 提出利用 DFB 激光芯片与集成式共焦法布里 -珀罗腔谐振器等组成共振反馈谐振腔, 实现功 率为 50 mW, 洛伦兹线宽仅 15.7 Hz, 同时获得超低噪声 (白噪声等级 5 Hz 2 /Hz) 输出, 其噪声水平比 普通 DFB 激光器和外腔激光器分别低了 5 个和 3 个数量级. 2015∼2018 年, 日本东北大学 Konosuke Aoyama 团队 [65,66] 提出一种相干光学负反馈方法降低单模半导体激光器线宽, 利用外腔负反馈镜片 将激光器线宽由 13.5 MHz 优化为 3 kHz, 频率调制 (FM) 噪声的能量密度降低 35 dB, 同时相对强度 噪声低于 −140 dB/Hz, 该系统可以保持窄线宽稳定输出超过一小时.…”

Performance improvement of optical negative feedback laser by reducing feedback loop length

“…While a current feedback technique that does not rely on increasing the cavity Q-factor has been proposed [24,25], it requires large feedback electrical circuits and the size of the laser system consequently becomes too large. To achieve a compact and very narrow spectral linewidth semiconductor laser, we have previously proposed an optical negative feedback semiconductor laser [26,27,28,29] that features a simple structure consisting of a single mode semiconductor laser and an optical filter. The optical filter acts as an optical frequency discriminator and converts the frequency noise of the semiconductor laser into electrical field amplitude modulated feedback light that is then fed back to the singlemode semiconductor laser.…”