Al-Alimi A W, Sarmani A R, Al-Mansoori M H, Abas A F, Alresheedi M T, Mahdi M A
Opt Express. 2018 Nov 12;26(23):30978-30990. doi: 10.1364/OE.26.030978.
We discover the technique of controlling the flatness in signal amplitude of a multiwavelength Brillouin-Raman fiber laser by employing an air-gap outside of the cavity. The structure that is adjustable within sub-millimeter length behaves as flexible optical feedback that provides modifiable portions of multiple Fresnel reflectivities. This is the main benchmark that allows the efficient management of gain competition between self-lasing modes and Brillouin Stokes waves that is vital for self-flattening initiation. When setting the Brillouin pump wavelength at 1529 nm and the air-gap distance to 0.4 mm, 296 Stokes lines are produced with a channel spacing of 0.158 nm. The lasing bandwidth is 46.60 nm that covers from 1529.16 to 1575.76 nm wavelength. In this case at Raman power of 950 mW, the intense Brillouin pump power of 2 dBm saturates the cascaded higher-orders lasing lines. As a result, the overall peak power discrepancy is maintained at just 1.8 dB where an average optical-signal-to-noise ratio of 20 dB is realized. To date, this is the widest bandwidth with the flattest spectrum attained in multiwavelength fiber lasers that incorporate a single Raman pump unit.
我们发现了一种通过在腔体外设置气隙来控制多波长布里渊 - 拉曼光纤激光器信号幅度平坦度的技术。在亚毫米长度内可调节的结构表现为灵活的光学反馈，可提供多个菲涅尔反射率的可修改部分。这是实现自激光模式与布里渊斯托克斯波之间增益竞争有效管理的主要基准，而这种增益竞争对于自平坦化的启动至关重要。当将布里渊泵浦波长设置为1529 nm且气隙距离设置为0.4 mm时，产生了296条斯托克斯线，通道间距为0.158 nm。激光带宽为46.60 nm，覆盖波长范围从1529.16到1575.76 nm。在这种情况下，当拉曼功率为950 mW时，2 dBm的强布里渊泵浦功率使级联的高阶激光线饱和。结果，总峰值功率差异仅维持在1.8 dB，实现了20 dB的平均光信噪比。迄今为止，这是在包含单个拉曼泵浦单元的多波长光纤激光器中获得的具有最平坦光谱的最宽带宽。
