We demonstrate quantum cascade laser (QCL) optical frequency combs emitting at λ ∼ 6 μm. A 5.5 μm-wide, 4.5 mm-long laser exhibits comb operation from −20 °C up to 50 °C. A maximum output power of 300 mW is achieved at 50 °C showing a robustness of the system. The laser output spectrum is ∼80 cm⁻¹ wide at the maximum current, with a mode spacing of 0.334 cm⁻¹, resulting in a total of 240 modes with an average power of 0.8 mW per mode. To achieve frequency comb operation, a plasmonic-waveguide approach is utilized. A thin, highly-doped indium phosphide (InP) layer is inserted in the top cladding design to compensate the positive dispersion of the system (material and waveguide). This approach can be further exploited to design QCL combs at even shorter wavelengths, down to 4 μm. Different ridge widths between 2.8 and 5.5 μm have been fabricated and characterized. All of the devices exhibit frequency comb operation. These observations demonstrate that the plasmonic-waveguide is a robust and reliable method for dispersion compensation of a semiconductor laser systems to achieve frequency comb operation.

中文翻译：

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基于等离激元增强的色散补偿，高性能量子级联激光器的频率在λ〜6μm处梳理。

我们证明量子级联激光器（QCL）的光学频率梳发射在λ〜6 μ米。阿5.5 μ从-20℃至最高米宽，4.5毫米长的激光展品梳操作至50℃。在50°C时达到300 mW的最大输出功率，显示了系统的坚固性。在最大电流下，激光输出光谱的宽度约为80 cm ^-1，模式间距为0.334 cm ^-1，总共产生了240个模式，每个模式的平均功率为0.8 mW。为了实现频率梳操作，利用了等离子体波导方法。在顶部覆层设计中插入了一层薄的高掺杂磷化铟（InP）层，以补偿系统（材料和波导）的正色散。这种方法可以进一步利用在甚至更短的波长来设计QCL梳子，降低到4 μ微米。2.8和5.5之间的不同脊宽度μ米已经制造和表征。所有设备均表现出频率梳操作。这些观察结果表明，等离子体波导是一种用于半导体激光系统色散补偿以实现频率梳操作的可靠而可靠的方法。