We demonstrate continuous frequency tuning in terahertz quantum cascade lasers with double metal waveguides using a Y-branched coupler. Two THz QCLs placed side-by-side couple by evanescent fields across the air gap between them. Each QCL waveguide comprises a 48-μm-wide coupler and S-bend section, which are connected to an 88-μm-wide Y-branch through an impedance matching tapered section. Photonic lattices are patterned on top of the coupler section in each QCL using focused ion-beam milling to control the spectral characteristics. The waveguide design used for individual QCL sections is optimized using finite element modeling and the spectral characteristics are modeled using a transfer matrix model. Continuous frequency tuning of ∼19 GHz is demonstrated while maintaining an output power of ∼4.2–4.8 mW and a heat sink temperature of 50 K. The tuning is controlled electrically through Stark shift and cavity pulling effects by driving both QCLs simultaneously and represents the widest electrically controlled continuous tuning performance from a THz QCL without significant change in output power.

中文翻译：

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具有光子晶格的耦合Y分支太赫兹量子级联激光器中具有接近恒定输出功率的连续频率调谐

我们演示了使用Y型分支耦合器在具有双金属波导的太赫兹量子级联激光器中进行连续频率调谐的方法。两个太赫兹QCL通过渐逝场并排放置，它们位于它们之间的气隙中。每个QCL波导均包括一个48μm宽的耦合器和一个S形弯曲部分，它们通过一个阻抗匹配的锥形部分连接到一个88μm宽的Y分支。使用聚焦离子束铣削来控制光谱特性，在每个QCL的耦合器部分的顶部图案化光子晶格。使用有限元建模优化了用于单个QCL截面的波导设计，并使用传输矩阵模型对光谱特性进行了建模。演示了约19 GHz的连续频率调谐，同时保持约4.2-4.8 mW的输出功率和50 K的散热器温度。