Controlling loss of waveguides for potential GaN terahertz quantum cascade lasers by tuning the plasma frequency of doped layers
Controlling loss of waveguides for potential GaN terahertz quantum cascade lasers by tuning the plasma frequency of doped layers
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DOI：
10.7567/jjap.57.081001
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发表时间：
2018-07
影响因子：
1.5
通讯作者：
Ke Wang;Tsung-Tse Lin;Li Wang;W. Terashima;H. Hirayama
中科院分区：
文献类型：
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作者：
Ke Wang;Tsung-Tse Lin;Li Wang;W. Terashima;H. Hirayama
通过理论计算，分析了潜在的GaN基太赫兹量子级联激光器(THZQCL)中双金属波导中不同掺杂层引起的波导损耗。光场可以很好地限制在有源QCL区域内。QCL有源区和n+接触层的平均电子密度应严格控制。通过降低QCL层中的电子密度，可以最大限度地降低低频(3 THz)的损耗。在中高太赫兹频段(∼3<；f<；15太赫兹)，重掺杂n+接触层的吸收占主导地位。因此，由电子密度决定的具有强吸收峰的体等离子体频率必须被调谐到偏离目标QCL频率。波导损耗加上腔镜损耗可以控制在低至∼24 cm−1。
We have analyzed the waveguide loss originating from various doping layers in double metal waveguides for potential GaN-based terahertz quantum cascade lasers (THz QCLs) by theoretical calculations. The optical field can be very well confined in the active QCL region. Average electron densities in the QCL active region and n+ contact layers should be controlled carefully. The loss in the low-frequency range (3 THz) can be minimized by decreasing the electron density in the QCL layer. In the middle- and high-THz-frequency ranges (∼3 < f < 15 THz), the absorption by the heavily doped n+ contact layer dominates the waveguide loss. Consequently, the bulk plasma frequency, which is determined by electron density and shows a strong absorption peak, must be tuned to deviate from the target QCL frequency. The waveguide loss plus the cavity mirror loss can be controlled to be as low as ∼24 cm−1.