Abstract-Gain measurement of terahertz quantum cascade laser via a master-oscillator power-amplifier configuration

Chenren Yu, Huan Zhu, Fangfang, Wang, Gaolei Chang, Haiqing Zhu, Jianxin Chen, Gangyi Xu, Li He,



https://www.sciencedirect.com/science/article/pii/S0022024819301551

We report a method to measure the net loss and gain of a terahertz quantum cascade laser (THz-QCL), which is based on a master-oscillator power-amplifier (MOPA) configuration. In the measurement, the master-oscillator (MO) section and power-amplifier (PA) section are separately biased. With the fixed seed power from the MO section, the output power of the device is measured at various bias voltage applied on the PA section, from which the net loss and gain is deduced as a function of bias. We demonstrate that gain clamping and gain saturation can be avoided in our measurement, which allow a complete evolution of the loss and gain characteristics. For a THz-QCL with the bound-to-continuum active region and the metal-metal waveguide, the measured maximal net gain is about 13.0-16.5 cm-1 at 2.58 THz at a 20 K, which is in qualitative agreement with the theoretical analysis.

Abstract-Terahertz master-oscillator power-amplifier quantum cascade laser with a grating coupler of extremely low reflectivity

Huan Zhu, Haiqing Zhu, Fangfang Wang, Gaolei Chang, Chenren Yu, Quan Yan, Jianxin Chen, Lianhe Li, A. Giles Davies, Edmund H. Linfield, Zhou Tang, Pingping Chen, Wei Lu, Gangyi Xu, and Li He

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-2-1942

A terahertz master-oscillation power-amplifier quantum cascade laser (THz-MOPA-QCL) is demonstrated where a grating coupler is employed to efficiently extract the THz radiation. By maximizing the group velocity and eliminating the scattering of THz wave in the grating coupler, the residue reflectivity is reduced down to the order of 10−3. A buried DFB grating and a tapered preamplifier are proposed to improve the seed power and to reduce the gain saturation, respectively. The THz-MOPA-QCL exhibits single-mode emission, a single-lobed beam with a narrow divergence angle of 18° × 16°, and a pulsed output power of 136 mW at 20 K, which is 36 times that of a second-order DFB laser from the same material.

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