Stable Single-Mode Operation of Distributed Feedback Quantum Cascade Laser by Optimized Reflectivity Facet Coatings - PubMed (original) (raw)

Stable Single-Mode Operation of Distributed Feedback Quantum Cascade Laser by Optimized Reflectivity Facet Coatings

Dong-Bo Wang et al. Nanoscale Res Lett. 2018.

Abstract

In this work, quantum cascade lasers (QCLs) based on strain compensation combined with two-phonon resonance design are presented. Distributed feedback (DFB) laser emitting at ~ 4.76 μm was fabricated through a standard buried first-order grating and buried heterostructure (BH) processing. Stable single-mode emission is achieved under all injection currents and temperature conditions without any mode hop by the optimized antireflection (AR) coating on the front facet. The AR coating consists of a double layer dielectric of Al2O3 and Ge. For a 2-mm laser cavity, the maximum output power of the AR-coated DFB-QCL was more than 170 mW at 20 °C with a high wall-plug efficiency (WPE) of 4.7% in a continuous-wave (CW) mode.

Keywords: Distributed feedback; Facet coating; Quantum cascade laser; Stable single mode.

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Conflict of interest statement

Authors’ Information

FQL is a professor in Key Laboratory of Semiconductor Materials Science at the Institute of Semiconductors, Chinese Academy of Sciences. He earned his MSc degree in Solid State Physics at the University of Science and Technology of China in 1990 and obtained his PhD degree in the Department of Physics, Nanjing University, in 1996. He has studied quantum cascade laser since 1996 using a solid source MBE in Beijing and realized a laser emitting at 5.1 μm in the end of 1999 and the room temperature operated quantum cascade laser emitting at ~ 3.54 μm in 2000. Recently, he has demonstrated the quantum dot cascade laser by two-step strain compensation active region and material grown technique. He is a winner of the National Outstanding Youth Fund in China.

Competing Interests

The authors declare that they have no competing interests.

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Figures

Fig. 1

Fig. 1

Schematic illustrating the model of finite DFB cavity with antireflection coating on the longitudinal optical mode profile

Fig. 2

Fig. 2

a The two red curves are the mode loss of high- and low-frequency mode respectively. The black curve is the differential mode loss between the two band-edge modes labeled as Δ. The inset shows the mode profile calculated for the low- and high-frequency modes, for a single period of the grating. b The calculated mode loss spectrum based on transfer matrix simulation with different AR coatings

Fig. 3

Fig. 3

Subthreshold DC spectrum of device measured at 30 °C

Fig. 4

Fig. 4

a, b Output power versus current of the DFB laser operated in CW mode at different heat sink temperatures between 20 and 90 °C along with _V_-I curves. c, d CW lasing spectra at different currents from 150 to 250 mA with a step of 25 mA at 20 °C

Fig. 5

Fig. 5

Single-mode emission spectra of the DFB laser at a driving 1.1 threshold current for different heat sink temperatures of 20–90 °C. The insert shows the linearly fit tuning characteristics of the lasing frequency with temperature

Fig. 6

Fig. 6

Wall-plug efficiency as a function of the electrical power dissipation for the 2-mm-long HR and AR-coated DFB-QCL

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