Theoretical and experimental study of optical gain and linewidth enhancement factor of type-I quantum-cascade lasers
| Autor: | Claire F. Gmachl, Jungho Kim, Deborah L. Sivco, A.Y. Cho, M. Lerttamrab, Federico Capasso, Shun Lien Chuang |
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| Rok vydání: | 2004 |
| Předmět: |
Physics
Kramers–Kronig relations Condensed matter physics Far-infrared laser Physics::Optics Condensed Matter Physics Laser Atomic and Molecular Physics and Optics law.invention Semiconductor laser theory Laser linewidth law Electrical and Electronic Engineering Atomic physics Quantum cascade laser Refractive index Lasing threshold |
| Zdroj: | IEEE Journal of Quantum Electronics. 40:1663-1674 |
| ISSN: | 0018-9197 |
| DOI: | 10.1109/jqe.2004.837666 |
| Popis: | A theoretical and experimental study of the optical gain and the linewidth enhancement factor (LEF) of a type-I quantum-cascade (QC) laser is reported. QC lasers have a symmetrical gain spectrum because the optical transition occurs between conduction subbands. According to the Kramers-Kronig relation, a zero LEF is predicted at the gain peak, but there has been no experimental observation of a zero LEF. There are other mechanisms that affect the LEF such as device self-heating, and the refractive index change due to other transition states not involved in lasing action. In this paper, the effects of these mechanisms on the LEF of a type-I QC laser are investigated theoretically and experimentally. The optical gain spectrum and the LEF are measured using the Hakki-Paoli method. Device self-heating on the wavelength shift in the Fabry-Perot modes is isolated by measuring the shift of the lasing wavelength above the threshold current. The band structure of a QC laser is calculated by solving the Schro/spl uml/dinger-Poisson equation self-consistently. We use the Gaussian lineshape function for gain change and the confluent hypergeometric function of the first kind for refractive index change, which satisfies the Kramers-Kronig relation. The refractive index change caused by various transition states is calculated by the theoretical model of a type-I QC laser. The calculated LEF shows good agreement with the experimental measurement. |
| Databáze: | OpenAIRE |
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