Abstract
Gain, spontaneous emission, and reflectance play important roles in setting the spectral output of homogeneously broadened lasers, such as semiconductor diode lasers. This paper provides a restricted-in-scope review of the steady-state spectral properties of semiconductor diode lasers. Analytic but transcendental solutions for a simplified set of equations for propagation of modes through a homogeneously broadened gain section are used to create a Fabry–Pérot model of a diode laser. This homogeneously broadened Fabry–Pérot model is used to explain the spectral output of diode lasers without the need for guiding-enhanced capture of spontaneous emission, population beating, or non-linear interactions. It is shown that the amount of spontaneous emission and resonant enhancement of the reflectance-gain (RG) product as embodied in the presented model explains the observed spectral output. The resonant enhancement is caused by intentional and unintentional internal scattering and external feedback.
Highlights
This work showed that the spectral output of a diode laser could be explained based on the reflectance-gain (RG) product and spontaneous emission as incorporated in a homogeneously broadened Fabry–Pérot model of a diode laser
These solutions are used in a Fabry–Pérot model of the output of a laser to understand the spectral output of homogeneously broadened lasers
Analytic solutions to a simplified set of coupled, non-linear rate equations that describe the amplification of light for steady-state propagation through a homogeneously broadened amplifier are given
Summary
This work showed that the spectral output of a diode laser could be explained based on the reflectance-gain (RG) product and spontaneous emission as incorporated in a homogeneously broadened Fabry–Pérot model of a diode laser. Analytic but transcendental solutions for the single-pass gain and for the amplified spontaneous emission are presented for the coupled non-linear rate equations. These solutions are used in a Fabry–Pérot model of the output of a laser to understand the spectral output of homogeneously broadened lasers. Göbel et al performed time and spectrally resolved measurements on an optically pumped Alx Ga1− x As/GaAs double quantum well laser and found results that could be explained by homogeneous gain saturation [4]. Experimental results are presented to demonstrate the dependence of spectral output on the RG product and amplified spontaneous emission
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