Small-Signal-Equivalent Circuits for a Semiconductor Laser (original) (raw)
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Two different forms of equivalent circuit models have been independently proposed for semiconductor laser amplifiers. These have interesting similarities in their equivalent circuits. This paper will compare the models in terms of derivation, completeness, applications, and computing speed. Results from the transmission line laser model. (TLLM) are presented and show the effects of input power, carrier inhomogeneities, and front facet reflectivity on two-input intermodulation distortion.
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We present a new largeismull signal equivalent circuit f o r semiconductor lasers, valid for above-as well as below-threshold operating condilions. based on the monomode rate equations atid a polynomial approximation of Fermi integral. The model is thus valid for conditions of large injection. Results obtained bv this model match perfectly those obtained by numerical integration of the rate equations. The equivalent circuit is easy to implement and solve on a nonlinear circuit analysis software such as SPICE and consequently allows the study of the parasitic effects as well as the laser behavior in complex circuits. Comparison between this model and previouslv published models is presented. The model is applied to the study of various heterojunction laser diodes, the experimental results of which have been published elsewhere.
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Pramana, 2008
This paper demonstrates theoretical characterization of intensity modulation of semiconductor lasers (SL's). The study is based on a small-signal model to solve the laser rate equations taking into account suppression of optical gain. Analytical forms of the small-signal modulation response and modulation bandwidth are derived. Influences of the bias current, modulation index and modulation frequency as well as gain suppression on modulation characteristics are examined. Computer simulation of the model is applied to 1.55-µm InGaAsP lasers. The results show that when the SL is biased far-above threshold, the increase of gain suppression increases both the modulation response and its peak frequency. The modulation bandwidth also increases but the laser damping rate decreases. Quantitative description of the relationships of both modulation bandwidth vs. relaxation frequency and maximum modulation bandwidth vs. nonlinear gain coefficient are presented.
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Large-signal analysis of analog intensity modulation of semiconductor lasers
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Large-signal analog intensity modulation of semiconductor lasers (SLs) is characterized based on numerical integration of the rate equations. The modulation dynamics are classified into seven types with regular and irregular signals. The classification is made in terms of the time trajectory of the laser intensity, phase portrait, and fast Fourier transform (FFT) spectrum. The operating region of each type is defined in a diagram of the modulation index versus modulation frequency. The accuracy of applying the approximate small-signal analysis to study analog modulation is assessed. The validity of identifying the dynamic types by the large-signal modulation response is examined. The laser emits continuous and regular signals under weak modulation. When the modulation index exceeds one half, the laser emits picosecond-pulses. Under strong modulation with frequencies around the relaxation frequency, both continuous and pulsed signals exhibit period-doubling.