Dhaka University Journal of Applied Science & Engineering

Semiconductor lasers are used as light sources in CD/DVD players, optical communication systems and other optical devices. But they often involve various noise and instability problems due to fluctuations of photon and electron numbers. In this paper, a numerical study has been done to understand the quantum noise characteristics of a semiconductor laser. Quantum noise is an intrinsic property of semiconductor lasers and impossible to control in principle. Hence analysis of noise characteristics for solitary lasers is important for noise largely limits the performance of the device. The rate equations for photon number and carrier number have been solved by considering self suppression coefficient of the laser. We consider Langevin noise sources for both photon number and carrier number to demonstrate the photon and carrier fluctuation. The rate equations are applied to typical 780-nm AlGaAs Fabry Perot semiconductor lasers operating in single mode by optimally choosing all the required parameters. Matlab is used to perform the numerical simulation. We analyze time-varying profiles of the fluctuating photon and carrier numbers for different injection current. The quantum noise of laser is calculated and presented through relative intensity noise (RIN) of the laser output. Frequency spectrum of the intensity noise is calculated with the help of fast Fourier transform (FFT). Transient behavior of the laser output is also demonstrated to understand noise characteristics of the device. Correspondence between the simulation data and practical result is also found.

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