First and second harmonics of the laser response to current modulation

Abstract

The nonsteady-state generalization of the laser current-voltage and power characteristic model is obtained and used to derive the small-signal systems of equations for first- and second-order laser distortion to current modulation. The model takes into account the heating of the electron-hole gas in the active region and intrinsic leakage current associated with escape of the particles through the heterojunctions. The intrinsic diode capacitances and general form impedance are included in the small-signal equations. The quantitative analysis of the laser response to the current modulation is carried out on the specific example of the 1.3 μm laser based on an InGaAsP compound. A dependence of the light first and second harmonics on the thickness of the cladding layer (due to change of the leakage current) is demonstrated. It is shown that for thicknesses larger than several microns the influence of the leakage is negligible. It is found that modulation of the electron-hole gas temperature (due to heating effect) dramatically increases the second harmonic just in the range of frequencies (<500 MHz) important for laser applications in the transmission of the analog video signals in cable television systems.