CLADISS: a longitudinal, multimode model for the analysis of the static, dynamic and stochastic behaviour of diode lasers with distributed feedback

A new computer model called CLADISS is presented for the analysis of multisection diode lasers. The model allows for the analysis of a wide variety of multisection devices with discrete or distributed internal reflections. The simulator can carry out a threshold, dc, ac, and a noise analysis. The threshold analysis determines the threshold of the various longitudinal modes of the laser. The power versus current and the wavelength versus current characteristics are found with the self-consistent dc analysis. In each of the dc bias points the dynamic ac analysis can calculate the FM and AM response of the laser, while the noise analysis can determine the frequency and intensity noise spectra, and the line shape of the longitudinal modes. Not only do the dc, ac, and noise analyses consider several longitudinal modes simultaneously, but they also take into account nonlinear gain suppression, spontaneous emission, and longitudinal spatial hole burning. CLADISS includes all of the longitudinal variations by dividing each laser section in many short segments. Both the optical field and carrier density are discretized according to this segmentation. To demonstrate the capabilities of CLADISS some nonlinear effects in DFB lasers are treated. We first consider instabilities induced in the side-mode suppression ratio by spatial hole burning. Next we discuss the effects of spatial hole burning and side modes on the FM response and on the linewidth. Finally, the model is used to calculate the linewidth floor due to the power dependence of the linewidth enhancement factor

Theoretical investigation of the 2nd order harmonic distortion in the AM-response of 1.55 mm F-P and DFB lasers

Numerical calculations of the second-order harmonic distortion in the amplitude modulation-response of Fabry-Perot and distributed feedback lasers are presented and the influence of several nonlinerities, such as longitudinal spatial hole burning, gain suppression, and relaxation oscillations is considered in detail. Our analysis is valid for modulation frequencies ranging from a few megahertz to well beyond the resonance frequency of the relaxation oscillation. The numerical calculation of the distortion is based on the laser model CLADISS [1] and consists of an extended small signal solution (up to second-order) of the set of coupled wave equations and the local carrier density rate equations. The distortion is investigated for Fabry-Perot lasers for which the effects of spontaneous emission and gain suppression can be clearly illustrated and for DFB lasers where the emphasis is on the influence of spatial hole burning and its combination with other nonlinearities. Various effects are discussed, e.g., the occurrence of a dip in the frequency dependence of the distortion resulting from the combination of spatial hole burning and relaxation oscillation contributions in some cases and the occurrence of a dip in the bias dependence when spatial hole burning and gain suppression contributions cancel each other

Coupling-coefficients in gain-coupled DFB lasers: inherent compromise between coupling strength and loss

A theoretical analysis of the gain-coupling coefficient kappa-(gain)L for DFB lasers with first-order, rectangular, gain, or loss gratings is presented. For the structure with gain grating, the dependence of kappa-(gain) on the modal gain g(mod) has been into account for the first time. In both structures, an inherent compromise between coupling strength and extra modal loss is found. The results show that significant kappa-(gain)L values are feasible, allowing to benefit from the unique features of gain-coupled DFB lasers

Linewidth rebroadening in DFB-lasers due to a bias dependent dispersion of the feedback

It is shown that a linewidth rebroadening in some lasers, observed at relatively low power levels, can be explained as a result of a wavelength and power dependence of the distributed reflections. This type of linewidth rebroadening can occur in lasers where the loss increases with frequency in the vicinity of the emission frequency and in which the loss increases with bias level