PICWaveA photonic IC, laser diode and SOA simulator 
Modelocked laser diodeSimulation with PICWave softwarePICWave can model a large variety of semiconductor lasers. We will show here how it can be used to simulate a modelocked laser diode.
Design of the modelocked laser cavity Design of the modelocked laser cavityIn this device modelocking relies on a saturable absorber. Both the laser and the saturable absorber are located within the laser cavity. The saturable absorber is modelled in PICWave by a gain section with a very short nonradiative recombination time.
The laser is defined by a 2D crosssection. The gain spectrum can be obtained in different ways, either defined manually or imported from a heterostructure model such as Harold. An example of importation of gain curves from Harold with WideBand Gain Fitting can be seen here. The passive modes of the laser are calculated with a fully vectorial XY mode solver: the FDM Solver. Numerous mode parameters can be calculated, including the effective index, group index and dispersion, as well as the confinement factor.
Simulation of the modelocked laser in the timedomainThe laser is modelled by PICWave in the timedomain. The laser is started from amplified spontaneous emission. You can see below the output of the laser in the time domain. You can clearly observe the Qswitching occurring at the beginning of the simulation. After 1.5ns, the modelocked laser reaches its steady state. Zooming on the steadystate, you can observe the expected train of Gaussianlike pulses, with a spacing of 16ps and a FWHM of 4ps.
Output of the modelocked laser in the frequency domainThe spectrum in the frequency domain is calculated for the steadystate. Zooming on a wavelength range of 10nm, you can clearly see the expected narrow mode lines with an overall approximately Lorentzian envelope profile. The wavelength spacing is 450pm, which corresponds to the expected value (cavity length: 640um, central wavelength: 1.475um, group index: 3.72).
