Ultra-broadband gain materials can be made by using selected area growth (SAG) techniques. Material gain peak along the waveguide can vary as much as 300nm (from 1300nm to 1600 nm) in InGaAsP/InP quantum well waveguides. This gain peak variation is obtained by both material composition changes and quantum well width changes. This kind of broad band materials can be used to make ultra broad tunable lasers, amplifiers, and wavelength converters. Due to large band gap variation, the current injection will not be constant along the waveguide. The average serial resistance perpendicular to the waveguide direction will play an important role in the current distribution. In our simulation, a large serial resistance device will have a uniform current injection, therefore a uniform carrier distribution. But for a small serial resistance device, the carrier distribution along the waveguide is mainly decided by the local waveguide material bandgaps.
By using the selective area growth (SAG) technique, the grating over growth technique, and the buried hetero-structure (BH) regrowth technique, we have successful fabricated integrated distributed feedback laser and electro-absorption modulator. A suitable tensile strain is introduced during the multiple quantum well (MQW) growth to compensate the compressive strain caused by the SAG effect. To obtain better control on the growth condition and grating coupling coefficient, a quaternary grating laser is used. The best DFB laser shows a threshold current of around 12 mA and slope efficiency up to 0.13 mW/mA from one facet.