Tunable multiple quantum well distributed Bragg reflector lasers

The properties that multiple-quantum-well (MQW) distributed feedback lasers offer for improved fabrication and performance characteristics in two- and three-section tunable distributed Bragg reflector (DBR) lasers are discussed. In these structures, an approximately 3000-angstrom-thick, 1.3-μm λ_PL (photoluminescence peak wavelength) InGaAsP layer serves as the largely continuous waveguide along the entire device length transparent at the approximately 1.5-μm wavelength of the laser operation. Gain in the first section is provided by a set of four InGaAs quantum wells with their 80-angstrom thickness chosen to provide the appropriate quantum shift for gain in the approximately 1.5-μm range. The advantages are: (1) lower propagation los in the active section, contributing to a higher η_d; (2) markedly improved coupling between the active and passive waveguide regions; and (3) a reduced linewidth-enhancement factor α for improved dynamic and noise characteristics.