Active Region Design With Different Crystal Orientations for High-Speed DFB Laser

Abstract

High-speed directly modulated distributed feedback (DFB) laser is crucial for high-speed optical communication systems. The modulation bandwidth and frequency chirp of such devices are primarily affected by the differential gain and linewidth enhancement factor (LEF) of the quantum wells (QWs) in the active region. In this work, the optical gain properties of long wavelength AlGaInAs-InP strained quantum wells (QWs) with different crystal orientations are numerically investigated using the multi-bands k.p theory, which considers both valence-band anisotropic and nonparabolicity. Compared to the QW laser grown on a conventional (001) substrate, a higher differential gain, and smaller LEF are observed for the laser grown on the (110) substrate with the ${\rm{(\bar{1}10)}}$ plane as the mirror facet. This is primarily due to the reduced effective mass of the valence band. The dynamic characteristics of (001)-and (110)-oriented DFB laser is theoretically studied using the one-dimensional traveling wave model (1D TWM) at ${\rm{25}}\;^\circ \text{C}$ and ${\rm{95}}\;^\circ \text{C}$. The simulation results show that the lower chirp and wider modulation bandwidth can be achieved for the QW laser grown on (110) substrate.

Keywords

• Crystal orientation
• differential gain
• linewidth enhancement factor
• –3 dB bandwidth