Semiconductor laser with regrown-lens-train unstable resonator: theory and design

The authors derive the geometrical optical properties of the fundamental mode of the unstable resonator consisting of a train of weak cylindrical lenses and obtain expressions for the effective distributed loss and the increase in threshold current due to the beam expansion. These properties are the same as for the continuous unstable resonator with a quadratic lateral variation of the index of refraction, to a very good approximation. The wave aberration introduced by passage through the lenses and through the output facet is not severe for stripe widths up to 170 mu m. The authors discuss the rationale for selecting a specific transverse structure for the regrown-lens-train laser and present the results of calculations of the waveguide modes and values of the effective index of refraction.>