A Confocal Laser Package Optimized for Minimum Reflections and Maximum Coupling.

Minimum optical feedback, from the coupling optics of semiconductor laser packages is required in order to reduce spectral instabilities and laser intensity noise. We report on the design considerations necessary for achieving return losses of > 50 dB. A simple formalism, based on Gaussian beam theory, is provided for the calculation of return loss in cases where the image of the reflecting surface is in the far-field of the laser. Data supporting the theoretical treatment are also presented. The trade-offs with respect to aberrations are discussed. In packages employing a 1.55 micron, multi-longitudinal mode CSBH laser we obtained a mean coupling efficiency of 66% with a standard deviation of 12%. System experiments at 590 Mb/s, using packaged 1.3micron EMBH multi-longitudinal mode lasers, into a link with transmission path dispersion as high as 91 ps/nm, show no measurable penalty attributable to reflections.