This book has been initially prepared as a special edition of Physica Status Solidi,
published as a festschrift in honor of Marc Ilegems, on the occasion of his retirement.
The editors however considered that the topic was important enough to deserve
a publication per se. Let me therefore state in a few words why should this
volume be of interest for a large audience, and then rephrase briefly what were the
achievements of Marc Ilegems that deserved to see his name associated to such a
book. I will then summarize the different chapters so the the reader may have a
proper overview of the content of this book.
The idea of going from a standard semiconductor laser to a vertical surface emitting
system appeared at the end of the 80th (the so-called VCSEL – Vertical Cavity
Surface Emitting Laser). Interesting preliminary work was accomplished by the
group of Franz Karl Reinhart at Ecole Polytechnique Fédérale, in Lausanne. The
idea is in fact quite simple and resides in the very high gain achievable in semiconductor
active layers together with the possibility to grow monolithic distributed
Bragg reflectors exhibiting reflectivities very close to 100%. It was then possible to
imagine, and later indeed realize, semiconductor lasers with a very small thickness
for the active layer.