Semiconductor Nanolasers

The semiconductor laser is among the most important inventions of the 20th century, having paved the way for our information society. More than sixty years after its demonstration, the laser remains a crucial enabling device for many emerging photonics applications. Present-day commercial semiconductor lasers, including edge-emitting lasers and VCSELs, use cavity mode volumes that are many times larger than the characteristic volume $V_{\lambda}= (\lambda/(2n))^{3}$, defined by a cube half-wave of wavelength $\lambda$ in a material with refractive index $n$. The theory of such macroscopic lasers is now well understood [1]. For future on-chip optical interconnects, e.g. between the cores of a computer, it is, however, essential to develop microscopic lasers with ultra-small footprints and ultra-low energy consumption. The emergence of point-defect cavities in photonic bandgap structures and nanofabrication technology developments have facilitated such a new generation of nanolasers with ultra-small mode volumes [2]–[5]. By virtue of enhanced light-matter coupling due to Purcell effects in nanocavities and a significant rate of spontaneous emission into the lasing mode, these nanolasers challenge existing laser theory. In particular, questions are raised about the correct description of the gain of the lasers, as well as the minimum level of quantum noise and the maximum modulation speed attainable.