Emission Properties of Optically-Injected Semiconductor Lasers at the Nanoscale

Introduction Semiconductor nanolasers are envisioned to be attractive candidates for future energy-saving optical communication networks. Their attractiveness relies in the dimensions of the optical cavity, well below the... [ view full abstract ]

Introduction
Semiconductor nanolasers are envisioned to be attractive candidates for future energy-saving optical communication networks. Their attractiveness relies in the dimensions of the optical cavity, well below the diffraction limit. First, this offers promises for a tighter integration of optoelectronic devices on a microchip. Then, optical cavities of subwavelength dimensions exhibit enhanced spontaneous emission, quantified by the beta- and Purcell factors. The Beta-factor quantifies the ratio of spontaneous emission coupled into the cavity mode. The Purcell factor (Fp) is proportional to the ratio between the cubed lasing wavelength and the cavity volume. Physically, the Purcell effect decreases the carrier lifetime and enhances by a factor Fp the rate of spontaneous emission that is coupled into the cavity mode. The increased spontaneous emission of nanolasers allows reaching much lower threshold currents, with stimulated emission being achieved without requiring population inversion.

Methods
The emission properties of optically-injected nanolasers are discussed with a novel rate equation model taking into account the zero point energy. When injecting light into the laser, the frequency of the slave laser will be pulled towards that of the master laser. In the particular case when the frequency of the master laser is close enough to the slave laser frequency and the master laser power is high enough, the slave laser will operate at the master laser frequency. This phenomenon, called injection locking, is known in various physical systems.

Results and discussion
In this work, we will show that the cavity’s volume widely impacts the injection-locking area. In particular, working below the diffraction limit leads to an enlargement of the locking area meaning that nanolasers theoretically need very low injected power to be locked. Impact of the spontaneous emission rate on the locking map will be presented. Under optical-injection, simulations point out that a stably-locked nanolaser can exhibit large modulation dynamics at injection rates that are by far much smaller than those used in edge-emitting macrolasers. These results will pave the way for the development of energy-saving directly-modulated optical sources in future high-speed optical networks.