No abstract

Shaping the light emission characteristics of laser systems is of great importance in various areas of science and technology. In a typical lasing arrangement, the transverse spatial profile of a laser mode tends to remain self-similar throughout the entire cavity. Going beyond this paradigm, we demonstrate here how to shape a spatially evolving mode such that it faithfully settles into a pair of bi-orthogonal states at the two opposing facets of a laser cavity. This was achieved by purposely designing a structure that allows the lasing mode to encircle a non-Hermitian exceptional point while deliberately avoiding non-adiabatic jumps. The resulting state transfer reflects the unique topology of the associated Riemann surfaces associated with this singularity. Our approach provides a route to developing versatile mode-selective active devices and sheds light on the interesting topological features of exceptional points.

We demonstrate the first few-mode semiconductor optical amplifier (FM SOA) that supports up to four waveguide modes. We show that each of the modes are confined to the waveguide, overlapping the quantum wells with approximately the same amount, leading to equalized gain for each of the four waveguide modes.

In this work, we report on laser diodes with intermixed InAlGaAs multi-quantum well (MQW) as the active gain medium. Using an impurity-free vacancy-enhanced disordering technique, several silicon nitride-capped InAlGaAs MQW samples are intermixed to different levels by varying the rapid-annealing temperatures from 730 °C to 830 °C. The intermixed laser diodes operate at wavelengths spanning from 1520 nm to 1400 nm, while exhibiting an increase in threshold current from 25 mA (as-grown) to 45 mA, and a decrease in slope efficiency from 0.101 W A −1 (as-grown) to 0.068 W A −1 as the intermixing extent is increased. For a sample that was annealed at 770 °C while only covered with a silicon dioxide film, the lasing wavelength is 1543 nm compared to 1550 nm for the as-grown laser wavelength, and the lasing threshold current is 26 mA with a slope efficiency of 0.08 W A −1 .