Temperature dependence of electroluminescence (EL) spectral intensity of the super-bright green and blue InGaN single-quantum-well (SQW) light-emitting diodes has been studied over a wide temperature range (T=15–300 K) under a weak injection current of 0.1 mA. It is found that when T is slightly decreased to 140 K, the EL intensity efficiently increases, as usually seen due to the improved quantum efficiency. However, with further decrease of T down to 15 K, it drastically decreases due to reduced carrier capture by SQW and trapping by nonradiative recombination centers. This unusual temperature-dependent evolution of the EL intensity shows a striking difference between green and blue SQW diodes owing to the different potential depths of the InGaN well. The importance of efficient carrier capture processes by localized tail states within the SQW is thus pointed out for enhancement of radiative recombination of injected carriers in the presence of the high-density dislocations.

Temperature and injection current dependence of electroluminescence (EL) spectral intensity of the superbright green and blue InGaN single-quantum-well (SQW) light-emitting diodes has been studied over a wide temperature range (T=15−300 K) and as a function of injection current level (0.1–10 mA). It is found that, when temperature is slightly decreased to 140 K, the EL intensity efficiently increases in both cases, as usually seen due to the improved quantum efficiency. However, with further decrease of temperature down to 15 K, unusual reduction of the EL intensity is commonly observed for both of the two diodes. At low temperatures the integrated EL intensity shows a clear trend of saturation with current, accompanying decreases of the EL differential quantum efficiency. We attribute the EL reduction due to trapping of injected carriers by nonradiative recombination centers. Its dependence on temperature and current shows a striking difference between the green and blue SQW diodes. That is, we find that the blue InGaN SQW diode with a smaller In concentration shows more drastic reduction of the EL intensity at lower temperatures and at higher currents than the green one. This unusual evolution of the EL intensity with temperature and current is due to less efficient carrier capturing by SQW. The carrier capture in the green and blue diodes also shows a keen difference owing to the different In content in the InGaN well. These results are analyzed within a context of rate equation model, assuming a finite number of radiative recombination centers. Importance of the efficient carrier capture processes by localized tail states within SQW at 180–300 K is thus pointed out for explaining the observed enhancement of radiative recombination of injected carriers in the presence of high-density misfit dislocations.

We theoretically and experimentally investigated the transition between modulation instability and Raman gain in a small silica microcavity with a large free-spectral range (FSR), which reveals that we can selectively switch from a four-wave mixing dominant state to a stimulated Raman scattering dominant state. Both the theoretical analysis and the experiment show that a Ramandominant region is present between transitions of Kerr combs with different free-spectral range spacings. We can obtain a stable Kerr comb and a stable Raman state selectively by changing the driving power, coupling between the cavity and the waveguide, and laser detuning. Such a controllable transition is achieved thanks to the presence of gain competition between modulation instability and Raman gain in silica whispering gallery mode microcavities.

By using nonlinear coupled mode equations, we numerically investigated the generation of a Kerr comb in a normal dispersion microcavity system, where mode coupling between two cavity modes is present. In contrast to previous studies, our model is rigorous in which we fully considered the mode coupling between two modes. We investigated the phase matching condition to obtain the suitable parameters needed to form a free-spectral-range (FSR)-selectable comb. Our calculations are in good agreement with existing experimental results, and enable us to obtain a good understanding of the phenomenon; moreover our model also allows us to reveal new phenomena. We investigated 1-FSR comb generation in detail and found that randomly oscillating behavior will appear when detuning is scanned, which has never before been clearly observed. This modeling approach will be a powerful tool that will assist dispersion engineering for Kerr comb generation and the frequency tuning needed to generate a deterministic mode-locked comb.

Microresonator-based optical frequency combs (known as microcombs or Kerr combs) have a large repetition frequency ranging typically from 10 to 1000 GHz, which is compatible with fast-scanning applications, including dual-comb spectroscopy and LiDAR. In this research, we numerically study dual-comb generation and soliton trapping in a single microresonator, whose two transverse modes are excited with orthogonally polarized dual pumping. The simulation model is described by using coupled Lugiato-Lefever equations (LLEs), which take account of cross-phase modulation and the difference in repetition frequencies. The numerical simulation calculates the dual-comb formation in a microresonator, whose microcombs propagate as soliton pulses and cause soliton trapping depending on the parameters. In the simulation, a trapped soliton is seeded by one of the original solitons in two transverse modes. In addition, we introduce an analytical solution for trapped solitons in coupled LLEs using a Lagrangian perturbation approach and clarify the relation between the parameters. Revealing the conditions of dual-comb soliton generation and soliton trapping is helpful in terms of optimizing the conditions for causing or avoiding these phenomena.