Ultra-wide and nearly flat-top gain spectrum in asymmetric quantum-well structure for InGaAs tunable lasers

For tunable quantum well lasers, it has been a huge challenge all along how to achieve an ultra-wide tuning spectrum far exceeding the full width at half maximum (FWHM) of gain in a classic quantum well and the uniform power output for all tunable wavelengths of the laser under a fixed injection power, especially based on a single well structure. In this paper, we are reporting some amazing results from a special asymmetrical InGaAs quantum well structure, with which both incredibly extremely-wide and nearly uniform gain spectra are obtained with a fixed injection power. The excellent gain characteristics may make above dream come ture for the InGaAs-based tunable lasers. The formation of the structure is associated with the Indium-rich island effect. The analysis showed that the spectrally-tunable range from this special well structure could be up to 6 times as broad as the FWHM of gain in the classic InGaAs well and the gain spectrum with quasi-rectangular feature in transverse electric mode was obtained as well. It enables nearly identical power output over the total spectrally tunable range of the laser to be realized with a fixed optical injection power.