Quantum Dot Lasers – Wavelength Control

Quantum dots, semiconductor particles small enough to contain single electrons, are a promising laser light source for specific applications. Although careful selection of the semiconductor material can effectively tune the output of quantum dot lasers, structural flaws tend to split the output into multiple wavelengths.

A group of researchers has proposed a possible solution in which two evanescently coupled microdisk optical resonators result in spectra with reduced mode-splitting.

It is not impossible to create defect-free lasers, but it would be costly and time-consuming. In comparison, the coupling is a faster, more flexible, and less expensive way to solve the problem. It is a ruse to avoid having to make perfect quantum dot lasers.

The researchers tested the theory using colloidal quantum dot (CQD) microdisk lasers made of cadmium selenide and measuring about 7.5 nanometers. Compared to the high-vacuum film processing methods required by some other inorganic quantum dot sources, CQDs are a promising photonic component that is relatively easy to fabricate using standard lithographic techniques and a variety of substrates.

Due to fabrication defects acting as asymmetric scattering centers, each CQD laser produced an imperfect output, with the resulting emission spectra split across a wavelength range as expected. It was a different story when the team combined two CQD lasers.

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