U.S. Team Develops PEC Etch-based Method To Tune Microdisk Lasers

Recently, a joint research team from Harvard Medical School (HMS) and MIT General Hospital in the United States said they have realized the tuning of microdisk laser outputs using PEC etching, which makes a new source of nanophotonics and biomedicine "very promising".
Microdisk lasers and nanodisk lasers have emerged as a promising light source and probe in fields such as nanophotonics and biomedicine. In several applications, such as on-chip photonic communication, on-chip bioimaging, biochemical sensing and quantum photonic information processing, they require laser output at a defined wavelength and with ultra-narrowband precision. However, large-scale fabrication of such precise wavelength micro- and nanodisk lasers remains challenging. Current nanofabrication processes introduce randomness in disk diameters, making it difficult to obtain set wavelengths in laser high-volume processing and production.
And now, a group of researchers from Harvard Medical School and the Wellman Center for Photomedicine at Massachusetts General Hospital have developed an innovative photoelectrochemical (PEC) etching technique that helps precisely tune the laser wavelengths of microdisk lasers with sub-nanometer precision.
The results are published in the journal Advanced Photonics.
Photoelectrochemical etching
The group's new approach enables the fabrication of microdisk lasers and nanodisk laser arrays with precise, predetermined emission wavelengths, according to the report. The key to this breakthrough is the use of PEC etching, which provides an efficient and scalable way to fine-tune the wavelength of microdisk lasers.
In the above results, the team succeeded in obtaining silicon dioxide-covered indium gallium arsenide phosphide microdisks on indium phosphide column structures. They then precisely tuned the laser wavelengths of these microdisks to defined values by photoelectrochemical etching in a dilute sulfuric acid solution.
They also investigated the mechanism and kinetics of specific photoelectrochemical (PEC) etching. Finally, they transferred the wavelength-tuned microdisk arrays onto polydimethylsiloxane substrates to produce separate, isolated laser particles with different laser wavelengths.
The resulting microdisks show an ultra-broadband bandwidth of laser emission, with on-column lasers less than 0.6 nm and isolated particles less than 1.5 nm.
Opening the door to biomedical and other applications
This result opens the door to many new nanophotonic and biomedical applications. For example, stand-alone microdisk lasers can serve as physical-optical barcodes for heterogeneous biological samples, enabling cell-type-specific labeling and targeting of specific molecules in multiplexed analyses.
Cell type-specific labeling is currently performed using conventional biomarkers such as organic fluorophores, quantum dots, and fluorescent beads, which have wide emission linewidths.
As a result, only a few specific cell types can be labeled simultaneously. In contrast, the ultra-narrowband light emission of microdisk lasers would be able to recognize a much larger number of cell types simultaneously.
The team tested and successfully demonstrated precisely tuned microdisk laser particles as biomarkers using them to label cultured normal breast epithelial cells MCF10A.With their ultra-broadband emission, these lasers could potentially revolutionize biosensing using well-established biomedical and optical techniques, such as cellular kinetic imaging, flow cytometry, and multihistology analysis.
The PEC etch-based technology marks a significant advancement in microdisk lasers. The scalability of the method, as well as its sub-nanometer precision, opens up new possibilities for the myriad applications of lasers in nanophotonic and biomedical devices, as well as in the barcoding of specific cell populations and analyzed molecules.