Researchers from the University of Illinois at Urbana-Champaign and Furukawa Electric Co. in Yokohama, Japan, have presented the results of their investigation into the modal characteristics of vertical-cavity surface-emitting lasers (VCSELs) with photonic crystal distributed Bragg reflector regions. The findings, which appeared in the Feb. 16 issue of Applied Physics Letters, suggest that a theoretical model of such characteristics may be used to improve the manufacture of single-mode VCSELs.The researchers compared the predicted and experimental modal properties of 850-nm VCSELs etched with a triangular array of one-, seven- or 19-hole photonic crystal defect structures. Although they considered only lasers that had airholes up to 10 µm in diameter and noted that the theoretical model may fail for larger apertures, they verified that it accurately predicts the dependence of single-mode behavior on properties such as etch depth and central defect diameter.