Single mode, low impedance 850-nm VCSELs with integrated mode filters

We present very simple implementations of mode filters that allow single mode operation of oxide-confined VCSELs with diameters 6 to 15 /spl mu/m. One implementation favored the fundamental mode by introducing mode selective reflectivity. The output mirror stack was terminated with an additional dielectric mirror pair in the center and with a quarter-wave dielectric in the outer region of the device. This mode filter was made by standard lithography and a selective etch. The second implementation favored the fundamental mode by introducing mode selective gain. While the oxide aperture defined the mode diameter, an additional current aperture provided gain to the center of the device only. This mode filter was made by standard lithography and a deep proton implant. In the study, we varied the mode filter diameter from well inside the oxide aperture to slightly outside the oxide aperture.