Improved performance of polarization-stable VCSELs by monolithic sub-wavelength gratings produced by soft nano-imprint lithography

We present a novel method for fabricating polarization-stable oxide-confined single-mode GaAs based vertical cavity surface emitting lasers (VCSELs) emitting at 850 nm using a new soft-lithography nano-imprint technique. A monolithic surface grating is etched in the output mirror of the laser cavity using a directly imprinted silica-based sol–gel imprint resist as an etch mask. The opto-electronic performance of these devices is compared to VCSELs fabricated by state-of-the-art electron-beam lithography. The lasers made using the soft nano-imprint technique show single-mode TM lasing at a threshold and laser slope similar to that of devices made by e-beam lithography. The soft nano-imprint technique also enables the fabrication of gratings with sub-wavelength pitch, which avoids diffraction losses in the laser cavity. The resulting single-mode VCSEL devices exhibit 29% enhanced efficiency compared to devices equipped with diffractive gratings.