Near-field spectroscopic characterization of a 10 μm aperture selectively oxidized vertical cavity surface emitting laser

We have characterized a 10 μm square aperture selectively oxidized 850 nm vertical cavity surface emitting laser (VCSEL) utilizing a near-field scanning optical microscope coupled to a spectrometer. We have obtained both spatially and spectrally resolved images of the VCSEL’s emission. The spatially resolved intensity distributions were measured for the transverse modes of the VCSELs in the near field and far field at three different excitation currents, at threshold as well as above threshold. We identify the modes as being Hermite–Gaussian. Two-dimensional maps of the total integrated intensity of the spectra reveal an inhomogeneous gain distribution. The relative intensities of the various individual modes as well as their spatial orientation reflect how the available gain of the cavity is used. The wavelengths of the transverse modes were observed to increase with increasing current; calculations show that a temperature-induced change in refractive index of the cavity is the factor contributing to this redshift.