| Hybrid VCSELs are fabricated for this study with various combinations of implant aperture width and depth, as well as different oxide aperture sizes, to create a variety of hybrid VCSELs that can be divided into two groups: the single mode structure and the high speed structure hybrid VCSELs. The VCSELs are grown on semi-insulating substrates to reduce the capacitance of the coplanar high speed probe pads.; The difference between the size of the oxide aperture radius and the size of the implant aperture radius, i.e., Δr = roxide − rimplant, has a profound effect on the modal characteristics of the VCSEL. By making the implant aperture smaller than the oxide aperture (Δr > 0), we can produce high power single mode operation by selectively injecting the current into the fundamental mode defined by the oxide apertures. If Δ r ≤ 0, the implant aperture will have no effect, and the hybrid VCSEL will perform like an oxide VCSEL.; The wavelength splitting between the fundamental mode (LP01) and the first higher order mode (LP11) of selectively oxidized, ion implanted, and single mode structure hybrid VCSELs grown on the same wafer is studied. Measured splittings show marked differences between the different laser structures due to the effects of index guiding and thermal lensing. Theoretical results were obtained using a vector optical mode solver and show good agreement with experimental results. For hybrid VCSELs with small oxide apertures, the LP01 and LP11 modes are influenced by the oxide index step, while for the hybrid VCSELs with larger oxide apertures, the modes are influenced by the index difference of the thermal lens.; The depth of the implant is also an important parameter in determining optical performance.; The high frequency modulation response for hybrid VCSELs is measured and compared to the theoretical response of the VCSEL derived through small signal analysis, with good agreement. For the two single mode structure wafers measured, the VCSELs with the implant aperture located farther away from the active region had the better response. The capacitance of the high speed structure VCSEL, where a deep (through the active region) and wide implant is used to reduce charge buildup underneath the oxide layers, and hence capacitance, is smaller than the capacitances of the other wafers due to reduction in the oxide capacitance. However, the capacitance of all the VCSEL wafers was increased because of the area of the bottom contact mesa and the photoresist bridge. (Abstract shortened by UMI.)... |
