Temperature-Dependent Impedance Characteristics of Temperature-Stable High-Speed 980-nm VCSELs

The temperature dependence of the impedance characteristics of high bit rate, highly temperature-stable 980-nm oxide-aperture vertical-cavity surface-emitting lasers (VCSELs) is investigated. A small-signal equivalent circuit model is fitted to measured small-signal reflection S11 and S21 scattering parameters across a large range of operating bias currents, temperatures, and oxide-aperture diameters to extract the circuit elements, -3 dB modulation bandwidth, relaxation resonance frequency, and parasitic cutoff frequency for each particular operating condition. The parasitic cutoff frequency of our small oxide-aperture diameter VCSELs is highly temperature insensitive from room temperature up to 85 °C, and does not limit our VCSELs' maximum data transmission rate. Finally, the dependence of the impedance characteristics and modulation bandwidth of our VCSELs on the oxide-aperture diameter is analyzed at 25 °C and 85 °C. The larger capacitance is the main reason of our larger aperture VCSELs, compared with smaller aperture VCSELs, have a lower parasitic cutoff frequency.