<title>High-speed modulation characteristics and small-signal circuit modeling of deeply implanted GRINSCH-VCSELs with graded heterointerfaces</title>

Abstract

The high frequency behavior of vertical-cavity surface-emitting lasers (VCSELs) has been investigated. The small-signal optical modulation response and the impedance characteristics of several different multiple-quantum-well (MQW) VCSEL device structures have been measured and modeled as a function of dc bias and frequency in the 0.13- to 20-GHz range. An equivalent circuit model describing the intrinsic and extrinsic response of the VCSEL was derived, and a good fit to the experimental impedance and modulation data has been achieved. The extrinsic model yields the VCSEL electrical transfer function from which the 3 dB corner frequency (attributed to RLC parasitics) can be evaluated. In some of the devices measured, the 3 dB cutoff frequency is higher than the 3 dB optical modulation bandwidth measured. It is demonstrated that the electrical circuit parasitics alone are not the limiting factor in obtaining the maximum modulation bandwidth from these devices. It is found that the output power roll-over effect due to thermal heating is also a significant limit in obtaining higher optical modulation frequencies. By fitting the model of the intrinsic modulation response to the measured data a maximum resonant relaxation frequency of over 22 GHz is obtained (for a device with an 11-micrometers -diameter active region). It is also found that the amplitude of the modulation in these MQW devices is significantly reduced as the current increases much above threshold, and that this attenuation of the amplitude is explained by the frequency roll-off of the electrical RC parasitics.