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7 February 2007 Modulation properties of VCSEL with intracavity modulator
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We have studied the modulation properties of VCSEL with intracavity multiple quantum well (MQW) electroabsorption modulator integrated into the top distributed Bragg reflector (DBR) [1]. Small signal analysis of rate equations for loss modulation shows an intrinsic high-frequency roll-off slope of 1/&ohgr; instead of 1/&ohgr;2 in directly modulated laser diodes, and consequently bandwidths in excess of 40 GHz are obtainable with this configuration [2]. Possible limiting factors to high bandwidth were examined by fitting high frequency characteristics to a multi-pole transfer function, and include RC delay and carrier drift-limited time of flight (TOF) in the modulator intrinsic region. Intracavity loss modulation shows a strong (+20dB) relaxation oscillation resonant feature in both theory and experiment. As demonstrated, this feature can be significantly reduced in amplitude using parasitics. We have extracted relative contribution of TOF and parasitic capacitance by varying the modulator intrinsic region width (105 and 210 nm) and lateral size of the modulator (18 and 12&mgr;m). It was estimated that the small size modulator exhibits parasitics f-3dB at 8GHz. To estimate the carrier TOF contribution to bandwidth limits, low temperature growth of a 210 nm absorber i-region and MQW was employed to reduce photogenerated carrier lifetime. Bandwidth limitations were found to be mostly due to diode and metallization capacitances, in addition to one pole set by the optoelectronic resonance frequency. We have used p-modulation doping of the gain region to increase the relaxation frequency. Pronounced active Q-switching was observed, yielding pulse widths of 40 ps at a 4 GHz rate.
© (2007) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
J. van Eisden, M. Yakimov, V. Tokranov, M. Varanasi, E. M. Mohammed, I. A. Young, and S. Oktyabrsky "Modulation properties of VCSEL with intracavity modulator", Proc. SPIE 6484, Vertical-Cavity Surface-Emitting Lasers XI, 64840A (7 February 2007);

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