| High-speed directly modulated vertical-cavity surface-emitting lasers (VCSELs) are highly desirable in cost-effective optical communication systems. As a transmitter for future digital and analog applications, the VCSEL has to be of high enough bandwidth and implemented with a low parasitic structure.; Low-parasitics oxide-confined VCSELs can be engineered with an additional proton implantation process. The implantation minimizes the capacitance introduced by the thin oxide layer. A parasitics model, validated experimentally, for the oxide-implant VCSELs suggests the possibility of a parasitics-free structure up to 40 GHz.; High-bandwidth VCSELs is achieved with the injection-locking technique. When the VCSEL is locked to the master laser, the frequency chirp can be reduced and the resonance frequency can be several times higher than its free running case. A 2 dB power penalty reduction at 10−9 bit-error-rate was demonstrated for a 50 km, 2.5 Gb/s optical link. For analog applications, our 94 ± 2 dB-Hz2/3 of third harmonic spur-free dynamic range (a 19 dB-Hz2/3 improvement from the free running case) is the record for 1.55 μm VCSELs. This improvement can be attained in a large injection parameter space.; The theory of an injection-locked laser has also been developed. The frequency response is recognized to be the same as that of a parasitic-limited laser. The theory predicts that the resonance frequency improves with a higher injection power and the damping is higher with a larger detuning. All these trends qualitatively match with our thorough experiments within the entire locking range. With the guidance of this model, one can readily identify the injection conditions for the desired performance improvement. In addition, the simulation shows that an injection-locked, directly-modulated VCSEL is feasible for a 50 km SMF-28 link at 10 Gb/s.; An injection-locked uncooled tunable VCSEL was demonstrated to have a reasonable modulation performance in a wide temperature range. The injection technique can lock the VCSEL to a designated wavelength and compensate the temperature-induced performance degradation. This concept can be extremely attractive for low-cost DWDM transmitters. |
