Optical communication systems require light sources that can be modulated with high speeds. However, the modulation bandwidth of laser diodes is typically limited by an intrinsic value, its relaxation resonance frequency. In order to circumvent this limitation, a number of methods have been proposed to boost the modulation speed, including optical injection locking, quantum dots lasers with large differential gain, push-pull modulation in composite lasers. This dissertation explores two new approaches for enhancing the direct modulation bandwidth of semiconductor quantum well laser diodes. Lasers with strong spontaneous emission have been shown to exhibit a high-speed performance theoretically. It is expected that such devices should have a modulation bandwidth on the order of several GHz under a sub-mA injection current. However, so far there has not been any experimentally observed verification of such enhanced behavior. In this work, we report on the experimental characterization of the intrinsic frequency response of metal-clad nanolasers. The probed nanolaser is optically pumped and modulated, allowing the emitted signal to be detected using a high-speed photodiode at each modulation frequency. Based on this technique, the prospect of high-speed operation of nanolasers is evaluated by measuring the ??-factor, which is an order of magnitude greater than that of other state-of-the-art directly modulated semiconductor lasers. In another experiment, we demonstrate that by tuning the gain-loss contrast between two coupled identical resonators a new degree of freedom to control the modulation frequency response is obtained. An electrically pumped microring laser system with a bending radius of 50 µm is fabricated on an InAlGaAs/InP MQW material. The integrated device was observed to lase in continuous-wave mode at room temperature with a threshold current of 27 mA. By tuning the pumping ratio between two coupled rings, our measured results clearly show a bandwidth broadening by up to 1.63 times, which matches well with laser rate equation model.
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Doctor of Philosophy (Ph.D.)
College of Optics and Photonics
Optics and Photonics
Optics and Photonics
Length of Campus-only Access
Doctoral Dissertation (Open Access)
Xu, Chi, "High Speed Modulation Characteristics of Semiconductor Nanolasers and Coupled Ring Laser Systems" (2021). Electronic Theses and Dissertations, 2020-. 589.