High-speed modulation of semiconductor lasers and properties of silver-coated quantum-dot lasers

摘要

There is currently a great deal of research interest in plasmonic lasers, in which the optical field is confined by a metal waveguide instead of the more traditional dielectric waveguide. These devices show great promise because of their strong optical confinement and scalability below the diffraction limit. Both of these attributes are critical to future optical interconnect and optical transmitter photonic integrated circuit applications, requiring large integration density of devices and minimal cross-talk between channels. To attain large integration density, there is also a desire for high-speed lasers that have a large direct modulation bandwidth and eliminate the need for external modulators. Nanoplasmonic lasers and their high-speed characteristics are thus an important topic of research.In this thesis, experimental techniques for characterizing the high-speed performance of a semiconductor laser using electrical modulation and relative intensity noise (RIN) spectrum measurement are presented. Reasonable agreement is shown between the results from the two methods, and the pros and cons of each are described. Measured properties of newly fabricated silver-coated and uncoated quantum-dot Fabry-P??rot lasers are also presented. Room temperature, continuous-wave lasing is demonstrated in several silver-coated devices. The modal gain and group index are extracted from observation of the below threshold amplified spontaneous emission (ASE) spectrum. A large group index of 3.9 is found for the silver-coated lasers with a waveguide width of 1.4 ??m (compared to 3.5 for the uncoated lasers), possibly indicating a plasmonic effect caused by the silver coating. An even larger group index of approximately 4.5 is observed in several silver-coated LEDs with a waveguide width of 10 ??m. Evidence for the presence of multiple lasing transverse modes for a 1.4 ??m waveguide width silver-coated laser is presented and discussed. Electrical modulation and RIN measurements of the uncoated and silver-coated lasers are also presented.