Design and fabrication of photonic crystal nanolasers

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Abstract

This thesis focuses on the design and fabrication of photonic crystal lasers and passive photonic crystal cavities to improve their efficiency and enhance the understanding of such nanoscale devices. The photonic crystal cavities are fabricated in an InP membrane and the lasers have embedded InAs quantum dots or InGaAsP/ InAlGaAs quantum well gain materials. The laser threshold is investigated experimentally for devices with a systematic design variation to optimize the cavityquality factor. The penetration depth into the mirror and the mirror phase change at the photonic crystal cavity end is numerically investigated for devices with systematic design variations using an equivalent FabryPerot model. The mirror phase is found to primarily be dependent on the change in resonance wavelength due to the design variations, while the penetration depth is found to increase as the Q-factor is increased due to gentler confinement of the cavity fields. Photonic crystal devices with a buried heterostructure gain medium are investigated experimentally for two different devices; a standard line defect laser and the Fano laser. In the Fano laser, one mirror is a standard termination of a line defect waveguide, while the other mirror is formed due to the the interference between a discrete nanocavity mode and the continuum of modes in an open waveguide. Numerical FDTD investigations are also carried out on equivalent cavities and open photonic crystal waveguides with buried heterostructures of varying lengths. The addition of the buried heterostructure to the line defect laser cavity redshifts the cavity resonance above the bandgap of the surrounding photonic crystal. Initial investigations confirm that confining the gain material to the line defect and waveguide are a of the Fanolasers eliminates the self-pulsing, previously observed in samples with active material in the nanocavity, thus enabling continuous-wave operation. The photonic crystal nanolasers promise exciting future opportunities with experimental realizations of novel device designs of ultracompact lasers with very low energy consumption enabling optical interconnects on the chip-scale.
Original languageEnglish
PublisherTechnical University of Denmark
Number of pages194
Publication statusPublished - 2020

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