Lasing and modified spontaneous emission in photonic crystal structures and microcavities

Citation

Lee, Reginald K. (2000) Lasing and modified spontaneous emission in photonic crystal structures and microcavities. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/kvvd-em02. https://resolver.caltech.edu/CaltechETD:etd-06102005-082207

Abstract

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Semiconductor light-emitting devices in the near-infrared (1.55 µm) based on microfabricated photonic crystal structures are demonstrated. The photonic structures consist of two-dimensional arrays of air holes patterned into an optically thin, airsuspended InGaAsP slab by high-resolution electron beam lithography and various dry etching techniques.

Two types of microcavities are examined. The first are larger hexagonally shaped cavities in the range of 10 to 20 µm in size and bounded by the photonic crystal structure. Cavity mode spontaneous emission at room temperature under optical pumping is used to demonstrate mode confinement due to the in-plane bandgap. No cavity mode peaks in the emission spectrum are seen if the in-plane bandgap is not spectrally aligned with the material emission. Pulsed lasing is also demonstrated with the lasing threshold at 66 mW peak incident optical pump power at a duty cycle of less than 1% in order to minimize membrane heating. Changes in the pump geometry is shown to result in controllable lasing mode switching. This behaviour is explained in terms of mode Q, lasing threshold and enhanced spontaneous emission into the mode.

The second type of microcavity consists of a single point defect into photonic lattice with a modal volume of [...]. Cavity quality factors up to 250 are demonstrated and suppressed spontaneous emission due to the bandgap except at the mode frequency is shown. Pulsed lasing at 143 K under optical pumping is demonstrated.

The fundamental modification of the spontaneous emission rate due to the in-plane bandgap in a photonic crystal slab structure with no microcavity is experimentally and numerically examined. Incomplete bandgaps are theoretically shown to be able to strongly inhibit spontaneous emission. High density of states points in the band-structure are seen to greatly enhance the spontaneous emission rate. Measurements using phase sensitive spectroscopy of the spontaneous emission rate from quantum wells in the photonic crystal slab show a greater than 10 times inhibition of the emission rate in the in-plane bandgap. Experimental evidence for saturation of the surface recombination at relatively low pumping levels is found.

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