Characteristics of two-dimensional photonic crystal lasers

Abstract

Ever since the advent of the laser in early sixties, the quest for the ultimate thresholdless laser has lured attentions of scientists all over the world. To realize the ultimate laser, the resonant laser cavity should meet two requirements: the size of the cavity should be an order of wavelength under consideration and the quality factor of the optical cavity should be high. In other words, one needs to have an ultra-small and low-loss resonant cavity whose nano-fabrication has been nontrivial. However, the concept of photonic bandgap based on photonic crystals together with the advancement of nano-fabrication opens up the new possibility of realistic multidimensional photon confinement. In this thesis, we propose and demonstrate a novel approach toward this ultimate thresholdless laser based on a two-dimensional triangular slab photonic crystal. The smallest possible resonant cavity from a two-dimensional photonic crystal can be created by introducing just one defect in an otherwise perfect crystal lattice. Also, by slightly modifying this cavity, we can additionally obtain novel properties such as high quality factor and nondegeneracy. In our modified single-cell two-dimensional photonic crystal slab structure, we find several resonant modes which are theoretically and experimentally studied. There exist four fundamental modes in the photonic band gap, doubly degenerate dipole and quadrupole modes, and nondegenerate hexapole and monopole modes. Among them, the monopole mode specifically attracts our interest because of its nondegeneracy, good coupling with the gain medium, and existence of the intensity minimum at the center of the cavity, which would open up the chance for the electrically-driven single-cell laser. The nondegenerate hexapole mode, a special type of whispering gallery mode, has a very high quality factor. We have fabricated two types of modified single-cell lasers, i.e., air-based free-standing and $SiO_2$-based epoxy-bonded structures. Rich...