Two dimensional photonic crystal lasers

In this article, we report on a two-dimensional (2D) photonic crystal (PhC) laser with a surface-emitting function. First of all, 2D PhC laser with triangular-lattice structure is described. A uniform 2D coherent lasing oscillation based on coupling of lightwaves propagating to six equivalent Gamma-X directions is successfully demonstrated. A large area 2D lasing oscillation over 300mum in diameter and correspondingly a very narrow divergence angle less than 2 degree are observed. Then, the properties of a square-lattice PhC laser are described where the geometry of unit cell structure is designed appropriately to control the polarization mode of emitted light of the device. As the band diagram of the square-lattice photonic crystal is influenced by the unit cell structure, the electromagnetic field distributions at individual band edges are strongly modified and become unified or linear by changing the structure from a circular to an elliptical geometry. We fabricate a laser with a square-lattice PhC of which unit cell structures are elliptical. In spite of the very large diameter, single wavelength at 1.3mum and linear polarization mode are observed at representative positions. These results encourage us to realize lasers with desirable features such as perfect single-mode emission over a large area, high output power, and surface emission with a very narrow divergence angle.