Two optical functional devices based on 2D photonic crystal are investigated. First of all, add-drop filtering devices based on single defects in 2D photonic crystal slabs are characterized. After describing basic characteristics of channel-drop function, we show the improvement of device characteristics through defect engineering. We also demonstrate the channel-add function of the device. Next, we describe a 2D large-area surface-emitting laser exhibiting single-longitudinal and single-lateral mode oscillation with narrow divergence angle based on the 2D coupling effect of lightwave in 2D photonic crystals. A method of controlling the polarization mode by changing the shape of the unit cell is also presented. These results indicate that 2D photonic crystals are useful for the realization of novel optical functional devices.
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 300 micrometers 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 1.3micrometers 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.
Semiconductor three- and two-dimensional photonic crystals and their effects on the control of photons are investigated for possible applications to optical chip and functional devices. On the three-dimensional crystal, the effect of the introduction of light-emitter into the three-dimensional photonic crystal is investigated, and also the design of single defect cavity is performed, which is important for the development of the optical chip. On the two-dimensional photonic crystals, an ultra-small channel-drop-filtering device using unique phenomena of trapping and emission of photons by single defects in the 2D photonic crystal slab is described. These results encourage us to develop ultra-small optical integrated circuits using photonic crystals.
Various important scientific and engineering applications, such as control of spontaneous emission, zero-threshold lasing, sharp bending of light, and trapping of photons, are expected by using photonic bandgap (PBG) crystals with artificially introduced defect states and/ or light-emitters. Realizing the maximum potential of photonic crystals requires the following steps: (i) construct a three-dimensional (3D) crystal with a complete photonic bandgap in the optical wavelength region; (ii) introduce an arbitrary defect into the crystal at an arbitrary position; (iii) introduce an efficient light-emitter; and, (iv) use an electronically conductive crystal, as this is desirable for actual device application. Although various approaches to constructing 3D crystals have been proposed and investigated, none of these reports satisfies the above requirements simultaneously. To develop complete 3D crystals at infrared (5-10um) to near-infrared wavelengths (1-2um), we stacked III-V semiconductor gratings into a diamond structure by means of wafer bonding and a laser-beam-assisted very precise alignment technique. Since the crystal is constructed with III-V semiconductors, which are widely used for optoelectronic devices, requirement (iii) is satisfied. Moreover, as the wafer bonding enables us to construct an arbitrary structure and to form an electronically conductive interface, all the above requirements (i)-(iv) will be satisfied. In this paper, we review our approach for creating full 3D photonic bandgap crystals at near-infrared wavelengths.
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