GaN Photonic-Crystal Surface-Emitting Laser
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1202-I12-03
GaN Photonic-Crystal Surface-Emitting Laser Susumu Yoshimoto1, Hideki Matsubara1, Kyosuke Sakai2, and Susumu Noda1, 3 1 Department of Electronic Science and Engineering, Kyoto University, Kyoto 615-8510, Japan. 2 Pioneering Research Unit for Next Generation, Kyoto University, Kyoto 615-8245, Japan. 3 Photonics and Electronics Science and Engineering Center, Kyoto University, Kyoto 615-8510, Japan.
ABSTRACT We introduce the lasing principle and important characteristics of photonic-crystal surface-emitting laser (PC-SELs). Specifically, we demonstrate two-dimensional coherent lasing oscillation with GaN PC-SELs, using a unique crystal growth technique called “air hole retained overgrowth” (AROG). Above the threshold, we obtained a two-dimensionally distributed nearfield pattern, and a distinctive far-field pattern with a divergence angle less than 1°. We also investigate a suitable sample structure for the reduction of the threshold current, where the PC structure is moved from an n-cladding layer to a p-cladding one. This is an important step towards the realization of novel light sources that can be integrated two dimensionally for a variety of new scientific and engineering applications in the blue to ultraviolet wavelengths.
INTRODUCTION There has been growing interest in photonic-crystal surface-emitting lasers (PC-SELs) [1–3] (Fig. 1). The lasing principle is based on the band-edge effect in a 2D PC, where the group velocity of light becomes zero and a 2D cavity mode is formed. The output power is coupled to the vertical direction by the PC, which gives rise to the surface-emitting function. PC-SELs have the following features: first, perfect, single longitudinal, and lateral mode oscillation can be achieved even when the lasing area becomes very large. Secondly, the polarization mode [2] and Surface emitting region Contact layer
Electrode
Upper clad Photonic crystal Carrier block Active layer Lower clad Substrate Electrode
Figure 1. Schematic structure of a PC-SEL.
beam pattern [3] can be controlled by appropriate design of the unit cell and/or lattice phase in the 2D PC. For example, unique beam patterns, including doughnut shapes with radial or tangential polarizations have been successfully generated, which lead to the realization of superhigh-resolution light sources that can be focused to a spot smaller than their wavelength [4, 5]. Recently, GaN PC-SELs have been realized in the blue-violet wavelengths [6] using a unique method called “air hole retained overgrowth” (AROG). The device successfully oscillated with a current injection at room temperature. A high-power laser beam in the blue to ultraviolet regime would greatly contribute to fields such as biomedical research and information technology. In this study, we overview the general characteristics of the PC-SEL, including the lasing principle and the unique beam patterns, and present the recent progress of GaN PC-SEL. LASING PRINCIPLE AND UNIQUE BEAM PATTERNS Figure 2 shows the lasing principle in (1) a triangular lattice photoni
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