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Novel Surface Emitting Laser Using High-Contrast Subwavelength Grating Michael C.Y. Huang, Mervin Ye Zhou Semiconductor diode lasers are widely used for a variety of applications, e.g., telecommunication, display, solid-state lighting, sensing, surveillance, printing, and imaging. It is desirable to have devices with light emission normal to the wafer surface so that light can be more efficiently extracted with simple, conventional optics. Vertical cavity surface emitting lasers (VCSELs) are a type of semiconductor laser diode with the emission beam perpendicular to the top surface. The laser resonator consists of two distributed Bragg reflector (DBR) mirrors parallel to the wafer surface for optical feedback, and in-between the two mirrors, an active gain region for the laser light generation. Due to the ultra-short gain region (several 10s nm), the reflectivity for both mirrors needs to be greater than 99.5%. Hence, the realization of VCSELs for wide wavelength regimes has been limited by challenges in choosing proper materials for making such highly reflective DBRs.
In this work we present a new class of surface emitting lasers utilizing a revolutionary, single-layer high-index-contrast sub-wavelength grating (HCG), instead of conventional a DBR or photonic crystal. The use of such a high-contrast grating dramatically reduces the required mirror epitaxial thickness by a factor of 20 and greatly simplifies VCSEL material requirements in terms of thickness control and composition accuracy. Our result demonstrates the first room-temperature continuous-wave (CW) operation of a subwavelength grating integrated VCSEL with a single wavelength and fixed polarization emission at 850 nm wavelength. Due to the polarization-dependent reflectivity of an HCG, lithographically-determined polarization is achieved, which will be critical for system stability and reliability. Moreover, we demonstrated a novel electrostatic actuated nano-electromechanical (NEMS) tunable surface emitting lasers utilizing a movable single-layer large-index-contrast HCG mirror. Single mode emission and continuous wavelength tuning were obtained at room-temperature under CW operation. The demonstration of an ultra-thin HCG mirror integrated VCSEL represents a significant impact for the future designs of VCSELs, photo-voltaic cells, and light emitting diodes at blue-green, 1.3-1.55 μm, and mid- to far infrared wavelengths.  References: A surface-emitting laser incorporating a high-index-contrast subwavelength grating, Michael C.Y. Huang, Y. Zhou and Connie J. Chang-Hasnain, Nature Photonics 1, 119 - 122 (2007) Nano electro-mechanical optoelectronic tunable VCSEL, Michael C. Y. Huang, Ye Zhou, and Connie J. Chang-Hasnain,Optics Express, Vol. 15, Issue 3, pp. 1222-1227
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