Journal of Crystal Growth 301–302 (2007) 163–167 Growth of GaAs with orientation-patterned structures for nonlinear optics Xiaojun Yu à , Luigi Scaccabarozzi, Angie C. Lin, Martin M. Fejer, James S. Harris Solid-State and Photonics Laboratory, CIS-X 126, Stanford University, Stanford, 94305-4075 CA, USA Available online 22 December 2006 Abstract Orientation-patterned AlGaAs/GaAs nonlinear waveguides have great potential for all optical-wavelength switching in wavelength division multiplexed optical networks. Unfortunately, the fabrication of such devices has been unsatisfactory due to the difficulties in the growth of GaAs on Ge, as well as regrowth of GaAs on orientation-patterned substrates. In this paper, we describe development of a growth technique of GaAs on Ge to suppress the generation of antiphase domain defects, which are a general characteristic of all polar- on-nonpolar growth. We fabricated low-loss nonlinear optical waveguides and demonstrated second-harmonic generation (SHG) that doubles the wavelength of 1550–775 nm. A record-high conversion efficiency of 43% W was achieved. These achievements provide a solid basis for the fabrication of highly efficient nonlinear optical devices. r 2007 Elsevier B.V. All rights reserved. PACS: 42.70.Mp; 42.65.Wi Keywords: A3. Molecular beam epitaxy; B2. Nonlinear optical materials; B2. Semiconductor gallium arsenide; B3. Nonlinear optical 1. Introduction Telecommunications is currently undergoing a very significant, large-scale transformation. Wavelength divi- sion multiplexed (WDM) techniques offer very effective utilization of the fiber bandwidth directly in the wavelength domain, rather than in the time domain. This approach requires fast signal switching between various wavelengths in the system to maximize capacity and minimize delay/ latency. Conventional wavelength switching is achieved in an optical switch with or without signal regeneration. The optoelectronic wavelength conversion technology is mature and widely deployed; however, it requires an optical to electrical to optical conversion process, which is very slow, consumes considerable power and requires a large number of expensive laser diodes. All optical frequency conversion provides a far better solution [1]. The nonlinear frequency conversion preserves both phase and amplitude informa- tion, and this is the only category of wavelength conversion that offers strict transparency. Efficient nonlinear frequency conversion can be achieved only in waveguide devices for this application, which has already been demonstrated in periodically poled lithium niobate (PPLN)-based difference frequency generation (DFG) waveguides [2]. GaAs is a more attractive material for nonlinear optical-wavelength conversion because of its high nonlinear coefficient, broad IR transparency range, and well-developed epitaxial growth technologies. Because of the isotropic nature of GaAs, birefringent phase matching (BPM) is not possible in conventional AlGaAs waveguides, thus various artificial approaches must be adopted, such as form-BPM [3–6], modal phase matching (MPM) [7,8], and quasi-phase matching (QPM) [9–11]. However, no efficient nonlinear waveguide devices based on GaAs/AlGaAs system have been built to date, regard- less of the phase matching approaches, because of high waveguide propagation losses. In a lossless waveguide, the generated nonlinear power increases quadratically with device length under undepleted pumps, while in a lossy waveguide, optical power is completely attenuated in a long waveguide, thus an optimal length (generally as short ARTICLE IN PRESS www.elsevier.com/locate/jcrysgro 0022-0248/$ - see front matter r 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jcrysgro.2006.11.315 à Corresponding author. E-mail address: xjyu@snowboard.stanford.edu (X. Yu).