Optical Characterization of Low Losses GaAs Waveguides Fabricated by Localized Vapour Phase Epitaxy

Abstract

The feasibility of very low losses GaAs waveguides has been recently demonstrated [1] using localized vapour phase epitaxy. This paper deals with the optical assessment (attenuation, polarization and electrical field mapping of the eigenmodes) of various structures grown using this process. Experimental growth conditions are discussed in details in [2]. In short, the guides are grown selectively on bare parts of a GaAs substrate otherwise covered by a dielectric film. Since the growth rate is strongly anisotropic, polygonal cross sections of various forms can be obtained. An additional feature is the possibility of modulating the doping level of the epilayer. Fig. 1 gives an example of 3 typical structures on (100) GaAs along <110> azimuth. Optical confinement is varied from one type to another by changing the doping sequence. With respect to the "classical" rib type structure, these guides have a much better lateral confinement.