Abstract: Low spherical aberration of a Mikaelian lens makes it suitable for focusing off-optical-axis light propagating in higher order modes. A Mikaelian lens can be used as a mode-size converter to expand light in a semiconductor waveguide before coupling light out of the waveguide. For example, a Mikaelian lens can be used in a waveguide to expand light from a 1 ?m wide multimode waveguide to a 20 ?m wide multimode grating coupler in a shorter distance than an adiabatic taper. 3D FDTD simulation results show that an embodiment of a 12 ?m long, subwavelength mode-size converter has comparable first-order mode transmission as a 600 ?m adiabatic taper.