(color online) Magnetic field distributions of the (a) fundamental and (b) first-order transverse TE WGMs. (c) Schematic diagram of waveguide-coupled square microcavity laser with square-ring-shaped injection window. (d) Wavelength interval and intensity ratio between two lasing modes versus injection current, with inset showing the lasing spectrum at an injection current of 90 mA. (e) Wavelength interval versus side length of square microlaser.