A microring resonator and methods critically couple a microring waveguide to an adjacent bus waveguide. A method of determining parameters of a critically coupled microring resonator includes modeling a coupled portion of the microring resonator as a U-shaped waveguide spaced apart from a straight waveguide by a gap and selecting a straight waveguide width and a gap size to optimize an output coupling ratio between the U-shaped waveguide and the straight waveguide. A method of producing the microring resonator includes using the determined parameters to produce, and a critically coupled microring resonator includes, a ring-shaped or microring waveguide spaced from the bus waveguide by a gap.