Serrodyne phase modulation is one of the most widely used frequency shifting techniques in a resonator micro-optic gyro (RMOG). However, to achieve high gyro performance, extraordinary linearity of the serrodyne waveform is critically required. In this paper, compact RMOG with an ultrashort micro-optic resonator using analog triangle phase modulation is proposed. Theoretical analysis on the effects of second and third order nonlinearity of the modulation waveform, along with quantitative calculation of errors induced by the modulating nonlinearity, is presented. Performances of the established RMOG system are experimentally demonstrated, with nonlinearity measurement of the generated and applied triangle waveform. The proposed scheme shows great capability in near-linear waveform generation with quite simple electrical elements.