In　order　to　solve　the　mutual　restricted　problem　between　modulation　bandwidth　and　high　Q　value　of　microring　electro-optic　modulator　which　used　intracavity　index　modulation　mechanism　in　the　device,　an　ultra-compact　coupling　modulation　based　electro-optic　modulator　was　proposed.　This　device　consists　of　trench-based　frustrated　total　internal　reflection　couplers　and　90°　waveguide　bends.　A　time　domain　dynamic　model　was　used　to　evaluate　the　device　performance,　and　the　results　show　that　the　modulation　phase　change　is　less　than　0.2　π,　the　state　modulation　depth　is　greater　than　0.96　(normalized　maximum　of　1.0),　and　the　modulation　bandwidth　is　greater　than　100　GHz.　This　high　speed　modulator　exhibits　a　small　chip　area　of　10　μm×15　μm　and　a　lower　power　consumption.　The　compact　device　configuration　shown　here　is　beneficial　to　the　extension　at　two-dimensional　directions,　and　may　be　potentially　utilized　in　large-scale　photonic　integrated　circuits.　©　2015,　Chinese　Optical　Society.　All　right　reserved.