The　structure　of　a　collinear　surface　acoustic　wave　(CSAW)　acousto-electro-optic　(AEO)　modulator　is　presented.　SAW　AEO　Coupled　wave　equations　are　given.　By　solving　these　equations,　conversion　efficiency　formula　of　CSAW　AEO　modulator　is　obtained.　Conversion　efficiency　as　the　function　of　acoustic　power　density　is　presented　in　x-cut　y-propagating　lithium　niobate　substrate　with　a　titanium　in-diffused　surface　waveguide.　Additional　electro-optic　port　can　change　the　center　frequency　of　the　modulator.　Relationship　between　conversion　efficiency　and　driving　frequency　is　also　presented.　Potential　applications　of　this　work　are　discussed.　©2010　IEEE.