Semiconductor　lasers　with　good　fundamental　transverse　mode　stability　have　important　applications　in　optical　communications,　light　sources,　biomedical　and　other　fields.　For　Fabry-Perot　(FP)　lasers,　lateral　mode　control　is　an　important　issue.　In　this　paper,　the　influence　of　the　side　double-trench　ridge　waveguide　structure　of　the　semiconductor　FP　laser　on　the　output　mode　characteristics　is　analyzed　theoretically.　The　device　is　modeled　and　calculated　using　matlab　software.　FP　laser　with　different　ridge　width　and　trench　width　are　designed　and　fabricated　using　the　double-trench　ridge　waveguide　structure.　The　influence　of　the　leakage　loss　of　the　double-trench　waveguide　structure　on　the　mode　output　characteristics　is　analyzed.　©　2023　SPIE.