Lasers　emitting　visible　light　based　on　high　harmonic　generation　(HHG)　have　significantly　enhanced　measurement　capabil-ities,　enabling　new　applications　across　precision　metrology,　attosecond　science,　and　ultrafast　time-resolved　spectroscopy.　This　paper　discusses　the　theoretical　framework　of　HHG　with　a　focus　on　nonlinear　effects,　examining　in　depth　second-harmonic　generation　(SHG)　and　third-harmonic　generation　(THG)　mechanisms,　as　well　as　a　thermal　nonlinear　model　for　pump　stability　analysis.　The　current　state　of　HHG　within　integrated　optical　circuits　is　reviewed,　with　a　particular　emphasis　on　its　implementation　in　high-index　doped　silica　glass　micro-ring　resonators　(HDSG　MRRs).　We　conclude　by　addressing　future　directions　for　optimizing　these　systems　to　expand　their　appli-cability　in　advanced　photonic　technologies,　highlighting　their　potential　for　innovation　in　both　applied　and　fundamental　sciences.　©　2025,　Electromagnetics　Academy.　All　rights　reserved.