Optical　feedback　for　either　the　excitation　or　the　signal　is　an　effective　approach　to　enhance　the　detection　sensitivity　of　Raman　scattering　spectroscopy.　A　combination　of　plasmonic　and　optical　feedback　schemes　may　supply　multifold　enhancement　mechanisms　with　further　improved　efficiency.　Herein,　a　plasmonic　Bragg　grating　(PBG)　consisting　of　periodically　distributed　silver　nanoslabs　coated　onto　the　sidewalls　of　the　grating　lines　is　reported.　Localized　surface　plasmons　excited　in　the　silver　nanoslabs　with　a　large　width/thickness　ratio　facilitate　enhanced　local　field　and　Raman　interaction.　Asymmetric　Bragg　diffraction　not　only　supplies　optical　feedback　along　the　grating　plane　to　extend　largely　the　laser-molecule　interaction　distance　but　also　enables　efficient　collection　of　the　Raman　signal　through　back-diffraction　into　the　detection　system.　Such　a　design　accomplishes　＂volume＂　surface-enhanced　Raman　scattering　with　a　modulation　depth　of　more　than　500　nm　and　strong　optical　feedback,　extending　largely　the　limited　interaction　distance　of　surface　plasmons.　With　respect　to　the　scheme　using　Ag　films　for　enhancement,　a　further　enhancement　factor　larger　than　2.8　x　10(3)　has　been　achieved　by　the　PBG　device　in　the　direct　detection　of　the　low-concentration　water　solution　of　R6G　molecules.　The　discovered　photophysics　is　potentially　important　for　practical　applications　in　in　situ　water　pollutant　detection.