Studying　the　noise　by　detectors　and　background　light,　we　find　that　the　influence　of　background　noise　on　the　detection　is　more　than　that　of　itself.　Therefore,　base　on　the　fiber　coupled　beam　splitting　technique,　the　small　area　detector　is　used　to　replace　the　large　area　detector.　It　can　achieve　high　signal-to-noise　ratio　(SNR)　and　reduce　the　speckle　interference　of　the　background　light.　This　technique　is　expected　to　solve　the　bottleneck　of　large　field　of　view　and　high　sensitivity.