To clean a GPON OLT SFP, first, power down the device and carefully remove the SFP module. Use a lint-free cloth or a fiber optic cleaning swab lightly moistened with isopropyl alcohol to clean the optical connector. Gently wipe the connector in a circular motion, avoiding excessive pressure. Allow it to dry completely before reinserting the module and powering up the device.SEESUO.COM ONEOCLEAN-E SC/FC/ST/LSH 2.5mm Pen One-Push Cleaner is recommend, it works so well