SMF, 1.31/1.55um, 10dB step 0~50dB, 1dB step 0~15dB The MN924C and MN9605C are high-precision optical attenuators designed for use with single mode optical fibers. A combined step attenuator and continuous attenuator permit highly accurate attenuation adjustment. The MN9605C has PC-type optical connectors, so that internally reflected light is thoroughly suppressed. It is precisely constructed for single-mode fiber use and can be used as a highly accurate 65 dB variable attenuator. - See more at: http://www.testequipmentconnection.com/38117/Anritsu_MN9605C.php#sthash.zOcAM2Ym.dpuf