This attenuator provides optimum performance for testing fiber optic transmission systems, sub systems and components. A combination of optical characteristics enables confident testing of high speed, high power systems which require superior power handling, ORL, PMD and PDL characteristics. Very flat wavelength response enables confident testing of CWDM / DWDM systems. The instrument wavelength setting is irrelevant in most practical situations. Excellent linearity and absolute accuracy enables precision linearity testing of sub systems and components. The patented metal free interchangeable connectors avoid critical contamination of connectors used in high power applications. Operational modes include: manual, relative, step, program, and remote control via a PC. The instrument can be preprogrammed with up to 15 different user programs for improved productivity. The PC software is used to provide external control. The combination of features provides superior value to the user.