The OLA-25 is a continuously variable optical attenuator designed for attenuating optical signals carried by single-mode fibers (9/125 /im) operating at 1300 and 1550 nm. The attenuator module is a neutral density filter placed in the broadened light beam between the input and output connections. The attenuation value is variable between 3 and 60 dB and depends on the position of the filter, which is set using the rotary control on the front panel. The actual attenuation includes the tosses of both test ports. It is displayed with a resolution of 0.1 dB on the LC display. The display error remains at < ± 0.2 dB. This accuracy is obtained by individual calibration of the display to match the attenuation filter characteristic. The OLA-25 is factory calibrated at 1300 and 1550 nm. it is set to the corresponding nominal wavelength using the slide switch. The OLA-25 is looped into the test circuit using test adapters, available for ai! standard 2.5 mm connector systems (DIN, FC, ST, etc.). Adapter cables can be used if different connectors are required. The test ports are physical contact (PC) types. This, together with the anti-reflex coated components in the attenuator module, guarantees a constant high return loss of > 23 dB. In normal operation the display of the OLA-25 is battery-powered. If the attenuation can be read directly from a bit error tester or optical power level meter in the test circuit, the display can be switched off, as the OLA-25 still functions as an attenuator in this mode.