The Acterna JDSU HA1 attenuator is a single-mode, ultra-high resolution, and programmable attenuator ideal for bit error rate testing and general laboratory work. The HA attenuators are ideal for use in such demanding applications as multichannel AM systems and high bit-rate digital pulse code modulation (PCM) systems. Discrete internal optical reflections are minimized to better than 60 dB, and cavity effects are virtually eliminated. All HA attenuators are offered with high return loss and low spectral ripple for CATV AM systems. The HA attenuators have a nominal resolution of 0.01 dB (0.001 dB for the HA1 series) and an extended attenuation range of 100 dB. The standard operating wavelength is 1200-1700 nm. The inherently linear design of these attenuators, combined with built-in calibration and offset functions, allows the user to match the display to an optical power meter over a wide power range. This feature is useful in tests requiring control of the absolute optical power source for the test device. The built-in beam blocking switch provides fast access from any attenuation setting to infinite attenuation ( > 90 dB).