The Agilent variable optical attenuator family features lowest insertion loss and excellent wavelength flatness over a complete attenuation range of 60 dB, for characterizing optical network components for telecomunication and data communication in systems. The power control feature in the Agilent's variable optical attenuator module (81576A and 81577A) enables the user to set the output power level of the attenuator. The model of 'attenuator plus power meter' eliminates measurement uncertainty of various instruments and optical components such as optical coupler in one system because the Agilent's test instrument provides complete specification in one module. It is ideal solution for test setup with BERT (bit error rate tester) or DCA (digital communication analyzer) where various power levels need to be precisely tested.