Product Overview The Keysight (Agilent) 81949A is a compact tunable laser source module that slots into the 8163A, 8164A/B and 8166A/B lightwave measurement system mainframes. It provides stable, mode-hop-free single frequency output across the C band, making it a practical source for DWDM component test, optical amplifier characterisation and transceiver verification where a compact, rack-friendly laser is needed. Because the module takes its power, control interface and