Agilent 81640A tunable laser repair

The Agilent 81640A is a C-band tunable laser module for the 8164/8166 mainframe. It covers the 1520–1570 nm window used in DWDM component testing, optical amplifier characterization, and coherent component measurement. This wavelength range means the 81640A sees heavy use in active telecom component test environments. Keysight support for the 81640A has ended. TEC control board failures are the primary repair case for the 81640A - the laser chip needs precise temperature stability to maintain wavelength accuracy and mode-hop-free tuning, and TEC failures cause the wavelength accuracy to degrade measurably before output power drops visibly. High-use units also show laser diode aging, which shows up as lower maximum output power, increased RIN, and reduced coherence length. Mainframe interface issues, mechanical shutter failures, and power supply problems are also seen. We test the 81640A in an 8164 mainframe, checking output power across the tuning range, wavelength accuracy at multiple set points, sweep quality, and GPIB communication. TEC assessment and repair, laser diode evaluation, output power characterization, and NIST-traceable wavelength calibration complete the service.