The PDLPro (PDLE-101) PDL Source/Emulator from General Photonics (Chino, CA) aids in testing to ensure that high speed fiber optic transceivers and coherent detection systems meet their stringent PDL tolerance specifications. The PDLE-101 is specifically designed for performance measurement of the PDL tolerance, tracking speed and recovery time of the PDL mitigation algorithm of a coherent detection system. Other applications include PDL emulation; code development for PDL compensation in coherent detection systems; and system PDL response testing. The PDLE-101 can generate individual PDL values between 0 dB and 20 dB, with a resolution of 0.1 dB for PDL tolerance testing. It can also generate variable PDL with a user-defined range, waveform, and speed for PDL tracking speed and recovery time tests.