Universal Bias Controller Testbed for DP-IQ Modulators in Coherent Optical Links

This paper presents the design, implementation, and testing of a testbed for the automatic bias controller (ABC) required in dual-polarization in-phase and quadrature (DP-IQ) modulators, like those used in coherent optical communication systems. The importance of controlling and adjusting the modulator bias signals is analyzed, as they directly impact the SNR of the demodulated signal. The operation of the testbed is demonstrated by implementing a bias adjustment algorithm that uses auxiliary signals or dithers. Finally, the performance of the testbed and ABC is experimentally validated by implementing a coherent optical communication system with DP-QPSK modulation at 10, 20, 100, and 128Gb/s data rates.