Intradyne coherent receiver (ICR) is an essential component for modern coherent systems. Critical parameters of ICR include frequency response, bandwidth, and gain imbalance. Conventionally one creates heterodyne beating between tunable laser source (TLS) and local oscillator, and sweeps frequency of TLS to measure those parameters. A complicated control loop aligns state of polarization (SoP) of TLS to 45/135 degree of principle axis of polarization beam splitter. Otherwise unequal amount of power will launch into two polarizations, leading to inaccurate result. To overcome this complexity, we present a novel scheme to characterize ICR using polarization-multiplexed laser source generated using internal components of coherent transmitter. The optical signals on two polarizations are modulated with sinusoidal signal at different frequencies. If frequency difference is larger than laser line width, the output at the coherent transmitter is a polarization-multiplexed laser source. This method allows on-board measurement of analog front-end of coherent receiver by connecting coherent transmitter with coherent receiver. Influence of automatic bias control and radio frequency amplifier is also discussed. Another method is to combine outputs of two separate TLSs with orthogonal polarization through a polarization beam combiner. Both methods lead to robust performance without active control of SoP. The measurement accuracy using polarization-multiplexed laser source is the same as that of the conventional method. The intrinsic resiliency to polarization change leads to simple setup and enables in-field characterization of ICR.
Qiang Wang, Yang Yue, Massimiliano Salsi, Bo Zhang, Andre Vovan, and Jon Anderson, "Characterization of coherent receiver using polarization-multiplexed source generated from coherent transmitter," Proc. SPIE 10130, Next-Generation Optical Communication: Components, Sub-Systems, and Systems VI, 101300F (Presented at SPIE OPTO: February 01, 2017; Published: 28 January 2017); https://doi.org/10.1117/12.2250982.
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