Coupling ratios design and their impact on the performance of binary driven QAM transmitters

The support of higher order modulation format such as 16-QAM and 64-QAMis an essential feature of next generation coherent optical transceivers to ensure a spectrally efficient and high capacity optical transmission [1–3]. In previous work, we have proposed an optical QAM transmitter scheme that employs QPSK modulators driven by binary electrical signals [4, 5]. This paper presents the design for the coupling ratio that considers the insertion loss of the optical components in order to generate a proper QAM symbol constellation with equally-spaced symbols.