Coherent optical module refers to a typically hot-pluggable coherent optical transceiver that uses coherent modulation (BPSK / QPSK / QAM) rather than amplitude modulation (RZ/ NRZ / PAM4) and is typically used in high-bandwidth data communications applications. Optical modules typically have an. Coherent optics are typically used for ultra-high bandwidth applications ranging anywhere from 100 Gigabit to 1 Terabit per second. Powerful digital signal processing chips (DSPs) are embedded within these systems to mitigate non-linear effects caused by fiber impairments, including chromatic. Everything You Need to Know About Coherent Optical Modulation Find us at www. com Page 2 Contents. IM-DD uses the amplitude of the signal to encode/decode information with a simple photo detector (the receiver) to measure its power. For example, light on = 1, light off = 0.