What is the time domain IQ skew of the 40G DQPSK receiver in optical transport network? Is it the time delay of the IQ channel ,or specifying the adjustment of the phase angle between the I and Q vectors?

The IQ timing skew of a receiver usually means the difference in the delay of the I & Q branches of the receiver.

There are currently no standards for optical DQPSK receivers in ITU-T at this time (although this is an active work item in Q6/15), however the OIF has an Implementation Agreement for a coherent receiver:



OIF-DPC-RX-01.1 - Implementation Agreement for Integrated Dual Polarization Intradyne Coherent Receivers, available at:



http://www.oiforum.com/public/docum...X-01.1.pdf

Which uses the term Channel skew in Table 7 of informative Appendix B to mean “Time difference between earliest and latest channel”, where the “channels” are XI, XQ, YI, YQ.