Method, device, and system for sending and receiving signal

The present invention relates to the technical field of communications, and disclosed are a method, device, and system for sending and receiving a signal, for solving the problem of poor digital signal quality and high implementation cost existing in signal transmission, particularly as follows: splitting a received digital signal into a first digital signal and a second digital signal; converting respectively the first digital signal and the second digital signal into an I analogue signal and a Q analogue signal; modulating respectively the I analogue signal and the Q analogue signal to two optical signals which are orthogonal in a polarization state; combining the two optical signals which are orthogonal in a polarization state into an optical signal and sending same to an ONU; and the ONU modulating correspondingly and sending same to a user terminal. Thus, the problem of poor digital signal quality and high implementation cost existing in signal transmission is solved.