A method of compensating for crosstalk in a mode division multiplexing passive optical network using a technique of transmitter-side crosstalk pre-compensation, performed at the Central Office, in which a downlink reference signal such as a training sequence or pilot signal is retrieved at the transmitter without being influenced by crosstalk effects on its uplink transmission. An uplink reference signal is transmitted in a quasi-single mode transmission along the optical fiber, and a plurality of optical signals input to transmission multiplexer are adapted based on the uplink reference signal to pre-compensate for crosstalk.