Abstract: 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.

Abstract: A mode division multiplexing passive optical network (PON) in which channel estimation/inversion is performed in the optical domain. The PON comprises a plurality of input channels; a multiplexer having a plurality of input ports connected to a respective one of the input channels; an optical fibre having an uplink end connected to an output port of the multiplexer, whereby the multiplexer outputs a mode multiplexed signal corresponding to the optical signals from the plurality of input channels. The PON includes an optical equalizer arranged to transfer power between optical signals having different modes to compensate for crosstalk between the different modes. In this system, compensation for crosstalk occurs in the optical domain, e.g. by using the optical equalizer to adapt the optical signals where necessary.