Point-to-multipoint (P2MP) transceivers offer apromisingsolution to transform present point-to-point optical access networks into scalable and flexible P2MP networks capable ofdynamically meeting, in a cost-effective and high energy consumption efficiency manner,the requirements associated with 5G-Advance and beyond networks, including largesignal transmission capacity, fast and dense connection, high network flexibility/adaptabilityand low latency. However, the previously reported P2MP optical transceivers based on either coherent XR optics orIMDD digital filter multiplexing (DFM) techniques are not suitable for implementing in low-latency and highly cost-sensitive IMDD-dominated optical access networks.This paper proposes, experimentally demonstrates and optimisesa novel P2MP flexible transceiver incorporating a new cascaded IFFT/FFT-based multi-channel aggregation/de-aggregation technique and an orthogonal digital filtering technique. The performancesof the proposed techniqueare extensively evaluated experimentally in an upstream 55.3Gb/s@25km IMDD PON.Itis shown that in comparison with the conventional DFM transceivers, the proposed transceivers can reduce the transmitter DSP complexity by a factor that approximatesto aggregated channel count,and simultaneouslyoffer additional physical layernetworksecurity,without requiring longdigital filter lengthsand greatly compromising upstream transmission performances/spectral efficienciesas well as differentialONU launch power dynamic ranges