This paper presents a new physical layer demonstrator for Optical Local Area Network. It offers a large total capacity to a large number of connected nodes without requiring optical amplifiers and achieves high modularity and scalability. A new multichannel Ethernet protocol tailored to the physical layer is also proposed. The physical layer configuration is based on a passive star coupler and combines the advantages of Frequency Division Multiplexing techniques and coherent heterodyne detection. Our experimental demonstrator is based on a 9*9 star coupler and a shared Local Oscillator. Two nodes are implemented and data are ASK modulated at 140 Mbit/s. Emission and detection schemes are simple: only one laser and one photodetector per node are required. Degradation caused by crosstalk has been measured and found to be negligible when channel separation is four times the bitrate. Experimental results show that our system has a potential total capacity of 6.5 Gbit/s and that more than 100 users can be connected to the network. The new multichannel Ethernet protocol simulations indicate considerable improvement of the performance when compared to a single Fast Ethernet channel protocol with the same total capacity.