We propose a new optical physical layer and protocol for optical Load Area Networks (LANs), which allow a large number of hosts to be connected while offering a large capacity and exhibiting a high degree of modularity and scalability. The physical layer of the optical LAN is first presented. It is based on a passive star topology and exploits the benefits of combining multichannel techniques together with coherent detection. It shows very simple emission and detection schemes requiring only one laser and one photodetector per node. The experimental setup of this physical layer has been implemented and is described. A new multichannel Ethernet protocol, tailored to the physical layer is also proposed and is presented in the second part of this paper. It results in a considerable improvement of the performance (transmission delay and packet loss), when compared to a single Fast Ethernet channel protocol with the same total capacity.