A loopback interconnect datacenter optical network (LIDON) is proposed for switching in datacenters with commercial devices. The intra- and inter-Pod switching in datacenters is accomplished with the Rack Expansion Module (REM) and the Loopback Interconnect Module (LIM) operating collectively. By developing the new functions of diagnostic ports of a wavelength selective switch, LIDON boasts several features, such as high path diversity and robust tolerance. Moreover, the scale of LIDON can be expanded by the proposed scheme to support the flexible switching volume. The feasibility of dividing intra- and inter-Pod signals was demonstrated by the filtering performance experiments. The simulations of the task completion time (TCT) for different services bore witness to the robust fault tolerance of LIDON.